## Thursday, January 31, 2013

### Type Ia single degenerate survivors must be overluminous

I noticed a paper on the arXiv today with exactly this title (well, except that I removed the superfluous capitalisation of words), that is due to be published in the Astrophysical Journal. The abstract of the paper says:
In the single-degenerate (SD) channel of a Type Ia supernovae (SN Ia) explosion, a main-sequence (MS) donor star survives the explosion but it is stripped of mass and shock heated. An essentially unavoidable consequence of mass loss during the explosion is that the companion must have an overextended envelope after the explosion. While this has been noted previously, it has not been strongly emphasized as an inevitable consequence. We calculate the future evolution of the companion by injecting $2$-$6\times10^{47}$ ergs into the stellar evolution model of a $1\,M_\odot$ donor star based on the post-explosion progenitors seen in simulations. We find that, due to the Kelvin-Helmholtz collapse of the envelope, the companion must become significantly more luminous ($10$-$10^3\, L_\odot$) for a long period of time ($10^3$-$10^4$ years). The lack of such a luminous "leftover" star in the LMC supernova remnant SNR 0609-67.5 provides another piece of evidence against the SD scenario. We also show that none of the stars proposed as the survivors of the Tycho supernova, including Tycho G, could plausibly be the donor star. Additionally, luminous donors closer than $\sim10$ Mpc should be observable with the Hubble Space Telescope starting $\sim2$ years post-peak. Such systems include SN 1937C, SN 1972E, SN 1986G, and SN 2011fe. Thus, the SD channel is already ruled out for at least two nearby SNe Ia and can be easily tested for a number of additional ones. We also discuss similar implications for the companions of core-collapse SNe.
Now, technical scientific papers are full of jargon and maybe the meaning of that paragraph isn't immediately clear to everyone (there's an accompanying Youtube video purporting to explain the content of the paper, but I didn't think it quite achieved that aim!). But I think this result is really quite interesting and probably important in a broader cosmological sense.

## Thursday, January 17, 2013

### New directions in a new year

Although we are already more than half-way through January, I'd like to say happy 2013 to all readers of this blog! Better late than never.

It won't have escaped the attention of regular visitors that the rate of posting new items here has significantly declined over the last few months, as exemplified by the belated new year's greetings. There is a good reason for this. It isn't that I haven't thought of any things to write about; on the contrary, I have had lots of ideas, but not enough time to write them up. Instead the hiatus has primarily been because I have been applying for a new postdoctoral job starting this coming October, and writing tailored job applications is an incredibly time-consuming process — much the same as in non-academic jobs, I suppose, though with the added annoyance that all the time spent writing in detail about what wonderful research you would do if hired is time not spent actually doing any research. Between those two competing claims for my attention and all the rest of real life, there was no time at all left for blogging.

However, the result of all this time spent applying is that I have now been offered, and accepted, a 2-year postdoc position to start in October at the University of Helsinki, in the group of Kari Enqvist. I have to say, I am very pleased about this, and not only because it means I needn't spend any further time on applications! In fact from a previous visit there, I know that the atmosphere in the Helsinki research group is one that I will enjoy very much.

I understand that to people outside academic physics circles, applying in about November (in fact some deadlines this year were even slightly earlier) for a job due to start fully 11 months later might seem a little odd. But that is the way the system works, and it probably isn't the only odd thing about physicists anyway. On the bright side though, it does mean that — as in this case — the question of where in the world one is moving to can all be settled by January, leaving plenty of time to plan the move, both in academic and purely logistical terms.

Anyway, now that this business is over, you can expect to see a slightly improved rate of posting here.