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An Atlas of K-Line Spectra for Cool Magnetic CP Stars: The Wing-Nib Anomaly (WNA)
We present a short atlas illustrating the unusual Ca II K-line profilesin upper main-sequence stars with anomalous abundances. Slopes of theprofiles for 10 cool, magnetic chemically peculiar (CP) stars changeabruptly at the very core, forming a deep ``nib.'' The nibs show thesame or nearly the same radial velocity as the other atomic lines. Thenear wings are generally more shallow than in normal stars. In threemagnetic CP stars, the K lines are too weak to show this shape, althoughthe nibs themselves are arguably present. The Ca II H lines also showdeep nibs, but the profiles are complicated by the nearby, strongHɛ absorption. The K-line structure is nearly unchanged withphase in β CrB and α Cir. Calculations, including NLTE, showthat other possibilities in addition to chemical stratification mayyield niblike cores.
| Winds from OB Stars: A Two-Component Scenario?
X-ray spectroscopy of several OB stars with massive winds has revealedthat many X-ray line profiles exhibit unexpectedly small blueshifts andare almost symmetric. Moreover, the hottest X-ray lines appear tooriginate closest to the star. These properties appear to beinconsistent with the standard model of X-rays originating in shockedmaterial in line-driven spherically symmetric winds. Here we raise thequestion, can the X-ray line data be understood in terms of atwo-component wind? We consider a scenario in which one component of thewind is a standard line-driven wind that emerges from a broad range oflatitudes centered on the equator. The second component of the windemerges from magnetically active regions in extensive polar caps. Theexistence of such polar caps is suggested by a recent model of dynamoaction in massive stars. We describe how the two-component model isconsistent with a variety of observational properties of OB star winds.
| Spectropolarimetry of the Classical T Tauri Star T Tauri
High-resolution (R~60,000) circular spectropolarimetry of the classicalT Tauri star T Tau is presented. The star was observed on 1997 November21 and 22. Analyzing 12 photospheric absorption lines, the meanlongitudinal magnetic field is found to be Bz=12+/-35 G. The3 σ upper limit of |Bz|<=105 G. Previously, T Tauwas reported to have a mean longitudinal field of 160+/-40 G. A strongmean magnetic field (~2.4 kG) has been reported on the surface of T Taubased on Zeeman broadening measurements in unpolarized light. Thepresent observations indicate that it is very unlikely that this fieldis dipolar in nature. In order to verify the observing techniques andanalysis methods used on T Tau, spectra of the Sun obtained by observingthe asteroid Vesta are analyzed in the same fashion. Here the meanlongitudinal field is Bz=-4+/-3 G, which is well within thelimits of previous observations. As a further check on our results, wealso present data for the magnetic Ap star 53 Cam, which gives a meanlongitudinal magnetic field that agrees well with the published fieldvariations for this star.
| T Tauri stellar magnetic fields: HeI measurements
We present measurements of the longitudinal magnetic field in thecircumstellar environment of seven classical T Tauri stars. Themeasurements are based on high-resolution circular spectropolarimetry ofthe HeIλ5876 emission line, which is thought to form in accretionstreams controlled by a stellar magnetosphere. We detect magnetic fieldsin BP Tau, DF Tau and DN Tau, and detect statistically significantfields in GM Aur and RW Aur A at one epoch but not at others. We detectno field for DG Tau and GG Tau, with the caveat that these objects wereobserved at one epoch only. Our measurements for BP Tau and DF Tau areconsistent, in terms of both sign and magnitude, with previous studies,suggesting that the characteristics of T Tauri magnetospheres arepersistent over several years. We observed the magnetic field of BP Tauto decline monotonically over three nights, and have detected a peakfield of 4 kG in this object, the highest magnetic field yet observed ina T Tauri star. We combine our observations with results from theliterature in order to perform a statistical analysis of themagnetospheric fields in BP Tau and DF Tau. Assuming a dipolar field, wedetermine a polar field of ~3 kG and a dipole offset of 40° for BPTau, while the field of DF Tau is consistent with a polar field of ~-4.5kG and a dipole offset of 10°. We conclude that many classical TTauri stars have circumstellar magnetic fields that are both strongenough and sufficiently globally ordered to sustain large-scalemagnetospheric accretion flows.
