- ID:
- ivo://CDS.VizieR/J/MNRAS/505/5253
- Title:
- A comparison of centering in ISS astrometry
- Short Name:
- J/MNRAS/505/5253
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- In the caviar software package, a standard tool for astrometry of images from the Cassini imaging science subsystem (ISS), Gaussian fitting is used to measure the centre of point-like objects, achieving a typical precision of about 0.2 pixels. In this work, we consider how alternative methods may improve on this. We compare three traditional centroiding methods: two-dimensional Gaussian fitting, median, and modified moment. Results using 56 selected images show that the centroiding precision of the modified moment method is significantly better than the other two methods, with standard deviations for all residuals in sample and line of 0.065 and 0.063 pixels, respectively, representing a factor of over 2 improvement compared to Gaussian fitting. Secondly, a comparison of observations using Cassini ISS images of Anthe is performed. Anthe results show a similar improvement. The modified moment method is then used to reduce all ISS images of Anthe during the period 2008-2017. The observed-minus-calculated residuals relative to the JPL SAT393 ephemeris are calculated. In terms of {alpha}xcos({delta}) and {delta} in the Cassini-centred international celestial reference frame, mean values of all residuals are close to 0km, and their standard deviations are less than 1km for narrow angle camera images, and about 4km for wide angle camera images.
« Previous |
1 - 10 of 58
|
Next »
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/437/1147
- Title:
- Amalthea and Thebe CCD astrometric obs.
- Short Name:
- J/A+A/437/1147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents the results of observations of Jupiter's satellites Amalthea and Thebe made in 1995, 1996 and 2001 at the Laboratorio Nacional de Astrofisica (LNA), Brazil. The observations were made in visible light wavelengths with a 1.6m reflector telescope and the light of Jupiter was covered by a mask placed near the CCD surface. The already published positions for 1995, whose astrometric reduction used the Galilean satellites, are now reduced using the stars in the CCD fields like the new positions of 1996 and 2001. The 2001 data are much better than those obtained in 1995, and that those from 1996 show large residuals. Considering the 310 frames observed, the mean residual is about 0.01" and the standard deviation is about 0.15".
- ID:
- ivo://CDS.VizieR/J/A+A/545/A144
- Title:
- Astrometric observations of Deimos
- Short Name:
- J/A+A/545/A144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Between July 2005 and July 2011 Mars Express performed 50 Deimos approaches. 156 SRC images were acquired and used for astrometric (positional) measurements of the small Martian satellite. For this study, we have developed a new technique, where the center-of-figure of the odd-shaped Deimos was determined by fitting the predicted to the observed satellite limb. The prediction of the limb was made based on the moon's known shape model. The camera pointing was verified and corrected by means of background star observations. We obtained a set of spacecraft- centered Deimos coordinates with accuracies between 0.6 and 3.6km (1 sigma). Comparisons with current orbit models indicate that Deimos is ahead or falling behind its predicted position along its track by as much as +3.7km or -4.4km, respectively, depending on the chosen model. Our data may be used to improve the orbit models of the satellite.
- ID:
- ivo://CDS.VizieR/J/A+AS/143/405
- Title:
- Astrometric observations of Helene
- Short Name:
- J/A+AS/143/405
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Astrometric photographic positions of the Saturnian satellite Helene obtained from 22 plates taken in 6 nights are presented. The observations are distributed between 5 missions in 1985 and 1987. All positions are compared with those calculated by Jacobson (1999, personal communication). The residuals have mean and standard deviation smaller than 0.25" and 0.30" respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/580/A28
- Title:
- Astrometric observations of Phobos
- Short Name:
- J/A+A/580/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mars Express (MEX) carried out 74 Phobos flybys at distances between 669 and 5579km from April 2008 to August 2011. Images taken with the Super Resolution Channel (SRC) were used to determine the Martian moon's spacecraft-centered right ascension and declination. Image positions of Phobos were measured using the control point and limb fit measurement techniques. Camera pointing and pointing drift were controlled by means of background star observations that were compared to the corresponding positions from the Tycho-2 catalog. Blurred and noisy images were restored by applying an image-based point spread function in a Richardson-Lucy deconvolution. Altogether, we provide 158 astrometric observations of Phobos with estimated uncertainties between 0.224 and 3.405km circular about the direction to the satellite. Control point measurements yield more accurate results than limb fit observations.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A104
- Title:
- Astrometric obs. of Phobos and Deimos in 1971
- Short Name:
- J/A+A/572/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate positional measurements of planets and satellites are used to improve our knowledge of their dynamics and to infer the accuracy of planet and satellite ephemerides. In the framework of the FP7 ESPaCE project, we provide positions of Mars, Phobos and Deimos taken with the U.S. Naval Observatory 26-inch refractor during the 1971 opposition of the planet. These 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 to provide the most accurate data.
