The Ca II infrared triplet as a stellar activity diagnostic

Busà, I.; Cuadrado, R. Aznar; Terranegra, L.; Andretta, V.; Gomez, M. T.

doi:10.1051/0004-6361:20065588

Cited by 65 publications

(71 citation statements)

References 46 publications

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“…The most widely studied relationship is that between H α core emission and the total surface flux in Ca ii H & K lines (Strassmeier et al 1990;Robinson et al 1990;Cincunegui et al 2007;Walkowicz & Hawley 2009). Several studies have obtained fluxes in other chromospheric indicators lines, such as the Ca ii infrared triplet, for binary (Montes et al 1995b(Montes et al , 1996b and single (Thatcher & Robinson 1993;López-Santiago et al 2005;Busà et al 2007) stars. The aforementioned studies were either centred on a specific spectral type range (Thatcher & Robinson 1993;Walkowicz & Hawley 2009) or analysed the relation between total fluxes, instead of that between each of the indicator lines.…”

Section: Flux-flux Relationshipsmentioning

confidence: 99%

Chromospheric activity and rotation of FGK stars in the solar vicinity

Martínez-Arnáiz¹,

Maldonado

Montes³

et al. 2010

A&A

116

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Context. Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. These spots clearly affect the spectral line profiles, and their perturbations alter the line centroids creating a radial velocity jitter that might "contaminate" the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star. Aims. We obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d ≤ 25 pc) cool (spectral types F to K) stars, to estimate their expected activity-related jitter. As a complementary objective, we attempt to obtain relationships between fluxes in different activity indicator lines, that permit a transformation of traditional activity indicators, i.e., Ca ii H & K lines, to others that hold noteworthy advantages.Methods. We used high resolution (∼50 000) echelle optical spectra. Standard data reduction was performed using the IRAF echelle package. To determine the chromospheric emission of the stars in the sample, we used the spectral subtraction technique. We measured the equivalent widths of the chromospheric emission lines in the subtracted spectrum and transformed them into fluxes by applying empirical equivalent width and flux relationships. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity (RV) jitter, we used empirical relationships between this jitter and the R HK index. Results. We measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected rotational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we used the measured chromospheric activity to estimate the expected RV jitter for the active stars in the sample.

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Section: Flux-flux Relationshipsmentioning

confidence: 99%

Chromospheric activity and rotation of FGK stars in the solar vicinity

Martínez-Arnáiz¹,

Maldonado

Montes³

et al. 2010

A&A

116

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“…This difference can be used as an indicator of a chromosphere and stellar activity (e.g. Andretta et al 2005;and Busà et al 2007). …”

Section: Semi-empirical Model Of β Cetmentioning

confidence: 99%

Chromosphere of K giant stars

Bério

Merle

Thévenin

et al. 2011

A&A

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Context. Interferometers provide accurate diameter measurements of stars by analyzing both the continuum and the lines formed in photospheres and chromospheres. Tests of the geometrical extent of the chromospheres are therefore possible by comparing the estimated radius in the continuum of the photosphere and the estimated radii in chromospheric lines. Aims. We aim to constrain the geometrical extent of the chromosphere of non-binary K giant stars and detect any spatial structures in the chromosphere. Methods. We performed observations with the CHARA interferometer and the VEGA beam combiner at optical wavelengths. We observed seven non-binary K giant stars (β and η Cet, δ Crt, ρ Boo, β Oph, 109 Her, and ι Cep). We measured the ratio of the radii of the photosphere to the chromosphere using the interferometric measurements in the H α and the Ca II infrared triplet line cores. For β Cet, spectro-interferometric observations are compared to a non-local thermal equilibrium (NLTE) semi-empirical model atmosphere including a chromosphere. The NLTE computations provide line intensities and contribution functions that indicate the relative locations where the line cores are formed and can constrain the size of the limb-darkened disk of the stars with chromospheres. We measured the angular diameter of seven K giant stars and deduced their fundamental parameters: effective temperatures, radii, luminosities, and masses. We determined the geometrical extent of the chromosphere for four giant stars (β and η Cet, δ Crt and ρ Boo). Results. The chromosphere extents obtained range between 16% to 47% of the stellar radius. The NLTE computations confirm that the Ca II/849 nm line core is deeper in the chromosphere of β Cet than either of the Ca II/854 nm and Ca II/866 nm line cores. We present a modified version of a semi-empirical model atmosphere derived by fitting the Ca II triplet line cores of this star. In four of our targets, we also detect the signature of a differential signal showing the presence of asymmetries in the chromospheres. Conclusions. It is the first time that geometrical extents and structure in the chromospheres of non-binary K giant stars are determined by interferometry. These observations provide strong constrains on stellar atmosphere models.

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“…The consequence of the coupling is that these Ca II lines are mostly collisionally controlled in the lower chromosphere and very sensitive to the local temperature (Cauzzi et al 2008). For these reasons, the Ca II IRT is studied as an indicator of chromospheric activity (Linsky et al 1979a;Foing et al 1989;Chmielewski 2000;Busà et al 2007) revealing itself as an interesting alternative for solar-type chromospheres studies and angular momentum evolution (Krishnamurthi et al 1998). These lines show attractive intrinsic characteristics such as:…”

Section: Introductionmentioning

confidence: 99%

“…The normalized indices Andretta et al 2005) and the use of equivalent widths (Busà et al 2007;Žerjal et al 2013) have a non straightforward physical interpretation since these approaches are not ideal representations of the chromospheric radiative losses.…”

Section: Introductionmentioning

confidence: 99%

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

Mello

Dutra-Ferreira

Ribas

2016

A&A

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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.

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The Ca II infrared triplet as a stellar activity diagnostic

Cited by 65 publications

References 46 publications

Chromospheric activity and rotation of FGK stars in the solar vicinity

Chromospheric activity and rotation of FGK stars in the solar vicinity

Chromosphere of K giant stars

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

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