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  • 1
    Publication Date: 2011-08-19
    Description: It is suggested that disk accretion provides the requisite external source to power the winds of T Tauri stars. As a test of this hypothesis, a potential accretion diagnostic for a representative sample of stars is compared to diagnostics of the wind strength. The luminosity of H-alpha, formed in the inner wind, and the luminosity of the forbidden emission lines, formed in the outer wind, are used as wind diagnostics, while the excess infrared luminosity is used as a potential accretion diagnostic. It is found that forbidden-line O I 6300 A and H-alpha line luminosities are correlated with each other over two orders of magnitude; this is interpreted as the indication of a wide range of mass-loss rates among the given sample of T Tauri stars. The luminosity of each of these lines is also found to be correlated with excess infrared luminosity. However, neither the forbidden nor the H-alpha luminosity is well correlated with the photospheric luminosity, leading to a conclusion that it is the disk, not the star, which primarily determines the strength of wind indicators in T Tauri stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 354; 687-700
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  • 2
    Publication Date: 2011-08-19
    Description: This paper presents a statistical study in which the observed total luminosity is compared quantitatively with an estimate of the stellar luminosity for a sample of 59 low-mass young stellar objects (YSOs) in the Taurus-Auriga complex. In 13 of the analyzed YSOs, luminosity excesses greater than 0.20 are observed together with greater than 0.6 IR excesses, which typically contribute the bulk of the observed excess luminosity and are characterized by spectral energy distributions which are flat or rise toward long wavelengths. The analysis suggests that YSOs showing the largest luminosity excesses typically power optical jets and/or molecular outflows or have strong winds, as evidenced by the presence of O I emission, indicating a possible correlation between accretion and mass-outflow properties.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 95; 534-542
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  • 3
    Publication Date: 2011-08-19
    Description: Properties of optical and molecular outflows associated with young stellar objects are discussed with emphasis placed on new results concerning outflow energetics, collimating structures, and the relationship between the outflow properties and the magnetic field geometry characterizing the host molecular clouds. Particular consideration is given to the IRAS observations of YSO mass outflows, which reveal extended far-IR emission associated with high-velocity molecular gas and in which a number of disk-like structures associated with YSO outflow sources were resolved. The disk axes appeared to lie along the direction of molecular outflows or stellar jets. The mass outflows showed a remarkable tendency to align along the direction of the magnetic fields which thread their host molecular clouds, suggesting that the cloud magnetic field must play an important role in determining the flattening (and perhaps the rotation) of protostellar structures.
    Keywords: ASTROPHYSICS
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  • 4
    Publication Date: 2011-08-19
    Description: An attempt is made to provide deep CCD images suitable for tracing the shock-excited and scattered-light components characterizing extended Herbig-Haro complexes. Tabular data include astrometric positions for all stars, shock-excited emission knots, prominent scattered-light patches, as well as an identification for all H-alpha emission objects within the CCD images. It is concluded that: (1) optical outflows are not always accompanied by molecular flows, (2) optical outflows show a higher degree of collimation than their molecular counterparts, and (3) the Herbig-Haro phenomenon is not restricted to low-mass young stellar objects.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 62; 39-69
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  • 5
    Publication Date: 2011-08-19
    Description: It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 1001-101
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  • 6
    Publication Date: 2011-08-16
    Description: Observations of a group of stars surrounding the Herbig Be-type star BD + 40.4124 suggest that this object is the brightest member of a relatively small stellar group. The age of this group is extremely small, probably less than 500,000 years.
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 173; Apr. 15
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  • 7
    Publication Date: 2011-08-16
    Description: A quantitative spectrophotometric study of the Herbig Ae and Be stars associated with nebulosity demonstrates that the majority have surface gravities appropriate to pre-main-sequence stars while the remainder have surface gravities characteristic of the zero-age main seee. This evidence, along with their gross spectroscopic and pc similarity to T Tauri-like stars and the fact that all these stars appear to be surrounded by circumstellar dust, places them among the youngest known stellar objects. The geometry of the circumstellar shells is discussed and the evidence seems to favor a nonspherical, possibly disklike shape. Finally, photographs taken with a 1-micron image-tube system reveal a large number of red stellar objects surrounding many of these stars. This suggests that the Herbig Ae and Be objects may be the brightest representatives of very recently formed stellar groups.-
    Keywords: SPACE SCIENCES
    Type: Astrophysical Journal; 173; Apr. 15
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  • 8
    Publication Date: 2011-08-16
    Description: Spectrophotometric observations of asymptotic giant and red giant branch stars in metal weak globular clusters
    Keywords: SPACE SCIENCES
    Type: ; 469-471. (
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  • 9
    Publication Date: 2011-08-16
    Description: Young cluster NGC 2264 pre-main sequence A and F stars four color and H beta observation, suggesting evidence of circumstellar gas shells
    Keywords: SPACE SCIENCES
    Type: ; TROPHYSICAL JOURNAL
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  • 10
    Publication Date: 2011-08-19
    Description: Further tests of the accretion disk hypothesis for FU Orionis objects are presented. High spectral resolution, high signal to noise, 5820-6830 A and 7500-9370 A spectra of V1057 Cyg reveal a correlation between linewidth and line transition lower excitation potential expected from this hypothesis. The magnitude of the effect compares favorably with that predicted by synthetic disk spectra. Additional evidence for previously documented spectral type and linewidth versus wavelength correlations is also presented. This kinematic evidence strongly supports the accretion disk hypothesis.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 349; 328-334
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