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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Magnetic field in a low-mass protostar disk - Millimeter polarimetry of IRAS 16293-2422

We have measured the millimeter polarization of IRAS 16293-2422, a low-mass protostar candidate embedded in the east streamer of the Rho Ophiuchi dark cloud. The source has a linear polarization at 1.1 mm of (2.8 +/- 0.5) percent at a position angle of 144 deg +/- 5 deg with a 19 arcsec beam. If this polarization is due to thermal emission from magnetically aligned nonspherical grains in a dust disk around the central (proto)star, then the magnetic field threads across the disk at a position angle of 54 deg +/- 5 deg projected on the sky. This direction is the same as that of the minor axis of the elongated circumstellar gas disk (of scale 1600 AU) and of the direction of one of the quadratic outflows. There is no positive evidence for a twisted magnetic field in the dust disk, which constrains the hydromagnetic models for molecular outflows, at least for this source.

Tamura, Motohide↗
NASA NTRS1994

Identification of a collapsing protostar

The globular molecular cloud B335 contains a single, deeply embedded, far-infrared source. Our recent observations of H2CO and CS lines toward this source provide direct kinematic evidence for collapse. Both the intensity and detailed shape of the line profiles match those expected from inside-out collapse inside a radius of 0.036 pc. The collapse began about 1.5 X 10(exp 5) years ago, similar to the onset of the outflow. The mass accretion rate is about 10 times the outflow rate, and about 0.4 solar mass should have now accumulated in the star and disk. Because B335 rotates only very slowly, any disk would still be very small (about 3 AU). The accretion luminosity should be adequate to power the observed luminosity. Consequently, we believe that B335 is indeed a collapsing protostar.

Evans, Neal J., II↗
NASA NTRS1994

Identification of a Collapsing Protostar

The globular molecular cloud B335 contains a single, deeply embedded far-infrared source. Our recent observations of H2CO and CS lines toward this source provide direct kinematic evidence for collapse. Both the intensity and detailed shape of the line profiles match those expected from inside-out collapse inside a radius of 0.036 pc. The collapse began about 1.5 x 10(exp 5) years ago, similar to the onset of the outflow. The mass accretion rate is about 10 times the outflow rate, and about 0.4 solar mass should have now accumulated in the star and disk. Because B335 rotates only, any disk would still be small (about 3 AU). The accretion luminosity should be adequate to power the observed luminosity. Consequently, we believe that B335 is indeed a collapsing protostar.

Evans, Neal J., II↗
NASA NTRS1998

Unraveling the 10 micron "silicate" feature of protostars: the detection of frozen interstellar ammonia

We present infrared spectra of four embedded protostars in the 750-1230 cm-1 (13.3-8.1 microns) range. For NGC 7538 IRS 9, a new band is reported at 1110 cm-1 (9.01 microns, and several others may be present near 785, 820, 900, 1030, and 1075 cm-1 (12.7, 12.2, 11.1, 9.71, and 9.30 microns). The band 1110 cm-1 is attributed to frozen NH3. Its position and width imply that the NH3 is frozen in a polar, H2O-rich interstellar ice component. The NH3/H2O ice ratio inferred for NGC 7538 IRS 9 is 0.1, making NH3 as important a component as CH3OH and CO2 in the polar ices along this line of sight. At these concentrations, hydrogen bonding between the NH3 and H2O can account for much of the enigmatic low-frequency wing on the 3240 cm-1 (3.09 microns) H2O interstellar ice band. The strength of the implied NH3 deformation fundamental at 1624 cm-1 (6.158 microns) can also account for the absorption at this position reported by ISO.

NASA Center ARC↗
NASA NTRS2008

High-velocity Interstellar Bullets in IRAS 05506+2414: A Very Young Protostar

We have made a serendipitous discovery of an enigmatic outflow source, IRAS 05506+2414 (hereafter IRAS 05506), as part of a multiwavelength survey of pre-planetary nebulae (PPNs). The HST optical and near-infrared images show a bright compact central source with a jet-like extension, and a fan-like spray of high-velocity (with radial velocities up to 350 km/s) elongated knots which appear to emanate from it. These structures are possibly analogous to the near-IR bullets'' seen in the Orion Nebula. Interferometric observations at 2.6 mm show the presence of a continuum source and a high-velocity CO outflow, which is aligned with the optical jet structure. IRAS 05506 is most likely not a PPN. We find extended NH3 (1,1) emission toward IRAS 05506; these data, together with the combined presence of far-IR emission, H2O and OH masers, and CO and CS J=2-1 emission, strongly argue for a dense, dusty star-forming core associated with IRAS 05506. IRAS 05506 is probably an intermediate-mass or massive protostar, and the very short timescale (200 yr) of its outflows indicates that it is very young. If IRAS 05506 is a massive star, then the lack of radio continuum and the late G to early K spectral type we find from our optical spectra imply that in this object we are witnessing the earliest stages of its life, while its temperature is still too low to provide sufficient UV flux for ionization.

star formation↗
NASA NTRS1968

Protostars.

Stellar formation taking into account angular momentum of interstellar cloud, discussing gravitational cloud contraction

Cameron, A. G. W.↗
NASA NTRS1978

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.↗
NASA NTRS1981

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.↗
NASA NTRS1981

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.↗
NASA NTRS1982

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.↗
NASA NTRS1984

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.↗
NASA NTRS1984

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.↗