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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.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| The nature of some doubtful open clusters as revealed by HIPPARCOS
We discuss the nature of some galactic open clusters by using propermotions and parallaxes from the Hipparcos and ACT catalogues. We showthat the clusters Collinder 399, Upgren 1, NGC 1252 and Melotte 227 donot exist. Collinder 132 is found to be mainly composed out of membersof an OB association, but there may be a star cluster present in thisarea too. Roeser & Bastian (1994) proposed that NGC 2451 consists oftwo star clusters. We show that NGC 2451 A definitively does exist, NGC2451 B may exist. A star cluster may also be present in the area ofRoslund 5. The Hipparcos data finally confirm the reality of Collinder135.
| CCD photometry of a delta Scuti variable in an open cluster. III. V 465 Persei in the alpha Persei cluster
We present the results of real-time CCD differential photometry for thedelta Scuti variable V 465 Per. The observations were performed forthirteen nights between November, 1994 and January, 1995. Total 3345points of differential V magnitudes were collected during theobservation period of 76.4 hours. From the Fourier analysis, we havedetected four frequencies as follows; f_1=14.040 c/d, f_2=17.208 c/d,f_3=33.259 c/d and f_4=13.721 c/d. Two frequencies of 12.50 c/d and33.49 c/d detected previously by Slovak (1978, ApJ 223, 192) maycorrespond to our f_1 and f_3, respectively. For each frequency,pulsation constants of Q_1=0.0520+/-0.008, Q_2=0.0425+/-0.006,Q_3=0.0220+/-0.003 and Q_4=0.0533+/-0.008 were derived from severalobservational properties of V 465 Per. Only the value of Q_3 is found tobe within the range of theoretical p-mode oscillations and the otherones show large differences relative to the theoretical values. The highQ-values might be interpreted as the occurrence of g-mode oscillationsin V 465 Per, even though it can not rule out the possibility ofsystematic errors (Breger 1990; Delta Scuti Star Newsletter, 2, 13)related to rotational velocity.
| UBVRI photometry of the FK5 Extension Catalogue Stars
UBVRI photometry in the Kron-Cousins system for 272 stars of theExtension Catalogue of the Fifth Fundamental Star Catalogue (FK5 stars)in the declination zone +7 deg to -90 deg is presented. Tables 1-2 arealso available 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 Based on observations made atthe European Southern Observatory, La Silla, Chile.
| γ Doradus and δ Scuti stars: cousins or twins?
γ Doradus stars are a group of slowly pulsating early F dwarfswith typical low frequencies near 1c/d. The pulsation modes are probablyg modes. These stars are slightly cooler than the typical δ Scutivariables, which pulsate with higher frequencies of typically 10c/d(mostly nonradial p modes). This paper examines the relationship betweenthe two groups of variables. Additional low-frequency variability hasbeen reported for fewer than 10% of the 300 δ Scuti starsexamined. In at least one case (1 Mon), the observational data areconsistent with an alternate interpretation in terms of a modeinteraction, f_1_-f_2_, between two p modes of higher frequency, ratherthan by the excitation of g modes. In several other stars (e.g. 4 CVn),the reported low-frequency variability may originate in the comparisonstar used. Arguments are given that for a number of stars the observedlow-frequency variations are caused by observational errors (such asinstrumental drift and transparency variations). A few δ Scutistars remain for which intrinsic γ Doradus-type variability mayalready have been discovered, although no case is well-studied. One ofthe best candidates is the star BI CMi, which is situated in the smallregion of overlap of the two groups of pulsators in theHertzsprung-Russell diagram. The star deserves further study.
| 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.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| 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.
| On the peculiarities of circumbinary envelopes in semi-detached close binaries and the modeling of their light curves.
Not Available
| The ellipsoidal variable stars
An annotated bibliography is presented for the ellipsoidal variableclass of noneclipsing close binaries, and a method is furnished for theanalysis of the light curves and spectroscopic data to determine thephysical parameters of such systems. Attention is given to confirmedellipsoidal variables, as well as suspected and rejected ones, and tothe characteristics of theoretical ellipsoidal light curves.
| Additional Variable Stars in the SRS Catalogue
Not Available
| 66th Name-List of Variable Stars
Not Available
| The frequency analysis of low amplitude delta Scuti stars. V - HD 188520
The paper analyzes HD188520 which is an A7IV/V star shown to be a newdelta Scuti variable. Photometry of this star is consistent with theA7/IV/V spectral classification; a frequency analysis of 502observations of HD188520 in a 60.5 hr period on 10 nights is presented.Two frequencies are present throughout the 66 day time-span of the dataset, although the alias at 3.760/day may be the correct lower frequency.It is suggested that the frequency at 4.762/day may result from g-modepulsation or ellipsoidal variability.
| Radial and non-radial oscillations in the very high metallicity Delta Scuti star HD 188136
The paper analyzes observations which show that HD 188136 is a DeltaScuti star. The metallicity index and the Sr4077 line which is nearly asstrong as H(delta) show that this star has a very high metallicity.Frequency analysis of 173 hr observations obtained on 30 nights in1978-79 was made; three frequencies were present throughout the entiredata set, one of which is due to a nonradial mode. It is suggested thatsince the Delta Scuti star evolves off the main sequence, it passesthrough a stage where radial and nonradial modes of the same k-valuecoincide.
| Four-color photoelectric photometry of two high-latitude clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..556E&db_key=AST
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Observation and Astrometry data
| Constellation: | Octant |
| Right ascension: | 20h06m04.82s |
| Declination: | -79°25'23.8" |
| Apparent magnitude: | 8.012 |
| Distance: | 128.866 parsecs |
| Proper motion RA: | 19.8 |
| Proper motion Dec: | -29.8 |
| B-T magnitude: | 8.283 |
| V-T magnitude: | 8.035 |
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INHABITED SKY
