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Asteroseismology of the β Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification
We report a multisite photometric campaign for the β Cephei star 12Lacertae. 750 h of high-quality differential photoelectricStrömgren, Johnson and Geneva time-series photometry were obtainedwith nine telescopes during 190 nights. Our frequency analysis resultsin the detection of 23 sinusoidal signals in the light curves. Ten ofthose correspond to independent pulsation modes, and the remainder arecombination frequencies. We find some slow aperiodic variability such asthat seemingly present in several β Cephei stars. We perform modeidentification from our colour photometry, derive the spherical degree lfor the five strongest modes unambiguously and provide constraints on lfor the weaker modes. We find a mixture of modes of 0 <=l<= 4. Inparticular, we prove that the previously suspected rotationally splittriplet within the modes of 12 Lac consists of modes of different ltheir equal frequency splitting must thus be accidental.One of the periodic signals we detected in the light curves is argued tobe a linearly stable mode excited to visible amplitude by non-linearmode coupling via a 2:1 resonance. We also find a low-frequency signalin the light variations whose physical nature is unclear; it could be aparent or daughter mode resonantly coupled. The remaining combinationfrequencies are consistent with simple light-curve distortions.The range of excited pulsation frequencies of 12 Lac may be sufficientlylarge that it cannot be reproduced by standard models. We suspect thatthe star has a larger metal abundance in the pulsational driving zone, ahypothesis also capable of explaining the presence of β Cepheistars in the Large Magellanic Cloud.
| 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.
| 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.
| λ Bootis stars with composite spectra
We examine the large sample of λ Boo candidates collected inTable 1 of Gerbaldi et al. (\cite{Gerbaldi2003}) to see how many of themshow composite spectra. Of the 132 λ Boo candidates we identify22 which definitely show composite spectra and 15 more for which thereare good reasons to suspect a composite spectrum. The percentage ofλ Boo candidates with composite spectra is therefore >17% andpossibly considerably higher. For such stars the λ Booclassification should be reconsidered taking into account the fact thattheir spectra are composite. We argue that some of the underabundancesreported in the literature may simply be the result of the failure toconsider the composite nature of the spectra. This leads to thelegitimate suspicion that some, if not all, the λ Boo candidatesare not chemically peculiar at all. A thorough analysis of even a singleone of the λ Boo candidates with composite spectra, in which thecomposite nature of the spectrum is duly considered, which woulddemonstrate that the chemical peculiarities persist, would clear thedoubt we presently have that the stars with composite spectra may not beλ Boo stars at all.Based on observations collected at ESO (Echelec spectrograph) and at TBL(Telescope Bernard Lyot) of the Pic du Midi Observatory (France).
| Far-Ultraviolet Observations of the Circumstellar Gas in the 2 Andromedae System
The A5 star β Pictoris is a possible young planetary system and hasthe best-studied circumstellar disk. Our visible and ultravioletobservations of 2 Andromedae indicated that this A3 star has βPictoris-like gas infall. We present the far-ultraviolet spectrum(905-1195 Å) of 2 And we obtained with the NASA-CNES-CSA FarUltraviolet Spectroscopic Explorer (FUSE). Unlike β Pic, 2 And'sFUSE spectrum does not show strong chromospheric emission lines from CIII and O VI. However, 2 And's FUSE spectrum contains manynonphotospheric lines that allow us to probe the circumstellar gas. Forexample, between 1120 and 1140 Å, we detected several Fe IIIabsorption lines arising from hyperfine levels of ground state, whichcannot be formed in the interstellar medium. These lines are gooddiagnostics of the circumstellar gas. We also detected circumstellar FeII, Cr III, Mn III, and O I (1D) lines. The simultaneouspresence of these species suggests that the circumstellar environment of2 And could include regions with different temperatures and densities.
