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Reconstructing the evolution of white dwarf binaries: further evidence for an alternative algorithm for the outcome of the common-envelope phase in close binaries
We determine the possible masses and radii of the progenitors of whitedwarfs in binaries from fits to detailed stellar evolution models anduse these to reconstruct the mass-transfer phase in which the whitedwarf was formed. We confirm the earlier finding that in the first phaseof mass transfer in the binary evolution leading to a close pair ofwhite dwarfs, the standard common-envelope formalism (theα-formalism) equating the energy balance in the system (implicitlyassuming angular momentum conservation) does not work. An algorithmequating the angular momentum balance (implicitly assuming energyconservation) can explain the observations. This conclusion is now basedon 10 observed systems rather than three. With the latter algorithm (theγ-algorithm) the separation does not change much for approximatelyequal-mass binaries. Assuming constant efficiency in the standardα-formalism and a constant value of γ, we investigate theeffect of both methods on the change in separation in general andconclude that when there is observational evidence for strong shrinkageof the orbit, the γ-algorithm also leads to this. We then extendour analysis to all close binaries with at least one white dwarfcomponent and reconstruct the mass-transfer phases that lead to thesebinaries. In this way we find all possible values of the efficiency ofthe standard α-formalism and of γ that can explain theobserved binaries for different progenitor and companion masses. We findthat all observations can be explained with a single value of γ,making the γ-algorithm a useful tool to predict the outcome ofcommon-envelope evolution. We discuss the consequences of our findingsfor different binary populations in the Galaxy, including massivebinaries, for which the reconstruction method cannot be used.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Search for Variability in the Equivalent Width of the HeI D3 Spectrum Line in Several Stars of Later Spectral Type
High resolution spectra with a high signal/noise ratio have beenobtained in the region of the HeI D line for 13 dwarfs of spectral typesA5 through K0. The variability in the equivalent width of this spectrumline was studied for five of these stars over a period of severalhundred days. Significant variability was observed for only one of thesestars, θ Cyg.
| HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations
We have discovered the first example of a star pulsating intrinsicallywith both γ Doradus and δ Scuti frequencies. The star, HD8801, is an Am metallic-line star that appears to be single. Since thevast majority of Am stars are members of binary systems with periodsless than 1000 days and also do not pulsate, HD 8801 possesses a veryunusual, if not unique, combination of physical properties. Ourphotometry, acquired with an automatic telescope at FairbornObservatory, resolves six independent pulsation periods between 0.048and 0.404 days. The two longest periods lie within the range of γDor variables, while the four shorter periods are within the range ofδ Sct stars. Eleven radial velocities, obtained over an 11 monthperiod, have a mean of 0.8+/-0.3 km s-1, providing noevidence for a spectroscopic companion. The star is on the main sequenceand lies within both the γ Dor and δ Sct instability strips.Pulsation constants computed for the six periods agree with pulsationconstants computed for other γ Dor and δ Sct variables. HD8801 is also the first confirmed case of a metallic-line star pulsatingwith γ Dor frequencies. Its projected rotational velocity of 55 kms-1 is typical for Am stars, which, as a group, rotate moreslowly than normal A stars. HD 8801's slow rotation compared to normal Astars does not appear to arise from either a binary companion orevolutionary expansion and thus remains a puzzle. The coexistence ofmetallicism and pulsation in several main-sequence stars near the rededge of the δ Sct strip contradicts recent models that predictpulsations only in more evolved stars.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| An Archive of IUE Low-Dispersion Spectra of the White Dwarf Stars
