Transcript JSK_PPV_poster - The Formation & Evolution of Planetary

Formation and Evolution of Planetary Systems
(FEPS): Cold Outer Disks Associated with
Sun-like Stars
http://feps.as.arizona.edu/
J.Serena Kim (Steward, U. of Arizona), D. C. Hines (Space Science Institute), D. E. Backman (NASA Ames/SOFIA), L. A. Hillenbrand (CalTech),
M. R. Meyer (Steward), J. Rodmann (MPIA), A. Moro-Martin (Princeton), J.M. Carpenter (CalTech), M.D. Silverstone (Steward), J. Bouwman (MPIA), E.
E. Mamajek (CfA), S. Wolf (MPIA), R. Malhotra (LPL, U of A), I. Pascucci (Steward), J. Najita (NOAO), D. L. Padgett (SSC), T. Henning (MPIA), T. Y.
Brooke (CalTech), M. Cohen (UC-Berkeley), S. E. Strom (NOAO), E. B. Stobie, C. W. Engelbracht, K. D. Gordon, K. Misselt, J. E. Morrison, J.
Muzerolle, & K. Y. L. Su (Steward)
Abstract
We present the discovery of Kuiper Belt (KB)-like debris systems
around three Sun-like stars based on observations with the
Spitzer Space Telescope as part of the legacy science program,
"The Formation and Evolution of Planetary Systems (FEPS)".
Two other debris disks systems suggested by observations with
ISO and IRAS are also confirmed. All five stars show infrared
emission excess at 70um compared to expected stellar
photospheres while no excess emission is detected at <33um.
These systems are relatively old (0.7 - 3 Gyr) among the FEPS
targets. We performed simple blackbody modeling for the
spectral energy distributions of the mid-infrared excess sources,
and interpret these systems as likely to possess debris belts
generated by planetesimal collisions similar to those in our
Kuiper-Belt. In this study we also report observations of the
relatively nearby system HD 13974 (at 11 pc), that is consistent
with stellar photosphere model within the uncertainties at 24um
and 70um.
Blackbody Model
Blackbody 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. 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). Here we use ~10 m grain size, which is the smallest grain size
that emit efficiently at 70 m.
Spitzer Data
Sample
70mm excess sources discussed here were selected from ~10% of FEPS
data, that were publicly available since April 2005.
IRAC (imaging at 3.6 m, 4.8 m, 8.0 m)
IRS
Figure 1.Flux density ratio of 24 m/Ks vs.
70 m/Ks of 37 sources with MIPS 70 m
detection (pink filled circles). Small dots are
not detected in 70 m. We used 1 sigma upper
limits for the 70 m non detection. Note that
HD 13974 has 70 m flux consistent with
photosphere (Kim et al. 2005).
(spectroscopy at 5 m - 35 m) - both Low and high resolution
MIPS (imaging at 24 m, 70 m, 160 m)
MIPS Data were reduced using MIPS_DAT pipeline (Gordon et al. 2005),
and the photometry were done using IDP3 (Schneider & Stobie 2002).
Figure 3.
70 m
Example 70 m
mosaic images
Figure 2.
Histogram of (observed - photospheric 70 m
fluxes) divided by  (random uncertainty). Four
excess sources (filled histogram) are easily noticed
in this histogram. Note that HD 8907 shows very
strong excess flux at 70 m, which was detected by
IRAS and ISO. HD 6963, HD 122652, HD 145229,
and HD 206374 discovered by FEPS program are
nearer to the rest of the stars without IR excess
(Kim et al. 2005).
5.2’
Table 1. Source properties, blackbody modeling results, Radiation blowout size (ablowout), and P-R drag time scale
Age
(Gyr)
d (pc)
Sp. Type
Tdust (K)
amin(m)
HD 6963
1-3
27
K0
57
HD 8907
0.3-1
34
F8
HD 13974
1-3
11
HD 122652
1-3
HD 145229
HD 206374
Source
RIN(AU)
log Mdust
(Mearth)
log LIR/L*
ablowout, Si
(m)
log(tP-R, Si)
(yr)
10
18
-4.9
-4.2
0.35
7.0
48
10
48
-3.1
-3.6
0.85
6.5
G0/(G9-K4)
55
10
>28
<-5.1
<-5.2
0.58
7.0
37
F8
56
10
31
-3.9
-4.1
0.68
6.8
0.3-1
33
G0
56
10
24
-4.5
-4.0
0.49
7.0
1-3
27
G6.5
57
10
>20
-4.7
<-4.5
0.43
6.9
Summary
On-going analysis with more complete data
Figure 4. Spectral energy distributions (SEDs) of HD 6963, HD 8907, HD
122652, HD 145229, HD 206374, and HD 13974. Blackbody model SEDs are
over-plotted with red dotted lines. (Kim et al. 2005)
Debris Disk Model (WH03) for HD 8907
a= 6um - 1mm
Astronomical silicate
Rin =42.5 AU
log (LIR/L*) =-3.6
Md = 0.02 Mearth
disk
star
2. As seen in Figure 1 & 2, the improved sensitivity of Spitzer allows us to
detect debris disk systems that are much fainter than those detected by
IRAS and ISO. The overall impression is that Kuiper-Belt (KB)-like systems
detectable by Spitzer and considered in this paper are less massive and more
distant than systems detected with IRAS and ISO.