| Magnetic field models for HD 116458 and HD 126515
We have modeled the magnetic fields of the slowly rotating stars HD116458 and HD 126515 using the “magnetic charge” technique.HD 116458 has a small angle between its rotation axis and dipole axis(β = 12°), whereas this angle is large for HD 126515 (β =86°). Both stars can be described with a decentered-dipole model,with the respective displacements being r = 0.07 and r = 0.24 in unitsof the stellar radius. The decentered-dipole model is able tosatisfactorily explain the phase relations for the effective field, Be(P), and the mean surface field, B s(P), for both stars, along with thefact that the B e(P) phase relation for HD 126515 is anharmonic. Wediscuss the role of systematic measurement errors possibly resultingfrom instrumental or methodical effects in one or both of the phaserelations. The displacement of the dipole probably reflects realasymmetry of the stellar field structure, and is not due to measurementerrors. Using both phase relations, B e(P) and B s(P), in the modelingconsiderably reduces the influence of the nonuniform distribution ofchemical elements on the stellar surface.
| 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.
| Model of the Magnetic Field of HD 187474
A model is constructed for the magnetic field of the star HD 187474,which has a very long axial rotation period P = 2345d. It turns out thatthe structure of the magnetic field is best described by a model of adisplaced (Δα = 0.1) dipole inclined to the axis of rotationby an angle β = 24°. The star is inclined to the line of sightby an angle i = 86°. Because of the displaced dipole the magnitudeof the magnetic field differs at the poles: Bp = +6300 and 11600 G. AMercator map of the distribution of the magnetic field over the surfaceis obtained. The 7 slowly rotating CP stars studied thus far have anaverage angle β = 62°, which equals the average value for arandom orientation of dipoles.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| NLTE ionization equilibrium of Nd II and Nd III in cool A and Ap stars
We investigate the formation of Nd ii- iii lines in the atmospheres ofA-type stars with a comprehensive atomic model including 1651 levels ofNd ii, 607 levels of Nd iii and the ground state of Nd iv. NLTE leads tooverionization of Nd ii which weakens the Nd ii lines relative to thecorresponding LTE line strengths at mild neodymium overabundance ([Nd/H]< 2.5) and amplifies them at higher [Nd/H] values. NLTE abundancecorrections grow with the effective temperature and reach 0.6 dex atT_eff = 9500 K for [Nd/H] = 2.5. The Nd iii lines are strengthenedcompared with LTE in all cases, and NLTE abundance corrections liebetween -0.3 dex and -0.2 dex for T_eff between 7500 K and 9500 K. NLTEeffects are larger for an inhomogeneous vertical abundance distributioncompared with a homogeneous one resulting in positive NLTE abundancecorrection up to 1.3 dex for the Nd ii lines and in negative ones downto -0.5 dex for the Nd iii lines. The neodymium distribution in theatmospheres of roAp stars γ Equ and HD 24712 is deduced from NLTEanalysis of the Nd ii and Nd iii lines and a strong evidence is foundfor the existence of enhanced Nd abundance layers abovelogτ5000 = -3.
| Abundances and chemical stratification analysis in the atmosphere of Cr-type Ap star HD 204411
We present results of an abundance and stratification analysis of theweakly magnetic chemically peculiar star HD 204411 based on the echellespectrum obtained with the high resolution spectrograph at the 3.55-mTelescopio Nazionale Galileo at the Observatorio del Roque de losMuchachos (La Palma, Spain). Atmospheric parameters obtained from thespectroscopy and spectrophotometry together with the Hipparcos parallaxshow that this star has already left the Main Sequence band. The upperlimit for the surface magnetic field derived from the differentialbroadening of the spectral lines with different magnetic sensitivity is750 G, which agrees with the recent detection of the weak effectivemagnetic field in this star. The best fit to the observed spectral lineprofiles was obtained with a combination of the rotational velocity v_esin i = 5.4 km s-1 and the radial-tangential macroturbulenceof 4.8 km s-1. The average abundances of HD 204411 aretypical for an Ap star of the Cr-type: C and O are deficient, Cr and Feare strongly overabundant. Sr, Y, Zr and the rare-earths, which usuallyhave large overabundances in cool Ap stars with strong magnetic fields,are either normal (Y, Ce) or only +0.5 dex overabundant in the weaklymagnetic star HD 204411. The chemical stratification analysis wasperformed for 5 elements, Mg, Si, Ca, Cr and Fe. Si, Ca and Fe show atendency to be concentrated below logτ5000=-1, while forMg we found marginal evidence for concentration in the upper atmosphere.This behaviour of Mg may be an artifact caused by the limited sample ofspectral lines and poor atomic data available for the Mg II lines usedin our analysis. Chromium, the most anomalous Fe-peak element, does notshow significant abundance gradients in the line-forming region.
