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

Abstract : 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 Eu = 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 Eu range, and yields Trot ≤ 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.
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https://hal-insu.archives-ouvertes.fr/insu-03717102
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Submitted on : Friday, July 8, 2022 - 8:52:12 AM
Last modification on : Tuesday, August 2, 2022 - 4:30:20 AM

### Citation

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⟩

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