Transcript ppt file - Universitat de Barcelona

UNIVERSITAT DE BARCELONA
IRAS 20343+4129, a puzzling massive star-forming region
Robert Estalella, Aina Palau, Maite Beltrán (UB)
Paul T. P. Ho (CfA), Henrik Beuther (MPIfA)
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Introduction: modes of star formation
(Megeath et al. 2005)
Observationally, there are
two modes of star formation
in molecular clouds:
clustered mode (e.g. Orion)
isolated mode (e.g. HHL 73)
Likely phenomena in clustered mode:
● interaction between sources
● outflows
● mergings of cloud cores
● compression front from high-mass stars
(Anglada et al. 1997)
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Introduction: the big question
Why do stars preferently form closely
packed rather than in isolation?
Nobody knows (up to now) the answer, but we can gain insight by:
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characterizing different cluster environments in their first stages of formation,
and
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studying the interaction between the members of these environments
Approach and strategy
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detect low-mass condensations:
high sensitivity
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first evolutionary stages:
mm/submm range
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high-mass star-forming regions farther away than 1 kpc: angular resolution: 2''-5''
Source selected from a sample of massive star-forming regions: IRAS 20343+4129
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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IRAS 20343+4129
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3200 L⊙ at 1.4 kpc in
Cygnus OB2
3 bright IR stars, brightest
infrared source IRS 3
coincident with a weak
cm source
IRS 1: the most luminous
and embedded object of
the association?
N-S bipolar outflow
(single dish)
0.05 pc
2MASS composite J, H, K image
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Continuum results (1 mm SMA)
cm source (white):
associated with IRS 3
1 mm emission (brown):
3 condensations:
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west: mm1-mm4, ~4 M⊙
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east: mm7, ~0.5 M⊙
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north:
mm6/IRS 1, ~0.2-0.5 M⊙
mm5/IRS 1N?
grey scale: 2MASS J image
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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CO (2-1) results (SMA)
low vel
Low velocity: associated with IRS 1, two elongated
structures at both sides of IRS 3
High velocity: bipolar molecular outflow in the
east-west direction driven by IRS 1.
No evidence of large-scale north-south outflow
high vel
grey scale: H2 cont + line at 2.12 µm (Kumar et al. 2002)
IRS 1 is at the center of
symmetry of the outflow
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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The bipolar outflow
Parameters of the outflow discovered toward IRS 1 compared to other outflows:
low
mass
high
mass
Parameters of IRS 1 outflow in between
low-mass and high-mass outflows
CO(2-1)
IRAM 30m
CO emission with IRAM 30 m (Beuther et al. 2002)
Large-scale blue lobe resolved out by the SMA
extended emission
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Cavity created by IRS 3
low res CO
Observations suggest that IRS 3 is
blowing up a shell of surrounding
material, and that the dust
condensations at both sides of IRS 3
are the result of accumulation of mass.
low vel CO
Snowplow
model from
Anglada et
al. (1995)
cont 1mm
IRS 3

assumptions:
Derived param.:
Rshell = 0.07 pc
vshell = 2 km/s
Pext  (3.3 km/s)2
n0 = 2300 cm-3
twind = 104 yr
Rmax = 0.08 pc
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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The nature of IRS 1
IRS 1:
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2MASS very bright magnitudes
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strong IR excess
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circumstellar mass at 1 mm
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outflow parameters
Is IRS 1 a high-mass B0 star? (too luminous)
Is IRS 1 a high-mass protostar? (too low circumstellar mass)
Is IRS 1 a low/intermediate-mass protostar?
SED for IRS 1 typical of Class I:
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1-2 µm: steep >0 profile
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10-100 µm: >0 profile
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Comparison with other SEDs of
Class I sources of different
luminosities scaled to the distance of
IRAS 20343+4129
IRS 1 is an intermediate-mass
Class I source
(IRS 13) 960 L⊙
(IRS 14) 250 L⊙
(IRAS 04016+2610) 4 L⊙
(but the circumstellar mass is low)
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Star formation: interactions, initial conditions
IRS 3 is driving a cavity and accumulating
the surrounding material in the walls
Interaction between sources could
have triggered star formation in
some cases
IRS 1 and IRS 3
could have formed
simultaneously
(IRS 3 may have
not triggered the
formation of IRS 1)
IRS 1
Initial conditions are
required to explain the
overall spatial distribution
of the sources
IRS 3
The most massive source has faint
mm emission associated
Other sources around it: different
properties at different wavelengths
This suggests continuous star formation,
and since Ns(IR) > Ns(mm), that
tlife(IR) > tlife(mm)
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Number of mm sources vs IR sources
Summary of high-mass protostellar objects observed with enough sensitivity to detect
low-mass condensations (< 1 M⊙) in the mm range, up to 2006:
Palau 2006, PhD thesis
See Aina’s presentation
Cesaroni 1999
Beuther & Schilke 2004
Median number of mm sources around high-mass protostars: 5
Median number of IR sources around high-mass stars: 15
(based on very poor statistics!)
Why?
Sensitivity problem?
Enough resolution and u-v coverage?
Massive enough regions?
Protostars already formed around the high-mass protostar?
Is star formation a continuous process?
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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Conclusions
IRAS 20343+4129 is a cluster environment with a variety of sources.
IRS 1, an intermediate-mass Class I source, driving an east-west
bipolar CO(2-1) outflow.
IRS 3, seems to drive an expanding shell pushing out the dust
condensations detected at both sides of this source.
Our observations suggest that star formation in this cluster
environments is a continuous process.
Interaction seems to be important in massive star-forming regions, but
initial conditions must be important as well to determine the final
distribution of young stellar objects in the cluster environment.
Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23
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