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http://hdl.handle.net/20.500.12386/31259
Titolo: | ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT). IV. Thioformaldehyde (H2CS) in protoplanetary discs: spatial distributions and binding energies | Autori: | CODELLA, CLAUDIO PODIO, LINDA GARUFI, ANTONIO Perrero, J. Ugliengo, P. FEDELE , DAVIDE Favre, C. Bianchi, E. Ceccarelli, C. Mercimek, S. BACCIOTTI, Francesca RYGL, Kazi Lucie Jessica TESTI, Leonardo |
Data pubblicazione: | 2020 | Rivista: | ASTRONOMY & ASTROPHYSICS | Numero: | 644 | Da pagina:: | A120 | Abstract: | Context. Planet formation starts around Sun-like protostars with ages ≤1 Myr, but the chemical compositions of the surrounding discs remains unknown. <BR /> Aims: We aim to trace the radial and vertical spatial distribution of a key species of S-bearing chemistry, namely H<SUB>2</SUB>CS, in protoplanetary discs. We also aim to analyse the observed distributions in light of the H<SUB>2</SUB>CS binding energy in order to discuss the role of thermal desorption in enriching the gas disc component. <BR /> Methods: In the context of the ALMA chemical survey of disk-outflow sources in the Taurus star forming region (ALMA-DOT), we observed five Class I or early Class II sources with the o-H<SUB>2</SUB>CS(7<SUB>1,6</SUB>-6<SUB>1,5</SUB>) line. ALMA-Band 6 was used, reaching spatial resolutions ≃40 au, that is, Solar System spatial scales. We also estimated the binding energy of H<SUB>2</SUB>CS using quantum mechanical calculations, for the first time, for an extended, periodic, crystalline ice. <BR /> Results: We imaged H<SUB>2</SUB>CS emission in two rotating molecular rings in the HL Tau and IRAS 04302+2247 discs, the outer radii of which are ~140 au (HL Tau) and 115 au (IRAS 04302+2247). The edge-on geometry of IRAS 04302+2247 allows us to reveal that H<SUB>2</SUB>CS emission peaks at radii of 60-115 au, at z = ±50 au from the equatorial plane. Assuming LTE conditions, the column densities are ~10<SUP>14</SUP> cm<SUP>-2</SUP>. We estimate upper limits of a few 10<SUP>13</SUP> cm<SUP>-2</SUP> for the H<SUB>2</SUB>CS column densities in DG Tau, DG Tau B, and Haro 6-13 discs. For HL Tau, we derive, for the first time, the [H<SUB>2</SUB>CS]/[H] abundance in a protoplanetary disc (≃10<SUP>-14</SUP>). The binding energy of H<SUB>2</SUB>CS computed for extended crystalline ice and amorphous ices is 4258 and 3000-4600 K, respectively, implying thermal evaporation where dust temperatures are ≥50-80 K. <BR /> Conclusions: H<SUB>2</SUB>CS traces the so-called warm molecular layer, a region previously sampled using CS and H<SUB>2</SUB>CO. Thioformaldehyde peaks closer to the protostar than H<SUB>2</SUB>CO and CS, plausibly because of the relatively high excitation level of the observed 7<SUB>1,6</SUB>-6<SUB>1,5</SUB> line (60 K). The H<SUB>2</SUB>CS binding energy implies that thermal desorption dominates in thin, au-sized, inner and/or upper disc layers, indicating that the observed H<SUB>2</SUB>CS emitting up to radii larger than 100 au is likely injected in the gas phase due to non-thermal processes. <P />Reduced datacubes are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/644/A120">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/644/A120</A> | URI: | http://hdl.handle.net/20.500.12386/31259 | URL: | https://www.aanda.org/articles/aa/full_html/2020/12/aa39309-20/aa39309-20.html http://arxiv.org/abs/2011.02305v1 |
ISSN: | 0004-6361 | DOI: | 10.1051/0004-6361/202039309 | Bibcode ADS: | 2020A&A...644A.120C | Fulltext: | open |
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