Star count analysis of the interstellar matter in the region of L1251

Abstract

We studied the ISM distribution in and around the star forming cloud L1251 with optical star counts. A careful calculation with a maximum likelihood based statistical approach resulted in B,V,R,I extinction distributions from the star count maps. A distance of 330+/-30 pc was derived. The extinction maps revealed an elongated dense cloud with a bow shock at its eastern side. We estimated a Mach number of M~2 for the bow shock. A variation of the apparent dust properties is detected, i.e. the Rv=Av/E{B-V} total to selective extinction ratio varies from 3 to 5.5, peaking at the densest part of L1251. The spatial structure of the head of L1251 is well modelled with a Schuster-sphere (i.e. n=5 polytropic sphere). The observed radial distribution of mass fits the model with high accuracy out to 2.5pc distance from the assumed center. Unexpectedly, the distribution of NH3 1.3 cm line widths is also well matched by the Schuster solution even in the tail of the cloud. Since the elongated head-tail structure of L1251 is far from the spherical symmetry the good fit of the linewidths in the tail makes it reasonable to assume that the present cloud structure has been formed by isothermal contraction.

arXiv comment9 pages, 9 figures, accepted in Astronomy & Astrophysics

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• The initial conditions of isolated star formation -- IX. Akari mapping of an externally heated pre-stellar core
• The outbursting protostar 2MASS~22352345+7517076 and its environment
• A search for cloud cores affected by shocked carbon chain chemistry in L1251
• The extinction curve in the visible and the value of Rv
• Cloud Motion and magnetic fields: Four clouds in the Cepheus Flare region
• On the relationship between the continuum of interstellar extinction curves, the 2200 Å bump, and the diffuse interstellar bands