Photometric observations of selected, optically bright quasars for Space Interferometry Mission and other future celestial reference frames

Photometric observations of 235 extragalactic objects that are potential targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R, I magnitudes at the 5% level are obtained at 1 - 4 epochs between 2005 and 2007 using the 1-m telescopes at Cerro Tololo Inter-American Observatory and Naval Observatory Flagstaff Station. Of the 134 sources which have V magnitudes in the Veron & Veron-Cetty catalog a difference of over 1.0 mag is found for the observed-catalog magnitudes for about 36% of the common sources, and 10 sources show over 3 mag difference. Our first set of observations presented here form the basis of a long-term photometric variability study of the selected reference frame sources to assist in mission target selection and to support in general QSO multi-color photometric variability studies.Comment: 40 pages, 13 figures, 4 table

Comparing Tycho-2 Astrometry with UCAC1

The Tycho-2 Catalogue, released in February 2000, is based on the ESA Hipparcos space mission data and various ground-based catalogs for proper motions. An external comparison of the Tycho-2 astrometry is presented here using the first U.S. Naval Observatory CCD Astrograph Catalog (UCAC1). The UCAC1 data were obtained from observations performed at CTIO between February 1998 and November 1999, using the 206 mm aperture 5-element lens astrograph and a 4k x 4k CCD. Only small systematic differences in position between Tycho-2 and UCAC1 up to 15 milliarcseconds (mas) are found, mainly as a function of magnitude. The standard deviations of the distributions of the position differences are in the 35 to 140 mas range, depending on magnitude. The observed scatter in the position differences is about 30% larger than expected from the combined formal, internal errors, also depending on magnitude. The Tycho-2 Catalogue has the more precise positions for bright stars (V <= 10 mag) while the UCAC1 positions are significantly better at the faint end (11 mag <= V <= 12.5 mag) of the magnitude range in common. UCAC1 goes much fainter (to R=16) than Tycho-2; however complete sky coverage is not expected before mid 2003.Comment: LaTeX, 8 pages, 3 PS figures, accepted by AJ (Aug 2000) see also http://ad.usno.navy.mil/ad/ucac/ request for UCAC1 CD-ROM: e-mail to [email protected] request for Tycho-2 CD-ROM: e-mail to [email protected] or [email protected]

The PPMXL catalog of positions and proper motions on the ICRS. Combining USNO-B1.0 and 2MASS

USNO-B1.0 and 2MASS are the most widely used full-sky surveys. However, 2MASS has no proper motions at all, and USNO-B1.0 published only relative, not absolute (i.e. on ICRS) proper motions. We performed a new determination of mean positions and proper motions on the ICRS system by combining USNO-B1.0 and 2MASS astrometry. This catalog is called PPMXL {VO-access to the catalog is possible via http://vo.uni-hd.de/ppmxl}, and it aims to be complete from the brightest stars down to about $V \approx 20$ full-sky. PPMXL contains about 900 million objects, some 410 million with 2MASS photometry, and is the largest collection of ICRS proper motions at present. As representative for the ICRS we chose PPMX. The recently released UCAC3 could not be used because we found plate-dependent distortions in its proper motion system north of -20$^\circ$ declination. UCAC3 served as an intermediate system for $\delta \leq -20^\circ$. The resulting typical individual mean errors of the proper motions range from 4 mas/y to more than 10 mas/y depending on observational history. The mean errors of positions at epoch 2000.0 are 80 to 120 mas, if 2MASS astrometry could be used, 150 to 300 mas else. We also give correction tables to convert USNO-B1.0 observations of e.g. minor planets to the ICRS system.Comment: 9 pages, 9 figure

Pilot/vehicle model analysis of visual and motion cue requirements in flight simulation

The optimal control model (OCM) of the human operator is used to predict the effect of simulator characteristics on pilot performance and workload. The piloting task studied is helicopter hover. Among the simulator characteristics considered were (computer generated) visual display resolution, field of view and time delay

Coronary artery grafting in infants

Coronary artery bypass grafting (CABG) with cardiac vale repair is an uncommon surgery in infants. CABG is technically demanding in infants due to the small size not only of the coronary arteries but also the potential graft arteries. The short and long-term outcome of surgery is not known and thus has largely been avoided. This article reports the case histories of two infants in whom CABG was undertaken successfully as a life-saving measure.peer-reviewe

Efficient Computation of the Nonlinear Schrödinger Equation with Time-Dependent Coefficients

open access articleMotivated by the limited work performed on the development of computational techniques for solving the nonlinear Schrödinger equation with time-dependent coefficients, we develop a modified Runge-Kutta pair with improved periodicity and stability characteristics. Additionally, we develop a modified step size control algorithm, which increases the efficiency of our pair and all other pairs included in the numerical experiments. The numerical results on the nonlinear Schrödinger equation with periodic solution verified the superiority of the new algorithm in terms of efficiency. The new method also presents a good behaviour of the maximum absolute error and the global norm in time, even after a high number of oscillations

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