Search Publications
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…
Evidence for Strong and Weak Turbulence Processes in the Source Region of a Local Type III Radio Burst
MacDowall, R. J.; Thejappa, G.
We present the Ulysses Unified Radio and Plasma Wave Experiment (URAP) observations of a local type III radio burst and the associated plasma wave activity generated in the vicinity of the spacecraft. These observations represent the first clear evidence of (1) the occurrence of ion-acoustic waves as well as whistlers in close association with Lan…
The Hubble Deep Field and the disappearing dwarf galaxies
Ferguson, Henry C.; Babul, Arif
Several independent lines of reasoning, both theoretical and observational, suggest that the very faint (B>~24) galaxies seen in deep images of the sky are small low-mass galaxies that have experienced a short epoch of star formation at redshifts 0.5<~z<~1 and have since faded into low-luminosity, low-surface-brightness objects. Such a sc…
Dissecting Capella's Corona: GHRS Spectra of the Fe XXI λ1354 and He II λ1640 Lines from Each of the Capella Stars
Brown, Alexander; Wood, Brian E.; Osten, Rachel A. +1 more
We report on moderate (λ/Δλ = 20,000) and high (λ/Δλ = 90,000) resolution spectra of the 104-day period Capella binary system (HD 34029) obtained with Hubble Space Telescope's Goddard High-Resolution Spectrometer (GHRS) on 1995 September 9 and 1996 April 9. The observations include a long-duration, moderate-resolution spectrum of the coronal Fe XX…
Radiative Transfer Models of Emission and Absorption in the H2O 6 Micron Vibration-Rotation Band toward Orion-BN-KL
Cernicharo, José; van Dishoeck, Ewine F.; Wright, Christopher M. +2 more
We report the spectrum of Orion-BN/KL between 5.3 and 7.2 µm observed with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory. H2O lines of the ν2=1-0 bending mode with λ < 6.3 µm (the R-branch) are observed in absorption, while lines with λ > 6.3 µm (the P-branch) are obse…