Pandora's Box

Middelkoop, Ronald; Huizing, Cornelis; Kuiper, Ruurd; Luit, E.J.

doi:10.29007/l7kx

Cited by 15 publications

(17 citation statements)

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“…The quantity S is sensitive to the integrated emission over these windows and the photospheric radiation transmitted by H and K instrumental passbands, both of which are color dependent (Middelkoop 1982). As mentioned in Section 1, Mittag et al (2013, hereafter M13) defined a new proxy, + R HK , which is converted from the S index by eliminating the photospheric contributions (Noyes et al 1984) and the socalled basal chromospheric flux (Schrijver 1987 (Middelkoop 1982). The photospheric flux in the HK bands  HK,phot , the basal chromospheric flux  HK,basal , and the continuum flux  RV were calculated from the B−V color index (Ramírez & Meléndez 2005).…”

Section: Determining the + R Hk Indexmentioning

confidence: 99%

“…The study of stellar activity in terms of different emission features originating from different parts of atmospheres has demonstrated the close connection between stellar activity, rotation, magnetic field, and inner stellar dynamo (Babcock 1958;Middelkoop 1982;Noyes et al 1984). The magnetic fields generated through magnetohydrodynamic processes control the structure and the energetic balance of stellar atmospheric plasma, bringing a variety of phenomena, e.g., inhomogeneous dark spots and bright faculae from the photosphere, emissions in the line cores from the chromosphere and the transition region, and thermal X-rays and eruptive flares from the coronal region (Catalano et al 1999).…”

Section: Introductionmentioning

confidence: 99%

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Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Zhang

et al. 2020

ApJS

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Monitoring chromospheric and photospheric indexes of magnetic activity can provide valuable information, especially the interaction between different parts of the atmosphere and their response to magnetic fields. We extract chromospheric indexes, S and + R HK , for 59,816 stars from LAMOST spectra in the LAMOST-Kepler program, and photospheric index, R eff , for 5575 stars from Kepler light curves. The log R eff shows positive correlation with log + R HK . We estimate the power-law indexes between R eff and + R HK for F-, G-, and K-type stars, respectively. We also confirm the dependence of both chromospheric and photospheric activity on stellar rotation. Ca II H and K emissions and photospheric variations generally decrease with increasing rotation periods for stars with rotation periods exceeding a few days. The power-law indexes in exponential decay regimes show different characteristics in the two activity-rotation relations. The updated largest sample including the activity proxies and reported rotation periods provides more information to understand the magnetic activity for cool stars.

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Section: Determining the + R Hk Indexmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Zhang

et al. 2020

ApJS

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“…Wilson scale with the calibration coefficients for NARVAL derived by Marsden et al (2014). To avoid color-dependence, S -index were transformed to R HK (Middelkoop 1982, Rutten 1984. To subtract the photospheric adjunct, we applied the correction formula of Noyes (1984).…”

Section: Chromospheric Activitymentioning

confidence: 99%

Magnetic activity of the young solar analog V1358 Orinis

Kriskovics

Kővári

Vida

et al. 2019

A&A

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Context. Young, fast rotating single stars can show dramatically different magnetic signatures and levels of magnetic activity as compared with the Sun. While losing angular momentum due to magnetic breaking and mass loss through stellar winds, the stars gradually spin down resulting in decreasing levels of activity. Studying magnetic activity on such solar analogues plays a key role in understanding the evolution of solar-like stars and allows a glimpse into the past of the Sun as well. Aims. In order to widen our knowledge of the magnetic evolution of the Sun and solar-like stars, magnetic activity of the young solar analogue V1358 Ori is investigated. Methods. Fourier analysis of long-term photometric data is used to derive rotational period and activity cycle length, while spectral synthesis is applied on high resolution spectroscopic data in order to derive precise astrophysical parameters. Doppler imaging is performed to recover surface temperature maps for two subsequent intervals. Cross-correlation of the consecutive Doppler maps is used to derive surface differential rotation. The rotational modulation of the chromospheric activity indicators is also investigated.Results. An activity cycle of ≈1600 days is detected for V1358 Ori. Doppler imaging revealed a surface temperature distribution dominated by a large polar cap with a few weaker features around the equator. This spot configuration is similar to other maps of young solar analogues from the literature, and supports recent model predictions. We detected solar-like surface differential rotation with a surface shear parameter of α = 0.016 ± 0.010 which fits pretty well to our recently proposed empirical relation between rotation and differential rotation. The chromospheric activity indicators showed a rotational modulation.

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“…emission from the photosphere, a so-called basal flux present even in the total absence of magnetic activity, and finally, the magnetic activity related emission in the line cores of the Ca II H&K absorption lines. Middelkoop (1982) and Rutten (1984) were the first to propose a method to convert the S MWO index into an absolute flux. To estimate the true chromospheric flux excess, i.e.…”

Section: R +mentioning

confidence: 99%

Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

Mittag

Schmitt

Schröder

2018

A&A

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The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R + HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 mainsequence stars with directly measured Mount Wilson S-indices and rotation periods. The R + HK values are derived from the respective S-indices and related to the rotation periods in various B − V -colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R + HK approaches zero, have a well-defined, colourdependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R + HK , rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.

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Pandora's Box

Cited by 15 publications

References 0 publications

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Magnetic Activity of F-, G-, and K-type Stars in the LAMOST–Kepler Field

Magnetic activity of the young solar analog V1358 Orinis

Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars

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