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A&A Supplement series, Vol. 122, May I 1997, 415-432

Received February 29, accepted August 9, 1996

Long-term tex2html_wrap_inline1518 monitoring of 12 southern hemisphere Long Period Variables

P. de Lavernytex2html_wrap1548 - H. Geoffray tex2html_wrap1550 - L. Jorda tex2html_wrap1552 - M. Kopp tex2html_wrap1554

Send offprint request: P. de Laverny (Uppsala Observatory)

tex2html_wrap1556  Uppsala Astronomical Observatory, Box 515, S-751 20 Uppsala, Sweden
tex2html_wrap1558  GRAAL, Université Montpellier II, F-34095 Montpellier Cedex 05, France
tex2html_wrap1560  ESO, Casilla 19001, Santiago 19, Chile
tex2html_wrap1562  ARPEGES, Observatoire de Paris, place J. Janssen, 92195 Meudon Principal Cedex, France
tex2html_wrap1564  DAEC, Observatoire de Paris, place J. Janssen, 92195 Meudon Principal Cedex, France


A program of tex2html_wrap_inline1520 photometric observations of twelve southern hemisphere Long Period Variables (LPV or Miras) has been carried out at the European Southern Observatory. Each star was observed on at least 11 occasions up to 29 over a 4-year period. A determination of their spectral types from the (V-tex2html_wrap_inline1524) and (tex2html_wrap_inline1526tex2html_wrap_inline1528) colours was also performed using the method described by Celis (1986b). We therefore present for the first time spectral type variations together with visible and colour light-curves for at least three successive cycles. New photometric parameters as visible and spectral type extrema are given. Spectral type variations are found in the range 1.3-4.5 subclasses. The variations during a cycle and from cycle-to-cycle are discussed and short-term declines with large amplitude are reported for R Oct and RY Hyi. We finally estimate the distance of these stars using a (tex2html_wrap_inline1532, P, Spectral type) relation. It is shown that rather good distances (mean error less than 30%) can be determined if the period of the stars is known and good UBVRI data are collected at the maximum of luminosity.gif

keywords: stars: late-type -- stars: AGB and post-AGB -- stars: variables -- stars: distances

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