A5017110401- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- History and Developments in Astronomy
- CCD and CMOS Imaging Sensors
- nanoparticles nucleation surface interactions
- Scientific Research and Discoveries
- Atmospheric Ozone and Climate
- Solidification and crystal growth phenomena
- Spectroscopy and Laser Applications
- Advanced Chemical Physics Studies
- Spectroscopy and Chemometric Analyses
- Pulsars and Gravitational Waves Research
- Photocathodes and Microchannel Plates
- Superconducting and THz Device Technology
- Phase Equilibria and Thermodynamics
- Astrophysical Phenomena and Observations
- Graph theory and applications
- Geophysics and Gravity Measurements
- Analytic Number Theory Research
Universidade de São Paulo
2014-2024
Museu de Astronomia e Ciências Afins
2004-2023
Instituto de Geofísica y Astronomía
2023
Universidade Cidade de São Paulo
2019-2022
Weatherford College
2021
Michigan State University
1998-2011
University of Copenhagen
2011
Indian Institute of Astrophysics
2011
Joint Institute for Nuclear Astrophysics
2008-2010
Osservatorio Astronomico di Padova
2010
We present the results of analysis "snapshot" spectra 253 metal-poor halo stars obtained in HERES survey. The snapshot have been with VLT/UVES and typically per pixel (ranging from 17 to 308), , –4980 Å. This sample represents major part complete 373 stars; however, CH strong content is not dealt here. are analysed using an automated line profile method based on Spectroscopy Made Easy (SME) codes Valenti & Piskunov. Elemental abundances moderate precision (absolute rms errors order 0.25 dex,...
We estimate the frequency of carbon-enhanced metal-poor (CEMP) stars among very stars, based on an analysis 349 with available high-resolution spectra observed as part Hamburg/ESO R-process Enhanced Star (HERES) survey. obtain that a lower limit 21% ± 2% [Fe/H] ≤ -2.0 exhibit [C/Fe] ≥ +1.0. These fractions are higher than those have been reported by recent examinations this question, substantially smaller samples stars. discuss source difference and suggest in order to take into account...
We combine spectroscopic, photometric, and astrometric information from APOGEE data release 17 $Gaia$ early 3 to perform a self-consistent characterization of $Gaia$-Sausage/Enceladus (GSE), the remnant last major merger experienced by Milky Way, considering stars globular clusters (GCs) altogether. Our novel set chemodynamical criteria select genuine GSE yields metallicity distribution function with median [Fe/H] $-1.22$ dex $0.23$ dispersion. Stars present an excess [Al/Fe] [Mg/Mn] (also...
We present a revised catalog of 2106 Galactic stars, selected without kinematic bias and with available radial velocities, distance estimates, metal abundances in the range -4.0 ≤ [Fe/H] 0.0. This update 1995 Beers & Sommer-Larsen includes newly derived homogeneous photometric velocities for number stars recently obtained high-resolution spectra, refined metallicities originally identified HK objective-prism survey (which account nearly half catalog) based on recent recalibration. A subset...
We have recalibrated a method for the estimation of stellar metal abundance, parameterized as [Fe/H], based on medium-resolution (1–2 Å) optical spectra (the majority which cover wavelength range 3700–4500 Å). The equivalent width Ca II K line (3933 function [Fe/H] and broadband B-V color, predicted from spectrum synthesis model atmosphere calculations, is compared with observations 551 stars high-resolution abundances available literature (a sevenfold increase in number calibration that...
We present a sample of 1777 bright (9 < B 14) metal-poor candidates selected from the Hamburg/ESO Survey (HES). Despite saturation effects in red portion HES objective-prism spectra, data were recoverable and quantitative selection criteria could be applied to select sample. Analyses medium-resolution (~2 Å) follow-up spectroscopy entire sample, obtained with several 2-4 m class telescopes, yielded 145 new stars metallicity [Fe/H] -2.0, which 79 have -2.5 17 -3.0. also C/Fe estimates for all...
We present a detailed study of Carbon-Enhanced Metal-Poor (CEMP) stars, based on high-resolution spectroscopic observations sample 18 stars. The stellar spectra for this were obtained at the 4.2m William Herschel Telescope (WHT) in 2001 and 2002, using Utrecht Echelle Spectrograph (UES), resolving power R ~52000 S/N ~ 40, covering wavelength range lambda-lambda 3700-5700 A. atmospheric parameters determined indicate temperatures ranging from 4750 C to 7100 K, log g 1.5 4.3, metallicities...
Abstract We analyze the dynamical properties of ∼1500 very metal-poor (VMP; [Fe/H] ≲ −2.0) halo stars, based primarily on medium-resolution spectroscopic data from HK and Hamburg/ESO surveys. These data, collected over past 30 yr, are supplemented by a number calibration stars other small samples, along with astrometric information Gaia DR2. apply clustering algorithm to 4D energy-action space sample, identify set 38 dynamically tagged groups (DTGs), containing between 5 member stars. Many...
ABSTRACT We present the first detailed chemical-abundance analysis of stars from dwarf-galaxy stellar stream Wukong/LMS-1 covering a wide metallicity range ($-3.5 \lt \rm [Fe/H] \lesssim -1.3$). find abundance patterns that are effectively indistinguishable bulk Indus and Jhelum, pair smaller streams proposed to be dynamically associated with Wukong/LMS-1. confirmed carbon-enhanced metal-poor star ($\rm [C/Fe] \gt +0.7$ $\rm \sim -2.9$) in strong enhancements Sr, Y, Zr, which is peculiar...
