Astrometric Reflector Research Articles

Observations of Five Major Uranian Satellites during 2013–2020 Based on Gaia DR3

A total of 10,339 positions of the five major Uranian satellites (Ariel, Umbriel, Titania, Oberon and Miranda) were collected at the Yunnan Observatories from 2013 to 2020 with the 1.0 m astrometric reflector. A median filtering method was applied to reduce the influence of the bright Uranus halo. All CCD observational data was analyzed by the newly developed CCD image-processing software with Gaia DR3 as the reference catalog. The impact of different exposure times on satellite positioning accuracy was evaluated. The observational positions of satellites were compared with theoretical positions from Institut de Mécanique Céleste et de Calcul des Éphémérides (DE441 and Lainey et al. 2015) and the mean offsets are from −0.″115 to 0.″103 in both R.A. and decl. for the five satellites. The standard deviation of the offsets are from 0.″008 to 0.″086 for the four greatest Uranian satellites and from 0.″037 to 0.″132 for Miranda in each direction. These precise observations of the five major Uranian satellites over an 8 yr period will be very useful for improving the orbital parameters of both Uranus and its five major satellites.

Optical and Near-infrared Continuum Emission Region Size Measurements in the Lensed Quasar FBQ J0951+2635

We present 10 seasons of Sloan Digital Sky Survey r-band monitoring observations and five seasons of H-band observations of the two-image system FBQ J0951+2635 from the Kaj Strand Astrometric Reflector at the United States Naval Observatory, Flagstaff Station. We supplement our light curves with six seasons of monitoring data from the literature to yield a 10 + 6 season combined data set, which we analyzed with our Monte Carlo microlensing analysis routine to generate constraints on the structure of this system’s continuum emission source and the properties of the lens galaxy. Complementing our optical light curves with the five-season near-infrared light curves, we ran a joint Monte Carlo analysis to measure the size of the continuum emission region at both wavelengths, yielding log(r 1/2 cm−1) = in the r band and in the H band at rest wavelengths of 2744 and 7254 Å, respectively, correcting for an assumed inclination angle of 60°. Modeling the accretion disk temperature profile as a power law T(r) ∝ r −β , we successfully constrain the slope for FBQ J0951+2635 to , shallower than, but nominally consistent with, the predictions of standard thin-disk theory, β = 0.75.

Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database

Abstract We present the United States Naval Observatory (USNO) Bright-star Astrometric Database (UBAD), a current-epoch high-accuracy astrometric catalog. The catalog consists of 364 bright northern hemisphere stars, including all but five such stars with either V < 3.5 or with I < 3.2 and V < 6, as well as a large fraction of slightly fainter stars; 36 of the brightest catalog stars are not included in Gaia Early Data Release 3 (EDR3). Observations were conducted with the USNO Flagstaff Station Kaj Strand 61 inch Astrometric Reflector. Target stars were imaged through a small 12.5 mag neutral-density spot, while the remainder of the stars in the field of view were unattenuated. This allowed for unsaturated images of the bright target stars to be calibrated directly against much fainter reference stars from Gaia EDR3. The median position errors are 1.9 mas in both R.A. and decl. at the catalog epoch of 2017.0, with 90% of catalog stars having errors less than 2.6 mas; systematic errors are 1–3 mas. Combining UBAD observations with Hipparcos-2 positions yields proper motions with median errors of 0.045 and 0.049 mas yr−1 in R.A. and decl., respectively, with 90% of stars having errors less than 0.1 mas yr−1; systematic errors are about 0.1 mas yr−1. Single-frame accuracy for positions of the target stars is typically 5–6 mas. Gaia EDR3 astrometry for these bright stars, which are heavily saturated in the Gaia observations, is validated over the magnitude range 2 ≲ G ≲ 6.

CCD Parallaxes for 309 Late-type Dwarfs and Subdwarfs

Abstract New, updated, and/or revised CCD parallaxes determined with the Strand Astrometric Reflector at the Naval Observatory Flagstaff Station are presented. Included are results for 309 late-type dwarf and subdwarf stars observed over the 30+ years that the program operated. For 124 of the stars, parallax determinations from other investigators have already appeared in the literature and we compare the different results. Also included here are new or updated VI photometry on the Johnson–Kron-Cousins system for all but a few of the faintest targets. Together with 2MASS JHK s near-infrared photometry, a sample of absolute magnitude versus color and color versus color diagrams are constructed. Because large proper motion was a prime criterion for targeting the stars, the majority turn out to be either M-type subdwarfs or late M-type dwarfs. The sample also includes 50 dwarf or subdwarf L-type stars, and four T dwarfs. Possible halo subdwarfs are identified in the sample based on tangential velocity, subluminosity, and spectral type. Residuals from the solutions for parallax and proper motion for several stars show evidence of astrometric perturbations.

