7 research outputs found
A terrestrial planet candidate in a temperate orbit around Proxima Centauri
At a distance of 1.295 parsecs, the red dwarf Proxima Centauri (α Centauri C, GL 551, HIP 70890 or simply Proxima) is the Sun’s closest stellar neighbour and one of the best-studied low-mass stars. It has an effective temperature of only around 3,050 kelvin, a luminosity of 0.15 per cent of that of the Sun, a measured radius of 14 per cent of the radius of the Sun and a mass of about 12 per cent of the mass of the Sun. Although Proxima is considered a moderately active star, its rotation period is about 83 days and its quiescent activity levels and X-ray luminosity are comparable to those of the Sun. Here we report observations that reveal the presence of a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface
State of the Field: Extreme Precision Radial Velocities
The Second Workshop on Extreme Precision Radial Velocities defined circa 2015
the state of the art Doppler precision and identified the critical path
challenges for reaching 10 cm/s measurement precision. The presentations and
discussion of key issues for instrumentation and data analysis and the workshop
recommendations for achieving this precision are summarized here.
Beginning with the HARPS spectrograph, technological advances for precision
radial velocity measurements have focused on building extremely stable
instruments. To reach still higher precision, future spectrometers will need to
produce even higher fidelity spectra. This should be possible with improved
environmental control, greater stability in the illumination of the
spectrometer optics, better detectors, more precise wavelength calibration, and
broader bandwidth spectra. Key data analysis challenges for the precision
radial velocity community include distinguishing center of mass Keplerian
motion from photospheric velocities, and the proper treatment of telluric
contamination. Success here is coupled to the instrument design, but also
requires the implementation of robust statistical and modeling techniques.
Center of mass velocities produce Doppler shifts that affect every line
identically, while photospheric velocities produce line profile asymmetries
with wavelength and temporal dependencies that are different from Keplerian
signals.
Exoplanets are an important subfield of astronomy and there has been an
impressive rate of discovery over the past two decades. Higher precision radial
velocity measurements are required to serve as a discovery technique for
potentially habitable worlds and to characterize detections from transit
missions. The future of exoplanet science has very different trajectories
depending on the precision that can ultimately be achieved with Doppler
measurements.Comment: 45 pages, 23 Figures, workshop summary proceeding
A candidate super-Earth planet orbiting near the snow line of Barnard’s star
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 imaging4,5,6, 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