Transcript feps_jan_2007_aas - The Formation & Evolution of Planetary

Placing our Solar System in Context
Latest Results from the FEPS
Spitzer Legacy Science Program
http://feps.as.arizona.edu/
D. Soderblom (STScI), & FEPS collaboration: M.R. Meyer (U. of Arizona, PI), L.A. Hillenbrand (Caltech, D.PI.), D. Backman (SETI)
S.V.W. Beckwith (STScI), J. Bouwman (MPIA), J.M. Carpenter (CalTech), M. Cohen (UC-Berkeley), S. Cortes (Steward), U. Gorti (NASA-Ames), T. Henning (MPIA),
D.C. Hines (Space Science Institute), D. Hollenbach (NASA-Ames), J. Serena Kim (Steward), J. Lunine (LPL), R. Malhotra (LPL), E. Mamajek (CfA), A. Moro-Martin (Steward), P. Morris (SSC),
J. Najita (NOAO), D. Padgett (SSC),I. Pascucci (Steward), J. Rodmann (MPIA), Wayne M. Schlingman (U. of Arizona), M.D. Silverstone (Steward), J.R. Stauffer (SSC), E. Stobie (Steward),
S. Strom (NOAO), D. Watson (Rochester), S. Weidenschilling (PSI), S. Wolf (MPIA), and E. Young (Steward)
Summary
Overall FEPS Goals
We present results from the Formation and Evolution of Planetary Systems (FEPS)
Spitzer Legacy Science Program. FEPS utilizes Spitzer observations of 336 sun-like
stars with ages from 3 Myr to 3 Gyr in order to construct spectral energy
distributions (SEDs) from 3-160 microns, as well as obtain high resolution midinfrared spectra. The SEDs yield constraints on the geometric distribution and mass
of dust while the spectra enable a search for emission from gas in circumstellar
disks as a function of stellar age. Our main goals are to study the transition from
primordial to debris disks at ages < 100 Myr, determine the lifetimes of gas-rich
disks in order to constrain theories of Jupiter-mass planet formation, and explore
the diversity of planetary architectures through studies of the range of observed
debris disk systems. We summarize recent results including: 1) the lifetime of inner
disks emitting in the IRAC bands from 3-8 microns from 3-30 Myr (Silverstone et al.
2006); 2) limits on the lifetime of gas-rich disks from analysis of a IRS high
resolution spectral survey (Pascucci et al. 2006), 3) detection of warm debris disks
using MIPS 24 and the IRS (Hines et al. 2006; Meyer et al. in prep); 4) physical
properties of old, cold debris disk systems detected with MIPS 70 (Hillenbrand et al.
in prep); and 5) exploration of the connection between debris and the presence of radial
velocity planets (Moro-Martin et al., submitted). A full program description can be found in
Meyer et al. (2006, PASP, in press).
Characterize transition from primordial to debris disks
IRAC (imaging at 3.6um, 4.8um, 8.0um)
Constrain timescale of gas disk dissipation
IRS
Examine the diversity of planetary systems
Distance (pc)
Targets
3-10 Myr
50/~140
80 - 60
Tau, Oph, Cha, Lup, Upper Sco
10-30 Myr
60/~160
60 - 160
Tau, Oph, Cha, Lup, Cen Crux
30-100 Myr
65/~130
40 - 180
IC2602, a Per
100-300 Myr
65/~100
20 - 120
Ursa Major, Castor, Pleiades
0.3-1 Gyr
65/~100
20 - 60
Field stars, Hyades
1-3 Gyr
50/~1000
20 - 60
Field stars
Dissipation of Gas-Rich Disks
(Silverstone et al. 2006; Pascucci et al. 2006)
Age range: 3 - 300 Myr
Among the 74 sources 3-30 Myr analyzed for continuum excess emission:
-- 5 excesses are detected in IRAC bands
-- 4 / 29 are in 3 – 10 Myr age bin
-- 1 / 45 in the 10 – 30 Myr age bin
Optically-thick disks typically dissipate in < 3 Myr from 0.3-3 AU.
Lack of gas emission-line detections in 15 stars 3-300 Myr old limit the
timescale for gas giant and ice giant planet formation as well migration
scenarios for the evolution of protoplanetary orbits.
