Validation of LAMOST stellar parameters with the PASTEL catalog

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) published its first data release(DRl)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(effective temperature T_(eff),surface gravity log g,metallicity[Fe/H]and radial velocity V_r)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 parameter measurements from problematic spectra and applying effective temperature constraints 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 T_(eff).We derive standard deviations of 110 K,0.19 dex and 0.11 dex for T_(eff),log g and[Fe/H]respectively when T_(eff)8000 K,and 4.91 km S~(-1) for V_r when T_(eff)10 000 K.Systematic errors are negligible except for those of V_r.In addition,metallicities in DR1 are systematically higher than those in PASTEL,in the range of PASTEL[Fe/H]-1.5.     

Automated estimation of stellar fundamental parameters from low resolution spectra: the PLS method

PLS (Partial Least Squares regression) is introduced into an automatic esti-mation of fundamental stellar spectral parameters. It extracts the most correlative spec-tral component to the parameters (Teff, log g and [Fe/H]), and sets up a linear regres-sion function from spectra to the corresponding parameters. Considering the properties of stellar spectra and the PLS algorithm, we present a piecewise PLS regression method for estimation of stellar parameters, which is composed of one PLS model for Teff, and seven PLS models for log g and [Fe/H] estimation. Its performance is investigated by large experiments on flux calibrated spectra and continuum normalized spectra at dif-ferent signal-to-noise ratios (SNRs) and resolutions. The results show that the piecewise PLS method is robust for spectra at the medium resolution of 0.23 nm. For low resolu-tion 0.5 nm and 1 nm spectra, it achieves competitive results at higher SNR. Experiments using ELODIE spectra of 0.23 nm resolution illustrate that our piecewise PLS models trained with MILES spectra are efficient for O ～ G stars: for flux calibrated spectra, the systematic offsets are 3.8%, 0.14dex, and -0.09 dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.44 dex and 0.38 dex, respectively; for continuum normalized spectra, the systematic offsets are 3.8%, 0.12dex, and -0.13 dex for Teff, log g and [Fe/H], with error scatters of 5.2%, 0.49 dex and 0.41 dex, respectively. The PLS method is rapid, easy to use and does not rely as strongly on the tightness of a parameter grid of templates to reach high precision as Artificial Neural Networks or minimum distance methods do.     

A Method of Estimating the [α/Fe] Ratios from Low-resolution Stellar Spectratwo

A method for the determination of [α/Fe] from low-resolution stellar spectra is presented. The proposed scheme includes the following three steps: firstly, the spectrum is decomposed by the multi-scale Haar wavelet, and the high-frequency components are removed to suppress the high-frequency noise; then, based on the correlation of the spectral data component with [α/Fe], the spectral features are selected by the LASSO (Least Absolute Shrinkage and Selection Operator) algorithm; finally, [α/Fe] is measured by the multiple linear regression method based on the MARCS stellar spectrum library. The effectiveness of the method is verified with the low-resolution stellar spectra of ELODIE, SDSS (Sloan Digital Sky Survey), LAMOST (Large Sky Area Multi-Object Fibre Spectroscopic Telescope), and four star clusters. The systematic deviations and accuracies are as follows: (0.04 dex, 0.064 dex) for the 317 ELODIE spectra; (0.16 dex, 0.065 dex) for the 412 SDSS spectra; (0.05 dex, 0.062 dex) for the 1276 LAMOST spectra (with the signal-noise ratio in the g band (SNRG) greater than 20). The averages of [α/Fe] obtained for the likely members of the globular star clusters (M13, M15) and open star clusters (NGC2420, M67) are in agreement with the literature values.     

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.     

The chemical composition of the Small Magellanic Cloud

The Small Magellanic Cloud is a close, irregular galaxy that has experienced a complex star formation history due to the strong interactions occurred both with the Large Magellanic Cloud and the Galaxy. Despite its importance, the chemical composition of its stellar populations older than ∼ 1–2 Gyr is still poorly investigated. I present the first results of a spectroscopic survey of ∼ 200 Small Magellanic Cloud giant stars performed with FLAMES@VLT. The derived metallicity distribution peaks at [Fe/H] ∼ –0.9/–1.0 dex, with a secondary peak at [Fe/H] ∼ –0.6 dex. All these stars show [α /Fe] abundance ratios that are solar or mildly enhanced (∼+0.1 dex). Also, three metal‐poor stars (with [Fe/H] ∼ –2.5 dex and enhanced [α /Fe] ratios compatible with those of the Galactic Halo) have been detected in the outskirts of the SMC: These giants are the most metal‐poor stars discovered so far in the Magellanic Clouds. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical spectrum of the bipolar nebula AFGL 2688

