We present new visible and near-infrared spectroscopic measurements for 252 near-Earth (NEO) and Mars-crossing (MC) objects observed from 1994 through 2002 as a complement to the Small Main-Belt Asteroid Spectroscopic Survey (SMASS, http://smass.mit.edu/). Combined with previously published SMASS results, we have an internally consistent data set of more than 400 of these objects for investigating trends related to size, orbits, and dynamical history. These data also provide the basis for producing a bias-corrected estimate for the total NEO population (Stuart and Binzel, 2004, Icarus 170, 295-311). We find 25 of the 26 Bus (1999, PhD thesis) taxonomic types are represented, with nearly 90% of the objects falling within the broad S-, Q-, X-, and C-complexes. Rare A-and E-types are more common in the MC than NEO population (about 5% compared to < 1%) and may be direct evidence of slow diffusion into MC orbits from the Flora and Hungaria regions, respectively. A possible family of MC objects (C-types) may reside at the edge of the 5:2 jovian resonance. Distinct signatures are revealed for the relative contributions of different taxonomic types to the NEO population through different source regions. E-types show an origin signature from the inner belt, C-types from the mid to outer belt, and P-types from the outer belt. S-and Q-types have effectively identical main-belt source region profiles, as would be expected if they have related origins. A lack of V-types among Mars-crossers suggests entry into NEO space via rapid transport through the ν6 and 3:1 resonances from low eccentricity main-belt orbits, consistent with a Vesta origin. D-types show the strongest signature from Jupiter family comets (JFC), with a strong JFC component also seen among the X-types. A distinct taxonomic difference is found with respect to the jovian Tisserand parameter T , where C-, D-, and X-type (most likely low albedo P-class) objects predominate for T 3. These objects, which may be extinct comets, comprise 4% of our observed sample, but their low albedos makes this magnitude limited fraction under-representative of the true value. With our taxonomy statistics providing a strong component to the diameter limited bias correction analysis of Stuart (2003, PhD thesis), we estimate 10-18% of the NEO population above any given diameter may be extinct comets, taking into account asteroids scattered into T < 3 orbits and comets scattered into T > 3 orbits. In terms of possible space weathering effects, we see a size-dependent transition from ordinary chondrite-like (Q-type) objects to S-type asteroids over the size range of 0.1 to 5 km, where the transition is effectively complete at 5 km. A match between the average surface age of 5 km asteroids and the rate of space weathering could constrain models for both processes. However, space weathering may proceed at a very rapid rate compared with collisional timescales. In this case, the presence or absence of a regolith may be the determining factor for whether or not an object appears "...

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We describe the construction of a highly reliable sample of ∼7,000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 deg 2 of northern sky. The majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than for most other wide-angle surveys; the photometric errors range from ∼0.03 mag at r = 15 to ∼0.20 mag at r = 18. Light curves include on average 250 -2data points, collected over about a decade. Using SDSS-based photometric recalibration of the LINEAR data for about 25 million objects, we selected ∼200,000 most probable candidate variables with r < 17 and visually confirmed and classified ∼7,000 periodic variables using phased light curves. The reliability and uniformity of visual classification across eight human classifiers was calibrated and tested using a catalog of variable stars from the SDSS Stripe 82 region, and verified using an unsupervised machine learning approach. The resulting sample of periodic LINEAR variables is dominated by 3,900 RR Lyrae stars and 2,700 eclipsing binary stars of all subtypes, and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. We discuss the distribution of these mostly uncataloged variables in various diagrams constructed with optical-to-infrared SDSS, 2MASS and WISE photometry, and with LINEAR light curve features. We find that combination of light curve features and colors enables classification schemes much more powerful than when colors or light curves are each used separately. An interesting side result is a robust and precise quantitative description of a strong correlation between the light-curve period and color/spectral type for close and contact eclipsing binary stars (β Lyrae and W UMa): as the color-based spectral type varies from K4 to F5, the median period increases from 5.9 hours to 8.8 hours. These large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars, and we make them publicly available.

We present a sample of ∼ 5, 000 RR Lyrae stars selected from the recalibrated LINEAR dataset and detected at heliocentric distances between 5 kpc and 30 kpc over ∼ 8, 000 deg 2 of sky. The coordinates and light curve properties, such as period and Oosterhoff type, are made publicly available. We analyze in detail the light curve properties and Galactic distribution of the subset of ∼ 4, 000 type-ab RR Lyrae stars, including a search for new halo substructures and the number density distribution as a function of Oosterhoff type. We find evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with the ratio of the type II and I subsamples of about 1:4, but with a weaker separation than for globular cluster stars. The wide sky coverage and depth of this sample allows unique constraints for the number density distribution of halo RRab stars as a function of galactocentric distance: it can be described as an oblate ellipsoid with the axis ratio q = 0.63 and with either a single or a double power law with a power-law index in the range −2 to −3. Consistent with previous studies, we find that the Oosterhoff type II subsample has a steeper number density profile than