scholarly journals Keck HIRES spectroscopy of SkyMapper commissioning survey candidate extremely metal-poor stars

2019 ◽  
Vol 485 (4) ◽  
pp. 5153-5167 ◽  
Author(s):  
A F Marino ◽  
G S Da Costa ◽  
A R Casey ◽  
M Asplund ◽  
M S Bessell ◽  
...  
Keyword(s):  
High Resolution ◽  
Galactic Halo ◽  
High Dispersion ◽  
Chemical Abundances ◽  
Data Survey ◽  
Current Sample

Abstract We present results from the analysis of high-resolution spectra obtained with the Keck HIRES spectrograph for a sample of 17 candidate extremely metal-poor (EMP) stars originally selected from commissioning data obtained with the SkyMapper telescope. Fourteen of the stars have not been observed previously at high dispersion. Three have [Fe/H] ≤ −3.0, while the remainder, with two more metal-rich exceptions, have −3.0 ≤ [Fe/H] ≤ −2.0 dex. Apart from Fe, we also derive abundances for the elements C, N, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, and Zn, and for n-capture elements Sr, Ba, and Eu. None of the current sample of stars is found to be carbon-rich. In general, our chemical abundances follow previous trends found in the literature, although we note that two of the most metal-poor stars show very low [Ba/Fe] (∼−1.7) coupled with low [Sr/Ba] (∼−0.3). Such stars are relatively rare in the Galactic halo. One further star, and possibly two others, meet the criteria for classification as a r-I star. This study, together with that of Jacobson et al. (2015), completes the outcomes of the SkyMapper commissioning data survey for EMP stars.

scholarly journals VLT/FLAMES high-resolution chemical abundances in Sculptor: a textbook dwarf spheroidal galaxy

2019 ◽  
Vol 626 ◽  
pp. A15 ◽  
Author(s):  
V. Hill ◽  
Á. Skúladóttir ◽  
E. Tolstoy ◽  
K. A. Venn ◽  
M. D. Shetrone ◽  
...  
Keyword(s):  
High Resolution ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Automated Analysis ◽  
Mass Function ◽  
Initial Mass Function ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Type Ia ◽  
Supernovae Type Ia

We present detailed chemical abundances for 99 red-giant branch stars in the centre of the Sculptor dwarf spheroidal galaxy, which have been obtained from high-resolution VLT/FLAMES spectroscopy. The abundances of Li, Na, α-elements (O, Mg, Si, Ca Ti), iron-peak elements (Sc, Cr, Fe, Co, Ni, Zn), and r- and s-process elements (Ba, La, Nd, Eu) were all derived using stellar atmosphere models and semi-automated analysis techniques. The iron abundances populate the whole metallicity distribution of the galaxy with the exception of the very low metallicity tail, −2.3 ≤ [Fe/H] ≤ −0.9. There is a marked decrease in [α/Fe] over our sample, from the Galactic halo plateau value at low [Fe/H] and then, after a “knee”, a decrease to sub-solar [α/Fe] at high [Fe/H]. This is consistent with products of core-collapse supernovae dominating at early times, followed by the onset of supernovae type Ia as early as ∼12 Gyr ago. The s-process products from low-mass AGB stars also participate in the chemical evolution of Sculptor on a timescale comparable to that of supernovae type Ia. However, the r-process is consistent with having no time delay relative to core-collapse supernovae, at least at the later stages of the chemical evolution in Sculptor. Using the simple and well-behaved chemical evolution of Sculptor, we further derive empirical constraints on the relative importance of massive stars and supernovae type Ia to the nucleosynthesis of individual iron-peak and α-elements. The most important contribution of supernovae type Ia is to the iron-peak elements: Fe, Cr, and Mn. There is, however, also a modest but non-negligible contribution to both the heavier α-elements: S, Ca and Ti, and some of the iron-peak elements: Sc and Co. We see only a very small or no contribution to O, Mg, Ni, and Zn from supernovae type Ia in Sculptor. The observed chemical abundances in Sculptor show no evidence of a significantly different initial mass function, compared to that of the Milky Way. With the exception of neutron-capture elements at low [Fe/H], the scatter around mean trends in Sculptor for [Fe/H] >  −2.3 is extremely low, and compatible with observational errors. Combined with the small scatter in the age-elemental abundances relation, this calls for an efficient mixing of metals in the gas in the centre of Sculptor since ∼12 Gyr ago.

scholarly journals A coma-free super-high resolution optical spectrometer using 44 high dispersion sub-gratings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hua-Tian Tu ◽  
An-Qing Jiang ◽  
Jian-Ke Chen ◽  
Wei-Jie Lu ◽  
Kai-Yan Zang ◽  
...  
Keyword(s):  
High Resolution ◽  
Spectral Resolution ◽  
Wavelength Region ◽  
Ultra Violet ◽  
High Spectral Resolution ◽  
Visible Range ◽  
High Dispersion ◽  
Charge Coupled Device ◽  
Wide Range ◽  
High Resolution Spectrometer