Based on echelle spectra obtained at the prime focus of the 6-m telescope, we have determined for the first time the detailed chemical composition of one of the components of the bipolar nebula identified with the intense infrared source AFGL 2688 by the model-atmosphere method. The iron abundance [Fe/H]=?0.59 dex derived for AFGL 2688 suggests that the object probably belongs to an intermediate population of the Galaxy. The stellar atmosphere exhibits high carbon and nitrogen abundances, [C/Fe]=+0.73 and [N/Fe]=+2.00, and C/O>1, confirming that the object is at the post-AGB stage. However, the detected overabundance of s-process elements (yttrium and barium) relative to iron is modest: [X/Fe]=+0.55. The lanthanides are even less enhanced: for La, Ce, Pr, and Nd, the mean abundance relative to iron is [la/Fe]=+0.26. This behavior of the heavy metals is consistent with the low intensity of the 21-μm band in the infrared spectrum of AFGL 2688; the intensity of this emission band is great in the spectra of all the studied PPN with large overabundances of s-process elements. An analysis of the radial velocities measured from spectral features originating in the atmosphere and in the circumstellar shell has revealed a high-velocity (～60 km s^?1) component of the stellar wind from AFGL 2688.     

Kinematics and stellar populations of the dwarf elliptical galaxy IC 3653

We present the first 3D observations of a diffuse elliptical galaxy (dE). The good quality data (S/N up to 40) reveal the kinematical signature of an embedded stellar disc, reminiscent of what is commonly observed in elliptical galaxies, though similarity of their origins is questionable. Colour map built from Hubble Space Telescope Advanced Camera for Surveys (ACS) images confirms the presence of this disc. Its characteristic scale (about 3 arcsec =250 pc) is about a half of galaxy's effective radius, and its metallicity is 0.1–0.2 dex larger than the underlying population. Fitting the spectra with synthetic single stellar populations (SSP), we found an SSP-equivalent age of 5 Gyr and nearly solar metallicity [Fe/H]  =−0.06  dex. We checked that these determinations are consistent with those based on Lick indices, but have smaller error bars. The kinematical discovery of a stellar disc in dE gives additional support to an evolutionary link from dwarf irregular galaxies due to stripping of the gas against the intracluster medium.     

Analysis and calibration of Ca ii triplet spectroscopy of red giant branch stars from VLT/FLAMES observations

We demonstrate that low-resolution Ca  ii triplet (CaT) spectroscopic estimates of the overall metallicity ([Fe/H]) of individual red giant branch (RGB) stars in two nearby dwarf spheroidal galaxies (dSphs) agree to ±0.1–0.2 dex with detailed high-resolution spectroscopic determinations for the same stars over the range  −2.5 < [Fe/H] < −0.5  . For this study, we used a sample of 129 stars observed in low- and high-resolution modes with VLT/FLAMES in the Sculptor and Fornax dSphs. We also present the data-reduction steps we used in our low-resolution analysis and show that the typical accuracy of our velocity and CaT [Fe/H] measurement is ∼2 km s⁻¹ and 0.1 dex, respectively. We conclude that CaT–[Fe/H] relations calibrated on globular clusters can be applied with confidence to RGB stars in composite stellar populations over the range  −2.5 < [Fe/H] < −0.5  .     

The determination of white dwarf parameters in dwarf novae by optical spectral modeling

This paper presents the results of a model analysis of optical spectra and determination of the parameters of three individual SU UMa and WZ Sge type dwarf novae.The moderate resolution spectra of TY Psc,FL Psc and V455 And were obtained at the 6-m BTA of the SAO RAS in the low state of these systems with the determination of white dwarf radiation.The theoretical spectra were calculated using the grid models of hydrogen dwarf atmospheres of white dwarfs by varying the parameters(T_(eff) and log g) to reach the best agreement with the observed ones.We highlight different effects of the parameters on the shape and intensity of the HI lines.Therefore,it is possible to unambiguously determine T_(eff) and log g from the analysis of observations.The fundamental parameters of white dwarfs(M and R) were found by comparing the parameters of atmospheres with theoretical models of the internal structure.The obtained parameters of the primaries of TY Psc,FL Psc and V455 And are consistent with the average values for SU UMa and WZ Sge systems.As a result,we demonstrate the efficiency of the method for determining the parameters of such systems based on the analysis of a limited set of observed optical spectra.     

