Is there large convective-core overshooting in Kepler targets KIC 2837475 and 11081729?

2020 ◽  
Vol 497 (4) ◽  
pp. 4042-4050
Author(s):  
Jianwei Zhang
Keyword(s):  
Internal Structure ◽  
Main Sequence ◽  
Normal Values ◽  
Independent Method ◽  
Observational Constraints ◽  
Main Sequence Stars ◽  
Convective Core ◽  
Best Fitting ◽  
Model Independent ◽  
Fitting Model

ABSTRACT The ratio of small-to-large separations r010 has been widely used in helioseismology and asteroseismology to investigate the internal structure of a star, as it is approximately independent of the structure of the outer layers. Several studies have used this tool to constrain the convective-core overshooting of main-sequence stars (i.e. 0.0 ≤ δov ≤ 0.2). This is consistent with the generally accepted values. However, Yang et al. have proposed that there is large convective-core overshooting in the Kepler targets KIC 2837475 and 11081729: 1.2 ≤ δov ≤ 1.6 and 1.7 ≤ δov ≤ 1.8, respectively. These are much larger than the normal values. Thus, the aim of this study is to re-investigate the ratios of the two stars using a model-independent method with the latest p-mode observations. Our results indicate that there is no robustness for including such a large convective-core overshooting while modelling these two stars. In fact, this leads to over-fitting, and the observational constraints of r010 prefer models with a normal convective-core overshooting (i.e. 0.0 ≤ δov ≤ 0.2) as the candidates for the best-fitting model of KIC 2837475 and 11081729.

scholarly journals A Spectroscopic Study of Blue Stragglers in M67

2008 ◽  
Vol 4 (S252) ◽  
pp. 391-397
Author(s):  
G. Q. Liu ◽  
L. Deng ◽  
M. Chávez ◽  
E. Bertone
Keyword(s):  
Effective Temperature ◽  
Spectral Properties ◽  
Main Sequence ◽  
Open Cluster ◽  
Observational Constraints ◽  
Photometric System ◽  
Main Sequence Stars ◽  
Complete Sample ◽  
Blue Stragglers ◽  
Fitting Method

AbstractSpectrophotometric observations of the complete sample of twenty four blue stragglers (BSs) in the old galactic open cluster M67 (NGC2682) have been collected, using the Guillermo Haro Observatory in Cananea, Mexico. All the calibrated spectra were re-calibrated by the Beijing Arizona Taipei Connecticut (BATC) photometric system which includes fluxes in 11 photometric bands covering ~3600–10000 Å. The goal of the current work is to provide observational constraints on spectral properties of BSs by determining the effective temperature (Teff) and surface gravity (log g). The overall results, obtained by applying the flux fitting method, indicate that Teff and surface gravities of BSs in M67 are fully compatible with those expected for main sequence stars.

scholarly journals Discovery of fossil magnetic fields in the intermediate-mass pre-main sequence stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 445-446
Author(s):  
Evelyne Alecian ◽  
Gregg A. Wade ◽  
Claude Catala
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Lower Mass ◽  
Convective Core

AbstractIt is now well-known that the surface magnetic fields observed in cool, lower-mass stars on the main sequence (MS) are generated by dynamos operating in their convective envelopes. However, higher-mass stars (above 1.5 M⊙) pass their MS lives with a small convective core and a largely radiative envelope. Remarkably, notwithstanding the absence of energetically-important envelope convection, we observe very strong (from 300 G to 30 kG) and organised (mainly dipolar) magnetic fields in a few percent of the A and B-type stars on the MS, the origin of which is not well understood. In this poster we propose that these magnetic fields could be of fossil origin, and we present very strong observational results in favour of this proposal.

scholarly journals Magnetic main sequence stars as progenitors of blue supergiants

2014 ◽  
Vol 9 (S307) ◽  
pp. 391-392
Author(s):  
I. Petermann ◽  
N. Castro ◽  
N. Langer
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Main Sequence ◽  
Mass Range ◽  
Main Sequence Stars ◽  
Core Mass ◽  
Hydrogen Burning ◽  
Sequence Band ◽  
Convective Core ◽  
The Right

AbstractBlue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3–30 M⊙ in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

scholarly journals Winds

1993 ◽  
Vol 137 ◽  
pp. 620-633
Author(s):  
K.B. MacGregor
Keyword(s):  
Mass Loss ◽  
Internal Structure ◽  
Physical State ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Present Review ◽  
Main Sequence Stars ◽  
Dynamical State ◽  
Stellar Interiors

AbstractIt is by now well known that most main sequence stars continuously lose mass as a consequence of the winds they emit. In addition to affecting the thermal and dynamical state of the stellar atmosphere, such mass loss can also induce changes in the interiors of stars. In the present review, we consider a few of the ways in which sustained, wind-like mass loss can alter the physical state of main sequence stellar interiors by examining the differences in internal structure, composition, and rotation between mass-losing and conservatively evolving stars.

scholarly journals Lithium Abundance, Diffusion and Turbulence

1995 ◽  
Vol 10 ◽  
pp. 459-460
Author(s):  
G. Michaud ◽  
G. Beaudet
Keyword(s):  
Main Sequence ◽  
Normal Values ◽  
Present Theory ◽  
Constant Mass ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Lithium Abundance ◽  
Calculated Curve ◽  
Fully Coupled

Richer & Michaud (1993) calculated a series of envelopes fully coupled to non-rotating, constant mass, stellar evolution models of hydrogen burning stars with masses in the range of 1.2 to 2.2 M⊙, typical of A and F main sequence stars. They included He settling. The location of the theoretically predicted gap of the Hyades agrees quite well with the observed one, a result obtained without the introduction of any free parameter. At temperatures above the gap, while the observed lithium abundances are within a factor of 2-3 of normal values, the theoretical calculated curve drops to very low values. Diffusion velocities being fairly small, any other physical process with larger or similar velocities can reduce the effect of diffusion and produce the observed results. Mass loss is one such process. Another difficulty with the present theory is the width of the gap. Observations show that the observed gap is wider than the calculated one in the Hyades. This also suggests that other physical processes play an important role.

The Internal Structure of Middle Main-Sequence Stars.

1962 ◽  
Vol 135 ◽  
pp. 770 ◽  
Author(s):  
Icko, Jr. Iben ◽  
John R. Ehrman
Keyword(s):  
Internal Structure ◽  
Main Sequence ◽  
Main Sequence Stars
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