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Deep SDSS optical spectroscopy of distant halo stars
摘要： Aims. We analyze a sample of tens of thousands of spectra of halo turno? stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population “in situ” out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as ?ux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each observed spectrum best. We used an optimization algorithm and evaluate model ?uxes by means of interpolation in a precomputed grid. In our analysis, we account for the spectrograph’s varying resolution as a function of ?ber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 2.5, con?rming the systematics identi?ed in the comparison with the SSPP. We ?nd that our metallicity estimates are signi?cantly more precise than the SSPP results. We also ?nd excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turno? stars as ?ux calibrators e?ciently excludes stars with high metallicities, but does not signi?cantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way.
关键词： techniques: spectroscopic,stars: atmospheres,methods: observational,Galaxy: halo,stars: Population II,stars: fundamental parameters
更新于2025-09-23 15:19:57
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The HARPS search for southern extra-solar planets
摘要： Context. We present radial-velocity measurements of eight stars observed with the HARPS Echelle spectrograph mounted on the 3.6-m telescope in La Silla (ESO, Chile). Data span more than ten years and highlight the long-term stability of the instrument. Aims. We search for potential planets orbiting HD 20003, HD 20781, HD 21693, HD 31527, HD 45184, HD 51608, HD 134060 and HD 136352 to increase the number of known planetary systems and thus better constrain exoplanet statistics. Methods. After a preliminary phase looking for signals using generalized Lomb-Scargle periodograms, we perform a careful analysis of all signals to separate bona-fide planets from signals induced by stellar activity and instrumental systematics. We finally secure the detection of all planets using the efficient MCMC available on the Data and Analysis Center for Exoplanets (DACE web-platform), using model comparison whenever necessary. Results. In total, we report the detection of twenty new super-Earth to Neptune-mass planets, with minimum masses ranging from 2 to 30 MEarth and periods ranging from 3 to 1300 days, in multiple systems with two to four planets. Adding CORALIE and HARPS measurements of HD20782 to the already published data, we also improve the characterization of the extremely eccentric Jupiter orbiting this visual companion of HD 20781.
关键词： techniques: radial velocities,stars: general,methods: data analysis,techniques: spectroscopic,planetary systems
更新于2025-09-19 17:15:36
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Data Reduction Pipeline of the TOU Optical Very High Resolution Spectrograph and Its sub-m?s?1?Performance
摘要： TOU is an extremely high resolution optical spectrograph (R = 100 000, 380–900 nm), which is designed to detect low-mass exoplanets using the radial velocity technique. We describe an IDL-based radial velocity (RV) data reduction pipeline for the TOU spectrograph and its performance with stable stars. This pipeline uses a least-squares fitting algorithm to match observed stellar spectra to a high-signal-to-noise template created for each star. By carefully controlling all of the error contributions to RV measurements in both the hardware and data pipeline, we have achieved ～0.9 m s?1 long-term RV precision with one of the most RV-stable stars, Tau Ceti, similar to what has been achieved with HARPS. This paper presents steps and details in our data pipeline on how to reach the sub-m s?1 RV precision and also all major error sources that contribute to the final RV measurement uncertainties. The lessons learned in this pipeline development can be applied to other environmentally controlled, very high resolution optical spectrographs to improve RV precision.
