תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Magnetic fields of chemically peculiar stars. I. The catalog of magnetic CP stars
This is the first paper of the series dedicated to the analysis of themagnetism of chemically peculiar (CP) stars of the upper Main Sequence.We use our own measurements and published data to compile a catalog ofmagnetic CP stars containing a total of 326 objects with confidentlydetected magnetic fields and 29 stars which are very likely to possessmagnetic field. We obtained the data on the magnetism of theoverwhelming majority of the stars solely based on the analysis oflongitudinal field component B e . The surface magneticfield, B s , has been measured for 49 objects. Our analysisshows that the number of magnetic CP stars decreases with increasingfield strength in accordance with exponential law, and stars with B e exceeding 5kG occur rarely (about 3% objects of ourlist).
| Line profile variations in rapidly oscillating Ap stars: resolution of the enigma
We have carried out the first survey of the pulsational line profilevariability in rapidly oscillating Ap (roAp) stars. We analysed highsignal-to-noise ratio time-series observations of 10 sharp-lined roApstars obtained with the high-resolution spectrographs attached to theVery Large Telescope and Canada-France-Hawaii Telescope. We investigatedin detail the variations of PrIII, NdII, NdIII and TbIII lines anddiscovered a prominent change of the profile variability pattern withheight in the atmospheres of all studied roAp stars. We show that, inevery investigated star, profile variability of at least one rare-earthion is characterized by unusual blue-to-red moving features, which wepreviously discovered in the time-resolved spectra of the roAp starγ Equ. This behaviour is common in rapidly rotating non-radialpulsators but is inexplicable in the framework of the standard obliquepulsator model of slowly rotating roAp stars. Using analysis of the lineprofile moments and spectrum synthesis calculations, we demonstrate thatunusual oscillations in spectral lines of roAp stars arise from thepulsational modulation of linewidths. This variation occursapproximately in quadrature with the radial velocity changes, and itsamplitude rapidly increases with height in stellar atmosphere. Wepropose that the linewidth modulation is a consequence of the periodicexpansion and compression of turbulent layers in the upper atmospheresof roAp stars. Thus, the line profile changes observed in slowlyrotating magnetic pulsators should be interpreted as a superposition oftwo types of variability: the usual time-dependent velocity field due toan oblique low-order pulsation mode and an additional linewidthmodulation, synchronized with the changes of stellar radius. Ourexplanation of the line profile variations of roAp stars solves thelong-standing observational puzzle and opens new possibilities forconstraining geometric and physical properties of the stellarmagnetoacoustic pulsations.Based on observations collected at the European Southern Observatory(Paranal, La Silla), at the Canada-France-Hawaii Telescope and on dataretrieved from the ESO Science Archive.E-mail: oleg@astro.uu.se
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The discovery of 8.0-min radial velocity variations in the strongly magnetic cool Ap star HD154708, a new roAp star
HD154708 has an extraordinarily strong magnetic field of 24.5kG. Using2.5h of high time resolution Ultraviolet and Visual Echelle Spectrograph(UVES) spectra we have discovered this star to be an roAp star with apulsation period of 8min. The radial velocity amplitudes in the rareearth element lines of NdII, NdIII and PrIII are unusually low -~60ms-1 - for an roAp star. Some evidence suggests that roApstars with stronger magnetic fields have lower pulsation amplitudes.Given the central role that the magnetic field plays in the obliquepulsator model of the roAp stars, an extensive study of the relation ofmagnetic field strength to pulsation amplitude is desirable.Based on observations collected at the European Southern Observatory,Paranal, Chile, as part of programme 075.D-0145.E-mail: dwkurtz@uclan.ac.uk
| Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
| Evolutionary state of magnetic chemically peculiar stars
