Recent Talks
List of all the talks in the archive, sorted by date.
Abstract
CANARY is a technical demonstrator for the proposed EAGLE instrument for European ELT. EAGLE will have twenty Integral Field Units patrolling a 5 arcminute field and requires a new form of adaptive optics to provide the required image quality for its 0.0375 arcsec image sampling: Laser Guide Star Multi-Object AO. This entails several significant technical innovations: open-loop control, atmospheric tomography, and new calibration methods. The CANARY demonstrator is currently in its first, natural guide star, phase, and the first results have been obtained on sky. CANARY Phase A is described and the first results are presented. The next, laser guide star, phase is then outlined.
Abstract
The RV method is responsible for discovering the majority of planets that orbit stars other than our Sun. However, one problem with this technique is that stellar jitter can cause RV variations that mimic or mask out a planet signature. There have been several instances in the past when stars have shown periodic RV variations which are firstly attributed to a planet and later found to be due to stellar spots, e.g. BD+20 1790 (Figueira, P et al. 2010) and CJ674 (Turnball et al. 204). So far the method of choice to overcome these problems is to avoid observing stars which show levels of high activity. However, this does not solve the problem: it merely avoids it. We have therefore been developing a code which separates out stellar jitter from the RVs to enable active planets to be looked at for planets. I will talk about our technique as well as show some exciting preliminary results.
Abstract
Fibrils are thin elongated features visible in the solar chromosphere in and around magnetized regions. Because of their visual appearance they have been traditionally considered a tracer of the magnetic field lines. In this work we challenge that notion for the first time by comparing their orientation to that of the magnetic field, obtained via high-resolution spectro-polarimetric observations of Ca II lines. The short answer to the question posed in the title is that mostly yes, but not always.
Abstract
The so called "dark ages" of the universe began about 400.000 years after the Big Bang as matter cooled down and space became filled with neutral hydrogen for hundreds of millions years. How the Universe was heated and reionized during the first billion years after the Big Bang is a question of topical interest in cosmology. I will show that current theoretical models on the formation and collapse of primordial stars suggest that a large fraction of massive stars should have imploded, forming high-mass black hole X-ray binaries. Then, I will review the recent observations of compact stellar remnants in the near and distant universe that support this theoretical expectation, showing that the thermal (UV and soft X-rays) and non-thermal (hard X-rays, winds and jets) emission from a large population of stellar black holes in high mass binaries heated the intergalactic medium over large volumes of space, complementing the reionization by their stellar progenitors. Feedback from accreting stellar black holes at that epoch would have prevented the formation of the large quantities of low mass dwarf galaxies that are predicted by the cold dark matter model of the universe. A large population of black hole binaries may be important for future observations of gravitational waves as well as for the existing and future atomic hydrogen radio surveys of HI in the early universe.
Abstract
In this talk, I will cover our contribution to the study of extremely red galaxy (ERG) populations presenting a multi-wavelength analysis of these objects, selected in the GOODS-South/Chandra Deep Field South field. By using all the photometric (from X-rays to radio) and spectroscopic information available on large deep samples of extremely red objects (EROs, 645 sources), infrared EROs (IEROs, 294 sources) and distant red galaxies (DRGs, 350 sources), we derive redshift distributions, identify AGN powered and star-formation powered galaxies (based on X-ray properties and a new IR AGN diagnostic developed by us), and, using the radio observations of this field, estimate robust (AGN- and dust-unbiased) star formation rate densities (SFRD) for these populations. Applying a redshift separation (1 ≤ z < 2 and 2 ≤ z ≤ 3) we find a significant rise (a factor of 1.5 — 3) of SFRD for EROs and DRGs toward high-z, while none is observed for IEROs. As expected, we find a significant overlap between the ERG populations, and investigate the properties of "pure" (galaxies that conform to only one of the three considered ERG criteria) and "combined" (galaxies conforming to all three criteria) sub-populations. We find ERG sub-populations with no AGN activity and intense star-formation rates. With average values of ~180 M⊙/yr at 2 ≤ z < 3, they reasonably contribute to the global star-formation rate density, reaching a > 20% level. Strong AGN behaviour is not observed in the ERG population, with AGN only increasing the average radio luminosity of ERGs by 10 — 20%. However, AGN are frequently found (in up to 27% of the ERG population), and would increase the SFRD estimate by over 100%. Thus, and while the contribution of SF processes to the radio luminosity in galaxies with AGN remains uncertain, a comprehensive identification of AGN in these populations is necessary to obtain meaningful results. The dust content to each population is also derived by correlating UV and Radio SFRs, giving a higher obscuration for more active SF sources. Also, know to be amongst the most massive galaxies in the high-z universe, I will show that ERGs may constitute up to 60% of the total mass in the universe at 1 ≤ z ≤ 3. Finally, preliminary and promising results are presented on the morphologies of ERGs (CAS and Gini/M20 parameters) based on the v1.9 ACS GOODS-S images.
