Planets around Stars Beyond the Main Sequence (Evolved Stars) 1.RV measurements of Giant Stars 2.Timing Variations a)Pulsar Planets b)Planets around oscillating stars c)Planets in eclipsing binaries Exoplanets around Giant stars Difficult on the main sequence, easier (in principle) for evolved stars Mass on main sequence A 1.9 M main sequence star A 1.9 M K giant star One way to detect planets around more massive stars with the RV method: Early Evidence for Planets around Giant stars (Hatzes & Cochran 1993) Frink et al P = 1.5 yrs M = 9 M J Planet around the giant star Iota Dra (M ~ 2.2 M Sun ) CFHT McDonald 2.1m McDonald 2.7m TLS The Planet around Pollux The RV variations of Gem taken with 4 telescopes over a time span of 26 years. The solid line represents an orbital solution with Period = 590 days, m sin i = 2.3 M Jup. Mass of star = 1.9 solar masses CFHTMcDonald 2.1m McDonald 2.7m TLS The Planet around Aldebaran The RV variations of Tau taken. The solid line represents an orbital solution with Period = 633 days, m sin i =5.3 M Jup. Mass of star = 1.06 solar masses DAO The first Tautenburg Planet: HD P = 471 d Msini = 14 M J M * = 3.5 M sun HD : Short Term Variations All Giant stars show stellar oscillations with periods of hours to days and amplitudes of m/s Period471 6 d RV Amplitude173 10 m/s e0.27 0.06 a1.5 2.2 AU m sin i14 M Jupiter Sp. Type K2 II III Mass3.5 M sun V sin i2.4 km/s HD HD b From Michaela Dllingers Ph.D thesis M sin i = 3.5 10 M Jupiter P = 272 d Msini = 6.6 M J e = 0.53 M * = 1.2 M P = 159 d Msini = 3 M J e = 0.03 M * = 1.15 M P = 477 d Msini = 3.8 M J e = 0.37 M * = 1.0 M P = 517 d Msini = 10.6 M J e = 0.09 M * = 1.84 M P = 657 d Msini = 10.6 M J e = 0.60 M * = 1.2 M P = 1011 d Msini = 9 M J e = 0.08 M * = 1.3 M M (M ) N Stellar Mass Distribution: Tautenburg Sample Mean = 1.4 M Median = 1.3 M ~20% of the intermediate mass stars have giant planets Johnson et al. (2010): Planets around retired A stars Johnson et al. also estimate that ~25% of stars with mass > 1.5 M sun have giant planets Eccentricity versus Period Blue points: Giant stars with planets Open points: Main sequence stars with planets M sin i (M jupiter ) N Planet Mass Distribution for Solar-type main sequence stars with P> 100 d Planet Mass Distribution for Giant and Main Sequence stars with M > 1.1 M More massive stars tend to have more massive planets and at a higher frequency There is believed to be a connection between metallicity and planet formation. Stars with higher metalicity tend to have a higher frequency of planets. Valenti & Fischer The Planet-Metallicity Connection Revisitied Planet-Metallicity Effect in Giant stars? [Fe/H] Percent Giant stars show no metallicity effect Maybe pollution can explain the metallicity-planet connection Giant hosting planet stars do not show a metallicity enhancement such as the planet hosting stars on the main sequence. Pasquini et al. (2007) hypothesize that the high metal content is due to pollution by planets. When the stars evolve to giants they have deeper convection zones which mixes the chemicals. Figure 1: Metal distribution for planet-hosting (P-H) giants (full line), P-H dwarfs with periods larger than 180 days (dashed line) and all P-H dwarfs (dotted). The giants show a distribution shifted to lower metallicity by about dex with respect to the dwarfs Pollution hypothesis: During planet formation the giant planets migrate in and collide with the star. They have a higher content of metals and thus pollute the outer layers of the stellar atmosphere. Because the convection zone for main sequence stars is not as deep, the polluted layers survive for some time. For giant stars that have a deep convection zone, this polluted layer gets mixed and one does not see a higher metal content. time Due to the orbital motion the distance the Earth changes. This causes differences in the light travel time Timing Variations: Pulsars Change in arrival time = a p m p sini M*cM*c a p, m p = semimajor axis, mass of planet time Main sequence lifetime ~ 10 million years Helium burning ~ 1 million years Carbon burning ~ 300 years Oxygen burning ~ 2/3 year Silicon burning ~ 2 days The Progenitors to Pulsars: Exploding Massive stars The burning stages of massive stars After Si burning the core collapses resulting in a supernova explosion. What is left behind is a neutron star. These Type II supernova Type Ia: Exploding White Dwarf that has accreted matter to send it over the Chandrasekhar Limit of ~ 1.4 M sun Energy output ergs Properties of Neutron Stars (Pulsars) Progenitor