Star catalogue comparison a tool to improve asteroidal prediction accuracy Dave Herald, TTSO4, April...
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Transcript of Star catalogue comparison a tool to improve asteroidal prediction accuracy Dave Herald, TTSO4, April...
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
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 infoFlags
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
• 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 inthe catalogs you draw good conclusions.
Access requirements• Occult 4.0.8.16 or later
• If Occult installed, can access from OccultWatcher – ver 3.2.0.5 or later
Any questions?