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|Wer beobachtet mit: BK Aurigae.|
|Chandra Observations of Coronal Emission from the Early G Supergiants α and β Aquarii|
We report Chandra detections of coronal X-rays from the early Gsupergiants α Aquarii (HD 209750: G2 Ib) and β Aquarii (HD204867: G0 Ib). Previous ROSAT observations of these archetypical``hybrid chromosphere'' stars were inconclusive, in the case of αAqr owing to a 38' mispointing, and for β Aqr because of a smallpositional discrepancy of the apparent source. The Chandra HighResolution Camera (HRC-I), with its superior spatial resolution andsensitivity, has obtained a positive detection of α Aqr andrecovered faint emission at the location of β Aqr, now wellseparated from the stronger source to the southeast that dominated theearlier ROSAT image. The coronal LX/LC IV luminosity ratiosof both supergiants are extremely depressed relative to early Gmain-sequence stars, continuing the ``X-ray deficiency syndrome''originally identified in late F/early G luminosity class III giants ofthe Hertzsprung gap.
|X-Rays from Hybrid Stars|
The late-type giants and supergiants of the ``hybrid chromosphere''class display signatures of cool (T<~2×104 K) windstogether with hot emission lines from species like C IV(T~105 K). A survey of such stars by Reimers et al. usingROSAT reported numerous X-ray detections (T~106 K),strengthening the (then heretical) idea that hot coronae and cool windscan coexist in luminous giants. However, several of the candidatesources were offset from the predicted stellar coordinates, calling intoquestion the identifications. In an effort to secure better knowledge ofthe X-ray luminosities of the hybrids, the ROSAT fields from the Reimerset al. survey were reexamined, exploiting the USNO-A2.0 astrometriccatalog to register the pointings to a few arcseconds accuracy. On thebasis of positional mismatches, at least two of the previously reporteddetections of key hybrid stars-γ Dra (K5 III) and β Aqr (G0Ib)-must be rejected. The new X-ray upper limits for these stars,combined with the remaining candidate detections (and nondetections)from the original survey, place the hybrids into the same ``X-raydeficient'' category as the ``noncoronal'' red giants like Arcturus(α Boo: K1.5 III) and Aldebaran (α Tau: K5 III). A few ofthe hybrid X-ray sources are exceptional, however. The archetype αTrA (K2 II-III), in particular, is securely detected in terms ofpositional coincidence, but its anomalous, contradictory coronalproperties suggest that an unseen companion-a young hyperactive Gdwarf-might dominate the X-ray emission.
|Magnetic field measurements on four yellow supergiants. I|
Multiyear high precision measurements of the longitudinal component ofthe magnetic field (Be) of four supergiants are reported: Aqr (G0 Ib),Aqr (G2 Ib), Gem (G8 Ib), and Peg (K2 Ib). The best measurementaccuracy, =0.8 G, was achieved for Peg. A Monte Carlo method was used totest the reliability of the derived measurement errors. The differencesbetween the observational errors and the calculated Monte Carlo errorswere 3.2%. For Aqr and Aqr no statistically significant value of themagnetic field was recorded when averaged over a night. For eGem thefollowing overnight average values of the magnetic field were recordedon five nights: 11.1±2.7 G, 9.8±2.5 G, -10.5±3.0 G,38.1±7.4 G, and 5.3±1.5 G. For Peg the magnetic fieldrecorded over two nights was -5.3±0.9 G and - 2.7±0.8 G.
|A Spectral Atlas of F and G Stars|
We present an atlas of a group of bright stars in the range of spectralclasses F--G and luminosity classes I--V. The spectra were obtainedwith spectral resolution R 15,000 within spectral region4500--6620 Å. Typical spectra of stars with different metallicity[Fe/H] are included. We also show the digital version of the spectraldata in FITS format.
