Implementation of New OPAL Tables in Eggleton's Stellar Evolution Code

Based on previous works of OPAL, we construct a series of opacity tables for various metallicities Z=0, 0.000 01, 0.000 03, 0.000 1, 0.000 3, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10(T/K) > 3.95 and Alexander's for log10(T/K) < 3.95. At log10(T/K) = 3.95, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.     

Implementation of New OPAL Tables in Eggleton''''s Stellar Evolution Code

Based on previous works of OPAL, we construct a series of opacity tables for various metallicities Z = 0, 0.000 01, 0.000 03, 0.000 1, 0.000 3, 0.001, 0.004, 0.01, 0.02,0.03, 0.04, 0.05, 0.06, 0.08 and 0.1. These tables can be easily used in Eggleton's stellar evolution code in place of the old tables without changing the code. The OPAL tables are used for log10 (T/K) ＞ 3.95 and Alexander's for log10 (T/K) ＜ 3.95. At log10 (T/K) - 3.95, the two groups' data fit well for all hydrogen mass fractions. Conductive opacities are included by reciprocal addition according to the formulae of Yakovlev and Urpin. A comparison of 1 and 5 M⊙ models constructed with the older OPAL tables of Iglesias and Rogers shows that the new opacities have most effect in the late stages of evolution, the extension of the blue loop during helium burning for intermediate-mass and massive stars.     

Effects of α-Enhancement on Stellar Evolution

Using Eggleton's code, we systematically show the differences in stellar evolution between the results based on the scaled-solar mixture and the α-enhanced metal mixture. As input, the OPAL high temperature opacities are used for log (T/K)>4.00, and the new Wichita State low temperature opacities, for log (T/K)≤4.00. Our calculations cover star masses ranging from 0.25 to 80.0 M⊙, spaced at Δlog M=0.10 or 0.05. The values of metallicities Z are 0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.06, 0.08 and 0.10. For a given Z, the initial hydrogen mass fraction is given by X=0.76-3.0Z. We show that α-enhancement can raise the stellar effective temperature and luminosity, and reduce the evolutionary age. Compared with some previous work, the effects of α-enhancement are more obviously demonstrated in our calculations.     

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 radiative and thermodynamic properties of the cosmic radiations using COBE FIRAS instrument data: Ⅲ. Galactic far-infrared radiation

Using the three-component spectral model describing the FIRAS average continuum spectra, the exact analytical expressions for thermodynamic and radiative functions of Galactic far-infrared radiation are obtained. The COBE FIRAS instrument data in the 0.15–2.88 THz frequency interval at the mean temperatures of T1= 17.72 K, T2= 14 K and T3= 6.73 K are used for calculating the radiative and thermodynamic functions, such as the total radiation power per unit area, total energy density, total emissivity, number density of photons, Helmholtz free energy density, entropy density, heat capacity at constant volume and pressure for the warm,intermediate-temperature and very cold components of the Galactic continuum spectra. The generalized Stefan-Boltzmann law for warm, intermediate-temperature and very cold components is constructed. The temperature dependence of each component is determined by the formula IS-B(T) = σ′ T6. This result is important when we construct the cosmological models of radiative transfer that can be applied inside the Galaxy. Within the framework of the three-component spectral model, the total number of photons in our Galaxy and the total radiation power(total luminosity) emitted from a surface of the Galaxy are calculated. Their values are N6Gtotal= 1.3780 × 108 and I3Gtotal(T) = 1.0482 × 106 W. Other radiative and thermodynamic properties of the Galactic far-infrared radiation(photon gas) of the Galaxy are calculated. The expressions for astrophysical parameters, such as the entropy density/Boltzmann constant and number density of the Galactic far-infrared photons are obtained. We assume that the obtained analytical expressions for thermodynamic and radiative functions may be useful for describing the continuum spectra of the far-infrared radiation for other galaxies.     

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 Al-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:T_(eff)~a= 6180 ± 50 K,T_(eff)~b=5865 ± 70 K, log g_a = 4.35 ± 0.12, log g_b = 4.45 ± 0.14, R_a = 1.262 ± 0.08 R_⊙, R_b = 1.006 ± 0.07 R_⊙,L_a = 2.09 ± 0.10 L_⊙and L_b = 1.08 ± 0.12 L_⊙, with spectral types F8 V 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 M_a = 1.17 ± 0.11 M_⊙and M_b = 1.06 ± 0.10 M_⊙.     

