stellar physics revealed by planetary transits

11 29 August 201229 August 2012 IAU SS13, Beijing

Stellar Physics Revealed by Stellar Physics Revealed by Planetary TransitsPlanetary Transits

Willie TorresWillie TorresHarvard-Smithsonian Center for AstrophysicsHarvard-Smithsonian Center for Astrophysics

IAU General Assembly, Special Session 13 High Precision Tests of Physics from High-Precision Photometry

Beijing, 29 August 2012


Selected TopicsSelected Topics

Accurate mass and radius determinations Accurate mass and radius determinations for low-mass starsfor low-mass stars Known disagreements between observations Known disagreements between observations

and stellar evolution theoryand stellar evolution theory Eclipsing binaries are by-products of transit Eclipsing binaries are by-products of transit

surveys: many new light curves availablesurveys: many new light curves available Circumbinary transiting planetsCircumbinary transiting planets

Spin-orbit alignment for planetary systemsSpin-orbit alignment for planetary systemsSpots on the host stars of transiting planets: Spots on the host stars of transiting planets: spot properties and distributionspot properties and distribution


Low-Mass Stars and the Low-Mass Stars and the Disagreements with ModelsDisagreements with Models

Many low-mass stars are both Many low-mass stars are both largerlarger and and coolercooler than predicted by stellar evolution theorythan predicted by stellar evolution theory Evidence has been accumulating for many years, mostly Evidence has been accumulating for many years, mostly

from double-lined eclipsing binaries (from double-lined eclipsing binaries (Lacy 1977, Popper 1997, Lacy 1977, Popper 1997,

Clausen 1999, Torres & Ribas 2002Clausen 1999, Torres & Ribas 2002, and many others), and many others) The vast majority of these binary systems have short The vast majority of these binary systems have short

orbital periods (mostly < 3 days)orbital periods (mostly < 3 days) Stellar activity has long been suspected as the underlying Stellar activity has long been suspected as the underlying

cause (tidal synchronization cause (tidal synchronization rapid rotation rapid rotation activity) activity)Magnetic fields inhibit convective energy transportMagnetic fields inhibit convective energy transport

Spot coverage reduces radiating surface areaSpot coverage reduces radiating surface area


CM Dra compared with models (Dotter et al. 2008)

Age and metallicity not Age and metallicity not well knownwell known

Population II star?Population II star?

Solar-metallicity Solar-metallicity models do not fitmodels do not fit

Age is not totally Age is not totally irrelevantirrelevant

Detailed studiesDetailed studies Feiden et al. 2011Feiden et al. 2011 Spada & Demarque 2012Spada & Demarque 2012 MacDonald & Mullan 2012MacDonald & Mullan 2012


Age and metallicity not Age and metallicity not well knownwell known

Population II star?Population II star?

Solar-metallicity models Solar-metallicity models do not fitdo not fit

Age is not totally Age is not totally irrelevantirrelevant

Detailed studiesDetailed studies Feiden et al. 2011Feiden et al. 2011 Spada & Demarque 2012Spada & Demarque 2012 MacDonald & Mullan 2012MacDonald & Mullan 2012

[Fe/H] = +0.50 fits, but [Fe/H] = +0.50 fits, but binary is unlikely to be binary is unlikely to be that metal-richthat metal-rich

CM Dra compared with models (Dotter et al. 2008)


If short-period binaries show disagreements with If short-period binaries show disagreements with theory, should long-period binaries behave better?theory, should long-period binaries behave better? Tidal forces should be much weakerTidal forces should be much weaker In principle the binary components should rotate more In principle the binary components should rotate more

slowly, and should be relatively inactiveslowly, and should be relatively inactive However, such long-period systems are rare among However, such long-period systems are rare among

eclipsing binaries (difficult to study)eclipsing binaries (difficult to study)

Two long-period eclipsing binaries recently found, Two long-period eclipsing binaries recently found, both as by-products of transit surveys:both as by-products of transit surveys: LSPM J1112+7626 (MEarth; Irwin et al. 2011)LSPM J1112+7626 (MEarth; Irwin et al. 2011) Kepler-16 (Doyle Kepler-16 (Doyle et alet al. 2011, Winn et al. 2011), a . 2011, Winn et al. 2011), a

system with a circumbinary transiting planet system with a circumbinary transiting planet


LSPM J1112+7626 (Irwin et al. 2011)

P = 41.032 days

Kepler-16

Age and metallicity unknown; secondary may still be active

(Doyle et al. 2011, Winn et al. 2011)

P = 41.079 days [Fe/H] = 0.30

Circumbinary planet

M4V

K5V

Dartmouth models (Dotter et al. 2008)


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] = +0.15 (Carter et al. 2011)

Photo-dynamical modeling of the Kepler light curve

Feiden et al. 2011

Age = 4.1 Gyr

This same model fits KOI-126 A

KOI-126 C

KOI-126 B

Triple System found by Kepler


Models are able to explain the larger radii and Models are able to explain the larger radii and cooler temperatures of late-type stars, but add free cooler temperatures of late-type stars, but add free parameters that must be tuned to each caseparameters that must be tuned to each case

