The frequency separations of stellar p-modes

2016

ApJ

The determination of the size of the convective core of main-sequence stars is usually dependent on the construction of models of stars. Here we introduce a method to estimate the radius of the convective core of main-sequence stars with masses between about 1.1 and 1.5 M ⊙ from observed frequencies of low-degree p-modes. A formula is proposed to achieve the estimation. The values of the radius of the convective core of four known stars are successfully estimated by the formula. The radius of the convective core of KIC 9812850 estimated by the formula is 0.140 ± 0.028 R ⊙ . In order to confirm this prediction, a grid of evolutionary models were computed. The value of the convective-core radius of the best-fit model of KIC 9812850 is 0.149 R ⊙ , which is in good agreement with that estimated by the formula from observed frequencies. The formula aids in understanding the interior structure of stars directly from observed frequencies. The understanding is not dependent on the construction of models.

Section: Introductionmentioning

confidence: 99%

Estimating the Radius of the Convective Core of Main-Sequence Stars From Observed Oscillation Frequencies

2016

ApJ

“…Although only a very limited number of modes ( l ≤ 3) are likely to be observed in solar‐like oscillations due to geometrical cancellation effects, the low‐degree p modes of the oscillations can penetrate deep into the interiors of stars (Dziembowski & Goode 1997) and each low‐degree p mode carries unique information about the stellar interior. Thus, asteroseismology has the capability to probe the interior of stars and to determine stellar fundamental parameters (Ulrich 1986; Gough 1987; Kjeldsen & Bedding 1995; Christensen‐Dalsgaard 2002; Yang & Bi 2007; Stello et al 2009a,b; Kallinger et al 2010a,b; Mosser et al 2010; Yang & Meng 2010).…”

Section: Introductionmentioning

confidence: 99%

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

Monthly Notices of the Royal Astronomical Society

Meng

et al. 2012

We calculated the populations of core‐helium‐burning (CHeB) stars and found that secondary red‐clump (SRC) stars can form a SRC peak in the distributions of the frequency of maximum seismic amplitude (νmax) and mean large‐frequency separation (Δν) of CHeB stars when metallicity Z≥ 0.02. The νmax and Δν of CHeB stars are dependent not only on He‐core mass but also on H‐shell burning. The SRC peak is composed of CHeB stars with mass roughly between the critical mass MHeF and MHeF+ 0.2, while He‐core mass is between about 0.33 and 0.36 M⊙. The location of the SRC peak can be affected by the mixing‐length parameter α, metallicity Z and overshooting parameter δov. A decrease in α or increase in Z or δov leads to a movement of the SRC peak towards a lower frequency. The change in Z and α only slightly affects the value of MHeF, but the variation in δov can affect the value of MHeF significantly. Thus the SRC peak might aid in determining the value of MHeF and calibrating δov. In addition, the effects of convective acceleration of SRC stars and the decrease in the νmax of ‘semidegenerate’ stars with mass result in the appearance of a shoulder between about 40 and 50 μHz in the νmax distribution. However, the convective acceleration of stars with M < MHeF leads to a deficit in the νmax distribution between about 9 and 20 μHz. Moreover, the value of the parameter b of the relation between νmax and Δν for populations with M > MHeF is obviously larger than that for populations with M < MHeF.

“…Fortunately, Δν and ν max also allow us to determine the fundamental parameters of stars (mass and radius) to within a few percent (Kjeldsen & Bedding 1995; Stello et al 2009a,b). Moreover, the properties of frequency separations have been studied by many investigators (Ulrich 1986; Gough 1987; Gabriel 1989; Roxburgh & Vorontsov 2000; Yang & Bi 2007; Yang & Meng 2009). Asteroseismic parameters Δν and ν max will be the primary parameters for asteroseismology.…”

Section: Introductionmentioning

confidence: 99%

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

Monthly Notices of the Royal Astronomical Society

Meng

et al. 2011

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.