Orbital period correction and light curve modeling of the W-subtype shallow contact binary OW Leo

Orbital period and multi-color light curves’investigation of OW Leo are presented for the first time.The orbital period of OW Leo is corrected from P=0.325545 days to P=0.32554052 days in our work,and the observational data from the All-Sky Automated Survey for Super Novae(ASAS-SN)are used to test the newly determined orbital period.Then,the phased light curves are calculated with the new period and the Wilson-Devinney program is applied to model the light curves,which reveal that OW Leo is a W-subtype shallow contact binary system(q=3.05,f=12.8%).The absolute physical parameters of the two component stars are estimated to be M₁=0.31(1)M_⊙,M₂=0.95(3)M_⊙,R₁=0.63(1)R⊙,R₂=1.04(1)R_⊙,L₁=0.43(1)L_⊙and L₂=1.01(2)L_⊙.The evolutionary status shows that the more massive star is less evolved than the less massive star.OW Leo has very low metal abundance,which means its formation and evolution are hardly influenced by any additional component.It is formed from an initially detached binary system through nuclear evolution and angular momentum loss via magnetic braking,and has passed a very long time of main sequence evolution.     

Brightness temperature for 166 radio sources

Using the database of the University of Michigan Radio Astronomy Observatory （UMRAO） at three radio frequencies （4.8, 8 and 14.5 GHz）, we determined the short-term variability timescales for 166 radio sources. The timescales are 0.15d （2007＋777） to 176.17 d （0528-250） with an average timescale of Atobs = 17.1 4- 16.5 d for the whole sample. The timescales are used to calculate the brightness temperatures, TB. The value of log TB is in the range of log TB = 10.47 to 19.06 K. In addition, we also estimated the boosting factor for the sources. The correlation between the polarization and the Doppler factor is also discussed.     

LASPM:the LAMOST stellar parameter pipeline for M-type stars and application to the sixth and seventh data release(DR6 and DR7)

The molecular-rich atmospheres of M type stars complicate our understanding to their atmospheric properties.Recently,great progress has been made in atmospheric modeling of M-type stars,and we take advantage of the updated BT-Settl model grid to develop a pipeline LAS PM to measure atmospheric parameters(T_(eff),log g,[M/H]) of M-type stars from low-resolution spectra.The pipeline was applied to the sixth and seventh data release(DR6 DR7) of Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST),which released atmospheric parameters for 610419 and 680 185 Mtype spectra,respectively.The key algorithm is to find the best-matching for templates in the synthetic spectral library for an observed spectrum,and then minimizing χ~2 through a linear combination of five best-matching templates.The intrinsic precisions of the parameters were estimated by using the multiple epoch observations for the same stars,which are 118 K,0.20 dex,0.29 dex for T_(eff),log g,and [M/H]respectively.The Teff and log g are consistent with the spectral and luminosity classifications by LAMOST 1D pipeline,and the loci of giants and dwarfs both on spectral index and color-magnitude diagrams show the validity.The metallicities of LASPM are also checked with the selected members of four open clusters(NGC 2632,Melotte 22,ASCC_16,and ASCC_19),which are consistent without any bias.Comparing the results between LASPM and the APOGEE Stellar Parameter and Chemical Abundance Pipeline(ASPCAP),there is a scatter of 73 K,0.22 dex,0.21 dex for T_(eff),log g,and [M/H],respectively.     

A Model of the Circumstellar Envelope of Luminous Blue Variables

The continuum energy distributions of the luminous blue variables R127 and R110 in the outburst phase are fitted with a circumstellar envelope model.Both stars show two peaks in their continuum, one near 1250A and the other in the optical band. We suggest that their UV and optical fluxes may have different origins: the UV flux comes from the central star while the optical flux comes from an expanding circumstellar envelope. We construct a model for LBVs consisting of two LTE atmosphere models with different temperatures, and find it to be in agreement with the observed spectral energy distributions of R127 and R110.According to our numerical experiments, R127‘s continuum is composed of fluxes from a circumstellar envelope of Teff = 8000K, R = 485R⊙, and log g = 1,and from a central star of Tef = 17000K, R = 135R⊙, and log g = 2.5 with a permeating factor f = 0.5; while R110‘s continuum can be fitted by a circumstellar envelope of Teff =7000K, R = 350R⊙, and logg = 0.5, and a central star of Teff =25 000 K, R = 27R⊙, and log g 3.0 with a permeating factor f = 0.65.Both models show that the non-spherically symmetric, optically thick regions are formed surrounding the central star in the outburst phase. The light of the central star is shielded by the circumstellar envelope so that the visual brightness increases with the decrease/increase of the temperature/radius of the optically thick regions.     

