Differential abundances of open clusters and their tidal tails: Chemical tagging and chemical homogeneity

Context. Well studied open clusters (OCs) of the solar neighborhood are frequently used as reference objects to test galactic and stellar theories. For that purpose, their chemical composition needs to be known with a high level of confidence. It is also important to clarify if each OC is chemically homogeneous and if it has a unique chemical signature. Aims. The aims of this work are (1) to determine accurate and precise abundances of 22 chemical species (from Na to Eu) in the Hyades, Praesepe, and Rupecht 147 by using a large number of stars at different evolutionary states, (2) to evaluate the level of chemical homogeneity of these OCs, and (3) to compare their chemical signatures. Methods. We gathered ∼800 high resolution and high signal-to-noise spectra of ∼100 members in the three clusters, which were obtained with the latest memberships based on Gaia DR2 data. We built a pipeline, which computes atmospheric parameters and strictly line-by-line differential abundances among twin stars in our sample. With this method, we were able to reach a very high precision in the abundances (0.01–0.02 dex in most of the elements). Results. We find large differences in the absolute abundances in some elements, which can be attributed to diffusion, non-local thermodynamic equilibrium (non-LTE) effects, or systematics in the analysis. For the three OCs, we find strong correlations in the differential abundances between different pairs of elements. According to our experiment with synthetic data, this can be explained by some level of chemical inhomogeneity. We compare differential abundances of several stars from the Hyades and Praesepe tails: The stars that differ more in chemical abundances also have distinct kinematics, even though they have been identified as members of the tail. Conclusions. It is possible to obtain high precision abundances using a differential analysis even when mixing spectra from different instruments. With this technique, we find that the Hyades and Preasepe have the same chemical signature when G dwarfs and K giants are considered. Despite a certain level of inhomogeneity in each cluster, it is still possible to clearly distinguish the chemical signature of the older cluster Ruprecht 147 when compared to the Hyades and Praesepe.

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Detailed chemical compositions of planet-hosting stars – I. Exploration of possible planet signatures

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1420 ◽

2020 ◽

Vol 495 (4) ◽

pp. 3961-3973 ◽

Cited By ~ 2

Author(s):

F Liu ◽

D Yong ◽

M Asplund ◽

H S Wang ◽

L Spina ◽

...

Keyword(s):

High Precision ◽

Chemical Evolution ◽

Planet Formation ◽

Scale Efficiency ◽

High Signal ◽

Chemical Compositions ◽

Condensation Temperature ◽

Differential Analysis ◽

Chemical Abundances ◽

Comparison Stars

ABSTRACT We present a line-by-line differential analysis of a sample of 16 planet-hosting stars and 68 comparison stars using high-resolution, high signal-to-noise ratio spectra gathered using Keck. We obtained accurate stellar parameters and high-precision relative chemical abundances with average uncertainties in Teff, log g, [Fe/H], and [X/H] of 15 K, 0.034 cm s−2 , 0.012 dex, and 0.025 dex, respectively. For each planet host, we identify a set of comparison stars and examine the abundance differences (corrected for Galactic chemical evolution effect) as a function of the dust condensation temperature, Tcond, of the individual elements. While we confirm that the Sun exhibits a negative trend between abundance and Tcond, we also confirm that the remaining planet hosts exhibit a variety of abundance–Tcond trends with no clear dependence upon age, metallicity, or Teff. The diversity in the chemical compositions of planet-hosting stars relative to their comparison stars could reflect the range of possible planet-induced effects present in these planet hosts, from the sequestration of rocky material (refractory poor) to the possible ingestion of planets (refractory rich). Other possible explanations include differences in the time-scale, efficiency and degree of planet formation, or inhomogeneous chemical evolution. Although we do not find an unambiguous chemical signature of planet formation among our sample, the high-precision chemical abundances of the host stars are essential for constraining the composition and structure of their exoplanets.

