arXiv subjects

Hu Zou

Publications and source records attributed to Hu Zou.

At least 199 records · Page 11Linked to original sources

arXiv2015

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.

astro-ph.SR↗

arXiv2015

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.

astro-ph.SR↗

arXiv2015

An Investigation of the Absolute Proper Motions of the SCUSS Catalog

Absolute proper motions for $\sim$ 7.7 million objects were derived based on data from the South Galactic Cap u-band Sky Survey (SCUSS) and astrometric data derived from uncompressed Digitized Sky Surveys that the Space Telescope Science Institute (STScI) created from the Palomar and UK Schmidt survey plates. We put a great deal of effort into correcting the position-, magnitude-, and color-dependent systematic errors in the derived absolute proper motions. The spectroscopically confirmed quasars were used to test the internal systematic and random error of the proper motions. The systematic errors of the overall proper motions in the SCUSS catalog are estimated as -0.08 and -0.06 mas/yr for μα cos δ and μδ, respectively. The random errors of the proper motions in the SCUSS catalog are estimated independently as 4.2 and 4.4 mas/yr for μα cos δ and μδ. There are no obvious position-, magnitude-, and color-dependent systematic errors of the SCUSS proper motions. The random error of the proper motions goes up with the magnitude from about 3 mas/yr at u < 18.0 mag to about 7 mas/yr at u = 22.0 mag. The proper motions of stars in SCUSS catalog are compared with those in the SDSS catalog, and they are highly consistent.

astro-ph.IM↗

arXiv2015

Capability of Quasar Selection by Combining the SCUSS and SDSS Observations

The South Galactic Cap $u$-band Sky Survey (SCUSS) provides a deep $u$-band imaging of about 5000 deg$^2$ in south Galactic cap. It is about 1.5 mag deeper than the SDSS $u$-band. In this paper we evaluate the capability of quasar selection using both SCUSS and SDSS data, based on considerations of the deep SCUSS $u$-band imaging and two-epoch $u$-band variability. We find that the combination of the SCUSS $u$-band and the SDSS $griz$ band allows us to select more faint quasars and more quasars at redshift around 2.2 than the selection only with the SDSS $ugriz$ data. Quasars have significant $u$-band variabilities. The fraction of quasars with large two-epoch variability is much higher than that of stars. The selection by variability can select both low-redshift quasars with ultraviolet excess and mid-redshift ($2 < z <3.5$) quasars where quasar selection by optical colors is inefficient. The above two selections are complementary and make full use of the SCUSS u-band advantages.

astro-ph.GA↗

arXiv2014

The 0.1<z<1.65 evolution of the bright end of the [OII] luminosity function

We present the [OII] luminosity function measured in the redshift range 0.1<z<1.65 with unprecedented depth and accuracy. Our measurements are based on medium resolution flux-calibrated spectra of emission line galaxies with the FORS2 instrument at VLT and with the SDSS-III/BOSS spectrograph. The FORS2 spectra and the corresponding catalog containing redshifts and line fluxes are released along with this paper. In this work we use a novel method to combine the aforementioned surveys with GAMA, zCOSMOS and VVDS, which have different target selection, producing a consistent weighting scheme to derive the [OII] luminosity function. The measured luminosity function is in good agreement with previous independent estimates. The comparison with two state-of-the-art semi-analytical models is good, which is encouraging for the production of mock catalogs of [OII] flux limited surveys. We observe the bright end evolution over 8.5 Gyr: we measure the decrease of log L* from 42.4 erg/s at redshift 1.44 to 41.2 at redshift 0.165 and we find that the faint end slope flattens when redshift decreases. This measurement confirms the feasibility of the target selection of future baryonic acoustic oscillation surveys aiming at observing [OII] flux limited samples.

astro-ph.GA↗

arXiv2014

The THU-NAOC Transient Survey: the Performance and the First-year Result

The Tsinghua University-National Astronomical Observatories of China (NAOC) Transient Survey (TNTS) is an automatic survey for a systematic exploration of optical transients (OTs), conducted with a 60/90 cm Schmidt telescope at Xinglong station of NAOC. This survey repeatedly covers ~ 1000 square degrees of the north sky with a cadence of 3-4 days. With an exposure of 60 s, the survey reaches a limited unfiltered magnitude of about 19.5 mag. This enables us to discover supernovae at their relatively young stages. In this paper, we describe the overall performance of our survey during the first year and present some preliminary results.

