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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly 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
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F stars
We test the hypothesis of Berthet (1992) {be91} which foresees that Amstars become giant metallic A and F stars (defined by an enhanced valueof the blanketing parameter Delta m_2 of the Geneva photometry) whenthey evolve. If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than 100kms(-1) , while the maximum rotational velocity for Am stars is about100 kms(-1) . The rate of tight binaries with periods less than 1000days is less than 30% among metallic giants, which is incompatible withthe value of 75% for Am stars - [Abt & Levy 1985] {ab85}).Therefore, the simplest way to explain the existence of giant metallic Fstars is to suggest that all normal A and early F stars might go througha short ``metallic" phase when they are finishing their life on the mainsequence. Besides, it is shown that only giant stars with spectral typecomprised between F0 and F6 may have a really enhanced Delta m_2 value,while all A-type giants seem to be normal. Based on observationscollected at Observatoire de Haute Provence (OHP), France.
| Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
| Accurate Positions Of Variable Stars Near The South Galactic Pole
Not Available
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| 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.
| Rapid oscillations of five stars in the spectral range A and F. I
The five stars HD 4849, HD 24712, HD 182475, HD 184552 and HD 215874 area small group of objects enclosed in a larger observational program forsearching of rapid oscillations. They have been observed with the 50 cmESO-telescope at La Silla (Chile). These objects are characterized as asuspected delta Scuti-type star, an Ap star, an A9 V star, an A1m starand an A9 III-IV star, respectively. For the first two stars theperiods, detected by other authors, were confirmed. For HD 182475 aperiod of 112.3 min has been estimated. In the case of HD 184552 anoscillation with a period of 163.3 min has been found. The star HD215874 shows unambiguously a variation with a period of 97.2 min.
| Empirical P-L-C relation for Delta Scuti stars - A catalogue
An extensive and up-to-date list of 192 Delta Scuti stars is presented.Empirical period - luminosity - color (P-L-C) relations are obtained forthe four lowest modes corresponding to radial pulsations. Agreement withpredicted values indicates that, in general, both Stroemgren photometriccalibration and pulsation theory work well for these stars.
| Quasi-160-minute oscillation period of Delta Scuti stars
The resonance power spectrum (or commensurability spectrum) computed for217 Delta Scuti stars indicates that the dominant (most commensurate)period for the total set of oscillation periods of these stars is 162.2+ or - 2.8 min. Within the error limits, this period coincidesapproximately with the 160-min period of global oscillations of the sun.
| Metallicism among A and F giant stars
132 stars considered as A and F giants have been studied for theirproperties in the Geneva photometric system. It is shown that thissystem to derive the temperature, absolute magnitude and Fe/H value forstars in this part of the HR diagram. 36 percent of the stars of oursample exhibit an enhanced value Delta m2 that can be interpreted interms of Fe/H. The red limit of stars having an enhanced Fe/H value is0.225 in B2-V1 or 6500 K in Teff. This corresponds to the limit definedby Vauclair and Vauclair (1982) where the diffusion timescale is equalto the stellar lifetime and permits the assumption that the diffusion isthe process responsible for the metallicism observed in the A and Fgiants.
| I.A.U. Archives of Unpublished Observations of Variable Stars - 1981-1984 Data
Not Available
| Differential photometry of the Delta SCT stars HR 151 and HR 239
Differential two-color photometry of the Delta Sct stars HR 151 (HD3326) and HR 239 (HD 4849) has led to a confirmation of the variabilityof HR 151 and a refinement of the period of HR 239. In addition,constraints on the radial overtone, k, and the spherical harmonic order,l, were determined for HR 239. Both these stars are of particularinterest as they have been considered to be possible Ap stars. If so,they may be the only two Ap stars that consistently show Delta Sctvariability, the case of the Ap classification of HR 151 being thestronger one.
| Revised list of pulsating stars with ultra-short periods
A comprehensive list of 178 known Delta Scuti and RR Lyrae-stars ispresented. Using this revised list a HR diagram for these ultra shortperiod pulsating stars is plotted and the blue and red edges of theresultant instability strip are determined. Selection effects arediscussed, and the PLC relationship of Breger (1979) is tested usingdata from this list. Stars lying outside the defined instability regionare discussed.
| The group of low-harmonic pulsating CP2 stars - HD 10088, a new candidate
The CP2 star HD 10088 was found to be pulsating in the fundamental orfirst overtone mode. Five CP2 stars are discussed as members of a groupof low-harmonic radially pulsating stars, a group which is clearlydistinct from the high overtone, non-radial oblique pulsators, a groupof eight stars established by Kurtz (1982).
| The Delta Scuti variability of three stars with AP spectral classifications, HR 151, 239 and 7461
Observations which show HR 151 and 7461 to be Delta Scuti stars andwhich confirm the Delta Scuti variability of HR 239 are presented. Allthree of these stars have been classified as Ap stars by at least onespectroscopist, but those classifications are insecure and need to bere-examined. If any of these stars are really magnetic Ap stars, thentheir Delta Scuti variability is of considerable interest.
| IAU Archives of Unpublished Observations of Variable Stars
Not Available
| Information on the Photoelectric Observations of Variable Stars Deposited at Odessa Astronomical Observatory
Not Available
| 65th Name-List of Variable Stars
Not Available
| Delta Scuti and related stars
An extensive review is given of the current status of our knowledge ofthe stars in the lower instability strip. Current problems areemphasized. Particular attention is given to the following areas: theconfusion concerning naming and the implied astrophysical properties(often erroneous), single and multiple periods, the effect of rotationand metallicism on pulsation, the nature of the so-called dwarfcepheids, and pulsation in Ap stars. Various reports of unusal andstrange effects are also discussed with personal, possibly biasedjudgment on their reality.
| The classification of intrinsic variables. VIII - Ultrashort period Cepheids
The photometric and astrometric data for ultrashort-period Cepheids withmaximum visual magnitudes brighter than 11.5 are collected anddiscussed. Most of these variables are high-mass, little-evolved starswhich, in the halo and disk populations, are blue stragglers. Theluminosities are calibrated from membership in disk and halo populationgroups; the visual magnitude equals 8(1-/c1/sub c) for disk stars, where(C1)sub c is a reddening- and temperature-free parameter.
| Observational evidence for the pulsational stability of some AP stars
Sixteen peculiar A type stars (one of them questionable) and two Amstars have been observed photometrically during a continuous observingrun of 2 to 4 hours each, to check them for pulsational stability. AllAp stars proved to be of constant brightness to within about thestandard duration of 0.002 to 0.003 mag, except for an eventuallong-term variability due to rotation. Therefore, no observationalevidence from this side can be brought up against diffusion as apossible mechanism responsible for peculiar atmospheres. Both Am starsalso proved to be of constant brightness. Four new pulsating variablestars have been discovered from observations in the program.
| HR 239 and HR 8676: Two delta Scuti-Type Variables
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | עוף החול |
| התרוממות ימנית: | 00h50m03.70s |
| סירוב: | -43°23'41.0" |
| גודל גלוי: | 6.48 |
| מרחק: | 96.993 פארסק |
| תנועה נכונה: | 9.9 |
| תנועה נכונה: | 10.1 |
| B-T magnitude: | 6.825 |
| V-T magnitude: | 6.512 |
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