A correlation between GALEX FUV magnitude and chromospheric activity among red giant stars

2018 ◽  
Vol 35 ◽  
Author(s):  
Graeme H. Smith
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Giant Stars ◽  
Chromospheric Activity ◽  
Chromospheric Emission ◽  
Red Giant Stars ◽  
Red Giant ◽  
Far Ultraviolet

AbstractIt is shown that upon combining GALEX far-ultraviolet and Johnson B magnitudes a resultant FUV–B colour can be obtained that for red giant stars of luminosity classes III and II correlates well with chromospheric emission in the cores of the Mg iih and k lines. Giant stars throughout the colour range 0.8 ≤ B – V ≤ 1.6 exhibit such a phenomenon. The main result of this paper is to show that GALEX far-ultraviolet photometry can provide information about the degree of chromospheric activity among red giant stars, and as such may offer a tool for surveying the evolution of chromospheric activity from the main sequence into the red giant phases of stellar evolution.

scholarly journals Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. II. Atomic Diffusion in M67 Stars

2019 ◽  
Vol 874 (1) ◽  
pp. 97 ◽  
Author(s):  
Diogo Souto ◽  
C. Allende Prieto ◽  
Katia Cunha ◽  
Marc Pinsonneault ◽  
Verne V. Smith ◽  
...  
Keyword(s):  
Main Sequence ◽  
Atomic Diffusion ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals Asteroseismic fingerprints of stellar mergers

2021 ◽  
Author(s):  
Nicholas Z Rui ◽  
Jim Fuller
Keyword(s):  
Stellar Evolution ◽  
Total Mass ◽  
Main Sequence ◽  
Red Giants ◽  
Giant Stars ◽  
Evolution Dynamics ◽  
Red Giant ◽  
Stellar Mergers ◽  
Gravity Mode ◽  
Spacing Measurement

Abstract Stellar mergers are important processes in stellar evolution, dynamics, and transient science. However, it is difficult to identify merger remnant stars because they cannot easily be distinguished from single stars based on their surface properties. We demonstrate that merger remnants can potentially be identified through asteroseismology of red giant stars using measurements of the gravity mode period spacing together with the asteroseismic mass. For mergers that occur after the formation of a degenerate core, remnant stars have over-massive envelopes relative to their cores, which is manifested asteroseismically by a g mode period spacing smaller than expected for the star’s mass. Remnants of mergers which occur when the primary is still on the main sequence or whose total mass is less than ≈2 M⊙ are much harder to distinguish from single stars. Using the red giant asteroseismic catalogs of Vrard et al. (2016) and Yu et al. (2018), we identify 24 promising candidates for merger remnant stars. In some cases, merger remnants could also be detectable using only their temperature, luminosity, and asteroseismic mass, a technique that could be applied to a larger population of red giants without a reliable period spacing measurement.

scholarly journals Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints

2015 ◽  
Vol 11 (A29B) ◽  
pp. 525-528
Author(s):  
Lagarde Nadège
Keyword(s):  
Spectroscopic Study ◽  
Stellar Evolution ◽  
Open Cluster ◽  
Stellar Populations ◽  
Red Giants ◽  
Seismic Properties ◽  
Giant Stars ◽  
Statistical Studies ◽  
Red Giant Stars ◽  
Red Giant

AbstractThe availability of asteroseismic constraints for a large sample of red-giant stars from the CoRoT and Kepler missions paves the way for various statistical studies of the seismic properties of stellar populations. We use a detailed spectroscopic study of 19 CoRoT red-giant stars (Morel et al. 2014) to compare theoretical stellar evolution models to observations of the open cluster NGC 6633 and field stars. This study is already published in Lagarde et al. (2015)

scholarly journals Harlow Shapley and Red Giant Stars

1988 ◽  
Vol 126 ◽  
pp. 481-482
Author(s):  
F. Martin ◽  
S.J. McCarthy
Keyword(s):  
Stellar Evolution ◽  
Variable Stars ◽  
Magellanic Clouds ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Harlow Shapley ◽  
Infrared Stars ◽  
Small Cloud

In five papers written between 1951 and 1955 Shapley considers the topic of red giant stars and reddish variable stars in the Magellanic Clouds. These works coincide with Shapley's final year as Director at Harvard and the first years of his retirement which extended a full score of years before his death in 1972. They include the following: Magellanic Clouds II (Supergiants/Red Variable Stars in the Small Cloud; January 1951); Magellanic Clouds IV (On Period Frequency Anomalies; February 1952); Magellanic Clouds VII (Star Colors and Luminosities in Five Constellations; March 1953); Magellanic Clouds VIII (On the Populations Characteristics of the Two Clouds; October 1953); and Magellanic Clouds XVI (Infrared Stars and Stellar Evolution; July 1955). These five papers, which appeared originally in the Proceedings of the National Academy of Science, may be found in the Harvard Reprint Series I as numbers 346, 360, 373, 376, and 425.

