A MASSIVE PROTOSTELLAR DISK

1
A MASSIVE PROTOSTELLAR DISK IN CEPHEUS A
REALLY??
Claudia Comito, MPIfR Bonn in collaboration
with Peter Schilke (MPIfR Bonn) Izaskun
Jimenez-Serra, Jesus Martin-Pintado (CSIC
Madrid) Helmut Wiesemeyer, Ian Martin Winters
(IRAM Grenoble)
2
THE SEARCH FOR ACCRETION DISKS AROUND MASSIVE
PROTOSTARS

• We know how low-mass stars form, but no
  universal paradigm explains the formation of
  massive stars (Mgt8Msun)
• Main hypotheses coalescence and accretion (must
  be through a disk)
• Observation of collimated outflows associated to
  massive stars suggests that accretion through
  rotating disks can happen for massive stars as
  well (see the Beuther et al. series)
• Problems massive protostars are RARE, FAR AWAY
  (dgt2kpc), live a SHORT LIFE in a MESSY
  ENVIRONMENT (clusters).
• Accretion disks around high-mass protostars are
  HARD TO SPOT!

3
THE CASE FOR THE CEPHEUS A (HW2) DISK

• Outflow in NE-SW direction observed in many
  molecular tracers. Powering source HW2?
• Distribution of H2O masers perpendicular to
  outflow direction, their velocity gradient
  suggests rotation (Torrelles et al. 1996)
• Other molecular species show same distribution
  (e.g., SiO).
• Torrelles suggests a 600AU diameter disk rotates
  around HW2.

Gomez et al. 1999 (OVRO data)
4
THE CASE FOR THE CEPHEUS A (HW2) DISK

• Outflow in NE-SW direction observed in many
  molecular tracers. Powering source HW2?
• Distribution of H2O masers perpendicular to
  outflow direction, their velocity gradient
  suggests rotation (Torrelles et al. 1996)
• Other molecular species show same distribution
  (e.g., SiO).
• Torrelles suggests a 600AU diameter disk rotates
  around HW2.

Gomez et al. 1999 (OVRO data)
5
PdBI OBSERVATIONS

• at 725 pc, 600 AU 0.8. The disk, if it
  exists, could be resolved with Plateau de Bure at
  1mm.
• in 2002/2003 and 2003/2004, proposed for 3
  setups and observed a number of molecular
  transitions in AB configuration.
• To determine feasibility of observations
• observed desired lines with single-dish
  telescopes (CSO, IRAM 30m) and estimated source
  size.
• modeled expected emission in PdBI beam
• verified that the required (high) spectral
  resolution would allow detection

6
SUMMARY OF OBSERVED FEATURES with PdBI in AB
configuration
SPECIES FREQUENCY REGION HPBW ()
SiO(2-1) 87 GHz Core large-scale flow 2 x 1.6
HCN(1-0) 89 GHz Core large-scale flow 1.9 x 1.8
H218O(313-220) 203 GHz Core 1 x 0.8
SO2(12-11) 203 GHz Core base of flow 1 x 0.8
13CO(2-1) 220 GHz Core large-scale outflow 0.9 x 0.7
CH3CN(12-11) 220 GHz Core base of flow 0.9 x 0.7
CH3OH(5-4) 241 GHz Core base of flow 0.7 x 0.6
7
RICH SPECTRUM SIGNATURE OF HOT-CORE CHEMISTRY
8
-18 km/sec
13CO
-2 km/sec
HCN 0 km/sec
9
-18 km/sec
13CO
-2 km/sec
HCN -13 km/sec
10
-18 km/sec
13CO
-2 km/sec
HCN -26 km/sec
11
SO2(12-11) 203 GHz 1x0.8
12
CH3CN(12-11) 220 GHz 0.9x0.7
13
(No Transcript)
14
(No Transcript)
15
SO2(12-11) 203 GHz 1x0.8
16
CH3CN(12-11) 220 GHz 0.9x0.7
17
DATA ANALYSIS IN PROGRESS!

• does the velocity gradient in, e.g., CH3CN
  really tell us about a rotating disk?
• Why is the central mass so small, when HW2 is
  supposed to be 8 Msun?
• IF a rotating disk exists, what is it rotating
  about? Why doesnt the dust peak coincide with
  the center of mass? (did we do it right?)
• HYPOTHESIS the disk may be rotating about 2 or
  more protostars at different stages of evolution
  (HW2, plus the source of the outflow, plus ???).

18
CONCLUSIONS

• Tiny example of observational approach to
  massive-star-formation studies.
• Problems high-mass protostars are far away, and
  have complicated environments. Complications are
• spatial they live in clusters, theyre
  difficult to single out
• kinematical phenomena like outflows are very
  common, their collective projection onto the
  plane of the sky results into a mighty mess.

We need the high spatial and spectral resolution
of mm interferometry to address these issues.
19
SO2(12-11) 203 GHz 1x0.8
20
Q ARE WE SEEING A ROTATING DISK ACCRETING ONTO A
PROTOSTAR? A MAYBE HOWEVER

• from fit of pv plots, IF a rotating disk exists,
  Mstar 1.5 Msun
• the 241 GHz dust emission suggests a mass of 1.2
  Msun

OUR MASSIVE PROTOSTELLAR DISK IS NOT THAT
MASSIVE AFTER ALL
21
(No Transcript)