Infrared observations of possible protostars
Energy distribution measurements on infrared objects located in H2 and gaseous nebulae regions
Becklin, E. E.↗
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Protostars.
Stellar formation taking into account angular momentum of interstellar cloud, discussing gravitational cloud contraction
Cameron, A. G. W.↗
The dynamical interaction of a newly formed protostar with infalling matter - The origin of interstellar grains
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Burke, J. R.↗
Conference on Protostars and Planets, University of Arizona, Tucson, Ariz., January 3-7, 1978, Proceedings
These papers deal with star formation, the origin of the solar system, and the possible formation of planets associated with other stars. Specific topics include chemical and isotopic anomalies in meteorites, laboratory analogs of interstellar dust, properties of dark globules, locations of newly formed stars in molecular clouds, O-star formation, observations of star-formation regions near supernova remnant W44, and equilibrium condensation of supernova ejecta. Other contributions discuss radio observations of molecular clouds associated with T Tauri stars, rotational velocities of pre-main-sequence stars, observational studies of star formation, characteristics of a possible preplanetary disk around the pre-main-sequence star MWC 349, calculations of the collapse of a rotating dusty protostellar cloud, a theory on the dynamics of dust particles in an incompressible turbulent fluid, and an analysis of the dynamical collapse of a model presolar nebula.
Gehrels, T.↗
Numerical three dimensional calculations of tidally induced binary protostar formation
The manner in which interstellar clouds fragment into subcondensations capable of becoming stars is still unknown. A variety of mechanisms may be responsible for cloud fragmentation. The considered investigation is concerned with a mechanism which is based on tidal forces due to a companion cloud. A 3D code is used to study the tidal effects of point sources of various masses located in the equatorial plane of an initially uniform density, uniformly rotating, isothermal gas cloud. It is found that tidal forces can be quite effective at inducing fragmentation in an initially uniform cloud, although the effects are most pronounced for low thermal energy clouds, perturbed by perhaps unreasonably large tidal forces. It is also seen that tidal forces may be much less efficient at preventing the collapse of a cloud than has previously been supposed.
Boss, A. P.↗
Fragmentation in a rotating protostar - A re-examination of comparison calculations
The self-gravitating collapse of a rotating, isothermal protostellar cloud has been recalculated with two independent fluid-dynamic computer codes, in three space dimensions, with improved spatial resolution compared to previous calculations. The results again predict fragmentation and formation of a binary protostellar system with properties similar to those obtained in the lower-resolution calculations. The results, however, are in disagreement with those obtained with a particle-dynamic code by Gingold and Monaghan (1981) for the collapse of a cloud from the same initial conditions. Possible explanations for the divergent results are discussed.
Bodenheimer, P.↗
Infrared spectra of protostars - Composition of the dust shells
Nearly complete 2 to 13 micron spectra are presented for 13 compact infrared sources associated with molecular clouds, along with partial spectra of six additional objects. The spectra are found to resemble blackbodies with superposed absorption features from 2.8 to 3.5 microns, at 6.0 and 6.8 microns, and in the silicate band centered near 9.7 microns. Correlations among the features are investigated in an attempt to confirm possible identifications. A good correlation between the deepest part of the absorption at 3.1 microns, its long wavelength wing, and the 6.0 micron features suggests that all may derive from large amorphous water ice particles. The relatively poor correlation between the 3.4 and 6.8 micron optical depths adds no evidence in support of the suggestion that these bands may be due to CH bonds
Willner, S. P.↗
Far-infrared and submillimeter observations of the low-luminosity protostars L1455 FIR and L1551 IRS 5 - The confinement of bipolar outflows
Far-IR observations of L1455 FIR and L1551 IRS 5 obtained in December, 1981, and in September, 1982, and January, 1983, respectively, using the H-1 and G-2 bolometer systems on the 91-cm telescope of the NASA Kuiper Aiborne Observatory are reported. Additional observations at 400 microns were obtained with UKIRT in November, 1981, (L1551) and with NASA IRTF in November, 1982 (L1455). The results are presented in tables and graphs, and L1455 and L1551 are compared with other objects in terms of central-star parameters, clouds, and overflows. The characteristics calculated for L1455 and L1551 include luminosity 1.5 and 23 solar luminosity, size less than 7 x 10 to the 16th cm, H2 density greater than or equal to 4 x 10 to the 5th and 1 x 10 to the 6th/cu cm, and 35-K dust cores of 0.2 and 0.7 solar mass, respectively. The bipolar appearance of the L1551 outflow is attributed to circumstellar material only.
Davidson, J. A.↗
Angular momentum transfer by gravitational torques and the evolution of binary protostars
The efficiency of angular momentum transport by gravitational torques is investigated semianalytically for two idealized models. The first model, a rotating ellipsoid embedded within another ellipsoid, is compared with numerical results for the fission instability of a radpidly-rotating polytrope. The fission instability is aborted by the rapid transfer of angular momentum outward by gravitational torques. The global rates of angular momentum transfer by gravitational torques in rotating gas clouds such as the presolar nebula are shown to be comparable to the rates assumed to be appropriate for transfer by turbulent stresses. The second model is a binary system embedded within a rotating ellipsoid. The binary orbital angular momentum decreases significantly when the phase angle with the ellipsoid is constant; the binary separation may then decrease by a factor of 100 within about an orbital period. For a variable phase angle, little secular loss of orbital angular momentum occurs. Binaries which form in the isothermal regime of the theory of hierarchical fragmentation will not undergo orbital decay, whereas very close binaries composed of nonisothermal fragments may decay and merge into single objects.
