2,048 research outputs found
A multi-transition submillimeter water maser study of evolved stars - detection of a new line near 475 GHz
Context: Maser emission from the H2O molecule probes the warm, inner
circumstellar envelopes of oxygen-rich red giant and supergiant stars.
Multi-maser transition studies can be used to put constraints on the density
and temperature of the emission regions.
Aims: A number of known H2O maser lines were observed toward the long period
variables R Leo and W Hya and the red supergiant VY CMa. A search for a new,
not yet detected line near 475 GHz was conducted toward these stars.
Methods: The Atacama Pathfinder Experiment telescope was used for a
multi-transition observational study of submillimeter H2O lines.
Results: The 5_33-4_40 transition near 475 GHz was clearly detected toward VY
CMa and W Hya. Many other H2O lines were detected toward all three target
stars. Relative line intensity ratios and velocity widths were found to vary
significantly from star to star.
Conclusions: Maser action is observed in all but one line for which it was
theoretically predicted. In contrast, one of the strongest maser lines, in R
Leo by far the strongest, the 437 GHz 7_53-6_60 transition, is not predicted to
be inverted. Some other qualitative predictions of the model calculations are
at variance with our observations. Plausible reasons for this are discussed.
Based on our findings for W Hya and VY CMa, we find evidence that the H2O
masers in the AGB star W Hya arise from the regular circumstellar outflow,
while shock excitation in a high velocity flow seems to be required to excite
masers far from the red supergiant VY CMa.Comment: 9 pages, 4 figures, Astronomy and Astrophyics (in press
Search for interstellar methoxyacetonitrile and cyanoethanol: insights into coupling of cyano- to methanol and ammonia chemistry
As part of an effort to study gas-grain chemical models in star-forming regions as they relate to molecules
containing cyanide (–C≡N) groups, we present here a search for the molecules 2-cyanoethanol (OHCH_2CH_2CN) and methoxyacetonitrile (CH_3OCH_2CN) in the galactic center region SgrB2. These species are structural isomers
of each other and are targeted to investigate the cross-coupling of pathways emanating from the photolysis products
of methanol and ammonia with pathways involving cyano-containing molecules. Methanol and ammonia ices are two of the main repositories of the elements C, O, and N in cold clouds and understanding their link to cyanide chemistry could give important insights into prebiotic molecular evolution. Neither species was positively detected, but the upper limits we determined allow comparison to the general patterns gleaned from chemical models. Our results indicate the need for an expansion of the model networks to better deal with cyanochemistry, in particular with respect to pathways including products of methanol photolysis. In addition to these results, the two main observational routes for detecting new interstellar molecules are discussed. One route is by decreasing detection limits at millimeter wavelength through spatial filtering with interferometric studies at the Atacama Large Millimeter Array (ALMA), and the second is by searching for intense torsional states at THz frequencies using the Herschel Space Observatory. 2-cyanoethanol and methoxyacetonitrile would both be good test beds for exploring the capabilities of ALMA and Herschel in the study of complex interstellar chemistry
The dynamical state of the First Hydrostatic Core Candidate Cha-MMS1
Observations of First Hydrostatic Core candidates, a theoretically predicted
evolutionary link between the prestellar and protostellar phases, are vital for
probing the earliest phases of star formation. We aim to determine the
dynamical state of the First Hydrostatic Core candidate Cha-MMS1. We observed
Cha-MMS1 in various transitions with the APEX and Mopra telescopes. The
molecular emission was modeled with a radiative transfer code to derive
constraints on the envelope kinematics. We derive an internal luminosity of
0.08 - 0.18 Lsol. An average velocity gradient of 3.1(0.1) km/s/pc over 0.08 pc
is found perpendicular to the filament in which Cha-MMS1 is embedded. The
gradient is flatter in the outer parts and at the innermost 2000 - 4000 AU.
