Dwarf planet

A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to planetary geologists is that they may be geologically active bodies, an expectation that was borne out in 2015 by the Dawn mission to and the New Horizons mission to Pluto. Astronomers are in general agreement that at least the nine largest candidates are dwarf planets: , , , , , , , , and . Of these nine plus the tenth-largest candidate , two have been visited by spacecraft (Pluto and Ceres) and seven others have at least one known moon (Eris, Haumea, Makemake, Gonggong, Quaoar, Orcus, and Salacia), which allows their masses and thus an estimate of their densities to be determined. Mass and density in turn can be fit into geophysical models in an attempt to determine the nature of these worlds. Only one, Sedna, has neither been visited nor has

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The post-infall evolution of a satellite galaxy

Pascale Jablonka, Matthew Luke Nichols, Yves Revaz

We describe a new method that only focuses on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo alters the chemodynamical evolution of dwarf galaxies. Using this method, we examine how a dwarf, similar to Sextans dwarf spheroidal, evolves in the corona of a Milky Way-like galaxy. We find that even at high perigalacticons the synergistic interaction between ram pressure and tidal forces transform a dwarf into a stream, suggesting that Sextans was much more massive in the past to have survived its perigalacticon passage. In addition, the large confining pressure of the hot corona allows gas that was originally at the outskirts to begin forming stars, initially forming stars of low metallicity compared to the dwarf evolved in isolation. This increase in star formation eventually allows a dwarf galaxy to form more metal rich stars compared to a dwarf in isolation, but only if the dwarf retains gas for a sufficiently long period of time. In addition, dwarfs that formed substantial numbers of stars post-infall have a slightly elevated [Mg/Fe] at high metallicity ([Fe/H] similar to -1.5).

Edp Sciences S A2015

Homogeneity in the early chemical evolution of the Sextans dwarf spheroidal galaxy

Pascale Jablonka, Carmela Lardo, Romain Ely Roland Lucchesi, Pierre North

We present the high-resolution spectroscopic analysis of two new extremely metal-poor star (EMPS) candidates in the dwarf spheroidal galaxy Sextans. These targets were preselected from medium-resolution spectra centered around the CaII triplet in the near-infrared and were followed-up at higher resolution with VLT/UVES. We confirm their low metallicities with [Fe/H] = -2.95 and [Fe/H] = -3.01, which place them among the most metal-poor stars known in Sextans. The abundances of 18 elements, including C, Na, the alpha, Fe-peak, and neutron-capture elements, are determined. In particular, we present the first unambiguous detection of Zn in a classical dwarf at extremely low metallicity. Previous indications were made of a large scatter in the abundance ratios of the Sextans stellar population around [Fe/H] similar to -3 when compared to other galaxies, particularly with very low observed [alpha /Fe] ratios. We took the opportunity of reanalyzing the full sample of EMPS in Sextans and find a [alpha /Fe] Milky Way-like plateau and a similar to 0.2 dex dispersion at fixed metallicity.

EDP SCIENCES S A2020

Solar System

The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. The largest of such objects are the eight planets, in order from the Sun: four terrestrial planets named

Planet

A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud

Natural satellite

A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body (or sometimes another natural satellite). Natural satellites ar

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