Turbulence, convection, and mixing in red giant stars: Some empirical approaches based on high resolution spectroscopy

1986 ◽  
Vol 118 (1-2) ◽  
pp. 227-235 ◽  
Author(s):  
Takashi Tsuji
Keyword(s):  
High Resolution ◽  
High Resolution Spectroscopy ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Empirical Approaches

scholarly journals Solar-like oscillations in subgiant and red-giant stars: mixed modes

2013 ◽  
Vol 9 (S301) ◽  
pp. 325-331 ◽  
Author(s):  
S. Hekker ◽  
A. Mazumdar
Keyword(s):  
High Resolution ◽  
Outer Part ◽  
Space Missions ◽  
Giant Stars ◽  
Internal Structures ◽  
Different Depths ◽  
Mixed Modes ◽  
Red Giant Stars ◽  
Red Giant

AbstractThanks to significant improvements in high-resolution spectrographs and the launch of dedicated space missions MOST, CoRoT and Kepler, the number of subgiants and red-giant stars with detected oscillations has increased significantly over the last decade. The amount of detail that can now be resolved in the oscillation patterns does allow for in-depth investigations of the internal structures of these stars. One phenomenon that plays an important role in such studies are mixed modes. These are modes that carry information of the inner radiative region as well as from the convective outer part of the star allowing to probe different depths of the stars.Here, we describe mixed modes and highlight some recent results obtained using mixed modes observed in subgiants and red-giant stars.

scholarly journals Stellar spectra analysis of giant stars: ARCTURUS

2020 ◽  
pp. 347-348
Author(s):  
Maria Rah
Keyword(s):  
High Resolution ◽  
Early Universe ◽  
Chemical Evolution ◽  
The Other ◽  
High Resolution Spectroscopy ◽  
Spectra Analysis ◽  
Stellar Spectra ◽  
Giant Stars ◽  
Low Metallicity ◽  
Red Giant

In this study, we analyzed the evolved red giant ARCTURUS using high-resolution spectroscopy that was taken by HARPS. The other names of this star is α Boo - Arcturus - HR 5340 - HD 124897 - HIP 69673. This evolved (log g = 1.66 dex) star shows low metallicity nature ([Fe/H] = -0.52), which could be employed to study the chemical evolution of the early universe.

scholarly journals Lithium in metal-poor red giants

2009 ◽  
Vol 5 (S268) ◽  
pp. 361-362
Author(s):  
Laimons Začs ◽  
Arturs Barzdis
Keyword(s):  
High Resolution ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Lithium Abundance ◽  
Giant Stars ◽  
Synthetic Spectra ◽  
Lithium Depletion ◽  
Red Giant Stars ◽  
Red Giant

AbstractThe lithium abundance was calculated for five metal-poor red giant stars from Li i doublet at 6707 Å by fitting the observed high-resolution spectra with synthetic spectra. The lithium abundance was found to be low in all stars, logϵ(Li) ≤ 1.8, confirming lithium depletion on the red giant and asymptotic giant branch.

scholarly journals Galactic or extragalactic chemical tagging for NGC 3201?

2018 ◽  
Vol 614 ◽  
pp. A146 ◽  
Author(s):  
B. Dias ◽  
I. Araya ◽  
J. P. Nogueira-Cavalcante ◽  
L. Saker ◽  
A. Shokry
Keyword(s):  
High Resolution ◽  
Globular Cluster ◽  
High Resolution Spectroscopy ◽  
Low Resolution ◽  
Element Abundances ◽  
Giant Stars ◽  
Mass Size ◽  
Red Giant ◽  
Process Element ◽  
Size Relation

