Updates on Boyajian’s Star

It’s been a busy few weeks for studies of the fascinating star announced by Tabetha Boyajian’s team, KIC 8462852.


It’s official!  Tabetha Boyajian is leading a Kickstarter effort to fund long-term monitoring of KIC 8462852 (I’m on the team!).  The idea is to purchase time on LCOGT, a private network of small telescopes around the world.  These professional instruments can provide regular brightness measurements of bright stars like KIC 8462, and will be able to provide us with an alert if it starts doing one of its mysterious dimming events again.  It’s an important effort, and exactly the sort of expensive, unknown-probability, uncertain-payoff science that is very hard for conservative time allocation committees and grant proposal panels to approve.

The logo for Tabetha Boyajian's Kickstarter campaign.

The logo for Tabetha Boyajian’s Kickstarter campaign.

But it’s also the sort of fun and fascinating science that plenty of people would be willing to kick a few bucks towards, and if “plenty” times “few” turns out to be enough, we’ll be able to ensure that we don’t miss the next event.  Please go to the site and help us out!

An Atlantic Article

Ross Andersen from the Atlantic, who wrote the article that made Boyajian’s star famous, saw the recent back-and-forth by Schaefer and Hippke.  First, Schaefer showed that Boyajian’s star seems to have undergone a “century-long-fade.”  Hippke wrote a rebuttal, Schaefer wrote an acid response, and Hippke came back with a more careful rebuttal.

Kim Cartier

Kimberly M. S. Cartier a.k.a. @AstroKimCartier

Rather than write his own summary for The Atlantic, would I like to write it myself, he wondered?  As luck would have it, my PhD student Kimberly Cartier, who is starting her final year in graduate school, is pursuing a career in science journalism.  Would Ross be interested in a piece co-written by the two of us?  Sure, he said.

So Kim and I quickly whipped up a Google Doc and pounded out a story.  After some back-and-forth with Ross for style and content, it went up on The Atlantic’s website.  I think it came out really well!

You can find more of Kim’s science outreach and journalism at Universe Today’s weekly space hangout, at her blog, occasionally on Monday mornings at 98.7 the Freq, on on twitter at @AstroKimCartier.

Green Bank Time!

The Green bank 100m telescope, the largest steerable telescope in the world.

The Green Bank 100m telescope, the largest steerable telescope in the world.

The event that started Boyajian’s Star’s fame was when Ross Andersen met with Andrew Siemion in Washington after Andrew’s testimony to Congress about the search for life in the universe. At the time, Andrew, Tabby, and I had just recently submitted a proposal to NRAO to use the Green Bank 100 m telescope to “listen” to Boyajian’s Star for alien transmissions.  Ross wrote a nice article on the Congressional event based on an interview with Andrew.

That “fun talk”, included Andrew mentioning our Green Bank proposal, and the rest is history.

But whatever happened to the Green Bank proposal? Well, the TAC met before Ross’s story broke, so all they had to go on was our short proposal explaining why the star was weird.  Our proposal was not as compelling as Ross’s article, and they turned us down, “with prejudice” as the lawyers say.

NRAO has a scale for ranking proposals, prioritized ‘A’ through ‘C’ for proposals that are awarded time, to ‘N’ for those for which there’s just not enough time.  It turns out, there’s also a sub-basement on the scale: N*, meaning something like “rejected not for lack of time, but because the proposal is not worthy, even if time were available.”

N* is what we got.  We got the feedback shortly after the news broke, and we decided to try again the next semester.  With a lot of astronomers’ eyes on the star, we could argue that if there were a simple exaplanation, it would have been forthcoming by now.  We also got to mention the Schaefer/Hippke flap, and address some of the TAC comments from the first round.

Well, apparently it worked!  We were just awarded 25 hours of ‘C’ time for 2016B, and Andrew tells me that this means we will almost certainly be able to observe.  I’m looking forward to the trip to West Virginia with Tabby and Andrew to do some radio astronomy!

That’s all for now.  Stay tuned…

Lodén 1 Part IV: Clusters in the Era of Gaia

So last time we established that the putative middle-aged, nearby cluster Lodén1 is neither middle-aged, nor nearby, nor a cluster.

(That, by the way, was basically the title of our paper, but the referee really disliked it (they thought it was confusing to call it a cluster then say it isn’t a cluster). Then the copyeditor went and changed all of our “amongst”s to “among”s.  Ah, well.)

We still need to take a look at NGC 2240 just in case, but frankly it’s pretty obviously not a real cluster, so it’s a low priority.  Also, Gaia is coming, and it will make this whole endeavor much easier.

The rest of this post is some thoughts by Jason Curtis on the topic:

While Lodén 1 does not appear to be a real cluster, the existence and recent realization that Ruprecht 147 is the oldest nearby cluster suggests that similar clusters might have also gone overlooked. As we say in our paper, “the utility of such clusters for stellar astrophysics demands that we find them.” This fall, the European Space Agency will begin releasing high-precision position and velocity data produced by its Gaia mission, starting with the brightest 2 million stars that were observed by the Hipparcos satellite in the early 1990s.

This first catalog will reach stars like the Sun at distances of up to 1000 light years, including the majority of the proposed candidates of Lodén 1 and the membership of Ruprecht 147. We expect that the improved proper motion precision will enhance our ability to determine the nature of unproven clusters like Lodén 1 and improve the membership identification of established clusters like Ruprecht 147.

Artist's impression of Gaia

Artist’s impression of Gaia

The stars that make up a cluster travel together through the galaxy, with little spread in position (e.g., clusters can span 10—20 light years) and velocity (typically 500 m/s, whereas the cluster itself can travel at tens of km/s relative to neighboring stars). Within a few years, Gaia will release 3D positions (coordinates and parallaxes) and 3D space motions (proper motions and radial velocities) for some 150 million stars, while fainter stars will still receive 3D positions and 2D proper motions. Even sparse star clusters like Ruprecht 147 are 2—3 times denser than the Solar neighborhood. This is not a huge contrast; however, the inclusion of ultra-high-precision proper motions from Gaia (which will see a 100—200x increase in precision over existing proper motions) will make finding sparse clusters easy!

Gaia’s measurements will let us….

  1. “Weigh” clusters by measuring velocity dispersion from proper motions
  2. Resolve internal structure of nearby clusters with parallaxes, and eliminate distance uncertainty for others
  3. Enable easy cluster identification by looking for over-densities in 5D phase space (3D positions—including parallax— and proper motions). Basically, stars are distributed throughout the Solar neighborhood and nearby galactic environment with a characteristic density or spacing. Clusters, even sparse clusters, should appear as over-densities given the expected high precision of the parallaxes. Furthermore, the stars in a given few parsec volume do not exhibit coherent proper motion. Together, these 5 position/motion components should yield new clusters, and new members of known clusters.

Lots to do, but first we should search for bound and moderately rich (N>20) systems that can immediately be characterized and targeted by space missions like TESS.

Our paper is now on the arXiv and will soon appear in the Astronomical Journal.

A Question for METI Critics

In a new paper (put putting forth an old argument) John Gertz argues that attempts to send deliberate signals for detection by alien civilizations is “unwise, unscientific, potentially catastrophic, and unethical.”  His rather caustic assault on METI-proponents is a pretty good summary of the extreme METI-opponent position. (METI = Messaging to ExtraTerrestrial Intelligences).

One thing that caught my eye that I had not heard before is that he obliquely proposes that something like an ethics review board weigh in on any powerful transmissions made by Earth.  He specifically mentions Arecibo radar pulses used to probe Solar System objects:

The asteroid detection radar problem is very easy to fix by adopting a standard of best practices that includes a provision for muting the radar during moments when the target occults a nearby star or transits the plane of the Milky Way.

The agent of our destruction?

The agent of our destruction?

I may be behind the times here, but this is the first time I’ve heard that the planetary science community should consider the ethical implications to the planet for their observations (as opposed to just the ethical implications of the deaths of any birds that happen to fly above the dish during transmission).

But Gertz interestingly does not mention laser AO programs, which send powerful laser beams to some of the nearest stars routinely.  Indeed, Kipping & Teachy recently showed how relatively powerful lasers from other worlds would be easily noticed as artificial signals even with our present technology, and searches for pulsed laser emission is one of the most promising SETI routes we have.  Tellis & Marcy have searched for lasers as weak as tens of Watts coming from tens of AU away from nearby stars.  I haven’t run the numbers, but it would surprise me if our laser AO systems, pointed right at nearby stars, were not detectable by an advanced alien civilization as being obviously artificial.

So my honest question to Gertz and other METI opponents is whether we should seriously be setting up review boards for laser AO and planetary radar?  What about the powerful arctic radars used to look for ICBMs that sweep across the sky? How powerful or coherent must a transmission be before we consider its ethical implications?

As a METI agnostic, I don’t have an answer to these questions; I’m genuinely curious to have this discussion.



Lodén 1, Part III: Neither Old, Nor Nearby, Nor a Cluster

Last time I described how the photometry of the stars in the purported cluster Lodén 1 didn’t seem to really implicate a cluster.

The next step was to get some radial velocities. Jason Curtis submitted a proposal to SALT—the South Africa Large Telescope—to use the Robert Stobie Spectrograph (RSS).  Lodén 1 is in the Southern Hemisphere, so we couldn’t use HET, but SALT is an HET clone, and in exchange for the plans and lessons learned on HET, the HET consortium, including Penn State, got institutional access to SALT for a few years.

