Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| The diagnosis of the mean quadratic magnetic field of Ap stars
Aims.We assess the validity of the method of determination of the meanquadratic field modulus and we explore its limits. Methods.Weanalyse high spectral resolution, high signal-to-noise spectra of a fewAp stars, and of a superficially normal main-sequence A star, recordedover a broad wavelength range with EMMI at the NTT.Results.Weintroduce a revised form of the regression equation describing thedependence of the second-order moment of the line profiles about theircentre, in natural light, on various parameters of the correspondingtransitions. We show that interpretation of the observed dependencesallows one to determine the mean quadratic magnetic field modulus of thestudied stars, and their v sin i. We explain why the contributions tothe quadratic field of the mean square magnetic field modulus and of themean square longitudinal field cannot in general be disentangled. Forthose stars of the sample that have resolved magnetically split lines,we show that the derived values of the quadratic field are mostlyconsistent with the values of the mean longitudinal magnetic field andof the mean magnetic field modulus at the observed phase. However thereare some hints that they may occasionally slightly underestimate theactual field. This suggests that the method is unlikely to yieldspurious field detections. In addition, we illustrate the importance forthis type of analyses of using, as far as possible, samples of lines ofa single ion, and to specify in the presentation of the results whichion was used.Conclusions.The results presented in this paper lendstrong support to the validity of the quadratic field diagnostic methodto obtain a realistic quantitative characterisation of the magneticfields Ap and related stars.
| Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars
Aims.We study the kinematic structure of peripheral areas of the UrsaMajoris stream (Sirius supercluster). Methods.We use diagrams ofindividual stellar apexes developed by us and the classical technique ofproper motion diagrams generalized to a star sample distributed over thesky. Results.Out of 128 cluster members we have identified threecorona (sub)structures comprised of 13, 13 and 8 stars. Thesubstructures have a spatial extension comparable to the size of thecorona. Kinematically, these groups are distinguished by their propermotions, radial velocities and by the directions of their spatialmotion. Coordinates of their apexes significantly differ from those ofthe apexes of the stream and its nucleus. Our analysis shows that thesesubstructures do not belong to known kinematic groups, such as Hyades orCastor. We find kinematic inhomogeneity of the corona of the UMa stream.
| High time resolution spectroscopy and magnetic variability of the cool Ap star HD965*
We present the results of an investigation of the magnetic Ap star HD965with high spectral and time resolution. We determine precise radialvelocities using spectra obtained with the Ultraviolet-Visual EchelleSpectrograph (UVES) on the European Southern Observatory Very LargeTelescope. Special attention is given to spectral lines of rare-earthelements which in rapidly oscillating Ap (roAp) stars exhibit thestrongest radial velocity variations with pulsation period. Careful timeseries analysis did not detect any convincing evidence of pulsation inHD965 with an upper limit in amplitude of 15-20 m s-1. Allproperties of HD965 are similar to the majority of roAp stars. A likelyreason for the apparent lack of pulsation could be connected with thegeometrical structure of the magnetic field and the aspect of the starat the time of observation. Longitudinal magnetic field measurements forHD965 showed that our UVES spectral observations were carried out whenthe longitudinal field was near zero and therefore, according to theoblique rotator model, near a time when the star was viewed from themagnetic equator. For a dipole oscillation aligned with the magneticfield, as is typical of roAp stars, no variation can be detected at thisaspect. We may, therefore, expect to detect rapid oscillations in HD965in the future, when the star will present one of the magnetic poles.
| The discovery of a luminous, rapidly oscillating Ap star, HD 116114, with a 21-minute pulsation period*
The discovery of a new rapidly oscillating Ap star, HD 116114, with apulsation period of 21 min, using high-resolution spectra obtained withthe Ultraviolet-Visual Echelle Spectrograph at the European SouthernObservatory's Very Large Telescope, is presented. The highest amplitudesof the radial velocity variations are between 50 and 125 ms-1 visible in the EuII lines. The spectral lines of LaII andthe core of the Hα line have amplitudes of about 30 ms-1. The frequency obtained for the oscillations is in goodagreement with theoretical predictions of longer-period, evolved roApstars. The distinction in luminosity between the roAp and noAp stars,and the suggestion that in all roAp stars the abundance of the secondions of Pr and Nd, relative to the abundance of the first ions, isanomalously high, need to be revised in the light of this discovery.
