1 29 August 2012IAU SS13, Beijing Stellar Physics Revealed by Planetary Transits Willie Torres Harvard-Smithsonian Center for Astrophysics IAU General Assembly, Special Session 13 High Precision Tests of Physics from High-Precision Photometry Beijing, 29 August 2012

2 29 August 2012IAU SS13, Beijing Selected Topics Accurate mass and radius determinations for low-mass stars Known disagreements between observations and stellar evolution theory Known disagreements between observations and stellar evolution theory Eclipsing binaries are by-products of transit surveys: many new light curves available Eclipsing binaries are by-products of transit surveys: many new light curves available Circumbinary transiting planets Circumbinary transiting planets Spin-orbit alignment for planetary systems Spots on the host stars of transiting planets: spot properties and distribution

3 29 August 2012IAU SS13, Beijing Low-Mass Stars and the Disagreements with Models Many low-mass stars are both larger and cooler than predicted by stellar evolution theory Evidence has been accumulating for many years, mostly from double-lined eclipsing binaries ( Lacy 1977, Popper 1997, Clausen 1999, Torres & Ribas 2002, and many others) Evidence has been accumulating for many years, mostly from double-lined eclipsing binaries ( Lacy 1977, Popper 1997, Clausen 1999, Torres & Ribas 2002, and many others) The vast majority of these binary systems have short orbital periods (mostly < 3 days) The vast majority of these binary systems have short orbital periods (mostly < 3 days) Stellar activity has long been suspected as the underlying cause (tidal synchronization  rapid rotation  activity) Stellar activity has long been suspected as the underlying cause (tidal synchronization  rapid rotation  activity) Magnetic fields inhibit convective energy transport Spot coverage reduces radiating surface area

4 29 August 2012IAU SS13, Beijing CM Dra compared with models (Dotter et al. 2008) Age and metallicity not well known Population II star? Solar-metallicity models do not fit Age is not totally irrelevant Detailed studies Feiden et al Feiden et al Spada & Demarque 2012 Spada & Demarque 2012 MacDonald & Mullan 2012 MacDonald & Mullan 2012

5 29 August 2012IAU SS13, Beijing Age and metallicity not well known Population II star? Solar-metallicity models do not fit Age is not totally irrelevant Detailed studies Feiden et al Feiden et al Spada & Demarque 2012 Spada & Demarque 2012 MacDonald & Mullan 2012 MacDonald & Mullan 2012 [Fe/H] = fits, but binary is unlikely to be that metal-rich CM Dra compared with models (Dotter et al. 2008)

6 29 August 2012IAU SS13, Beijing If short-period binaries show disagreements with theory, should long-period binaries behave better? Tidal forces should be much weaker Tidal forces should be much weaker In principle the binary components should rotate more slowly, and should be relatively inactive In principle the binary components should rotate more slowly, and should be relatively inactive However, such long-period systems are rare among eclipsing binaries (difficult to study) However, such long-period systems are rare among eclipsing binaries (difficult to study) Two long-period eclipsing binaries recently found, both as by-products of transit surveys: LSPM J (MEarth; Irwin et al. 2011) LSPM J (MEarth; Irwin et al. 2011) Kepler-16 (Doyle et al. 2011, Winn et al. 2011), a system with a circumbinary transiting planet Kepler-16 (Doyle et al. 2011, Winn et al. 2011), a system with a circumbinary transiting planet

7 29 August 2012IAU SS13, Beijing LSPM J (Irwin et al. 2011) P = days Kepler-16 Age and metallicity unknown; secondary may still be active (Doyle et al. 2011, Winn et al. 2011) P = days [Fe/H] =  0.30 Circumbinary planet M4V K5V Dartmouth models (Dotter et al. 2008)

8 29 August 2012IAU SS13, Beijing Current models do agree with the measurements of at least one low-mass system: KOI-126 BC Pair of M dwarfs with P = 1.77 days in a 33.9-day orbit around a G dwarf [Fe/H] = (Carter et al. 2011) Photo-dynamical modeling of the Kepler light curve Feiden et al Age = 4.1 Gyr This same model fits KOI-126 A KOI-126 C KOI-126 B Triple System found by Kepler

9 29 August 2012IAU SS13, Beijing Models are able to explain the larger radii and cooler temperatures of late-type stars, but add free parameters that must be tuned to each case  (magnetic inhibition parameter; Mullan & MacDonald 2001)  (magnetic inhibition parameter; Mullan & MacDonald 2001)  ML, and spot filling factor  (Chabrier et al. 2007)  ML, and spot filling factor  (Chabrier et al. 2007) Systematic effects play an important role in measuring masses and radii of low-mass stars (e.g., spots change with time, and can affect the results) High-precision photometry and continuous coverage (e.g., Kepler, CoRoT) is an advantage Photo-dynamical modeling in multiple systems can alleviate some of the problems caused by spots

