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We applied the newly developed rose diagram overlay method to detect the layered structure of 88 nearby open clusters (=500 pc) on the three projections after the distance correction of their member stars, based on the catalog in literature. The results show that with the rose diagram overlay method, a total of 74 clusters in our sample have a layered structure, while the remaining clusters are without a clear layered structure. We for the first time defined the layered structure parameters for the sample clusters. Meanwhile, we found that the layered circle core area (s) has a strong positive correlation with the number of cluster members, while the kernel instability index (1) has a strong negative correlation with the number of cluster members. Our study provides a novel perspective for the detection of the layered structure of open clusters. [ABSTRACT FROM AUTHOR]

We present the revised and high-quality CCD time series observations in 2017 and 2018 of the W UMa-type contact binary BH Cas. The combination of our new determinations of minimum times and those collected from the literatures reveal a long-term period increase with a rate of dP/dt = +3.27 × 10−7 day yr−1, which can be accounted for by angular momentum transfer as the less-massive component loses its mass to the more massive one. One cyclical oscillation (A′ = 0.00300 day and P′ = 20.09 yr) superimposed on the long-term period increase tendency is attributed to one additional object that orbits BH Cas. The low-resolution spectra of this source are observed at phase ∼0.0 and ∼0.5 in 2018 and 2019, and the spectral types are identified as K3V ± 1 and G8V ± 2. According to the luminosity contributions and spectra at these phases, the spectral type of the primary star is close to K3V ± 1. We infer a cool spot on the hotter and less-massive component to fit the asymmetry of light curves. In addition, changes in the location, temperature, and area of spots on the secondary star in different observations may indicate that the magnetic field activity of the secondary is more active than that of the primary. Such strong spot activities and optical flare are both detected at the same time from a W UMa-type star for the first time. With the XMM-Newton observations taken in 2003 and 2012, the X-ray light curve is obtained and the X-ray spectra can be well described with a blackbody or a bremsstrahlung model. The soft X-ray luminosity of BH Cas is estimated as (8.8–9.7) × 1030 erg s−1. [ABSTRACT FROM AUTHOR]

In this paper, we present an analysis of the pulsating behavior of Kepler target KIC 10284901. The Fourier transform of the high-precision light curve reveals seven independent frequencies for its light variations. Among them, the first two frequencies are main pulsation modes: F0 = 18.994054(1) day−1 and F1 = 24.335804(4) day−1; the ratio F0/F1 = 0.7805 classifies this star as a double-mode high-amplitude δ Scuti (HADS) star; another two frequencies, fm1 = 0.4407 day−1 and fm2 = 0.8125 day−1, are detected directly, and the modulations of fm1 and fm2 to F0 and F1 modes (seen as quintuplet structures centered on these two modes in the frequency spectrum) are also found. This is the first detection of a double-modulation effect in the HADS stars. The features of the frequency pattern and the ratio (fm1/fm2 ≈ 1:2), as well as the cyclic variation of amplitude of the two dominant pulsation modes, which seem to be similar to that in Blazhko RR Lyrae stars, indicate this modulation might be related to the Blazhko effect. A preliminary analysis suggests that KIC 10284901 is in the bottom of the HADS instability strip and situated in the main sequence. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Tsinghua University-Ma Huateng Telescope for Survey (TMTS) has been constantly monitoring the northern sky since 2020 in search of rapidly variable stars. To find variable white dwarfs (WDs), the TMTS catalogue is cross-matched with the WD catalogue of Gaia EDR3, resulting in over 3000 light curves of WD candidates. The WD TMTS J17184064+2524314 (hereafter J1718) is the second ZZ Ceti star discovered among these common sources. Based on the light curves from TMTS, follow-up photometric observations, and Transiting Exoplanet Survey Satellite , 10 periods and three combination periods are detected. A rotation period of 25.12 ± 0.18 h is derived, according to the identified rotational splitting. Our spectroscopic observation indicates that this WD belongs to DA type with T eff = 11 670 ± 604 K, log  g = 8.16 ± 0.36, M = 0.70 ± 0.23 M⊙, and age = 0.51 ± 0.34 Gyr. Based on core-parametrized asteroseismological model grids (≥14 million), we derive the best-fitting solution of T eff = 11 640 ± 20 K, log  g = 8.267 ± 0.008, and M = 0.750 ± 0.005 M⊙ for J1718, consistent with the spectral fitting results. For this WD, the corresponding carbon and oxygen abundances in the core are 0.43 and 0.57, respectively. The distance derived from the intrinsic luminosity given by asteroseismology is 64 ± 15 pc, in accord with the distance of 70.1 ± 0.2 pc from Gaia DR3 within the uncertainties. [ABSTRACT FROM AUTHOR]

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, fm = 0.3193 d−1, is found in LC data with a signal-to-noise ratio of 6.2. A weak modulation of fm 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. [ABSTRACT FROM AUTHOR]

