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  • Other Sources  (14)
  • ASTROPHYSICS  (14)
  • 1
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    On the nature of the material surrounding Vega (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of Vega at 193 microns indicate that the far-infrared emission from the circumstellar material discovered by IRAS (Aumann et al. 1984) may decline more rapidly than a Planck spectrum at wavelengths greater than 100 microns. This suggests that the emitting particles may be smaller than the millimeter-sized objects proposed by Aumann et al. (1984). Small grains would be driven from the stellar system by radiation pressure, or their orbits would decay as a result of Poynting -Robertson drag. In order to maintain a state of dynamic equilibrium, a continuous supply of new particles would be required. It is hypothesized that the small grains are ejected by sublimation of volatile material from larger comet-like bodies in a partially coalesced preplanetary disk. A reservoir containing less than a few hundred earth masses could sustain the source over the lifetime of the star.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 285; 808-812
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  • 2
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    Far-infrared and submillimeter observations of the multiple cores in S255, W3, and OMC-1 - Evidence for fragmentation? (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The two cores of the S255 cloud were mapped at 60, 100, 185, and 400 microns and 40-400 microns maps were made of the cores and S255, OMC-1 and W3. Absolute flux densities were determined with an accuracy of 30 percent. The luminosities and masses of the S255 cores were equivalent to those of the other objects, including the concentration of a compact H II region around young objects. The densified regions are regarded as typical of areas where massive objects are forming. The observed 1.4-4 km/sec velocity differences between two cores in any one cloud indicates that the angular momentum of the original clouds, which drove the collapse of the cores, is transferred to the massive young stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 284; 637-642
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  • 3
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    On the far-IR and sub-mm spectra of spiral galaxies (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Photometric measurements of three Virgo cluster spirals (NGC4254, NGC4501, and NGC4654) at 160-microns (far-infrared) and 360-microns (submillimeter) wavelengths are compared with theoretical models and observations at other wavelengths. It is shown that the data at the observed wavelengths do not fit any of interstellar dust grain models very well; four possibilities are given in order to explain discrepancies: the observed wavelength points are incorrect; previously observed data is incorrect; both data are incorrect; and the premise of the analysis is incorrect - a composite far-infrared spectrum of normal spiral galaxies is meaningless because they vary considerably in their far-infrared properties. It is also noted that the observed data are inconsistent with models having large cold grains.
    Keywords: ASTROPHYSICS
    Type: Physics and Chemistry of Interstellar Molecular Clouds - MM and Sub-MM Observations in Astrophysics; Sept. 22-25, 1988; Zermatt; Switzerland
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  • 4
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    Far-infrared detection of low-luminosity star formation in the Bok globule B335 (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Measurements of far-infrared intensities in the Bok globule B335, made with higher spatial and spectral resolution than two earlier studies, are described. The NASA 3-m Infrared Telescope Facility was used in February 1981 and the Kuiper Airborne Observatory 0.9-m telescope was used in October 1981 and August 1982 for the observations. The far-infrared source in B335 was revealed to be more compact than previously assumed, ruling out the interstellar radiation field as the dominant heat source. The new far-infrared size, luminosity, and temperature derived suggest that these may be the first observations of low-mass star formation embedded deeply within a Bok globule. The far-infrared source does not have a near-infrared or radio continuum counterpart. High angular resolution at submillimeter wavelengths will be critical in further studies of low-mass star formation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 274; L43-L47
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  • 5
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    Far-infrared and submillimeter observations of the low-luminosity protostars L1455 FIR and L1551 IRS 5 - The confinement of bipolar outflows (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 277; L13-L16
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  • 6
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    Star Formation in Globules (1984)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The low mass star formation process was studied by application of submillimeter and supplementing far-infrared continuum observations by molecular line observations to the discovery and analysis of compact cores in molecular clouds with low luminosity. These dense regions are likely to be the sites where a cloud has recently collapsed or is still collapsing to form a star. Observations show that nonisotropic effects must play an important role in star formation. Four low luminosity sources embedded in the clouds L1551, B335, L1455 and L723 are presented. All these sources exhibit collimated bipolar molecular outflows of varying strengths. Data on the outflows are combined with determinations of mass, luminosity and temperature of the dust in the dense cores surrounding these embedded energy sources, to infer the evolutionary stage of the object. The possible role of the cores in channeling or generating the outflow is examined.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center Airborne Astron. Symp.; p 186-193
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  • 7
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    Far-infrared and submillimeter wavelength observations of star-forming dense cores. II - Images (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: This paper reports on far-infrared and submillimeter wavelength observations of low-mass protostellar candidates. The data set comprises emission maps of nine sources observed over a wavelength range 100-800 microns. The emission is extended at all wavelengths longer than 100 microns. The apparent size of the emission regions is weakly correlated with the beam size and is consistent with an underlying specific intensity profile which is scale-free. The observed emission maps are not circular, but have a mean aspect ratio of 1.3, and the position angles are similar to those determined from maps of molecular emission. The observational results are used in conjunction with theoretical considerations to constrain the physical properties of the putative protostellar envelopes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 555-569
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  • 8
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    The luminosity of the Galactic center (1992)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: High signal-to-noise 50- and 90-micron continuum maps of the central 5 x 4 arcmin of the Galaxy made from observations on the Kuiper Airborne Observatory are presented. Dust and luminosity distribution models which are consistent with the data are presented. These data are consistent with a flared disk of dust, centered on the position of Sgr A*, having a central cavity wth a radius of 1 pc. Strong evidence is found for a large amount of dust between the northern and eastern ionized arms located within the cavity. It is argued that this 'tongue' of dust is optically thick at UV and visible wavelengths. Both smooth and clumped dust distributions, consistent with the disk and central cavity, are considered. For the smooth distribution, the dust heating is found to be consistent with the data only for a central UV source of a few x 10 exp 6 solar luminosities.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 387; 189-211
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  • 9
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    Polarization of the far-infrared emission from the thermal filaments of the Galactic center arc (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The polarization of the 100 micron continuum emission has been measured at 14 positions in the dense, warm molecular cloud associated with the arched filaments, or the 'bridge', of the radio arc near the Galactic center. At all positions the percent polarization is found to be quite large, ranging up to 6.5 percent. The polarization is interpreted in terms of thermal emission by magnetically aligned dust grains. The directions of the polarization vectors then indicate that the magnetic field is (1) parallel to the long dimension of the thermal radio filaments, and (2) very uniform on scales of 1-10 pc. Of several explanations for the inferred field geometry, the simplest is that it results from the unusually large dynamical shear in the emitting cloud.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 399; 1; p. L63-L66.
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  • 10
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    Far-infrared and submillimeter-wavelength observations of star-forming dense cores. I - Spectra (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Far-infrared and submillimeter photometry of 10 low-mass star formation regions containing embedded IRAS sources is presented. These new observations define the peak of the spectral energy distributions of these objects and provide more precise estimates of their bolometric luminosities. Two new sources, L1527 and L483, are among the reddest known low-mass objects, with spectral energy distribution peaks at 100-200 microns and extremely steep IRAS slopes. These cold sources have spectra which are similar to blackbodies of 30-40 K but have significant excess emission on the Wien side. Models of the spectral energy distributions using a spherically symmetric core structure indicate that these sources have visual extinctions greater than 1000 mag. However, models with these large extinctions predict too little near-infrared emission. A nonspherically symmetric distribution of circumstellar material may play a role in the generation of the extra near-infrared emission.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 366; 203-220
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