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Contribution of White Dwarfs to Cluster Masses

Highlights of Astronomy ◽

10.1017/s1539299600021651 ◽

1998 ◽

Vol 11 (1) ◽

pp. 430-432

Author(s):

Ted Von Hippel

Keyword(s):

Stellar Evolution ◽

Mass Fraction ◽

Globular Clusters ◽

White Dwarfs ◽

Literature Search ◽

Galactic Disk ◽

Dynamical Evolution ◽

Open Clusters ◽

Solar Neighborhood ◽

Current Evidence

The study of cluster white dwarfs (WDs) has been invigorated recently bythe Hubble Space Telescope (HST). Recent WD studies have been motivated by the new and independent cluster distance (Renzini et al. 1996), age (von Hippel et al. 1995; Richer et al. 1997), and stellar evolution (Koester & Reimers 1996) information that cluster WDs can provide. An important byproduct of these studies has been an estimate of the WD mass contribution in open and globular clusters. The cluster WD mass fraction is of importance for understanding the dynamical state and history of star clusters. It also bears an important connection to the WD mass fractions of the Galactic disk and halo. Current evidence indicates that the open clusters (e.g. von Hippel et al. 1996; Reid this volume) have essentially the same luminosity function (LF) as the solar neighborhood population. The case for the halo is less clear, despite the number of very good globular cluster LFs down to nearly 0.1 solar masses (e.g. Cool et al. 1996; Piotto, this volume), as the field halo LF is poorly known. For most clusters dynamical evolution should cause evaporation of the lowest mass members, biasing clusters to have flatter present-day mass functions (PDMFs) than the disk and halo field populations. Dynamical evolution should also allow cluster WDs to escape, though not in the same numbers as the much lower mass main sequence stars. The detailed connection between cluster PDMFs and the field IMF awaits elucidation from observations and the new combined N-body and stellar evolution models (Tout, this volume). Nevertheless, the WD mass fraction of clusters already provides an estimate for the WD mass fraction of the disk and halo field populations. A literature search to collect cluster WDs and a simple interpretive model follow. This is a work in progress and the full details of the literature search and the model will be published elsewhere.

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Using non-solar-scaled opacities to derive stellar parameters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833753 ◽

2018 ◽

Vol 620 ◽

pp. A54 ◽

Cited By ~ 4

Author(s):

C. Saffe ◽

M. Flores ◽

P. Miquelarena ◽

F. M. López ◽

M. Jaque Arancibia ◽

...

Keyword(s):

High Precision ◽

Chemical Species ◽

Model Atmosphere ◽

Condensation Temperature ◽

Spectroscopic Methods ◽

Fundamental Parameters ◽

Evolved Stars ◽

Solar Type ◽

Scaled Models ◽

Previous Step

Aims. In an effort to improve spectroscopic methods of stellar parameters determination, we implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We wanted to compare the results with the usual solar-scaled method using a sample of solar-type and evolved stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying non-solar-scaled opacities and model atmospheres. Our sample is composed of 20 stars, including main sequence and evolved objects. The stellar parameters were determined by imposing ionization and excitation equilibrium of Fe lines, with an updated version of the FUNDPAR program, together with plane-parallel ATLAS12 model atmospheres and the MOOG code. Opacities for an arbitrary composition and vmicro were calculated through the opacity sampling (OS) method. We used solar-scaled models in the first step, and then continued the process, but scaled to the abundance values found in the previous step (i.e. non-solar-scaled). The process finishes when the stellar parameters of one step are the same as in the previous step, i.e. we use a doubly iterated method. Results. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g, and [Fe/H] amount to 26 K, 0.05 dex, and 0.020 dex for the stars in our sample. These differences can be considered the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. We note that some chemical species could also show an individual variation greater than those of the [Fe/H] (up to ~0.03 dex) and varying from one species to another, obtaining a chemical pattern difference between the two methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the solution found with the classical solar-scaled method indeed cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We discuss in the text the significance of the differences obtained when using solar-scaled versus non-solar-scaled methods. Conclusions. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as the analysis of condensation temperature Tc trends), we consider its application to be worthwhile. To date, this is probably one of the most precise spectroscopic methods for stellar parameter derivation.

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Considerations for atmospheric retrieval of high-precision brown dwarf spectra

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2289 ◽

2020 ◽

Vol 497 (4) ◽

pp. 5136-5154

Author(s):

Anjali A A Piette ◽

Nikku Madhusudhan

Keyword(s):

