Oxford University Press : Linking chromospheric activity and magnetic field properties for late-type dwarf stars

Brown, E.L.; Jardine, M.M.; Marsden, S.C.; Mengel, M.W.; See, V.; Dahlkemper, M.N.; Petit, P.; Vidotto, A.A.; Jeffers, S.V.; Morin, J.; Boro Saikia, S.

doi:10.1093/mnras/stac1291

Article
Report number	arXiv:2205.03108
Title	Linking chromospheric activity and magnetic field properties for late-type dwarf stars
Author(s)	Brown, E.L. (Queensland U.) ; Jeffers, S.V. (Gottingen, Max Planck Inst.) ; Marsden, S.C. (Queensland U.) ; Morin, J. (U. Montpellier 2, LUPM) ; Boro Saikia, S. (Vienna U.) ; Petit, P. (IRAP, Toulouse) ; Jardine, M.M. (St. Andrews U.) ; See, V. (ESTEC, Noordwijk ; Exeter U.) ; Vidotto, A.A. (TCD, Dublin ; Leiden Observ.) ; Mengel, M.W. (Queensland U.) ; Dahlkemper, M.N. (Gottingen U. ; CERN)
Publication	2022-07-02
Imprint	2022-05-06
Number of pages	20
In:	Mon. Not. R. Astron. Soc. 514 (2022) 4300-4319
DOI	10.1093/mnras/stac1291 (publication)
Subject category	astro-ph.SR ; Astrophysics and Astronomy
Abstract	Spectropolarimetric data allow for simultaneous monitoring of stellar chromospheric $\log{R^{\prime}_{\rm{HK}}}$ activity and the surface-averaged longitudinal magnetic field, $B_l$, giving the opportunity to probe the relationship between large-scale stellar magnetic fields and chromospheric manifestations of magnetism. We present $\log{R^{\prime}_{\rm{HK}}}$ and/or $B_l$ measurements for 954 mid-F to mid-M stars derived from spectropolarimetric observations contained within the PolarBase database. Our magnetically active sample complements previous stellar activity surveys that focus on inactive planet-search targets. We find a positive correlation between mean $\log{R^{\prime}_{\rm{HK}}}$ and mean $\log\|B_l\|$, but for G stars the relationship may undergo a change between $\log{R'_{\rm{HK}}}\sim-4.4$ and $-4.8$. The mean $\log{R^{\prime}_{\rm{HK}}}$ shows a similar change with respect to the $\log{R^{\prime}_{\rm{HK}}}$ variability amplitude for intermediately-active G stars. We also combine our results with archival chromospheric activity data and published observations of large-scale magnetic field geometries derived using Zeeman Doppler Imaging. The chromospheric activity data indicate a slight under-density of late-F to early-K stars with $-4.75\leq\log{R'_{\rm HK}}\leq-4.5$. This is not as prominent as the original Vaughan-Preston gap, and we do not detect similar under-populated regions in the distributions of the mean $\|B_l\|$, or the $B_l$ and $\log{R'_{\rm HK}}$ variability amplitudes. Chromospheric activity, activity variability and toroidal field strength decrease on the main sequence as rotation slows. For G stars, the disappearance of dominant toroidal fields occurs at a similar chromospheric activity level as the change in the relationships between chromospheric activity, activity variability and mean field strength.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0) publication: © 2022-2025 The Author(s) (License: CC-BY-4.0)

$Bottom: HR diagram of the sample of PolarBase stars selected for our study. Circles denote single objects, stars denote binary or multiple star systems where the measured $\log R'_{\rm HK}$ may be impacted by the presence of companions, and triangles indicate binary or multiple systems where the $B_l$ and $\log R^{\prime}_{\rm HK}$ are known to be impacted by blending. Filled markers are taken to be main sequence stars. Open markers have significant \ion{Li}{i} absorption lines present in their spectra, suggesting that they may be young stars. Markers with reduced opacity are stars with noisy spectra, for which it is not clear if the stars have strong \ion{Li}{i} lines. The Sun is indicated with the usual symbol in red. Top: Histogram showing the breakdown of the sample by spectral classification.$ $Top: HR diagrams showing (left to right) mean chromospheric activity ($\log R^{\prime}_{\rm HK}$), amplitude of chromospheric activity variability ($\log \Delta R^{\prime}_{\rm HK}$) and number of observations used to measure the mean $\log R^{\prime}_{\rm HK}$. Bottom: HR diagrams showing (left to right) the mean, unsigned surface--averaged longitudinal magnetic field strength ($\log|B_l|$), amplitude of magnetic field strength variability ($\log \Delta B_l$) and number of observations used to measure the mean $|B_l|$. For all plots, the marker shapes and fill-styles are the same as in Figure \ref{fig:HRD}. \ion{Li}{i} abundant stars, which we take to be young stars, are indicated by open markers, while mature stars are shown by filled markers. Stars for which we were unable to determine if significant \ion{Li}{i} lines were present are shown by filled markers with a reduced opacity. Circles denote single objects, while star symbols indicate binaries for which $B_l$ measurements do not appear to be impacted by blending between companions, and triangles represent binaries for which $B_l$ is known to be impacted.$ $Mean chromospheric activity versus mean unsigned longitudinal field strength for our sample, separated by spectral type. Marker shapes and fill-styles are the same as in Figure \ref{fig:HRD}. Marker color scales with the number of observations. We take the number of observations as the average of the number of $\log R^{\prime}_{\rm HK}$ observations and $4\times B_l$ observations (since $4\times$ Stokes {\it{I}} observations are required to measure $B_l$). The grey shaded histograms above and to the right of each plot show the distributions of the mean $\log|B_l|$ and $\log R^{\prime}_{\rm HK}$ across each sample of main sequence stars. The black line histograms indicate the distributions of data for young, lithium rich stars only. The dashed lines indicate the limits of possible reduced populations in the activity distributions; the lines are red for the F and K stars because we did not find the reduced populations to be significant with respect to the histogram uncertainties in Figure \ref{fig:AppA}. The solid black line shown for G stars indicates a continuous piece-wise linear fit to the data.$ Show more plots

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Записът е създаден на 2022-05-20, последна промяна на 2023-01-31

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