Exoplanets in orbit around red dwarf stars have been studied extensively in recent years. These stars have effective surface temperatures ranging from 2400 to 3700 K (more than 2000 degrees cooler than the Sun) and masses ranging from 0.08 to 0.45 solar masses. In this context, a team of researchers led by Borja Toledo Padrón, a Severo Ochoa-La Caixa doctoral student at the Instituto de Astrofisica de Canarias (IAC) specializing in the search for planets around these types of stars, discovered a super-Earth orbiting the star GJ 740, a red dwarf star 36 light years from Earth.
The planet orbits its star with a period of 2.4 days and has a mass that is roughly three times that of Earth. Because the star is so close to the Sun, and the planet is so close to the star, this new super-Earth may be the subject of future research with very large diameter telescopes by the end of this decade. The study’s findings were recently published in the journal Astronomy and Astrophysics.
Researchers report the discovery of a super-Earth orbiting the star GJ 740, a red dwarf star situated some 36 light years from Earth.
“This planet has the second-shortest orbital period around this type of star. The mass and period point to a rocky planet with a radius of about 1.4 Earth radii, which could be confirmed in future TESS observations “Borja Toledo Padrón, the article’s first author, explains. The data also indicate the presence of a second planet with an orbital period of 9 years and a mass comparable to that of Saturn (close to 100 Earth masses), though its radial velocity signal could be due to the star’s magnetic cycle (similar to that of the Sun), so more data are needed to confirm that the signal is due to a planet.
The Kepler mission, recognized as one of the most successful in detecting exoplanets using the transit method (which is the search for small variations in the brightness of a star caused by planets orbiting around it transiting between it and ourselves), discovered a total of 156 new planets around cool stars. According to its data, this type of star has an average of 2.5 planets with orbital periods of less than 200 days.
“The search for new exoplanets around cool stars is driven by the smaller difference between the planet’s mass and the star’s mass compared with stars in warmer spectral classes (which facilitates the detection of the planets’ signals), as well as a large number of this type of stars in our Galaxy,” comments Borja Toledo Padrón.
Cool stars are also a good place to look for planets using the radial velocity method. Using spectroscopic observations, this method detects small variations in the velocity of a star caused by the gravitational attraction of a planet in orbit around it. Since the discovery of the first radial velocity signal of an exoplanet around a cool star in 1998, a total of 116 exoplanets have been discovered using the radial velocity method.
“The main difficulty of this method is related to the intense magnetic activity of this type of stars, which can produce spectroscopic signals very similar to those due to an exoplanet,” says Jonay I. González Hernández, an IAC researcher who is a co-author of this article.
The study is part of the project HADES (HArps-n red Dwarf Exoplanet Survey), in which the IAC is collaborating with the Institut de Ciències de l’Espai (IEEC-CSIC) of Catalonia, and the Italian program GAPS (Global Architecture of Planetary Systems), whose objective is the detection and characterization of exoplanets around cool stars, in which are being used HARPS-N, on the Telescopio Nazionale Galileo (TNG) at the Roque de Los Muchachos Observatory (Garafía, La Palma).
This discovery was made possible by a six-year observing campaign with HARPS-N, which was supplemented by measurements with the CARMENES spectrograph on the 3.5m telescope at Calar Alto Observatory (Almera) and HARPS on the 3.6m telescope at La Silla Observatory (Chile), as well as photometric support from the ASAP and EXORAP surveys. IAC researchers Alejandro Suárez Mascareo and Rafael Rebolo are also involved in this project.