CCD Strip Research Articles

Quasi-periodic line-of-sight velocity variations at the bases of polar coronal holes

Spatial and temporal variations in the line-of-sight velocities and brightnesses measured in the Hα and FeI 6564 A Hβ and FeI 4864 A NiI 4857 A lines at the bases of polar coronal holes are analyzed. Time series with durations of 43–120 min were recorded using a CCD strip (3700 pixels 200×7 µm in size) and a CCD array (256×1024 pixels 24 µm in size). Quasi-stationary upward flows (with radial velocities reaching 3 km/s in the photosphere and 12–15 km/s in the chromosphere) were observed near dark points at the boundaries of the chromospheric network. The acoustic 3-min and 5-min oscillations are amplified in the coronal hole, and reach 1 km/s in the photosphere and 3–4 km/s in the chromosphere. The spectra of fluctuations of the line-of-sight velocity exhibit significant maxima at low frequencies, clustering near 0.4, 0.75, and 1 mHz.

Pluto-Charon Stellar Occultation Candidates: 2000–2009

We have completed a search for candidates for occultations by Pluto and Charon over the years 2000 through 2009. Using the DE405 ephemeris and the Plu006 orbit model for Pluto and Charon, we searched for stars that lie within 10 of their respective apparent motions. The images used were CCD strip scans taken at the George R. Wallace Astrophysical Observatory, reaching a depth of 15th to 17th magnitude. As Pluto-Charon enter the Galactic plane, a dramatic increase in the number of stellar appulses will occur. We identify 486 appulses by Pluto and 479 appulses by Charon over this period, with the frequency peaking in 2007. Further astrometry will be necessary to determine which of these appulses will have minimum separations small enough (less than 034 for Pluto or 031 for Charon) to produce an occultation visible from Earth.

Triton Stellar Occultation Candidates: 2000–2009

As part of our ongoing program of predictions and observations of stellar occultations by solar system bodies, we have completed a search for candidates for occultations by Triton over the decade 2000 to 2009. Star positions near Triton's projected orbit as determined by the DE405 ephemeris and NEP016 orbit model were measured on (unfiltered) CCD strip scans recorded with the 0.6 m telescope at the George R. Wallace Astrophysical Observatory to a depth of 16th to 18th magnitude, depending on the quality of individual strip scans. Within 10 of the predicted orbit of Triton during this period, 128 stars were found, including 12 stars brighter than 14th magnitude. Only appulses with geocentric minimum separations of less than about 037 will result in an occultation visible from Earth, but potential errors in the ephemeris and in the positions of our candidates preclude accurate prediction of actual occultation events without further astrometry.

Improved Astrometric Calibration Regions along the Celestial Equator

We present improved and highly accurate International Celestial Reference System (ICRS) equatorial positions for 1,268,732 stars in 16 astrometric calibration regions located around the celestial equator. Each region is about 76 × 32 in area (~24.3 deg2), contains a large number of stars (18,767 to 263,810), has stellar densities ranging from 765 to 10,772 stars deg-2, covers a wide range in magnitude (9.5 < R < 17.8, or equivalently 10.0 < V < 18.3), and is complete to magnitude R ~ 17.2 (V ~ 17.7). All of the observations were taken in 1994–1998 (mean epoch ~J1996.0) with the Flagstaff Astrometric Scanning Transit Telescope. Furthermore, each region was observed many times with overlapped CCD strip scans, and these data were reduced to star positions using differential reductions. The reference-star positions were taken from the ACT catalog of accurate star positions and proper motions. The star positions presented herein are typically accurate to ±26 mas (±12 mas precision) in both right ascension and declination, except for the faintest stars, whose errors are about 2 times larger. Similarly, magnitudes were determined for the astrometric calibration stars using standard photometric reductions, and accuracies of ±18 mmag (±10 mmag precisions) were achieved (about ±46 mmag for the faintest stars). There is little variation among the individual astrometric calibration regions in terms of the positional and photometric accuracies achieved. In addition, the positions and magnitudes presented in this paper supersede those given in 1997 by Stone, insofar as they are considerably more accurate, are rigorously placed in the ICRS, include many more stars in the low Galactic regions, and have had accurate proper motions computed for them as well. The proper motions are accurate to about ±6 mas yr-1 and should maintain the accuracy of the positions for many years to come. Concerning possible applications, the positions and magnitudes of the stars in the astrometric calibration regions can be used to calibrate single and mosaicked CCD detectors, as well as to optimize techniques for reducing star measures on astrographic plates to star positions and magnitudes. As a consequence, the positions, proper motions, and magnitudes put forth in this paper are made available to interested users.

