73 research outputs found
Radio-millimetre investigation of galactic infrared dark clouds
This paper presents follow-up observations of the mid-Infrared dark clouds
selected from the ISOGAL inner Galaxy sample. On-the-fly maps of 13CO, C18O and
the 1.2 mm continuum emission have been obtained a the IRAM 30-m telescope. A
preliminary analysis of the physico-chemical conditions at works in the clouds
is given and molecular depletion onto cold grains is discussed.Comment: 16 pages, 12 figures, to be published in A&
Early phase of massive star formation: A case study of Infrared dark cloud G084.81-01.09
We mapped the MSX dark cloud G084.81-01.09 in the NH3 (1,1) - (4,4) lines and
in the J = 1-0 transitions of 12CO, 13CO, C18O and HCO+ in order to study the
physical properties of infrared dark clouds, and to better understand the
initial conditions for massive star formation. Six ammonia cores are identified
with masses ranging from 60 to 250 M_sun, a kinetic temperature of 12 K, and a
molecular hydrogen number density n(H2) ~ 10^5 cm^-3. In our high mass cores,
the ammonia line width of 1 km/s is larger than those found in lower mass cores
but narrower than the more evolved massive ones. We detected self-reversed
profiles in HCO+ across the northern part of our cloud and velocity gradients
in different molecules. These indicate an expanding motion in the outer layer
and more complex motions of the clumps more inside our cloud. We also discuss
the millimeter wave continuum from the dust. These properties indicate that our
cloud is a potential site of massive star formation but is still in a very
early evolutionary stage
Stellar sources in the ISOGAL intermediate bulge fields
We present a study of ISOGAL sources in the "intermediate" galactic bulge
( 2, 1--4), observed by
ISOCAM at 7 and 15 . In combination with near-infrared (I, J, K) data of DENIS survey, complemented by 2MASS data, we discuss the nature of
the ISOGAL sources, their luminosities, the interstellar extinction and the
mass-loss rates. A large fraction of the 1464 detected sources at 15
are AGB stars above the RGB tip, a number of them show an excess in
([7]-[15]) and (K-[15]) colours, characteristic
of mass-loss. The latter, especially (K-[15]), provide
estimates of the mass-loss rates and show their distribution in the range
10 to 10 M/yr.Comment: 16 pages, accepted for publication in Astronomy and Astrophysic
Physical Characteristics of a Dark Cloud in an Early Stage of Star Formation toward NGC 7538: an Outer Galaxy Infrared Dark Cloud?
In the inner parts of the Galaxy the Infrared Dark Clouds (IRDCs) are
presently believed to be the progenitors of massive stars and star clusters.
Many of them are predominantly devoid of active star formation and for now they
represent the earliest observed stages of massive star formation. Their Outer
Galaxy counterparts, if present, are not easily identified because of a low or
absent mid-IR background. We characterize the ambient conditions in the Outer
Galaxy IRDC candidate G111.80+0.58, a relatively quiescent molecular core
complex in the vicinity of NGC7538. We conduct molecular line observations on a
number of dense cores and analyze the data in terms of excitation temperature,
column and volume density, mass and stability. The temperatures (15-20K) are
higher than expected from only cosmic ray heating, but comparable to those
found in massive cores. Star forming activity could be present in some cores,
as indicated by the presence of warm gas and YSO candidates. The observed
super-thermal line-widths are typical for star forming regions. The velocity
dispersion is consistent with a turbulent energy cascade over the observed size
scales. We do not find a correlation between the gas temperature and the
line-width. The LTE masses we find are much larger than the thermal Jeans mass
and fragmentation is expected. In that case the observed lines represent the
combined emission of multiple unresolved components. We conclude that
G111.80+0.58 is a molecular core complex with bulk properties very similar to
IRDCs in an early, but not pristine, star forming state. The individual cores
