The interpretation of cyclical photometric variations in certain dwarf Me-type stars

Budding, E.

doi:10.1007/bf00643052

Cited by 102 publications

(73 citation statements)

References 10 publications

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“…Altogether, 20 light curves in V and I C with sufficiently large rotational modulation above the noise level were found suitable for the analysis. For the starspot modeling and spot temperature determination we used our own computer code, based on Budding's (1977) equations, that assumes circular spot(s) which are homogenously cooler and thus darker than the surrounding photosphere. Only the spot's area and location (longitude and latitude) were adopted as free parameters.…”

Section: Methodsmentioning

confidence: 99%

Time-series photometric spot modeling

Oláh

Strassmeier

Kővári

et al. 2001

A&A

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Abstract. We analysed all the existing photometric observations of V833 Tau and found long-term variability on time scales of ≈70 years, 6.5 years and 2.4 years. Using V and IC-band data from 1990-2000, we obtained starspot surface distributions from 20 suitable light curves. We found that the spot-area changes generally follow the long-term light variations. Spot temperatures are determined for each of the datasets and an average value of 1230 K ± 270 K relative to the photosphere is found. This value agrees with previous results from TiO modeling (1330 K ± 110 K). Small scale spot temperature and area changes are recovered during 1997-1999, that we explain with a variable spot/faculae ratio. A powerful flare in UBV (RI)C was observed in 1993 November. A 10 000 K fit yielded a total emitted flare energy of more than 10 34 ergs from an area of about 1.3% of the stellar surface, 60% of it in the V (RI)C bands. The flare characteristics are compared to another, 100-times smaller flare observed earlier in 1983.

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Section: Methodsmentioning

confidence: 99%

Time-series photometric spot modeling

Oláh

Strassmeier

Kővári

et al. 2001

A&A

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“…We modeled the DS light curve folded on the 1.15 day period using a model based on the formalism developed by Budding (1977). The EUV variability is assumed to be produced by a circular spot on the photosphere of GD 394 as it moves relative to the line of sight and over the rotation period of the white dwarf.…”

Section: Ight Curve Modelingmentioning

confidence: 99%

Adding More Mysteries to the DA White Dwarf GD 394

Dupuis

Chayer

Vennes

et al. 2000

ApJ

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We present spectroscopic and timing analyses of the hot DA white dwarf GD 394 showing abundance inhomogeneities across its surface. Lick Hamilton echelle, International Ultraviolet Explorer (IUE), HST GHRS, and Hopkins Ultraviolet Telescope (HUT) spectra show dominant Si III and Si IV features, while Extreme Ultraviolet Explorer (EUV E) spectra show evidence of a host of trace element opacities. We report the detection of Si III j4552 triplet with a measured radial velocity of 27 km s~1 in agreement with far ultraviolet (FUV) line velocities, but indicating a silicon abundance (Si/H \ 2 ] 10~5) a factor of 10 larger than measured in the FUV range [Si/H \ (2È7) ] 10~6]. E †ective temperature measurements based on Lyman continuum (EUV E) and Lyman line series (HUT) are systematically cooler (*T D [4000 K) than measurements based on medium-dispersion Balmer line spectroscopy, an e †ect attributed to yet unidentiÐed opacities. A timing analysis of EUV E deep-survey and scanner time series, as well as spectrometer data, shows GD 394 to be variable in the extreme ultraviolet (EUV) with an amplitude of 25% and a period of 1.150^0.003 days. The EUV variability suggests abundance inhomogeneities in the atmosphere, and we explore di †erent models to explain its origin.

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“…Since discovered as a variable star by Guthnick (1929), SV Cam has been observed by Wood (1946), Van Woerden (1957), Hilditch et al (1979) and Patkos (1982). The light curves have been analysed by Zeilik et al (1988), Budding (1977), Budding & Zeilik (1987) and Djurasević (1998), using spot modelling techniques. According to these authors, a single active darkspotted region covers a significant part of the stellar surface at high latitudes and is responsible for the migration waves which tend to fall into two longitude sectors, 45…”

Section: Target Starsmentioning

confidence: 99%

A spectroscopic study of the eclipsing binaries SV Camelopardalis and XY Ursae Majoris

Özeren

Gunn

Doyle³

et al. 2001

A&A

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Abstract. High-resolution spectroscopic observations of the eclipsing RS CVn-type active close binaries SV Camelopardalis and XY Ursae Majoris reveal excess emission components in the Hα and Hβ lines. We have used the spectral subtraction technique to separate the excess emission from the photospheric background and find that in both stars the excess emission is associated with the secondary, cooler component. Analysis of the EWHα/EW Hβ ratio indicates that in both cases the emission is probably associated with surface plage regions or prominences viewed against the stellar disks. We find no evidence of excess absorption features associated with extended prominence-like material in these systems.

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The interpretation of cyclical photometric variations in certain dwarf Me-type stars

Cited by 102 publications

References 10 publications

Time-series photometric spot modeling

Time-series photometric spot modeling

Adding More Mysteries to the DA White Dwarf GD 394

A spectroscopic study of the eclipsing binaries SV Camelopardalis and XY Ursae Majoris

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