arXiv subjects

Zhen-Yu Wu

Publications and source records attributed to Zhen-Yu Wu.

At least 19 recordsLinked to original sources

arXiv2022

The Aligned Orbit of WASP-148b, the Only Known Hot Jupiter with a Nearby Warm Jupiter Companion, from NEID and HIRES

We present spectroscopic measurements of the Rossiter-McLaughlin effect for WASP-148b, the only known hot Jupiter with a nearby warm-Jupiter companion, from the WIYN/NEID and Keck/HIRES instruments. This is one of the first scientific results reported from the newly commissioned NEID spectrograph, as well as the second obliquity constraint for a hot Jupiter system with a close-in companion, after WASP-47. WASP-148b is consistent with being in alignment with the sky-projected spin axis of the host star, with $λ=-8^{\circ}.2^{{+8^{\circ}.7}}_{-9^{\circ}.7}$. The low obliquity observed in the WASP-148 system is consistent with the orderly-alignment configuration of most compact multi-planet systems around cool stars with obliquity constraints, including our solar system, and may point to an early history for these well-organized systems in which migration and accretion occurred in isolation, with relatively little disturbance. By contrast, previous results have indicated that high-mass and hot stars appear to more commonly host a wide range of misaligned planets: not only single hot Jupiters, but also compact systems with multiple super-Earths. We suggest that, to account for the high rate of spin-orbit misalignments in both compact multi-planet and isolated-hot-Jupiter systems orbiting high-mass and hot stars, spin-orbit misalignments may be caused by distant giant planet perturbers, which are most common around these stellar types.

astro-ph.EP↗

arXiv2022

Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No evidence for Temporal Variation of the Spin-Orbit Angle

We present 12 new transit light curves and 16 new out-of-transit radial velocity measurements for the XO-3 system. By modelling our newly collected measurements together with archival photometric and Doppler velocimetric data, we confirmed the unusual configuration of the XO-3 system, which contains a massive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric ($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \pm 0.00145\,$day) orbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\odot}$). Furthermore, we find no strong evidence for a temporal change of either $V\sin i_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit profile (and thus orbital angular momentum vector of XO-3b). We conclude that the discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\circ} \pm 15.0^{\circ}$ (Hebrard et al. 2008); $37.3^{\circ} \pm 3.7^{\circ}$ (Winn et al. 2009); $37.3^{\circ} \pm 3.0^{\circ}$ (Hirano et al. 2011)) may have stemmed from systematic noise sources.

astro-ph.EP↗

arXiv2022

New analysis of the fraction of observable nights at astronomical sites based on FengYun-2 satellite data

The fraction of observable nights is an essential parameter for selecting astronomical sites. In recent years, meteorological satellite data have played an essential role in recognising and providing statistics of observable nights. We present a method to estimate the fraction of observable nights based on the FengYun-2 series of geostationary meteorological satellites and weather records of multiple astronomical sites. We have calculated the fraction of observable nights at 27 sites in Indonesia and two astronomical sites in China to validate the method. The results derived from our method show good agreement with previous works. Furthermore, we have derived the yearly distribution of the fraction of observable nights above China, which indicates the area near 40$^{\circ}$N has more observable nights than other areas in China.

astro-ph.IM↗

arXiv2021

Transiting Exoplanet Monitoring Project (TEMP). VI. The Homogeneous Refinement of System Parameters for 39 Transiting Hot Jupiters with 127 New Light Curves

