This week we had some distinguished visitors from Germany: Wolfgang Hillebrandt (Max Planck Institut für Astrophysik) and Fritz Roepke and Michael Fink (Würzburg). They’re experts in the theory of supernova explosions — 3-D hydrodynamics and radiation transfer. I read papers like theirs to get a sense of what’s possible in current models and what kinds of assumptions people make, and I talk to them to get a sense of how far-fetched these assumptions really are.
We gathered in a conference room and conducted a little “mini-meeting” with short (10-15 minute) presentations and plenty of time for discussion. I presented notes on the status of the SkyMapper supernova search (“almost there!”), while my RSAA colleagues Mike Childress and Brad Tucker talked about their forays into the study of type Ia supernova host galaxies and environments. Fang Yuan and Chiaki Kobayashi talked more about the role of supernovae in the chemical evolution of galaxies and the implications of some of Chiaki’s models for the class of “calcium-rich” transients which Fang has been studying. (They’re called that because their nebular spectra, showing the innermost core of supernova ejecta, show lots of calcium but not much iron or oxygen. The photospheric spectra of these events, taken while they are still near their brightest point, have a variety of appearances, and it’s not currently known whether they are thermonuclear supernovae, core-collapse supernovae, or something else entirely.)
There was some lively exchange regarding the question of how to reliably measure the mass ejected in each of a sample of type Ia supernova explosions. (Check here for a quick review of the subject. While the historically-favored “single-degenerate” model requires a white dwarf to be near the Chandrasekhar limit when it explodes, models with exploding sub-Chandrasekhar or super-Chandrasekhar white dwarfs are getting more attention these days.) The technique I’ve been using in my recent work involves a careful accounting of all radiation emitted from the ultraviolet through the near infrared (wavelengths between 300 nm and 2200 nm) during a critical period of the SN’s evolution (between 60 and 120 days after explosion). Wolfgang showed some attempts by his group to reconstruct the masses of simulated supernova explosions using a similar technique, with very mixed results. While it is good to be aware of the limitations of one’s measurements, I think my own fitting procedure is less prone to the kind of difficulties Wolfgang’s group faced, so I agreed to try and fit some of their models to see how close I could get to the answers in the back of the book.
(In tangentially related news, “That Paper” on super-Chandrasekhar-mass supernovae has been accepted! You can find a pre-print here.)
While the formal mini-meeting took place on Wednesday, Wolfgang stayed through Thursday night (including pizza at Brian’s), Michael gave a talk on explosion models of rapidly rotating white dwarfs on Friday, and Fritz and Michael both came to RSAA drinks on Friday, so there was plenty of time for ongoing discussion.