O18O and C18O observations of rho Oph A

Abstract

Observations of the (N_J=1_1-1_0) ground state transition of O_2 with the Odin satellite resulted in a about 5 sigma detection toward the dense core rho Oph A. At the frequency of the line, 119 GHz, the Odin telescope has a beam width of 10', larger than the size of the dense core, so that the precise nature of the emitting source and its exact location and extent are unknown. The current investigation is intended to remedy this. Telluric absorption makes ground based O_2 observations essentially impossible and observations had to be done from space. mm-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Although the Earth's atmosphere is entirely opaque to low-lying O_2 transitions, it allows ground based observations of the much rarer O18O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, rho Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C18O (J=3-2) line can be expected to help identify the O_2 source on the basis of its line shape and Doppler velocity. Line opacities were determined from observations of optically thin 13C18O (J=3-2) at selected positions. During several observing periods, two C18O intensity maxima in rho Oph A were searched for in the 16O18O (2_1-0_1) line at 234 GHz with the 12m APEX telescope. Our observations resulted in an upper limit on the integrated O18O intensity of < 0.01 K km/s (3 sigma) into the 26.5" beam. We conclude that the source of observed O_2 emission is most likely confined to the central regions of the rho Oph A cloud. In this limited area, implied O_2 abundances could thus be higher than previously reported, by up to two orders of magnitude.

7 pages, 6 figures (5 colour), Astronomy & Astrophysics

References in corpus (5)

• The chemical composition of the Sun
• Laboratory evidence for efficient water formation in interstellar ices
• Molecular oxygen in the rho Ophiuchi cloud
• Mobility of D atoms on porous amorphous water ice surfaces under interstellar conditions
• Oxygen in dense interstellar gas - the oxygen abundance of the star forming core rho Oph A

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• H2O line mapping at high spatial and spectral resolution - Herschel observations of the VLA1623 outflow
• Linking interstellar and cometary O${}_2$: a deep search for ${}^{16}$O${}^{18}$O in the solar-type protostar IRAS 16293--2422
• Gas and dust in the star-forming region rho Oph A: II. The gas in the PDR and in the dense cores
• Characterizing three-dimensional magnetic field, turbulence, and self-gravity in the star-forming region L1688
• CO-to-H_2 Conversion Factor of Molecular Clouds using X-Ray Shadows
• The physical and chemical properties of the $\rho$ ophiuchi A dense core
• A new constraint on the molecular oxygen abundance at $z\sim 0.886$