Estimates of Active Region Area Coverage through Simultaneous Measurements of He I $\lambda \lambda$ 5876 and 10830 Lines

Abstract

Simultaneous, high-quality measurements of the neutral helium triplet features at 5876~Å and 10830~Å, respectively, in a sample of solar-type stars are presented. The observations were made with ESO telescopes at the La Silla Paranal Observatory under program ID 088.D-0028(A) and MPG Utility Run for FEROS 088.A-9029(A). The equivalent widths of these features combined with chromospheric models are utilized to infer the fractional area coverage, or filling factor, of magnetic regions outside of spots. We find that the majority of the sample is characterized by filling factors less than unity. However, discrepancies occur among the coolest K-type and warmest and most rapidly rotating F-type dwarf stars. We discuss these apparently anomalous results and find that in the case of K-type stars they are an artifact of the application of chromospheric models best suited to the Sun than to stars with significantly lower $T_{\mathrm{eff}}$. The case of the F-type rapid rotators can be explained with the measurement uncertainties of the equivalent widths, but they may also be due to a non-magnetic heating component in their atmospheres. With the exceptions noted above, preliminary results suggest that the average heating rates in the active regions are the same from one star to the other, differing in the spatially integrated, observed level of activity due to the area coverage. Hence, differences in activity in this sample are mainly due to the filling factor of active regions.

Accepted for publication in The Astrophysical Journal

References in corpus (22)

• Kepler Mission Design, Realized Photometric Performance, and Early Science
• Rotation Periods of 34,030 Kepler Main-Sequence Stars: The Full Autocorrelation Sample
• Rotation and differential rotation of active Kepler stars
• Water Vapour Absorption in the Clear Atmosphere of an exo-Neptune
• Rotation periods of 12 000 main-sequence Kepler stars: Dependence on stellar spectral type and comparison with v sin i observations
• New measurements of rotation and differential rotation in A-F stars: Are there two populations of differentially rotating stars?
• Solar cycle variation in solar irradiance
• Do stellar magnetic cycles influence the measurement of precise radial velocities?
• Variability of the transitional T Tauri star T Chamaeleontis
• Transit mapping of a starspot on CoRoT-2 - Probing a stellar surface by planetary transits
• TW Hya: Spectral Variability, X-Rays, and Accretion Diagnostics
• The GAPS Programme with HARPS-N at TNG VIII: Observations of the Rossiter-McLaughlin effect and characterisation of the transiting planetary systems HAT-P-36 and WASP-11/HAT-P-10
• Active cool stars and He I 10830 Å: the coronal connection
• Activity Analyses for Solar-Type Stars Observed With Kepler. I. Proxies of Magnetic Activity
• The cause of spatial structure in solar He I 1083 nm multiplet images
• Helium line formation and abundance in a solar active region
• Chromospheres in Metal-Poor Stars Evidenced from the He I 10830A Line
• The EUV spectrum of the Sun: SOHO CDS NIS radiances during solar cycle 23
• Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation I: non-thermal transport of helium ions
• Helium line formation and abundance during a C-class flare
• Enhancement of the helium resonance lines in the solar atmosphere by suprathermal electron excitation II: non-Maxwellian electron distributions
• The 10830 He I Absorption Line Among Metal-Poor Subdwarfs

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