High Precision ◽

Thermal Emission ◽

Simulated Data ◽

Brown Dwarfs ◽

High Signal ◽

Temperature Structure ◽

Wide Field ◽

Brown Dwarf ◽

Data Set ◽

Stellar Objects

ABSTRACT Isolated brown dwarfs provide remarkable laboratories for understanding atmospheric physics in the low-irradiation regime, and can be observed more precisely than exoplanets. As such, they provide a glimpse into the future of high-signal-to-noise ratio (SNR) observations of exoplanets. In this work, we investigate several new considerations that are important for atmospheric retrievals of high-quality thermal emission spectra of sub-stellar objects. We pursue this using an adaptation of the h y dra atmospheric retrieval code. We propose a parametric pressure–temperature (P–T) profile for brown dwarfs consisting of multiple atmospheric layers, parametrized by the temperature change across each layer. This model allows the steep temperature gradient of brown dwarf atmospheres to be accurately retrieved while avoiding commonly encountered numerical artefacts. The P–T model is especially flexible in the photosphere, which can reach a few tens of bar for T-dwarfs. We demonstrate an approach to include model uncertainties in the retrieval, focusing on uncertainties introduced by finite spectral and vertical resolution in the atmospheric model used for retrieval (∼8 per cent in the present case). We validate our retrieval framework by applying it to a simulated data set and then apply it to the HST/WFC3 (Hubble Space Telescope’s Wide-Field Camera 3) spectrum of the T-dwarf 2MASS J2339+1352. We retrieve sub-solar abundances of H2O and CH4 in the object at ∼0.1 dex precision. Additionally, we constrain the temperature structure to within ∼100 K in the photosphere. Our results demonstrate the promise of high-SNR spectra to provide high-precision abundance estimates of sub-stellar objects.

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Development of high-precision distributed wireless microseismic acquisition stations

10.5194/gi-2018-17 ◽

2018 ◽

Author(s):

Shuaiqing Qiao ◽

Hongmei Duan ◽

Qisheng Zhang ◽

Qimao Zhang ◽

Shuhan Li ◽

...

Keyword(s):

Data Acquisition ◽

High Precision ◽

Oil And Gas ◽

Data Communication ◽

Microseismic Monitoring ◽

Acquisition System ◽

Seismic Exploration ◽

High Signal ◽

Control Board ◽

High Data

Abstract. In recent years, owing to the shortage of oil and gas resources and increased difficulty in mining, traditional (wired) microseismic monitoring equipment has been unable to meet the needs of energy exploitation. Therefore, it is necessary to develop new high-precision seismic exploration and data acquisition systems. In this study, we combined advance acquisition systems with wireless technology to develop a new wireless microseismic acquisition system. The hardware circuit of the acquisition system mainly included a data acquisition board and a main control board. High-precision analog-to-digital conversion and digital filtering technologies were used to provide data with high signal-to-noise ratios, resolution, and fidelity to the acquisition stations. Key technologies were integrated into the ARM of the main control board. Reliable GPS technology was employed to realize synchronous acquisitions among various acquisition stations, and WIFI technology was used to achieve wireless data communication between acquisition stations and the central station, thus improving the data transmission speed and accuracy. After conducting a series of evaluation tests, it was found that the system was stable, convenient to use, and had high data accuracy, therefore providing significant support for the solution to problems encountered in current oil and gas exploration processes, such as the complicated environment and inconvenient construction.

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Observational Constraints on Mode Excitation in δ-Scuti Stars In Open Clusters

International Astronomical Union Colloquium ◽

10.1017/s0252921100018789 ◽

1993 ◽

Vol 137 ◽

pp. 746-748 ◽

Cited By ~ 2

Author(s):

S. Frandsen ◽

H. Kjeldsen

Keyword(s):

Internal Structure ◽

High Precision ◽

Open Clusters ◽

Stellar Structure ◽

Observational Constraints ◽

Sensitive Measure ◽

Mode Excitation ◽

Scuti Stars ◽

Δ Scuti Stars

The special opportunities offered by δ-Scuti stars are the following: -They regularly oscillate in several modes, and with high precision observations one has measured of the order 5 modes (Michel and Baglin 1991-The excitation is a very delicate and therefore a very sensitive measure of the internal structure.-They are found in open clusters which constitute a very rich scenario for tests of the theory of stellar structure and evolution. This makes it feasible to observe several stars simultaneously and gain more results than for single stars.-The brightness is moderately high and still they live long enough to be present in a variety of clusters and in the field as well.

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Assessing positive matrix factorization model fit: a new method to estimate uncertainty and bias in factor contributions at the measurement time scale

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-497-2009 ◽

2009 ◽

Vol 9 (2) ◽

pp. 497-513 ◽

Cited By ~ 23

Author(s):

J. G. Hemann ◽

G. L. Brinkman ◽

S. J. Dutton ◽

M. P. Hannigan ◽

J. B. Milford ◽

...

