“where to study planet formation? the nearest, youngest stars”
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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? - PowerPoint PPT PresentationTRANSCRIPT
“Where to Study Planet Formation?
The Nearest, Youngest Stars”
Eric MamajekHarvard-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?
stellar age?
birth environment?
etc…
Is our Earth & Solar System “normal” ?
Pulsar Planets
Hot JupitersEccentric Jupiters
Multi-planet Systems
Neptunes
High Mass Star Planets
Low Mass Star Planets
Normal Jupiters
Super-Earths
Transiting Hot Jupiters
Star+planetary system formation paradigm (cartoon)
T. Greene (2001)
Is this a normal outcome?
Early hints: protoplanetary disks are nearly ubiquitous!
1990s:
Circumstellar gas and
dust appears to be
common around
<1 Myr stars.
HST resolves disks.
2000s:
Spitzer Space Telescope
(3-160um) now showing
diversity of spectral energy
distributions (disk geometries,
dust properties, etc.)
Evolution of Circumstellar Disks
M. Meyer (U. Arizona)
Reservoir of solids needed to regenerate short-lived dust grains
around older (>10 million year-old) stars
Need Samples of
Different ages to
Study disk evolution!
(Burrows et al. 1997)
“Stars”
“Planets”
“Brown Dwarfs”
Lu
min
osit
y
Age
Sun (Now)
X
Jupiter (Now)
X
Finding the Nearest, Youngest Stars
Nearby Young Stars (& Groups)
Why do we care?
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)
Eta Cha cluster(Mamajek et al. 1999, 2000,
Lyo et al. 2003)
Discovered w/
ROSAT & Hipparcos
Galactic Star-Formation: census of clusters
is not complete, even within 100 pc! Can make
complete stellar censuses, study dynamics, etc.
Substellar Objects: best chance to image
luminous young planets and brown dwarfs
Theoretical
Isochrones
Problem
for deriving
ages:
Main
Sequence
stars
evolve very
slowly!
Activity
Scales with
Rotation…
Rotation
slows
with age
Mamajek &
Hillenbrand
(2008, in prep.)
Rotation period ~ age^0.5
(Skumanich 1972,
Barnes 2007)
* Sun
<100 Myr
~600 Myr
Lithium
Depletion
Li burned at
~1-2 MK in stellar
interiors…
Li depletion rate
varies with Mass
(secondary effects
are metallicity &
rotation)
Why we need
optical
Spectroscopy!
* Sun
Stellar Aggregates in the Solar Neighborhood(1997)
Stellar Aggregates in the Solar Neighborhood(2007)Nearby younglow-mass starsare X-ray luminous& Li-rich. Thosein groups are co-moving…
Key: ROSAT All-Sky Survey (X-ray)Hipparcos/Tycho-2(astrometry)
Mamajek (2005, 2006)Zuckerman & Song (2004), Torres et al. (2006)
Mu Oph
group (Mamajek 2006)
~120 Myr
~173 pc
Epsilon Cha
group
(Mamajek+ 2000,
Feigelson+ 2003)
~5 Myr
~115 pc
Eta Cha
group
(Mamajek+ 2000,
Feigelson+ 2003)
~7 Myr
~97 pc
32 Ori
group
(Mamajek,
in prep.)
~25 Myr
~95 pc
Our nearest OB association/Star-forming Complex: the “big picture”
32 Ori Group @ d = 95 pc
(Mamajek, in prep.)First northern pre-MS stellar group within 100 pc!
32 Ori Group
~25 Myr
Follow-up: Spitzer Cycle 4 survey for disks at 3-24um with
IRAC & MIPS (Mamajek, Meyer, Kim)
Snapshot of Disk Evolution across the Mass Spectrum at 5 Myr
Disk
Fraction
>2.5 Mo 1.5-2.5 Mo 0.5-1.5 Mo <0.5 Mo
Carpenter, Mamajek, Meyer, Hillenbrand (2006)
FEPS
Dusty Debris Common Around Normal Stars
CAIs Vesta/Mars LHB Chondrules Earth-Moon
Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008).