|Space Telescope Imaging Spectrograph Survey of Far-Ultraviolet Coronal Forbidden Lines in Late-Type Stars|
We describe an extensive search with the Space Telescope ImagingSpectrograph (STIS) for ultraviolet coronal (T>106 K)forbidden lines in a sample of 29 F-M dwarfs, giants, and supergiants.Measuring coronal lines in the 1150-1700 Å band with STIS hasimportant advantages of superior velocity resolution and an absolutewavelength calibration compared with using the Chandra or XMM-Newtongrating spectrometers to observe permitted transitions of the same ionstages in the kilovolt X-ray region. Fe XII λλ1242, 1349(T~2×106 K) and Fe XXI λ1354 (107 K)are well known from solar studies and have been reported in previousstellar work. A search for other coronal forbidden lines in the1200-1600 Å region was largely negative. The few candidateidentifications (e.g., Ar XIII λ1330 and Ca XV λ1375) aretoo faint to be diagnostically useful. We add new dwarfs to the list ofFe XII detections, including the nearby solar twin α Cen A (G2 V).Clear detections of Fe XXI were obtained in dMe stars, active giants, ashort-period RS CVn binary, and possibly in active solar-type dwarfs. Wedeveloped a semiempirical method for removing the C I blend thatpartially affects the Fe XXI λ1354 profile. As discussed recentlyby Johnson et al., Capella (α Aur; G8 III+G1 III) displays clearFe XXI variability between Goddard High-Resolution Spectograph (GHRS)and STIS observations 4 yr apart, which is apparently due to asubstantial decline in the contribution from the G8 primary. We presentan alternative model of the GHRS and STIS era profiles using informationin the two sets of line shapes jointly, as well as knowledge of thebehavior of Fe XXI profiles of other late-G ``clump'' giants similar toCapella G8. The full survey sample also provides a context for theapparent variability: the Fe XXI flux of the G8 star in the GHRSspectrum is nearly identical (in LFeXXI/Lbol) toother clump giants of similar LX/Lbol, but it haddropped at least a factor of 6 in the STIS measurement. The He IIλ1640 Bα feature-which is thought to be responsive tocoronal irradiation-also showed significant changes between the GHRS andSTIS epochs, but the decrease in the G8 star was much smaller than FeXXI. The Fe XII flux displays a correlation with the ROSAT 0.2-2 keVX-ray flux that can be described by an α=0.5 power law. Fe XXIexhibits a steeper, perhaps linear (α=1), correlation with theROSAT flux down to an activity level ofLX/Lbol~10-5, below which detections ofthe coronal forbidden line are rare. There is no evidence of large,systematic Doppler shifts in either Fe XII λ1242 or Fe XXIλ1354. This suggests that the emissions arise dominantly inconfined structures, analogous to magnetic loops on the Sun, ratherthan, say, in a hot wind. The Fe XII and Fe XXI line widths generallyare close to thermal (FWHM~40-90 km s-1 atT~106.2-107.0 K), except for the Hertzsprung-gapgiants 31 Comae (G0 III) and Capella G1 and the K1 subgiant primary ofHR 1099, all of which show evidence for excess broadening in Fe XXI (FeXII is obscured in these objects by broad N V λ1242 features). Ifthe excess broadening is rotational, it implies that the hot coronae of``X-ray-deficient'' 31 Com and Capella G1 are highly extended, contraryto the compact structures suggested by recent density estimates in anumber of active coronal sources.
