Precise determination of fundamental parameters of six exoplanet host stars and their planets

The aim of this paper is to determinate the fundamental parameters of six exoplanet host （EH） stars and their planets. Because techniques for detecting exo- planets yield properties of the planet only as a function of the properties of the host star, we must accurately determine the parameters of the EH stars first. For this rea- son, we constructed a grid of stellar models including diffusion and rotation-induced extra-mixing with given ranges of input parameters （i.e. mass, metallicity and initial rotation rate）. In addition to the commonly used observational constraints such as the effective temperature Tell, luminosity L and metallicity [Fe/H], we added two obser- vational constraints, the lithium abundance log N （Li） and the rotational period Prot. These two additional observed parameters can set further constraints on the model due to their correlations with mass, age and other stellar properties. Hence, our estimations of the fundamental parameters for these EH stars and their planets have a higher preci- sion than previous works. Therefore, the combination of rotational period and lithium helps us to obtain more accurate parameters for stars, leading to an improvement in knowledge about the physical state of EH stars and their planets.

Absolute parameters of the three totally-eclipsing W UMa stars NSVS 2443858,NSVS 780649 and V1098 Her

We present the first photometric analysis of three totally-eclipsing W UMa binaries,NS VS2443858,NSVS 780649 and V1098 Her.The absolute astrophysical parameters of the stellar components were determined by means of Gaia distances and light curve solutions.The results show that:(ⅰ)Two of the systems,NSVS 2443858 and V1098 Her,are of A subtype while the obtained temperature of the secondary component of NSVS 780649 indicates that it is a W-subtype system;(ⅱ)The estimated mass ratios approach the lower limit of the mass ratio assumed by researchers in recent years so our targets could be classified as extreme mass ratio binary(EMRB)systems;(ⅲ)All the systems have deep contact configurations,so they also are deep low mass ratio(DLMR)systems;(ⅳ)The components of our systems are stars of F and G spectral type and undergo total eclipses;(ⅴ)The sum 0.871 M⊙of the component masses of NSVS 780649 is below the mass limit of 1.0-1.2 M⊙assumed for the known contact binary stars.

Physical and geometrical parameters of CVBS Ⅺ: Cou 1511(HIP 12552)

Model atmospheres of the close visual binary star Cou 1511 （HIP 12552） are constructed using grids of Kuruz＇s blanketed models to build the individual synthetic spectral energy distributions （SEDs） for both components. These synthetic SEDs are combined together for the entire system and compared with the observational one following A1-Wardat＇s complex method for analyzing close visual binary stars. The entire observational SED of the system is used as a reference for comparison between the synthetic SED and the observed one. The parameters of both components are derived as： Teff = 6180 4- 50 K, Tebfr = 5865 ＋ 70 K, log 9a = 4.35 ± 0.12, log 9b = 4.45± 0.14, Ra = 1.262 ± 0.08 R⊙^eff, Rb = 1.006 ± 0.07 R⊙^ett, La = 2.09 -4- 0.10 L⊙ and Lb = 1.08 ± 0.12 L⊙, with spectral types F8V and G1.5V for components （a, b） respectively and age of 3.0 ± 0.9 Gyr. A modified orbit of the system is built and the masses of the two components are calculated as Ma = 1.17 ±0.11 Me and Mb = 1.06 ± 0.10 Me.

Spectral classification of stars based on LAMOST spectra

In this work, we select spectra of stars with high signal-to-noise ratio from LAMOST data and map their MK classes to the spectral features. The equivalent widths of prominent spectral lines, which play a similar role as multi-color photometry, form a clean stellar locus well ordered by MK classes. The advantage of the stellar locus in line indices is that it gives a natural and continuous classification of stars consistent with either broadly used MK classes or stellar astrophysical parameters. We also employ an SVM-based classification algorithm to assign MK classes to LAMOST stellar spectra. We find that the completenesses of the classifications are up to 90% for A and G type stars, but they are down to about 50% for OB and K type stars. About 40% of the OB and K type stars are mis-classified as A and G type stars,respectively. This is likely due to the difference in the spectral features between late B type and early A type stars or between late G and early K type stars being very weak. The relatively poor performance of the automatic MK classification with SVM suggests that the direct use of line indices to classify stars is likely a more preferable choice.

