arXiv subjects

Yang Huang

Publications and source records attributed to Yang Huang.

At least 307 records · Page 17Linked to original sources

arXiv2015

The LAMOST Survey of Background Quasars in the Vicinity Fields of the M 31 and M 33 - III. Results from the 2013 Regular Survey

In this work, we report new quasars discovered in the vicinity fields of the Andromeda (M31) and Triangulum (M33) galaxies with the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope, also named Guoshoujing Telescope) during the 2013 observational season, the second year of Regular Survey. In total, 1330 new quasars are discovered in an area of $\sim$133 deg$^2$ around M31 and M33. With $i$ magnitudes ranging from 14.79 to 20.0, redshifts from 0.08 to 4.85, the 1330 new quasars represent a significant increase of the number of identified quasars in the vicinity fields of M31 and M33. Up to the moment, there are in total 1870 quasars discovered by LAMOST in this area (see also Huo et al. 2010, 2013). The much enlarged sample of known quasars in this area can potentially be utilized to construct a precise astrometric reference frame for the measurement of the minute proper motions of M31, M33 and the associated substructures, vital for the understanding of the formation and evolution of M31, M33 and the Local Group of galaxies.Meanwhile, amongst the sample, there are in total 45, 98 and 225 quasars with $i$ magnitudes brighter than 17.0, 17.5 and 18.0 respectively. In the aforementioned brightness bins, 15, 35 and 84 quasars are reported here for the first time, 6, 21 and 81 are reported in Huo et al. (2010, 2013), while 0, 1 and 6 are from the Sloan Digital Sky Survey, and 24, 41 and 54 are from the NED database. These bright quasars provide an invaluable sample for the kinematics and chemistry study of the interstellar/intergalactic medium of the Local Group.

astro-ph.GA↗

arXiv2015

On the metallicity gradients of the Galactic disk as revealed by LSS-GAC red clump stars

Using a sample of over 70, 000 red clump (RC) stars with $5$-$10$% distance accuracy selected from the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC), we study the radial and vertical gradients of the Galactic disk(s) mainly in the anti-center direction, covering a significant disk volume of projected Galactocentric radius $7 \leq R_{\rm GC} \leq 14$ kpc and height from the Galactic midplane $0 \leq |Z| \leq 3$ kpc. Our analysis shows that both the radial and vertical metallicity gradients are negative across much of the disk volume probed, and exhibit significant spatial variations. Near the solar circle ($7 \leq R_{\rm GC} \leq 11.5$ kpc), the radial gradient has a moderately steep, negative slope of $-0.08$ dex kpc$^{-1}$ near the midplane ($|Z| < 0.1$ kpc), and the slope flattens with increasing $|Z|$. In the outer disk ($11.5 < R_{\rm GC} \leq 14$ kpc), the radial gradients have an essentially constant, much less steep slope of $-0.01$ dex kpc $^{-1}$ at all heights above the plane, suggesting that the outer disk may have experienced an evolution path different from that of the inner disk. The vertical gradients are found to flatten largely with increasing $R_{\rm GC}$. However, the vertical gradient of the lower disk ($0 \leq |Z| \leq 1$ kpc) is found to flatten with $R_{\rm GC}$ quicker than that of the upper disk ($1 < |Z| \leq 3$ kpc). Our results should provide strong constraints on the theory of disk formation and evolution, as well as the underlying physical processes that shape the disk (e.g. gas flows, radial migration, internal and external perturbations).

astro-ph.GA↗

arXiv2015

Joint Wireless Information and Power Transfer for an Autonomous Multiple Antenna Relay System

Considering a three-node multiple antenna relay system, this paper proposes a two-phase amplify-and-forward (AF) relaying protocol, which enables the autonomous relay to simultaneously harvest wireless power from the source information signal and from an energy signal conveyed by the destination. We first study this energy-flow-assisted (EFA) relaying in a single-input single-output (SISO) relay system and aim at maximizing the rate. By transforming the optimization problem into an equivalent convex form, a global optimum can be found. We then extend the protocol to a multiple antenna relay system. The relay processing matrix is optimized to maximize the rate. The optimization problem can be efficiently solved by eigenvalue decomposition, after linear algebra manipulation. It is observed that the benefits of the energy flow are interestingly shown only in the multiple antenna case, and it is revealed that the received information signal and the energy leakage at the relay can be nearly separated by making use of the signal space, such that the desired signal can be amplified with a larger coefficient.