| The calcium isotopic anomaly in magnetic CP stars
Chemically peculiar stars in the magnetic sequence can show the sameisotopic anomaly in calcium previously discovered for mercury-manganesestars in the non-magnetic sequence. In extreme cases, the dominantisotope is the exotic 48Ca. Measurements of Ca II linesarising from 3d-4p transitions reveal the anomaly by showing shifts upto 0.2 Å for the extreme cases - too large to be measurementerrors. We report measurements of miscellaneous objects, including twometal-poor stars, two apparently normal F-stars, an Am-star, and theN-star U Ant. Demonstrable anomalies are apparent only for the Ap stars.The largest shifts are found in rapidly oscillating Ap stars and in oneweakly magnetic Ap star, HD 133792. We note the possible relevance ofthese shifts for the GAIA mission.Based on observations obtained at the European Southern Observatory, LaSilla and Paranal, Chile (ESO programme Nos. 65.L-0316, 68.D-0254 and266.D-5655).
| Radial velocity variations in pulsating Ap stars. V. 10 Aquilae
We have used precise stellar radial velocities to study the pulsationalmotion of the rapidly oscillating Ap star 10 Aql.Observations were made on three separate nights using the highresolution spectrograph of the Harlan J. Smith 2.7 m telescope atMcDonald Observatory. A high radial velocity precision was achieved byusing an iodine gas absorption cell. The integrated radial velocitymeasurements using the full wavelength region covered by iodineabsorption lines (5000-6300 Å) failed to detect any coherentpulsational velocity variations to a level of 2.5-5 m s-1. Ananalysis over a much narrower wavelength range revealed that pulsationalradial velocity variations are indeed present in 10Aql, but only in 5 spectral lines. The amplitude of thesevariations ranged from about 100 m s-1 to as high as 398 ms-1 for an unidentified feature at λ5471.40 Å.Other spectral features showing pulsational radial velocity variationsare tentatively identified as Sm II and Tm II.Based on observations collected at McDonald Observatory.
| Rotational periods of four roAp stars
Forty-five new measurements of the mean longitudinal magnetic fields andmean equivalent widths of 4 roAp stars have obtained using the MuSiCoSspectropolarimeter at Pic du Midi observatory. These new high-precisiondata have been combined with archival measurements in order to constrainthe rotational periods of HD 12098, HD 24712 = HR 1217, HD 122970 and HD176232 = 10 Aql. We report a revised rotational period for HD 24712(Prot = 12.45877 ± 0.00016 d, crucial forinterpretation of upcoming MOST observations of this star), newrotational periods for HD 12098 and HD 122970 (Prot=5.460± 0.001 d and Prot=3.877 ± 0.001 d,respectively) and evidence for an extremely long period for HD 176232.Table 1 is only available in electonic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or via http: / /cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/L55
| Radial velocity variations in pulsating Ap stars - III. The discovery of 16.21-min oscillations in β CrB
We present the analysis of 3 h of a rapid time series of precisestellar radial velocity (RV) measurements (σ= 4.5 ms-1) of the cool Ap star β CrB. The integrated RVmeasurements spanning the wavelength interval 5000-6000 Åshowsignificant variations (false alarm probability = 10-5) witha period of 16.21 min (ν= 1028.17 μHz) and an amplitude of 3.54+/- 0.56 m s-1. The RV measured over a much narrowerwavelength interval reveals one spectral feature at λ6272.0Åpulsating with the same 16.21-min period and an amplitude of 138+/- 23 m s-1. These observations establish β CrB to be alow-amplitude rapidly oscillating Ap star.
