CARMENES science preparation: characterisation of M dwarfs with low-resolution spectroscopy and search for low-mass wide companions to young stars

Francisco Javier Alonso Floriano

Astrophysics Department

Year 2015

Preparación científica de CARMENES : caracterización de enanas M con espectroscopía de baja resolución y búsqueda de compañeros separados poco masivos de estrellas jóvenes

The mass ratio between rocky planets and M-type dwarfs is much lower than between rocky planets and stars like the Sun. This fact has made them prime targets for the detection of Earth-like planets in the habitable zone using the Doppler method. However, M stars show more observational diffi- culties than hotter stars. Their maximum emission occurs at infrared wavelengths, which causes a low surface brightness in the optical range, especially for the lowest-mass subtypes. In addition, the molecular bands that fill their spectra, and the increase on activity and rotation that occurs from mid-subtypes, complicate the radial velocity determinations. For exoplanetary hunting, it translates into a great consumption of telescope time, and the construction of expensive high-resolution infrared spectrographs. To make this effort worthwhile, that is, to find a significant amount of exoplanets in the habitable zone of M dwarfs, an intense scientific preparation is needed to enable the selection of the best candidates. However, the detection of exo-Earths in the habitable zone does not imply the habitability of such planets. Recent investigations force us to raise the possibility that these planets do not maintain enough water to harbour life as we know it, or even that stellar activity sterilizes their surfaces. To solve these issues, it is necessary to investigate the planet formation and evolution, which requires planet searches around young M stars.

This work is focused on the study of low-mass objects that can be targets of exoplanet searches with near-infrared spectrographs in general and CARMENES in particular. The CARMENES con- sortium comprises 11 institutions from Germany and Spain that are building a high-resolution spec- trograph (R = 82,000) with two channels, visible (0.55–1.05 μm) and infrared (0.95–1.7 μm), for the 3.5m Calar Alto telescope. It will observe a sample of 300 M dwarfs in 600 nights of guaranteed time during at least three years, starting in January 2016. The final sample will be chosen from the ∼2200 M dwarfs included in the CARMENCITA input catalogue. For these stars, we have obtained and collected a large amount of data: spectral types, radial and rotational velocities, photometry in several bands, etc. Part of the effort of the science preparation necessary for the final selection of targets for CARMENES and other near-infrared spectrographs has been collected in two publica- tions, which are presented in this PhD thesis.

Useful information

Supervisors: David Montes Gutiérrez, José A. Caballero Hernández (CAB)
University: Universidad Complutense de Madrid, Facultad de Ciencias Físicas; Centro de Astrobiología
Reading date: 05/11/2015