A new astrometric measurement and reduction of USNO photographic observations of Phobos and Deimos: 1967–1997

Context. Accurate positional measurements of planets and satellites are used to improve our knowledge of both their orbits and their dynamics and to infer the accuracy of the planet and satellite ephemerides. Aims. In the framework of the European FP7 ESPaCE program, we provide the positions of Mars, Phobos, and Deimos taken with the US Naval Observatory 61-inch astrometric reflector and 26-inch refractor from 1967 to 1997. Methods. Four hundred twenty five astrophotographic plates were measured with the digitizer of the Royal Observatory of Belgium and reduced through an optimal process that includes image, instrumental, and spherical corrections using the UCAC4 catalog to provide the most accurate equatorial (RA, Dec) positions. Results. We compared the observed positions of the planet Mars and its satellites with the theoretical positions from INPOP13c and DE430 planetary ephemerides and from NOE MarsSatV1_0 and MAR097 satellite ephemerides. The rms residuals in RA and Dec of one position are less than 62 mas or about 20 km at the opposition of Mars. The rms intersatellite residuals in RA and Dec of one position are less than 40 mas or about 13 km at Mars. This accuracy is comparable to the most recent CCD observations. We also fitted the NOE model to the new computed positions and compared the orbital evolution of Phobos and Deimos with those derived from the same model, but only fitted to spacecraft data. Our results show that astrophotographic plate data can now compete with those of old spacecraft.

SPECKLE INTERFEROMETRY AT THE USNO FLAGSTAFF STATION: OBSERVATIONS OBTAINED IN 2008 AND NINE NEW ORBITS

Results are presented for 299 speckle interferometric observations of double stars, obtained in 2008 at the USNO Flagstaff Station using the 1.55 m Kaj Strand Astrometric Reflector. Separations range from 015 to 988, with a median of 222. This observing run concentrated on neglected systems, as well as systems in need of improved orbital elements; new orbital solutions have been determined for nine systems as a result.

SPECKLE INTERFEROMETRY AT THE USNO FLAGSTAFF STATION: OBSERVATIONS OBTAINED IN 2003-2004 AND 17 NEW ORBITS

Results are presented for 353 speckle interferometric observations of double stars, obtained in 2003 and 2004 at the USNO Flagstaff Station using the 1.55 m Kaj Strand Astrometric Reflector. Separations range from 012 to 742, with a median of 042. These two observing runs concentrated on systems in need of improved orbital elements, and new solutions have been determined for 17 systems as a result.

CCD astrometric observations of Phoebe in 2003–2004

In 2003-2004, we obtained 115 new observations of Phoebe, the 9th Saturnian faint satellite (visual magnitude of about 16.5). We used a large CCD detector (2048 x 2048 pixels) mounted on the 1.56 m astrometric reflector at the Sheshan Station, near Shanghai. In our reduction, an up-to-date catalogue of stars, UCAC2 (Zacharias et al. 2004), was chosen to ensure a proper astrometric calibration. A comparison of our observations to three recently available, high quality ephemerides, including the JPL SAT185 by Jacobson (2004b), has shown that most of our observed positions of Phoebe present an accuracy of some tens of mas, which appears to be a very high level for such a faint satellite.

Re-determination of Phoebe's orbit

In order to improve the orbit of Phoebe, the ninth satellite of the Saturnian system, 101 new observations were made by our research team in 2003, using a CCD detector of large size (2048×2048 pixels) mounted on the 1.56 m astrometric reflector at the Sheshan Station of Shanghai Astronomical Observatory. We fitted a numerical integration of its orbit to all of the collected Earth-based astrometric observations from 1904 to 2003, including the newest precise data sets from Qiao & Tang and from Peng et al. A new set of initial conditions of Phoebe has been obtained, leading to an improved orbit of this satellite.

Preliminary Parallaxes of 40 L and T Dwarfs from the US Naval Observatory Infrared Astrometry Program

