Long-term variations in the spottedness of BY Dra M dwarfs

Alekseev, I. Yu.; Kozhevnikova, A. V.

doi:10.1134/s1063772917030015

Cited by 19 publications

(17 citation statements)

References 14 publications

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“…The uncertainty was computed from 10 6 random resamplings of the input parameters according to their quoted uncertainties. The lower inclination value that we find, contrary to other studies (Zboril 2003;Morin et al 2008;Alekseev & Kozhevnikova 2017), arises from the different projected velocity and stellar radius used. In particular, projected rotational velocities of 5.0 and 6.5 km s −1 (Delfosse et al 1998;Reiners & Basri 2007) and stellar radii of 0.30 and 0.37 R (Delfosse et al 2000;Pettersen 1980) were reported.…”

Section: The Active Star Yz CMIcontrasting

confidence: 99%

“…Zboril (2003) computed spot solutions from light curves taken in different seasons, and found a typical spot coverage between 10% and 25% of the surface, resulting from a single spot at a co-latitude ∼15−35 deg from the pole and temperature ∼500 K cooler than the surrounding photosphere, all assuming an inclination ranging from 60 deg to 75 deg. Similarly, Alekseev & Kozhevnikova (2017) used 11 epochs of observations over 30 years of broadband photometry to compute the spottedness of YZ CMi. The authors assumed an effective temperature of 3300 K and an inclination of i = 60 deg, obtaining two belts of spots 210 ± 70 K cooler than the photosphere, which were mainly located at latitudes of 12−15 deg, and covering up to 38% of the stellar surface.…”

Section: The Active Star Yz CMImentioning

confidence: 99%

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The CARMENES search for exoplanets around M dwarfs

Baroch

Morales

Ribas

et al. 2020

A&A

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Context. Variability caused by stellar activity represents a challenge to the discovery and characterization of terrestrial exoplanets and complicates the interpretation of atmospheric planetary signals. Aims. We aim to use a detailed modeling tool to reproduce the effect of active regions on radial velocity measurements, which aids the identification of the key parameters that have an impact on the induced variability. Methods. We analyzed the effect of stellar activity on radial velocities as a function of wavelength by simulating the impact of the properties of spots, shifts induced by convective motions, and rotation. We focused our modeling effort on the active star YZ CMi (GJ 285), which was photometrically and spectroscopically monitored with CARMENES and the Telescopi Joan Oró. Results. We demonstrate that radial velocity curves at different wavelengths yield determinations of key properties of active regions, including spot-filling factor, temperature contrast, and location, thus solving the degeneracy between them. Most notably, our model is also sensitive to convective motions. Results indicate a reduced convective shift for M dwarfs when compared to solar-type stars (in agreement with theoretical extrapolations) and points to a small global convective redshift instead of blueshift. Conclusions. Using a novel approach based on simultaneous chromatic radial velocities and light curves, we can set strong constraints on stellar activity, including an elusive parameter such as the net convective motion effect.

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Section: The Active Star Yz CMIcontrasting

confidence: 99%

Section: The Active Star Yz CMImentioning

confidence: 99%

The CARMENES search for exoplanets around M dwarfs

Baroch

Morales

Ribas

et al. 2020

A&A

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“…In order to maintain this cycle, the star performs tens of times more turnovers than the Sun or other slowly rotating G-M dwarfs with cyclic activity. The considerable amplitude of the cycle (more than 0.2 m ) indicates an increasing of the star spottedness, up to 38% of its total area in the maximum of the activity (Alekseev and Kozhevnikova, 2017). The large area and high flare energy are features of difference in the activity of this star from those typical for the Sun and other low-mass stars.…”

Section: Discussionmentioning

confidence: 82%

Long-Term Cyclic Variability of YZ CMi in the Context of Solar and Stellar Physics

Bondar

Katsova

2018

Geomagn. Aeron.

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Manifestations of activity on the YZ CMi (M4.5Ve) flare star which has a rotation period of 2.77 days and belongs to a group of activity-saturated stars, are considered from long-term photometric data together with photographic measurements from 1926 to 2009. Long-term changes in yearly mean brightness of the star are found on a time scale of 27.5 years with an amplitude of 0.2 − 0.3 m that indicate variations in development of surface inhomogeneities and a large degree of surface spottedness in the maximum activity. Spots are distributed unevenly over the surface, their concentration is higher at certain longitudes spaced by intervals equal to 0.6 phases of the rotation period. The recovery of active longitude (a possible "flip-flop" effect) occurs over a period of about 6 years. We note differences in activity of this star from typical for the Sun and solar-like stars, which are associated with its dynamic characteristics P cyc and P rot and its inner structure.

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“…We have used the results derived for 40 dK-dM stars from photographic data series (Bondar', 1995(Bondar', , 2013, from photometric researches by Alekseev and Kozhevnikova (2017) and Messina et al (2002). For 9 stars (Bondar' 2019) the available data series were added by data from photometric catalogs.…”

Section: G-m Dwarfs With Cyclic Activity On Long-term Intervalsmentioning

confidence: 99%

“…A certain number of stars with cycles longer than the solar one are known, but most of the studied objects were investigated from the modern databases on a limited time interval; therefore, cycles of no longer than 10-15 years were found for these stars (Savanov, 2012 The long-term variations in brightness of several dozens of cool K-M dwarfs were studied from photographic archives and broadband photometry (Bondar', 1995(Bondar', , 2013Alekseev and Bondar', 1998;Alekseev and Kozhevnikova, 2017); for some of them the activity of photospheric starspots similar to the observed on the Sun has been found or suspected.…”

Section: Introductionmentioning

confidence: 99%

Cycles on the Solar-type Stars and Cooler Dwarfs

2019

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Features of the development of activity cycles in the solar-type stars and fast-rotating cool dwarfs have been considered for 65 stars observed in some decades. Cycles with duration of 7-18 years compared to the solar cycle were found for about 50% of the studied stars. In cooler dwarfs with rotation periods of less than 5 days, cyclic changes in brightness occur on longer scales, up to 80 years. Activity of the highest level is produced on K dwarfs; their main cycles are long and have the highest amplitudes. Both old and young solar-type stars show a similar tendency in increasing the cycle length with a slower rotation. No evidence for a relation between the rotation period and duration of cycles was found for cool dwarfs with P rot < 5 days.

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Long-term variations in the spottedness of BY Dra M dwarfs

Cited by 19 publications

References 14 publications

The CARMENES search for exoplanets around M dwarfs

The CARMENES search for exoplanets around M dwarfs

Long-Term Cyclic Variability of YZ CMi in the Context of Solar and Stellar Physics

Cycles on the Solar-type Stars and Cooler Dwarfs

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