Kelu-1 is a Binary L Dwarf: First Brown Dwarf Science from Laser Guide Star Adaptive Optics

(Abridged) We present near-IR imaging of the nearby L dwarf Kelu-1 obtained with the Keck sodium laser guide star adaptive optics (LGS AO) system as part of a high angular resolution survey for substellar binaries. Kelu-1 was one of the first free-floating L dwarfs identified, and the origin of its overluminosity compared to other similar objects has been a long-standing question. Our images clearly resolve Kelu-1 into a 0.29'' (5.4 AU) binary, and a previous non-detection by HST demonstrates that the system is a true physical pair. Binarity explains the properties of Kelu-1 that were previously noted to be anomalous compared to other early-L dwarfs. We estimate spectral types of L1.5-L3 and L3-L4.5 for the two components, giving model-derived masses of 0.05-0.07 Msun and 0.045-0.065 Msun for an estimated age of 0.3-0.8 Gyr. More distant companions are not detected to a limit of 5-9 Mjup. The presence of lithium absorption indicates that both components are substellar, but the weakness of this feature relative to other L dwarfs can be explained if only Kelu-1B is Li-bearing. Determining whether both or only one of the components possesses lithium could constrain the age of Kelu-1 (and other Li-bearing L binaries) with higher precision than is possible for most ultracool field objects. These results are the first LGS AO observations of brown dwarfs and demonstrate the potential of this new instrumental capability for substellar astronomy.Comment: 24 pages, Astrophysical Journal, in press (Nov 20, 2005 issue). Note that Figure 1 of the PDF version is degraded by arxiv.org, but the Postscript version is fine. Version 2 includes very minor changes to match the published versio

A Spectro-photometric Analysis of Cool White Dwarfs in the Gaia and Pan-STARRS Footprint

We present a spectro-photometric analysis of 2880 cool white dwarfs within 100 pc of the Sun and cooler than Teff = 10,000 K, with grizy Pan-STARRS photometry and Gaia trigonometric parallaxes available. We also supplement our data sets with near-infrared JHK photometry, when available, which is shown to be essential for interpreting the coolest white dwarfs in our sample. We perform a detailed analysis of each individual object using state-of-the-art model atmospheres appropriate for each spectral type including DA, DC, DQ, DZ, He-rich DA, and the so-called IR-faint white dwarfs. We discuss the temperature and mass distributions of each subsample, as well as revisit the spectral evolution of cool white dwarfs. We find little evidence in our sample for the transformation of a significant fraction of DA stars into He-atmosphere white dwarfs through the process of convective mixing between Teff = 10,000 K and 6500 K, although the situation changes drastically in the range Teff = 6500 - 5500 K where the fraction of He-atmosphere white dwarfs reaches 45%. However, we also provide strong evidence that at even cooler temperatures (Teff < 5200 K), most DC white dwarfs have H atmospheres. We discuss a possible mechanism to account for this sudden transformation from He- to H-atmosphere white dwarfs involving the onset of crystallization and the occurrence of magnetism. Finally, we also argue that DQ, DZ, and DC white dwarfs may form a more homogeneous population than previously believed.Comment: Accepted for publication in MNRAS (21 pages, 20 figures

Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition

We present the results of a Hubble Space Telescope NICMOS imaging survey of 22 T-type field brown dwarfs. Five are resolved as binary systems with angular separations of 0"05-0"35, and companionship is established on the basis of component F110W-F170M colors (indicative of CH4 absorption) and low probabilities of background contamination. Prior ground-based observations show 2MASS 1553+1532AB to be a common proper motion binary. The properties of these systems - low multiplicity fraction (11[+7][-3]% resolved, as corrected for sample selection baises), close projected separations (a = 1.8-5.0 AU) and near-unity mass ratios - are consistent with previous results for field brown dwarf binaries. Three of the binaries have components that span the poorly-understood transition between L dwarfs and T dwarfs. Spectral decomposition analysis of one of these, SDSS 1021-0304AB, reveals a peculiar flux reversal between its components, as its T5 secondary is ~30% brighter at 1.05 and 1.27 micron than its T1 primary. This system, 2MASS 0518-2828AB and SDSS 1534+1615AB all demonstrate that the J-band brightening observed between late-type L to mid-type T dwarfs is an intrinsic feature of this spectral transition, albeit less pronounced than previously surmised. We also find that the resolved binary fraction of L7 to T3.5 dwarfs is twice that of other L and T dwarfs, an anomaly that can be explained by a relatively rapid evolution of brown dwarfs through the L/T transition, perhaps driven by dynamic (nonequilibrium) depletion of photospheric condensates.Comment: ~40 pages, 17 figures, accepted for publication to ApJ. Note that emulateapj style file cuts off part of Table

