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Публикации по объекту
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.
| An Improved Infrared Passband System for Ground-based Photometry: Realization
We describe new simulations and field trials of the new infraredpassband system developed and discussed by Young, Milone, & Stagg,who discussed and illustrated the state of infrared photometry andsuggested ways in which it could be improved. In particular, theypresented a new set of passbands that minimize the dependence of thephotometry on the water vapor bands of the atmospheric windows, whichdefined the edges of many previous infrared passbands, especially whenused at sites and under conditions for which they were not designed. Inthis paper, we present numerical simulations for three atmosphericmodels, demonstrate a measure of the signal-to-noise ratio in the newpassbands for these models, and present observational data obtained at arelatively low-elevation site. The latter demonstrate the utility ofthis system for most astronomical sites where photometry can beperformed, and permit the transformation of observations to this system.Publications of the Rothney Astrophysical Observatory, No. 74.
| Magnetic Field and Chemical Composition of the Peculiar Star HD 10221
We analyzed the chemical composition of the chemically peculiar (CP)star HD 0221=43 Cas using spectra taken with the NES spectrograph of the6-m telescope with a spectral resolution of 45 000. The Hβ lineprofile corresponds most closely to T eff = 11 900 K and log g = 3.9.The rotational velocity is v e sin i = 27 ± 2 km s-1, and themicroturbulence is ξ t = 1 km s-1. The results of our abundancedetermination by the method of synthetic spectra show that the star haschemical anomalies typical of SrCrEu stars, although its effectivemagnetic field is weak, B e < 100 G. For silicon, we obtained anabundance distribution in atmospheric depth with a sharp jump of 1.5 dexat an optical depth of log τ 5000 = -0.3 and with siliconconcentration in deep atmospheric layers. Similar distributions werefound in the atmospheres of cooler stars with strong and weak magneticfields. A comparison of the chemical peculiarities in HD 10221 withknown CP stars with magnetic fields of various strengths leads us toconclude that a low rotational velocity rather than amagnetic field isthe determining factor in the formation mechanism of chemical anomaliesin the atmospheres of CP stars.
| 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.
| Magnetic field measurements on four yellow supergiants. I
Multiyear high precision measurements of the longitudinal component ofthe magnetic field (Be) of four supergiants are reported: Aqr (G0 Ib),Aqr (G2 Ib), Gem (G8 Ib), and Peg (K2 Ib). The best measurementaccuracy, =0.8 G, was achieved for Peg. A Monte Carlo method was used totest the reliability of the derived measurement errors. The differencesbetween the observational errors and the calculated Monte Carlo errorswere 3.2%. For Aqr and Aqr no statistically significant value of themagnetic field was recorded when averaged over a night. For eGem thefollowing overnight average values of the magnetic field were recordedon five nights: 11.1±2.7 G, 9.8±2.5 G, -10.5±3.0 G,38.1±7.4 G, and 5.3±1.5 G. For Peg the magnetic fieldrecorded over two nights was -5.3±0.9 G and - 2.7±0.8 G.
| 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.
| 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.
| On the influence of Stark broadening on Cr I lines in stellar atmospheres
Using the semiclassical perturbation method, electron-, proton-, andionized helium-impact line widths and shifts for the nine Cr i spectrallines from the 4p^7P^0{-}4d^7D multiplet were calculated for a perturberdensity of 1014 cm-3 and for temperatures T = 2500{-} 50 000 K. The results were used to investigate the influence ofStark broadening effect in the Cr-rich Ap star β CrB atmosphere online shapes of these lines. It was found that the contribution of protonand He ii collisions to the line width and shift is significant andcomparable, and is sometimes even larger than electron-impactcontribution depending of the electron temperature. Moreover, not onlythe Stark line width, but also the Stark shift may contribute to theblue as well as to the red asymmetry of the same line depending on theelectron-, proton-, and He ii density in stellar atmosphere. The resultswere used to investigate the influence of Stark broadening effect on Cri line shapes in the atmosphere of the Cr-rich Ap star β CrB.
| 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).
| 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
| 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.
