CH3OH and Its Deuterated Species in the Disk/Envelope System of the Low-Mass Protostellar Source B335

By Keith Cowing
Status Report
May 29, 2024
Filed under , , , , , , , , ,
CH3OH and Its Deuterated Species in the Disk/Envelope System of the Low-Mass Protostellar Source B335
Moment 0 maps of the CH3OH (183,15−182,16, A, Eu=447 K), CH2DOH (42,2−41,3, e0, Eu/=38 K), CHD2OH (41,2−40,1, o1-e0, Eu=32 K), and CH3OD (51−40, E, Eu=49 K) emission. The integrated velocity range is from -0.2 km−1 to 14.5 km s−1 . The systemic velocity is 8.34 km s−1 (Yen et al. 2015). Contour levels are every 3σ from 3σ, where σ is 1.5 mJy beam−1 , 3.0 mJy beam−1 , 3.0 mJy beam−1 , and 2.0 mJy beam−1 , respectively. The spectra are obtained within each rectangle area (0. ′′03×0. ′′05) to calculate the temperature and the column density. The numbers represent the offsets from the continuum peak (0. ′′0). The white cross mark show the continuum peak position (α2000, δ2000) = (19h 37m00s .90, +7◦ 34′ 09.”49). The red ellipse in each map represents the beam size. The red and blue arrows in the panel (a) show the directions of the red- and blue-shifted outflow. — astro-ph.GA

Deuterium fractionation in the closest vicinity of a protostar is important in understanding its potential heritage to a planetary system.

Here, we have detected the spectral line emission of CH3OH and its three deuterated species, CH2DOH, CH2DOH, and CH3OD, toward the low-mass protostellar source B335 at a resolution of 0.”03 (5 au) with Atacama Large Millimeter/submillimeter Array. They have a ring distribution within the radius of 24 au with the intensity depression at the continuum peak.

We derive the column densities and abundance ratios of the above species at 6 positions in the disk/envelope system as well as the continuum peak. The D/H ratio of CH3OH is ~[0.03-0.13], which is derived by correcting the statistical weight of 3 for CH2DOH. The [CHD2OH]/[CH2DOH] ratio is derived to be higher ([0.14-0.29]).

On the other hand, the [CH2DOH]/[CH3OD] ratio ([4.9-15]) is higher than the statistical ratio of 3, and is comparable to those reported for other low-mass sources. We study the physical structure on a few au scale in B335 by analyzing the CH3OH (183,15-182,16, A) and HCOOH (120,12-110,11) line emission. Velocity structures of these lines are reasonably explained as the infalling-rotating motion.

The protostellar mass and the upper limit to centrifugal barrier are thus derived to be 0.03-0.07 M_{\odot} and <7 au, respectively, showing that B335 harbors a young protostar with a tiny disk structure. Such youth of the protostar may be related to the relatively high [CH2DOH]/[CH3OH] ratio.

Yuki Okoda, Yoko Oya, Nami Sakai, Yoshimasa Watanabe, Ana López-Sepulcre, Takahiro Oyama, Shaoshan Zeng, Satoshi Yamamoto

Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2405.16744 [astro-ph.GA] (or arXiv:2405.16744v1 [astro-ph.GA] for this version)
Submission history
From: Yuki Okoda
[v1] Mon, 27 May 2024 01:28:58 UTC (4,701 KB)

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) 🖖🏻