$O^{18}$O and $C^{18}$O observations ofρOphiuchi A

Abstract

Context. Contrary to theoretical expectation, surprisingly low concentrations of molecular oxygen, O 2 , have been found in the interstellar medium. Telluric absorption makes ground based O 2 observations essentially impossible and observations had to be done from space. Millimetre-wave telescopes on space platforms were necessarily small, which resulted in large, several arcminutes wide, beam patterns. Observations of the (N J = 1 1 −1 0 ) ground state transition of O 2 with the Odin satellite resulted in a 5σ detection toward the dense core ρ 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.Aims. The precise nature of the emitting source and its exact location and extent are therefore unknown. The current investigation is intended to remedy this. Methods. Although the Earth's atmosphere is entirely opaque to low-lying O 2 transitions, it allows ground based observations of the much rarer 16 O 18 O in favourable conditions and at much higher angular resolution with larger telescopes. In addition, ρ Oph A exhibits both multiple radial velocity systems and considerable velocity gradients. Extensive mapping of the region in the proxy C 18 O (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 13 C 18 O (J = 3−2). During several observing periods, two C 18 O intensity maxima in ρ Oph A were searched for O 18 O in the (2 1 −0 1 ) line at 234 GHz with the 12 m APEX telescope. These positions are associated also with peaks in the mm-continuum emission from dust.

Gas and dust in the star-forming regionρ Oph A

“…However, as shown by Liseau et al (2010) on the basis of C 18 O (3−2) and 13 C 18 O (3−2) observations of ρ Oph A, optical depths do exceed unity even in the rare isotopologues of CO. In those cases, the observed radiation does not carry information about the entire core but is restricted to layers closer to the surface, leading to erroneous estimates of the overall temperature and density distribution.…”

“…4.2). The nominal offset of the C 18 O (3−2) map (Liseau et al 2010) is at (−45 · 1, +3 · 0), which was applied to the line data to align with the continuum maps. As already mentioned, the pointing accuracy of the APEX telescope is 2 rms.…”

Deuterated formaldehyde inρOphiuchi A

“…Earlier, Loinard et al (2002) reported a high D 2 CO/H 2 CO ratio toward the VLA 1623 source. The existence of D 2 CO in several positions of this 2 × 3 cloud core formed the incentive of the present study as an excellent source to delineate the distribution of H 2 CO, HDCO, and D 2 CO as we know the distribution of the dust (Motte et al 1998) and the gas in terms of C 18 O (Liseau et al 2010). Here we report on mapping observations of the ρ Oph A cloud core in several frequency settings that cover most of the low-energy H 2 CO, HDCO, and D 2 CO lines in the 1.3 millimeter band using the 12 m APEX telescope (Güsten et al 2006).…”

“…Moreover, it was in the direction of this cloud core that Larsson et al (2007), using the Odin satellite, detected the 119 GHz line from molecular oxygen as well as the ammonia ground state line at 572 GHz (Liseau et al 2003). More recently, while searching for the 234 GHz O 18 O line Liseau et al (2010) detected several lines due to D 2 CO toward the millimeter continuum peaks. This study also includes C 18 O(3−2) mapping observations.…”

Detection of interstellar hydrogen peroxide

“…The ρ Oph A molecular cloud, at a distance of about 120 pc, has been the subject of several studies. Continuum observations (André et al 1993;Motte et al 1998) and C 18 O observations (Liseau et al 2010) revealed …”