WISE J104915.57−531906.1 is a L/T brown dwarf binary located 2 pc from the Sun. The pair contains the closest known brown dwarfs and is the third closest known system, stellar or sub-stellar. We report comprehensive follow-up observations of this newly uncovered system. We have determined the spectral types of both components (L8±1, for the primary, agreeing with the discovery paper; T1.5±2 for the secondary, which was lacking spectroscopic type determination in the discovery paper) and, for the first time, their radial velocities (V rad ∼23.1, 19.5 km s −1 ) using optical spectra obtained at the Southern African Large Telescope (SALT) and other facilities located at the South African Astronomical Observatory (SAAO). The relative radial velocity of the two components is smaller than the range of orbital velocities for theoretically predicted masses, implying that they form a gravitationally bound system. We report resolved near-infrared JHK S photometry from the IRSF telescope at the SAAO which yields colors consistent with the spectroscopically derived spectral types. The available kinematic and photometric information excludes the possibility that the object belongs to any of the known nearby young moving groups or associations. Simultaneous optical polarimetry observations taken at the SAAO 1.9-m give a non-detection with an upper limit of 0.07%. For the given spectral types and absolute magnitudes, 1 Gyr theoretical models predict masses of 0.04-0.05 M ⊙ for the primary, and 0.03-0.05 M ⊙ for the secondary. Subject headings: brown dwarfs -infrared: stars -solar neighborhood -stars: low-mass -stars: individual (WISE J104915.57−531906.1, G 171−22, HD 55383) 1 Based on observations made with the Southern African Large Telescope (SALT).

A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogendeficient. Almost all of these H-deficient central stars (CSs) display spectra with strong carbon and helium lines. Most of them exhibit emission line spectra resembling those of massive WC stars. Therefore these stars are classed as CSPNe of spectral type [WC]. Recently, quantitative spectral analysis of two emission-line CSs, PB 8 and IC 4663, revealed that these stars do not belong to the [WC] class. Instead PB 8 has been classified as [WN/WC] type and IC 4663 as [WN] type. In this work we report the spectroscopic identification of another rare [WN] star, the CS of Abell 48. We performed a spectral analysis of Abell 48 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. We find that the expanding atmosphere of Abell 48 is mainly composed of helium (85 per cent by mass), hydrogen (10 per cent), and nitrogen (5 per cent). The residual hydrogen and the enhanced nitrogen abundance make this object different from the other [WN] star IC 4663. We discuss the possible origin of this atmospheric composition.

No abstract

Growth, annual exploitation (u), and natural mortality (v) of bluegills Lepomis macrochirus and redear sunfish L. microlophus were investigated on Lake Panasoffkee, Florida, during 1998 and 1999 to assess the potential benefits of several minimum size limits. The average u of 15.0‐cm total length (TL) or larger fish was 0.14 for bluegills and redear sunfish during the 2‐year period. For both species, exploitation increased up to threefold as fish size increased (e.g., u = 0.37 for bluegills ≥23.0 cm TL in 1999). Total annual mortality (A) was 0.64 for bluegills and 0.68 for redear sunfish. Natural mortality estimates were 0.50 (78% of A) for bluegills and 0.55 (81% of A) for redear sunfish. Simulations predicted that minimum size limits would decrease average total yield and harvest for both bluegills and redear sunfish, but that a 20.3‐cm minimum length limit could slightly increase the number of fish harvested over 20.0 cm TL. A 22.9‐cm minimum length limit was predicted to greatly reduce yield without creating a measurable increase in the harvest of fish over the size limit. Lake Panasoffkee sunfishes incurred record levels of estimated effort and harvest in 1998–1999, but size‐selective exploitation acted essentially as a minimum size limit, resulting in no predicted benefit for a 20.3‐cm limit. Separation of fishing mortality and natural mortality allowed us to conclude that natural mortality had a greater influence on Lake Panasoffkee sunfish population abundance and fishing quality than did fishing mortality, so a minimum size limit was not recommended. Estimates of exploitation, natural mortality, and growth rates are more valuable than measures of size structure and angler catch when considering or evaluating harvest restrictions.

Aims. We report first results from our extensive survey of the very small (H > 21.5 mag) near-Earth asteroids. Our aim was to obtain photometric lightcurves for these faint, fast moving objects and to measure their rotation periods and amplitudes of light variations. These parameters can be used to make statistical analysis of the still little known population of the smallest asteroids, test present theories of the YORP effect as well as to study their spin limits, which are connected with their internal structure. Methods. Due to the faintness of the targets and the expected short periods of rotation, observations were performed with the large, 10-m SALT telescope in SAAO (South Africa). For most asteroids, V filter images with exposure times of 5-60 s were obtained with the instrument's SALTICAM's CCD camera. Even though the non-sidereal tracking was not available, the SALTICAM's relatively large field-of-view of 8 × 8 helped to perform the relative photometry of the fast-moving targets. Results. The presented asteroids have synodic periods ranging from 77 s to 44 min, effective diameters from 21 to 94 m, and significantly elongated shapes.