In this paper, the high-precision light curves of the Kepler target KIC 5950759 are analyzed. The Fourier analysis of the long cadence (LC) light curve reveals three independent frequencies. Two of them are main pulsation modes: F0 = 14.221373(21) d −1 and F1 = 18.337249(44) d −1 . The third independent frequency, f m = 0.3193 d −1 , is found in LC data with a signal-to-noise ratio of 6.2. A weak modulation of f m to F0 and F1 modes (triplet structures centered on F0 and F1) are detected both in long and short cadence data. This is the first detection of the modulation effect in a double-mode high-amplitude δ Scuti (HADS) star. The most possible cause of the modulation effect in the light curves is amplitude modulation with the star's rotation frequency of 0.3193 d −1 . The preliminary analysis suggests that KIC 5950759 is in the bottom of the HADS instability strip and likely situated in the main sequence. Spectroscopic observations are necessary to verify the true nature of the modulation terms.

No abstract

We carried out photometric observations of the SX Phe star BL Cam in 2014, 2017 and 2018 using Nanshan 1-m telescope. In addition to the dominated frequency of 25.5790(3) cd −1 and its two harmonics, an independent frequency of 25.247 (2) cd −1 , which is a nonradial mode frequency, was detected from the data in 2014. A total of 123 new times of light maxima were determined from our light curves in the three years, which, together with that published in the literature, were used to analyze the O−C diagram. The change rate of the main period was derived as (1/P)(dP/dt) = -2.39 (8)×10 −8 yr −1 , which is lower than that published in previous literature. A periodical change with a period of 14.01 (9) yr was found in the residuals of the O−C curve fitting. If it was caused by the light-time effect, BL Cam should be a binary system. The mass of the companion was restricted as low as that of a brown dwarf. No evidence of the triple system suggested by previous authors was shown in our analysis.

No abstract

No abstract

Homogeneous metallicities and continuous high-precision light curves play key roles in studying the pulsation properties of RR Lyrae stars. By cross matching LAMOST DR6 with the Kepler and K2 fields, we have determined seven and 50 non-Blazhko RRab stars, respectively, that have homogeneous metallicities determined from low-resolution spectra of the LAMOST–Kepler/K2 survey. The Fourier decomposition method is applied to the light curves of these stars provided by the Kepler space-based telescope to determine the fundamental pulsation periods and parameters. The calculated amplitude ratios of R 21, R 31 and the phase differences of ϕ 21, ϕ 31 are consistent with the parameters of RRab stars in both globular clusters and the Large Magellanic Cloud. We find a linear relationship between the phase differences ϕ 21 and ϕ 31, which is in good agreement with the results in the literature. As far as the amplitude, we find that the amplitude of primary frequency A 1 and the total amplitude A tot follow either a cubic or linear relationship. For the rise time, we do not find its relevance with the period of the fundamental pulsation mode P1, or A tot and ϕ 21. However, it might follow a linear relationship with R 31. Based on the homogeneous metallicities, we have derived a new calibration formula for the period–ϕ 31–[Fe/H] relation, which agrees well with previous studies.

KIC 10417986 is a short orbital period (0.0737 d) ellipsoidal variable star with a δ Sct and γ Dor hybrid pulsations component discovered by Kepler. The ground-based spectroscopic observations were carried out in the winters of 2020 and 2021 to investigate the binary nature of this star. We derive the orbital parameters using the rvfit code with a result of K 1 = 29.7 ± 1.5 kms-1, γ = -18.7 ± 1.7 kms-1, and confirm an orbital period of 0.84495 d instead of the result given by Kepler. The atmospheric parameters of the primary are determined by the synthetic spectra fitting technique with the estimated values of T eff = 7411 ± 187 K, log g = 4.2 ± 0.3 dex, [M/H] = 0.08 ± 0.09 dex and vsini = 52 ± 11 kms-1. KIC 10417986 is a circular orbit binary system. From the single-lined nature and mass function of the star, the derived orbital inclination is 26 ± 6°, and the mass of the secondary is 0.52 -0.09 +0.18 M ⊙, which should be a late-K to early-M type star. Fourteen frequencies are extracted from Kepler light curves, of which six independent frequencies in the high-frequency region are identified as the p-mode pulsations of δ Sct star, and one independent frequency in the low-frequency region (f 2= 1.3033 cd-1) is probably the rotational frequency due to the starspots rather than the ellipsoidal effect.

We perform a detailed analysis of the Kepler target KIC 5768203 based on the Kepler and Transiting Exoplanet Survey Satellite (TESS) data. Three independent frequencies are detected by Fourier analysis of the Kepler long-cadence data: two pulsation frequencies f P0 = 7.807874(2) day−1 and f P1 = 9.970035(6) day−1, which have amplitudes below 1.4 mmag in the Kepler band, and one modulation frequency f rot = 0.45813(1) day−1. Based on a period ratio of 0.7803, f P0 and f P1 are supposed to be radial frequencies. However, further confirmation is needed. Based on the triplets and phase variations of the two pulsation frequencies, the star is possibly a δ Sct pulsator in a binary system. The modulation frequency f rot and its four harmonics could be attributed to the stellar rotation and surface spots. With the rotation frequency f rot, the rotation velocity of the star is estimated to be 75(3) km s−1. By analyzing the phase diagram without pulsations, it is inferred that there are starspots (or clusters of starspots) of large area on the surface of KIC 5768203. These starspots are slowly evolving in position and brightness over the course of the Kepler long-cadence observations. The finding of the rotation frequency in the TESS data implies the long-term presence of starspots on the surface of KIC 5768203.