The South Africa Large Telescope.

The South Africa Large Telescope.

The telescope was still working out its growing pains, so we never got all of the observations we asked for, and the reduction pipeline improved as we went along, but in the end we got some nice spectra of two classes of stars: Lodén’s original candidates, and the members identified by Kharchenko.

Eunkyu Han, now a graduate student at Boston University.

Eunkyu Han, now a graduate student at Boston University.

The reduction and analysis was done by Eunkyu Han, at the time a post-baccalaureate researcher for our group, and now a graduate student in Phil Muirhead’s group at Boston University.  Eunkyu did a lot of work reducing all of the data from SALT down to just the number we wanted: the radial velocity  Thanks a lot to the SALT staff for helping us with the reductions and wavelength solutions on this relatively new and untested instrument!

These medium resolution spectra measure radial velocities to a km/s or so.  This is enough to see if they’re all roughly the same (in the case of a co-moving group of stars in a cluster) or basically random (as we’d expect for field stars).  This is what they look like:

Medium-resolution spectrum of Lodén's candidate 5. All of this light is roughly in the orange portion of the spectrum, with yellow off the left hand side and deep red off the right hand side. The deep lines marked "Na D" are where the star is dark, exactly at the color of those orange sodium street lamps. This is due to sodium in the star's atmosphere. The inverse-Eiffel-Tower shape on the right is from hydrogen in the star's atmosphere. The difference in the wavelengths of these lines as we observe them and as they are in the lab tells us how fast the star is moving towards or away from us. We actually used the narrow lines marked in red to make this determination. (The blue line shows where the Earth's atmosphere messes with the measurements).

Medium-resolution spectrum of Lodén’s candidate 5.

All of this light is roughly in the orange portion of the spectrum, with yellow off the left hand side and deep red off the right hand side. The deep lines marked “Na D” are where the star is dark, exactly at the color of those orange sodium street lamps. This is due to sodium in the star’s atmosphere. The inverse-Eiffel-Tower shape on the right is from hydrogen in the star’s atmosphere. The difference in the wavelengths of these lines as we observe them and as they are in the lab tells us how fast the star is moving towards or away from us. We actually used the narrow lines marked in red to make this determination. (The blue line shows at which wavelengths the Earth’s atmosphere messes with the measurements—you can see why we avoided those regions!).

So, is there a cluster of stars all at the same velocity, distinct from “the field”?  Or does it look basically like you’d expect for random stars?  Here’s Eunkyu’s result (in black) and what we expect from a random collection of stars in that direction (from Jason Curtis):

Radial velocity distribution of candidate Lodén 1 members. Nothing to see here; move along…

Radial velocity distribution of candidate Lodén 1 members. Nothing to see here; move along…

Yeah, there’s not much there.  There is a peak, but it’s about where you expect to find one, anyway.  We plotted up the stars in that peak and found… nothing that looks like a coeval sequence in the photometry.


  • We looked at the colors of the stars, and found lots of A stars, so its not old.
  • We looked at a color magnitude diagram, and nothing stood out from the field, so if anything is there, it’s not bright, so it’s not nearby.
  • And looking at the motions of the stars, it’s exactly what you expect from the field.

In short, the old, nearby cluster Lodén 1 is neither old, nor nearby, nor a cluster.

Paging Linda Richman…

Paging Linda Richman…

So this one didn’t pan out, but, as we wrote in the paper, “The potential utility that would come with the discovery of a new 2 Gyr star cluster at a distance of only 360 pc was sufficiently high that it warranted careful inspection and disproof.”

We did get into a semantic argument with the referee about whether if there is any cluster or association in the field that Gaia might find, it would be Lodén 1 or not.  We decided not; your mileage may vary.

Next time: Final thoughts, and cluster hunting in the era of Gaia.


Lodén 1, Part II: Proving a Negative

Last time, I described how Jason Curtis proved that the long-forgotten cluster Ruprecht 147 was actually an important benchmark in stellar astrophysics.

We wanted to know if two other entries in WEBDA — Lodén 1 and NGC 2240 — might be similarly useful.

We were pretty skeptical.  Neither “cluster” has a proper motion that distinguishes it from the field.  This means that there is no indication that the stars in those overdensities on the sky are moving as a group—the only reason to think that there might be a cluster there is that there seem to be more bright stars in the region than one would expect by chance.  But it’s a big sky—chance has lots of opportunities to fool you.

Lodén 1 was first noticed by L. O. Lodén in 1980, in his search for “hidden” clusters in the southern galactic plane.  Lodén noted an “evident concentration of late-type stars…and main sequence A–F stars” whose physical association was “not confirmed by strongly suspected.”  Kharchenko’s 2005 analysis put the cluster at 175 pc and 2.5 billion years old— very useful if true, but somewhat inconsistent with Lodén’s note that the cluster contains A stars (though they could be blue stragglers, of course).  A later paper by the Kharchenko group put the cluster at 200 million years old and over 750 pc away, further confusing the issue.  We suspected that the reason the two fits came out so differently was that the Kharchenko algorithm was trying to fit field stars, and so had a GIGO problem.

Part of a figure from Eunkyu and Jason Curtis's paper

Part of a figure from Eunkyu and Jason Curtis’s paper showing color-magnitude diagrams for Lodén’s “field 1” and a control field at the same Galactic latitude.

Jason Curtis did a lot of work putting isochrones down on color-magnitude diagrams for stars in the field.  The above figure shows the Kharchenko et al. 2005 isochrones for the “cluster” in gray, and in red the same isochrone shifted out to 500 pc.  The left panel shows Lodén’s field 1 (the location of the purported cluster), and the right shows a nearby control field at the same Galactic latitude.

The right panel shows “field stars”— the colors (x-axis) and brightness (y-axis) of the random stars along this line of sight in the Galactic plane.  The red (high J-K) stars are mostly intrinsically bright, background K giants at a variety of distances (farther away makes you fainter, moving you down in the graph).  The blue stars (J-K near 0) are mostly hot, young stars randomly strewn along the line of sight.  There is no clustering along either isochrone line because there is no coeval cluster of stars in this region—if there were, you would expect to see an overdensity of points along those or some similar isochrone.

The left hand panel shows the Lodén 1 field, and you’d be hard pressed to tell it was any different from the control.  True, there are a few more bright stars: not really any more red giants, but there are 7–10 blue stars with J < 9.25 or so, while the control field only has 3.  Those are presumably the blue stars that caught Lodén’s attention in the first place.

For reference, here’s how Ruprecht 147 looks:

Color-magnitude diagrams for Ruprecht 147 and a control field.

Color-magnitude diagrams for Ruprecht 147 and a control field.

Its control field looks very different (it’s farther from the plane, so the field stars are typically more distant) but the cluster field has the unmistakable presence of a cluster: lots of stars on the Main Sequence, a healthy but smaller red giant branch population, and even a few blue stragglers (the bright blue stars off of the red line).

If you squint, you can try to make the Lodén 1 stars fall on the red line there, but the numbers are all wrong: given the number of giants, there are way too few Main Sequence stars for this to be real.  The control field actually has a more convincing coeval sequence.

So there doesn’t appear to be anything obvious here.  But that doesn’t mean that Lodén was wrong, just that the cluster doesn’t stand out very well from the field.  To really be sure, we need to see if there are any comoving stars in the field.  We can use catalog data to see in which direction on the sky the stars are moving, and see if there is a subset of them all going in the same direction.  Ruprecht 147 stands out nicely by this metric:

Proper motion diagram for Ruprecht 147

Proper motion diagrams for Ruprecht 147 field and control. Blue cross gives representative error bars.

Here the motions in the north and east directions are plotted ((0,0) is no motion) for all of the stars in the Ruprecht 147 field (left) and its control field (right).  The red circle marks the position in proper-motion space of the cluster.  The control field reveals that field stars generally have zero proper motion — this is because they are typically very distant, so they seem to move very slowly across the sky. The more nearby field stars have large proper motion (they are farther from (0,0)), but there aren’t very many of those, so there’s not much contamination in the red circle.  The cluster itself has a bunch of stars moving southward at a bit over 20 milliarcseconds per year; the overdensity is obvious in the figure above.

How about Lodén 1?

Lodén 1 proper motion diagram

Proper motion diagrams for Lodén 1 (left) and control field (right)

Yikes.  There is no obvious overdensity.  If this cluster is real, its is not moving significantly through the plane.

At the referee’s request, Jason Curtis did some heriocs trying to see if there was an overdensity buried in there, using the control field as a guide.  Noting convincing came out.

But these things are important if they’re real, and we should give some deference to Lodén’s intuition on this.  The real test would be to measure the two missing components to these stars’ motions and positions: their radial velocities and distances.  The distances will have to wait for Gaia, but the radial velocities we could do ourselves.

Next time: Eunkyu collects radial velocities, and pronounces her verdict.

Lodén 1, Part I: Finding new, nearby, old open clusters

Jason Curtis, soon to be an NSF postdoctoral fellow a Columbia University

Jason Curtis, soon to be an NSF postdoctoral fellow a Columbia University

Jason Curtis’s PhD thesis is on the “old”, nearby open cluster Ruprecht 147.  I first came across this cluster when naively looking for an “old” (> 1 billion years) open benchmark cluster to compare field stars with, as part of the GPI target selection group when I was a postdoc at Berkeley.

