The mass and radius of the M-dwarf in the short period eclipsing binary RR Caeli

We present new photometry and spectroscopy of the eclipsing white dwarf - M-dwarf binary star RR Cae. We use timings of the primary eclipse from white-light photo-electric photometry to derive a new ephemeris for the eclipses. We find no evidence for any period change greater than Pdot/P ~ 5E-12 over a timescale of 10 years. We have measured the effective temperature of the white dwarf, T_WD, from an analysis of two high resolution spectra of RR Cae and find T_WD = (7540 +- 175)K. We estimate a spectral type of M4 for the companion from the same spectra. We have combined new spectroscopic orbits for the white dwarf and M-dwarf with an analysis of the primary eclipse and cooling models for helium white dwarfs to measure the mass and radius of the M-dwarf. The mass of the M-dwarf is (0.182 - 0.183) +- 0.013 Msun and the radius is (0.203 - 0.215) +- 0.013 Rsun, where the ranges quoted for these values reflect the range of white dwarf models used. In contrast to previous studies, which lacked a spectroscopic orbit for the white dwarf, we find that the mass and radius of the M-dwarf are normal for an M4 dwarf. The mass of the white dwarf is (0.440 +-0.022) Msun. With these revised masses and radii we find that RR Cae will become a cataclysmic variable star when the orbital period is reduced from its current value of 7.3 hours to 121 minutes by magnetic braking in 9-20 Gyr. We note that there is night-to-night variability of a few seconds in the timing of primary eclipse caused by changes to the shape of the primary eclipse. We speculate as to the possible causes of this phenomenon. (Abridged)Comment: Accepted for publication in MNRAS. The paper contains 10 figures and 3 table

Does risk matter for farm businesses? The effect of crop insurance on production and diversification.

We use a large increase in Federal crop insurance subsidies as a natural experiment to identify the impact of risk on acreage and diversification decisions. Subsidy increases induced greater crop insurance coverage, which reduced farmers' financial risks. Did this change in the risk environment alter production decisions? We merged crop insurance participation data with farm-level Agricultural Census data from 1992 and 1997 to examine how harvested acreage and diversification changed in response to the policy-induced change in insurance coverage. The difference in differences empirical approach controls for unobservable heterogeneity and our results are robust across multiple definitions of our key variables and various fixed effects. We find that changes in the risk environment caused larger farms to expand while smaller farms shrank. Regardless of size, producers showed some evidence of using diversification as a method to mitigate risk. However, risk does not seem to have large overall effects.Risk and Uncertainty,

THE IMPORTANCE OF INCOME RISK IN LABOR ALLOCATION DECISIONS

Previous research has found that on-farm income variability helps determine off-farm labor supply. However, unobserved heterogeneity of farms or regions may have biased earlier results. In this study, we use an exogenous increase in Federal crop insurance subsidies as a natural experiment to identify the importance of risk in off-farm labor supply. The subsidy increases induced greater participation in crop insurance programs and thereby reduced farmers' financial risks. By merging county-level crop insurance participation data with farm-level Agricultural Census data from 1992 and 1997 we can compare the off-farm labor decisions of individual farms before and after the subsidy and thereby control for unobserved heterogeneity. Unlike previous studies, we find that on-farm risk does not affect the labor allocation decisions of farm households.Labor and Human Capital,

Simultaneous X-ray/optical observations of GX 9+9 (4U 1728-16)

We report on the results of the first simultaneous X-ray (RXTE) and optical (SAAO) observations of the luminous low mass X-ray binary (LMXB) GX 9+9 in 1999 August. The high-speed optical photometry revealed an orbital period of 4.1958 hr and confirmed previous observations, but with greater precision. No X-ray modulation was found at the orbital period. On shorter timescales, a possible 1.4-hr variability was found in the optical light curves which might be related to the mHz quasi-periodic oscillations seen in other LMXBs. We do not find any significant X-ray/optical correlation in the light curves. In X-rays, the colour-colour diagram and hardness-intensity diagram indicate that the source shows characteristics of an atoll source in the upper banana state, with a correlation between intensity and spectral hardness. Time-resolved X-ray spectroscopy suggests that two-component spectral models give a reasonable fit to the X-ray emission. Such models consist of a blackbody component which can be interpreted as the emission from an optically thick accretion disc or an optically thick boundary layer, and a hard Comptonized component for an extended corona.Comment: 19 pages, 13 figures; accepted for publication in MNRA

Nova Scorpii 1941 (V697 Sco): A Probable Intermediate Polar

V697 Sco, the remnant of Nova Scorpii 1941 and currently at V ~ 20.0, is found from photometric observations to have the characteristics of an intermediate polar (IP) with an orbital period (Porb) of 4.49 h and a rotation period (Prot) of 3.31 h. It therefore appears to be a member of the rare class of IPs where Prot ~ Porb, which are probably discless systems. The prominence of the modulation at 0.5 Prot, and its orbital sidebands, indicates two-pole accretion.Comment: To appear in the November 2002 issue of PAS

Farm Growth, Consolidation, and Diversification: Washington Dairy Industry

Farm Management, Q12,

Numerical model of swash motion and air entrapment within coarse-grained beaches

Copyright 2012 Elsevier B.V., All rights reserved.Peer reviewedPublisher PD