scholarly journals A Keck/Deimos Survey of Red Giant Branch Stars in the Outskirts of M31

2006 ◽  
pp. 286-291 ◽  
Author(s):  
Annette M. N. Ferguson ◽  
Scott Chapman ◽  
Rodrigo Ibata ◽  
Mike Irwin ◽  
Geraint Lewis ◽  
...  
Keyword(s):  
Red Giant ◽  
Giant Branch Stars

scholarly journals On the precision of full-spectrum fitting of simple stellar populations – I. Well-sampled populations

2020 ◽  
Vol 498 (2) ◽  
pp. 2814-2832
Author(s):  
Randa Asa’d ◽  
Paul Goudfrooij
Keyword(s):  
Random Noise ◽  
Star Clusters ◽  
Stellar Populations ◽  
Asymptotic Giant Branch ◽  
Full Spectrum ◽  
Red Giant ◽  
Set Up ◽  
Age Range ◽  
Spectrum Fitting ◽  
Giant Branch Stars

ABSTRACT We investigate the precision of the ages and metallicities of 21 000 mock simple stellar populations (SSPs) determined through full-spectrum fitting. The mock SSPs cover an age range of 6.8 < log (age/yr) < 10.2, for three wavelength ranges in the optical regime, using both Padova and MIST isochrone models. Random noise is added to the model spectra to achieve S/N ratios between 10 and 100 per wavelength pixel. We find that for S/N ≥ 50, this technique can yield ages of SSPs to an overall precision of ∆log (age/yr)∼01 for ages in the ranges 7.0 ≤ log (age/yr) ≤ 8.3 and 8.9 ≤ log (age/yr) ≤ 9.4. For the age ranges of 8.3 ≤ log (age/yr) ≤ 8.9 and log (age/yr) ≥ 9.5, which have significant flux contributions from asymptotic giant branch and red giant branch stars, respectively, the age uncertainty rises to about ±0.3 dex. The precision of age and metallicity estimation using this method depends significantly on the S/N and the wavelength range used in the fitting. We quantify the systematic differences in age predicted by the MIST and Padova isochrone models, due to their different assumptions about stellar physics in various important (i.e. luminous) phases of stellar evolution, which needs to be taken in consideration when comparing ages of star clusters obtained using these popular models. Knowing the strengths and limitations of this technique is crucial in interpreting the results obtained for real star clusters and for deciding the optimal instrument set-up before performing the observations.

scholarly journals The Magellanic Edges Survey I: Description and first results

2020 ◽  
Vol 497 (3) ◽  
pp. 3055-3075
Author(s):  
L R Cullinane ◽  
A D Mackey ◽  
G S Da Costa ◽  
S E Koposov ◽  
V Belokurov ◽  
...  
Keyword(s):  
Target Selection ◽  
Radial Distance ◽  
Large Magellanic Cloud ◽  
Disc Model ◽  
Observation Strategy ◽  
First Results ◽  
Mass Estimate ◽  
Red Clump ◽  
Red Giant ◽  
Giant Branch Stars

ABSTRACT We present an overview of, and first science results from, the Magellanic Edges Survey (MagES), an ongoing spectroscopic survey mapping the kinematics of red clump and red giant branch stars in the highly substructured periphery of the Magellanic Clouds. In conjunction with Gaia astrometry, MagES yields a sample of ~7000 stars with individual 3D velocities that probes larger galactocentric radii than most previous studies. We outline our target selection, observation strategy, data reduction, and analysis procedures, and present results for two fields in the northern outskirts (>10° on-sky from the centre) of the Large Magellanic Cloud (LMC). One field, located in the vicinity of an arm-like overdensity, displays apparent signatures of perturbation away from an equilibrium disc model. This includes a large radial velocity dispersion in the LMC disc plane, and an asymmetric line-of-sight velocity distribution indicative of motions vertically out of the disc plane for some stars. The second field reveals 3D kinematics consistent with an equilibrium disc, and yields Vcirc = 87.7 ± 8.0 km s−1 at a radial distance of ~10.5 kpc from the LMC centre. This leads to an enclosed mass estimate for the LMC at this radius of (1.8 ± 0.3) × 1010 M⊙.

