K2 light curve of HD 3167. Top: the full K2 light curve. Both the numerous, shallow transits of HD 3167 b and three deeper transits of HD 3167 c are evident in the light curve by eye. Bottom left: K2 light curve (grey dots) phase folded on the transits of HD 3167 b, and best-fit transit model (thick purple line). Bottom right: K2 light curve (grey dots) phase folded on the transits of HD 3167 c, and best-fit transit model (thick purple line). Credit: Vanderburg et al., 2016.
NASA’s Kepler spacecraft continues its fruitful exoplanet hunt with the newest discovery of 2 super-Earth-sized alien worlds. The newly detected planets are orbiting a nearby sun-sized star HD 3167, 150 light years away. Although Kepler has lost 2 of its 4 reaction wheels and therefore cannot be precisely pointed toward stars, it is still capable of detecting new exoworlds. The spacecraft is now in its extended mission K2, during which it has already found over 100 new planets. HD 3167 system is the latest addition to the vast collection.
HD 3167 was observed by Kepler between Jan 3 and Mar 23, 2016 during Campaign 8 of its K2 mission. This observation campaign allowed a team to detect 2 transit signals that could be planets circling around this nearby star. “We identified 2 planet candidates transiting HD 3167 after processing pixel-level data to produce a light curve, removing systematic effects due to Kepler’s unstable pointing, and searching for planets using a Box Least Squares periodogram search,” the researchers wrote.
To confirm the planetary status of these candidates, the team conducted follow-up with Tillinghast Reflector Echelle Spectrograph (TRES) on the 1.5 m telescope at the Fred L. Whipple Observatory on Mt. Hopkins, Arizona and Robo-AO adaptive optics system at the 2.1 m telescope at the Kitt Peak National Observatory, Arizona. They also used statistical techniques to validate the planetary nature of the transiting signals.
The confirmed exoplanets received designation HD 3167 b and HD 3167 c. With a radius of ~1.6 Earth radii, HD 3167 b is the inner planet, orbiting the host star in just slightly less than one day. The outer planet is nearly 3X bigger than Earth and has an orbital period of ~30 days. HD 3167 could be an excellent target for further follow-up observations as it is one of the closest and brightest stars hosting multiple transiting planets. This system is highly suitable for precise radial velocity observations to measure the planets’ masses.
“If HD 3167 b is rocky with a mass of about four Earth masses, it should induce radial velocity variations with a semiamplitude of about 3 ms−1. Depending on its composition, HD 3167 c could induce radial velocity variations with a semiamplitude of anywhere between 1 ms−1 and 3 ms−1. These signals should be readily detectable with modern spectrographs,” the paper reads.
The team also emphasized that the outer planet is one of the best currently known small planets for atmospheric characterization with transit transmission spectroscopy. However, they also noted that the short period of HD 3167 b makes it likely that spectroscopic observations of HD 3167 c’s atmosphere might overlap with a transit of the inner planet.”This could be an efficient way to rule out a hydrogen-dominated atmosphere for HD 3167 b. Observers should be cautious, however, to ensure that a transit of HD 3167 b not interfere with out-of-transit observations necessary for calibration,” the researchers concluded.
http://phys.org/news/2016-07-super-earth-sized-planets-orbiting-nearby-star.htmljCp
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