The CARMENES search for exoplanets around M dwarfs

Abstract

Despite their activity, low-mass stars are of particular importance for the search of exoplanets by the means of Doppler spectroscopy, as planets with lower masses become detectable. We report on the discovery of a planetary companion around HD 180617, a bright (J = 5.58 mag), low-mass (M = 0.45M⊙) star of spectral type M2.5 V. The star, located at a distance of 5.9 pc, is the primary of the high proper motion binary system containing vB 10, a star with one of the lowest masses known in most of the twentieth century. Our analysis is based on new radial velocity (RV) measurements made at red-optical wavelengths provided by the high-precision spectrograph CARMENES, which was designed to carry out a survey for Earth-like planets around M dwarfs. The available CARMENES data are augmented by archival Doppler measurements from HIRES and HARPS. Altogether, the RVs span more than 16 yr. The modeling of the RV variations, with a semi-amplitude of K = 2.85-0.25+0.16 m s-1, yields a Neptune-like planet with a minimum mass of 12.2-1.4+1.0 M⊕ on a 105.90-0.10+0.09 d circumprimary orbit, which is partly located in the host star’s habitable zone. The analysis of time series of common activity indicators does not show any dependence on the detected RV signal. The discovery of HD 180617 b not only adds information to a currently hardly filled region of the mass-period diagram of exoplanets around M dwarfs, but the investigated system becomes the third known binary consisting of M dwarfs and hosting an exoplanet in an S-type configuration. Its proximity makes it an attractive candidate for future studies.

The CARMENES search for exoplanets around M dwarfs

“…This spectrograph is operated at the 3.5 m telescope on Calar Alto, Spain, and has been taking data since January 2016 (Quirrenbach et al 2016(Quirrenbach et al , 2018Reiners et al 2018a). So far CARMENES has been used in the discovery of several new planets (Reiners et al 2018b;Kaminski et al 2018;Ribas et al 2018;Luque et al 2018;Nagel et al 2019). All of these discoveries estimated the mass of the host star with the same procedure that we present in this work, even though Reiners et al (2018b), Kaminski et al (2018), and Ribas et al (2018) used slightly older data than those used in this work.…”

The CARMENES search for exoplanets around M dwarfs

“…The main goal of CARMENES is to discover and characterize Earth-like planets around an initial sample of about 300 M dwarfs (Reiners et al 2018b). To date, the program has already confirmed eight planet candidates from large-scale photometric and spectroscopic surveys (e.g., Trifonov et al 2018;Sarkis et al 2018) and detected more than ten new planets (e.g., Reiners et al 2018a;Kaminski et al 2018;Luque et al 2018Luque et al , 2019Ribas et al 2018;Nagel et al 2019;Perger et al 2019;Zechmeister et al 2019;Morales et al 2019).…”

Detection and characterization of an ultra-dense sub-Neptunian planet orbiting the Sun-like star K2-292

“…The instrument consists of two channels: the visual channel (VIS) obtains spectra at a resolving power of R = 94 600 in the wavelength range from 0.52 µm to 0.96 µm, while the near-infrared (NIR) channel yields spectra of R = 80 400 from 0.96 µm to 1.71 µm. CARMENES performance, data reduction and wavelength calibration are described in Reiners et al (2018) and Kaminski et al (2018).…”

“…Therefore, we do not consider for the RV computation those spectra whose signal-to-noise ratio per spectral sampling element, averaged over each order, is smaller than 40. Furthermore, to achieve the highest RV precision, we correct the spectra from telluric absorption using Molecfit Kausch et al 2015) following the method presented in Nortmann et al (2018) and Salz et al (2018).…”