Absolute Dimensions of the F-Type Eclipsing Binary Star Vz Cephei

Torres, Guillermo; Lacy, Claud H.

doi:10.1088/0004-6256/137/1/507

Cited by 8 publications

(5 citation statements)

References 47 publications

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“…For the exception, VZ Cep, the observed masses and radii are well reproduced by the Y 2 models, but the observed temperature of the secondary component is about 250 K lower than predicted (Torres et al 2009). Therefore, it is also less luminous than predicted, which is in general not the case for the rest of the sample.…”

Section: Saw Nomentioning

confidence: 57%

Absolute dimensions of solar-type eclipsing binaries

Clausen¹,

Bruntt

Claret

et al. 2009

A&A

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Context. The influence of stellar activity on the fundamental properties of stars around and below 1 M is not well understood. Accurate mass, radius, and abundance determinations from solar-type binaries exhibiting various levels of activity are needed for a better insight into the structure and evolution of these stars. Aims. We aim to determine absolute dimensions and abundances for the solar-type detached eclipsing binary V636 Cen, and to perform a detailed comparison with results from recent stellar evolutionary models. Methods. uvby light curves and uvbyβ standard photometry were obtained with the Strömgren Automatic Telescope, radial velocity observations with the CORAVEL spectrometer, and high-resolution spectra with the FEROS spectrograph, all at ESO, La Silla. Stateof-the-art methods were applied for the photometric and spectroscopic analyses. Results. Masses and radii that are precise to 0.5% have been established for the components of V636 Cen. The 0.85 M secondary component is moderately active with starspots and Ca ii H and K emission, and the 1.05 M primary shows signs of activity as well, but at a much lower level. We derive a [Fe/H] abundance of −0.20 ± 0.08 and similar abundances for Si, Ca, Ti, V, Cr, Co, and Ni. Corresponding solar-scaled stellar models are unable to reproduce V636 Cen, especially its secondary component, which is ∼10% larger and ∼400 K cooler than predicted. Models adopting significantly lower mixing-length parameters l/H p remove these discrepancies, seen also for other solar-type binary components. For the observed [Fe/H], Claret models for l/H p = 1.4 (primary) and 1.0 (secondary) reproduce the components of V636 Cen at a common age of 1.35 Gyr. The orbit is eccentric (e = 0.135 ± 0.001), and apsidal motion with a 40% relativistic contribution has been detected. The period is U = 5 270 ± 335 yr, and the inferred mean central density concentration coefficient, log(k 2 ) = −1.61 ± 0.05, agrees marginally with model predictions. The measured rotational velocities, 13.0 ± 0.2 (primary) and 11.2 ± 0.5 (secondary) km s −1 , are in remarkable agreement with the theoretically predicted pseudo-synchronous velocities, but are about 15% lower than the periastron values. Conclusions. V636 Cen and 10 other well-studied inactive and active solar-type binaries suggest that chromospheric activity, and its effect on envelope convection, is likely to cause radius and temperature discrepancies, which can be removed by adjusting the model mixing length parameters downwards. Noting this, the sample may also lend support to theoretical 2D radiation hydrodynamics studies, which predict a slight decrease of the mixing length parameter with increasing temperature/mass for inactive main sequence stars. More binaries are, however, needed for a description/calibration in terms of physical parameters and level of activity.

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Section: Saw Nomentioning

confidence: 57%

Absolute dimensions of solar-type eclipsing binaries

Clausen¹,

Bruntt

Claret

et al. 2009

A&A

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“…The differences for IM Vir are shown in Figure 1, and are less than 0.5 km s −1 for the primary but reach values as large as 13 km s −1 for the secondary. Similarly large differences have been found occasionally for other systems using the same instrumentation (e.g., AD Boo, GX Gem, VZ Cep; Clausen et al 2008;Lacy et al 2008;Torres & Lacy 2009). We have applied these differences as corrections to the raw velocities of IM Vir.…”