The cluster was listed in the online open cluster database WEBDA as being nearby (within 500 pc) and “old” (globular cluster astronomers would call it “intermediate aged”— 10 Gyr is old!).  This was based on work by Kharchenko et al. in 2005 who used “known” stellar associations’ proper motions to find new members (fitting their brightnesses and colors with stellar isochrones) and pin down their cluster parameters in a uniform way.  But they had not looked hard at Ruprecht 147 itself, and its fit seemed poor to me—the isochrone passed through the blue stragglers, for instance.

Distances and ages of clusters in WEBDA. The blue open circle is where I had found Ruprecht 147 (in the database) in 2007. The closed circle is Jason Curtis's value. What's that red point?

Distances and ages of clusters in WEBDA. The blue open circle is where I had found Ruprecht 147 (in the database) in 2007. The closed circle is Jason Curtis’s value. What’s that red point?

It turns out that prior to Kharchenko’s work, it wasn’t even clear than Ruprecht 147 was a real cluster.  Jason’s paper beautifully traces out the history here, but basically the overdensity of stars in Sagittarius that marks the cluster was noticed over 150 years ago by John Herschel, but not really believed to be anything other than an asterism by most observers since.  Jaroslav Ruprecht “rediscovered” the cluster about 50 years ago (accidentally giving it a new name), and both that entry and Herschel’s have been dutifully copied from catalog to catalog ever since.

After much work, Jason Curtis established that Kharchenko was absolutely correct that many stars in the area share a common proper motion: the cluster is real, truly nearby, and truly not young.  His refined cluster parameters (300 pc and 3Gyr) are reflected in the figure above (the blue “C13” point).  As you can see, Ruprecht 147 is superlatively old and nearby, much closer than M67 and much older than Praesepe, two critical benchmarks in stellar astrophysics.  With over 100 members, Ruprecht 147 is poised to become a similarly important object of study (which is one thing Jason will work on as an NSF postdoctoral fellow at Columbia University in Marcel Agüeros’s group).

Ruprecht 147 had escaped notice for so long because it sits in Sagittarius—one of the densest regions of stars in the sky—and because it is so close that its stars are scattered over many square degrees.  Its age also hurts it: all of its O, B, and A stars have long since evolved past the giant phase and are now gone or too faint to notice (the remaining 5 or 6 A stars are blue stragglers) so there are few bright stars to draw they eye’s attention like in Praesepe.  It was the Tycho proper motions that made it stand out to the point that Kharchenko’s algorithms proved it to be real.

That figure also shows two other objects, NGC 2240 and Lodén 1, that might be similarly important, if real.  What are they?  Could they be new benchmarks in stellar astrophysics?

Jason Curtis and I put former Penn State undergraduate (and, later, baccalaureate researcher) Eunkyu Han on the case, and her paper is now ready for publication.

More in the next installment

Twenty Years of Precise RVs III: What Keck Gave Us

Last time I wrote about my summary of the Lick Planet Search at the  at the OHP2015 conference; today I’ll finish up with what we learned from Keck.

In the mid-1990’s, Geoff and Paul were strengthening their connections to UC Berkeley, where with Gibor Basri they were using the Lick Observatory facilities.

Geoff and Paul in their UC Berkeley office circa 1994.

Geoff and Paul in their UC Berkeley office circa 1994.

Having connections via UC Santa Cruz and Berkeley, they were able to plan to extend their planet search to the new new HIRES spectrograph at Keck Observatory, which was, like the Lick Hamilton spectrograph, designed by Steve Vogt

Of course, HIRES was going to need an iodine cell; here are Geoff’s instructions to SFSU glass blower Mylan Healy for its construction.

Notes on the construction of the iodine cell for Keck for SFSU glass blower Mylan Healy.

Notes on the construction of the iodine cell for Keck for SFSU glass blower Mylan Healy.


Debra Fischer joined the team as a postdoc in 1997, a couple years before I arrived in 1999.  Here she is working to get a Fourier Transform Spectrograph scan of the Keck iodine cell:

Debra getting an FTS scan of the Keck iodine cell.

Debra getting an FTS scan of the Keck iodine cell.

HIRES proved to be capable of more precise velocities than the Hamilton, regularly achieving 1-3 m/s precision on stable stars.

One of the biggest benefits of a long survey is that you can detect loooooooooong period planets.  This culminated in a few significant discoveries I talked about at OHP: the 10th good Jupiter analog, announced by Sharon Wang (who is going to work with Paul in DC as a DTM Fellow this fall):

HD 37605 b and c, discovered with Keck and HET velocities.

HD 37605 b and c, discovered with Keck and HET velocities.

And many more such planets were announced by Katherina Feng (now a grad student at UCSC).  Here’s one some with large period ratios (the largest known between planets in a system — including in the solar system!)

HD 187123 b & c, which are the planets with the highest known well-measured period ratio

HD 187123 b & c, which are the planets with the highest known well-measured period ratio

I also had some comments about activity cycles, but I’ll save those for another post, another time.  If you’d like to learn more, my contribution to the conference proceedings is on the arXiv and on the OHP2015 site.

And there’s a link to video of my talk here.

Twenty Years of Precise RVs II: Early days at Lick

Last post I described the OHP2015 meeting in France, where I gave a talk.

My contribution to the conference proceedings just went live, and you can read them on the arXiv or on the OHP2015 site. For a “personal history” of the same material, told with greater authority and detail see Paul Butler’s post on the Pale Red Dot site.

The Lick Planet Search begin in the late ’80’s at the Shane 120-inch telescope on Mount Hamilton, in the mountains above San Jose (you can see the dome of the Great Refractor from the 101 freeway in San Jose).

The Shane 120-inch at Lick Observatory on Mount Hamilton, above San Jose. I spent many, many (too many) nights on that mountain in my many (too many) years in graduate school.

The Shane 120-inch at Lick Observatory on Mount Hamilton, above San Jose. I spent many, many (too many) nights on that mountain in my many (too many) years in graduate school.

The spectrograph lives in a basement room beneath the siderostat shed seen here. On nights when other instruments were in use (like those using the laser, seen here), the spectrograph could still be accessed with an auxiliary telescope.  The shed opens, and the siderostat reflects starlight up into the port in the side of the dome.  A small, 0.6 meter telescope is housed inside the dome, and feeds the spectrograph by sending light down into the slit room in the basement, where a pickoff mirror sends the light into the path normally used for light from the 3-meter.

View of the siderostat from the perspective of the port in the side of the dome. This mirror feeds the small "CAT": Coudé Auxiliary Telescope.

View of the siderostat from the perspective of the port in the side of the dome. This mirror feeds the small “CAT”: Coudé Auxiliary Telescope.


The work to extract precise RVs from the spectrograph was largely done at San Francisco State University by Geoff Marcy, Paul Butler, and their students and colleagues. The primary problem is that the instrument was not stable, and the “instrumental profile” or “line spread function” varied with temperature, pressure, position of its various components, and (trickiest of all) the illumination of the slit (which varies from exposure to exposure).  Working with Jeff Valenti at CU Boulder, Marcy & Butler determined that they could use the precisely known spectrum of the iodine lines (obtained at the McMath FTS in 1991) to determine the instrumental profile simultaneously with the velocity of the star by modeling the spectrum.  This was a significant computational burden at the time, but it worked.

Paul Butler at SFSU circa 1988

Paul Butler at SFSU circa 1988

The Doppler lab at SFSU. The wall is lined with diagnostic plots from the Lick Planet Search.

The Doppler lab at SFSU. The wall is lined with diagnostic plots from the Lick Planet Search.

The original cell was designed by Paul Butler and Geoff Marcy, and blown by SFSU glass blower Mylan Healy:

The original iodine cell for Lick.

The original iodine cell for Lick.

Paul Butler, a chemistry masters student at SFSU, tested many different compounds to replace hydrogen fluoride, the original gas used by Bruce Campbell and Gordon Walker to get below 20 m/s precision at DAO.  HF is notoriously dangerous to work with, and molecular iodine had been suggested by Robert Howard at the Carnegie Institution of Washington, inspired by work by Beckers in the late ’70s.  Similar work was also being done by Libberecht and Hatzes & Cochran.  Paul spent months trying many compounds many of them “explosive, deadly poisonous, or both” before settling on iodine.

Since pure iodine is a solid at STP, the gas cell is evacuated and heated to ensure complete sublimation of the small amount of iodine within.  The blue cylinder in the picture is thermal insulation, and the wires are for the temperature controller that kept the cell at constant temperature.  The arm held the cell in the path of the light.

Fancy picture of the iodine cell in position at Lick Observatory. I think that's Debra Fischer's hand. Image copyright Laurie Hatch, used with permission.

Fancy picture of the iodine cell in position at Lick Observatory. I think that’s Debra Fischer’s hand. The beam is shown bouncing off of the slit plate, behind which is the spectrograph room. Image copyright Laurie Hatch, used with permission.

Another technical hurdle was a spectrograph that delivered high resolution, a broad bandpass, and a high-quality, linear detector.  The Hamilton spectrograph fit the bill.  It was built (and later upgraded) by Steve Vogt (one of Geoff Marcy’s thesis advisers) seen here holding a spooky glowing orb of some kind 1.


