Contributing to the EE Cep campaign

Introduction

EE Cephei (R.A.: 22 09 22.757, Dec.: +55 45 24.184, J2000.0) is a variable star of spectral type Be5 III (Mikolajewski & Graczyk 1999, Mikolajewski et al. 2005), with a period of 2050 days (approximately 5.6 years; Meinunger 1976), and an eclipse duration of about 40 days.

Its variability was detected in 1952 (Romano 1956) and soon it was identified as an eclipsing binary system (Romano & Perissinotto 1966). Up to date we have observed a total of 12 eclipses which however present large differences in their duration and depth (see Fig. 1). Mikolajewski & Graczyk (1999) suggested the presence of an opaque disk surrounding the secondary, which is either a low-mass star or a close binary system. A tilt in the disk and a possible precession of the rotation axis of the main Be star (Pieńkowski et al. 2020) can explain the different shapes of its eclipses (see Fig. 2)

Figure 1: All light curves from EE Cep, in various bands and colors (source: EE Cep 2020).

Figure 2: The proposed model for EE Cep. A thick disk (or rings) passes in front of the primary star Be which rotates around its axis and due to the precession it exhibits different parts of its
surface (Pieńkowski et al. 2020).

Until today three major observing campaigns have been organized in order to uncover the mysteries of EE Cep: in 2003, 2009 and 2014 (Galan et al. 2012, 2014). Despite the wealth of the data collected we still miss a consistent description for the system (Pieńkowski et al. 2020).

Contribution to the current campaign

We have participated in the last international campaign of 2014 with a number of CCD measurements that cover the whole duration of the eclipse. Our results have been published in the 9th Panhellenic Conference on Amateur Astronomy (Maravelias et. al. 2015 – in Greek). In Fig. 3 we show the light curve from these observations.

EE Cep light curve 2014
Figure 3: The light curve of EE Cep during its 2014 eclipse from HAAA’ members’ observations.

Given this experience we are carefully monitoring the current eclipse of 2020, using private and remote telescopes to secure observations at every possible occasion. Our observations will be forwarded to the international observing campaign of 2020-2021 (see the site for more details regarding observations), while we plan to publish our results in a forthcoming paper.

Stay tuned !

References

  • Meinunger 1976, Mitteilungen ueber Veraenderliche Sterne, vol. 7, p. 97
  • Mikolajewski & Graczyk 1999, Monthly Notices of the Royal Astronomical Society, vol. 303, p. 521
  • Mikolajewski et al. 2005, Astrophysics and Space Science, vol. 296, p. 451
  • Gałan et al. 2012, Astronomy & Astrophysics, vol. 544, p. 53
  • Gałan et al. 2014, Information Bulletin On Variable Stars, no. 6111, p. 1
  • Pieńkowski et al. 2020, arXiv:2001.05891
  • Romano 1956, Coelum Periodico Bimestrale per la Divulgazione dell’Astronomia, vol. 24, p. 135
  • Romano & Perissinotto 1966, Memorie della Societa Astronomia Italiana, vol. 37, p. 255
  • Maravelias et al. 2015, The light curve of EE Cephei during the 2014 eclipse, Proceedings of the 9th Panhellenic Conference on Amateur Astronomy, Sparta, 9-11 Ocotber 2015, p. 115 [in Greek]