ABSTRACT
The closet exoplanets to the Sun provide opportunities for detailed characterization of planets outside the Solar System. We report the discovery, using radial velocity measurements, of a compact multiplanet system of super-Earth exoplanets orbiting the nearby red dwarf star GJ 887. The two planets have orbital periods of 9.3 and 21.8 days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8-day planet is ~350 kelvin. The planets are interior to, but close to the inner edge of, the liquid-water habitable zone. We also detect an unconfirmed signal with a period of ~50 days, which could correspond to a third super-Earth in a more temperate orbit. Our observations show that GJ 887 has photometric variability below 500 parts per million, which is unusually quiet for a red dwarf.
ABSTRACT
Barnard's star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs1, it is the closest single star to the Sun; only the three stars in the α Centauri system are closer. Barnard's star is also among the least magnetically active red dwarfs known2,3 and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging4-6, astrometry7,8 and direct imaging9, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard's star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard's star, making it an excellent target for direct imaging and astrometric observations in the future.
ABSTRACT
We present a very large f/1.O prime focus, all-spherical, all-fused-silica catadioptric camera. It contains a two-element airspaced corrector, an f/0.76 primary mirror, and a singlet final element. It accommodates a chromatic range from 0.3 to 1.1µm or more without refocus. It is optimized with an external entrance pupil but can be reoptimized for other pupil distances. In spite of its 30-in. (76.2-cm) focal length, it delivers 12.6-µm (rms) average image diameters to a 3.6-in.- (9.1-cm-) diameter flat focal surface. It is thus well matched to the (7-15µm) pixels and to the size of a (2 × 2) mosaic of today's largest available CCD's.
ABSTRACT
We have developed a multichannel spectrophotometric detector system using a 1024 element self-scanned silicon photodiode array, which is now in routine operation with the high-dispersion coudé spectrograph of the University of Texas McDonald Observatory 2.7-m telescope. We discuss operational considerations in the use of such arrays for high precision and low light level spectrophotometry. A detailed description of the system is presented. Performance of the detector as measured in the laboratory and on astronomical program objects is described, and it is shown that these arrays are highly effective detectors for high dispersion astronomical spectroscopy.
