Spot activity in the RS CVn binary DM Ursae Majoris

Rosario, M. J.; Heckert, P. A.; Mekkaden, M. V.; Raveendran, A. V.

doi:10.1111/j.1365-2966.2008.14372.x

Cited by 6 publications

(13 citation statements)

References 23 publications

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“…Because of the small temperature variation during the years with available V − I C , we cannot estimate the contribution of the changes of temperature origin in the overall light variation. However, the B − V color index, which also reflects the temperature variability as seen from the rotationally modulated light and color index curves in Rosario et al (2009), does not show the long-term change evident in V color. This is at least suggestive that some other mechanism is responsible for that variation (see Fig.…”

Section: Temperatures and Luminosities From Long-term Photometrymentioning

confidence: 91%

“…5. DM UMa showed nearly constant mean B − V during the 28 years of observation (but still rotationally modulated) while its V magnitude changed more than 0. m 6 in total (Rosario et al 2009). The low inclination of about 40…”

Section: Cyclic Brightness and Color Changesmentioning

confidence: 99%

“…The derived temperatures, given in Table 6, are precise to within about 50 K (see also Sect. 2.4) based on the error estimates of V − I C given by Rosario et al (2009). Figure 5 shows the effective temperatures at maximum and minimum brightness of the modulated light curves, parallel with the light and color index curves.…”

Section: Temperatures and Luminosities From Long-term Photometrymentioning

confidence: 99%

“…The star has a 28 year photometric dataset collected from the literature together with a long series of new observations taken between 1988−2009, all presented by Rosario et al (2009). The secondary component is not detected, the mass function is low (≈0.016, Crampton et al 1979).…”

Section: Introduction and Target Starsmentioning

confidence: 99%

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Magnitude-range brightness variations of overactive K giants

Oláh

Moór

Kővári

et al. 2014

A&A

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Context. Decades-long, phase-resolved photometry of overactive spotted cool stars has revealed that their long-term peak-to-peak light variations can be as large as one magnitude. Such brightness variations are too large to be solely explained by rotational modulation and/or a cyclic, or pseudo-cyclic, waxing and waning of surface spots and faculae as we see in the Sun. Aims. We study three representative, overactive spotted K giants (IL Hya, XX Tri, and DM UMa) known to exhibit V-band light variations between 0. m 65-1. m 05. Our aim is to find the origin of their large brightness variation. Methods. We employ long-term phase-resolved multicolor photometry, mostly from automatic telescopes, covering 42 yr for IL Hya, 28 yr for XX Tri, and 34 yr for DM UMa. For one target, IL Hya, we present a new Doppler image from NSO data taken in late 1996. Effective temperatures for our targets are determined from all well-sampled observing epochs and are based on a V − I C color-index calibration.Results. The effective temperature change between the extrema of the rotational modulation for IL Hya and XX Tri is in the range 50-200 K. The bolometric flux during maximum of the rotational modulation, i.e., the least spotted states, varied by up to 39% in IL Hya and up to 54% in XX Tri over the course of our observations. We emphasize that for IL Hya it is just about half of the total luminosity variation that can be explained by the photospheric temperature (spots/faculae) changes, while for XX Tri it is even about one third. The long-term, 0. m 6 V-band variation of DM UMa is more difficult to explain because little or no B − V color index change is observed on the same timescale. Placing the three stars with their light and color variations into H-R diagrams, we find that their overall luminosities are generally too low compared to predictions from current evolutionary tracks. Conclusions. A change in the stellar radius due to strong and variable magnetic fields during activity cycles likely plays a role in explaining the anomalous brightness and luminosity of our three targets. At least for IL Hya, a radius change of about 9% is suggested from m bol and T eff , and is supported by independent v sin i measurements.

