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Emission Line and Ultraviolet to X-Ray Continuum Correlations: Constraints on the Anisotropy of the Ionizing Continuum in Active Galactic Nuclei
Wang, Ting-Gui; Zhou, You-Yuan; Lu, You-Jun
Anisotropic emission of the ionizing continuum is a general prediction of accretion disk models. In this paper, we present the results of correlation analysis of the UV emission line and UV to X-ray continuum properties for a large sample of broad emission line AGNs observed with ROSAT, IUE, and HST. We find strong correlations between the C IV/Ly…
Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri
Ballester, Gilda E.; Krist, John E.; Crisp, David +14 more
Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 µm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2".…
Induced Massive Star Formation in the Trifid Nebula?
Acosta-Pulido, J.; Cernicharo, J.; Cox, P. +7 more
The discovery of new gamma Doradus stars from the HIPPARCOS mission
Eyer, L.; Aerts, C.; Kestens, E.
We present a classification of 39 new variable stars with spectral type between A2 and F8 discovered by Hipparcos with the aim to find new gamma Doradus stars. We have used a multivariate classification scheme and report the discovery of 14 new gamma Doradus variables among this unbiased sample. Our results point out the biased nature towards hot …
The Absolute Magnitude of RR Lyrae Stars Derived from the Hipparcos Catalogue
Yoshii, Yuzuru; Tsujimoto, Takuji; Miyamoto, Masanori
The present determination of the absolute magnitude MV(RR) of RR Lyrae stars is twofold, relying upon Hipparcos proper motions and trigonometric parallaxes separately. First, applying the statistical parallax method to the proper motions, we find V(RR)>=0.69+/-0.10 for 99 halo RR Lyrae stars with <[Fe/H>=-1.58. Second, applying…
The Host Galaxy of the Gamma-Ray Burst 971214
Piro, L.; Frontera, F.; Bloom, J. S. +13 more
We report on Hubble Space Telescope (HST) observations of the host galaxy of GRB 971214, taken 4 months after the burst. The redshift of the proposed host galaxy at z=3.418, combined with optical and radio observations of the burst afterglow, implies the extremely large isotropic energy release from the burst in γ-rays of Eγ~3×1053…
M87: A Misaligned BL Lacertae Object?
Kriss, Gerard A.; Dopita, Michael A.; Hartig, George F. +5 more
The nuclear region of M87 was observed with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) at six epochs, spanning 18 months, after the HST image quality was improved with the deployment of the corrective optics (COSTAR) in 1993 December. From the FOS target acquisition data, we have established that the flux from the opti…
Intraday variability in X-ray selected BL Lacertae objects
Wagner, S. J.; Heidt, J.
We present a study of the intraday variability behaviour of two samples of X-ray selected BL Lac objects, the EMSS and EXOSAT samples consisting of 22 and 11 sources, respectively. In both samples we were able to detect intraday variability in less than 40% of the sources only. The duty cycle (the fraction of time, when a BL Lac object is variable…
HST observations of the QSO pair Q1026-0045A,B
Petitjean, Patrick; Smette, Alain; Surdej, Jean +3 more
The spatial distribution of the Lyalpha forest is studied using new HST data for the quasar pair Q 1026-0045 A and B at z_em = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and corresponds to transverse linear separations between lines of sight of ~ 300h(-1}_{50) kpc (q_o = 0.5) over the redshift range 0.833 < z < 1.438. …
Spectral analyses of WC stars in the LMC
Hillier, D. J.; Hamann, W. -R.; Koesterke, L. +1 more
Spectra of six Wolf-Rayet stars in the Large Magellanic Cloud (LMC) of the subtype WC4, the dominant WC spectral type in the LMC, are taken with the Faint Object Spectrograph (FOS) on board the Hubble Space Telescope (HST). They are analyzed by means of non-LTE models for spherically expanding atmospheres computed using standard assumptions. Compl…