We report on a dedicated effort to identify and study metal-poor stars strongly enhanced in r-process elements ([r/Fe] > 1 dex; hereafter r-II stars), the Hamburg/ESO R-process Enhanced Star survey (HERES). Moderate-resolution (~2A) follow-up spectroscopy has been obtained for giant candidates selected from objective-prism (HES) as well HK sharp-lined with [Fe/H] < -2.5dex. For several hundred confirmed giants brighter than B~16.5mag (most of them HES), ``snapshot'' spectra (R~20,000; S/N~30...
We obtain estimates of stellar atmospheric parameters for a previously published sample 1777 relatively bright (9 < B 14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel et al. analysis these stars was only able to derive [Fe/H] and [C/Fe] subset sample, due limitations in methodology then available. A new spectroscopic pipeline has been used Teff, log g, [Fe/H], almost entire dataset. This is very local - about 90% are located within 0.5 kpc Sun. consider...
We report medium-resolution (1–2 Å) spectroscopy and broadband (UBV) photometry for a sample of 39 bright stars (the majority which are likely to be giants) selected as metal-deficient candidates from an objective-prism survey concentrating on Galactic latitudes below |b| = 30°, the Luminous Stars Extension (LSE) Drilling & Bergeron. Although primary purpose LSE was select OB (hence concentration low latitudes), small number giant noted during this provide interesting information metal-weak...
We report broadband UBV and/or BVRCIC CCD photometry for a total of 1857 stars in the thick-disk and halo populations Galaxy. The majority our targets were selected as candidate field horizontal-branch or other A-type (FHB/A, N = 576), low-metallicity (N 1221), from HK Hamburg/ESO objective-prism surveys. Similar data small number additional samples are also reported. These being used several purposes. In case FHB/A candidates they to accurately separate lower gravity FHB various higher...
A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ∼ 3000) optical spectra have been obtained for 302 the candidate "weak-metal" stars selected by Bidelman & MacConnell. We use these data to calibrate recently developed generalization Sloan Extension Galactic Exploration and Understanding (SEGUE) Stellar Parameter Pipeline, obtain estimates atmospheric parameters (Teff, log g, [Fe/H]) non-Sloan Digital Sky Survey/SEGUE data; we also [C/Fe]. The abundance measurements...
We present a comprehensive abundance analysis of two newly-discovered carbon-enhanced metal-poor (CEMP) stars. HE2138-3336 is s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] ratio measured thus far, if NLTE corrections are included ([Pb/Fe] +3.84). HE2258-6358, -2.67, exhibits enrichments in both s- r-process elements. These stars were selected from sample candidate Hamburg/ESO objective-prism survey, followed up medium-resolution (R ~ 2,000) spectroscopy GEMINI/GMOS....
We obtain a new determination of the metallicity distribution function (MDF) stars within ∼5–10 kpc Sun, based on recently improved co-adds ugriz photometry for Stripe 82 from Sloan Digital Sky Survey. Our estimate uses methodology developed previously by An et al. to study in situ halo stars, but is factor two larger sample than available before, with much-improved photometric errors and zero-points. The newly obtained MDF can be divided into multiple populations peak metallicities at...
We report on the discovery of seven low-metallicity stars selected from Hamburg/ESO Survey, six which are extremely metal-poor (EMP, [Fe/H] ⩽ −3.0), with four having −3.5. Chemical abundances or upper limits derived for these based high-resolution (R ∼ 35,000) Magellan/MIKE spectroscopy, and in general agreement those other very reported literature. Accurate metallicities abundance patterns this metallicity range particular importance studies shape distribution function Milky Way's halo...
Abstract We present results from a medium-resolution ( R ∼ 2000) spectroscopic follow-up campaign of 1694 bright V < 13.5), very metal-poor star candidates the RAdial Velocity Experiment (RAVE). Initial selection low-metallicity targets was based on stellar parameters published in RAVE Data Releases 4 and 5. Follow up accomplished with Gemini-N Gemini-S, ESO/NTT, KPNO/Mayall, SOAR telescopes. The wavelength coverage for most observed spectra allows determination carbon α -element...
Abstract In the first billion years after its formation, Galaxy underwent several mergers with dwarf satellites of various masses. The debris Gaia-Sausage/Enceladus (GSE), galaxy responsible for last significant merger Milky Way, dominates inner halo and has been suggested to be progenitor both Hercules-Aquila Cloud (HAC) Virgo Overdensity (VOD). We combine SEGUE, APOGEE, Gaia, StarHorse distances characterize chemodynamical properties verify link between HAC, VOD, GSE. find that orbital...
The Na I near-infrared feature has been used to indicate the dwarf/giant population in composite systems, but its interpretation is still an issue of contention. In order try understand behavior this controversial feature, we study spectra cool stars by means both observed and synthetic spectra.
We develop and test a method for the estimation of metallicities ([Fe/H]) carbon abundance ratios ([C/Fe]) carbon-enhanced metal-poor (CEMP) stars based on application artificial neural networks, regressions, synthesis models to medium-resolution (1–2 Å) spectra J - K colors. calibrate this by comparison with determinations 118 available high-resolution analyses reported in recent literature. The network regression approaches make use previously defined set line-strength indices quantifying...