Brown Dwarfs

First Observations Of Warm And Cold Methanol In Class 0/I Proto-brown Dwarfs

By Keith Cowing
Press Release
May 19, 2023
Filed under , , , , ,
First Observations Of Warm And Cold Methanol In Class 0/I Proto-brown Dwarfs
An edge-on view of the internal density (left) and temperature (right) structure of a proto-BD predicted by the brown dwarf formation model (Machida & Basu 2019). White dotted lines mark the expected warm corino region close to the jet launching zone. — astro-ph.GA

We present results from the first molecular line survey to search for the fundamental complex organic molecule, methanol (CH3OH), in 14 Class 0/I proto-brown dwarfs (proto-BDs). IRAM 30-m observations over the frequency range of 92-116 GHz and 213-280 GHz have revealed emission in 14 CH3OH transition lines, at upper state energy level, Eupper∼7-49 K, and critical densities, ncrit of 105 to 109 cm−3.

The most commonly detected lines are at Eupper< 20 K, while 11 proto-BDs also show emission in the higher excitation lines at Eupper∼21-49 K and ncrit∼105 to 108 cm−3. In comparison with the brown dwarf formation models, the high excitation lines likely probe the warm (∼25-50 K) corino region at ∼10-50 au in the proto-BDs, while the low-excitation lines trace the cold (< 20 K) gas at ∼50-150 au. The column density for the cold component is an order of magnitude higher than the warm component.

The CH3OH ortho-to-para ratios range between ∼0.3-2.3. The volume-averaged CH3OH column densities show a rise with decreasing bolometric luminosity among the proto-BDs, with the median column density higher by a factor of ∼3 compared to low-mass protostars. Emission in high-excitation (Eupper> 25 K) CH3OH lines together with the model predictions suggest that a warm corino is present in ∼78\% of the proto-BDs in our sample.

The remaining show evidence of only the cold component, possibly due to the absence of a strong, high-velocity jet that can stir up the warm gas around it.

B. Riaz, W.-F. Thi, M. N. Machida

Comments: Accepted in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2305.04991 [astro-ph.GA] (or arXiv:2305.04991v1 [astro-ph.GA] for this version)
Submission history
From: Basmah Riaz
[v1] Mon, 8 May 2023 18:54:31 UTC (2,240 KB)
Astrobiology, Astrochemistry

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