PESSTO meeting Thursday

(NB: I’m now some time behind and am sleepily waiting for the first of three flights that will eventually take me back to Australia. I do have a buffer of posts which I will continue to put up; while not exactly current, I wouldn’t say they’re stale.)

I arrived first thing in the morning and met Nancy Elias-Rosa, our host and meeting organizer in Barcelona, and Andreas Pastorello, an Italian core-collapse supernova expert from Padova. The latter seemed to want sneak previews of everything I was going to talk about later.


  • First up was Stefano Valenti, a postdoc from the Padova group about to take a new position at LCOGT in Santa Barbara. He’s responsible for the spectroscopic reduction pipeline the PESSTO observers use, consisting mostly of IRAF tasks glued together with Python, and walked us through how to use it. It seems pretty well put together, but I wasn’t able to download and install the routines due to access permission issues from the website on which the code download is hosted. (This was fixed later.) I’ll need to know how this works later if I’m going to help reduce data during observing shifts, something I really ought to be helping out with.
  • Stephen Smartt, PESSTO’s ESO PI, gave an overview of lessons learned during operations so far. First, La Silla observatory offers little to no on-site support and the observers are expected to get it right themselves, so standard procedures internal to the collaboration (enshrined in a user manual) will prove essential to regular operations. Second, we need to do better at selecting good follow-up targets — i.e., telling the weirdos from prosaic-looking things. Finally, in a similar vein, we should try to minimize time used for spectroscopic screening and instead prioritize follow-up.
  • Pastorello touched on a similar theme: PESSTO science has been carved up under the direction of several science PIs, who say what observations they want, but communication between PIs and observers needs to be improved so that the most interesting possible data are taken. The PESSTO “marshal”, a software suite which tracks candidates through a classification and observation workflow, should help with this. We also need to coordinate with other spectroscopic observing programs, preferably via standard things like VOevents or RSS feeds which the marshal can read.
  • Dave Young from Queen’s University Belfast (Smartt’s group) gave a demo of the marshal. It’s visually quite slick and reminds me of Gmail. There are various queues or tags which you can give a transient to get different people to look at it: an “inbox” of unclassified new things, an “archive” of things put aside, and other states related to follow-up, along with currently observed magnitudes, spectroscopic types, and free text comments from scientists with their opinions on the object. Good work!
  • Massimo Turatto talked about the Asiago Supernova Program, an ongoing follow-up program which has been around for a while. Various funding cuts and effective hiring freezes are having a big impact on their program, so they’re responding as best they can, enabling remote observing and cutting on-site support staff. They have about 45 nights a year, and provided first classification for over 100 supernovae last year, although their temporal coverage can be uneven and it can thus take them a while to classify a new thing. Turatto also mentioned a web thing called GELATO which you can use to classify supernovae.
  • I gave the standard SkyMapper progress report: still waiting for the vibrations to be fixed, but after that we should be good to go. There were few questions (not much to question me on, really), except whether the candidates would be made public.


After a beer with mostly Belfast people, there was a collaboration dinner at a Catalan restaurant in Ciutat Vella called Can Culleretes (“since 1796”). They catered to my vegetarian tastes especially, and the house wine was dry but drinkable.

I sat at the end of the table near Seppo Mattila, a Finn interested in interactions of supernovae (including SNe Ia) with their environments. While the first third or so of our conversation was about what working for Brian was like and whether his wines were any good, the remainder was about interacting supernovae in a general sense. He brought my attention to a new class of interacting supernovae, “SNe Ibn”. These are what they sound like: supernovae which show no sign of hydrogen, but have narrow emission lines from helium in their spectra.

Normally narrow lines come from circumstellar material beyond the shock formed by the blast wave of the supernova ejecta; that blast wave emits strongly in X-rays, which ionize the surrounding medium. The lines from the shock themselves are broader, and their width reflects the speed at which the shock is expanding. So these are supernovae going off in a dense medium which is almost entirely hydrogen-free. The progenitors must be fairly evolved, perhaps AGB stars, which got rid of their hydrogen long ago but sloughed off large amounts of helium in the years just before they exploded. It goes to show that lack of hydrogen lines don’t necessarily mean the supernova isn’t interacting with its environment. (Sometimes you can detect non-thermal X-ray or radio emission coming directly from the shock, but the emission is much weaker than the optical emission and the supernova has to be very nearby to have much hope of an upper limit telling you anything.)

I’m still wondering what impact this might have on my picture for SN 2007if and how much of its luminosity could actually come from 56Ni. If you can have strong interactions without hydrogen, why not helium as well? — why not a pure carbon-oxygen interaction, such as those predicted by some models under the double-degenerate progenitor scenario for SNe Ia, which freezes out sometime after maximum light? Or could some of the energy be generated by a shock interaction that freezes out in the first few hours after explosion, then trapped by the dense ejecta until maximum light?

Mattila and Valenti are, it turns out, still postdocs, though Mattila’s position has a longer term like mine does (and research start-up funds, like a mid-career fellowship). It’s an eye-opener to come face to face with these people whose names you keep seeing on papers — I usually assume they’re faculty if I don’t already know otherwise, so it’s a sober reminder to see how much really good work is being done by young people living on soft money.


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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