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  • 1
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    The Beta Pictoris circumstellar disk. XV - Highly ionized species near Beta Pictoris (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Temporal variations of the Fe II, Mg II, and Al III circumstellar lines towards Beta Pictoris have been detected and monitored since 1985. However, the unusual presence of Al III ions is still puzzling, since the UV stellar flux from an A5V star such as Beta Pic is insufficient to produce such an ion. In order to better define the origin of such a phenomenon, new observations have been carried out to detect faint signatures of other highly ionized species in the short UV wavelength range, where the stellar continuum flux is low. These observations reveal variations not only near the C IV doublet lines, but also in C I and Al II lines, two weakly ionized species, not clearly detectable until now. In the framework of an infalling body scenario, highly ionized species would be created in the tail, far from the comet head, by collisions with ambient gas surrounding the star, or a weak stellar wind. Spectral changes have also been detected near a CO molecular band location, which, if confirmed, would provide the first molecular signature around Beta Pictoris.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 267; 1; p. 187-193.
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  • 2
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    Studies of H I and D I in the local interstellar medium (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: High-dispersion IUE spectra are presented of the hydrogen Ly-alpha chromospheric emission line of two nearby late-type stars, Capella and Lambda And. Both interstellar H I and D I Ly-alpha absorption can be seen against the chromospheric line, and the density, velocity dispersion, and bulk velocity of the gas in those lines of sight are derived. Limits are placed on the D/H ratio. The results are consistent with the current picture of the local interstellar medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 356; 223-228
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  • 3
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    A Type Stars as Probes of the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: With the aim to sample the Local Interstellar Medium (LISM), it was proposed to use A stars as targets. The Mg II UV lines seem to be the best interstellar absorption candidates. Several hundreths of A stars can be reached within 100 pc. First preliminary results (20 lines of sight) are presented, based on previous Copernicus and actual IUE observations.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 75-80
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  • 4
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    Deuterium Abundance in the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 84-88
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  • 5
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    Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to Beta Cma (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The line of sight to Beta CM a was probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. The density was found to be bar N sub H approximately .002/cu cm. Two separate regions were distinguished: (1) A local nearby HI region extends over a few parsecs from the Sun with a density of the order of 0.1/cu cm and a temperature of 11000 to 12500 K; (2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e., of approximately 0.1 cu cm and it contains only elements in low ionization state. All the ata are coherent with the picture of a cloud in ionization equilibrium at T approximately 23000 deg K.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 80-83
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  • 6
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    The interstellar medium on the Gamma Cassiopeiae line of sight (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The interstellar medium on the Gamma Cas line of sight is studied through the observations of O I, H2, H I, D I, and Ar I absorption features with the Copernicus satellite. By using the velocity structure of the line of sight previously determined through atomic nitrogen, it is demonstrated that these neutrals are located in the same physical regions and that the O I and Ar I abundances could be solar, on the average, relative to N I in all components. The 1066.660 A Ar I line profile is contaminated by an unidentified line, already detected in the spectrum of Zeta Pup. Furthermore, a peculiar behavior of the Ar I abundance in the different components is reported, possibly associated with high-velocity interstellar gas present on the line of sight. It is concluded that the Gamma Cas line of sight could intercept a dense cloud which has been engulfed and disrupted by a shock.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 242
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  • 7
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    The gaseous component of the disk around Beta Pictoris (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 293; L29-L33
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  • 8
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    The ratio of deuterium to hydrogen in interstellar space. IV - The lines of sight to Delta, Epsilon, and Iota Orionis (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Deuterium absorption features in spectra of Delta, Epsilon, and Iota Ori obtained with Copernicus are analyzed. The Iota Ori line-of-sight analysis, which is quite detailed because of the high-velocity H I components superposed on the deuterium features, gives a D/H ratio (which is uncertain because of a complex profile) of 0.000014. A D/H ratio of the order of 7 millionths is determined for Delta and Epsilon Ori. For the complex line profiles involved, one may regard this as a formal lower limit. Several attempts were made to increase the ratio N(D I)/N(H I) in the context of reasonable models for the line of sight, but with no success; the derived values are therefore regarded as actual values, not lower limits. Since the derived value is an average on the line of sight, the possibility cannot be ruled out that the true ratios N(D I)/N(H I) in individual nearby components differ from the mean values. The mean value for these two directions is lower by a factor of 4 than the best value for the Zeta Pup line of sight (the highest yet derived for path lengths greater than 50 pc).
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 229
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  • 9
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    Implications of high-velocity interstellar H I absorption features (1979)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Contributions to the interstellar H I column density at high velocities from immediate postshock gas and from the cooling gas behind a shock are compared. The detection of high-velocity H I in L-epsilon and L-delta for Iota Ori is reported and interpreted as cooling gas behind a shock of 100 km/s velocity. The immediate postshock gas should be observable for shock velocities greater than 200 km/s and permits direct determination of the velocities of adiabatic shocks in the interstellar medium. It is pointed out that interstellar L-alpha and L-beta lines may not have purely Lorentzian profiles if high-velocity H I is a widespread phenomenon.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 229
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  • 10
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    Transient components in the Lyman lines of hot stars Evidence for the ejection of shells or puffs on very short timescales (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The existence of H I transient components in the stellar wind of Epsilon Per toward eight early type stars observed by the Copernicus satellite is systematically investigated. It is shown that such transient components are indeed present in the spectra of five of these stars and have characteristics very similar to the one found in the case of Epsilon Per. It is shown that such components can be interpreted in terms of coherent 'puffs' or shells of matter ejected by the stars. They would be caused by an increase of the stellar mass loss rate by a factor of 1.5 to 3 during one hour or less, and would be accelerated more slowly than the quiet wind. It is suggested that such events must be due to instabilities in these stars which are all slightly evolved stars ranging in spectral types between O9 and B1. The instabilities are probably similar to those in Beta Cephei stars, i.e., nonradial pulsations.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 137; 1 Au
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