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Visual observations of Perseid meteors carried out in 1953-83 at the Onsala Space Observatory are analyzed to study the fine structure of the Perseid meteor stream maximum. Observed hourly rates are corrected for weather conditions and to a zenithal value. The Perseid activity curve is studied (1) for all observed Perseids, (2) for Perseids of app. magnitude 2.0 or brighter. The activity curve for
We investigate the observed depletion of red giants in the cores ofpost-core-collapse globular clusters. In particular, the evolutionaryscenario we consider is a binary consisting of two low-mass stars whichundergoes two common-envelope phases. The first common-envelope phaseoccurs when the primary is a red giant resulting in a helium white dwarfand main-sequence star in a detached binary. The sec
We present deep Hubble Space Telescope ACS observations of the G1 clump, a distinct stellar overdensity lying at similar to 30 kpc along the southwestern major axis of M31, close to the G1 globular cluster ( from the work of Ferguson and coworkers). Our well-populated color-magnitude diagram reaches similar to 7 mag below the red giant branch tip with 90% completeness, and allows the detection of
The evolution of the Solar neighbourhood is followed using a unique,magnitude complete and kinematically unbiased sample of 14,000 F, G, andK dwarfs. Metallicity, age, space motion and galactic orbits have beendetermined for all stars. The result is a detailed view of the complexevolution of the local Milky Way, which must be matched by any model forthe chemical and dynamical evolution of the Gala
We present a qualitative physical model of the origin of two very brightUV lines of Fe II at 2507-2509 Å, present in high-resolutionspectra of gaseous condensations (blobs) close to the central star ofeta Carinae. The spectra have been obtained with the Hubble SpaceTelescope (HST). The model is based on a type of Bowen mechanism withselective photoexcitation of Fe II by a broad HLyalpha profile,ge
We show that the Galactic thick disk reaches at least solar metallicities and that it experienced strong chemical enrichment during a period of ~3 Gyr, ending around 8-9 Gyr ago. This finding puts further constraints on the relation and interface between the thin and thick disks and their formation processes. Our results are based on a detailed elemental abundance analysis of 261 kinematically sel
Photoinduced Ba L x-rays were measured, in the excitation energy range of 5.6-30 keV, by using high-brilliance undulator radiation. The obtained intensity ratios, the excitation-energy independent L beta(4)/L beta(3), L eta/L beta(1), L iota/L alpha(1,2), L beta(6)/ L alpha(1,2) and L beta(2,15)/L alpha(1,2) as well as the excitation- energy dependent L beta(1)/L alpha(1,2), L beta(3)/L alpha(1,2)
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We consider possible schemes for the resonance-enhanced two-photon ionization (RETPI) of Ne and Ar atoms under the action of bichromatic radiation of intense resonance lines of HI, HeI, and HeII in a radiation-rich astrophysical plasma. The ionization rate is comparable to or exceeds the recombination rate in rarified astrophysical plasma, which leads to the accumulation of singly ionized ions wit
Previously, weak emission lines had been detected at red wavelengths inthe spectra of a limited sample of mid to late B type main sequencestars. A fuller description of the occurrence and origins of these lineshas yet to be forwarded, in part due to the lack of observationsdetailing the spectral transitions involved. To address this deficiency,we present a line list of weak emission features found
Both the Fe II UV emission in the 2000-3000 Å region [Fe II(UV)]and resonance emission line complex of Mg II at 2800 Å areprominent features in quasar spectra. The observed Fe II(UV)/Mg IIemission ratios have been proposed as means to measure the buildup ofthe Fe abundance relative to that of the alpha-elements C, N, O, Ne,and Mg as a function of redshift. The current observed ratios show largesca
Using a numerical simulation of compressible convection with radiativetransfer mimicking the solar photosphere, we compare the velocity fieldderived from granule motions to the actual velocity field of the plasma.We thus test the idea that granules may be used to trace large-scalevelocity fields at the sun's surface. Our results show that this isindeed the case provided the scale separation is suf
P-mode oscillations in the Sun and stars are excited stochasticly by Reynolds stress and entropy fluctuations produced by convection in their outer envelopes. The excitation increases with increasing effective temperature (until envelope convection ceases in the F stars) and also increases with decreasing gravity.
We present the FERRUM Project, an international collaboration aiming at a production and evaluation of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of astrophysical relevance. The results obtained include measurements and calculations of permitted and forbidden lines of Fe II. The data have been applied to both emission
We have used the Cerro Tololo Inter-American Observatory telescopes andspectrographs to record emission lines in eta Carinae from 3093 to8956 Å with a gap between 4432 and 5696 Å. A resolving powerof about 20,000 was used throughout. Accurate wavelengths, peakintensities relative to the local continuum, and line identificationsare presented. The data are briefly discussed with respect to the state
Within the framework of a simple model of photophysical processes in the Weigelt blobs in the vicinity of the luminous blue variable (LBV) star eta Carinae, we explain the presence of the fluorescent < O I > 8446-angstrom and forbidden [O I] 6300-angstrom lines as well as the absence of the allowed O I 7774-angstrom line in spectra recorded with the Hubble Space Telescope (HST)/STIS instrument (Gu
We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K dwarf, with [Me/H]>0.1 dex. The selection of stars was based on their kinematics as well as on their uvby-beta photometry. One sample of stars on rather eccentric orbits traces the chemical evolution interior to the solar orbit and another, on circular orbits,
