arXiv subjects

H. -B. Yuan

Publications and source records attributed to H. -B. Yuan.

26 records · Page 2Linked to original sources

arXiv2014

A three dimensional extinction map of the Galactic Anticentre from multi-band photometry

We present a three dimensional extinction map in $r$ band. The map has a spatial angular resolution, depending on latitude, between 3 -- 9\,arcmin and covers the entire XSTPS-GAC survey area of over 6,000\,$\rm deg^2$ for Galactic longitude $\rm 140 \leq$ $l$ $ \leq 220°$ and latitude $\rm -40\leq$ $b$ $ \leq 40°$. By cross-matching the photometric catalog of the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) with those of 2MASS and WISE, we have built a multi-band photometric stellar sample of about 30 million stars and applied spectral energy distribution (SED) fitting to the sample. By combining photometric data from the optical to the near-infrared, we are able to break the degeneracy between the intrinsic stellar colours and the amounts of extinction by dust grains for stars with high photometric accuracy, and trace the extinction as a function of distance for low Galactic latitude and thus highly extincted regions. This has allowed us to derive the best-fit extinction and distance information of more than 13 million stars, which are used to construct the three dimensional extinction map. We have also applied a Rayleigh-Jeans colour excess (RJCE) method to the data using the 2MASS and WISE colour $(H-W2)$. The resulting RJCE extinction map is consistent with the integrated two dimensional map deduced using the best-fit SED algorithm. However for individual stars, the amounts of extinction yielded by the RJCE method suffer from larger errors than those given by the best-fit SED algorithm.

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arXiv2014

RR Lyrae in XSTPS: The halo density profile in the North Galactic Cap

We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XDSS). The area we consider is located in the North Galactic Cap, covering 376.75 sq deg at RA $\approx$ 150 deg and Dec $\approx$ 27 deg down to a magnitude limit of i $\approx$ 19. Using the variability information afforded by the multi-epoch nature of our XDSS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them and estimate the detection efficiency. The majority of our candidates have more than 12 observations and for these we are able to calculate periods. These also allows us to estimate our contamination level, which we predict is between 30% to 40%. Finally we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the South Galactic Cap using the Watkins et al. (2009) and Sesar et al. (2010) RRL data-sets, after accounting for possible contamination in our data-set from Sagittarius stream members. We consider non-spherical double power law models of the halo density profile and again find agreement with literature data-sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material.

astro-ph.GA↗

arXiv2014

HST and LAMOST discover a dual active galactic nucleus in J0038+4128

We report the discovery of a kiloparsec-scale dual active galactic nucleus (AGN) in J0038+4128. From the Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC2) images, we find two optical nuclei with a projection separation of 4.7 kpc (3.44 arcsec). The southern component (J0038+4128S) is spectroscopically observed with the HST Goddard High Resolution Spectrograph in the UV range and is found to be a Seyfert 1 galaxy with a broad Ly alpha emission line. The northern component (J0038+4128N) is spectroscopically observed during the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (also named the Guoshoujing Telescope) pilot survey in the optical range. The observed line ratios as well as the consistency of redshift of the nucleus emission lines and the host galaxy's absorption lines indicate that J0038+4128N is a Seyfert 2 galaxy with narrow lines only. These results thus confirm that J0038+4128 is a Seyfert 1-Seyfert 2 AGN pair. The HST WFPC2 F336W/U-band image of J0038+4128 also reveals for the first time for a dual AGN system two pairs of bi-symmetric arms, as are expected from the numerical simulations of such system. Being one of a few confirmed kiloparsec-scale dual AGNs exhibiting a clear morphological structure of the host galaxies, J0038+4128 provides an unique opportunity to study the co-evolution of the host galaxies and their central supermassive black holes undergoing a merging process.

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arXiv2013

Spectroscopic Observations of Planetary Nebulae in the Northern Spur of M31

We present spectroscopy of three planetary nebulae (PNe) in the Northern Spur of the Andromeda Galaxy (M31) obtained with the Double Spectrograph on the 5.1 m Hale Telescope at the Palomar Observatory. The samples are selected from the observations of Merrett et al. Our purpose is to investigate formation of the substructures of M31 using PNe as a tracer of chemical abundances. The [O III] 4363 auroral line is detected in the spectra of two objects, enabling temperature determinations. Ionic abundances are derived from the observed collisionally excited lines, and elemental abundances of nitrogen, oxygen, and neon as well as sulphur and argon are estimated. Correlations between oxygen and the alpha-element abundance ratios are studied, using our sample and the M31 disk and bulge PNe from the literature. In one of the three PNe, we observed relatively higher oxygen abundance compared to the disk sample in M31 at similar galactocentric distances. The results of at least one of the three Northern Spur PNe might be in line with the proposed possible origin of the Northern Spur substructure of M31, i.e. the Northern Spur is connected to the Southern Stream and both substructures comprise the tidal debris of the satellite galaxies of M31.