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| 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.
| Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters
We present the first investigation of the structure of the stellarsurface magnetic field using line profiles in all four Stokesparameters. We extract the information about the magnetic field geometryand abundance distributions of the chemically peculiar star 53 Cam bymodelling time-series of high-resolution spectropolarimetricobservations with the help of a new magnetic Doppler imaging code. Thiscombination of the unique four Stokes parameter data andstate-of-the-art magnetic imaging technique makes it possible to inferthe stellar magnetic field topology directly from the rotationalvariability of the Stokes spectra. In the magnetic imaging of 53 Cam wediscard the traditional multipolar assumptions about the structure ofmagnetic fields in Ap stars and explore the stellar magnetic topologywithout introducing any global a priori constraints on the fieldstructure. The complex magnetic model of 53 Cam derived with ourmagnetic Doppler imaging method achieves a good fit to the observedintensity, circular and linear polarization profiles of strongmagnetically sensitive Fe II spectral lines. Such an agreement betweenobservations and model predictions was not possible with any earliermultipolar magnetic models, based on modelling Stokes I spectra andfitting surface averaged magnetic observables (e.g., longitudinal field,magnetic field modulus, etc.). Furthermore, we demonstrate that even thedirect inversion of the four Stokes parameters of 53 Cam assuming alow-order multipolar magnetic geometry is incapable of achieving anadequate fit to our spectropolarimetric observations. Thus, as a mainresult of our investigation, we discover that the magnetic fieldtopology of 53 Cam is considerably more complex than any low-ordermultipolar expansion, raising a general question about the validity ofthe multipolar assumption in the studies of magnetic field structures ofAp stars. In addition to the analysis of the magnetic field of 53 Cam,we reconstruct surface abundance distributions of Si, Ca, Ti, Fe and Nd.These abundance maps confirm results of the previous studies of 53 Cam,in particular dramatic antiphase variation of Ca and Ti abundances.Based on observations obtained with the Bernard Lyot telescope of thePic du Midi Observatory and Isaac Newton Telescope of the La PalmaObservatory.
| Some Comments on the Magnetic Braking of CP Stars
The low rotation velocities of magnetic CP stars are discussed.Arguments against the involvement of the magnetic field in the loss ofangular momentum are given: (1) the fields are not strong enough inyoung stars in the stage of evolution prior to the main sequence; (2)there is no significant statistical correlation between the magneticfield strength and the rotation period of CP stars; (3) stars with shortperiods have the highest fields; (4) a substantial number of stars withvery low magnetic fields (B e P>25 days, which form 12% of the total,probably lie at the edge of the velocity distribution for low massstars. All of these properties conflict with the hypothesis of magneticbraking of CP stars.
| Spatial Distribution of Magnetic CP Stars
The spatial distribution of magnetic CP stars is studied using thecatalog of CP stars compiled by the Special Astrophysical Observatory ofthe Russian Academy of Sciences. It is shown that the overwhelmingmajority of these objects are at distances closer than 500 pc from thesun. The axes of rotation and the magnetic axes of the field CP starsare distributed randomly, while a preferential orientation of themagnetic axes in certain directions is seen for stars that are membersof open clusters. The closeness of the magnetic models for CP stars thatare members of clusters may be evidence that there is a general factorwhich influences the origin of magnetic fields in stars. The magneticfield of the galaxy may be such a factor.
| 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
| Discovery of a 14.5 kG magnetic field in the NGC 2516 star HD 66318
We have been searching for magnetic Ap stars in open clusters, in orderto clarify the time evolution of magnetic fields in middle main sequencestars from the ZAMS to the TAMS. We have discovered that the star HD66318 in the open cluster NGC 2516 has an extraordinarily large magneticfield: the measured mean longitudinal component Bl ~ 4.5 kG,and the mean field modulus Bs ~ 14.5 kG. This star thus hasone of the largest fields so far discovered in a non-degenerate star,and the largest field known in a current Ap star cluster member.We estimate that HD 66318 has completed about 16 +/- 5% of its mainsequence life. It thus appears to contradict the hypothesis of Hubrig etal. that magnetic fields are only found in stars that have completed atleast 30% of their main sequence lifetimes.There is no indication that the spectrum or brightness of the star isvariable, and the spectral lines are very sharp. The star probably has avery long rotation period (years).We have modelled some parts of the observed spectrum, assuming that thechemical composition is uniform both horizontally and vertically, andusing a simple multipolar expansion for the field structure; althoughour model does not reproduce exactly the observed spectrum, it is clearthat the atmospheric chemical composition of the star is very peculiar,with Ti, Cr and Fe overabundant by between 1.5 and 2.5 dex. Both La IIand III are apparently about 4 dex overabundant. In contrast, evidencefor the presence of other rare earths is difficult to find in thespectrum. It appears that Ce III, Pr III, Nd II and III, and Eu II aredetected with inferred overabundances ranging between 1.5 and 5 dex, butfor most of these elements, the abundance of the non-detected ionizationstate is significantly lower than that inferred for the detected state.HD 66318 thus seems to exhibit strong discrepancies between abundancesdeduced for different ionization states of rare earths, a phenomenon sofar found only in somewhat cooler stars.Even within one ionization state it has not been found possible to fitmost observed lines with a single value of abundance. For example, whenwe fit medium strength lines of Fe II, the calculated strong lines ofthis ion are deeper than observed, and the calculated weak lines areless deep than observed. This situation is probably due to strongvertical abundance stratification of most of the elements studied.Finally, HD 66318 also shows a new form of core-wing anomaly in Hαin which the observed line profile falls below the computed one in thecore. These characteristics clearly suggest that the atmosphericstructure of HD 66318 is not closely similar to that of a normal mainsequence A star of similar parameters.This paper is based on data obtained at the European SouthernObservatory VLT during observing runs 68.D-0403 and DDT-269.D-05022.
