J/AJ/98/2086 J/AJ/98/2086 CCD photometry of NGC 2257 RR Lyrae A R Walker Astron. J. 98 2086 1989 1989AJ.....98.2086W Photometry, CCD Stars, variable Extensive B and V band CCD photometry for 33 cluster and nine field RR Lyrae variables near the old LMC cluster NGC 2257 provide accurate mean magnitudes for the stars, and hence distances for the cluster and field populations. The mean magnitudes for the two groups differ by 0.17mag. This is interpreted as a distance effect rather than a difference in metal abundance or evolutionary state. The field stars thus average 3.7kpc more distant from us than cluster stars, and 4.1kpc more distant than the plane of the LMC as defined by the de Vaucouleurs and Freeman incline plane model. In addition the field stars occupy less than 9kpc in depth; however, the data are not inconsistent with the LMC field RR Lyrae, taken as a whole, forming a spherical rather than a planar system. From the period-amplitude diagram, both the cluster and field variables have metal abundance of [Fe/H]=-1.8+/-0.1. There is little evidence for any gross spread in metal abundance among the field variables, although periods for two short-period and, presumably, metal-rich RRab stars are confirmed. The new light curves extend previous work on period changes for the cluster variables and have allowed revised periods and rates of period change to be calculated. Two possible double-mode (RRd) field variables were found to have incorrect periods and are actually RRabb stars. Photometry for 462 stars, reaching to V~21 and sampling the cluster to its very center, have been used to prepare a color-magnitude of the evolved stars in NGC 2257. This shows a richly populated blue horizontal branch, the width of which measurements of the dispersion of absolute magnitudes of RR Lyrae in galactic globular clusters by Sandage. The asymptotic giant branch is early separated from the red giant branch allowing accurate numbers of stars in the various stages of evolution to be counted. These counts are compared with those for galactic globular clusters, with the result that NGC 2257 appears to be indistinguishable from its local counterparts such as M3.

NGC 225706 30.4 -64 19

Seq Star sequential number --- Xoff X offset from star 78 (Alcaino I) (+ is West) number=1 Alcaino I in Alcaino & Alvarado, 1988AJ.....95.1724A. arcsec Yoff Y offset from star 78 (Alcaino I) (+ is North) number=1 Alcaino I in Alcaino & Alvarado, 1988AJ.....95.1724A. arcsec Vmag V magnitude mag B-V B-V colour index mag Star Star number --- Per Period number=1 The period given here is that adopted by NHH (Nemec et al., 1985ApJS...57..329), and corresponds to the epoch given by these authors (Tables V, VI of Nemec et al., 1985ApJS...57..329). The phase at maximum light in February 1988 (column Phase) corresponds to this ephemeris. See text for revised periods and period change rates for many of these stars. d Type Variable type --- <Vmag> Intensity mean V magnitude mag u_<Vmag> Uncertainty flag on <Vmag> --- <Bmag> Intensity mean B magnitude mag u_<Bmag> Uncertainty flag on <Bmag> --- <Bmag>-<Vmag> <Bmag> minus <Vmag> mag u_<Bmag>-<Vmag> Uncertainty flag on <Bmag>-<Vmag> --- <B-V> B-V magnitude mean mag u_<B-V> Uncertainty flag on <B-V> --- AV V amplitude mag u_AV Uncertainty flag on AV --- AB B amplitude mag u_AB Uncertainty flag on AB --- Rise Rise time to maximum (in phase units) --- u_Rise Uncertainty flag on Rise --- Phase Phase at the maximum light --- Marie-Jose Wagner, Patricia Bauer CDS 1997Apr29 UNKNOWN UNKNOWN Prepared via OCR at CDS. J_AJ_98_2086.xml