1,422 research outputs found
New Measurements of the Radio Photosphere of Mira based on Data from the JVLA and ALMA
We present new measurements of the millimeter wavelength continuum emission
from the long period variable Mira ( Ceti) at frequencies of 46 GHz, 96 GHz,
and 229 GHz (~7 mm, 3 mm, and 1 mm) based on observations obtained
with the Jansky Very Large Array (JVLA) and the Atacama Large
Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities
are consistent with a radio photosphere model derived from previous
observations, where flux density, . The stellar disk
is resolved, and the measurements indicate a decrease in the size of the radio
photosphere at higher frequencies, as expected if the opacity decreases at
shorter wavelengths. The shape of the radio photosphere is found to be slightly
elongated, with a flattening of ~10-20%. The data also reveal evidence for
brightness non-uniformities on the surface of Mira at radio wavelengths. Mira's
hot companion, Mira B was detected at all three observed wavelengths, and we
measure a radius for its radio-emitting surface of
cm. The data presented here highlight the power of the JVLA and ALMA for the
study of the atmospheres of evolved stars.Comment: Accepted to ApJ; 27 pages, 7 figure
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
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
Initial phases of massive star formation in high infrared extinction clouds. II. Infall and onset of star formation
The onset of massive star formation is not well understood because of
observational and theoretical difficulties. To find the dense and cold clumps
where massive star formation can take place, we compiled a sample of high
infrared extinction clouds, which were observed previously by us in the 1.2 mm
continuum emission and ammonia. We try to understand the star-formation stages
of the clumps in these high extinction clouds by studying the infall and
outflow properties, the presence of a young stellar object (YSO), and the level
of the CO depletion through a molecular line survey with the IRAM 30m and APEX
12m telescopes. Moreover, we want to know if the cloud morphology, quantified
through the column density contrast between the clump and the clouds, has an
impact on the star formation occurring inside it. We find that the HCO+(1-0)
line is the most sensitive for detecting infalling motions. SiO, an outflow
tracer, was mostly detected toward sources with infall, indicating that infall
is accompanied by collimated outflows. The presence of YSOs within a clump
depends mostly on its column density; no signs of YSOs were found below 4E22
cm-2. Star formation is on the verge of beginning in clouds that have a low
column density contrast; infall is not yet present in the majority of the
clumps. The first signs of ongoing star formation are broadly observed in
clouds where the column density contrast between the clump and the cloud is
higher than two; most clumps show infall and outflow. Finally, the most evolved
clumps are in clouds that have a column density contrast higher than three;
almost all clumps have a YSO, and in many clumps, the infall has already
halted. Hence, the cloud morphology, based on the column density contrast
between the cloud and the clumps, seems to have a direct connection with the
evolutionary stage of the objects forming inside
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