Transcript The Pluto “Smackdown” and The “New” Solar System

“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?
stellar age?
birth environment?
etc…
Is our Earth & Solar System “normal” ?
Super-Earths
Neptunes
High Mass Star Planets
Low Mass Star Planets
Multi-planet Systems
Transiting Hot Jupiters
Normal Jupiters
Eccentric Jupiters
Hot Jupiters
Pulsar Planets
Star+planetary system formation paradigm (cartoon)
Is this a normal outcome?
T. Greene (2001)
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
Need Samples of
Different ages to
Study disk evolution!
Reservoir of solids needed to regenerate short-lived dust grains
M. Meyer (U. Arizona)
around older (>10 million year-old) stars
Sun (Now)
X
“Stars”
“Brown Dwarfs”
“Planets”
Jupiter (Now)
X
(Burrows et al. 1997)
Age
Finding the Nearest, Youngest Stars
Why do we care?
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)
Eta Cha cluster
Galactic Star-Formation: census of clusters
(Mamajek et al. 1999, 2000,
is not complete, even within 100 pc! Can make
Lyo et al. 2003)
complete stellar censuses, study dynamics, etc.
Discovered w/
ROSAT & Hipparcos
Theoretical
Isochrones
Problem
for deriving
ages:
Main
Sequence
stars
evolve very
slowly!
Activity
Scales with
<100 Myr
Rotation…
~600 Myr
Rotation
slows
with age
Rotation period ~ age^0.5
* Sun
(Skumanich 1972,
Barnes 2007)
Mamajek &
Hillenbrand
(2008, in prep.)
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
* Sun
optical
Spectroscopy!
Stellar
Aggregates in
the Solar
Neighborhood
(1997)
Stellar
Aggregates in
the Solar
Neighborhood
(2007)
Nearby young
low-mass stars
are X-ray luminous
& Li-rich. Those
in groups are comoving…
Key: ROSAT All-Sky
Survey (X-ray)
Hipparcos/Tycho-2
(astrometry)
Mamajek (2005, 2006)
Zuckerman & Song
(2004),
Torres et al. (2006)
Eta Cha
Epsilon Cha
group
group
(Mamajek+ 2000,
(Mamajek+ 2000,
Feigelson+ 2003)
Feigelson+ 2003)
~7 Myr
~5 Myr
~97 pc
~115 pc
Mu Oph
32 Ori
group
group
(Mamajek 2006)
(Mamajek,
~120 Myr
in prep.)
~173 pc
~25 Myr
~95 pc
Our nearest OB association/Star-forming Complex: the “big picture”
32 Ori Group @ d = 95 pc
First northern pre-MS stellar group within 100 pc!
(Mamajek, in prep.)
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)
Dusty Debris Common Around Normal Stars
CAIs Vesta/Mars
Chondrules
Earth-Moon
LHB
Primary sources of
Dust grains: ~10-100km
Planetesimals
Fraction
w/24um
Excess
FEPS
To be a detectable
“excess”: ~10^3 X
Solar system
zodiacal dust!
Age
Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008).
2M1207:
A young
“planetary mass object”
gone wrong…
Substellar Binary 2M1207
2M1207 “A”:
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”:
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”?
Because we know…
…we think we know…
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
the 2M1207A
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!
Brighter
2M1207 “A”
“B” Predicted
Luminosity
Temperature & Age
“B” Predicted
Luminosity & Age
Dimmer
2M1207 “B”
<- Hotter
Mohanty, Jayawardhana, Huelamo,
Mamajek (2007; ApJ 657, 1064)
Cooler ->
Temperature [K]
Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007)
Predictions:
Resolved disk?
Polarization?
KH15D-type eclipses?
Afterglow of a protoplanetary collision?
(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?
(Mamajek & Meyer,
2007 ApJ, 668, L175)
Analytical Estimate of Protoplanet Growth
Mass
Time
Disk Surface Density
Lodato et al.
(2005)
Orbital Radius
Primary Mass
Conclusion: one can form a small gas giant
around 2M1207A within ~10 Myr, but at ~< 5 AU!
“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?
James Webb Space Telescope
(JWST) 6.5-meter, ~2013
Giant Magellan Telescope
(GMT) 25-meter, ~2015
Can exoplanets be imaged?
Why do we care?
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 MMT/AO + Clio
15” FOV; 4.5um;
Altair (A7V, 8 pc)
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
“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)
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)
Background star;
equivalent in
brightness to a
planet of ~5 M_Jup
Clio 3-5um
+
+
+
Imager
(InSb 320x256 array)
MMT 6.5-m
f/5 Adaptive Optics
Secondary
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)
Conclusions
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
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 debris
disk systems at large radii - we need more nearby young targets!