106 research outputs found
A New Component in the Radio Continua of PNe
A byproduct of experiments designed to map the CMB is the recent detection of a new component of foreground galactic emission. The anomalous foreground at 10–30 GHz, unexplained by traditional emission mechanisms, correlates with 100 mum dust emission, and is thus presumably due to dust.Is the anomalous foreground ubiquitous in the Galaxy? I will present evidence obtained with the CBI and SIMBA+SEST supporting the existence of the new component in the ISM at large, and in specific objects, in the form of a 31 GHz excess over free-free emission in PNe
Molecular abundances in carbon-rich circumstellar envelopes
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
Molecular excitation in the Eagle nebula's fingers
Context: The M16 nebula is a relatively nearby Hii region, powered by O stars
from the open cluster NGC 6611, which borders to a Giant Molecular Cloud.
Radiation from these hot stars has sculpted columns of dense obscuring material
on a few arcmin scales. The interface between these pillars and the hot ionised
medium provides a textbook example of a Photodissociation Region (PDR).
Aims: To constrain the physical conditions of the atomic and molecular
material with submillimeter spectroscopic observations.
Methods: We used the APEX submillimeter telescope to map a ~3'x3' region in
the CO J=3-2, 4-3 and 7-6 rotational lines, and a subregion in atomic carbon
lines. We also observed C18O(3-2) and CO(7-6) with longer integrations on five
peaks found in the CO(3-2) map. The large scale structure of the pillars is
derived from the molecular lines' emission distribution. We estimate the
magnitude of the velocity gradient at the tips of the pillars and use LVG
modelling to constrain their densities and temperatures. Excitation
temperatures and carbon column densities are derived from the atomic carbon
lines.
Results: The atomic carbon lines are optically thin and excitation
temperatures are of order 60 K to 100 K, well consistent with observations of
other Hii region-molecular cloud interfaces. We derive somewhat lower
temperatures from the CO line ratios, of order 40 K. The Ci/CO ratio is around
0.1 at the fingers tips.Comment: 4 pages, APEX A&A special issue, accepte
Physical properties of Southern infrared dark clouds
It is commonly assumed that cold and dense Infrared Dark Clouds (IRDCs)
likely represent the birth sites massive stars. Therefore, this class of
objects gets increasing attention. To enlarge the sample of well-characterised
IRDCs in the southern hemisphere, we have set up a program to study the gas and
dust of southern IRDCs. The present paper aims at characterizing the continuuum
properties of this sample of objects. We cross-correlated 1.2 mm continuum data
from SIMBA@SEST with Spitzer/GLIMPSE images to establish the connection between
emission sources at millimeter wavelengths and the IRDCs we see at 8 m in
absorption against the bright PAH background. Analysing the dust emission and
extinction leads to a determination of masses and column densities, which are
important quantities in characterizing the initial conditions of massive star
formation. The total masses of the IRDCs were found to range from 150 to 1150
(emission data) and from 300 to 1750 (extinction
data). We derived peak column densities between 0.9 and 4.6
cm (emission data) and 2.1 and 5.4 cm
(extinction data). We demonstrate that the extinction method fails for very
high extinction values (and column densities) beyond A values of
roughly 75 mag according to the Weingartner & Draine (2001) extinction relation
model B. The derived column densities, taking into account
the spatial resolution effects, are beyond the column density threshold of 3.0
cm required by theoretical considerations for massive
star formation. We conclude that the values for column densities derived for
the selected IRDC sample make these objects excellent candidates for objects in
the earliest stages of massive star formation.Comment: Accepted for publication in Astronomy & Astrophysic
Submillimeter spectroscopy of southern hot cores: NGC6334(I) and G327.3-0.6
High-mass star-forming regions are known to have a rich molecular spectrum
from many species. Some of the very highly excited lines are emitted from very
hot and dense gas close to the central object(s). The physics and chemistry of
the inner cores of two high mass star forming regions, NGC6334(I) and
G327.3-0.6, shall be characterized. Submillimeter line surveys with the APEX
telescope provide spectra which sample many molecular lines at high excitation
stages. Partial spectral surveys were obtained, the lines were identified,
physical parameters were determined through fitting of the spectra. Both
sources show similar spectra that are comparable to that of the only other high
mass star forming region ever surveyed in this frequency range}, Orion-KL, but
with an even higher line density. Evidence for very compact, very hot sources
is found.Comment: APEX A&A special issue, accepte
Looking for the S-Z Effect towards Distant ROSAT Clusters of Galaxies
We report on observations of the Sunyaev-Zeldovich effect towards X-ray ROSAT
clusters taken with a double channel (1.2 and 2 mm) photometer installed at the
focus of the 15m SEST antenna in Chile. This paper describes the first results
obtained for the high-z clusters S1077, A2744 and S295. Marginal detections
were found for A2744 and at 1 mm for S1077. We discuss these data in terms of
contamination of sources along the line of sight and give a constraint on the
amplitude of the kinematic effect.Comment: 17 pg Latex file (using aasms4.sty) gzip'd tar'd uuencoded file
including 1 ps figure, ApJ Letter in pres
Circumstellar masers in the Magellanic Clouds
We have searched for 22 GHz H2O and 43/86/129 GHz SiO masers in bright IRAS
point sources in the SMC and LMC, to test whether the kinematics of the mass
loss from these stars depends on metallicity. H2O masers were detected in the
red supergiants IRAS04553-6825 and IRAS05280-6910, and tentatively in the
luminous IR object IRAS05216-6753 and the AGB star IRAS05329-6708. SiO masers
were detected in IRAS04553-6825. The outflow velocity increases between the H2O
masing zone near the dust-formation region and the more distant OH masing zone
from 18 to 26 km/s for IRAS04553-6825 and from 6 to 17 km/s for IRAS05280-6910.
The total sample of LMC targets is analysed in comparison with circumstellar
masers in the Galactic Centre. The photon fluxes of circumstellar masers in the
LMC are very similar to those in the Galactic Centre. The expansion velocities
in the LMC appear to be 20% lower than for similarly bright OH masers in the
Galactic Centre, but the data are consistent with no difference in expansion
velocity. OH/IR stars in the LMC appear to have slower accelerating envelopes
than OH/IR stars in the Galactic Centre. Masers in the LMC have blue-asymmetric
emission profiles. This may be due to the amplification of stellar and/or
free-free radiation, rather than the amplification of dust emission, and may be
more pronounced in low metallicity envelopes. SiO maser strength increases with
the photometric amplitude at 2.2 micron but is independent of the photometric
amplitude at 10 micron. This suggests a strong connection between shocks in the
dust-free SiO masing zone and the dust formation process. Appendices describe
H2O maser emission from R Dor in the Milky Way, optical echelle spectroscopy of
IRAS04553-6825, and the properties of masers in the Galactic Centre (Abridged).Comment: 19 pages, 17 figures. Accepted for publication in Astronomy &
Astrophysics Main Journa
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