A method to estimate stellar ages from kinematical data

Almeida-Fernandes, F.; Rocha-Pinto, Helio J.

doi:10.1093/mnras/sty119

Cited by 21 publications

(5 citation statements)

References 102 publications

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“…As stars age there is an increasing probability of kinematic disturbances as they orbit the Galactic centre that results in an overall increase in stellar Galactic velocity and the velocity dispersion of stars in general [142][143][144]. Therefore, it is possible to estimate the age of a star based on its kinematics alone [145,146]. This is especially useful for stars, such as M-dwarfs, in which it is difficult to derive isochronal, gyrochronological, chemical, or astroseismological age values.…”

Section: Radius Mass and Agementioning

confidence: 99%

“…We utilise The LHS 1903 planetary system the methodology of ref. [146] that allows for age estimates based on kinematic-age probability distributions that were formalised and bench-marked using a sample of 9000 stars in the Geneva-Copenhagen Survey that have known isochronal ages. For this study, we computed the age of LHS 1903 using the Galactic U, V, and W velocity, and eccentricity, and Gaia DR3 Galactic reference coordinates [107].…”

Section: Radius Mass and Agementioning

confidence: 99%

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LHS 1903 provides evidence for gas-depleted formation of planets around M-dwarfs

Wilson,

Simpson,

Cameron

et al. 2023

Preprint

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Many important advances in planet formation theory have come from the discovery of unexpected planets. The thousands of discovered exoplanets have unveiled demographic trends, such as the bimodality of planetary radius distribution known as the radius valley. Modelling these trends can probe underlying processes, e.g. the formation environment and atmospheric evolution. Here, we report the discovery and characterisation of a four-planet system around the kinematically thick-disk M-dwarf LHS 1903 with orbital periods of 2.16, 6.23, 12.57, and 29.32 days that becomes the only known M-dwarf hosting four small, well-characterised planets spanning the radius valley. We utilise high-precision transit photometry from the Transiting Exoplanet Survey Satellite (TESS) and the CHaracterising ExOPlanets Satellite (CHEOPS) to measure the radii of LHS 1903 b, c, d, and e (1.382+/-0.046, 2.046^+0.078_-0.074, 2.500^+0.078_-0.077, and 1.732^+0.059_-0.058 R_oplus). Combined with HARPS-N radial velocity data, we determine the planetary bulk densities (1.24^+0.21_-0.19, 0.53^+0.11_-0.09, 0.38^+0.09_-0.08, and 1.11^+0.33_-0.31 rho_oplus). Our compositional analysis finds that planet b is rocky, planets c and d have extended atmospheres, and LHS 1903 e does not have a gaseous envelope. Our discovery that planet e, the longest-period well-characterised terrestrial M-dwarf planet, lacks an extended atmosphere causes tension with thermally-driven mass loss radius valley predictions, but supports a gas-depleted formation explanation. The observed broken atmospheric-mass fraction trend is at odds with current formation theory, but provides further evidence for a gas-depleted formation environment for terrestrial M-dwarf planets.

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Section: Radius Mass and Agementioning

confidence: 99%

Section: Radius Mass and Agementioning

confidence: 99%

LHS 1903 provides evidence for gas-depleted formation of planets around M-dwarfs

Wilson,

Simpson,

Cameron

et al. 2023

Preprint

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“…These values are provided in the GALAH VAC and computed with the tool galpy (Bovy 2015). As a star evolves, these parameters are known to increase their average values: this process of dynamical heating is caused by interactions with different substructures of the Galaxy, such as spiral arms, giant molecular clouds, or the Galactic bar (e.g., Aumer et al 2016;Mackereth et al 2019;Almeida-Fernandes & Rocha-Pinto 2018).…”

Section: Kinematic Propertiesmentioning

confidence: 99%

Lithium, masses, and kinematics of young Galactic dwarf and giant stars with extreme [α/Fe] ratios

Borisov

Prantzos

Charbonnel

2022

A&A

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Context. Recent spectroscopic explorations of large Galactic stellar samples stars have revealed the existence of red giants with [α/Fe] ratios that are anomalously high, given their relatively young ages. Aims. We revisit the GALAH DR3 survey to look for both dwarf and giant stars with extreme [α/Fe] ratios, that is, the upper 1% in the [α/Fe]-[Fe/H] plane over the range in [Fe/H] between -1.1 and +0.4 dex. We refer to these outliers as "exαfe" stars. Methods. We used the GALAH DR3 data along with their value-added catalog to trace the properties (chemical abundances, masses, ages, and kinematics) of the exαfe stars. We applied strict criteria to the quality of the determination of the stellar parameters, abundances, and age determinations to select our sample of single stars. We investigated the effects of secular stellar evolution and the magnitude limitations of the GALAH survey to understand the mass and metallicity distributions of the sample stars. Here, we also discuss the corresponding biases in previous studies of stars with high -albeit not extreme -[α/Fe] in other spectroscopic surveys. Results. We find both dwarf and giant exαfe stars younger than 3 Gyr, which we refer to as "y-exαfe" stars. Dwarf y-exαfe stars exhibit lithium abundances similar to those of young [α/Fe]-normal dwarfs at the same age and [Fe/H]. In particular, the youngest and most massive stars of both populations exhibit the highest Li abundances, A(Li)∼3.5 dex (i.e., a factor of 2 above the protosolar value), while cooler and older stars exhibit the same Li depletion patterns increasing with both decreasing mass and increasing age. In addition, the [Fe/H] and mass distributions of both the dwarf and giant y-exαfe stars do not differ from those of their [α/Fe]normal counterparts found in the thin disk and they share the same kinematic properties, with lower eccentricities and velocities with respect to the local standard of rest than old stars of the thick disk. Conclusions. We conclude that y-exαfe dwarf and giant stars are indeed young, their mass distribution shows no peculiarity, and they differ from young [α/Fe]-normal stars by their extreme [α/Fe] content only. However, their origins still remain unclear.

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“…This evolution results in a statistical correlation known as disk heating (Wielen 1977), a net increase in Galactic space motions with time. Almeida-Fernandes & Rocha-Pinto (2018) summarize some mechanisms that can explain the fluctuations that a star can encounter when traveling around the Galactic center: encounters with giant molecular clouds, interaction with non-axisymmetric Galactic structures, interactions with satellite galaxies, etc.…”

Section: Kinematical Features As a Proxy For Old Agesmentioning

confidence: 99%

New Candidates for Chromospherically Young, Kinematically Old Stars

Pereira

Rocha-Pinto

2019

Proc. IAU

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Roughly speaking, young stars are associated to intense chromospheric activity (CA), whereas it decreases with stellar aging. However, some objects that show high kinematical components – in turn, associated to older stars – reveal CA similar to that of young ones; we call these stars chromospherically young and kinematically old (CYKOs). One hypothesis that could explain their occurrence is the merge of a short-period binary, from which the outcome would be a chromospherically active, kinematically evolved star. Considering that they evolved separately, we expect them to be lithium depleted, and therefore we look for CYKO stars by analyzing their lithium content (λ 6707 Å). We present a preliminary list of 48 stars matching this criteria, aiming to either confirm or discard the coalescence of a short-period pair hypothesis.

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A method to estimate stellar ages from kinematical data

Cited by 21 publications

References 102 publications

LHS 1903 provides evidence for gas-depleted formation of planets around M-dwarfs

LHS 1903 provides evidence for gas-depleted formation of planets around M-dwarfs

Lithium, masses, and kinematics of young Galactic dwarf and giant stars with extreme [α/Fe] ratios

New Candidates for Chromospherically Young, Kinematically Old Stars

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