FEPS The Formation and Evolution of Planetary Systems: The First Results from a Spitzer Legacy Progr

1
FEPS (The Formation and Evolution of Planetary
Systems) The First Results from a Spitzer Legacy
Program
J.Serena Kim (Steward Obs.) FEPS collaboration
(M.R.Meyer (PI), D. Backman (NASA-Ames, D.P.I.) ,
S.V.W. Beckwith (STScI), J. Bouwman (MPIA),
J.M. Carpenter (Caltech), M. Cohen (UC-Berkeley),
U. Gorti (NASA-Ames), T. Henning (MPIA), L.
Hillenbrand (Caltech, D.P.I.), D. C. Hines
(Steward), D. Hollenbach (NASA-Ames), J. Lunine
(LPL), R. Malhotra (LPL), E. Mamajek (Steward),
A. Moro-Martin (Steward), P. Morris (SSC), J.
Najita (NOAO), D. Padgett (SSC), I. Pascucci
(MPIA), J. Rodmann (MPIA), M.D. Silverstone
(Steward), D. Soderblom (STScI), J.R. Stauffer
(SSC), E. Stobie (Steward), S. Strom (NOAO), D.
Watson (Rochester), S. Weidenschilling (PSI), S.
Wolf (MPIA), and E. Young (Steward))
Abstract We present 3-160um photometry obtained
with the IRAC and MIPS instruments,
spectro-photometry from 5-35um using IRS low
resolution spectrograph, and IRS high resolution
spectrum of HD105. Our report includes updates
on new detections at 70um and 160um of the
candidate debris disk around HD 105 (G0V, 30 Myr
old) as well as a newly discovered debris disk,
HD 150706 (G3V, 1 Gyr old). We also place
preliminary upper limits on the remnant molecular
gas in the disk surrounding HD 105.
30- 10 Myr 45 to ??? AU 1x10-7 Msun

• The FEPS Spitzer Legacy Program
• Goals
• Characterize transition from primordial to
  debris disks
• Constrain timescale of gas disk dissipation
• Examine the diversity of planetary systems
• Try to answer a question Is our Solar System
  Unique?
• Targets

700- 300 Myr 20 to lt100 AU 6.9x10-8 Msun
Figure 1. MIPS 70 160um images of HD 105 and
HD 150706.
Figure 2. SED for HD 105 and HD 150706.
Representative models for the dust debris
surrounding HD 105 (RIN/ROUT 45/300 AU
aMIN/aMAX 5/100um) and HD 150706 (RIN/ROUT
20/100 AU aMIN/aMAX 1/100um) are also shown.
Table 1. FEPS targets
No lines detected for HD 105 Mass in H2 lt 4 Mjup.
lt- Figure 3. Mgas upper limits for HD 105
Table 2. Adopted stellar and derived
circumstellar properties
Figure 4. SED for HD 161897, HD 157664, and HD
47875. Kurucz models are overplotted.

• HD 150706
• Grain size 0.3 or 1 um (smaller than HD
  105s case)
• Inner radius 45 or 20 AU with outer radius lt
  100 AU.
• P-R drag time scale for 1 um grains at 20AU lt 1
  Myr (ltlt age of
• the star 700Myr ) -gt suggest regeneration of
  small grains via
• collision.
• HD 150706 is less likely to have gas-rich disk
  compared to HD 105.
• FOR BOTH HD 105 HD 150706
• Lack of circumstellar materials in the inner disk
  suggest
• Something is preventing dust at 20-40AU from
  reasching the sublimation radius in the inner
  disk
• a lack of significant numbers of colliding
  planetesimals inside of 20-45AU.
• These suggest that the inner region is
  relatively clear of small bodies, consistent with
  timescale of terrestrial planet formation (e.g.,
  Kenyon Bromley 2004)
• The presence of gt 1 large planet lt 20-40AU from
  a star may explain the iner edge of the outer
  dust disk (e.g., Moro-Martin Malhotra 2003)

• Models
• Toy Model based on Backman Paresce (1993)
• Assumptions The IR excess emission is from
  grains
• orbiting, and in thermal equilibrium with
  radiation from the
• centeral stars.
• The model RIN and ROUT of HD 105 and HD 150706
  containing cold materials are calculated with
  assumptions regarding grain compositions, size
  distributions, and spatial distributions.
  Without mineralogical features in the observed
  IRS spectra, the solution is not an unique model,
  but a range of models.
• DDS (Debris Disk Simulator) following Wolf
  Hillenbrand (2003)
• parameters and Assumptions
• - Initial input parameters are based on results
  from Toy models
• - grain composition astronomical silicates
  graphite in the ISM
• ratio and surface density distribution
  proportional to r0.
• Mdisk was adjusted to match the peak flux in the
  IR excesses.
• grain size distribution n(a) a-p power-law
  exponent, amin amax,
• and RIN and ROUT were varied to find the range
  of values.
• Models are relatively insensitive to the radial
  density distribution
• exponent.

HD 105 Range of fitting results (amin RIN are
degenerated) Grain size (amin) 0.3,
5, 8 um Inner radius (RIN) 1000,
120, 42 AU Best fit models Adopting amin
5 um, allowing grain size distribution up to
100 or 1000um, RIN range 120 45 AU (32 AU for
amin 8um). amax and ROUT are not well
constrained. The mass in grains lt 1mm for
these models 9x10-8 and 4x10-8 Msun. PR drag
time scale (assuming grain density of 2.5 g/cm3)
lt 15 Myr for 5um grain at 45 AU ( lt 30 Myr,
the stellar age) -gt suggest any such small
grains are regenerated, perhaps, via
collisions of planetesimals. However given the
optical depth of dust (15-300AU2, the radiating
cross-sectional area), the time scale for dust
to collide is lt 1Myr. -gt suggest that
collisions as well as P-R drag are important in
determining the actual size distribution of
dust as well as its radial surface
density profile. Gas Mass Upper limit for H2 lt
4 MJUPITER (Fig. 3) note IRS High resolution
data of HD 105 are still under analysis
References Backman, D. E. Paresce, F. 1993,
Protostars and Planets III. 1253 Keynon, S.J.
Bromley, B.C. 2004, ApJ, 602, L133 Meyer, M.R. et
al. 2004. ApJS, in press Moro-Martin, A.
Malhotra, R. 2003, AJ, 125, 2255 Wolf, S.
Hillenbrand, L.A. 2003, ApJ, 596, 603