The Variable Stars Data Analysis From TNTS

The Tsinghua University-NAOC Transient Survey (TNTS) is a four-year project aiming at detecting extremely early supernovae, designed to scan the sky area of about 2000 square degrees every 3-4 days, allowing us to detect astronomical phenomenon such as supernovae, variables, and AGN/quasars. In this paper, we report the first 2-year photometry of 600 sky fields of about 1300 square degrees from the TNTS, aiming at detecting stellar variabilities. The photometry was carried out in a clear filter with a 0.6-m Schmidt telescope located at Xinglong station of NAOC. Thanks to the relatively short cadence and broad synoptic coverage, we totally detected 1237 variable stars including 299 new ones, with brightness< 18.0 mag, and magnitude variations) 0.1 mag on a timescale from a few hours to few hundred days. Among such detections, we tentatively identified 661 RR Lyrae stars,431 binaries,72 Semiregular pulsators,29 Mira stars and so on based on their time-series variability index Js and their phased diagrams. We found that 14 RR Lyrae stars show the Blazhko effect and 67 contact eclipsing binary exhibits the O’Connell effect in light of their phase diagrams. Follow-up observations are needed for further investigations of their properties. Since the period and amplitude of light variations of RR Lyrae variables depend on their chemical compositions, their photometric observations can be used to investigate distribution of metallicity along the direction perpendicular to the Galactic disk. We find that the metallicity of RR Lyrae stars shows large scatter at regions closer to the Galactic plane (e.g.,-3.0< [Fe/H]< 0) but tends to converge at [Fe/H]～-1.7 at larger Galactic latitudes. This variation may be related to that the RRAB Lyrae stars in the Galactic halo come from globular clusters with different metallicity and vertical distances, i.e. OoⅠ and OoⅡ populations, favoring for the dual-halo model.