Sct-type pulsations in eclipsing binary systems: RZ Cas

Abstract

We present the results of a three‐continent multisite photometric campaign carried out on the Algol‐type eclipsing binary system RZ Cas, in which the primary component has recently been discovered to be a δ Sct‐type pulsator. The present observations include, for the first time, complete simultaneous Strömgren uvby light curves together with a few Crawford Hβ data collected around the orbital phase of the first quadrature. The new observations confirm the pulsational behaviour of the primary component. A detailed photometric analysis, based on these observations, is presented for both binarity and pulsation. The results indicate a semidetached system where the secondary fills its Roche lobe. The appearance of the light curves reveals the presence of the mass stream from the secondary component and a hotspot where this stream impacts on the surface of the primary star. There are also some indications of chromospheric activity in the secondary. On the other hand, the pulsational behaviour out‐of‐primary eclipse can be well described with only one frequency at 64.1935 cd−1 similar to the main peak found by Ohshima et al. The existence of multiperiodicity is not confirmed in our data. Concerning the mode identification, our results indicate non‐radial pulsation in a high radial order (n= 6), with l= 2, |m|= 1, 2 as the most suitable. However, additional effects must be taken into account in the predictions. Moreover, the pulsation amplitude in the u band is larger than in b and v, which is unusual among the δ Sct‐type variables. This can be explained as due to pulsation in a high n value and close to the blue edge of the δ Sct region. On the other hand, the early data of Ohshima et al. have also been analysed and similar results are found concerning the frequency content and pulsational amplitude. Finally, a revision of all the photometric out‐of‐primary‐eclipse data sets available in the literature is made together with some additional unpublished data leading to interesting findings relative to changes taking place in the pulsation amplitudes and frequencies from season to season. Furthermore, multiperiodicity is probably present in some epochs.

Delta Scuti stars: Observational aspects

“…This raises the question whether their pulsation is different. Some of these stars have unusually short pulsation periods, e.g., the 22-minute period of RZ Cas (Rodríguez et al 2004). In fact, RZ Cas also shows a λ Boo-type abundance pattern (Narusawa et al 2006).…”

Detection of a classicalδScuti star in the new eclipsing binary system HIP 7666

“…We therefore propose that the primary component is a δ Scuti pulsator. There are only a very few known normal δ Scuti stars that are members of detached eclipsing binary systems (see Rodríguez 2002;Rodríguez et al 2004). Recent investigations have demonstrated the existence of a group of A-F pulsating stars located in the δ Scuti instability strip and with the same observational characteristics as δ Scuti stars but in a different evolutionary stage.…”

“…non-radial modes with l = |m|); -during the eclipses, the components act as a spatial filter which causes phase and amplitude modulation of the nonradial mode and makes the mode identification more accurate (Mkrtichian et al 2002); -the pulsating component can be correctly identified if there is evidence that the pulsations are most clearly present during one of both minima. Rodríguez et al (2004) recently summarized the status of the eclipsing binaries with a δ Scuti component: only about a dozen cases are presently known. About 30% consist of eclipsing binaries with a classical δ Scuti pulsator while the rest defines a distinct class of δ Scuti pulsators, called the oscillating EA stars (Mkrtichian et al 2002).…”

In search of RR Lyrae type stars in eclipsing binary systems

“…Cepheids, for example, have been found in galactic EBs (Freyhammer et al 2005;Antipin et al 2007) as well as in the LMC (Alcock et al 2002;Lepischak & Welch 2004;Guinan et al 2005); there are more than 30 known δ-Scuti type components in EBs (see e.g. Dallaporta et al 2002;Rodríguez et al 2004;Christiansen et al 2007), and several other types such as slowly pulsating B stars (Pigulski & Michalska 2007;Pilecki & Szczygiel 2007 obtained with the HST Fine Guidance Sensor (Benedict et al 2002) that estimated its absolute magnitude of M = 0.61 ± 0.1.…”