Mon. Not. R. Astron. Soc., 476, 4949-4964 (2018/June-1)
The ALMA-PILS survey: the sulphur connection between protostars and comets: IRAS 16293-2422 B and 67P/Churyumov-Gerasimenko.
DROZDOVSKAYA M.N., VAN DISHOECK E.F., JORGENSEN J.K., CALMONTE U., VAN DER WIEL M.H.D., COUTENS A., CALCUTT H., MULLER H.S.P., BJERKELI P., PERSSON M.V., WAMPFLER S.F. and ALTWEGG K.
Abstract (from CDS):
The evolutionary past of our Solar system can be pieced together by comparing analogous low-mass protostars with remnants of our Protosolar Nebula - comets. Sulphur-bearing molecules may be unique tracers of the joint evolution of the volatile and refractory components. ALMA Band 7 data from the large unbiased Protostellar Interferometric Line Survey are used to search for S-bearing molecules in the outer disc-like structure, ∼60 au from IRAS 16293-2422 B, and are compared with data on 67P/Churyumov-Gerasimenko (67P/C-G) stemming from the ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instrument aboard Rosetta. Species such as SO2, SO, OCS, CS, H2CS, H2S, and CH3SH are detected via at least one of their isotopologues towards IRAS 16293-2422 B. The search reveals a first-time detection of OC33S towards this source and a tentative first-time detection of C36S towards a low-mass protostar. The data show that IRAS 16293-2422 B contains much more OCS than H2S in comparison to 67P/C-G; meanwhile, the SO/SO2 ratio is in close agreement between the two targets. IRAS 16293-2422 B has a CH3SH/H2CS ratio in range of that of our Solar system (differences by a factor of 0.7-5.3). It is suggested that the levels of UV radiation during the initial collapse of the systems may have varied and have potentially been higher for IRAS 16293-2422 B due to its binary nature; thereby, converting more H2S into OCS. It remains to be conclusively tested if this also promotes the formation of S-bearing complex organics. Elevated UV levels of IRAS 16293-2422 B and a warmer birth cloud of our Solar system may jointly explain the variations between the two low-mass systems.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
astrochemistry - comets: general - stars: protostars - ISM: molecules
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