cs.IT↗

arXiv2015

Joint Wireless Information and Power Transfer in a Three-Node Autonomous MIMO Relay Network

This paper investigates a three-node amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network, where an autonomous relay harvests power from the source information flow and is further helped by an energy flow in the form of a wireless power transfer (WPT) at the destination. An energy-flow-assisted two-phase relaying scheme is proposed, where a source and relay joint optimization is formulated to maximize the rate. By diagonalizing the channel, the problem is simplified to a power optimization, where a relay channel pairing problem is solved by an ordering operation. The proposed algorithm, which iteratively optimizes the relay and source power, is shown to converge. Closed-form solutions can be obtained for the separate relay and source optimizations. Besides, a two-phase relaying without energy flow is also studied. Simulation results show that the energy-flow-assisted scheme is beneficial to the rate enhancement, if the transmit power of the energy flow is adequately larger than that of the information flow. Otherwise, the scheme without energy flow would be preferable.

cs.IT↗

arXiv2015

Stellar loci III: Photometric metallicities for half million FGK stars of Stripe 82

We develop a method to estimate photometric metallicities by simultaneously fitting the dereddened colors u-g, g-r, r-i and i-z from the SDSS with those predicted by the metallicity-dependent stellar loci. The method is tested with a spectroscopic sample of main-sequence stars in Stripe 82 selected from the SDSS DR9 and three open clusters. With 1 per cent photometry, the method is capable of delivering photometric metallicities precise to about 0.05, 0.12, and 0.18 dex at metallicities of 0.0, -1.0, and -2.0, respectively, comparable to the precision achievable with low-resolution spectroscopy at a signal-to-noise ratio of 10. We apply this method to the re-calibrated Stripe 82 catalog and derive metallicities for about 0.5 million stars of colors 0.3 < g-i < 1.6 mag and distances between 0.3 -- 18 kpc. Potential systematics in the metallicities thus derived, due to the contamination of giants and binaries, are investigated. Photometric distances are also calculated. About 91, 72, and 53 per cent of the sample stars are brighter than r = 20.5, 19.5, and 18.5 mag, respectively. The median metallicity errors are around 0.19, 0.16, 0.11, and 0.085 dex for the whole sample, and for stars brighter than r = 20.5, 19.5, and 18.5 mag, respectively. The median distance errors are 8.8, 8.4, 7.7, and 7.3 per cent for the aforementioned four groups of stars, respectively. The data are publicly available. Potential applications of the data in studies of the distribution, (sub)structure, and chemistry of the Galactic stellar populations, are briefly discussed. The results will be presented in future papers.

astro-ph.GA↗

arXiv2015

Determination of the Local Standard of Rest using the LSS-GAC DR1

We re-estimate the peculiar velocity of the Sun with respect to the local standard of rest using a sample of local stars within 600 pc of the Sun, selected from the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC). The sample consists of 94332 FGK main-sequence stars with well-determined radial velocities and atmospheric parameters. To derive the LSR, two independent analyses are applied to the data. Firstly, we determine the solar motion by comparing the observed velocity distribution to that generated with the analytic formulism of Schonrich & Binney that has been demonstrated to show excellent agreement with rigorous torus-based dynamics modelling by Binney & McMillan. Secondly, we propose that cold populations of thin disc stars, selected by applying an orbital eccentricity cut, can be directly used to determine the LSR without the need of asymmetric drift corrections. Both approaches yield consistent results of solar motion in the direction of Galactic rotation, V_sun, that are much higher than the standard value adopted hitherto, derived from Stromgren's equation. The newly deduced values of V_sun are 1-2 km/s smaller than the more recent estimates derived from the Geneva-Copenhagen Survey sample of stars in the solar neighbourhood (within 100 pc). We attribute the small difference to the presence of several well-known moving groups in the GCS sample that, fortunately, hardly affect the LSS-GAC sample. The newly derived radial and vertical components of the solar motion agree well with the previous studies. In addition, for all components of the solar motion, the values yielded by stars of different spectral types in the LSS-GAC sample are consistent with each other, suggesting that the local disk is well relaxed and that the LSR reported in the current work is robust. Our final recommended LSR is, (U,V,W)_sun = (7.01+/-0.20, 10.13+/-0.12, 4.95+/-0.09) km/s.

