On the Observational History of Chi Cygni (Abstract)

Volume 29 number 1 (2001)

Eric Broens

Vereniging voor Sterrenkunde Werkgroep Veranderlijke Sterren Wateringstraat 143 B-2400 Mol Belgium

Christiaan Sterken

University of Brussels (VUB) Pleinlaan 2 B-1050 Brussels Belgium

Chris Koen

South African Astronomical Observatory P. O. Box 9 Observatory 7935 Cape South Africa

Abstract

(Abstract only) Since its discovery in 1686 by Gottfried Kirch, chi Cygni has attracted the attention of many observers. Until 1738 the star was mainly monitored by G. Kirch and C. Kirch, and occasionally by Cassini and Halley. Later on, Le Gentil, Pigott, and Olbers, among others, provided series of observations, although these had long interruptions in between. During the 19th century significant contributions came from Argelander and contemporaries. In the second half of the 19th century, J. Schmidt obtained observations covering nearly 40 years! From the end of the 19th century on, amateurs have gathered an uninterrupted series of observations. An analysis of the available observations since the discovery date yields substantial cycle-to-cycle variations in the pulsation period with quite strong evidence for a linearly increasing period. A quadratic fit Tmax = T0 + PE + 0.5 (dP/dE) E2 over the complete range of available data yields a period change dP/dE = 0.014 day/century (P = 405.27 days), implying that chi Cygni's pulsation period has increased by about 4 days since the discovery date three centuries ago.