Physical and geometrical parameters of VCBS XIII: HIP 105947

The best physical and geometrical parameters of the main sequence close visual binary system(CVBS), HIP 105947, are presented. These parameters have been constructed conclusively using Al-Wardat’s complex method for analyzing CVBSs, which is a method for constructing a synthetic spectral energy distribution(SED) for the entire binary system using individual SEDs for each component star. The model atmospheres are in its turn built using the Kurucz(ATLAS9) line-blanketed plane-parallel models. At the same time, the orbital parameters for the system are calculated using Tokovinin’s dynamical method for constructing the best orbits of an interferometric binary system. Moreover, the mass-sum of the components, as well as the ?θ and ?ρ residuals for the system, is introduced. The combination of Al-Wardat’s and Tokovinin’s methods yields the best estimations of the physical and geometrical parameters. The positions of the components in the system on the evolutionary tracks and isochrones are plotted and the formation and evolution of the system are discussed.

NSVS 2569022:a peculiar binary among W UMa stars with extremely small mass ratios

Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total eclipse of W subtype and the mass ratio is well-determined. Its extremely small value of only 0.077 implies that the target will probably experience instability and a possible merger. This value ranks NSVS 2569022 in sixth place among binaries with the smallest mass ratio. Based on an empirical relation of ＂period - total mass＂ for low mass-ratio binaries, we estimate the global parameters of NSVS 2569022： masses M1 = 1.17 M⊙ and M2 = 0.09 M⊙; radii R1 = 1.19 R⊙ and R2 = 0.38 R⊙; luminosities L1 = 1.73 L⊙ and L2 = 0.17L⊙. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out to be a peculiar binary among W UMa stars with extremely small mass ratios due to its unexpectedly small fill-out factor of only 0.014 （slightly overcontact configuration）.

Stellar parameters of main sequence turn-off star candidates observed with LAMOST and Kepler

Main sequence turn-off （MSTO） stars since their ages can be robustly estimated from have advantages as indicators of Galactic evolution atmospheric parameters. Hundreds of thousands of MSTO stars have been selected from the LAMOST Galactic survey to study the evolution of the Galaxy, and it is vital to derive accurate stellar parameters. In this work, we select 150 MSTO star candidates from the MSTO star sample of Xiang that have asteroseismic parameters and determine accurate stellar parameters for these stars by combining asteroseismic parameters deduced from Kepler photometry and atmospheric parameters deduced from LAMOST spectra. With this sample, we examine the age determination as well as the contamination rate of the MSTO star sample. A comparison of age between this work and Xiang shows a mean difference of 0.53 Gyr （7%） and a dispersion of 2.71 Gyr （28%）. The results show that 79 of the candidates are MSTO stars, while the others are contaminations from either main sequence or sub-giant stars. The contamination rate for the oldest stars is much higher than that for younger stars. The main cause for the high contamination rate is found to be the relatively large systematic bias in the LAMOST surface gravity estimates.

Automatic determination of stellar atmospheric parameters and construction of stellar spectral templates of the Guoshoujing Telescope (LAMOST)

A number of spectroscopic surveys have been carried out or are planned to study the origin of the Milky Way. Their exploitation requires reliable automated methods and softwares to measure the fundamental parameters of the stars. Adopting the ULySS package, we have tested the effect of different resolutions and signal-to- noise ratios （SNR） on the measurement of the stellar atmospheric parameters （effective temperature Teff, surface gravity log g, and metaUicity [Fe/H]）. We show that ULySS is reliable for determining these parameters with medium-resolution spectra （R ～2000）. Then, we applied the method to measure the parameters of 771 stars selected in the commissioning database of the Guoshoujing Telescope （LAMOST）. The results were compared with the SDSS/SEGUE Stellar Parameter Pipeline （SSPP）, and we derived precisions of 167 K, 0.34dex, and 0.16dex for Teff, logg and [Fe/H] respectively. Furthermore, 120 of these stars are selected to construct the primary stellar spectral template library （Version 1.0） of LAMOST, and will be deployed as basic ingredients for the LAMOST automated parametrization pipeline.

