We can tell what stars are made of by the colors missing from their spectra, but that’s not really true for hot, rapidly rotating stars. These stars lack convective envelopes, so they lack magnetic dynamos, so they do not spin down as they age. As a result of their rapid rotation, the Doppler shift blurs out their lines and its hard to get a precise measurement of their abundances (except hydrogen, whose lines are so deep you can’t miss them, even blurred out).
But one astronomer’s trash is another’s treasure. These rapidly rotating stars make great sources of light for calibrating spectrographs because you can be sure that any spectral features you *do* see are due to your instrument, not the star. And these stars can be very bright, so it’s a quick test.
The problem is that not all hot stars rotate quickly enough to be “good” calibrators. For instance, here’s what a small portion of a rapid rotator looks like:
This star’s spectrum is flat (or slightly sloped) in this small region of the blue. The overall mountain shape is the response of the spectrograph, which this star lets you model. The “fuzz” is photon noise—by chance some channels get more photons than others. The spike in the middle is a “cosmic ray” event—a high energy particle from somewhere in the dome struck the detector and caused a spike. The only thing here that’s due to the star are some barely perceptible wiggles.
Here’s a “bad” calibrator star, that is not spinning fast enough to be a “good” calibrator:
Not smooth at all! Those “bites” taken out are due to elements in the star’s atmosphere absorbing certain shades of blue light, and the bowl shape is due to the way different parts of the stellar surface are moving towards and away from us as the star rotates.
So which stars are “good” and which are “bad” for calibrating high resolution spectrographs Published values of their rotation speeds turn out to be an unreliable guide for this, so observers over the years make lists of “good” hot star calibrators. For instance, when I need a “good” hot star, I ask Howard Isaacson at Berkeley, who has a list carefully compiled by Kelsey Clubb. At Berkeley, Kelsey Club went through the California Planet Survey’s library of hot star spectra and separated the wheat from the chaff, which is really useful!
This sort of list isn’t usually publishable—it’s not the sort of scientific advance or discovery that usually warrants a peer-reviewed paper. But it is the sort of thing scientists should share and that Kelsey should get credit for.
Now, thanks to the new AAS journal “Research Notes of the American Astronomical Society”, we have a good way to share the list. This new journal is not peer reviewed, but it is free, curated, and has a science editor who accepts papers. They can only be 1,000 words, have one figure or table, and they do not have to be new or novel or anything—just interesting.
But why not just put it to the arXiv, and skip the 1,000 word limit thing? Well, Geoff Bower asked the same thing on the Twitter, and I came up with two big reasons: RNAAS will curate machine-readable tables, which is great, and as a AAS journal, if your result is (unlike this one) newsworthy, it might get picked up by AAS Nova. Editor Chris Lintott points out a third:
Permanent DoI too, which helps with long term archiving.
— chrislintott (@chrislintott) March 23, 2018
Anyway, as a journal that emphasizes utility and curates tables, it is the perfect place for Kelsey’s list, so that’s where we published it. You can find it here.
I was actually worried this would happen. When RNAAS came out, and then when Overleaf linked directly to it for submissions, I got worried I’d like it too much:
This is cool:https://t.co/mUKNqhvSXv
If I ever find some free time, this combination of Overleaf and RNASS might prove to be pretty potent.
— Jason Wright (@Astro_Wright) November 10, 2017
and (despite my misspelling of RNAAS) I was right. I’ve now submitted or supervised five of these. Here are the others:
I may have a problem…