Alessi 95 and the short period Cepheid SU Cassiopeiae

TL;DR

This study characterizes the open cluster Alessi 95 and confirms SU Cas as a cluster member, providing precise measurements of its parameters and demonstrating consistency across multiple distance estimation methods.

Contribution

The paper establishes detailed parameters for Alessi 95 and confirms SU Cas as a cluster member using combined photometric, spectroscopic, and new observational data.

Findings

Alessi 95 has a mean reddening of E(B-V)=0.35

Distance to Alessi 95 is approximately 429 pc

SU Cas's properties are consistent with overtone pulsation and cluster membership

Abstract

The parameters for the newly-discovered open cluster Alessi 95 are established on the basis of available photometric and spectroscopic data, in conjunction with new observations. Colour excesses for spectroscopically-observed B and A-type stars near SU Cas follow a reddening relation described by E(U-B)/E(B-V)=0.83+0.02*E(B-V), implying a value of R=Av/E(B-V)~2.8 for the associated dust. Alessi 95 has a mean reddening of E(B-V)_(B0)=0.35+-0.02 s.e., an intrinsic distance modulus of Vo-Mv=8.16+-0.04 s.e. (+-0.21 s.d.), d=429+-8 pc, and an estimated age of 10^8.2 yr from ZAMS fitting of available UBV, CCD BV, NOMAD, and 2MASS JHKs observations of cluster stars. SU Cas is a likely cluster member, with an inferred space reddening of E(B-V)=0.33+-0.02 and a luminosity of <Mv>=-3.15+-0.07 s.e., consistent with overtone pulsation (P_FM=2.75 d), as also implied by the Cepheid's light curve parameters, rate of period increase, and Hipparcos parallaxes for cluster stars. There is excellent agreement of the distance estimates for SU Cas inferred from cluster ZAMS fitting, its pulsation parallax derived from the infrared surface brightness technique, and Hipparcos parallaxes, which all agree to within a few percent.