The THU-NAOC transient survey: the performance and results from the first year

The Tsinghua University-National Astronomical Observatories, Chinese Academy of Sciences （NAOC） Transient Survey is an automatic survey that conducts a systematic exploration of optical transients. This project utilizes a 60/90 cm Schmidt telescope at the Xinglong Station of NAOC. This survey repeatedly covers - 1000 square degrees of the northern sky with a cadence of 34 d. With an exposure of 60 s, the survey reaches a limiting unfiltered magnitude of about 19.5 mag, which enables us to discover supernovae in their relatively young stages. We describe the overall performance of our survey during the first year and present some preliminary results.

Testing and data reduction of the Chinese Small Telescope Array(CSTAR) for Dome A,Antarctica

The Chinese Small Telescope Array （CSTAR） is the first Chinese astronomical instrument on the Antarctic ice cap. The low temperature and low pressure testing of the data acquisition system was carried out in a laboratory refrigerator and on the 4500 m Pamirs high plateau, respectively. The results from the final four nights of test observations demonstrated that CSTAR was ready for operation at Dome A, Antarctica. In this paper, we present a description of CSTAR and the performance derived from the test observations.

Multicolor photometry of the galaxy cluster A98: substructures and star formation properties

An optical photometric observation with the Beijing-Arizona-Taiwan- Connecticut （BATC） multicolor system is carried out for A98 （z =0.104）, a galaxy cluster with two large enhancements in X-ray surface brightness. Spectral energy distributions （SEDs） covering 15 intermediate bands are obtained for all sources detected down to V - 20 mag in a field of 58′× 58′. After star-galaxy separation with colorcolor diagrams, a photometric redshift technique is applied to the galaxy sample for further membership determination. The color-magnitude relation is taken as a further restriction of the early-type cluster galaxies. As a result, a list of 198 faint member galaxies is achieved. Based on the newly generated sample of member galaxies, the dynamical substructures, A98N, A98S, and A98W, are investigated in detail. A separate galaxy group, A98X, is also found to the south of the main concentration of A98, which is gravitationally unbound to A98. For 74 spectroscopically confirmed member galaxies, the environmental effect on the star formation history is investigated. The bright galaxies in the core region are found to have shorter time scales of star formation, longer mean stellar ages, and higher interstellar medium metallicities, which can be interpreted in the context of the hierarchical cosmological scenario.

Old stellar population synthesis:new age and mass estimates for Mayall II = G1

Mayall Ⅱ = G1 is one of the most luminous globular clusters （GCs） in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population （SSP） models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ～1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates （of order 10^7M⊙） indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster＇s exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, （1.65±0.63） × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.

A Fourteen-Band Photometric Study of A2443

We present a multi-color photometric study of the galaxy cluster A2443 （z = 0.108） with the Beijing-Arizona-Taiwan-Connecticut （BATC） system. The spectral energy distributions （SEDs） in 14 intermediate bands are obtained for 5975 detected from -ldeg^2 of the BATC images. Color-color diagrams are used for star-galaxy separation, then a photometric redshift technique is applied to the galaxy sample for cluster membership determination. There are 301 galaxies with photometric redshifts between 0.08 and 0.14 determined as member candidates of A2443, including 289 new ones. Based on this enlarged sample, the luminosity function and color magnitude relation of the cluster are studied. With an evolutionary synthesis model, we find that the fainter galaxies tend to have longer time scales of star formation than the brighter ones. Morphologically, we show an elongated spatial distribution associating with the galaxy cluster ZwCl 2224.2＋1651, which contains more blue galaxies. This result indicates that galaxy cluster ZwCl 2224.2＋1651 may be falling into A2443, and cluster-cluster interaction could have triggered star formation activities in ZwCl 2224.2＋1651.

Estimating the Metallicity of Old Star Clusters in M33

Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.

