New sub-Neptune exoplanet orbiting nearby star detected

Using the radial velocity method, an international team of astronomers has discovered a new extrasolar planet orbiting a nearby star known as GI 410. The newfound alien world was classified as a sub-Neptune exoplanet with a mass of at least 8.4 Earth masses. The discovery was reported April 4 on the pre-print server arXiv.

The radial velocity (RV) method of detecting an exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an unseen exoplanet as it orbits the star. Thanks to this technique, more than 600 exoplanets have been detected so far.

Now, a group of astronomers led by Andres Carmona of the Grenoble Alpes University in France reports another exoplanet detection using the RV technique. The discovery was made with the SPIRou near-infrared spectropolarimeter at the Canada–France–Hawaii Telescope (CFHT). The observations were complemented by data from the optical velocimeter SOPHIE at the Haute-Provence Observatory.

“We have monitored the star in the near-infrared with the spectropolarimeter and velocimeter SPIRou and in the optical with the velocimeter SOPHIE. The SPIRou RVs show a robust periodic signal at P=6.020±0.004 days. The signal is recovered in the raw LBL [line-by-line] data and in the two PCA [principal component analysis] methods used to correct the LBL RVs for systematics and telluric correction residuals,” the researchers explain.

The newly detected planet, which received designation GI 410 b, has a minimum mass of 8.4 Earth masses and orbits its host every 6.02 days, at a distance of some 0.053 AU from it. However, given that GI 410 b does not transit its parent star, its radius still remains unknown.

The host star GI 410, which is located about 39 light years away, is about half the size and mass of the sun. The star has an effective temperature at a level of 3,842 K and its age was estimated to be 480 million years, therefore it is one of the youngest stars nearby.

Given that GI 410 b is located very close to its host, the astronomers underlined that it may have an active interaction with the high-energy radiation and the stellar wind particle fluxes from GI 410. They calculated that GI 410 b may receive 20.4 times more than Earth’s insolation.

Besides the detection of Gl 410 b, tentative evidence for two additional planetary signals was found at 2.99 and 18.7 days. However, further observations are required in order to confirm the planetary nature of these signals.

“Further measurements and improvements in the methods to recover the data in the |Vtot|<10 km/s region are required to fully exploit all the measurements taken and ultimately confirm or refute the planetary nature of these signals,” the authors of the paper conclude.

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