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arXiv2013

LSS-GAC - A LAMOST Spectroscopic Survey of the Galactic Anti-center

As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC) will survey a significant volume of the Galactic thin/thick disks and halo in a contiguous sky area of ~ 3,400sq.deg., centered on the Galactic anti-center (|b| <= 30°, 150 <= l <= 210°), and obtain λλ3800--9000 low resolution (R ~ 1,800) spectra for a statistically complete sample of >= 3M stars of all colors, uniformly and randomly selected from (r, g - r) and (r, r - i) Hess diagrams obtained from a CCD imaging photometric survey of ~ 5,400sq.deg. with the Xuyi 1.04/1.20 m Schmidt Telescope, ranging from r = 14.0 to a limiting magnitude of r = 17.8 (18.5 for limited fields). The survey will deliver spectral classification, radial velocity Vr and stellar parameters (effective temperature Teff, surface gravity log g and metallicity [Fe/H]) for millions of Galactic stars. Together with Gaia which will provide accurate distances and tangential velocities for a billion stars, the LSS-GAC will yield a unique dataset to study the stellar populations, chemical composition, kinematics and structure of the disks and their interface with the halo, identify streams of debris of tidally disrupted dwarf galaxies and clusters, probe the gravitational potential and dark matter distribution, map the 3D distribution of interstellar dust extinction, search for rare objects (e.g. extremely metal-poor or hyper-velocity stars), and ultimately advance our understanding of the assemblage of the Milky Way and other galaxies and the origin of regularity and diversity of their properties. ... (abridged)

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arXiv2012

Atmospheric Extinction Coefficients and Night Sky Brightness At the Xuyi Observational Station

We present measurements of the optical broadband atmospheric extinction coefficients and the night sky brightness at the Xuyi Observational Station of Purple Mountain Observatory (PMO). The measurements are based on CCD imaging data taken in the Sloan Digital Sky Survey g, r and i bands with the Xuyi 1.04/1.20m Schmidt Telescope for the Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC), the photometric part of the Digital Sky Survey of the Galactic Anti-center (DSS-GAC). The data were collected in more than 130 winter nights from 2009 to 2011. We find that the atmospheric extinction coefficients for the g, r and i bands are 0.70, 0.55 and 0.38 mag/airmass, respectively, based on observations taken in several photometric nights. The night sky brightness determined from images of good quality has median val- ues of 21.7, 20.8 and 20.0 mag/arcsec2 and reaches 22.1, 21.2 and 20.4 mag/arcsec2 under the best observing conditions for the g, r and i bands, respectively. The relatively large extinction coefficients compared with other good astronomical observing sites are mainly due to the relatively low elevation (i.e. 180 m) and high humidity of the Station.

astro-ph.IM↗

arXiv2010

Three-dimensional chemically homogeneous and bi-abundance photoionization models of the "super-metal-rich" planetary nebula NGC 6153

Deep spectroscopy of the planetary nebula (PN) NGC\,6153 shows that its heavy element abundances derived from optical recombination lines (ORLs) are ten times higher than those derived from collisionally excited lines (CELs), and points to the existence of H-deficient inclusions embedded in the diffuse nebula. In this study, we have constructed chemically homogeneous and bi-abundance three-dimensional photoionization models, using the Monte Carlo photoionization code {\sc mocassin}. We attempt to reproduce the multi-waveband spectroscopic and imaging observations of NGC\,6153, and investigate the nature and origin of the postulated H-deficient inclusions, as well as their impacts on the empirical nebular analyses assuming a uniform chemical composition. Our results show that chemically homogeneous models yield small electron temperature fluctuations and fail to reproduce the strengths of ORLs from C, N, O and Ne ions. In contrast, bi-abundance models incorporating a small amount of metal-rich inclusions ($\sim 1.3$ per cent of the total nebular mass) are able to match all the observations within the measurement uncertainties. The metal-rich clumps, cooled down to a very low temperature ($\sim 800$~K) by ionic infrared fine-structure lines, dominate the emission of heavy element ORLs, but contribute almost nil to the emission of most CELs. We find that the abundances of C, N, O and Ne derived empirically from CELs, assuming a uniform chemical composition, are about 30 per cent lower than the corresponding average values of the whole nebula, including the contribution from the H-deficient inclusions. Ironically, in the presence of H-deficient inclusions, the traditional standard analysis of the optical helium recombination lines, assuming a chemically homogeneous nebula, overestimates the helium abundance by 40 per cent.

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arXiv2009

Electron Temperatures of Planetary Nebulae Determined from the He I Discontinuities

We have used the He I discontinuities at 3421A to determine the electron temperatures, designated Te(He I), for a sample of five Galactic planetary nebulae (PNe). We compared Te(He I) with the electron temperatures derived from the hydrogen Balmer jump at 3646A, designated Te(H I), and found that Te(He I) are generally lower than Te(H I). There are two possible interpretations, a) the presence of substantial He+2 zone, or b) the presence of hydrogen-deficient cold clumps within diffuse nebulae. A series of photoionization models were constructed to test the two scenarios. We found that the observed Te(He I)/Te(H I) discrepancies are beyond the predictions of chemically homogeneous models. Our modelling shows that the presence of a small amount of hydrogen-deficient inclusions seems to be able to reproduce the observed intensities of He I discontinuities. We stress the value of He I discontinuities in investigating nebular physical conditions. Albeit with some observational and technical limitations, He I discontinuities should be considered in future modelling work.

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