Issue |
Astron. Astrophys. Suppl. Ser.
Volume 136, Number 2, April II 1999
|
|
---|---|---|
Page(s) | 333 - 361 | |
DOI | https://doi.org/10.1051/aas:1999218 | |
Published online | 15 April 1999 |
High density molecular clumps around protostellar candidates
Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
Send offprint request to: R. Cesaroni
Received:
20
November
1998
Accepted:
20
January
1999
There are several indications that strong
H2O maser emission arises at the very beginning of the
evolution of a massive star and disappears when an Hii region
becomes detectable in the radio continuum.
If this is the case, one expects to find dense hot molecular gas
surrounding embedded far IR sources coincident with H2O masers.
In order to test this hypothesis, we
have used the Pico Veleta 30-m radiotelescope to search for molecular
line emission towards a sample of 12 H2O
masers located in regions of massive star formation,
but not directly associated with bright compact radio Hii regions,
with the intention to identify the sites of newly born massive
(proto)stars in their earliest stages and to study their properties.
Our main goals were: a) to confirm the hypothesis that the H2O masers
not associated with compact radio continuum emission
are indeed located at the centre of high density clumps within a molecular
cloud; b) to use several molecular transitions
(namely: (), CS(
), C34S(
), C34S(
, C34S
),
HCN(
), (
), (
),
(
), CH3OH(
), CH3OH(
))
in order to derive information on
the size, kinematics, temperature, density, and ionisation degree
of the molecular gas in the places where star formation
has just begun, as well as to search for the presence of outflows
on scale sizes of 10″ - 30″.
In this paper we present the large amount of data obtained at Pico Veleta
in a compressed way, but still sufficiently ample
to give usable informations for
further studies. General results from a first analysis of the data are
also presented.
Our first goal is amply verified since in all cases and in molecules
tracing high density gas
we find a barely resolved peak at the position of the maser,
confirming the validity of our selection criteria.
Our sample thus provides a valid reference list of
regions of massive star formation in their earliest phases.
As far as the second goal is concerned, the large variety of intensity ratios
of different molecules, as well as of other derived parameters, point out
that the molecular clumps where star formation is taking place are far from
identical and that chemical evolution and influence of the newborn star may
amply affect the line intensity ratios.
In some cases small scale (seconds of arc) outflows were detected, not
necessarily related to the minute of arc scale outflows present in the same
regions.
More detailed studies of each region are presented in separate papers.
Key words: ISM: clouds / ISM: molecules / radio lines: interstellar
© European Southern Observatory (ESO), 1999