(magnetic inhibition parameter; Mullan & MacDonald 2001)(magnetic inhibition parameter; Mullan & MacDonald 2001) ML ML , and spot filling factor , and spot filling factor (Chabrier et al. 2007) (Chabrier et al. 2007)

Systematic effects play an important role in Systematic effects play an important role in measuring masses and radii of low-mass stars measuring masses and radii of low-mass stars (e.g., spots change with time, and can affect the (e.g., spots change with time, and can affect the results)results)

High-precision photometry and continuous High-precision photometry and continuous coverage (e.g., coverage (e.g., KeplerKepler, , CoRoTCoRoT) is an advantage) is an advantage

Photo-dynamical modeling in multiple systems can Photo-dynamical modeling in multiple systems can alleviate some of the problems caused by spotsalleviate some of the problems caused by spots


Spin-Orbit AlignmentSpin-Orbit Alignment

Transiting planet observations can provide Transiting planet observations can provide information on the orientation of the stellar information on the orientation of the stellar spin axis relative to the planetary orbitspin axis relative to the planetary orbit Rossiter-McLaughlin effectRossiter-McLaughlin effect Observation of spot anomaliesObservation of spot anomalies

Obliquity measurements can tell us about the Obliquity measurements can tell us about the efficiency of tidal interactions, energy efficiency of tidal interactions, energy dissipation, and have a bearing on planet dissipation, and have a bearing on planet migration theoriesmigration theories


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 axisOrbital axis

Queloz et al. (2000), Ohta, Taruya, & Suto (2005), Gaudi & Winn (2007)

The Rossiter-McLaughlin Effect


R-M observations are relatively easy for hot R-M observations are relatively easy for hot Jupiters transiting bright and rapid rotatorsJupiters transiting bright and rapid rotators

A (Rp/R*)2 v sin i


WASP-15HAT-P-2

WASP-17

WASP-8

HAT-P-1 HAT-P-7


Two broadly different migration mechanisms Two broadly different migration mechanisms proposed for hot Jupitersproposed for hot Jupiters Interactions with a flat circumstellar disk Interactions with a flat circumstellar disk

Low obliquities Low obliquities Dynamical processes (e.g., planet-planet scattering) Dynamical processes (e.g., planet-planet scattering)

High obliquitiesHigh obliquities

Winn et al. (2010) first noticed that hot Jupiters Winn et al. (2010) first noticed that hot Jupiters orbiting early-type stars tend to be misaligned, orbiting early-type stars tend to be misaligned, while those around cool stars are notwhile those around cool stars are not Initial obliquities were nearly random (scattering), and Initial obliquities were nearly random (scattering), and

low obliquities result from subsequent tidal interactionslow obliquities result from subsequent tidal interactions

Albrecht et al. (2012) provided additional support Albrecht et al. (2012) provided additional support for the scattering processfor the scattering process

Migration and Stellar PropertiesMigration and Stellar Properties


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


Spots on the Host Stars of Transiting PlanetsSpots on the Host Stars of Transiting Planets

A nuisance: they interfere with the determination of A nuisance: they interfere with the determination of planet propertiesplanet properties They cause variations in transit depth, biasing the radiusThey cause variations in transit depth, biasing the radius They produce chromatic effects that can be mistaken for They produce chromatic effects that can be mistaken for

atmospheric absorptionatmospheric absorption They cause anomalies in individual light curvesThey cause anomalies in individual light curves They can bias transit timing measurementsThey can bias transit timing measurements

An opportunity to learn about the planet, its orbit, An opportunity to learn about the planet, its orbit, and the parent starand the parent star Stellar rotation period (Stellar rotation period (Silva-Valio 2008Silva-Valio 2008)) Spot distribution (Spot distribution (Lanza et al. 2009; DLanza et al. 2009; Déésert et al. 2011sert et al. 2011)) Spin-orbit alignment (Spin-orbit alignment (Nutzman et al. 2011, Deming et al. 2011; Nutzman et al. 2011, Deming et al. 2011;

Sanchis-Ojeda et al. 2011, 2012Sanchis-Ojeda et al. 2011, 2012))


Porb/Prot = 0.1

1

2

3

Aligned axes

Time


Time

Misaligned axes

1

2

3


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 Rp = 4.7 R

Mp = 26 M

Known to be misaligned (λ = 103º) from R-M measurements

Prot 30.5 days

Spot anomalies seem to occur at two specific phases of the transit


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

is = 80º

is = 168º

Sanchis-Ojeda et al. (2011)


A Butterfly Diagram for HAT-P-A Butterfly Diagram for HAT-P-11?11?

Spot distribution as a function of timeHAT-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)


SummarySummary

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)

stellar physics revealed by planetary transits

Documents

lowmass system

solarmetallicity models

period eclipsing binaries

distributionlowmass

modelsmany lowmass stars

shortperiod binaries

current models

eclipsing binaries difficult