603 research outputs found
Using ages and kinematic traceback: the origin of young local associations
Over the last decade, several groups of young (mainly low-mass) stars have
been discovered in the solar neighbourhood (closer than ~100 pc), thanks to
cross-correlation between X-ray, optical spectroscopy and kinematic data. These
young local associations offer insights into the star formation process in
low-density environments, shed light on the substellar domain, and could have
played an important role in the recent history of the local interstellar
medium. Ages estimates for these associations have been derived in the
literature by several ways. In this work we have studied the kinematic
evolution of young local associations and their relation to other young stellar
groups and structures in the local interstellar medium, thus casting new light
on recent star formation processes in the solar neighbourhood. We compiled the
data published in the literature for young local associations, including the
astrometric data from the new Hipparcos reduction. Using a realistic Galactic
potential we integrated the orbits for these associations and the Sco-Cen
complex back in time. Combining these data with the spatial structure of the
Local Bubble and the spiral structure of the Galaxy, we propose a recent
history of star formation in the solar neighbourhood. We suggest that both the
Sco-Cen complex and young local associations originated as a result of the
impact of the inner spiral arm shock wave against a giant molecular cloud. The
core of the giant molecular cloud formed the Sco-Cen complex, and some small
cloudlets in a halo around the giant molecular cloud formed young local
associations several million years later. We also propose a supernova in young
local associations a few million years ago as the most likely candidate to have
reheated the Local Bubble to its present temperature.Comment: 9 pages, 5 figures. Invited talk, to appear in "The Ages of Stars",
Proceedings of the IAU Symposium 258, Baltimore USA 13-17 Oct 2008, eds D.
Soderblom et al., CUP in pres
De las opiniones a los argumentos
La actividad consiste en inferir la definición del término "light" a partir de productos asà etiquetados y de otros estándar. Pero en las primeras respuestas pesan mucho más los supuestos que los datos que proporcionan esos envases. Lo que se pretende precisamente es que los alumnos y alumnas aprendan a distinguir las opiniones de los argumentos, a cuestionarse lo que dan por hecho y a desarrollar razonamientos claros y precisos
Characterisation of Galactic carbon stars and related stars from Gaia-EDR3
We extend here a previous investigation on the characteristics of Galactic
carbon stars using more accurate EDR3 astrometry measurements. Based on a much
larger statistics, we confirm that N- and SC-type carbon stars share a very
similar luminosity function, while the luminosities of J-type stars (Mbol) are
fainter by half a magnitude on average. R-hot type carbon stars have
luminosities throughout the RGB, which favours the hypothesis of an external
origin for their carbon enhancement. Moreover, the kinematic properties of a
significant fraction of the R-hot stars are compatible with the thick-disc
population, in contrast with that of N- and SC-type stars, which would belong
mostly to the thin disk. We also derive the luminosity function of a large
number of Galactic extrinsic and intrinsic (O-rich) S stars and show that the
luminosities of the latter are typically higher than the predicted onset of the
third dredge-up during the AGB for solar metallicity. This result is consistent
with these stars being genuine thermally pulsing AGB stars. On the other hand,
using the so-called Gaia-2MASS diagram, we show that the overwhelming majority
of the carbon stars identified in the LAMOST survey as AGB stars are probably
R-hot and/or CH-type stars. Finally, we report the identification of 2660 new
carbon stars candidates that we identified through their 2MASS photometry,
their Gaia astrometry, and their location in the Gaia-2MASS diagram.Comment: 14 pages, 16 figures, accepted for publication in A&
Constraining the thin disc initial mass function using Galactic classical Cepheids
Context: The Initial Mass Function (IMF) plays a crucial role on galaxy evolution and its implications on star formation theory make it a milestone for the next decade. It is in the intermediate and high mass ranges where the uncertainties of the IMF are larger. This is a major subject of debate and analysis both for Galactic and extragalactic science. Aims: Our goal is to constrain the IMF of the Galactic thin disc population using both Galactic Classical Cepheids and Tycho-2 data. Methods: For the first time the Besan\c{c}on Galaxy Model (BGM) has been used to characterise the Galactic population of the Classical Cepheids. We have modified the age configuration in the youngest populations of the BGM thin disc model to avoid artificial discontinuities in the age distribution of the simulated Cepheids. Three statistical methods, optimized for different mass ranges, have been developed and applied to search for the best IMF that fits the observations. This strategy allows us to quantify variations in the Star Formation History (SFH), the stellar density at Sun position and the thin disc radial scale length. A rigorous treatment of unresolved multiple stellar systems has been undertaken adopting a spatial resolution according to the catalogues used. Results: For intermediate masses, our study favours a composite field-star IMF slope of for the local thin disc, excluding flatter values such as the Salpeter IMF (). Moreover, a constant Star Formation History is definitively excluded, the three statistical methods considered here show that it is inconsistent with the observational data. Conclusions: Using field stars and Galactic Classical Cepheids, we have found, above , an IMF steeper than the canonical stellar IMF of associations and young clusters. This result is consistent with the predictions of the Integrated Galactic IMF
Spiral structure parameters in the solar neighbourhood
Two samples of O- and B-type stars and Cepheids with Hipparcos data have been used to characterize galactic rotation and spiral arm kinematics in the solar neighbourhood. An extensive set of simulations has been performed in order to assess the capabilities of the method and its sensitivity to sample errors and biases in the adopted parameters
Modeling the evolution of the Milky Way from Gaia DR3
Galactic stellar populations are good tracers of the history of the Milky Way. Their study via Gaia astrometric and photometric data should allow to pinpoint the star formation history (SFH) in the disc and halo in a self-consistent dynamical model. Population synthesis models are efficient tools to measure the SFH from the distribution of the stars in the Hess diagram, thanks to different locations of stars according to their age and metallicity. We present the iterative strategy planned to fit the IMF and the SFH of the thin disk using the BGMFast scheme (del Alcazar et al., see poster) based on approximate bayesian computation (ABC) performed with HPC tools and, at the same time, the attempt to keep the self-consistent dynamical model by fitting the gravitational potential of the Milky Way to the stellar kinematics and densities from Gaia data (Robin et al., 2022)
Detection of satellite remnants in the Galactic Halo with Gaia III. Detection limits for Ultra Faint Dwarf Galaxies
We present a method to identify Ultra Faint Dwarf Galaxy (UFDG) candidates in
the halo of the Milky Way using the future Gaia catalogue and we explore its
detection limits and completeness. The method is based on the Wavelet Transform
and searches for over-densities in the combined space of sky coordinates and
proper motions, using kinematics in the search for the first time. We test the
method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot
(GUMS) as a background, and use a library of around 30 000 UFDGs simulated as
Plummer spheres with a single stellar population. For the UFDGs we use a wide
range of structural and orbital parameters that go beyond the range spanned by
real systems, where some UFDGs may remain undetected. We characterize the
detection limits as function of the number of observable stars by Gaia in the
UFDGs with respect to that of the background and their apparent sizes in the
sky and proper motion planes. We find that the addition of proper motions in
the search improves considerably the detections compared to a photometric
survey at the same magnitude limit. Our experiments suggest that Gaia will be
able to detect UFDGs that are similar to some of the known UFDGs even if the
limit of Gaia is around 2 magnitudes brighter than that of SDSS, with the
advantage of having a full-sky catalogue. We also see that Gaia could even find
some UFDGs that have lower surface brightness than the SDSS limit.Comment: Accepted for publication in MNRA
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