| The heterogeneous class of lambda Bootis stars
We demonstrate that it is arduous to define the lambda Boo stars as aclass of objects exhibiting uniform abundance peculiarities which wouldbe generated by a mechanism altering the structure of their atmosphericlayers. We collected the stars classified as lambda Boo up to now anddiscuss their properties, in particular the important percentage ofconfirmed binaries producing composite spectra (including our adaptiveoptics observations) and of misclassified objects. The unexplained RVvariables (and thus suspected binaries), the known SB for which we lackinformation on the companion, the stars with an UV flux inconsistentwith their classification, and the fast rotating stars for which noaccurate abundance analysis can be performed, are also reviewed.Partly based on observations collected at the CFH Telescope (Hawaii) andat TBL of the Pic du Midi Observatory (France).Table \ref{tab5} is only available in electronic form athttp://www.edpsciences.org
| Kinematics of Hipparcos Visual Binaries. II. Stars with Ground-Based Orbital Solutions
This paper continues kinematical investigations of the Hipparcos visualbinaries with known orbits. A sample, consisting of 804 binary systemswith orbital elements determined from ground-based observations, isselected. The mean relative error of their parallaxes is about 12% andthe mean relative error of proper motions is about 4%. However, even 41%of the sample stars lack radial velocity measurements. The computedGalactic velocity components and other kinematical parameters are usedto divide the stars with known radial velocities into kinematical agegroups. The majority (92%) of binaries from the sample are thin diskstars, 7.6% have thick disk kinematics and only two binaries have halokinematics. Among them, the long-period variable Mira Ceti has a verydiscordant {Hipparcos} and ground-based parallax values. From the wholesample, 60 stars are ascribed to the thick disk and halo population.There is an urgent need to increase the number of the identified halobinaries with known orbits and substantially improve the situation withradial velocity data for stars with known orbits.
| Far-Ultraviolet Observations of the Circumstellar Gas in the 2 Andromedae System
The A5 star β Pictoris is a possible young planetary system withthe best-studied circumstellar disk. Our visible and ultravioletobservations of 2 Andromedae indicated that this A3 star has ``βPictoris-like'' gas infall. We present the far-ultraviolet spectrum (905-- 1195 Å)\ of 2 And we obtained with the NASA-CNES-CSA FarUltraviolet Spectroscopic Explorer (FUSE). Unlike β Pic, 2 And'sFUSE spectum does not show strong chromospheric emission lines fromC 3 and O 6. However, 2 And's FUSE spectrum contains manynon-photospheric lines that allow us to probe the circumstellar gas. Forexample, between 1120 and 1140 Å,\ we detected several Fe 3absorption lines arising from hyper-fine levels of ground state, whichcannot arise in the interstellar medium and can be used as diagnosticsof the circumstellar gas. We also detected circumstellar Fe 2,Cr 3, and Mn 3 lines that are sufficiently strong to allowcircumstellar gas velocity determinations.
| 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
| 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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
| ICCD Speckle Observations of Binary Stars. XXIII. Measurements during 1982-1997 from Six Telescopes, with 14 New Orbits
We present 2017 observations of 1286 binary stars, observed by means ofspeckle interferometry using six telescopes over a 15 year period from1982 April to 1997 June. These measurements constitute the 23dinstallment in CHARA's speckle program at 2 to 4 m class telescopes andinclude the second major collection of measurements from the MountWilson 100 inch (2.5 m) Hooker Telescope. Orbital elements are alsopresented for 14 systems, seven of which have had no previouslypublished orbital analyses.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| The long-term behaviour of the pulsation periods and amplitudes of the β Cephei star 16 (EN) Lacertae
The blue-light observations of this pulsating and eclipsing variable(BCEP+EA) cover an interval from 1950 to 1992. The out-of-eclipse (thatis, pulsational) variation contains three sinusoidal terms with variableamplitudes. In our 1996 paper (JP96), based on the 1950-1983 data, weshowed that for the first two terms, having frequencies equal to about5.9112 and 5.8551d-1, the amplitudes varied with time-scalesof the order of 50yr. The remaining term formed a doublet with constantamplitudes and frequencies close to 5.5033d-1, resulting in abeat-period of 1.85yr. In the present paper we confirm this pictureusing additional data, derive improved values of the time-scales andrefine the parameters of the doublet. In addition, we determine theyear-to-year variation of the epochs of maximum light of the first twoterms. This allows us to account for (1) the ground-based blue-filterobservations that were not extensive enough to be used in the analysis,and (2) the Hp magnitudes from the Hipparcos mission. In particular, wedemonstrate that the period of 0.171203d, given in the HipparcosVariability Annex, is spurious.