基于深度学习的LAMOST星系星族参数测量

星系的光谱包含其内部恒星的年龄和金属丰度等信息, 从观测光谱数据中测量这些信息对于深入了解星系的形成和演化至关重要. LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope)巡天发布了大量的星系光谱, 这些高维光谱与它们的物理参数之间存在着高度的非线性关系. 而深度学习适合于处理多维、海量的非线性数据, 因此基于深度学习技术构建了一个8个卷积层$+$4个池化层$+$1个全连接层的卷积神经网络, 对LAMOST Data Release 7 (DR7)星系的年龄和金属丰度进行自动估计. 实验结果表明, 使用卷积神经网络通过星系光谱预测的星族参数与传统方法基本一致, 误差在0.18dex以内, 并且随着光谱信噪比的增大, 预测误差越来越小. 实验还对比了卷积神经网络与随机森林回归模型、深度神经网络的参数测量结果, 结果表明卷积神经网络的结果优于其他两种回归模型.     

High Resolution Optical Spectroscopy of Hot Post-AGB Star Candidates LS IV-04 1 and LB3116

We present LTE analysis of high resolution optical spectra for B-type hot PAGB stars LS IV-04 1 and LB3116 (LSE 237). The spectra of these high Galactic latitude stars were obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph. The standard 1D LTE analysis with line-blanketed LTE model atmospheres and spectral synthesis provided fundamental atmospheric parameters of T_eff= 15 000±1000 K, log g= 2.5±0.2, ξ = 5.0±1.0 km s^?1, [M/H] = ?1.81 dex, and v sin i= 5 km s^?1 for LSIV-04 1 and T_eff= 16 000±1000 K, log g= 2.5±0.1, v sin i= 25 km s^?1, and [Fe/H] = ?0.93 dex for LB 3116. Chemical abundances of ten different elements were obtained. For LS IV-04 1, its derived model temperature contradicts with previous analysis results. The upper limits for its nitrogen and oxygen abundances were reported for the first time. The magnesium, silicon and calcium were overabundant (i.e. [Mg/Fe] = 0.8 dex, [Si/Fe] = 0.5 dex, [Ca/Fe] = 0.9 dex). With its metal-poor photosphere and V_LSR ≈ 96 km s^?1, LSIV-04 1 is likely a population II star and most probably a PAGB star. LTE abundances of LB 3116 were reported for the first time. The spectrum of this helium rich star shows 0.9 dex enhancement in the nitrogen. The photosphere of the star is slightly deficient in Mg, Si, and S. (i.e. [Mg/Fe] = ?0.2 dex, [Si/Fe] = ?0.4 dex, [S/Fe] = ?0.2 dex). The Al is slightly enhanced. The phosphorus is overabundant, i.e. [P/Fe] ≈ 1.7 ± 0.47 dex, hence LB3116 may be the first example of a PAGB star which is rich in phosphorus. With its high radial velocity (i.e.V_LSR = 73 km s^?1), and the deficiencies observed in C, Mg, Si, and S indicate that LB 3116 is likely a hot PAGB star at high galactic latitude.     

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-tonoise ratios(SNR) on the measurement of the stellar atmospheric parameters(effective temperature Teff,surface gravity log g,and metallicity [Fe/H]) . We show that ULySS is reliable for determ...     

Observational restrictions on sodium and aluminium abundance variations in evolution of the galaxy

In this paper we construct and analyze the uniform non-LTE distributions of the aluminium ([Al/Fe]-[Fe/H]) and sodium ([Na/Fe]-[Fe/H]) abundances in the sample of 160 stars of the disk and halo of our Galaxy with metallicities within ?4.07 ≤ [Fe/H] ≤ 0.28. The values of metallicity [Fe/H] and microturbulence velocity ξ _turb indices are determined from the equivalent widths of the Fe II and Fe I lines. We estimated the sodium and aluminium abundances using a 21-level model of the Na I atom and a 39-level model of the Al I atom. The resulting LTE distributions of [Na/Fe]-[Fe/H] and [Al/Fe]-[Fe/H] do not correspond to the theoretical predictions of their evolution, suggesting that a non-LTE approach has to be applied to determine the abundances of these elements. The account of non-LTE corrections reduces by 0.05–0.15 dex the abundances of sodium, determined from the subordinate lines in the stars of the disk with [Fe/H] ≥ ?2.0, and by 0.05–0.70 dex (with a strong dependence on metallicity) the abundances of [Na/Fe], determined by the resonance lines in the stars of the halo with [Fe/H] ≤ ?2.0. The non-LTE corrections of the aluminium abundances are strictly positive and increase from 0.0–0.1 dex for the stars of the thin disk (?0.7 ≤ [Fe/H] ≤ 0.28) to 0.03–0.3 dex for the stars of the thick disk (?1.5 ≤ [Fe/H] ≤ ?0.7) and 0.06–1.2 dex for the stars of the halo ([Fe/H] ≤ ?2.0). The resulting non-LTE abundances of [Na/Fe] reveal a scatter of individual values up to Δ[Na/Fe] = 0.4 dex for the stars of close metallicities. The observed non-LTE distribution of [Na/Fe]-[Fe/H] within 0.15 dex coincides with the theoretical distributions of Samland and Kobayashi et al. The non-LTE aluminium abundances are characterized by a weak scatter of values (up to Δ[Al/Fe] = 0.2 dex) for the stars of all metallicities. The constructed non-LTE distribution of [Al/Fe]-[Fe/H] is in a satisfactory agreement to 0.2 dex with the theoretical data of Kobayashi et al., but strongly differs (up to 0.4 dex) from the predictions of Samland.     

