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ISOPHOT boosts dust masses in spiral galaxies
Siebenmorgen, R.; Chini, R.; Zota, V. +1 more
We report photometry with ISO between 60 and 200 -um of six galaxies. Three of them are active and the extension of their spectra beyond the IRAS bands up to 200 -um confirms our previous conception that most of the dust there is warm and has a fairly uniform temperature of phantom {0}im30K. In the other three galaxies which are inactive, we detec…
Type II radio emissions in the frequency range from 1-14 MHz associated with the April 7, 1997 solar event
St. Cyr, O. C.; Thompson, B. J.; Kaiser, M. L. +4 more
We present an analysis of radio emissions associated with the April 7, 1997 solar eruptive event. The event consisted of a filament disappearance, a complex two-phase coronal mass ejection (CME), and a C6.9, 2N flare. At the same time, intermittent type II radio emissions in the frequency range 1-10 MHz, corresponding to an altitude range of 2-15 …
The LMC distance modulus from HIPPARCOS RR Lyrae and classical Cepheid data
Luri, X.; Figueras, F.; Torra, J. +2 more
The LM method \cite{luri96}, designed to exploit the Hipparcos data to obtain luminosity calibrations, is applied to derive luminosity calibrations for RR Lyrae and classical Cepheids. From these calibrations the distance to the Large Magellanic Cloud (LMC) is estimated. The distance moduli provided by the two calibrations are in good agreement, g…
The fine structure of the Pleiades luminosity function and pre-main sequence evolution
Meusinger, H.; Piskunov, A. E.; Schilbach, E. +2 more
The luminosity function (LF) of the Pleiades cluster stars was constructed for the study of the LF fine structure related to pre-MS stellar evolution. Theoretical luminosity functions based on present-day pre-MS and MS stellar models were constructed and compared with observations. We tested both power- and log-normal laws describing the cluster s…
WFPC2 Studies of the Crab Nebula. II. Ionization Structure of the Crab Filaments
Ballester, Gilda E.; Crisp, David; Holtzman, Jon A. +15 more
Narrowband images of the Crab Nebula taken with the Hubble Space Telescope (HST) WFPC2 show the morphology and ionization structure of the filaments in great detail. At HST resolution, low- and high-ionization emission from filaments in the Crab differ in two complementary respects. First, low-ionization emission is found to be concentrated in ver…
The Problem of HIPPARCOS Distances to Open Clusters. II. Constraints from Nearby Field Stars
Stauffer, John R.; Pinsonneault, Marc H.; Soderblom, David R. +4 more
This paper examines the discrepancy between distances to nearby open clusters as determined by parallaxes from Hipparcos compared to traditional main-sequence fitting. The biggest difference is seen for the Pleiades, and our hypothesis is that if the Hipparcos distance to the Pleiades is correct, then similar subluminous zero-age main-sequence (ZA…
Models of the ISO 3-µm Reflection Spectrum of Jupiter
Feuchtgruber, H.; Drossart, P.; Knacke, R. F. +3 more
A spectrum of Jupiter in the 3-µm region obtained with the Infrared Space Observatory (ISO) shows evidence for the long-sought spectral signature of NH3ice particles in the jovian atmosphere. We calculated Jupiter 3-µm reflection spectrum, including multiple scattering by spherical cloud particles. Models containing reflecti…
A Hubble Space Telescope Study of Extragalactic OB Associations
Macri, Lucas M.; Gibson, Brad K.; Stetson, Peter B. +9 more
We present a study of OB associations, identified by objective means, in seven spiral galaxies observed with the Hubble Space Telescope as part of the Key Project on the distance scale. The properties of the associations, including their size distribution and average diameter, and the luminosity function of their brightest stars, do not vary signi…
An Asymmetric Arcsecond Radio Jet from Circinus X-1
Wu, Kinwah; van Paradijs, Jan; Fender, Robert +4 more
In observations with the Australia Telescope Compact Array, we have resolved the radio counterpart of the unusual X-ray binary Circinus X-1 into an asymmetric, extended structure on arcsecond scales. In order to quantify the asymmetry, we have redetermined as accurately as possible both the optical and radio coordinates of the source. The extended…
The Intervening and Associated O VI Absorption-Line Systems in the Ultraviolet Spectrum of H1821+643
Tripp, Todd M.; Savage, Blair D.; Lu, Limin
GHRS and FOS ultraviolet spectra of the bright QSO H1821+643 (m_V = 14.2, z_em = 0.297) reveal the presence of strong O vi lambdalambda1031.93, 1037.62 absorption systems at z_abs = 0.225 and 0.297, the latter being at the redshift of the QSO itself. Ground-based galaxy redshift measurements by us and others reveal two emission-line galaxies near …