Transcript Identifying Low Luminosity Embedded Sources

Spitzer Observations of
Molecular Clouds:
Identifying Low Luminosity Embedded Sources
Tracy Huard
University of Maryland
Collaborators
Michael Dunham, Neal Evans
Tyler Bourke, Phil Myers
Lori Allen
Lee Mundy
Chang Won Lee, Miryang Kim
(Univ of TX at Austin)
(SAO)
(NOAO)
(Univ of MD)
(Korea Astronomy and
Space Science Inst.)
c2d (and GB) Science Goals
• Complete database for nearby (< 350 pc) regions
– Low mass star and substar formation
• Follow evolution: starless cores to planet-forming disks
• Coordinate with FEPS team
– ensure complete coverage of 0 to 1 Gyr
• Cover range of other variables
– mass, rotation, turbulence, environment, …
– separate these from evolution.
The c2d Sample
Chapman et al. (2007); Merin et al. (2008)
B59;
Brooke et al. (2007)
Padgett et al. (2008);
Allen et al. (2008)
Young et al. (2005);
Porras et al. (2007);
Alcala et al. (2008)
Harvey et al. (2006);
Harvey et al. (2007a);
Harvey et al. (2007b)
L1251B/E
Lee et al. (2006)
Jorgensen et al. (2006);
Rebull et al. (2007);
Lai et al. (2008)
The Gould Belt sample
Gutermuth et al. 2008 ApJL
in
progress…
Matthews et al.
Hatchell et al.
Harvey et al. 2008 ApJ
Peterson et al.
Kirk et al. 2009
Cloud
Auriga
Cepheus
Chamaeleon I
Chamaeleon II
Chamaeleon III
Corona Australis
IC5146E
IC5146NW
Lupus I
Lupus III
Lupus IV
Lupus V
Lupus VI
Musca
Ophiuchus
Perseus
Scorpius
Serpens (c2d)
Serpens-Aquila
dist area
mass
mass(YSO)/
[pc] [sq deg] [Msun] N(YSO) mass(total)
300
300
200
178
200
130
950
950
150
200
150
150
150
160
125
250
130
260
260
1.91
1.40
0.82
1.04
2.55
0.85
0.25
0.32
1.39
1.34
0.37
1.70
0.98
1.04
6.60
3.86
1.41
0.85
9.33
5000
2700
920
660
1500
300
3700
5500
540
950
190
720
470
390
3200
6700
640
2400
22000
172
133
93
26
4
45
93
39
13
69
12
44
46
13
292
385
10
227
1442
0.017
0.024
0.048
0.019
0.001
0.063
0.012
0.004
0.012
0.035
0.030
0.030
0.047
0.017
0.044
0.028
0.008
0.044
0.031
Summary of
Star Formation
In Nearby
Clouds
Evans et al. 2009
Allen et al., in prep.
L1014:
A TypicalAStarless
Typical Starless
Core… Or
Core
Maybe Not!
•
•
•
DSS R-band image
Dust prevents us from
seeing stars behind the
core, as well as the
interior of the core
Previousallows
Spitzer
infrared
us to see
surveys
many
background
did not findstars,
any
protostars
plus
one embedded
source
L1014-IRS:
Radiative Transfer Models
•
•
(Proto)stellar blackbody and disk required
to match Spitzer observations
Models constrain internal luminosity
Lint = Lstar + Ldisk ~ 0.09 Lsun
(not directly observable)
•
Accretion Luminosity:
L acc ~
•

•
Young et al. (2004)
•
Ý
GM M
acc
R
In the standard model (collapse of
isothermal sphere),
Mdot ~ 2 x 10-6 Msun year-1
(Shu, Adams, & Lizano 1987)
Collapse at this rate onto an object on the
stellar/substellar boundary (M = 0.08 Msun)
with typical protostellar radius gives
Lacc ~ 1.6 Lsun
How do you explain this object?
L1014-IRS:
Confirmation of its Embeddedness
CO outflow detected with orientation similar to near-IR nebulosity,
and Vlsr consistent with association with L1014 at 200 pc.
With luminosity of 0.025 - 0.050 Lsun and age of 105 years,
L1014-IRS is consistent with having a mass of 20-25 MJupiter
Chabrier et al. 2000
Huard et al. 2006
Bourke et al. 2005
L1014: High-resolution Extinction Map
Near-IR colors of background stars used to construct a high angular resolution
map of extinction. (NICE method; e.g., Lada et al. 2004)
Av = [2, 5, 10, 15, 20, 25, 30, 35]
30''
30''
Questions…
How common are sources like L1014-IRS ?
Do they typically form in isolation or in systems ?
What are their physical properties ?
L1014-IRS is not unique
IRAM04191 (Dunham et al. 2006)
Lint ~ 0.08 Lsun
L1521 (Bourke et al. 2006)
Lint ~ 0.06 Lsun
VeLLO Candidates
JHK
4.5, 8, 24
DSS R
8,24,70
Contours
350 m
CB130-3
L673-7
L328-IRS: Poster here by Chang Won Lee discussing
a VeLLO wanna-be.