| The spectroscopic signature of roAp stars
To reliably determine the spectroscopic signature of rapidly oscillatingchemically peculiar (roAp) stars it is also necessary to investigate asample of non pulsating chemically peculiar (noAp) as well as presumably``normal'' stars. We describe in this study the sample ofspectroscopically investigated stars and comment on the techniques usedfor the analysis. In particular we discuss ionization disequilibria ofrare earths in roAp stars that distinguish them from noAp stars. In thelight of the recently discovered pulsation of β CrB we seearguments that all magnetic CP2 stars up to a transition temperature ofabout 8100 K may be pulsating.Based on observations obtained at the European Southern Observatory (LaSilla, Chile), the Canadian-French-Hawaii telescope, the South AfricaAstronomical Observatory, The Crimean Astrophysical Observatory and onnumerous SIMBAD interrogations.
| Abundance Analysis of the Silicon Star HR 6958
The elemental composition of the chemically peculiar star HR6958 hasbeen studied with emphasis on doubly ionized rare earths. A visualregion spectrum taken with the ELODIE spectrograph at the Haute-ProvenceObservatory was analyzed. A total of 40 elements including Pr III , Nd III , Tb III , Dy III , Ho III , and Er III were identified andtheir abundances computed. He is deficient by over 1dex with respect tothe Sun; the light elements (C-Ca), except for Si, have solarabundances; the iron group elements (Sc-Fe) are overabundant by 1 dex to2dex, with Ti and Cr highly overabundant; and the lanthanide rare earthsare overabundant by 3dex to 4dex. This abundance pattern with Hedeficient, Si, Ti, Cr, Sr, and Pr overabundant indicates that HR6958 isa member of Si stars.
| Measuring stellar magnetic fields from high resolution spectroscopy of near-infrared lines
Zeeman splitting of otherwise degenerate levels provides astraight-forward method of measuring stellar magnetic fields. In theoptical, the relative displacements of the Zeeman components are quitesmall compared to the rotational line broadening, and thereforeobservations of Zeeman splitting are usually possible only for ratherstrong magnetic fields in very slowly rotating stars. However, themagnitude of the Zeeman splitting is proportional to the square of thewavelength, whereas rotational line broadening mechanisms are linear inwavelength; therefore, there is a clear advantage in using near-infraredspectral lines to measure surface stellar magnetic fields. We haveobtained high resolution (R >= 25 000) spectra in the 15 625-15 665Å region for two magnetic chemically peculiar stars, viz. HD176232 and HD 201601, and for the suspected magnetic chemically peculiarstar HD 180583, as part of a pilot study aimed at determining theaccuracy with which we can measure stellar magnetic fields using theZeeman splitting of near-infrared lines. We confirm that in principlethe magnetic field strength can be estimated from the magneticintensification of spectral lines, i.e. the increase in equivalent widthof a line over the zero-field value. However, due to line blending aswell as the dependence of this intensification on abundance and fieldgeometry, accurate estimates of the magnetic field strengths can beobtained only by modelling the line profiles by means of spectralsynthesis techniques. Using this approach, we find a 1.4 kG magneticfield modulus in HD 176132 and an upper limit of 0.2 kG in HD 180583.The very weak infrared lines in the spectrum of HD 201601 are consistentwith a 3.9 kG field modulus estimated from the splitting of the Fe II6149.258 Å line seen in an optical spectrum. Finally, we wouldlike to draw attention to the fact that there are no sufficientlydetailed and reliable atomic line lists available for the near-infraredregion that can be used in high resolution work; a large fraction of thefeatures observed in our spectra remains to be identified.Based on observations made with the NASA Infrared Telescope Facility.
| 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
| On the influence of Stark broadening on Si I lines in stellar atmospheres
We study the influence of Stark broadening and stratification effects onSi I lines in the rapidly oscillating (roAp) star 10 Aql, where the SiI,6142.48 Å and 6155.13 Å lines are asymmetrical andshifted. First we have calculated Stark broadening parameters using thesemiclassical perturbation method for three Si I lines: 5950.2 Å,6142.48 Å and 6155.13 Å. We revised the synthetic spectrumcalculation code taking into account both Stark width and shift forthese lines. From the comparison of our calculations with theobservations we found that Stark broadening + the stratification effectcan explain asymmetry of the Si I 6142.48 Å and 6155.13 Ålines in the atmospere of roAp star 10 Aql.