Paul calls the Hamilton “arguably the first modern echelle spectrometer”.

The Lick Planet Search really took off within days of the announcement by Mayor & Queloz of the discovery of 51 Peg b.  Geoff and Paul immediately confirmed the discovery, devoting what little computing power they had access to to analyzing data just for that star from a single observing run. The ensuing attention gave them access to more computing power, and in short order they announced the next nine exoplanet discoveries (most already in their unanalyzed data!).

The Lick Planet Search spanned 25 years, and owes its success to almost innumerable observers (we tried to track down all their names and thank them in the acknowledgements here).  Of special note are Debra Fischer, who ran and improved the program for years, and John Johnson, who did his thesis using the Hamilton.

The Lick Planet Search was still producing until one fateful day that the temperature controller partially failed.  Unfortunately, the part that failed was the part that turned the heater off, and as a result the insulation was melted and the cell badly damaged.

The sad fate of the Lick iodine cell.

The sad fate of the Lick iodine cell.

My understanding is that Geoff Marcy donated the cell to the Smithsonian.

In total, the Lick Planet Search made 14,000 observations of 386 stars. Debra published the entire radial velocity archive in 2014, ensuring that its legacy will be maintained.

Next post: the planet search moves to Keck.


1 Yes, I know it’s a mirror.

Twenty Years of Precise RVs I: A meeting in France

In October of last year, a lot of exoplanet astronomers gathered in Observatoire de Haute-Provence (OHP), France, for OHP2015, a conference on “Twenty years of giant exoplanets”. Many thanks to SOC chair Isabelle Boisse, and LOC chair François Bouchy for their efforts putting it together.

For those who don’t know, OHP is where the field of exoplanetary astronomy got jump-started with the discovery of 51 Pegasi b by Michel Mayor and Didier Queloz using the ELODIE instrument (which we got to see when touring the facilities). Today, the same telescope uses the SOPHIE instrument to continue the precise RV tradition there.  The site itself reminded me a lot of Lick Observatory, actually (which is not too surprising; both are very near regions world-renowned for vineyards growing similar grapes).  bandeau_image_OHP_CNRS_900pxI had never been, and it was neat to get to travel to France and make minimal use of my high school French.  We stayed in the dormitories and got to visit a local fromagerie.

What I liked about the conference is that it focused on the first class of exoplanets discovered (pulsar planets aside), which is one that often gets forgotten when we focus on the (much more numerous) smaller and potentially terrestrial bodies being found by Kepler and at low amplitudes by RV.  These are the mature, presumably gas-giant planets orbiting at tenths to tens of AU from ordinary stars.

I was asked to talk about the 20 years of precise RVs at Lick and Keck observatories.  I started working with Geoff Marcy in 1999 or 2000, less than 5 years after the discovery of 51 Peg b, when there were still only a small number of exoplanets known.  I had heard enough stories from Geoff, Paul Butler, Debra Fischer, and Jeff Valenti, that I felt I could cover the territory pretty well.

So,I asked around and put together many slides of “vintage” photos showing things like the original Lick iodine cell and the lab at San Francisco State University where Marcy, Butler, and others got that planet search running.

I’ll blog about the content of my talk in future installments, but if you’re curious you can see my talk itself here:

Talk at OHP

Talk at OHP

I also recommend this “personal history” of the same material, told with greater authority and detail by Paul Butler on the Pale Red Dot site.

Next time: where it all started.

AAS Ethics Investigations

In a previous post I laid out my feedback to the AAS on its new draft Code of Ethics.  I’m glad the AAS is addressing this, and especially glad that they are engaging the membership to craft a strong code that will improve our society.

My second concern in that piece was that the new investigative and punitive powers this policy gives the AAS seemed in need of revision (for instance a single person appoints the entire committee)  I wrote that it would help to know that similar committees in allied field’s professional societies work well, and have restricted their most vigorous efforts to severe cases, held a sense of proportion in their actions, and acted primarily to protect the powerless.

To satisfy my curiosity, I checked some of astronomy’s allied fields’ professional societies to see if any have standing committees charged with investigating, adjudicating, and punishing ethical breaches, including sexual harassment.

I could not find any.  The American Physical Society and American Chemical Society don’t seem to have any bodies that handle adjudication of ethical breaches.  Indeed, the APS doesn’t seem to address non-scientific misconduct (like harassment) at all, having, at most, a statement on treatment of subordinates.  In contrast, I am proud that the AAS is leading on this.

The ACS has a more thorough ethics program, with a committee whose job is to educate and provide resources for the community.  I would like to see the AAS do this as well.

But in my quick search I couldn’t find any body at ACS responsible for investigations of wrongdoing (the Ethics Committee itself serves as a resource “but not as an adjudication body”.)

The American Geophysical Union’s Ethics Committee was the closest to an exception.  It provides an easy-to-find link for people to submit complaints of violations, and serves to investigate allegations.  Some features of this committee (and what I like about them in parentheses):

  • The chair of the committee determines which allegations to bring to the full committee (discretion to investigate)
  • The committee is composed of at least one member from committees responsible for outreach, meetings, and publications, and one AGU editor in chief, one editors, and one associate editor. Additional members can be added as appropriate for specific allegations (guaranteed broad representation and appropriate expertise on the committee)
  • Members are appointed by their respective committees, in consultation with AGU leadership (distribution of power)
  • It is not a standing committee; it convenes only as needed (it is not their job to go find work to do)
  • The committee’s recommendations at the end of an investigation go to the AGU board of directors, which decides punishment. (separation of powers)

I find many features of this setup appealing, and indeed many of them are in the current version of the Code of Ethics.  Of course, its possible that this model doesn’t work well, or is missing important features that would be important for the AAS to include. I encourage the AAS Ethics Task Force to contact the AGU (including those who have brought complaints to the AGU Ethics Committee) see how well it works, and to consider whether to adopt components of this model in the AAS Code of Ethics.

Whether they agree with me or not, I encourage all AAS members to give their feedback to the AAS here.

AAS Ethics Policy

The late unpleasantness in astronomy has rightly led the American Astronomical Society to take a new look at its ethics policy (here) which was adopted in its current form in 2010.  The current code lacks any enforcement mechanism, and so a new draft has been adopted that includes one (you can read it here).

I like the current version of the AAS Ethics Statement, but it is primarily aspirational.  I have three major concerns with the revised version.

My first concern is the following language, in the preamble:

Upon acceptance or renewal of AAS membership, all members will be asked to acknowledge that they have read this Code of Ethics and will strive to abide by these as an AAS member. (emphasis mine)

This bit about “striving to abide by these [sic]” is new, and problematic.  It takes what was an aspirational ethics statement and turns it into a code of ethics, and one that members must pledge to follow as a condition of renewing their membership.

Now, I understand that the AAS would like the statement to have some teeth so that it can sanction very bad actors, and I get that having members promise to follow a code gives the AAS a basis for admonishing and correcting bad behavior.

Now, if the code truly contained, as it states, “the minimal standards of ethical behavior relating to the profession” then this wouldn’t be a big problem, but there’s a lot more in there than that (and there always was — the “minimal standards” language is in the current ethics statement as well).

For instance, the ethics statement (and the new code) states that

Scientists should…promote equality of opportunity and treatment regardless of gender, race, ethnic and national origin, religion, age, marital status, sexual orientation, gender identity and expression, disabilities, veteran status, etc.

I’m fully behind this statement—I agree with it and I’m proud that my professional society has this as official policy.  But the Code of Ethics isn’t a policy statement of the society, it is a set of professional norms that the AAS wants all of its members to agree to when the renew their memberships.

I’m sure there are lots of astronomers who do not agree with the quoted statement (in deed, if not in word).  It’s one thing to require these astronomers to acknowledge that the AAS would like them to promote equality (as the current ethics statement does). It’s another to require it of them as a condition of membership, which is what the new language does.  Indeed, taken literally, members who do not promote such equality (by, say, doing nothing at all on the topic) are in violation of the code of ethics. 

My second concern is the new investigative and punitive powers this policy gives the AAS.  Under the new policy the AAS gets a Committee on Ethics that receives complaints, can investigate them, and can act on them with outcomes ranging from no action, to admonishment, to expulsion from the society.  All of the committee members are appointed by the AAS president.

I’d really like to know if this is modeled on a successful committee in some closely allied field’s professional society, or is this something new we’re trying in light of recent events? For instance, it does seem sub-optimal that the entire Committee on Ethics will be appointed by a single person (the president). After all, the president could be accused of a violation!

There have been (mostly anonymous) whisperings that the AAS is gearing up for a “witch hunt.” I find such whisperings to be rather paranoid (after all, the salient feature of a witch hunt is that, unlike unethical astronomers, witches don’t actually exist).  But this is not to say that a process of investigation and punishment cannot get out of hand or be abused. It would help to know that similar committees have restricted their best efforts to severe cases, held a sense of proportion in their actions, and acted primarily to protect the powerless.

My third concern is this language:

Any AAS member or meeting attendee who experiences or witnesses a violation of the AAS Code of Ethics should report that violation to the AAS Committee on Ethics.

I presume this is just poor drafting, but just to put a fine point on what’s wrong here: taken literally, this unqualified statement means that all members should report all violations of the code of ethics to the AAS that they “experience[] or witness[]”.  Combined with the language that led to my first concern, this implies that it is a requirement of membership to report event the most minor infractions (such as not promoting equality).  Yikes.