Metallicity Distributions of Elliptical Galaxies and Globular Cluster Systems

Gradients of absorption line indices are studied and mean stellar metallicities are estimated for 46 elliptical galaxies. The mean stellar metallicities range from 〈 [Fe/H] 〉 ≃ =0.8 to +0.2 and ellipticals with smaller central velocity dispersions tend to have lower 〈 [Fe/H] 〉 thus the mass-metallicity relation holds not only for the galaxy center but also for the whole part of the galaxy. There is an evidence that the magnesium is enhanced systematically in all ellipticals by 0.2 dex with respect to the iron. Giant elliptical galaxies show lack of metal-poor stars (the G-dwarf problem). Metal-poor globular clusters of ellipticals formed well in advance of the formation of metal-rich ones which formed simultaneously with the bulk of stars of mother galaxies under the influence of galaxy chemical enrichment. The bimodal [Fe/H] distribution of globular clusters does not necessarily mean that elliptical galaxies formed by the mergers of disc galaxies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Linear nonadiabatic pulsation models of the double-mode Cepheid V371 Per

A recently found double-mode Cepheid with the shortest known period in our Galaxy and abnormal period ratio,V371 Per,is investigated by linear nonadiabatic pulsation models.V371 Per is likely to be crossing the instability strip for the first time,because the mass derived from pulsation models is larger than the evolution mass for the second or higher crossing objects.This result seems to support the conclusion obtained from spectroscopic observation.We also found that models with observed period and period ratio of V371 Per need to have mass and T_(eff) in a narrow range which shifts as heavy element abundance Z changes.We have checked the agreement between T_(eff) ranges estimated observationally and derived from pulsation models using observational Z.We found that those ranges overlap marginally.We need more spectroscopic estimations of T_(eff) and [Fe/H],and more photometric monitoring to estimate the evolutional period change for confirmation of our result.     

Analysis of UBV photometry in selected area 133

We interpret the de‐reddened UBV data for the field SA 133 to deduce the stellar density and metallicity distribution functions. The logarithmic local space density for giants, D*(0) = 6.40, and the agreement of the luminosity function for dwarfs and sub‐giants with the one of Hipparcos confirms the empirical method used for their separation. The metallicity distribution for dwarfs gives a narrow peak at [Fe/H] = +0.13 dex, due to apparently bright limiting magnitude, V_o = 16.5, whereas late‐type giants extending up to z ∼ 4.5 kpc from the galactic plane have a multimodal distribution. The metallicity distribution for giants gives a steep gradient d[Fe/H]/dz = –0.75 dex kpc^–1 for thin disk and thick disk whereas a smaller value for the halo, i.e. d[Fe/H]/dz = –0.45 dex kpc^–1. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of galactic subsystems in light of the magnesium abundance in field stars: The thin disk

