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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…
Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle
Whitelock, Patricia A.; Feast, Michael W.
The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period-luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145-200d in the general Solar neighbourhood have a n…
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…
Solar spicules and macrospicules observed by SUMER
Wilhelm, K.
Motivated by recent observations of spicules and macrospicules in the far-ultraviolet (FUV) wavelength range with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) on the Solar and Heliospheric Observatory (SOHO), a generation mechanism for spicules and macrospicules is outlined which deviates significantly from most of …
Hα emitting galaxies and the cosmic star formation rate at z =~ 2.2
Oliva, E.; van der Werf, P. P.; Moorwood, A. F. M. +1 more
An infrared imaging survey in narrow band filters around 2.1 mu m has yielded ~ 10 candidate Hα emitting galaxies at z =~ 2.2 of which 6 have been subsequently confirmed spectroscopically with ISAAC at the ESO VLT. The survey reached a limiting line flux of ~ 5x10-17 erg cm-2 s-1 and covered 100 arcmin2 …
Galactic globular clusters as a test for very-low-mass stellar models
Zoccali, M.; Piotto, G.; Cassisi, S. +2 more
We make use of the `Next Generation' model atmospheres of Allard et al. and Hauschildt, Allard & Baron to compute theoretical models for low- and very-low-mass stars for selected metallicities in the range Z=0.0002 to 0.002. On this basis, we present theoretical predictions covering the sequence of H-burning stars as observed in Galactic globu…
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…
A 0.4-20 mu m spectroscopic study of the clumped wind of WR 147
Hillier, D. J.; Crowther, P. A.; Willis, A. J. +4 more
We present a detailed spectroscopic study of the WN8(h)+B0.5 V binary system WR 147 using a non-LTE model that incorporates advances in line blanketing and allows for clumping in the wind. Ground-based optical and near-infrared observations, and high-resolution spectra obtained with the ISO Short Wavelength Spectrometer are combined for this study…