Boss, A. P.↗
Absorption features in the 5-8 micron spectra of protostars
High signal-to-noise ratio spectra in the range of 5-8 microns of four sources embedded in molecular clouds are examined using low-temperature laboratory measurements of the 5-8-micron spectra of simple molecules and their mixtures. The absorption, apparent in all four sources, is characterized by highly distinct features ranging from two relatively narrow bands at 6.0 and 6.8 microns in W33A to a broad, shallow, and partially structured feature extending from 5.2 to 7.8 microns in Mon R2-IRS2, BN, and NGC2264. The first feature (W33A) is explained by the OH bending mode in H2O and the CH deformation modes in saturated hydrocarbons; while the second feature (Mon R2-IRS2-type) is explained by the presence of a mixture of saturated and unsaturated hydrocarbons possibly containing strongly electronegative groups.
Tielens, A. G. G. M.↗
Protostars and planets II
Various papers on the formation of stars and planets are presented. The general topics addressed include: molecular clouds and star formation, young stellar objects and circumstellar disks, chemistry and grains in molecular clouds and the solar nebula, formation of giant planets, and models of the solar nebula and other planetary systems. Individual papers address: molecular cloud cores, physical conditions in isolated dark globules, rotation in dark clouds, and turbulence in molecular clouds. Also discussed are: fragmentation and hierarchical structure in the interstellar medium, formation of bound stellar clusters, ambient radiation field of young solar systems, and magnetic fields.
Black, D. C.↗
Protostars and planets - Overview from a planetary perspective
Today the simultaneous formation of a star and planetary system is understood to be natural and coupled consequences of the collapse of an interstellar cloud of molecular gas and dust. Ideas put forward to account for the existence of the solar system seem generally applicable to star formation throughout the universe. If this is indeed the case, then planetary systems should be present in large numbers throughout the universe. Even the gross structural features of the planetary system in the solar system seem largely to be the result of nearly deterministic processes, rather than the result of chance alone; many planetary systems throughout the universe may resemble this one. This chapter summarizes and examines some of the implications of ideas about the formation of stars and planetary systems.
Levy, E. H.↗
Candidate solar-type protostars in nearby molecular cloud cores
IRAS data have been used to examine the vicinity of nearly 100 dense clumps of molecular gas observed in lines of CO and NH3. More than one-third of these molecular cloud 'cores' contain infrared sources that appear to be newly formed, or forming, low mass stars. While about one-third of the infrared sources are associated with visible stars and have properties that resemble T Tauri stars, the remainder of the infrared sources have no optical counterparts and are probably embedded within the molecular cloud itself. These invisible sources lie close to the molecular cloud peaks and have cold, massive shells of material around them. Some of the cores without infrared sources have gas properties similar to those with embedded sources and so may be on the verge of gravitational collapse. The selection of the IRAS sample and its properties are described. The spectral energy distributions of the sources and their nature are discussed along with their physical properties, the properties of cores with and without infrared sources, and the time scale for the evolution of the sources.
Beichman, C. A.↗
The temperature structure in accretion flows onto massive protostars
Radiation transfer problems involved in the infall of dust and gas during star formation are studied. Dust properties are discussed, and modifications of spherical radiative transfer equations are presented that permit forward scattering by dust to be treated for the small size of the star relative to the inner radius of the shell. A procedure for deriving the stellar radiation field incident on the inner edge of the shell is developed. The temperature correction procedure of Cassinelli and Hartmann (1975) for extended stellar atmospheres is modified so that the multitemperature nature of the grains in the cloud may be derived. Temperature distributions for three schematic models in which the density is prespecified are discussed. Radiative acceleration of grains is addressed, showing that the proper mean opacity differs by a large factor from the Rosseland mean opacity that is commonly used. Emergent fluxes for the models are given.
Wolfire, Mark G.↗
Theory of collapse and protostar formation
Interstellar clouds must increase in density by a factor of more than 10 to the 20th in order to form stars. Because observations of the phases intermediate between dense interstellar clouds and pre-main-sequence stars are difficult, theoretical solutions presently provide the primary means for exploring the collapse phase of protostellar formation. The mathematical formulation of the protostellar collapse problem is presented, and various methods employed in solving the equations are outlined. This tutorial emphasizes the numerical approach to the study of the nonlinear time-dependent evolution of collapsing interstellar clouds, including self-gravitation, rotation, and radiative transfer. Results are summarized for the restricted cases of spherical and axisymmetric symmetry, as well as for fully three-dimensional evolutions, and briefly compared to observations of star formation.
Boss, A. P.↗
Two micron morphology of candidate protostars
Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.
Tamura, Motohide↗
A submillimeter protostar mear LkH-alpha 198
We present submillimeter and millimeter line and continuum observations of the region around LkH-alpha 198 and V376 Cas. The continuum data reveal the presence of a very cool object, LkH-alpha 198 MM located approximately 19 sec northwest of LkH-alpha 198. LkH-alpha 198 MM is not visible in the near-IR. The CO maps suggest that the mm-source, rather than LkH-alpha 198 or its IR companion LkH-alpha 198B, may drive the large CO outflow seen in this cloud or that both drive outflows which are roughly aligned with each other. In addition V376 Cas appears to power a small bipolar CO outflow.
Sandell, Goran↗
Protostars and Disks
The research concentrated on high angular resolution (arc-second scale) studies of molecular cloud cores associated with very young star formation. New ways to study disks and protoplanetary systems were explored. Findings from the areas studied are briefly summarized: (1) molecular clouds; (2) gravitational contraction; (3) jets, winds, and outflows; (4) Circumstellar Disks (5) Extrasolar Planetary Systems. A bibliography of publications and submitted papers produced during the grant period is included.
Ho, Paul↗