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Re: Any "on line" Star Position Computation available ?
From: Paul Hirose
Date: 2011 Jun 15, 11:17 -0700
From: Paul Hirose
Date: 2011 Jun 15, 11:17 -0700
ICRS coordinates of Diphda at epoch J2000.0:
00 43 35.371451 -17 59 11.77811 FK6 (VizieR) [1]
00 43 35.22827 -17 59 12.0627 HIP2 (SIMBAD) [2]
00 43 35.3709 -17 59 11.783 HIP2 (Hirose) [3]
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.143s .28" SIMBAD - Hirose
[1] The FK6 catalog values don't require any correction for epoch or
reference frame.
[2] The Hipparcos catalogs (the original reduction and the improved 2007
reduction) give the ICRS position at epoch J1991.25. The coordinates on
this line are the SIMBAD's adjustment to epoch J2000.0.
[3] Hipparcos second reduction (2007) coordinates from VizieR,
transformed from epoch J1991.25 to J2000.0 by Hirose.
As Kermit already observed, the SIMBAD coordinates don't agree with the
others. Why? I think SIMBAD applied the proper motion correction twice.
Look at the corrections to transform from 1991.25 to 2000.0 (HIP2 values):
232.55 mas/yr * 8.75 yr / cos dec = 2140 mas = .143s
31.99 mas/yr * 8.75 yr = 280 mas = .28"
These values are identical to the anomalies in the SIMBAD coordinates.
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