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Magnetic fields of chemically peculiar stars. I. The catalog of magnetic CP stars
This is the first paper of the series dedicated to the analysis of themagnetism of chemically peculiar (CP) stars of the upper Main Sequence.We use our own measurements and published data to compile a catalog ofmagnetic CP stars containing a total of 326 objects with confidentlydetected magnetic fields and 29 stars which are very likely to possessmagnetic field. We obtained the data on the magnetism of theoverwhelming majority of the stars solely based on the analysis oflongitudinal field component B e . The surface magneticfield, B s , has been measured for 49 objects. Our analysisshows that the number of magnetic CP stars decreases with increasingfield strength in accordance with exponential law, and stars with B e exceeding 5kG occur rarely (about 3% objects of ourlist).
| The primordial binary population. II.. Recovering the binary population for intermediate mass stars in Scorpius OB2
We characterize the binary population in the young and nearby OBassociation Scorpius OB2 (Sco OB2)using available observations of visual, spectroscopic, and astrometricbinaries with intermediate-mass primaries. We take into accountobservational biases by comparing the observations with simulatedobservations of model associations. The available data indicate a largebinary fraction (> 70% with 3σ confidence), with a largeprobability that all intermediate mass stars in ScoOB2 are part of a binary system. The binary systems have amass ratio distribution of the form f_q(q) ∝ qγ_q,with γq ≈ -0.4. Sco OB2 has asemi-major axis distribution of the form f_a(a) ∝aγ_a with γa ≈ -1.0 (Öpik'slaw), in the range 5 {R}_ȯ⪉ a ⪉ 5× 106{R}_ȯ. The log-normal period distribution of Duquennoy & Mayor[1991, A&A, 248, 485] results in too few spectroscopic binaries,even if the model binary fraction is 100%. Sco OB2 isa young association with a low stellar density; its current populationis expected to be very similar to the primordial population. The factthat practically all stars in Sco OB2 are part of abinary (or multiple) system demonstrates that multiplicity is afundamental factor in the star formation process, at least forintermediate mass stars.Appendix A is only available in electronic form at http://www.aanda.org
| Magnetic-field dependence of chemical anomalies in CP stars
The dependence of the degree of anomaly of parameter Z of Genevaphotometry ( Z0 = Z CP ℒ Z norm.) on theaverage surface magnetic field Bs is analyzed. The Z0 value isproportional to the degree of anomaly of chemical composition. It wasfound that Bs → 0 corresponds Z0 → ‑0.010÷‑0.015, i.e., part of CP stars are virtually devoid of magneticfield, but exhibit chemical anomalies. This effect may be due toselection whereby only objects with strong chemical anomalies areclassified as CP stars, thereby producing a deficit of stars withrelatively weak anomalies. Moreover, CP stars have other sources ofstabilization of their atmospheres besides the magnetic field, e.g.,slow rotation. Formulas relating Z0 to Bs are derived.
| Searching for links between magnetic fields and stellar evolution: II. The evolution of magnetic fields as revealed by observations of Ap stars in open clusters and associations
Context: The evolution of magnetic fields in Ap stars during the mainsequence phase is presently mostly unconstrained by observation becauseof the difficulty of assigning accurate ages to known field Ap stars. Aims: We are carrying out a large survey of magnetic fields in clusterAp stars with the goal of obtaining a sample of these stars withwell-determined ages. In this paper we analyse the information availablefrom the survey as it currently stands. Methods: We select from theavailable observational sample the stars that are probably (1) clusteror association members and (2) magnetic Ap stars. For the stars in thissubsample we determine the fundamental parameters T{eff},L/L_ȯ, and M/M_ȯ. With these data and the cluster ages weassign both absolute age and fractional age (the fraction of the mainsequence lifetime completed). For this purpose we have derived newbolometric corrections for Ap stars. Results: Magnetic fields arepresent at the surfaces of Ap stars from the ZAMS to the TAMS.Statistically for the stars with M > 3 M_ȯ the fields declinewith advancing age approximately as expected from flux conservationtogether with increased stellar radius, or perhaps even faster than thisrate, on a time scale of about 3×107 yr. In contrast,lower mass stars show no compelling evidence for field decrease even ona timescale of several times 108 yr. Conclusions: Study ofmagnetic cluster stars is now a powerful tool for obtaining constraintson evolution of Ap stars through the main sequence. Enlarging the sampleof known cluster magnetic stars, and obtaining more precise rms fields,will help to clarify the results obtained so far. Further fieldobservations are in progress.Tables 2 and 3 are only available in electronic form athttp://www.aanda.org
| A brown dwarf desert for intermediate mass stars in Scorpius OB2?
