Fine structure of the chromospheric activity in Solar-type stars – The Hα line

Abstract

Abstract.A calibration of Hα as both a chromospheric diagnostic and an age indicator is presented, complementing the works previously done on this subject (Herbig 1985;Pasquini & Pallavicini 1991). The chromospheric diagnostic was built with a statistically significant sample, covering nine years of observations, and including 175 solar neighborhood stars. Regarding the age indicator, the presence of stars for which very accurate ages are determined, such as those belonging to clusters and kinematic groups, lends confidence to our analysis. We also investigate the possibility that stars of the same age might have gone through different tracks of chromospheric decay, identifying -within the same age range -effects of metallicity and mass. These parameters, however, as well as age, seem to be significant only for dwarf stars, losing their meaning when we analyze stars in the subgiant branch. This result suggests that, in these evolved stars, the emission mechanism cannot be magnetohydrodynamical in nature, in agreement with recent models (Fawzy et al. 2002c, and references therein). The Sun is found to be a typical star in its Hα chromospheric flux, for its age, mass and metallicity. As a byproduct of this work, we developed an automatic method to determine temperatures from the wings of Hα, which means the suppression of the error inherent to the visual procedure used in the literature.

Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: a chemo-chronological analysis

“…The table lists the flux in the centre of the Hα line (F Hα ), computed by Lyra & Porto de Mello (2005) and used as a chromospheric activity indicator (the larger the value of F Hα , the higher the level of chromospheric activity). The uncertainty for this parameter is 0.5 × 10 5 erg cm −2 s −1 .…”

“…Lyra & Porto de Mello (2005) applied this method to solar neighbourhood stars, and values of T Hα eff for our sample were used as a third T eff indicator, with an uncertainty σ(T Hα eff ) = 50 K.…”

Spectroscopic properties of cool Ursa Major group members

“…However, it is possible to address the chromospheric infilling of the Hα core. Lyra & Porto de Mello (2005) argue that there are even some advantages compared to Ca II H&K. Fuhrmann (2004) note that the Hα cores of Ursa Major stars are filled-in by about 10% compared to inactive main-sequence stars of similar effective temperature. The present work allows one to verify this behaviour for a larger sample of UMa group members.…”

“…To more reliably compare the chromospheric infilling of UMa group members with that of other stellar groups, in particular the Pleiades and the Hyades, the chromospheric flux is measured according to the method of Lyra & Porto de Mello (2005). They showed that members of different stellar groups display a different average level of chromospheric flux.…”

“…The normalized spectra are integrated in both the Hα core (W Hα ) with a width of 1.7 Å and Willstrop's band (6550-6600 Å; W 50 ). The absolute flux in the Hα core F Hα is calculated from the ratio of W Hα to W 50 , using the absolute flux calibration and the (V − R) − T eff calibration given by Lyra & Porto de Mello (2005). Finally, photospheric flux is subtracted from F Hα using the lower envelope in their Fig.…”