3. HD 13974 has a MIPS 70 m flux consistent with photospheric emission
within 1  total uncertainty (including 20% absolute calibration uncertainty).
The upper limit of log(LIR/L*) is < -5.2, similar to that of inferred for the
solar systems' KB.
4. Simple blackbody grain modeling of our 5 excess SEDs yielded log(LIR/L*)
< -4.5 -3.5, color temperatures between 55 - 58 K, and inner radii of outer
disks between 18 and 46 AU.
5. A solar system KB evolution model predicts Spitzer 70 m fluxes (see Kim
et al. 2005, Backman et al. 2006) from hypothetical planetesimal
assemblages around our target stars that are within factors of 2 - 3 of the
observed fluxes. We infer that these systems have outer remnant
planetesimal belts that are consistent in scale and starting masses to our KB.
6. The absence of a disk around the ~1 Gyr old star HD 13974 suggests that
either this object does not contain the parent bodies that produce infraredemitting debris, or perhaps the debris has been cleared out already.
7. We placed upper limits on warm dust masses interior to RIN for each of
these systems, and showed that the depletion of the disk < RIN is significant.
We commented on several possible causes for RIN. We speculate that the RIN
of exo-KBs presented in this study could be explained by the existence of
one or more Jupiter mass planets at 10 - 20 AU from each star.
Debris Disk Model: Wolf & Hillenbrand (2003)
Figure 5.
Spectral energy distribution (SED) of HD 8907. The model SED
is a fit from detailed modeling using WH03 models (see section 4.2 Kim et al.
2005). Blue filled circles are IRAC data, red filled circles are MIPS data, box
points are ISO fluxes, and filled upside-down-triangles are 3  upper limits of
2.9mm and 3.1mm (Carpenter et al. 2005). The spectrum (green) is IRS spectrum.
~10 - 20 AU
~20-40 AU
--- KB-like disk only
log (age)
Figure 6.(preliminary)
Fraction of 70 m excess
sources vs. age using nearly complete FEPS data (~320 sources).
Note the peak is > 1 Gyr old age bin. Black solid line includes all
sources with 70m excess, while blue line include ONLY KB-like
excess sources. Stay tuned for upcoming paper!
Disk Radius (AU)
<0.1 0.3-1 1-10 30-100
Dusty Disk lifetime
While inner disks are seen in
mostly young sources (Silverstone
et al. 2005, Bouwman et al. 2006
for hot and warm disks in the FEPS
sample), cold outer disks like our
KB are seen in old (1 - 4 Gyr) sunlike stars.
3-10
10-30
Age (Myr)
1. The five excess sources have SEDs that are consistent with photospheric
models out to 33 m, but show clear excesses at 70 m, which was the
selection criterion. We find that these stars are all "old" (three sources
are in our 1 - 3 Gyr age bin, while two are in the 0.3 - 1 Gyr age bin).
Nexcess/Ntot (%)
(Kim et al. 2005)
100-300
1 Gyr-4 Gyr
References
Backman, D. E. & Paresce, F. 1993, Protostars and Planets III. 1253
Backman et al. 2005, in preparation
Bouwman et al. 2006, in preparation
Carpenter et al. 2005, ApJ, 129, 1049
Gordon et al. 2005, PASP, in press
Hillenbrand et al. 2005, in preparation
Kim et al. 2005, ApJ, 632, 659
Meyer, M.R. et al. 2004. ApJS, 154, 422
Schneider, G. & Stobie, E. 2002, ADASS, 11, 382 (IDP3)
Silverstone et al. 2005, ApJ, submitted
Wolf, S. & Hillenbrand, L.A. 2003, ApJ, 596, 603 (WH03)