are close to virial equilibrium and some contain sufficient material to form
massive stars and star clusters. The ambient conditions suggest that turbulence
is involved in supporting the cores against gravitational collapse.Comment: Accepted for publication in A&A -- 19 pages, 9 figures -- high
resolution available at
http://www.astro.rug.nl/~frieswyk/Data/Research/OGIRDC/index.htm
ISOGAL: A deep survey of the obscured inner Milky Way with ISO at 7 and 15 micron and with DENIS in the near-infrared
The ISOGAL project is an infrared survey of specific regions sampling the
Galactic Plane selected to provide information on Galactic structure,stellar
populations,stellar mass-loss and the recent star formation history of the
inner disk and Bulge of the Galaxy. ISOGAL combines 7 and 15 micron ISOCAM
observations - with a resolution of 6'' at worst - with DENIS IJKs data to
determine the nature of the sources and theinterstellar extinction. We have
observed about 16 square degrees with a sensitivity approaching 10-20mJy,
detecting ~10^5 sources,mostly AGB stars,red giants and young stars. The main
features of the ISOGAL survey and the observations are summarized in this
paper,together with a brief discussion of data processing and quality. The
primary ISOGAL products are described briefly (a full description is given in
Schuller et al. 2003, astro-ph/0304309): viz. the images and theISOGAL-DENIS
five-wavelength point source catalogue. The main scientific results already
derived or in progress are summarized. These include astrometrically calibrated
7 and 15um images,determining structures of resolved sources; identification
and properties of interstellar dark clouds; quantification of the infrared
extinction law and source dereddening; analysis of red giant and (especially)
AGB stellar populations in the central Bulge,determining luminosity,presence of
circumstellar dust and mass--loss rate,and source classification,supplemented
in some cases by ISO/CVF spectroscopy; detection of young stellar objects of
diverse types,especially in the inner Bulge with information about the present
and recent star formation rate; identification of foreground sources with
mid-IR excess. These results are the subject of about 25 refereed papers
published or in preparation.Comment: A&A in press. 19 pages,10 Ps figures; problems with figures fixe
ISOGAL Survey of Baade's Windows in the Mid-infrared
The ISOGAL mid-infrared survey of areas close to the Galactic Plane aims to
determine their stellar content and its possible bearing on the history of the
Galaxy. The NGC6522 and Sgr I Baade's Windows of low obscuration towards the
inner parts of the Bulge represent ideal places in which to calibrate and
understand the ISOGAL colour-magnitude diagrams.
The survey observations were made with the ISOCAM instrument of the ISO
satellite. The filter bands chosen were LW2(~7 microns) and LW3(~15 microns).
The results presented here show that most of the detected objects are late
M-type giants on the AGB, with a cut-off for those earlier than M3-M4. The most
luminous members of these two Bulge fields at 7 microns are the Mira variables.
However, it is evident that they represent the end of a sequence of increasing
15 micron dust emission which commences with M giants of earlier sub-type.
In observations of late-type giants the ISOCAM 15 micron band is mainly
sensitive to the cool silicate or aluminate dust shells which overwhelm the
photospheric emission. However, in ordinary M-giant stars, the 7 micron band is
not strongly affected by dust emission and may be influenced instead by
absorption. The nu2 band of water at 6.25 microns and the SiO fundamental at
7.9 microns are likely contribitors to this effect.
A group of late M stars has been found which vary little or not at all but
have infrared colours typical of well-developed dust shells. Their luminosities
are similar to those of 200-300 day Miras but they have slightly redder
[7]-[15] colours which form an extension of the ordinary M giant sequence.
The Mira dust shells show a mid-infrared [7]-[15] colour-period relation. ca
700 days.Comment: 13 pages 15 figure
Infrared Dark Clouds in the Small Magellanic Cloud?
