Searches for planets around massive stars are essential for developing general understanding of planet formation and evolution of the planetary systems. The main objective of the Pennsylvania - Torun Planet Search is detection of planets around G-K subgiants and giants through precision radial velocity (RV) measurements with iodine absorption cell using HET HRS spectrograph. However, the long period radial velocity variations of red giants may also have other than planetary nature (e.g. a non-radial pulsations or rotational modulation in presence of starspots). In this work we present bisector analysis of cross-correlation functions (CCF) constructed from the spectra used for radial velocity determination but cleaned from the iodine lines for the second red giant with planets from our survey HD 102272.
High fidelity iodine spectra provide the wavelength and instrument calibration needed to extract precise radial velocities (RVs) from stellar spectral observations taken through iodine cells. Such iodine spectra are usually taken by a Fourier Transform Spectrometer (FTS). In this work, we investigated the reason behind the discrepancy between two FTS spectra of the iodine cell used for precise RV work with the High Resolution Spectrograph (HRS) at the Hobby-Eberly Telescope. We concluded that the discrepancy between the two HRS FTS spectra was due to temperature changes of the iodine cell. Our…
Detecting exoplanets around giant stars sheds light on the later-stage evolution of planetary systems. We observed the M giant HD 18438 and the K giant HD 158996 as part of a Search for Exoplanets around Northern circumpolar Stars (SENS) and obtained 38 and 24 spectra from 2010 to 2017 using the high-resolution Bohyunsan Observatory Echelle Spectrograph (BOES) at the 1.8m telescope of Bohyunsan Optical Astronomy Observatory in Korea. We obtained precise RV measurements from the spectra and found long-period radial velocity (RV) variations with period 719.0 days for HD 18438 and 820.2 days for …
Long-term stellar activity variations can affect the detectability of long-period and Earth-analogue extrasolar planets. We have, for 54 stars, analysed the long-term trend of five activity indicators: log$R'_\mathrm{HK}$, the cross-correlation function (CCF) bisector span, CCF full-width-at-half-maximum, CCF contrast, and the area of the Gaussian fit to the CCF; and studied their correlation with the RVs. The sign of the correlations appears to vary as a function of stellar spectral type, and the transition in sign signals a noteworthy change in the stellar activity properties where earlier t…
We have been conducting a exoplanet search survey using Bohyunsan Observatory Echelle Spectrograph (BOES) for the last 18 years. We present the detection of exoplanet candidate in orbit around HD 18438 from high-precision radial velocity (RV) mesurements. The target was already reported in 2018 (Bang et al. 2018). They conclude that the RV variations with a period of 719 days are likely to be caused by the pulsations because the Lomb-Scargle periodogram of HIPPARCOS photometric and Ha EW variations for HD 18438 show peaks with periods close to that of RV variations and there were no correlatio…
The HARPS search for southern extra-solar planets. XXXI. Magnetic activity cycles in solar-type stars: statistics and impact on precise radial velocities
上下文通过径向速度测量寻找太阳系外行星依赖于恒星光球的稳定性。目标。我们的目标是表征磁活动周期的统计特性，并研究它们对光谱测量的影响，如径向速度，线平分线和线形。方法.我们使用的数据从HARPS高精度行星搜索样本包括304 FGK恒星超过7年。我们获得高精度的Ca II H & K色球活动测量，并将其转换为R'HK指数使用更新的校准考虑到恒星金属丰度。我们研究R'HK变异作为时间的函数，并寻找可能的相关性与径向速度和线形参数。结果我们根据Ca II H & K变化的幅度和时间尺度对恒星进行分类，并尽可能确定活动周期。我们发现，在太阳附近，39 +/-8%的老太阳型恒星没有任何活动周期（或者只有非常弱的活动周期），而61 +/-8%的恒星有活动周期。非循环星几乎只在G矮星中发现，平均活动水平log R'HK <-4.95。磁周期振幅一般随活动水平的降低而降低。相当一部分恒星的径向速度和线形参数与活动周期相关，表现出很小的变化。径向速度对磁循环的敏感性随着温度的升高而增加，而晚K矮星几乎不敏感。结论.活动周期确实会引起长周期、低幅度的径向速度变化，其水平高达~25 m/s。因此，在寻找长周期系外行星时必须谨慎。然而，这些影响可以被校正到高精度的径向速度数据，同时测量钙II H & K通量和线形参数的去趋势。（节录）
A Machine Learning approach for correcting radial velocities using physical observables
Institut de Ciències de l’Espai (ICE, CSIC)（空间科学研究所（西班牙国家研究委员会））；Institut d’Estudis Espacials de Catalunya (IEEC)（加泰罗尼亚空间研究所）；University of Warwick（华威大学）；Instituto de Astrofísica de Andalucía (IAA-CSIC)（安达卢西亚天体物理研究所（西班牙国家研究委员会））；The Open University（开放大学）；Max Planck Institut für Sonnensystemforschung (MPS)（马克斯·普朗克太阳系研究所）；Zentrum für Astronomie der Universität Heidelberg（海德堡大学天文中心）；Georg-August-Universität Göttingen（哥廷根大学）
