MPA SN meeting, day 4

Again, I’m not going to cover every talk so please don’t get too upset if you’re reading this and your talk isn’t here. (I consider this to be an unlikely event since most of the people explicitly following this blog aren’t astronomers.)


  • Jeff Silverman talked about studies of the late-time optical spectra of SNe Ia from the Berkeley SN Ia follow-up program. These are mostly, if not entirely, spectra in their nebular phase, and the goal is to measure the widths and radial velocity offsets of lines from ionized iron. Doing so is supposed to help us get a better idea if these supernovae are spherically symmetric (so that no net velocity offset is expected) or asymmetric (so that you get an offset and it correlates with other observables in ways your favorite asymmetry models predict). The results were vaguely suggestive but didn’t look too clean; the error bars on the velocities were so wide you could have put them on either side of the plot without much penalty. Jeff also talked for about 30 seconds about his studies of 2002ic-like SNe Ia (see below).
  • Dan Milisavljevic (now at CfA) gave a great talk about his observational studies of SNe IIb (a transition case between SNe II and SNe Ib with weak but not absent hydrogen), in which he showed that the discovery rate is almost certainly affected by classification bias: the spectrum changes, and it can change quickly, over about a week, instead of the weeks to months it has been known to take other spectroscopically similar SNe. Solution: more, and earlier, spectroscopic follow-up.
  • Dan’s colleague and previous supervisor Rob Fesen reported on their work together on studying the Cassiopeia A core-collapse supernova remnant. They plastered the entire remnant with optical long-slit spectra, I’m guessing because they didn’t have an IFU big enough to cover the whole remnant efficiently, and reconstructed its entire 3-D geometry. This was utterly fascinating and much more detailed than Dan’s quick report on that remnant at last year’s meeting in Sydney, which with some dismay I note I never covered here. Jets of high-velocity iron punching through the outer shock, and inner bubbles of hot gas within the shock’s confines… but one of the best things about this talk was Rob’s excitement in describing what they’d found (“like a kid at Christmas”, some people said at coffee).
  • Carlos Badenes gave a great review of X-ray observations of SN remnants, which was necessarily quick but has got me interested in the details. For one thing, he says that you can reconstruct the 56Ni mass of a SN Ia just from the X-ray emission in the remnant, and that on this basis both Kepler’s remnant and SNR 0509-67.5 (the one Schaefer & Pagnotta 2012 think is a double-degenerate merger) are bright, 1991T-like SNe with ~1 solar mass of nickel. Which of course fits right in with my whole super-Chandra thing.


I had some good discussions with Roger Chevalier, my old first-year astronomy professor at UVA, about 2002ic-like SNe, i.e., what look like thermonuclear SNe going off in a dense medium (remember that SN Ia progenitors are relatively old stars and are supposed to have cleaned out their environment long prior to the explosion). As far as either of us seem to know the jury isn’t out on these guys yet. But the recent Dilday et al. 2012 result claims that PTF11kx, an example of this kind of event, is a single-degenerate explosion in a symbiotic system (loosely, a white dwarf plus a red giant). Roger seemed to think the glow of the shocked gas in this event was too bright for a symbiotic system, but that’s about the only thing he found conclusive.

Several talks on Monday alluded to a new mystery result from Jeff Silverman about the frequency of 2002ic-like SNe Ia. When I pressed him about it at coffee, Jeff said he had found several more of these rare events in the PTF search, but he claims that the late-time spectra don’t tell you much of anything useful because they stop evolving after a while. I’m not sure that in itself doesn’t tell you anything. However, it is discouraging to think that the shock interaction of the SN ejecta with the medium produces so much light that it drowns out the SN nebular spectrum, which would be our best shot at identifying whether they’re core-collapse events or truly thermonuclear.

Later in the evening there was a collaboration dinner for those members of PESSTO who happened to be in Garching for this meeting (the formal PESSTO collaboration meeting is next week). I spent most of the time at the table with Stephen Smartt, Stefan Taubenberger and a few others talking about PESSTO operations and upcoming proposals for ESO telescope time to support them.


About Richard

I'm an American scientist who is building a new life in Australia. This space will contain words about science and math, but also philosophy, policy, literature, my travels, occasional rants, all sorts of things I find strange and awesome. The views expressed in this blog do not necessarily reflect the opinions of my employer at the time (currently University of Sydney), though personally, I think they should.
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