We present 127 new transit light curves for 39 hot Jupiter systems, obtained over the span of five years by two ground-based telescopes. A homogeneous analysis of these newly collected light curves together with archived spectroscopic, photometric, and Doppler velocimetric data using EXOFASTv2 leads to a significant improvement in the physical and orbital parameters of each system. All of our stellar radii are constrained to accuracies of better than 3\%. The planetary radii for 37 of our 39 targets are determined to accuracies of better than $5\%$. Compared to our results, the literature eccentricities are preferentially overestimated due to the Lucy-Sweeney bias. Our new photometric observations therefore allow for significant improvement in the orbital ephemerides of each system. Our correction of the future transit window amounts to a change exceeding $10\,{\rm min}$ for ten targets at the time of JWST's launch, including a $72\,{\rm min}$ change for WASP-56. The measured transit mid-times for both literature light curves and our new photometry show no significant deviations from the updated linear ephemerides, ruling out in each system the presence of companion planets with masses greater than $0.39 - 5.0\, rm M_{\oplus}$, $1.23 - 14.36\, \rm M_{\oplus}$, $1.65 - 21.18\, \rm M_{\oplus}$, and $0.69 - 6.75\, \rm M_{\oplus}$ near the 1:2, 2:3, 3:2, and 2:1 resonances with the hot Jupiters , respectively, at a confidence level of $\pm 1\,σ$. The absence of resonant companion planets in the hot Jupiter systems is inconsistent with the conventional expectation from disk migration.

astro-ph.EP↗

arXiv2021

Chemical abundances of three new Ba stars from the Keck/HIRES spectra

Based on high resolution, high signal-to-noise (S/N) ratio spectra from Keck/HIRES, we have determined abundances of 20 elements for 18 Ba candidates. The parameter space of these stars are in the range of 4880 $\leq$ $\rm{T_{eff}}$ $\leq$ 6050 K, 2.56 $\leq$ log $g$ $\leq$ 4.53 dex and -0.27 $\leq$ [Fe/H] $\leq$ 0.09 dex. It is found that four of them can be identified as Ba stars with [s/Fe] $>$ 0.25 dex (s: Sr, Y, Zr, Ba, La, Ce and Nd), and three of them are newly discovered, which includes two Ba giants (HD 16178 and HD 22233) and one Ba subgiant (HD 2946). Our results show that the abundances of $α$, odd and iron-peak elements (O, Na, Mg, Al, Si, Ca, Sc, Ti, Mn, Ni and Cu) for our program stars are similar to those of the thin disk, while the distribution of [hs/ls] (hs: Ba, La, Ce and Nd, ls: Sr, Y and Zr) ratios of our Ba stars is similar to those of the known Ba objects. None of the four Ba stars show clear enhancement in carbon including the known CH subgiant HD 4395. It is found that three of the Ba stars present clear evidences of hosting stellar or sub-stellar companions from the radial velocity data.

astro-ph.SR↗

arXiv2020

A catalogue of 74 new open clusters found in Gaia Data-Release 2

Based on astrometric data from Gaia DR2, we employ an unsupervised machine learning method to blindly search for open star clusters in the Milky Way within the Galactic latitude range of |b| < 20 degrees. In addition to 2,080 known clusters, 74 new open cluster candidates are found. In this work, we present the positions, apparent radii, parallaxes, proper motions and member stars of these candidates (https://cdsarc.u-strasbg.fr/ftp/vizier.submit//new_OC/). Meanwhile, to obtain the physical parameters of each candidate cluster, stellar isochrones are fit to the photometric data. The results show that the apparent radii and the observed proper motion dispersions of these new candidates are consistent with those of open clusters previously identified in Gaia DR2.

astro-ph.GA↗

arXiv2019

A neural document language modeling framework for spoken document retrieval

Recent developments in deep learning have led to a significant innovation in various classic and practical subjects, including speech recognition, computer vision, question answering, information retrieval and so on. In the context of natural language processing (NLP), language representations have shown giant successes in many downstream tasks, so the school of studies have become a major stream of research recently. Because the immenseness of multimedia data along with speech have spread around the world in our daily life, spoken document retrieval (SDR) has become an important research subject in the past decades. Targeting on enhancing the SDR performance, the paper concentrates on proposing a neural retrieval framework, which assembles the merits of using language modeling (LM) mechanism in SDR and leveraging the abstractive information learned by the language representation models. Consequently, to our knowledge, this is a pioneer study on supervised training of a neural LM-based SDR framework, especially combined with the pretrained language representation methods.

