Recent Talks
List of all the talks in the archive, sorted by date.
Abstract
Measuring the Aerosol Optical Depth (AOD) is of particular importance in monitoring aerosol contributions to global radiative forcing and air quality. Most measuring methods are based on direct or indirect observation of sunlight and thus are only available for use during daylight hours. Attempts have been made to measure AOD behavior at night from star photometry, and more recently moon photometry. Star photometry method uses spectrally calibrated stars as reference targets this provides somewhat more flexibility than a sun photometer but there are low-signal and calibration issues which can make these measurements problematic. Moon photometry is only possible when the moon is present in the sky. We suggest a complementary method, based on the observation of artificial sky glow generated by light pollution. The methodology requires (1) the implementation of an heterogeneous 3D light pollution model and (2) the design of an automated light pollution spectrometer which will be presented here. The instrument designated as the Spectrometer for Aerosol Night Detection (SAND) is now in its third version. Basically, SAND-3 is an automated CCD based, long-slit spectrometer protected from inclement weather by an acrylic dome. SAND have been used successfully in many astronomical sites along with some urban sites. Our first day/night (continuity) AOD measurements comparisons with AERONET/AEROCAN sunphotometer data will be shown for Sherbrooke university (Quebec, Canada) atmospheric optical observatory.
Abstract
An analysis of the impact of seismic and volcanic activity was carried out at selected astronomical sites, namely the observatories of El Teide (Tenerife, Canary Islands), Roque de los Muchachos (La Palma, Canary Islands), Mauna Kea (Hawaii) and Paranal (Chile) and the candidate site of Cerro Ventarrones/Armazones (Chile). In this sense, we studied the impact of seismicity, volcanic ash clouds, lava flows and ground deformation. Hazard associated with volcanic activity is low or negligible at all sites, whereas seismic hazard is very high in Chile and Hawaii. The lowest geological hazard in both seismic and volcanic activity was found at Roque de los Muchachos observatory, in the island of La Palma.
Abstract
It has been recently shown that the chemical composition of the Sun is anomalous when compared to most nearby stars of very similar fundamental parameters, so-called solar twins. Compared to these stars, the Sun is deficient in refractory elements relative to volatiles, a finding that we speculate is a signature of the terrestrial planet formation that occurred around the Sun but not in the majority of solar twins. I will discuss these and newer related results, the strengths and weaknesses of our planet formation interpretation, as well as our plans for future observations that can help us better understand the nature of the abundance trends found.
Abstract
Nature is one of the world's leading scientific journals, publishing many papers that receive wide attention by the general public. But, Nature is very selective —> < 7% of submitted papers are published. In order to maximize your chances of getting published, papers should present fundamental new physical insights, or startling observations/results. Theory papers pose additional problems, as we want only those papers that are likely to be the correct explanation, and not simply exploring parameter space. The writing should be clear, concise and directed at the level of a graduate course in the subject. I encourage authors to contact me in advance of submission of a paper, both to ascertain the appropriateness of the result for Nature, and to ensure that the writing is close to our standards. Posting to ArXiv is and always has been allowed, but authors should discuss the specifics with their institutional public affairs officers before doing so. Lapses in professional ethics seem to be on the rise? I will discuss some examples, and what we should be doing to keep astronomy clean.
Abstract
Short-lived nuclides (SLNs) were incorporated to the solar nebula at the time of condensation of the first minerals from the vapor phase. The study of the isotopic ratios preserved in primitive meteorites provides clues on the stellar sources that produced these SLN, being supernovae and Asymptotic Giant Branch stars (AGBs) candidates. On the other hand, stellar grains were also preserved in primitive meteorites and Interplanetary Dust Particles (IDPs). Their survival demonstrates that the solar nebula was not so hot as first researchers proposed in the 60s. Interestingly, the available stellar grain abundances in primitive meteorites (chondrites) depend of the physico-chemical processes suffered by their parent bodies: metamorphism, aqueous alteration, etc. An evaluation of the primordial presolar grain abundances in the protoplanetary disk at the time these materials formed would allow a comparison with the derived from theoretical models. For gaining insight on these processes we should study the most primitive meteorites (the chondrites), but also even more pristine materials arrived from comets, particularly these captured in the stratosphere as IDPs, or collected from 81P/Wild 2 comet by Stardust (NASA) spacecraft.
Abstract
The properties of molecular clouds associated with 10 H II regions were studied using CO observations. We identified 142 dense clumps within our sample and measured and calculated physical properties of the clumps such as size, excitation temperature, line widths, density and mass. We found that our sources are divided into two categories: those that show a size-line width relation ("type I") and those which do not show any relation ("type II"). Type II sources have larger line widths in general. Investigating the relation between the line width and other parameters shows that while the MLTE (Local Thermodynamic Equilibrium mass) increases with ΔV (line width) for both 12CO(2-1) and 13CO(2-1) lines in type I sources, no relation was found for type II sources. No relation between column density and line width was found for either category. We also investigated how the characteristics of the clumps vary with distance from the HII region. We found no relation between mass distribution of the clumps and distance from the ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas. Only the projected distance is measured in our study which is equal or smaller than the true value. Therefore we compared the results by a Monte Carlo simulation of a central heating source and found that for small distances the relation is very scattered, which is consistent with our results. No relation was found between line width and distance from the H II region which probably indicates that the internal dynamics of the clumps is not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars may have a more important role.