We have applied the unsharp-masking technique to the 24 m image of the
Small Magellanic Cloud (SMC), obtained with the Spitzer Space Telescope, to
search for high-extinction regions. This technique has been used to locate very
dense and cold interstellar clouds in the Galaxy, particularly infrared dark
clouds (IRDCs). Fifty five candidate regions of high-extinction, namely
high-contrast regions (HCRs), have been identified from the generated
decremental contrast image of the SMC. Most HCRs are located in the southern
bar region and mainly distributed in the outskirts of CO clouds, but most
likely contain a significant amount of H2. HCRs have a peak-contrast at 24
m of 2 - 2.5 % and a size of 8 - 14 pc. This corresponds to the size of
typical and large Galactic IRDCs, but Galactic IRDCs are 2 - 3 times darker at
24 m than our HCRs. To constrain the physical properties of the HCRs, we
have performed NH3, N2H+, HNC, HCO+, and HCN observations toward one of the
HCRs, HCR LIRS36-EAST, using the Australia Telescope Compact Array and the
Mopra single-dish radio telescope. We did not detect any molecular line
emission, however, our upper limits to the column densities of molecular
species suggest that HCRs are most likely moderately dense with n ~ 10^{3}
cm-3. This volume density is in agreement with predictions for the cool atomic
phase in low metallicity environments. We suggest that HCRs may be tracing
clouds at the transition from atomic to molecule-dominated medium, and could be
a powerful way to study early stages of gas condensation in low metallicity
galaxies. Alternatively, if made up of dense molecular clumps < 0.5 pc in size,
HCRs could be counterparts of Galactic IRDCs, and/or regions with highly
unusual abundance of very small dust grains.Comment: accepted for publication in the Astronomical Journa
Herschel observations of deuterated water towards Sgr B2(M)
Observations of HDO are an important complement for studies of water, because
they give strong constraints on the formation processes -- grain surfaces
versus energetic process in the gas phase, e.g. in shocks. The HIFI
observations of multiple transitions of HDO in Sgr~B2(M) presented here allow
the determination of the HDO abundance throughout the envelope, which has not
been possible before with ground-based observations only. The abundance
structure has been modeled with the spherical Monte Carlo radiative transfer
code RATRAN, which also takes radiative pumping by continuum emission from dust
into account. The modeling reveals that the abundance of HDO rises steeply with
temperature from a low abundance () in the outer envelope
at temperatures below 100~K through a medium abundance () in
the inner envelope/outer core, at temperatures between 100 and 200~K, and
finally a high abundance () at temperatures above 200~K in
the hot core.Comment: A&A HIFI special issue, accepte
Herschel observations of EXtra-Ordinary Sources: The Terahertz spectrum of Orion KL seen at high spectral resolution
We present the first high spectral resolution observations of Orion KL in the
frequency ranges 1573.4 - 1702.8 GHz (band 6b) and 1788.4 - 1906.8 GHz (band
7b) obtained using the HIFI instrument on board the Herschel Space Observatory.
We characterize the main emission lines found in the spectrum, which primarily
arise from a range of components associated with Orion KL including the hot
core, but also see widespread emission from components associated with
molecular outflows traced by H2O, SO2, and OH. We find that the density of
observed emission lines is significantly diminished in these bands compared to
lower frequency Herschel/HIFI bands.Comment: Accepted for publication in the Herschel HIFI special issue of
Astronomy and Astrophysics Letters, 5 pages, 3 figure
Herschel observations of extra-ordinary sources: Detection of Hydrogen Fluoride in absorption towards Orion~KL
We report a detection of the fundamental rotational transition of hydrogen
fluoride in absorption towards Orion KL using Herschel/HIFI. After the removal
of contaminating features associated with common molecules ("weeds"), the HF
spectrum shows a P-Cygni profile, with weak redshifted emission and strong
blue-shifted absorption, associated with the low-velocity molecular outflow. We
derive an estimate of 2.9 x 10^13 cm^-2 for the HF column density responsible
for the broad absorption component. Using our best estimate of the H2 column
density within the low-velocity molecular outflow, we obtain a lower limit of
~1.6 x 10^-10 for the HF abundance relative to hydrogen nuclei, corresponding
to 0.6% of the solar abundance of fluorine. This value is close to that
inferred from previous ISO observations of HF J=2--1 absorption towards Sgr B2,
but is in sharp contrast to the lower limit of 6 x 10^-9 derived by Neufeld et
al. (2010) for cold, foreground clouds on the line of sight towards G10.6-0.4.Comment: 5 pages, 3 figures, paper to be published in the Herschel special
issue of A&A letter
- …