Statistics – Computation
Scientific paper
Feb 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010ycat..35159032a&link_type=abstract
VizieR On-line Data Catalog: J/A+A/515/A32. Originally published in: 2010A&A...515A..32A
Statistics
Computation
Positional Data, Occultations, Planets
Scientific paper
The catalog consists of (RA, DEC) star positions in the ICRS (J2000) at mean epoch of observation, proper motions and R magnitudes (J, H and K magnitudes are also furnished in the case of 2MASS stars). The mean epoch of observation is given as Modified Julian Date. The position error at mean epoch of observation, the estimated (x,y) error from CCD frame measurements and the number of contributing positions in the WFI mosaics are also furnished. Two flags are included. One indicates if the star belongs to the UCAC2 or 2MASS catalogs. The other flag indicates astrometric position multiplicity in the WFI mosaic solutions (see details in Sect. 4.4 of the paper). For refined astrometry, the user should only use stars with this flag equal to zero. The position error is estimated from repeatability, by the standard deviation (mean error) of contributing individual CCD positions about the final catalog star positions (last iteration in global mosaic solution - see Sect. 4.3 of the paper). By default, multiple entry flagged stars have no position error estimates. Complementary to these position errors, the (x,y) errors from CCD frame measurements (2-D Gaussian fits to the star image profiles) and the number of contributing positions per star in the WFI mosaics may also be used to weight the positions. Proper motions were computed using the 2MASS as first epoch. If it was not a 2MASS star, the USNO B1.0 catalog was used instead. If it was neither a 2MASS nor a USNO B1.0 star, no proper motion was computed. The second epoch position came from the WFI astrometry. Since only two epochs/positions were used in computations, no proper motion error estimates could be derived. For UCAC2 stars, proper motions were directly extracted from that catalog. The catalog flag allows for the identification of the star catalog used as first epoch. The observations were made with a broad-band R filter (ESO#844 with lambdacentral=651.725nm and deltalambda=162.184nm at FWHM). The magnitudes were derived from PSF photometry, but since they were calibrated in the UCAC2 system, magnitude zero-point errors up to 0.3 might be expected for R>17. The infrared magnitudes were extracted from the 2MASS catalog. Their typical errors are less than 0.6, 0.040 and 0.040 for magnitudes J, H and K, respectively. The catalog is divided by year. The sky coverage of the catalog for each year is displayed in Table 1 and in Fig. 1 of the paper (for more details, see Sect. 3). There are small gaps without catalog stars between the years (see Fig. 1), corresponding to sky regions where, as seen from Earth, the Sun is too close to Pluto's direction at date. For each year, the catalog entries are ordered by crescent declination.
Each prediction table contains the date and instant of stellar occultation (UTC), the ICRS (J2000) star coordinates at the event date (that is, corrected by proper motion), the closest apparent geocentric distance between star and body, the position angle of the shadow across the Earth (clockwise, zero at North), the velocity in km/s, the distance to the Earth (AU), longitude of the sub-solar point, local solar time, DE418 and plu017 ephemerides offsets in (RA, DEC) for the central instant, the catalog proper motion, the catalog and multiplicity flags, the estimated star catalog position errors, the proper motions and the magnitudes R*, J*, H* and K*. Magnitudes are normalized to a reference shadow velocity v of 20km/s (the typical shadow velocity around the Pluto opposition). Magnormalized=mag+2.5log_10(v/20). These normalized magnitudes may bring forward faint stars involved in slow events, thus allowing for longer integration time, and consequently reasonably good signal-to-noise ratios (SNRs) without loss of spatial resolution in diameter measurements and in probing atmosphere altitudes in the light curves, in spite of the faintness of the targets. Note however that Pluto's important contribution to the total recorded flux will then be an issue in those situations, so that a case by case estimation of the SNR must be conducted for those candidates. The prediction tables are divided by body and year, with entries in chronological order. The reference ephemerides used for Pluto and its satellites were DE418 and plu017 ephemerides.
(7 data files).
Andrei Alexander H.
Assafin Marcelo
Braga-Ribas Felipe
Camargo I. B. J.
da Silva Neto Dario N.
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