Oral Presentation
Detection of A Hot Corino in the Prototypical Warm Carbon-Chain Chemistry Source IRAS 15398−3359
Presenter: Yuki Okoda (RIKEN)
IRAS 15398-3359 is a low-mass Class 0 protostellar source in the Lupus 1 molecular cloud (Tbol=44 K, d=155 pc). This source is known to be rich in carbon-chain species such as C4H, C4H2, CH3CCH, and HC5N (Sakai et al. 2009). The infalling-rotating envelope and the Keplerian disk are identified by using the CCH and SO line emission, respectively (Okoda et al. 2018). Complex organic molecules including high excitation CH3OH lines were not detected in the previous observations, and hence, it was recognized as a WCCC source.
We have conducted observations toward this source at a resolution of 30 au as part of the ALMA large program FAUST (Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars). We detect nine CH3OH lines including the high excitation lines with the upper state energies up to 500 K. This is the first detection of such high excitation CH3OH lines in this source. The CH3OH rotational temperature and the column density are derived to be 119^{+20}_{-26} K and 3.2^{+2.5}_{-1.0}×10^{18} cm^{-2}, respectively. The beam filling factor is also derived to be 0.018^{+0.005}_{-0.003}, suggesting that the emitting region of CH3OH is much smaller than the synthesized beam size. The emitting region of three high excitation lines, 18_{3,15}-18_{2,16}, A, 19_{3,16}-19_{2,17}, A, and 20_{3,17}-20_{2,18}, A, is located within the 50 au area around the protostar, and seems to have a slight extension toward the northwest. Toward the continuum peak, we also detect one emission line from CH_2DOH and two features of multiple CH_3OCHO lines. These results in combination with previous reports indicate that IRAS 15398-3359 is a hybrid source showing both hot corino chemistry rich in complex organic molecules on small scales and warm carbon-chain chemistry (WCCC) rich in carbon-chain species on large scales.
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