Recent Talks
List of all the talks in the archive, sorted by date.
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.
Abstract
Two-dimensional stellar kinematics obtained with the integral-field spectrograph SAURON allow the classification of early-type galaxies into 'slow' and 'fast' rotators, different from their morphological classification into ellipticals and lenticulars. Most fast rotators, including lenticular as well as many elliptical galaxies, are consistent with oblate axisymmetric disk-like systems. On the other hand, the slow-rotator ellipticals show clear deviations from axisymmetry, which can be modeled with our extension of Schwarzschild's orbit superposition method to triaxial geometry. Besides galaxies, I show that Schwarzschild's method can also be used to model in detail globular clusters such as ω Cen and M15. The recovered internal orbital structure of ω Cen reveals besides a signature of tidal interaction, also a central stellar disk, supporting its origin as the nucleus of a stripped dwarf galaxy. The formally best-fit Schwarzschild model for M15 includes an intermediate-mass black hole, but we cannot exclude a model in which dark remnants make up the dark mass in the collapsed core.
Abstract
CALIFA is the largest IFS survey ever performed up to date. Recently started, it will observe ~600 galaxies in the Local Universe with PPAK at the 3.5m of the Calar Alto Observatory, sampling most of the size of these galaxies and covering the optical wavelength range between 3700-7100 Å, using to spectroscopic setups. The main goal of this survey is to characterize the spatially resolved spectroscopic properties (both the stellar and ionized gas components) of all the population of galaxies at the current cosmological time, in order to understand in detail the how is the final product of the evolution of galaxies. To do so, the sample will cover all the possible galaxies within the color-magnitude diagram, down to MB ~ -18 mag, from big dry early-types to active fainter late-type galaxies. The main science drivers of the survey is to understand how galaxies evolve within the CM-diagram, understanding the details the process of star formation, metal enrichment, migrations and morphological evolution of galaxies.
Abstract
For most persistent low mass X-ray binaries (LMXBs) and transients in outbursts the optical emission is dominated by reprocessing of the X-rays in the outer accretion disk. This has severely hampered any dynamical studies and thereby our knowledge of their system parameters. A new avenue opened thanks to the discovery of narrow high-excitation emission components arising from the irradiated companion star. These lines are most prominent in the Bowen region (a blend of N III and C III lines between 4630 and 4650 Å). In this talk I will discuss this new technique, give an overview of the main results of our survey on the optically brightest LMXBs, and discuss the implications for their system parameters. Furthermore, I will point out the main limitations of this technique and how they might be overcome.
Abstract
A new method of imaging in the visible has given the highest resolution images ever taken anywhere. It needs a natural guide star of only 18.5 mag (I band). This talk will show how it can be done on the WHT, the VLT and even on the GTC.
Abstract
Developed since 2006 by the IAC and UPCT, FASTCAM is an optical camera which takes advantage of recently available low noise and fast read-out CCDs (with integration times ~30 ms) to perform speckle imaging of astrophysical sources. At high enough speed rate, the atmospheric turbulence - classically responsible for image degradation , i.e. seeing- can be frozen in the image, which permits us to implement "lucky imaging techniques". In this shared talk, we will review the principle and objectives of the instrument (mainly oriented so far towards the study of brown dwarfs), we will present the results obtained in different campaigns at the NOT and WHT telescopes stressing the effort towards high contrast and high resolution optical imaging potential which can be further enhanced with post-processing techniques. In this talk we will also discuss some ideas for future projects and scientific applications, possibly in conjunction with the GTC.Upcoming talks
- UNDARK kick offThursday October 10, 2024 - 9:15 GMT+1 (Aula)
- TBDDr. Nikki ArendseThursday October 17, 2024 - 10:30 GMT+1 (Aula)
Recent Colloquia
Recent Talks
