Analysis of a Proper-Motion Selected Sample of Stars in the Ursa Minor Dwarf Spheroidal Galaxy
نویسنده
چکیده
We have studied the stellar population and internal structure of the core of the Ursa Minor dwarf spheroidal galaxy, using a sample of stars selected to be members based on their proper motions. In agreement with previous studies, we find Ursa Minor to be dominated by an old, metal-poor stellar population. A small number of stars with high membership probabilities lie redward of the red giant branch. The brightest (V ∼< 18) such stars are known to be Carbon stars, rather than metal-rich first-ascent giants. A number of stars with high membership probabilities lie blueward of the red giant branch, and are more luminous than the horizontal branch. We speculate that these are post-horizontal branch stars. There may also be one or two stars in the post-AGB phase. Spectroscopy of the candidate post-HB and post-AGB stars is required to determine their nature. We recover the internal substructure in Ursa Minor that has been noted by several authors in the last 15 years. Using a variety of twoand three-dimensional statistical tests, we conclude that this substructure is statistically significant at the 0.005 level. There is no evidence that the regions of density excess have stellar populations that differ from the main body of Ursa Minor. The crossing time for a typical density excess is only ∼ 5×10 yr. They are therefore clearly not due to intermediate age star-forming bursts. We conclude that they are instead due to tidal interactions between the Galaxy and Ursa Minor. Subject headings: galaxies: dwarf — galaxies: individual (Ursa Minor dSph) — galaxies: stellar content — galaxies: structure — Local Group
منابع مشابه
A photometrically and kinematically distinct core in the Sextans dwarf spheroidal galaxy
We present the line of sight radial velocity dispersion profile of the Sextans dwarf spheroidal galaxy (dSph), based on a sample of 88 stars extending to about 1 (∼ 1.5kpc). Like the Draco and Ursa Minor dSphs, Sextans shows some evidence of a fall-off in the velocity dispersion at large projected radii, with significance p = 0.96. Surprisingly, the dispersion at the very centre of Sextans is c...
متن کاملThe Low-Mass Stellar IMF at High Redshift: Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy
Low-mass stars, those with main-sequence lifetimes that are of order the age of the Universe, provide unique constraints on the Initial Mass Function (IMF) when they formed. Star counts in systems with simple star-formation histories are particularly straightforward to interpret, and those in ‘old’ systems allow one to determine the low-mass stellar IMF at large look-back times and thus at high...
متن کاملBlue straggler stars in dwarf spheroidal galaxies
Blue straggler star (BSS) candidates have been observed in all old dwarf spheroidal galaxies (dSphs), however whether or not they are authentic BSSs or young stars has been a point of debate. To both address this issue and obtain a better understanding of the formation of BSSs in different environments we have analysed a sample of BSS candidates in two nearby Galactic dSphs, Draco and Ursa Mino...
متن کاملThe Star Formation History and the spatial distribution of stellar populations in the Ursa Minor Dwarf Spheroidal Galaxy
As a part of a project devoted to the study of the Ursa Minor dSph, the star formation history of the galaxy is presented in this paper. The analysis uses wide field photometry, encompassing about 1◦× 1◦ (the total covered area being 0.75 deg), which samples the galaxy out to its tidal radius. Derivation of the SFH has been performed using the synthetic partial model technique. The resulting SF...
متن کامل