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 4.0.8.16 or later
• If Occult installed, can access from
OccultWatcher – ver 3.2.0.5 or later
Any questions?