Solar mass

Abstract: Stellar clusters are born embedded within giant molecular clouds (GMCs) and during their formation and early evolution are often only visible at infrared wavelengths, being heavily obscured by dust. Over the last 15 years advances in infrared detection capabilities have enabled the first systematic studies of embedded clusters in galactic molecular clouds. In this article we review the current state of empirical knowledge concerning these extremely young protocluster systems. From a survey of the literature we compile the first extensive catalog of galactic embedded cluster properties. We use the catalog to construct the mass function and estimate the birthrate for embedded clusters within roughly 2 Kpc of the Sun. We find that the embedded cluster birthrate exceeds that of visible open clusters by an order of magnitude or more indicating a high infant mortality rate for protocluster systems. Less than 4-7% of embedded clusters survive emergence from molecular clouds to become bound clusters of Pleiades age. The vast majority (90%) of stars that form in embedded clusters form in rich clusters of 100 or more members with masses in excess of 50 solar masses. We review the role of embedded clusters in investigating the nature of the IMF which, in one nearby example, has been measured over the entire range of stellar and substellar mass, from OB stars to subsellar objects near the deuterium burning limit. We also review the role embedded clusters play in the investigation of circumstellar disk evolution and the important constraints they provide for understanding the origin of planetary systems. Finally, we discuss current ideas concerning the origin and dynamical evolution of embedded clusters and the implications for the formation of bound open clusters.

Abstract: We have detected a pulsar with a pulsation period that varies systematically between 0.058967 and 0.059045 sec over a cycle of 0.3230 d. Approximately 200 independent observations over 5-minute intervals have yielded a well-sampled velocity curve which implies a binary orbit with projected semimajor axis sin i = 1.0 solar radius, eccentricity e = 0.615, and mass function f(m) = 0.13 solar mass. No eclipses are observed. We infer that the unseen companion is a compact object with mass comparable to that of the pulsar. In addition to the obvious potential for determining the masses of the pulsar and its companion, this discovery makes feasible a number of studies involving the physics of compact objects, the astrophysics of close binary systems, and special- and general-relativistic effects.

Abstract: Results are presented from a survey for 1.3 mm radiation toward 86 stars in the Taurus-Auriga dark clouds, including classical T Tauri stars, stars in T associations, and a few weak emission-line stars or naked T Tauri stars. The results show that 42 percent of the stars have detectable emission from small particles. The aggregate particle masses are found to be between 0.00001 and 0.01 solar mass, suggesting total disk masses between 0.001 and 1 solar mass. For several source between 1.3 and 2.7 mm, the spectral indices indicate that the particle emissivities are weaker functions of frequency, compared to the usual case of interstellar grains. Particle growth via adhesion in the dense disks is proposed to explain this result. The results show that disks more massive than the minimum mass of the protosolar system commonly accompany the birth of solar-mass stars, indicating that planetary systems are probably common in the Galaxy. 59 refs.

Abstract: We describe results from a fully self-consistent three-dimensional hydrodynamical simulation of the formation of one of the first stars in the Universe. In current models of structure formation, dark matter initially dominates, and pregalactic objects form because of gravitational instability from small initial density perturbations. As they assemble via hierarchical merging, primordial gas cools through ro-vibrational lines of hydrogen molecules and sinks to the center of the dark matter potential well. The high-redshift analog of a molecular cloud is formed. As the dense, central parts of the cold gas cloud become self-gravitating, a dense core of approximately 100 M (where M is the mass of the Sun) undergoes rapid contraction. At particle number densities greater than 10(9) per cubic centimeter, a 1 M protostellar core becomes fully molecular as a result of three-body H2 formation. Contrary to analytical expectations, this process does not lead to renewed fragmentation and only one star is formed. The calculation is stopped when optical depth effects become important, leaving the final mass of the fully formed star somewhat uncertain. At this stage the protostar is accreting material very rapidly (approximately 10(-2) M year-1). Radiative feedback from the star will not only halt its growth but also inhibit the formation of other stars in the same pregalactic object (at least until the first star ends its life, presumably as a supernova). We conclude that at most one massive (M 1 M) metal-free star forms per pregalactic halo, consistent with recent abundance measurements of metal-poor galactic halo stars.