Context: .The photospheres of about 5-10% of the upper main sequencestars exhibit remarkable chemical anomalies. Many of these chemicallypeculiar (CP) stars have a global magnetic field, the origin of which isstill a matter of debate. Aims: .We present a comprehensivestatistical investigation of the evolution of magnetic CP stars, aimedat providing constraints to the theories that deal with the origin ofthe magnetic field in these stars. Methods: .We have collectedfrom the literature data for 150 magnetic CP stars with accurateHipparcos parallaxes. We have retrieved from the ESO archive 142 FORS1observations of circularly polarized spectra for 100 stars. From thesespectra we have measured the mean longitudinal magnetic field, anddiscovered 48 new magnetic CP stars (five of which belonging to the rareclass of rapidly oscillating Ap stars). We have determined effectivetemperature and luminosity, then mass and position in the H-R diagramfor a final sample of 194 magnetic CP stars. Results: .We foundthat magnetic stars with M > 3 ~M_ȯ are homogeneouslydistributed along the main sequence. Instead, there are statisticalindications that lower mass stars (especially those with M ≤2~M_ȯ) tend to concentrate in the centre of the main sequence band.We show that this inhomogeneous age distribution cannot be attributed tothe effects of random errors and small number statistics. Our datasuggest also that the surface magnetic flux of CP stars increases withstellar age and mass, and correlates with the rotation period. For starswith M > 3~M_ȯ, rotation periods decrease with age in a wayconsistent with the conservation of the angular momentum, while for lessmassive magnetic CP stars an angular momentum loss cannot be ruledout. Conclusions: .The mechanism that originates and sustains themagnetic field in the upper main sequence stars may be different in CPstars of different mass.
| The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode
We undertook a time-series photometric multisite campaign for therapidly oscillating Ap (roAp) star HD 99563 and also acquired mean lightobservations over four seasons. The pulsations of the star, which showflatter light maxima than minima, can be described with a frequencyquintuplet centred on 1557.653 μHz and some first harmonics of it.The amplitude of the pulsation is modulated with the rotation period ofthe star that we determine with 2.91179 +/- 0.00007 d from the analysisof the stellar pulsation spectrum and of the mean light data. We breakup the distorted oscillation mode into its pure spherical harmoniccomponents and find it is dominated by the l= 1 pulsation, and also hasa notable l= 3 contribution, with weak l= 0 and 2 components. Thegeometrical configuration of the star allows us to see both pulsationpoles for about the same amount of time; HD 99563 is only the fourthroAp star for which both pulsation poles are seen and only the thirdwhere the distortion of the pulsation modes has been modelled. We pointout that HD 99563 is very similar to the well-studied roAp star HR 3831.Finally, we note that the visual companion of HD 99563 is located in theδ Scuti instability strip and may thus show pulsation. We showthat if the companion was physical, the roAp star would be a2.03-Msolar, object, seen at a rotational inclination of44°, which then predicts a magnetic obliquity .
| 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.
| HD 12098 - A new northern hemisphere roAp star
We present the analysis of 65 hours of high speed photometricobservations of HD 12098 taken from State Observatory, Naini Tal andGurushikhar Observatory, Mt. Abu on sixteen nights spanning fromNovember 1999 to November 2000. HD 12098 is the first rapidlyoscillating Ap star discovered from the ``Naini Tal-Cape survey fornorthern hemisphere roAp stars". It is the 32nd in the complete list. HD12098 exhibits one predominant mode of oscillation at nu1 =2.1738 mHz. The second-most significant frequency in our data is atnu2 = 2.1641 mHz with a 1 cycle/day alias ambiguity. We arguethat nu2 is a rotational sidelobe of nu1, ratherthan an independent pulsation mode. Evidence for the presence of twoother frequencies at 2.1807 and 2.3056 mHz is also presented.
| 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.
| 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.
| Hβ photometry of southern CP2 stars: is the uvbybeta luminosity calibration also valid for peculiar stars?
