11 research outputs found
High-J v=0 SiS Maser Emission in IRC+10216: A New Case of Infrared Overlaps
We report on the first detection of maser emission in the J=11-10, J=14-13
and J=15-14 transitions of the v=0 vibrational state of SiS toward the C-rich
star IRC+10216. These masers seem to be produced in the very inhomogeneous
region between the star and the inner dust formation zone, placed at 5-7 R*,
with expansion velocities below 10 km/s. We interpret the pumping mechanism as
due to overlaps between v=1-0 ro-vibrational lines of SiS and mid-IR lines of
C2H2, HCN and their 13C isotopologues. The large number of overlaps found
suggests the existence of strong masers for high-J v=0 and v=1 SiS transitions,
located in the submillimeter range. In addition, it could be possible to find
several rotational lines of the SiS isotopologues displaying maser emission.Comment: 4 pages, 1 figure, published in the ApJ Letter
Understanding the chemical complexity in Circumstellar Envelopes of C-Rich AGB stars: The case of IRC +10216
Abstract The circumstellar envelopes of carbon-rich AGB stars show a chemical complexity that is exemplified by the prototypical object IRC +10216, in which about 60 different molecules have been detected to date. Most of these species are carbon chains of the type C n H, C n H 2 , C n N, HC n N. We present the detection of new species (CH 2 CHCN, CH 2 CN, H 2 CS, CH 3 CCH and C 3 O) achieved thanks to the systematic observation of the full 3 mm window with the IRAM 30m telescope plus some ARO 12m observations. All these species, known to exist in the interstellar medium, are detected for the first time in a circumstellar envelope around an AGB star. These five molecules are most likely formed in the outer expanding envelope rather than in the stellar photosphere. A pure gas phase chemical model of the circumstellar envelope is reasonably successful in explaining the derived abundances, and additionally allows to elucidate the chemical formation routes and to predict the spatial distribution of the detected species
Understanding the Chemical Complexity in Circumstellar Envelopes of C-rich AGB Stars: the Case of IRC +10216
The circumstellar envelopes of carbon-rich AGB stars show a chemical
complexity that is exemplified by the prototypical object IRC +10216, in which
about 60 different molecules have been detected to date. Most of these species
are carbon chains of the type CnH, CnH2, CnN, HCnN. We present the detection of
new species (CH2CHCN, CH2CN, H2CS, CH3CCH and C3O) achieved thanks to the
systematic observation of the full 3 mm window with the IRAM 30m telescope plus
some ARO 12m observations. All these species, known to exist in the
interstellar medium, are detected for the first time in a circumstellar
envelope around an AGB star. These five molecules are most likely formed in the
outer expanding envelope rather than in the stellar photosphere. A pure gas
phase chemical model of the circumstellar envelope is reasonably successful in
explaining the derived abundances, and additionally allows to elucidate the
chemical formation routes and to predict the spatial distribution of the
detected species.Comment: 4 pages, 4 figures; to appear in Astrophysics and Space Science,
special issue of "Science with ALMA: a new era for Astrophysics" conference,
November, 13-17 2006, ed. R. Bachille
Si-BEARING MOLECULES TOWARD IRC+10216: ALMA UNVEILS THE MOLECULAR ENVELOPE OF CWLeo
We report the detection during the ALMA Cycle 0 of SiS rotational lines in
high-vibrational states as well as SiO and SiC lines in their ground
vibrational state, towards IRC+10216. The spatial distribution of these
molecules shows compact emission for SiS and a more extended emission for SiO
and SiC, and also proves the existence of an increase in the SiC
emission at the outer shells of the circumstellar envelope. We analyze the
excitation conditions of the vibrationally excited SiS using the population
diagram technique and we used a large velocity gradient model to compare with
the observations. We found moderate discrepancies between the observations and
the models that could be explained if SiS lines detected are optically thick.
Additionally, the line profiles of the detected rotational lines in the high
energy vibrational states show a decreasing linewidth with increasing energy
levels. This may evidence that these lines could be excited only in the inner
shells, i.e. the densest and hottest, of the circumstellar envelope of
IRC+10216.Comment: 20 pages, 3 figures. Published in ApJ