| Magnetic intensification of spectral lines
We present an in-depth investigation of the increase in equivalent widthof saturated lines under the influence of strong magnetic fields, aptlycalled ``magnetic intensification''. Assuming 20 different Zeemanpatterns (with the number of components ranging from 3 to 45) for afictitious Fe II line at 4500 Å in a 10 000 K, log g = 4.0 Kuruczatmosphere, we calculate equivalent widths as a function of magneticfield strength, field angle and line strength (abundance). The increaseover the zero field equivalent width is found to always fall below then/2 relation suggested by Babcock (\cite{bab49}), where n is the numberof Zeeman components. After a discussion of the behaviour of variousZeeman patterns we turn to the influence of anomalous dispersion onmagnetic intensification. Changes in line blanketing due to magneticdesaturation appear to be of negligible size. Finally we show thatmagnetic intensification leads to apparent enhanced abundances and tovirtual abundance variations in magnetic stars with dipolar surfacemagnetic field configurations.
| The magnetic B and A stars - their cause and cure
Not Available
| Radial velocity study of the roAp star HR 1217
We analyse 1160 high-dispersion echelle spectra of the roAp star HR 1217obtained over two 2-week runs. Radial velocities were obtained bycross-correlating with three different templates: a spectrum of a normalstar, a spectrum of HR 1217 itself and a spectrum containing only linesof rare-earth elements. We show that rotational modulation is present inthe radial velocities calculated using the normal star template and therare-earth template, but with opposite phases. The roAp pulsations arenot detected in the radial velocities from the normal star template, areweakly present in the radial velocities using a template of the staritself and are of large amplitude in the radial velocities obtainedusing a template containing only rare-earth lines. The pulsationfrequencies are, as far as we can tell, identical to those obtainedphotometrically, although only the mode of largest amplitude is detectedindependently. These observations confirm that the pulsations in roApstars are strongly concentrated at the magnetic poles, which is also thelocation where the rare-earth elements are overabundant. A strongcore-wing anomaly is present in the Hα profile of the star.
| New Magnetic Chemically Peculiar Stars
Not Available
| Magnetic survey of bright northern main sequence stars
The first results of a systematic search for magnetic fields in thebrightest upper main sequence (MS) stars are presented. The main goal isto survey the stars with about the same detection limit and to improveexisting statistics of their magnetism. The target list contains 57upper MS stars and represents well B0.5-F9 stars. High-resolution Zeemanspectra were obtained for 30 stars of the list. The accuracy of themagnetic field measurements ranges from 20 to 300 G depending mainly onspectral class. In the majority of studied stars we did not detectmagnetic fields. In some stars we suspect the presence of a weakmagnetic field. These are the best candidates for more extensivestudies. A particular case is the star chi Dra where we probablydetected the global magnetic field. The longitudinal field strength isB_l= -54+/-12 G. Further observations of this star are needed to confirmthe detection and to ascertain if the magnetic field is variable withthe period of rotation. Based on observations collected at the 1 mtelescope of the Special Astrophysical Observatory (Nizhnij Arkhyz,Russia).