We present Hβ photometry of 233 southern CP2 stars (covering themagnetic Ap stars according to the definition by Preston 1974) brighterthan V < 8.5 mag from the list of Bidelman & MacConnell (1973).Absolute magnitudes derived from this photometry together with alreadyexisting uvby photometry is confronted with Hipparcos results availablefor a common subset of 152 stars. In order to compare peculiar withnormal stars, we identified a sample of 1147 normal B to F-type starsusing their published uvbybeta and Hipparcos data. For our analysis wedivide both samples into three temperature as well as two Hipparcosparallax accuracy groups. The error distribution of both samples provedto be statistically comparable. As a result the absolute magnitudes forthe B-type CP2 stars show up to be significantly too bright by anaverage of 0.5 mag using the actual photometric calibration. On theother hand, the photometric absolute magnitudes for cool A to F-type CP2stars are up to three magnitudes fainter as compared to Hipparcos. Basedon observations at ESO-La Silla and with the Hipparcos satellite
| 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.
| Lithium on the surface of cool magnetic CP stars I. Summary of spectroscopic observations with three telescopes
We present new results of observations of the 6708 Ä line in twelveCP stars made with three telescopes: the ESO CAT telescope, the CrimeanObservatory (CrAO) 2.6-m telescope, and the Nordic Optical Telescope(NOT). Unique profile and wavelength variations of the line at 6708Ä were discovered in two stars, HD 60435 and HD 83368. We presentarguments in favour of the identification of this feature with theresonant Li i line. According to the incidence and variability of thisline, spectra of twelve stars were divided in four groups: Group 1 - theline is remarkably variable in intensity and wavelength; this groupincludes the stars HD 83386 and HD 60435; Group 2 - the line is variableto a lesser extent; includes beta CrB and HD 188041; Group 3 - the lineis not variable; includes 33 Lib, HD 134214, HD 166473 and gamma Equ;Group 4 - the line is not present; includes HD 42659, HD 80316, HD118022 and HD 128898. The behaviour in Groups 1-3 can be explained bythe existence of Li rich spots on the star's surface using the obliquerotator model with different inclination and magnetic obliquity for eachstar. For HD 83368 we have found a tight correlation between thevisibility of the spots and the orientation of the dipole pulsationmode. Based on observations collected at the European SouthernObservatory, La Silla, Chile, the Nordic Optical Telescope, La Palma,Spainand the Shajn Telescope, Crimean Astrophysical Observatory,Ukraine}
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| CP2 stars as viewed by the UVBY H_beta system
The aim of this work is to study the capacity of the uvby H_βsystem for detecting the chemically peculiar (CP) stars based on theeffect that peculiar features in the flux distribution have on all theStromgren-Crawford indices. Our study focuses on the classical magneticpeculiar stars (CP2), though Am stars (CP1) are also included forcomparison with cool CP2 stars. Satisfactory results were obtained forhot CP2 stars: the definition of a new index p, which is a linearcombination of uvby H_β colours, allowed us to separate a highpercentage of hot CP2 stars from normal stars. According to this newindex, 60 new CP2 candidates are proposed. The working sample wasextracted from The General Catalogue of Ap and Am stars by \cite[Rensonet al. (1991)]{ren91}. Photometric observations to enlarge the sample ofCP2 stars with complete uvby H_β photometry were carried out. Theseobservations are also reported in the present paper. The new index p isalso used to correct the reddening of early CP2 stars computed as ifthey were normal stars. Tables 2, 3 and 7 are also available inelectronic form from CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Evolutionary estimates for 10 magnetic AP stars calculated from their rigid rotator geometries.