Validation of LAMOST stellar parameters with the PASTEL catalog

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） published its first data release （DR1） in 2013, which is currently the largest dataset of stellar spectra in the world. We combine the PASTEL catalog and SIMBAD radial velocities as a testing standard to validate stellar parameters （effec- tive temperature Tefr, surface gravity log g, metallicity [Fe/H] and radial velocity Vr） derived from DR1. Through cross-identification of the DR1 catalogs and the PASTEL catalog, we obtain a preliminary sample of 422 stars. After removal of stellar param- eter measurements from problematic spectra and applying effective temperature con- straints to the sample, we compare the stellar parameters from DR1 with those from PASTEL and SIMBAD to demonstrate that the DR1 results are reliable in restricted ranges of Tefr. We derive standard deviations of 110 K, 0.19 dex and 0.11 dex for Tell, log 9 and [Fe/H] respectively when Teff〈 8000 K, and 4.91 km s-1 for Vr when Teff 〈 10 000 K. Systematic errors are negligible except for those of Vr. In addition, metallicities in DR1 are systematically higher than those in PASTEL, in the range of PASTEL [Fe/H] 〈 -1.5.

A comparison of stellar atmospheric parameters from the LAMOST and APOGEE datasets

We have compared stellar parameters, including temperature, gravity and metallicity, for common stars in the LAMOST DR2 and SDSS DR12/APOGEE datasets. It is found that the LAMOST dataset provides a more well-defined red clump feature than the APOGEE dataset in the Teff versus log g diagram. With this advantage, we have separated red clump stars from red giant stars, and attempt to establish calibrations between the two datasets for the two groups of stars. The results show that there is a good consistency in temperature with a calibration close to the one-to-one line, and we can establish a satisfactory metallicity calibration of[Fe/H]APOGEE= 1.18[Fe/H]LAMOST ＋ 0.11 with a scatter of ～ 0.08 dex for both the red clump and red giant branch samples. For gravity, there is no correlation for red clump stars between the two datasets, and scatters around the calibrations of red giant stars are substantial. We found two main sources of scatter in log g for red giant stars. One is a group of stars with 0.00253 × Teff- 8.67 〈 log g 〈 2.6 located in the forbidden region, and the other is the contaminated red clump stars, which could be picked out from the unmatched region where stellar metallicity is not consistent with position in the Teff versus log g diagram. After excluding stars in these two regions,we have established two calibrations for red giant stars, log g APOGEE = 0.000615 ×Teff,LAMOST＋ 0.697 × log g LAMOST- 2.208（σ = 0.150） for [Fe/H] 〉-1 and log gAPOGEE= 0.000874×Teff,LAMOST＋0.588×log g LAMOST-3.117（σ = 0.167）for [Fe/H] 〈-1. The calibrations are valid for stars with Teff = 3800- 5400 K and log g = 0- 3.8 dex, and are useful in work aiming to combine the LAMOST and APOGEE datasets in a future study. In addition, we find that an SVM method based on asteroseismic log g is a good way to greatly improve the accuracy of gravity for these two regions, at least in the LAMOST dataset.

On the LSP3 estimates of surface gravity for LAMOST-Kepler stars with asteroseismic measurements

Asteroseismology allows for deriving precise values of the surface gravity of stars. The accurate asteroseismic determinations now available for the large number of stars in the Kepler fields can be used to check and calibrate surface gravities that are currently being obtained spectroscopically for a huge number of stars targeted by large-scale spectroscopic surveys, such as the on-going Large Sky Area Multi-Object Fiber Spectroscopic Telescope （LAMOST） Galactic survey. The LAMOST spectral surveys have obtained a large number of stellar spectra in the Kepler fields. Stellar atmospheric parameters of those stars have been determined with the LAMOST Stellar Parameter Pipeline at Peking University （LSP3）, by template matching with the MILES empirical spectral library. In the current work, we compare surface gravities yielded by LSP3 with those of two asteroseismic samples-- the largest Kepler asteroseismic sample and the most accurate Kepler asteroseismic sample. We find that LSP3 surface gravities are in good agreement with asteroseismic values of Hekker et al., with a dispersion of -0.2 dex. Except for a few cases, asteroseismic surface gravities ofHuber et al. and LSP3 spectroscopic values agree for a wide range of surface gravities. However, some patterns in the differences can be identified upon close inspection. Potential ways to further improve the LSP3 spectroscopic estimation of stellar atmospheric parameters in the near future are briefly discussed. The effects of effective temperature and metallicity on asteroseismic determinations of surface gravities for giant stars are also discussed.

