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“Where to Study Planet Formation? The Nearest, Youngest Stars”. Eric Mamajek Harvard-Smithsonian Center for Astrophysics. Space Telescope Science Institute - 17 January 2008. Some “Big Questions”. How do planetary systems vary by the following: stellar mass? stellar multiplicity?
Harvard-Smithsonian Center for Astrophysics
Space Telescope Science Institute - 17 January 2008
How do planetary systems vary by the following:
Is our Earth & Solar System “normal” ?
High Mass Star Planets
Low Mass Star Planets
Transiting Hot Jupiters
Is this a normal outcome?
T. Greene (2001)
Circumstellar gas and
dust appears to be
<1 Myr stars.
HST resolves disks.
Spitzer Space Telescope
(3-160um) now showing
diversity of spectral energy
distributions (disk geometries,
dust properties, etc.)
Need Samples of
Different ages to
Study disk evolution!
Reservoir of solids needed to regenerate short-lived dust grains
around older (>10 million year-old) stars
M. Meyer (U. Arizona)
(Burrows et al. 1997)
Nearby Young Stars (& Groups)
Substellar Objects: best chance to image
luminous young planets and brown dwarfs
Disk Evolution: ~3-100 Myr is interesting
age range for planet formation. Photospheres of
low-mass stars are bright; easier to detect disks.
Some disks are resolvable! (e.g. Beta Pic)
Galactic Star-Formation: census of clusters
is not complete, even within 100 pc! Can make
complete stellar censuses, study dynamics, etc.
Eta Cha cluster
(Mamajek et al. 1999, 2000,
Lyo et al. 2003)
ROSAT & Hipparcos
Rotation period ~ age^0.5
(2008, in prep.)
Li burned at
~1-2 MK in stellar
Li depletion rate
varies with Mass
are metallicity &
Why we need optical
are X-ray luminous
& Li-rich. Those
in groups are co-moving…
Key: ROSAT All-Sky Survey (X-ray)
Mamajek (2005, 2006)
Zuckerman & Song (2004),
Torres et al. (2006)
(Mamajek+ 2000, Feigelson+ 2003)
32 Ori group
(Mamajek, in prep.)
First northern pre-MS stellar group within 100 pc!
Follow-up: Spitzer Cycle 4 survey for disks at 3-24um with
IRAC & MIPS (Mamajek, Meyer, Kim)
>2.5 Mo 1.5-2.5 Mo 0.5-1.5 Mo <0.5 Mo
Carpenter, Mamajek, Meyer, Hillenbrand (2006)
CAIs Vesta/Mars LHB
Primary sources of
Dust grains: ~10-100km
To be a detectable
“excess”: ~10^3 X
Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008).
“planetary mass object”
* discovered by J. Gizis (2002) in 2MASS.
* ~8 Million year old TW Hya group member
* distance = 53 +- 1 pc
* ~25 Jupiter mass brown dwarf accretor
* discovered by G. Chauvin et al. (2004)
* common motion with “A” confirmed (HST)
* ~late L-type spectrum, no methane
* ~0.01 X luminosity of “A”
* 0.8” separation => 41 AU
What is the mass and origin of “B”?
The infrared colors and spectrum of “B” …its temperature (1600K)
“A” and “B” have common motion …“A” and “B” are coeval and bound
The distance to the 2M1207 system …the luminosity of “B” (1/50,000x Sun)
The distance and 3D motion of
…its age, as it appears to be a
member of the ~8 Million-year-old
“TW Hydra Association”
Any combination of two of these variables
(temperature, luminosity, age)should allow
us to uniquely estimate the mass!
Temperature & Age
Luminosity & Age
Mohanty, Jayawardhana, Huelamo,
Mamajek (2007; ApJ 657, 1064)
(e.g. Stern 1994, Zhang & Sigurdsson 2003, Anic, Alibert, & Benz 2007)
Radius ~50,000 km
Mass ~ tens of Earths
Closer-in unseen giant?
(Mamajek & Meyer,
2007 ApJ, 668, L175)
Mass Time Disk Surface Density
Lodato et al.
Orbital Radius Primary Mass
Conclusion: one can form a small gas giant
around 2M1207A within ~10 Myr, but at ~< 5 AU!
might constitute a new class of object
seen by the next generation of observatories!
Can we see the lingering afterglows of titanic protoplanetary accretion events?
James Webb Space Telescope Giant Magellan Telescope
(JWST) 6.5-meter, ~2013 (GMT) 25-meter, ~2015
Imaging Planets w/ MMT
NO extrasolar planet has been yet imaged!
Our knowledge of exoplanet atmospheres is limited to a few transiting “Hot Jupiters”.
No extrasolar objects with photospheres with
Teff < 650K (T8.5 type) are known -
i.e. new atmospheric chemistry & physics
Previous surveys mostly limited to near-IR --
We are exploring L & M-bands (3.5-4.8 um) where giant planet spectra are predicted to peak
MMT/AO + Clio
15” FOV; 4.5um; Altair (A7V, 8 pc)
& M. Meyer
Heinze+ (FGK *s)
Apai+, (M*s <6pc),
So far no
5” (30AU @ 6 pc)
brightness to a
planet of ~5 M_Jup
(InSb 320x256 array)
Apodized Phase Plate
f/5 Adaptive Optics
+ phase plate
~0.3 Gyr ~3 pc
with phase plate
(Mamajek et al.)
The nearest, youngest stars can provide the best targets for studying planet formation and disk evolution “up close”.
Something is wrong with the infamous “planetary
mass companion” 2M1207b - it is either way too hot or way to
We are using MMT/AO + Clio imaging in the thermal IR to search for planets around nearby stars (so far no detections). Apodized phase plate optic is allowing us to probe at smaller orbital radii (~0.5”; ~5 AU @ 10 pc)
Future looks bright for studying giant planets and dusty debris
disk systems at large radii - we need more nearby young targets!