|Polaris: Amplitude, Period Change, and Companions|
Polaris has presented us with the rare phenomenon of a Cepheid with apulsation amplitude that has decreased over the last 50 yr. In thisstudy we have used this property to see whether the amplitude decreaseduring the last 15 yr has had any effect on upper atmosphere heating. Weobtained IUE high- and low-resolution spectra but found no change ineither the Mg II chromospheric emission or the flux at 1800 Åbetween 1978 and 1993 when the pulsation amplitude dropped by 50% (from2.8 to 1.6 km s-1). The energy distribution from 1700 Åthrough V, B, R(KC), and I(KC) is like that of a nonvariable supergiantof the same color rather than a full amplitude Cepheid in that it hasmore flux at 1800 Å than the full amplitude Cepheid δ Cep.Polaris also has a rapidly changing period (3.2 s yr-1), incommon with other overtone pulsators. We argue that this is a naturalconsequence of the different envelope locations that dominate pulsationgrowth rates in fundamental and overtone pulsation. In fundamental modepulsators, the deeper envelope is more important in determining growthrates than for overtone pulsators. For fundamental mode pulsators,evolutionary changes in the radius produce approximately linear changesin period. In overtone pulsators, pulsation reacts to small evolutionarychanges in a more unstable way because the modes are more sensitive tohigh envelope features such as opacity bumps, and the growth rates forthe many closely spaced overtone modes change easily. Finally, the upperlimit to the X-ray flux from an Einstein observation implies that thecompanion in the astrometric orbit is earlier than F4 V. The combinationof upper and lower limits on the companion from IUE and Einsteinrespectively catch the companion mass between 1.7 and 1.4Msolar. The X-ray limit is consistent with the more distantcompanion α UMi B being a physical companion in a hierarchaltriple system. However the X-ray limits require that the even moredistant companions α UMi C and D are too old to be physicallyassociated with Polaris.
|A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars|
Rotational velocity vsin i and mean radial velocity are presented for asample of 231 Ib supergiant stars covering the spectral region F, G andK. This work is the second part of the large survey carried out with theCORAVEL spectrometer to establish the behavior of the rotation for starsevolving off the main sequence (De Medeiros & Mayor 1999). Thesedata will add constraints to the study of the rotational behavior inevolved stars, as well as solid information concerning tidalinteractions in binary systems and on the link between rotation,chemical abundance and activity in stars of intermediate masses. Basedon observations collected at the Haute-Provence Observatory,Saint-Michel, France and at the European Southern Observatory, La Silla,Chile Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/97
|Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics|
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|The proper motions of fundamental stars. I. 1535 stars from the Basic FK5|
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
|The Radial Velocity and Spectral Line Bisector Variability of Polaris|
We present precise stellar radial velocity measurements for theCepheid-type star Polaris taken in 1992-1993. The peak-to-peak amplitudeof the pulsations was 1.555+/-0.056 km s-1 in epoch 1992.4and 1.517+/-0.047 km s-1 in epoch 1993.2. These amplitudesare comparable to the one measured by Dinshaw et al. in 1987.75 andrecent measurements by Kamper & Fernie for 1995-1997. Consequently,these do not support the continued drop in pulsational amplitude firstextrapolated by Dinshaw et al. A periodogram analysis for our datayields a pulsational period of 3.9726769°+/-0.00011°, slightlyhigher than the value found by Dinshaw et al. and consistent with thevalue derived from the Kamper & Fernie data. The pulsational periodof Polaris may thus be increasing. Residual radial velocity measurementsafter removal of the component due to radial pulsations show thepresence of a 40 day period with a 2K amplitude of about 400 ms-1, first reported by Dinshaw et al. Spectral line bisectorsof the Sc II λ5526 and Mg I λ5528 lines also showvariations with the 40 day period, strongly indicating that this periodis indeed real. The presence of line bisector variations excludes alow-mass companion object as a cause of the residual radial velocityvariations. Two models are considered for the residual radial velocityand bisector span variations: starspots and nonradial pulsations.Although both can reproduce the amplitude and shape of the residualradial velocity variations, the spot models considered were unable toreproduce the overall shape and amplitude of the bisector spanvariations. The best-fit spot model was provided by a single spot with atemperature 500 K cooler than the photosphere with a macroturbulentvelocity of zero in the spot. If surface features do exist on Polarisand are responsible for the residual radial variations for this star,then possibly they have a temperature structure and distribution morecomplicated than the simple models considered here. The best fit to allthe observed variations was provided by a nonradial m=4 mode, althoughthese were not entirely satisfactory having a phase shift of about 0.25between the observed and predicted bisector variations. Possibleexplanations for this shift include temperature effects, a sourcefunction originating in a dynamic stellar atmosphere, or a differentpulsation mode than the one that was considered. Although the exactpulsational mode is yet to be identified, we believe that the residualradial velocity variations are due to a long-period pulsation mode.Supporting evidence comes from the fact that three different residualvariations with periods near 40 days have now been seen in Polaris andit is unlikely that these variations are due to rotational modulation bysurface features on a star that is differentially rotating.
|Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions|
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
|Excitation and visibility of high-degree modes in stars|
Observational evidence for excitation of non-radial modes in stars isconfronted with the results of linear stability surveys for stellarmodels. We consider various types of pulsators on the upper mainsequence as well as stars in the Cepheid strip. Our stability surveycovers the whole range of spherical harmonic degrees, l, whereinstability is found. There is fair agreement between the theoreticalinstability strip and the location of ζ Oph stars, but the observedand calculated periods do not agree in some stars. We suggest thateither pulsation is not responsible for the ζ Oph phenomenon orelse there are serious errors in mode identification in these cases. Wedo not find instability at long periods for early B-type stars,supporting the idea that pulsation is not responsible for the periodicvariations in Be stars. The agreement between the observed andcalculated periods of high-degree modes in δ Sct stars is not verysatisfactory. This is attributed to problems in mode identification. Wediscuss unstable modes of high degree in Cepheid models as a possiblemechanism for the low-amplitude radial velocities seen in some starswithin the instability strip. We find, however, that the observedperiods are at least a factor of 2 longer than the calculated periods.Finally, we discuss the possibility of observing modes of high degreephotometrically. We suggest that a large number of high-degree modes maybecome detectable by future space-borne photometric missions. Theconfusion arising from these modes may greatly reduce the value of suchobservations for asteroseismology. However, they will be very importantin studying the mechanism of mode selection.
|Far-Ultraviolet Continuum of G-Type Stars: A Signature of the Temperature Minimum Region|
The main results of a program of systematic comparison between observedand computed UV spectral energy distributions of field G-type stars areillustrated. We constructed the UV observed energy distributions for 53G stars, starting from the IUE Uniform Low Dispersion Archive (ULDA) andcomputed the corresponding theoretical fluxes by using the atmosphericparameters from the Catalogue of [Fe/H] Determinations (1996 edition)and a Kurucz grid of model fluxes. From the comparison betweenobservations and classical models, a UV excess shortward of 2000 Åis evident for all the program stars. The UV continuum in the region1600-2000 Å can be described by synthetic fluxes computed fromsemiempirical models based on the temperature minimum concept. Valuesfor the T_min/T_eff ratio on the order of 0.80 are suitable for theinterpretation of the observed fluxes. The residual discrepanciesshortward of 1600 Å are suggested to be effects of thechromosphere, on the basis of a comparison with the Maltby et al.semiempirical model of the Sun.
|A Precision Velocity Study of Photometrically Stable Stars in the Cepheid Instability Strip|
Results of a precision Doppler velocity survey of 15 stars that lie inor near the Cepheid instability strip are presented. Previous studieshave shown that these stars are photometrically stable. Long-term radialvelocity precision of 15 m s-1 has been achieved with the use of aniodine absorption cell and a high-resolution cross-dispersed echellespectrometer. The stars show a variety of behavior from stability (atthe level of 30 m s-1) to variability from 50 m s-1 to a few km s-1.Periodograms of many of the program stars show significant peaks at50-80 days that are not associated with radial pulsation. Previouslyundetected binary companions have been found around two of the stars.Line profiles are compared to delta Cep.