Context. The origin of the globular cluster (GC) NGC 3201 is under debate. Its retrograde orbit points to an extragalactic origin, but no further chemical evidence supports this idea. Light-element chemical abundances are useful to tag GCs and can be used to shed light on this discussion. Aims. Recently it was shown that the CN and CH indices are useful to identify GCs that are anomalous to those typically found in the Milky Way. A possible origin of anomalous clusters is the merger of two GCs and/or the nucleus of a dwarf galaxy. We aim to derive CN and CH band strengths for red giant stars in NGC3201 and compare these with photometric indices and high-resolution spectroscopy and discuss in the context of GC chemical tagging. Methods. We measure molecular band indices of S(3839) and G4300 for CN and CH, respectively from low-resolution spectra of red giant stars. Gravity and temperature effects are removed. Photometric indices are used to indicate further chemical information on C+N+O or s-process element abundances that are not derived from low-resolution spectra. Results. We found three groups in the CN–CH distribution. A main sequence (S1), a secondary less-populated sequence (S2), and a group of peculiar (pec) CN-weak and CH-weak stars, one of which was previously known. The three groups seem to have different C+N+O and/or s-process element abundances, to be confirmed by high-resolution spectroscopy. These are typical characteristics of anomalous GCs. The CN distribution of NGC 3201 is quadrimodal, which is more common in anomalous clusters. However, NGC 3201 does not belong to the trend of anomalous GCs in the mass-size relation. Conclusions. The globular cluster NGC 3201 shows signs that it can be chemically tagged as anomalous: it has an unusual CN–CH relation, indications that pec-S1-S2 is an increasing sequence of C+N+O or s-process element abundances, and a multi-modal CN distribution that seems to correlate with s-process element abundances. The non-anomalous characteristics are that it has a debatable Fe-spread and it does not follow the trend of mass size of all anomalous clusters. Three scenarios are postulated here: (i) if the sequence pec-S1-S2 has increasing C+N+O and s-process element abundances, NGC 3201 would be the first anomalous GC outside of the mass-size relation; (ii) if the abundances are almost constant, NGC 3201 would be the first non-anomalous GC with multiple CN–CH anti-correlation groups; or (iii) it would be the first anomalous GC without variations in C+N+O and s-process element abundances. In all cases, the definition of anomalous clusters and the scenario in which they have an extragalactic origin must be revised.

scholarly journals Chemical similarities between the Galactic bulge and local thick disk red giant stars: analysis from optical data

2009 ◽  
Vol 5 (S265) ◽  
pp. 342-343
Author(s):  
Alan Alves-Brito ◽  
Jorge Meléndez ◽  
Martin Asplund
Keyword(s):  
High Resolution ◽  
Thick Disk ◽  
Elemental Abundance ◽  
Optical Data ◽  
Galactic Bulge ◽  
Open Problems ◽  
Chemical Enrichment ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

AbstractThe Galactic structure and composition remain as one of the greatest open problems in modern astrophysics. We show here that there are chemical similarities between the Galactic bulge and local thick disk red giant stars. This finding puts strong constraints on the IMF, SFR and chemical enrichment timescale of the bulge and thick disk. Our results are based upon a detailed elemental abundance analysis of 80 high S/N and high resolution optical spectra of giant stars, in the range −1.5 < [Fe/H] < +0.5.

High-resolution spectra of stars in globular clusters. VI - Oxygen-deficient red giant stars in M13

1991 ◽  
Vol 101 ◽  
pp. 1693 ◽  
Author(s):  
Jeffery A. Brown ◽  
George Wallerstein ◽  
J. B. Oke
Keyword(s):  
High Resolution ◽  
Globular Clusters ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

Isolating Red Giant Stars in M31's Elusive Outer Spheroid

1998 ◽  
Vol 116 (2) ◽  
pp. 707-722 ◽  
Author(s):  
David B. Reitzel ◽  
Puragra Guhathakurta ◽  
Andrew Gould
Keyword(s):  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

Ellipsoidal Variability and Long Secondary Periods in MACHO Red Giant Stars

2006 ◽  
Vol 650 (1) ◽  
pp. L55-L58 ◽  
Author(s):  
A. Derekas ◽  
L. L. Kiss ◽  
T. R. Bedding ◽  
H. Kjeldsen ◽  
P. Lah ◽  
...  
Keyword(s):  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

Dust clouds around red giant stars: Evidence of sublimating comet disks?

Icarus ◽  
1989 ◽  
Vol 81 (1) ◽  
pp. 24-30 ◽  
Author(s):  
John J. Matese ◽  
Daniel P. Whitmire ◽  
Ray T. Reynolds
Keyword(s):  
Giant Stars ◽  
Dust Clouds ◽  
Red Giant Stars ◽  
Red Giant
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