arXiv subjects

T. K. Sridharan

Publications and source records attributed to T. K. Sridharan.

59 records · Page 4Linked to original sources

arXiv2002

IRAS 05358+3543: Multiple outflows at the earliest stages of massive star formation

We present a high-angular-resolution molecular line and millimeter continuum study of the massive star formation site IRAS 05358+3543. The most remarkable feature is a highly collimated (collimation factor ~10) and massive (>10 M_sun) bipolar outflow of 1 pc length, which is part of a quadrupolar outflow system. The three observed molecular outflows forming the IRAS 05358+3543 outflow system resemble, in structure and collimation, those typical of low-mass star-forming regions. They might therefore, just like low-mass outflows, be explained by shock entrainment models of jets. We estimate a mass accretion rate of 10^{-4) M_sun/yr, sufficient to overcome the radiative pressure of the central object and to build up a massive star, lending further support to the hypothesis that massive star formation occurs similarly to low-mass star formation, only with higher accretion rates and energetics.

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arXiv2001

Massive molecular outflows

We present a mapping study of massive molecular outflows in 26 high-mass star-forming regions at 11'' spatial resolution. Bipolar morpholgy is found in 80% of the sources and the collimation is higher than previously thought. Additionally, we find that well known low-mass correlations continue up to the high-mass regime, and accretion rates are around 10^(-4) Msun/yr rising as high as 10^(-3) Msun/yr. A tight correlation between the outflow and the core mass is established, implying that the accretion rate is a rather linear function of the initial core mass. All the data suggest that massive outflows are qualitatively similar and just quantitatively enhanced compared to their low mass counterparts.

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arXiv2001

Massive molecular outflows

Well established correlations of low-mass flows show a continuity in the high-mass regime, and mean accretion rates for L>1000 Lsun are dM/dt~10^(-4) Msun/yr. We also present a tight correlation between outflow masses and core masses, which implies that the accretion rate is to first order a linear function of the core mass. All those results support the idea that similar physical processes drive outflows of all masses.

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arXiv2001

High-Mass Proto-Stellar Candidates - I : The Sample and Initial Results

We describe a systematic program aimed at identifying and characterizing candidate high-mass proto-stellar objects (HMPOs). Our candidate sample consists of 69 objects selected by criteria based on those established by Ramesh & Sridharan (1997) using far-infrared, radio-continuum and molecular line data. Infrared-Astronomical-Satellite (IRAS) and Midcourse-Space-Experiment (MSX) data were used to study the larger scale environments of the candidate sources and to determine their total luminosities and dust temperatures. To derive the physical and chemical properties of our target regions, we observed continuum and spectral line radiation at millimeter and radio wavelengths. We imaged the free-free and dust continuum emission at wavelengths of 3.6 cm and 1.2 mm, respectively, searched for H2O and CH3OH maser emission and observed the CO 2-1 and several NH3 lines toward all sources in our sample. Other molecular tracers were observed in a subsample. The presented results indicate that a substantial fraction of our sample harbors HMPOs in a pre-UCHII region phase, the earliest known stage in the high-mass star formation process.

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arXiv2001

High-Mass Proto-Stellar Candidates - II : Density structure from dust continuum and CS emission

We present a detailed 1.2 mm continuum and CS spectral line study of a large sample of 69 massive star forming regions in very early stages of evolution, most of them prior to building up an ultracompact HII region. The continuum data show a zoo of different morphologies and give detailed information on the spatial distributions, the masses, column densities and average densities of the whole sample. Fitting the radial intensity profiles shows that three parameters are needed to describe the spatial distribution of the sources: constant emission from the center out to a few arcsec radius followed by a first power law intensity distribution which steepens further outside into a second power law distribution. The mean inner power law intensity index mi (I~r^(-mi)) is 1.2 corresponding to density indices p (n~r^(-p)) of 1.6. In total the density distribution of our massive star formations sites seem to be not too different from their low-mass counterparts, but we show that setting tight constrains on the density indices is very difficult and subject to many possible errors. The local densities we derive from CS calculations are higher (up to one order of magnitude) than the mean densities we find via the mm-continuum. Such inhomogeneous density distribution reflects most likely the ubiquitous phenomenon of clumping and fragmentation in molecular clouds. Linewidth-mass relations show a departure from virial equilibrium in the stages of strongly collapsing cores.

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