- ID:
- ivo://CDS.VizieR/J/A+A/383/1054
- Title:
- Astrometry of Pluto and Saturn in 1995-2001
- Short Name:
- J/A+A/383/1054
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work, we publish astrometric positions of Pluto and satellites of Saturn obtained with the Bordeaux and Valinhos CCD meridian circles. These observations are used to test the DE403 and DE405 ephemerides.
- ID:
- ivo://CDS.VizieR/J/A+AS/130/77
- Title:
- Astrometry of Satellites of Uranus
- Short Name:
- J/A+AS/130/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table7 contains standard Co-ordinates (J2000.0) in arcseconds relative to the reference satellite. The numbers of the satellites 1-5 correspond to the conventional designation of the satellites I-V.
- ID:
- ivo://CDS.VizieR/J/other/PSS/210.1
- Title:
- Astrometry of the 5 largest Uranian sat.
- Short Name:
- J/other/PSS/210.
- Date:
- 14 Dec 2021 08:12:44
- Publisher:
- CDS
- Description:
- We present the astrometry of the five largest satellites of Uranus from observations spread over almost three decades with photographic plates and CCDs (mainly), taken at the Pico dos Dias Observatory - Brazil. All positions presented here are obtained from the reanalysis of measurements and images used in previous publications. Reference stars are those from the Gaia Early Data Release 3 (Gaia EDR3) allowing, in addition to a higher accuracy, a larger number of positions of the largest satellites as compared to our previous works. From 1982 to 1987, positions were obtained from photographic plates. From 1989 to 2011, CCDs were used. On average, we obtained {Delta}{alpha}cos{delta}=-11(+/-52) milli-arcseconds and {delta}{delta}=-14 (+/-43) milli-arcseconds for the differences in the sense observation minus ephemerides (DE435+ura111). Comparisons with different ephemerides (DE440, INPOP21a, INPOP19a and NOE-7-2013-MAIN) and results from stellar occultations indicate a possible offset in the (Solar System) barycentric position of the Uranian system barycenter. Overall, our results are useful to improve dynamical models of the Uranian largest satellites as well as the orbit of Uranus.
- ID:
- ivo://CDS.VizieR/I/256
- Title:
- Carlsberg Meridian Catalogs
- Short Name:
- I/256
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This composite catalogue contains 180812 positions and magnitudes of 176591 stars north of declination -40deg, 155005 proper motions, and 25848 positions and magnitudes of 184 Solar System objects obtained with the Carlsberg Automatic Meridian Circle on La Palma during the period May 1984 to May 1998. It includes Carlsberg Meridian Catalogues Numbers 1 to 11 (CMC1-11); i.e. it comprises all the observations made since the instrument began operation on La Palma. The positions of the stars are for the epoch of observation and the equinox J2000.0, and are referred to the new International Celestial Reference Frame. The limiting magnitude is V=15.4. The catalogue mainly comprises positions and proper motions for the following programmes: 36000 International Reference Stars 30000 faint reference stars in a global net 18000 reference stars in the fields of radio sources 17000 stars in the Lick Northern Proper Motion catalogue 5000 reference stars for calibration of Schmidt plates 2600 stars in the Gliese catalogue of nearby stars 5000 stars in nearby OB associations 10500 F-type stars within 100 pc 9000 G-type dwarfs and giants, K-type giants stars within 300 pc 2200 unbiassed sample of K/M-type dwarf stars 19400 reference stars near Veron-Cetty galaxies 4700 variable stars (12-14 mag) in GCVS 12400 stars (11-14 mag) with pm>0".18/yr in NLTT and several smaller programmes mainly aimed at galactic kinematics. Positions and magnitudes of 12 novae and 8 supernovae which occurred in the years 1991 to 1998 are included. The catalogue also contains observations of the following Solar System objects: Callisto, Ganymede, Rhea, Titan, Iapetus, Hyperion, Uranus, Oberon, Neptune, Pluto and 173 minor planets and Comet P/Wild2. The mean error of a catalogue position in the zenith is 0".09 in right ascension and declination in CMC1-6, improving to 0".06 in CMC7-11. The accuracy in magnitude is 0.05 mag in CMC1-10, improving to 0.03 mag in CMC11. The mean error of the proper motions, derived by combining the position in this catalogue with those at earlier epochs, is typically in the range 0".003 to 0".004 per year. Cross-references are given to DM, AGK, SAO, HD and the double star catalogues ADS and WDS. The catalogue also contains 12216 mean annual observed positions of the FK5 stars used to transfer the instrumental system to the FK5 frame in the years 1984 to 1995. A compilation of all the meteorological data collected in the years 1984-1998, including the atmospheric extinction, is appended. This catalogue supersedes the previous versions which were numbered <I/126> (CMC1 and 2), <I/133> (CMC3), <I/147> (CMC4), <I/170> (CMC5), <I/189> (CMC6), <I/205> (CMC7) and <I/213> (CMC8).