| A statistical analysis of the magnetic structure of CP stars
We present the results of a statistical study of the magnetic structureof upper main sequence chemically peculiar stars. We have modelled asample of 34 stars, assuming that the magnetic morphology is describedby the superposition of a dipole and a quadrupole field, arbitrarilyoriented. In order to interpret the modelling results, we haveintroduced a novel set of angles that provides one with a convenient wayto represent the mutual orientation of the quadrupolar component, thedipolar component, and the rotation axis. Some of our results aresimilar to what has already been found in previous studies, e.g., thatthe inclination of the dipole axis to the rotation axis is usually largefor short-period stars and small for long-period ones - see Landstreet& Mathys (\cite{Landstreet2000}). We also found that forshort-period stars (approximately P<10 days) the plane containing thetwo unit vectors that characterise the quadrupole is almost coincidentwith the plane containing the stellar rotation axis and the dipole axis.Long-period stars seem to be preferentially characterised by aquadrupole orientation such that the planes just mentioned areperpendicular. There is also some loose indication of a continuoustransition between the two classes of stars with increasing rotationalperiod.
| Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four ofwhich might in fact be Am stars, and give their orbital elements. Fourof them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. Thetwelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339,HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD216533. Rough estimates of the individual masses of the components of HD65339 (53 Cam) are given, combining our radial velocities with theresults of speckle interferometry and with Hipparcos parallaxes.Considering the mass functions of 74 spectroscopic binaries from thiswork and from the literature, we conclude that the distribution of themass ratio is the same for cool Ap stars and for normal G dwarfs.Therefore, the only differences between binaries with normal stars andthose hosting an Ap star lie in the period distribution: except for thecase of HD 200405, all orbital periods are longer than (or equal to) 3days. A consequence of this peculiar distribution is a deficit of nulleccentricities. There is no indication that the secondary has a specialnature, like e.g. a white dwarf. Based on observations collected at theObservatoire de Haute-Provence (CNRS), France.Tables 1 to 3 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/394/151Appendix B is only available in electronic form athttp://www.edpsciences.org
| 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
| Abundance stratification and pulsation in the atmosphere of the roAp star boldmath gamma Equulei
We present the evidence for abundance stratification in the atmosphereof the rapidly oscillating Ap star gamma Equ. Ca, Cr, Fe, Ba, Si, Naseem to be overabundant in deeper atmospheric layers, but normal tounderabundant in the upper layers with a transition in the typical lineforming region of -1.5
| Vertical Chromium Distribution in the Atmospheres of CP Stars. II. Modeling
Vertical chromium distributions in the atmospheres of several Ap and Amstars are fitted using detailed modeling of the profiles of CrII lines.The vertical distributions obtained for Ap stars are consistent withBabel's results of an investigation of Cr lines in the spectrum of theAp star 53 Cam. It is shown that the observational data cannot beinterpreted in terms of the hypothesis that microturbulent velocityvaries with depth.
| Vertical Chromium Distribution in the Atmosphere of a Chemically Peculiar Star. I. Diagnostics
On the basis of CCD spectrograms obtained with high resolution at theCoudé focus of the 2.6-m telescope of the Crimean AstrophysicalObservatory, Cr II lines lying in the wings of the H hydrogen line areinvestigated. Vertical chromium stratification in the atmospheres of twonormal and eight chemically peculiar stars is diagnosed using the methodof spectral synthesis. An increase in Cr abundance with depth is foundfor the cool Ap stars CrB, HR 7575, Equ, and 10 Aql. Some increase in Crabundance in the upper layers of the atmosphere is presumed for all Amstars and for both HgMn components of 46 Dra. The verticalchromium distribution in the atmospheres of the hot, spotted Ap stars 17Com and 2 CVn is evidently uniform.
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| The Naini Tal - Cape survey for pulsations in chemically peculiar A-type stars. I. Methods and preliminary results
A new survey for pulsating, chemically peculiar A- and F-type stars inthe northern hemisphere has been initiated using the 1-m telescope atUttar Pradesh State Observatory in Naini Tal. The survey is primarilystructured to reveal high-overtone pulsations in chemically peculiar A-Fstars, but it is also revealing low-overtone delta Scuti-type pulsationsin stars with peculiar colours. This paper describes the scope andmethods of the survey. Preliminary observations of 28 candidate starsare presented and the discovery of three new pulsators, HD 12098, HD13038 and HD 13079, is announced. Null results for the remaining 25stars are also discussed.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ג'ירף |
| התרוממות ימנית: | 08h01m42.40s |
| סירוב: | +60°19'28.0" |
| גודל גלוי: | 6.01 |
| מרחק: | 98.425 פארסק |
| תנועה נכונה: | -33 |
| תנועה נכונה: | -20.3 |
| B-T magnitude: | 6.221 |
| V-T magnitude: | 6.031 |
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