118411365
The photometric system of the Tsinghua-NAOC 80-cm telescope at NAOC Xinglong Observatory
The Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at the Xinglong Observatory of NAOC, with the main scientific goals of monitoring various transients in the universe such as supernovae, gamma-ray bursts, novae, variable stars, and active galactic nuclei. We present a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations taken on 12 photometric nights, spanning the period from 2004 to 2012, we derived an accurate transformation equation between the instrumental ubvri magnitudes and standard Johnson UBV and Cousins RI magnitudes. In particular, the color terms and the extinction coefficients of different passbands are well determined. With these data, we also obtained the limiting magnitudes and the photometric precision of TNT. It is worthwhile to point out that the sky background at the Xinglong Observatory became gradually worse over the period from 2005 to 2012 (e.g., ~21.4 mag vs. ~20.1 mag in the V band).
119237976
A large sample of low surface brightness disc galaxies from the SDSS – II. Metallicities in surface brightness bins
We study the spectroscopic properties of a large sample of low surface brightness galaxies (LSBGs) [with B-band central surface brightness μ0(B) > 22 mag arcsec −2 ] selected from the Sloan Digital Sky Survey Data Release 4 (SDSS-DR4) main galaxy sample. A large sample of disc-dominated high surface brightness galaxies [HSBGs, with μ0(B) < 22 mag arcsec −2 ] are also selected for comparison simultaneously. To study them in more details, these sample galaxies are further divided into four subgroups according to μ0(B) (in units of mag arcsec −2 ): very low surface brightness galaxies (vLSBGs) (24.5–22.75), intermediate low surface brightness galaxies (iLSBGs) (22.75–22.0), intermediate high surface brightness galaxies (iHSBGs) (22.0–21.25) and very high surface brightness galaxies (vHSBGs) (<21.25). The diagnostic diagram from spectral emission-line ratios shows that the active galactic nucleus fractions of all the four subgroups are small (<9 per cent). The 21 032 star-forming galaxies with good-quality spectroscopic observations are further selected for studying their dust extinction, strong-line ratios, metallicities and stellar mass–metallicity relations. The vLSBGs have lower extinction values and have less metal-rich and massive galaxies than the other subgroups. The oxygen abundances of our LSBGs are not as low as those of the H II regions in LSBGs studied in literature, which could be because our samples are more luminous, and because of the different metallicity calibrations used. We find a correlation between 12 + log(O/H) and μ0(B) for vLSBGs, iLSBGs and iHSBGs but show that this could be a result of correlation between μ0(B) and stellar mass and the well-known mass–metallicity relation. This large sample shows that LSBGs span a wide range in metallicity and stellar mass, and they lie nearly on the stellar mass versus metallicity and N/O versus O/H relations of normal galaxies. This suggests that LSBGs and HSBGs have not had dramatically different star formation and chemical enrichment histories.
2927391
A large sample of low surface brightness disc galaxies from the SDSS – I. The sample and the stellar populations
We present the properties of a large sample (12 282) of nearly face-on low surface brightness (LSB) disc galaxies selected from the main galaxy sample of SDSS-DR4. These properties include B-band central surface brightness μ 0 (B), scalelengths h, integrated magnitudes, colours and distances D. This sample has μ 0 (B) values from 22 to 24.5 mag arcsec -2 with a median value of 22.42 mag arcsec -2 , and disc scalelengths ranging from 2 to 19 kpc. They are quite bright with M B taking values from -18 to -23 mag with a median value of -20.08 mag. There exist clear correlations between log h and M B , log h and log D, log D and M B . However, no obvious correlations are found between μ 0 (B) and log h, colours, etc. The correlation between colours and log h is weak even though it exists. Both the optical-optical and optical-NIR colour-colour diagrams indicate that most of them have a mixture of young and old stellar populations. They also satisfy colour-magnitude relations, which indicate that brighter galaxies tend generally to be redder. The comparison between the LSBGs and a control sample of nearly face-on disc galaxies with higher surface brightness (HSB) with μ 0 (B) from 18.5 to 22 mag arcsec -2 show that, at a given luminosity or distance, the observed LSB galaxies tend to have larger scalelengths. These trends could be seen gradually by dividing both the LSBGs and HSBGs into two subgroups according to surface brightness. A volume-limited subsample was extracted to check the incompleteness of surface brightness. The only one of the property relations having an obvious change is the relation of log h versus μ 0 (B), which shows a correlation in this subsample.
14830508
SDSS J121811.0+465501.2: A New Low Surface Brightness Galaxy with Low Metallicity
We have serendipitously found a new nearby low surface brightness (LSB) galaxy from the SDSS database. We estimate the oxygen abundance of its H II region SDSS J121811.0+465501.2 from its electron temperature, as well as that of another H II region, SDSS J135440.5+535309.6, located in the irregular LSB galaxy UGC 8837. These two extragalactic H II regions were classified as stars in the SDSS DR4 database and were found occasionally by us in the automatic recognition and classification of stellar spectra. Their optical spectra show obvious emission lines, i.e., strong [O III] λλ4959, 5007 and Balmer emission lines, but very weak [N II] λλ6548, 6583 and [S II] λλ6317, 6731, which could indicate that they are metal-poor star-forming regions. The derived oxygen abundances of the two objects are 12 + log(O/H) ~ 7.88 ± 0.30 and 7.70 ± 0.30, respectively. The host of the H II region SDSS J121811.0+465501.2 is identified as a new nearly edge-on LSB disk galaxy (almost without a bulge), with a B-band central surface brightness μ0(B) of 23.68 mag arcsec-2 and an inclination angle of ~75° by using the GIM2D software to analyze its g- and r-band images independently. It is a nearby dwarf galaxy with redshift z ~ 0.00157, disk scale length ~0.40 kpc, and B-band absolute magnitude MB ~ -13.51 mag. The very low oxygen abundances of these two objects confirm the low metallicities of LSB galaxies.
