COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3215

                                                         Konkoly Observatory
                                                         Budapest
                                                         14 July 1988

                                                         HU ISSN 0374 - 0676


      COORDINATED ULTRAVIOLET, OPTICAL AND RADIO OBSERVATIONS
                       OF EI Eri (=HD 26337)
                      CALL FOR OBSERVATIONS

From 16 to 19 September 1988, the G5 IV single-line noneclipsing RS CVn-type
system EI Eri (=HD 26337) will be concurrently observed with IUE, VLA, VLBI
and several optical ground-based instruments with the main purpose of determining 
the size, location and physical characteristics of large-scale atmospheric
structures.
   The scheduled observations will provide high-resolution line profiles of
Mg II h and k (IUE) and other lines at optical wavelengths, UV and optical
continuum fluxes versus orbital or rotation phase. Radio fluxes and maps with
VLA and VLBI will be also obtained to synthesize a 3-dimensional picture
of EI Eri atmosphere, from photospheric up to coronal levels. We
aim at covering two consecutive full orbital cycles in order to isolate short-
term flare-like variations from those due to quasi-stable atmospheric structures, 
such as cool starspots, bright plages or coronal features, as they move
across the projected stellar disc following the star's rotation.
   The scientific rationale of this program is extensively discussed in several
recent reviews (e.g., Linsky 1983, Rodono 1986a, 1986b) and papers related
to past observation campaigns on other stars, (Rodono et al. 1986, 1987,
Butler et al, 1986, Byrne et al. 1987, Andrews et al. 1988, Walter et al.
1987, Linsky et al. 1988, Neff et al. 1988). Essential data and information on
previous photometry and spectroscopy of EI Eri may be found in Hall et al.
(1987) and Fekel et al. (1987), respectively,
   Unfortunately, EI Eri is not suitable for extensive ground-based coverage
in September. However, we call for systematic optical photometry and
spectroscopy that are already available or might be obtained in the fall of
1988. The interested observers are kindly requested to contact one of the
undersigned about their observation plan and/or results.


MARCELLO RODONO               JAMES E. NEFF (Code 681)

Astrophysical Observatory     Goddard Space Flight Center
Viale Andrea Doria 6,         Greenbelt, MD 20771, USA
95125 Catania,                Telex: 710-828-9716
Italy                         SPAN address: 6169 ::NEFF
Telex: 970359 (ASTRCT I)
Fax: 39-95-330592
SPAN address: 38982::MARCELLO



References:

Andrews, A.D., et al, 1988, Astron. Astrophys., in press. [BIBCODE 1988A&A...204..177A ]
Butler, C.J., et al., 1986, Nature 321, 679. [BIBCODE 1986Natur.321..679B ]
Byrne, P.B., et al., 1987, Astron. Astrophys, 180, 172. [BIBCODE 1987A&A...180..172B ]
Fekel, F.C., Quigley, R., Gillies, K., and Africano, J.L., 1987, Astron. J,
      94, 726. [BIBCODE 1987AJ.....94..726F ]
Hall, D.S., et al., 1987, Astron. J. 94, 723. [BIBCODE 1987AJ.....94..723H ]
Linsky, J.L., 1983, in 3rd Cambridge Workshop on Cool Stars, Stellar Systems
      and the Sun, eds. S.L. Baliunas, L. Hartmann, Springer-Verlag, Berlin,
      p. 244. [BIBCODE 1984LNP...193..244L ]
Linsky, J.L., et al., 1988, Astron. Astrophys., in press. [BIBCODE 1989A&A...211..173L ]
Neff, J.E., et al., 1988, Astron. Astrophys., submitted. [BIBCODE 1989A&A...215...79N ]
Rodono, M., 1986a, in Highlights of Astronomy, ed, J.P. Swings, Reidel,
      Dordrecht, p. 429. [BIBCODE 1986HiA.....7..429R ]
Rodono, M., 1986b, in 4th Cambridge Workshop on Cool Stars, Stellar System and
      the Sun, eds. M. Zeilik, D.M. Gibson, p. 456. [BIBCODE 1986LNP...254..475R ]
Rodono, M. et al., 1986, Astron. Astrophys. 165, 135. [BIBCODE 1986A&A...165..135R ]
Rodono, M. et al., 1987, Astron. Astrophys. 176, 267. [BIBCODE 1987A&A...176..267R ]
Walter, F.M. et al., 1987, Astron. Astrophys. 186, 241. [BIBCODE 1987A&A...186..241W ]