High-resolution images of T Tau and its infrared companion have been reconstructed from near-and mid-infrared data collected at the Hale 5 m telescope. The near-infrared (1-5 fim) results were obtained by two dimensional speckle imaging and the mid-infrared (10-20 ¡im) results were derived from shift and add procedures applied to slit scans. The spectral energy distributions of the separated components were constructed from 1 to 20 [im data collected in less than half a year (1990 September to 1991 January). The spectral energy distribution of the optical component (T Tau N) is interpreted as containing two distinct constituents, a photosphere and a surrounding disk of circumstellar material. Measurements at a number of infrared wavelengths over the period 1985 December to 1991 January show a 2 mag color-independent change in the brightness of the infrared component (T Tau S). We propose that this may have been caused by an increase in accretion onto T Tau S and model the spectral energy distribution of T Tau S as being dominated by an accretion disk.

Infrared broadband photometry of the cool brown dwarf Gliese 229B extending in wavelength from 0.8 to 10.5 /zm is reported. These results are derived from both new data and reanalyzed, previously published data. Existing spectral data reported have been rereduced and recalibrated.The close proximity of the bright Gliese 229A to the dim Gliese 229B required the use of special techniques for the observations and also for the data analysis. We describe these procedures in detail. The observed luminosity between 0.8 and 10.5/zm is (4.9+-0.6)× 10 -6 L®. The observed spectral energy distribution is in overall agreement with a dust-free model spectrum by Tsuji et al. for Teff_900 K. If this model is used to derive the bolometric correction, the best estimate of the bolometric luminosity is 6.4X 10 -6 L e and 50% of this luminosity lies between 1 and 2.5/zm. Our best estimate of the effective temperature is 900 K. From the observed near-infrared spectrum and the spectral energy distribution, the brightness temperatures (Tg) are estimated. The highest, T 8 = 1640 K, is seen at the peak of the J band spectrum, while the lowest, T8_<600 K, is at 3.4/_m, which corresponds to the location of the fundamental methane band.

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SDSS 1257+5428 is a white dwarf in a close orbit with a companion that has been suggested to be a neutron star. If so, it hosts the closest known neutron star, and its existence implies a great abundance of similar systems and a rate of white-dwarf neutron-star mergers similar to that of the type Ia supernova rate. Here, we present high signal-to-noise spectra of SDSS 1257+5428, which confirm an independent finding that the system is in fact composed of two white dwarfs, one relatively cool and with low mass, and the other hotter and more massive. With this, the demographics and merger rate are no longer puzzling (various factors combine to lower the latter by more than two orders of magnitude). We show that the spectra are fit well with a combination of two hydrogen model atmospheres, as long as the lines of the higher-gravity component are broadened significantly relative to what is expected from just pressure broadening. Interpreting this additional broadening as due to rotation, the inferred spin period is short, about 1 minute. Similarly rapid rotation is only seen in accreting white dwarfs that are magnetic; empirically, it appears that in non-magnetized white dwarfs, accreted angular momentum is lost by nova explosions before it can be transferred to the white dwarf. This suggests that the massive white dwarf in SDSS 1257+5428 is magnetic as well, with B ≃ 10 5 G. Alternatively, the broadening seen in the spectral lines could be due to a stronger magnetic field, of ∼ 10 6 G. The two models can be distinguished by further observations. Subject headings: white dwarfs: general -white dwarfs: individual (SDSS 1257+5428)

Human exploration of the Moon is associated with substantial risks to astronauts from space radiation. On the surface of the Moon, this consists of the chronic exposure to galactic cosmic rays and sporadic solar particle events. The interaction of this radiation field with the lunar soil leads to a third component that consists of neutral particles, i.e., neutrons and gamma radiation. The Lunar Lander Neutrons and Dosimetry experiment aboard China’s Chang’E 4 lander has made the first ever measurements of the radiation exposure to both charged and neutral particles on the lunar surface. We measured an average total absorbed dose rate in silicon of 13.2 ± 1 μGy/hour and a neutral particle dose rate of 3.1 ± 0.5 μGy/hour.