关键词： techniques: radial velocities,planets and satellites: detection,instrumentation: spectrographs,techniques: spectroscopic
更新于2025-09-19 17:15:36
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Benchmark stars for <i>Gaia</i> Fundamental properties of the Population II star HD?140283 from interferometric, spectroscopic, and photometric data
摘要： Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD 140283 is the closest and brightest metal-poor Population II halo star (distance = 58 pc and V = 7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD 140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of θ1D = 0.353 ± 0.013 milliarcsec. Using photometry from the literature we derived the bolometric flux in two ways: a zero reddening solution (AV = 0.0 mag) of Fbol of 3.890 ± 0.066 × 10?8 erg s?1 cm?2, and a maximum of AV = 0.1 mag solution of 4.220 ± 0.067 × 10?8 erg s?1 cm?2. The interferometric Teff is thus between 5534 ± 103 K and 5647 ± 105 K and its radius is R = 2.21 ± 0.08 R⊙. Spectroscopic measurements of HD 140283 were obtained using HARPS, NARVAL, and UVES and a 1D LTE analysis of Hα line wings yielded Teff spec = 5626 ± 75 K. Using fine-tuned stellar models including diffusion of elements we then determined the mass M and age t of HD 140283. Once the metallicity has been fixed, the age of the star depends on M, initial helium abundance Yi, and mixing-length parameter α, only two of which are independent. We derive simple equations to estimate one from the other two. We need to adjust α to much lower values than the solar one (～2) in order to fit the observations, and if AV = 0.0 mag then 0.5 ≤ α ≤ 1. We give an equation to estimate t from M, Yi (α), and AV. Establishing a reference α = 1.00 and adopting Yi = 0.245 we derive a mass and age of HD 140283: M = 0.780 ± 0.010 M⊙ and t = 13.7 ± 0.7 Gyr (AV = 0.0 mag), or M = 0.805 ± 0.010 M⊙ and t = 12.2 ± 0.6 Gyr (AV = 0.1 mag). Our stellar models yield an initial (interior) metal-hydrogen mass fraction of [Z/X]i = ?1.70 and log g = 3.65 ± 0.03. Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Yi, and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results.
关键词： stars: fundamental parameters,techniques: spectroscopic,surveys,stars: individual: HD 140283,techniques: interferometric,stars: Population II
更新于2025-09-19 17:15:36
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Spatial deconvolution of spectropolarimetric data: an application to quiet Sun magnetic elements
摘要： Context. One of the difficulties in extracting reliable information about the thermodynamical and magnetic properties of solar plasmas from spectropolarimetric observations is the presence of light dispersed inside the instruments, known as stray light. Aims. We aim to analyze quiet Sun observations after the spatial deconvolution of the data. We examine the validity of the deconvolution process with noisy data as we analyze the physical properties of quiet Sun magnetic elements. Methods. We used a regularization method that decouples the Stokes inversion from the deconvolution process, so that large maps can be quickly inverted without much additional computational burden. We applied the method on Hinode quiet Sun spectropolarimetric data. We examined the spatial and polarimetric properties of the deconvolved profiles, comparing them with the original data. After that, we inverted the Stokes profiles using the Stokes Inversion based on Response functions (SIR) code, which allow us to obtain the optical depth dependence of the atmospheric physical parameters. Results. The deconvolution process increases the contrast of continuum images and makes the magnetic structures sharper. The deconvolved Stokes I profiles reveal the presence of the Zeeman splitting while the Stokes V profiles significantly change their amplitude. The area and amplitude asymmetries of these profiles increase in absolute value after the deconvolution process. We inverted the original Stokes profiles from a magnetic element and found that the magnetic field intensity reproduces the overall behavior of theoretical magnetic flux tubes, that is, the magnetic field lines are vertical in the center of the structure and start to fan when we move far away from the center of the magnetic element. The magnetic field vector inferred from the deconvolved Stokes profiles also mimic a magnetic flux tube but in this case we found stronger field strengths and the gradients along the line-of-sight are larger for the magnetic field intensity and for its inclination. Moreover, the discontinuity between the magnetic and non magnetic environment in the flux tube gets sharper. Conclusions. The deconvolution process used in this paper reveals information that the smearing induced by the point spread function (PSF) of the telescope hides. Additionally, the deconvolution is done with a low computational load, making it appealing for its use on the analysis of large data sets.
