Theoretical uncertainties on the radius of low- and very-low-mass stars

Tognelli, E.; Moroni, Pier Giorgio Prada; Degl’Innocenti, S.

doi:10.1093/mnras/sty195

Cited by 31 publications

(37 citation statements)

References 56 publications

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“…Stellar models have been computed using the most recent version of the Pisa stellar evolutionary code (see e.g., Tognelli et al 2011) described in detail in previous papers (see Randich et al 2018;Tognelli et al 2018, and references therein). We simply recall the main aspects relevant for the present analysis.…”

Section: Pms Isochronesmentioning

confidence: 99%

When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster

Jeřabková

Beccari

Boffin

et al. 2019

A&A

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Context. Recently published high-quality OmegaCAM photometry of the 3x3 deg around the Orion Nebula Cluster (ONC) in r, and i filters revealed three well-separated pre-main sequences in the color-magnitude diagram (CMD). The objects belonging to the individual sequences are concentrated toward the center of the ONC. The authors concluded that there are two competitive scenarios: a population of unresolved binaries and triples with an exotic mass ratio distribution, or three stellar populations with different ages (≈ 1 Myr age differences). Aims. We use Gaia DR2 in combination with the photometric OmegaCAM catalog to test and confirm the presence of the putative three stellar populations. We also study multiple stellar systems in the ONC for the first time using Gaia DR2. Methods. We selected ONC members based on parallaxes and proper motions and take advantage from OmegaCAM photometry that performs better than Gaia DR2 photometry in crowded regions. We identify two clearly separated sequences with a third suggested by the data. We used Pisa stellar isochrones to estimate ages of the stellar populations with absolute magnitudes computed using Gaia parallaxes on a star by star basis. Results. 1) We confirm that the second and third sequence members are more centrally concentrated toward the center of the ONC. In addition we find an indication that the parallax and proper motion distributions are different among the members of the stellar sequences. The age difference among stellar populations is estimated to be 1-2 Myr. 2) We use Gaia proper motions and other measures to identify and remove as many unresolved multiple system candidates as possible. Nevertheless we are still able to recover two well-separated sequences with evidence for the third one, supporting the existence of the three stellar populations. 3) Due to having ONC members with negligible fore-or background contamination we were able to identify a substantial number of wide binary objects (separation between 1000-3000 au) and with relative proper motions of the binary components consistent with zero. This challenges previously inferred values that suggested no wide binary stars exist in the ONC. Our inferred wide-binary fraction is ≈ 5%. Conclusions. We confirm the three populations correspond to three separated episodes of star formation. Based on this result, we conclude that star formation is not happening in a single burst in this region. In addition we identify 5% of wide-binary stars in the ONC that were thought not to be present.

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Section: Pms Isochronesmentioning

confidence: 99%

When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster

Jeřabková

Beccari

Boffin

et al. 2019

A&A

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“…Our results show that both squared visibilities and closure phases are in good agreement with a binary system of ∼38 mas separation between the components and a K-band flux ratio of ∼5%. This configuration implies masses for the tentative binary AB Dor Ca/Cb of 0.072 ± 0.013 M and 0.013 ± 0.001 M , according to the PMS evolutionary models of Chabrier et al (2000), Baraffe et al (2015) and Tognelli et al (2018). It is worth noting that, with these masses, one of the objects would lie near the hydrogen-burning limit (AB Dor Ca), while AB Dor Cb would lie at the frontier between brown dwarfs and planets.…”

Section: Discussionmentioning

confidence: 74%

“…In Fig. 5 we represent the cooling curves of AB Dor Ca/Cb (models by Tognelli et al 2018) compared with published AB Dor C photometric measurements (Close et al 2005;Luhman & Potter 2006;Close et al 2007;Boccaletti et al 2008) for the two scenarios considered: 1) the (old) single-object scenario (with AB Dor C as a single object of 0.090 M ) and 2) the (new) binary scenario resulting from our detection (with AB Dor C as a binary with estimated masses of 0.072 M and 0.013 M , according to the parameters given in Table 2). Published magnitudes at J, H, and K bands are shown for the two mostconsidered age ranges in the literature: 75 ± 25 Myr (Janson et al 2007;Boccaletti et al 2008) and 120 ± 20 Myr (Luhman et al 2005;Ortega et al 2007), being the latter being favored by the recent works of Bell et al (2015) and Gagné et al (2018).…”

Section: Binary Hypothesis and Photometrymentioning

confidence: 99%

“…Differences in bolometric luminosity or in magnitudes could highlight two scenarios. On one hand, a discrepancy in luminosity would suggest problems in the fundamental physics used to compute very low-mass stars models, in particular due to the adopted equation of state, outer boundary conditions, magnetic fields, and surface spots (Siess 2001;Chabrier et al 2007;di Criscienzo et al 2010;Feiden & Chaboyer 2013;Somers & Pinsonneault 2015;Tognelli et al 2018). On the other hand, a difference visible only in magnitudes should point out for the need for more accurate synthetic spectra, which, especially in the case of low-and very low-mass stars, still represents a challenging task.…”