We have produced an archive of the ultraviolet low-dispersion spectrafor the full set of white dwarf stars observed with the InternationalUltraviolet Explorer (IUE) satellite over the course of its 18 yrmission. This archive contains the spectra of 322 individual degeneratestars which have been processed to optimize the signal-to-noise for eachstar. In particular, all spectra have been corrected for residualtemporal and thermal effects and placed on the Hubble Space TelescopeFaint Object Spectrograph absolute flux scale using procedures describedby Massa & Fitzpatrick. Wherever possible, multiple observations ofindividual stars have been co-added to further enhance signal-to-noiseand have been combined into a single spectrum including the full 1150 to3150 Å wavelength region observed by IUE. The contents of thisspectral archive are described and the details of data reductionprocedures are provided, along with the url for access to the electronicfiles of the processed spectra.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Resolving Sirius-like binaries with the Hubble Space Telescope
We present initial results from a Hubble Space Telescope ultravioletimaging survey of stars known to have hot white dwarf companions whichare unresolved from the ground. The hot companions, discovered throughtheir EUV or UV emission, are hidden by the overwhelming brightnesses ofthe primary stars at visible wavelengths. Out of 17 targets observed, wehave resolved eight of them with the Wide Field Planetary Camera 2,using various ultraviolet filters. Most of the implied orbital periodsfor the resolved systems are hundreds to thousands of years, but in atleast three cases (56 Persei, ζ Cygni and RE J1925-566) it shouldbe possible to detect the orbital motions within the next few years, andthey may eventually yield new dynamically determined masses for thewhite dwarf components. The 56 Persei and 14 Aurigae systems are foundto be quadruple and quintuple, respectively, including the known opticalcomponents as well as the newly resolved white dwarf companions. Themild barium star ζ Cygni, known to have an 18-year spectroscopicperiod, is marginally resolved. All of these newly resolved Sirius-typebinaries will be useful in determining gravitational redshifts andmasses of the white dwarf components.
| On the formation of oxygen-neon white dwarfs in close binary systems
The evolution of a star of initial mass 10 Msun, andmetallicity Z = 0.02 in a Close Binary System (CBS) is followed from itsmain sequence until an ONe degenerate remnant forms. Restrictions havebeen made on the characteristics of the companion as well as on theinitial orbital parameters in order to avoid the occurrence of reversalmass transfer before carbon is ignited in the core. The system undergoesthree mass loss episodes. The first and second ones are a consequence ofa case B Roche lobe overflow. During the third mass loss episode stellarwinds may play a role comparable to, or even more important than Rochelobe overflow. In this paper, we extend the previously existingcalculations of stars of intermediate mass belonging to close binarysystems by following carefully the carbon burning phase of the primarycomponent. We also propose different possible outcomes for our scenarioand discuss the relevance of our findings. In particular, our mainresult is that the resulting white dwarf component of mass 1.1 M_sunmore likely has a core composed of oxygen and neon, surrounded by amantle of carbon-oxygen rich material. The average abundances of theoxygen-neon rich core are X(O16)=0.55,X(Ne20)=0.28, X(Na23)=0.06 andX(Mg24)=0.05. This result has important consequences for theAccretion Induced Collapse scenario. The average abundances of thecarbon-oxygen rich mantle are X(O16)=0.55, andX(C12)=0.43. The existence of this mantle could also play asignificant role in our understanding of cataclysmic variables.
| Pulsation behavior of classical Am star 60 Tauri
Five nights photoelectric photometric observations through v and y bandsconfirm the pulsation of classical Am δ Scuti variable 60 Tau.Power spectrum of light curves shows multi-period pulsation behavior of60 Tau and two pulsation modes f1=13.0364 andf2=11.8521 cycles per day are definitely identified.Classical Am star 60 Tau is a complicated pulsation δ Scutivariable. Considering the pulsation constant Q, 60 Tau is identified tobe low overtone f or p1 modes tendentiously.
| Extreme Ultraviolet Astronomy
Astronomical studies in the extreme ultraviolet (EUV) band of thespectrum were dismissed during the early years of space astronomy asimpossible, primarily because of the mistaken view that radiation inthis band would be absorbed by the interstellar medium. Observations inthe 1980s from sounding rockets and limited duration orbital spacecraftbegan to show the potential of this field and led to the deployment oftwo spacecraft devoted to EUV astronomy: the UK Wide Field Camera andthe Extreme Ultraviolet Explorer. The instrumentation in these missions,although quite limited in comparison with instrumentation in otherfields of space astronomy, provided unique and far-reaching results.These included new information on solar system topics, stellarchromospheres and corona, white dwarf astrophysics, cataclysmicvariables, the interstellar medium, galaxies, and clusters of galaxies.We summarize these findings herein.
| Cool Companions to Hot White Dwarfs
Low-mass companions to high-mass stars are difficult to detect, which ispartly why the binary fraction for high-mass stars is still poorlyconstrained. Low-mass companions can be detected more easily however,once high-mass stars turn into white dwarfs. These systems are alsointeresting as the progenitors of a variety of intensely studiedinteracting binary systems, like novae, CVs, symbiotics, Ba and CHgiants, Feige 24-type systems, and dwarf carbon stars. We describe anear-IR photometric search for cool red dwarf companions to hot whitedwarfs (WDs). IR photometry offers a sensitive test for low-massmain-sequence (MS) companions. Our sample of EUV-detected WDs offersseveral advantages over previous (largely proper motion-selected) WDsamples: (1) the high WD temperatures(24,000=2 Msolar, we thusprovide a photometric measure of the binary fraction of high-mass starsthat would be difficult to perform in high-mass main-sequence stars. Weestimate that 90% of the companions are of type K or later.
| The Three-dimensional Structure of the Warm Local Interstellar Medium. I. Methodology
In this first in a series of papers, we develop a methodology forconstructing three-dimensional models of the local interstellar cloud(LIC) and adjacent warm clouds in the local interstellar medium (LISM).Our models are based on the column density of neutral hydrogen gas(NHI) inferred primarily from measurements of the deuteriumcolumn density toward nearby stars obtained from the analysis of HubbleSpace Telescope ultraviolet spectra. We also use values ofNHI inferred from spectra of hot white dwarfs and B-typestars obtained by the Extreme Ultraviolet Explorer satellite. These verydifferent methods give consistent results for the three white dwarfstars in common. We assume that along each line of sight allinterstellar gas moving with a speed consistent with the LIC velocityvector has a constant density, NHI=0.10 cm-3, andextends from the heliosphere to an edge determined by the value ofNHI moving at this speed. A number of stars have velocitiesand/or depletions that indicate absorption by other warm clouds in theirlines of sight. On this basis α Cen A and B and probably alsoɛ Ind lie inside the Galactic center (G) cloud, HZ 43 and 31 Comlie inside what we call the north Galactic pole cloud, and β Cet islocated inside what we call the south Galactic pole cloud. We show thelocations of these clouds in Galactic coordinates. The Sun is locatedvery close to the edge of the LIC toward the Galactic center and thenorth Galactic pole. The absence of Mg II absorption at the LIC velocitytoward α Cen indicates that the distance to the edge of the LIC inthis direction is <=0.05 pc and the Sun should leave the LIC and perhapsenter the G cloud in less than 3000 yr. Comparison of LIC and totalvalues of NHI toward pairs of stars with separations between0.9d and 20 deg reveals a pattern of good agreement so long as bothstars lie within 60 pc of the Sun. Thus the LIC and perhaps also othernearby warm clouds have shapes that are smooth on these angular scales.In our second paper we will therefore fit the shape of the LIC with aset of smooth basis functions (spherical harmonics).
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A Catalog of Spectroscopically Identified White Dwarfs
A catalog of 2249 white dwarfs which have been identifiedspectroscopically is presented complete through 1996 April. Thiscompilation is the fourth edition of the Villanova Catalog ofSpectroscopically Identified White Dwarfs. For each degenerate star, thefollowing data entries with references are provided: (1) a catalogcoordinate designation or WD number, in order of right ascension; (2)the right ascension and declination for epoch 1950.0; (3) the spectraltype based upon the new system; (4) a catalog symbol denoting binarymembership; (5) a list of most names known to exist for a given star;(6) proper motion and position angle; (7) broadband UBV photometry, V,B-V, U-B (8) multichannel spectrophotometry, v(MC), g-r (9)Strömgren narrowband photometry, y, b-y, u-b (10) an absolutevisual magnitude based upon the best available color-magnitudecalibration or trigonometric parallax; (11) the observed radial velocityuncorrected for gravitational redshift or solar motion; and (12) thetrigonometric parallax with mean error when available. Notes for unusualor peculiar stars and a coded Reference Key alphabetized by the firstauthor's last name are presented, as well as an expanded tablecross-referencing all names to the catalog WD number. An introductionand full descriptions of the entries are provided in the text.
| Evidence for an ionization gradient in the local interstellar medium: EUVE observations of white dwarfs
We present an enlarged and homogeneous set of interstellar hydrogen andhelium column densities obtained through continuum and ionization edgesfitting of nearby hot white dwarfs observed with the Extreme UltravioletExplorer (EUVE). We compare the HI columns towards the targets and theirlocations relative to the soft X-ray cavity contours drawn by Snowden etal. (1998). We then use the inferred ionization degrees of hydrogen andhelium (available towards 17 objects) as a database for a search ofsystematic trends in the local interstellar medium. We find that theionization degree of helium does not show any trend, with a constantvalue around 40%. At variance with helium, hydrogen ionization varieswithin the Local Bubble: there is an ionization increase along thegeneral direction of the Canis Major cavity. These results areconsistent with hydrogen being ionized by the Canis Major hot starsAdara and Mirzam. However, the co-existence of fully neutral hydrogenand strongly ionized helium along some l-o-s remains to be explained.
| Hot White Dwarfs in the Extreme-Ultraviolet Explorer Survey. IV. DA White Dwarfs with Bright Companions
We present an analysis of optical, ultraviolet, and X-ray spectralproperties of a sample of 13 hot hydrogen-rich (DA) white dwarfs, eachpaired with a luminous unresolved companion. Using low-dispersionInternational Ultraviolet Explorer spectra, ROSAT photometry, andExtreme-Ultraviolet Explorer photometry and spectroscopy, we estimatethe effective temperature, mass, and distance of the white dwarfs.Additionally, we examine the question of their atmospheric composition.We establish orbital properties for most binaries by means ofhigh-dispersion optical spectroscopy obtained with the Hamilton echellespectrograph at Lick Observatory; the same data help uncover evidence ofactivity in some of the secondary stars that is also notable in ROSATX-ray measurements. In particular, we find high-amplitude (>20 kms-1) velocity variations in only two stars (HD 33959C and HR 8210),low-amplitude variations in four additional objects (HD 18131, HR 1608,theta Hya, and BD +27 deg1888), and no variations (<2 km s-1) in theremainder. We have observed Ca H and K in emission in four (BD +08deg102, HD 18131, HR 1608, and EUVE J0702+129) of the six objects thatwere also detected in the 0.52-2.01 keV ROSAT PSPC band, while thesource of the hard X-ray emission in HD 33959C remains unknown; otherinvestigators have noted some evidence of activity in the remaining0.52-2.01 keV detection, HD 217411. Properties of the white dwarfs arealso investigated; EUV spectroscopy shows the effect of a low heavyelement abundance in the atmosphere of the white dwarf in HD 33959C andof a high heavy element abundance in HD 223816; measurements of allother objects are apparently consistent with emission from pure-hydrogenatmospheres. However, current data do not constrain well the white dwarfparameters, and, to remedy the situation, we propose to obtainspectroscopy of the complete H Lyman line series.
| Sirius B: A New, More Accurate View
Long-standing questions regarding the temperature, gravity, mass, andradius of the well-known white dwarf Sirius B are considered in light ofnew data. Recently obtained Extreme Ultraviolet Explorer (EUVE)observations and reprocessed IUE NEWSIPS data have produced a new,well-defined effective temperature of 24,790 +/- 100 K and a surfacegravity of log g = 8.57 +/- 0.06 for Sirius B. A new Hipparcos parallaxfor the Sirius system of pi = 0."37921 +/- 0."00158 is used inconjunction with the above spectroscopic results and the previouslypublished gravitational redshift to yield a mass of 0.984 +/- 0.074Mȯ and a radius of R = 0.0084 +/- 0.00025Rȯ for the whitedwarf. Combining these results with the existing astrometric mass forSirius B gives a refined mass estimate of M = 1.034 +/- 0.026 Mȯ.The mass and radius for Sirius B are found to be consistent with thetheoretical mass-radius relation for a carbon-core white dwarf. The EUVEspectrum is also used to determine a firm upper limit of He/H = 1.8 x10-5 for the helium mixing ratio in the photosphere of Sirius B. IUEechelle spectra of Sirius B provide an estimate of log NH I = 17.72 +/-0.1 for the interstellar H I column to this star.
| The Stellar Extreme-Ultraviolet Radiation Field
The local extreme ultraviolet (EUV) radiation field from stellar sourceshas been determined by combining the EUV spectra of 54 stars, taken withthe spectrometers aboard the Extreme Ultraviolet Explorer satellite. Theresultant spectrum over the range 70-730 A is estimated to be 95%complete above 400 A and 90% complete above 200 A. The flux contributedby two B stars and three hot white dwarfs dominate the spectrum exceptat the shortest wavelengths, where an assortment of EUV source typescontribute. The high electron densities measured toward nearby stars canbe accounted for by photoionization from this radiation field, but thespectrum is too soft to explain the overionization of helium withrespect to hydrogen recently measure in the Local Cloud.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Catalogue of cataclysmic binaries, low-mass X-ray binaries and related objects (Sixth edition)
The catalogue lists coordinates, apparent magnitudes, orbitalparameters, stellar parameters of the components and other characteristcproperties of 318 cataclysmic binaries, 47 low-mass X-ray binaries and49 related objects with known or suspected orbital periods together witha comprehensive selection of the relevant recent literature. In additionthe catalogue contains a list of references to published finding chartsfor 394 of the 414 objects. A cross-reference list of alias objectdesignations concludes the catalogue. Literature published before 30June 1997 has, as far as possible, been taken into account. Thecatalogue is available in electronic form only via the CDS at ftp130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| CCD photometry of a delta Scuti variable in an open cluster. III. V 465 Persei in the alpha Persei cluster
We present the results of real-time CCD differential photometry for thedelta Scuti variable V 465 Per. The observations were performed forthirteen nights between November, 1994 and January, 1995. Total 3345points of differential V magnitudes were collected during theobservation period of 76.4 hours. From the Fourier analysis, we havedetected four frequencies as follows; f_1=14.040 c/d, f_2=17.208 c/d,f_3=33.259 c/d and f_4=13.721 c/d. Two frequencies of 12.50 c/d and33.49 c/d detected previously by Slovak (1978, ApJ 223, 192) maycorrespond to our f_1 and f_3, respectively. For each frequency,pulsation constants of Q_1=0.0520+/-0.008, Q_2=0.0425+/-0.006,Q_3=0.0220+/-0.003 and Q_4=0.0533+/-0.008 were derived from severalobservational properties of V 465 Per. Only the value of Q_3 is found tobe within the range of theoretical p-mode oscillations and the otherones show large differences relative to the theoretical values. The highQ-values might be interpreted as the occurrence of g-mode oscillationsin V 465 Per, even though it can not rule out the possibility ofsystematic errors (Breger 1990; Delta Scuti Star Newsletter, 2, 13)related to rotational velocity.
