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|Title:||Water and interstellar complex organics associated with the HH 212 protostellar disc. On disc atmospheres, disc winds, and accretion shocks||Authors:||CODELLA, CLAUDIO
Lee, C. -F.
Pineau des Forêts, G.
RYGL, Kazi Lucie Jessica
|Issue Date:||2018||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||617||First Page:||A10||Abstract:||Context. The unprecedented combination of high-sensitivity and high angular resolution provided by the ALMA interferometer allows us to shed light on the processes leading to the formation of the jet-disc system associated with a Sun-like mass protostar. <BR /> Aims: We investigate the physical and chemical properties of the gas associated with water and interstellar complex organic molecules around a protostar on solar system scales. <BR /> Methods: The HH 212 protostellar system, in Orion B, has been mapped, thanks to ALMA-Band 7 Cycle 1 and Cycle 4 observations of dueterated water (HDO) and acetaldehyde (CH<SUB>3</SUB>CHO) emission with an angular resolution down to 0.''15 (60 au). <BR /> Results: Many emission lines due to 14 CH<SUB>3</SUB>CHO and 1 HDO transitions at high excitation (E<SUB>u</SUB> between 163 and 335 K) have been imaged in the inner 70 au region. The local thermal equilibrium analysis of the CH<SUB>3</SUB>CHO emission leads to a temperature of 78 ± 14 K and a column density of 7.6 ± 3.2 × 10<SUP>15</SUP> cm<SUP>-2</SUP>, which, when N<SUB>H<SUB>2</SUB></SUB> of 10<SUP>24</SUP> cm<SUP>-2</SUP> is assumed, leads to an abundance of X<SUB>CH<SUB>3</SUB>CHO</SUB> ≃ 8 × 10<SUP>-9</SUP>. The large velocity gradient analysis of the HDO emission also places severe constraints on the volume density, n<SUB>H<SUB>2</SUB></SUB> ≥ 10<SUP>8</SUP> cm<SUP>-3</SUP>. The line profiles are 5-7 km s<SUP>-1</SUP> wide, and CH<SUB>3</SUB>CHO and HDO both show a ±2 km s<SUP>-1</SUP> velocity gradient over a size of 70 au (blue-shifted emission towards the north-west and red-shifted emission towards the south-east) along the disc equatorial plane, in agreement with what was found so far using other molecular tracers. <BR /> Conclusions: The kinematics of CH<SUB>3</SUB>CHO and HDO are consistent with the occurrence of a centrifugal barrier, that is, the infalling envelope-rotating disc ring, which is chemically enriched through low-velocity accretion shocks. The emission radius is 60 au, in good agreement with what was found before for another interstellar complex organic molecule such as NH<SUB>2</SUB>CHO. We support a vertical structure for the centrifugal barrier, suggesting the occurrence of two outflowing, expanding, and rotating rings above and below (of about 40-45 au) the optically thick equatorial disc plane. It is tempting to speculate that these rings could probe the basis of a wind launched from this region.||URI:||http://hdl.handle.net/20.500.12386/28360||URL:||https://www.aanda.org/articles/aa/abs/2018/09/aa32765-18/aa32765-18.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201832765||Bibcode ADS:||2018A&A...617A..10C||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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