MIPS (imaging at 24um, 70um, 160um)
Blackbody Debris Disk Models
From Protostellar Disks to Mature Planetary Systems
Primordial Disks:
- gas rich
- opacity is dominated by primordial grains.
Transition Disks:
- very short time scale
- planetesimals grow
N*/Ntot
(spectroscopy at 5um - 35um) - both Low and high resolution
Is our Solar System common or rare?
Sample
Age
Spitzer Observations
Debris disks:
- no detection of gas
- Poynting-Robertson (P-R) drag time scale is
shorter than the age of system, therefore
pristine grains in a disk had been spiraled into
the star. Therefore, we expect no residual
ISM dust left over from formation.
- opacity is dominated by 2nd generation grains
produced by collisions of planetesimals.
See recent review by Meyer et al. (2006).
Warm Disks (Hines et al. 2006; Meyer et al. in prep)
24 micron excess emission:
Initially identified through [8] – [24] micron colors.
Dispersion in locus of colors for non-disked sources sets 3-sigma limits.
Limits for detection in dust mass: ~10-4 – 10-6 Mearth
HD 12039: A warm disk dominated by grains larger than 7 microns at
T~110K around R = 4-6 AU, similar to the properties of our own asteroid
belt. The star is 30Myr old. The P-R drag time is < 2 Myrs. Dust mass is
about 2 x 10-6 Mearth. Hines et al. (2006).
Preliminary models are based on color temperatures of excess flux measured in
IRS and MIPS bands fluxes. The relation between grain temperature, position,
and primary stellar luminosity (Backman & Paresce 1993) is for blackbody
grains larger than the longest wavelength of observation. Grain albedo is
assumed to be zero. Lack of data beyond the peak of emission prevents useful
characterization of outer boundary (ROUT). Information from mineralogical
features can be used to help characterizing grain size (Bouwman et al. in prep).
The total radiating masses can be considered lower limits, calculated for single
particle size and fixed grain density (e.g., 10 um radius and density 2.5 g/cm3).
Note that the Poynting-Robertson drag lifetime of a 100 um-radius grain of
density 2.5 g/ cm3 at r = 20AU around 1 LSUN star is ~ 7 x 107 yrs.
References
Backman, D. E. & Paresce, F. 1993, Protostars and Planets III. 1253
Beichman et al. 2005, ApJ, 622, 1160.
Bryden et al. 2006, ApJ, 636, 1098.
Gorlova et al. 2006, ApJ, 649, 1028.
Gorti and Hollenbach, 2004, ApJ, 613, 424.
Greaves et al. 2006, MNRAS, 366, 283.
Hollenbach et al. 2005, ApJ, 631, 1180
Hines et al. 2006, ApJ, 638, 1070.
Kenyon and Bromley, 2006, AJ, 131, 1837
Kim et al. 2005, ApJ, 632, 659-669
Meyer, M. R. et al. 2004. ApJS, 154, 422.
Meyer, Backman, Weinberger, and Wyatt, 2006, PPV, in press (astro-ph/0606399).
Pascucci et al. 2006, ApJ, 651, 1177.
Rieke et al. 2005, ApJ, 620, 1010.
Silverstone et al. 2006, ApJ, 639, 1138.
Stauffer et al. 2005, AJ, 130, 1834
Cold Kuiper Belt-like disks
(Hillenbrand et al. in prep; Moro-Martin et al. submitted)
Age range: 300 Myr – 3 Gyr
adust: ~10 micron with P-R drag time scales of 10um silicate grains: 2 – 30 Myr.
Radiation blowout sizes (aMIN, silicate): ~0.3 – 0.7 micron
Ldust/L*: ~10-4 with Mdust: from blackbody models: 10-10 – 10-11 Msun
RIN : ~20 - >30 AU ( > RSUBLIMATION, icy grains)
We find Kuiper-Belt like debris disks in 13 new objects for a total of 31 sources with
70 micron excess in the FEPS sample.
Some sources appear to have extended debris disks with multi-temperature dust
models required.
Figure 1:
[2Mass Ks] - IRAC [3.6um] vs. IRAC
[4.5um] - [8.0um] color-color diagram
• 74 young targets from the FEPS sample
• Five apparent excess targets appear above
and to the right of the locus of photospheres
in this diagram are optically-thick disks.