After all, what about people who are being harassed or abused and are fearful of retribution if they report? Or have trauma as a result? Are they in violation of the code of ethics if they don’t report their trauma to strangers at the AAS? Obviously they should not be, but if the language in this document seems to say that they are, then the language is far too broad.

To take another example of infractions that the AAS wants to know about:

“All people encountered in one’s professional life should be treated with respect. At no time is abusive, demeaning, humiliating or intimidating behavior acceptable“

As an aspirational platitude, that’s fine, which is why I’m OK with it in the current ethics statement.  As a professional norm that constitutes a basis for investigation and punishment, as in the new code of ethics, this is very problematic, because it’s not literally true.

To take just one example, if a junior member of our society is severely harassed (or worse) by a senior member, one can’t really expect that junior member to treat that senior member with respect. I can easily imagine situations where a junior member vents about the harassment on Twitter or some other public forum in impolite and unprofessional ways. The harasser could then point to the language of this document and report that the victim is violating the ethics code, and have them sanctioned! (Indeed, they have to report it!)


Again, I understand what the AAS is trying to do here, but trying to implement professional norms like this is hard and needs to be done carefully.  Imprecise language will lead to overly broad and so unenforceable rules, which will then be applied unevenly or not all.

We do need to have a hard conversation about ethics in our society and the AAS should be able to take action against bad actors.  I don’t think this current policy fits the bill.  It may be just a few tweaks before it’s in good shape; I’m not sure.

Whether they agree with me or not, I encourage all AAS members to give their feedback to the AAS here.

Mercedes Richards (1955-2016)

We are in mourning at PSU astronomy.  Our colleague Prof. Mercedes Richards died yesterday from complications of a chronic medical condition.

Mercedes Richards

Mercedes Richards. Image by Wendy Estep and Sara Brennen.

I first met Prof. Richards when I visited Penn State as prospective faculty. The interview was supposed to be about my exoplanet work, but we ended up talking about stars and stellar clusters.  After I was hired, it was always a pleasure to stop by her office for her thoughts on stellar activity, stellar evolution, spectroscopy, and teaching.  Her home in College Township is just a few doors down from ours, and the Richardses were always warm and welcoming neighbors.

Mercedes Tharam Davis was raised in Kingston, Jamaica, where her father, a police detective, and her mother, an accountant, taught her the power of deductive reasoning and care in one’s work.  She received her BSc in Physics from the University of the West Indies before moving to Toronto, where she earned her MSc (at York) and PhD (U Toronto) in astronomy.  She joined the faculty at the University of Virginia in 1987, and came to Penn State as a full Professor in 2002.

Prof. Richards is especially well known for her pioneering work in tomography of binary star systems and CVs.  By strutinizing spectroscopic and photometric time series of stars and compact objects in close orbit, Prof. Richards could create three-dimensional “movies” of mass-exchange systems, answering important questions about how mass transfer occurs.

Her research has been recognized with a Fullbright Distinguished Chair, and the Musgrave Medal.  The latter has been awarded occasionally by the Institute of Jamaica for over 100 years for achievement in art, science, or literature; Prof. Richards was just the 14th scientist to be so honored.

Prof. Richards’s service to the profession is exemplary.  She served as President of IAU Commission 42, a Councillor of the AAS, and organized numerous international conferences.  She served as our assistant department head from 2003-2008.

Prof. Richards’s dedication to students of all ages is well known.  Her introductory astronomy class was one of the most popular on campus.  She was a founder and director of SEECoS, a high school science outreach program of Penn State, and a Harlow Shapely Lecturer for the AAS.

I’m going to miss Dr. Richards; she has served as a role model educator, researcher, and scientist for me since my arrival.

Prof. Richards is survived by her husband Donald, who is a professor of statistics at Penn State and occasional co-author with her, and two daughters, Chandra and Suzanne.  They have always been joyful presences at department events, and our hearts and thoughts are with them today.

Oz in popular culture

Some spoilers for the Oz books below.

I’ve been reading the Oz books with my 5 year-old daughter, Georgia, before bed every night. I knew people called them classic American mythology, but I thought that was primarily based on the 1939 film, and a bit on The Wiz! and Wicked. I knew that the other books had many adaptations, but their cultural impact I thought must be small because I’d never seen or heard of their characters or plots.

Instead, what I’ve found is that, although clearly 100 years old, they have aged very well, and seem to have had broad and deep influence on popular culture beyond the first book’s adaptation in film.

We’re on the third book now, Ozma of Oz, and the number of popular culture echoes I’ve identified is already large. There is a strong theme of “animated people,” “talking animals,” and transformation in the books, but somehow each one that’s introduced seems fresh:

  •  Jack Pumpkinhead was the first one I noticed strongly—Jack the Pumpkin King from the Nightmare Before Christmas is clearly based on him.
  • The Tin Woodman’s origin in the books is very different than implied in the film. He’s not an animated statue—he’s a clumsy axeman who keeps amputating body parts, and having them replaced with tin ones, until nothing’s left; the transformation left him without any heart. He’s a cyborg that has lost his humanity. From the Skywalkers to countless cyborg films, this theme is now common in film.
    Jack Pumpkinhead with some familiar and less-familiar characters from Oz from The Marvelous Land of Oz
  • The “group of friends that heedlessly head into adventure and peril, and prevail through luck” storyline is used a lot. The books are serial, and there’s lots of unlikely coincidence and favorite characters meeting and teaming up to please fans of the books (as Baum admits in an author’s introduction). Baum probably didn’t start this, of course, but it’s a great and early example of the form in American popular culture that’s thriving today in this Golden Age of television.
  • Tiktok is a robot. Baum makes it clear he can think, has memory, is trustworthy and has empathy, but is not alive.  He’s a great exploration of what that could mean—in what sense is he not alive when the Tin Woodman is? Where modern characters like Data make this tension an explicit plot point, Baum prefers to simply assert the contradiction, like the droids in Star Wars.
  • The jolly but sinister Nome King and his nome army in his Underworld Kingdom is a direct ancestor of the dwarf (and goblin?) kingdoms of Middle Earth.  The description of the underworld halls read like they could have been the basis for Jackson’s film adaptations of LOTR.
  • I detected echoes of Princess Langwidere in the Fireys in Labyrinth, but she’s also a metaphor for moodiness and the inconstancy of personality.  The theme of trying on someone else’s personality and/or face is another cinema favorite.
  • Unlike the film version with her “mid-Atlantic” accent, the book version of Dorothy is a hick, a Mark Twain-ian noble uneducated rural American. She’s got a great line about why, unlike the haughty Princess Ozma, she’s not too proud to beg for an audience with the Nome King: “I’m only a little girl from Kansas, and we’ve got more dignity at home than we know what to do with.”
  • The Gump is basically a zombie, a reanimated monster from found parts. He’s clearly based on Frankenstein’s monster, but with full memory and faculties from his old life.  At the end of the book he begs to be disassembled because he’s an unnatural abomination. A great example of how Baum can explore some pretty dark themes with a cheery tone.
  • The brainless but wise and faithful Scarecrow seems to me an echo of Sancho Panza.  A similar character from another American myth is Jar Jar Binks; Julia suggests Inspector Gadget as another.
  • The idea for the Hungry Tiger is brilliant, but I can’t think of any similar characters since.  He’s a bloodthirty predator with morals.  He’s always growling threateningly about how hungry he is, how much he wants to eat the other characters, how much he’d love to find a fat baby to devour.  But he knows that it would do no good—eventually he’d get hungry again, and then he’d be responsible for a needless, innocent death.  So he’s always hungry.  This isn’t really Baum moralizing—the Cowardly Lion happily, regularly heads into the forest to find dinner.  This is sort of like the “reformed vampire” trope, except that the rationale is different: the Hungry Tiger would gladly take a life to permanently satisfy his hunger.

In some ways, the mores of the Oz books were ahead of their time.

  • For instance, there is a lot of gender-bending.  There’s a hen named “Bill” because she was misgendered as a chick (Dorothy calls her “Billina” because “Putting the ‘eena‘ on the end makes it a girl’s name, you see”). And there’s even a sex-change of a major character I can’t write more about without major spoilers (can you spoil a 100 year-old classic American myth?)
  • Oz is basically ruled by women:
    • The witches ruling the cardinal kingdoms of Oz at the opening of the books are all women.  When we finally see another “fairy land”, Ev, we find it is ruled by the feckless Princess Langwidere.
    • In the second book, General Jinjur leads her army of women (volunteers recruited from all four cardinal kingdoms) to depose the Scarecrow from the Emerald City (recall the Wizard installs the scarecrow as his successor before departing in his balloon). She’s basically a feminist Social Justice Warrior out to overthrow the unjust patriarchy, and she briefly succeeds!

General Jinjur’s army conquers the Emerald City, deposing the Scarecrow

In other ways, there’s a lot of retrograde material:

  • Slavery is a thing, explicitly.  Our heroes chastise the Nome King for having (human!) slaves, but among their number are Tiktok and the Saw Horse, both of whom obediently and happily serve the “masters” that animated them.
  • General Jinjur’s army of women is incompetent because of their femininity— they’re armed only with knitting needles and motivated primarily by the prospect of raiding the Emerald City for gemstones to make jewelry with.
  • Men are always the muscle.
  • For an American classic, democratic principles are surprisingly absent. Rule by birthright is the norm, with the occasional usurper by force or trickery (the Wizard, General Jinjur).

