Absolute parameters and physical nature of two W-UMa type binaries:V1123 Tau and V1128 Tau

We present high-precision, multi-band CCD photometry of two less-studied close binaries V1123 Tau and V1128 Tau. Complete covered light curves and a number of new times of light minima of the two eclipsing systems were obtained, based on which, revised orbital elements and new ephemerides were given. By adopting the Wilson-Devinney method, the light curves were analyzed. The photometric solutions confirm the W UMa-type nature of the binary systems. With the less-massive secondary slightly cooler than the primary, V1123 Tau could be classified as an A- type contact system. While V1128 Tau is typically considered a W-type W UMa star, the surface temperature of its secondary component is determined to be absolutely higher than the primary by about 270 K. Combining with the results of radial-velocity solutions, we determined absolute parameters of the two systems. The mass, radius and luminosity for each component of V1123 Tau were derived as： 1.36 ±0.05M⊙, 1.37 ± 0.02R⊙, and 2.01± O.07L⊙ and 0.40±0.02M⊙, 0.80±0.01R⊙, and 0.67±0.04L⊙, respectively. For V1128 Tau, the absolute parameters were computed to be 1.09±0.03M⊙, 1.01±0.01R⊙, and 1.34±0.06Le and 0.58 ± 0.01M⊙, 0.76±0.01R⊙, and 0.91±0.05L⊙, respectively. Based on these results, the evolutionary status and the physical nature of the two binary systems are discussed, while also connecting with the theoretical models.

Physical Parameters of W UMa Type Contact Binaries and Their Stability of Mass Transfer

In this study,we determined the physical parameters of W UMa type contact binaries and their stability of mass transfer with different stellar mass ranges over a broad space by applying the basic dynamical evolution equations of the W UMa type contact binaries using accretor and donor masses between 0.079 and 2.79 M_(⊙).In these systems,we have studied the three subclasses of W UMa systems of A-,B-and W-type contact binaries using the initial and final mass ranges and we investigated different stellar and orbital parameters for the subclasses of W UMa systems.We examined the stability of the W UMa type contact binaries using the orbital parameters such as critical mass ratio,Roche lobe radius of the donor star and mass ratio of these systems.Thus,we computed the observed and calculated physical parameters of A-,B-and W-type W UMa systems.Moreover,we determined the combined and color temperatures to classify the three subclasses of the systems.Also,we presented the result of the internal stellar structure and evolution of W UMa type contact binaries by using the polytropic model.

Spectroscopic Study of Late-type Emission-line Stars Using the Data from LAMOST DR6

Low-mass emission-line stars belong to various evolutionary stages,from pre-main-sequence young stars to evolved stars.In this work,we present a catalog of late-type(F0 to M9)emission-line stars from the LAMOST Data Release 6.Using the scipy package,we created a Python code that finds the emission peak at Hαin all latetype stellar spectra.A data set of 38,152 late-type emission-line stars was obtained after a rigorous examination of the photometric quality flags and the signal-to-noise ratio of the spectra.Adopting well-known photometric and spectroscopic methods,we classified our sample into 438 infrared(IR)excess sources,4669 post-main-sequence candidates,9718 Fe/Ge/Ke sources,and 23,264 d Me sources.From a crossmatch with known databases,we found that 29,222 sources,comprising 65 IR excess sources,7899 Fe/Ge/Ke stars,17,533 dMe stars,and3725 PtMS candidates,are new detections.We measured the equivalent width of the major emission lines observed in the spectra of our sample of emission-line stars.Furthermore,the trend observed in the line strengths of major emission lines over the entire late-type spectral range is analyzed.We further classified the sample into four groups based on the presence of hydrogen and calcium emission lines.This work presents a large data set of late-type emission-line stars,which can be used to study active phenomena in late-type stars.