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Astron. Astrophys. 342, 167-172 (1999)

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1. Introduction

[FORMULA] Cygni (HD 187796 = HR 7564 = BD+32 3593) is famous for having the largest visual amplitude amongst the well-observed Mira variables. In early July 1686, Gottfried Kirch planned observations of Nova 11 Vulpeculae (discovered 16 years earlier), and at this occasion he compared the surrounding field with Bayer's Uranometria atlas made in 1603. He could not find the star that was designed by Bayer as [FORMULA] Cygni (even Flamsteed took the star 17 Cyg for [FORMULA] Cygni) and, consequently, Kirch kept this region under close surveillance. On October 19, 1686 he found [FORMULA] Cygni again as a star of about fifth magnitude. This appearance was the first reliable historical time of maximum of this variable, and [FORMULA] Cygni is thus one of the oldest known variable stars.

From the discovery date till 1738 the star was mainly monitored by G. Kirch and Christfried Kirch, and-rather occasionally-also by Cassini and Halley. But the really significant observational contributions were made by Argelander and contemporaries (specifically J. Schmidt-who was one of the first who systematically monitored the star through its phase of minimum light-and who provided an almost continuous sequence of observations covering a time interval of nearly 40 years from 1845 to 1884). From the beginning of the [FORMULA] century the star was observed almost uninterruptedly by different observers, particularly by amateur astronomers. Fig. 1 illustrates the evolution of the number of magnitude estimates as a function of time, and Fig. 2 shows the light curves available since 1865.

[FIGURE] Fig. 1. Evolution of the number of magnitude estimates as a function of time.

[FIGURE] Fig. 2. Light curves of [FORMULA] Cygni available since 1865. Note that the minima are not always well-covered (data from Sterken & Broens 1998, Broens et al. 1998).

The bulk of the historical data, transformed to the V scale of the Johnson UBV sytem, has been published by Sterken & Broens (1998) and Broens et al. (1998).

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998