Papers by Sergey Malafeev
We studied the temperature distribution in cores of giant molecular clouds on the basis of high q... more We studied the temperature distribution in cores of giant molecular clouds on the basis of high quality CH_3C_2H J=13-12 maps obtained on the IRAM 30-m telescope. These maps could be deconvolved into several distinct clumps. The dependence of temperature on the projected distance from the clump center was analyzed. These dependencies were compared with model calculations of temperatures which would be derived for optically thin CH_3C_2H emission from a spherically symmetric cloud with power law temperature and density gradients. In this way we found that the radial temperature dependence in these clumps can be fitted by a power law with -0.3 ... -0.4 indices. This dependence is in agreement with the theoretically expected one for a centrally heated optically thin cloud.
Proceedings of the International Astronomical Union, 2005
We found that in regions of high mass star formation the CS emission correlates well with the dus... more We found that in regions of high mass star formation the CS emission correlates well with the dust continuum emission and is therefore a good tracer of the total mass while the N2H + distribution is frequently very different. This is opposite to their typical behavior in low-mass cores. The behavior of other high density tracers varies from source to source but most of them are closer to CS. Radial density profiles in massive cores are fitted by power laws with indices about −1.6, as derived from the dust continuum emission. The radial temperature dependence on intermediate scales is close to the theoretically expected one for a centrally heated optically thin cloud. The velocity dispersion either remains constant or decreases from the core center to the edge. Several cores including those without known embedded IR sources show signs of infall motions. They can represent the earliest phases of massive protostars. There are implicit arguments in favor of small-scale clumpiness in the cores.
Proceedings of the International Astronomical Union, 2005
We summarize the results of our studies of chemical differentiations in regions of high mass star... more We summarize the results of our studies of chemical differentiations in regions of high mass star formation based on molecular line and dust continuum observations. The results reveal significant differences between high-mass and low-mass cores. In particular, in the former ones N2H+ abundance drops in the vicinity of bright YSOs while CS is a good tracer of total mass. Understanding high mass star formation (HMSF) is still a challenge for astrophysics. And in order to investigate physical processes in these regions it is important to know their chemical features since molecular emission is the primary probe of the physical conditions in interstellar clouds. It is now well established that the central parts of dense low mass cloud cores suffer strong depletion of many molecules (in particular, CO, HCO+ and CS) onto dust grains (e.g. Caselli et al. 1999, 2002, Tafalla et al. 2002, Bergin et al. 2001). On the other hand, N2H+ is an excellent tracer of dust continuum emission (Caselli et al. 2002), implying that this species does not deplete out. The situation is different in HMSF cores as shown below. Our observations of a sample of HMSF cores in lines of several high density tracers (CS, N2H+, HCN, HNC, HCO+, their isotopes, etc.) and in dust continuum emission at 1.2 mm reveal certain relationships between them which are different from those seen in cold low mass cores (Zinchenko et al. 1995, 1998, Pirogov et al. 2003, Pirogov et al., in preparation, Zinchenko et al., in preparation). Here we summarize the main results. The most striking feature is a strong difference in many cases between N2H+ distribution and distributions of most other species. CS, HCN and HCO+ usually follow well dust continuum emission while N2H+ does not. This is opposite to the situation in cold low-mass cores. The variations of the CS(5-4)/N2H+ intensity ratio reach more than an order of magnitude, as shown in Figure 1 where we plot this ratio in dependence on the distance from the CS/dust peak for one of the sources. HNC distribution is usually intermediate between CS and N2H+ ones.
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Papers by Sergey Malafeev