cs.CL↗

arXiv2018

Transiting Exoplanet Monitoring Project (TEMP). I. Refined System Parameters and Transit Timing Variations of HAT-P-29b

We report the photometry of six transits of the hot Jupiter HAT-P-29b obtained from 2013 October to 2015 January. We analyze the new light curves, in combination with the published photometric, and Doppler velocimetric, and spectroscopic measurements, finding an updated orbital ephemeris for the HAT-P-29 system, $T_{\rm C}[0]= 2456170.5494(15)\,[\rm{BJD_{TDB}}]$ and $P=5.723390(13) \,{\rm days}$. It is $17.63\,{\rm s}$ ($4.0\,σ$) longer than the previously published value, amounting to errors exceeding $2.5\,\rm{hrs}$ at the time of writing (on UTC 2018 June 1). The measured transit mid-times for HAT-P-29b show no compelling evidence of timing anomalies from a linear model, which rules out the presence of a perturbers with masses greater than $0.6$, $0.7$, $0.5$, and $0.4\,{\rm M_\oplus}$ near the $1:2$, $2:3$, $3:2$, and $2:1$ resonances with HAT-P-29b, respectively.

astro-ph.EP↗

arXiv2018

Transiting Exoplanet Monitoring Project (TEMP). IV. Refined System Parameters, Transit Timing Variations and Orbital Stability of the Transiting Planetary System HAT-P-25

We present eight new light curves of the transiting extra-solar planet HAT-P-25b obtained from 2013 to 2016 with three telescopes at two observatories. We use the new light curves, along with recent literature material, to estimate the physical and orbital parameters of the transiting planet. Specifically, we determine the mid-transit times (T$_{C}$) and update the linear ephemeris, T$_{C[0]}$=2456418.80996$\pm$0.00025 [$\mathrm{BJD}_\mathrm{TDB}$] and P=3.65281572$\pm$0.00000095 days. We carry out a search for transit timing variations (TTVs), and find no significant TTV signal at the $ΔT=$80 s-level, placing a limit on the possible strength of planet-planet interactions ($\mathrm{TTV_{G}}$). In the course of our analysis, we calculate the upper mass-limits of the potential nearby perturbers. Near the 1:2, 2:1, and 3:1 resonances with HAT-P-25b, perturbers with masses greater than 0.5, 0.3, and 0.5 $\mathrm{M_{\oplus}}$ respectively, can be excluded. Furthermore, based on the analysis of TTVs caused by light travel time effect (LTTE) we also eliminate the possibility that a long-period perturber exists with $M_{\rm p}> 3000 \,\mathrm{M_{J}}$ within $a=11.2\,{\rm AU}$ of the parent star.

astro-ph.EP↗

arXiv2017

Transiting Exoplanet Monitoring Project (TEMP). III. On the Relocation of the Kepler-9~b Transit

The Kepler-9 system harbors three known transiting planets. The system holds significant interest for several reasons. First, the outer two planets exhibit a period ratio that is close to a 2:1 orbital commensurability, with attendant dynamical consequences. Second, both planets lie in the planetary mass "desert" that is generally associated with the rapid gas agglomeration phase of the core accretion process. Third, there exist attractive prospects for accurately measuring both the sky-projected stellar spin-orbit angles as well as the mutual orbital inclination between the planets in the system. Following the original \textit{Kepler} detection announcement in 2010, the initially reported orbital ephemerides for Kepler-9~b and c have degraded significantly, due to the limited time base-line of observations on which the discovery of the system rested. Here, we report new ground-based photometric observations and extensive dynamical modeling of the system. These efforts allow us to photometrically recover the transit of Kepler-9~b, and thereby greatly improve the predictions for upcoming transit mid-times. Accurate ephemerides of this system are important in order to confidently schedule follow-up observations of this system, for both in-transit Doppler measurements as well as for atmospheric transmission spectra taken during transit.

