Transcript PowerPoint file - Departament d`Astronomia i Meteorologia

IRAS 20343+4129: A Puzzling High-Mass Protostar Candidate
Aina Palau, Robert Estalella,
Departament d'Astronomia i Meteorologia, Universitat de Barcelona
and
Paul T.P. Ho, Henrik Beuther
Harvard-Smithsonian Center for Astrophysics
Abstract
IRAS 20343+4129 is a massive protostar candidate, at a distance of 1.4 kpc, displaying strong dust and CO (2-1) emission from single-dish observations. Two strong IR sources lie
inside the IRAS ellipsoid error: IRS 1 and IRS 3. With the SMA observations, we have discovered a high-velocity bipolar outflow in the EW direction clearly associated with IRS 1, the
most embedded source in the region. Surprisingly, only weak continuum emission is found toward IRS 1, and the strongest millimeter condensations are not associated with any IR
source, but are coincident with low-velocity extended gas and H2 emission features at both sides of IRS 3. This suggests that dust is associated with the walls of an expanding cavity
which could be produced by an opening outflow or, alternatively, by a stellar wind emanating from IRS 3. High-angular resolution observations play a key role in disentangling the
contributions from multiple sources in intermediate/high-mass star forming regions.
Introduction
Observations
IRAS 20343+4129 is a high-mass star forming region at a distance of 1.4 kpc and has a luminosity of 3200 L. A bright-rimmed feature 1′ southwest of the
IRAS source has been detected at cm wavelengths (Miralles et al. 1994, Carral et al. 1999), and in the H2 (2.12 μm) emission line (Kumar et al. 2002).
Dense gas tracers such HCO+ and NH3 and cm emission have been detected toward IRAS 20343+4129 (Richards et al. 1987; Miralles et al. 1994).
Kumar et al. (2002) find three bright NIR nebulous stars: IRS 1 and IRS 3 (the latter associated with the cm source) lying inside the IRAS error ellipsoid,
and IRS 2 located to the north. Emission in a fan-shape morphology, extending southward from IRS 1 and surrounding IRS 3, seems to trace a cavity.
Single-dish observations revealed three peaks of mm and submm continuum emission and outflow emission coming from two different sources (Beuther et
al. 2002a, 2002b; Williams et al. 2004), suggesting that star formation is taking place simultaneously in several locations of the cloud.
The observations were carried out at 230 GHz with the
SMA with 5 antennas on 2003 July 30 and 31, and with 6
antennas on 2003 August 3. Typical system temperature
was around 200 K. The rms noise at 1.3 mm was 2 mJy
beam-1. The correlator was set to the standard mode, with
0.8125 MHz (or 1.06 km s-1) per channel. Standard
passband and gain calibration was performed in IDL using
the MIR package, and imaging with the MIRIAD package.
The synthesized beam was 3.5  2.6.
Fig. 2.- 2MASS composite
image of J, H, and Ks
filters), at the same scale
than Fig. 1. Red objects,
as IRS 1, are the most
embedded. The dashed
box shows the region
mapped in Figs. 4, 5, and
6.
Fig. 1.- H2 emission at
2.12 μm from Kumar et al.
(2002).
Note
the
3
sources, IRS 1, 2, and 3,
the H2 emission surrounding IRS 3 with a fan-shape
morphology,
and
the
arched structure to the
West. The dashed box
shows the region mapped
in Figs. 4, 5, and 6.
Fig. 4.- SMA continuum emission
at 230 GHz (brown contours),
superposed on the 2MASS J-band
image (grey scale). Contours are 3, 3, 6, 9, 12, 15, and 18 times the
rms of the map, 2 mJy beam-1.
The synthesized beam is 3.5 
2.6, at P.A.=-38. Also shown is
the 3.6 cm emission obtained with
the VLA (white contours), with a
peak intensity of 0.6 mJy beam-1.
Crosses correspond to IR sources
from 2MASS PSC.
Results: Continuum Emission
Weak continuum emission at 230 GHz (at a 6  level) is found associated with IRS 1 with a flux density of 18.3 mJy. For a
dust temperature between 20 K (from NH3 Miralles et al. 1994) and 44 K (derived from the SED, Sridharan et al. 2002), the
mass of gas and dust toward IRS 1 results in 0.3-0.6 M.
The strongest condensations in the field are coincident with one of the peaks detected in single-dish, northwest of IRS 3, and
are not associated with any IR source. The emission there contains several peaks, with a total flux density of 170 mJy, which
corresponds to 5.6 M for a Td of 20 K. Since the flux density from single-dish measurements is 1 Jy, 83% of the flux has
been filtered out by the interferometer. On the other hand, the eastern condensation detected at a 6  level corresponds to a
single-dish emission peak, that is, almost all the emission picked up with the single-dish is resolved by the SMA. Thus, this
eastern peak detected in single-dish is not constituted by compact sources but rather extended emission, while the western
peak contains more compact millimeter emission.
The only VLA cm source in the field is found toward IRS 3. From our millimeter observations we can only set an upper limit of
4  = 8 mJy for the emission at 1 mm toward IRS 3.
