Instrumental effects and the Stroemgren photometric system

in Astronomy and Astrophysics. Supplement Series (1987), 71

The extent to which the use of different photometers can affect results on stellar color indices was investigated by simultaneously observing a sample of widely different stars with several uvby ... [more ▼]

The extent to which the use of different photometers can affect results on stellar color indices was investigated by simultaneously observing a sample of widely different stars with several uvby photometric systems available at the ESO, La Silla, Chile. In one instance, the ESO 50-cm telescope and the four-channel photometer at the Danish 50-cm telescope were used simultaneously. The reductions were performed separately on each data set, using a linear color transformation procedure. The results agree with theoretical investigations which showed that substantial errors can arise from the nonconformity of passbands. It is emphasized that it is necessary to use separate color transformations for various stellar types and classes and for different interstellar reddenings. [less ▲]

UVBY observations of A, F, G and K field stars

in Astronomy and Astrophysics. Supplement Series (1987), 69

Photoelectric data in the uvby system have been obtained for about 800 southern stars of the Hipparcos Input Catalog (Grenon, 1982, 1985). Most of the stars are F and G main sequence and fall in the ... [more ▼]

Photoelectric data in the uvby system have been obtained for about 800 southern stars of the Hipparcos Input Catalog (Grenon, 1982, 1985). Most of the stars are F and G main sequence and fall in the magnitude range V = 8-11. [less ▲]

BW Vulpeculae - A coordinated campaign of photoelectric photometry from thirteen observatories

in Astronomy and Astrophysics. Supplement Series (1986), 66

This paper contains the fully reduced observational data on the Beta Cep star BW Vul, which were obtained in the summer of 1982 during an international campaign at thirteen observatories in the northern ... [more ▼]

This paper contains the fully reduced observational data on the Beta Cep star BW Vul, which were obtained in the summer of 1982 during an international campaign at thirteen observatories in the northern hemisphere. Useful measurements were made during a total of 486 hours. All observations have been assigned proper weights and were binned in time intervals of 90 seconds. In this manner the observations were combined into single data points which resulted in about 6000 mean differential measurements. A preliminary ephemeris for 1982 is derived, and a mean lightcurve is given. The results indicate a fair degree of stability in the shape and in the amplitude of the lightcurve. Possible variations exist in the morphology of the stillstand phenomenon. [less ▲]

Photometric variability of some early-type stars

in Astronomy and Astrophysics. Supplement Series (1986), 63

Photometric observations of 12 variable early type stars are presented. The properties of individual stars are discussed, and an attempt is made to interpret their variability. The information presented ... [more ▼]

Photometric observations of 12 variable early type stars are presented. The properties of individual stars are discussed, and an attempt is made to interpret their variability. The information presented on the stars includes the HD number and other identification, the observing runs, the periodicity of the variations, an error estimate, and a tentative classification of each star. [less ▲]

On the shape of the UVBY lightcurves of CP stars

in Astronomy and Astrophysics. Supplement Series (1985), 60

The authors present the lightcurves in the Strömgren system of 56 CP stars. The observational data have been fitted by a sine wave and its first harmonic. The least-square parameters are tabulated and it ... [more ▼]

The authors present the lightcurves in the Strömgren system of 56 CP stars. The observational data have been fitted by a sine wave and its first harmonic. The least-square parameters are tabulated and it is shown that such a fit describes very well the CP variations in most cases, the only exceptions being due to observational uncertainties. [less ▲]

New period determinations for variable CP stars

in Astronomy and Astrophysics. Supplement Series (1985), 59

Periods, or improved determinations of periods, are presented for 29 CP stars observed at La Silla in 1977-1982. The PHOT2 program's algorithm makes possible the bringing together of different observing ... [more ▼]

Periods, or improved determinations of periods, are presented for 29 CP stars observed at La Silla in 1977-1982. The PHOT2 program's algorithm makes possible the bringing together of different observing runs, through an improved reduction of the data to a common standard system. It is noted that, in many instances, magnetic observations would be required for the resolution of ambiguities, especially in the presence of quasi-symmetric double waves. [less ▲]

The ultraviolet spectrum of the Be star HD 50138

in Astronomy and Astrophysics. Supplement Series (1985), 60

The ultraviolet spectrum of the B8 Ve star HD 50138, recorded during the December 1978-January 1982 period with IUE, is analyzed. The spectrum is found to be crowded by absorption lines, mostly those of ... [more ▼]

