Day 3/5, Session 1: Transit Observations


Hi all and welcome to my, Nathan Mayne‘s, digest of the Wednesday morning session at the Exoclimes conference in Aspen. A session dominated by observers, which after a couple of days of complicated models presented by theorists, is rather refreshing…Or is it?

First David K. Sing reviews current observational techniques focussing on transit spectroscopy which includes:

  • The transmission spectrum (planetary radius against wavelength).
  • The emission spectrum (thermal emission from the planet).
  • The phase curve (flux changes caused by contrast in temperature between the day, facing the star, and night side of the planet)

These features can then be used to derive a surprisingly extensive list of parameters for the planet (given a few assumptions). For example, we can infer the composition of the planet, its mass and even whether a surface hot-spot on a tidally-locked hot Jupiter is offset by zonal winds! At this point I am feeling extremely positive-this looks easy!

Now, back to theory for a couple of talks. Vivian Parmentier presented a detailed analysis of the TiO (and VO) content of a tidally-locked hot Jupiter. Conclusion: it is present (but can be trapped on the night side), but unsurprisingly exhibits fluctuations (damn dynamics whatever happened to the steady state problems we all learnt in textbooks?).

In a change to the schedule our second theoretical interloper, Kevin Heng, discussed the problem of hot Jupiters having inflated radii. Kevin starts by defending his use of the “primitive equations” (a simplified form of the dynamical equations GCMs use to predict planetary climates). Kevin shows that the inflation of hot Jupiters is linked to their insolation, and advocates ohmic dissipation as a method of injecting energy deep in the hot Jupiter (see talk by Emily Rauscher).

The next talk is a very exciting talk by Kevin Stevenson on recent Spitzer observations of…SENSITIVE INFORMATION DELETED…..

After a quick break, it was time for a few shorter talks. The next five speakers, Jayne Birkby, Ian Crossfield, Catherine Huitson, Avi Mandell and Paul Anthony Wilson (he likes adding the Anthony), will all be speaking about transit or eclipse spectroscopy.

Jayne Birkby begins by plunging me into depression, it seems these observations are not so easy after all. Even The GTC at 10.4m requires the same level of coercion as I do to go and see a musical. She list a large number of systematics (too many for this post). However, the take home message is: it can be done.

Ian Crossfield continues the melancholy by addressing the carbon rich (infered from a weak H2O absorption) Wasp-12 b and presenting another set of devilishly difficult to perform observations. After having to chuck out half the observations (technical issues) and fighting valiantly for every photon the final message is: it can be done.

Catherine Huitson then explains that the flux across the Na spectral feature is an excellent probe of the upper atmosphere of hot Jupiters. For HD189′ examination of the wavelengths about the detected Na line show presence of a hot upper atmosphere or thermosphere as well as continuum scattering caused by an unknown particle, possibly M and M’s (my speculation). Adam Showman points out the assumptions in the model presented mean that ionised hydrogen is not accounted for and the temperatures are possibly overestimates, everyone nods in agreement as usually happens when Adam Showman makes a comment.

Paul Wilson then explains observations using a tunable filter (giving me nightmares about my old practical physics class by saying “Fabry-Perot”) and a long slit spectrograph on the GTC. He detects K in one (HAT-P1 b) but is defeated by observing conditions for TrES-2 b. Paul, like Catherine Huitson, also finds evidence of a hot thermosphere (Adam Showman mentions the previous discrepancy). Bottom line on performing such observations: it can be done.

Finally,  Avi Mandell explains the work required to obtain milli-mag photometry using HST WFC3 (I miss doing star formation observations where 0.1 mag is enough).

Conclusion: these observations can be done. They are just really hard!


About Author

I am a Postdoctoral researcher at the University of Exeter. I started working with Prof. Isabelle Baraffe in November 2011 on a project to model the atmospheres of Hot Jupiters using a Global Circulation Model (GCM). My research history includes a Masters level research project on Surface Plasmon Resonance, a PhD in Stellar ages and observational astrophysics and a postdoctoral project on radiative transfer in brown dwarf accretion discs. (More)