John D. Gross

Analysis of the rotation period of asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger - search for the YORP effect

Context. The spin state of small asteroids can change on a long timescale by the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect, the net torque that arises from anisotropically scattered sunlight and proper thermal radiation from an irregularly-shaped asteroid. The secular change in the rotation period caused by the YORP effect can be detected by analysis of asteroid photometric lightcurves. Aims. We analyzed photometric lightcurves of near-Earth asteroids (1865) Cerberus, (2100) Ra-Shalom, and (3103) Eger with the aim to detect possible deviations from the constant rotation caused by the YORP effect. Methods. We carried out new photometric observations of the three asteroids, combined the new lightcurves with archived data, and used the lightcurve inversion method to model the asteroid shape, pole direction, and rotation rate. The YORP effect was modeled as a linear change in the rotation rate in time dω/dt .V alues of dω/dt derived from observations were compared with the values predicted by theory. Results. We derived physical models for all three asteroids. We had to model Eger as a nonconvex body because the convex model failed to fit the lightcurves observed at high phase angles. We probably detected the acceleration of the rotation rate of Eger dω/dt = (1.4 ± 0.6) × 10 −8 rad d −2 (3σ error), which corresponds to a decrease in the rotation period by 4. 2m s yr −1 . The photometry of Cerberus and Ra-Shalom was consistent with a constant-period model, and no secular change in the spin rate was detected. We could only constrain maximum values of |dω/dt| < 8 × 10 −9 rad d −2 for Cerberus, and |dω/dt| < 3 × 10 −8 rad d −2 for Ra-Shalom.

A BVRCIC Survey of W Ursae Majoris Binaries

We report on a BVRcIc survey of field W Ursae Majoris binary stars and present accurate colors for 606 systems that have been observed on at least three photometric nights from a robotic observatory in southern Arizona. Comparison with earlier photometry for a subset of the systems shows good agreement. We investigate two independent methods of determining the interstellar reddening, although both have limitations that can render them less effective than desired. A subset of 101 systems shows good agreement between the two reddening methods.

Heterogeneity of preferences for local public goods: The case of private expenditure on public education

Abstract Revealed preference techniques are used to investigate the degree of heterogeneity of local public good preferences by testing the hypothesis that demographic characteristics are correlated with preferences for expenditure on public education. The test relies on a goodness-of-fit index which is on an estimation of wasted consumer expenditure. We use bootstrap techniques to estimate the distribution of the test statistic. Preference heterogeneity is found to be common, however Democrat-Protestant households are found to have similar tastes, and, to a lesser extent, so are households with school-age children where at least one other trait is held in common. Republicans exhibit the greatest degree of preference heterogeneity.

Two Simple Algorithms for Generating a Subset of Data Consistent with WARP and Other Binary Relations

The authors give two algorithms which partition data into two subsets, a set consistent with the weak axiom of revealed preference (WARP) and its complement. Their main contribution is a very fast, but inexact, algorithm. The authors also describe an exact algorithm which will be impractical for large data sets. These same algorithms may be applied to several other binary relationships such the nonparametric production axioms. Since violations of WARP are also violations of the strong and generalized axioms, these algorithms are a logical first step in computing subsets consistent with these relations.

The Absolute Dimensions of the Overcontact Binary FI Bootis

UBVRCIC photometry of the W UMa eclipsing binary FI Bootis has been obtained and analyzed simultaneously with previously published photometry and radial velocities. The analysis of the light and radial velocity curves shows that the system is an A-type W UMa system consisting of stars with masses 0.82 and 0.31 M⊙.