Michael Margulis

The formation and early dynamical evolution of bound stellar systems

We present the results of numerical N-body calculations which simulate the dynamical evolution of young clusters as they emerge from molecular clouds. We follow the evolution of initially virialized stellar systems of 50 and, in some cases, 100 stars from the point in time immediately after the stars have formed in a cloud until a time long after all the residual star-forming gas has been dispersed from the system. By varying the star formation efficiency and the gas dispersal time for each model, we determined the combination of these parameters which result in the production of bound stellar groups after the gas not used in star formation is completely dispersed.

An unusual outflow around IRAS 16293-2422

The dense dusty molecular cloud core associated with the unusual protostellar source IRAS 16293-1422 (IRAS 1629A) was observed in the J = 2-1 transition of (C-12)O and (C-13)O. These observations indicate that IRAS 1629A is a source of an unusual high-velocity molecular outflow with four separate emission lobes. The morphology and velocity structure of the lobes may suggest the presence of a dual jet or double bipolar outflow system originating from the vicinity of IRAS 1269A. These observations resolve the outflowing gas into numerous high-velocity clumps which are either being continuously accelerated from low to high velocity along the entire length of the flow or are undergoing free-flow expansion. 28 references.

Molecular outflows in the Monoceros OB1 molecular cloud

Observations of J = 1-0 emission from CO in nine suspected molecular outflows in the Monoceros OB1 molecular cloud are presented. It is found that, if the five sources which are confirmed to be outflows conserve momentum as they evolve, they will sweep up at least 0.6 percent of the mass of the entire cloud before coming into pressure equilibrium with the ambient gas. This number indicates that it should take at most 160 episodes of similar outflow activity in order to sweep up the bulk of the Mon OB1 cloud to highly supersonic speeds.

Young stellar objects in the Monoceros OB1 molecular cloud

Detailed results of an IRAS survey of a large portion of the Monoceros OB1 molecular cloud for discrete far-IR sources are presented. IRAS spectral energy distributions are constructed for 27 of the 30 sources identified in the region. Many are bright class I energy distributions, indicating that star formation is still occurring in the complex which produced the visible cluster, NGC 2264. Far-IR luminosities are calculated for each source, and the bolometric luminosity functions for class I and class II sources in the Mon OB1 cloud are found to be significantly different. Of all class I and II sources more luminous than 5 solar, 50 percent of class I sources are more luminous than 60 solar while only 4 percent of class II sources are. An attempt is made to determine the type of young stellar object in the cloud with which molecular outflows are associated. 35 refs.

Observations of molecular and atomic clouds in M31

The first coordinated CO and H I observations of M31 made with identical and sufficiently high angular and velocity resolutions to resolve individual GMCs have been obtained. Extensive observations of a star-forming complex located within a portion of a spiral arm about 7 kpc from the center of M31 are reported. The distribution of both atomic and molecular gas is clearly correlated in both space and velocity. The H I line widths are typically around 25 km/s and usually a factor of two broader than CO lines detected along the same lines of sight. The molecular clouds are associated with H II regions and appear to be active sites of star formation. Comparison of H I and CO observations suggest that molecular clouds form from atomic gas on relatively short time scales within a spiral arm. 52 references.

A study of the stellar population in the Lynds 1641 dark cloud: a possible dense cluster associated with IRAS 05338―0624

Sensitive images obtained at 1.6 and 2.2 microns reveal a possible dense cluster of stars associated with IRAS 05338-0624 and located within an optically thick molecular core; the visual extinction suffered by cluster members ranges from 7 to 40 mag. A circular region of diameter 70 arcsec (0.16 pc at a distance of 480 pc) contains 20 stellar objects or semistellar knots. Assuming that the depth of the region is comparable to its projected size leads to an estimated stellar density of 6800/cu pc. The ratio of stellar to molecular material contained within the core must lie between 4 percent and 43 percent. It is likely that this cluster will emerge from its parent core as a bound group. 18 refs.

An unbiased survey for high-velocity gas in the Monoceros OB1 molecular cloud

In order to make an unbiased survey for high-velocity gas in a single molecular cloud, a sensitive and uniformly sampled map of CO (J = 1-0) emission over a large fraction of the Mon OB1 (NGC 2264) molecular cloud was obtained. High-velocity line wings were detected on profiles over about 10 percent of the region surveyed. Complete maps of the 12, 25, 60 and 100-micron far-infrared emission from the Mon OB1 cloud were constructed as well by coadding the appropriate IRAS survey fields. 18 references.

A spectacular molecular outflow in the Monoceros OB1 molecular cloud

Detailed observations of CO, CS, IR continuum, and H2 emission from a large, highly collimated, bipolar outflow in the Monoceros OB1 molecular cloud are presented. The CO observations suggest that molecular gas in the outflow is contained in a shell with higher velocity material situated interior to lower velocity material. The velocities of outflow emission are found to increase with increasing distance from the center of the outflow. Additional detections include shock-excited molecular hydrogen emission from the blueshifted lobe of the outflow and six 2-micron sources in the direction of the outflow. Near-IR and IRAS observations suggest that the driving source for the outflow must have a bolometric luminosity below about 4.5 solar luminosities. It is concluded that the flow is probably not driven by stellar radiation from a central source. 41 refs.

A study of the stellar population in the Lynds 1641 dark cloud - deep near-infrared imaging

Deep H and K photometry of a selection of IRAS point sources in the L1641 cloud is presented. Using these data in combination with IRAS data and previously published near-infrared photometry for sources in this region, it is found that the L1641 cloud contains newly born stars embedded within cores of unusually large visual extinction. A comparison of the properties of cores in L1641 with those in the Taurus-Auriga star-forming complex reveals that L1641 contains cores with higher visual extinctions, larger ammonia (J, K) = (1, 1) line widths, greater kinetic temperatures, and probably higher optical depths at 100 microns than any cores in Taurus-Auriga. These results are qualitatively consistent with recent suggestions that the process of protostellar collapse in cores in the L1641 cloud is dominated by gravity while this process is dominated by magnetic fields in Taurus-Auriga. 20 refs.

Very high velocity emission from molecular outflows

Very low noise spectra of emission from the J = 1 - 0 transition of CO in nine molecular outflows are presented. All the spectra exhibit emission at higher velocities than has been found from more noisy spectra of these outflows taken in the past. In the cases of AFGL 490, NGC 2071, L723 and S140 the highest velocity emission observed may comprise a component in the line wings distinct from the lower velocity wing emission which arises from the swept-up outflowing molecular gas. It is possible that the very high velocity emission observed may arise from gas entrained in the driving winds of these outflows. The outflows which exhibit the most striking high-velocity emission are probably the youngest in our sample. This is consistent with a picture in which molecular outflows are driven by winds which do not blow for their entire lifetimes. In addition, the gas moving at very high velocities in some outflows may carry a considerable amount of mechanical energy, perhaps as much as has been attributed to lower velocity gas in these outflows from analysis of more noisy spectra taken in the past. 19 refs.