Orbital eccentricities as indicators of stellar populations

Cubarsi, Rafael; Stojanović, M.; Ninković, S.

doi:10.1051/0004-6361/202040017

Cited by 2 publications

(1 citation statement)

References 52 publications

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“…The majority of particles are in highly circular orbits, as is both intuitively expected and observationally grounded, as far as the Milky Way stellar population is concerned (e.g. Cubarsi, Stojanović, & Ninković, 2021). The ones whose orbits are significantly eccentric (with lower circularity values) inhabit, almost exclusively, inner to central regions of the galaxy.…”

Section: Galaxy Evolution and The Motions Of Starsmentioning

confidence: 84%

Dynamical aspects of Galactic habitability in N-body simulations

Mitrašinović,

Vukotić,

Micic

et al. 2023

Publ. Astron. Soc. Aust.

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Recent studies of Galactic evolution revealed that the dynamics of the stellar component might be one of the key factors when considering galactic habitability. We run an N-body simulation model of the Milky Way, which we evolve for 10 Gyr, to study the secular evolution of stellar orbits and the resulting galactic habitability related properties, i.e., the density of the stellar component and close stellar encounters. The results indicate that radial migrations are not negligible, even in a simple axisymmetric model with mild levels of dynamical heating, and that the net outward diffusion of the stellar component can populate galactic outskirts with habitable systems. Habitable environment is also likely even at sub-Solar galactocentric radii, because the rate of close encounters should not significantly degrade habitability. Stars that evolve from non-circular to stable nearly circular orbits typically migrate outwards, settling down in a broad Solar neighbourhood. The region between $R \approx 3$ kpc and $R \approx 12$ kpc represents the zone of radial mixing, which can blur the boundaries of the Galactic Habitable Zone (GHZ), as it has been conventionally understood. The present-day stable population of the stars in the Solar neighbourhood originates from this radial mixing zone, with most of the stars coming from the inner regions. The Solar system can be considered as a typical Milky Way habitable system because it migrated outwards from the metal-rich inner regions of the Disk and has a circular orbit in the present epoch. We conclude that the boundaries of the GHZ cannot be sharply confined for a given epoch because of the mixing caused by the stellar migrations and secular evolution of stellar orbits.

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Section: Galaxy Evolution and The Motions Of Starsmentioning

confidence: 84%

Dynamical aspects of Galactic habitability in N-body simulations

Mitrašinović,

Vukotić,

Micic

et al. 2023

Publ. Astron. Soc. Aust.

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Orbital eccentricities as indicators of stellar populations

Cubarsi

Stojanović

Ninković

2021

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Context. In previous work, we showed how the planar and vertical eccentricities of disc stars, e and e′, could be used as indicators of the stars’ kinematic populations. For a local stellar sample drawn from the Gaia DR2 catalogue, these populations were represented geometrically in the eccentricity diagram, e′2 vs. e2, approximately separated by straight lines. Aims. In the current work, we propose a new relationship between the star’s perpendicular velocity and its vertical eccentricity, allowing for a reevaluation of the critical vertical eccentricity and maximum height, zmax, specific to each population component. Methods. We approximated the local potential function to be consistent with the actual shape of the curve that relates the maximum vertical speed of a star and its maximum height. The curve corresponds to a non-linear restoring vertical force, where the stiffness decreases with an increase in the maximum height. The constants involved in this fitting, together with the population velocity dispersions, determine the specific region for each population in the eccentricity diagram. Results. The new classification determines 88% of the sample is made up of thin disc stars and 9% of thick disc stars, whereby 3% of the stars have been relabelled, by providing thinner thin and thick discs. Nested thin disc subsamples allow us to estimate Strömberg’s asymmetric drift equation, leading to a heliocentric velocity of the circular orbit of Vc ≈ −12.9 km s−1, an absolute rotation velocity of Θc ≈ 227 km s−1, and a rotation component of the Galactocentric velocity of the Sun at Θ⊙ ≈ 240 km s−1. Conclusions. The thin disc stars of our local sample are characterised based on values 0 ≤ e ≤ 0.32, 0 ≤ e′ ≤ 0.09, and zmax = 0.7 kpc. Disc stars satisfy 0 ≤ e ≤ 0.44, 0 ≤ e′ ≤ 0.18, zmax = 1.5 kpc. The maximum vertical peculiar velocity for disc stars is found to be w0 = 115 km s−1. The assumed potential provides a stellar density of the disc vanishing at z0 = 1.8 kpc. The approximate behaviour in the local disc is that a small decrease in the stiffness is associated with a relative decrease in the limiting velocity, which produces a thinner disc and a loss of stars in the local cylinder, both in a similar proportion to the limiting velocity.

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Orbital eccentricities as indicators of stellar populations

Cited by 2 publications

References 52 publications

Dynamical aspects of Galactic habitability in N-body simulations

Dynamical aspects of Galactic habitability in N-body simulations

Orbital eccentricities as indicators of stellar populations

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