| The 5200-Åflux depression of chemically peculiar stars - II. The cool chemically peculiar and λ Bootis stars
After establishing the synthetic Δa photometric system in thefirst paper of this series, we now present model atmospheres computedwith individual abundances for a representative sample of chemicallypeculiar (CP) stars and either confirm or redetermine their inputparameters through comparisons with photometric, spectrophotometric andhigh-resolution spectroscopic data. The final models obtained from thisprocedure were used to compute synthetic Δa indices which werecompared with observations. The observed behaviour of Δa isreproduced for several types of CP stars: models for Am stars shownegligible (or marginally positive) values of a few mmag, while forλ Bootis stars - and for metal deficient A stars in general - weobtain negative values (as low as -12 mmag in one case). For the coolestCP2 stars with effective temperatures below about 8500 K, we obtain mild(~+10 mmag) to moderately large (~+30 mmag) flux depressions inagreement with observations. However, Δa values for slightlyhotter members of the CP2 group (for which still Teff <10000 K) are underestimated from these new models. The effect of themicroturbulence parameter on the Δa index is revisited and itsdifferent role in various types of CP stars for reproducing the fluxdepression at 5200 Åis explained. We also provide reasons whymodels based on enhanced microturbulence and scaled solar abundancecould not explain the observed flux depression for all types of CPstars. We discuss potential improvements of the current models includingthe possibility of still missing line opacities (unidentified andautoionization lines), modifications due to an explicit account of aglobal stellar magnetic field, and the effect of vertical abundancestratification.
| 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.
| Magnetic Model of HD 2453
A model is constructed for the magnetic field of the star HD 2453, whichhas a very long rotation period (P=521d). It is found that the structureof the field corresponds to the model of a dipole shifted by r=0.09Rfrom the center. The angle of inclination of the axis of the dipole tothe axis of rotation, =5°; that is, the star is viewed almost fromits equator of rotation and magnetic equator. This explains the lowamplitude of the phase dependence of the magnetic field, Be(P), and thelow amplitude of the photometric variability. The field at the magneticpoles is equal to Bp=+4400 and -7660 G. The magnetic field parametersturn out to be close to those obtained by Landstreet and Mathys assuminga dipole-quadrupole-octupole model. A Mercator map of the magnetic fielddistribution of HD 2453 is produced.
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| 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.
| Probable detection of radial magnetic field gradients in the atmospheres of Ap stars
For the first time the possible presence of radial gradients of magneticfields in the atmospheres of three magnetic Ap stars has been criticallyexamined by measurements of the mean magnetic field modulus fromspectral lines resolved into magnetically split components lying on thedifferent sides of the Balmer jump. A number of useful diagnostic linesbelow and above the Balmer discontinuity, only slightly affected byblends, with simple doublet and triplet Zeeman pattern have beenidentified from the comparison between synthetic spectra computed withthe SYNTHMAG code and the high resolution and S/N spectra obtained inunpolarized light with the ESO VLT UVES spectrograph. For all threestars of our sample, HD 965, HD 116114 and 33 Lib, an increase of themagnetic field strength of the order of a few hundred Gauss has beendetected bluewards of the Balmer discontinuity. These results should betaken into account in future modelling of the geometric structure of Apstar magnetic fields and the determination of the chemical abundances inAp stars with strong magnetic fields.Based on observations obtained at the European Southern Observatory,Paranal, Chile (ESO program No. 70.D-0470).
| Stellar activity and magnetism studied by optical interferometry
By means of numerical simulations, we investigate the ability of opticalinterferometry, via the fringe phase observable, to address stellaractivity and magnetism. To derive abundance maps and stellar rotationaxes, we use color differential interferometry which couples highangular resolution to high spectral resolution. To constrain magneticfield topologies, we add to this spectro-interferometer a polarimetricmode. Two cases of well-known Chemically Peculiar (CP) stars (βCrBand α2CVn) are simulated to derive instrumentalrequirements to obtain 2D-maps of abundance inhomogeneities and magneticfields. We conclude that the near-infrared instrument AMBER of the VLTIwill allow us to locate abundance inhomogeneities of CP stars largerthan a fraction of milliarcsecond whereas the polarimetric mode of theFrench GI2T/REGAIN interferometer would permit one to disentanglevarious magnetic field topologies on CP stars. We emphasize the crucialneed for developing and validating inversion algorithms so that futureinstruments on optical aperture synthesis arrays can be optimally used.
| Calculation of synthetic spectra of stars with consideration for magnetic field effect and stratification of chemical elements with depth
The computer code SynthM of spectrum synthesis in magnetic stellaratmospheres under the assumption of LTE in plane-parallel atmosphere isdescribed. The comparison of calculated Stokes IQUV shows good agreementbetween SynthM and N. Piskunov's SynthMag codes. We carried out testcalculation of synthetic profiles of selected lines observed in spectrumof β CrB. SynthM code allows one to calculate synthetic spectrawith present abundances stratification. The code allows us to use twobuilt-in analytical models of stellar magnetic field configuration.Also, it is possible to use arbitrary model of magnetic fieldconfiguration by setting the modulus and direction of field for eachintegrating node of a surface grid.
