SIMBAD references

2014ApJ...783...72F - Astrophys. J., 783, 72 (2014/March-2)

Weak maser emission of methyl formate toward Sagittarius B2(N) in the green bank telescope PRIMOS survey.

FAURE A., REMIJAN A.J., SZALEWICZ K. and WIESENFELD L.

Abstract (from CDS):

A non-LTE radiative transfer treatment of cis-methyl formate (HCOOCH3) rotational lines is presented for the first time using a set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5-30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH3-He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. A total of 49 low-lying transitions of methyl formate, with upper levels below 25 K, are identified. These lines are found to probe a presumably cold (∼30 K), moderately dense (∼104/cm3), and extended region surrounding Sgr B2(N). The derived column density of ∼4x1014/cm2 is only a factor of ∼10 larger than the column density of the trans conformer in the same source. Provided that the two conformers have the same spatial distribution, this result suggests that strongly non-equilibrium processes must be involved in their synthesis. Finally, our calculations show that all detected emission lines with a frequency below 30 GHz are (collisionally pumped) weak masers amplifying the continuum of Sgr B2(N). This result demonstrates the importance and generality of non-LTE effects in the rotational spectra of complex organic molecules at centimeter wavelengths.

Abstract Copyright:

Journal keyword(s): astrochemistry - ISM: molecules - masers - molecular data - molecular processes

Simbad objects: 4

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2020.01.25-00:24:19

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