| Atmospheric parameters and chemical composition of the ultra-cool roAp star HD 213637
A high-resolution spectrum obtained with the UVES instrument at the ESOVLT is used to determine atmospheric parameters and chemical compositionof the roAp star HD 213637. Resolved Zeeman split lines are discoveredin the spectrum of this star, indicating a mean field modulus of 5.5 kG.Effective temperature, Teffv{6400} determined from theprofiles of the hydrogen Hα and Hβ lines, makes HD 213637one of the coolest (ro)Ap stars known, suggesting that the class ofmagnetic chemically peculiar stars extends to lower effectivetemperatures than previously thought. Furthermore, the low temperatureof HD 213637 poses serious challenge to some excitation mechanismssuggested as an explanation of the roAp phenomenon. This peculiar staris also unique in its evolutionary stage: it is either located near thevery end of its main sequence life or has already ascended the giantbranch. Abundance analysis reveals that HD 213637 is iron-deficient andhas abundance pattern typical of the cool pulsating Ap stars. Aninconsistency between abundances derived from the weak and strongspectral lines and the lines of different ions provide a clear evidencefor prominent vertical abundance stratification of many chemicalspecies, notably Na, Mg, Ca, Fe, Pr, Nd, Tb, and Er.Based on observations obtained at the European Southern Observatory,VLT.
| Magnetic field measurements of Ap stars. Discovery of a strong magnetic field in HD 18610
HD 18610 was included in our project on abundance determination ofrapidly oscillating (roAp) and non-oscillating (noAp) cool chemicallypeculiar stars. Already a preliminary investigation of the raw spectraindicated the presence of an intense magnetic field which was confirmedby a more detailed analysis.To determine the magnetic field strength we primarily used the Fe IIline at 6149.26 Å, a strong line which is split in a anomalousZeeman doublet. HD 18610 is a Cr-Eu-Sr non-pulsating Ap star with aTeff and log g typical for roAp stars. The classification ofthis star as a CP2 star (Preston \cite{Preston}) was confirmed withDelta a photometry by Maitzen & Vogt (\cite{MV83}). In the presentinvestigation we derived a mean magnetic field modulus of |vec {B}|=5700 +/- 200 G.
| Discovery of rapid radial velocity variations in the roAp star 10 Aql and possible pulsations of β CrB
We report discovery of radial velocity variations in rare earth spectrallines of the roAp star 10 Aql with amplitudes of between 30 and 130 ms-1 and periods of about 11 min. Radial velocity variationswith amplitude 70 m s-1 may also have been detected in onespectral line of Fe I in β CrB. If confirmed, our results mayindicate that all Ap stars in a certain temperature range pulsate, whichmeans that roAp stars do not exist as a separate class but are onlydistinguished by higher pulsational amplitudes.
| 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
| On the excitation mechanism in roAp stars
We investigate a model for the excitation of high-order oscillations inroAp stars. In this model we assume that the strong concentration ofmagnetic field about the magnetic poles is enough to suppressconvection. Thus the model considered is composed of two polar regions,in which convection is presumed to be suppressed totally, and anequatorial region, where the convection is unaffected. This model isgenerated by building pairs of locally spherically symmetricalequilibria to represent the polar and equatorial regions of the star,which are patched together below the base of the convection zone.Gravitational settling of heavy elements is taken into account bychoosing appropriate chemical composition profiles for both the polarand equatorial regions. Our results indicate that the composite model isunstable against axisymmetric non-radial high-order modes of pulsationthat are aligned with the magnetic poles. The oscillations are excitedby the κ mechanism acting principally in the hydrogen ionizationzones of the polar regions. The effect of the lateral inhomogeneity onthe second frequency differences is also investigated; we find that theperturbation to them by the inhomogeneity is of the same order as thesecond differences themselves, thereby hindering potential attempts touse such differences to identify the degrees of the modes in astraightforward way.