These features suggest solid-body rotation beyond 4000 AU and slower,
differential rotation beyond 8000 AU. The origin of the flatter gradient in the
innermost parts is unclear. The classical infall signature is detected in HCO+
3-2 and CS 2-1. The radiative transfer modeling indicates a uniform infall
velocity in the outer parts of the envelope. An infall velocity field scaling
with r^(-0.5) is consistent with the data for r < 9000 AU. The infall
velocities are 0.1 - 0.2 km/s at r > 3300 AU and 0.04 - 0.6 km/s at r < 3300
AU. Both the internal luminosity of Cha-MMS1 and the infall velocity field in
its envelope are consistent with predictions of MHD simulations for the first
core phase. There is no evidence for a fast, large-scale outflow stemming from
Cha-MMS1 but excess emission from the high-density tracers CS 5-4, CO 6-5, and
CO 7-6 suggests the presence of higher-velocity material at the inner core. Its
internal luminosity excludes Cha-MMS1 being a prestellar core. The kinematical
properties of its envelope are consistent with Cha-MMS1 being a first core
candidate or a very young Class 0 protostar.(abridged).Comment: Accepted for publication in A&A. 27 pages, 22 figures, 13 tables. A
version with high-resolution figures is available on request to the first
autho
APEX telescope observations of new molecular ions
Hydrides are key ingredients of interstellar chemistry since they are the
initial products of chemical networks that lead to the formation of more
complex molecules. The fundamental rotational transitions of light hydrides
fall into the submillimeter wavelength range. Using the APEX telescope, we
observed the long sought hydrides SH+ and OH+ in absorption against the strong
continuum source Sagittarius B2(M). Both, absorption from Galactic center gas
as well as from diffuse clouds in intervening spiral arms over a large velocity
range is observed. The detected absorption of a continuous velocity range on
the line of sight shows these hydrides to be an abundant component of diffuse
clouds. In addition, we used the strongest submillimeter dust continuum sources
in the inner Galaxy to serve as background candles for a systematic census of
these hydrides in diffuse clouds and massive star forming regions of our Galaxy
and initial results of this survey are presented.Comment: To appear in Spectroscopy of Molecular Ions in the Laboratory and in
Space (SMILES 2010), AIP Conference Proceedings, in pres
Observations of extragalactic masers in bright IRAS sources
We report the first results of an ongoing survey at 22 GHz with the 100-m
Effelsberg telescope to search for water maser emission in bright IRAS sources.
We have detected water vapor emission in IC 342. The maser, associated with a
star forming region ~10-15 arcsec west of the nucleus, consists of a single 0.5
km/s wide feature and reaches an isotropic luminosity of 0.01 L(sun) (D = 1.8
Mpc). Our detection raises the detection rate among northern galaxies with IRAS
point source fluxes S(100micron) > 50 Jy to 16%.Comment: 6 pages, 3 figures. Proceeding of the conference "SRT: the impact of
large antennas on Radio Astronomy and Space Science", Cagliari, Italy, 7-10
Nov. 2001, Eds. Porceddu et al. Needs srt_style.st
The innermost region of the water megamaser radio galaxy 3C403
The standard unified scheme of active galactic nuclei requires the presence
of high column densities of gas and dust potentially obscuring the central
engine. So far, few direct subarcsecond resolution studies of this material
have been performed toward radio galaxies. The goal of this paper is to
elucidate the nuclear environment of the prototypical X-shaped Fanaroff-Riley
type II radio galaxy 3C403, the only powerful radio galaxy known to host a
water megamaser. Very Large Array A-array and single-dish Green Bank and
Effelsberg 1.3 cm measurements were performed to locate and monitor the water
maser emission. Very Long Baseline Interferometry 6 cm continuum observations
were taken to analyze the spatial structure of the nuclear environment at even
smaller scales, while the CO J=1-0 and 2-1 transitions were observed with the
IRAM 30-m telescope to search for thermal emission from a spatially extended,
moderately dense gas component.[abridged]Comment: 11 pages, 12 figures, accepted by A&A. For a version with high
quality figures, see http://erg.ca.astro.it/~atarchi/3C403
Interstellar HOCN in the Galactic center region
Aims. Our aim is to confirm the interstellar detection of cyanic acid, HOCN,
in the Galactic center clouds. It has previously been tentatively detected only
in Sgr B2(OH).
Methods. We used a complete line survey of the hot cores Sgr B2(N) and (M) in
the 3 mm range, complemented by additional observations carried out with the
IRAM 30 m telescope at selected frequencies in the 2 mm band and towards four
additional positions in the Sgr B2 cloud complex in the 2 and 3 mm bands. The
spectral survey was analysed in the local thermodynamical equilibrium
approximation (LTE) by modeling the emission of all identified molecules
simultaneously. This allowed us to distinguish weak features of HOCN from the
rich line spectrum observed in Sgr B2(N) and (M). Lines of the more stable (by
1.1 eV) isomer isocyanic acid, HNCO, in these sources, as well as those of HOCN
and HNCO towards the other positions, were analysed in the LTE approximation as
well.
Results. Four transitions of HOCN were detected in a quiescent molecular
cloud in the Galactic center at a position offset in (R.A., decl.) by
(20'',100'') from the hot core source Sgr B2(M), confirming its previous
tentative interstellar detection. Up to four transitions were detected toward
five other positions in the Sgr B2 complex, including the hot cores Sgr B2(M),
(S), and (N). A fairly constant abundance ratio of ~ 0.3 - 0.8 % for HOCN
relative to HNCO was derived for the extended gas components, suggesting a
common formation process of these isomers
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