I present estimates of the evolutionary states (effective temperatures,masses, radii, luminosities and ages) of 10 magnetic Ap stars, andsubsequent constraints on the evolution of magnetic fields in theseobjects. Using rotational axis inclinations (sin i) reported by Leroy etal. (1996A&A...311..513L), combined with apparent rotationalvelocities (vsin i) and rotational periods (P_rot_) obtained from avariety of sources, the radii of these stars have been calculatedassuming rigid rotation. From the positions of these objects in theradius-effective temperature (log(R/Rsun_)-log(T_eff_)) planeI obtain their evolutionary states using the model evolutionarycalculations by Schaller et al. (1992A&AS...96..269S). The stars inthis study span the entire width of the main sequence, showing notendancy to cluster near the ZAMS or the TAMS. In this respect theseresults are consistent with the conclusion of North(1993IAUCo.138..577N) (who reports that the Ap (CP2) stars appear to bedistributed uniformly along the width of the main sequence) andinconsistent with that of Hubrig & Mathys (1994AN....315..343H) (whosuggest that the magnetic Ap stars may be near the end of their mainsequence life). When the magnetic field strengths of these stars aregraphed versus the fraction of main sequence evolution completed, nocorrelation is evident. However, it is of interest to note that strongmagnetic fields do exist in Ap stars at all evolutionary states (fromthe ZAMS to the TAMS), and that more than 70% of the stars discussed inthis paper have polar magnetic field strengths between 3 and 6kG. Asimilar graph of the magnetic axis obliquity angle β of each starversus age shows that intermediate values of β exist for stars asold as 10^9^yr. This indicates that, if β does evolve towardasymptotic values as suggested by Mestel et al. (1981MNRAS.195..979M),the timescale for this evolution is quite long, at least for stars with~5kG surface magnetic fields and rotational periods near 10 days.
| The oblique dipole pulsation mode of the rapidly oscillating AP star HD80316
New high-speed photometric observations of the rapidly oscillating Apstar HD80316 suggest that its principal pulsation mode is an obliquedipole mode with a frequency of either 2251.68 or 2254.47 muHz (P=7.4min). Rotationally split frequency triplets give two choices for therotation period, P_rot=2.085+/-0.005 or 4.163+/-0.010d, which agree withpossible rotation periods derived independently from mean lightobservations. Both frequency triplet possibilities show the sum of therotational inclination, i, and the magnetic obliquity, beta, to begreater than 90 deg. This makes HD80316 only the third roAp star, afterHR3831 and HD6532, to have a polarity-reversing dipole pulsation. Thetwo possible rotation periods are so close to multiples of 1 d^-1 thatalias problems in our single-site observations preclude a definitesolution for the oscillations of this star. Further progress requiresmultisite observations, or long-term single-site observations to sampleall rotation phases.
| The discovery of a frequency quintuplet and distorted dipole mode in the rapidly oscillating AP star HD 6532
We have analysed 77 h of new, multisite observations of HD 6532 obtainedin 1994, along with 20 h of observations from 1984 and 90 h from 1985. Afrequency quintuplet with frequency separations equal to exactly therotation frequency, and two harmonic frequencies, give a completesolution. The amplitude spectrum of the residuals shows white noise withits highest peaks of amplitude 0.1 mmag. We interpret the frequencyquintuplet in terms of a distorted oblique dipole mode, which we modelwith a spherical harmonic series that is primarily dipolar with smallradial and quadrupole contributions. This model does not fully describethe rotational modulation of pulsation amplitude and phase, which leadsus to suggest that a completely decentred dipole model needsdevelopment. HD 6532 is only the second roAp star, after HR 3831, with apolarity-reversing pulsation mode which has been studied in sufficientdetail to characterize the geometry of the mode.
| A kinematical study of rapidly oscillating AP stars.
A kinematical study of rapidly oscillating Ap (roAp) stars and of asample of apparently similar Ap stars that show no pulsation isperformed, with a view to investigating possible differences between thetwo groups. The mean absolute magnitudes of the stars of both samples,derived through the mean parallax method, are at most marginallydifferent. From the consideration of the velocity ellipsoid parametersand of the mean orbital elements characterizing their motion in theGalaxy, the roAp stars appear significantly older than theirnon-pulsating counterparts.
| Linear polarimetry of AP stars. VI. A modified dipolar model consistent with the observations.
