2,254 research outputs found
Comparison of submillimeter and ultraviolet observations of neutral carbon toward Zeta Ophiuchi
We have observed the ^3P_1 → ^3P_0 ground state transition of C_I emission toward ζ Oph. We compare this observation with predictions made from Copernicus ultraviolet absorption measurements of the population of the ^3P_1 level and with millimeter wave observations of CO
The abundances of atomic carbon and carbon monoxide compared with visual extinction in the Ophiuchus molecular cloud complex
We have observed emission from the 492 GHz lines of C I toward six positions in the Ophiuchus molecular
cloud complex for which accurate visual extinctions are available. We find that the column density of C I
increases with A_v to greater than 2 x 10^(17) cm^(-2) at 100 mag, the column-averaged fractional abundance
reaches a peak of about 2.2 x 10^(-5) for A_v in the range 4-11 mag and the column-averaged abundance ratio
of C I to CO decreases with A_v from about 1 at 2 mag to greater than ~0.03 at 100 mag. These results imply
that, while C I is not the primary reservoir of gaseous carbon even at cloud edges, its fractional abundance
remains high for at least 10 mag into the cloud and may be significant at even greater depths
Chlorine in dense interstellar clouds - The abundance of HCl in OMC-1
We report the first detection of a chlorine-bearing molecular species in the interstellar medium via emission
from the J = 1 → 0 transition of HCl at 625.9 GHz toward OMC-1. The relative strengths, widths, and velocities
of the resolved hyperfine components are consistent with moderate optical depth emission originating from dense, quiescent molecular cloud material (V_(LSR) = 9 km s^(-1)). The overall emission strength implies a fractional abundance of f(HCl/H_2) ~ (0.5-5.0) x 10^(-8), depending on the density of the emitting region. This is approximately an order of magnitude below previous theoretical estimates and a factor of 3-30 below the cosmic abundance of Cl. Recent laboratory work suggests that the lowered fractional abundance of HCl is caused by a combination of depletion onto grains with gas-phase loss processes such as the reaction of HCl with C^+
First detection of the ground-state J_K = 1_0 → 0_0 submillimeter transition of interstellar ammonia
The J_K = 1_0 → 0_0 transition of ammonia at 572.5 GHz has been detected in OMC-1 from NASA's Kuiper Airborne Observatory. The central velocity of the line (V_(LSR)≈ 9 km s^(-1)) indicates that it originates in the molecular cloud material, not in the hot core. The derived filling factor of ≳ 0.09 in a 2' beam implies a source diameter of ≳ 35" if it is a single clump. This clump area is much larger than that derived from observations of the 1_1 inversion transition. The larger optical depth in the
1_0 → 0_0 transition (75-350) can account for the increased source area and line width as compared
with those seen in the 1_1 inversion transition
First detection of the ground state JK = 1 sub 0 going to 0 sub 0 submillimeter transition of interstellar ammonia
The JK = 1 sub 0 approaching O sub 0 transition of ammonia at 572.5 GHz was detected in OMC-1 from NASA's Kuiper Airborne Observatory. The central velocity of the line (VLSR approximately = 9 km/s) indicates that it originates in the molecular cloud material, not the hot core. The derived filling factor of approximately 0.09 in a 2' beam implies a source diameter of approximately 35" if it is a single clump. This clump area is much larger than that derived from observations of the sub 1 inversion transition. The larger optical depth in the 1 sub 0 approaching 0 sub 0 transition (75-350) can account for the increased source area and linewidth as compared with those seen in the 1 sub 0 inversion transition
Ground-based searches for interstellar H_(2)D^+
We present ground-based searches for the 1_(10) - 1_(11) line of interstellar H_(2)D^(+) at 372 GHz which are more sensitive than those obtained from the Kuiper Airborne Observatory by factors of 3-4 for extended sources and by more than two orders of magnitude for compact sources. The line was not detected in a variety of interstellar clouds, including NGC 2264 toward which a possible detection had been suggested previously. The inferred H_(2)D^(+) abundance limits of 10^(-10) - 10^(-11) are still consistent with, but approach the abundances predicted by chemical models. Simultaneous observations of the DCO^(+) 3-2 and N_(2)H^(+) 4-3 lines have been used to place additional limits on the H_(3)^(+) abundance, and suggest 10^(-11) < x(H_(3)^(+))< 10^(-9). The N_(2)H^(+) data also indicate that for NGC 2264, but perhaps not for the other sources, gas-phase N_2 contains a substantial fraction of the available nitrogen in the cloud
Lunar photo study Final report, 1 Dec. 1964 - 1 Oct. 1965
Photometric properties of realistic lunar models and evaluation of photographs of models dusted with copper oxid
Interstellar H^+_3: possible detection of the 1_(10)→1_(11) transition of H_2D^+
An interstellar line has been detected in emission at the expected submillimeter wavelength of the 1_(10)→1_(11) transition of H_(2)D^+, the deuterated version of the primary ion (H^(+)_(3)) in the favored ion-molecule reaction scheme for interstellar gas phase chemistry. The strength of the line is in approximate agreement with the theoretically anticipated H_(2)D^+ abundance
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