Section: Spectroscopic Observations and Reductionsmentioning

confidence: 57%

Absolute Dimensions of the G7+k7 Eclipsing Binary Star Im Virginis: Discrepancies With Stellar Evolution Models

Morales

Torres

Marschall

et al. 2009

ApJ

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We report extensive spectroscopic and differential photometric BVRI observations of the active, detached, 1.309-day double-lined eclipsing binary IM Vir, composed of a G7-type primary and a K7 secondary. With these observations we derive accurate absolute masses and radii of M 1 = 0.981 ± 0.012 M ⊙ , M 2 = 0.6644 ± 0.0048 M ⊙ , R 1 = 1.061 ± 0.016 R ⊙ , and R 2 = 0.681 ± 0.013 R ⊙ for the primary and secondary, with relative errors under 2%. The effective temperatures are 5570 ± 100 K and 4250 ± 130 K. The significant difference in mass makes this a favorable case for comparison with stellar evolution theory. We find that both stars are larger than the models predict, by 3.7% for the primary and 7.5% for the secondary, as well as cooler than expected, by 100 K and 150 K, respectively. These discrepancies are in line with previously reported differences in low-mass stars, and are believed to be caused by chromospheric activity, which is not accounted for in current models. The effect is not confined to low-mass stars: the rapidly-rotating primary of IM Vir joins the growing list of objects of near-solar mass (but still with convective envelopes) that show similar anomalies. The comparison with the models suggests an age of 2.4 Gyr for the system, and a metallicity of [Fe/H] ≈ −0.3 that is consistent with other indications, but requires confirmation.

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“…With masses around 1.3 solar masses, CO And is an important addition to well-studied main-sequence systems in the mass interval (approximately1.1-1.7 solar masses) where convective overshooting is ramped up in evolutionary models. Only GX Gem and BW Aqr are listed by Torres & Lacy (2009) to be in a similar evolutionary state, both of them more massive than CO And.…”

Section: Discussionmentioning

confidence: 99%

“…As in previous work with similar spectroscopic material (see, e.g., Torres & Lacy 2009), we have used numerical simulations to assess the systematic errors in our velocities that may result from residual line blending in our narrow spectral window, or from shifts of the spectral lines in and out of this window as a function of orbital phase. Briefly, we generated synthetic composite spectra matching our observations by combining copies of the templates for each star, shifted to the appropriate velocities for each of the exposures as predicted by a preliminary orbital solution, and scaled to the observed light ratio.…”

Section: Spectroscopic Observations and Orbital Solutionmentioning

confidence: 99%

Absolute Properties of the Eclipsing Triple Star Co Andromedae: Constraints on Convective Core Overshooting

Lacy

Torres

Claret

et al. 2010

The Astronomical Journal

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Accurate absolute properties have been determined for the eclipsing triple star CO And (F8+F8) based on extensive differential photometry obtained by three robotic observatories and CfA spectroscopy. The eclipsing binary star orbit is circular with a period of 3.655 days. The triple nature of this system is revealed by more than a century of timings of minimum light, and by the presence of third light in the photometric orbits. The masses of the eclipsing pair are 1.289 ± 0.007 and 1.264 ± 0.007 solar masses, and the corresponding radii are 1.727 ± 0.021 and 1.694 ± 0.017 solar radii. These stars are synchronously rotating and are near the end of their main-sequence phase, at an age of about 3.6 Gyr. The much fainter widely separated third body appears to have a mass of about 0.8 solar masses. The distance to the system is 377 ± 25 pc.

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Absolute Dimensions of the F-Type Eclipsing Binary Star Vz Cephei

Cited by 8 publications

References 47 publications

Absolute dimensions of solar-type eclipsing binaries

Absolute dimensions of solar-type eclipsing binaries

Absolute Dimensions of the G7+k7 Eclipsing Binary Star Im Virginis: Discrepancies With Stellar Evolution Models

Absolute Properties of the Eclipsing Triple Star Co Andromedae: Constraints on Convective Core Overshooting

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