Search for exoplanets around northern circumpolar stars III. Long-period radial velocity variations in HD 18438 and HD 158996

Tae Yang Bang, Byeong Cheol Lee, Gwang Hui Jeong, Inwoo Han, Myeong Gu Park

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

Detecting exoplanets around giant stars sheds light on the later-stage evolution of planetary systems. We observed the Mgiant HD18438 and the Kgiant HD158996 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 1.8mtelescope 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 HD 158996. We checked the chromospheric activities using Caii H and Hα lines, HIPPARCOS photometry and line bisectors to identify the origin of the observed RV variations. In the case of HD 18438, we conclude that the observed RV variations with period 719.0 days are likely to be caused by the pulsations because the periods of HIPPARCOS photometric and Hα EW variations for HD 18438 are similar to that of RV variations in Lomb-Scargle periodogram, and there are no correlations between bisectors and RV measurements. In the case of HD 158996, on the other hand, we did not find any similarity in the respective periodograms nor any correlation between RV variations and line bisector variations. In addition, the probability that the real rotational period can be as longer than the RV period for HD 158996 is only about 4.3%. Thus we conclude that observed RV variations with a period of 820.2 days of HD 158996 are caused by a planetary companion, which has the minimum mass of 14.0 MJup, the semi-major axis of 2.1 AU, and eccentricity of 0.13 assuming the stellar mass of 1.8 M. HD 158996 is so far one of the brightest and largest stars to harbor an exoplanet candidate.

Original languageEnglish
Pages (from-to)17-25
Number of pages9
JournalJournal of the Korean Astronomical Society
Volume51
Issue number1
DOIs
StatePublished - 2018

Keywords

  • Stars: Individual: HD 18438, HD 158996
  • Techniques: Radial velocities

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