A Comparison of Stellar Evolution with Binary Systems

Abstract

We have compared stellar evolution models with the three intermediate-mass binary systems V2291 Oph, a Aur, and g And, whose masses are determined accurately within 7%. These systems were recently regarded by and coworkers as systems that favor evolution with moderate overshoot mixing Schro der from the convective cores. While they assumed a standard Population I metallicity for these binaries, we have taken into account the available heavy-element abundance data in the literature. We have taken two approaches for each system. First, assuming no core overshooting, we have adjusted helium abundance for each binary to obtain the best Ðt. Second, adopting a helium abundance from a standard metallicity-helium relation, we have estimated a required extent of core overshooting Our results l ov . indicate that the required extent of core overshooting is less than which is smaller than the D0.15H p , extent estimated by and his collaborators. The main reason for the di †erence is attributed to Schro der the fact that we have taken into account published estimates of metallicity for each system. We have found that to obtain a good Ðt with red components we have to modify the ratio of mixing length to pressure scale height for each system. The required ratio is found to be smaller for a metal-poor system and vice versa.

Using binaries containing giants to constrain theories of stellar and tidal evolution

“…The inferred age is log t = 8.778 −0.012 +0.031 which means that it is not as well determined as the previous case. This should be compared with the models computed by Iwamoto & Saio (1999): these authors found that core overshooting is not necessary to explain the astrophysical parameters of η And if models with subsolar metallicity are adopted; their mixing length parameter is very similar to ours (1.40). The approximately solar composition also requires some changes in the input physics.…”

“…The mixinglength parameter was increased to 1.85 and the final solution is better than that by adopting the models with subsolar metallicity since the inferred age is log t = 8.918 −0.020 +0.003 . Comparing our models with Z = 0.018 with those by Iwamoto & Saio (1999) (both adopting core overshooting), the mixing-length parameter is similar, as the core overshooting parameter (α ov = 0.20 and 0.15, respectively).…”

“…Schröder, Pols & Eggleton (1997) analysed V2291 Oph and found an acceptable fit by adopting Z = 0.02 and a moderate amount of core overshooting α ov ≈ 0.27. Iwamoto & Saio (1999), on the other hand, using the same astrophysical parameters but adopting a different chemical composition (Z = 0.03 according to Marshal 1996), also found a good match. In both cases, a larger value of the mixing-length parameter was adopted (2.0 and 2.3, respectively).…”

“…The masses of the primary and secondary inferred from these observations and from the spectroscopic studies by Gordon are 2.59 ± 0.30 M and 2.34 ± 0.22 M . The astrophysical parameters of η And have been used to test the capability of evolutionary stellar models (Schröder et al 1997;Iwamoto & Saio 1999). In both works the primary seems to be in the core helium burning phase while the secondary is in the ascending giant branch.…”

THE ROLE OF TYPE Ia SUPERNOVAE IN CHEMICAL EVOLUTION. I. LIFETIME OF TYPE Ia SUPERNOVAE AND METALLICITY EFFECT

“…Figure 17 shows the adopted stellar lifetime function as a function of initial mass and metallicity, which is provided by Kodama & Arimoto (1997). The stellar evolution tracks are calculated with the code described in Iwamoto & Saio (1999) with the core overshooting. Because of the coarse mass grid, there is a tiny irregularity at 1.8M ⊙ (Z = 0.004, 0.008), 2.0M ⊙ (Z = 0.02), 2.2M ⊙ (Z = 0.0001-0.002), and 3.3M ⊙ (Z = 0.0002) in the table, which we have smoothed with interpolation.…”