Photometric Variability in the CSTAR Field: Results From the 2008 Data Set

The Chinese Small Telescope ARray (CSTAR) is the first telescope facility built at Dome A, Antarctica. During the 2008 observing season, the installation provided long-baseline and high-cadence photometric observations in the i-band for 18,145 targets within 20 deg2 CSTAR field around the South Celestial Pole for the purpose of monitoring the astronomical observing quality of Dome A and detecting various types of photometric variability. Using sensitive and robust detection methods, we discover 274 potential variables from this data set, 83 of which are new discoveries. We characterize most of them, providing the periods, amplitudes and classes of variability. The catalog of all these variables is presented along with the discussion of their statistical properties.Comment: 38 pages, 11 figures, 4 tables; Accepted for publication in ApJ

Eclipsing Binaries From the CSTAR Project at Dome A, Antarctica

The Chinese Small Telescope ARray (CSTAR) has observed an area around the Celestial South Pole at Dome A since 2008. About $20,000$ light curves in the i band were obtained lasting from March to July, 2008. The photometric precision achieves about 4 mmag at i = 7.5 and 20 mmag at i = 12 within a 30 s exposure time. These light curves are analyzed using Lomb--Scargle, Phase Dispersion Minimization, and Box Least Squares methods to search for periodic signals. False positives may appear as a variable signature caused by contaminating stars and the observation mode of CSTAR. Therefore the period and position of each variable candidate are checked to eliminate false positives. Eclipsing binaries are removed by visual inspection, frequency spectrum analysis and locally linear embedding technique. We identify 53 eclipsing binaries in the field of view of CSTAR, containing 24 detached binaries, 8 semi-detached binaries, 18 contact binaries, and 3 ellipsoidal variables. To derive the parameters of these binaries, we use the Eclipsing Binaries via Artificial Intelligence (EBAI) method. The primary and the secondary eclipse timing variations (ETVs) for semi-detached and contact systems are analyzed. Correlated primary and secondary ETVs confirmed by false alarm tests may indicate an unseen perturbing companion. Through ETV analysis, we identify two triple systems (CSTAR J084612.64-883342.9 and CSTAR J220502.55-895206.7). The orbital parameters of the third body in CSTAR J220502.55-895206.7 are derived using a simple dynamical model.Comment: 41 pages, 12 figures; published online in ApJ

Microbial reduction and precipitation of vanadium (V) in groundwater by immobilized mixed anaerobic culture

Vanadium is an important contaminant impacted by natural and industrial activities. Vanadium (V) reduction efficiency as high as 87.0% was achieved by employing immobilized mixed anaerobic sludge as inoculated seed within 12 h operation, while V(IV) was the main reduction product which precipitated instantly. Increasing initial V(V) concentration resulted in the decrease of V(V) removal efficiency, while this index increased first and then decreased with the increase of initial COD concentration, pH and conductivity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the decreased microbial diversity. V(V) reduction was realized through dissimilatory reduction process by significantly enhanced Lactococcus and Enterobacter with oxidation of lactic and acetic acids from fermentative microorganisms such as the enriched Paludibacter and the newly appeared Acetobacterium, Oscillibacter. This study is helpful to detect new functional species for V(V) reduction and constitutes a step ahead in developing in situ bioremediations of vanadium contamination. (C) 2015 Elsevier Ltd. All rights reserved.National Natural Science Foundation of China (NSFC) [41440025, 21307117]; Beijing Excellent Talent Training Project [2013D009015000003]; Beijing Higher Education Young Elite Teacher Project [YETP0657]SCI(E)[email protected]

Exoplanets in the Antarctic Sky I. The first data release of AST3-II (CHESPA) and new found variables within the southern CVZ of TESS

Located at Dome A, the highest point of the Antarctic plateau, the Chinese Kunlun station is considered to be one of the best ground-based photometric sites because of its extremely cold, dry, and stable atmosphere. A target can be monitored from there for over 40 days without diurnal interruption during a polar winter. This makes Kunlun station a perfect site to search for short-period transiting exoplanets. Since 2008, an observatory has existed at Kunlun station, and three telescopes are working there. Using these telescopes, the AST3 project has been carried out over the last 6 yr with a search for transiting exoplanets as one of its key programs (CHESPA). In the austral winters of 2016 and 2017, a set of target fields in the southern continuous viewing zone (CVZ) of TESS were monitored by the AST3-II telescope. In this paper, we introduce the CHESPA and present the first data release containing photometry of 26,578 bright stars (m(i) <= 15). The best photometric precision at the optimum magnitude for the survey is around 2 mmag. To demonstrate the data quality, we also present a catalog of 221 variables with a brightness variation greater than 5 mmag from the 2016 data. Among these variables, 179 are newly identified periodic variables not listed in the AAVSO database (https://www.aavso.org/), and 67 are listed in the Candidate Target List. These variables will require careful attention to avoid false-positive signals when searching for transiting exoplanets. Dozens of new transiting exoplanet candidates will be released in a subsequent paper

Exoplanets in the Antarctic Sky. II. 116 Transiting Exoplanet Candidates Found by AST3-II (CHESPA) within the Southern CVZ of TESS

