A survey of HDCO and D2CO towards Class 0/I proto-brown dwarfs. Issue 3 (11th June 2022)

• Record Type: Journal Article
• Authors: Riaz, B; Thi, W-F
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 514:Issue 3(2022)
• Page Start: 3604
• Page End: 3611
• Publication Date: 2022-06-11
• Subjects: astrochemistry -- brown dwarfs -- stars: evolution -- stars: formation -- ISM: abundances -- ISM: molecules; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1573
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Deuterium fractionation can constrain the physical and chemical conditions at the early stage of brown dwarf formation. We present IRAM 30-m observations over a wide frequency range of 213–279 GHz of singly and doubly deuterated species of formaldehyde (HDCO and D2 CO) towards Class 0/I proto-brown dwarfs (proto-BDs). Multiple low-excitation HDCO and D2 CO transition lines with upper energy level ≤40 K are detected. The D2 CO/HDCO, HDCO/H2 CO, and D2 CO/H2 CO abundance ratios range between 0.01 and 2.5 for the proto-BDs, similar to the range seen in low-mass protostars. The highest ratios of D2 CO/HDCO ∼1.3–2.5 are measured for two Stage 0 proto-BDs. These objects could possess a warm corino, similar to the few hot corino cases reported among Class 0 protostars. The mean D2 CO/HDCO, D2 CO/H2 CO, and HDCO/H2 CO ratios for the proto-BDs are comparatively higher than the range predicted by the current gas-grain chemical models, indicating that HDCO and D2 CO are formed via grain surface reactions in the dense and cold interiors of the proto-BDs at an early formation stage.