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

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

Corresponding author: M. Kun, kun@konkoly.hu

Received: 24 April 2002
Accepted: 6 November 2002

Abstract

Lynds 1340, a molecular cloud forming intermediate-mass stars, has been mapped in the NH₃(1,1) and (2,2) transitions with the Effelsberg 100-m telescope. We observed the whole area of the cloud where C¹⁸O emission was detected earlier, at a 40″ grid, with additional positions towards the C¹⁸O peaks and optically invisible IRAS point sources. Our observations covered an area of 170 arcmin², corresponding to about 5.15 pc² 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 , about 6% of the mass traced by C¹⁸O. 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 NH₃, ¹³CO, C¹⁸O and obey the line width–size relation . Comparison of sizes, densities and nonthermal line widths of ammonia cores with those of C¹⁸O and ¹³CO structures supports the scenario in which core formation has been induced by turbulent fragmentation. The typical physical properties of the NH₃ cores of L 1340,  pc,  K,  km s^-1, and   are close to those of the high-mass star forming Perseus and Orion B clouds.