Outflow 20--2000 AU from a High-Mass Protostar in W51-IRS2

We present the results of the first high angular resolution observations of SiO maser emission towards the star forming region W51-IRS2 made with the Very Large Array (VLA) and Very Long Baseline Array (VLBA). Our images of the water maser emission in W51-IRS2 reveal two maser complexes bracketing the SiO maser source. One of these water maser complexes appears to trace a bow shock whose opening angle is consistent with the opening angle observed in the distribution of SiO maser emission. A comparison of our water maser image with an image constructed from data acquired 19 years earlier clearly shows the persistence and motion of this bow shock. The proper motions correspond to an outflow velocity of 80 km/s, which is consistent with the data of 19 years ago (that spanned 2 years). We have discovered a two-armed linear structure in the SiO maser emission on scales of ~25 AU, and we find a velocity gradient on the order of 0.1 km/s/AU along the arms. We propose that the SiO maser source traces the limbs of an accelerating bipolar outflow close to an obscured protostar. We estimate that the outflow makes an angle of <20 degrees with respect to the plane of the sky. Our measurement of the acceleration is consistent with a reported drift in the line-of-sight velocity of the W51 SiO maser source.Comment: 19 pages, 5 figures (including 3 color). Accepted for publication in ApJ (April 1, 2001 issue

The mass ratio distribution of short period double degenerate stars

Short period double degenerates (DDs) are close white dwarf - white dwarf binary stars which are the result of the evolution of interacting binary stars. We present the first definitive measurements of the mass ratio for two DDs, WD0136+768 and WD1204+450, and an improved measurement of the mass ratio for WD0957-666. We compare the properties of the 6 known DDs with measured mass ratios to the predictions of various theoretical models. We confirm the result that standard models for the formation of DDs do not predict sufficient DDs with mass ratios near 1. We also show that the observed difference in cooling ages between white dwarfs in DDs is a useful constraint on the initial mass ratio of the binary. A more careful analysis of the properties of the white dwarf pair WD1704+481.2 leads us to conclude that the brighter white dwarf is older than its fainter companion. This is the opposite of the usual case for DDs and is caused by the more massive white dwarf being smaller and cooling faster. The mass ratio in the sense (mass of younger star)/(mass of older star) is then 1.43+-0.06 rather than the value 0.70+-0.03 given previously.Comment: Accepted for publication in MNRA

A technique for passive attitude control of solar oriented interplanetary spacecraft

Passive damping technique for attitude control of solar orientated interplanetary spacecraf

The triple degenerate star WD1704+481

WD1704+481 is a visual binary in which both components are white dwarfs. We present spectra of the H-alpha line of both stars which show that one component (WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf components. Thus, WD1704+481 is the first known triple degenerate star. From radial velocity measurements of the close binary we find an orbital period of 0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white dwarfs predicted by the mass ratio and gravitational redshift difference combined with theoretical cooling curves are 0.39+-0.05 solar mass and 0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first example of a double degenerate in which the less massive white dwarf is composed of helium and the other white dwarf is composed of carbon and oxygen.Comment: 5 pages, 4 figure

Orbital periods of the binary sdB stars PG0940+068 and PG1247+554

We have used the radial velocity variations of two sdB stars previously reported to be binaries to establish their orbital periods. They are PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are 0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for PG0940+068. The nature of the companions is not constrained further by our data.Comment: 5 pages, 2 figure

Exact ground states of a staggered supersymmetric model for lattice fermions

We study a supersymmetric model for strongly interacting lattice fermions in the presence of a staggering parameter. The staggering is introduced as a tunable parameter in the manifestly supersymmetric Hamiltonian. We obtain analytic expressions for the ground states in the limit of small and large staggering for the model on the class of doubly decorated lattices. On this type of lattice there are two ground states, each with a different density. In one limit we find these ground states to be a simple Wigner crystal and a valence bond solid (VBS) state. In the other limit we find two types of quantum liquids. As a special case, we investigate the quantum liquid state on the one dimensional chain in detail. It is characterized by a massless kink that separates two types of order.Comment: 21 pages, 6 figures, v2: largely rewritten version with more emphasis on physical interpretatio

The 3-53 keV Spectrum of the Quasar 1508+5714: X-rays from z = 4.3

We present a high-quality X-ray spectrum in the 3--53 keV rest-frame band of the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z > 4. A simple power-law model with an absorption column density equal to the Galactic value in the direction of the source provides an excellent and fully adequate fit to the data; the measured power-law photon index Gamma = 1.42 (+0.13,-0.10). Upper limits to Fe K alpha line emission and Compton-reflection components are derived. We offer evidence for both X-ray and radio variability in this object and provide the first contemporaneous radio spectrum (alpha = -0.25). The data are all consistent with a picture in which the emission from this source is dominated by a relativistically beamed component in both the X-ray and radio bands.Comment: 8 pages, TeX, 2 postscript figures; to appear in ApJ Letter

Ohio Livestock Waste Management Guide

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