On the direct imaging of Exoplanets Sebastian Perez Stellar Coffee - December 2008
Outline Exoplanets overview Direct Imaging: - Observing strategy - Angular differential imaging HR8799 Fomalhaut beta Pictoris Conclusions
Exoplanets overview 329 planets detected so far! 11 directly imaged: 2M1207 b * AB Pic b * GQ Lupi b * SCR 1845 b * UScoCTIO 108 b (Bejar et al. 01/2008) CT Cha b * (Schmidt et al. 09/2008) HR 8799 b,c,d (Marois et al. 16/11/2008) Fomalhaut b (Kalas et al. 19/11/2008) beta Pic b (Lagrange et al. 21/11/2008) (*) observed with NACO on Yepun, VLT 3
Detection Radial velocity, transits, microlensing: - limited to small/moderate planet-star separations Direct imaging: - Jupiter-like planets with wide orbits - key step towards imaging Earth-like planets What do we look at? Gravitational potential energy turned into heat (infra-red) Problems: - we need really good resolution (AO) - huge luminosity contrast between planet and hot star L visible = 10 9 L L infrared = 10 4 L due to reduced stellar flux and thermal radiation from gravitational contraction of the planet
Credit: ESO A3V A5V A5V
Why A-type stars? Can support heavier and larger discs. May form more massive planets at wider separations: perfect for direct imaging! Young A-star discs can have many times the minimum mass solar nebula (0.01 solar mass, estimated by Weindenschilling 1977) Extreme example: Gomez s Hamburger * disc ~ 0.1 solar mass radius ~ 3000 au (*) discovered by Arturo Gomez at CTIO in 1985 6
Imaging technique Take a mix of many unsaturated images (0.1s) and saturated ones (~30s). Once the star s emission is effectively cancelled, the next strong thermal emission will be thermal emission from zodiacal dust (Brian May 2007). Problem: AO is limited by quasi-static speckle artefacts. Solution: Angular Differential Imaging! (Marois et al. 2006) (*) discovered by Arturo Gomez at CTIO in 1985
HR 8799 Marois et al. 2008 arxiv:0811.2606v1 A5V star, about 40 pc away. Keck (2004, 2008) ADI + Gemini (2007) revealed: 3 planets! M b 7 M Jupiter M c 10 M Jupiter M d 10 M Jupiter JHK bands - NIRC2/Keck 8
Marois et al. 2008 arxiv:0811.2606v1
Fomalhaut Kalas et al. 2008 arxiv:0811.1994v2 A3V star, at 7.7 pc away, 100-300 Ma old. Belt was detected in 2004. Truncated in the inner edge, centred 15 au away from the star. A planet would explain this feature! Planet detected with HST by analysing 2004-2008 data (R-band) located at 120 au from the star M planet 3M J to avoid disruption of the belt. R band - WFPC2/HST
R band - ACS/HST
Beta Pictoris Lagrange et al. 2008 arxiv:0811.3583l A6V star at 20 pc away. Prototype of young (20 Ma) planetary systems (Smith and Terrile 1984). Inner region (<50 au) of debris disc is odd: - void of material - tilted inner disc - UV spectra shows loads of carbon a Jupiter size planet at > 6 au would explain the situation.. Colliding planetesimals with giant planet on a slightly inclined orbit! J-band/ESO 3.6-m Beuzit et al. (1997) T-ReCS/Gemini - Telesco et al. (2005)
Dynamical simulations show that the gravitational perturbation of a giant planet at ~10 au can account for the evaporated bodies.
field of view ~ 13 x 13 arcsec 3.6 microns/naco Lagrange et al. (2008)
Conclusions Direct imaging of Jupiter-like planets is a key step towards imaging Earth-like planets. We live in a fortunate time when space exploration could realise the dreams of past generations, of finding Earth-like planets and life independent of the Earth. - Woolf and Angel (1998) ARA&A
Life on Earth Spectroscopic evidence nco 2 + nh 2 O + 2n photons > (H 2 CO) n + no 2 We need life to sustain oxygen (Woolf & Angel 1998). Oxygen is in equilibrium with ozone (absorption at 9.7 microns). Second indicator of life is methane: produced by decomposition of organic matter
Life on Earth Spectroscopic evidence nco 2 + nh 2 O + 2n photons > (H 2 CO) n + no 2 We need life to sustain oxygen (Woolf & Angel 1998). Oxygen is in equilibrium with ozone (absorption at 9.7 microns). Second indicator of life is methane: produced by decomposition of organic matter