Characterizing VeLLOs
L1014
IRAM04191
Lint ~ 0.09 Lsun
strong dust emission
weak outflow
no infall
no depletion
no deuteration
Young et al. 2004
Bourke et al. 2005
Huard et al. 2006
Crapsi et al. 2005
Lint ~ 0.08 Lsun
strong dust emission
large outflow
infall
depletion
deuteration
Dunham et al. 2006
Belloche et al. 2002
Andre et al. 1999
L1521
Lint ~ 0.06 Lsun
strong dust emission
outflow?
infall
depletion
deuteration
Bourke et al. 2006
Crapsi et al. 2004
Despite having similar Lint, the envelopes/outflows
Dunham et al. 2008
of known VeLLOs differ significantly.
Identifying Low-Luminosity Sources
•
Set of criteria to select sources with rising/flat SEDs
•
24 µm detection with S/N ≥ 3
•
70 µm detection
•
LIR  0.5 Lsun (Lint < 1 Lsun)
•
Filter out galaxies (Harvey et al. 2007)
Dunham et al. 2008
•
Visual Inspection
49 Candidate Low-Luminosity
Embedded Sources in Cores
27 Qualify as VeLLO Candidates
Poster here by Miryang Kim extends search
criteria to larger Gould’s Belt sample of clouds.
Identifying More Candidates that are Embedded
•
Rising/flat SED from IRAC to MIPS-1
•
24 µm detection with S/N ≥ 3
•
Characterize distribution of sources with extinction
•
Comparison to near-IR images
Eradicating “vermin” (galaxies)
Criteria to remove exgal
background developed by
c2d and IRAC GTO
(P. Harvey and R. Gutermuth).
Applied to full 5.3 sq. deg. of
SWIRE ELAIS-N1.
Generally, predicts 0 to 1 per
sq. deg.
Harvey et al. 2007
YSO candidates
Point-like galaxies
Blue are extended galaxies
Stars removed already
AGB stars
Standard Evolutionary Scenario
Single isolated low-mass star
n~104-105
outflow
n~105-108 cm-3
T~10-300 K
cm-3
T~10 K
infall
Factor 1000
smaller
Core collapse
t=0
t=105 yr (?)
Class I
Class 0
Formation planets
Protostar with disk
t=106-107 yr
Solar system
Note change of axes!
t>108 yr
Identifying More Candidates that are Embedded
Identifying More Candidates that are Embedded
1006 vermin
Identifying More Candidates that are Embedded
220 vermin
117 candidate embedded sources
(44 identified as YSO)
450 vermin
Identifying More Candidates that are Embedded
69 vermin
143 candidate embedded sources
(65 identified as YSO)
228 vermin
Identifying More Candidates that are Embedded
log S (24 µm; 140 pc) = (0.87 ± 0.20) log Lint - (10.05 ± 0.17)
Dunham et al. (2008)
Identifying More Candidates that are Embedded
log S (24 µm; 140 pc) = (0.87 ± 0.20) log Lint - (10.05 ± 0.17)
Dunham et al. (2008)
117 Sources qualify as VeLLO candidates in Auriga
Identifying More Candidates that are Embedded
log S (24 µm; 140 pc) = (0.87 ± 0.20) log Lint - (10.05 ± 0.17)
Dunham et al. (2008)
117 Candidate candidate proto-brown dwarfs in Auriga
Deep Near-IR Imaging
~7 good-weather nights were used to obtain deep JHKs observations
of Auriga and Perseus with NEWFIRM on the 4-meter telescope at
KPNO. Awaiting the release of the data processing pipeline…
16 orbits on HST will be used (September/October) to obtain deep H
observations of 6 very good VeLLO candidates.
Questions…
How common are sources like L1014-IRS ?
L1014-IRS is certainly not unique
At least two other confirmed VeLLOs, several more unpublished cases
Currently, 27 of 49 low luminosity (< 1 Lsun) candidates in cores are VeLLOs
VeLLOs may be a significant fraction of
low-luminosity (< 1 Lsun) protostars (~30-50%)
Questions…
Do they typically form in isolation or in systems ?
Requires a similar search in the large molecular clouds
Currently, 12 of 43 low luminosity (< 1 Lsun) candidates in clouds could be VeLLOs
27 of 49 low luminosity (< 1 Lsun) candidates in cores could be VeLLOs
VeLLOs may comprise a similar fraction of low-luminosity
sources in clouds and isolated cores.
…but MORE works needs to be done here!
Poster here by Miryang Kim extends the Dunham et al. 2008
search criteria to the larger Gould’s Belt sample of clouds.
Questions…
What are their physical properties ?
…MUCH MORE works needs to be done here!
Summary
L1014-IRS was the first VeLLO discovered. Since then, two more
confirmed VeLLOs have been discovered in cores IRAM04191 and
L1521F.
The three confirmed VeLLOs demonstrate varied envelope/outflow
properties. More confirmed VeLLOs need to be modeled in detail before
the physical properties of this class of sources may be characterized.
VeLLOs may constitute a significant fraction (~30-50%) of low-luminosity
(< 1Lsun) protostars, independent of environment (cluster vs isolation).
However, MORE work needs to be done in confirming VeLLO candidates
and associating them with neighbors before conclusions can be drawn.
We are searching for more VeLLO candidates, in a statistical way, using
MIPS 24 µm and extinction maps. Deep near-IR imaging is being used
to identify specific sources as VeLLO candidates.