Abstract
A Friedman-like cosmological model, based on noncommutative geometry, is presented. Its Planck level is totally nonlocal with no space and no time. The dynamics on this level is strongly probabilistic which makes the initial singularity statistically insignificant. Space, time and the standard dynamics emerge when one goes from the non-commutative regime (on the Planck level) to the usual "commutative physics".
Abstract
Survey operations with the VISTA telescope with it wide field near IR camera started in Feb 2010, following a science verification phase that started in Oct, 2009. I will describe this new 4.2m wide field telescope and the ESO VISTA Public survey program. I will give details of all ESO six public surveys which will be used for a range of galactic and extragalactic science. I am the PI of the largest, by area, VISTA survey, I will focus my talk on the VISTA Hemisphere Survey and I will show how this survey will be used to find quasars in the Epoch of Reionization at redshift greater than 7. The VISTA Hemisphere Survey (VHS) has been been awarded 300 clear nights on the 4.2m ESO VISTA telescopes. VHS observations started i February, 2010 and the survey will take 5 years to complete. The VHS will cover the whole southern celestial hemisphere (dec<0) to a depth 4 magnitudes fainter than 2MASS/DENIS in at least two wavebands J and K. In the South Galactic Cap, 5000 square degrees will be imaged deeper, including H band, and will have supplemental deep multi-band grizY imaging data provided by the Dark Energy Survey (DES). The remainder of the high galactic latitude sky will be imaged in YJHK and combined with ugriz wavebands from the VST ATLAS, SDSS BOSS and Skymapper optical surveys. The medium term scientific goals include: a huge expansion in our knowledge of the lowest-mass and nearest stars; deciphering the merger history and genesis of our own Galaxy; measurement of large-scale structure out to z=1 and measuring the properties of Dark Energy; discovery of the first quasars with z > 7. In my talk, I will describe the scientific motivation and methodology of the search for quasars with z > 7.
Abstract
La Astronomía, quizá la ciencia organizada más antigua, presente en todas las culturas, que en este Siglo XXI es fundamentalmente Astrofísica, intenta penetrar en el conocimiento de la naturaleza y evolución del Universo, en su conjunto y en detalle. En tan desmesurada aventura, la clave para avanzar sigue siendo la observación astronómica. Y Canarias ha tenido la suerte de que la atmosfera de sus cumbres posea condiciones excepcionales para la observación astronómica. Por eso los observatorios del Instituto de Astrofísica de Canarias (IAC) reúnen la batería más completa de telescopios. Estos observatorios de Canarias constituyen una reserva astronómica mundial, protegida por ley, donde tienen telescopios e instrumentos más sesenta instituciones de dieciocho países. En el Observatorio del Roque de los Muchachos, además, acaba de entrar en operación el Gran Telescopio Canarias, construido por España. Siendo, con sus 10.4 m. de apertura, el mayor y más avanzado telescopio óptico-infrarrojo del momento. Pronto, esperamos, que a él también venga el Telescopio Europeo Extremadamente Grande (E-ELT) de 42 m., haciendo de en nuestras Islas el centro de gravedad de esta rama de la Ciencia.
La Astrofísica demanda la última tecnología para sus instrumentos en tierra y espacio. Por eso es germen de desarrollo tecnológico e industrial. Lo que supone riqueza económica y social. Sin dejar de ser por ello, como toda ciencia básica, fuente de cultura, al tratar de dar respuestas a las preguntas fundamentales del ser humano, y dotarle de nuevas cosmovisiones.
Abstract
The study of the Milky is expected to have a major impact on our understanding of how galaxies form and evolve. "Near-field cosmology" is being vigorously pursued through a series of major surveys of the Galaxy's stellar content (2-MASS, SDSS, RAVE, Hermes, Apogee, Gaia) that are either in hand or pending. It will be argued that what we want to know is deeply buried in these data and can only be extracted by comparing the surveys with a hierarchy of dynamical models of ever increasing complexity. Work currently being done to build such hierarchical models will be described, and some early results from this work will be summarised.Upcoming talks
- Coloquio con Isabel Pérez Grande (AEE)Dr. Isabel Pérez GrandeTuesday November 26, 2024 - 10:30 GMT (Aula)
- Revisiting mass transfer and accretion in symbiotic binaries in the Gaia eraDr. Jaroslav MercThursday November 28, 2024 - 10:30 GMT (Aula)
Recent Colloquia
Recent Talks
