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 2011. 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 • PPMXL – 900M stars, whole sky, with proper motions. Essentially 2MASS + USNO-B1, adjusted to ICRS reference frame. • Announced . Not yet available on VizieR, so haven’t assessed it yet. • Likely to be better than UCAC3 for faint stars – but UCAC4 is expected to be better 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 Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 Ex 6 Ex 7 Ex 8 May 7 Anneliese – mag 6.5 over Melbourne #1 May 7 Anneliese – mag 6.5 over Melbourne #2 • 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 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 220.127.116.11 or later • If Occult installed, can access from OccultWatcher – ver 18.104.22.168 or later Any questions?