We present JHKS observations of 22 intermediate-mass stars inthe Scorpius-Centaurus OB association, obtained with the NAOS/CONICAsystem at the ESO Very Large Telescope. This survey was performed todetermine the status of (sub)stellar candidate companions of Sco OB2member stars of spectral type A and late-B. The distinction betweencompanions and background stars is made on the basis of a comparison toisochrones and additional statistical arguments. We are sensitive tocompanions with an angular separation of 0.1''-11'' (13-1430 AU) and thedetection limit is K_S=17 mag. We detect 62 stellar components of which18 turn out to be physical companions, 11 candidate companions, and 33background stars. Three of the 18 confirmed companions were previouslyundocumented as such. The companion masses are in the range 0.03{M}_ȯ ≤ M ≤ 1.19 {M}_ȯ, corresponding to mass ratios0.06 ≤ q ≤ 0.55. We include in our sample a subset of 9 targetswith multi-color ADONIS observations from Kouwenhoven et al. (2005,A&A, 430, 137). In the ADONIS survey secondaries with KS< 12 mag were classified as companions; those with KS >12 mag as background stars. The multi-color analysis in this paperdemonstrates that the simple K_S=12 mag criterion correctly classifiesthe secondaries in 80% of the cases. We reanalyse the total sample(i.e. NAOS/CONICA and ADONIS) and conclude that of the 176 secondaries,25 are physical companions, 55 are candidate companions, and 96 arebackground stars. Although we are sensitive (and complete) to browndwarf companions as faint as K_S=14 mag in the semi-major axis range130-520 AU, we detect only one, corresponding to a brown dwarf companionfraction of 0.5 ± 0.5% (M ⪆ 30 {M_J}). However, the number ofbrown dwarfs is consistent with an extrapolation of the (stellar)companion mass distribution into the brown dwarf regime. This indicatesthat the physical mechanism for the formation of brown dwarf companionsaround intermediate mass stars is similar to that of stellar companions,and that the embryo ejection mechanism does not need to be invoked inorder to explain the small number of brown dwarf companions amongintermediate mass stars in the Sco OB2 association.Based on observations collected at the European Southern Observatory,Chile. Program 073.D-0354(A). Appendix A is only available in electronicform at http://www.aanda.org
| The search for the origin of the Local Bubble redivivus
We present a new unbiased search and analysis of all B stars in thesolar neighbourhood (within a volume of 400 pc diameter) using theArivel data base to track down the remains of the OB associations, whichhosted the supernovae (SNe) responsible for the Local Bubble (LB) in theinterstellar gas. We find after careful dereddening and by comparisonwith theoretical isochrones, that besides the Upper Scorpius the UpperCentaurus Lupus and Lower Centaurus Crux subgroups are the youngeststellar associations in the solar neighbourhood with ages of 20-30 Myr,in agreement with previous work. In search for the `smoking gun' of theorigin of the LB, we have traced the paths of the associations back intothe past and found that they entered the present bubble region 10-15 Myrago. We argue that the LB began to form then and estimate that 14-20 SNehave gone off since. It is shown that the implied energy input issufficient to excavate a bubble of the presently observed size.
| Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
| Evolutionary state of magnetic chemically peculiar stars
Context: .The photospheres of about 5-10% of the upper main sequencestars exhibit remarkable chemical anomalies. Many of these chemicallypeculiar (CP) stars have a global magnetic field, the origin of which isstill a matter of debate. Aims: .We present a comprehensivestatistical investigation of the evolution of magnetic CP stars, aimedat providing constraints to the theories that deal with the origin ofthe magnetic field in these stars. Methods: .We have collectedfrom the literature data for 150 magnetic CP stars with accurateHipparcos parallaxes. We have retrieved from the ESO archive 142 FORS1observations of circularly polarized spectra for 100 stars. From thesespectra we have measured the mean longitudinal magnetic field, anddiscovered 48 new magnetic CP stars (five of which belonging to the rareclass of rapidly oscillating Ap stars). We have determined effectivetemperature and luminosity, then mass and position in the H-R diagramfor a final sample of 194 magnetic CP stars. Results: .We foundthat magnetic stars with M > 3 ~M_ȯ are homogeneouslydistributed along the main sequence. Instead, there are statisticalindications that lower mass stars (especially those with M ≤2~M_ȯ) tend to concentrate in the centre of the main sequence band.We show that this inhomogeneous age distribution cannot be attributed tothe effects of random errors and small number statistics. Our datasuggest also that the surface magnetic flux of CP stars increases withstellar age and mass, and correlates with the rotation period. For starswith M > 3~M_ȯ, rotation periods decrease with age in a wayconsistent with the conservation of the angular momentum, while for lessmassive magnetic CP stars an angular momentum loss cannot be ruledout. Conclusions: .The mechanism that originates and sustains themagnetic field in the upper main sequence stars may be different in CPstars of different mass.
| The primordial binary population. I. A near-infrared adaptive optics search for close visual companions to A star members of Scorpius OB2
We present the results of a near-infrared adaptive optics survey withthe aim to detect close companions to Hipparcos members in the threesubgroups of the nearby OB association Sco OB2: Upper Scorpius (US),Upper Centaurus Lupus (UCL) and Lower Centaurus Crux (LCC). We havetargeted 199 A-type and late B-type stars in the KS band, anda subset also in the J and H band. We find 151 stellar components otherthan the target stars. A brightness criterion is used to separate thesecomponents into 77 background stars and 74 candidate physical companionstars. Out of these 74 candidate companions, 41 have not been reportedbefore (14 in US; 13 in UCL; 14 in LCC). The angular separation betweenprimaries and observed companion stars ranges from 0.22'' to 12.4''. Atthe mean distance of Sco OB2 (130 pc) this corresponds to a projectedseparation of 28.6 AU to 1612 AU. Absolute magnitudes are derived forall primaries and observed companions using the parallax andinterstellar extinction for each star individually. For each object wederive the mass from KS, assuming an age of 5 Myr for the USsubgroup, and 20 Myr for the UCL and LCC subgroups. Companion starmasses range from 0.10 Mȯ to 3.0 Mȯ. Themass ratio distribution follows f(q) = q-Γ withΓ=0.33, which excludes random pairing. No close (ρ ≤3.75'') companion stars or background stars are found in the magnituderange 12 mag≤ KS ≤ 14 mag. The lack of stars withthese properties cannot be explained by low-number statistics, and mayimply a lower limit on the companion mass of 0.1Mȯ. Close stellar components with KS >14mag are observed. If these components are very low-mass companion stars,a gap in the companion mass distribution might be present. The smallnumber of close low-mass companion stars could support theembryo-ejection formation scenario for brown dwarfs. Our findings arecompared with and complementary to visual, spectroscopic, andastrometric data on binarity in Sco OB2. We find an overall companionstar fraction of 0.52 in this association. This is a lower limit sincethe data from the observations and from literature are hampered byobservational biases and selection effects. This paper is the first steptoward our goal to derive the primordial binary population in Sco OB2.Full Table 1 is only available in electronic form athttp://www.edpsciences.orgBased on observations collected with the ADONIS instrument at theEuropean Southern Observatory, La Silla, Chile (65.H-0568(A) and67.D-0220(A)).