10 29 August 2012IAU SS13, Beijing Spin-Orbit Alignment Transiting planet observations can provide information on the orientation of the stellar spin axis relative to the planetary orbit Rossiter-McLaughlin effect Rossiter-McLaughlin effect Observation of spot anomalies Observation of spot anomalies Obliquity measurements can tell us about the efficiency of tidal interactions, energy dissipation, and have a bearing on planet migration theories

11 29 August 2012IAU SS13, Beijing The obliquity (or spin-orbit angle  ) is the angle between the spin axis of the host star and the axis of the orbit of the planet. Typically we can only measure its projection on the plane of the sky, λ. Transiting planet Stellar spin axis Orbital axis

Queloz et al. (2000), Ohta, Taruya, & Suto (2005), Gaudi & Winn (2007) The Rossiter-McLaughlin Effect

13 29 August 2012IAU SS13, Beijing R-M observations are relatively easy for hot Jupiters transiting bright and rapid rotators A  (R p /R * ) 2  v sin i

14 29 August 2012IAU SS13, Beijing WASP-15 HAT-P-2 WASP-17 WASP-8 HAT-P-1 HAT-P-7

15 29 August 2012IAU SS13, Beijing Two broadly different migration mechanisms proposed for hot Jupiters Interactions with a flat circumstellar disk  Low obliquities Interactions with a flat circumstellar disk  Low obliquities Dynamical processes (e.g., planet-planet scattering)  High obliquities Dynamical processes (e.g., planet-planet scattering)  High obliquities Winn et al. (2010) first noticed that hot Jupiters orbiting early-type stars tend to be misaligned, while those around cool stars are not Initial obliquities were nearly random (scattering), and low obliquities result from subsequent tidal interactions Initial obliquities were nearly random (scattering), and low obliquities result from subsequent tidal interactions Albrecht et al. (2012) provided additional support for the scattering process Migration and Stellar Properties

16 29 August 2012IAU SS13, Beijing For hot Jupiters, systems with high obliquities tend to be associated with hotter stars Albrecht et al. (2012) Obliquities measured via the R-M effect

17 29 August 2012IAU SS13, Beijing Spots on the Host Stars of Transiting Planets A nuisance: they interfere with the determination of planet properties They cause variations in transit depth, biasing the radius They cause variations in transit depth, biasing the radius They produce chromatic effects that can be mistaken for atmospheric absorption They produce chromatic effects that can be mistaken for atmospheric absorption They cause anomalies in individual light curves They cause anomalies in individual light curves They can bias transit timing measurements They can bias transit timing measurements An opportunity to learn about the planet, its orbit, and the parent star Stellar rotation period ( Silva-Valio 2008 ) Stellar rotation period ( Silva-Valio 2008 ) Spot distribution ( Lanza et al. 2009; Désert et al ) Spot distribution ( Lanza et al. 2009; Désert et al ) Spin-orbit alignment ( Nutzman et al. 2011, Deming et al. 2011; Sanchis-Ojeda et al. 2011, 2012 ) Spin-orbit alignment ( Nutzman et al. 2011, Deming et al. 2011; Sanchis-Ojeda et al. 2011, 2012 )

18 29 August 2012IAU SS13, Beijing P orb /P rot = Aligned axes Time

19 29 August 2012IAU SS13, Beijing Time Misaligned axes 1 2 3

20 29 August 2012IAU SS13, Beijing Starspots, spin-orbit alignment, and active latitudes in the HAT-P-11 exoplanetary system (Sanchis-Ojeda et al. 2011) Out-of-transit variability from Kepler K4V star with a “super-Neptune” Orbital period = 4.9 days R p = 4.7 R  M p = 26 M  Known to be misaligned (λ = 103º) from R-M measurements P rot  30.5 days Spot anomalies seem to occur at two specific phases of the transit

21 29 August 2012IAU SS13, Beijing Spot distribution on HAT-P-11 Two preferred phases  Two preferred latitudes? Planetary transits of active stars allow us to constrain the three-dimensional stellar obliquity  (not just λ) based on the observed pattern of spot anomalies and a simple geometrical model Latitude = ±19.7º Latitude = 67º i s = 80º i s = 168º Sanchis-Ojeda et al. (2011)

22 29 August 2012IAU SS13, Beijing A Butterfly Diagram for HAT-P-11? Spot distribution as a function of time HAT-P-11 The Sun If the active latitudes change with time analogously to the “butterfly diagram” of the Sun’s activity, future Kepler observations should reveal changes in the preferred phases of spot-crossing anomalies Sanchis-Ojeda et al. (2011)

23 29 August 2012IAU SS13, Beijing Summary Accurate measurements of stellar properties (masses, radii) are enabled by the many new light curves resulting from transit surveys, and photo- dynamical modeling in special configurations (triples, circumbinary transiting planets) Spot anomalies detected with high-precision photometry are now a common and useful tool for measuring rotation periods and obliquities in transiting systems (complementary to the R-M effect). They can also serve to characterize the spot distribution. R. Sanchis-Ojeda KOI-126 Carter et al. (2011)