NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has been brought out of hibernation and has resumed surveying the sky at 3.4 and 4.6 μm. The scientific objectives of the NEOWISE reactivation mission are to detect, track, and characterize near-Earth asteroids and comets. The search for minor planets resumed on 2013 December 23, and the first new near-Earth object (NEO) was discovered 6 days later. As an infrared survey, NEOWISE detects asteroids based on their thermal emission and is equally sensitive to high and low albedo objects; consequently, NEOWISE-discovered NEOs tend to be large and dark. Over the course of its three-year mission, NEOWISE will determine radiometrically derived diameters and albedos for ∼2000 NEOs and tens of thousands of Main Belt asteroids. The 32 months of hibernation have had no significant effect on the mission's performance. Image quality, sensitivity, photometric and astrometric accuracy, completeness, and the rate of minor planet detections are all essentially unchanged from the prime mission's post-cryogenic phase.

We present the results of a program to acquire photometry for 86 late M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M 5.8 versus [5.8]À[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one-parameter family in T eff. Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of 5 ($70M J to $15M J), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 m fluxes to be lower than expected, from which we infer a stronger CO fundamental band at $4.67 m. This suggests that equilibrium CH 4 /CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of K s , IRAC 3.6 m, and 4.5 m bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M K s versus K s À[4.5] relation, which shows a smooth progression over spectral type, and splits the M, L, and T types cleanly.

We report the discovery of T dwarf companions to the nearby stars HN Peg (G0V, 18.4 pc, τ ∼ 0.3 Gyr) and HD 3651 (K0V, 11.1 pc, τ ∼ 7 Gyr). During an ongoing survey of 5 ′ ×5 ′ fields surrounding stars in the solar neighborhood with the Infrared Array Camera aboard the Spitzer Space Telescope, we identified these companions as candidate T dwarfs based on their mid-infrared colors. Using near-infrared spectra obtained with SpeX at the NASA Infrared Telescope Facility, we confirm the presence of methane absorption that characterizes T dwarfs and measure spectral types of T2.5±0.5 and T7.5±0.5 for HN Peg B and HD 3651 B, respectively. By comparing our Spitzer data to images from the Two-Micron All-Sky Survey obtained several years earlier, we find that the proper motions of HN Peg B and HD 3651 B are consistent with those of the primaries, confirming their companionship. HN Peg B and HD 3651 B have angular separations of 43. ′′ 2 and 42. ′′ 9 from their primaries, which correspond to projected physical separations of 795 and 476 AU, respectively. A comparison of their luminosities to the values predicted by theoretical evolutionary models implies masses of 0.021 ± 0.009 and 0.051 ± 0.014 M ⊙ for HN Peg B and HD 3651 B. In addition, the models imply an effective temperature for HN Peg B that is significantly lower than the values derived for other T dwarfs at similar spectral types, which is the same behavior reported by Metchev & Hillenbrand for the young late-L dwarf HD 203030 B. Thus, the temperature of the L/T transition appears to depend on surface gravity. Meanwhile, HD 3651 B is the first substellar companion directly imaged around a star that is known to harbor a close-in planet from radial velocity surveys. The discovery of this companion supports the notion that the high eccentricities of close-in planets like the one near HD 3651 may be the result of perturbations by low-mass companions at wide separations.