The Exciting Star of the Berkeley 59/Cepheus OB4 Complex and Other Chance Variable Star Discoveries

TL;DR

This study investigates various variable stars in the Berkeley 59/Cepheus OB4 complex, providing new spectroscopic and photometric data, identifying key stellar properties, and exploring cluster membership and star evolution.

Contribution

The paper offers new spectroscopic and photometric observations of variable stars, including the first detailed analysis of the ionizing star and cluster parameters in Berkeley 59.

Findings

BD+66 1673 is an O5 V((f))n star, likely ionizing the complex.

Cluster age estimated at ~2 million years, distance ~883 pc, reddening E(B-V)=1.38.

Identification of eclipsing binaries and their classifications, including a possible cataclysmic variable.

Abstract

A study is presented regarding the nature of several variable stars sampled during a campaign of photometric monitoring from the Abbey Ridge Observatory: 3 eclipsing binaries, 2 semiregulars, a luminous Be star, and a star of uncertain classification. For one of the eclipsing systems, BD+66 1673, spectroscopic observations reveal it to be an O5 V((f))n star and the probable ionizing star of the Berkeley 59/Cep OB4 complex. An analysis of spectroscopic observations and BV photometry for Berkeley 59 members in conjunction with published observations imply a cluster age of ~2 Myr, a distance of d = 883+-43 pc, and a reddening of E(B-V) =1.38+-0.02. Two of the eclipsing systems are Algol-type, but one appears to be a cataclysmic variable associated with an X-ray source. ALS 10588, a B3 IVn star associated with the Cepheid SV Vul, is of uncertain classification, although consideration is given to it being a slowly pulsating B star. The environmental context of the variables is examined using spectroscopic parallax, 2MASS photometry, and proper motion data, the latter to evaluate the membership of the variable B2 Iabe star HDE 229059 in Berkeley 87, an open cluster that could offer a unique opportunity to constrain empirically the evolutionary lineage of young massive stars. Also presented are our null results for observations of a sample of northern stars listed as Cepheid candidates in the Catalogue of Newly Suspected Variables.