OK, what modern influences from Oz have I missed?  I haven’t finished Ozma of Oz yet, so please don’t give any major spoilers in the comments if you’ve read past me, but go ahead and name characters I haven’t met.

AstroWright Group Science at #AAS227

AAS 227

It’s that time of year again! I’m not there at AAS myself, but here is some of the science I’m involved in to some degree.  Put them on your schedule with the AAS meeting app!

Tuesday oral, 10am, Sun D:

fabienne105.02 PSU Hubble Fellow Fabienne Bastien on using “flicker” to derive stellar gravities (and, so, masses) from Kepler and K2 light curves.  10am in Sun D.

Screen Shot 2013-11-06 at 9.38.47 AM.pngimage_normal.png 105.03 Right after Fabienne(!), NSF Graduate Fellow Jason Curtis (@jcwaalaaa) talks on what’s up with Ruprecht 147, the closest intermediate-age open cluster (a crucial test for gyrochronology!).  10am in Sun D. Stellar astronomers: Jason is on the job market this year.

Tuesday poster:

mccrady137.14 MINERVAn Nate McCrady (@natemccrady) presents all the latest science with Project MINERVA in the poster session.

Brendan138.26 Atmospheric escape and star-planet interactions in hot Jupiters: Brendan Miller (@brendanpmiller) presents new Chandra observations of HD 97658 and HAT-P-11 in the poster session.

Rachel Worth 138.30  PSU grad student Rachel Worth (@RachelJWorth) has results on Proxima Centauri’s Influence on Planet Formation in Alpha Centauri.  While you’re at her poster, ask her about lithopanspermia.  Dynamicists and astrobiologists: Rachel is on the job market this year.

Wednesday oral 2pm Sun D:

HgmRH_IK 220.03D Sharon (Xuesong) Wang (@sharonxuesong) gives her dissertation talk on solving the precise radial velocity issues at Keck and HET observatories. If you ever wondered about the nitty gritty of how precise iodine RVs are made, this is the talk for you.  Observational exoplaneteers: Sharon is on the job market this year!

Wednesday posters:

Julia Kregenow 245.08 Penn State teaches more undergraduates astronomy than any college in the country, including lots of Web courses.  How much do the students in those Web courses learn?  More than you think (as long as it’s done right.)  Julia Kregenow on how to keep learning gains high in Web instruction (spoiler alert: MOOCs aren’t doing it right).

Kim Cartier 250.03 A meta-poster! Kimberly Cartier (@AstroKimCartier) gives important advice on good poster design — in poster form!

Thursday oral 10am Osceola B:

Kim Cartier 306.06 Kimberly Cartier again!  This time talking about near-IR spectroscopy of WASP-103b at secondary eclipse, work she is doing with Ming Zhao and Thomas Beatty.

Friday oral 2pm Osceola 4:

Sam Halverson427.01D Finally, fans of fiber optic radial velocity work should not miss Sam Halverson’s dissertation talk on photonic systems for high precision radial velocity measurements, in particular his novel use of ball scramblers for very high scrambling gains at high efficiency.  Instrumentalists: Sam is on the job market this year!


When you get promoted and/or tenure at Penn State, the libraries hold a ceremony for you, where a book of your choice gets added to their special collection with a plate on the inside cover commemorating your achievement.  They ask that you choose a book (they’ll buy it if they don’t have it) with some significance, and they post a short blurb about it on their website.

At the ceremony, President Barron told how he instituted the same tradition at Florida State when he was president there. He also acknowledged the hard work and sacrifice of the newly promoted’s families, since he knows promotion is a team effort.  I was very pleased to hear that.

My terribly amateurish attempt to get a photo of President Barron thanking the families of the newly promoted for their sacrifice.

My terribly amateurish attempt to get a photo of President Barron thanking the families of the newly promoted for their sacrifice.

Here’s my book and blurb:

My book and blurb, to be added to the library's special collection

My book and blurb, to be added to the library’s special collection

The blurb in more detail:

A wise frog once asked "What's so amazing / that keeps us stargazing? / And what do we think we might see?"  For me, the answers to those questions were found in this book, which I checked out of my elementary school library over and over. In a fast-moving field where books are often out-of-date before their first printing, Our Universe had amazing longevity. Its popularity, aided by a friendly layout, compelling text, and beautiful illustrations, helped teach the world about the facts and mysteries of the universe.  Over the years it inspired many people, me included, to pursue a career in astronomy.

I know I’m not the only astronomer that was inspired by Our Universe. The copy at Lockwood Elementary school was effectively mine, because I kept renewing it over and over. I always knew I wanted to study astronomy, but this book gave me the background to start to understand what that meant.

Today, I can really appreciate the care of the graphic design that went into this book, drawing me in first with the pictures, then they layout and infographics, and eventually all that black-on-white text.

For an older generation of astronomers, the inspiration was Cosmos.  How many others of my generation owe their careers, in part, to Gallant’s book? Who do the young’uns today point to?

Leave your inspirations in the comments below.

KIC 8462852: Where’s the Flux?

A little over a year ago, Tabby Boyajian gave a seminar here at the Center for Exoplanets and Habitable Worlds about her research. While she was here, she showed me some crazy light curves from Kepler spotted by her team of PlanetHunters:

8462852_all 8462852_q1 8462852_q13 8462852_q8 8462852_q16_q17

Did I have any idea what it might be she wondered?  We tossed around ideas, but I was stumped.  Tabby’s team had spectra, which helped rule out some possibilities: it’s clearly an F star, and the “fuzz” in the second panel above is due to its 0.88 d rotation period.  But those dips are crazy!

One can think of lots of ways stars can behave oddly like this, but almost all of them invoke young stars.  This star is moving too fast to have formed recently, and doesn’t show any infrared signs of a big disk that you would associate with the material that could cause those dips.  And there aren’t any star forming regions in that part of the sky, anyway.  How could an old star do this?

Interestingly, I had been working on a paper about detecting transiting megastructures with Kepler.  The idea is that if advanced alien civilizations build planet-sized megastructures — solar panels, ring worlds, telescopes, beacons, whatever — Kepler might be able to distinguish them from planets.  Luc Arnold wrote a nice paper about this, and I was turning my blog post on the topic into a proper journal article.

One of the things that occurred to me is that a civilization that would build one megastructure would eventually build more.  The star might be surrounded by them (a Dyson swarm).  What would that look like?

If they were small, it might be a flickering, or even just a general dimming.  But if they were very large, you would get dips.  It would look maybe like Kenworthy and Mamajek’s giant ring system, but without the obvious symmetries.

The analogy I have is watching the shadows on the blinds of people outside a window passing by. If one person is going around the block on a bicycle, their shadow will appear regularly in time and shape (like a regular transiting planet). But crowds of people ambling by — both directions, fast and slow, big and large — would not have any regularity about it at all.  The total light coming through the blights might vary like — Tabby’s star.

My philosophy of SETI (section 2.3 of this paper) is that you should reserve the alien hypothesis as a last resort. One of the reasons not stated in that link is analogous to Cochran’s Commandment to planet hunters prior to 51 Peg b‘s discovery:

Thou shalt not embarrass thyself and thy colleagues by claiming false planets.

It would be such a big deal if true, it’s important that you be absolutely sure before claiming you’ve detected something, lest everybody lose credibility.  Much more so for SETI.

But from a SETI perspective, one should focus one’s resources on the best targets.  Looking for astronomical anomalies is a reasonable way to focus one’s search. There is no inconsistency between assuming purely natural explanations for all phenomena, and targeting SETI efforts at the most astrophysically inexplicable phenomena.

I found Tabby’s star to be inexplicable, so I contacted Andrew Siemion at the Berkeley SETI Research Center. I told him we had a very strange star, and how does one go about doing a radio SETI search?


The Green Bank 100m telescope

Andrew was initially skeptical, but he quickly agreed that this is a great target.  He, Tabby, some of the PlanetHunters, and I put in a Green Bank Telescope proposal to do a classical, radio-SETI search (à la Contact), and I went to work on my paper.

Then a few things happened.  First, Tabby’s team published up KIC8462852 (that’s the name of the star) with the appropriate subtitle “Where’s the Flux?” (we call it “the WTF star” internally, although I more commonly call it “Tabby’s star” or “LGM-2”.).

This is such a cool object.  I really want to know what’s going on.  Kudos to the whole PlanetHunters team for such an amazing find.

Tabby’s team tentatively settles on a plausible but contrived natural explanation for it: a swarm of comets recently perturbed by the passage of a nearby star.  I would put low odds on that being the right answer, but it’s the best one I’ve seen so far (and much more likely than aliens, I’d say).  If I had to guess I’d say the star is young, despite all appearances.  I can’t back that up.

Anyway, a few weeks later, Andrew gave some congressional testimony, and while down there met Ross Andersen of the Atlantic.  Andrew told Ross about Tabby’s star, Ross interviewed Tabby, then Ross interviewed me (we know each other from an earlier story), and then Ross wrote up an article about Tabby’s star.  Ross’s story is well written and plays up the megastructure angle in a compelling way.

The internet went aflutter.  I’m glad for Phil Plait’s sober take — he gets it just right.  The British tabloids did their predictable thing (I won’t link — they couldn’t even be bothered to get my name right, much less convey the proper sense of proportion).  And it’s all still taking off.

