Issue |
A&A
Volume 366, Number 3, February II 2001
|
|
---|---|---|
Page(s) | 873 - 890 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20000358 | |
Published online | 15 February 2001 |
Disks and outflows around intermediate-mass stars and protostars*
1
Observatorio Astronómico Nacional (IGN), Campus Universitario, Apdo. 1143, 28800 Alcalá de Henares (Madrid), Spain
2
Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, Domaine Universitaire, 38406 St Martin d'Hères Cedex, France
3
Universidad Complutense de Madrid, Av. Arcos de Jalón s/n, 28037 Madrid, Spain
4
Nobeyama Radio Observatory, Nobeyama, Minamimaki, Minamisaku, Nagano, 384-1305, Japan
5
Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
A. Fuente
Received:
28
July
2000
Accepted:
14
November
2000
In order to study the existence and evolution of circumstellar disks
around intermediate-mass stars (),
we have obtained single-dish and interferometric continuum images
at 2.6 mm and 1.3 mm of the intermediate-mass protostar
NGC 7129 FIRS 2
and of the Herbig Be stars LkHα 234 and HD 200775.
These objects are representative of the different stages of the
pre-main sequence evolution with ages ranging from a few 103
to 8 106 years.
Single-dish and interferometric observations of
the outflows associated with these sources are also presented.
In NGC 7129 FIRS 2, two millimeter sources are required
to fit the interferometric 1.3 mm continuum emission.
Only the most intense of these millimeter objects, FIRS 2 -MM1,
seems to be associated with the CO outflow. The second and weaker
source, FIRS 2 -MM2, does not present any sign of stellar activity.
The single-dish map of the CO outflow
presents an unusual morphology with the blue and red lobes separated
by an angle of 82
. The CO
interferometric
image shows that this unusual morphology is the result of the superposition
of two outflows, one of them associated with FIRS 2 -MM1 (the blue lobe in
the single-dish map) and the other (the red lobe) with a new
infrared source (FIRS 2 -IR) which is not detected in the
millimeter continuum images.
The interferometric 1.3 mm continuum image of NGC 7129 FIRS 1
reveals that LkHα 234 is a member of a cluster of
embedded objects. Two millimeter clumps
are detected in this far-infrared source. The strongest
is spatially coincident with the mid-infrared companion of
LkH α 234, IRS 6.
A new millimeter clump, FIRS 1 -MM1,
is detected at an offset (
, 3.0'')
from LkHα 234.
We have not detected any compact
source towards LkHα 234 with a limit for the mass of a
circumstellar disk, MD
< 0.1
.
The comparison of the interferometric CO
and continuum images reveals that IRS 6 very likely
drives the energetic molecular
outflow detected towards NGC 7129 FIRS 1 and the [SII] jet.
The extremely young object FIRS 1 -MM1 (it has not been
detected in the near-and mid-infrared) turns out to be
the driving source of the H2 jet.
There is no evidence for the existence of a
bipolar outflow associated with LkHα 234.
We have not detected 1.3 mm continuum emission towards HD 200775.
Our observations imply a 3-σ upper limit of < 0.002
for the mass of a circumstellar disk.
This is the lowest upper limit obtained so far in a Herbig Be star.
Thus our observations provide new important information on
three protostars (IRS 6, FIRS 1 -MM1 and FIRS 2 -MM1),
one infrared star (FIRS 2 -IR) and two Herbig Be stars.
The luminosities of the protostars are
consistent with being intermediate-mass objects
(
-
). They are surrounded by
thick envelopes with masses ranging between ∼
and drive energetic outflows.
Circumstellar disks and bipolar outflows are not detected toward the
Herbig Be stars. We have obtained an upper limit for the disk/stellar
mass ratio,
, of < 0.02 in LkHα 234 and of < 0.0002
in HD 200775. Our limit in HD 200775 implies that in evolved Herbig Be
stars the
ratio is more than two orders of magnitude lower than
in T Tauri and Herbig Ae stars. We propose that in massive stars
(
≥ 5
) both the dispersal of the outer disk and the
energetic mass-loss, occur early in the stellar evolution
before the star becomes visible. Some mechanisms for the dispersal of the outer
disk are discussed.
Key words: stars: formation / fundamental parameters / pre-main sequence / ISM: abundances / clouds / molecules
© ESO, 2001
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