|BA II lines as luminosity indicators: s-Cepheids and non-variable supergiants|
Ba II line equivalent widths appear to be well correlated with theabsolute magnitudes for yellow supergiants. Two Ba II lines 5853.6Angstroms and 6141.7 Angstroms were applied for investigation of thepossible relation between their equivalent widths and Mv forsmall-amplitude Cepheids and non-variable supergiants.
|The ROSAT all-sky survey catalogue of optically bright late-type giants and supergiants|
We present X-ray data for all late-type (A, F, G, K, M) giants andsupergiants (luminosity classes I to III-IV) listed in the Bright StarCatalogue that have been detected in the ROSAT all-sky survey.Altogether, our catalogue contains 450 entries of X-ray emitting evolvedlate-type stars, which corresponds to an average detection rate of about11.7 percent. The selection of the sample stars, the data analysis, thecriteria for an accepted match between star and X-ray source, and thedetermination of X-ray fluxes are described. Catalogue only available atCDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle|
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
|Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
|A catalogue of [Fe/H] determinations: 1996 edition|
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Determinations of Metal Abundances from ROSAT Observations|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..382B&db_key=AST
|The Comparable Analysis of the Cepheids and Non-Variable Supergiants from the Instability STRIP.I.|
|A uvbyβ photometric calibration of iron abundances in supergiant stars.|
A photometric reddening-free calibration for [Fe/H] valid for giant andsupergiant stars of intermediate temperature, has been obtained usingthe Stroemgren uvbyβ system. Galactic supergiants, supergiants inthe Magellanic Clouds and Galactic metal deficient red giants withspectroscopic determinations of [Fe/H] were used as calibrators. Thecalibration can be used to predict [Fe/H] with an accuracy of 0.33 dex,valid for stars with 0.14<[m_1_]<0.70 in the iron abundance range-2.5<[Fe/H]<+0.3. This shows the potential of supergiant stars astracers of iron abundances in other galaxies. Evidence that Galacticluminous F-G stars are intrinsically bluer than their counterparts inthe Magellanic Clouds is offered.
|Hybrid stars and the reality of "dividing lines" among G to K bright giants and supergiants.|
We present results of pointed ROSAT PSPC observations of 15 hybridstars/candidates, which have been analyzed in a homogenous way. 7 ofthese stars were observed in X-rays for the first time. 12 out of 15hybrid stars have been detected as X-ray sources, some of them close tothe detection limit. We conclude that essentially all hybrid stars asdefined by the simultaneous presence of transition region line emissionand cool stellar winds are X-ray sources if exposed sufficiently deep.The X-ray luminosities of hybrid stars cover a range between 2x10^27^and ~10^30^erg/s. Their X-ray surface fluxes can be as low as =~20erg/cm^2^/s and thus considerably lower than those of normal luminosityclass (LC) III giants. X-ray spectra of hybrid stars tend to be harderthan that of normal LC III giants, moreover, the X-ray brightest starshave the hardest spectra. We find that for K II giants the normalizedX-ray flux versus C IV flux obeys a power law with an exponent a=2.9,steeper than among normal giants (1.5). Hybrid K II stars are X-rayunderluminous by a factor of 5 to 20 compared to LC III giants at thesame level of normalized CIV flux f_CIV_/f_bol_; hybrid G supergiantsare even more X-ray deficient. We reanalyze the CaII wind dividing lineand find it vertical at B-V=1.45 for LC III giants. It is nearlyhorizontal between B-V=1.45 and 1.0 (at M_bol_=~-2...-3), and not welldefined for supergiants with B-V<1.0. We therefore suggest thatpossibly all LC II and Ib G and K giants are hybrid stars and that the"dividing line" concept in its simplest form is not valid for G/K giantsbrighter than M_bol_=~-2. Hybrid stars are supposed to be evolvedintermediate mass stars and their coronal activity may in principle bedetermined by the individual history of each star.