scholarly journals Lithium abundance in lower red giant branch stars of Omega Centauri

2018 ◽  
Vol 618 ◽  
pp. A134 ◽  
Author(s):  
A. Mucciarelli ◽  
M. Salaris ◽  
L. Monaco ◽  
P. Bonifacio ◽  
X. Fu ◽  
...  
Keyword(s):  
High Resolution ◽  
Globular Clusters ◽  
Stellar System ◽  
The Other ◽  
Large Telescope ◽  
Lithium Abundance ◽  
Very Large Telescope ◽  
Red Giant ◽  
Giant Branch Stars ◽  
Branch Star

We present Li, Na, Al, and Fe abundances of 199 lower red giant branch star members of the stellar system Omega Centauri, using high-resolution spectra acquired with FLAMES at the Very Large Telescope. The A(Li) distribution is peaked at A(Li) ∼ 1 dex with a prominent tail towards lower values. The peak of the distribution well agrees with the lithium abundances measured in lower red giant branch stars in globular clusters and Galactic field stars. Stars with A(Li) ∼ 1 dex are found at metallicities lower than [Fe/H] ∼ –1.3 dex but they disappear at higher metallicities. On the other hand, Li-poor stars are found at all metallicities. The most metal-poor stars exhibit a clear Li–Na anti-correlation, where about 30% of the sample have A(Li) lower than ∼0.8 dex, while these stars represent a small fraction of normal globular clusters. Most of the stars with [Fe/H] > –1.6 dex are Li poor and Na rich. The Li depletion measured in these stars is not observed in globular clusters with similar metallicities and we demonstrate that it is not caused by the proposed helium enhancements and/or young ages. Hence, these stars formed from a gas already depleted in lithium. Finally, we note that Omega Centauri includes all the populations (Li-normal/Na-normal, Li-normal/Na-rich, and Li-poor/Na-rich stars) observed, to a lesser extent, in mono-metallic GCs.

scholarly journals Neutron-capture elements in dwarf galaxies

2019 ◽  
Vol 631 ◽  
pp. A171 ◽  
Author(s):  
Á. Skúladóttir ◽  
C. J. Hansen ◽  
S. Salvadori ◽  
A. Choplin
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Dwarf Galaxies ◽  
Core Collapse ◽  
Chemical Abundances ◽  
Relative Contribution ◽  
History Of ◽  
Red Giant ◽  
Process Element ◽  
Giant Branch Stars

The heavy elements (Z >  30) are created in neutron (n)-capture processes that are predicted to happen at vastly different nucleosynthetic sites. To study these processes in an environment different from the Milky Way, we targeted the n-capture elements in red giant branch stars in the Sculptor dwarf spheroidal galaxy. Using ESO VLT/FLAMES spectra, we measured the chemical abundances of Y, Ba, La, Nd, and Eu in 98 stars covering the metalliticy range −2.4 < [Fe/H] < −0.9. This is the first paper in a series about the n-capture elements in dwarf galaxies, and here we focus on the relative and absolute timescales of the slow (s)- and rapid (r)-processes in Sculptor. From the abundances of the s-process element Ba and the r-process element Eu, it is clear that the r-process enrichment occurred throughout the entire chemical evolution history of Sculptor. Furthermore, there is no evidence for the r-process to be significantly delayed in time relative to core-collapse supernovae. Neutron star mergers are therefore unlikely the dominant (or only) nucleosynthetic site of the r-process. However, the products of the s-process only become apparent at [Fe/H] ≈ −2 in Sculptor, and the s-process becomes the dominant source of Ba at [Fe/H] ≳ −2. We tested the use of [Y/Mg] and [Ba/Mg] as chemical clocks in Sculptor. Similarly to what is observed in the Milky Way, [Y/Mg] and [Ba/Mg] increase towards younger ages. However, there is an offset in the trends, where the abundance ratios of [Y/Mg] in Sculptor are significantly lower than those of the Milky Way at any given age. This is most likely caused by metallicity dependence of yields from the s-process, as well as by a different relative contribution of the s-process to core-collapse supernovae in these galaxies. Comparisons of our results with data of the Milky Way and the Fornax dwarf spheroidal galaxy furthermore show that these chemical clocks depend on both metallicity and environment.

