[LINK] On the discovery of Groombridge 34 Ab

[rfmcdonald]

The Dragon's Gaze alerted me to the news that a super-Earth has been found orbiting Groombridge 34A or Gliese 15A, one of a binary pair of red dwarf stars (Wikipedia, Sol Station) a mere 11.7 light years away. The paper's abstract is as follows.

We report the discovery of a low-mass planet orbiting Gl 15 A based on radial velocities from the Eta-Earth Survey using HIRES at Keck Observatory. Gl 15 Ab is a planet with minimum mass Msini = 5.35 ± 0.75 M⊕, orbital period P = 11.4433 ± 0.0016 days, and an orbit that is consistent with circular. We characterize the host star using a variety of techniques. Photometric observations at Fairborn Observatory show no evidence for rotational modulation of spots at the orbital period to a limit of ~0.1 mmag, thus supporting the existence of the planet. We detect a second RV signal with a period of 44 days that we attribute to rotational modulation of stellar surface features, as confirmed by optical photometry and the Ca II H & K activity indicator. Using infrared spectroscopy from Palomar-TripleSpec, we measure an M2 V spectral type and a sub-solar metallicity ([M/H] = -0.22, [Fe/H] = -0.32). We measure a stellar radius of 0.3863 ± 0.0021 R⊙ based on interferometry from CHARA.

Universe Today's Shannon Hall writes at greater length.

Gliese 15 is a binary system, with two cool, dim red dwarfs orbiting each other. Although red dwarfs are the most common type of star in the galaxy, they’re so intrinsically faint that not a single one (including the closest star to the Sun, Proxima Centauri) is visible to the naked eye.

Although Gliese 15A might appear faint from Earth, it is overwhelmingly bright compared to its barely reflective exoplanet. So unfortunately we can’t easily see the exoplanet directly. But it does leave an imprint on its host star. Its small gravitational tug makes Gliese 15A wobble ever so slightly as both orbit a mutual center of mass, known as the barycenter.

The star’s movement is then imprinted on its spectrum. As Gliese 15A moves away from the Earth, its spectral lines stretch to redder wavelengths. But as it moves toward the Earth, its spectral lines compress to shorter wavelengths.

The change is minute. But the Keck 10-meter telescope, with an extremely high-resolution detector, can see such small changes. And from this tiny wobble, Andrew Howard and colleagues calculated that the planet is 5.35 times the mass of Earth and orbits its star in only 11.44 days, making it a hot super-Earth. And remember, it’s only 11.7 light-years away.