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With the continuous development of large optical surveys, a large number of light curves of late-type contact binary systems (CBs) have been released. Deriving parameters for CBs using the the WD program and the PHOEBE program poses a challenge. Therefore, this study developed a method for rapidly deriving light curves based on the Neural Networks (NN) model combined with the Hamiltonian Monte Carlo (HMC) algorithm (NNHMC). The neural network was employed to establish the mapping relationship between the parameters and the pregenerated light curves by the PHOEBE program, and the HMC algorithm was used to obtain the posterior distribution of the parameters. The NNHMC method was applied to a large contact binary sample from the Catalina Sky Survey, and a total of 19,104 late-type contact binary parameters were derived. Among them, 5172 have an inclination greater than 70 deg and a temperature difference less than 400 K. The obtained results were compared with the previous studies for 30 CBs, and there was an essentially consistent goodness-of-fit (R2) distribution between them. The NNHMC method possesses the capability to simultaneously derive parameters for a vast number of targets. Furthermore, it can provide an extremely efficient tool for rapid derivation of parameters in future sky surveys involving large samples of CBs.

Low mass-ratio (q) contact binary systems are progenitors of stellar mergers such as blue straggles (BS) or fast-rotating FK Com stars. In this study, we present the first light curve analysis of two newly identified low mass-ratio contact binary systems, TIC 55007847 and TIC 63597006, that are identified from TESS. Both stars are classified as A-subtype contact binaries. We obtained the precise orbit periods for the two objects by using the O-C method, i.e. P=0.6117108 d for TIC 55007847 and P=0.7008995 d for TIC 63597006, respectively, and found an obvious periodic signal in the O-C curve of TIC 63597006. We suggest that the periodic signal comes from a third body. We further use the Markov Chain Monte Carlo (MCMC) method with PHOEBE to derive the photometric solutions for the two binaries. The photometric solution for this object shows that the contribution of the third body is about 6%. Our analysis revealed that TIC 55007847 has an extremely low mass ratio of q=0.08. By calculating the ratio of spin angular momentum to the orbital angular momentum Js/Jo, we found that TIC 55007847 is very close to the instability threshold with Js/Jo = 0.31, indicating that it may merge into a single, fast-rotating star in the future. For TIC 63597006, q=0.14 and Js/Jo=0.15. This object is in a relatively stable evolutionary status at present.

Contact binary may be the progenitor of a red nova that eventually produces a merger event and have a cut-off period around 0.2 days. Therefore, a large number of contact binaries is needed to search for the progenitor of red novae and to study the characteristics of short-period contact binaries. In this paper, we employ the Phoebe program to generate a large number of light curves based on the fundamental parameters of contact binaries. Using these light curves as samples, an autoencoder model is trained, which can reconstruct the light curves of contact binaries very well. When the error between the output light curve from the model and the input light curve is large, it may be due to other types of variable stars. The goodness of fit (R2) between the output light curve from the model and the input light curve is calculated. Based on the thresholds for global goodness of fit (R2), period, range magnitude, and local goodness of fit (R2), a total of 1322 target candidates were obtained.

Starting from more than 11,200 short-period (less than 0.5 days) EW-type eclipsing binary candidates with the All-Sky Automated Survey for Supernovae (ASAS-SN) V-band light curves, we use MCMC and neural networks (NNs) to obtain the mass ratio ($q$), orbital inclination ($incl$), fill-out factor ($f$) and temperature ratio ($T_s/T_p$). After cross-matching with the Gaia DR3 database, the final sample contains parameters of 2,399 A-type and 8,712 W-type contact binaries (CBs). We present the distributions of parameters of these 11,111 short-period CBs. The mass ratio ($q$) and fill-out factor ($f$) are found to obey log-normal distributions, and the remaining parameters obey normal distributions. There is a significant period-temperature correlation of these CBs. Additionally, the temperature ratio (${T_s}$/${T_p}$) tends to increase as the orbital period decreases for W-type CBs. There is no significant correlation between them for A-type CBs. The mass ratio and fill-out factor ($q-f$) diagram suggest there is no significant correlation between these two parameters. A clear correlation exists between the mass ratio and radius ratio. The radius ratio increases with the mass ratio. Moreover, the deep fill-out CBs tend to fall on the upper boundary of the $q$$-$${R_s}$/${R_p}$ distribution, while the shallow fill-out CBs fall on the lower boundary., Comment: 15 pages, 8 figures, 1 table.Accepted for publication in ApJS. The full dataset will be available with the ApJS article

