* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Wasp-17b: An Ultra-Low Density Planet in a Probable Retrograde
International Ultraviolet Explorer wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Circumstellar habitable zone wikipedia , lookup
Observational astronomy wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Spitzer Space Telescope wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Astrobiology wikipedia , lookup
Extraterrestrial life wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Nebular hypothesis wikipedia , lookup
Planets in astrology wikipedia , lookup
Discovery of Neptune wikipedia , lookup
Exoplanetology wikipedia , lookup
Planet Nine wikipedia , lookup
Satellite system (astronomy) wikipedia , lookup
Definition of planet wikipedia , lookup
Planets beyond Neptune wikipedia , lookup
IAU definition of planet wikipedia , lookup
Wasp-17b: An Ultra-Low Density Planet in a Probable Retrograde Orbit Anderson, D. R. et al., ApJ 709, 159-167 Thomas Kupfer March 29, 2011 Astrophysical Background Formation of planetary systems SuperWASP Observations Photometric observations Spectroscopic observations Results Discussion Outlook Formation of planetary systems ◮ Gravitational collapse of a molecular cloud ◮ Conservation of the angular momentum of the cloud ⇒ A disk is formed with the new star in the center ◮ In the disk planets can be formed http://astrobiology.nasa.gov/nai/ seminars/detail/117 Formation of planetary systems ◮ Gas giants supposed to be formed beyond the frost line ◮ Angular momentum of star and planets derive from parent molecular cloud ⇒ Close alignment between the stellar spin and the planetary orbit axis is expected SuperWASP (Wide Angle Search for Planets) ◮ Consists of two robotic observatories (SuperWASP North and South) ◮ Each observatory consists of eight 200mm lenses ◮ Aim is to observe the entire sky up to 15 Magnitude and look for transiting planets ◮ 26 proved planet detections http://wasp.astro.keele.ac.uk/ Photometric Observations ◮ WASP-17 was observed by WASP-South over two years (2006 – 2008) ⇒ Resulting in 15 509 usable photometric measurements ◮ They found a transit at 3.7 day periodicity ◮ Follow up observations with the EulerCAM over 6 hours Spectroscopic Observations http://www.isdc.unige.ch/result.cgi?061127 novaX ◮ 41 spectra were obtained using the CORALIE spectrograph mounted at the Euler Swiss Telescope ◮ 3 additional spectra with HARPS spectrograph Rossiter–McLaughlin effect http://www.naoj.org/Pressrelease/2010/12/20/index.html ◮ When the planet obscures a part of the star blue- or red-shifted light is ”obscured” ⇒ Leading to an ”annomalous” radial velocity ◮ The shape of the effect is sensitive to the path of the planet relative to the stars spin axis Rossiter–McLaughlin effect in WASP-17 ◮ Three RV measurements during the transits suggest large spin-orbit misalignment ◮ first and third in transit-point are discrepant by 6σ and 3.8σ for a prograde orbit ⇒ First planet found to be in a probable retrograde orbit Stellar and System Parameter ◮ From spectroscopy WASP-17 is a F6 star ◮ System Parameter were determined in a Markov-Chain Monte Carlo analysis ◮ Planet is in a 3.735 days orbit with a separation of ∼ 0.05 AU Parameters Extra constraints eccentricity λ (deg) MP (MJup ) RP (RJup ) ρP (ρJup ) Case 1 ... 0.129 −147 0.490 1.74 0.092 Case 2 MS Prior 0.237 −148.7 0.496 1.51 0.144 Case 3 e=0 0 (fixed) −149.3 0.498 1.97 0.0648 Discussion ◮ WASP-17b the least dense planet known with a density of 0.06 – 0.14 ρJupiter ◮ Radius of 1.5 – 2 RJupiter larger than predicted by standard evolution models Possible Explanations: ◮ Enhanced atmospheric opacity can delay radius shrinkage BUT 10 times solar insufficient to account for planets size ◮ Additional energy source is necessary ◮ Because of tidal dissipation orbital energy is deposited within the planet ⇒ Leading to an inflated planet which could account for the radius of WASP-17b Discussion ◮ Planet is in a close and retrograde orbit ◮ Supposed to be formed outside the ice boundary (∼ 3 AU) and in a prograde orbit Possible Explanations: ◮ Migration of the planet due to tidal interaction with the gas disk BUT Not able to produce a retrograde orbit ◮ Additional planet – planet or star – planet scattering is necessary to produce highly eccentric and retrograde orbit ⇒ A combination of tidal dissipation and scattering are necessary to produce such a system Outlook ◮ Further RV measurements and imaging are necessary to search for stellar and planetary companions ◮ Due to low surface gravity the planet has the largest known atmospheric scale hight for a planet (1100 – 2100 km) ⇒ good prospect for transmission spectroscopy ⇒ WASP-17b is an example that the formation or planetary systems could be quite complicated