Gravité de surface

En astronomie, la gravité de surface est l'intensité du champ gravitationnel à la surface d'un objet astrophysique (planète, étoile ou autre). Ce concept est également utilisé, quoique de façon légèrement différente, dans la physique des trous noirs où il règle la vitesse à laquelle le champ gravitationnel au sens classique du terme diverge à l'approche de la surface du trou noir, c'est-à-dire de son horizon. En physique stellaire et substellaire (naines brunes, exoplanètes massives), l'usage est d'utiliser le logarithme décimal de la valeur exprimée dans le système CGS (cm/s²). Formule newtonnienne Dans le cadre de la mécanique classique, la gravité de surface \kappa est donnée par la formule habituelle du champ gravitationnel d'un objet sphérique, à savoir : :\kappa=\frac{GM}{R^2}=\frac{\mu}{R^2}, où :

G est la constante de gravitation ;
M est la masse de l'objet considéré ;
R est son rayon, l'objet é

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (5)

Publications associées

Chargement

Personnes associées (1)

Personnes associées

Chargement

Unités associées (2)

Unités associées

Chargement

Concepts associés (34)

Concepts associés

Chargement

Cours associés (7)

Cours associés

Chargement

Séances de cours associées (9)

Séances de cours associées

Chargement

The Tenth Data Release Of The Sloan Digital Sky Survey: First Spectroscopic Data From The Sdss-Iii Apache Point Observatory Galactic Evolution Experiment

Arnaud Borde, Johan Comparat, Timothée Guy Olivier Delubac, Ginevra Favole, Jean-Paul Richard Kneib, Bo Ma, David Schlegel, Yue Shen, Zheng Zheng

The Sloan Digital Sky Survey (SDSS) has been in operation since 2000 April. This paper presents the Tenth Public Data Release (DR10) from its current incarnation, SDSS-III. This data release includes the first spectroscopic data from the Apache Point Observatory Galaxy Evolution Experiment (APOGEE), along with spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS) taken through 2012 July. The APOGEE instrument is a near-infrared R similar to 22,500 300 fiber spectrograph covering 1.514-1.696 mu m. The APOGEE survey is studying the chemical abundances and radial velocities of roughly 100,000 red giant star candidates in the bulge, bar, disk, and halo of the Milky Way. DR10 includes 178,397 spectra of 57,454 stars, each typically observed three or more times, from APOGEE. Derived quantities from these spectra (radial velocities, effective temperatures, surface gravities, and metallicities) are also included. DR10 also roughly doubles the number of BOSS spectra over those included in the Ninth Data Release. DR10 includes a total of 1,507,954 BOSS spectra comprising 927,844 galaxy spectra, 182,009 quasar spectra, and 159,327 stellar spectra selected over 6373.2 deg(-2).

Iop Publishing Ltd2014

Chargement

Tracing the formation of the Milky Way through ultra metal-poor stars

Pascale Jablonka, Nicolas Lawrence Etienne Longeard

We use Gaia DR2 astrometric and photometric data, published radial velocities and MESA models to infer distances, orbits, surface gravities, and effective temperatures for all ultra metal-poor stars ([Fe/H] < -4.0 dex) available in the literature. Assuming that these stars are old (> 11 Gyr) and that they are expected to belong to the Milky Way halo, we find that these 42 stars (18 dwarf stars and 24 giants or sub-giants) are currently within similar to 20 kpc of the Sun and that they map a wide variety of orbits. A large fraction of those stars remains confined to the inner parts of the halo and was likely formed or accreted early on in the history of the Milky Way, while others have larger apocentres (> 30 kpc), hinting at later accretion from dwarf galaxies. Of particular interest, we find evidence that a significant fraction of all known UMP stars (similar to 26 per cent) are on prograde orbits confined within 3 kpc of the Milky Way plane (J(z) < 100 km s(-1) kpc). One intriguing interpretation is that these stars belonged to the massive building block(s) of the proto-Milky Way that formed the backbone of the Milky Way disc. Alternatively, they might have formed in the early disc and have been dynamically heated, or have been brought into the Milky Way by one or more accretion events whose orbit was dragged into the plane by dynamical friction before disruption. The combination of the exquisite Gaia DR2 data and surveys of the very metal-poor sky opens an exciting era in which we can trace the very early formation of the Milky Way.

OXFORD UNIV PRESS2019

Chargement

The Pristine survey - V. A bright star sample observed with SOPHIE

Pascale Jablonka, Carmela Lardo

With the aim of probing the properties of the bright end of the Pristine survey and its effectiveness in selecting metal-poor stars, we selected a sample of bright candidate metal-poor stars combining Pristine CaHK photometry with APASS gi photometry, before the Gala second data release became available, These stars were observed with the SOPHIE spectrograph at the 1.93 in telescope of Observatoire de Haute Provence and we used photometry and parallaxes from Gaia DR2 to derive their atmospheric parameters. Chemical abundances were determined from the spectra for 40 stars of the sample. Eight stars were confirmed to be very metal-poor ([Fe/H] < -2.0), as expected from the photometric estimate. No star was found with [Fe/H] < -3.0, although for nine stars the photometric estimate was below this value. Three multiple systems are identified from their multipeaked cross-correlation functions, Two metal-poor stars with [Fe/H] approximate to -1.0 have an age estimate of about 4 Gyr. Accretion from a satellite galaxy is a possible explanation for these 'young metal-poor stars', but they could also be field blue stragglers. Galactic orbits for our sample of stars allowed us to divide them into three classes that we label 'Halo', 'Thick', and 'Thin' and tentatively identify as halo, thick disc, and thin disc. We present a new method for deriving photometric metallicities, effective temperatures, and surface gravities by combining Gala parallaxes, photometry, and Pristine CaHK photometry. Comparison with spectroscopic metallicities shows a very good agreement and suggests that we can further improve the efficiency of Pristine CaHK in selecting metal poor stars.

OXFORD UNIV PRESS2019

Chargement

Étoile

vignette|Le Soleil, l’étoile la plus proche de la Terre, vu lors d'une éruption en ultraviolets avec de fausses couleurs. Une étoile est un corps céleste plasmatique qui rayonne sa propre lumière par

Stellar classification

In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffr

Naine blanche

vignette| est une naine blanche visible comme un petit point en bas à gauche de , beaucoup plus brillante. Si ce système était observé dans le domaine des rayons X, Sirius B apparaîtrait alors plus br

PHYS-207(a): General physics : quanta

Ce cours est une introduction à la mécanique quantique. En partant de son développement historique, le cours traite les notions de complémentarité quantique et le principe d'incertitude, le processus de mesure, l'équation de Schrödinger, ainsi que des éléments de physique atomique et moléculaire.

PHYS-323: Astrophysics II

Ce cours est une introduction à la physique stellaire. On y expose les notions indispensables à la compréhension du fonctionnement d'une étoile et à la construction de modèles de structure interne et d'évolution stellaires. On donne aussi des clés d'interprétation des spectres stellaires.

PHYS-106(b): General physics : thermodynamics

Le but du cours de Physique générale est de donner à l'étudiant les notions de base nécessaires à la compréhension des phénomènes physiques. L'objectif est atteint lorsque l'étudiant est capable de prévoir quantitativement les conséquences de ces phénomènes avec des outils théoriques appropriés