Hot Jupiter Radii andSpectroscopic Transits

PHY 688, Lecture 25Mar 25, 2009

Mar 25, 2009 PHY 688, Lecture 25 2

Outline• Review of previous lecture:

– hot Jupiters• surface temperature gradients• winds• phases and optical albedo

• Radii

• Spectroscopic transits– the Rossiter-McLaughlin Effect

Mar 25, 2009 PHY 688, Lecture 25 3

Previously in PHY 688…

Mar 25, 2009 PHY 688, Lecture 25 4

Atmospheric Dynamics of Hot Jupiters

Mar 25, 2009 PHY 688, Lecture 25 5

Non-Uniform Planet Surface Brightness

(Knutson et al. 2007)

HD 189733 at 8 µm

• hot Jupiters aretidally locked to theirhost stars:– orbital and rotation

period are the same(~1–5 days)

– sub-stellar point doesnot change

• however, peak planetbrightness does notcoincide withmoment of secondaryeclipse– redistribution of heat

Mar 25, 2009 PHY 688, Lecture 25 6

HD 189733b Brightness Map• brightest spot is

not at the sub-stellar point

• brightest andfaintest spot onHD 189733b areon the samehemisphere!

• temperaturedifference is~350 K

(Knutson et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 7

Non-Uniformity in BrightnessDepends on Incident Flux

• in fact, HD 189733b has a relatively homogenized day-night atmosphere– ~350 K difference in temperature– pL planet, no temperature inversion

• much larger day-night contrast inferred on υ And b,HD 179949b– ~1400 K at υ And b– pM planets, temperature inversions

Mar 25, 2009 PHY 688, Lecture 25 8

Radiative(Newtonian)

Cooling• temperature disturbance

relaxes toward radiativeequilibriumexponentially, with timeconstant trad

• for atmospheric P, T:

!

trad~P

g

cP

4"T 3

(Fortney et al. 2008)

Mar 25, 2009 PHY 688, Lecture 25 9

Winds:Cooling vs.Advection

• advection time scaletadvec = Rp/U– Rp – planet radius– U – wind speed

• balance of cooling vs.advection decides windspeed U

• winds of several km/sec(~ sound speed) expectedfrom 2D and 3Ddynamical models

(Fortney et al. 2008)

U

!

"Tday–night

"Trad~ 1# e# tadvec / trad

Mar 25, 2009 PHY 688, Lecture 25 10

Winds: trad/tadvecRatio DependsAlso on Depth

• ratio is higher in the loweratmosphere– especially in pM planets with

stratospheres:

• smaller day-night contrast (moreredistribution of heat) in:– deeper layers– pL planets

(Fortney et al. 2008)

!

"Tday–night

"Trad~ 1# e# tadvec / trad

Mar 25, 2009 PHY 688, Lecture 25 11

Observations in Optical Reflected Light:Phases of Hot Jupiters

(Rowe et al. 2006)

Mar 25, 2009 PHY 688, Lecture 25 12

HD 209458b: No Phase Variation Seen

(Rowe et al. 2006)

MOST satellite data HD 209458: original time series

standard star: original time series

HD 209458: folded to P = 3.52 d

HD 209458: folded, binned and zoomed

0.02

0

05×10–4

region of expectedsecondary eclipse

Mar 25, 2009 PHY 688, Lecture 25 13

Hot Jupiters are Very Dark in the Optical

• 500–800 nm opacity dominated by neutral alkali lines

Mar 25, 2009 PHY 688, Lecture 25 14

Outline• Review of previous lecture:

– surface temperature gradients– winds– phases and optical albedo

• Radii

• Spectroscopic transits– the Rossiter-McLaughlin Effect

Mar 25, 2009 PHY 688, Lecture 25 15

From Lecture 17: Radius vs. Mass:Comparison with Known Planets

• for polytropes

• n = 1.5 for browndwarfs

• n = 0.5–1.0 for 0.1–1MJup planets

• (n = 0: uniformdensity)

• icy/rocky cores inNeptune, Uranus?

• the hot Jupiter HD209458b has a largerradius than non-irradiated planets

(Guillot 2006)

!

R"M

1#n

3#n

olivine (Mg,Fe)2SiO4 planetH2O planet

Mar 25, 2009 PHY 688, Lecture 25 16

Sizes and Structure of Giant Planets:Very Hot Jupiters Are Larger

(Charbonneau et al. 2007)

pM planet

pL planet

Mar 25, 2009 PHY 688, Lecture 25 17

Radii of VeryHot Jupiters

• some large radii cannot beexplained by coreless planetmodels with high-altitudestratospheres:– extra internal power source?

