Characteristics of solar-like oscillations of clusters simulated by stellar population synthesis

Abstract

Using a stellar population‐synthesis method, we studied the distributions of νmax and Δν of simulated clusters with various ages and metallicities. Except for the confirmed peak (RC peak) of Δν of red‐clump (RC) stars, i.e. core helium‐burning stars, one sees a gap and a main‐sequence (MS) peak in the distributions of νmax and Δν of young clusters. The gap corresponds mainly to the Hertzsprung‐gap phase of evolution. The RC peak is caused by the fact that the radii of many RC stars near the zero‐age horizontal branch are concentrated in a certain range. The MS peak also results from the fact that many MS stars located in a certain mass range have an approximate radius in the early phase of the MS. The MS peak barely exists in the simulated clusters with age ≲ 1.0 Gyr. The location of the MS peak moves to a lower frequency with increasing age or metallicity, which may be applied to constrain the age and metallicity of young clusters. For simulated clusters with Z= 0.02, the frequency of the location of the dominant RC peak increases with age when age < 1.2 Gyr, and then decreases with age when age > 1.2 Gyr, but scarcely varies when age > 2.4 Gyr. This is relative to the degeneracy of the hydrogen‐exhausted core at the time of helium ignition. In addition, the RC peak is not sensitive to the metallicity, especially for clusters with age > 2.4 Gyr. Asteroseismical observations of clusters with age ≲ 2.4 Gyr may aid in testing the theory of degeneracy of hydrogen‐exhausted cores. Moreover, for clusters with 1.1 M⊙ < Mhook < 1.3 M⊙ there is a MS gap and a peak on the left of the MS gap in the distributions of νmax and Δν, which may be applied to constrain the central hydrogen abundance of stars in the MS gap and the peak.

Characteristics of solar-like oscillations of secondary red-clump stars

“…Furthermore, it has been identified that non‐uniform distributions of ν max and Δν of red giants result from red‐clump [core helium‐burning (CHeB)] stars (Miglio et al 2009; Huber et al 2010; Mosser et al 2010; Yang et al 2010; Hekker et al 2011b). The dominant peak in the distributions of ν max and Δν, which is located around 30 and 4 μHz for ν max and Δν, respectively, is mainly composed of stars that are close to the zero‐age horizontal branch (ZAHB: Yang et al 2010, 2011a). Stars with ν max > 40 μHz are mainly red‐clump stars with mass larger than 2.0 M ⊙ (Huber et al 2010).…”

“…Moreover, the values of νmax and ∆ν of red giants of clusters NGC 6811, NGC 6819, and NGC 6791 have also been extracted by Stello et al (2010a) and Hekker et al (2011a). For an ensemble of stars, the νmax and ∆ν can be applied to investigate many interesting questions about the Galaxy or stellar clusters (Miglio et al 2009(Miglio et al , 2012Miglio 2011;Yang et al , 2011aHuber et al 2010;Mosser et al 2010;Hekker et al 2011a,b;Stello et al 2010aStello et al ,b, 2011. These studies advanced our understanding of the theory of stellar structure and evolution.…”

Grids of rotating stellar models with masses between 1.0 and 3.0M⊙

“…Then, just as the case of 1.0 M ⊙ models, the rotational mixing begins to play a dominant role. The rotating models exhibit a higher effective temperature and an approximately equal luminosity compared to the non-rotating ones when they evolved into the same evolutionary state [for instance the beginning of the MS hook (Yang et al 2011a) in the HR diagram]. Moreover, for the star with M = 1.4 M ⊙ , Fig.…”

Asteroseismic analysis ofKeplertarget KIC 2837475

“…Asteroseismology has proved to be a powerful tool for determining fundamental star parameters, diagnosing internal structures of stars, and probing physical processes in stellar interiors (Eggenberger et al 2005;Yang & Bi 2007b;Stello et al 2009;Christensen-Dalsgaard & Houdek 2010;Yang et al 2010Yang et al , 2011aYang et al , 2012Silva Aguirre et al 2011Liu et al 2014;Chaplin et al 2014;Metcalfe et al 2014;Guenther et al 2014).…”