I’ve decided to take it relatively easy this week, and spend some time just trying to organize my efforts and dig myself out from underneath the enormous pile of papers and projects in various stages of completion. It can’t be a good sign when Google Chrome has 40 threads running to keep track of all your tabs. The weather remains cold but sunny, it’s going to be a good week.
We had our weekly SN Tea today, a supernova-oriented journal club which I chair, with abstracts of interesting papers we’ve read. There were quite a few this week, about core-collapse supernovae about which I’m still learning more than I care to admit. I read and presented this awesome paper from Tanaka et al., about probing the 3-D structure of core-collapse SNe using spectropolarimetry. That’s kind of a mouthful to say, but the authors explain it really well and I hope to say more about this paper in a little bit. Until then, interested nerds please click.
Another paper presented was this one by Dessart et al., with the vague and vaguely pretentious title “On the nature of supernovae Ib and Ic.” These are the explosions of evolved stars, like the white dwarf progenitors of SNe Ia, but which haven’t collapsed to a fully electron degenerate core. Since SNe Ib have helium emission lines and SNe Ic don’t, you might think it’s because SN Ic progenitors have blown all their helium off into space and are therefore older, more highly evolved stars than SN Ib progenitors. But the authors argue using a relatively simple (1-D) simulation that the strength of the helium line we observe depends in part on the temperature and ionization of the helium gas, which in turn depends on how the material acting as a heat source (56Ni, just like in SNe Ia) is distributed through the ejecta. SNe Ib and Ic could therefore be stars of the same overall mass and age, but which explode differently, in such a way that SNe Ib have a lot of 56Ni in the outer layers where you find the helium, whereas for SNe Ic it’s all found near the center (though not at the center, chances are there’s a neutron star there). This too, I think, is kind of cool.
H-R Diagram Images and Other Educational Stuff
After tea, I ate a late lunch at my desk and started browsing astrobites, a digest of grad-student-level summaries of astronomy papers; it’s good to have some idea of what’s exciting outside one’s own field. The first astro-bite I ran into was this one, discussing the heavily star-oriented mystery of “blue stragglers”. I don’t really know a whole lot about stars, which I see as a bit of a liability when I study exploding stars! (Just remember that in the “particle physics with telescopes” approach to SN Ia Hubble diagram cosmology, you aren’t required to know much, if anything, about stars or even galaxies.) So I figured it would be good to learn.
I got to the point where the summary explained that blue stragglers are defined by their position on the Hertzsprung-Russell (H-R) diagram, one of the foundational infographics of astronomy which you learn about as an undergraduate. My knowledge of stars comprises one important factoid: the lifetime of stars gets shorter as the stars themselves become bluer and more luminous, i.e., as you go up and to the left on the H-R diagram. People talk about all kinds of things like convective vs. radiative envelopes, “third dredge-up”, AGB stars, horizontal branch stars, etc., which jargon I am still slowly imbibing from the rarefied atmosphere up here on Mt. Stromlo. After a moment’s reflection I realized I’d have trouble labeling the specific parts of the H-R diagram, other than the main sequence (where most normal stars hang out) and the red giant branch (where red giants live).
So I Googled for some good images I could post on my office wall and absorb osmotically. I found this sweet hi-res, full-color spread; there are many versions of this image floating around, which people have stolen, copied, or annotated, so it must be pretty famous among H-R aficionados. I don’t know the original source; maybe a popular textbook, or a back issue of Physics Today? It’s linked to this interesting and informative blog by a high-school astronomy teacher in Pennsylvania, which has all kinds of cool images, displays, interactive widgets and videos, so those readers keen on learning Astronomy 101 kinds of stuff can start there. For the observational categories, rather than the theoretical overview, I found this, which turned out to be from a previous astrobite.
It was somewhere around here that I thought some of these links might be at a level where my non-astronomer friends might be interested in them, and that I should post them here. So here they are. Enjoy!
One final note: while astrobites are mostly written by grad students, I’m becoming aware of an increasing number of blogs being written by young faculty-level astronomers of about my vintage — to share their knowledge not just with the general public, but other astronomers. The trend is discussed in this astrobetter post. One good example I found via this post and now enjoy reading each day through RSS feed is Hogg’s Research, by the eponymous galaxy expert and Bayesian inference stalwart David Hogg of NYU. (He’s also on Twitter, but not Facebook, as far as I can tell; Brian is on both.) I’ve always just used Facebook for strictly personal shares and kept work out of it, but increasingly scientists are using mainstream social media professionally. There’s so much going on that I feel like I need a definite strategy for using social media to keep the signal-to-noise high, but there must be advantages or else so many people wouldn’t be doing it these days.
Anyway, I’ve run into David at numerous conferences on survey astronomy at this point, and while I don’t know him too well personally, I can confidently say that he’s got a provocative and coherent vision for how astronomical data analysis should be done, and his group puts forth a steady stream of things that are just plain cool and produce interesting results. “Camp Hogg”‘s motto: “We Don’t Throw Away Data.” One good example is The Thresher, a piece of software which does so much more than co-add images (it’s a long story). There are plenty of examples on the blog; he doesn’t (usually) post the answers, he just tells you the kinds of directions he’s taking (and of course asks you to cite the blog if you use anything he puts there). He makes a point of posting something short about his research activities every day — usually no more than a paragraph.
Besides showing the arc of one’s work and branding it as one’s own in others’ awareness, it’s probably a good idea as a sort of running lab notebook to identify themes and branches for one’s own benefit. I might try something like this tagged as “Astronomy, Research” with additional “Technical” tags as necessary.