• stratospheric heat trap• tidal heating• damping or orbital eccentricity

and apparent resetting ofplanet age?

– host stars are giga-years old (Fortney et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 18

Are Very Hot Jupiters Younger?

(Fortney et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 19

Jupiter’s Evolution in the Solar System

Mar 25, 2009 PHY 688, Lecture 25 20

Radii of VeryHot Jupiters

• some large radii cannot beexplained by coreless planetmodels with high-altitudestratospheres:– extra internal power source?

• stratospheric heat trap• tidal heating• damping or orbital eccentricity

and apparent resetting ofplanet age?

– host stars are giga-years old

– preferential evaporation ofneutral helium?

(Fortney et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 21

Larger Radii through Evaporation ofNeutral Helium

• material evaporated form planetcarries both H and He

• H is ionized, He is not– this depends strongly in strength of

EUV emission from host star– 10,000K temperature is in between

ionization points• strong planetary magnetic field

could limit loss of charged H ionswithout affecting neutral He loss

• decrease of mean molecular weightat constant entropy: larger radius

(Hansen & Barman 2007)

Mar 25, 2009 PHY 688, Lecture 25 22

Outline• Review of previous lecture:

– surface temperature gradients– winds– phases and optical albedo

• Radii

• Spectroscopic transits– the Rossiter-McLaughlin Effect

Mar 25, 2009 PHY 688, Lecture 25 23

Rossiter-McLaughlin Effect• change of apparent radial velocity of host star during

transit of secondary companion• Rossiter (1924), McLaughlin (1924): “rotational” effect

Mar 25, 2009 PHY 688, Lecture 25 24

Rossiter-McLaughlin Effect

• first detected ineclipsing binary stars– as in bottom panel

• effective Dopplershift of (absorption)line changesdepending on thepart of the host starthat is occulted

(Gaudi & Winn 2007)

Mar 25, 2009 PHY 688, Lecture 25 25

RM Effect Geometry

• seek to measure angle λ between projected stellarrotation axis and planetary orbital axis

(Ohta et al. 2005)

• note: ΩS sin IS here is the same as Vs sin Isand V sin Is in the following slides: theprojected stellar spin rate

Mar 25, 2009 PHY 688, Lecture 25 26

RM Effect Geometry

• shape of deviation from normal radial velocity signaturedepends on λ

(Gaudi & Winn 2007)

Mar 25, 2009 PHY 688, Lecture 25 27

RM Effect Geometry• shape of deviation from normal radial velocity signature depends

on λ– differentiate prograde vs. retrograde planetary orbits

(Ohta et al. 2005)

Mar 25, 2009 PHY 688, Lecture 25 28

RM Effect Magnitude

• depends on stellar rotation rate and planet-starradius ratio γ = Rp/Rs– photometric measurements of transit give precise and

independent measure of γ

(for γ << 1)

(Gaudi & Winn 2007)

Mar 25, 2009 PHY 688, Lecture 25 29

Observations of RM Effect Due toPlanet Transits

• first observed inHD 209458b in2000

• shown here forTrES-1– only third such

observation– independent Vssin

Is constrain fromshape of stellarspectral lines (Narita et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 30

RM Effect in TrES-1

(Narita et al. 2007)

Mar 25, 2009 PHY 688, Lecture 25 31

Summary of RM Effect Observationsfor Transiting Planets

• measure projectedspin-orbit angle λ

• infer constraints onactual spin-orbitangle ψ

• ψpeak < 22º at 95%confidence

• broadly consistentwith planetformation in a disk,no major orbitaldisturbance

(Fabrycky & Winn 2009)

Mar 25, 2009 PHY 688, Lecture 25 32

• very sensitive to– V sin Is (projected stellar

rotation velocity)– Rp, Rs– a (orbital semi-major axis)– i (orbital inclination)

• shown is plot of

for various parameters p

• useful for– studying planet atmospheres– detecting/confirming wide

planets

The RM Effect: Other Applications

(Ohta et al. 2005)

Mar 25, 2009 PHY 688, Lecture 25 33

Using the RM Effect to ProbeAtmospheric Composition

• employ the strong Rp/Rs dependence

(Dreizler et al. 2009)

Mar 25, 2009 PHY 688, Lecture 25 34

Detecting Exo-Earth’s through theRM Effect

(Gaudi & Winn 2007)

Earth’s r.v. andRM signature

• note: i and I are the same variablein the top equation above