New analytical possibilities of a steeloscope fitted with a multielement photodetector

It is shown that the use of a multielement photodetector (CCD strip) as an attachment to a steeloscope eliminates the subjectivity of visual analysis, makes it possible to obtain operative information on measurement results, extends the spectral range of the device, and improves the working conditions of analysts.

New Variables in the Sloan Digital Sky Survey Calibration Fields

The US Naval Observatory 0.2 m Flagstaff Astrometric Scanning Transit Telescope was used to obtain astrometric information in 16 equatorial fields in support of the Sloan Digital Sky Survey. Each field is approximately 76 × 32 in size and was scanned ~10 times with overlapping CCD strip scans; star positions accurate to ±50 mas in each coordinate and magnitudes good to ±0.011 mag were determined. As an ancillary project, this database was searched for new variables, and the results of that search are presented here. Approximately 1500 new variables have been discovered, and accurate coordinates for ~100 previously identified variables and suspected variables are given.

Astrometric Calibration Regions Along the Celestial Equator

view Abstract Citations (14) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astrometric Calibration Regions Along the Celestial Equator Stone, Ronald C. Abstract This paper presents accurate J2000 equatorial coordinates and magnitudes for 661 591 stars observed in 16 astrometric calibration regions located around the celestial equator. The size of each region is about 7.6°×3.2&deg and includes large numbers of stars (18 799 to 91 058 stars) at high stellar densities (770 to 3720 stars deg-1) and with magnitudes 9.5<R<17.8 mag. The positions and magnitudes were determined from overlapped CCD strip scans made in 1994-1996 and are internally accurate to ±18 mas, respectively, in right ascension and declination, and ±0.011 mag in magnitude for the brighter stars (R<15 mag), and these errors are about 3 times larger for the faintest stars. The true errors in these positions and magnitudes are probably ±41 and ±50 mas in right ascension and declination and ±0.018 mag for the magnitudes. Each star was observed 8-11 times in the observing program, and all the positions were determined directly in the extragalactic reference frame. A full description of the reduction methods is given as well as particulars about the resulting catalog of star positions and magnitudes. Because these regions are large in size, contain high densities of stars with accurate positions and magnitudes, and are accessible from both hemispheres, they are useful for many practical purposes which are discussed in Sec. 7 of this paper. Publication: The Astronomical Journal Pub Date: December 1997 DOI: 10.1086/118689 Bibcode: 1997AJ....114.2811S Keywords: ASTROMETRY; INSTRUMENTATION: DETECTORS full text sources ADS |

Pluto-Charon Stellar Occultation Candidates: 1996-1999

view Abstract Citations (6) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Pluto-Charon Stellar Occultation Candidates: 1996-1999 McDonald, S. W. ; Elliot, J. L. Abstract With the hope of finding stellar occultation events that can be used to answer fundamental questions about Pluto and Charon, we have extended our previous search for stellar-occultation candidates for these bodies to include the years 1996 to 1999. The data for this work are CCD strip scans to about 17.5 R magnitude for stars close to Pluto's and Charon's ephemerides (DE403). We list 60 stars within 1.0 arcsec of Pluto's ephemeris and 64 within 1.0 arcsec of Charon's ephemeris over these four years. In addition, we list our predictions for stars that have been previously published as Pluto and/or Charon occultation candidates [Mink et al AJ, 101, 2255 (1991); Dunham et al AJ, 102, 1464 (1991)]. Four events involve stars brighter than 15th magnitude and minimum separations less than 0.31 arcsec. An appulse with a minimum geocentric separation less than 0.35 arcsec will result in a stellar occultation observable from Earth, but further astrometry and photometry will be necessary to refine individual predictions for identification of actual occultations. Finder charts are included to aid in further studies and prediction refinement. Publication: The Astronomical Journal Pub Date: August 1996 DOI: 10.1086/118054 Bibcode: 1996AJ....112..788M Keywords: OCCULTATIONS; PLANETS AND SATELLITES: PLUTO; PLANETS AND SATELLITES: CHARON full text sources ADS | data products SIMBAD (86)

Triton stellar occultation candidates: 1995-1999

We have completed a search for candidates for stellar occultations by Triton over the years 1995-1999. CCd strip scan images provided star positions in the relevant sky area to a depth of about 17.5 R magnitude. Over this time period, we find that Triton passes within 1.0 arcsec of 75 stars. Appulses with geocentric minimum separations of less than 0.35 arcsec will result in stellar occultations, but further astrometry and photometry is necessary to refine individual predictions for identification of actual occultations. Finder charts are included to aid in further studies and prediction refinement. The two most promising potential occultations, Tr176 and Tr180, occur in 1997.