astro-ph.IM↗

arXiv2014

Spectral Energy Distributions and Masses of 304 M31 Old Star Clusters

This paper presents CCD multicolor photometry for 304 old star clusters in the nearby spiral galaxy M31. Of which photometry of 55 star clusters is first obtained. The observations were carried out as a part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March, using 15 intermediate-band filters covering 3000--10000 Å. Detailed comparisons show that our photometry is in agreement with previous measurements. Based on the ages and metallicities from Caldwell et al. and the photometric measurements here, we estimated the clusters' masses by comparing their multicolor photometry with stellar population synthesis models. The results show that the sample clusters have masses between $\sim 3\times10^4 M_\odot$ and $\sim 10^7 M_\odot$ with the peak of $\sim 4\times10^5 M_\odot$. The masses here are in good agreement with those in previous studies. Combined with the masses of young star clusters of M31 from Wang et al., we find that the peak of mass of old clusters is ten times that of young clusters.

astro-ph.GA↗

arXiv2014

Estimation of Absolute Magnitude-dependent Galactic Model Parameters In Intermediate Latitude With SDSS and SCUSS

Based on SDSS and South Galactic Cap of u-band Sky Survey (SCUSS) early data, we use star counts method to estimate the Galactic structure parameters in an intermediate latitude with 10,180 main-sequence (MS) stars in absolute magnitude interval of $4 \leq M_r \leq 13$. We divide the absolute magnitude into five intervals:$4 \leq M_r < 5$, $5 \leq M_r < 6$, $6 \leq M_r < 8$, $8 \leq M_r < 10$, $10 \leq M_r \leq 13$, and estimate the Galactic structure parameters in each absolute magnitude interval to explore their possible variation with the absolute magnitude. Our study shows the parameters depend on absolute magnitude. For the thin disk, the intrinsic faint MS stars have large local space density and they tend to stay close to the Galactic plane. A plausible explanation is that faint MS stars with long lifetime experience long gravitational interaction time result in a short scaleheight. However, for the thick disk, the parameters show a complex trend with absolute magnitude, which may imply the complicated original of the thick disk. For the halo, the intrinsic faint MS stars have large local density and small axial ratio, which indicate a flattened inner halo and a more spherical outer halo.

astro-ph.GA↗

arXiv2014

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 square degree 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-second integrations in the i-band. Photometric precision reaches about 4 mmag at 20-second cadence at i=7.5, and is about 20 mmag at i=12. Using robust detection methods, ten 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.

astro-ph.EP↗

arXiv2013

Gradients of Stellar Population Properties and Evolution Clues in a Nearby Galaxy M 101

Multi-band photometric images from ultraviolet and optical to infrared are collected to derive spatially resolved properties of a nearby Scd type galaxy M 101. With evolutionary stellar population synthesis models, two-dimensional distributions and radial profiles of age, metallicity, dust attenuation, and star formation timescale in the form of the Sandage star formation history are obtained. When fitting with the models, we use the IRX-$A_\mathrm{FUV}$ relation, found to depend on a second parameter of birth rate b (ratio of present and past-averaged star formation rate), to constrain the dust attenuation. There are obvious parameter gradients in the disk of M101, which supports the theory of an "inside-out disk" growth scenario. Two distinct disc regions with different gradients of age and color are discovered, similar to another late-type galaxy NGC 628. The metallicity gradient of the stellar content is flatter than that of H {\sc ii} regions. The stellar disk is optically thicker inside than outside and the global dust attenuation of this galaxy is lower, compared with galaxies of similar and earlier morphological type. We highlight that a variational star formation timescale describes the real star formation history of a galaxy. The timescale increases steadily from the center to the outskirt. We also confirm that the bulge in this galaxy is a disk-like pseudobulge, whose evolution is likely to be induced by some secular processes of the small bar with relatively young age, rich metal, and much dust.

astro-ph.CO↗

arXiv2012

Metal Abundance and Kinematical Properties of M81 Globular Cluster System

In this paper, we presented metal abundance properties of 144 M81 globular clusters. These globulars consist of the largest globular cluster sample in M81 till now. Our main results are: the distribution of metallicities are bimodal, with metallicity peaks at [Fe/H]\sim-1.51 and -0.58, and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution as the metal-rich ones in M31 do; like our Galaxy and M31, the globular clusters in M81 have a small radial metallicity gradient. These results are consistent with those obtained based on a small sample of M81 globular clusters. In addition, this paper showed that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists, and that rotation is present in the metal-rich globular cluster subsample, while the metal-poor globular cluster subsample shows no evidence for rotation. The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii. The results of this paper confirm the conclusion of Schroder et al. that M81's metal-rich globular clusters at intermediate projected radii were associated with a thick disk of M81.