Results: CO(2-1)
Table 1. Energetics of the outflow driven by IRAS 20343+4129 IRS 1
s-1
Fig. 5.- Zero-order moment of the low velocity
CO(2-1) emission. Velocities have been
integrated from 8 to 14 km s-1. Contours range
from 8 to 64 Jy beam-1 km s-1, increasing in
steps of 8 Jy beam-1 km s-1. Grey scale, the
same as in Fig. 4.
CO(2-1) emission extends from -8 up to 38 km
(the
systemic velocity is 11.2 km s-1). The integrated
emission for the low-velocities, from 8 to 14 km s-1
reveals two filamentary structures associated with the
fan-shape structure found in H2. From the low-velocity
map, it is also clear the association of CO(2-1) with
IRS 1, as well as the presence of weak low-velocity
components westwards of the CO(2-1) main emission.
Regarding the high velocities, these are present only in
the immediate surroundings of IRS 1. Blue velocities
have been integrated from -4 to 6 km s-1, while red
velocities from 16 to 38 km s-1. The high-velocity CO(21) emission has a bipolar structure, with the center at
the position of IRS 1, and elongated in the EW
direction. No CO(2-1) emission is detected toward IRS
2 and 3. Note that these two sources are detected in
the visible, and thus could be older than IRS 1.
From the position-velocity plot toward IRS1 in the EW
direction, we find weak high-velocity gas at 12 km s-1
from the systemic velocity at position offsets from IRS
1 up to 7, or 10000 AU. Such velocities at these
distances would imply a central mass of 1000 M to be
gravitationally bound, and hence the bipolar structure
seen in CO(2-1) toward IRS 1 is tracing an outflow
motion.
Wing
Red
Blue
V range
Age
Mass
Momentum
Momentum rate
(km s-1)
(yr)
( M )
(M km s-1)
(M yr-1 km s-1)
0.24
3.3
6.9  10-4
0.28
3.8
8.1  10-4
14
Discussion
• Small scale outflow discovered toward IRS 1
While the large-scale NS outflow seen in single-dish at relatively low velocities is resolved out by the SMA, we have detected a
CO compact bipolar outflow in the EW direction clearly associated with IRS 1. This outflow is consistent with IRS 1 being a
low/intermediate-mass protostar (Bontemps et al. 1996). Little dust emission is seen toward IRS 1, corresponding to an upper
limit for the circumstellar mass of 0.3-0.6 M, typical for low-mass protostars. However, the IRAS luminosity is 3200 L, rising the
question of what is the origin of such a high luminosity since, from the 2MASS data, IRS 1 is the most embedded source in the
region.
• Nature of the dust condensations at both sides of IRS 3
The strongest dust condensations are associated with CO low-velocity gas and H2 emission features, and fall at the edges of the
blue lobe large-scale outflow. We interpret these dust condensations as a consequence of an accumulation of mass in the walls
of an expanding cavity, advancing against the surrounding medium. This cavity could be the blue lobe of a progressively
opening angle outflow or could be produced by a stellar wind emanating from the cm source associated with IRS 3.
• Single-dish versus SMA
Fig. 3.- Single-dish 1.2 mm
(grey scale) and CO (2-1)
wing emission (solid contours, 8 to 9 km s-1; dashed
contours, 13 to 15 km s-1)
from Beuther et al. (2002b),
at the same scale than
Figs. 1 and 2. The dashed
box shows the region
mapped in Figs. 4, 5, and 6.
With a single-dish instrument one would have never seen the small-scale outflow from IRS 1, whereas it is quite prominent with
the SMA. The SMA interferometer is particularly useful for small, probably less massive outflows, which are overwhelmed by the
extended outflows in the single-dish observations.
4700
Fig. 6.- Integrated high-velocity
CO (2-1) emission (contours). Red
contours (16 to 38 km s-1) and
blue contours (-4 to 6 km s-1)
begin at 2 Jy beam-1 km s-1 and
increase in steps of 5 Jy beam-1
km s-1. Grey scale, the same as in
Fig. 4.
Fig. 7.- Position-velocity plot along the
east-west direction, centered on IRS 1.
Contours are -30, -9, -3, 3, 9, 30, 60, 90,
120, 150, and 180 times 0.08 Jy beam-1.
The lines mark the position of IRS 1 and
the systemic velocity, 11.2 km s-1.
References
Beuther, H., Schilke, P., Menten, K.M., et al. 2002a, ApJ, 566, 945
Beuther, H., Schilke, P., Sridharan, T.K., et al. 2002b, A&A, 383, 892
Bontemps, S., André, P., Terebey, S., & Cabrit, S. 1996, A&A, 311, 858
Carral, P., Kurtz, S., Rodríguez, L. F., et al. 1999, RevMexAA, 35, 97
Kumar, M.S.N., Bachiller, R., & Davis, C.J. 2002, ApJ, 576, 313
Miralles, M.P., Rodríguez, L.F., & Scalise, E. 1994, ApJS, 92, 173
Richards, P.J., Little, L.T., Toriseva, M., & Heaton, B.D. 1987, MNRAS, 228, 43
Sridharan, T. K., Beuther, H., Schilke, P., et al. 2002, ApJ, 566, 931
Williams, S. J., Fuller, G. A., Sridharan, T. K. 2004, A&A, 417, 115