Keyword(s):

Matrix Factorization ◽

Time Scale ◽

Synthetic Data ◽

Chemical Species ◽

Positive Matrix Factorization ◽

Pollution Source ◽

Model Fit ◽

Receptor Model ◽

Positive Matrix ◽

Factor Contribution

Abstract. A Positive Matrix Factorization receptor model for aerosol pollution source apportionment was fit to a synthetic dataset simulating one year of daily measurements of ambient PM2.5 concentrations, comprised of 39 chemical species from nine pollutant sources. A novel method was developed to estimate model fit uncertainty and bias at the daily time scale, as related to factor contributions. A circular block bootstrap is used to create replicate datasets, with the same receptor model then fit to the data. Neural networks are trained to classify factors based upon chemical profiles, as opposed to correlating contribution time series, and this classification is used to align factor orderings across the model results associated with the replicate datasets. Factor contribution uncertainty is assessed from the distribution of results associated with each factor. Comparing modeled factors with input factors used to create the synthetic data assesses bias. The results indicate that variability in factor contribution estimates does not necessarily encompass model error: contribution estimates can have small associated variability across results yet also be very biased. These findings are likely dependent on characteristics of the data.

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Comparison of errors between a differential and a classical abundance analysis

Canadian Journal of Physics ◽

10.1139/cjp-2016-0877 ◽

2017 ◽

Vol 95 (9) ◽

pp. 855-857

Author(s):

Henrique Reggiani ◽

Jorge Meléndez

Keyword(s):

Measurement Errors ◽

Signal To Noise Ratio ◽

High Signal ◽

Differential Analysis ◽

Analysis Method ◽

Chemical Abundances ◽

Differential Abundance ◽

Low Metallicity ◽

Low Levels ◽

Differential Abundance Analysis

The differential abundance analysis method can improve the precision of stellar chemical abundances. The method compares the equivalent widths of a certain line in a star with the same line in a star considered to be a standard representative of its class, using high resolution and high signal to noise ratio spectra. The method has achieved great results by reducing the measurement errors to unprecedentedly low levels. However, to date, there has not been a consistent analysis on the actual improvements of this method when compared to a classical analysis in metal-poor stars. Here we present a comparison between the errors of a classical stellar analysis and a differential analysis among low-metallicity stars.

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Mixing in Magnetized Interiors of Solar-Type Stars: Frequently Asked Questions

Highlights of Astronomy ◽

10.1017/s1539299600013599 ◽

2002 ◽

Vol 12 ◽

pp. 301-303

Author(s):

Paul Charbonneau

Keyword(s):

Angular Momentum ◽

Turbulent Mixing ◽

Chemical Species ◽

Light Element ◽

Open Clusters ◽

Short Paper ◽

Angular Momentum Transport ◽

Solar Type ◽

Element Evolution ◽

Seismic Measurements

AbstractThis short paper discusses various issues pertaining to the redistribution of angular momentum and mixing of chemical species in the radiative interior of solar-type stars. Results obtained to date indicate that models combining magnetically-mediated angular momentum transport with turbulent mixing of chemical species offer the best hope of explaining the observed rotation and light element evolution in open clusters, without doing excess violence to seismic measurements of the solar internal differential rotation.

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The Spiral Structure in the Solar Neighborhood

Frontiers in Astronomy and Space Sciences ◽

10.3389/fspas.2021.671670 ◽

2021 ◽

Vol 8 ◽

Author(s):

L. G. Hou

Keyword(s):

Spiral Structure ◽

Open Clusters ◽

Solar Neighborhood ◽

High Mass ◽

Mass Star ◽

Giant Molecular Clouds ◽

Star Formation Region ◽

Spiral Arms ◽

Different Types ◽

Better Than

The spiral structure in the solar neighborhood is an important issue in astronomy. In the past few years, there has been significant progress in observation. The distances for a large number of good spiral tracers, i.e., giant molecular clouds, high-mass star-formation region masers, HII regions, O-type stars, and young open clusters, have been accurately estimated, making it possible to depict the detailed properties of nearby spiral arms. In this work, we first give an overview about the research status for the Galaxy’s spiral structure based on different types of tracers. Then the objects with distance uncertainties better than 15% and <0.5 kpc are collected and combined together to depict the spiral structure in the solar neighborhood. Five segments related with the Perseus, Local, Sagittarius-Carina, Scutum-Centaurus, and Norma arms are traced. With the large dataset, the parameters of the nearby arm segments are fitted and updated. Besides the dominant spiral arms, some substructures probably related to arm spurs or feathers are also noticed and discussed.

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