astro-ph.CO↗

arXiv2012

Age and mass studies for young star clusters in M31 from SEDs-fit

In this paper, we present photometry for young star clusters in M31, which are selected from Caldwell et al. These star clusters have been observed as part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March. The BATC images including these star clusters are taken with 15 intermediate-band filters covering 3000--10000 Å. Combined with photometry in the {\sl GALEX} far- and near-ultraviolet, broad-band $UBVRI$, SDSS $ugriz$, and infrared $JHK_{\rm s}$ of Two Micron All Sky Survey, we obtain their accurate spectral energy distributions (SEDs) from 1538-20000 Å. We derive these star clusters' ages and masses by comparing their SEDs with stellar population synthesis models. Our results are in good agreement with previous determinations. The mean value of age and mass of young clusters ($<2$ Gyr) is about 385 Myr and $2\times 10^4 {M_\odot}$, respectively. There are two distinct peaks in the age distribution, a highest peak at age $\sim$ 60 Myr and a secondary peak around 250 Myr, while the mass distribution shows a single peak around $10^4 {M_\odot}$. A few young star clusters have two-body relaxation times greater than their ages, indicating that those clusters have not been well dynamically relaxed and therefore have not established the thermal equilibrium. There are several regions showing aggregations of young star clusters around the 10 kpc ring and the outer ring, indicating that the distribution of the young star clusters is well correlated with M31's star-forming regions. The young massive star clusters (age $\leq 100$ Myr and mass $\geq 10^4 {M_\odot}$) show apparent concentration around the ring splitting region, suggesting a recent passage of a satellite galaxy (M32) through M31 disk.

astro-ph.CO↗

arXiv2012

Type IIn Supernova SN 2010jl: Optical Observations for Over 500 Days After Explosion

We present extensive optical observations of a Type IIn supernova (SN) 2010jl for the first 1.5 years after the discovery. The UBVRI light curves demonstrated an interesting two-stage evolution during the nebular phase, which almost flatten out after about 90 days from the optical maximum. SN 2010jl has one of the highest intrinsic H_alpha luminosity ever recorded for a SN IIn, especially at late phase, suggesting a strong interaction of SN ejecta with the dense circumstellar material (CSM) ejected by the progenitor. This is also indicated by the remarkably strong Balmer lines persisting in the optical spectra. One interesting spectral evolution about SN 2010jl is the appearance of asymmetry of the Balmer lines. These lines can be well decomposed into a narrow component and an intermediate-width component. The intermediate-width component showed a steady increase in both strength and blueshift with time until t ~ 400 days after maximum, but it became less blueshifted at t ~ 500 days when the line profile appeared relatively symmetric again. Owing to that a pure reddening effect will lead to a sudden decline of the light curves and a progressive blueshift of the spectral lines, we therefore propose that the asymmetric profiles of H lines seen in SN 2010jl is unlikely due to the extinction by newly formed dust inside the ejecta, contrary to the explanation by some early studies. Based on a simple CSM-interaction model, we speculate that the progenitor of SN 2010jl may suffer a gigantic mass loss (~ 30-50 M_sun) in a few decades before explosion. Considering a slow moving stellar wind (e.g., ~ 28 km/s) inferred for the preexisting, dense CSM shell and the extremely high mass-loss rate (1-2 M_sun per yr), we suggest that the progenitor of SN 2010jl might have experienced a red supergiant stage and explode finally as a post-red supergiant star with an initial mass above 30-40 M_sun.

astro-ph.SR↗

arXiv2012

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 (BATC) system of 15 intermediate bands. Within the BATC viewing field of 58'* 58', there are 368 galaxies with known spectroscopic redshifts, including 238 member galaxies (called sample I). Based on the spectral energy distributions (SEDs) of 1376 galaxies brighter than iBATC = 19:5, photometric redshift technique and the color-magnitude relation of earlytype 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 dynamically 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 evidences for morphology and luminosity segregations are found in both samples. With the evolutionary synthesis model PEGASE, environmental effect on the star formation properties is confirmed. Faint galaxies in low-density region tend to have longer time scales of star formation, smaller mean stellar ages, and lower metallicities of interstellar medium, which is in agreement with the context of hierarchical cosmological scenario.