| Photometric Measurements of the Fields of More than 700 Nearby Stars
In preparation for optical/IR interferometric searches for substellarcompanions of nearby stars, we undertook to characterize the fields ofall nearby stars visible from the Northern Hemisphere to determinesuitable companions for interferometric phase referencing. Because theKeck Interferometer in particular will be able to phase-reference oncompanions within the isoplanatic patch (30") to about 17th magnitude atK, we took images at V, r, and i that were deep enough to determine iffield stars were present to this magnitude around nearby stars using aspot-coated CCD. We report on 733 fields containing 10,629 measurementsin up to three filters (Gunn i, r and Johnson V) of nearby stars down toabout 13th magnitude at V.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| New lambda Bootis stars with a shell
We publish here the second part of our spectroscopic survey at highdispersion of some known and suspected lambda Bootis stars with a viewto detecting circumstellar shell features. Eight stars of our sampleexhibit such features. These stars are fast rotators, a result which isin line with Hohlweger and Rentzsch-Holm's study (1995). The analysis ofthe photometric data has allowed us to confirm the exclusion of a fewstars misclassified from the lambda Bootis group.
| Beta Pic-like circumstellar disk gas surrounding HR 10 and HD 85905
We present high spectral resolution observations of the absorption linesof Ca II and Na I associated with the circumstellar gas disk surroundingthe two A-type shell stars HR 10 and HD85905. Data taken over two four-night periods in January andNovember 1997 reveal substantial changes in the circumstellar absorptionline profiles between successive observations of both stars. Suchvariable features have both blue and red-shifted velocities up to 50 kms(-1) away from the central absorbing component, and are similar tothose routinely observed in the beta Pictoris system. The sporadicpresence of the circumstellar absorption components observed towardsboth HR 10 and HD 85905 may be explained by the infalling evaporatingcomet model developed for the beta Pictoris system by Beust {et al./}(\cite{beust90}). We note that variable circumstellar absorptionfeatures have also been detected in rapidly rotating A-type stars, suchthat they may be suffering irregular mass-loss that could give rise tosimilar circumstellar disks and shells.
| Rotation modulation or/and pulsation in O Andromedae. I. The photometric results of an international multisite multitechnique campaign
We present the photometry of a month-long international campaign on thevariable Be star o Andromedae. Excellent time coverage and photometricprecision permit a critical comparison for the first time between thepulsational and the rotational modulation hypotheses. A multiperiodicanalysis of data taken many years apart shows sets of close frequencies.The amplitude ratio between the ultraviolet and visible variations iswhat is expected for early-type star pulsation. But, the total amplitudeand the order of importance of the frequencies is very different betweenobservation campaigns. A simple double wave periodic curve accounts formost of the light variation: a rotation/modulation model is considered,with activity variations in or just above the photosphere. Any modelmust explain the observed changes in the amplitudes of the frequencecorresponding to the period and its first harmonic. A very simple modelwith two stable photospheric activity "features" is insufficient toexplain the small variations observed around the mean values of theperiod and its light amplitude. Thus we propose that the photosphere,which is very probably oblate and seen almost equator-on, is dividedinto zonal bands undergoing differential rotation.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Detection of beta Pictoris--like Gaseous Infall in 2 Andromedae
Ultraviolet observations of 2 Andromedae with the Goddard HighResolution Spectrograph on board the Hubble Space Telescope (HST)clearly reveal the existence of circumstellar gas, in addition topreviously known anomalous interstellar features, in the line of sighttoward this nearby star. We also detect varying, redshifted Ca IIabsorptions, which we interpret as gaseous infalls. These variable Ca IIabsorption features and the presence of circumstellar absorptions fromAl III lambda lambda 1854.716 and 1862.790 and from excitedfine-structure levels of Fe II near 2600 Angstroms seen in 2 And aresimilar to those observed in spectra of beta Pic.
