Issue |
A&A
Volume 544, August 2012
|
|
---|---|---|
Article Number | A53 | |
Number of page(s) | 16 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361/201016235 | |
Published online | 27 July 2012 |
International observational campaigns of the last two eclipses in EE Cephei: 2003 and 2008/9⋆,⋆⋆
1
Toruń Centre for Astronomy, Nicolaus Copernicus
University, ul. Gagarina
11, 87-100
Toruń,
Poland
e-mail: cgalan@astri.uni.torun.pl; mamiko@astri.uni.torun.pl; tomtom@astri.uni.torun.pl
2
Olsztyn Planetarium and Astronomical Observatory,
Al. Marszałka J. Piłsudskiego 38,
10-450
Olsztyn,
Poland
3
Universidad de Concepción, Departamento de
Astronomia, Casilla
160-C, Concepción,
Chile
4
Institute of Physics, Faculty of Science, Ss. Cyril and Methodius
University, PO Box
162, 1000
Skopje, FYROM,
Macedonia
5
Institute of Astronomy and National Astronomical Observatory,
Bulgarian Academy of Sciences, 72
Tsarigradsko Shose Blvd., 1784
Sofia,
Bulgaria
6
Institute for Astronomy, Astrophysics, Space Applications and
Remote Sensing, NOA PO Box
20048, 11810
Athens,
Greece
7
Dept. of Physics and Earth Science, University of North
Alabama, Florence,
35632
AL,
USA
8
David Dunlap Observatory, Department of Astronomy and
Astrophysics, University of Toronto, 50 St. George St., Toronto, ON
M5S 3H4,
Canada
9
International Centre for Astronomical and Medico-Ecological
Research, Terskol,
Russia
10
Variable Star and Exoplanet Section ofCzech Astronomical
Society, Czech Republic
11
Altan Observatory, Velka Upa 193, Pec pod Snezkou, Czech
Republic
12
Tadeusz Banachiewicz Astronomical Observatory,
Wȩglówka, 32-412
Wiśniowa,
Poland
13
Max Planck Institute for Astronomy, Königstuhl 17, 69117
Heidelberg,
Germany
14
Department of Earth and Space Sciences, University of California
at Los Angeles, 595, Charles E.
Young Dr. East
CA
90095,
USA
15
Mt. Suhora Observatory, Pedagogical Univ.,
ul. Podchora¸żych 2,
30-084
Kraków,
Poland
16
Rolling Hills Observatory Clermont, FL,
USA
17
University of Hawaii Maui College, Kahului, Hawaii
18
Instituto de Astronomia, Universidad Catolica del
Norte, Av. Angamos
0610, Antofagasta,
Chile
19
Department of Astrophysics, Astronomy and Mechanics, National and
Kapodistrian University of Athens, 157 84 Zografos, Athens, Greece
20
Instituto de Astronomá, Universidad Nacional Autónoma de México
Apdo. postal 70264, Ciudad Universitaria, México
D.F. 04510,
México
21
Department of Experimental Physics and Astronomical Observatory,
University of Szeged, Dom ter
9, 6720
Szeged,
Hungary
22
Pulkovo Astronomical Observatory, Russian Academy of
Sciences, Pulkovskoe sh.
65, 196140
St. Petersburg,
Russia
23
Space Research Centre, Polish Academy of Sciences,
Bartycka 18A, 00-716
Warsaw,
Poland
24
Nicolaus Copernicus Astronomical Center,
Rabiańska 8, 87-100
Toruń,
Poland
25
Observatorio Astronómico “Las Pegueras”, NAVAS DE ORO
(Segovia), Spain
26
Hopkins Phoenix Observatory, 7812 West Clayton Drive, Phoenix, 85033-2439
Arizona,
USA
27
Observatory and Planetarium of Johann Palisa, VŠB – Technical
University of Ostrava, 17.