Estimating stellar atmospheric parameters based on Lasso features

With the rapid development of large scale sky surveys like the Sloan Digital Sky Survey （SDSS）, GAIA and LAMOST （Guoshoujing telescope）, stellar spectra can be obtained on an ever-increasing scale. Therefore, it is necessary to estimate stel- lar atmospheric parameters such as Teff, log g and [Fe/H] automatically to achieve the scientific goals and make full use of the potential value of these observations. Feature selection plays a key role in the automatic measurement of atmospheric parameters. We propose to use the least absolute shrinkage selection operator （Lasso） algorithm to select features from stellar spectra. Feature selection can reduce redundancy in spectra, alleviate the influence of noise, improve calculation speed and enhance the robustness of the estimation system. Based on the extracted features, stellar atmospheric param- eters are estimated by the support vector regression model. Three typical schemes are evaluated on spectral data from both the ELODIE library and SDSS. Experimental results show the potential performance to a certain degree. In addition, results show that our method is stable when applied to different spectra.

Three-dimensional orbit and physical parameters of HD 6840

HD 6840 is a double-lined visual binary with an orbital period of N7.5 years. By fitting the speckle interferometric measurements made by the 6 m BTA telescope and 3.5 m WIYN telescope, Balega et al. gave a preliminary astrometric orbital solution of the system in 2006. Recently, Griffin derived a precise spectroscopic orbital solution from radial velocities observed with OPH and Cambridge Coravel. However, due to the low precision of the determined orbital inclination, the derived component masses are not satisfying. By adding the newly collected astrometric data in the Fourth Catalog of Interferometric Measurements of Binary Stars, we give a three-dimensional orbit solution with high precision and derive the preliminary physical parameters of HD 6840 via a simultaneous fit including both astrometric and radial velocity measurements.

Photometric observations and light curve solutions of the W UMa stars NSVS 2244206,NSVS 908513,CSS J004004.7+385531 and VSX J062624.4+570907

Photometric observations in Sloan 9＇ and i＇ bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7＋385531 and VSX J062624.4＋570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factors within 0.15-0.26. Their components are G-K spectral types and are almost in thermal contact. They are also relatively close in size and luminosity： the radius ratios r2/r1 are within 0.75-0.90; the luminosity ratios 12/11 are within 0.53-0.63. The results of the light curve solution of CSS J004004.7＋385531 imply the weak limb-darkening effect of its primary component and possible presence of additional absorbing features in the system.

Neutrino luminosity of stars with different masses

Neutrinos play an important role in stellar evolution.They are produced by nuclear reactions or thermal processes.Using the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),we study stellar neutrino luminosity with different masses.The neutrino luminosities of stars with different initial masses at different evolutionary stages are simulated.We find that the neutrino flux of a star with 1 M⊙ mass at an evolutionary age of 4.61×10^9 yr is consistent with that of the Sun.In general,neutrinos are produced by nuclear reactions,and the neutrino luminosity of stars is about one or two magnitudes lower than the photo luminosity.However,neutrino luminosity can exceed photo luminosity during the helium flash which can occur for stars with a mass lower than 8 M⊙.Although the helium flash does not produce neutrinos,plasma decay,one of the thermal processes,can efficiently make neutrinos during this stage.Due to the high mass-loss rate,a star with a mass of 9 M⊙ does not undergo the helium flash.Its neutrinos mainly originate from nuclear reactions until the end of the AGB stage.At the end of the AGB stage,its neutrino luminosity results from plasma decay which is triggered by the gravitational energy release because of the stellar core contracting.

Stellar loci IV.red giant stars

In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The stars span a range of 0.55-1.2 mag in color g-i,-0.3--2.5 in metallicity[Fe/H],and have values of surface gravity log g smaller than 3.5 dex.As in the case of main-sequence(MS)stars,the intrinsic widths of loci of red giants are also found to be quite narrow,a few mmag at maximum.There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars.The colors of red giants are less sensitive to metallicity than those of MS stars.With good photometry,photometric metallicities of red giants can be reliably determined by fitting the u-g,g-r,r-i,and i-z colors simultaneously to an accuracy of 0.2-0.25 dex,comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10.By comparing fitting results to the stellar loci of red giants and MS stars,we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry.The technique achieves completeness of~70 per cent and efficiency of~80 per cent in selecting metal-poor red giant stars of[Fe/H]≤-1.2.It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.