关键词： Sun: photosphere,techniques: polarimetric,methods: statistical,methods: data analysis,Sun: magnetic fields,techniques: spectroscopic
更新于2025-09-19 17:15:36
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An Empirical Template Library for FGK and Late-type A Stars Using LAMOST Observed Spectra
摘要： We present an empirical stellar spectra library created using spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR5. This library represents a uniform data set ranging from 3750 through 8500 K in effective temperature (Teff), from ?2.5 through +1.0 dex in metallicity ([Fe/H]), and from 0 to 5.0 dex in gravity (log g). The spectra in the library have resolutions R ～ 1800, with well-calibrated fluxes and rest-framed wavelengths. Using a large number of red stars observed by LAMOST, we generated denser K-type templates to fill in data missing from current empirical spectral libraries, particularly the late K type. For K giants, we calibrated the spectroscopic surface gravities against the asteroseismic surface gravities. To verify the reliability of the parameters labeled for this library, we performed an internal cross-validation using a χ2 minimization method to interpolate the parameters of each individual spectrum using the remaining spectra in the library. We obtained precisions of 41 K, 0.11 dex, and 0.05 dex for Teff, log g, and [Fe/H], respectively, which means the templates are labeled with correct stellar parameters. Through external comparisons, we confirmed that measurements of the stellar parameters through this library can achieve accuracies of approximately 125 K in Teff, 0.1 dex in [Fe/H] and 0.20 dex in log g without systematic offset. This empirical library is useful for stellar parameter measurements because it has large parameter coverage and full wavelength coverage from 3800 to 8900 ?.
关键词： methods: statistical,techniques: spectroscopic,methods: data analysis
更新于2025-09-19 17:15:36
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Classification of large-scale stellar spectra based on deep convolutional neural network
摘要： Classification of stellar spectra from voluminous spectra is a very important and challenging task. In order to better classify stellar spectra, inspired by the principle of deep convolutional neural network (CNN), we propose a supervised algorithm for stellar spectra classification based on 1D stellar spectra convolutional neural network (1D SSCNN). In 1D SSCNN, we modify the traditional 2D convolutional neural network into 1D network to adapt to the spectral classification. On the basis of using convolution algorithm, the spectral features are extracted and used for classification. We first use the stellar spectra data to train a 1D SSCNN to obtain a well-trained model, and then we apply the well-trained model to classify the unknown spectra. To evaluate the performance of the proposed algorithms, we apply 1D SSCNN to classify three spectral types: F-type spectra, G-type spectra, and K-type spectra and 10 subclasses of K-type spectra: A0-type, A5-type, F0-type, F5-type, G0-type, G5-type, K0-type, K5-type, M0-type, and M5-type spectra from Sloan Digital Sky Survey (SDSS). Our 1D SSCNN algorithm obtain higher classification accuracy compared with support vector machine (SVM), random forest (RF), and artificial neural network (ANN).
关键词： methods: statistical,stars: statistics,methods: data analysis,astronomical data bases: miscellaneous,techniques: spectroscopic
更新于2025-09-19 17:15:36
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Simultaneous UV- and ion processing of astrophysically relevant ices
摘要： Context. Interstellar ices are known to be simultaneously processed by both cosmic-ray bombardment and UV photolysis. Our knowledge of the effects of energetic processing on relevant icy samples is mainly based on laboratory investigations. In the past 35 years many experiments have been performed to study these effects separately but, to the best of our knowledge, never simultaneously. Aims. The aim of this work is to study the effects of simultaneous processing of ices by both cosmic rays and UV photons to investigate to what extent the combined effect of ion bombardment and UV photolysis influences the chemical pathways. Methods. We carried out the simultaneous processing of CH3OH:N2 ice held at 16 K by 200 keV H+ ions and Lyman-alpha 10.2 eV UV photons. The samples were analyzed by in situ transmission infrared spectroscopy. The un-combined processes of UV irradiation and bombardment by H+ ions of CH3OH:N2 ice were also studied. This mixture was chosen because the effects of ion bombardment and UV photolysis on methanol and nitrogen have been extensively studied in previous investigations. This mixture enables one to investigate whether simultaneous processing (a) influences the destruction of original species; (b) influences the formation of new species; or (c) causes synergistic effects since Lyman-alpha photons have a very low efficiency in breaking the dinitrogen bond because N2 is almost transparent at Lyman-alpha wavelengths. Results. After processing a CH3OH:N2 sample, the intensity of the methanol bands was observed to decrease at the same rate in all cases. After ion bombardment, species such as CO2, CO, H2CO, CH4, N2O, HNCO, and OCN? are formed in the ice mixture. After UV photolysis, species such as CO2, CO, H2CO, and CH4 are formed, but no N-bearing species are detected. Spectra of ices processed by both UV photons and ions were compared with spectra of ices bombarded only by ions. We find that there are no differences in the band area and profile of N-bearing species for the two types of experiment at the same ion fluence; therefore, the addition of UV irradiation to ion bombardment does not affect the abundance of N-bearing species. The initial formation rate of CH4, within the experimental uncertainties, is the same in all cases studied, while the saturation value of CH4 is higher for UV photolysis than for ion bombardment when they act separately. In the case of simultaneous processing, when the dose (eV/16u) given by UV photons is similar to the dose given during ion bombardment, the saturation value of CH4 reaches a value intermediate between the value obtained after UV photolysis and ion bombardment separately. Conclusions. Our results confirm that when UV photolysis and ion bombardment act separately, their effects are very similar from a qualitative point of view, while significant quantitative difference may exist. In the case of simultaneous processing we did not detect any synergistic effect, but in some instances the behavior of newly formed species (such as CH4) can significantly depend on the UV/ions dose ratio.