scholarly journals Revealing the tidal scars of the Small Magellanic Cloud

2020 ◽  
Vol 495 (1) ◽  
pp. 98-113 ◽  
Author(s):  
Michele De Leo ◽  
Ricardo Carrera ◽  
Noelia E D Noël ◽  
Justin I Read ◽  
Denis Erkal ◽  
...  
Keyword(s):  
Centre Of Mass ◽  
Proper Motions ◽  
Dynamical Models ◽  
Tidal Disruption ◽  
Kinematic Data ◽  
Close Proximity ◽  
Outward Motion ◽  
Red Giant ◽  
Giant Branch Stars ◽  
Stellar Kinematic

ABSTRACT Due to their close proximity, the Large and Small Magellanic Clouds (LMC/SMC) provide natural laboratories for understanding how galaxies form and evolve. With the goal of determining the structure and dynamical state of the SMC, we present new spectroscopic data for ∼3000 SMC red giant branch stars observed using the AAOmega spectrograph at the Anglo-Australian Telescope. We complement our data with further spectroscopic measurements from previous studies that used the same instrumental configuration as well as proper motions from the Gaia Data Release 2 catalogue. Analysing the photometric and stellar kinematic data, we find that the SMC centre of mass presents a conspicuous offset from the velocity centre of its associated H i gas, suggesting that the SMC gas is likely to be far from dynamical equilibrium. Furthermore, we find evidence that the SMC is currently undergoing tidal disruption by the LMC within 2 kpc of the centre of the SMC, and possibly all the way into the very core. This is revealed by a net outward motion of stars from the SMC centre along the direction towards the LMC and an apparent tangential anisotropy at all radii. The latter is expected if the SMC is undergoing significant tidal stripping, as we demonstrate using a suite of N-body simulations of the SMC/LMC system disrupting around the Milky Way. Our results suggest that dynamical models for the SMC that assume a steady state will need to be revisited.

scholarly journals High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6681

2017 ◽  
Vol 846 (1) ◽  
pp. 23 ◽  
Author(s):  
Erin M. O’Malley ◽  
Alexei Knaizev ◽  
Andrew McWilliam ◽  
Brian Chaboyer
Keyword(s):  
High Resolution ◽  
Red Giant ◽  
Giant Branch Stars

scholarly journals THE CHEMICAL COMPOSITION OF RED GIANT BRANCH STARS IN THE GALACTIC GLOBULAR CLUSTERS NGC 6342 AND NGC 6366

2016 ◽  
Vol 152 (1) ◽  
pp. 21 ◽  
Author(s):  
Christian I. Johnson ◽  
Nelson Caldwell ◽  
R. Michael Rich ◽  
Catherine A. Pilachowski ◽  
Tiffany Hsyu
Keyword(s):  
Chemical Composition ◽  
Globular Clusters ◽  
Galactic Globular Clusters ◽  
Red Giant ◽  
Giant Branch Stars

scholarly journals Observations of Lithium in red giant stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 301-309
Author(s):  
Verne V. Smith
Keyword(s):  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Asymptotic Giant Branch Stars ◽  
Multiple Sources ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Red Giant ◽  
First Time ◽  
Giant Branch Stars

AbstractConnections between observations of the lithium abundance in various types of red giants and stellar evolution are discussed here. The emphasis is on three main topics; 1) the depletion of Li as stars ascend the red giant branch for the first time, 2) the synthesis of 7Li in luminous and massive asymptotic giant branch stars via the mechanism of hot-bottom burning, and 3) the possible multiple sources of excess Li abundances found in a tiny fraction of various types of G and K giants.

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