We report first results from the CHinese Exoplanet Searching Program from Antarctica (CHESPA)-a wide-field high-resolution photometric survey for transiting exoplanets carried out using telescopes of the AST3 (Antarctic Survey Telescopes times 3) project. There are now three telescopes (AST3-I, AST3-II, and CSTAR-II) operating at Dome A-the highest point on the Antarctic Plateau-in a fully automatic and remote mode to exploit the superb observing conditions of the site, and its long and uninterrupted polar nights. The search for transiting exoplanets is one of the key projects for AST3. During the austral winters of 2016 and 2017 we used the AST3-II telescope to survey a set of target fields near the southern ecliptic pole, falling within the continuous viewing zone of the TESS mission. The first data release of the 2016 data, including images, catalogs, and light curves of 26,578 bright stars (7.5 <= m(i) <= 15), was presented in Zhang et al. The best precision, as measured by the rms of the light curves at the optimum magnitude of the survey (m(i) = 10), is around 2 mmag. We detect 222 objects with plausible transit signals from these data, 116 of which are plausible transiting exoplanet candidates according to their stellar properties as given by the TESS Input Catalog, Gaia DR2, and TESS-HERMES spectroscopy. With the first data release from TESS expected in late 2018, this candidate list will be timely for improving the rejection of potential false-positives

Planetary transit candidates in the CSTAR field: analysis of the 2008 data

The Chinese Small Telescope ARray (CSTAR) is a group of four identical, fully automated, static 14.5 cm telescopes. CSTAR is located at Dome A, Antarctica and covers 20 deg2 of sky around the South Celestial Pole. The installation is designed to provide high-cadence photometry for the purpose of monitoring the quality of the astronomical observing conditions at Dome A and detecting transiting exoplanets. CSTAR has been operational since 2008, and has taken a rich and high-precision photometric data set of 10,690 stars. In the first observing season, we obtained 291,911 qualified science frames with 20 s integrations in the i band. Photometric precision reaches 4 mmag at 20 s cadence at i = 7.5 and is 20 mmag at i = 12. Using robust detection methods, 10 promising exoplanet candidates were found. Four of these were found to be giants using spectroscopic follow-up. All of these transit candidates are presented here along with the discussion of their detailed properties as well as the follow-up observations

Quantification of the Influence of Citrate/Fe(II) Molar Ratio on Hydroxyl Radical Production and Pollutant Degradation during Fe(II)-Catalyzed O2 and H2O2 Oxidation Processes

Ligand-enhanced hydroxyl radical (&bull;OH) production is an important strategy for Fe(II)-catalyzed O2 and H2O2 oxidation processes. However, the influence of the molar ratio of ligands to Fe(II) on &bull;OH production remains elusive. This study employed citrate and inorganic dissolved Fe(II) (Fe(II)dis) as the representative ligand and Fe(II) species, respectively, to quantify this relationship. Results showed that &bull;OH production was highly dependent on the citrate/Fe(II) molar ratio. For instance, for the oxygenation of Fe(II)dis, the &bull;OH accumulations were 2.0&ndash;8.5, 3.4&ndash;28.5 and 8.1&ndash;42.3 &mu;M at low (0.25&ndash;0.5), moderate (0.5&ndash;1), and high (1&ndash;2) citrate/Fe(II) molar ratios, respectively. At low citrate/Fe(II) molar ratio (&lt;0.5), inorganic Fe(II)dis mainly contributed to &bull;OH production, with the increase in the citrate/Fe(II) molar ratio to a high level (1&ndash;2), Fe(II)-citrate complex turned to the electron source for &bull;OH production. The change in Fe(II) speciation with the increase of citrate/Fe(II) molar ratio elevated &bull;OH production. For pollutant degradation, 1 mg/L phenol was degraded by 53.6% within 40 min during oxygenation of Fe(II)-citrate system (1:1) at pH 7. Our results suggest that a moderate molar ratio of ligand/Fe(II) (0.5&ndash;1) may be optimal for Fe(II)-catalyzed O2 and H2O2 oxidation processes

Effects of riboflavin and desferrioxamine B on Fe(II) oxidation by O2

Flavins and siderophores secreted by various plants, fungi and bacteria under iron (Fe) deficient conditions play important roles in the biogeochemical cycling of Fe in the environment. Although the mechanisms of flavin and siderophore mediated Fe(III) reduction and dissolution under anoxic conditions have been widely studied, the influence of these compounds on Fe(II) oxidation under oxic conditions is still unclear. In this study, we investigated the kinetics of aqueous Fe(II) (17.8 μM) oxidation by O2 at pH 5‒7 in the presence of riboflavin (oxidized (RBF) and reduced (RBFH2)) and desferrioxamine B (DFOB) as representative flavins and siderophores, respectively. Results showed that the addition of RBF/RBFH2 or DFOB markedly accelerates the oxidation of aqueous Fe(II) by O2. For instance, at pH 6, the rate of Fe(II) oxidation was enhanced 20‒70 times when 10 μM RBFH2 was added. The mechanisms responsible for the accelerated Fe(II) oxidation are related to the redox reactivity and complexation ability of RBFH2, RBF and DFOB. While RBFH2 does not readily complex Fe(II)/Fe(III), it can activate O2 and generate reactive oxygen species, which then rapidly oxidize Fe(II). In contrast, both RBF and DFOB do not reduce O2 but react with Fe(II) to form RBF/DFOB-complexed Fe(II), which in turn accelerates Fe(II) oxidation. Furthermore, the lower standard reduction potential of the Fe(II)-DFOB complex, compared to the Fe(II)-RBF complex, correlates with a higher oxidation rate constant for the Fe(II)-DFOB complex. Our study reveals an overlooked catalytic role of flavins and siderophores that may contribute to Fe(II)/Fe(III) cycling at oxic-anoxic interfaces