MOLECULAR LINE OBSERVATIONS OF MCLD 123.5+24.9 IN THE POLARIS CIRRUS

Journal Article · Wed Feb 01 04:00:00 EST 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/745/2/195· OSTI ID:22011714

Shimoikura, Tomomi; Dobashi, Kazuhito; Sakurai, Tohko; Nishiura, Shingo ^[1]; Takano, Shuro ^[2]; Hirota, Tomoya ^[3]

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1. Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan)
2. Nobeyama Radio Observatory, National Astronomical Observatory of Japan, 462-2 Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)
3. National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)

In this paper, we present results of millimeter-wave observations with various molecular lines made toward MCLD 123.5+24.9 in the Polaris cirrus using the 45 m telescope at Nobeyama Radio Observatory. MCLD 123.5+24.9 is one of the rare dense cores forming in diffuse cirrus clouds where star formation may rarely take place. In order to investigate the structure, dynamics, the evolutionary stage of MCLD 123.5+24.9, we observed this core in 17 emission lines from 13 different molecular species. Emission lines of CS, CCS, and HC{sub 3}N are strongly detected all over the core, while those of SO and N{sub 2}H{sup +} are weak or remain undetected, indicating that MCLD 123.5+24.9 is in an early stage of core evolution in terms of chemical composition. Based on comparison of the fractional abundances of CCS and HC{sub 3}N, which are considered indicators of chemical age, with those of other cores with and without star formation as well as with model calculations in the literature, we suggest that MCLD 123.5+24.9 is in a phase prior to star formation. From the C{sup 18}O data obtained, we derived the total molecular mass of MCLD 123.5+24.9 to be {approx}3 M{sub Sun} at an assumed distance of 150 pc. There are three subcores in MCLD 123.5+24.9, called CS-A, CS-B, and CS-C. We derived their masses to be 0.2-0.6 M{sub Sun }. We also investigated the dynamical stability of MCLD 123.5+24.9 and the subcores by applying the virial theorem to find that MCLD 123.5+24.9 is not gravitationally bound as a whole, while the individual subcores are in the virial equilibrium and can collapse with a small increase of external pressure imposed on their surfaces.

• OSTI ID: 22011714
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 745; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
CHEMICAL COMPOSITION
EMISSION
EQUILIBRIUM
MASS
NITRILES
STAR EVOLUTION
STARS
TELESCOPES
VIRIAL THEOREM