astro-ph.EP↗

arXiv2016

SCUSS u-Band Emission as a Star-Formation-Rate Indicator

We present and analyze the possibility of using optical ${\it u}$-band luminosities to estimate star-formation rates (SFRs) of galaxies based on the data from the South Galactic Cap ${\it u }$ band Sky Survey (SCUSS), which provides a deep ${\it u}$-band photometric survey covering about 5000 $deg^2$ of the South Galactic Cap. Based on two samples of normal star-forming galaxies selected by the BPT diagram, we explore the correlations between ${\it u}$-band, H$α$, and IR luminosities by combing SCUSS data with the Sloan Digital Sky Survey (SDSS) and ${\it Wide}$-${\it field\ Infrared\ Survey\ Explorer}$ (${\it WISE}$). The attenuation-corrected ${\it u}$-band luminosities are tightly correlated with the Balmer decrement-corrected H$α$ luminosities with an rms scatter of $\sim$ 0.17 dex. The IR-corrected ${\it u }$ luminosities are derived based on the correlations between the attenuation of ${\it u}$-band luminosities and ${\it WISE}$ 12 (or 22) $μ$m luminosities, and then calibrated with the Balmer-corrected H$α$ luminosities. The systematic residuals of these calibrations are tested against the physical properties over the ranges covered by our sample objects. We find that the best-fitting nonlinear relations are better than the linear ones and recommended to be applied in the measurement of SFRs. The systematic deviations mainly come from the pollution of old stellar population and the effect of dust extinction; therefore, a more detailed analysis is needed in the future work.

astro-ph.GA↗

arXiv2012

Multicolor Photometry of the Nearby Galaxy Cluster A119

This paper presents multicolor optical photometry of the nearby galaxy cluster Abell 119 (z = 0:0442) with the Beijing-Arizona-Taiwan-Connecticut (BATC) system of 15 intermediate bands. Within the BATC viewing field of 58'* 58', there are 368 galaxies with known spectroscopic redshifts, including 238 member galaxies (called sample I). Based on the spectral energy distributions (SEDs) of 1376 galaxies brighter than iBATC = 19:5, photometric redshift technique and the color-magnitude relation of earlytype galaxies are applied to select faint member galaxies. As a result, 117 faint galaxies were selected as new member galaxies. Combined with sample I, an enlarged sample (called sample II) of 355 member galaxies is obtained. Spatial distribution and localized velocity structure for two samples demonstrate that A119 is a dynamically complex cluster with at least three prominent substructures in the central region within 1 Mpc. A large velocity dispersion for the central clump indicates a merging along the line of sight. No significant evidences for morphology and luminosity segregations are found in both samples. With the evolutionary synthesis model PEGASE, environmental effect on the star formation properties is confirmed. Faint galaxies in low-density region tend to have longer time scales of star formation, smaller mean stellar ages, and lower metallicities of interstellar medium, which is in agreement with the context of hierarchical cosmological scenario.

astro-ph.GA↗

arXiv2011

Independent determination of the systematic and random errors of the proper motions in the PPMXL catalog using quasars

Using a sample of 117053 quasars identified in the PPMXL catalog, the systematic errors of the proper motions in the PPMXL catalog are estimated independently as -2.0 and -2.1 mas yr$^{-1}$ in $μ_α\cosδ$ and $μ_δ$, respectively. For objects with SDSS $r$ magnitude between 16.0 and 21.0 mag and SDSS $g-r$ color between -0.4 and 1.2, there are no obvious magnitude and color dependence in the systematic errors of the proper motions in the PPMXL catalog. The random errors of the proper motions in the PPMXL catalog change from $\sim4.0$ to $\sim8.0$ mas yr$^{-1}$ along with the increase of the magnitude of the objects. No color dependence in the random errors of the proper motions in the PPMXL catalog is found. There are obvious right ascension $α$ dependence of the systematic errors in both components of the proper motions in the PPMXL catalog. For quasars with declination $δ>0$, the systematic errors of $μ_δ$ in the PPMXL catalog increase linearly with $δ$ with a slope of 0.07 mas yr$^{-1}$ deg$^{-1}$. For comparison, using a subsample of quasars identified both in the PPMXL and SDSS DR7 catalogs, the systematic errors of the USNO-SDSS proper motions in the SDSS DR7 catalog are derived as 0.9 and 0.5 mas yr$^{-1}$ in $μ_α\cosδ$ and $μ_δ$, respectively. There are no obvious magnitude, color, and $α$ dependence in the systematic errors of the USNO-SDSS proper motions. For quasars with declination $δ>0$, the systematic errors of $μ_δ$ in the SDSS DR7 catalog increase linearly with $δ$ with a slope of 0.03. The random errors of the USNO-SDSS proper motions change from $\sim2.5$ to $\sim6.0$ mas yr$^{-1}$ along with the change of the magnitude and color of the objects.