Semi-detached binaries are in the stage of mass transfer and play a crucial role in studying mass transfer physics between interacting binaries. Large-scale time-domain surveys provide massive light curves of binary systems, while Gaia offers high-precision astrometric data. In this paper, we develop, validate, and apply a pipeline that combines the MCMC method with a forward model and DBSCAN clustering to search for semi-detached binary and estimate its inclination, relative radius, mass ratio, and temperature ratio using light curve. We train our model on the mock light curves from PHOEBE, which provides broad coverage of light curve simulations for semi-detached binaries. Applying our pipeline to TESS sectors 1-26, we have identified 77 semi-detached binary candidates. Utilizing the distance from Gaia, we determine their masses and radii with median fractional uncertainties of ~26% and ~7%, respectively. With the added 77 candidates, the catalog of semi-detached binaries with orbital parameters has been expanded by approximately 20%. The comparison and statistical results show that our semi-detached binary candidates align well with the compiled samples and the PARSEC model in Teff-L and M-R relations. Combined with the literature samples, comparative analysis with stability criteria for conserved mass transfer indicates that ~97.4% of samples are undergoing nuclear-timescale mass transfer, and two samples (GO Cyg and TIC 454222105) are located within the limits of stability criteria for dynamical- and thermal-timescale mass transfer, which are currently undergoing thermal-timescale mass transfer. Additionally, one system (IR Lyn) is very close to the upper limit of delayed dynamical-timescale mass transfer.

We present the results from a spectroscopic monitoring campaign to obtain reverberation-mapping measurements and investigate the broad-line region kinematics for active galactic nuclei (AGN) of Mrk~817 and NGC~7469. This campaign was undertaken with the Lijiang 2.4-meter telescope, the median spectroscopic sampling is 2.0 days for Mrk~817 and 1.0 days for NGC~7469. We detect time lags of the broad emission lines including H$\beta$, H$\gamma$, He~{\sc ii} and He~{\sc i} for both AGNs, and including Fe~{\sc ii} for Mrk~817 with respect to the varying AGN continuum at 5100~\AA. Investigating the relationship between line widths and time lags of the broad emission lines, we find that the BLR dynamics of Mrk~817 and NGC~7469 are consistent with the virial prediction. We estimate the masses of central supermassive black hole (SMBH) and the accretion rates of both AGNs. Using the data of this campaign, we construct the velocity-resolved lag profiles of the broad H$\gamma$, H$\beta$, and He~{\sc i} lines for Mrk~817, which show almost the same kinematic signatures that the time lags in the red wing are slightly larger than the time lags in the blue wing. For NGC~7469, we only clearly construct the velocity-resolved lag profiles of the broad H$\gamma$ and H$\beta$, which show very similar kinematic signatures to the BLR of Mrk~817. These signatures indicate that the BLR of Keplerian motion in both AGNs seemingly has outflowing components during the monitoring period. We discuss the kinematics of the BLR and the measurements including SMBH mass and accretion rates., Comment: 19 pages, 11 figures, accepted for publication in ApJ

Observing a telluric standard star for correcting the telluric absorption lines of spectrum will take a significant amount of precious telescope time, especially in the long-term spectral monitoring project. Beyond that, it's difficult to select a suitable telluric standard star near in both time and airmass to the scientific object. In this paper, we present a method of correcting the telluric absorption lines by combining the advantages of long slit spectroscopy. By rotating the slit, we observed the scientific object and a nearby comparison star in one exposure, so that the spectra of both objects should have the same telluric transmission spectrum. The telluric transmission spectrum was constructed by dividing the observed spectrum of comparison star by its stellar template, and was used to correct the telluric absorption lines of the scientific object. Using the long slit spectrograph of Lijiang 2.4-meter telescope, we designed a long-term spectroscopic observation strategy, and finished a four-year spectroscopic monitoring for a pair of objects (an active galactic nuclei and an non-varying comparison star). We applied this method to correct the telluric absorption lines of the long-term monitored spectra by Lijiang 2.4-meter telescope, and investigated the variation of the telluric absorptions at Lijiang Observatory. We found that the telluric absorption transparency is mainly modulated by the seasonal variability of the relative humidity, airmass and seeing. Using the scatter of the [O~III] $\lambda$5007 fluxes emitted from the narrow-line region of active galactic nuclei as an indicator, we found that the correction accuracy of the telluric absorption lines is 1%., Comment: 15 pages, 10 figure, accepted for publication in RAA (Research in Astronomy and Astrophysics)