We present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager on the US naval Observatory (USNO) 1.55 m Strand Astrometric Reflector. The results presented here are based on observations obtained between 2000 September and 2002 November; about half of the objects have an observational time baseline of t 1:3 yr and half t 2:0 yr. Despite these short time baselines, the astrometric quality is sufficient to produce significant new results, especially for the nearer T dwarfs. Seven objects are in common with the USNO optical CCD parallax program for quality control and seven in common with the European Southern Observatory 3.5 m New Technology Telescope parallax program. We compare astrometric quality with both of these programs. Relative to absolute parallax corrections are made by employing Two Micron All Sky Survey and/or Sloan Digital Sky Survey photometry for reference-frame stars. We combine USNO infrared and optical parallaxes with the best available California Institute of Technology (CIT) system photometry to determine MJ , MH, and MK values for 37 L dwarfs between spectral types L0 and L8 and 19 T dwarfs between spectral types T0.5 and T8 and present selected absolute magnitude versus spectral type and color diagrams, based on these results. Luminosities and temperatures are estimated for these objects. Of special interest are the distances of several objects that are at or near the L-T dwarf boundary so that this important transition can be better understood. The previously reported early to mid T dwarf luminosity excess is clearly confirmed and found to be present at J, H, and K. The large number of objects that populate this luminosity-excess region indicate that it cannot be due entirely to selection effects. The T dwarf sequence is extended to MJ 16:9 by 2MASS J041519 0935, which, at d 5:74 pc, is found to be the lluminous LOG (L=L )pa

ASTROMETRY OF SINGLE-CHORD OCCULTATIONS: APPLICATION TO THE 1993 TRITON EVENT

ABSTRACT This paper outlines a method for reducing astrometric data to derive the closest approach time and distance to the center of an occultation shadow for a single observer. The method applies to CCD frames, strip scans, or photographic plates and uses a set of field stars of unknown positions to define a common coordinate system for all frames. The motion of the occulting body is used to establish the transformation between this common coordinate system and the celestial coordinate system of the body's ephemeris. This method is demonstrated by application to the Tr60 occultation by Triton on 1993 July 10 UT. Over an interval of 4 nights that included the occultation time, 80 frames of Triton and Tr60 were taken near the meridian with the U.S. Naval Observatory (USNO) 60-inch astrometric reflector. Application of the method presented here to these data yields a closest approach distance of 359 ± 133 km (corresponding to 0.017 ± 0.0076 arcsec) for the occultation chord obtained with the Kuiper Airborne Observatory (KAO). Comparison of the astrometric closest approach time with the KAO light-curve midtime shows a difference of 2.2 ± 4.1 sec. Relative photometry of Triton and Tr60, needed for photometric calibration of the occultation light curve, is also presented.

B, V photometry of Thebe (JXIV)

Thebe (JXIV), a small inner moon of Jupiter, was discovered by Synnott in 1980 from Voyager images. It orbits in a severe environment of bombardment by high-energy charged particles trapped in Jupiter's magnetosphere and other contaminants originating on Io. Since Thebe is too small for its surface to be affected by endogenic processes, Thebe's surface is useful as a probe for the remote sensing of this environment. B and V photometry of Thebe was obtained relative to Amalthea (JV). A TI 800 × 800 CCD chip was used with the USNO 61-in. astrometric reflector at Flagstaff. The results show Thebe to be 0.5 mag brighter in V on the leading side, near the eastern elongation, than on the trailing side, near the western elongation, suggesting synchronous rotation. A mean opposition magnitude, V = 15.7, is obtained when combining these results with Millis' photometry of JV. The average albedo in V, 0.04, is similar to that of JV and agrees with Synnott's discovery observations. A ( B - V) of 1.3 makes Thebe one of the reddest moons in the Solar System and suggests that it too has been resurfaced by sulfur from Io. Contrary to expectations, Thebe is found to be 0.2 mag bluer than Amalthea, suggesting other contaminants. Thebe also shares several photometric patterns with the Galileans and, thus, links the inner satellite system with the Galilean system. This suggests that the magnetospheric processes which have modified the surfaces of the Galileans have also modified the surfaces of the inner satellites. An implication of this conclusion is that the leading faces of the innermost satellites, Adrastea (JXV) and Metis (JXVI), should be darkened and reddened.

Observational status of the USNO trigonometric parallax program

Since 1983, a TI 800×800 CCD has been routinely used on the 1.5-m astrometric reflector during dark time to measure parallaxes of faint (V≥16.0) stars. The rest of the time remains devoted to the fine grain (Kodak type IIIa emulsions) photographic parallax program, which now uses magnitude compensating filters to extend the range of the program to V=0. Sufficient data are now available to evaluate the precisions of these programs. For CCD fields, the mean error for the relative parallax ranges from ±0".0025 for fields with relatively few observations to ±0".0005 for intensively observed fields such as vB10. The photographic program is now producing relative parallaxes with average mean errors of ±0".0026 compared to ±0".0038 previously obtained with coarse grain emulsions.

Research on the Errors in Determination of Precise Optical Positions of Radio Sources

To link the optical reference frame to extragalactic radio frame, an observation program is in progress in Purple Mountain Observatory (PMO) and Shanghai Observatory. In this program, 70 extragalactic sources will be observed with the 1.56 m astrometric reflector in Shanghai. The secondary reference stars are determined with the twin astrograph (D = 40 cm, f = 300 cm) in PMO, and about 50 radio stars and some bright extragalactic sources will be observed with the twin astrograph.