The YNEV stellar evolution and oscillation code

We have developed a new stellar evolution and oscillation code YNEV,which calculates the structures and evolutions of stars,taking into account hydrogen and helium burning.A nonlocal turbulent convection theory and an updated overshoot mixing model are optional in this code.The YNEV code can evolve low-and intermediate-mass stars from the pre-main sequence to a thermally pulsing asymptotic branch giant or white dwarf.The YNEV oscillation code calculates the eigenfrequencies and eigenfunctions of the adiabatic oscillations for a given stellar structure.The input physics and numerical scheme adopted in the code are introduced.Examples of solar models,stellar evolutionary tracks of low-and intermediate-mass stars with different convection theories(i.e.mixing-length theory and nonlocal turbulent convection theory),and stellar oscillations are shown.     

More than two hundred and fifty thousand spectroscopic binary or variable star candidates discovered by LAMOST

About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than10 km s^-1 and they are possible spectroscopic binary or variable candidates(SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s^-2. The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g～4.621 and lower T ～ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has logg around 4.171 cm s^-2 that includes binaries and pulsating stars such as δSet and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage.The last group is composed of giants or supergiants with log g around 2.461 cm s^-2 that may be evolved pulsating stars. One target(C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.     

Physical properties of γ Doradus pulsating stars and their relationship with long-period δ Scuti variables

We present LAMOST data on 168 γ Doradus(γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period(P), temperature(T), gravitational acceleration(log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to7280 K. They are slightly more metal poor than the Sun with a metallicity range from-0.4 to 0. On the H-R and log g-T diagrams, both the γ Dor and δ Scuti(δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct(P 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables(P 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33γ Dor stars are identified as candidates of binary or multiple systems.     

Analysis of the 3C 445 soft X-ray spectrum as observed by Chandra high-energy gratings

We present a detailed analysis of the soft X-ray emission of 3 C 445 using an archival Chandra High Energy Transmission Grating(HETG) spectrum. Highly-ionized H-and He-like Mg, Si and S lines, as well as a resolved low-ionized Si Kα line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X radiative recombination continua(RRC) feature in the spectrum seems to prefer a photoionized environment. The spectrum is subsequently modeled with a photoionization model, and the results are compared with those of a collisional model. Through a detailed analysis of the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are log ξ = 3.3_(-0.3)~(+0.4) erg cm s~(-1), n H = 5_(-4.5)~(+15)× 10~(10) cm~(-3) and NH = 2.5_(-1.7)~(+3.8)× 10~(20) cm~(-2).According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred radial distance(6 × 10~(14)-8 × 10~(15) cm), we suggest the emission lines originating from matter are located in the broad line region(BLR).     

Linear Correlations between Peak Frequency of Gyrosynchrotron Spectrum and Photosphere Magnetic Fields

The gyrosynchrotron spectra are computed in a nonuniform magnetic field case, taking into account the self-and gyroresonanceabsorption. It is found that the peak frequency νp of the gyrosynchrotron spectrum systematically increases with the increasing photosphere magnetic field strength B0 and increasing viewing angle θ. It is also found for the first time that there are good positive linear correlations between νp and B0, and between log νp and log θ, with linear correlation coefficient 0.99 between νp and B0 and 0.95 between log νp and log θ. We apply the correlations to analyze two burst events observed with OVSA and find that the evolution tendencies of the photosphere magnetic field strength B0 estimated from the above expression are comparable with the observational results of SOHO/MDI. We also give a comparison of the diagnostic results of coronal magnetic field strength in both uniform and nonuniform source models.     

