ExoZodical Emission and ExoPlanets:

Ground-based Challenges

C. Beichman (NASA Exoplanet Science Institute)

With lots of help from A. Tanner (Georgia State), G. Bryden (JPL), S. Lawler (Wesleyan/UBC)

R. Akeson (NExScI), D. Ciardi (NExScI), C. Lisse (JHU), Mark Wyatt (Cambridge)

Stars are a billion times brighter…

…than the planet

…hidden in the glare.

Like this firefly.

Near-IR Interferometry

Results• PTI and CHARA indicate

Vega, Leo and Lep have a 1-2% near-infrared excess

• Companions (none known), dust scattering or emission– Scattering produces too much mid-infrared flux emission from host

dust is the most likely explanation

• 2 to 10 m flux ratio requires small, hot, non-silicate grains– Dust needs to be near sublimation radius– Grain size below radiation pressure blowout radius lifetime problem?

• Transient event (comet sublimation, recent asteroid collision)– Minimum mass ~ breakup of single 10 km radius body

• Generated by collisions in planetesimal belt at < 1 AU

Fit to both baselinediam = 1.32 ± 0.013 masflux = 2.4 ± 1.3%

Keck Nulling Key Project

• In 2007, NASA HQ allocated the majority of the NASA Keck time to exozodi survey of nearby stars

Keck Interferometer

• 3 teams were competitively selected – Phil Hinz, Univ of Arizona– Marc Kuchner, Goddard Space Flight Center– Gene Serabyn, Jet Propulsion Laboratory

• Observational programs cover known debris disk systems and nearby main sequence stars

Observing Summary• 8 runs Feb. ‘08 – Jan. ‘09: 32 interferometer nights• 44/46 targets observed• No excess for 40 targets (F/F<0.1-1%)• 3-5× improvement over Spitzer photometry (0.5-2%)

Colavita et al (2009, PASP in press)

MIDI

Keck Nuller

Spitzer51 Ophiuchus:A PictorisAnalog Measuredwith the KeckInterferometer Nuller

Stark et al. 2009, ApJ

Simultaneous fit to Spitzer, MIDI, andKeck Nuller data

10 parameter modelwith 2 dust clouds:

1) inner ring of large grains (“birth ring”)

2) small particles (maybe meteoroids)

Stark et al. 200951 Ophiuchus

HD 69830 from Ground & Space

• Spitzer IRS shows disk small, hot grains at 1 AU (outside of outermost planet) at 1,400x zodi– NO evidence for variability

• Unresolved with Gemini @ 11 m (0.3” 4 AU)

• MIDI resolves emission, but exact distribution ambiguous, 0.25 -1 AU (Smith, Wyatt and Haniff 2009)

LBTI ExoZodi Science• MMT nulling experiments

indicate detection of disks with an uncertainty of 25-75 zodi

• The larger apertures and faster correction of the LBT will improve this limit by a factor of 6

• LBTI could characterize debris disks with an uncertainty of ~3-10 zodi around nearby stars.

• Planned survey of 60 stars once LBTI becomes operational

Detection of a 390±70 zody dust disk around β Leo and a non-detection around o Leo with an uncertainty of 50 zodi.

Nulling observations with the MMT(Phil Hinz)

Origin of Hot Dust Disks• Wyatt et al (2006) suggest hot disks rare (<1-2%)• Long term decline due to dissipation at few AU implies mature systems may be clean (few Zodi)• Hot dust disk in mature stars may be LHB analogs

Wyatt et al. 2006

What we can measure with IRS

HD69830

Ages of our sample stars

Our solar system????? TPF

Limit

Ground-based Zodi Survey Prospects • Space-based (Spitzer,

JWST) cannot get below 1000 Zodi at 10 m

• Ground based observations at few hundred Zodi, 3-4x Spitzer

• LBTI will go below 100 SS, perhaps as low as 10 SS, approaching TPF limit

• Modest extrapolation with theory may satisfy concerns

LBTI Limits