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

Jackson, R. J.; Jeffries, R. D.

doi:10.1093/mnras/stu2076

Cited by 37 publications

(43 citation statements)

References 51 publications

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“…However, the availability of the necessary photometry and spectral information is far from uniform, leading to uncertainties. Furthermore, the impact of the detailed accretion history, activity, rotation and magnetic field on the location of TTS in the HR diagram may be larger than previously thought (Baraffe et al 2012;Somers & Pinsonneault 2014;Jackson & Jeffries 2014;Bouvier et al 2016). While we cannot escape these issues, we decided to adopt the stellar masses adopted in the studies referred above whenever available.…”

Section: On the Use Of Hα As An Accretion Discriminatormentioning

confidence: 85%

A search for passive protoplanetary discs in the Taurus–Auriga star-forming region

Duchêne

Becker

Yang

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We conducted a 12-month monitoring campaign of 33 T Tauri stars (TTS) in Taurus. Our goal was to monitor objects that possess a disk but have a weak Hα line, a common accretion tracer for young stars, to determine whether they host a passive circumstellar disk. We used medium-resolution optical spectroscopy to assess the objects' accretion status and to measure the Hα line. We found no convincing example of passive disks; only transition disk and debris disk systems in our sample are non-accreting. Among accretors, we find no example of flickering accretion, leading to an upper limit of 2.2% on the duty cycle of accretion gaps assuming that all accreting TTS experience such events. Combining literature results with our observations, we find that the reliability of traditional Hα-based criteria to test for accretion is high but imperfect, particularly for low-mass TTS. We find a significant correlation between stellar mass and the full width at 10 per cent of the peak (W 10% ) of the Hα line that does not seem to be related to variations in free-fall velocity. Finally, our data reveal a positive correlation between the Hα equivalent width and its W 10% , indicative of a systematic modulation in the line profile whereby the high-velocity wings of the line are proportionally more enhanced than its core when the line luminosity increases. We argue that this supports the hypothesis that the mass accretion rate on the central star is correlated with the Hα W 10% through a common physical mechanism.

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Section: On the Use Of Hα As An Accretion Discriminatormentioning

confidence: 85%

A search for passive protoplanetary discs in the Taurus–Auriga star-forming region

Duchêne

Becker

Yang

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Starspots have a similar affect on lithium burning timescales (Jackson & Jeffries 2014a;Somers & Pinsonneault 2015), which is perhaps not surprising given the deep connection between starspots and magnetic inhibition of convection (Biermann 1941;Deinzer 1965). Nevertheless, if magnetic fields are directly influencing the structure of young stars, they should leave an imprint on the observed lithium abundance distribution in young stellar populations.…”

Section: Lithium Depletionmentioning

confidence: 93%

Magnetic inhibition of convection and the fundamental properties of low-mass stars

Feiden

2016

A&A

292

290

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When determining absolute ages of identifiably young stellar populations, results strongly depend on which stars are studied. Cooler (K, M) stars typically yield ages that are systematically younger than warmer (A, F, G) stars by a factor of two. I explore the possibility that these age discrepancies are the result of magnetic inhibition of convection in cool young stars by using magnetic stellar evolution isochrones to determine the age of the Upper Scorpius subgroup of the Scorpius-Centaurus OB Association. A median age of 10 Myr consistent across spectral types A through M is found, except for a subset of F-type stars that appear significantly older. Agreement is shown for ages derived from the Hertzsprung-Russell diagram and from the empirical mass-radius relationship defined by eclipsing multiple-star systems. Surface magnetic field strengths required to produce agreement are of order 2.5 kG and are predicted from a priori estimates of equipartition values. A region in the HR diagram is identified that plausibly connects stars whose structures are weakly influenced by the presence of magnetic fields with those whose structures are strongly influenced by magnetic fields. The models suggest this region is characterized by stars with rapidly thinning outer convective envelopes where the radiative core mass is greater than 75% of the total stellar mass. Furthermore, depletion of lithium predicted from magnetic models appears in better agreement with observed lithium equivalent widths than predictions from non-magnetic models. These results suggest that magnetic inhibition of convection plays an important role in the early evolution of low-mass stars and that it may be responsible for noted age discrepancies in young stellar populations.

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“…Yet precise measurements of K-and M-dwarfs in eclipsing binary systems have shown that, for a given mass, the radii of stars with 0.2 < M/M < 0.8 are 10-15 per cent larger than predicted by current evolutionary models. Hence, for a given luminosity, the effective transiting exoplanets that are discovered around them and alter the age-dependence of lithium depletion in their photospheres (Jackson & Jeffries 2014a;Somers & Pinsonneault 2014.…”

Section: The Radii Of Low-mass Starsmentioning

confidence: 99%

TheGaia-ESO Survey: Stellar radii in the young open clusters NGC 2264, NGC 2547, and NGC 2516

Jackson¹,

Jeffries²,

Randich³

et al. 2016

A&A

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Context. Rapidly rotating, low-mass members of eclipsing binary systems have measured radii that are significantly larger than predicted by standard evolutionary models. It has been proposed that magnetic activity is responsible for this radius inflation. Aims. By estimating the radii of low-mass stars in three young clusters (NGC 2264, NGC 2547, NGC 2516, with ages of ∼5, ∼35 and ∼140 Myr respectively), we aim to establish whether similar radius inflation is seen in single, magnetically active stars. Methods. We use radial velocities from the Gaia-ESO Survey (GES) and published photometry to establish cluster membership and then combine GES measurements of projected equatorial velocities with published rotation periods to estimate the average radii for groups of fast-rotating cluster members as a function of their luminosity and age. The average radii are compared with the predictions of both standard evolutionary models and variants that include magnetic inhibition of convection and starspots. Results. At a given luminosity, the stellar radii in NGC 2516 and NGC 2547 are larger than predicted by standard evolutionary models at the ages of these clusters. The discrepancy is least pronounced and not significant ( 10 per cent) in zero age main sequence stars with radiative cores, but more significant in lower-mass, fully convective pre main-sequence cluster members, reaching 30 ± 10 per cent. The uncertain age and distance of NGC 2264 preclude a reliable determination of any discrepancy for its members. Conclusions. The median radii we have estimated for low-mass fully convective stars in the older clusters are inconsistent (at the 2-3σ level) with non-magnetic evolutionary models and more consistent with models that incorporate the effects of magnetic fields or dark starspots. The available models suggest this requires either surface magnetic fields exceeding 2.5 kG, spots that block about 30 per cent of the photospheric flux, or a more moderate combination of both.

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

Cited by 37 publications

References 51 publications

A search for passive protoplanetary discs in the Taurus–Auriga star-forming region

A search for passive protoplanetary discs in the Taurus–Auriga star-forming region

Magnetic inhibition of convection and the fundamental properties of low-mass stars

TheGaia-ESO Survey: Stellar radii in the young open clusters NGC 2264, NGC 2547, and NGC 2516

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