| ICCD Speckle Observations of Binary Stars. XVII. Measurements During 1993-1995 From the Mount Wilson 2.5-M Telescope.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1639H&db_key=AST
| ICCD Speckle Observations of Binary Stars. XVI. Measurements During 1982-1989 from the Perkins 1.8-M Telescope.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1623F&db_key=AST
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| A consolidated catalogue of lambda Bootis stars
lambda Bootis stars challenge our understanding of diffusion andaccretion processes related to stars and their circumstellarenvironment, and they are interesting components of the classicalinstability strip. Attempts to derive group properties with statisticalmethods are severely limited by the small number of unambiguouslyidentified lambda Bootis stars. In general, the subject appears to beobscured by incorrect memberships and it is therefore essential toprovide a sufficiently large catalogue of definitive group membersbefore modeling the lambda Bootis phenomenon. This paper describes thefirst steps towards this goal, based on our current knowledge of wellinvestigated members, leading to a concise definition of lambda Bootisstars: {Pop I hydrogen burning metal poor (except of C,N,O and S) A-typestars.} The definition does not depend on phenomenological features,like flux depressions, colour excesses, v sin i values, etc. Based on anew homogeneous catalogue with 45 lambda Bootis stars, we discussclassification criteria which can be used for a spectroscopic andphotometric all-sky survey for lambda Bootis stars in the field and inclusters of different ages. Based on observations obtained atESO-La,Silla, CTIO, Observatoire de Haute-Provence, OsservatorioAstronomico di Padua-Asiago, Univ. Toronto Southern Observatory,Observatorio do Pico dos Dias-LNA/CNPq/MCT (Brazil). Table 1 is alsoavailable 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.
| Properties and nature of Be stars. 17. V360 Lac = HD 216200 is a B3e + F9IV: binary.
An analysis of an extensive collection of photometric and spectroscopicobservations of the little studied bright Be star V360 Lac lead to thefollowing main conclusions: (1) V360 Lac is a binary system consistingof a B3e primary and a F9IV secondary which probably fills the Rochelobe and losses mass towards the primary. Radial-velocity curves of bothcomponents were obtained. (2) The light variations arise fromsuperposition of variations on at least three time scales: phase-lockedorbital brightness and colour changes with two minima; sinusoidalvariation with a 322.24^d^ period and low-amplitude rapid changes with apossible period of 1.6738^d^. (3) A tentative solution of the B and Vlight curves which assumes the semi-detached configuration and presenceof a disk around the primary, combined with the orbital solution, leadsto preliminary basic physical elements of the system which areconsistent with the radiative properties of the binary components.
| Amplitude monitoring of the β Cephei star 16 Lacertae.
Based on new observations, it is shown here that the amplitude of one ofthe three well known and stable short periods in the β Cep variable16 Lac has changed: while the radial mode P_1_=0.16917d is near itslower amplitude level and the amplitude variation of the non-radial modeP_3_=0.18173d is still probably in phase with the orbital period, theamplitude of the NR mode P_2_=0.17077d has increased progressively by afactor two in the last ten years. The observed phase of P_2_ shows thatat least for this period, the previous ephemeris is no longer valid.Various hypotheses are proposed to account for the observed amplitudesvariations.
| A High-Resolution Survey of Interstellar Ca II Absorption
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..533W&db_key=AST
| Detection of Accreting, Circumstellar Gas in a lambda Bootis Star: 131 Tauri
We present IUE high-dispersion spectra of the lambda Boo star, 131 Tau(HD 38545), confirming the presence of shell spectral features and alsoproviding the first detection of accreting, circumstellar gas in thespectrum of a lambda Boo star. Accreting gas can be followed in themid-UV Fe II transitions to +80 km s-1 relative to the star.Circumstellar material can be followed to +60 km s-1 relative to thestar in Zn II and is detected, albeit with low S/N, in Si II, Al II, andC I. The IUE data for 131 Tau were compared with archival spectra ofother lambda Boo stars with optical detections of narrow absorptionfeatures, which have previously been interpreted as signatures ofcircumstellar gas. We find that the circumstellar absorption in 131 Taumore closely resembles similar features that are routinely observed inbeta Pic and recently detected in other field A-shell stars.
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