The study of the architecture of planetary systems, and in particular that of the spin-orbit angle (which is the inclination of the planetary orbit with respect to the stellar rotation axis) can unveil important details on the dynamical evolution of planetary systems. In particular, young planets typically migrate radially, changing their distance to the host star and interacting with the
About 20% of the exoplanets discovered so far (October 2021) were found with measurements of radial velocity (data from https://exoplanets.nasa.gov/). This method is based on spectroscopic observations of stars with planets, from which it is possible to measure the Doppler effect produced by periodic oscillations of the star, due to the gravitational attraction between star and planet along the orbit of
Hot Jupiters are gaseous giant planets that orbit very close to their stars (within a typical distance of less than 0.1 Astronomical Units, AU, where 1 AU is the average distance between Earth and Sun, about 150 million of km). These planets are of great interest for astronomers both because of the effects due to the intense incident stellar radiation,
M stars are the most common stars in the Universe. They have a mass ranging between 0.6 and 0.08 Solar masses in the main sequence, and an effective temperature ranging between 3900 K and 2400 K. In these stars, the signals due to the presence of planets, such as radial velocity (periodic oscillations of the star from its rest position
About 19.3% of the 4001 exoplanets confirmed to date were discovered with the technique of the radial velocity (from https://exoplanets.nasa.gov/). This method consists in using time series of spectroscopic observations in order to measure the periodic oscillations of the position of stars due to the presence of orbiting exoplanets. In fact, in a planetary system both the planets and the
In the last years, stars of spectral class M (which are stars with effective temperatures between 2400 and 3700 K and masses between 0.08 and 0.45 solar masses) have been extensively observed for the search of exoplanets. This both because they are the most abundant class of stars in the Galaxy, and because the low star/planet mass ratio, compared to
The mechanisms involved in the formation of planets are still not completely understood. The most widely accepted model that describe the formation of gaseous planets is the core-accretion model. In this paradigm, the formation of these planets starts with the formation of a large rocky core by the coagulation of planetesimals, followed by the accretion of a large gaseous envelope
Some of the exoplanets known so far belong to classes that do not exist in our Solar System. For instance, the class of the Hot Jupiters, i.e., gaseous giant planets orbiting at close distances from their stars (typically less than 0.5 AU, Astronomical Unit, where a 1 AU is the average distance between Sun and Earth, about 150 million km).
The “Ultra-Short Period” (USP) exoplanets have very close orbits and orbital periods shorter than one day. These planets typically have a radius smaller than 2 Earth radii and a terrestrial composition, sometime with an excess of iron. Four hypotheses have been made to explain the formation and evolution of USP planets. The main hypothesis is that these planets originate
Low mass star (in particular M-type star, with a mass between 0.075 and 0.5 solar masses) are typical targets for the search and study of exoplanets. In these stars, in fact, the radial velocity method is more efficient than in stars with higher mass. Radial velocity consists in detecting periodic oscillations in the stellar spectra due to the motion of