The USNO-B Catalog

USNO-B is an all-sky catalog that presents positions, proper motions, magnitudes in various optical passbands, and star/galaxy estimators for 1,042,618,261 objects derived from 3,643,201,733 separate observations. The data were obtained from scans of 7,435 Schmidt plates taken for the various sky surveys during the last 50 years. USNO-B1.0 is believed to provide all-sky coverage, completeness down to V = 21, 0.2 arcsecond astrometric accuracy at J2000, 0.3 magnitude photometric accuracy in up to five colors, and 85% accuracy for distinguishing stars from non-stellar objects. A brief discussion of various issues is given here, but the actual data are available from http://www.nofs.navy.mil and other sites.Comment: Accepted by Astronomical Journa

Solar System Objects Observed in the SDSS Commissioning Data

We discuss measurements of the properties of about 10,000 asteroids detected in 500 deg2 of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r < 21.5, with a baseline of 5 minutes. Extensive tests show that the sample is at least 98% complete, with the contamination rate of less than 3%. We find that the size distribution of asteroids resembles a broken power-law, independent of the heliocentric distance: D^{-2.3} for 0.4 km < D < 5 km, and D^{-4} for 5 km < D < 40 km. As a consequence of this break, the number of asteroids with r < 21.5 is ten times smaller than predicted by extrapolating the power-law relation observed for brighter asteroids (r < 18). The observed counts imply that there are about 530,000 objects with D>1 km in the asteroid belt, or about four times less than previous estimates. The distribution of main belt asteroids in the 4-dimensional SDSS color space is bimodal, and the two groups can be associated with S (rocky) and C (carbonaceous) asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids and suggests the existence of two distinct belts: the inner rocky belt, about 1 AU wide (FWHM) and centered at R~2.8 AU, and the outer carbonaceous belt, about 0.5 AU wide and centered at R~3.2 AU. The colors of Hungarias, Mars crossers, and near-Earth objects are more similar to the C-type than to S-type asteroids, suggesting that they originate in the outer belt. (abridged).Comment: 89 pages, 31 figures, submitted to A

Exploring the Extremes: Characterizing a New Population of Old and Cold Brown Dwarfs

International audienceMapping out the populations of thick disk and halo brown dwarfs is important for understanding the metallicity dependence of low-temperature atmospheres and the substellar mass function. Recently, a new population of cold and metal-poor brown dwarfs has been discovered, with T eff ≲ 1400 K and metallicity ≲−1 dex. This population includes what may be the first known “extreme T-type subdwarfs” and possibly the first Y-type subdwarf, WISEA J153429.75−104303.3. We have conducted a Gemini YJHK/Ks photometric follow-up campaign targeting potentially metal-poor T and Y dwarfs, utilizing the GNIRS and Flamingos-2 instruments. We present 14 near-infrared photometric detections of eight unique targets: six T subdwarf candidates, one moderately metal-poor Y dwarf candidate, and one Y subdwarf candidate. We have obtained the first-ever ground-based detection of the highly anomalous object WISEA J153429.75−104303.3. The F110W − J color of WISEA J153429.75−104303.3 is significantly bluer than that of other late T and Y dwarfs, indicating that WISEA J153429.75−104303.3 has an unusual spectrum in the 0.9-1.4 μm wavelength range which encompasses the J-band peak. Our J-band detection of WISEA J153429.75−104303.3 and corresponding model comparisons suggest a subsolar metallicity and temperature of 400-550 K for this object. JWST spectroscopic follow-up at near-infrared and mid-infrared wavelengths would allow us to better understand the spectral peculiarities of WISEA J153429.75−104303.3, assess its physical properties, and conclusively determine whether or not it is the first Y-type subdwarf

DIVISION G COMMISSION 45: STELLAR CLASSIFICATION

International audienceCommission 45 is solidly anchored in the beginnings of the IAU. It evolved out of Commission 29, which was one of the original commissions and whose title and emphasis was the Spectral Classification of Stars (Transactions of the IAU, Volume I, 1922). C29 was formed with W.S. Adams (Pasadena) as president. Its first members were Miss Cannon, R.H. Curtiss, A. Fowler, A. de Gramont, M. Hamy, H.F. Newall, J.S. Plaskett, H.N. Russell, all very much part of the history of stellar spectroscopy. In the 1922 Transactions report it was recognized the Harvard System of spectral classification ``has already been adopted by international agreement. . .'

Multiplicity Survey of 20 Y Dwarfs with NIRCam Kernel Phase Interferometry

JWST Proposal. Cycle 1, ID. #247