Marvin E. Germain

The Third US Naval Observatory CCD Astrograph Catalog (UCAC3)

The second US Naval Observatory (USNO) CCD Astrograph Catalog, UCAC2 was released in 2003 July. Positions and proper motions for 48,330,571 sources (mostly stars) are available on 3 CDs, supplemented with Two Micron All Sky Survey photometry for 99.5% of the sources. The catalog covers the sky area from -90° to +40° 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 (0.2 m) Twin Astrograph equipped with a 4K CCD camera. The precision of the positions are 15–70 mas, depending on magnitude, with estimated systematic errors of 10 mas or below. Proper motions are derived by using over 140 ground- and space-based catalogs, including Hipparcos/Tycho and the AC2000.2, as well as yet unpublished remeasures of the AGK2 plates and scans from the NPM and SPM plates. Proper-motion errors are about 1–3 mas yr-1 for stars to 12th magnitude, and about 4–7 mas yr-1 for fainter stars to 16th magnitude. The observational data, astrometric reductions, results, and important information for the users of this catalog are presented.

The First US Naval Observatory CCD Astrograph Catalog

The USNO CCD Astrograph (UCA) started an astrometric survey in 1998 February at Cerro Tololo, Chile. This first, preliminary catalog (UCAC1) includes data taken up to 1999 November with about 80% of the Southern Hemisphere covered. Observing continues, and full sky coverage is expected by mid-2003 after moving the instrument to a Northern Hemisphere site in early 2001. The survey is performed in a single bandpass (579–642 nm), a twofold overlap pattern of fields, and with a long and a short exposure on each field. Stars in the magnitude range 10–14 have positional precisions of ≤20 mas. At the limiting magnitude of R ≈ 16 mag, the positional precision is 70 mas. The UCAC aims at a density (stars per square degree) larger than that of the Guide Star Catalog (GSC) with a positional accuracy similar to Tycho. The UCAC program is a major step toward a high-precision densification of the optical reference frame in the post–Hipparcos era, and the first stage, the UCAC1 contains over 27 million stars. Preliminary proper motions are included, which were derived from Tycho-2, Hipparcos, and ground-based transit circle and photographic surveys for the bright stars (V ≤ 12.5 mag) and the USNO A2.0 for the fainter stars. The accuracy of the proper motions varies widely, from 1 to over 15 mas yr-1. The UCAC1 is available on CD-ROM from the US Naval Observatory.

Stellar Angular Diameters of Late-Type Giants and Supergiants Measured with the Navy Prototype Optical Interferometer

We have measured the angular diameters of 50 F, G, K, and M giant and supergiant stars using the Navy Prototype Optical Interferometer at wavelengths between 649 and 850 nm and using three baselines with lengths up to 37.5 m. Uniform-disk diameters, obtained from fits to the visibility amplitude, were transformed to limb-darkened diameters through the use of limb-darkening coefficients for plane-parallel stellar atmosphere models. These limb-darkened diameters are compared with those measured with the Mark III optical interferometer and with those computed by the infrared flux method. Sources of random and systematic error in the observations are discussed.

Astrophysical Quantities of Cepheid Variables Measured with the Navy Prototype Optical Interferometer

We present mean angular diameters for two cepheid variables, alpha Ursae Minoris and zeta Geminorum, determined with the Navy Prototype Optical Interferometer (NPOI). We present linear radii for these cepheids and two additional cepheids, delta Cephei and eta Aquilae, previously observed at the NPOI. We find the limb-darkened angular diameter of alpha Ursae Minoris and of zeta Geminorum to be 3.28 +/- 0.02 and 1.55 +/- 0.09 milliarcseconds respectively. Using trigonometric parallaxes, we find the linear radii of alpha Ursae Minoris, zeta Geminorum, delta Cephei and eta Aquilae to be 46 (+/- 3), 60 (+25, -14), 45 (+8, -6), and 69 (+28, -15) Solar radii respectively. We compare the pulsation periods and linear radii of this sample of cepheids, which range in period from three to 11 days, to theoretical and empirical period-radius and period-radius-mass relations found in the literature. We find that the observed diameter of alpha Ursae Minoris is in excellent agreement with the predicted diameter as determined from both surface brightness techniques and theory only if alpha Ursae Minoris is a first overtone pulsator.We present mean angular diameters for two Cepheid variables, ? UMi and ? Gem, determined with the Navy Prototype Optical Interferometer (NPOI). We present linear radii for these Cepheids and two additional Cepheids, ? Cep and ? Aql, previously observed at the NPOI. We find the limb-darkened angular diameters of ? UMi and of ? Gem to be 3.28 ? 0.02 and 1.55 ? 0.09 mas, respectively. Using trigonometric parallaxes, we find the linear radii of ? UMi, ? Gem, ? Cep, and ? Aql to be 46 ? 3, 60, 45, and 69 R?, respectively. We compare the pulsation periods and linear radii of this sample of Cepheids, which range in period from 3 to 11 days, to theoretical and empirical period-radius and period-radius-mass relations found in the literature. We find that the observed diameter of ? UMi is in excellent agreement with the predicted diameter as determined from both surface brightness techniques and theory only if ? UMi is a first-overtone pulsator.

