Research on asteroseismology

I have intensively worked in the field of asteroseismology, observing several pulsating stars of RR Lyrae and δ Scuti type. These observations were obtained in the frame of various international campaigns of observations for some interesting targets.

The international campaign on V1162 Ori was initiated in 1999 by Chris Sterken, and its goal was follow-up observations on this High-amplitude delta Scuti Star (HADS), in order to recover its multiple periodicities. The target appeared to have many pulsation frequencies as expected.

V1162 Ori is a High-amplitude delta Scuti Star (HADS), which was the first target ever observed from the University of Athens Observatory (images after Arentoft et al. 2001). Comparison of simultaneous light curves from Athens (0.4 m telescope) and SAAO (1-m telescope) shows that high photometric accuracy can be obtained from a light polluted area.

Pulsations of the peculiar subdwarf B star KPD 2109+4401 were investigated in Zhou et al., 2006, MNRAS, 367, 179 and in Reed et al., 2006, MmSAI, 77, 476. Continuous observations recovered the basic harmonics of this target.

The unique photometric behavior of the peculiar subdwarf B star KPD 2109+4401.

A similar case was the investigation of the double-mode nature of the HADS star GSC 0144:3031 (Poretti et al., 2005, A&A, 440, 1097). The new observations of GSC 0144-3031 confirm the existence of pure radial double–mode pulsators. Detailed models have been calculated and compared with the observed period ratios and the physical parameters determined on the basis of multicolour photometry. Our models suggest that double-mode HADS stars constitute a very homogeneous class of variable stars.

GSC 0144:3031 was intesively investigated from the University of Athens Observatory.

The pulsating star SZ Lyn is a perfect example of a HADS within a binary system. This target was observed for several years (2001-2015) and the O-C diagram has revealed the binary nature of this system (Gazeas et al., 2004, CoAst, Vol. 145, 49 and Gazeas et al., 2004, CoAst, Vol. 144, 26).

The High Amplitude delta Scuti Star SZ Lyn is a member of a binary system. The O-C diagram revealed the existance of an invisible companion, with an orbital period of ~1180 days.

The prototype pulsator RR Lyr, as well as the very similar pulsator XZ Cyg, were observed between 2004-2006 in order to study the Blazhko effect in pulsating stars. The Blazhko project is still running, coordinated by K. Kolenberg since 2004. Some preliminary results from the first run of observations are published in Kolenberg et al., 2006, A&A, 459, 577, where it is shown that the Blazhko period is changing over time, changing the shape, amplitude and phase of pulsations of the RR Lyr-type stars.

The prototype pulsator RR Lyr shows perfectly the so called Blazhko effect. Each light curve is slightly different than the previous one.

Publications

Publications and scientific announcements released after the results of asteroseismology reseach are:

Arentoft, T.; Sterken, C.; Knudsen, M. R.; Handler, G.; Niarchos, P.; Gazeas, K.; Manimanis, V.; Moalusi, M. B.; Vuthela, F. F.; Van Cauteren, P., "Irregular amplitude variations and another abrupt period change in the δ Scuti star V 1162 Ori", 2001, A&A, 378, 33

Arentoft, T.; Sterken, C.; Handler, G.; Freyhammer, L. M.; Bruch, A.; Niarchos, P.; Gazeas, K.; Manimanis, V.; van Cauteren, P.; Poretti, E.; Dawson, D. W.; Liu, Z. L.; Zhou, A. Y.; Du, B. T.; Shobbrook, R. R.; Garrido, R.; Fried, R.; Akan, M. C.; Ibanoglu, C.; Evren, S.; Tas, G.; Johnson, D.; Blake, C.; Kurtz, D. W., "V 1162 Ori: A multiperiodic delta Scuti star with variable period and amplitude", 2001, A&A 374, 1056

Zhou, A.-Y.; Reed, M. D.; Harms, S.; Terndrup, D. M.; An, D.; Zola, S.; Gazeas, K. D.; Niarchos, P. G.; Ogloza, W.; Baran, A.; Wolf, G. W., “Resolving the pulsations of the subdwarf B star KPD 2109 + 4401”, 2006, MNRAS, 367, 179

Reed, M. D.; Zhou, A.-Y.; Harms, S. L.; Wolf, G. W.; Terndrup, D. M.; An, D.; Kilkenny, D.; Chen, C.-W.; Chen, W.-P.; Lin, H.-C.; Zola, S.; Baran, A.; Ogloza, W.; Siwak, M.; Gazeas, K. D.; Niarchos, P. G.. “Follow-up observations of pulsating subdwarf B stars”, 2006, MmSAI, 77, 476

Poretti, E.; Suárez, J. C.; Niarchos, P. G.; Gazeas, K. D.; Manimanis, V. N.; van Cauteren, P.; Lampens, P.; Wils, P.; Alonso, R.; Amado, P. J.; Belmonte, J. A.; Butterworth, N. D.; Martignoni, M.; Martín-Ruiz, S.; Moskalik, P.; Robertson, C. W., “The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class”, 2005, A&A, 440, 1097

Gazeas, K.D., Niarchos, P.G., Boutsia, K.A., “SZ Lyn: New BVRI CCD observations and improved pulsational and orbital elements”, 2004, CoAst, Vol. 144, 26

Gazeas, K.D., Niarchos, P.G., Boutsia, K.A., “SZ Lyn: New pulsational and orbital elements based on old and recent photometric observations”, 2004, CoAst, Vol. 145, 49

Kolenberg, K., Smith, H. A., Gazeas, K. D., Elmaslı, A., Breger, M., Guggenberger, E., van Cauteren, P., Lampens, P., Reegen, P., Niarchos, P. G., Albayrak, B., Selam, S. O., Özavci, I., Aksu, O., “The Blazhko effect of RR Lyrae in 2003-2004”, 2006, A&A, 459, 577

Pigulski, A., Handler, G., Michalska, G., Kołaczkowski, Z., Kopacki, G., Narwid, A., Vanhollebeke, E., Steślicki, M., Lefever, K., Gazeas, K. D., de Meester, W., Vanautgaerden, J., Leitner, A., de Ridder, J., van Helshoecht, V., Gielen, C., Vandenbussche, B., Saesen, S., Reed, M. D., Eggen, J. R., Gelven, G. A., Desmet, M., Puga Antolín, E., Aerts, C., Schmidt, E., Huygen, R., Lorenz, D., Vučković, M., Broeders, E., Bauwens, E., Verhoelst, T., Deroo, P., Lenz, P., Dehaes, S., Ladjal, D., Steininger, B., Davignon, G., Beck, P., Yakut, K., Drummond, R., Fu, J.-N., Jiang, X.-J., Zhang, C., Provencal, J., Decin, L., “The ongoing 2005 - 2006 campaign on β Cephei stars in NGC 6910 and χ Persei (NGC 884)”, 2007, CoAst, 150, 191