| A Study of Rare Earth Elements in the Atmospheres of Chemically Peculiar Stars. Pr III and Nd III Lines
We determine the abundances of Pr and Nd in the atmospheres of magneticand non-magnetic chemically peculiar stars from the lines of rare earthelements in the first and second ionization states. The computations forthe magnetic stars take into account the influence of the magnetic fieldon line formation. We studied the influence of errors in thestellar-atmosphere parameters and the atomic parameters of the spectrallines on the accuracy of abundance determinations. Within the derivedaccuracy, ionization equilibrium is satisfied in the atmospheres ofnon-pulsating magnetic and non-magnetic stars (so that abundancesderived separately from lines of first and second ions agree). For allthe pulsating magnetic (roAp) stars studied, the abundances derived fromlines of second ions are 1.0 to 1.7 dex higher than those derived fromfirst ions. The violation of ionization equilibrium in the atmospheresof pulsating stars is probably due to, first, considerable enrichment ofPr and Nd in the uppermost atmospheric layers, and second, a higherlocation for the layer of enhanced elemental abundance in roAp starsthan in non-pulsating stars. Two objects from the list of non-pulsatingmagnetic stars, HD 62140 and HD 115708, exhibit anomalies of their Prand Nd lines characteristic of roAp stars. The differences in the rareearth anomalies for the pulsating and non-pulsating peculiar stars canbe used as a selection criterion for candidate roAp stars.
| 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.
| The core-wing anomaly of cool Ap stars. Abnormal Balmer Profiles
The profiles of Hα in a number of cool Ap stars are anomalous.Broad wings, indicative of temperatures in the range 7000-8000 K endabruptly in narrow cores. The widths of these cores are compatible withthose of dwarfs with temperatures of 6000 K or lower. This profile hasbeen known for Przybylski's star, but it is seen in other cool Ap stars.The Hβ profile in several of these stars shows a similar core-winganomaly (CWA). In Przybylski's star, the CWA is probably present athigher Balmer members. We are unable to account for these profileswithin the context of LTE and normal dwarf atmospheres. We conclude thatthe atmospheres of these stars are not ``normal''. This is contrary to anotion that has long been held. Based on observations obtained at theEuropean Southern Observatory, Paranal, Chile (ESO programme No.65.I-0644) and the South African Astronomical Observatory (SAAO).}
| 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
| Observing roAp Stars with WET: A Primer
We give an extensive primer on roAp stars -- introducing them, puttingthem in context and explaining terminology and jargon, and giving athorough discussion of what is known and not known about them. Thisprovides a good understanding of the kind of science WET could extractfrom these stars. We also discuss the many potential pitfalls andproblems in high-precision photometry. Finally, we suggest a WETcampaign for the roAp star HR 1217.
| Abundance analyses of roAp stars. VI. 10 Aql and HD 122970
In this sixth paper in a sequence on abundance analyses of roAp stars wepresent the results for two further members of this group, which arefairly similar and have only a small magnetic field. The analysis of 10Aql and HD 122970 did not require, for the first time in this long termproject, the development of tools and hence was rather straight-forward.We reanalyzed Sm, Eu and Gd in HD 203932, because better atomicparameters have become available with vald-2; and for Eu we also took\hfs effects into account. Similar to the five roAp stars analysed sofar (alpha Cir: Kupka et al. 1996, HD 203932: Gelbmann et al. 1997,gamma Equ: Ryabchikova et al. 1997a, HD 24712: Ryabchikova et al. 1997b,and HD 166473: Gelbmann et al. 2000) we find nearly solar abundances ofFe and Ni, and a definite overabundance of Cr and especially Co, withlarge overabundances of rare earth elements. This pattern seems to be acommon property of chemically peculiar (CP2, Ap) stars. HD 101065(Przybylski's star), another roAp star, has a similar peculiaritypattern, except of iron (Cowley et al. 2000) which is underabundant. 10Aql and HD 122970 provide another example for the anomalous linestrengths of the second ions of rare earth elements resulting in anabundance increase of up to 2 dex (!) compared to values obtained fromlines of the first ions. As we mentioned in an earlier paper, thisanomaly yet is not found in non-roAp and ``normal'' stars. Based onobservations obtained at Crimea and McDonald Observatories
| Rapidly oscillating Ap stars versus non-oscillating Ap stars
The positions in the HR diagram and the kinematic characteristics ofrapidly oscillating and non-oscillating chemically peculiar stars areobtained using new Hipparcos proper motions and parallaxes, and our ownradial velocity measurements. We find that rapidly oscillating stars, asa group, are (-0.47 +/- 0.34) mag above the zero-age main sequence(ZAMS), while the non-oscillating stars are (-1.20 +/- 0.65) mag abovethe ZAMS and so appear slightly more evolved on average. From thecomparison of the kinematical characteristics, we conclude that bothgroups are very similar. The results of radial velocity measurementsindicate that there is a real deficiency of binaries among rapidlyoscillating stars. Presently, no such star is known to be aspectroscopic binary.
