The 0.4-$M_{\odot}$ eclipsing binary CU Cancri

Ribas, I.

doi:10.1051/0004-6361:20021609

Cited by 142 publications

(224 citation statements)

References 48 publications

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“…Since the properties of the more massive primary star appear to be well reproduced by the models (as expected from previous experience; see Andersen 2003), suspicion falls on our theoretical understanding of stars under a solar mass. Similar evidence has been presented over the last several years (e.g., Popper 1997;Clausen et al 1999a;Torres & Ribas 2002;Ribas 2003;Dawson & De Robertis 2004;López-Morales & Ribas 2005), but in fact indications go as far back as the work by Hoxie (1973), Lacy (1977), and others. All of these studies have shown that theoretical calculations for stars less massive than the Sun tend to underestimate the radius by as much as 10%-20%.…”

Section: Comparison With Evolutionary Modelssupporting

confidence: 80%

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar‐Type Stars

Torres

Lacy

Marschall

et al. 2006

ApJ

102

117

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We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P ¼ 2:35 days). A third star is visible in the spectrum, and the system is a hierarchical triple. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the Hipparcos mission (abscissa residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components: M Aa ¼ 1:282 AE 0:015 M , R Aa ¼ 1:615 AE 0:017 R , and T Aa eA ¼ 6180 AE 100 K for the primary (star Aa), and M Ab ¼ 0:9315 AE 0:0068 M , R Ab ¼ 0:974 AE 0:020 R , and T Ab eA ¼ 5300 AE 150 K for the secondary (Ab). The mass of the tertiary is determined to be M B ¼ 0:925 AE 0:036 M and its effective temperature is T B eA ¼ 5670 AE 150 K. Current stellar evolution models agree well with the properties of the primary but show a very large discrepancy in the radius of the secondary, in the sense that the predicted values are $10% smaller than observed (a $5 effect). In addition, the temperature is cooler than predicted, by some 200 K. These discrepancies are quite remarkable given that the star is only 7% less massive than the Sun, the calibration point of all stellar models. We identify the chromospheric activity as the likely cause of the effect. Inactive stars agree very well with the models, while active ones such as V1061 Cyg Ab appear systematically too large and too cool.

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Section: Comparison With Evolutionary Modelssupporting

confidence: 80%

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar‐Type Stars

Torres

Lacy

Marschall

et al. 2006

ApJ

102

117

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“…However, radii of single inactive M dwarfs measured by interferometry are in excellent agreement with models from Baraffe et al (1998). Thus, the discrepancies pointed out by Torres & Ribas (2002) and Ribas (2003) only concern fast-rotating stars, confirming that rotation strongly affects the internal structure of those objects. …”

Section: Activitymentioning

confidence: 72%

Mass-radius relation of low and very low-mass stars revisited with the VLTI

Demory¹,

Ségransan²,

Forveille

et al. 2009

A&A

161

129

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We measured the radii of 7 low and very low-mass stars using long baseline interferometry with the VLTI interferometer and its VINCI and AMBER near-infrared recombiners. We use these new data, together with literature measurements, to examine the luminosityradius and mass-radius relations for K and M dwarfs. The precision of the new interferometric radii now competes with what can be obtained for double-lined eclipsing binaries. Interferometry provides access to much less active stars, as well as to stars with much better measured distances and luminosities, and therefore complements the information obtained from eclipsing systems. The radii of magnetically quiet late-K to M dwarfs match the predictions of stellar evolution models very well, providing direct confirmation that magnetic activity explains the discrepancy that was recently found for magnetically active eclipsing systems. The radii of the early K dwarfs are reproduced well for a mixing length parameter that approaches the solar value, as qualitatively expected.

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“…While these three determinations are not completely independent, their consistency despite the widely different ingredients reinforces our conclusion that the model ΔT eff is at least ∼ 250 K too small. Stellar evolution models have been shown previously to overestimate the effective temperatures of low-mass stars in eclipsing binaries by up to ∼ 200 K (e.g., Torres & Ribas 2002;Ribas 2003). The study of V1061 Cyg by Torres et al (2006) suggested that the problem is not confined to M dwarfs, but extends up to masses almost as large as that of the Sun (0.93 M in the case of V1061 Cyg B).…”

Section: Discussionmentioning

confidence: 99%

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

Torres

Lacy

2008

The Astronomical Journal

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We present new V-band differential photometry and radial velocity measurements of the unevolved, 1.18 day period, F+G-type, double-lined eclipsing binary VZ Cep. We determine accurate values for the absolute masses, radii, and effective temperatures as follows: M A = 1.402 ± 0.015 M , R A = 1.534 ± 0.012 R , and T eff = 6690 ± 160 K for the primary, and M B = 1.1077 ± 0.0083 M , R B = 1.042 ± 0.039 R , and T eff = 5720 ± 120 K for the secondary. A comparison with current stellar evolution models suggests an age of 1.4 Gyr for a metallicity that is near solar. The temperature difference between the stars, which is much better determined than the absolute values, is found to be ∼ 250 K larger than predicted by theory. If all of this discrepancy is attributed to the secondary (which would then be too cool compared to models), the effect would be consistent with similar differences found for other low-mass stars, generally believed to be associated with chromospheric activity. However, the radius of VZ Cep B (which unlike the primary, still has a thin convective envelope) appears normal, whereas in other stars affected by activity the radius is systematically larger than predicted. Thus, VZ Cep poses a challenge not only to standard theory but also to our understanding of the discrepancies in other low-mass systems.

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The 0.4-$M_{\odot}$ eclipsing binary CU Cancri

Cited by 142 publications

References 48 publications

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar‐Type Stars

The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models for Active and Inactive Solar‐Type Stars

Mass-radius relation of low and very low-mass stars revisited with the VLTI

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

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