In recent years, an exhaustive study of red dwarf stars has been carried out to find exoplanets orbiting them. These stars have effective surface temperatures between 2400 and 3700 K (more than 2000 degrees cooler than the Sun) and masses between 0.08 and 0.45 solar masses. In this context, a team of researchers led by Borja Toledo Padrón, doctoral student Severo Ochoa-La Caixa at the Instituto de Astrofísica de Canarias (IAC), specializing in the search for planets around this type of star, discovered a super – Earth orbiting the star GJ 740, a red dwarf star about 36 light years from Earth.
The planet revolves around its star with a period of 2.4 days and its mass is approximately 3 times the mass of Earth. Because the star is so close to the Sun, and the planet so close to the star, this new super-Earth could be the subject of future research with very large-diameter telescopes towards the end of this decade. The results of the study were recently published in the journal Astronomy and astrophysics.
“It is the planet with the second shortest orbital period around this type of star. The mass and period suggest a rocky planet, with a radius of about 1.4 Earth radius, which could be confirmed in future observations with the TESS satellite “, explains Borja Toledo Padrón, the first author of the article. The data also indicates the presence of a second planet with an orbital period of 9 years, and a mass comparable to that of Saturn (nearly 100 earth masses), although its radial velocity signal may be due to the magnetic cycle of the star (similar to that of the Sun), so more data is needed to confirm that the signal is really 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 the transit between it and us planets orbiting it), discovered a total of 156 new planets around cool stars. From its data, it has been estimated that this type of star hosts an average of 2.5 planets with orbital periods of less than 200 days. “The search for new exoplanets around cold stars is motivated by the smaller difference between the mass of the planet and the mass of the star compared to stars of the warmer spectral classes (which makes it easier to detect signals from the planets ), as well as by the large number of stars in our galaxy, ”comments Borja Toledo Padrón.
Cold stars are also an ideal target for finding planets using the radial speed method. This method is based on the detection of small variations in the speed of a star due to the gravitational pull of a planet orbiting around it, using spectroscopic observations. Since the discovery in 1998 of the first radial speed signal from an exoplanet around a cold star, so far a total of 116 exoplanets have been discovered around this class of stars using the radial speed method. . “The main difficulty of this method is linked to the intense magnetic activity of this type of star, which can produce spectroscopic signals very similar to those due to an exoplanet”, explains Jonay I. González Hernández, researcher at the IAC who is co-author of this article.
The study is part of the HADES project (HArps-n red Dwarf Exoplanet Survey), in which the IAC collaborates with the Institute of 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 cold stars, in which HARPS-N is used, on the Telescopio Nazionale Galileo (TNG) at the Roque de los Muchachos Observatory (Garafía , La Palma). This detection was possible thanks to a six-year observation campaign with HARPS-N, completed by measurements with the CARMENES spectrograph on the 3.5 m telescope of the Calar Alto (Almería) and HARPS observatory, on the 3.6 m telescope of the La Silla observatory (Chile), as well as the photometric support for the ASAP and EXORAP surveys. IAC researchers Alejandro Suárez Mascareño and Rafael Rebolo are also participating in this work.
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