Can we really use chemical properties of red-giant stars as age indicators?

2017 ◽  
Vol 13 (S334) ◽  
pp. 325-326
Author(s):  
Nadège Lagarde ◽  
A. C. Robin ◽  
C. Reylé
Keyword(s):  
Stellar Evolution ◽  
European Space Agency ◽  
Chemical Properties ◽  
Transport Processes ◽  
Giant Stars ◽  
Space Agency ◽  
Stellar Photosphere ◽  
Red Giant Stars ◽  
Red Giant ◽  
Stellar Masses

AbstractThe cornerstone mission of the European Space Agency, Gaia, together with forthcoming complementary surveys (CoRoT, Kepler, K2, APOGEE and Gaia-ESO), will revolutionize our understanding of the formation and history of our Galaxy, providing accurate stellar masses, radii, ages, distances, as well as chemical properties for a very large sample of stars across different Galactic stellar populations. Using improved population synthesis approach and new stellar evolution models we attempt to evaluate the possibility to derive ages of clump stars from their chemical properties. A new version of the Besançon Galaxy models (BGM) is used in which new stellar evolutionary tracks are computed from the stellar evolution code STAREVOL. The effects of mixing on chemical composition of the stellar photosphere has a significant impact on the determined stellar age from the observed [C/N] ratio. We clearly show that transport processes occurring in red-giant stars should be taken into account in the determination of ages for future Galactic archaeology studies.

scholarly journals Chemical Abundances of Main-sequence, Turnoff, Subgiant, and Red Giant Stars from APOGEE Spectra. I. Signatures of Diffusion in the Open Cluster M67

2018 ◽  
Vol 857 (1) ◽  
pp. 14 ◽  
Author(s):  
Diogo Souto ◽  
Katia Cunha ◽  
Verne V. Smith ◽  
C. Allende Prieto ◽  
D. A. García-Hernández ◽  
...  
Keyword(s):  
Main Sequence ◽  
Open Cluster ◽  
Chemical Abundances ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant

scholarly journals Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era

2020 ◽  
Vol 633 ◽  
pp. A34 ◽  
Author(s):  
C. Charbonnel ◽  
N. Lagarde ◽  
G. Jasniewicz ◽  
P. L. North ◽  
M. Shetrone ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Mixing Processes ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Good Tracer ◽  
The Impact ◽  
Maximum Likelihood Technique ◽  
Evolution Status

Context. Li is extensively known to be a good tracer of non-standard mixing processes occurring in stellar interiors. Aims. We present the results of a new large Li survey in red giant stars and combine it with surveys from the literature to probe the impact of rotation-induced mixing and thermohaline double-diffusive instability along stellar evolution. Methods. We determined the surface Li abundance for a sample of 829 giant stars with accurate Gaia parallaxes for a large sub-sample (810 stars) complemented with accurate HIPPARCOS parallaxes (19 stars). The spectra of our sample of northern and southern giant stars were obtained in three ground-based observatories (Observatoire de Haute-Provence, ESO-La Silla, and the Mc Donald Observatory). We determined the atmospheric parameters (Teff, log(g) and [Fe/H]), and the Li abundance. We used Gaia parallaxes and photometry to determine the luminosity of our objects and we estimated the mass and evolution status of each sample star with a maximum-likelihood technique using stellar evolution models computed with the STAREVOL code. We compared the observed Li behaviour with predictions from stellar models, including rotation and thermohaline mixing. The same approach was used for stars from selected Li surveys from the literature. Results. Rotation-induced mixing accounts nicely for the Li behaviour in stars warmer than about 4200 K, independently of the mass domain. For stars with masses lower than 2 M⊙ thermohaline mixing leads to further Li depletion below the Teff of the RGB bump (about 4000 K), and on the early asymptotic giant branch, as observed. Depending on the definition we adopt, we find between 0.8 and 2.2% of Li-rich giants in our new sample. Conclusions.Gaia puts a new spin on the understanding of mixing processes in stars, and our study confirms the importance of rotation-induced processes and of thermohaline mixing. However asteroseismology is required to definitively pinpoint the actual evolution status of Li-rich giants.

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