Dusty, young and chaotic – the HR 8799 system with the new LBT AO system

Hi folks, for one week only I’ll be MCing astrojc while Emma is off wedding planning.

This week’s paper is on the HR 8799 system. Three planets were directly imaged around this young star in 2008 with a fourth, closer companion identified in 2010. The system also has a disk inside the orbit of the closest companion (planet e) and a more distant outer disk beyond the orbits of the planets. Spectroscopic observations indicate that the planets are cool, around the temperature of the transition between the L spectral class and the T spectral class. However there are indications of some non-equilibrium chemistry and thicker clouds than field L and T dwarfs (which are often higher mass brown dwarfs).

The paper in question is one of two studying HR 8799 with the new AO system on the LBT. It presents H band photometry of the system along with a companion paper containing 3.3 micron observations.  The papers indicate that the planets are indeed atmospherically strange, showing little methane absorption compared to field brown dwarfs of similar temperatures (the onset of methane in the spectrum is the signature of the L to T transition). As was previously known, planet b is significantly fainter and redder than most known L dwarfs. The paper also models the orbits of the planets indicating that the orbits are not stable on a timescale comparable to the age of the host star.

So what shall we talk about,

1) The LBT AO system and the two instruments used for this detection (PISCES and LBTI)

2) The strange atmospheric chemistry of these objects

3) The dynamics of the system. I’m no expert on this part, what does it mean for formation models?

So come along everyone for #astrojc at 8pm BST on Thursday