Section: Binary Hypothesis and Photometrymentioning

confidence: 99%

“…Mass versus age at constant K s magnitude: 8.43 ± 0.16 (blue; Ca) and 11.7 ± 0.3 (red; Cb) and the corresponding binary system (green; Ca+Cb). A dashed-dotted line represents the measured dynamical mass of 0.090 M(Azulay et al 2017), while the shadowed gray area represents the age range (44-66 Myr) resulting from the intersection of this measured dynamical mass with the measured Ca+Cb magnitude, according to the models byTognelli et al (2018). The irregularities in the model are more likely a product of the interpolation than a real physical effect.…”

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confidence: 99%

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Evidence of a Substellar Companion to AB Dor C

Climent

Berger

Guirado

et al. 2019

ApJL

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Studies of fundamental parameters of very low-mass objects are indispensable to provide tests of stellar evolution models that are used to derive theoretical masses of brown dwarfs and planets. However, only objects with dynamically determined masses and precise photometry can effectively evaluate the predictions of stellar models. AB Dor C (0.090 M ) has become a prime benchmark for calibration of theoretical evolutionary models of low-mass young stars. One of the ambiguities remaining in AB Dor C is the possible binary nature of this star. We observed AB Dor C with the VLTI/AMBER instrument in low-resolution mode at the J, H and K bands. The interferometric observables at the K-band are compatible with a binary brown dwarf system with tentative components AB Dor Ca/Cb with a K-band flux ratio of 5% ± 1% and a separation of 38 ± 1 mas. This implies theoretical masses of 0.072 ± 0.013 M and 0.013 ± 0.001 M for each component, near the hydrogen-burning limit for AB Dor Ca, and near the deuterium-burning limit, straddling the boundary between brown dwarfs and giant planets, for AB Dor Cb. The possible binarity of AB Dor C alleviates the disagreement between observed magnitudes and theoretical mass-luminosity relationships.

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Asteroseismic age estimates of RGB stars in open clusters

Valle

Dell’Omodarme

Tognelli

et al. 2018

A&A

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Context. Open clusters (OCs) provide a classical target to calibrate the age scale and other stellar parameters. Despite their wide use, some issues remain to be explored in detail. Aims. We performed a theoretical investigation focused on the age estimate of red giant branch (RGB) stars in OCs based on mixed classical surface (Teff and [Fe/H]) and asteroseismic (Δν and νmax) parameters. We aimed to evaluate the performances of three widely adopted fitting procedures, that is, a pure geometrical fit, a maximum likelihood approach, and a single stars fit, in recovering stellar parameters. Methods. A dense grid of stellar models was computed, covering different chemical compositions and different values of the mixing-length parameter. Artificial OCs were generated from these data by means of a Monte Carlo procedure for two different ages (7.5 and 9.0 Gyr) and two different choices of the number of stars in the RGB evolutionary phase (35 and 80). The cluster age and other fundamental parameters were then recovered by means of the three methods previously mentioned. A Monte Carlo Markov chain approach was adopted for estimating the posterior densities of probability of the estimated parameters. Results. The geometrical approach overestimated the age by about 0.3 and 0.2 Gyr for true ages of 7.5 and 9.0 Gyr, respectively. The value of the initial helium content was recovered unbiased within the large random errors on the estimates. The maximum likelihood approach provided similar biases (0.1 and 0.2 Gyr) but with a variance reduced by a factor of between two and four with respect to geometrical fit. The independent fit of single stars showed a very large variance owing to its neglect of the fact that the stars came from the same cluster. The age of the cluster was recovered with no biases for 7.5 Gyr true age and with a bias of −0.4 Gyr for 9.0 Gyr. The most important difference between geometrical and maximum likelihood approaches was the robustness against observational errors. For the first fitting technique, we found that estimations starting from the same sample but with different Gaussian perturbations on the observables suffer from a variability in the recovered mean of about 0.3 Gyr from one Monte Carlo run to another. This value was as high as 45% of the intrinsic variability due to observational errors. On the other hand, for the maximum likelihood fitting method, this value was about 65%. This larger variability led most simulations – up to 90% – to fail to include the true parameter values in their estimated 1σ credible interval. Finally, we compared the performance of the three fitting methods for single RGB-star age estimation. The variability owing to the choice of the fitting method was minor, being about 15% of the variability caused by observational uncertainties. Conclusions. Each method has its own merits and drawbacks. The single star fit showed the lowest performances. The higher precision of the maximum likelihood estimates is partially negated by the lower protection that this technique shows against random fluctuations compared to the pure geometrical fit. Ultimately, the choice of the fitting method has to be evaluated in light of the specific sample and evolutionary phases under investigation.

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Theoretical uncertainties on the radius of low- and very-low-mass stars

Cited by 31 publications

References 56 publications

When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster

When the tale comes true: multiple populations and wide binaries in the Orion Nebula Cluster

Evidence of a Substellar Companion to AB Dor C

Asteroseismic age estimates of RGB stars in open clusters

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