Meredith L. Rawls edited More Discussion.tex  almost 9 years ago

Commit id: d24b35e3a037b7c592bcde9fb1ebe3150ab23035

deletions | additions      

       

Figures \ref{fig:emission1} and \ref{fig:emission2} investigate whether magnetic activity has any appreciable effect on absorption lines in either star. Following the approach of \citet{fro12}, we plot each target spectrum (colored line) on top of a model (dotted line), and show the difference below (solid black line). The model spectrum is a PHOENIX BT-Settl stellar atmosphere like the one described in Section \ref{bf} \citep{all03,asp09}, with $T_{\rm{eff}} = 5000$ and $\log g = 3.0$. It has been convolved to a lower resolution much closer to that of the ARCES and TRES spectrographs.  We examine a selection of the strongest {\rm Fe}\kern 0.1em{\sc i} lines which fall in the disentangled wavelength region and are either prone to Zeeman splitting in the presence of strong magnetic fields \citep{har73}, or not \citep{sis70}. The non-magnetic lines serve as a control. We find none of the six panels of {\rm Fe}\kern 0.1em{\sc i} absorption lines in either star show any significant deviation from the model spectrum. Thus, there is no apparent Zeeman broadening, which is unsurprising for evolved red giants. Magnetic fields must be quite strong to produce this effect. However, the H$\alpha$ and {\rm Ca}\kern 0.1em{\sc ii} absorption lines, which can be indicators of chromospheric activity, are somewhat more interesting. The H$\alpha$ line appears significantly deeper and broader than the model in both stars. While net emission is typically associated with activity, \citet{rob90} shows several examples of main sequence stars with increased H$\alpha$ absorption due to chromospheric heating, although they caution  it is difficult to separate the photospheric and chromospheric contributions to the line. The Still, the  increased H$\alpha$ absorption equivalent width is slightly more pronounced in Star 1 than Star 2, which suggests Star 1 may be more magnetically active. It is unclear whether the {\rm Ca}\kern 0.1em{\sc ii} doublet shows signs of excess broadening or increased equivalent width, but these lines certainly do not have \emph{smaller} equivalent widths than the model as we would expect in the case of chromospheric activity \citep{fro12}.