astro-ph.GA↗

arXiv2011

Kinematics and Stellar Population Properties of the Andromeda Galaxy by the Spectroscopic Observations of the Guoshoujing Telescope

The Andromeda galaxy was observed by the Guoshoujing Telescope (GSJT, formly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope -- LAMOST) during the 2009 commissioning phase. Due to the absence of standard stars for flux calibration, we use the photometric data of 15 intermediate bands in the Beijing-Arizona-Taipei-Connecticut (BATC) survey to calibrate the spectra. Total 59 spectra located in the bulge and disk of the galaxy are obtained. Kinematic and stellar population properties of the stellar content are derived with these spectra. We obtain the global velocity field and calculate corresponding rotation velocities outer to about 7 kpc along the major axis. These rotation velocity measurements complement those of the gas content, such as the H {\sc i} and CO. The radial velocity dispersion presents that the stars in the bulge are more dynamically thermal and the disk is more rotation-supported. The age distribution shows that the bulge was formed about 12 Gyr ago, the disk is relatively younger, and the ages of some regions along the spiral arms can reach as young as about 1 Gyr. These young stellar populations have relatively richer abundance and larger reddening. The overall average metallicity of the galaxy approximates the solar metallicity and a very weak abundance gradient is gained. The reddening map gives a picture of a dust-free bulge and a distinct dusty ring in the disk.

astro-ph.CO↗

arXiv2011

Stellar Population Properties and Evolution Analysis of NGC 628 with the Panchromatic Photometry

Panchromatic spectral energy distribution (SED) from the ultraviolet (UV), optical to infrared (IR) photometry of NGC 628, combined with the evolutionary stellar population synthesis, is used to derive the spatially resolved age, metallicity and reddening maps. These parameter distributions show that the bulge of this galaxy is a disk-like pseudobulge, which has the S{é}rsic index close to the exponential law, rich gas, and a young circumnuclear ring structure. We also discover the disk has two distinct regions with different radial age and metallicity gradients. The inner region is older and has a much steeper age gradient than the outer region of the disk. Both these two regions and the central young structure can be seen in the radial profile of the optical color. Based on the age and reddening distributions, we consider that the pseudobulge and disk are likely to have grown via the secular evolution, which is the redistribution of mass and energy through the angular momentum transport caused by the non-axisymmetric potential of the spirals. However, possible gas accretion events could affect the outer region of the disk, due to abundant H{\sc i} gas accumulating in the outer disk.

astro-ph.CO↗

arXiv2011

The i-band Sky brightness and Transparency at Dome A, Antarctica

Based on the observations of the Chinese Small Telescope ARray (CSTAR), the i band observing conditions at Antarctic Dome A have been investigated. The over all variations of sky brightness and transparency are calculated and subsequently cloud cover, contributions to the sky background from various factors including aurorae are derived. The median sky brightness of moonless clear nights is about 20.5 mag arcsec$^{-2}$ in the SDSS i band at the South Celestial Pole, which contains the diffused Galactic light of about 0.06 mag. There are no thick clouds in the year of 2008. Relatively strong aurorae are detected by their brightening the normal sky, which contribute up to about 2 of the observed images.

astro-ph.IM↗

arXiv2011

The sky brightness and transparency in i-band at Dome A, Antarctica

The i-band observing conditions at Dome A on the Antarctic plateau have been investigated using data acquired during 2008 with the Chinese Small Telescope ARray. The sky brightness, variations in atmospheric transparency, cloud cover, and the presence of aurorae are obtained from these images. The median sky brightness of moonless clear nights is 20.5 mag arcsec^{-2} in the SDSS $i$ band at the South Celestial Pole (which includes a contribution of about 0.06 mag from diffuse Galactic light). The median over all Moon phases in the Antarctic winter is about 19.8 mag arcsec^{-2}. There were no thick clouds in 2008. We model contributions of the Sun and the Moon to the sky background to obtain the relationship between the sky brightness and transparency. Aurorae are identified by comparing the observed sky brightness to the sky brightness expected from this model. About 2% of the images are affected by relatively strong aurorae.

astro-ph.IM↗