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all the photometric out‐of‐primary‐eclipse data sets available in the literature is made together with some additional unpublished data leading to interesting findings relative to changes taking place in the pulsation amplitudes and frequencies from season to season.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.

Abstract. Airglow observations with a Spectral AirglowTemperature Imager (SATI), installed at the Sierra Nevada Observatory (37.06 • N, 3.38 • W) at 2900-m height, have been used to investigate the presence of tidal variations at mid-latitudes in the mesosphere/lower thermosphere region. Diurnal variations of the column emission rate and vertically averaged temperature of the O 2 Atmospheric (0-1) band and of the OH Meinel (6-2) band from 5 years (1998)(1999)(2000)(2001)(2002)(2003) of observations have been analysed. From these observations a clear tidal variation of both emission rates and rotational temperatures is inferred. It is found that the amplitude of the daily variation for both emission rates and temperatures is greater from late autumn to spring than during summer. The amplitude decreases by more than a factor of two during summer and early autumn with respect to the amplitude in the winter-spring months. Although the tidal modulations are preferentially semidiurnal in both rotational temperatures and emission rates during the whole year, during early spring the tidal modulations seem to be more consistent with a diurnal modulation in both rotational temperatures and emission rates. Moreover, the OH emission rate from late autumn to early winter has a pattern suggesting both diurnal and semidiurnal tidal modulations.

Context. BL Cam is an extreme field multiperiodic short-period low-metallicity high-amplitude SX Phe-type variable where its probably complex pulsational content is subject of controversies. Aims. A comprehensive study has been carried out to investigate the nature and pulsational properties of this object. Methods. The analysis is based on new photometric data collected during the last few years at different sites, as well as on all available previously published data. Frequency analyses have been performed on a number of reliable data sets to analyse the pulsational content. In addition, the classical O−C method was used to study the behaviour of the main period. Results. Our frequency analysis confirms some aspects on the multiperiodicity of BL Cam, previously found by other authors, showing a number of secondary modes close to the main frequency f 0 = 25.5769 cd −1 . The secondary modes present eventual amplitude variations. However, the main frequency exhibits no significant changes in its amplitude and seems to correspond to the fundamental mode of radial pulsation. Abrupt changes sometimes observed in the light curves could be due to spurious activity on or close to the star's photosphere. We confirm the existence of a secondary frequency at 31.6 or 32.6 cd −1 , with variable amplitude, and with the possibility of both frequencies being intrinsic to the star. More than one hundred of new times of light maxima have been determined in the present work. These together with those available in the literature allow us a more discriminating analysis of the O-C diagram. This shows that the observed variations of the main period can be described by two terms: (i) a secular increase of the main period at a rate of dP/Pdt = 117(±3) × 10 −9 yr −1 ; and (ii) a perturbation from a companion star in a rather eccentric orbit with a period of 10.5(±0.2) yr causing a light time semi-amplitude of 148(±12) s. . Most display visual peak-to-peak amplitudes larger than ∼0.m 3 with short periods ( < ∼ 0. d 08) and some belong to double or multiple systems. SX Phe stars have typical Population II characteristics, i.e. they belong to the halo and old disk populations of the Galaxy with low metallicities and high spatial motions. However, they show surprisingly large masses (∼1.0−1.2 M ) and relatively young ages (∼2−5 Gyr) (see e.g., Nemec & Mateo 1990), characteristics which are still not fully explained by stellar evolution theory. The field SX Phe stars are pulsating variables located in the Lower Instability Strip, mixed with Population I δ Sct-type variables. Recent reviews for the highamplitude members of this class can be found in Rodríguez (2003Rodríguez ( , 2004.The discovery in the 1980's of three SX Phe variables in the globular cluster ω Cen (Rodríguez & López-González 2000) confirmed that SX Phe and Population I δ Sct variables are different. At present, we know that the majority of the SX Phe variables located in globular clusters belong to their blue straggler (BS) population. These stars are bluer and brigh...

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Abstract.A comprehensive frequency analysis of 57 Tau, supposed only a static pulsational arrangement, is presented based on 54 nights of photometric data collected between 1981 and 1995 (althogether 232 hours). The presence of individual frequencies is confirmed by intercomparing four subsets of this data set, however, the uncertainties in data coming from the sparse nights and low signal weaken the conclusion on some results. The entire data base is then used to resolve closely spaced peaks. Twelve frequencies are indentified using this process. Further multisite observations are recommended to confirm the present frequency solution. Two periods, with a high probability of being real, are found in the low frequency domain. They are suggested to arise from binarity or g modes, as in γ Dor stars. Single unusual cycles, possessing large amplitude, or displaying asymmetry, have been localized. A coherent frequency at 29.83 c/d with variable amplitude was found. The nonstandard behaviour of the light variation indicates that nonlinear and/or nonstationary processes could be very important in the investigation of δ Scuti observations.