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Properties and nature of Be stars. XIX. Spectral and light variability of 60 Cygni
Harmanec, P.; Huang, L.; Cao, H. +11 more
An analysis of electronic spectra secured between 1992 and 1999 at the Haute Provence, Ondřejov and Dominion Astrophysical Observatories and of differential UBV measurements of 60 Cyg obtained between 1984 and 1999 at Hvar, San Pedro Mártir, Toronto and Xinglong Observatories, the all-sky Hipparcos satellite H_p photometry transformed to Johnson V…
HE 2-113: A Multipolar Planetary Nebula with Rings around a Cool Wolf-Rayet Star
Sahai, Raghvendra; Nyman, Lars-Åke; Wootten, Alwyn
We present Hα imaging and molecular-line (CO) observations of He 2-113, an object which belongs to a rare class of planetary nebulae with Wolf-Rayet type central stars. The Hα images, obtained with the Hubble Space Telescope Wide-Field Planetary Camera 2, show that He 2-113 has an overall bipolar shape and two bright, knotty, compact ringlike stru…
Face-on Galaxies NGC 524 and NGC 6340: Chemically Decoupled Nuclei and Inclined Circumnuclear Disks
Sil'chenko, O. K.
The central regions of the early-type disk galaxies NGC 524 and NGC 6340 have been investigated with the Multipupil Field Spectrograph at the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We confirm the existence of chemically distinct stellar nuclei in these galaxies, which had been claimed earlier. Th…
The structure of Algol's corona: a consistent scenario for the X-ray and radio emission
Schmitt, J. H. M. M.; Micela, G.; Favata, F. +2 more
We present a systematic analysis of the four known large X-ray flares detected to date on the eclipsing binary system Algol, using an approach based on hydrodynamic simulations of decaying flaring loops including sustained heating. This method yields, for the large BeppoSAX Algol flare of Aug. 1997 (where a geometrical estimate of the size of the …
Far-Ultraviolet Echoes from the Frontier between the Solar Wind and the Local Interstellar Cloud
Ben-Jaffel, L.; Ratkiewicz, R.; Puyoo, O.
We propose that first-order Fermi acceleration of Lyα photons should occur at the interface region between the solar and interstellar winds. In this process, photons are Doppler-shifted toward shorter wavelengths each time they are scattered by hydrogen neutrals that have been decelerated by charge exchange with protons in the transition region wr…
Network and internetwork: a compared multiwavelength analysis
Falchi, A.; Cauzzi, G.; Falciani, R.
We analyze the temporal behavior of Network Bright Points (NBPs) using a set of data acquired during coordinated observations between ground-based observatories (mainly at the NSO/Sacramento Peak) and the Michelson Doppler Interferometer onboard SOHO. We find that, at any time during the observational sequence, all the NBPs visible in the NaD_2 im…
Background and Scattered-Light Subtraction in the High-Resolution Echelle Modes of the Space Telescope Imaging Spectrograph
Sembach, Kenneth R.; Howk, J. Christopher
We present a simple, effective approach for estimating the on-order backgrounds of spectra taken with the highest resolution modes of the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope. Our scheme for determining the on-order background spectrum for STIS E140H and E230H observations uses moderate-order polynomial f…
Structure and dynamics of an active region loop system observed on the solar disc with SUMER on SOHO
Marsch, E.; Lanzafame, A. C.; Brooks, D. H. +3 more
In this paper we present and discuss spectra obtained by SUMER on SOHO from an active region loop system observed on the solar disc, close to the central meridian, on July 26th, 1996. The region was observed with a spatial resolution of about 2arcsec by 2arcsec in emission lines forming in the transition region and inner corona, with the aim of in…
Possible solar cycle variations in the convection zone
Basu, Sarbani; Antia, H. M.
Using data from the Global Oscillations Network Group (GONG) that covers the period from 1995 to 1998 we study the change in frequencies of solar oscillations with solar activity. From these frequencies we attempt to determine any possible variation in solar structure with solar activity. We do not find any evidence of a change in the convection z…
Near-Surface Flow Fields Deduced Using Correlation Tracking and Time-Distance Analyses
Duvall, T. L., Jr.; De Rosa, Marc; Toomre, Juri
Near-photospheric flow fields on the Sun are deduced using two independent methods applied to the same time series of velocity images observed by SOI-MDI on SOHO. Differences in travel times between f modes entering and leaving each pixel measured using time-distance helioseismology are used to determine sites of supergranular outflows. Alternativ…