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  • ASTROPHYSICS  (27)
  • 1
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    The CI pressure shift and gravitational redshift of the cool DBQA5 white dwarf LDS678A (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A high resolution ultraviolet spectrum of the helium rich degenerate LDS 678A, obtained with the International Ultraviolet Explorer (IUE) satellite is presented. LDS 678A is the coolest metallic line generate (DQ or DZ) yet observed with the IUE scale. These observations provide a detailed line profile of the strong C I 2479 absorption line with equivalent width (W sub 2479 = 2.35 plus or minus 0.06 angstroms) from which theoretical line profile fits yield a C abundance (log C/He = 6.4). The presence of carbon in a helium rich atmosphere lends credence to the notion that LDS 678A is a transitional case between the DB white dwarfs with nearly pure helium atmospheres and the helium rich DQ white dwarfs which exhibit carbon bands. Corrected for an inferred pressure shift for the C I line, a gravitational redshift is deduced from which a most probable mass of 0.55 solar mass is derived.
    Keywords: ASTROPHYSICS
    Type: ESA, Evolution in Astrophysics: IUE Astronomy in the Era of New Space Missions; p 467-470
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  • 2
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    Spectrophotometric and model-atmosphere analyses of the hot DO and DAO white dwarfs from the Palomar-Green survey (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Recent optical and spectrophotometric observations of all currently known DAO and DO hot white dwarf candidates from the Palomar-Green Survey are presented. The optical observations were carried out using the Kitt Peak National Observatory Intensified Image Dissector Scanner (IIDS) system, the Multiple Mirror Telescope (MMT), and two photon-counting Reticon systems. Ultraviolet spectrophotometry was obtained using the International Ultraviolet Explorer (IUE) short-wavelength and long-wavelength cameras. The following spectroscopic subgroups were identified in the observations: the cool DO stars with spectra showing H I features together with He II + H blends; the hot DO stars, with spectra exhibiting weak He II (+H) lines; and hydrogen-rich DAO stars with broad H lines and sharp H II lines at 4686 A. A fourth subgroup of stars resembling PG 1159 with He at He II lines at 4686, and a C, N ion blend in the optical spectrum were also found. The spectroscopic data were analyzed in terms of a grid of hot, high-gravity LTE model atmospheres composed of a mixture of hydrogen and helium, and atmospheric parameters are deduced for each class of objects. On the basis of the model atmosphere analysis, the local space density of the DO stars is estimated to be 1.9-3.0 x 10 to the -7th per cubic pc, depending on the scale height.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 58; 379-411
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  • 3
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    The cosmological evolution and luminosity function of X-ray selected active galactic nuclei (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The cosmological evolution and the X-ray luminosity function of X-ray selected active galactic nuclei (AGNs) are derived and discussed. The sample used consists of 31 AGNs extracted from a fully identified sample of X-ray sources from the Einstein Observatory Medium Sensitivity Survey and is therefore exclusively defined by its X-ray properties. The distribution in space is found to be strongly nonuniform. The amount of cosmological evolution required by the X-ray data is derived in the framework of pure luminosity evolution and is found to be smaller than the amount determined from optically selected samples. The X-ray luminosity function is derived. It can be satisfactorily represented by a single power law only over a limited range of absolute luminosities. Evidence that the luminosity function flattens at low luminosity or steepens at high luminosity, or both, is presented and discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 4
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    Discovery of carbon stars in the Draco dwarf spheroidal galaxy (1982)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A grating prism survey of the Draco dwarf spheroidal galaxy that is 97% areally complete has led to the discovery of three carbon stars. Membership of these stars in Draco is firmly established from luminosity, proper motion, and radial velocity considerations. Optical and preliminary infrared photometry suggest that the Draco carbon stars are more closely related to the CH stars in omega Cen than to the luminous carbon stars found in the Fornax and Carina dwarfs. One of the carbon stars possesses an unusual emission line spectrum which might be indicative of either a very hot degenerate companion or a preplanetary evolutionary stage. Carbon stars have now been located in all four of the dwarf spheroidals that have been examined using transmission grating prism techniques. The rarity of these stars in galactic globulars, systems with which the dwarf spheroidals are often compared, indicates a fundamental population difference whose cause is not yet fully understood.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 254
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  • 5
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    1E 0104.2 + 3153 - A broad absorption-line QSO viewed through a giant elliptical galaxy (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The optical identification of the X-ray source 1E 0104.2 + 3153 is complicated by the close projection of a broad absorption-line (BAL) QSO (z = 2.027) 10 arcsec from a giant elliptical galaxy (z = 0.111) at the center of a compact group of galaxies. At only 1.2 de Vaucouleur radii (16 kpc for H sub 0 = 100 km/s Mpc) this QSO-galaxy projection is the closest yet discovered. Based upon current observations, the source of the X-ray emission cannot be conclusively determined. Present in the BAL QSO spectrum are extremely strong Ca II H and K absorption lines due to the intervening galaxy, the first optical detection of the cold interstellar medium in an elliptical galaxy. The strength of these lines (EW = 2 and 1 A) requires observation through several interstellar clouds in the line of sight to the QSO. By its proximity to the central regions of the elliptical galaxy and the relative distances of the galaxy and QSO, this QSO is a particularly good candidate for observing dramatic transient gravitational lensing phenomena due to halo stars in the foreground galaxy.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 277; 43-50
