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.
15020605
The type Ia supernova 1997br in ESO 576-G40
The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35 ± 0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measuring the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epochs. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.
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.
119270494
Multiwavelength study of nearly face-on low surface brightness disk galaxies
We study the ages of a large sample (1802) of nearly face-on disk low surface brightness galaxies (LSBGs) using the evolutionary population synthesis (EPS) model PEGASE with an exponentially decreasing star formation rate to fit their multiwavelength spectral energy distributions (SEDs) from far-ultraviolet (FUV) to near-infrared (NIR). The derived ages of LSBGs are 1–5 Gyr for most of the sample no matter if constant or varying dust extinction is adopted, which are similar to most of the previous studies on smaller samples. This means that these LSBGs formed the majority of their stars quite recently. However, a small part of the sample (~2%–3%) has larger ages of 5–8 Gyr, meaning their major star forming process may have occurred earlier. At the same time, a large sample (5886) of high surface brightness galaxies (HSBGs) are selected and studied using the same method for comparisons. The derived ages are 1–5 Gyr for most of the sample (97%) as well. These results probably mean that these LSBGs have not much different star formation histories from their HSBGs counterparts. However, we should notice that the HSBGs are generally about 0.2 Gyr younger, which could mean that the HSBGs may have undergone more recent star forming activities than the LSBGs.
1567381
The structure of the Galactic halo : SDSS versus SuperCOSMOS
The halo structure at high Galactic latitudes near both the north and south poles is studied using Sloan Digital Sky Survey (SDSS) and SuperCOSMOS data. For the south cap halo, the archive of the SuperCOSMOS photographic photometry sky survey is used. The coincident source rate between SuperCOSMOS data in B J band from 16.5 to 20.5 mag and SDSS data is about 92 per cent, in a common sky area in the south. While that in the R F band is about 85 per cent from 16.5 to 19.5 mag. Transformed to the SuperCOSMOS system and downgraded to the limiting magnitudes of SuperCOSMOS, the star counts in the North Galactic Cap from SDSS show up to an 16.9±6.3 per cent asymmetric ratio (defined as relative fluctuations over the rotational symmetry structure) in the B J band, and up to 13.5 ± 6.7 per cent asymmetric ratio in the R F band. From SuperCOSMOS Bj and R F bands, the structure of the Southern Galactic hemisphere does not show the same obvious asymmetric structures as the northern sky does in both the original and downgraded SDSS star counts. An axisymmetric halo model with n = 2.8 and q = 0.7 can fit the projected number density from SuperCOSMOS fairly well, with an average error of about 9.17 per cent. By careful analysis of the difference of star counts between the downgraded SDSS northern halo data and SuperCOSMOS southern halo data, it is shown that no asymmetry can be detected in the South Galactic Cap at the accuracy of SuperCOSMOS, and the Virgo overdensity is likely a foreign component in the Galactic halo.
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.
119772144
Microscopic study of the ground state properties of light nuclei
Ground state properties of light isotopes from helium to oxygen, such as binding energies, spin parities, rms radii, and halo phenomena are studied systematically by the Skyrme Hartree-Fock model with fit E{sub {sigma} } as the effective interaction. Since the particle number of the studied system is rather small, pairing interactions between identical nucleons are treated with the particle number conservation method. The results of the calculation show that most of the ground state properties can be well described. Some unsuccessful points of the calculation are pointed out. {copyright} {ital 1997} {ital The American Physical Society}
2493678
Large-scale structures in the distribution of X-ray selected AGN
We are searching for large-scale structures in the distribution of AGN discovered by the ROSAT All-Sky Survey. The RASS detected > 60000 X-ray objects, of which approximately 35% are AGN at z < 0.5. The surface density in the extragalactic sky is approximately 0.5 AGN/deg^2, which has not been reached until now by any other survey for this redshift range. We efficiently single out the AGN among all the RASS sources using the Hamburg/RASS database of optical identifications, which contains presently 13867 entries. 
Follow-up spectroscopy of RASS AGN candidates identified in selected areas of the northern sky is underway to determine the spatial distribution of the AGN in these areas. In every area structures reminiscent of clusters and filaments are found on scales 50 - 100 h^{-1}Mpc. These structures have a similar size as the serendipitously discovered groups of AGN in optical surveys at higher redshifts. Samples of low redshift AGN drawn from the RASS are large enough to be used with samples of higher redshift to study evolutionary effects in the large-scale distribution of AGN.
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.
11077788
A GRB Follow-up System at the Xinglong Observatory and Detection of the High-Redshift GRB 060927 ⋆
A gamma-ray burst (GRB) optical photometric follow-up system at the Xinglong Observatory of National Astronomical Observatories of China (NAOC) has been constructed. It uses the 0.8-m Tsinghua-NAOC Telescope (TNT) and the 1-m EST telescope, and can automatically respond to GRB Coordinates Network (GCN) alerts. Both telescopes slew relatively fast, being able to point to a new target field within ~1 min upon a request. Whenever available, the 2.16-m NAOC telescope is also used. In 2006 the system responded to 15 GRBs and detected seven early afterglows. In 2007 six GRBs have been detected among 18 follow-up observations. TNT observations of the second most distant GRB 060927 (z = 5.5) are shown, which started as early as 91 s after the GRB trigger. The afterglow was detected in the combined image of the first 19×20 s unfiltered exposures. This GRB follow-up system has joined the East-Asia GRB Follow-up Observation Network (EAFON).
54983794
Experimental Test of the Prototype LLRF Systems for PAL-XFEL
Two prototype LLRF systems were developed in collaboration with Pohang Accelerator Laboratory(PAL) and domestic companies. They are focused on the control of single klystron system to obtain mainly analogue performance. The low power test of the developed LLRF showed good performance previously. We experimentally tested LLRF in the klystron systems to see performance in the high power situation. They showed performance around the prototype specification for short time and relatively long time. During test some bugs are discovered and fixed..