The Cepheid Impostor HD 18391 and its Anonymous Parent Cluster

Abstract

New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variablity previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small-amplitude variability at a level of ΔV = 0.016+-0.002 is indicated, with a period of P=123.04+-0.06 d. A weaker second signal may be present at P=177.84+-0.18 with ΔV = 0.007+-0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of E(B-V) = 1.02, is associated with heavily-reddened B-type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ~10 arcmin to the west and 1661+-73 pc distant. The cluster has nuclear and coronal radii of r_n=3.5 arcmin and R_c=14 arcmin, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid-like pulsation, provided that it follows the semi-period-luminosity relation expected of such objects. Its inferred luminosity as a cluster member is M_V=-7.76+-0.10, its age (9+-1)x10^6 years, and its evolutionary mass ~19 M_{\sun}. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period-luminosity relation closely, much like another Cepheid impostor, V810 Cen.

Accepted for Publication (Astronomische Nachrichten)

References in corpus (5)

• Rate of Period Change as a Diagnostic of Cepheid Properties
• Binary and Multiple O-Type Stars in the Cas OB6 Association
• Reddenings of FGK supergiants and classical Cepheids from spectroscopic data
• Galactic clusters with associated Cepheid variables. VII. Berkeley 58 and CG Cassiopeiae
• The hot stars in orbit around the M31 central supermassive black hole: are they young or old?

Cited by in corpus (6)

• The atmospheric parameters and spectral interpolator for the stars of MILES
• The PL calibration for Milky Way Cepheids and its implications for the distance scale
• The Origin of the Young Pulsar PSR J0826+2637 and Its Possible Former Companion HIP 13962
• WR 38/38a and the ratio of total-to-selective extinction in Carina
• Extinction in the Star Cluster SAI~113 and Galactic Structure in Carina
• Painting a Family Portrait of the Yellow Super- and Hypergiants in the Milky Way I. Constraining the Distances and Luminosities