A study of the Mg II 2796.34 Å emission line in late–type normal and RS CVn stars

Cardini, D.; Cassatella, A.; Badiali, M.; Altamore, A.; Fernández-Figueroa, M. J.

doi:10.1051/0004-6361:20030913

Cited by 4 publications

(2 citation statements)

References 30 publications

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“…The Mg ii k line fluxes were obtained through the method described in Cardini et al (2003), which consists in a direct integration of the observed profiles, as measured above the photospheric flux level. The estimated relative uncertainty on the measured fluxes is AE15%.…”

Section: Sample and Data Processingmentioning

confidence: 99%

Color, Rotation, Age, and Chromospheric Activity Correlations in Late‐Type Main‐Sequence Stars

Cardini¹,

Cassatella

2007

ApJ

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A study of the rotation-activity-age relationships in a large sample of single late-type main-sequence stars is carried out, based on rotation period data from the literature, on our measurements of the Mg ii k line chromospheric flux in IUE high-resolution spectra, and on Hipparcos parallaxes. The analysis of the rotation period data of open clusters and field stars indicates that the rotational period decreases linearly with increasing mass in stars of the same age and evolves as a power of age as t 0:45 . This information has enabled us to disentangle the role of age in the chromospheric activityYrotation relationship, as well as to analyze the behavior of the Mg ii emission flux in terms of ''activity evolutionary paths'' and of ''activity isochrones.'' It is shown that the Mg ii emission maintains a saturated level in very young stars until a certain age that depends on stellar mass, while at later stages it decays at a faster rate for more massive stars. We have also determined the convection turnover time from observational data and analyzed the relationship between the Mg ii emission flux and the Rossby number. We reach the conclusion that there is no clear advantage in using the Rossby number instead of stellar age in describing the chromospheric Mg ii losses, at least with the convective turnover time values currently in use.

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Section: Sample and Data Processingmentioning

confidence: 99%

Color, Rotation, Age, and Chromospheric Activity Correlations in Late‐Type Main‐Sequence Stars

Cardini¹,

Cassatella

2007

ApJ

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“…In addition to normal stars, we consider here a sample of 29 very active evolved stars of the RS CVn type. They have been selected following the criteria given in Cardini et al (2003) (hereafter Paper II) and further selected following the criteria illustrated above.…”

Section: Sample Of Starsmentioning

confidence: 99%

Mg II chromospheric radiative loss rates in cool active and quiet stars

Cardini¹

2005

A&A

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Abstract. The Mg  k emission line is a good indicator of the level of chromospheric activity in late-type stars. We investigate the dependence of this activity indicator on fundamental stellar parameters. To this purpose we use IUE observations of the Mg  k line in 225 late-type stars of luminosity classes I-V, with different levels of chromospheric activity. We first re-analyse the relation between Mg  k line luminosity and stellar absolute magnitude, performing linear fits to the points. The ratio of Mg  surface flux to total surface flux is found to be independent of stellar luminosity for evolved stars and to increase with decreasing luminosity for dwarfs. We also analyse the Mg  k line surface flux-metallicity connection. The Mg  k emission level turns out to be not dependent on metallicity. Finally, the Mg  k line surface flux-temperature relation is investigated by treating separately, for the first time, a large sample of very active and normal stars. The stellar surface fluxes in the k line of normal stars are found to be strongly dependent on the temperature and slightly dependent on the gravity, thus confirming the validity of recently proposed models. In contrast, data relative to RS CVn binaries and BY Dra stars, which show very strong chromospheric activity, are not justified in the framework of a description based only on acoustic waves and uniformly distributed magnetic flux tubes so that they require more detailed models.

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A star under multiple influences

Kővári,

Strassmeier,

Kriskovics

et al. 2024

A&A

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Close binaries with magnetically active components are astrophysical laboratories for studying the effects of binarity on activity. Of particular interest are binary and multiple star systems that contain a solar-type active component with an internal structure similar to the Sun, allowing us to study how the dynamo of a solar-type star would work under different conditions. We have conducted a comprehensive investigation of V815\,Her using photometric and spectroscopic data to understand the origin of the activity and what influences it in the short and long term. Using space photometry we performed light curve modeling in order to derive astrophysical and orbital parameters for the eclipsing binary subsystem V815\,Her B. Using archival photometric data covering a century we carried out a time frequency analysis. Spectral synthesis was applied to determine the basic astrophysical parameters of the rapidly rotating primary using high-resolution STELLA spectra recorded in 2018. Photometric analysis of archived data revealed multiple cycles on timescales between sim 6.5 and sim 26 years, some of which may be harmonic. From TESS photometry we obtained an orbital solution for the V815\,Her B subsystem. By placing the primary component on the Hertzsprung$-$Russell-diagram, we could deduce an age of approx 30\,Myr, in line with the high Li-6707 abundance. The STELLA spectra covering the 200 day-long observing season enabled us to create 19 time-series Doppler images, which revealed a constantly changing spotted surface on a timescale of a few weeks. From the consecutive image pairs we built up the average cross-correlation function map to measure the surface differential rotation of the spotted star, from which we derive a weak solar-type surface shear. We found evidence that the V815\,Her B component previously apostrophized as a "third body" is actually an eclipsing close binary subsystem of two M dwarfs with a period of 0.5\,d, that is, V815\,Her is a 2+2 hierarchical quadruple system. The system is apparently young, only a few times ten million years old, consistent with the spotted primary V815\,Her Aa being a zero-age main-sequence star. Spot activity on the primary was found to be vivid. Fast starspot decay suggests that convective-turbulent erosion plays a more significant role in such a rapidly rotating star. The weak surface shear of V815\,Her Aa due to differential rotation is presumably confined by tidal forces of the close companion V815\,Her Ab. The slowly increasing photometric cycle of about 6.5 years on average is interpreted as a spot cycle of V815\,Her Aa, which is probably modulated by the eccentric wide orbit.

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A study of the Mg II 2796.34 Å emission line in late–type normal and RS CVn stars

Cited by 4 publications

References 30 publications

Color, Rotation, Age, and Chromospheric Activity Correlations in Late‐Type Main‐Sequence Stars

Color, Rotation, Age, and Chromospheric Activity Correlations in Late‐Type Main‐Sequence Stars

Mg II chromospheric radiative loss rates in cool active and quiet stars

A star under multiple influences

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