A systematic Search for high-mass Stars in Cygnus X

Principal Investigators:
Sylvain Bontemps (Observatoire de Bordeaux)
Frederique Motte (SAp/Saclay)
Nicola Schneider-Bontemps (SAp/Saclay)

Massive stars(> 10 Msun) have a direct influence on their environment because they inject large quantities of energy into the interstellar medium via their radiation and stellar winds and ultimately as supernovae. These dynamical processes can trigger individual or cluster mode star formation due to induced collapse of molecular cloud fragments at the edges of expanding HII regions and supernova shells or direct compression of globules.

Similar to the situation of investigating low mass stars 15 years ago, it is now of prime interest to study in a statistical way 'real' massive protostars, which means the youngest ones still accreting material (without HII region). Thanks to new millimeter cameras which are capable to map large sky fields, comprehensive and unbiased surveys can be undertaken to search for protostellar objects (pre-infall objects and protostars).

We thus started a multiwavelength study program in the Cygnus X region to study the massive star formation capacity of such a Giant Molecular Cloud.

Cygnus X

Cygnus X is one the most active, nearby Giant Molecular Cloud (GMC) complex with ongoing high-mass star formation, located between l=75° and 85°). It contains the well-known bright IR sources DR21, DR21(OH), S106, W75 and AFGL2591 and the richest known OB association of the Galaxy (Cygnus OB2) and numerous HII regions.

The discussion on the nature of Cygnus X has remained controversial since the earliest observations of this region. There are two different scenarios:

1. Cygnus X is a large Stroemgren sphere surrounding the Cyg OB2 association and all objects are located at approximately the same distance, i.e., that of the Cyg OB 2 cluster (1/7 kpc).

2. The other view suggests that the large number of objects seen in Cygnus X is a by chance superposition of star formation sites because the local spiral arm is seen tangentially.

This Figure shows an Halpha image (courtesy of William McLaughlin (willmclaughlin.astrodigitals.com) of the Galactic plane in the Cygnus X direction. In this optical image, the large-scale dark pattern known as the "Great Cygnus Rift" and the bright, well-known reflection nebulae North America nebula (NGC7000), Pelican nebula (IC5070), and IC1318 are most prominent. The molecular gas distribution is traced with CO emission line observations from the low angular resolution (8.7 arcmin) survey from the Center for Astrophysics (Cfa) and is overlayed as white contours.

The dashed polyon shows the area which was surveyed with the KOSMA 3m telescope in the 13CO 2-1 and 3-2 and 12CO 3-2 lines.

Click to see a higher resolution image

Data Sets/Status of the project

IRAM 30m mm-Continuum Observations with MAMBO
We started the project by mapping the region around the well-known radio sources DR21 and W75 in the 1.3mm continuum using the 117 channel MAMBO-II camera at the IRAM 30m telescope. We then extended the observed area to neighbouring regions, including DR17-23 and - further to the west - L889 and IC 1318 b/c. In total, approximately 3 square degrees are covered (Motte et al., in prep.) with something like 100 protostars detected.

First results are published in the IAU 227 (2005) proceedings.

IRAM 30m multiline observations
At the positions of peak dust continuum emission, different sets of molecular lines were observed with the IRAM 30m telescope in order to determine the temperature (H2CO, N2H+, CH3CN), density (CS), outflow activity (SiO) and infall features (HCO+, CS, N2H+).

IRAM Plateau de Bure observations
The most interesting protostars extracted from our mm-continuum survey and the IRAM 30m multiline observations were observed in different molecular line tracers at the PdB as follow-ups.