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2019-05-10 How feedback from massive stars shapes the hierarchical star cluster assembly in globally collapsing molecular clouds
Area: Astrofísica
Investigador Invitado Alejandro González-Samaniego
Filiación Institucional IRYA-Morelia
Resumen: Ver resumen It is well known that most stars form in groups or clusters, which in
turn form from Molecular Clouds (MC), but it is still not clear how the
structural properties of the clusters are affected by the feedback from
their massive stars while they are still connected to their parent MCs.
Here we present results from hydrodynamical simulations in which we study
stellar cluster formation within a MC undergoing global hierarchical
collapse, focusing on the effect of feedback from the photoionizing
radiation from massive stars. We show that the feedback from the newly
formed stars strongly affects the morphology and dynamics of the gas
that continues to fall onto the cluster-forming clump. In particular,
we find that the resulting stellar sub-clusters (or "groups") are more
extended in simulations that include feedback than the ones obtained in
control simulations without feedback, and that infalling motions of the
stars forming in the periphery are reduced by this effect. Age gradients
in groups can be erased or modified due to the effect of the feedback
from massive stars.
   
Lugar-Hora Auditorio del Centro de Información - 12:00
   
2019-05-31 The Contribution of Dwarf Planets to the Delivery of Low Inclination Comets in the Solar System and Beyond
Area: Astrofísica
Investigador Invitado Marco A. Muñoz Gutierrez
Filiación Institucional Academia Sinica de Taiwan
Resumen: Ver resumen Through a large set of numerical simulations, we explored the dynamical effect that dozens of dwarf planet sized objects have on the secular evolution of debris disks particles, both considering generic cold debris disks and the Solar System's Kuiper belt. In the latter case, we used a bias-free orbital representation of the cometary nuclei (with diameters above 2 km), the so-called L7 synthetic model from CFEPS, which consists of three dynamical sub-populations: the Classical, the Resonant, and the Scattering. The dynamical evolution of the Kuiper belt particles is studied under the gravitational influence of the Sun and the four giant planets, as well as of the 34 largest known trans-Neptunian objects (TNOs), those with absolute magnitude H < 4. Over a 1 Gyr time-scale, we analyze the secular influence of the DPs over debris disk particles and their contribution to the injection rate of new low inclination comets (or Jupiter Family Comets in the case of the Solar System). We found that DPs globally increase the number of JFCs by 12%, when compared with the number of comets produced by the giant planets alone. When considering each population separately, we find that the increment produced by the presence of DPs is 15% and 10% for the Classical and Resonant populations, respectively, while for the Scattering population the increment is marginal but noticeable. Given the rate of escapes from the Kuiper belt (enhanced by DPs) and a recent estimate of the injection rate of new comets (required to maintain the observed population of JFCs in steady state), we find the upper limits to the number of objects of each population, by assuming each one supplies the 100% of the observed JFCs; the results are 5.7 x 10^7 , 8.1 x 10^7 , and 28 x 10^7 for the Scattering, Resonant, and Classical populations, respectively. We also provide some constrains on the fractional contribution of each population separately. Finally, we found that the Plutinos are the most important source of comets which were originally in a resonant configuration, where the presence of Pluto alone enhances by 10% the number of JFCs.
   
Lugar-Hora Auditorio del Centro de Información - 12:00
   
2019-06-28 TBD
Area: Astrofísica
Investigador Invitado TBD
Filiación Institucional tbd
Resumen: Ver resumen TBD
   
Lugar-Hora Auditorio del Centro de Información - 12:00
   
2019-07-05 Gaia wide binaries challenging a Newtonian prediction
Area: Astrofísica
Investigador Invitado Xavier Hernández
Filiación Institucional IA-UNAM
Resumen: Ver resumen Under Newtonian dynamics, the relative motion of the components of a binary star should
follow a Keplerian scaling with separation. Once orientation effects and a distribution
of ellipticities are accounted for, dynamical evolution can be
modelled to include the effects of Galactic tides and stellar mass perturbers.
This furnishes a prediction for the
relative velocity between the components of a binary and their projected separation.
Taking a carefully selected sample of ~100 solar neighbourhood wide binaries from
the Hipparcos catalogue, we identify these same stars in the recent Gaia DR2, to test
the prediction mentioned using the latest and most accurate astrometry available. The
results are consistent with the Newtonian prediction for projected separations below 7000 AU,
but inconsistent with it at larger separations, where accelerations are expected to be lower
than the critical $a_{0}=1.2 \times 10^{-10} $ { m s$^{-2}$} value of MONDian gravity.
This result challenges Newtonian gravity at low accelerations and shows the appearance
of gravitational anomalies of the type usually attributed to dark matter at galactic scales,
now at much smaller stellar scales. Preliminary result with a sample of ~30,000 wide binary
candidates from the full Gaia DR2 are consistent with previous determinations,
mass cuts of the larger sample do not follow detailed Newtonian expectations in the low
acceleration regime, but also do not follow simple MONDian gravity expectations. Thus,
the detailed phenomenology observed currently lacks a clear explanation.
   
Lugar-Hora Auditorio del Centro de Información - 12:00
   
2019-07-12 Efectos de rotación en estrellas masivas
Area: Astrofísica
Investigador Invitado Anabel Arrieta Ostos
Filiación Institucional Universidad Iberoamericana
Resumen: Ver resumen Las estrellas masivas producen la mayoría de los elementos pesados de la galaxia, ionizan el gas y sus vientos comprimen el medio interestelar induciendo la formación estelar. Se sabe mucho sobre los procesos físicos que las forman y de los que gobiernan su evolución sin embargo hay todavía mucho por entender. En años recientes se han encontrado evidencia de un mayor número de estrellas masivas de las que predecían los modelos de función inicial de masa. Incluso las masas estimadas son mayores a las que se pensaba. Por esta razón es importante continuar con el estudio de estas e ir incorporando nuevos mecanismos físicos a su evolución.

En esta plática se resume el trabajo que estamos realizando en la Universidad Iberoamericana y el Instituto Politécnico Nacional en materia de espectroscopía de estrellas masivas con el objetivo de entender cómo afecta la rotación de la estrella en la geometría de los vientos y la pérdida de masa.
   
Lugar-Hora Auditorio del Centro de Información - 12:00


Última modificación :
05-07-2010 a las 14:08 por Webmaster

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