AbstractUnlike the single grating Czerny–Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

scholarly journals Masses and ages for metal-poor stars

2019 ◽  
Vol 627 ◽  
pp. A173 ◽  
Author(s):  
M. Valentini ◽  
C. Chiappini ◽  
D. Bossini ◽  
A. Miglio ◽  
G. R. Davies ◽  
...  
Keyword(s):  
High Resolution ◽  
Seismic Data ◽  
Age Determination ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Abundance Pattern ◽  
Halo Stars ◽  
Stellar Ages ◽  
First Results ◽  
Detailed Chemical

Context. Very metal-poor halo stars are the best candidates for being among the oldest objects in our Galaxy. Samples of halo stars with age determination and detailed chemical composition measurements provide key information for constraining the nature of the first stellar generations and the nucleosynthesis in the metal-poor regime. Aims. Age estimates are very uncertain and are available for only a small number of metal-poor stars. We present the first results of a pilot programme aimed at deriving precise masses, ages, and chemical abundances for metal-poor halo giants using asteroseismology and high-resolution spectroscopy. Methods. We obtained high-resolution UVES spectra for four metal-poor RAVE stars observed by the K2 satellite. Seismic data obtained from K2 light curves helped improve spectroscopic temperatures, metallicities, and individual chemical abundances. Mass and ages were derived using the code PARAM, investigating the effects of different assumptions (e.g. mass loss and [α/Fe]-enhancement). Orbits were computed using Gaia DR2 data. Results. The stars are found to be normal metal-poor halo stars (i.e. non C-enhanced), and an abundance pattern typical of old stars (i.e. α and Eu-enhanced), and have masses in the 0.80−1.0 M⊙ range. The inferred model-dependent stellar ages are found to range from 7.4 Gyr to 13.0 Gyr with uncertainties of ∼30%−35%. We also provide revised masses and ages for metal-poor stars with Kepler seismic data from the APOGEE survey and a set of M4 stars. Conclusions. The present work shows that the combination of asteroseismology and high-resolution spectroscopy provides precise ages in the metal-poor regime. Most of the stars analysed in the present work (covering the metallicity range of [Fe/H] ∼ −0.8 to −2 dex) are very old >9 Gyr (14 out of 19 stars), and all of the stars are older than >5 Gyr (within the 68 percentile confidence level).

scholarly journals Multiple retrograde substructures in the Galactic halo: A shattered view of Galactic history

2019 ◽  
Vol 631 ◽  
pp. L9 ◽  
Author(s):  
Helmer H. Koppelman ◽  
Amina Helmi ◽  
Davide Massari ◽  
Adrian M. Price-Whelan ◽  
Tjitske K. Starkenburg
Keyword(s):  
High Resolution ◽  
Clustering Algorithm ◽  
Galactic Halo ◽  
High Energy ◽  
Galaxy Mergers ◽  
Chemical Abundance ◽  
Distinct Structure ◽  
Halo Stars ◽  
Energy Part ◽  
Hydrodynamical Simulations

Aims. Several kinematic and chemical substructures have been recently found amongst Milky Way halo stars with retrograde motions. It is currently unclear how these various structures are related to each other. This Letter aims to shed light on this issue. Methods. We explore the retrograde halo with an augmented version of the Gaia DR2 RVS sample, extended with data from three large spectroscopic surveys, namely RAVE, APOGEE, and LAMOST. In this dataset, we identify several structures using the HDBSCAN clustering algorithm. We discuss their properties and possible links using all the available chemical and dynamical information. Results. In concordance with previous work, we find that stars with [Fe/H] < −1 have more retrograde motions than those with [Fe/H] > −1. The retrograde halo contains a mixture of debris from objects like Gaia-Enceladus, Sequoia, and even the chemically defined thick disc. We find that the Sequoia has a smaller range in orbital energies than previously suggested and is confined to high energy. Sequoia could be a small galaxy in itself, but since it overlaps both in integrals-of-motion space and chemical abundance space with the less bound debris of Gaia-Enceladus, its nature cannot yet be fully settled. In the low-energy part of the halo, we find evidence for at least one more distinct structure: Thamnos. Stars in Thamnos are on low-inclination, mildly eccentric retrograde orbits, moving at vϕ ≈ −150 km s−1, and are chemically distinct from the other structures. Conclusions. Even with the excellent Gaia DR2 data, piecing together all the fragments found in the retrograde halo remains challenging. At this point, we are very much in need of large datasets with high-quality high-resolution spectra and tailored high-resolution hydrodynamical simulations of galaxy mergers.

