Anchoring the distance scale via X-ray/infrared data for Cepheid clusters: SU Cas

Abstract

New X-ray (XMM-Newton) and JHK[subscript s] (Observatoire du Mont-Megantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J −H) = 0.08 [plus or minus] 0.02 and d = 405 [plus or minus] 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d = 414 [plus or minus] 5([sigma][subscript x-bar]) [plus or minus] 10([sigma]) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators ([delta] Cep, [zeta] Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H[subscript 0].