listopadu 15, 708
33
Ostrava-Poruba, Czech
Republic
28
Instytut Astronomiczny, Uniwersytet Wrocławski,
Kopernika 11, 51-622
Wrocław,
Poland
29
Astronomical Observatory, Jagiellonian Univ.,
ul. Orla 171, 30-244
Kraków,
Poland
30
Las Cumbres Observatory, 6740 Cortona Drive Suite 102, Goleta, CA
93117,
USA
31
National Centre for Nuclear Research, 00-681
Warsaw,
Poland
32
Leiden Observatory, PO Box 9513, 2300 RA
Leiden, The
Netherlands
33
Furzehill House, Ilston, Swansea, SA2 7LE, UK
34
Variable Star Section of the British Astronomical Association,
Furzehill House, Ilston, Swansea, SA2
7LE, UK
35
INAF, Osservatorio Astronomico di Padova,
via dell Osservatorio 8, 36012
Asiago ( VI), Italy
36
Special Astrophysical Observatory of the Russian AS,
369167
Nizhnij Arkhyz,
Russia
37
GRAS Observatory, Mayhill, New
Mexico, USA
38
Department of Physics and Space Sciences, 150 W. University Blvd,
Florida Institute of Technology, Melbourne, FL
32901,
USA
39 Green Island Observatory (B34),
North Cyprus
40
Hankasalmi Observatory, Jyvaskylan Sirius ry, Vertaalantie 419,
40270
Palokka,
Finland
41
Nicolaus Copernicus Astronomical Center, Bartycka 18,
00-716
Warsaw,
Poland
42 Sonoita Research Observatory/AAVSO, USA
43
Department of Physics and Astronomy, Box 516, 751 20
Uppsala,
Sweden
44
Centrum Hewelianum, PKFM “Twierdza Gdańsk”, ul. 3 Maja 9a,
80-802
Gdańsk,
Poland
45
University of Ljubljana, Faculty of Mathematics and Physics,
Jadranska 19,
1000
Ljubljana,
Slovenia
Received:
30
November
2010
Accepted:
17
April
2012
Context. EE Cep is an unusual long-period (5.6 yr) eclipsing binary discovered during the mid-twentieth century. It undergoes almost-grey eclipses that vary in terms of both depth and duration at different epochs. The system consists of a Be type star and a dark dusty disk around an invisible companion. EE Cep together with the widely studied ε Aur are the only two known cases of long-period eclipsing binaries with a dark, dusty disk component responsible for periodic obscurations.
Aims. Two observational campaigns were carried out during the eclipses of EE Cep in 2003 and 2008/9 to verify whether the eclipsing body in the system is indeed a dark disk and to understand the observed changes in the depths and durations of the eclipses.
Methods. Multicolour photometric data and spectroscopic observations performed at both low and high resolutions were collected with several dozen instruments located in Europe and North America. We numerically modelled the variations in brightness and colour during the eclipses. We tested models with different disk structure, taking into consideration the inhomogeneous surface brightness of the Be star. We considered the possibility of disk precession.
Results. The complete set of observational data collected during the last three eclipses are made available to the astronomical community. The 2003 and 2008/9 eclipses of EE Cep were very shallow. The latter is the shallowest among all observed. The very high quality photometric data illustrate in detail the colour evolution during the eclipses for the first time. Two blue maxima in the colour indices were detected during these two eclipses, one before and one after the photometric minimum. The first (stronger) blue maximum is simultaneous with a “bump” that is very clear in all the UBV(RI)C light curves. A temporary increase in the I-band brightness at the orbital phase ~0.2 was observed after each of the last three eclipses. Variations in the spectral line profiles seem to be recurrent during each cycle. The Na i lines always show at least three absorption components during the eclipse minimum and strong absorption is superimposed on the Hα emission.
Conclusions. These observations confirm that the eclipsing object in
EE Cep system is indeed a dark, dusty disk around a low luminosity object. The primary
appears to be a rapidly rotating Be star that is strongly darkened at the equator and
brightened at the poles. Some of the conclusions of this work require verification in
future studies: (i) a complex, possibly multi-ring structure of the disk in EE Cep; (ii)
our explanation of the “bump” observed during the last two eclipses in terms of the
different times of obscuration of the hot polar regions of the Be star by the disk; and
(iii) our suggested period of the disk precession
(~11–12 Porb) and predicted depth of about
2 for the
forthcoming eclipse in 2014.
Key words: binaries: eclipsing / circumstellar matter / stars: emission-line, Be / planetary systems
Appendix A is available in electronic form at http://www.aanda.org
Tables B.1–B.36 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/544/A53
© ESO, 2012
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