arXiv subjects

Xiao-Feng Wang

Publications and source records attributed to Xiao-Feng Wang.

21 records · Page 2Linked to original sources

arXiv2016

The underlying driver for the \civ Baldwin effect in QSOs with $0<z<5$

Broad emission lines is a prominent property of type I quasi-stellar objects (QSOs). The origin of the Baldwin effect for \civ $\lambda1549~$Å broad emission lines, i.e., the luminosity dependence of the \civ equivalent width (EW), is not clearly established. Using a sample of 87 low-$z$ Palomar-Green (PG) QSOs and 126 high-$z$ QSOs across the widest possible ranges of redshift ($0<z<5$), we consistently calculate \hb-based single-epoch supermassive black hole (SMBH) mass and the Eddington ratio to investigate the underlying driver of the \civ Baldwin effect. An empirical formula to estimate the host fraction in the continuum luminosity at 5100 Å is presented and used in \hb-based \mbh calculation for low-$z$ PG QSOs. It is found that, for low-$z$ PG QSOs, the Eddington ratio has strong correlations with PC1 and PC2 from the principal component analysis, and \civ EW has a strong correlation with the optical \feii strength or PC1. Expanding the luminosity range with high-$z$ QSOs, it is found that \civ Baldwin effect exists in our QSOs sample. Using \hb-based single-epoch SMBH mass for our QSOs sample, it is found that \civ EW has a strong correlation with the Eddington ratio, which is stronger than that with the SMBH mass. It implies that the Eddington ratio seems to be a better underlying parameter than the SMBH mass to drive the \civ Baldwin effect.

astro-ph.GA↗

arXiv2012

The Photometric System of Tsinghua-NAOC 80-cm Telescope at NAOC Xinglong Observatory

Tsinghua-NAOC (National Astronomical Observatories of China) Telescope (hereafter, TNT) is an 80-cm Cassegrain reflecting telescope located at Xinglong bservatory of NAOC, with 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 in this paper a systematic test and analysis of the photometric performance of this telescope. Based on the calibration observations on twelve photometric nights, spanning the period from year 2004 to year 2012, we derived an accurate transformation relationship 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 Xinglong Observatory may become gradually worse over the period from year 2005 to year 2012 (e.g., $\sim$21.4 mag vs. $\sim$20.1 mag in the V band).

astro-ph.IM↗

arXiv2009

Deconvolution density estimation with heteroscedastic errors using SIMEX

In many real applications, the distribution of measurement error could vary with each subject or even with each observation so the errors are heteroscedastic. In this paper, we propose a fast algorithm using a simulation-extrapolation (SIMEX) method to recover the unknown density in the case of heteroscedastic contamination. We show the consistency of the estimator and obtain its asymptotic variance and then address the practical selection of the smoothing parameter. We demonstrate that, through a finite sample simulation study, the proposed method performs better than the Fourier-type deconvolution method in terms of integrated squared error criterion. Finally, a real data application is conducted to illustrate the use of the method.

math.ST↗