4,320 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
Characterizing the chemical pathways for water formation -- A deep search for hydrogen peroxide
In 2011, hydrogen peroxide (HOOH) was observed for the first time outside the
solar system (Bergman et al., A&A, 2011, 531, L8). This detection appeared a
posteriori quite natural, as HOOH is an intermediate product in the formation
of water on the surface of dust grains. Following up on this detection, we
present a search for HOOH in a diverse sample of sources in different
environments, including low-mass protostars and regions with very high column
densities, such as Infrared Dark Clouds (IRDCs). We do not detect the molecule
in any other source than Oph A, and derive 3 upper limits for the
abundance of HOOH relative to H lower than in Oph A for most sources. This
result sheds a different light on our understanding of the detection of HOOH in
Oph A, and shifts the puzzle to why this source seems to be special. Therefore
we rediscuss the detection of HOOH in Oph A, as well as the implications of the
low abundance of HOOH, and its similarity with the case of O. Our chemical
models show that the production of HOOH is extremely sensitive to the
temperature, and favored only in the range 2030 K. The relatively high
abundance of HOOH observed in Oph A suggests that the bulk of the material lies
at a temperature in the range 2030 K.Comment: 18 pages, 3 figures, invited refereed paper at the Faraday Discussion
16
Exciting Maser Science with New Instruments - the Promise of the EVLA
In the near future, the Expanded Very Large Array (EVLA) will allow surveys
for maser sources with unprecedented sensitivity, spectral coverage and
spectroscopic capabilities. In particular, comprehensive surveys for many maser
species with simultaneous sensitive continuum imaging and absorption studies
will give a comprehensive radio picture of star formation in the Galactic plane
and elsewhere. Very efficient EVLA surveys for H2O megamasers in Active Galacic
Nuclei will be possible to practically arbitrary redshifts.
EVLA and Atacama Large Millimeter Array (ALMA) studies of H2O and SiO masers
will serve as high resolution probes of the innermost envelopes of oxygen-rich
evolved stars and HCN masers of carbon-rich stars.
Farther in the future, the Square Kilometer Array (SKA) promises the
detection of OH gigamasers at all conceivable redshifts and maser astrometry
with unprecedented accuracy.Comment: 10 pages, incl. 4 figures, iaus.cls, to appear the Procedings of IAU
Symp. 242 (Astrophysical masers and their environments) eds. J. Chapman & W.
Baan Replaced version with a few typos correcte
Aluminium oxide in the optical spectrum of VY Canis Majoris
We report the first identification of the optical bands of the B-X system of
AlO in the red supergiant VY CMa. In addition to TiO, VO, ScO, and YO, which
were recognized in the optical spectrum of the star long time ago, AlO is
another refractory molecule which displays strong emission bands in this
peculiar star. Simulating the bands of AlO, we derive a rotational temperature
of the circumstellar gas of Trot=700K. By resolving individual rotational
components of the bands, we derive the kinematical characteristics of the gas,
finding that the emission is centered at the stellar radial velocity and its
intrinsic width is 13.5 km/s (full width at half maximum). It is the narrowest
emission among all (thermal) features observed in VY CMa so far. The
temperature and line widths suggest that the emission arises in gas located
within ~20 stellar radii, where the outflow is still being accelerated. This
result contradicts equilibrium-chemistry models which predict substantial AlO
abundances only to within a few stellar radii. We argue that non-equilibrium
models involving propagation of shocks are needed to explain the observations.Comment: to appear in A&
Familial cases of a submicroscopic Xp22.2 deletion : genotype-phenotype correlation in microphthalmia with linear skin defects syndrome
Purpose: Microphthalmia with linear skin defects syndrome (MLS or MIDAS, OMIM #309801) is a rare X-linked male-lethal disorder characterized by microphthalmia or other ocular anomalies and skin lesions limited to the face and neck. However, inter-and intrafamilial variability is high. Here we report a familial case of MLS.
Methods: A mother and daughter with MLS underwent a complete ophthalmological examination, and extensive imaging, including anterior segment pictures, corneal topography and keratometry, autofluorescence, infrared reflectance and red free images, as well as spectral-domain optical coherence tomography. The mother also underwent full-field flash electroretinography. In addition, high-resolution array comparative genomic hybridization analysis was performed in both as well as in the maternal grandparents of the proband.
Results: Microphthalmia and retinal abnormalities were noted in the proband and the mother, whereas only the mother presented with scars of the typical neonatal linear skin defects. Array comparative genomic hybridization analysis revealed a 185-220 kb deletion on chromosome band Xp22.2 including the entire HCCS gene.
Conclusions: The identification of a deletion including HCCS led to the diagnosis of MLS in these patients. Retinal abnormalities can be part of the ocular manifestations of MLS
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