Measuring the Atmospheric Influence on Differential Astrometry: a Simple Method Applied to Wide Field CCD Frames

Sets of short exposure, guided CCD frames are used to measure the noise added by the atmosphere to differential astrometric observations. Large nightly variations that are correlated with the seeing have been found in the data obtained over 2 years at the KPNO and CTIO 0.9-meter telescopes. The rms noise added by the atmosphere, after a linear transformation of the raw $x,y$ data, is found to be 3 to 7 mas, normalized to 100 seconds exposure time and a field of view of 20 arcminutes near the zenith. An additional nearly constant noise (base-level) of 8.5 mas = 0.012 pixel is found for the KPNO and 6.0 mas = 0.015 pixel for the CTIO telescope. This implies that a ground-based, all sky, astrometric survey from guided CCD frames is more likely limited by the base-level noise than by the atmosphere and could reach an accuracy better than 10 mas under good seeing conditions.Comment: 12 pages LaTeX incl. tables, no figures, accepted by PASP, scheduled for Dec.9

The Twin Astrographic Catalog (TAC) Version 1.0

A first version of the Twin Astrographic Catalog (TAC) of positions for 705,679 stars within $-18^{\circ} \le \delta \le 90^{\circ}$ has been produced. The sky coverage of the TAC is complete to over 90\% in that area. The limiting magnitude is about B=11.5. Positions are based on $4912$ plates taken with the U.S. Naval Observatory Twin Astrograph (blue, yellow lens) at epochs 1977--1986. The TAC is supplemented by proper motions which are obtained from a combination with a re--reduced Astrographic Catalog (AC). Some AC zones are available now and a complete northern hemisphere is expected by fall 1996. Proper motions of almost all TAC stars will be generated as the AC work progresses. The average precision of a catalog position is 90 mas per coordinate at epoch of observation. A large fraction of that error is introduced by the currently available reference stars. The inherent precision of the TAC data is considerably better. The precision of the proper motions is currently 2.5 to 4 mas/yr. Magnitude--dependent systematic errors have been found and preliminarily corrected. The final reduction of this plate material will be performed with the Hipparcos catalog in 1997. The TAC is about 3 times more precise than the PPM or ACRS in the northern hemisphere at current epochs and contains about 3 times more stars. The TAC has a higher star density than the Tycho catalog and provides independent, high precision positions for a large fraction of the Tycho stars at an epoch about 10 years earlier than the Tycho mean epoch. The TAC version 1.0 data are released as the AC zones become available. For latest information, look at the US Naval Observatory World Wide Web page http://aries.usno.navy.mil/ad/tac.html.Comment: 22 pages LaTex, accepted by AJ, scheduled for Nov., no figures provided, needs aasms4.st

"The Levy Institute Measure of Economic Well-Being"

Our measure of economic well-being is motivated by the conviction that there is substantial room for improving existing official measures of the level and distribution of household economic well-being. The definition of the scope of our measure is guided by an extended concept of income that fundamentally reflects the resources that a household can command for facilitating current consumption or acquiring financial and physical assets. In the contemporary United States, three main institutions--markets, the government, and the household--mediate such command. The measure therefore attempts to integrate the following components: money income, wealth, noncash transfers from the business and government sectors, some forms of public consumption, and household production. We discuss conceptual issues relevant to each of the components and outline an approach for combining them.

"Household Wealth and the Measurement of Economic Well-Being in the United States"

The standard official measure of household economic well-being in the United States is gross money income. The general consensus is that such measures are limited because they ignore other crucial determinants of well-being. We modify the standard measure to account for one such determinant: household wealth. We then analyze the level and distribution of economic well-being in the United States during the 1980s and 1990s, using the standard measure and a measure that differs from the standard in that income from wealth is calculated as the sum of lifetime annuity from nonhome wealth and imputed rental-equivalent for owner-occupied homes. Our findings indicate that the level and distribution of economic well-being is substantially altered when money income is adjusted for wealth. Over the 1989Ð2000 period, median well-being appears to increase faster when these adjustments are made than when standard money income is used. This adjustment also widens the income gap between African Americans and whites, but increases the relative well-being of the elderly. Adding imputed rent and annuities from household wealth to household income considerably increases measured inequality and the share of income from wealth in inequality. However, both measures show about the same rise in inequality over the period. Our results contradict the assertion that the Òworking richÓ have replaced the rentiers at the top of the economic ladder.

The Levy Institute Measure of Economic Well-Being United States, 1989-2001

The picture of economic well-being depends crucially on how it is measured. We introduce a new measure of economic well-being that includes public consumption, income from wealth, and household production. The differences in scope and method between our measure and standard income lead to substantially different findings regarding economic well-being. The average U.S. household appears to be much better off in 2001 relative to 1989 according to our measure in comparison to money income. In contrast to official measures, our measure shows that racial disparity increased. The increase in measured inequality was higher than indicated by the official measures.

Brorfelde Schmidt CCD Catalog (BSCC)

The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars, north of +49 deg Declination with precise positions and V, R photometry. The catalog has been constructed from the reductions of 18,667 CCD frames observed with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog was used for astrometric and photometric reference stars. Errors of individual positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range. External comparisons with 2MASS and SDSS reveal possible small systematic errors in the BSCC of up to about 30 mas. The catalog is supplemented with J, H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550 MB ASCII, compressed) will be made available at the Strasbourg Data Center (CDS).Comment: 16 pages, 22 figures, 2 tables, accepted by A

URAT: astrometric requirements and design history

The U.S. Naval Observatory Robotic Astrometric Telescope (URAT) project aims at a highly accurate (5 mas), ground-based, all-sky survey. Requirements are presented for the optics and telescope for this 0.85 m aperture, 4.5 degree diameter field-of-view, specialized instrument, which are close to the capability of the industry. The history of the design process is presented as well as astrometric performance evaluations of the toleranced, optical design, with expected wavefront errors included.Comment: 12 pages, 7 figures, SPIE 2006 Orlando conf. proc. Vol. 626

The second US Naval Observatory CCD Astrograph Catalog (UCAC2)

The second USNO CCD Astrograph Catalog, UCAC2 was released in July 2003. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with 2MASS photometry for 99.5% of the sources. The catalog covers the sky area from -90 to +40 degrees declination, going up to +52 in some areas; this completely supersedes the UCAC1 released in 2001. Current epoch positions are obtained from observations with the USNO 8-inch Twin Astrograph equipped with a 4k CCD camera. The precision of the positions are 15 to 70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by utilizing over 140 ground-and space-based catalogs, including Hipparcos/Tycho, the AC2000.2, as well as yet unpublished re-measures of the AGK2 plates and scans from the NPM and SPM plates. Proper motion errors are about 1 to 3 mas/yr for stars to 12th magnitude, and about 4 to 7 mas/yr for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.Comment: accepted by AJ, AAS LaTeX, 14 figures, 10 table