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  • 6
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    Two hot, low-field magnetic DA white dwarfs (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two hot stars discovered in the Palomar Green survey which were found to exhibit peculiarly broad and strong Balmer lines possibly indicative of low magnetic fields are discussed. The stars, PG 1658+441 and PG 0136+251, were found to have extended trough-shaped Balmer and Lyman-alpha line profiles when compared to nonmagnetic dwarfs of similar temperatures. Further observations of PG 1658+441 show it to correspond to a 30,000 K pure hydrogen atmosphere and confirm its nature as a magnetic object with a longitudinal field strength of about 0.7 megagauss and a mean surface field of about 2.3 megagauss. PG 0136+251 is found to be a hotter star (40,000-50,000 K) with weaker lines. Although no strong evidence for magnetic line splitting was obtained, it is argued that neither a high surface gravity nor very rapid rotation can account for the Balmer line shapes. Results thus extend the range of magnetic degenerates to include very hot white dwarfs, and demonstrate the usefulness of line-widths as indicators of possible low-field magnetic sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
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  • 7
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    IUE results on the AM Herculis stars CW 1103, E1114, and PG 1550 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: IUE data are presented on three AM Her stars (CW 1103 + 254, E1114 + 182, and PG 1550 + 191) which are used in conjunction with optical and IR fluxes to study the accretion characteristics of these systems in relation to other polars.The time-resolved IUE spectra of CW 1103 show that the column contributes little to the UV, while the white dwarf, with a temperature of approximately 13,000 K and a distance of approximately 140 pc, is the dominant source of light. Thus, CW 1103 at its normal state is basically very similar to VV Pup at its low accretion state, except for increased IR emission that is not connected to the accretion column or the secondary. E1114 also appears to be a low UV emitter, but better data are needed to constrain the observed temperature. On the other hand, PG 1550 has a steeper UV distribution, with a possibility for a hot Rayleigh-Jeans component at wavelengths less than 1600 A. This source is very similar to E1405-451 and AM Her itself.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 321-327
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  • 8
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    The new eclipsing magnetic binary system E 1114 + 182 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A comprehensive analysis of E 1114 + 182, the first eclipsing AM Herculis binary system and the shortest-period eclipsing cataclysmic variable known, is presented. The time-resolved X-ray observations which led to the system's recognition as an AM Her system with a roughly 90 minute orbital period are reported. The current optical photometric and polarimetric ephemeris and a description of the system's phase-modulated properties are given. The detailed photometric eclipse profile and the highly variable spectroscopic behavior are addressed. This information is used to determine systemic parameters and derive new information on the line emission regions. The data put severe constraints on current torque models for keeping the binary and white dwarf rotation in phase.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 293; 303-320
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  • 9
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    Detection and analysis of photospheric CNO features in the ultraviolet spectrum of the hot DO white dwarf PG 1034 + 001 (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analysis of PG 1034 + 001 extended to include the high-dispersion IUE spectra and the high-resolution optical multiple-mirror telescope echelle spectra is discussed. The observations reveal the presence of absorption lines (C IV at 1548 and 1551 A, N V at 1238 and 1242 A, and O V at 1371 A) from highly ionized species with large redshifts (+ 40-50) km/s) relative to the interstellar lines. The results of a preliminary abundance analysis of the photospheric lines, together with the results of a search of sharp shortward-shifted features are presented. An interpretation of the observed abundances is made in terms of selective radiative forces acting in a high-temperature photosphere. Some speculations on the evolutionary status of DO stars like PG 1034 + 001 are given.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 292; 477-483
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  • 10
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    Discovery of oxygen in the PG 1159 degenerate stars - A direct evolutionary link to O VI planetary nebula nuclei and confirmation of pulsation theory (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The discovery of strong O VI absorption/emission lines in five members of the PG 1159 degenerate stars is reported. It is shown that the optical spectra are dominated by C IV, O VI, and He II, with no detectable N lines. It is confirmed that the planetary nebula-central star, K1-16, which is found to be a pulsating star by Grauer and Bond (1984), is a member of the spectroscopic group. The detection of strong oxygen features in the photospheres of the objects provides support of the prediction of Starrfield et al. (1984). The properties of the PG 1159 stars are compared with the so-called O VI central stars of planetary nebulae and both groups of stars are found to have similar spectral features, temperatures, and luminosities. The implications of the O VI/PG 1159 evolutionary link are assessed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 292; 471-476
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