119256368
The properties of a large sample of low surface brightness galaxies from SDSS
A large sample of low surface brightness (LSB) disk galaxies is selected from SDSS with B-band central surface brightness mu_0(B) from 22 to 24.5 mag arcsec^(-2). Some of their properties are studied, such as magnitudes, surface brightness, scalelengths, colors, metallicities, stellar populations, stellar masses and multiwavelength SEDs from UV to IR etc. These properties of LSB galaxies have been compared with those of the galaxies with higher surface brightnesses. Then we check the variations of these properties following surface brightness.
14866078
The asymmetric structure of the Galactic halo
Using the stellar photometry catalogue based on the latest data release (DR4) of the Sloan Digital Sky Survey (SDSS), a study of the Galactic structure using star counts is carried out for selected areas of the sky. The sample areas are selected along a circle at a Galactic latitude of +60 ◦ , and 10 strips of high Galactic latitude along different longitudes. Direct statistics of the data show that the surface densities of l from 180 ◦ to 360 ◦ are systematically higher than those of l from 0 ◦ to 180 ◦ , defining a region of overdensity (in the direction of Virgo) and another one of underdensity (in the direction of Ursa Major) with respect to an axisymmetric model. It is shown by comparing the results from star counts in the (g r) colour that the density deviations are due to an asymmetry of the stellar density in the halo. Theoretical models for the surface density profile are built and star counts are performed using a triaxial halo of which the parameters are constrained by observational data. Two possible reasons for the asymmetric structure are discussed.
119229799
Cosmological parameter estimation from CMB and X-ray cluster after Planck
. We investigate constraints on cosmological parameters in three 8-parameter models with the summed neutrino mass as a free parameter, by a joint analysis of CCCP X-ray cluster data, the newly released Planck CMB data as well as some external data sets including baryon acoustic oscillation measurements from the 6dFGS, SDSS DR7 and BOSS DR9 surveys, and Hubble Space Telescope Ho measurement. We find that the combined data strongly favor a non-zero neutrino masses at more than 3 sigma confidence level in these non-vanilla models. Allowing the CMB lensing amplitude A(L) to vary, we find A(L) > 1 at 3 sigma confidence level. For dark energy with a constant equation of state w, we obtain w < -1 at 3 sigma confidence level. The estimate of the matter power spectrum amplitude 08 is discrepant with the Planck value at 2 sigma confidence level, which reflects some tension between X-ray cluster data and Planck data in these non-vanilla models. The tension can be alleviated by adding a 9% systematic shift in the cluster mass function.
119755058
Relativistic Hartree-Fock model with short range correlation in nuclear matter
We introduce the form factor and short range correlation in the relativistic Hartree-Fock approximation (RHFU) to study the properties of nuclear matter. We treat the short range correlation with the unitary correlation operator method (UCOM). In this framework, we can perfectly reproduce the equation of state of pure neutron matter obtained by the relativistic Brueckner-Hartree-Fock theory with the Bonn potential. We apply the RHFU model to symmetric nuclear matter. The contribution of ρ meson is cut down largely by the form factor of the size in the realistic nucleon-nucleon interaction. The short range correlation has a significant effect on the Fock energies of pion and ρ meson exchange interaction.
32197965
Optical Afterglow Observations of the Unusual Short-Duration Gamma-Ray Burst GRB 040924
The 1 m telescope at Lulin Observatory and the 0.76 m Katzman Automatic Imaging Telescope at Lick Observatory were used to observe the optical afterglow of the short-duration (1.2-1.5 s) gamma-ray burst GRB 040924. This object has a soft high-energy spectrum, thus making it an exceptional case, perhaps actually belonging to the short-duration tail of the long-duration GRBs. Our data, combined with other reported measurements, show that the early R-band light curve can be described by two power laws with index α = -0.7 (at t = 16-50 minutes) and α = -1.06 (at later times). The rather small difference in the spectral indices can be explained more easily by an afterglow model invoking a cooling break than by one with a jet break.
14520300
Distance Determination of Variable Galactic Sources
We have developed a timing analysis method to determine the distances of variable galactic X-ray sources based on the method advanced by Trumper and Schonfelder in 1973. The light-curve of the halo produced by the scattering of X-rays off the interstellar dust is delayed and smeared by the dust grains. This method utilizes the differences between the power density spectra of the point source and the halo. We present the details of this method and our first applications of this method to the Chandra data of X-ray binary Cyg X-3.
95137172
Soft x-ray imaging and spectroscopy of single nanocrystals
Resonant photoemission electron microscopy (PEEM) at the Fe L3,2 absorption edge was utilized to image single γ-Fe2O3 nanocrystals of 10 nm average diameter (∼20 000 Fe atoms) and to record soft x-ray absorption spectra of individual particles. Within the spectral resolution of the experiment, no damage to the individual nanoparticles occurs during repeated, prolonged exposure to the intense x-ray beam. Furthermore, no differences in the position or shape of the soft x-ray absorption spectrum of a single nanocrystal and the ensemble are observed within the experimental resolution. PEEM contrast images and soft x-ray absorption spectra, however, show strong intensity variations between different particles reflecting the size distribution of the sample. This proof-of-principle experiment successfully demonstrates the applicability of x-ray spectromicroscopy to the study of nanoscale systems on a hitherto unachieved length scale.