astro-ph.GA↗

arXiv2011

Orbits of nearby planetary nebulae and their interaction with the interstellar medium

We present and analyze the orbits of eight nearby planetary nebulae (PNs) using two different Galactic models. The errors of the derived orbital parameters are determined with a Monte Carlo method. Based on the derived orbital parameters, we find that Sh 2-216, DeHt 5, NGC 7293, A21, and Ton 320 belong to the thin-disk population, and PG 1034+001 and A31 belong to the thick-disk population. PuWe 1 probably belongs to the thick-disk population, but its population classification is very uncertain due to the large errors of its derived orbital parameters. The PN-ISM interactions are observed for the eight PNs in our sample. The position angles of the proper motions of the PNs are consistent with the directions of the PN-ISM interaction regions. The kinematic ages of PNs are much smaller than the time for them to cross the Galactic plane. Using the models of Borkowski et al. and Soker et al., the PN-ISM interaction can be used to derive the local density of ISM in the vicinity of evolved PNs. According to the three-dimensional hydrodynamic simulations of Wareing et al. (WZO), Sh 2-216, A21, and Ton 320 are in the WZO 3 stage, PG 1034+001 and NGC 7293 are in the WZO 1 stage, and PuWe 1 is in the WZO 2 stage.

astro-ph.GA↗

arXiv2011

Multicolor Photometry Study of the Galaxy Cluster A2589: Dynamics, Luminosity Function and Star Formation History

In this paper we present a multicolor photometry for A2589 ($z=0.0414$) with 15 intermediate bands in the Beijing-Arizona-Taiwan-Connecticut (BATC) system which covers an optical wavelength range from 3000 Å to 10000 Å. The spectral energy distributions (SEDs) for more than 5000 sources are achieved down to {\it V} $\sim$ 20 mag in about 1 deg$^{2}$ field. A2589 has been also covered by the Sloan Digital Sky Survey (SDSS) in photometric mode only. A cross-identification of the BATC-detected galaxies with the SDSS photometric catalog achieves 1199 galaxies brighter than $i=19.5$ mag, among which 68 member galaxies with known spectroscopic redshifts are found. After combining the SDSS five-band photometric data and the BATC SEDs, the technique of photometric redshift is applied to these galaxies for selecting faint member galaxies. The color-magnitude relation is taken as a further restriction of early-type cluster galaxies. As a result, 106 galaxies are newly selected as member galaxies. Spatial distribution of member galaxies shows a north-south elongation which agrees with the X-ray brightness profile and the orientation of central cD galaxy, NGC 7647. No substructures are detected on the basis of positions and radial velocities of cluster galaxies, indicating that A2589 is a well-relaxed system. The luminosity function of A2589 exhibits a peak at $M_{R} \sim -20$ mag and a dip at $M_{R} \sim -19 $ mag. The low-density outer regions are the preferred habitat of faint galaxies. With the evolutionary population synthesis model, PEGASE, the environmental effect on the star formation properties for 68 spectroscopically confirmed member galaxies is studied. The outlier faint galaxies tend to have longer time scales of star formation, shorter mean stellar ages, and lower metallicities of interstellar medium, which can be interpreted in the context of hierarchical cosmological scenario.

