INAOE | Astrofísica | Seminarios
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2017-01-20 Casting shadows on a fiery sky: obscuration events in active galactic nuclei
Investigador Invitado Jacobo Ebrero
Filiación Institucional ESAC, Madrid, Spain
Resumen: Ver resumen Active galactic nuclei (AGN) are characterised by their X-ray emission, which is known to vary at short and long timescales. While their variability can sometimes be due to intrinsic variations in the accretion flow, in other occasions it may attributed to the passage of intervening material across our line of sight. The monitoring of such obscuring or eclipsing events are of particular interest as they can be useful to probe the dynamics and physical properties of the matter in the vicinity of the central supermassive black hole.

These events have been reported as short eclipses, possibly due to the passing of broad line region clouds, as well as longer periods compatible with a long-lasting stream of material intersecting our line of sight. In fact, systematic studies of these kind of obscuration events show that they may be more common than previously thought, happening regularly in a majority of AGN, but they have passed unnoticed due to the lack of continuous monitoring.
Lugar-Hora - 12:00
2017-01-25 Is there really such a thing as Dark Matter?
Investigador Invitado Xavier Hernandez
Filiación Institucional IA-UNAM
Resumen: Ver resumen I will review a number of scalings and astronomical observations which suggest that
the gravitational anomalies usually ascribed to the presence of an as yet undetected and
hypothetically dominant dark matter, might instead signal a change in the character of
gravity in the low acceleration regime. Such ideas lead to testable predictions in a number
of low acceleration astronomical systems, which I will describe. Spanning over 11 orders of
magnitude in mass, from wide binary stellar systems, through globular clusters, elliptical
and spiral galaxies, observations consistently suggest a change in gravity associated to
the local acceleration scale.
Lugar-Hora - 12:00
2017-01-26 Resolving Debris Discs with ALMA
Investigador Invitado Mark Booth
Filiación Institucional AIU, Jena, Alemania
Resumen: Ver resumen Debris discs were first detected 3 decades ago when it was noticed that IRAS observations of a number of stars showed an infra-red excess above the stellar photosphere. These observations were quickly followed-up by a resolved image of the dust around beta Pictoris, clearly demonstrating it to be an edge on disc. But few other discs were resolved until much more recently. Resolved images allow us to determine the radial distribution of dust in the disc. By looking for signatures in these resolved images they can tell us about the dynamical history of the planetary system and where planets might orbit today. Much work along these lines has been done in the optical and infrared, but these observations are dominated by small grains that are affected by transport forces whereas sub-mm and mm observations have the benefit of being most sensitive to larger grains that trace the 'birth-ring' of planetesimals that are more useful for constraining dynamical effects of planets. ALMA has revolutionised such observations by giving us both high resolution and high sensitivity at long wavelengths. I will demonstrate its benefits by focusing on observations of two systems: HR 8799 and epsilon Eridani. HR 8799 is a massive A star and the only system so far where multiple planets have been directly imaged. Our observations allow us to see the inner edge of the disc for the first time. By comparing this with the expectations from dynamical simulations we find that either the planets orbits have changed during the evolution of the system or there must be an extra planet in the system beyond those so far detected. Epsilon Eridani is the nearest star to us known to have a debris discs at just 3.2pc away - this results in the disc being too large to fit within the ALMA primary beam. Because of this we focus our observations on the northern part of the disc. With our high resolution we are able to resolve the width of this disc, finding it to be one of the narrowest detected with a fractional width comparable to the Solar System. This suggests the possibility of a planet interior to the disc shaping the inner and outer edges as Neptune is thought to do to our own Kuiper belt.
Lugar-Hora - 12:00
2017-01-27 Yair Krongold
Investigador Invitado Yair Krongold
Filiación Institucional IA-UNAM
Resumen: Ver resumen tbd
Lugar-Hora - 12:00

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

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