| Radiative lifetime, oscillator strength and Landé factor calculations in doubly ionized europium (Eu III)
A set of transition probabilities has been calculated for Eu IIItransitions of astrophysical interest particularly for the study ofchemically peculiar stars. They were obtained taking configurationinteraction and core-polarization effects into account. The accuracy ofthe new scale of oscillator strengths, which differs substantially fromprevious results, has been assessed through comparisons with recenttime-resolved laser-induced fluorescence measurements of radiativelifetimes.
| Characteristic Features of the Spectrum of the Unique roAp Star HD 101065 near the 6708 Å Lithium Resonance Doublet
Synthetic spectrum of the peculiar roAp star HD 101065(Przybylski’s Star) have been computed in the wavelength interval6705.8 6708.7 Å in order to describe the observed spectrum in thevicinity of the 6708 Å lithium line. Our detailed computations ofthe synthetic spectrum allowing for the hyperfine structure of thelithium line, lithium isotopic composition, and blending due to lines ofrare-earth elements (CeII, NdII, SmII, and others) have yieldedestimates of the atmospheric lithium abundance of the star and its6Li/7Li isotopic ratio.
| Target Selection for SETI. I. A Catalog of Nearby Habitable Stellar Systems
In preparation for the advent of the Allen Telescope Array, the SETIInstitute has the need to greatly expand its former list of ~2000targets compiled for Project Phoenix, a search for extraterrestrialtechnological signals. In this paper we present a catalog of stellarsystems that are potentially habitable to complex life forms (includingintelligent life), which comprises the largest portion of the new SETItarget list. The Catalog of Nearby Habitable Systems (HabCat) wascreated from the Hipparcos Catalogue by examining the information ondistances, stellar variability, multiplicity, kinematics, and spectralclassification for the 118,218 stars contained therein. We also make useof information from several other catalogs containing data for Hipparcosstars on X-ray luminosity, Ca II H and K activity, rotation, spectraltypes, kinematics, metallicity, and Strömgren photometry. Combinedwith theoretical studies on habitable zones, evolutionary tracks, andthird-body orbital stability, these data are used to remove unsuitablestars from HabCat, leaving a residue of stars that, to the best of ourcurrent knowledge, are potentially habitable hosts for complex life.While this catalog will no doubt need to be modified as we learn moreabout individual objects, the present analysis results in 17,129Hipparcos ``habstars'' near the Sun (75% within 140 pc), ~2200 of whichare known or suspected to be members of binary or triple star systems.
| 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.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| Lithium and rotation in F and G dwarfs and subgiants
Lithium abundances have been determined in 127 F and G Pop I stars basedon new measurements of the equivalent width of the lambda 6707 ÅLi I line from their high resolution CCD spectra. Distances and absolutemagnitudes of these stars have been obtained from the HipparcosCatalogue and their masses and ages derived, enabling us to investigatethe behaviour of lithium as a function of these parameters. Based ontheir location on the HR diagram superposed on theoretical evolutionarytracks, the sample of the stars has been chosen to ensure that they havemore or less completed their Li depletion on the main sequence. A largespread in the Li abundances is found at any given effective temperatureespecially in the already spun down late F and early G stars. Thisspread persists even if the ``Li-dip'' stars that have evolved from themain sequence temperature interval 6500-6800 K are excluded. Stars inthe mass range up to 2 M/Msun when divided into threemetallicity groups show a linear correlation between Li abundance andmass, albeit with a large dispersion around it which is not fullyaccounted for by age either. The large depletions and the observedspread in Li are in contrast to the predictions of the standard stellarmodel calculations and suggest that they are aided by non-standardprocesses depending upon variables besides mass, age and metallicity.The present study was undertaken to examine, in particular, the effectsof rotation on the depletion of Li. No one-to-one correlation is foundbetween the Li abundance and the present projected rotational velocity.Instead the observed abundances seem to be dictated by the rotationalhistory of the star. However, it is noted that even this interpretationis subject to the inherent limitation in the measurement of the observedLi EQW for large rotational velocities.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/409/251
| 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
| 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.
| 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.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Северная Корона |
| Прямое восхождение: | 15h27m49.70s |
| Склонение: | +29°06'21.0" |
| Видимая звёздная величина: | 3.68 |
| Расстояние: | 34.965 парсек |
| Собственное движение RA: | -181.5 |
| Собственное движение Dec: | 85.2 |
| B-T magnitude: | 3.99 |
| V-T magnitude: | 3.672 |
Каталоги и обозначения:
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INHABITED SKY