Late-time photometry of two nearby type II-P supernovae: 2004dj and 2004et

We present late-time photometry for two bright type II-P supernovae （SNe） 2004dj and 2004et, extending over 400 d after the explosion, which are measured with a set of intermediate-band filters that have the advantage of tracing the strength variations of some spectral features. Although these two SNe II-P exhibit similar photometric evolution at earlier times, they diverge during the nebular phase. SN 2004dj shows a slow late-time decline rate with - 0.7 ±0.1 mag （100d）^-1 during the period ranging from t ≈ 200 - 300 d after the explosion, while SN 2004et shows a much faster decline rate at a comparable phase, e.g., 1.3 ± 0.1 mag （100d）^-1. The steeper decay rate seen in SN 2004et is likely due to dust formation in the explosion ejecta. Based on intermediate-band photometry, we derived the evolution of the feature lines [e.g., Hα] of SNe 2004dj and 2004et which are similar in flux at comparable phases but perhaps with significantly different decay rates. The origin of the observed variations in the continuum and the feature lines is briefly discussed.

Variable stars in the field of open cluster NGC 2126

We report the results of a time-series CCD photometric survey of variable stars in the field of open cluster NGC 2126. In about a one square degree field covering the cluster, a total of 21 variable candidates are detected during this survey, of which 16 are newly found. The periods, classifications and spectral types of 14 newly discovered variables are discussed, which consist of six eclipsing binary systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or δ Scuff star. In addition, there are two variable candidates, the properties of which cannot be determined. By a method based on fitting observed spectral energy distributions of stars with theoretical ones, the membership probabilities and the fundamental parameters of this cluster are determined. As a result, five variables are probably members of NGC 2126. The fundamental parameters of this cluster are determined as： metallicity to be 0.008 Z, age log（t） = 8.95, distance modulus （m - M）0 = 10.34 and reddening value E（B - V） = 0.55 mag.

South Galactic Cap u-band Sky Survey(SCUSS):Project Overview

The South Galactic Cap u-band Sky Survey （SCUSS） was established in 2009 in order to provide a photometric input catalog for target selection of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） project. SCUSS is an international cooperative project between National Astronomical Observatories, Chinese Academy of Sciences, and Steward Observatory at the University of Arizona, using the 90 inch （2.3 m） Bok telescope on Kitt Peak. The telescope is equipped with a prime focus camera that is composed of a mosaic of four 4096 × 4096 CCDs and has a field of view of about 1 deg2. From 2009 to 2013, SCUSS performed a sky survey of an approximately 5000 deg2 field of the South Galactic Cap in u band, including the Galactic anticenter area and the SDSS-IV extended imaging area. The limiting magnitude of SCUSS is deeper than 23 mag （at a signal-to-noise ratio of 5）. In this paper, we briefly describe the goals of this project, method of observations and data reduction, and we also introduce current and potential scientific activities related to the SCUSS project.

Multicolor photometry of the nearby galaxy cluster A119

This paper presents multicolor optical photometry of the nearby galaxy cluster Abell 119 （z = 0.0442） with the Beijing-Arizona-Taiwan-Connecticut system of 15 intermediate bands. Within the BATC field of view of 58＇× 58＇, there are 368 galaxies with known spectroscopic redshifts, including 238 member galaxies （called sample I）. Based on the spectral energy distributions of 1376 galaxies brighter than iBATC ---- 19.5, the photometric redshift technique and the color-magnitude relation of early-type galaxies are applied to select faint member galaxies. As a result, 117 faint galaxies were selected as new member galaxies. Combined with sample I, an enlarged sample （called sample II） of 355 member galaxies is obtained. Spatial distribution and localized velocity structure for two samples demonstrate that A119 is a dynami- cally complex cluster with at least three prominent substructures in the central region within 1 Mpc. A large velocity dispersion for the central clump indicates a merging along the line of sight. No significant evidence for morphology or luminosity segrega- tions is found in either sample. With the PEGASE evolutionary synthesis model, the environmental effect on the properties of star formation is confirmed. Faint galaxies in the low-density region tend to have longer time scales of star formation, smaller mean stellar ages, and lower metallicities in their interstellar medium, which is in agreement with the context of the hierarchical cosmological scenario.

Discovery of 13 New Variable Stars in the Field of the Open Cluster NGC 2168 (M35)

A wide-field time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2168 was carried out using the BATC Schmidt telescope. In total 13 new variable stars are discovered with three W UMa systems,one EA type and two EB type eclipsing binaries （one of them could be a W UMa system）, and seven pulsating stars including three candidates of δ Scuti stars.