Screen Shot 2015-10-15 at 9.15.14 AM

I’m really glad that Tabby’s star is getting so much media coverage.  It’s a great mystery!

But I am a bit embarrassed about the less responsible reporting overstating the evidence here — especially since we didn’t have anything ready to show our professional colleagues so that they can give reporters informed takes on it.

I usually don’t post papers prior to acceptance, but we have a favorable referee’s report and everyone’s asking, so since the Internet seems to be eating this up, I asked co-author Kim Cartier to post it to the arXiv.

You can find it here. Section 4 is what you are looking for.

Eugene Commins (1932-2015)

Eugene Commins died on Saturday.

Eugene Commins

Eugene Commins

I only knew Prof. Commins as a professor whose courses had to be taken. They were not formally required for astronomy students, but the word was that if you were a Berkeley grad student and didn’t take is courses, you would regret having missed an amazing opportunity, and if you did take them you would always remember them.

He had a brilliant career, too. Read about it here:

Something only touched on there, though, were how his courses changed the students. I still remember many of the problems he assigned. Some of them totally changed the way I think about the world and physics. Here’s one (by fellow Berkeley grads can correct my memory):

This calculation is purely classical, but the quantum analog yields the same result.

Consider the paths of the gas particles in this room. Now, consider their future motions if an electron on the surface of a star at the edge of the observable universe is instantaneously displaced by 1 cm. How long until their paths are qualitatively different as a result of that displacement?

Path to solution:

  • For this rough, order-of-magnitude calculation, treat them as a set of identical hard spheres traveling ballistically and undergoing elastic collisions.
  • Calculate the particles’ typical speed
  • Calculate the particles’ typical masses
  • Calculate the particles’ typical sizes
  • Calculate the particles’ typical separation
  • Calculate the change in acceleration from that electron’s displacement on a particle
  • Calculate the differential acceleration (tides) from the electron’s displacement on neighboring particles
  • Calculate the relative change in lateral position the particle will experience during its travel between particles
  • Calculate the change in the angle the particle will experience upon scattering due to the electron’s displacement
  • Calculate the number of scatterings until the change in lateral displacement is equal to the size of a particle
  • Calculate the time it takes to experience this number of scatterings.

I don’t remember the quantitative answer, but it’s absurdly small. The reason is that the change in angle grows geometrically with each scattering (i.e. it grows by a constant factor each time). As a result, it takes something like dozens or hundreds of scatterings before two particles that would have collided miss each other instead. Because particles collide many times per second, the time it takes for this to happen is far less than a second.

The lesson is that the idea of calculating the future of the universe, or even a tabletop experiment that is sensitive to small perturbations, is impossible. In order to get the paths of the gas particles in this room correct for less than a second, one needs to know the position of every particle in the universe to much better than a cm.

So if the universe (or even just this room) is a simulation (if we are in a Matrix), then either the physics is being faked, or the computer doing the simulating is, itself, a super-universe-sized affair.

Professor Emeritus Commins was 85.

Update: Marshall Perrin found the problem:


I was pretty close!  I had the point of the problem wrong (though not its implications) and the distance to the star (off by 109, but that hardly changes the answer at all!)

Ethics and Radicalism

A while back I posted on “Ethics and Evil,” about the perils of following one’s beliefs to their logical conclusions.  I focused on the fact that all knowledge is provisional, so one must always keep in mind that one’s closely held beliefs might be wrong.  The boldness with which we act should be proportional to the moral intensity of a situation, which might be greater for us in contexts we feel strongly about, but it should also be tempered by the magnitude of the evil we would perpetuate if we were wrong in our ethical assessment.

Today in the New York Times’ excellent “The Stone” series is another argument along these lines about veganism and animal rights by Bob Fischer and James McWilliams.  The hook is a (to me rather unconvincing) analogy about interrupting an opera to help a distressed audience member, but the gist of the argument is that people with strong, extreme positions, like vegans, should be willing to accept baby steps and half-measures, like giving farm chickens bigger cages.  It is, in short, an argument about not letting the perfect be the enemy of the good.  “Absolute certainty and purity of principle,” they write, “can be detrimental to moral decision-making.”

What I find fascinating about this particular argument is that it explicitly argues for a compromise position even granting that the vegan radicals are right.  Referring to an uncompromising vegan that demands a global adoption of veganism:

[he] isn’t crazy: he’s making the same inference that slavery abolitionists made in the 19th century. They claimed, as many animal activists do now, that it was pointless to call for the reform of an unjust institution. You don’t fix unjust institutions; you dismantle them. Entirely. Now.

The analogy to slavery is obviously flawed in an important way, since most people would give humans much more moral standing than, say, a chicken.  But aside from this huge difference in moral intensity, the analogy is a good one. Today, in depictions about the antebellum south, the absolutist abolitionists are often presented unquestioningly as the obviously rational good guys. But at the time, their “ask” — that white America voluntarily “give up” its single most valuable asset (i.e. free its enslaved people) — seemed crazy and impossible, even to supporters of the movement.  It took the Civil War to make it happen. It’s possible that in 100 years we will look back on today’s carnivores with a similar puzzlement and disgust to the way we look on those slaveowners today.

Presidential candidate Bernie Sanders is interrupted during a campaign stop by Black Lives Matter activists

Presidential candidate Bernie Sanders is interrupted during a campaign stop by Black Lives Matter activists

I’ve been thinking a lot about the role of radicals in society lately, and whether one can morally both agree with them and not do what they demand.

Fischer and McWilliams again:

We’re not saying that the activists should become more moderate. The point here isn’t that the activist’s principles are mistaken, but rather that those principles have to coexist with other moral commitments, and with the reality of the world as we find it, if he or she is to honor the beings for whom those principles were designed.

Of course, it is reasoning like this that lead many opponents of slavery to resist abolition.  On the other hand, many of those people also voted for Lincoln, who, more or less, spouted lines like this to get elected.  Back to the first hand, the radical abolitionists were right in a deep way that justified the Civil War. On the other hand, the moderates’ and incrementalists’ caution was not unwarranted: the costs (to white America, especially) were terrible, and if voters had known what they were getting into, they might have not chosen to vote for Lincoln.

Two famous, uncompromising radicals of the Civil Rights Era.

Two famous, uncompromising radicals of the Civil Rights Era. If you don’t think MLK was a radical, please read his works in full, or just start with John Johnson’s post here.

I’m sure about this much: we need radicals.  As the cliché goes, we should never doubt that a small group of radicals can change the world, “indeed, it is the only thing that ever has.”  Behind every accommodationist, incrementalist reformer like LBJ or FDR were uncompromising radicals pushing them.  These radicals widened the Overton Window to give them political cover, and made life miserable for them until they used that cover to do “the right thing”.   As FDR supposedly told labor leaders upon taking office: “I agree with you, I want to do it, now make me do it.”

This dynamic is not always as explicit or made with the mutual understanding as the FDR quote suggests. Today, hearing radicals and sympathetic moderates discuss things is a fascinating exercise in talking past each other (see, for instance, this game attempt by a befuddled Washington reporter to understand a supporter of Black Lives Matter here, or Hillary Clinton’s discussion with activists here).

So I’m still ambivalent about this. I think I buy Fischer and McWilliams’s apologia for a position of compromise and moderation, even when one agrees with a radical position.  And I stand by my earlier point about the perils of unwarranted certitude and a caution to consider the expectation value of harm you are causing (a tiny chance of error times a huge amount of evil can still be very evil).

But then I find myself haunted by the analogy to the abolitionists: is this all just an intellectual veneer around moral cowardice?

I don’t have an answer.  I’m still mulling it over.


What is the h-index of SETI?

The SETI literature, like the literature in many fields, is very heterogeneous.  Some papers are classic, seminal, and/or revelatory.  Others are just embarrassing.  And of course lots are in between.

It’s hard to do a comparison with other fields, but my general impression of it was that it is very small (very few papers, even fewer refereed papers, and very very few authors), rather cloistered (most of the citations to SETI papers are by other SETI papers), stale (most of the important papers are from decades ago) and outside of mainstream astrophysics (many of the most cited papers are in non-astrophysics journals or unrefereed conference proceedings).

To see if these impressions are correct, I tried to compile a SETI bibliography, and see what the most cited papers are.  But it’s surprisingly difficult to get ADS to return a good list of SETI papers.  Searching for (SETI or “extraterrestrial intelligence”) (the latter is an AAS keyword) yields fewer papers than searching on those two separately and merging the results, which feels like a bug in ADS.

Anyway, merging those two lists, I get 1408 abstracts.  Ever. The earliest is Freeman Dyson’s 1960 paper, but that’s wrong because the 1959 Cocconi & Morrison paper is seminal (it established radio SETI as a real possibility). Clearly that first approach is missing important papers.

So I went through and added to my list all of the papers that cite Dyson’s, Cocconi’s, and Kardashev’s 1964 papers.  I looked at the most cited of the SETI papers among those, and added in papers that reference them.  I then hunted through the references in other highly cited SETI papers and picked out good ones.

Even towards the end of this exercise I was regularly adding new, clearly relevant papers.  A comprehensive bibliography will be difficult to generate (if you have one that is ADS compatible, let me know!)

