Probing the structure of a birthplace of intermediate-mass stars: Ammonia cores in Lynds 1340

M. Kun; J. G. A. Wouterloot; L. V. Tóth

doi:doi:10.1051/0004-6361:20021640

Free access

Issue		A&A Volume 398, Number 1, January IV 2003


Page(s)		169 - 180
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20021640

A&A 398, 169-180 (2003)
DOI: 10.1051/0004-6361:20021640

Probing the structure of a birthplace of intermediate-mass stars: Ammonia cores in Lynds 1340

M. Kun¹, J. G. A. Wouterloot² and L. V. Tóth^{3, 4}

¹ Konkoly Observatory, 1525 Budapest, PO Box 67, Hungary
² Joint Astronomy Centre, 660 N. A'ohoku Place, University Park, 96720 Hilo, Hawaii, USA
³ Department of Astronomy, Loránd Eötvös University, 1117 Budapest, Pázmány Péter sétány 1, Hungary
⁴ Helsinki University Observatory, PO Box 14, 00014 University of Helsinki, Finland

(Received 24 April 2002 / Accepted 6 November 2002 )

Abstract
Lynds 1340, a molecular cloud forming intermediate-mass stars, has been mapped in the NH ₃(1,1) and (2,2) transitions with the Effelsberg 100-m telescope. We observed the whole area of the cloud where C ¹⁸O emission was detected earlier, at a 40 $\arcsec$ grid, with additional positions towards the C ¹⁸O peaks and optically invisible IRAS point sources. Our observations covered an area of 170 arcmin ², corresponding to about 5.15 pc ² at a distance of 600 pc, and revealed 10 ammonia cores. The cores, occupying some 7% of the mapped area, probably represent the highest density regions of L 1340. Their total mass is ~80 $M_{\odot}$ , about 6% of the mass traced by C ¹⁸O. Six cores are associated with optically invisible IRAS point sources. Their average nonthermal line width is 0.78 km s ^-1, while the same quantity for the four starless cores is 0.28 km s ^-1. We suggest that the narrow-line cores are destined to form low-mass stars, whereas small groups of intermediate-mass stars are being formed in the turbulent cores. The features traced by NH ₃, ¹³CO, C ¹⁸O and $\ion{H}{i}$ obey the line width-size relation $\Delta v_{{\rm NT}} \propto R_{1/2}^{0.41}$ . Comparison of sizes, densities and nonthermal line widths of ammonia cores with those of C ¹⁸O and ¹³CO structures supports the scenario in which core formation has been induced by turbulent fragmentation. The typical physical properties of the NH ₃ cores of L 1340, $\langle R_{1/2} \rangle=0.08$ pc, $\langle T_{{\rm kin}} \rangle=13.8$ K, $\langle \Delta v_{{\rm total}} \rangle=0.64$ km s ^-1, and $\langle M \rangle=9$ $M_{\odot}$ are close to those of the high-mass star forming Perseus and Orion B clouds.

Key words: stars: formation -- ISM: molecules -- ISM: individual objects: L 1340

Offprint request: M. Kun, kun@konkoly.hu

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