Fine structure of the age-chromospheric activity relation in solar-type stars

Abstract

Context. Strong spectral lines are useful indicators of stellar chromospheric activity. They are physically linked to the convection efficiency, differential rotation, and angular momentum evolution and are a potential indicator of age. However, for ages > 2 Gyr, the age-activity relationship remains poorly constrained thus hampering its full application. Aims. The Ca II infrared triplet (IRT lines, λλ 8498, 8542, and 8662) has been poorly studied compared to classical chromospheric indicators. We report in this paper absolute chromospheric fluxes in the three Ca II IRT lines, based on a new calibration tied to up-to-date model atmospheres. Methods. We obtain the Ca II IRT absolute fluxes for 113 FGK stars from high signal-to-noise ratio (S/N) and highresolution spectra covering an extensive domain of chromospheric activity levels. We perform an absolute continuum flux calibration for the Ca II IRT lines anchored in atmospheric models calculated as an explicit function of effective temperatures (T eff ), metallicity ([Fe/H]), and gravities (log g) avoiding the degeneracy usually present in photometric continuum calibrations based solely on color indices. Results. The internal uncertainties achieved for continuum absolute flux calculations are ≈ 2% of the solar chromospheric flux, one order of magnitude lower than for photometric calibrations. Using Monte Carlo simulations, we gauge the impact of observational errors on the final chromospheric fluxes due to the absolute continuum flux calibration and find that T eff uncertainties are properly mitigated by the photospheric correction leaving [Fe/H] as the dominating factor in the chromospheric flux uncertainty. Conclusions. Across the FGK spectral types, the Ca II IRT lines are sensitive to chromospheric activity. The reduced internal uncertainties reported here enable us to build a new chromospheric absolute flux scale and explore the ageactivity relation from the active regime down to very low activity levels and a wide range of T eff , mass, [Fe/H], and age.

Revisiting the 16 Cygni planet host at unprecedented precision and exploring automated tools for precise abundances

“…We inspected the chromospheric signature of other classical indicators along the spectral coverage of our observations such as Ca II H & K (Mamajek & Hillenbrand 2008;Lorenzo-Oliveira et al 2016a), Hβ (Montes et al 2001), and Ca II infrared triplet (Lorenzo-Oliveira et al 2016b). All of these show the same behavior found by Hα lines; 16 Cyg A and B are chromospherically older than the Sun (age > 4-5 Gyr) and the activity differences between the components are negligible.…”

The MUSCLES Treasury Survey. IV. Scaling Relations for Ultraviolet, Ca ii K, and Energetic Particle Fluxes from M Dwarfs

“…In the optical, the Ca IIresonance lines at 3933 Å(Ca IIK) and 3968 Å(Ca IIH), the Na I D resonance lines at 5890 and 5896 Å, Hαat 6563 Å, and the Ca IIinfrared triplet (IRT) at 8498, 8542, and 8662 Åare known to be good indicators of stellar chromospheric activity (e.g., Walkowicz & Hawley 2009;Gomes da Silva et al 2011;Lorenzo-Oliveira et al 2016, and references therein). However, Hαand Na I D are only good indicators of stellar activity for very active stars Díaz et al 2007;Walkowicz & Hawley 2009) and will not be considered here, because many of our target stars are optically inactive.…”

The Solar Twin Planet Search

“…expect that the log R HK (T eff ) is a better indicator of activity evolution of most inactive and old stars. The use of B-V color probably collapses the effective temperature and metallicity effects, which might give more direct information about the absolute continuum flux distribution (see, e.g., Lorenzo-Oliveira et al 2016a). This effect is more evident in inactive stars where the chromospheric/photospheric contrast is weaker.…”

“…The first parametrization of the activity-age relation was performed by Skumanich (1972), where the chromospheric emission of the Ca ii H & K lines was used as activity indicator. While there are other important magnetic activity tracers such as high-energy coronal emissions (Ribas et al 2005;Booth et al 1012), Mg ii H & K (Oranje & Zwaan 1985;Buccino & Mauas 2008), Hα (Pasquini & Pallavicini 1991;Lyra & Porto de Mello 2005), Hβ (Montes et al 2001), and the Ca ii infrared triplet (Busà et al 2007;Lorenzo-Oliveira et al 2016a), the Ca ii H & K lines are widely used because they are readily measurable from ground-based observatories, and also because a consistent and ready-to-use absolute flux calibration is available in the literature.…”

“…Therefore, the most convenient way to rule out the effects of other variables on Ca ii activity levels (Rutten & Schrijver 1987;Rocha-Pinto & Maciel 1998;Gray et al 2006;Lovis et al 2011;Lorenzo-Oliveira et al 2016a), minimizing biases in the age-activity correlation, is the study of chromospheric activity evolution of open clusters members (Soderblom et al 1991;Mamajek & Hillenbrand 2008), wide binaries (Garcés et al 2011;Desidera et al 2006), or field stellar twins with similar mass and metallicity. In this work we adopted the last option, reassessing the age-chromospheric activity relation using a large sample of solar twins (Ramírez et al 2014).…”