Physical properties and molecular composition of the region of massive star formation L379IRS1

Kalenskii, S.; Shchurov, M.

Авторы: Kalenskii S., Shchurov M.
Сборник: 6th Zermatt ISM Symposium, Conditions and Impact of Star Formation From Lab to Space, September 7–11, 2015, Zermatt, Switzerland, Abstract Book
Тезисы
Год издания: 2015
Первая страница: 149
Аннотация: Region of massive star formation L379IRS1 (IRAS18265-1517) is located in a dark cloud L379 at a distance of 2 kpc from the Sun. Submillimeter observations showed that IRS1 consists of two clumps situated 0.2 pc north and 0.14 pc south of IRS1, connected by an arc of emission west of IRS1. Each clump probably harbors a B0–5 protostar, which drives a bipolar outflow. Class I methanol masers, detected at 36, 44, 132 GHz and some other frequencies are associated with the northern outflow. We observed L379IRS1 in 7 spectral bands in the 1-mm, 2-mm, and 3-mm spectral regions with the IRAM 30-m radio telescope. As a result, spectral lines of 25 molecules were detected, beginning from simple diatomic and triatomic species, such as CS, SiO or OCS, to complex eight-atom and nine-atom molecules, such as CH3OCHO or CH3OCH3. Rotational diagrams built from methanol and methyl cyanide lines made it possible to determine the temperature of a quescent gas in the region, which turned to be about 40 − 50 K. In addition to this quescent warm gas there is a hot component, which shows itself in the presence of high-excitation lines of methanol and methyl cyanide, in the existence of molecules that form in hot regions, and in the existence of water vapour masers, as well as Class II methanol masers at 6.7 GHz. Probably, one of the hot regions is a hot core, located near the southern submm peak and related to a group of methanol masers at 6.7 GHz. High-excitation lines detected in some other directions may be related to other hot cores or to hot postshock gas in the lobes of bipolar outflows. Rotational diagrams allowed us to determine the column densities and abundances of methanol and methyl cyanide in the quescent gas. The abundance of methanol proved to be about 10−9 and that of methyl cyanide, about 10−11, which is typical for dense cores of molecular clouds. In addition, we found that the column densities of A- and E-methanol in L379IRS1 are virtually the same. Column densities of other observed molecules were calculated assuming that all molecular-level populations correspond to a temperature of 40 K. The molecular composition of the warm gas proved to be close to that in another region of massive star formation, DR21(OH). However, the content of SO2 in these regions is very different. Its column density in L379IRS1 is by a factor of 20 lower than that in DR21(OH). As the abundance ratios SO2/CS and SO2/OCS, which can be used as chemical clocks, are much lower in L379IRS1 than in DR21(OH), L379IRS1 should be younger than DR21(OH).
Добавил в систему: Рудницкий Георгий Михайлович

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