Constraining the Properties of Delta Scuti Stars Using Spectroscopic Eclipsing Binary Systems

Abstract

Many stars exhibit stellar pulsations, favoring them for asteroseismic analyses. Interpreting the oscillations requires some knowledge of the oscillation mode geometry (spherical degree, radial and azimuthal orders). The δ Scuti stars (1.5 -2.5 M ⊙ ) often show just one or few pulsation frequencies.Although this may promise a successful seismological analysis, we may not know enough about either the mode or the star to use the oscillation frequency to improve the determination of the stellar model, or probe the star's structure. For the observed frequencies to be used successfully as seismic probes of these objects, we need to concentrate on stars for which we can reduce the number of free parameters in the problem, such as binary systems or open clusters. We investigate how much our understanding of a δ Scuti star is improved when it is in a detached eclipsing binary system instead of being a single field star. We use singular value decomposition to explore the precision we expect in stellar parameters (mass, age and chemical composition) for both cases. We examine how the parameter uncertainties propagate to the luminosity -effective temperature diagram and determine when the effort of obtaining a new measurement is justified. We show that for the single star, a correct identification of the oscillation mode is necessary to produce strong constraints on the stellar model properties, while for the binary system the observations without the pulsation mode provide the same or better constraints on the stellar parameters. In the latter case, the strong constraints provided by the binary system not only allow us to detect an incorrectly-identified oscillation mode, but we can also constrain the oscillation mode geometry by comparing the distribution of possible solutions with and without including the oscillation frequency as a constraint.

A seismic and gravitationally bound double star observed byKepler

“…We assume that the model behaves linearly locally, and so we can use a simple inversion method to calculate the parameter changes (dP) to make to an initial guess of the parameters P 0 in order to bring the model observables into line with the simulated observations, see Creevey et al (2011). (This involves calculating the Jacobian matrix dF/dP evaluated at the solution, where F are the observables, such as luminosity ratio and frequency ratios.)…”

Asteroseismology of Eclipsing Binary Stars

“…Classical pulsators in eclipsing binary stars offer the possibility to alleviate this problem. Creevey et al (2011) found that eclipsing binaries constrain fundamental properties of a star equally well or better than what is possible for a pulsating δ Scuti star with correct mode identification ( Figure 4). Conversely, the correct mode identification can be inferred by comparing solutions assuming different mode identifications, and identifying those solutions which yield the best match to the binary constraints.…”

“…Dashed lines mark the exact input solution, the box show the initial guess values, and the error bar mark the input uncertainties for the eclipsing binary solution. From Creevey et al (2011).…”

Multiple star systems observed with CoRoT andKepler

“…The promise of working on δ Scuti stars in EBs is the possibility to perform mode identification, enabled by precise knowledge of the mass and radius of the pulsating star [14]. This is notoriously tricky to achieve, but would specify precise constraints on stellar theory.…”