New <i>BVR</i> photometry of six prominent RS Canum Venaticorum binaries

Padmakar,; Pandey, S. K.

doi:10.1051/aas:1999272

Cited by 22 publications

(19 citation statements)

References 25 publications

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“…Korhonen et al 2001), not bluer. This socalled anticorrelation between the V light curve and the B − V colour index curve has been observed by several investigators (Padmakar & Pandey 1999, and references therein). The cause of the anticorrelation is under debate.…”

Section: B − V Coloursupporting

confidence: 64%

BVphotometry of UX Ari in the period 1987–2002

Ulvås

Henry

2003

A&A

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Abstract. We present 14.3 years of previously unpublished photometric observations of UX Ari. The observations were obtained between 1987.9 and 2002.2 using the T3 0.4-metre Automatic Photoelectric Telescope at Fairborn Observatory and consist of 1228 B band and 1213 V band measurements. The comparison star was 62 Ari. We have analyzed the new data together with previously published photometric observations. The V magnitude shows variations with dominant periods of about 12 and 25 years, where the longest period seems to correspond to an activity cycle. The previously reported anticorrelation between the B − V colour and V magnitude variations is confirmed.

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Section: B − V Coloursupporting

confidence: 64%

BVphotometry of UX Ari in the period 1987–2002

Ulvås

Henry

2003

A&A

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“…For IM Peg, values of ∆T 920 K (Poe & Eaton 1985) and ∆T 1130 K (Padmakar & Pandey 1999) are reported.…”

Section: Resultsmentioning

confidence: 99%

Measuring starspot temperature from line depth ratios

Catalano

Biazzo

Frasca

et al. 2002

A&A

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Abstract.Gray and collaborators have recently demonstrated that line-depth ratios are a powerful tool for temperature discrimination, able to resolve differences ≤10 K. The method has been applied to detect temperature variations in the 5-15 K range due to activity cycles (e.g. Gray et al. 1996aGray et al. , 1996b or to rotation modulation produced by large surface features, called "star-patches", like that detected in ξ Boo A by Toner & Gray (1988). Cool starspots of a few tenths of the stellar surface produce bumps in a line profile, which migrate through the line profile allowing Doppler-imaging in fast rotating stars. In the hypothesis that in slowly-rotating stars the passage of dark spots produces modulation of the center line depth of different amount in lines of different sensitivity to temperature, we have made test observations on three active binaries of the RS CVn type. Based on observations made at the Catania Astrophysical Observatory at a resolution R = 14 000, we show that line-depth ratios can be effectively used to determine spot temperatures of active binary systems. Using, on average, ten line pairs, selected in the 6100-6300 Å wavelength range, with the help of observations of 30 main sequence and giant stars, we have derived a calibration relation of line-depth ratios (LDR) in an absolute temperature scale, taking into account the gravity effect in the calibration relation. Single LDRs converted to temperature through the calibration relations have led to clear rotational modulation of the average surface temperature with amplitudes of 177 K, 119 K, and 127 K for VY Ari, IM Peg and HK Lac, with average estimated errors of about 10 K. We show that the observed temperature variation amplitude allows us to define a minimum fractional spotted area coverage as a function of spot-photosphere temperature ratio. Adopting the maximum value of average temperature, determined from the LDRs, as that of the unspotted photosphere, we computed the average spot temperature corresponding to the minimum spot coverage. Although not univocally constrained, the temperature difference (∆T = T ph − T sp ) obtained for the three systems, ∆T = 890 K for VY Ari, ∆T = 750 K for IM Peg, and ∆T = 810 K for HK Lac, are in good agreement with values derived with other methods.

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“…The differential V magnitudes given in Table 1 are plotted in Fig. 1 along with those compiled by Ulvas & Henry (2003), which in addition to their own data, include those obtained by Hall et al (1975), Hall (1977), Landis et al (1978), Guinan et al (1981), Sarma & Prakasa Rao (1984), Mohin & Raveendran (1989), Strassmeier et al (1989), Raveendran & Mohin (1995) and Padmakar & Pandey (1996). The previously reported observations indicated a fairly smooth variation for the mean V magnitude of UX Ari with a period around 25 years (Ulvas & Henry 2003).…”

Section: New Bv Photometrymentioning

confidence: 95%

Bluer colour of UX Arietis at fainter visual magnitudes

Rosario

Raveendran

Mekkaden

2007

A&A

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Aims. The RS CVn star UX Ari appears bluer when it is fainter, which is unusual for a spotted star; we aim to resolve this unusual behaviour of the object. Also the data available in the literature indicate that the mean V magnitude of UX Ari varies by about 25 years; we want to confirm whether this is indeed true. Methods. The most important parameter in understanding the colour variation is the relative brightnesses of the component stars of UX Ari. We use all spectroscopic information available in the literature to obtain a reasonable value for this parameter. We also present new BV photometry of UX Ari obtained on 58 nights during 2001-07. Results. The V magnitudes of UX Ari we obtained are significantly fainter than those reported in the literature, and they are not consistent with a 25-year period for the mean light level. The increased fractional contribution by the hotter G-type component to the total light in the blue spectral region as the active star becomes faint, seems to be the real cause for the bluer colour of UX Ari at fainter visual magnitudes.

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New BVR photometry of six prominent RS Canum Venaticorum binaries

Cited by 22 publications

References 25 publications

BVphotometry of UX Ari in the period 1987–2002

BVphotometry of UX Ari in the period 1987–2002

Measuring starspot temperature from line depth ratios

Bluer colour of UX Arietis at fainter visual magnitudes

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