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Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| On the elemental abundance and isotopic mixture of mercury in HgMn stars
Optical region spectra of 31 HgMn stars have been studied for theabundance and isotope mixture of mercury. In the course of theinvestigation the lines Hg I lambda 4358 and Hg Ii lambda lambda3984,6149 have been studied, with abundances established for all threelines in several HgMn stars. The mercury isotope mixture has beendetermined from high resolution spectra of the lambda 3984 line.Possible signs of an ionization anomaly have been detected by thecomparison of the abundance derived from the Hg I line and the Hg Iilines in seven of the observed HgMn stars. A possible correlation of themercury abundance with Teff has been detected. Possible signsof a weak anticorrelation of the manganese and mercury abundance in HgMnstars have been found, which could be interpreted as a sign ofinhomogeneous surface distribution of these elements. For a number ofthe HgMn stars in this study the mercury abundance and isotope mixtureare reported for the first time.
| 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
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| 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
| 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 (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Manganese abundances in mercury-manganese stars
We use exact curve-of-growth analysis and spectral synthesis to deducethe abundance of Mn from high signal-to-noise ratio visible-regionechelle spectra of selected Mn i and MnII lines in 24 HgMn stars. Theresults are compared with the Mn abundances derived from UV resonancelines by Smith & Dworetsky. We find excellent agreement for severalunblended Mn lines and confirm the temperature dependence of the Mnabundance found by Smith & Dworetsky. The MnII lines at lambdalambda 4206 and 4326 are much stronger than one would predict from themean Mn abundances. The lack of agreement is greatest for stars with thestrongest MnII lines. Using ad hoc multicomponent fits to the profilesof sharp-lined stars, we show that most of the discrepancies can beexplained by hyperfine structure that desaturates the lines, with fullwidths of the order of 0.06-0.09 A.
| 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.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Orbital elements of binary systems with a chemically peculiar star
When binary systems with a chemically peculiar (CP) star are comparedwith normal-star binary systems, they present: a lower incidence, adeficiency of short periods, rather eccentric orbits, and companions oflow mass. Unfortunately these results are based on a relatively small (~ 50) number of CP-star binary systems with known orbital parameters anda similar analysis has not yet been carried out for helium-peculiarstars, as there is only one helium-weak star with known orbitalelements. With the aim to contribute to the study of binary systemswhose brightest component is a CP star, we have performed spectroscopicobservations and determined the orbital elements for seven of thesesystems. Of these we have included two helium-weak and two helium-strongstars. The values found for the orbital elements confirm the deficiencyof short periods and the lack of circular orbits for CP stars: only HD15144 has an orbital period shorter than 3 days (the orbital perioddistribution of normal stars peaks at 3 days) and a circular orbit. Asto helium-peculiar stars, we have determined orbital periods longer than12 days and large eccentricity values (0.26-0.40). As O-A star binarysystems have circular orbits only when their orbital periods are lessthan two days, we conclude that CP-star binary systems are characterisedonly by long orbital periods with respect to normal stars. Probably asmall component separation and/or a massive companion, which areassociated with short orbital periods, is responsible for such a strongatmospheric mass motion on the stellar surface to prevent the elementseparation which is at the basis of the CP star phenomenon. Theamplitude of the radial velocity curve of the helium-strong star HD36485 is only 8 km s(-1) , one of the smallest known values for a CPstar, which appears to be consistent with the small ( ~ 10(deg) )inclination of the rotational axis. Partially based on observationscollected at the European Southern Observatory, LaSilla Chile.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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 (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra V. Mercury.
Atmospheric mercury abundances are derived for a sample of 40main-sequence, late-B stars, of which 14 are classified normal, and 26are known chemically peculiar stars of HgMn or related He-weak types.The observational material for this study comprises co-added,short-wavelength IUE spectra encompassing the HgII λ1942resonance line, coupled with a selection of new and publishedmeasurements (equivalent widths and centroid wavelengths) of the opticalHgII λ3984 and HgI λ4358 lines. The analysis includes anexplicit treatment of the isotopic and hyperfine structure of theselines, and allows for star-to-star variations in the isotopiccomposition of mercury within the framework of an assumed,mass-dependent fractionation model. The relative isotopic abundances ofmercury (as defined by a dimensionless mix parameter, q) are determinedusing the graphical method pioneered by White et al. In agreement withprevious studies, q is found to be strongly anti-correlated witheffective temperature, in the sense that the coolest stars are dominatedby the heaviest isotopes (e.g., ^202^Hg and ^204^Hg). New isotopic-mixparameters for three programme stars - 87 Psc (q=0.3), 28 Her (q=2.8),and HR 7775 (q=1.5) - reinforce that anti-correlation. Syntheticreconstruction of the λ3984 line in those programme stars forwhich high-resolution spectra are available tends to confirm theisotopic mixtures derived using the graphical method, and lends validityto the mass-dependent fractionation model in general. However, theλ3984 feature observed in the cool HgMn star HR 7775 can only besatisfactorily reproduced by using a tailored isotopic mixture, whichdeparts significantly from that predicted by the q-formalism. Theλ1942 resonance line is detected in 10 normal B stars, for whichthe mean isotope-summed mercury abundance of 1.96+/-0.34dex (on thescale where logN(H)=12) exceeds the meteoritic value by nearly 3σ.The mercury abundances derived for the HgMn stars vary between ~5 and7dex, except for two objects (53 Tau and HR 2676) in which theabundances are consistent with those observed in the normal stars. TheHe-weak stars in the programme (33 Gem, HR 6000, 36 Lyn, and 46 Aql)appear to be mildly enriched in mercury, but to an extent rendereduncertain by unknown isotopic-mix parameters. The abundances obtainedfrom the optical and ultraviolet lines agree to within their estimatederrors, which lends weight to the view that the metastable lower levelof λ3984 (5d^9^6s^2^^2^D_5/2_) is not overpopulated with respectto its LTE value. The isotope-summed mercury abundances are notcorrelated with the effective temperatures, surface gravities, or degreeof isotopic fractionation of the programme stars; nor is there evidencefor systematic changes in the surface mercury abundances of HgMn starsalong evolutionary tracks in the H-R diagram.
