FAUST VI. VLA 1623-2417 B: A new laboratory for astrochemistry around protostars on 50 au scale

C. Codella (1) , A. López-Sepulcre (1) , S. Ohashi , C. J. Chandler , M. de Simone (1) , L. Podio , C. Ceccarelli (1) , N. Sakai , F. Alves , A. Durán , D. Fedele , L. Loinard , S. Mercimek , N. Murillo , Y. Zhang , E. Bianchi (1) , M. Bouvier (1) , G. Busquet , P. Caselli , F. Dulieu (2) , S. Feng , T. Hanawa , D. Johnstone , B. Lefloch (1) , L. T. Maud , G. Moellenbrock , Y. Oya , B. Svoboda , S. Yamamoto

1 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
2 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique

The ALMA interferometer, with its unprecedented combination of high-sensitivity and high-angular resolution, allows for (sub-)mm wavelength mapping of protostellar systems at Solar System scales. Astrochemistry has benefited from imaging interstellar complex organic molecules in these jet-disk systems. Here we report the first detection of methanol (CH₃OH) and methyl formate (HCOOCH₃) emission towards the triple protostellar system VLA1623-2417 A1+A2+B, obtained in the context of the ALMA Large Program FAUST. Compact methanol emission is detected in lines from E_u = 45 K up to 61 K and 537 K towards components A1 and B, respectively. LVG analysis of the CH₃OH lines towards VLA1623-2417 B indicates a size of 0${_{.}^{\prime\prime}}$11-0${_{.}^{\prime\prime}}$34 (14-45 au), a column density N(CH₃OH) = 10¹⁶-10¹⁷ cm^-2, kinetic temperature ≥ 170 K, and volume density ≥ 10⁸ cm^-3. An LTE approach is used for VLA1623-2417 A1, given the limited E_u range, and yields T_rot ≤ 135 K. The methanol emission around both VLA1623-2417 A1 and B shows velocity gradients along the main axis of each disk. Although the axial geometry of the two disks is similar, the observed velocity gradients are reversed. The CH₃OH spectra from B shows two broad (4-5 km s^-1) peaks, which are red- and blue-shifted by ~ 6-7 km s^-1 from the systemic velocity. Assuming a chemically enriched ring within the accretion disk, close to the centrifugal barrier, its radius is calculated to be 33 au. The methanol spectra towards A1 are somewhat narrower (~ 4 km s^-1), implying a radius of 12-24 au.

Mots clés: astrochemistry; ISM: molecules; stars: formation; Individual object: VLA 1623; 2417; Astrophysics - Astrophysics of Galaxies; Astrophysics - Solar and Stellar Astrophysics

Domaines: Planète et Univers [physics]

C. Codella, A. López-Sepulcre, S. Ohashi, C. J. Chandler, M. de Simone, et al.. FAUST VI. VLA 1623-2417 B: A new laboratory for astrochemistry around protostars on 50 au scale. Monthly Notices of the Royal Astronomical Society, 2022, ⟨10.1093/mnras/stac1802⟩. ⟨insu-03717102⟩