Chao-Jian Wu

CCD Photometry of Candidate RR Lyrae Stars in the Sloan Digital Sky Survey

We present unfiltered CCD photometry of a sample of 71 candidate RR Lyrae stars during 2003 and 2004, out of 148 candidate stars that were selected from Sloan Digital Sky Survey (SDSS) commissioning data by Ivezic and coworkers. We obtain light curves of 69 candidate stars and present a catalog of their positions, amplitudes, periods, types, and mean magnitudes. We confirm that the 69 stars are true RR Lyrae variables based on periods and light curves, for the first time for 41 of them. We identify 57 type ab, 11 type c, and 1 type d (double-mode) in our sample. The double-mode RR Lyrae star shows properties similar to globular cluster stars and are unlike field stars of the Galactic halo in the Petersen diagram. We also find one RR Lyrae star that is related to Pal 5 and recover another. In our sample, only two candidate stars do not have a reasonable light curve. We conclude that the ratio of contamination in our sample is less than ~8%, which shows that the criteria used by Ivezic and coworkers to select RR Lyrae stars from the SDSS two-epoch data are reliable.

The shallow-decay phase in both the optical and X-ray afterglows of Swift GRB 090529A: energy injection into a wind-type medium?

The energy injection model is the usual choice for interpreting the shallow-decay phase in Swift gamma-ray burst (GRB) X-ray afterglows. However, very few GRBs have simultaneous signatures of energy injection in their optical and X-ray afterglows. Here, we report on the optical observations of GRB 090529A from 2000 s to ∼10 6 s after the burst, in which an achromatic decay is seen at both wavelengths. The optical light curve shows a decay from 0.37 to 0.99, with a break at ∼10 5 s. In the same time interval, the decay indices of the X-ray light curve changed from 0.04 to 1.2. Comparing these values with the closure relations, the segment after 3 × 10 4 s is consistent with the prediction of the forward shock in an interstellar medium without any energy injection. The shallow-decay phase between 2000 and 3 × 10 4 s could be a result of the external shock in a wind-type medium with an energy injection under the condition of νo <ν c <ν x. However, the constraint of the spectral region is not consistent with the multiband observations. For this shallow-decay phase, other models are also possible, such as energy injection with evolving microphysical parameters, a jet viewed off-axis, etc.

Molecular Gas and Star-formation in Low Surface Brightness Galaxies

We have obtained CO(J=2-1) spectra of nine face-on low surface brightness galaxies(LSBGs) using the JCMT 15-meter telescope and observed Ha images using the 2.16-meter telescope of NAOC. As no CO has been detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) x 10^7 Msun. Their star formation rates are mainly lower than 0.4 Msun/yr and star formation efficiencies are lower than 1.364 x 10^10 /yr. Our results show that the absence of molecular gas content is the direct reason for the low star formation rate. The low star formation efficiency probably resulted from the low efficiency of HI gas transforming to H2 gas.

An Hα Imaging Survey of the Low-surface-brightness Galaxies Selected from the Fall Sky Region of the 40% ALFALFA H i Survey

We present the observed H

The LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) in the Southern Galactic Cap. I. The Spectroscopic Redshift Catalog

\alpha

FGK 22 μm excess stars in LAMOST DR2 stellar catalog

flux and derived star formation rates (SFRs) for a fall sample of low

A New Serial-direction Trail Effect in CCD Images of the Lunar-based Ultraviolet Telescope

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The LAMOST Complete Spectroscopic Survey of Pointing Area at Southern Galactic Cap

surface

The debris disk candidates: eleven 24 μm excess stars in the Spitzer SWIRE fields

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The stellar masses of galaxies from the 3.4 μm band of the WISE All-Sky Survey

brightness galaxies (LSBGs). The sample is selected from the fall sky region of the 40