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On the relationship between the δ Scuti and γ Doradus pulsators
We searched for δ Scuti-type pulsations amongst known andcandidate γ Doradus stars. The motivations for such a project comefrom the need to understand the relationship of these two classes ofpulsator better, from the present poor knowledge of the hot border ofthe γ Doradus phenomenon, and from the exciting prospects forasteroseismology should stars be found which have both types ofpulsation excited. We acquired 270h of observations and monitored atotal of 26 stars. One target, HD 209295, turned out to be a member ofboth classes of pulsating star, but this object is peculiar in the sensethat it is a close binary. We classify six of our targets as new bonafide γ Doradus stars, whereas nine more are good γ Doraduscandidates, and three turned out to be ellipsoidal variables. One of ourprogramme stars was found to be a δ Scuti star, with no additionalγ Doradus variations. Furthermore, one star was already known tobe a bona fide γ Doradus star, and we could not find anunambiguous explanation for the variability of five more stars. Theanalysis of our data together with improved knowledge of stars from theliterature enabled us to revise the blue border of the γ Doradusphenomenon towards cooler temperatures. This new blue edge is muchbetter defined than the previous one and extends from a temperature ofabout 7550K on the ZAMS to 7400K one magnitude above it. Five bona fideγ Doradus stars we observed are located inside the δ Scutiinstability strip, but none of them exhibited observable δ Scutipulsations. We therefore suggest that γ Doradus stars are lesslikely to be δ Scuti pulsators compared with other normal stars inthe same region of the lower instability strip. In addition, we showthat there is a clear separation between the pulsation constants Q ofδ Scuti and γ Doradus stars. The γ Doradus stars knownto date all have Q>0.23d.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| The position corrections of 1400 stars observed with PA II in San Juan.
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| 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.
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