Fractionw/24umExcess
Age
Primary sources of
Dust grains: ~10-100km
Planetesimals
To be a detectable
“excess”: ~10^3 X
Solar system
zodiacal dust!
2M1207:
A young
“planetary mass object”
gone wrong…
Substellar Binary 2M12072M1207 “A”: * 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
2M1207 “B”: * discovered by G. Chauvin et al. (2004) with VLT/NACO * 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”?
B
A
Because we know… …we think we know…
The distance to the 2M1207 system …the luminosity of “B” (1/50,000x Sun)
The infrared colors and spectrum of “B” …its temperature (1600K)
The distance and 3D motion of
the 2M1207A
…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!
“A” and “B” have common motion …“A” and “B” are coeval and bound
Temperature [K]
Lu
min
osit
y
2M1207 “A”
2M1207 “B”
“B” Predicted
Temperature & Age
“B” Predicted
Luminosity & Age
Mohanty, Jayawardhana, Huelamo,
Mamajek (2007; ApJ 657, 1064)
Cooler -><- Hotter
Dimmer
Brighter
Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007)
Predictions:Resolved disk?
Polarization?
KH15D-type eclipses?
Afterglow of a protoplanetary collision?
(Mamajek & Meyer,
2007 ApJ, 668, L175)
?
(e.g. Stern 1994, Zhang & Sigurdsson 2003, Anic, Alibert, & Benz 2007)
Predictions:Radius ~50,000 km
Mass ~ tens of Earths
Lower gravity
Higher Z
Closer-in unseen giant?
Mass Time Disk Surface Density
Orbital Radius Primary Mass
Analytical Estimate of Protoplanet Growth
Conclusion: one can form a small gas giant
around 2M1207A within ~10 Myr, but at ~< 5 AU!
Lodato et al.
(2005)
James Webb Space Telescope Giant Magellan Telescope(JWST) 6.5-meter, ~2013 (GMT) 25-meter, ~2015
“Hot Protoplanet Collision Afterglows” 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?
Can exoplanets be imaged?
Why do we care?
MMT/AO + Clio
15” FOV; 4.5um;
Altair (A7V, 8 pc)
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
Imaging Planets w/ MMT
“Still looking” to image an exoplanet• Giant planets should be brightest in
IR (~5 um), especially young ones
• Searches in near-IR with adaptive optics on large telescopes or HST have thus far only upper limits on the numbers of <13 Jupiter mass companions to nearby stars
• Surveys @ VLT, Keck, HST, MMT• (e.g., Macintosh et al. 2001, 2003, Metchev
et al. 2003, Chauvin et al. 2004, 2005, Masciadri et al. 2005, Hinz et al. 2006, Biller et al. 2007, Apai et al. 2007, Kaspar et al. 2007, Heinze PhD Thesis, Mamajek et al., in prep.)
• Jupiters are rare at ~>30 AU
Radial Velocity Searches Imaging
(D. Apai,
M. Meyer)
Background star;
equivalent in
brightness to a
planet of ~5 M_Jup
Digital Snapshots with MMT f/15 AO+CLIO (L&M-band imager)
P. Hinz, A. Heinze M. Kenworthy, E. Mamajek, D. Apai& M. Meyer
Surveys:Heinze+ (FGK *s)Apai+, (M*s <6pc),Mamajek+ (A*s <25pc)So far no planets…
5” (30AU @ 6 pc)
MMT 6.5-m f/5 Adaptive Optics
Secondary
Clio 3-5um
Imager(InSb 320x256 array)
+ ++
Apodized
Phase Plate
1” radius
MMT/AO
+ Clio
+ phase plate
~1 hr
Dec. 2006
Sirius
~0.3 Gyr ~3 pc
Following up
Nearest northern
A-type stars
with phase plate
(Mamajek et al.)
(M. Kenworthy)
ConclusionsThe 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 dim. Why?
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 debrisdisk systems at large radii - we need more nearby young targets!