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U BV photoelectric photometry of the 1H/2H double mode cepheid CO Aurigae
We performed new U BV photoelectric photometry of the double modecepheid CO Aur. A careful time series analysis, by means of variousalgorithms, of our light curves of CO Aur enabled us to confirm the twopreviously known periodicities (Antonello et al. 1986) and their ratioof about 0.800. This ratio can be explained if CO Aur is a double modecepheid pulsating in the first and second overtone (1H/2H); only twosuch stars are known in our galaxy. From the analysis of present data,the high stability of the periods stated by Fuhrmann et al. (1984) isfully confirmed; there is no clear evidence of variations of other lightcurve parameters. Within the limits of our photoelectric data, thesecondary periodicity of CO Aur has a perfectly sinusoidal shape. Wealso performed a time series analysis of the Tycho epoch photometry inB_T and V_T; and the high stability of the first period of CO Aur isconfirmed by the Tycho datasets too.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| CO AUR and the double mode Cepheids
New photoelectric observations confirm that CO Aur is a short period,double mode Cepheid, with the period ratio indicating the excitation offirst and second overtones. The Fourier analysis of double mode Cepheidlight curves confirms the importance of the phase differenceφ21 for the determination of the pulsational mode of aCepheid.
| Untersuchungen zum Lichtwechsel des doppeltperiodischen δ-Cephei-Sterns CO Aurigae.
Conventional Argelander estimations of eight hundred photographic platesof Sonneberg Observatory are made. The light curve elements of thedouble period cepheid are improved and found to be stable within theobservational accuracy.
| A photometric investigation of RV Tauri and yellow semiregular variables
Results are presented for DDO and UBV photoelectric photometry of 52 RVTau and semiregular variables and candidates. CN abundances, effectivetemperatures, surface gravities, absolute visual magnitudes, and massestimates are derived in the framework of the spectroscopic groupingsproposed by Preston et al. (1963). The photometry suggests a furtherdivision of Preston's group A, and a possible physical connection isindicated between this group and the semiregular variables. Thespectroscopic groups are shown to be well separated in the DDOcolor-color diagrams when mean colors are used for individual stars. Anupper limit of about 3 solar masses is determined for stars in eachgroup. A correlation between derived iron abundances and published IRexcesses obtained from flux measurements at 3.6 and 11.3 microns isfound which supports the contention that dust production incircumstellar shells increases with increasing metallicity.
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