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 imaging4-6, 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.

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 angstroms derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi=0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the persistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stromgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 degrees in phase.

Air pollution impact of a suburban highway segment.

Design traffic volumes, vehicle emission factors and meterological data are used to assess the impact of a suburban limited-access highway segment. Mesoscale effects are determined by emission inventory techniques. Microscale effects are determined using a pollutant dispersion model developed by the California Division of Highways. The air pollution impact of the highway segment is small, and should not be considered a significant criteria for decisions concerning construction of the highway.