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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?

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Where to study planet formation the nearest youngest stars
“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
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
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
Evolution of Circumstellar Disks

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)


Sun (Now)

X

“Stars”

“Brown Dwarfs”

Luminosity

“Planets”

Jupiter (Now)

X

Age

(Burrows et al. 1997)



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)

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)

Discovered w/

ROSAT & Hipparcos


Theoretical

Isochrones

Problem

for deriving

ages:

Main

Sequence

stars

evolve very

slowly!


Activity

Scales with

Rotation…

Rotation

slows

with age

<100 Myr

~600 Myr

Rotation period ~ age^0.5

(Skumanich 1972,

Barnes 2007)

* Sun

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 optical

Spectroscopy!

* Sun



Stellar Aggregates in the Solar Neighborhood

(2007)

Nearby young

low-mass stars

are X-ray luminous

& Li-rich. Those

in 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)


Epsilon Cha group

(Mamajek+ 2000, Feigelson+ 2003)

~5 Myr

~115 pc

Eta Cha

group

(Mamajek+ 2000,

Feigelson+ 2003)

~7 Myr

~97 pc

Mu Oph

group

(Mamajek 2006)

~120 Myr

~173 pc

32 Ori group

(Mamajek,

in prep.)

~25 Myr

~95 pc



32 ori group @ d 95 pc
32 Ori Group @ d = 95 pc picture”

(Mamajek, in prep.)

First northern pre-MS stellar group within 100 pc!


32 ori group
32 Ori Group picture”

~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 picture”

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 picture”

CAIs Vesta/Mars LHB

Chondrules Earth-Moon

Primary sources of

Dust grains: ~10-100km

Planetesimals

To be a detectable

“excess”: ~10^3 X

Solar system

zodiacal dust!

Fraction

w/24um

Excess

FEPS

Rieke et al. (2005); Gorlova et al. (2006); Siegler et al. (2007); Meyer et al. (2008).

Age


2M1207: picture”

A young

“planetary mass object”

gone wrong…


Substellar binary 2m1207
Substellar Binary 2M1207 picture”

A

2M1207 “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


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

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!


Brighter know…

2M1207 “A”

“B” Predicted

Temperature & Age

“B” Predicted

Luminosity & Age

Luminosity

2M1207 “B”

Dimmer

<- Hotter

Cooler ->

Temperature [K]

Mohanty, Jayawardhana, Huelamo,

Mamajek (2007; ApJ 657, 1064)


Edge-on Gray Dust Disk hypothesis (Mohanty et al. 2007) know…

Predictions:

Resolved disk?

Polarization?

KH15D-type eclipses?


Afterglow of a protoplanetary collision? know…

(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 know…

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” know…

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



Why do we care? know…

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)


Still looking to image an exoplanet
“Still looking” to image an exoplanet know…

  • 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 know…

Radial Velocity Searches

(D. Apai,

M. Meyer)


Digital Snapshots with MMT know… 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 know…

Imager

(InSb 320x256 array)

+

+

+

MMT 6.5-m

Apodized Phase Plate

f/5 Adaptive Optics

Secondary

1” radius


MMT/AO know…

+ 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
Conclusions know…

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!


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