Pulsaciones no-radiales, no-adiabáticas en estrellas pre-enanas blancas PG1159

Desde hace algunos años, en nuestro Observatorio se ha comenzado el estudio de las pulsaciones estelares en estrellas enanas blancas. Hasta ahora, todos los cálculos han sido realizados dentro de la aproximación adiabática (Córsico, A. H. 1998, 2003). En esta Tesis nos proponemos generalizar el código de pulsaciones adiabáticas no-radiales desarrollado por Córsico, A. H.(1998), relajando la condición de adiabaticidad, de manera que permita calcular pulsaciones no-radiales, no-adiabáticas de estrellas pre-enanas blancas y enanas blancas. La importancia de relajar la condición de adiabaticidad se debe a que esta aproximación, si bien es útil para predecir con gran exactitud el valor de los períodos de oscilación de un dado modelo estelar, no proporciona información acerca de cuáles, de los infinitos modos posibles que conforman el espectro de pulsación, pueden llegar a alcanzar amplitudes lo suficientemente grandes como para ser observados en estrellas reales. Y esto es lo que pretendemos analizar aquí.Facultad de Ciencias Astronómicas y Geofísica

Pulsaciones no-radiales, no-adiabáticas en estrellas pre-enanas blancas PG1159

Desde hace algunos años, en nuestro Observatorio se ha comenzado el estudio de las pulsaciones estelares en estrellas enanas blancas. Hasta ahora, todos los cálculos han sido realizados dentro de la aproximación adiabática (Córsico, A. H. 1998, 2003). En esta Tesis nos proponemos generalizar el código de pulsaciones adiabáticas no-radiales desarrollado por Córsico, A. H.(1998), relajando la condición de adiabaticidad, de manera que permita calcular pulsaciones no-radiales, no-adiabáticas de estrellas pre-enanas blancas y enanas blancas. La importancia de relajar la condición de adiabaticidad se debe a que esta aproximación, si bien es útil para predecir con gran exactitud el valor de los períodos de oscilación de un dado modelo estelar, no proporciona información acerca de cuáles, de los infinitos modos posibles que conforman el espectro de pulsación, pueden llegar a alcanzar amplitudes lo suficientemente grandes como para ser observados en estrellas reales. Y esto es lo que pretendemos analizar aquí.Facultad de Ciencias Astronómicas y Geofísica

d1005+68: A New Faint Dwarf Galaxy in the M81 Group

We present the discovery of d1005+68, a new faint dwarf galaxy in the M81 Group, using observations taken with the Subaru Hyper Suprime-Cam. d1005+68's color-magnitude diagram is consistent with a distance of $3.98_{-0.43}^{+0.39}$ Mpc, establishing group membership. We derive an absolute $V$-band magnitude, from stellar isochrone fitting, of $M_{V} = -7.94_{-0.50}^{+0.38}$, with a half-light radius of $r_{h} = 188_{-41}^{+39}$ pc. These place d1005+68 within the radius-luminosity locus of Local Group and M81 satellites and among the faintest confirmed satellites outside the Local Group. Assuming an age of 12 Gyr, d1005+68's red giant branch is best fit by an isochrone of [Fe/H] $= -1.90 \pm 0.24$. It has a projected separation from nearby M81 satellite BK5N of only 5 kpc. As this is well within BK5N's virial radius, we speculate that d1005+68 may be a satellite of BK5N. If confirmed, this would make d1005+68 one of the first detected satellites-of-a-satellite.Comment: 7 pages, 4 figures, 1 table, additional affiliations include

Characterizing dw1335-29, a recently discovered dwarf satellite of M83

The number, distribution, and properties of dwarf satellites are crucial probes of the physics of galaxy formation at low masses and the response of satellite galaxies to the tidal and gas dynamical effects of their more massive parent.To make progress, it is necessary to augment and solidify the census of dwarf satellites of galaxies outside the Local Group. M\"uller et al. (2015) presented 16 dwarf galaxy candidates near M83, but lacking reliable distances, it is unclear which candidates are M83 satellites. Using red giant branch stars from the HST/GHOSTS survey in conjunction with ground-based images from VLT/VIMOS, we confirm that one of the candidates, dw1335-29-- with a projected distance of 26 kpc from M83 and a distance modulus of $(m - M)_0 = 28.5^{+0.3}_{-0.1}$ -- is a satellite of M83. We estimate an absolute magnitude $M_V = -10.1 \pm{0.4}$, an ellipticity of $0.40^{+0.14}_{-0.22}$, a half light radius of $656^{+121}_{-170 }$ pc, and [Fe/H] = $-1.3^{+0.3}_{-0.4}$. Owing to dw1335-29's somewhat irregular shape and possible young stars, we classify this galaxy as a dwarf irregular or transition dwarf. This is curious, as with a projected distance of 26 kpc from M83, dw1335-29 is expected to lack recent star formation. Further study of M83's dwarf population will reveal if star formation in its satellites is commonplace (suggesting a lack of a hot gas envelope for M83 that would quench star formation) or rare (suggesting that dw1335-29 has a larger M83-centric distance, and is fortuitously projected to small radii).Comment: 7 pages, 5 figures, accepted for publication in MNRA

The GHOSTS survey. II. The diversity of Halo Color and Metallicity Profiles of Massive Disk Galaxies

We study the stellar halo color properties of six nearby massive highly inclined disk galaxies using Hubble Space Telescope Advanced Camera for Surveys and Wide Field Camera 3 observations in both F606W and F814W filters from the GHOSTS survey. The observed fields, placed both along the minor and major axis of each galaxy, probe the stellar outskirts out to projected distances of ~ 50-70 kpc from their galactic centre along the minor axis. The 50% completeness levels of the color magnitude diagrams are typically at two mag below the tip of the red giant branch. We find that all galaxies have extended stellar halos out to ~ 50 kpc and two out to ~ 70 kpc. We determined the halo color distribution and color profile for each galaxy using the median colors of stars in the RGB. Within each galaxy we find variations in the median colors as a function of radius which likely indicates population variations, reflecting that their outskirts were built from several small accreted objects. We find that half of the galaxies (NGC 0891, NGC 4565, and NGC 7814) present a clear negative color gradient, reflecting a declining metallicity in their halos; the other have no significant color or population gradient. In addition, notwithstanding the modest sample size of galaxies, there is no strong correlation between their halo color/metallicity or gradient with galaxy's properties such as rotational velocity or stellar mass. The diversity in halo color profiles observed in the GHOSTS galaxies qualitatively supports the predicted galaxy-to-galaxy scatter in halo stellar properties; a consequence of the stochasticity inherent in the assembling history of galaxies.Comment: Accepted by MNRAS, 31 pages, 18 figures. Appendix added and some editions to match accepted version. Conclusions unchange