astro-ph.GA↗

arXiv2014

Relative Flux Calibration of the LAMOST Spectroscopic Survey of the Galactic Anti-center

We have developed and implemented an iterative algorithm of flux calibration for the LAMOST Spectroscopic Survey of the Galactic anti-center (LSS-GAC). For a given LSS-GAC plate, the spectra are first processed with a set of nominal spectral response curves (SRCs) and used to derive initial stellar atmospheric parameters (effective temperature $T_{\rm eff}$, surface gravity log\,$g$ and metallicity [Fe/H]) as well as dust reddening $E(B-V)$ of all targeted stars. For each of the sixteen spectrographs, several F-type stars of good signal-to-noise ratios (SNRs) are then selected as flux standard stars for further, iterative spectral flux calibration. Comparison of spectrophotometric colours, deduced from the flux-calibrated spectra, with the photometric measurements yields average differences of 0.02$\pm$0.07 and $-$0.04$\pm$0.09\,mag for the $(g-r)$ and $(g-i)$, respectively. The relatively large negative offset in $(g-i)$ is due to the fact that we have opted not to correct for the telluric bands, most notably the atmospheric A-band in the wavelength range of $i$-band. Comparison of LSS-GAC multi-epoch observations of duplicate targets indicates that the algorithm has achieved an accuracy of about 10 per cent in relative flux calibration for the wavelength range 4000 -- 9000\,Å. The shapes of SRC deduced for the individual LAMOST spectrographs are found to vary by up to 30 per cent for a given night, and larger for different nights, indicating that the derivation of SRCs for the individual plates is essential in order to achieve accurate flux calibration for the LAMOST spectra.

astro-ph.GA↗

arXiv2014

The LAMOST Stellar Parameter Pipeline at Peking University --- LSP3

We introduce the LAMOST Stellar Parameter Pipeline at Peking University --- LSP3, developed and implemented for the determinations of radial velocity $V_{\rm r}$ and stellar atmospheric parameters (effective temperature $T_{\rm eff}$, surface gravity log\,$g$, metallicity [Fe/H]) for the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC). We describe the algorithms of LSP3 and examine the accuracy of parameters yielded by it. The precision and accuracy of parameters yielded are investigated by comparing results of multi-epoch observations and of candidate members of open and globular clusters, with photometric calibration, as well as with independent determinations available from a number of external databases, including the PASTEL archive, the APOGEE, SDSS and RAVE surveys, as well as those released in the LAMOST DR1. The uncertainties of LSP3 parameters are characterized and quantified as a function of the spectral signal-to-noise ratio (SNR) and stellar atmospheric parameters. We conclude that the current implementation of LSP3 has achieved an accuracy of 5.0\,km\,s$^{-1}$, 150\,K, 0.25\,dex, 0.15\,dex for the radial velocity, effective temperature, surface gravity and metallicity, respectively, for LSS-GAC spectra of FGK stars of SNRs per pixel higher than 10. The LSP3 has been applied to over a million LSS-GAC spectra collected hitherto. Stellar parameters yielded by the LSP3 will be released to the general public following the data policy of LAMOST, together with estimates of the interstellar extinction $E(B-V)$ and stellar distances, deduced by combining spectroscopic and multi-band photometric measurements using a variety of techniques.

astro-ph.GA↗

arXiv2014

LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC): target selection and the first release of value-added catalogues