Abstract
Since 2003 there has been a new period of excavation and research on Stonehenge. With two excavations inside Stonehenge and many more around it, archaeologists now have a new chronology for this famous monument as well as the prehistoric monuments with which it is associated. While theories of its use as an astronomical observatory were proposed in the late 20th century, current approaches re-interpret Stonehenge’s astronomical alignments as calendrical indicators for the timing of social gatherings, in which Stonehenge was part of a larger complex of monuments in wood and stone, centered on a short stretch of the River Avon. Many of these other monuments were also designed to mark astronomical events but these have received less attention than their more famous stone counterpart. In 2009 the Stonehenge Riverside Project, which has been conducting most of the new research, discovered a new stone circle, named as Blue stonehenge, next to the River Avon at the end of Stonehenge’s avenue.
Abstract
Recent observations of the rotation curve of M31 show a rise of the outer part that cannot be understood in terms of standard dark matter models or perturbations of the galactic disc by M31's satellites. In this talk, we show a possible explanation of this dynamical feature based on the influence of the magnetic field within the thin disc. We have considered standard mass models for the luminous mass distribution, a Navarro-Frenk-White model to describe the dark halo, and we have added up the contribution to the rotation curve of a magnetic field in the disc. We have found a significant improvement of the fit in the outer part when magnetic effects are considered. Our best-fit requires a field strength of ~ 4μG which is compatible with the observations of the magnetic fields in M31.
Abstract
Contrary to popular belief, on very large distance scales visible matter stubbornly refuses to "fall" according to the laws of gravity of both Newton and Einstein. The paradox has led to the introduction of dark matter, purporting to explain the observed surplus of gravitational pull. The logical possibility remains that there is no dark matter, what you see is all there is, and that the paradox simply signals the break down of the Einstein-Newton theory of gravity. I will review alternative theories of gravity that do away with the need for dark matter. Surprisingly Solar system gravitational experiments, such as those associated with the LISA Pathfinder mission, might settle the score between the two approaches.
Abstract
Understanding the composition and the nature of any asteroid approaching the Earth, and consequently potentially hazardous, is a matter of general interest, both scientific and practical. The potentially hazardous asteroid 1999 RQ36 is especially accessible to spacecraft and is the primary target of NASA's OSIRIS-REx sample return mission. Spectra of this asteroid point to the most primitive meteorites (CIs and CMs) as the most likely analogs. Asteroid (3200) Phaethon is also particularly interesting. Together with 2005 UD and 2001 YB5, is one of the only 3 near-Earth asteroids with associated meteor showers, which mostly come from comets. There is evidence of the presence of hydrated minerals on its surface, usually associated with organic material. Both asteroids are classified as "B". B-type asteroids are found mostly in the middle and outer main belt and are believed to be primitive and volatile-rich. We combine dynamical and spectral information to identify the most likely main-belt origin of these two objects.
Abstract
In this talk we present spectroscopy of asteroids 24 Themis and 65 Cybele in the 2-4 μ region obtained with the NASA 3.5m IRTF telescope. Their spectra are very similar, and present the typical water ice band at 3.1 μ and additional absorption bands in the 3.2-3.4 μ region that can be attributed to solid organics, showing that there is a small amount of water ice and solid organics widely distributed across their surface. Spectra in the 6-25 μ region obtained with SPITZER of 65 Cybele also show that its surface is covered by a fine anhydrous silicate grains mantle as other outer belt asteroids like the Trojans are. This dust mantle, with a small amount of water ice and complex organic solids, is similar to comet surface where non-equilibrium phases coexist. The presence of water-ice and anhydrous silicates is indicative that hydration did not happened or is incomplete, suggesting that the temperatures were always sufficiently low. This is the first detection of water ice and and solid organics in the surface of an asteroid and suggest that these materials are much more abundant than expected in the surface of asteroids with semi-major axis a > 3 AU. The cosmogonical and astrobiological relevance of this discovery will be discussed.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
