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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] ------- ------ .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. --