As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anti-centre (LSS-GAC) aims to survey a significant volume of the Galactic thin/thick discs and halo for a contiguous sky area of over 3,400 deg$^2$ centred on the Galactic anti-centre ($|b| \leq 30^{\circ}$, $150 \leq l \leq 210^{\circ}$), and obtain $λλ$3700 -- 9000 low resolution ($R \sim 1,800$) spectra for a statistically complete sample of $\sim 3$\,M stars of all colours down to a limiting magnitued of $r$ $\sim$ 17.8\,mag (to 18.5\,mag for limited fields). Together with Gaia, the LSS-GAC will yield a unique dataset to advance our understanding of the structure and assemblage history of the Galaxy, in particular its disk(s). In addition to the main survey, the LSS-GAC will also target hundreds of thousands objects in the vicinity fields of M\,31 and M\,33 and survey a significant fraction (over a million) of randomly selected very bright stars (VB; $r \le 14$ mag) in the northern hemisphere. During the Pilot and the first year Regular Surveys of LAMOST, a total of 1,042,586 [750,867] spectra of a signal to noise ratio S/N(7450Å) $\ge$ 10 [S/N(4650Å) $\ge$ 10] have been collected. In this paper, we present a detailed description of the target selection algorithm, survey design, observations and the first data release of value-added catalogues (including radial velocities, effective temperatures, surface gravities, metallicities, values of interstellar extinction, distances, proper motions and orbital parameters) of the LSS-GAC.

astro-ph.SR↗

arXiv2014

Stellar color regression: a spectroscopy based method for color calibration to a few mmag accuracy and the recalibration of Stripe 82

In this paper, we propose a spectroscopy based Stellar Color Regression (SCR) method to perform accurate color calibration for modern imaging surveys, taking advantage of millions of stellar spectra now available. The method is straightforward, insensitive to systematic errors in the spectroscopically determined stellar atmospheric parameters, applicable to regions that are effectively covered by spectroscopic surveys, and capable of delivering an accuracy of a few millimagnitudes for color calibration. As an illustration, we have applied the method to the SDSS Stripe 82 data (Ivezic et al; I07 hereafter). With a total number of 23,759 spectroscopically targeted stars, we have mapped out the small but strongly correlated color zero point errors present in the photometric catalog of Stripe 82, and improve the color calibration by a factor of 2 -- 3. Our study also reveals some small but significant magnitude dependence errors in z-band for some CCDs. Such errors are likely to be present in all the SDSS photometric data. Our results are compared with those from a completely independent test based on the intrinsic colors of red galaxies presented by I07. The comparison as well as other tests shows that the SCR method has achieved a color calibration internally consistent at a level of about 5 mmag in u-g, 3 mmag in g-r, and 2 mmag in r-i and i-z, respectively. Given the power of the SCR method, we discuss briefly the potential benefits by applying the method to existing, on-going, and up-coming imaging surveys.

astro-ph.IM↗

arXiv2014

Stellar loci I. Metallicity dependence and intrinsic widths

Stellar loci are widely used for selection of interesting outliers, reddening determinations, and calibrations. However, hitherto the dependence of stellar loci on metallicity has not been fully explored and their intrinsic widths are unclear. In this paper, by combining the spectroscopic and re-calibrated imaging data of the SDSS Stripe 82, we have built a large, clean sample of dwarf stars with accurate colors and well determined metallicities to investigate the metallicity dependence and intrinsic widths of the SDSS stellar loci. Typically, one dex decrease in metallicity causes 0.20 and 0.02 mag decrease in colors u-g and g-r, and 0.02 and 0.02 mag increase in colors r-i and i-z, respectively. The variations are larger for metal-rich stars than for metal-poor ones, and for F/G/K stars than for A/M ones. Using the sample, we have performed two dimensional polynomial fitting to the u-g, g-r, r-i, and i-z colors as a function of color g-i and metallicity [Fe/H]. The residuals, at the level of 0.029, 0.008, 0.008 and 0.011 mag for the u-g, g-r, r-i, and i-z colors, respectively can be fully accounted for by the photometric errors and metallicity uncertainties, suggesting that the intrinsic widths of the loci are at maximum a few mmag. The residual distributions are asymmetric, revealing that a significant fraction of stars are binaries. In a companion paper, we will present an unbiased estimate of the binary fraction for field stars. Other potential applications of the metallicity dependent stellar loci are briefly discussed.

astro-ph.SR↗

arXiv2014

Stellar loci II. a model-free estimate of the binary fraction for field FGK stars

