Περίληψη:
Context. Recent progress in the seismic interpretation of field beta Cep
stars has resulted in improvements of the physics in the stellar
structure and evolution models of massive stars. Further asteroseismic
constraints can be obtained from studying ensembles of stars in a young
open cluster, which all have similar age, distance and chemical
composition.
Aims. To improve our comprehension of the beta Cep stars, we studied the
young open cluster NGC 884 to discover new B- type pulsators, besides
the two known beta Cep stars, and other variable stars.
Methods. An extensive multi-site campaign was set up to gather accurate
CCD photometry time series in four filters (U, B, V, I) of a field of
NGC 884. Fifteen different instruments collected almost 77 500 CCD
images in 1286 h. The images were calibrated and reduced to transform
the CCD frames into interpretable differential light curves. Various
variability indicators and frequency analyses were applied to detect
variable stars in the field. Absolute photometry was taken to deduce
some general cluster and stellar properties.
Results. We achieved an accuracy for the brightest stars of 5.7 mmag in
V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in
the amplitude spectra is 50 mu mag in the V band. Our campaign confirms
the previously known pulsators, and we report more than one hundred new
multi- and mono- periodic B-, A- and F-type stars. Their interpretation
in terms of classical instability domains is not straightforward,
pointing to imperfections in theoretical instability computations. In
addition, we have discovered six new eclipsing binaries and four
candidates as well as other irregular variable stars in the observed
field.
Συγγραφείς:
Saesen, S.
Carrier, F.
Pigulski, A.
Aerts, C.
Handler,
G.
Narwid, A.
Fu, J. N.
Zhang, C.
Jiang, X. J. and
Vanautgaerden, J.
Kopacki, G.
Steslicki, M.
Acke, B. and
Poretti, E.
Uytterhoeven, K.
Gielen, C.
Ostensen, R.
De
Meester, W.
Reed, M. D.
Kolaczkowski, Z.
Michalska, G. and
Schmidt, E.
Yakut, K.
Leitner, A.
Kalomeni, B.
Cherix,
M.
Spano, M.
Prins, S.
Van Helshoecht, V.
Zima, W. and
Huygen, R.
Vandenbussche, B.
Lenz, P.
Ladjal, D. and
Antolin, E. Puga
Verhoelst, T.
De Ridder, J.
Niarchos, P.
and Liakos, A.
Lorenz, D.
Dehaes, S.
Reyniers, M. and
Davignon, G.
Kim, S. -L.
Kim, D. H.
Lee, Y. -J.
Lee, C.
-U.
Kwon, J. -H.
Broeders, E.
Van Winckel, H. and
Vanhollebeke, E.
Waelkens, C.
Raskin, G.
Blom, Y.
Eggen,
J. R.
Degroote, P.
Beck, P.
Puschnig, J.
Schmitzberger,
L.
Gelven, G. A.
Steininger, B.
Blommaert, J.
Drummond,
R.
Briquet, M.
Debosscher, J.