astro-ph.GA↗

arXiv2009

The orbits of open clusters in the Galaxy

We present and analyze kinematics and orbits for a sample of 488 open clusters in the Galaxy. The velocity ellipsoid for our present sample is derived as ($σ_{U}$, $σ_{V}$, $σ_{W})$=$(28.7$, 15.8, 11.0) km s$^{-1}$ which represents a young thin disc population. We also confirm that the velocity dispersions increase with the age of cluster subsample. The orbits of open clusters are calculated with three Galactic gravitational potential models. The errors of orbital parameters are also calculated considering the intrinsic variation of the orbital parameters and the effects of observational uncertainties. The observational uncertainties dominate the errors of derived orbital parameters. The vertical motions of clusters calculated using different Galactic disc models are rather different. The observed radial metallicity gradient of clusters is derived with a slope of $b=-0.070\pm0.011$ dex kpc$^{-1}$. The radial metallicity gradient of clusters based on their apogalactic distances is also derived with a slope of $b=-0.082\pm0.014$ dex kpc$^{-1}$. The distribution of derived orbital eccentricities for open clusters is very similar to the one derived for the field population of dwarfs and giants in the thin disc.

astro-ph.GA↗

arXiv2009

Variable Stars in the Field of the Open Cluster NGC 2126

We report the results of a time-series CCD photometric survey of variable stars in the field of the open cluster NGC 2126. In about one square degree field covering the cluster, a total number of 21 variable candidates are detected during this survey, of which 16 are newly found. The periods, classifications and spectral types of 14 newly discovered variables are discussed, which consist of six eclipsing binaries systems, three pulsating variable stars, three long period variables, one RS CVn star, and one W UMa or $δ$ Scuti star. In addition, there are two variable candidates, the properties of which cannot be determined in this paper. By a method based on fitting spectral energy distributions(SEDs) of stars with theoretical ones, the membership probabilities and the fundamental parameters of this cluster are determined. As a result, five variables are probably members of NGC 2126. The fundamental parameters of the this cluster are determined as: the metallicity to be 0.008 $Z_\odot$, the age $\log(t)$= 8.95, the distance modulus $(m-M)_{0}$= 10.34 and the reddening value $E(B-V)$=0.55 mag.

astro-ph.SR↗

arXiv2007

BATC 13-band Photometry of Open Cluster NGC 7789

We present 13-band CCD intermediate-band spectrophotometry of a field centered on the open cluster NGC 7789 from 400 to nearly 1000 nm, taken with Beijing-Arizona-Taiwan-Connecticut (BATC) Multi-Color Survey photometric system. By comparing observed spectral energy distributions of NGC 7789 stars with theoretical ones, the fundamental parameters of this cluster are derived: an age of $1.4\pm0.1$ Gyr, a distance modulus $(m-M)_{0}=11.27\pm0.04$, a reddening $E(B-V)=0.28\pm0.02$, and a metallicity with the solar composition $Z=0.019$. When the surface density profile for member stars with limiting magnitudes of 19.0 in the BATC $e$ band ($λ_{\textrm{eff}}=4925$ Å) is fitted by King model, the core radius $R_{c}=7.52\arcmin$ and the tidal radius $R_{t}=28.84\arcmin$ are derived for NGC 7789. The observed mass function (MF) for main sequence stars of NGC 7789 with masses from 0.95 to 1.85 $M_{\odot}$ is fitted with a power-law function $ϕ(m)\propto m^α$ and the slope $α=-0.96$ is derived. Strong mass segregation in NGC 7789 is reflected in the significant variation of the concentration parameters $C_{0}=\log (R_{t}/R_{c})$ for member stars of NGC 7789 within different mass ranges: $C_{0}=1.02$ for most of massive stars; $C_{0}=0.37$ for the lowest-mass MS stars. Strong mass segregation in NGC 7789 is also indicated in the significant variation of the slopes $α$ in different spatial regions of the cluster: the MF for stars within the core region has $α=-0.71$, much flatter than that for stars in external regions of the cluster ($α=-1.20$).

astro-ph↗