We propose a Stellar Locus OuTlier (SLOT) method to determine the binary fraction of main-sequence stars statistically. The method is sensitive to neither the period nor mass-ratio distributions of binaries, and able to provide model-free estimates of binary fraction for large numbers of stars of different populations in large survey volumes. We have applied the SLOT method to two samples of stars from the SDSS Stripe 82, constructed by combining the re-calibrated SDSS photometric data with respectively the spectroscopic information from the SDSS and LAMOST surveys. For the SDSS spectroscopic sample, we find an average binary fraction for field FGK stars of $41%\pm2%$. The fractions decrease toward late spectral types, and are respectively $44%\pm5%$, $43%\pm3%$, $35%\pm5%$, and $28%\pm6%$ for stars of $g-i$ colors between 0.3 -- 0.6, 0.6 -- 0.9, 0.9 -- 1.2, and 1.2 - 1.6\,mag. A modest metallicity dependence is also found. The fraction decreases with increasing metallicity. For stars of [Fe/H] between $-0.5$ - 0.0, $-1.0$ - $-0.5$, $-1.5$ - $-1.0$, and $-2.0$ - $-1.5$\,dex, the inferred binary fractions are $37%\pm3%$, $39%\pm3%$, $50%\pm9%$, and $53%\pm20%$, respectively. We have further divided the sample into stars from the thin disk, the thick disk, the transition zone between them, and the halo. The results suggest that the Galactic thin and thick disks have comparable binary fractions, whereas the Galactic halo contains a significantly larger fraction of binaries. Applying the method to the LAMOST spectroscopic sample yields consistent results. Finally, other potential applications and future work with the method are discussed.

astro-ph.SR↗

arXiv2014

On Legendrian foliations in contact manifolds II: Deformation theory

Using the structural theorems developed in [Hua13], we study the deformation theory of coisotropic submanifolds in contact manifolds, under the assumption that the characteristic foliation is nonsingular. In the "middle" dimensions, we find an interesting relationship with foliation theory. Some elementary applications of contact geometry in foliation theory are explored.

math.SG↗

arXiv2014

Non-existence of certain singularities in Legendrian foliations

In this paper we show that the singular locus of a Legendrian foliation as defined in [Hua13] is a compact submanifold whose connected components are of codimension at most two. As a consequence, given any closed $(n+1)$-dimensional coisotropic submanifold $W$ in a contact $(2n+1)$-manifold, the contact structure in a sufficiently small neighborhood of $W$ is uniquely determined by the characteristic (Legendrian) foliation.

math.SG↗

arXiv2014

A topological grading on bordered Heegaard Floer homology

In this paper, we construct a canonical grading on bordered Heegaard Floer homology by homotopy classes of nonvanishing vector fields. This grading is a generalization of our construction of an absolute grading on Heegaard Floer homology and it extends the well-known grading with values in a noncommutative group defined by Lipshitz-Ozsváth-Thurston.

math.GT↗

arXiv2013

On Legendrian foliations in contact manifold I: Singularities and neighborhood theorems

In this note we study several aspects of coisotropic submanifolds of a contact manifold. In particular we give a structure theorem for the singularity of the characteristic foliation of a coisotropic submanifold. Moreover we establish the existence and uniqueness results of germs of contact structures near Legendrian foliations, which is a special case of coisotropic submanifold. This note can be thought of as an attempt to generalize the study of surfaces in three-dimensional contact geometry to higher dimensions.

math.SG↗

arXiv2013

Mapping the three-dimensional multi-band extinction and diffuse interstellar bands in the Milky Way with LAMOST

With modern large scale spectroscopic surveys, such as the SDSS and LSS-GAC, Galactic astronomy has entered the era of millions of stellar spectra. Taking advantage of the huge spectroscopic database, we propose to use a "standard pair" technique to a) Estimate multi-band extinction towards sightlines of millions of stars; b) Detect and measure the diffuse interstellar bands in hundreds of thousands SDSS and LAMOST low-resolution spectra; c) Search for extremely faint emission line nebulae in the Galaxy; and d) Perform photometric calibration for wide field imaging surveys. In this contribution, we present some results of applying this technique to the SDSS data, and report preliminary results from the LAMOST data.

astro-ph.GA↗

arXiv2013

1/4-Pinched Contact Sphere Theorem

Given a closed contact 3-manifold with a compatible Riemannian metric, we show that if the sectional curvature is 1/4-pinched, then the contact structure is universally tight. This result improves the Contact Sphere Theorem in [EKM12], where a 4/9-pinching constant was imposed. Some tightness results on positively curved contact open 3-manifold are also discussed.

math.DG↗