V439 Cygni: Insights into the Nature of an Exotic Variable Star (Abstract)

Volume 41 number 1 (2013)

David G. Turner

Saint Mary’s University, Halifax, NS B3H 3C3, Canada; turner@ap.smu.ca

Abstract

(Abstract only) V439 Cyg is a 12th magnitude irregular variable in the core of the very young cluster Berkeley 87 that has defied straightforward characterization in previous years. Prior to the last thirty years it was an irregular variable that displayed occasional erratic 0.5-magnitude flareups lasting several days. In 1959 it was classified as a late-type carbon star from an objective-prism survey, but a photometric study of the cluster in 1982 and an image-tube spectrum in 1983 revealed it to be a highly-reddened early-type star. Attempts to study the star spectroscopically have been hampered by its peculiar nature. The star always exhibits emission in the lower Balmer series hydrogen lines superposed on an almost featureless continuum. But the spectral veiling of V439 Cyg sometimes lifts, revealing characteristics of a very rapidly-rotating star that recently displays features of a nitrogen-enriched B0 dwarf. The star’s light variability apparently ceased thirty years ago, yet it remains an exotic example of slightly evolved massive stars that display the effects of CNO-processed elements in stellar cores mixed into their surface layers. Is V439 Cyg an example of a merged binary?