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A Tentative Detection of the Cosmic Infrared Background at 3.5 µm from COBE/DIRBE Observations
Dwek, E.; Arendt, R. G.
Foreground emission and scattered light from interplanetary dust (IPD) particles and emission from Galactic stellar sources are the greatest obstacles to determining the cosmic infrared background (CIB) from diffuse sky measurements in the ~1-5 µm range. We use ground-based observational limits on the K-band intensity of the CIB in conjuncti…
Temperature Dependence of Ultraviolet Line Average Doppler Shifts in the Quiet Sun
Chae, J.; Yun, H. S.; Poland, A. I.
The existence of prevailing redshifts in the UV lines formed in the solar transition region raises an important question concerning its physical origin and its role in the mass and energy balance of the outer solar atmosphere. A series of UV spectral lines observed by SUMER has been analyzed to obtain the spatial average of Doppler shifts in the q…
HIPPARCOS subdwarfs and globular cluster ages: the distance and age of M 92
Pont, F.; Turon, C.; Mayor, M. +1 more
A new determination of the distance and age of the old globular cluster M 92 (NGC 6341) is obtained from a consideration of a set of more than 500 subdwarf candidates with Hipparcos parallaxes. Precise [Fe/H] values are derived for most stars using the equivalent width of the Coravel cross-correlation function. We examine at some length the biases…
Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
di Benedetto, G. P.
I report on the implementation of the empirical surface brightness technique using the near-infrared Johnson broadband { (V-K)} colour as suitable sampling observable aimed at providing accurate effective temperatures of 537 dwarfs and giants of A-F-G-K spectral-type selected for a flux calibration of the Infrared Space Observatory (ISO). The surf…
Quiet Sun EUV transient brightenings and turbulence. A panoramic view by EIT on board SOHO
Berghmans, D.; Clette, F.; Moses, D.
Since January 1996, the Extreme-Ultraviolet Imaging Telescope (EIT, onboard SOHO) has produced unique image sequences covering a wide field of view with a high temporal resolution, in the He Ii transition region line and in several Fe coronal emission lines. Using two sequences acquired with cadences of the order of one minute and with durations r…
Geomagnetic storms caused by coronal mass ejections (CMEs): March 1996 through June 1997
St. Cyr, O. C.; Paswaters, S. E.; Simnett, G. M. +7 more
(1) All but two geomagnetic storms with Kp ≥ 6 during the operating period (March 1996 through June 1997) of the Large Angle Spectroscopic Coronagraph (LASCO) experiment on the Solar and Heliospheric Observatory (SOHO) spacecraft can be traced to Coronal Mass Ejections (CMEs). (2) These geomagnetic storms are not related to high speed solar wind s…
Evolved Massive Stars in the Local Group. II. A New Survey for Wolf-Rayet Stars in M33 and Its Implications for Massive Star Evolution: Evidence of the ``Conti Scenario'' in Action
Massey, Philip; Johnson, Olivia
We expect the evolution of massive stars to be strongly influenced by mass loss and hence to be sensitive to metallicity. It should be possible to test this ``Conti scenario'' be comparing the populations of evolved massive stars among the Local Group galaxies, but such investigations have been hampered by incompleteness. In a previous paper, we p…
Deuterium Abundance in the Local ISM and Possible Spatial Variations
Linsky, Jeffrey L.
Excellent HST/GHRS spectra of interstellar hydrogen and deuterium Lyman-alpha absorption toward nearby stars allow us to identify systematic errors that have plagued earlier work and to measure accurate values of the D/H ratio in local interstellar gas. Analysis of 12 sightlines through the Local Interstellar Cloud leads to a mean value of D/H = (…
The Ultraviolet Spectra of LINERs: A Comparative Study
Filippenko, Alexei V.; Ho, Luis C.; Maoz, Dan +3 more
Imaging studies have shown that ~25% of LINER galaxies display a compact nuclear UV source. As part of a program to study the nature of LINERs and their connection to the active galaxy phenomenon, we compare the Hubble Space Telescope UV (1150-3200 Å) spectra of seven such UV-bright LINERs. Data for three of the galaxies (NGC 404, 4569, and 5055) …
X-ray coronal changes during Halo CMEs
St. Cyr, O. C.; Webb, D. F.; Lemen, J. R. +2 more
Using the Yohkoh soft X-ray images, we examine the coronal structures associated with “halo” coronal mass ejections (CMEs). These may correspond to events near solar disk center. Starting with a list of eleven confirmed halo CMEs over the time range from December 1996 through May 1997, we find seven with surface features identifiable in soft X-ray…