Data from our compiled catalog of spectroscopically determined magnesium abundances in stars with accurate parallaxes are used to select thin-disk dwarfs and subgiants according to kinematic criteria. We analyze the relations between the relative magnesium abundances in stars, [Mg/Fe], and their metallicities, Galactic orbital elements, and ages. The [Mg/Fe] ratios in the thin disk at any metallicity in the range ?1.0 dex <[Fe/H] < ?0.4 dex are shown to be smaller than those in the thick disk, implying that the thin-disk stars are, on average, younger than the thick-disk stars. The relative magnesium abundances in such metal-poor thin-disk stars have been found to systematically decrease with increasing stellar orbital radii in such a way that magnesium overabundances ([Mg/Fe] > 0.2 dex) are essentially observed only in the stars whose orbits lie almost entirely within the solar circle. At the same time, the range of metallicities in magnesium-poor stars is displaced from ?0.5 dex < [Fe/H] < +0.3 dex to ?0.7 dex < [Fe/H] < +0.2 dex as their orbital radii increase. This behavior suggests that, first, the star formation rate decreases with increasing Galactocentric distance and, second, there was no star formation for some time outside the solar circle, while this process was continuous within the solar circle. The decrease in the star formation rate with increasing Galactocentric distance is responsible for the existence of a negative radial metallicity gradient (grad _R[Fe/H] = ?0.05 ± 0.01 kpc^?1) in the disk, which shows a tendency to increase with decreasing age. At the same time, the relative magnesium abundance exhibits no radial gradient. We have confirmed the existence of a steep negative vertical metallicity gradient (grad _Z[Fe/H] = ?0.29 ± 0.06 kpc^?1) and detected a significant positive vertical gradient in relative magnesium abundance (grad _Z[Mg/Fe] = 0.13 ± 0.02 kpc^?1); both gradients increase appreciably in absolute value with decreasing age. We have found that there is not only an age-metallicity relation, but also an age-magnesium abundance relation, in the thin disk. We surmise that the thin disk has a multicomponent structure, but the existence of a negative trend in the star formation rate along the Galactocentric radius does not allow the stars of its various components to be identified in the immediate solar neighborhood.     

Abundances in Przybylski's star

We have derived abundances for 54 elements in the extreme roAp star HD 101065. ESO spectra with a resolution of about 80 000, and S/N of 200 or more were employed. The adopted model has T _eff=6600 K, and log( g )=4.2. Because of the increased line opacity and consequent low gas pressure, convection plays no significant role in the temperature structure. Lighter elemental abundances through the iron group scatter about standard abundance distribution (SAD) (solar) values. Iron and nickel are about one order of magnitude deficient while cobalt is enhanced by 1.5 dex. Heavier elements, including the lanthanides, generally follow the solar pattern but enhanced by 3 to 4 dex. Odd-Z elements are generally less abundant than their even-Z neighbours. With a few exceptions (e.g. Yb), the abundance pattern among the heavy elements is remarkably coherent, and resembles a displaced solar distribution.     

Spectroscopy of the W Virginis star V1 (K 307 ) in the globular cluster M12

High-resolution CCD spectra have been obtained for the first time for the W Virginis star V1 (K 307) in the globular cluster M12 and its closest neighbor K 307b (m _pg=14^m; the angular distance from the W Vir star is δ<1 arcsec). We determined the fundamental parameters (T _eff=5600 K, logg=1.3, and T _eff=4200 K, logg=1.0 for the W Vir star and the neighboring star, respectively) and their detailed chemical composition. The derived metallicities of the two stars ([Fe/H]=?1.27 and ?1.22 relative to the solar value) are in good agreement with the metallicities of other cluster members. Changed CNO abundances were found in the atmosphere of the W Vir star: a small carbon overabundance, [C/Fe]=+0.30 dex, and a large nitrogen overabundance, [N/Fe]=+1.15 dex, with oxygen being underabundant, [O/Fe]≈?0.2 dex. The C/O ratio is ≥1. Na and the α-process elements Mg, Al, Si, Ca, and Ti are variously enhanced with respect to iron. We found an enhanced abundance of s-process metals relative to iron: [X/Fe]=+0.34 for Y, Zr, and Ba. The overabundance of the heavier metals La, Ce, and Nd with respect to iron is larger: [X/Fe]=+0.49. The largest overabundance was found for the r-process element europium, [Eu/Fe]=+0.82. The spectrum of the W Vir star exhibits the Hα and Hβ absorption-emission profiles and the He I λ5876 Å emission line, which are traditionally interpreted as a result of shock passage in the atmosphere. However, the radial velocities determined from absorption and emission features are in conflict with the formation pattern of a strong shock. The high luminosity log L/L _⊙ = 2.98, the chemica peculiarities, and the spectral peculiarity are consistent with the post-AGB evolution in the instability strip. The pattern of relative elemental abundances [X/Fe]in the atmosphere of the neighboring star K 307b is solar. Statistically significant differences were found only for sodium and α-process elements: the mean overabundance of light metals is [X/Fe]=+0.35.     

Physical parameters of the binary star CM draconis components

Spectra of the eclipsing binary star CM Dra consisting of two M dwarfs are discussed in detail. High-resolution echelle spectra (R = 47000) obtained using the 4.2 m William Hershel telescope are used. The temperatures and metallicities of both components in the binary system are determined using the stellar spectra simulation: T = 3100 ± 100 K, logg = 5.0 ± 0.2, [M/H] = ?0.5 ± 0.2 dex. The estimated values are in good agreement with the results obtained by other researchers.