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  • 1
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    The Galactic halo and local intergalactic medium toward PKS 2155-304 (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Low-resolution UV observations of the bright, low-redshift BL Lac object PKS 2155-304 have been obtained by the HST's high-resolution spectrograph. Attention is here given to results on the number of intergalactic H I Ly-alpha components in the line-of-sight toward this object. The highest-redshift of the observed Ly-alpha systems furnishes a lower limit on the distance of the BL Lac object; this distance is consistent with the approximate redshift deduced from CCD imagery of the probable host galaxy for PKS 2155-304.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 409; 1; p. 199-204.
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  • 2
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    Partially Crystalline Silicate Dust in Protostellar Disks (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: We examine the infrared emission of the Herbig Ae/Be stars and show that some possess characteristics indicative of partially crystalline grains similar to those seen in Beta Pictoris and some solar system comets.
    Keywords: Astronomy
    Type: From Stardust to Planetesimals: Contributed Papers; 19-22; NASA-CP-3343
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  • 3
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    Newly identified main-sequence A stars with circumstellar dust (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The IRAS Faint Source Survey data base and the ADDSCAN/SCANPI software are used to search for systems with circumstellar dust in two samples: all of the 62 A stars in Woolley's catalog, which lie near the main sequence and are typically within 25 pc of the sun, and all A stars in the Bright Star Catalogue with mV in the range 4-5 and v sin i not less than 100 km/s. In the first sample, 11 nearby A stars having (12)-(25) and (25)-(60) colors consistent with circumstellar dust are found. The analysis of the second sample demonstrates that the use of the FSS data base increases the likelihood of identifying A stars with circumstellar dust fainter than mV = 4. Three more new dusty systems are found in this sample. Beta Pictoris (A5 IV-V) is the only star within 25 pc of the sun that displays IR colors indicative of both warm and cool dust. It is inferred from the absence of cool dust in the vast majority of the systems that the dust disks of these stars are much less extended than that seen around Beta Pictoris.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 396; 2, Se
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  • 4
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    Accreting Gas and Dust in Pre-Main Sequence Disk Systems (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Infrared spectroscopy of pre-main sequence stars with dusty protostellar disks provide information about the evolution of refractory materials in such systems. These systems exhibit varying degrees of strength and structure in the silicate emission band situated at 10 microns wavelength. Band strength is affected by the mean grain size, while band structure is determined by the chemical composition and degree of crystallinity. In some objects, the silicate band is strong and featureless, similar to that seen in the interstellar medium. In others, the band is often weaker, and exhibits structure consistent with the presence of crystalline olivine. In these latter objects, the band is similar to that of some solar system comets. The strength and structure of the silicate band may be related to the processing history of the system.
    Keywords: Astrophysics
    Type: Formulation and Evolution of Solids in Space; 513-520
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  • 5
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    The (BETA) Pictoris Phenomenon Among Herbig Ae/Be Stars (1996)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: We present a survey of high dispersion UV and optical spectra of Herbig Ae/Be (HAeBe) and related stars. We find accreting, circumstellar gas over the velocity range +100 to +400 km/s, and absorption profiles similar to those seen toward Beta Pic, in 36% of the 33 HAeBe stars with IUE data as well as in 3 non-emission B stars. We also find evidence of accretion in 7 HAeBe stars with optical data only. Line profile variability appears ubiquitous. As a group, the stars with accreting gas signatures have higher v sin i than the stars with outflowing material, and tend to exhibit large amplitude (greater than or equal to 1(sup m)) optical light variations. All of the program stars with polarimetric variations that are anti-correlated with the optical light, previously interpreted as the signature of a dust disk viewed close to equator-on, also show spectral signatures of accreting gas. These data imply that accretion activity in HAeBe stars is preferentially observed when the line of sight transits the circumstellar dust disk. Our data imply that the spectroscopic signatures of accreting circumstellar material seen in Beta Pic are not unique to that object, but instead are consistent with interpretation of Beta Pic as a comparatively young A star with its associated circumstellar disk.
