Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Feiden, Gregory A.; Chaboyer, Brian

doi:10.1088/0004-637x/789/1/53

Cited by 112 publications

(106 citation statements)

References 87 publications

(224 reference statements)

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“…This explanation has recently been shown to be satisfactory for three well-characterized systems (MacDonald & Mullan 2014), although the internal magnetic field needed might be too strong compared with analytical arguments (Feiden & Chaboyer 2014). However, this scenario usually requires a relatively fast rotation rate to maintain a dynamo-fast rotation rate that is enforced by tidal synchronization in short-period binaries.…”

Section: Inflated Radius Of Koi-189 Bmentioning

confidence: 99%

SOPHIE velocimetry ofKeplertransit candidates

Díaz

Montagnier

Leconte

et al. 2014

A&A

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We present the radial-velocity follow-up of two Kepler planetary transiting candidates (KOI-189 and KOI-686) carried out with the SOPHIE spectrograph at the Observatoire de Haute Provence. These data promptly discard these objects as viable planet candidates and show that the transiting objects are in the regime of very low-mass stars, where a strong discrepancy between observations and models persists for the mass and radius parameters. By combining the SOPHIE spectra with the Kepler light curve and photometric measurements found in the literature, we obtain a full characterization of the transiting companions, their orbits, and their host stars. The two companions are in significantly eccentric orbits with relatively long periods (30 days and 52.5 days), which makes them suitable objects for a comparison with theoretical models, since the effects invoked to understand the discrepancy with observations are weaker for these orbital distances. KOI-189 b has a mass M = 0.0745 ± 0.0033 M and a radius R = 0.1025 ± 0.0024 R . The density of KOI-189 b is significantly lower than expected from theoretical models for a system of its age. We explore possible explanations for this difference. KOI-189 b is the smallest hydrogen-burning star with such a precise determination of its fundamental parameters. KOI-686 b is larger and more massive (M = 0.0915 ± 0.0043 M ; R = 0.1201 ± 0.0033 R ), and its position in the mass-radius diagram agrees well with theoretical expectations.

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Section: Inflated Radius Of Koi-189 Bmentioning

confidence: 99%

SOPHIE velocimetry ofKeplertransit candidates

Díaz

Montagnier

Leconte

et al. 2014

A&A

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“…It is hypothesized that fully convective M dwarfs, generally those with spectral types M4 and later, are unable to efficiently shed angular momentum through the interaction between the stellar wind and the stellar magnetic field, and therefore spin down more slowly over time (Stassun et al 2011). Also, some M dwarfs appear to have inflated radii, which may also be a consequence of magnetic activity (e.g., Feiden & Chaboyer 2014, Jackson & Jeffries 2014, Han et al 2017.…”

Section: Introductionmentioning

confidence: 99%

The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment

Gilhool

Blake

Terrien

et al. 2017

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We present the results of a spectroscopic analysis of rotational velocities in 714 M-dwarf stars observed by the SDSS-III Apache Point Galactic Evolution Experiment (APOGEE) survey. We use a template-fitting technique to estimate v i sin while simultaneously estimating g log , M H [ ], and T eff . We conservatively estimate that our detection limit is 8 km s −1 . We compare our results to M-dwarf rotation studies in the literature based on both spectroscopic and photometric measurements. Like other authors, we find an increase in the fraction of rapid rotators with decreasing stellar temperature, exemplified by a sharp increase in rotation near the M4 transition to fully convective stellar interiors, which is consistent with the hypothesis that fully convective stars are unable to shed angular momentum as efficiently as those with radiative cores. We compare a sample of targets observed both by APOGEE and the MEarth transiting planet survey and find no cases where the measured v i sin and rotation period are physically inconsistent, requiring i sin 1 > . We compare our spectroscopic results to the fraction of rotators inferred from photometric surveys and find that while the results are broadly consistent, the photometric surveys exhibit a smaller fraction of rotators beyond the M4 transition by a factor of ∼2. We discuss possible reasons for this discrepancy. Given our detection limit, our results are consistent with a bimodal distribution in rotation that is seen in photometric surveys.

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“…There is growing observational evidence from fast-rotating, magnetically active stars in tidally-locked eclipsing binaries, young clusters and the field, that magnetic activity may increase the radii of low-mass stars (Lopez-Morales 2007; Morales, Ribas & Jordi 2008;Jackson, Jeffries & Maxted 2009;Stassun et al 2012). The mechanism by which it does so is still unclear; but could include the magnetic stabilisation of the star against convection (Gough & Tayler 1966;Moss 1968;Mullan & Macdonald 2001;Feiden & Chaboyer 2013), a reduction in convective efficiency due to a turbulent dynamo (Feiden & Chaboyer 2014) or the blocking of emergent flux by dark, magnetic starspots (Spruit 1982;Spruit & Weiss 1986;Jackson & Jeffries 2014). If PMS stellar radii are increased by magnetic activity, they could have lower central temperatures and hence less Li depletion at a given age.…”

Section: Introductionmentioning

confidence: 99%

The effect of star-spots on the ages of low-mass stars determined from the lithium depletion boundary

Jackson

Jeffries

2014

Monthly Notices of the Royal Astronomical Society

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In a coeval group of low-mass stars, the luminosity of the sharp transition between stars that retain their initial lithium and those at slightly higher masses in which Li has been depleted by nuclear reactions, the lithium depletion boundary (LDB), has been advanced as an almost model-independent means of establishing an age scale for young stars. Here we construct polytropic models of contracting pre-main sequence stars (PMS) that have cool, magnetic starspots blocking a fraction β of their photospheric flux. Starspots slow the descent along Hayashi tracks, leading to lower core temperatures and less Li destruction at a given mass and age. The age, τ LDB , determined from the luminosity of the LDB, L LDB , is increased by a factor (1 − β) −E compared to that inferred from unspotted models, where E ≃ 1 + d log τ LDB /d log L LDB and has a value ∼ 0.5 at ages < 80 Myr, decreasing to ∼ 0.3 for older stars. Spotted stars have virtually the same relationship between K-band bolometric correction and colour as unspotted stars, so this relationship applies equally to ages inferred from the absolute K magnitude of the LDB. Low-mass PMS stars do have starspots, but the appropriate value of β is highly uncertain with a probable range of 0.1 < β < 0.4. For the smaller β values our result suggests a modest systematic increase in LDB ages that is comparable with the maximum levels of theoretical uncertainty previously claimed for the technique. The largest β values would however increase LDB ages by 20-30 per cent and demand a re-evaluation of other age estimation techniques calibrated using LDB ages.

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Magnetic Inhibition of Convection and the Fundamental Properties of Low-Mass Stars. Ii. Fully Convective Main-Sequence Stars

Cited by 112 publications

References 87 publications

SOPHIE velocimetry ofKeplertransit candidates

SOPHIE velocimetry ofKeplertransit candidates

The Rotation of M Dwarfs Observed by the Apache Point Galactic Evolution Experiment

The effect of star-spots on the ages of low-mass stars determined from the lithium depletion boundary

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