Astrochemistry of protoplanetary disks: HCN and H_2CO
Abstract
Protoplanetary disks are the birthplace of planets. The chemical composition of nascent planets is thus directly linked to the composition and distribution of the material in disks. We present observations of simple organic species detected in protoplanetary disks, including HCN and H_2CO. We used ALMA to observe the two HCN isotopologues, namely H13CN and HC15N, in a sample of six protoplanetary disks with different stellar type and disk structure properties. We measured the 14N/15N isotpic ratios and find values between 80 to 160, with no systematic differences between the disks. We also present SMA and ALMA observations of multiple emission lines of H_2CO towards the disk around Herbig Ae star HD163296. We derive the first measurement of the ortho-to-para ratio of H_2CO in a protoplanetary disk, finding a disk-averaged o/p ratio of 1.8 - 2.8, depending on the assumed disk structure. The derived rotational temperature of ∼24 K is consistent with H_2CO coming from the colder regions in the disk, where the dominant formation pathway is likely grain surface chemistry. We end with a brief discussion about the future directions of disk chemistry studies, inspired by the remarkable structure seen in the dust continuum emission by the DSHARP ALMA Large Program.
- Publication:
-
Memorie della Societa Astronomica Italiana
- Pub Date:
- 2019
- Bibcode:
- 2019MmSAI..90..519G
- Keywords:
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- Stars: abundances;
- Stars: atmospheres;
- Stars: Population II;
- Galaxy: globular clusters;
- Galaxy: abundances;
- Cosmology: observations