Effect of magnetic activity saturation in chromospheric flux-flux relationships

Martínez-Arnáiz, R.; López‐Santiago, J.; Crespo‐Chacón, I.; Montes, D.

doi:10.1111/j.1365-2966.2011.18584.x

Cited by 79 publications

(64 citation statements)

References 76 publications

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“…As expected, we find a correlation between the equivalent widths of the Hα line, the rest of Balmer lines, and the Ca H & K doublet (at least for the seven brightest targets; e.g., Martínez-Arnáiz et al 2011). To our knowledge, this is the first time that the calcium doublet is investigated down to the M spectral type in σ Orionis (Muzerolle et al 2003 tabulated equivalent widths of Hγ and the calcium infrared triplet at 8500-8660 Å, but not of the Ca H & K doublet).…”

Section: Resultssupporting

confidence: 51%

Stars and brown dwarfs in theσ Orionis cluster

Caballero

Cabrera-Lavers

García-Álvarez

et al. 2012

A&A

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Context. Although many studies have been performed so far, there are still dozens of low-mass stars and brown dwarfs in the young σ Orionis open cluster without detailed spectroscopic characterisation. Aims. We look for unknown strong accretors and disc hosts that were undetected in previous surveys. Methods. We collected low-resolution spectroscopy (R ∼ 700) of ten low-mass stars and brown dwarfs in σ Orionis with OSIRIS at the Gran Telescopio Canarias under very poor weather conditions. These objects display variability in the optical, infrared, Hα, and/or X-rays on time scales of hours to years. We complemented our spectra with optical and near-/mid-infrared photometry. Results. For seven targets, we detected lithium in absorption, identified Hα, the calcium doublet, and forbidden lines in emission, and/or determined spectral types for the first time. We characterise in detail a faint, T Tauri-like brown dwarf with an 18 h-period variability in the optical and a large Hα equivalent width of -125 ± 15 Å, as well as two M1-type, X-ray-flaring, low-mass stars, one with a warm disc and forbidden emission lines, the other with a previously unknown cold disc with a large inner hole. Conclusions. New unrevealed strong accretors and disc hosts, even below the substellar limit, await discovery among the list of known σ Orionis stars and brown dwarfs that are variable in the optical and have no detailed spectroscopic characterisation yet.

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Section: Resultssupporting

confidence: 51%

Stars and brown dwarfs in theσ Orionis cluster

Caballero

Cabrera-Lavers

García-Álvarez

et al. 2012

A&A

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“…Therefore, the correlations between different chromospheric activity indicators and the relation of excess chromospheric emission with other activity indicators had gained lot of attention (e.g. Schrijver, Dobson & Radick 1992;Montes et al 1995Montes et al , 1996Martínez-Arnáiz et al 2011). In fact, this topic need further investigation, e.g., need complex physical models to interpret the correlations, which is beyond the scope of this paper.…”

Section: Correlations Between Activity Indicatorsmentioning

confidence: 96%

Stellar activity with LAMOST – II. Chromospheric activity in open clusters

Fang

Zhao

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We use the LAMOST spectra of member stars in Pleiades, M34, Praesepe, and Hyades to study how chromospheric activity vary as a function of mass and rotation at different age. We measured excess equivalent widths of Hα, Hβ , and Ca ii K based on estimated chromospheric contributions from old and inactive field dwarfs, and excess luminosities are obtained by normalizing bolometric luminosity, for more than 700 late-type stars in these open clusters. Results indicate two activity sequences in cool spot coverage and Hα excess emission among GK dwarfs in Pleiades and M dwarfs in Praesepe and Hyades, paralleling with well known rotation sequences. A weak dependence of chromospheric emission on rotation exists among ultra fast rotators in saturated regime with Rossby number Ro 0.1. In the unsaturated regime, chromospheric and coronal emission show similar dependence on Ro, but with a shift toward larger Ro, indicating chromospheric emission gets easily saturated than coronal emission, and/or convective turnover time-scales based on X-ray data do not work well with chromospheric emission. More interestingly, our analysis show fully convective slow rotators obey the rotation-chromospheric activity relation similar to hotter stars, confirming the previous finding. We found correlations among Hα, Hβ , and Ca ii K emissions, in which Hα losses are more important than Ca ii K for cooler and more active stars. In addition, a weak correlation is seen between chromospheric emission and photospheric activity that shows dependency on stellar spectral type and activity level, which provides some clues on how spot configuration vary as a function of mass and activity level.

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“…Up to now stellar activity has been studied for the young objects with activity close to saturation and less active stars observed during execution of exoplanet search programmes (for example, Wright et al 2004;Martínez-Arnáiz et al 2011). Previously, we Fig.…”

Section: Relationship Between the LI Abundance Rotation And The Chrmentioning

confidence: 99%

Activity and the Li abundances in the FGK dwarfs

Mishenina

Soubiran

Kovtyukh

et al. 2012

A&A

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Aims. The aim of the present study is to determine the Li abundances for a large set of the FGK dwarfs and to analyse the connections between the Li content, stellar parameters, and activity. Methods. The atmospheric parameters, rotational velocities and the Li abundances were determined from a homogeneous collection of the echelle spectra with high resolution and a high signal-to-noise ratio. The rotational velocities v sin i were determined by calibrating the cross-correlation function. The effective temperatures T eff were estimated by the line-depth ratio method. The surface gravities log g were computed by two methods: the iron ionization balance and the parallax. The LTE Li abundances were computed using synthetic spectra method. The behaviour of the Li abundance was examined in correlation with T eff , [Fe/H], as well as with v sin i and the level of activity in three stellar groups of the different temperature range. Results. The stellar parameters and the Li abundances are presented for 150 slow rotating stars of the lower part of the main sequence. The studied stars show a decline in the Li abundance with decreasing temperature T eff and a significant spread, which should be due to the difference of age of stars. The correlations between the Li abundances, rotational velocities v sin i, and the level of the chromospheric activity were discovered for the stars with 6000 > T eff > 5700 K, and it is tighter for the stars with 5700 > T eff > 5200 K. The target stars with T eff < 5200 K do not show any correlation between log A(Li) and v sin i. The relationship between the chromospheric and coronal fluxes in active with detected Li as well as in less active stars gives a hint that there exist different conditions in the action of the dynamo mechanism in those stars. Conclusions. We found that the Li-activity correlation is evident only in a restricted temperature range and the Li abundance spread seems to be present in a group of low chromospheric activity stars that also show a broad spread in the chromospheric vs. coronal activity.

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Effect of magnetic activity saturation in chromospheric flux-flux relationships

Cited by 79 publications

References 76 publications

Stars and brown dwarfs in theσ Orionis cluster

Stars and brown dwarfs in theσ Orionis cluster

Stellar activity with LAMOST – II. Chromospheric activity in open clusters

Activity and the Li abundances in the FGK dwarfs

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