    Keywords: Astronomy
    Type: Astronomy and Astrophysics Supplement Series; Volume 120; 157-177
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  • 6
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    C IV and Si IV in IUE spectra of normal B8-A0 stars: UV identified Be/Ae stars (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Archival IUE high dispersion spectra of 42 B6-A2 stars within 200 pc were surveyed. Five of the program stars show significant C IV and Si IV absorption. All of the stars with detected C IV have v sin i less than or = 190 km/sec. Sharp absorption cores are present in Si II lambda 1533 in 3 of the objects, indicating that these are previously unrecognized shell stars. Three of the stars have variable or asymmetric C IV profiles which are consistent with the C IV and Si IV being produced in stellar winds. One star has C IV in the form of a shortward-shifted discrete absorption component, similar to those observed in Be stars. The data are compared with similar data for Be and B shell stars.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 397-400
    Format: application/pdf
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  • 7
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    Recurrent shell infall events in a B0.5e star: HD 58978 1979-1988 (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Infall from the circumstellar envelope onto the bright B0.5 IVe star, HD 58978 was studied. The IUE data indicate that the star was surrounded by a low and moderately ionized circumstellar shell at least 12 times between 1979 and 1988. During 6 of these episodes, the signatures of cool circumstellar material were redshifted with respect to the photosphere by 20 to 80 km/sec. The data indicate that the transition from infall to minimal shell absorption can occur in under 10 days, and are consistent either with infall phases lasting up to 6 months, or with infall episodes shorter than 10 to 15 days. The long term behavior of the shell episodes is compared with variability in the stellar wind.
    Keywords: ASTRONOMY
    Type: ESA, A Decade of UV Astronomy with the IUE Satellite, Volume 1; p 257-260
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  • 8
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    The very high rotators in the late-B and early-A stars: Shell stars with Si IV and C IV features the case of HD 119921 (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Study of several stars in the late B and early A spectral types shows that very high rotators are associated with shell characteristics (sometimes not detected at all in the visible spectra) and also with C IV and some Si IV spectral absorption features which can be explained by circumstellar phenomena superimposed over stellar metallic blends. These particularities are evidenced by comparison with other spectra of low and high rotators in the same spectral range. HD 119921, a star with similar characteristics to the other ones of the sample, is given special attention. A possible scenario is suggested to explain the observed superionization features.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 283-286
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  • 9
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    Stellar winds in two massive Herbig Be stars (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: A survey of the IUE archival spectra of Herbig Be stars, revealed 2 stars, HD 200775 and HD 259431, with winds which differ from those seen in more evolved stars and from the winds observed in the cooler Herbig Ae stars. The winds are strong, show a wide range of ionization from C IV to Mg II and Si II, and exhibit pronounced ionization gradients as a function of radial velocity. These winds are present at v sin i less than or = 100 km/sec, suggesting that winds from massive pre-main sequence Be stars extend to higher latitudes than those observed in more evolved stars. The presence of well-developed discrete absorption components, together with stronger winds than can be accounted for based on the stellar luminosity, suggests that mechanisms other than simple radiation pressure are important in initiating and driving stellar winds from these stars.
    Keywords: ASTRONOMY
    Type: ESA, Proceedings of the Celebratory Symposium on a Decade of UV Astronomy with the IUE Satellite, Volume 2; p 109-111
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  • 10
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    A search for Beta Pictoris analogs (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results are presented of the survey of known shell stars detected by the Infrared Astronomy Satellite (IRAS) at sufficient bandpasses to permit evaluation of the nature of the infrared excess, and having archival International Ultraviolet Explorer (IUE) high dispersion spectra suitable for identifying stars with infalling circumstellar plasma. Detection of infall in shell stars with infrared signatures of circumstellar dust is described. One star which shows infalling plasma, but apparently no circumstellar dust is described. The implications for the understanding of Beta Pictoris and similar systems are discussed.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 227-230
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