The ultraviolet spectrum of the B8 Ve star HD 50138, recorded during the December 1978-January 1982 period with IUE, is analyzed. The spectrum is found to be crowded by absorption lines, mostly those of singly ionized iron peak elements. In addition there are broad lines essentially due to superionized species (Si IV, C IV) and a P Cygni profile for the Mg II doublet, similar to that seen in the star AB Aur. A few Fe II emission lines are also detected. The slowly expanding envelope surrounding HD 50138 appears to be decelerated outward with a decreasing ionization. The physical state of this envelope seems to suffer strong variations: a double structure was detected for some of the absorption lines in 1978-1979, and is interpreted as due to an outburst. A net increase of the excitation in 1980 is also observed and vanishes in 1982. In order to explain the unusual profiles of the Mg II lines, a possible fluorescence mechanism driven by Ly-beta is discussed. An accurate list of line identification is also provided. [less ▲]

Photoelectric photometry of the peculiar emission-line star GG Carinae

in Astronomy and Astrophysics. Supplement Series (1984), 55

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of ... [more ▼]

The first extensive sets of photoelectric observations of the peculiar emission-line star GG Carinae were obtained from 1977 to 1981, in both the standard UBV and Strömgren systems. A Fourier analysis of 767 independent measurements leads to the determination of a period P = 31[SUP]d[/SUP].020 for the light variations. Different physical arguments based on the analysis of the present photoelectric - as well as previous photographic - data clearly indicate, however, that the true period is P = 62[SUP]d[/SUP].039. The resulting composite lightcurve displays two distinct maxima and minima with a total light amplitude Deltam â ¡ 0.5 mag. Additional interesting features are noticed in the mean lightcurve. Although it is not possible to classify GG Carinae among any known type of variable stars, the light variations of this object are similar to those observed for beta Lyrae-type systems. [less ▲]

UBV photometry of the minor planets 86 Semele, 521 Brixia, 53 Kalypso and 113 Amalthea

in Astronomy and Astrophysics. Supplement Series (1983), 52

The asteroids were observed photometrically during the 1980 and 1981 oppositions, respectively. The V lightcurve of 86 Semele displays two asymmetric maxima and minima with a total amplitude DeltaV = 0.18 ... [more ▼]

The asteroids were observed photometrically during the 1980 and 1981 oppositions, respectively. The V lightcurve of 86 Semele displays two asymmetric maxima and minima with a total amplitude DeltaV = 0.18 mag. Its synodic rotation period is P[SUB]s[/SUB] = 16h38m02" ± 16" and the color indices B-V = 0.690 ± 0.011 and U-B = 0.320 ± 0.015 mag. 521 Brixia is a slow rotator (P[SUB]s[/SUB] > 24h) showing light variations greater than DeltaV â 0.09 mag and with color indices B-V = 0.714 ± 0.008 and U-B = 0.337 ± 0.011 mag. 53 Kalypso rotates with a period P[SUB]s[/SUB] = 26h33m ± 4m with a total light amplitude DeltaV > 0.10 mag and color indices B-V = 0.692 ± 0.015 and U-B = 0.341 ± 0.022 mag. The lightcurve of 113 Amalthea shows large amplitude variations (DeltaV > 0.26 mag) with a broad minimum and the rotation period is greater than 12h with color indices B-V = 0.888 ± 0.012 and U-B = 0.487 ± 0.019 mag. [less ▲]

Further spectroscopic observations of 25 quasi-stellar objects

in Astronomy and Astrophysics. Supplement Series (1981), 46

Spectroscopic observations are reported for 25 quasars suspected of having line profiles which are indicative of mass outflow from the central quasar. The quasars were selected on the basis of optical ... [more ▼]

Spectroscopic observations are reported for 25 quasars suspected of having line profiles which are indicative of mass outflow from the central quasar. The quasars were selected on the basis of optical variability and/or the presence of P Cygni spectral profiles, and large emission redshift, and observed on widened spectrograms obtained at the Cassegrain focus of the ESO 3.6-m telescope at La Silla during December 1977 and July 1978. Observations confirm the previously detected emission and absorption redshifts for most of the quasars, and reveal previously undetected lines and absorption redshifts in a few cases. [less ▲]