Trigonometric stellar parallaxes determined with the Zô-sè 40-cm refractor

As a preparation for the parallax and proper motion program of the Shanghai Observatory 1.56 m astrometric reflector, since 1980 an experimental program has been performed with the Zô-sè 40-cm refractor. All the plates of the series have been taken by the end of 1985. Up to now, seven series of those have been reduced and the others are being processed. The reduced results are given and compared with those of other observatories.

The Parallax And Proper Motion Program Of The Shanghai Observatory 1.56-M Astrometric Reflector

The main properties of the 1.56-m astrometric reflector of Shanghai Observatory are described. Some principles of selecting program stars are presented. The experimental program that has been performed with the Zô-sè 40-cm refractor since 1980 is outlined. Accuracies which are expected to be obtained for new program parallaxes are discussed.

Astrometry with small telescopes

At the Quonochontaug Observatory of the University of Rhode Island, we specialize in the development of simple seeing limited optical telescopes. Our main instrument is a heavy Serrier trussed f/10.7, .4-m astrometric reflector which provided the last-minute astrometry in the successful prediction of the occultation of SAO 120774 by Herculina in 1978. It is similar in design to the U. S. Naval Observatory 1.5-m reflector. Its scale of 47.1“/mm makes it potentially more powerful than the Lick .5-m, f/7 astrograph. However, its field of view of 1.3° × 1.7° is insufficient to capture enough AGK3R reference stars which are needed to consistently provide tenth-of-a-second-of-arc accuracy. To solve this problem, a .24-.32-m, f/6.3 lensless Schmidt was developed to provide a 3.8° field at 135”/mm and is mounted on the .4-m telescope. It can be used by itself and/or to provide a secondary reference frame for the main instrument. The measures from the plates and film are reduced by a suite of interactive computer programs which allows one to choose the proper reduction model based on the Eichhorn criterion. Over 100 positions of stars, asteroids, comets and supernovae have been provided with these instruments, and a regular observing program including participation in the IHW is underway.

Recent trigonometric parallaxes from two hemispheres

Both southern and northern hemisphere parallax results are reported for a number of stars including several white dwarfs, the central star of NGC7293, Barnard's star, and several other red dwarfs. The 1 meter astrometric reflector of the McCormick Observatory is described and some preliminary results are briefly discussed.

U.S. Naval Observatory parallaxes of faint stars. VI

view Abstract Citations (70) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS U.S. Naval Observatory parallaxes of faint stars. List VI. Dahn, C. C. ; Harrington, R. S. ; Riepe, B. Y. ; Christy, J. W. ; Guetter, H. H. ; Kallarakal, V. V. ; Miranian, M. ; Walker, R. L. ; Vrba, F. J. ; Hewitt, A. V. ; Durham, W. S. ; Ables, H. D. Abstract Trigonometric parallaxes determined at the U.S. Naval Observatory from plate material obtained with the 1.55-m astrometric reflector are listed. Included are parallax determinations for 89 single stars and for both components of four common-proper-motion binary systems. Of these, 94 are considered 'definitive' in the sense that they are based on sufficient plate material (generally, 40-50 plates per series) covering a sufficient time interval (average of 4.6 yr per series); thus further precision can be expected to accrue only as (approximately) the square root of the total number of plates employed in the solution. Publication: The Astronomical Journal Pub Date: February 1982 DOI: 10.1086/113115 Bibcode: 1982AJ.....87..419D Keywords: Astrometry; Stellar Motions; Stellar Parallax; Stellar Spectrophotometry; Tables (Data); Astronomical Observatories; Binary Stars; Data Reduction; Reference Stars; Astronomy full text sources ADS | data products SIMBAD (100) GCPD (1) Related Materials (9) Part 1: 1970PUSNO..20c...1R Part 2: 1972PUSNO..20f...1R Part 3: 1975PUSNO..24a...1H Part 4: 1976PUSNO..24c...1D Part 5: 1980AJ.....85..454H Part 6: 1981AJ.....86.1414H Part 8: 1985AJ.....90..123H Part 9: 1988AJ.....95..237D Part 10: 1993AJ....105.1571H

Trigonometric stellar parallaxes

I derive some satisfaction from the fact that the general judgment of astrometric work with reflectors as being inferior to that carried out with the long focus refractors, which existed for most of this century, is no longer generally accepted, and that the USNO 61-inch astrometric reflector has contributed to this.If, however, van Maanen had continued his parallax work with the 60-inch Mt. Wilson reflector, or stayed within the small coma free field of the 100-inch telescope, his contributions to the parallax field would have been more justly appreciated.