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Ultraviolet Galaxy Counts from Space Telescope Imaging Spectrograph Observations of the Hubble Deep Fields
Ferguson, Henry C.; Brown, Thomas M.; Gardner, Jonathan P.
We present galaxy counts in the near-ultraviolet (NUV; 2365 Å) and far-ultraviolet (FUV; 1595 Å) obtained from Space Telescope Imaging Spectrograph observations of portions of the Hubble Deep Field-North (HDF-N), the Hubble Deep Field-South (HDF-S), and a parallel field near the HDF-N. All three fields have deep (AB>29) optical imaging, and we …
The Optical Gravitational Lensing Experiment: Red Clump Stars as a Distance Indicator
Udalski, A.
We present relation of the mean I-band brightness of red clump stars on metallicity. Red clump stars were proposed to be a very attractive standard candle for distance determination. The calibration is based on 284 nearby red giant stars whose high-quality spectra made it possible to determine accurate individual metal abundances. High-quality par…
Unveiling the Active Nucleus of Centaurus A
Marconi, Alessandro; Koekemoer, Anton; Capetti, Alessandro +4 more
We report new Hubble Space Telescope WFPC2 and NICMOS observations of the center of the nearest radio galaxy Centaurus A (NGC 5128) and discuss their implications for our understanding of the active nucleus and jet. We detect the active nucleus in the near-IR (K and H) and, for the first time, in the optical (I and V), deriving the spectral energy…
Evidence for a Black Hole and Accretion Disk in the LINER NGC 4203
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +5 more
We present spectroscopic observations from the Hubble Space Telescope that reveal for the first time the presence of a broad pedestal of Balmer line emission in the LINER galaxy NGC 4203. The emission-line profile is suggestive of a relativistic accretion disk and is reminiscent of double-peaked transient Balmer emission observed in a handful of o…
Identification of the Coronal Sources of the Fast Solar Wind
Romoli, M.; Giordano, S.; Antonucci, E. +2 more
The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on 1996 April 6-9 with the Ultraviolet Coronagraph Spectrometer aboard the Solar and Heliospheric Observatory spacecraft, identifies the interplume lanes and background coronal hole regions as the channels in which the fast solar wind is preferentially ac…
Testing Comptonizing Coronae on a Long BeppoSAX Observation of the Seyfert 1 Galaxy NGC 5548
Maraschi, L.; Piro, L.; Perola, G. C. +6 more
We test accurate models of Comptonization spectra over the high-quality data of the BeppoSAX long look at NGC 5548, allowing for different geometries of the scattering region, different temperatures of the input soft photon field, and different viewing angles. We find that the BeppoSAX data are well represented by a plane-parallel or hemispherical…
Eclipsing Binaries as Astrophysical Laboratories: Internal Structure, Core Convection, and Evolution of the B-Star Components of V380 Cygni
Fitzpatrick, Edward L.; Guinan, Edward F.; Jordi, Carme +4 more
New photometric solutions have been carried out on the important eccentric eclipsing system V380 Cygni (B1.5 II-III+B2 V) from UBV differential photoelectric photometry obtained by us. The photometric elements obtained from the analysis of the light curves have been combined with the spectroscopic solution recently published by Popper & Guinan…
The Hubble Space Telescope Key Project on the Extragalactic Distance Scale. XXVII. A Derivation of the Hubble Constant Using the Fundamental Plane and Dn-σ Relations in Leo I, Virgo, and Fornax
Kelson, Daniel D.; Illingworth, Garth D.; Huchra, John P. +18 more
Using published photometry and spectroscopy, we construct the fundamental plane and Dn-σ relations in Leo I, Virgo, and Fornax. The published Cepheid period-luminosity (PL) relations to spirals in these clusters fixes the relation between angular size and metric distance for both the fundamental plane and Dn-σ relations. Usin…
Reconciling Spectroscopic Electron Temperature Measurements in the Solar Corona with In Situ Charge State Observations
Esser, Ruth; Edgar, Richard J.
It has been a puzzle for quite some time that spectroscopic measurements in the inner corona indicate electron temperatures far too low to produce the ion fractions observed in situ in the solar wind. In the present Letter, we show that in order to reconcile the two sets of measurements, a number of conditions have to exist in the inner corona: (1…
A Spectroscopic Redshift for the Cl 0024+16 Multiple Arc System: Implications for the Central Mass Distribution
Ellis, Richard; Broadhurst, Tom; Frye, Brenda +1 more
We present a spectroscopic redshift of z=1.675 for the well-known multiply lensed system of arcs seen in the z=0.39 cluster Cl 0024+16. In contrast to earlier work, we find that the lensed images are accurately reproduced by a projected mass distribution which traces the locations of the brightest cluster elliptical galaxies, suggesting that the m…