Grids of stellar models including second harmonic and colors:solar composition(Z = 0.0172,X = 0.7024)

Grids of stellar evolution are required in many fields of astronomy/astrophysics,such as planet hosting stars,binaries,clusters,chemically peculiar stars,etc.In this study,a grid of stellar evolution models with updated ingredients and recently determined solar abundances is presented.The solar values for the initial abundances of hydrogen,heavy elements and mixing-length parameter are 0.0172,0.7024 and 1.98,respectively.The mass step is small enough(0.01 M_⊙)that interpolation for a given star mass is not required.The range of stellar mass is 0.74 to10.00 M_⊙.We present results in different forms of tables for easy and general application.The second stellar harmonic,required for analysis of apsidal motion of eclipsing binaries,is also listed.We also construct rotating models to determine the effect of rotation on stellar structure and derive fitting formulae for luminosity,radius and the second harmonic as a function of rotational parameter.We also compute and list colors and bolometric corrections of models required for transformation between theoretical and observational results.The results are tested for the Sun,the Hyades cluster,the slowly rotating chemically peculiar Am stars and eclipsing binaries with apsidal motion.The theoretical and observational results along isochrones are in good agreement.The grids are also applicable to rotating stars provided that equatorial velocity is given.     

He-shell flashes on the surface of oxygen-neon white dwarfs

Accretion induced collapse(AIC)may be responsible for the formation of some interesting neutron star binaries(e.g.,millisecond pulsars,intermediate-mass binary pulsars,etc).It has been suggested that oxygen-neon white dwarfs(ONe WDs)can increase their mass to the Chandrasekhar limit by multiple He-shell flashes,leading to AIC events.However,the properties of He-shell flashes on the surface of ONe WDs are still not well understood.In this article,we aim to study He-shell flashes on the surface of ONe WDs in a systematic approach.We investigated the long-term evolution of ONe WDs accreting He-rich material with various constant mass-accretion rates by time-dependent calculations with the stellar evolution code Modules for Experiments in Stellar Astrophysics(MESA),in which the initial ONe WD masses range from 1.1 to 1.35 M_⊙.We found that the mass-retention efficiency increases with the ONe WD mass and the mass-accretion rate,whereas both the nova cycle duration and the ignition mass decrease with the ONe WD mass and the mass-accretion rate.We also present the nuclear products in different accretion scenarios.The results presented in this article can be used in the future binary population synthesis studies of AIC events.     

Galaxy properties derived with spectral energy distribution fitting in the Hawaii-Hubble Deep Field-North

We compile multi-wavelength data from ultraviolet to infrared(IR) bands as well as redshift and source-type information, for a large sample of 178 341 sources in the Hawaii-Hubble Deep Field-North field. A total of 145 635 sources among the full sample are classified/treated as galaxies and have redshift information available. We derive physical properties for these sources utilizing the spectral energy distribution fitting code CIGALE that is based on Bayesian analysis. Through various consistency and robustness checks, we find that our stellar-mass and star-formation rate(SFR) estimates are reliable, which is mainly due to two facts. Firstly, we adopt the most up-to-date and accurate redshifts and point spread functionmatched photometry; and secondly, we make sensible parameter choices with the CIGALE code and take into account the influences of mid-IR/far-IR data, star-formation history models, and AGN contribution. We release our catalog of galaxy properties publicly(including, e.g., redshift, stellar mass, SFR, age, metallicity, dust attenuation). It is the largest of its kind in this field and should facilitate future relevant studies on the formation and evolution of galaxies.     

Tri-Phonic Helioseismology: Comparison of Solar p Modes Observed by the Helioseismology Instruments Aboard SOHO

The three helioseismology instruments aboard SOHO observe solar p modes in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series of two months duration are compared and confirm that the instruments indeed observe the same Sun to a high degree of precision. Power spectra of 108 days are compared showing systematic differences between mode frequencies measured in intensity and in velocity. Data coverage exceeds 97% for all the instruments during this interval. The weighted mean differences (V-I) are −0.1 μHz for l=0, and −0.16 μHz for l=1. The source of this systematic difference may be due to an asymmetry effect that is stronger for modes seen in intensity. Wavelet analysis is also used to compare the shape of the forcing functions. In these data sets nearly all of the variations in mode amplitude are of solar origin. Some implications for structure inversions are discussed.