5,449 research outputs found
Discovery of Water Vapor in the High-redshift Quasar APM 08279+5255 at z = 3.91
We report a detection of the excited 2_(20)-2_(11) rotational transition of para-H_2O in APM 08279+5255 using the IRAM Plateau de Bure Interferometer. At z = 3.91, this is the highest-redshift detection of interstellar water to date. From large velocity gradient modeling, we conclude that this transition is predominantly radiatively pumped and on its own does not provide a good estimate of the water abundance. However, additional water transitions are predicted to be detectable in this source, which would lead to an improved excitation model. We also present a sensitive upper limit for the hydrogen fluoride (HF) J = 1-0 absorption toward APM 08279+5255. While the face-on geometry of this source is not favorable for absorption studies, the lack of HF absorption is still puzzling and may be indicative of a lower fluorine abundance at z = 3.91 compared with the Galactic interstellar medium
On the structure of hot absorption spectra of polyatomic molecules: Solvent effect on the transition energy gap.
Models for Dense Molecular Cloud Cores
We present a detailed model for the thermal balance, chemistry, and radiative
transfer within quiescent dense molecular cloud cores that contain a central
protostar. Large variations in the gas temperature are expected to affect the
gas-phase chemistry dramatically; with the predicted H2O abundance varying by
more than a factor of 1000 within cloud cores. Based on our predicitions for
the thermal and chemical structure of the cores, we have constructed
self-consistent radiative transfer models to compute line strengths and
profiles for transitions of various isotopomers of CO, H2O, and OI. We predict
the high lying transitions of water to be in absorption, and low gain maser
emission at 183 GHz. We predict the 63 micron line of OI to be in absorption
against the continuum for many sources. Finally, our model can also account
successfully for recent ISO observations of absorption in rovibrational
transitions of water toward the source AFGL 2591.Comment: 36 pages, 18 figures, LaTex, Accepted for publication by ApJ (11/97
557 GHz Observations of Water Vapor Outflows from VY CMa and W Hydrae
We report the first detection of thermal water vapor emission in the 557 GHz,
ground state transition of ortho-HO toward VY Canis
Majoris. In observations obtained with the Submillimeter Wave Astronomy
Satellite (SWAS), we measured a flux of Jy, in a spectrally resolved
line centered on a velocity km s with a full width half
maximum of km s, somewhat dependent on the assumed line shape.
We analyze the line shape in the context of three different radial outflow
models for which we provide analytical expressions. We also detected a weaker
557 GHz emission line from W Hydrae. We find that these and other HO
emission line strengths scale as suggested by Zubko and Elitzur (2000).Comment: Astrophysical Journal Letters, accepte
ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
(abbreviated) We aim to study the inner wind of the well-known AGB star CW
Leo. Different diagnostics probing different geometrical scales have pointed
toward a non-homogeneous mass-loss process: dust clumps are observed at
milli-arcsec scale, a bipolar structure is seen at arcsecond-scale and
multi-concentric shells are detected beyond 1". We present the first ALMA Cycle
0 band 9 data around 650 GHz. The full-resolution data have a spatial
resolution of 0".42x0".24, allowing us to study the morpho-kinematical
structure within ~6". Results: We have detected 25 molecular lines. The
emission of all but one line is spatially resolved. The dust and molecular
lines are centered around the continuum peak position. The dust emission has an
asymmetric distribution with a central peak flux density of ~2 Jy. The
molecular emission lines trace different regions in the wind acceleration
region and suggest that the wind velocity increases rapidly from about 5 R*
almost reaching the terminal velocity at ~11 R*. The channel maps for the
brighter lines show a complex structure; specifically for the 13CO J=6-5 line
different arcs are detected within the first few arcseconds. The curved
structure present in the PV map of the 13CO J=6-5 line can be explained by a
spiral structure in the inner wind, probably induced by a binary companion.
From modeling the ALMA data, we deduce that the potential orbital axis for the
binary system lies at a position angle of ~10-20 deg to the North-East and that
the spiral structure is seen almost edge-on. We infer an orbital period of 55
yr and a binary separation of 25 au (or ~8.2 R*). We tentatively estimate that
the companion is an unevolved low-mass main-sequence star. The ALMA data hence
provide us for the first time with the crucial kinematical link between the
dust clumps seen at milli-arcsecond scale and the almost concentric arcs seen
at arcsecond scale.Comment: 22 pages, 18 Figures, Astronomy & Astrophysic
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