First results from the Goddard High-Resolution Spectrograph - The Galactic halo and the Ly-alpha forest at low redshift in 3C 273

1991 ◽  
Vol 377 ◽  
pp. L21 ◽  
Author(s):  
Simon L. Morris ◽  
Ray J. Weymann ◽  
Blair D. Savage ◽  
Ronald L. Gilliland
Keyword(s):  
High Resolution ◽  
Galactic Halo ◽  
First Results

scholarly journals The Composition of Warm Giants in M 71 and M 5

1988 ◽  
Vol 126 ◽  
pp. 497-498
Author(s):  
Catherine A. Pilachowski ◽  
Christopher Sneden
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
High Dispersion ◽  
High Signal ◽  
Signal To Noise

In 1979 a disturbing controversy arose in the field of globular cluster research when Cohen (1980) and Pilachowski, Canterna, and Wallerstein (1980) announced the results of the first high dispersion studies of the composition of giants in the globular clusters M 71 and 47 Tucanae. In contrast to earlier studies, which found metallicities of typically −0.3 and −0.5 dex, these investigators obtained values of −1.3 and −1.1. Since then, many have attempted to redetermine the abundances of M 71 and 47 Tuc to explain the discrepant results. These efforts have all suffered from the absence of high signal-to-noise, high resolution spectra of stars with temperatures above 4300 K.

The Nature of the Triangulum-Andromeda Stellar Structures

2018 ◽  
Vol 14 (S344) ◽  
pp. 122-124
Author(s):  
J. V. Sales Silva ◽  
H. Perottoni ◽  
K. Cunha ◽  
H. J. Rocha-Pinto ◽  
D. Souto ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinematic Analysis ◽  
Dwarf Galaxies ◽  
Galactic Disk ◽  
Thin Disk ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
The Galaxy ◽  
Stellar Halo ◽  
Debris Cloud

AbstractThe outer stellar halo is home to a number of substructures that are remnants of former interactions of the Galaxy with its dwarf satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as a debris cloud by Rocha-Pinto et al., (2004) using 2MASS M giants. Would be these structures related to dwarf galaxies or to the galactic disk? To uncover the nature of these stars we performed a high-resolution spectroscopic study (R = 40,000) along with a kinematic analysis using Gaia data. We determined the atmospheric parameters and chemical abundances of Ca and Mg for the 13 TriAnd candidate stars along with their respective orbits. Our results indicate that the TriAnd stars analyzed have a galactic nature but that these stars are not from the local thin disk.

scholarly journals Simultaneous IUE Ground-Based Spectroscopic Observations of the Variable LMC Star R 71

1982 ◽  
Vol 98 ◽  
pp. 443-443 ◽  
Author(s):  
B. Wolf ◽  
I. Appenzeller ◽  
O. Stahl
Keyword(s):  
High Resolution ◽  
Velocity Field ◽  
Low Temperature ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
High Dispersion ◽  
Outflow Velocity ◽  
Photometric Observations ◽  
Type Variable ◽  
Visual Light

Using the IUE satellite we obtained high resolution UV spectrograms (1200 < λ < 3200 Å) of the S Dor type variable R 71 in the LMC. The IUE observations were supplemented by coordinated groundbased high dispersion spectroscopy and by photometric observations. From these observations we derive for the minimum state of R 71 the following stellar parameters: L = 2.0 × 105 L⊙, R ≈ 81 R⊙, Teff ≈ 13 600 K. For the expanding envelope we find a surprisingly low temperature of only about 6000 K and an apparently decelerated velocity field with a maximum outflow velocity of ~ 127 km s−1. The minimum state mass loss rate is in the order of 3 × 10−7 M⊙ y−1. Our results support the suggestion that the visual light variations of the S Dor type variables are produced by strong density variations of the expanding envelopes of these objects. A detailed study is forthcoming in Astronomy & Astrophysics.

scholarly journals Chemical abundances of the H II regions NGC 5461 and NGC 5471 in M 101, Derived from echelle spectrophotometry

2003 ◽  
Vol 212 ◽  
pp. 730-731
Author(s):  
Valentina Luridiana ◽  
César Esteban ◽  
Manuel Peimbert ◽  
Antonio Peimbert
Keyword(s):  
High Resolution ◽  
Spectroscopic Data ◽  
H Ii Regions ◽  
Correction Factors ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Photo Ionization

We present high resolution spectroscopic data of the two giant extragalactic H ii regions NGC 5461 and NGC 5471 in M 101. We calculate the physical conditions in the two nebulae with a large number of diagnostics, and determine their chemical abundances by applying ionization correction factors (icfs) to the observed ionic abundances. The comparison of the icfs based on photo-ionization models (Luridiana & Peimbert 2001; Luridiana et al. 1999) to those computed following the prescriptions by Mathis & Rosa (1991) shows large discrepancies for several elements, including nitrogen, neon and chlorine.

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