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Subaru Fov Case Study

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3.3 Locating the FoV
The central coordinates of the Subaru FoV are α2000 = 13:26:21.127 and δ2000 = -42:49:09.02, located approximately ∼ 15 kpc from the center of NGC5128 towards the NE. I use the two
AO guide stars45 and the cardinal points as reference, in order to locate the FoV of the
Subaru images on the HST images (see figure 3.3). The position angles (PA) of the two

The term “guide stars” refers always to the foreground AO guide stars in the lower right corner of the HST
(see figure 3.3) and/or the Subaru images (see figure 3.2). With the term “unresolved guide star” I also refer to the same sources, in this case, however, the quoted information (e.g. proper motion, magnitude etc.) is obtained from lower resolution images in which …show more content…

The insignificant change in their
PA and projected separation between the epochs of the Subaru and the HST data (i.e. ∼
15 years) could be either due to the combination of the different– but negligible– proper motions of the two projected members, or due to the “capture” of a close physical binary in an orbital configuration similar to that on the HST images. In a, time-wise, random observation though, the former appears more likely to be the case.
Additionally, the total proper motion of the unresolved guide star (G.S.) quoted in the
UCAC4 catalog (Zacharias et al., 2013), namely, ∼ 24.2 ± 14.3 mas and ∼ −34.5 ± 12.0 mas in RA and Dec, respectively, is negligible. In principal, this can account for the small ob- served change in PA and projected separation (i.e. ∼ 0.3 degrees and ∼ 60 mas, respec- tively), which is in any case within the uncertainties. Most importantly, however, the neg- ligible proper motion of the G.S. is a good indication that the HST field stars47 are expected roughly at the same, with respect to the two guide stars, positions on the Subaru NIR im- ages as

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