Star catalogue comparison a tool to improve asteroidal prediction accuracy Dave Herald, TTSO4, April 2010, Canberra

before HIPPARCOS Accuracies generally worse than 0.2 Systematic errors in both RA and Dec A good prediction had an uncertainty of ~1000km

Hipparcos Removed systematic errors Precision of Hipparcos ~0.001 for 100,000 stars (most stars brighter than ~8) Proper motions determined from motions over the 4-year mission duration

Tycho2 Part of Hipparcos Lower precision ~.02 Coverage to about mag 12 Proper motions – from comparison with old astrometric catalogues

Results from Hipparcos/Tycho2 Hipparcos/Tycho2 removed major source of uncertainty Asteroid orbits improved after several years, as observations in the Hipparcos reference frame grew in number Typical uncertainty <200km

UCAC2 First post-Hipparcos large-scale astrometric catalogue covering the ecliptic [-90° to +45°] Coverage – mags 8 to 16 Accuracy – better than Tycho2 Proper motions from comparison with old catalogues

Recent catalogues UCAC3 – 101M stars, whole sky. Has some specific issues affecting up to 5% of stars UCAC4 – due in Whole sky CMC14 – 95M stars, +50° to -30°. Similar accuracy to UCAC. No proper motions PPMX – 18M stars, whole sky. Independent measures included for ~half the stars. Similar accuracy to UCAC 2MASS – near-infrared catalogue. 470M sources. Whole sky. Similar accuracy to UCAC for many stars. No proper motions

Recent catalogues

Compare catalogues Positions always differ Catalogue errors become apparent Assess commonalities and differences Compare formal uncertainties Identify existence of relevant notes in the source catalogues

Comparison screen

Comparison Graphic

Comparison text 1 Magnitudes Current position

Comparison text 2 Uncertainty info Flags

Comparison text 3 Catalogue positions

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Ex 8

May 7 Anneliese – mag 6.5 over Melbourne #1

Nice observation consistent with PPM position – BUT residuals from NICE generally not good. Prefer PPMX to Hipparcos. Plan on south shift in path of 0.4 path widths May 7 Anneliese – mag 6.5 over Melbourne #2

Nice tool! Yes, that is the way to go for your application. Putting together all available catalog data for a specific star is advisable and with your knowledge of star catalogs and the individual positions and motions given in the catalogs you draw good conclusions.

Access requirements Occult or later If Occult installed, can access from OccultWatcher – ver or later

Any questions?