| On the effective temperatures, surface gravities, and optical region fluxes of the CP stars
We determined effective temperatures and surface gravities for 17magnetic Chemically Peculiar (mCP) stars by comparing optical regionspectrophotometry and Hγ profiles with the predictions of ATLAS9model atmospheres. Although solar composition models can fit the energydistributions of the normal and many Mercury-Manganese stars, theycannot match the optical energy distributions of the mCP stars,especially the lambda 5200 broad, continuum regions. The role ofmetallicity and microturbulence to provide appropriate energydistributions which fit those observed for the mCP stars isinvestigated. Using metal-rich models with the opacity distributionfunctions for microturbulent velocities of 4 and 8 km s-1,their lambda 5200 broad, continuum features are often fit as part ofthis process. For some stars it is impossible to fit simultaneously boththis feature and the line blanketing in the Hγ region. Thissuggests that this continuum feature is produced by elements other thanthose which contribute most of the general line blanketing. A systematicdifference in the temperatures found by the photometric andspectrophotometric approaches is discovered for the hotter mCP stars. Aninvestigation of 10 Mercury-Manganese stars shows a similar effect. Thismay be due to the photospheric compositions becoming less solar withincreasing temperature.
| Parallaxes versus p-Modes: Comparing HIPPARCOS and Asteroseismic Results for Pulsating AP Stars
The p-mode eigenfrequency spacings of 12 rapidly oscillating Ap (roAp)stars provide estimates of their radii. By combining these withindependent estimates of their effective temperatures via Hβphotometry, Martinez predicted luminosities for all but one of thissample. Hipparcos parallaxes, and hence luminosities, are now availablefor the entire sample. While we obtain general agreement between the twosets of measurements, Hipparcos finds systematically larger parallaxesthan predicted by asteroseismology. If the Hipparcos parallaxes and theinterpretation of the p-mode spacings are both correct, this suggeststhe roAp stars are systematically cooler than expected from the Hβcalibration. Other explanations (e.g., systematic overestimates of theradii if Ap stars actually have globally metal-poor compositions andmagnetic perturbations of the pulsational frequencies) are unlikely toaccount for the discrepancy. Lower temperatures for the roAp stars wouldshift many of them beyond the classical instability strip in the H-Rdiagram, implying that the He II ionization mechanism cannot beresponsible for their pulsation. However, it is essential to ensure thatboth the Hipparcos parallaxes and the asteroseismic models do not suffersome systematic bias. We identify one case (HD 166473) where theparallax in the Tycho Catalogue must be wrong, giving a luminosity of~0.4 L_solar for a late A star, and another (alpha Cir) where Hipparcospredicts a temperature 1000 K cooler than a detailed model of thestellar spectrum.
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | わし座 |
| Right ascension: | 18h58m46.90s |
| Declination: | +13°54'24.0" |
| Apparent magnitude: | 5.89 |
| Distance: | 74.349 parsecs |
| Proper motion RA: | 1.2 |
| Proper motion Dec: | -51 |
| B-T magnitude: | 6.216 |
| V-T magnitude: | 5.927 |
Catalogs and designations:
|
INHABITED SKY