Diameters of δ Cephei and η Aquilae Measured with the Navy Prototype Optical Interferometer

We have measured the diameters of the Cepheid variables δ Cephei (18 nights) and η Aquilae (11 nights) with the Navy Prototype Optical Interferometer. The primary results of these observations are the mean angular diameters θLD of these Cepheids: 1.520 ± 0.014 milliseconds of arc (mas) for δ Cep and 1.69 ± 0.04 mas for η Aql. We also report limb-darkened diameters for the check stars in this program: for β Lac, θLD = 1.909 ± 0.011 mas and for 12 Aql, θLD = 2.418 ± 0.010 mas. When combined with radius estimates from period-radius relations in the literature, the Cepheid angular diameters suggest distances slightly smaller than, but still consistent with, the Hipparcos distances. Pulsations are weakly detected at a level of ~1.5 to 2 σ for both Cepheids.

Speckle Interferometry at the US Naval Observatory. V.

The results of 1544 speckle interferometric observations of 637 binary stars, ranging in separation from 025 to 525, are tabulated. These observations were obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, with an intensified CCD detector. This is the fifth in a series of papers presenting measures obtained with this system and covers the period 1998 January 1 through December 31. Random errors for all measures are estimated to be 17.6 mas in separation and 055/ρ in position angle, where ρ is the separation in arcseconds.

Speckle Interferometry at the US Naval Observatory. IV.

The results of 1314 speckle interferometric observations of 625 binary stars, ranging in separation from 02 to 52 with a limiting secondary magnitude of V = 11, are tabulated. These observations were obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, with an intensified CCD detector. This is the fourth in a series of papers presenting measures obtained with this equipment and covers the period 1997 January 1 through December 31. Random errors for all measures are estimated to be 18 mas in separation and 057/ρ in position angle, where ρ is the separation in arcseconds.

Speckle Interferometry at the US Naval Observatory. II.

Position angles and separations resulting from 2406 speckle interferometric observations of 547 binary stars are tabulated. This is the second in a series of papers presenting measures obtained using the 66 cm refractor at the US Naval Observatory in Washington, DC, with an intensified CCD detector. Program stars range in separation from 02 to 38, with Δm ≤ 2.5 mag and a limiting magnitude of V = 10.0. The observation epochs run from 1993 January through 1995 August. Random errors are estimated to be 14 mas in separation and 052/ρ in position angle, where ρ is the separation in arcseconds. The instrumentation and calibration are briefly described. Aspects of the data analysis related to the avoidance of systematic errors are also discussed.

SYSTEMATIC EFFECTS IN ICCD-BASED SPECKLE INTERFEROMETRY OF DOUBLE STARS

Speckle interferometric observations of double stars enjoy considerably higher weight in orbital solutions than visual observations. This is justified on the basis of their higher precision and impersonal nature. It is crucial, therefore, that sources of systematic error in speckle observations are identified and controlled to a level commensurate with their low random errors. Accurate calibration is of primary importance. Other sources of systematic error that affect ICCD-based speckle interferometry include imperfect CCD charge transfer efficiency, fixed pattern noise, and nonuniform background in the autocorrelation function. All of these errors and their remedies are discussed. The restoration of observations compromised by fixed pattern noise is evaluated, and results for 30 such observations are given.

Estimating errors in stellar angular diameters: does the NPOI see the pulsation of δ Cephei?

We examine our measured Cepheid diameters and the uncertainties as estimated from observations of calibrators and check stars, using (delta) Cephei, for which we have the most data, as our example. The mean limb-darkened diameter of (delta) Cep is 1.520 +/- 0.014 mas. The pulsation is only weakly seen, if at all, a tantalizing result that however does not determine the distance with useful precision. The longer baselines currently under construction will provide both high-precision diameters and a post-facto check of our uncertainty estimates.