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?