关键词： astrochemistry,ISM: molecules,techniques: spectroscopic,molecular processes,methods: laboratory
更新于2025-09-19 17:15:36
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The GAPS programme with HARPS-N at TNG
摘要： Aims. We observed the τ Boo system with the HARPS-N spectrograph to test a new observational strategy aimed at jointly studying asteroseismology, the planetary orbit, and star-planet magnetic interaction. Methods. We collected high-cadence observations on 11 nearly consecutive nights and for each night averaged the raw FITS files using a dedicated software. In this way we obtained spectra with a high signal-to-noise ratio, used to study the variation of the Ca ii H&K lines and to have radial velocity values free from stellar oscillations, without losing the oscillations information. We developed a dedicated software to build a new custom mask that we used to refine the radial velocity determination with the HARPS-N pipeline and perform the spectroscopic analysis. Results. We updated the planetary ephemeris and showed the acceleration caused by the stellar binary companion. Our results on the stellar activity variation suggest the presence of a high-latitude plage during the time span of our observations. The correlation between the chromospheric activity and the planetary orbital phase remains unclear. Solar-like oscillations are detected in the radial velocity time series: we estimated asteroseismic quantities and found that they agree well with theoretical predictions. Our stellar model yields an age of 0.9 ± 0.5 Gyr for τ Boo and further constrains the value of the stellar mass to 1.38 ± 0.05 M☉.
关键词： planetary systems,techniques: spectroscopic,stars: activity,stars: individual: τ Boo,asteroseismology
更新于2025-09-19 17:15:36
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Using near-infrared spectroscopy for characterization of transiting exoplanets
摘要： Context. We propose a method for observing transiting exoplanets with near-infrared high-resolution spectrometers. Aims. We aim to create a robust data analysis method for recovering atmospheric transmission spectra from transiting exoplanets over a wide wavelength range in the near-infrared. Methods. By using an inverse method approach, combined with stellar models and telluric transmission spectra, the method recovers the transiting exoplanet’s atmospheric transmittance at high precision over a wide wavelength range. We describe our method and have tested it by simulating observations. Results. This method is capable of recovering transmission spectra of high enough accuracy to identify absorption features from molecules such as O2, CH4, CO2, and H2O. This accuracy is achievable for Jupiter-size exoplanets at S/N that can be reached for 8 m class telescopes using high-resolution spectrometers (R > 20 000) during a single transit, and for Earth-size planets and super-Earths transiting late K or M dwarf stars at S/N reachable during observations of less than 10 transits. We also analyse potential error sources to show the robustness of the method. Conclusions. Detection and characterization of atmospheres of both Jupiter-size planets and smaller rocky planets looks promising using this set-up.
关键词： methods: data analysis,infrared: planetary systems,planets and satellites: atmospheres,techniques: spectroscopic
更新于2025-09-19 17:15:36