•The typical error is plotted as a cross in the upperleft of this figure (Silverstone et al. 2006).
•The lack of sources with optically-thin excess
places constraints on the during of the transition
time between thick and thin from 0.3-3 AU.
Figure 3:
Observed 24 micron flux
divided by the expected 24
micron photospheric flux as a
function of star age for all
FEPS targets within 100 pc.
Figure 4: SED of HD 12039
Upper limits represent the measured on source flux density + 3 times the
uncertainty including calibration uncertainty. Blackbody dust model is the best
fit emission model for blackbody grains. Model_11AU allows for grains to exist
to 11 AU and violates the 3sigma upper limit at 70 microns. Lower spectrum is
everything divided by the Kurucz model, showing departure from the
photosphere at 12-14 microns (Hines et al. 2006).
Figure 6:
Excess emission distributions for a sub-set
of the debris disk sources.
Residual Spitzer emission after removal of stellar
contribution. The blue lines are fits to the 33-70
um excess, the red lines are fits to the 24-33 um
emission, and the green lines are composite fits
when excess emission is detected at three or
more wavelengths (Hillenbrand et al. in prep).
Figure 2:
Gas Surface Density Upper Limits From Non-detections of Gas Emission Lines
We searched for emission lines of H2, [FeII], [SI], and [SiII] using the high resolution mode of the Spitzer
IRS, as well as sub-mm lines of CO with the SMT in Arizona. No emission lines were detected. Applying the
models of Gorti and Hollenbach (2004) and following Hollenbach et al. (2005) we placed upper limits to the
gas surface density for 15 FEPS targets with optically-thin (or lacking) dust disk signatures. The ages of the
targets ranged from 3-300 Myr. Our results suggest that there is not enough gas in these systems to form
gas giants (Jupiter mass), nor ice giants (Neptune mass). Furthermore, it is unlikely there is enough gas
left in the terrestrial planet zone (0.3-3 AU) to damp eccemtricities of forming proto-planets as requred in
some models (Pascucci et al. 2006).
Figure 7:
Warm Dust Radii vs. Cool Dust Radii
Rinner determined from blackbody grain fit to 24-33 um color
temperature and limit on Router from 70 um constraints.
Figure 5:
Evolution of 24 Micron Excess Selected as 3-sigma Excess in [8]-[24] color:
The fraction of FEPS stars with 24 micron excess selected from a sub-sample of the data for stars within 100
parsecs [light green squares] is compared to recent results from the literature as a function of age. The red
squares are from Gorlova et al. (2006; see also Stauffer et al. 2005), Siegler et al. (in press), and Bryden et al.
(2006). The light [dark] blue circles are from Rieke et al. (2005) [Hernandez et al. (in press)] respectively. The
dark green square is a compilation of Padgett et al., Bouwman et al., and Carpenter et al. (all in press). Also
indicated at the top of the chart are major epochs in the formation and evolution of our solar system. While the
excess fractions for the FGK stars track below the early type stars (though they are sensitive to SMALLER
amounts of dust as detected as a fraction of the photosphere), the open cluster data (red squares < 100 Myr) are
consistent with the field star data (light green squares). The ensemble of the data is broadly consistent with
models for terrestrial planet formation (e.g. Kenyon and Bromley 2006) and the history of our solar system
(Meyer et al. in preparation). A full analysis of the distribution of dust as a function of temperature and stellar
Figure 8:
70 Micron Dust excess as a function of age for stars with and without planets:
While there was a preliminary suggestion of a correlation between the presence of a planet and the frequency and
magnitude of detected debris dust from Beichman et al. (2005), we are unable to confirm a correlation based on
statistical analysis of both the Bryden et al. (2006) and FEPS samples. The frequency of massive debris disks (>
x100 soloar system levels) in both samples is 10-15 % regardless of the presence of known radial velocity planets.
This is consistent with the notion that the conditions to generate debris (presence of planetesimal belts with at
least one large oligarch) are less stringent than those required to form gas giant planets (cf. Greaves et al. 2006;
Najita et al. in prep). Solid line model in left panel from Kenyon and Bromley. One planet host star in the FEPS
sample, HD 38528, shown at right, has a debris disk at 70 microns. Modelling of the planet and dust disk
dynamics is underway (Moro-Martin et al. in preparation).