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. IV. Gallium.
An analysis is presented of the ultraviolet gallium resonance lines inInternational Ultraviolet Explorer (IUE) spectra of 40 normal,superficially normal, and HgMn-type late-B stars. Gallium abundances arederived by fitting the GaIIλ1414, and GaIIIλλ1495,1534 lines with synthetic spectra computed under the conventionalassumptions of local thermodynamic equilibrium (LTE) and atmosphericchemical homogeneity. We find that the derived upper limits on thegallium abundances of the normal and superficially normal stars areconsistent with the solar value. However, gallium is overabundant inessentially all HgMn stars, including the cooler examples such as HR4072, χ Lup, and ι CrB, where the enhancements are relativelymoderate and unambiguous identification of the resonance lines dependscritically on newly available laboratory wavelengths. Furthermore, thegallium overabundances in the HgMn stars exhibit a loose correlationwith effective temperature, similar in most respects to those identifiedfor manganese and copper in the same stars except for the presence ofthe anomalously Ga-rich, cool HgMn star HR 7775. We show that asystematic discrepancy between the abundances derived from the Ga^+^ andGa^2+^ ions in the hotter HgMn stars (T_eff_>12000K) can be explainedby radiative transfer effects in the presence of a stratification ofgallium at optical depths above logτ_0_=~0. This `stratificationmodel' can also account for the anomalously shaped Gaiii λ1495profiles observed in the extreme cases of μ Lep, HR 2844, and HR 7143(as demonstrated in a previous paper), and is consistent with publishedpredictions of radiative diffusion theory for non-magnetic stars.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| 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.
| The position corrections of 1400 stars observed with PA II in San Juan.
Not Available
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. 3: Copper and zinc
Atmospheric abundances of copper and zinc are derived for a sample of 40normal, superficially normal, and HgMn-type main-sequence late-B starsby local thermodynamic equilibrium (LTE) spectrum-synthesis analysis ofco-added high-resolution International Ultraviolet Explorer (IUE)spectra. In the normal and superficially normal stars, the abundances ofthese elements are generally consistent with their solar values, towithin the limits of observational and analytical error. In most (butnot all) HgMn stars, copper is found to be overabundant and, moreover,exhibits a pronounced positive correlation with effective temperaturesimilar to that seen for manganese. Zinc is typically deficient in theHgMn stars with underabundances of 2 dex or more in many cases, althoughit is apparently overabundant in three program stars and present atessentially solar abundance in three others. There appears to be nocharacteristic distinguishing those HgMn stars which are zinc-rich orzinc-normal from those that are zinc-deficient. These results providefurther evidence for the existence of a sub-group of hot, mild HgMnstars characterized, in the context of this work, by relatively moderateoverabundances of copper when compared with other 'genuine' HgMn starsof similar effective temperature. While the copper abundance correlationwith effective temperature would appear to be a possible signature ofradiative diffusion in the atmospheres of HgMn stars, the inexplicablydichotomous behavior of zinc in the same objects could prove difficultto reconcile with existing parameter-free models of this mechanism.
| Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part Two - Magnesium Aluminium and Silicon
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...276..393S&db_key=AST
| Elemental Abundances in Normal Late B-Stars and Hgmn-Stars from Co-Added IUE Spectra - Part One - Iron Peak Elements
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..335S&db_key=AST
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| Physical data of the fundamental stars.
Not Available
| Carbon and nitrogen in B2 to A2 main-sequence stars
Carbon abundances are derived from the C II resonance doublet at 1335 Ain 108 main-sequence stars between 9000 and 21000 K from IUE archivaldata. Only alpha Leo and psi sq 2 Aqr are strongly carbon deficient(factors 14 and 50, resp.). The N I lines at 1493 and 1495 A weremeasured in 28 sharp-lined stars below 16500 K. Nitrogen anomalies arefound in 5 stars, but seem uncorrelated to the C abundances. Fourmechanisms for the depletion of carbon are discussed, but none issatisfactory.
| Observed and computed spectral flux distribution of non-supergiant O9-G8 stars. III - Determination of T(eff) for the stars in the Breger Catalogue
The effective temperatures and angular diameters of nonsupergiant O9-G8stars are determined from visible spectrophotometry. The results, whichrefer to 302 stars included in the Breger Catalogue, are derived fromthe comparison between the observed flux distributions and thepredictions of Kurucz's models (1979). The uncertainties to be expectedin individual results are discussed; their sizes are of the order of 5percent in effective temperature and 10 percent in angular diameter.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
| Four-colour photometry of B stars north of B = + 45 deg and comparison with the south
Four-color photometry of 33 Henry Draper B stars north of b = + 45 degis presented. Most are little-reddened B or intermediate-A stars. A newAm star is discovered. The new measures essentially complete uvbyphotometry of all HD B stars within 45 deg of either galactic pole. Thenorthern and southern cones of HD B stars are compared, and selectioneffects deduced. Far from the galactic plane, it appears that B starsmay be equally distributed north and south of the plane; closer to thesun, an asymmetry associated with Gould's Belt is evident.
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