An Update of the Catalog of Radial Velocity Standard Stars from the APOGEE DR17

We present an updated catalog of 46,753 radial velocity(RV)standard stars selected from the APOGEE DR17.These stars cover the Northern and Southern Hemispheres almost evenly,with 62%being red giants and 38%being main sequence stars.These RV standard stars are stable on a baseline longer than 200 days(with 54%longer than one year and 10%longer than five years)with a median stability better than 215 m s~(-1).The average number of observations of those stars is 5 and each observation is required to have signal-to-noise ratio greater than50 and RV measurement error smaller than 500 m s~(-1).Based on the new APOGEE RV standard star catalog,we have checked the RV zero-points(RVZPs)for current large-scale stellar spectroscopic surveys including RAVE,LAMOST,GALAH and Gaia.By careful analysis,we estimate their mean RVZP to be+0.149 kms~(-1),+4.574 km s~(-1)(for LRS),-0.031 km s~(-1)and+0.014 kms~(-1),respectively,for the four surveys.In the RAVE,LAMOST(for MRS),GALAH and Gaia surveys,RVZP exhibits a systematic trend with stellar parameters(mainly[Fe/H],T_(eff),log g,G_(BP)-G_(RP)and G_(RVS)).The corrections to those small but clear RVZPs are of vital importance for these massive spectroscopic surveys in various studies that require extremely high RV accuracies.

High-α-Metal-Rich stars in the LAMOST-MRS survey and its connection with the galactic bulge

We report the detection of a large sample of high-α-metal-rich stars on the low giant branch with 2.6<log g<3.3 dex in the LAMOST-MRS survey.This special group corresponds to an intermediate-age population of 5-9 Gyr based on the[Fe/H]-[C/N]diagram and age-[C/N]calibration.A comparison group is selected to have a solarαratio at super metallicity,which is young and has a narrow age range around 3 Gyr.Both groups have thin-disk like kinematics but the former shows slightly large velocity dispersions.The special group shows a larger extension in a vertical distance toward 1.2 kpc,a second peak at smaller Galactic radius and a larger fraction of super metal rich stars with[Fe/H]>0.2 than the comparison group.These properties strongly indicate its connection with the outer bar/bulge region at R=3-5 kpc.A tentative interpretation of this special group is that its stars were formed in the X-shaped bar/bulge region,close to its corotation radius,where radial migration is the most intense,and brings them to present locations at 9 kpc and beyond.Low eccentricities and slightly outward radial excursions of its stars are consistent with this scenario.Its kinematics(cold)and chemistry([α/Fe]~0.1)further support the formation of the instability-driven X-shaped bar/bulge from the thin disk.

Two New r-process-enhanced Stars with [Fe/H] >-0.6 dex from the LAMOST-MRS Survey

We report the discovery of two r-process-enhanced stars with [Fe/H]>-0.6 dex selected from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) survey.Three candidate stars have been selected from the LAMOST medium-resolution(R~ 7500) spectroscopic survey,and the follo wed-up high signal-to-noise ratio and high-resolution(R~31,500) spectra are obtained with the ARC Echelle Spectrograph mounted on the3.5 m telescope at the Apache Point Observatory,which allow us for the determination of stellar atmospheric parameters and abundances of 20 elements.Among these three r-process-enhanced candidate stars,TYC 1710-933-1 and TYC 2858-372-1 have [Eu/Fe] higher than 0.3 dex and [Ba/Eu] lower than 0.0 dex,thus,can be identified as new r-process-enhanced objects.TYC 2858-372-1 shows similar r+s-process pattern to the Sun.TYC 1710-933-1 presents enhancement of the r-process elements of Nd and Eu.Our work indicates that the enrichment mechanisms of the heavy neutron-capture elements are complicated for metal-rich stars.

Absolute physical parameters of three poorly studied detached eclipsing binaries

The photometric and spectroscopic data for three double-lined detached eclipsing binaries were collected from the photometric and spectral surveys.The light and radial velocity curves of each binary system were simultaneously analyzed using Wilson-Devinney(WD)code,and the absolute physical and orbital parameters of these binaries were derived.The masses of both components of ASASSN-V J063123.82+192341.9 were found to be M1=1.088±0.016 and M20.883±0.016 M⊙;those of ASAS J011416+0426.4 were determined to be M1=0.934±0.046 and M2=0.754±0.043 M⊙;and those of MW Aur were derived to be M1=2.052±0.196 and M21.939±0.193 M⊙.Finally,the evolutionary status of these detached binaries was discussed based on their absolute parameters and the theoretical stellar models.