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Section: Temperatures and Luminosities From Long-term Photometrymentioning

confidence: 91%

Section: Cyclic Brightness and Color Changesmentioning

confidence: 99%

Section: Temperatures and Luminosities From Long-term Photometrymentioning

confidence: 99%

Section: Introduction and Target Starsmentioning

confidence: 99%

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Magnitude-range brightness variations of overactive K giants

Oláh

Moór

Kővári

et al. 2014

A&A

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“…4 are not consistent with the general understanding that the light modulations in RS CVn binaries are caused by starspots that are cooler than the ambient photosphere, in which case we would have observed a redder colour for V711 Tau at fainter visual magnitudes. From an analysis of an extensive multicolour photometry of the single-lined, active RS CVn binary DM UMa, Rosario et al (2009) found that there are excess fluxes in U and B bands, which increase as the star becomes fainter, but they compensate only partially for the greater reduction in flux in those bands caused by spot activity.…”

Section: (B -V) Colour Variationmentioning

confidence: 99%

Orbital period modulation and spot activity in the RS CVn binary V711 Tauri

Muneer

Jayakumar

Rosario

et al. 2010

A&A

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Aims. We attempt to establish the real nature of the orbital period variation and its relation to the spot activity of V711 Tau, and determine why the (B − V) colour of the star appears to be nearly independent of its V magnitude. We wish to verify whether existing predictions in the literature for the long-term spot activity of the star are true or not by making extended photometric observations, and whether the broad component of Hα emission originates in more localised active regions, as suggested by some chromospheric models, by searching for any correlation between the base-line width of the emission and the light modulation. Methods. We obtained new radial velocities of the G-type component of V711 Tau on 42 nights during 2004−09, and BV photometry of V711 Tau on 202 nights during the years 1993−2009. We measured the equivalent widths of two well resolved lines of the G-type component from 13 of the spectra obtained by us. We also measured the equivalent widths and base-line widths of Hα emission from 21 spectra obtained during 2008−09. We analyse these along with relevant information available in the literature. Results. The available radial velocity data of V 711 Tau are consistent with a sinusoidal modulation of its orbital period; the period of modulation is found to be 36.3 ± 1.9 yr. The fractional light-loss over a photometric cycle is found to vary with an average period of 14.1 ± 0.3 yr. It appears that physical processes linked to the magnetic activity of the spotted star are responsible for the variation in the orbital period. The excess reduction in the B band flux relative to that in V band caused by spot activity is almost compensated for by the fractional increase in the contribution by the hotter companion to the total light in the blue spectral region, and thereby makes the (B − V) colour of the binary system nearly independent of its V magnitude. We find that the ratio of the radii of the components derived from their v sin i values, which is usually quoted in the literature, is substantially larger than that implied by the ratio of their brightnesses in V band. There is a slight indication from the V band data that the spot activity in V711 Tau has a component that is fixed in the orbital frame of reference. The equivalent width and base-line width of Hα emission do not show any obvious correlation with the V band light curve.

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Some findings from the longitudinal migration of starspots

Kaya,

Dal

2024

Publ. Astron. Soc. Aust.

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We present results regarding the longitudinal migrations of cool stellar spots that exhibit remarkable oscillations and explore their possible causes. We conducted analyses using high-quality data from nine target systems of various spectral types, spanning from F to M, which were observed by the Kepler Satellite. The systems in which the behaviour of the spots was examined are as follows: KIC 4357272, KIC 6025466, KIC 6058875, KIC 6962018, KIC 7798259, KIC 9210828, KIC 11706658, KIC 12599700, and KIC 8669092. Basic stellar parameters were calculated from light curve analysis using the PHOEBE V.0.32 software, and light curves were modelled to obtain sinusoidal variations occurring out-of-eclipses phases, induced by rotational modulation. Subsequently, we calculated the minimum times of the obtained sinusoidal variations using the Fourier transform. The distributions of θ min corresponding to these minimum times over time were computed using linear fits to determine the longitudinal migrations of the spotted areas. We then compared the longitudinal migration periods with the stellar parameters found in the literature. In addition, we also found a secondary variation in the spot migrations apart from the linear models. Our results revealed that the longitudinal migration periods vary in relation to the B – V colour index of the stars.

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Spot activity in the RS CVn binary DM Ursae Majoris

Cited by 6 publications

References 23 publications

Magnitude-range brightness variations of overactive K giants

Magnitude-range brightness variations of overactive K giants

Orbital period modulation and spot activity in the RS CVn binary V711 Tauri

Some findings from the longitudinal migration of starspots

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