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Supernova 1991T and the Value of the Hubble Constant
Gibson, Brad K.; Stetson, Peter B.
Based on multiepoch Hubble Space Telescope observations, we present the discovery of 16 high-quality Cepheid candidates in NGC 4527. Corrected for metallicity effects in the Cepheid period-luminosity relation, we derive a distance, including both random (r) and systematic (s) uncertainties, of 13.0+/-0.5(r)+/-1.2(s) Mpc. Our result is then used to…
Spectroscopy of B-type emission-line stars with compact dusty envelopes: HD 85567, Hen 3-140, and Hen 3-1398
Miroshnichenko, A. S.; Levato, H.; Bjorkman, K. S. +1 more
We report the results of our spectroscopic observations (3600-5900 Å, R =~ 16 000 and 5750-8750 Å, R =~ 11 000) of three southern emission-line B-type stars associated with IRAS sources, HD 85567, Hen 3-140, and Hen 3-1398, whose nature and evolutionary state are not well-established yet. We also obtained new multicolour photometry of HD 85567 (UB…
Gravitational microlensing by low-mass objects in the globular cluster M22
Casertano, Stefano; Livio, Mario; Albrow, Michael D. +4 more
Gravitational microlensing offers a means of determining directly the masses of objects ranging from planets to stars, provided that the distances and motions of the lenses and sources can be determined. A globular cluster observed against the dense stellar field of the Galactic bulge presents ideal conditions for such observations because the pro…
Infrared Surface Brightness Fluctuations of the Coma Elliptical Galaxy NGC 4874 and the Value of the Hubble Constant
Graham, James R.; Liu, Michael C.
We have used the Keck I telescope to measure K-band surface brightness fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma Cluster. We use deep Hubble Space Telescope (HST) WFPC2 optical imaging to account for the contamination due to faint globular clusters and improved analysis techniques to derive measurements of the SBF…
Circumstellar Carbonaceous Material Associated with Late-Type Dusty WC Wolf-Rayet Stars
Tielens, A. G. G. M.; Chiar, J. E.
We have studied the 5-8.5 µm infrared spectra of the late-type Wolf-Rayet stars WR 118, WR 112, and WR 104, the WN star WR 147, the B5 hypergiant Cygnus OB2 No. 12, and the Galactic center luminous blue variable Pistol Star using the Short Wavelength Spectrometer on the Infrared Space Observatory. We attribute an absorption feature at 6.2 &m…
How to determine the thermal electron density and the magnetic field strength from the Cluster/Whisper observations around the Earth
Krasnoselskikh, V.; Fergeau, P.; Décréau, P. M. E. +11 more
The Wave Experiment Consortium, WEC, is a highly integrated package of five instruments used to study the plasma environment around the Earth. One of these instruments, the Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation, Whisper, aims at the thermal electron density evaluation and natural wave monitoring in the 4…
HST Observations of Saturnian Satellites during the 1995 Ring Plane Crossings
Nicholson, Philip D.; French, Richard G.; McGhee, Colleen A. +1 more
In May, August, and November 1995, Hubble Space Telescope (HST) observations during Saturn's ring-plane crossings allowed us to view saturnian satellites normally hidden to Earth-based observers in the glare of the rings. New measurements of Janus, Epimetheus, Prometheus, and Pandora have been combined to form revised orbital solutions using all t…
XMM-Newton optical monitor observations of LMC X-3
Page, M. J.; Soria, R.; Wu, K. +1 more
We study the optical counterpart of the black-hole X-ray binary LMC X-3, by using XMM-Newton/OM observations carried out during a low-hard X-ray state. We derive a better constraint for the temperature, mass and radius of the companion star, and we show that the star is likely to be a ~ B5 subgiant filling its Roche lobe. Taking into account the e…
Long-term monitoring of active stars. IX. Photometry collected in 1993
Messina, S.; Rodonò, M.; Cutispoto, G.
As a part of an extensive program focused on the global properties and evolution of active stars, high-precision UBV(RI)_c and UBV photometry of 31 selected stars is presented. The UBV(RI)_c observations were collected at the European Southern Observatory over the 31 December 1992-18 January 1993 and the 20 November-3 December 1993 intervals. Addi…
XMM-Newton first-light observations of the Hickson galaxy group 16
Arnaud, M.; Clavel, J.; Priedhorsky, W. +40 more
This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentra…