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A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| Photometric Period Variation of V 1379 AQL
V 1379 Aql is an eclipsing binary consisting a hot subdwarf (sdB) and ared giant star (K0 III/IV). According to the brightness variationoutside of eclipses, the giant component is a chromospherically activestar. The dark and cool active structures on this component and theirevolution cause the variation of the total light of the system.Photometric observations spanning 16 years yield the variations of thephotometric period and the mean brightness. There is a correlationbetween them. We suggest that the photometric period decreases as thelatitude of the active region moves toward the equator.
| The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| 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.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| Beyond the iron group: Heavy metals in hot subdwarfs
We report the discovery of strong photospheric resonance lines of GaIII, Ge IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdBand sdOB stars at temperatures ranging from 22 000 K to 40 000 K. Linesof other heavy elements are also detected, however in these cases moreatomic data are needed. Based on these discoveries, we present ahypothesis to explain the apparent lack of silicon in sdB stars hotterthan 32 000 K. The existence of triply ionised Ge, Sn, and Pbsuggests that rather than silicon sinking deep into the photosphere, itis removed from the star in a fractionated stellar wind. This hypothesisprovides a challenge to diffusion models of sdB stars.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. These observations areassociated with program #8635 and #5319.
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| Discovery of a spectroscopic binary comprising two hot helium-rich subdwarfs
Helium-rich subdwarf B (He-sdB) stars form a very small fraction of thepopulation of hot subdwarf stars in our Galaxy. They have been foundboth in the field of our Galaxy as well as in globular clusters. Theevolution of these rare stars has recently been the subject of muchdebate involving both binary and single star evolution models. We reportour serendipitous discovery that the prototype - PG1544+488 - is a binary containing two low-mass helium-rich hotsubdwarfs. This discovery challenges existing evolutionary models forHe-sdB stars and suggests that they may be formed through close binaryevolution and following the ejection of a common envelope.Based on observations made with the William Herschel and Isaac NewtonTelescopes operated on the island of La Palma by the Isaac Newton Groupin the Spanish Observatorio del Roque de los Muchachos of the Institutode Astrofísica de Canarias and with the NASA-CNES-CSA FarUltraviolet Spectroscopic Explorer.
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| The Evolution of Cool Algols
We apply a model of dynamo-driven mass loss, magnetic braking, and tidalfriction to the evolution of stars with cool convective envelopes; inparticular, we apply it to binary stars where the combination ofmagnetic braking and tidal friction can cause angular momentum loss fromthe orbit. For the present we consider the simplification that only onecomponent of a binary is subject to these nonconservative effects, butwe emphasize the need in some circumstances to permit such effects inboth components.The model is applied to examples of (1) the Sun, (2) BYDra binaries, (3) Am binaries, (4) RS CVn binaries, (5) Algols, and (6)post-Algols. A number of problems regarding some of these systems appearto find a natural explanation in our model. There are indications fromother systems that some coefficients in our model may vary by a factorof 2 or so from system to system; this may be a result of the chaoticnature of dynamo activity.
| The tidal effects on the lithium abundance of binary systems with giant component
We analyse the behavior of lithium abundance as a function of effectivetemperature, projected rotational velocity, orbital period andeccentricity for a sample of 68 binary systems with giant component andorbital period ranging from about 10 to 6400 days. For these binarysystems the Li abundances show a gradual decrease with temperature,paralleling the well established result for single giants. We have alsoobserved a dependence of lithium content on rotation. Binary systemswith moderate to high rotation present also moderate to high Li content.This study shows also that synchronized binary systems with giantcomponent seem to retain more of their original lithium than theunsynchronized systems. For orbital periods lower than 100 to 250 days,typically the period of synchronization for this kind of binary systems,lithium depleted stars seems to be unusual. The suggestion is made thatthere is an ``inhibited zone" in which synchronized binary systems withgiant component having lithium abundance lower than a threshold levelshould be unusual. Based on observations collected at ESO, La Silla.
| The comparative accuracy of photographic observations of radio stars observed at the Engelhardt Astronomical Observatory
At the Engelhardt Astronomical Observatory (EAO), we observedphotographic positions of 113 Galactic Radio Sources (GRS) in the systemPPM catalogue (Rizvanov & Dautov 1998). Analysis of their accuracyis made by comparison with the Hipparcos catalogue (Perryman et al.1997) and astrometric catalogue of radio stars in the radio window fromthe article of Walter et al. (1991). Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/375/670
| A Complete Survey of Case A Binary Evolution with Comparison to Observed Algol-type Systems
We undertake a comparison of observed Algol-type binaries with a libraryof computed Case A binary evolution tracks. The library consists of 5500binary tracks with various values of initial primary massM10, mass ratio q0, and period P0,designed to sample the phase-space of Case A binaries in the range-0.10<=logM10<=1.7. Each binary is evolved using astandard code with the assumption that both total mass and orbitalangular momentum are conserved. This code follows the evolution of bothstars to the point where contact or reverse mass transfer occurs. Theresulting binary tracks show a rich variety of behavior that we sortinto several subclasses of case A and case B. We present the results ofthis classification, the final mass ratio, and the fraction of timespent in Roche Lobe overflow for each binary system. The conservativeassumption under which we created this library is expected to hold for abroad range of binaries, where both components have spectra in the rangeG0 to B1 and luminosity classes III to V. We gather a list of relativelywell-determined, observed hot Algol-type binaries meeting thiscriterion, as well as a list of cooler Algol-type binaries, for which weexpect significant dynamo-driven mass loss and angular momentum loss. Wefit each observed binary to our library of tracks using aχ2-minimizing procedure. We find that the hot Algolsdisplay overall acceptable χ2, confirming theconservative assumption, while the cool Algols show much less acceptableχ2, suggesting the need for more free parameters, such asmass and angular momentum loss.
| On the Formation of Helium Double Degenerate Stars and Pre-Cataclysmic Variables
The evolution of low-mass (M<2.5 Msolar) binaries throughthe common envelope phase has been studied for systems in which onemember is on its first ascent of the red giant branch. Three-dimensionalhydrodynamical simulations have been carried out for a range of redgiant masses (1-2 Msolar) with degenerate helium cores(0.28-0.45 Msolar) and companions (0.1-0.45Msolar) for initial orbital periods ranging from ~15 to 1000days. The results suggest that these low-mass binary systems can survivethe common envelope phase provided that the helium degenerate core ismore massive than about 0.2-0.25 Msolar and that the mass ofthe red giant progenitor is <~2 Msolar. Specificapplications are made to observed double helium degenerate systems,pre-cataclysmic variables, and subdwarf B stars in order to placeconstraints on progenitor systems evolving through the common envelopephase. For the observed short-period double degenerate systems, it isfound that evolutionary scenarios involving two phases of commonenvelope evolution are not likely and that a scenario involving anAlgol-like phase of mass transfer followed by a common envelope phase isviable, suggesting that the first-formed white dwarf is often reheatedby nuclear burning on its surface. A formation mechanism for twosubdwarf B stars observed in eclipsing short-period binaries withlow-mass main-sequence stars is also described.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Radio star catalogue observed in San Juan (RSSJ95)
Using the data observed in San Juan with the photoelectric AstrolabeMark II of the Beijing Astronomical Observatory from February, 1992 toMarch, 1997, the radio star catalogue in San Juan(RSSJ95) has beencompiled. There are 69 radio stars in this catalogue. The positions ofthe radio stars are for the epoch of observation and the equinox J2000.0and a system close to that of the system FK5. The mean precisions are+/-2.2 ms and +/-0.035'' in right ascensions and declinations,respectively. The magnitudes of stars are from 0.9 to 10.7. Thedeclinations are from -2fdg 5 to -60(deg) . The mean epoch is 1995.1.Finally, the comparison results between the Hipparcos catalogue andRSSJ95 are given.
| KPD 0422+5421: a new short-period subdwarf B/white dwarf binary
The subdwarf B (sdB) star KPD 0422+5421 was discovered to be asingle-lined spectroscopic binary with a period ofP=0.0901795+/-(3x10^-7) d (2 h 10 min). The UB light curves display anellipsoidal modulation with amplitudes of ~0.02 mag. The sdB starcontributes nearly all of the observed flux. This and the absence of anyreflection effect suggest that the unseen companion star is small (i.e.R_comp~0.01R_solar) and therefore degenerate. We modelled the UB lightcurves and derived i=78.05 deg+/-0.50 deg and a mass ratio ofq=M_comp/M_sdB=0.87+/-0.15. The sdB star fills 69 per cent of its Rochelobe. These quantities may be combined with the mass function of thecompanion [f(M)=0.126+/-0.028M_solar] to derive M_sdB=0.72+/-0.26M_solarand M_comp=0.62+/- 0.18M_solar. We used model spectra to derive theeffective temperature, surface gravity and helium abundance of the sdBstar. We found T_eff=25000+/-1500 K, log g=5.4+/-0.1 and [He/H]=-1.0.With a period of 2 h 10 min, KPD 0422+5421 has one of the shortest knownorbital periods of a detached binary. This system is also one of only afew known binaries that contain a subdwarf B star and a white dwarf.Thus KPD 0422+5421 represents a relatively unobserved, and short-lived,stage of binary star evolution.
| Infrared flux excesses from hot subdwarfs. II. 72 more objects
In our search, started in February, 1994, for JHK excess fluxes amongthe hot subdwarf population as an indicator for the presence of binarycompanions, results for 72 more hot objects (=63 hot subdwarfs + 1Horizontal Branch B star + 7 white dwarfs + 1 non-subdwarf object)observed with the Carlos Sanchez CVF IR photometer (in June and October,1994), are presented. The exact number of binary hot subdwarfs hasgained renewed importance after the recent discovery of pulsators withG-F companions. The total number of candidates we propose may help toset some constraints; for example, out of 41 objects with excesses, 13may have G-type binary companions. From our new sample, 14 discoveriesof binary candidates have been found: BD+25 4655, Feige 108, HD 4539, HD149382, HD 216135, KPD 2109+440, LSI+63 198, LSIV+10 9, LSV+22 38, PG0011+221, PG 0116+242, PG 0314+103, PG 2151+100 and TON 139. Besides, 2more from reanalysis of February, 1994, data - BD+37 1977 and BD+481777, may now be found to be IR excess candidates. Two suspectedbinaries, PB 8555 and SB 7, are also confirmed. By fitting \cite[Kurucz(1993)]{kur93} model spectra and assuming zero-age main sequencecompanions, we find upper limits on the subdwarf gravities. Thedistributions of upper limits on log(g), mostly between about 5.25 and6.5, are nearly identical for both sdBs and sdOs. Figure~1 is onlyavailable in the electronic version of the paper(http://www.edpsciences.com)
| The age-mass relation for chromospherically active binaries. III. Lithium depletion in giant components
We present a study of the lithium abundances of a sample of evolvedcomponents of Chromospherically Active Binary Systems. We show that asignificant part of them have lithium excesses, independently of theirmass and evolutionary stage. Therefore, it can be concluded that Liabundance does not depend on age for giant components of CABS. Theseoverabundances appear to be closely related to the stellar rotation, andwe interpret them as a consequence of the transfer of angular momentumfrom the orbit to the rotation as the stars evolve in and off the MainSequence, in a similar way as it happens in the dwarf components of thesame systems and in the Tidally Locked Binaries belonging to the Hyadesand M67. Based on observations collected with the 2.2\,m telescope ofthe German-Spanish Observatorio de Calar Alto (Almeria, Spain), and withthe 2.56\,m Nordic Optical Telescope in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrof\'\i sica de Canarias(La Palma, Spain)
| Further discussion of binary star radio survey data
Statistical information on 8280 individual radio observations of binarystars, predominantly at 8.4 GHz using the Parkes 64 m antenna, ispresented. Three main groups are distinguished: (i) RS CVn stars, (ii)classical Algol binaries (EA2s) and (iii) detached pairs of generallyearly type (ETBs). The RS CVn stars more frequently gave rise todetectable fluxes, while the ETBs, in this data, are a small and ratherheterogeneous class. The Algols' emission appears to increase nearconjunction phases, though we cannot clearly distinguish any specialproperty of the Algols' phase-dependent behaviour which is not alsoshared by the RS CVn binaries. Both these categories' data show abimodal, phase-dependent pattern to the distribution of detections,suggesting both binary types share similar underlying physicalproperties, though there could also be other factors at play. The samplesizes of the Algols and particularly the ETB detections are too smallfor effective, discriminatory statistics, however.
| The EC 14026 stars - VIII. PG 1336-018: a pulsating sdB star in an HWVir-type eclipsing binary
The sdB star PG 1336-018 is found to be a very short-period eclipsingbinary system, remarkably similar to the previously unique system HWVir. In addition, and unlike HW Vir, the sdB star in the PG 1336 systemshows rapid oscillations of the type found in the recently discoveredsdB pulsators, or EC 14026 stars. The orbital period, 0.101 0174 d, isone of the shortest known for a detached binary. Analysis ofphotoelectric and CCD photometry reveals pulsation periods near 184 and141 s, with semi-amplitudes of ~0.01 and ~0.005 mag respectively. Bothoscillations might have variable amplitude, and it is probable thatother frequencies are present with amplitudes ~0.003 mag or less. The184- and 141-s pulsations are in the range of periods predicted bymodels for hot horizontal-branch stars. Analysis of medium-dispersionspectrograms yields T_eff=33 000+/-1000 K and log g=5.7+/-0.1 for thesdB primary star, a radial velocity semi-amplitude K_1=78+/-3 km s^-1and a system velocity gamma=6+/-2 km s^-1. Spectrograms from the IUEFinal Archive give T_eff=33 000+/-3000 K and E(B-V)=0.05 for log g=6.0models. The derived angular radius leads to a distance of 710+/-50 pcfor the system, and an absolute magnitude for the sdB star of+4.1+/-0.2. A preliminary analysis of U, V and R light curves indicatesthe orbital inclination to be near 81 deg and the relative radii to ber_1=0.19 and r_2=0.205. Assuming the mass of the sdB primary to be 0.5Msolar leads to a mass ratio q=0.3 for the system, and indicates thatthe secondary is a late-type dwarf of type ~M5. As with HW Vir, it isnecessary to invoke small limb-darkening coefficients and high albedosfor the secondary star to obtain reasonable fits to the observed lightcurves.
| Photospheric and chromospheric activity in the late-type giant component of the evolved binary system HD 185510
UBV photometry and moderate resolution Hα spectrophotometry of theevolved binary system HD 185510 (sdB + K0 III), performed at CataniaAstrophysical Observatory, is presented and discussed. Thespectrophotometric data were collected in 1991, 1993, and 1994, whilethe photometric light curves were obtained in 1993, 1994 and 1995.>From the B and V photometry we determine a new photometricrotational period of 26(d) .23, confirming the asynchronous rotation ofthe cool giant component. The spectroscopic data confirm the vsin ivalue of 15 Km s(-1) measured by Fekel et al. (1993) and clearly reveala filled-in Hα line with appreciable variations. The excessemission of the line, observed at any orbital phase, is found to beanticorrelated with the V light curve and is primarily ascribed to thechromospheric activity on the cool star. The primary total eclipse isclearly visible in the U band, but undetectable in the V band. >Fromthe U observations we determined a total duration of the primary eclipse(from 1(st) to 4(rd) contact) of 1(d) .3883, with the ingress lastingonly 27 minutes. This new accurate monitoring and timing of the eclipseallowed us to improve the system solution which leads to R_C=8.8Rsun, T_C=4800K, R_H=0.11 Rsun, T_H=30000K for thecool and hot star respectively. The evolution of HD185510B is discussedalso in relation to the evolutionary status of HD 185510A and thesynchronization time scale. HD 185510B is probably a sdB near the zeroage extended horizontal branch, resulting from an enhanced mass loss inlate case B or case A mass exchange with a possible common envelopephase. A small amount (15-20%) of mass loss from the system which canaccount for the strong IR excess is suggested. The complete U B Vphotometric data set is available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| San Juan radio star catalogue and comparison with HIPPARCOS catalogue.
Not Available
| Alignment of rotational axes in asynchronous late type binaries
41 RS CVn and BY Dra type binaries with reliable orbital and physicalparameters have been found to rotate asynchronously with the orbitalrevolution. For this sample inclinations of the rotational axes, i_r, ofthe primaries and the orbital inclinations, i_o, are independentlydetermined to test the alignment between the equatorial and the orbitalplanes. The observed difference Delta i=| {i_o} - {i_r}| measures adeviation from coplanarity of these planes. It turns out that mostasynchronous systems prove to be misaligned, especially when theinfluence of the position angle is taken into account. Thus, thegenerally accepted assumption that rotational axes are perpendicular toorbital planes is not valid for asynchronous RS CVn and BY Dra typebinaries. The influence of the position angle of the observer on thederived values of Delta i can be studied only by statistical methods.The distribution of the observed Delta i is compared wih the expectedvalues of Delta i() e for two cases: a) the rotational axes are randomlyinclined to the orbital planes, and b) the rotational axes areperpendicular to the orbital planes. The best fit to our observed sampleof asynchronous binaries is obtained for the case a), while for thesynchronous RS CVn and BY Dra type binaries the rotational axes areperpendicular to their orbital planes. The appendix is available onlyelectronically with the on-line publication athttp://link.springer.de/link/service/journals/00230
| S1040 in M67: A Post--Mass Transfer Binary with a Helium Core White Dwarf
We have obtained spectra of the yellow giant S1040 in the open clusterM67 using the Goddard High-Resolution Spectrograph (GHRS) and the FaintObject Spectrograph on the Hubble Space Telescope. S1040 is asingle-lined spectroscopic binary with a 42.8 day period that occupies a"red straggler" position in the M67 color-magnitude diagram (CMD), 0.2mag blueward of the giant branch. A detection of S1040 at 1620 A withthe Ultraviolet Imaging Telescope provided evidence that the secondaryis a hot white dwarf and thus that the anomalous location of S1040 inthe CMD is likely due to a prior episode of mass transfer. Our GHRSspectrum shows a broad Ly alpha absorption profile that confirms thewhite dwarf identification of the S1040 secondary. A model atmospherefit to the GHRS spectrum yields Teff = 16,160 K, log g = 6.7, and a massof about 0.22 Msolar, for an assumed cluster distance of 820 pc and areddening of E(B - V) = 0.02. The unusually low mass derived for thewhite dwarf implies that it must have a helium core and that a masstransfer episode must have begun while the progenitor was on the lowergiant branch. We construct a plausible mass transfer history for S1040in which it originated as a short-period (~2 days) binary and evolvedthrough a blue straggler phase to reach its current state.
| Rotational Velocities of Late-Type Stars
A calibration based on the results of Gray has been used to determineprojected rotational velocities for 133 bright stars with spectral typesof F, G, or K, most of which appear in {\it The Bright Star Catalogue}.The vast majority have {\it v} sin {\it i} $\leq$ 10 km s$^{-1}$ and,thus, are slow rotators. With the new calibration, projected rotationalvelocities have been determined for a sample of 111 late-type stars,most of which are chromospherically active. Some of the stars have hadtheir rotational velocities measured for the first time. (SECTION:Stars)
| The structure of roundchroms in close binary systems
The determination of common chromospheres - roundchroms - for 32 closebinary systems, all of RS CVn type, is described; the main parameters ofthese roundchroms - volumes, electron concentrations and masses, areestimated. Three types of roundchroms are established according to theirstructure. The empirical relationship between their electronconcentration n_e and intercomponent distance a - n_e = K a^-0.80,discovered earlier, is confirmed by data for over fifty close binarysystems. This law holds promise for the determination of component radiiof close binary systems and some parameters of their roundchroms.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נשר |
| התרוממות ימנית: | 19h39m38.82s |
| סירוב: | -06°03'49.5" |
| גודל גלוי: | 8.33 |
| מרחק: | 235.294 פארסק |
| תנועה נכונה: | 23.4 |
| תנועה נכונה: | -27.7 |
| B-T magnitude: | 9.749 |
| V-T magnitude: | 8.448 |
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