Mass: 8-20 M sun Remnant mass: < 3 M sun (otherwise it becomes a black hole) Pressure support: Neutron degeneracy pressure Radius: ~10 km Density: 200 million tons/cm 3 Magnetic field strength: ~ Gauss Periods: 1.5 millisecs to 8.5 s Rotation period of B : P = secs These are very stable clocks! The Lighthouse Beacons of Pulsars PSR B P = 0.7s Vela P = s Crab P = s Why do they think it is a planet? Checked the barycentric correction of the Earth: Ok 300 other pulsars observed and no 6 month periodicity was found. If it is due to the wrong barycentric why was it not seen in the other pulsars? Possible problems Pulsars have a rotational instability. Unlikely, especially since it is periodic The barycentric correction is in fact wrong.hmmmmmm initial position of the pulsar used in the barycentric motion of the Earth was off by 7 arcmin They detected the ellipticity of the Earth 98 d orbit removed, 66 d orbit remains 66 d orbit removed, 98 d orbit remains The radiation from the star is due to the rotational energy loss from the star: dE/dt = I d /dt = 2 /P d /dt = rate of rotational change dE/dt ~ 4 x 10 7 ergs cm 2 s 1 Solar radiation at Earth = 1.42 x 10 6 ergs cm 2 s 1 This is about 30 times the flux at the Earth, so the temperature of the planets should be ~670 K, comparable to Mercury Pulsar with a 0.3 Msun mass companion in a 191 d orbit After removing the timing variations of the stellar companion there are additional variations in the residuals Phinney 1993: Period variations due to planet Mearth with P > 15 yrs. Thorsett et al : Variations are consistent either with a planet at ~10 AU, or a star at ~50 AU orbit This planet is uncertain. Currently there is only one pulsar with planetary companions Origin of the Pulsar Planets 1. First Generation Planets: These rocks are remnants of planets (maybe giant planets) that survived the supernova explosion 2. Second Generation Planets: Planets that formed in the debris disk left behind after the supernova explosion Unfortunately, we only have one example of a pulsar with planets, until we find more such systems the nature of pulsar planets will be unknown. Optical Light Curves of ZZ Ceti Stars Searching for Planets Around Oscillating White Dwarfs Mullally et al. (2008, ApJ, 676, 573) looked at a sample of 15 pulsating white dwarfs One can also use stellar oscillations as clocks for timing variations One, GD 66 looks promising: Arrival time variations consistent with a ~2 M Jup companion in a 4.5 year orbitbut one has to be careful: Evolutionary changes can cause period changes Unstable modes can cause period changes Beating of modes can cause period changes (WD stars tend to be multiperiodic pulsators). But the amplitude of the mode shows variations Subdwarf B Stars (sdB) sdB stars are believed to be core He-burning stars of 0.5 M on the extended horizontal branch that have lost their envelope T eff ~ K Periods 100 250 secs V391 Peg O-C for two pulsation frequencies look the same Prototype sdB pulsating star Sub-stellar Objects in Strange Places: The Sub-stellar companion to the sdB star HD found with traditional radial velocity variations A 8-20 M Jup mass object in a 2.9 d orbital periodso why is this interesting? P = 2.9 days a = 0.05 AU (assuming a 2 solar mass star) = 10 solar radii. On giant branch: Stellar radius R sun At one point this companion was in the envelope of the star! sdB stars Planets around the cataclysmic eclipsing binary NN Ser White Dwarf: Mass: Solar masses Temperature = K Orbital Period 3.12 hours M4 Dwarf companion: Mass: 0.11 Solar masses Temperature ~ 3000 K NN Ser is an eclipsing system. If there are additional companions around one or both stars this will change the expected time of the eclipse. Mass transfer One planet fit to the variations in the eclipse timing: Two planet fit: P 1 = 15.5 years M 1 = 6.9 M Jup P 2 = 7.7 years M 2 ~ 2 M Jup 2:1 resonance These planets have to be circumbinary planets: Formation scenarios: First or Second Generation planets First Generation: Planets formed with stars, but these would have to have survived the supernova explosion Second Generation: Planets formed after the common envelope phase X Planets around the cataclysmic eclipsing binary DP Leo White Dwarf companion with Mass > 1 Solar mass Companion is a cool star that is transfering mass to the W.D. Orbital Period = 89 minutesDP Leo is a post Common Envelope star (CE). During the evolution of the W.D. the secondary was in the envelope of the companion star. Timing variations can also be used on transiting planets Kepler-9b