Following the LAMOST Spectroscopic Survey and the Xuyi’s Photometric Survey of the Galactic Anti-center, we plan to carry out a time-domain survey of the Galactic Anti-center (TDS-GAC) to study variable stars by using the Nanshan 1-meter telescope. Before the beginning of TDS-GAC, a precursive sky survey (PSS) has been executed. The goal of the PSS is to optimize the observation strategy of TDS-GAC and to detect some strong transient events, as well as to find some short time-scale variable stars of different types. By observing a discontinuous sky area of 15.03deg2 with the standard Johnson-Cousin-Bessel V filter, 48 variable stars are found and the time series are analyzed. Based on the behaviors of the light curves, 28 eclipsing binary stars, 10 RR Lyraes, 3 periodic pulsating variables of other types have been classified. The rest 7 variables stay unclassified with deficient data. In addition, the observation strategy of TD-GAC is described, and the pipeline of data reduction is tested. [ABSTRACT FROM AUTHOR]

Tsinghua University-Ma Huateng Telescope for Survey (TMTS) aims to discover rapidly evolving transients by monitoring the northern sky. The TMTS catalogue is cross-matched with the white dwarf (WD) catalogue of Gaia EDR3, and light curves of more than a thousand WD candidates are obtained so far. Among them, the WD TMTS J23450729+5813146 is one interesting common source. Based on the light curves from the TMTS and follow-up photometric observations, periods of 967.113, 973.734, 881.525, 843.458, 806.916, and 678.273 s are identified. In addition, the TESS observations suggest a 3.39-h period but this can be attributed to the rotation of a comoving M dwarf located within 3 arcsec. The spectroscopic observation indicates that this WD is DA type with T eff = 11 778 ± 617 K, log  g  = 8.38 ± 0.31, mass = 0.84 ± 0.20 M⊙, and age = 0.704 ± 0.377 Gyr. Asteroseismological analysis reveals a global best-fitting solution of T eff = 12 110 ± 10 K and mass = 0.760 ± 0.005 M⊙, consistent with the spectral fitting results, and oxygen and carbon abundances in the core centre are 0.73 and 0.27, respectively. The distance derived from the intrinsic luminosity given by asteroseismology is 93 parsec, which is in agreement with the distance of 98 parsec from Gaia DR3. Additionally, kinematic study shows that this WD is likely a thick-disc star. The mass of its zero-age main sequence is estimated to be 3.08 M⊙ and has a main sequence plus cooling age of roughly 900 Myr. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the optical observations of a subluminous Type Ia supernova (SN Ia) 2017fzw, which exhibited high photospheric velocity (HV) at B-band maximum light. The absolute B-band peak magnitude was determined to be M m a x B = − 18.65 ± 0.13 mag, similar to 91bg-like SNe Ia. An estimation of the rate of decline for the B-band light curve was determined to be Δ m 15 (B) = 1.60 ± 0.06 mag. The spectra of SN 2017fzw were similar to those of 91bg-like SNe Ia, with prominent Ti ii and Si ii  λ 5972 features at early phases, gradually transitioning to spectra resembling normal (mainly HV subclass) SNe Ia at later phases, with a stronger Ca ii NIR feature. Notably, throughout all phases of observation, SN 2017fzw displayed spectral evolution characteristics that were comparable to those of HV SNe Ia, and at peak brightness, the Si ii  λ 6355 velocity was determined to be 13,800 ±   415 km s − 1 and a more pronounced Ca ii NIR feature was also detected. Based on these findings, we classify SN 2017fzw as a transitional object with properties of both normal and 91bg-like SNe Ia, providing support for the hypothesis of a continuous distribution of supernovae between these two groups. [ABSTRACT FROM AUTHOR]

A rigorous treatment of the refractive scintillation caused by a two-component interstellar scattering medium and a Kolmogorov form of density spectrum is discussed. It is assumed that the interstellar scattering medium is composed of a thin screen ISM and an extended interstellar medium. We conclude that the refractive scintillation caused by this two-component ISM scattering gives a more satisfactory explanation for the observed flux density variation than the single extended medium model along the line of sight to the pulsar PSR B0136+57. [ABSTRACT FROM AUTHOR]

Fast radio bursts (FRBs) are highly dispersed, millisecond-duration radio bursts 1-3 . Recent observations of a Galactic FRB 4-8 suggest that at least some FRBs originate from magnetars, but the origin of cosmological FRBs is still not settled. Here we report the detection of 1,863 bursts in 82 h over 54 days from the repeating source FRB 20201124A (ref.  9 ). These observations show irregular short-time variation of the Faraday rotation measure (RM), which scrutinizes the density-weighted line-of-sight magnetic field strength, of individual bursts during the first 36 days, followed by a constant RM. We detected circular polarization in more than half of the burst sample, including one burst reaching a high fractional circular polarization of 75%. Oscillations in fractional linear and circular polarizations, as well as polarization angle as a function of wavelength, were detected. All of these features provide evidence for a complicated, dynamically evolving, magnetized immediate environment within about an astronomical unit (AU; Earth-Sun distance) of the source. Our optical observations of its Milky-Way-sized, metal-rich host galaxy 10-12 show a barred spiral, with the FRB source residing in a low-stellar-density interarm region at an intermediate galactocentric distance. This environment is inconsistent with a young magnetar engine formed during an extreme explosion of a massive star that resulted in a long gamma-ray burst or superluminous supernova., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)