| Identification of soft high galactic latitude RASS X-ray sources. I. A complete count-rate limited sample
We present a summary of spectroscopic identifications for a completesample of bright soft high galactic latitude X-ray sources drawn fromthe ROSAT All-Sky Survey which have PSPC count-rates CR > 0.5 {ctss}(-1) and hardness ratios HR1 < 0. Of a total of 397 sources, 270had catalogued counterparts although most of these were not previouslyknown as X-ray sources; of the remaining 127 sources neither X-ray noroptical properties were previously known. Of the whole sample of verysoft X-ray sources 155 were also discovered by the Wide-Field-Camera onboard ROSAT. We present spectroscopic identifications of 108 sources andother identifications for further 18 sources; 1 source remainsunidentified so far. In practically all cases a unique opticalcounterpart exists facilitating identification. The largest sourceclasses are AGN, magnetic cataclysmic variables, and hot white dwarfs.Based in part on observations with the ESO/MPI 2.2m telescope at LaSilla, Chile
| Behaviour of calcium abundance in Am-Fm stars with evolution
Calcium abundance in the atmosphere of Am stars is examined as afunction of their evolutionary state within the main sequence. Newspectroscopic abundances as well as abundances obtained photometricallyby Guthrie (1987) are used, since they are mutually quite consistent.The main result of this work is that, contrary to earlier suggestions,calcium abundance does not tend to be larger in evolved Am stars than inunevolved ones, for objects distributed along a given evolutionary trackin the HR diagram. The trend appears to be the reverse, if it is presentat all. For our whole sample of Am stars, there is a significantcorrelation between calcium abundance and effective temperature, in thesense that the cooler objects are the most Ca-deficient, hence have themost pronounced Am peculiarity. This implies an apparent correlationbetween calcium deficiency and age, although the lack of Am starsyounger than log t = 8.6 seems real. Our results are fully consistentwith the low rate of Am stars observed in young clusters and withtheoretical predictions of time-dependent radiative diffusion (Alecian1996). Based on observations collected at Observatoire de Haute Provence(CNRS), France, and on data from the ESA HIPPARCOS astrometry satellite.
| An Optical Atlas of Extreme Ultraviolet Explorer (EUVE) Sources
The Extreme Ultraviolet Explorer (EUVE) has been detecting EUV sourcessince its launch in June 1992. Positions of 540 sources have been madeavailable to the community by the EUVE team. We have extracted 7' X 7'images centered on these 540 EUVE sources from the Space TelescopeScience Institute digitized sky archives. We present these images asmosaic finder charts to aid observers trying to identify EUVE sources,or to characterize known sources. (SECTION: Atlases)
| The chemical composition and binarity of beta Crateris
A detailed abundance analysis of the bright A-type star betaCrt ispresented. It is found that most of the abundances are essentiallysolar, indicating that the star is not a hot Am star. The only prominentanomalies are an underabundance of Al and overabundances of S, Sr andBa. The barium overabundance is the most prominent and has importantimplications for the past history of this supposed binary system. Thepresence of the ROSAT-discovered white dwarf companion could indicatethat the A-type star may have accreted material from the white dwarfprogenitor. There are indications in the literature that the system is arelatively short-period binary. However, the radial velocitymeasurements presented in this paper show no apparent velocity changes,and do not support this hypothesis. It may be that the system is a widelong-period binary, or not even physically associated. Additional radialvelocity measurements are required to investigate the orbit of thissystem.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | פגסוס |
| התרוממות ימנית: | 21h26m26.70s |
| סירוב: | +19°22'32.0" |
| גודל גלוי: | 6.07 |
| מרחק: | 46.041 פארסק |
| תנועה נכונה: | 80.4 |
| תנועה נכונה: | 17.5 |
| B-T magnitude: | 6.347 |
| V-T magnitude: | 6.093 |
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INHABITED SKY