While some Ap variables display a linear polarization variation verysimilar to that computed for a pure magnetic dipole, several Ap starsshow conspicuous peculiarities which must be interpreted in terms ofdepartures from the standard, oblique rotator model (we have shownpreviously that abundances anomalies are not sufficient to explain oddpolarization diagrams). We have designed an inversion method, based on aresidues minimization process, which allows us to build the map of themagnetic peculiarities at the surface of non-dipolar stars. As thelinear polarization is but weakly sensitive to the variations of thefield modulus, we interpret the polarization anomalies in terms ofinclination changes of the lines of force within their meridian plane.Keeping the magnetic equator as a plane of symmetry, we show that it issufficient to assume slightly expanded lines of force, over some partsof the magnetic equator, to explain most peculiar polarization curves(Figs. 2 to 7). Such regions, where the lines of force expand outwards,seem to occur preferentially in the vicinity of the rotation poles forthose stars having a β angle not far from 90deg. In the case ofβ CrB, which was studied previously in detail (Leroy, 1995), thisregion nearly coincides with the equatorial patch of enhanced fieldstrength, which must be postulated to explain the surface fieldmeasurements. The present study, which also provides unambiguousdeterminations of the i and β angles for 15 stars, marks theprovisional end of our investigation based on broadband linearpolarization measurements. We expect that similar measurements, having agood spectral resolution, will be available soon: they will yield moresevere observational constraints enabling a more detailed modeling work.However, we think that the series of articles which ends with thepresent paper has demonstrated the great value of linear polarizationdata and may have opened fruitful research tracks bearing on themagnetic structure of Ap stars.
| The p-mode spectra of the roAp stars
Not Available
| Linear polarimetry of AP stars. V. A general catalogue of measurements.
A systematic program of broadband linear polarimetry, bearing on 55 Apstars, has been developed during the 4 last years, at the Pic du MidiObservatory. While separate data have been already published, we presentin this paper a complete catalogue of our observational material,including more than 400 measurements. We complement these data withanother 100 measurements, obtained previously by other authors, so as toget a synthetic view of the phenomenon. Most of the observations havebeen dedicated to a small number (15) of stars, which show conspicuouschanges of the linear polarization, so that it is possible to knowaccurately the time variation of the Stokes parameters: we expect thatthese new data will really improve our knowledge of the magneticconfiguration, after a proper analysis which is currently beingdeveloped. For the other 40 stars, the polarization is either too small,or strongly contaminated by the interstellar polarization, so thatbroadband polarimetry is not very effective. Anyway, this firstsystematic investigation on the linear polarization of Ap stars will bea useful starting point for future measurements which should be madewith higher spectral resolution. Finally, our measurements have providednew determinations of the rotation period for several stars.
| VRI photometry of wide double stars with A- type primaries.
We are presenting VRI photometry of 93 wide visual double stars havinglate B- or A- type primaries, taken from the Annex of Double andMultiple Stars of the HIPPARCOS Input Catalogue. Spectral types havebeen estimated for most of the primaries and for the majority of thesecondaries. 40% of them probably have common origin components, forwhich we calculated photometric parallaxes and some orbital valuesestimates.
| Observations of Pulsating AP Stars in South Africa
Not Available
| Catalogue of CP stars with references to short time scale variability
A catalogue was compiled which contains all references in the literaturesince 1962 related to variations of CP stars on time scales shorter thanthe rotation period. The role of this catalogue lies in the unbiasedlisting of all available references, and not in a critical evaluation.
| Discovery of 10.5-minute Oscillations in the Ap SrEu Star HD 9289
Not Available
| The 71st Name-List of Variable Stars
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | נחש מים |
| התרוממות ימנית: | 09h18m25.03s |
| סירוב: | -20°22'16.2" |
| גודל גלוי: | 7.779 |
| מרחק: | 133.69 פארסק |
| תנועה נכונה: | 48 |
| תנועה נכונה: | -42.2 |
| B-T magnitude: | 8.142 |
| V-T magnitude: | 7.809 |
קטלוגים וכינוים:
|
