The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies
L. Fossati, S. E. Marcelja, D. Staab, P. E. Cubillos, K. France, C. A. Haswell, S. Ingrassia, J. S. Jenkins, T. Koskinen, A. F. Lanza, S. Redfield, A. Youngblood, G. Pelzmann
过去对拥有热彗星的恒星的紫外线和光学观测表明，其中一些恒星的色球活动非常低，明显低于基底水平。对于WASP-13，观察结果表明，明显缺乏活性可能是由来自干预ISM的吸收引起的。受这一结果的启发，我们研究了ISM吸收对主序星晚型星活动测量（S和logR' $_{\rm HK}$指数）的影响。为此，我们采用合成恒星光球光谱结合不同量的色球发射和ISM吸收。我们提出了ISM吸收的影响，通过改变几个仪器，恒星，和ISM参数的活动测量。我们发现，当恒星和ISM谱线之间的相对速度小于30-40 km/s，ISM Ca Ⅱ柱密度logN $_{\rm CaII}$ >12时，ISM吸收对活度测量有显著影响。银河ISM吸收的直接测量和三维地图表明，沿着大多数视线，通常在大约100 pc的距离处可以达到logN $_{\rm CaII}$ =12的ISM Ca II柱密度。特别是，对于距离大于100 pc的类太阳恒星，我们预计logR' $_{\rm HK}$值的凹陷（偏差）大于0.05-0.1 dex，大约与该参数的典型测量和校准不确定性相同。这项工作表明，由ISM吸收引入的偏见时，必须始终考虑测量活动的恒星躺在超过100 pc。我们还考虑了多个ISM吸收分量的影响。我们讨论的相关性，这一结果的系外行星研究。
英文摘要：
Past UV and optical observations of stars hosting hot Jupiters have shown that some of these stars present an anomalously low chromospheric activity, significantly below the basal level. For WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening ISM. Inspired by this result, we study the effect of ISM absorption on activity measurements (S and logR'$_{\rm HK}$ indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental, stellar, and ISM parameters. We find that for relative velocities between the stellar and ISM lines smaller than 30-40 km/s and for ISM CaII column densities logN$_{\rm CaII}$>12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM CaII column density of logN$_{\rm CaII}$=12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the logR'$_{\rm HK}$ value larger than 0.05-0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies.
Magnetic activity in cool stars: manifestations and relevance to exoplanets
Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系统研究所）；Centro de Rádio Astronomia e Astrofísica Mackenzie, Universidade Presbiteriana Mackenzie（麦肯齐射电天文学与天体物理学中心，麦肯齐长老会大学）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学，巴黎西岱大学，法国原子能和替代能源委员会，法国国家科学研究中心，天文信息与管理实验室）；Leibniz-Institut für Astrophysik Potsdam (AIP)（波茨坦莱布尼茨天体物理研究所）；HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly Observatory（匈牙利研究网络地球与天文学研究中心，孔科利天文台）；Instituto de Astronomía y Física del Espacio (IAFE, UBA-CONICET)（空间天体物理学与天体物理研究所）；The Catholic University of America（美国天主教大学）；The Hakubi Center for Advanced Research, Kyoto University（京都大学博雅教育研究中心）；Department of Physics, Kyoto University（京都大学物理学系）；University of Helsinki（赫尔辛基大学）
Refined Telluric Absorption Correction for Low-Resolution Ground-Based Spectroscopy: Resolution and Radial Velocity Effects in the O2 A-Band for Exoplanets and K I Emission Lines