|The RIASS coronathon: Joint X-ray and ultraviolet observations of normal F-K stars|
Between 1990 August and 1991 January the ROSAT/IUE All Sky Survey(RIASS) coordinated pointings by the International Ultraviolet Explorer(IUE) with the continuous X-ray/EUV mapping by the Roentgensatellit(ROSAT). The campaign provided an unprecedented multiwavelength view ofa wide variety of cosmic sources. We report findings for F-K stars, alarge proportion of the RIASS targets. Forty-eight of our 91'Coronathon' candidates were observed by the IUE during the campaign.For stars missed by the IUE, we supplemented the ROSAT survey fluxeswith archival UV spectra and/or follow-on observations.
|Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.|
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
|Radio continuum emission from stars: a catalogue update.|
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
|A CaII and MgII luminosity/emission-width data base.|
The so-called Wilson-Bappu relationship (hereinafter W-B) is anempirical linear relation established in 1957. Formally simple, thisrelation links two observable parameters of a star: the CaII K line coreemission width with the absolute magnitude of the star havingchromospheric activity. Other Luminosity/Emission-width relationshipswere established on the basis of other chromospheric lines like MgII(2795.5A and 2802.7A) and Lyα (1215.9A). All these resonance linesare used as a diagnostic of physical properties of stellarchromospheres. We have reanalysed all the available data connected withthe CaII K and the MgII k line widths in the literature from 1957 untiltoday to be able to prepare a database containing all the essentialinformation needed to study and to understand empirical stellar activityrelationships.
|Spectral classifications in the near infrared of stars with composite spectra. I. The study of MK standards.|
Up to now the spectral classifications of the cool components ofcomposite spectra obtained in the 3800-4800A wavelength region have beenvery disparate. These disparities are due to the fact that the spectraof the evolved cool component are strongly veiled by that of the hotterdwarf component, which makes a classification very difficult. We proposeto study these systems in the near infrared (8380-8780A). In thisspectral domain the magnitude difference between the spectra of thecomponents is in general sufficiently large so that one observespractically only the spectrum of the cool component. In this first paperwe provide, for a sample of MK standards, the relations between theequivalent width (Wlambda_ ) of certain lines and thespectral classifications. For the cool G, K and M type stars, the linesconsidered are those of the calcium triplet (Ca II 8498, 8542 and 8662),of iron (Fe I 8621 and 8688), of titanium (Ti I 8426 and 8435) and ofthe blend λ8468. The use of certain line intensity ratiospermits, after eliminating partially the luminosity effects, a firstapproach to the spectral type. For the hotter stars of types O, B, A andF we study the behavior of the hydrogen lines (P12 and P14), the calciumlines (Ca II 8498 and 8542) as well as those of the oxygen (O I 8446).The latter line presents a very characteristic profile for stars of lowrotation and therefore in Am stars, which are frequently found among thecomposite spectrum binaries. Among the cooler stars of our sample, only6% present real anomalies with respect to the MK classifications. Thisresult is very encouraging for undertaking the classification of asample of composite spectra. The spectra were taken at the Observatoirede Haute-Provence (OHP) with the CARELEC spectrograph at the 193 cmtelescope, with a dispersion of 33 A/mm.
|Calibrations of Mv, (Fe/H), and log G for yellow supergiant stars from O I 7774 and uvby-beta data|
New calibrations of the absolute magnitude Mv from O I 7774data are derived from narrow-band photometry and low dispersionspectroscopy for AO-G2 low and high luminosity stars. The nonlineardependence of Mv from the equivalent width W(OI) and therelevance of the stellar temperature in the calibration are confirmed inagreement with previous calibrations obtained from high resolutionspectroscopy. Also functional formulas to estimate (Fe/H) and log g fromuvby-beta data for FO-G3 supergiants are offered. These calibrationspredict iron abundances and gravities for yellow supergiants withuncertainties not much higher than good spectroscopic determinations.