Interestingly, the most cited paper on my initial list is “The merging history of the Milky Way” by Unavane, Wyse, and Gilmore, but that’s clearly a mistake — it does have “extraterrestrial intelligence” as a keyword, but there’s nothing in the paper about that as far as I can tell.  I guess the keyword was set by mistake.  I threw that one out.  I similarly tossed out several other highly cited papers that weren’t really SETI papers.

So, I think I’ve caught the bulk of things, though we’ll be both incomplete and contaminated with non-SETI papers.  Let’s see what we have:


(Note that this list is totally uncurated for papers with fewer than 20 citations, so don’t give the total number of abstracts on that list any credence.  If you have an ADS library with SETI papers in it, send me a link and I’ll toss them in with mine.)

Sorting by citations, we can see which papers really matter (assuming I haven’t missed any big ones).   


Jill Tarter

The first one: Jill Tarter’s prescient and seminal paper reappraising M dwarfs for their habitability, with 134 citations.  The logic in this paper is a driving force behind HPF here at Penn State, so, thank you Jill! (134 citations).

Next up: Cocconi & Morrison (1959) : the birth of radio SETI. (108)

Third, Cordes & McLaughlin, on fast radio transients (88 citations).

Cordes also holds 7th for the effects of interstellar scattering on signal propagation.  58 citations.

5th is Charlie Lineweaver’s paper on the Galactic Habitable Zone, which is about complex life, not necessarily ETIs (85 citations)

6th is Rare Earth, by Ward and Brownlee.  Again, mostly astrobiology, not SETI.  Only 73 citations, despite the splash it caused.

Number 7 is Harwit on photon orbital angular momentum in astronomy.  This paper mentions SETI, but all of the citations are about photon polarization.(63)

8th is Jill’s review article on SETI from 2001.  Thanks again Jill! (55)

9th is Kardashev’s classic paper on the types of civilizations. (54)

10th is Meléndez’s paper on the solar twin HIP 56948. (52) He also has number 20 for HD 98618 (39), and 21 for HIP 56948 again (37).  These papers all mention SETI in passing, but are really about solar twins, and most of the citations come from that.

11th is Hart’s notorious “we are alone” paper.  A common foil for SETI papers, as evidenced by its 52 citations.

12th is Gott’s controversial paper on the Copernican principle.  A fun paper, but I think most statisticians have major issues with his probability theory (as do I).

13th is is Turnbull and Tarter’s target selection for SETI paper.  50 citations.


Freeman Dyson

14th is Brin’s paper on “The Great Silence”, reviewing the Fermi Paradox.  A very good paper, as it must be to get 49 citations reviewing well-worn and contentious territory.

15th is Dyson’s 1960 paper describing his namesake spheres.  47 citations.

16th is Tipler’s “Debbie Downer” paper “Extraterrestrial intelligent beings do not exist” reiterating many of Hart’s arguments, but with von Neumann machines.  Another common foil paper.

17th is Jack Welch’s paper on the Allen telescope Array (43)

18th is a review by Horneck on exobiology.

19th is “Galileon hairs of Dyson spheres, Vainshtein’s coiffure and hirsute bubbles”.  I can’t make heads or tails of this one — something about alternative theories of gravity?  Not sure what this one is about.  But 41 citations.

22nd is Chyba & Hand’s review article on astrobiology.  It mentions ETIs in passing.  34 citations.sagan.jpg

23rd is Newman & Sagan’s paper modeling the spread of intelligence in the galaxy as a diffusion problem.  The limit they calculate for very long timescales is wrong by orders of magnitude (see Section 5.1 of our paper), but the approach is seminal and not too bad for fast ships. 32 citations.

24th is Schwartz & Townes on using “optical masers” for SETI — in 1961 (Nature, 32 citations).  Now a big part of SETI, funded to the tune of $1M/yr.

25th is a paper by Frisch on “G-star astropauses”.  Not sure what this is about, but he takes a genuine SETI angle (something about interstellar pressure affecting the development of life).

26th is Ball 1973: “The Zoo Hypothesis”.  We are only apparently alone because we’re in a zoo.  Sort of like the prime directive.  Influential paper.  31 citations.

27th is Bracewell’s 1960 paper in Nature about communicating with ET.  I’m not familiar with it.

28 marks the first appearance of JBIS, a common destination for SETI papers.  It’s Jim Annis’s “Astrobiological phase transition” argument. I like this paper a lot, because it provides a plausible reason that other civilizations might not be much older than we are (though I don’t buy the argument myself).  I’m happy to have contributed a couple of his 28 citations.

29 is a book by Barry Parker on alien life and SETI that I’m not familiar with. 28 citations.

So number of citations and number of papers have crossed.  The h index of SETI is 28, in what I think is a pretty generous definition of “SETI” (Jill’s paper at #1, Rare Earth, and Charlie Lineweaver’s Galactic Habitable Zone paper are really about complex life in general, not ETIs.).  I may have missed important papers; if you know of any I should have included, please let me know.

So my sense is that SETI is a small field is, not surprisingly, validated. An h index of 28 is good for a scientist, but minuscule for a field of astronomy.  Even if I’m missing a few important papers, I don’t think I’m off by enough to change this conclusion.

So what’s next to increase SETI’s h index?

Cordes, Lazio, and Sagan on scintillation in SETI signals has 27 citations, so needs only 2 more.  Horowitz & Sagan’s description of the META radio survey also needs two more.  I’ll have to read about it so I can cite it.

Mario Livio has an ApJ paper about the number and age of ETIs in the Milky Way.  I should read it.

Sagan has a 1973 book with 23 citations on communication with ETIs, “CETI”.

Andrew Howard

Andrew Howard

And Andrew Howard’s PhD thesis paper on nanosecond optical SETI has 22 citations.

My own papers have 9, 8, and 3 citations.  Hopefully they’ll be useful enough to eventually improve the field’s h index.

So, what has this exercise taught me?  Consider papers with more than 20 citations:

Only two in the last 5 years: the hirsute bubbles paper, and the discovery of HIP 56948.

In the decade before that (2001-2010) there were 13 well-cited papers, of which 3 are about solar twins or M dwarfs, and two are SETI review articles.

In the decade before that there are 10.  There are 4 papers from the 80’s, 5 from the 70’s, and 4 from the 60’s.

The four oldest papers on this list were all published in either Nature or Science within a 3 year span.

So things are pretty reasonably spread out, with the more recent decades having more well-cited papers.  This is likely because they present results useful in other contexts, while the older papers are strictly focused on SETI, and so don’t get referenced outside the field.

So my impression of SETI being stale, of having had a heydey in the 60’s and 70’s that has died out, wasn’t really right. SETI is stronger than ever.

The other aspects will take a more detailed analysis to work out.

Scientifically Accurate Twinkle Twinkle Little Star

Reposting this from its original home, with minor edits:

Singing to our kids: Twinkle Twinkle Little Star…how I wonder what you..

HEY, what a second, we’re astronomers! None if this “how I wonder” stuff about facts established 100 years ago for OUR little prodigy.

Inspired by a Girl Scout poster we saw in Oakland with insipid, inaccurate doggerel, Julia Kregenow and I wanted a better version.  Here is Julia’s updated version (with some contributions from me). We last updated these back in 2012 (long before that Weinersmith guy put his out…)

Scientifically Accurate Twinkle Twinkle Little Star

Twinkle Twinkle Little Star
I know exactly what you are

Opaque ball of hot dense gas
Million times our planet’s mass
Looking small because you’re far
I know exactly what you are

Fusing atoms in your core
Hydrogen, helium, carbon and more [note the double-time (“hy-dro-gen- -he-li-um- -car-bon-and – more”)]
With such power you shine far
Twinkle twinkle little star

Classed by their spectroscopy
Oh, Be A Fine Girl Kiss Me
Bright when close and faint when far
I know exactly what you are

Smallest ones burn cool and slow
Still too hot to visit, though
Red stars dominate by far
Twinkle twinkle little star

Largest ones are hot and blue
Supernova when they’re through
Then black hole or neutron star
I know exactly what you are

Our Sun’s average as stars go
Formed 5 billion years ago
Halfway through its life so far
Twinkle twinkle little star

Sunspots look dark but they’re bright
Slightly cooler so less light
Temporary surface scar
I know exactly what you are

Swelling up before it’s dead
Cooling off and growing red
Then its end is not so far
Twinkle twinkle giant star

Outer layers float away
Planetary Nebulae2
Wispy gas is gossamer
I know exactly what you were

Interstellar medium
Recycled ad nauseam
Gas and dust are spread afar
Twinkle twinkle little star

Forming from collapsing clouds
Cold and dusty gas enshrouds
Spinning, heating protostar
I know exactly what you are

Two stars make a binary
Or a triple if there’s three
Some are solo just like ours
Twinkle twinkle little stars

Often forming multiply3
Clusters bound by gravity
Open type or globular4
I know exactly what you are

Two hundred billion stars all stay
Bound up in the Milky Way
Dusty spiral with a bar
Twinkle twinkle little star

Stars have planets orbiting
Rocky or gassy, moons or rings
Earth’s unique with life so far
I know exactly what you are.

Lyrics copyright Julia Kregenow and Jason Wright, 2011, 2012. If you reproduce these lyrics in whole or in part, please include the copyright and credit this original source.

1[Say the elements in double time so it scans]
4[“GLAH-byoo-LAHR” — sorry!]