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe 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/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are 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/404/913
| Astrometric radial velocities. III. Hipparcos measurements of nearby star clusters and associations
Radial motions of stars in nearby moving clusters are determined fromaccurate proper motions and trigonometric parallaxes, without any use ofspectroscopy. Assuming that cluster members share the same velocityvector (apart from a random dispersion), we apply a maximum-likelihoodmethod on astrometric data from Hipparcos to compute radial and spacevelocities (and their dispersions) in the Ursa Major, Hyades, ComaBerenices, Pleiades, and Praesepe clusters, and for theScorpius-Centaurus, alpha Persei, and ``HIP 98321'' associations. Theradial motion of the Hyades cluster is determined to within 0.4 kms-1 (standard error), and that of its individual stars towithin 0.6 km s-1. For other clusters, Hipparcos data yieldastrometric radial velocities with typical accuracies of a few kms-1. A comparison of these astrometric values withspectroscopic radial velocities in the literature shows a good generalagreement and, in the case of the best-determined Hyades cluster, alsopermits searches for subtle astrophysical differences, such as evidencefor enhanced convective blueshifts of F-dwarf spectra, and decreasedgravitational redshifts in giants. Similar comparisons for the ScorpiusOB2 complex indicate some expansion of its associations, albeit slowerthan expected from their ages. As a by-product from the radial-velocitysolutions, kinematically improved parallaxes for individual stars areobtained, enabling Hertzsprung-Russell diagrams with unprecedentedaccuracy in luminosity. For the Hyades (parallax accuracy 0.3 mas), itsmain sequence resembles a thin line, possibly with wiggles in it.Although this main sequence has underpopulated regions at certaincolours (previously suggested to be ``Böhm-Vitense gaps''), suchare not visible for other clusters, and are probably spurious. Futurespace astrometry missions carry a great potential for absoluteradial-velocity determinations, insensitive to the complexities ofstellar spectra. Based on observations by the ESA Hipparcos satellite.Extended versions of Tables \ref{tab1} and \ref{tab2} are available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.125.8) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/446
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| New variable chemically peculiar stars identified in the HIPPARCOS archive
Since variability of chemically peculiar (CP) stars plays an importantrole for the astrophysical explanation of their outstanding behaviour,we have identified new variable CP stars listed in Renson's catalogueusing the extensive Hipparcos Variability Annex. From the 293 objectsfound, 33 were excluded because they are no CP stars and/or have noperiod listed, half of the remaining stars are newly identified and halfhad been already included in the catalogue of variable CP stars by\cite[Catalano & Renson (1997).]{Ca} Most of the newly identifiedvariability is due to an apparent magnetic field coupled with stellarrotation (oblique rotator model). The constraints of this model arefulfilled for all but three CP2 stars. Variations of bona fide Am-Fmstars are exclusively explained by eclipses of binary systems.Furthermore eight candidates of the >~mma Doradus group (pulsatingAm-Fm stars) were detected. Based on data from the ESA Hipparcosastrometry satellite. Table 1 is also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia\break http://cdsweb.u-strasbg.fr/Abstract.html
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable 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
| The Southern Vilnius Photometric System. IV - The E region standard stars
This paper is the fourth in a series on the extension of the Vilniusphotometric system to the Southern Hemisphere. Observations were made of60 stars in the Harvard Standard E regions to increase a set of standardstars.
| Radial velocities and axial rotation for a sample of chemically peculiar stars.
As part of a systematic project we have determined radial velocities andprojected rotational velocities for a sample of 186 chemically peculiarstars which have been observed by the Hipparcos' satellite. The purposeis to provide necessary data to study the space velocities of peculiarstars.
| 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.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
| Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| The evolution of the magnetic fields of AP stars - Magnetic observations of stars in the Scorpius-Centaurus association
Data concerning the positions, photometry, proper motions, and radialvelocities have been compiled for a sample of Ap and Bp stars toward theScorpius-Centaurus association. Probable members of the association areidentified, and new magnetic observations of 13 of these member Ap starsin the mass range 2.5-4.5 solar masses are presented. These magneticobservations are compared with similar data for a sample of old field Apstars. No evidence is found for a significant difference between thedistributions of magnetic field strengths of the two samples, suggestingthat little or no evolution of the magnetic fields in Ap stars occurs ona time scale of a few x 10 to the 8th yr.
| Secondary standards for the Stromgren UVBY system
Observations of 158 E region stars have been made in the Stromgrensystem, using the 46-cm reflector at Cape Town. They are mostly brighterthan eighth magnitude and are intended for use as secondary standardsfor the four-color system. The E region relative zero points are definedwith a precision of + or - 0.001 mag, and the internal standard errorsof the colors life between + or - 0.001 and + or - 0.002 mag.
| Photometric standard stars for the UBV and (RI)KC systems.
Not Available
| Spectral classification from the ultraviolet line features of S2/68 spectra. III - Early A-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33...15C&db_key=AST
| VRI standards in the E regions
Not Available
| Standard Stars for VRI Photometry with S25 Response Photocathodes [Errata: 1974MNSSA..33....1C]
Not Available
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