Recent Talks
List of all the talks in the archive, sorted by date.
Abstract
I will present a short introduction to speckle imaging and the so-called speckle holography technique. Subsequently, I will present results of speckle observations with the VLT (NACO) and Keck (NIRC) telescopes. The experiments demonstrate that in the observed targets speckle imaging combined with holographic image reconstruction provides imaging quality that can compete with and even supersede current adaptive optics (AO) imaging systems. Speckle imaging is a way to achieve reliable, high-quality, diffraction limited imaging capacity at relatively low costs. I will discuss what would be the estimated performance of speckle cameras at the WHT and GTC and sketch possible concepts.
Abstract
Using the k-means cluster analysis algorithm, we carry out an unsupervised classification of all galaxy spectra in the seventh and final Sloan Digital Sky Survey data release (SDSS/DR7). Except for the shift to rest-frame wavelengths and the normalization to the g-band flux, no manipulation is applied to the original spectra. The algorithm guarantees that galaxies with similar spectra belong to the same class. We find that 99% of the galaxies can be assigned to only 17 major classes, with 11 additional minor classes including the remaining 1%. The classification is not unique since many galaxies appear in between classes; however, our rendering of the algorithm overcomes this weakness with a tool to identify borderline galaxies. Each class is characterized by a template spectrum, which is the average of all the spectra of the galaxies in the class. These low-noise template spectra vary smoothly and continuously along a sequence labeled from 0 to 27, from the reddest class to the bluest class. Our Automatic Spectroscopic K-means-based (ASK) classification separates galaxies in colors, with classes characteristic of the red sequence, the blue cloud, as well as the green valley. When red sequence galaxies and green valley galaxies present emission lines, they are characteristic of active galactic nucleus activity. Blue galaxy classes have emission lines corresponding to star formation regions. We find the expected correlation between spectroscopic class and Hubble type, but this relationship exhibits a high intrinsic scatter. Several potential uses of the ASK classification are identified and sketched, including fast determination of physical properties by interpolation, classes as templates in redshift determinations, and target selection in follow-up works (we find classes of Seyfert galaxies, green valley galaxies, as well as a significant number of outliers). The ASK classification is publicly accessible through various Web sites.
Abstract
We present recent theoretical and empirical results concerning the accuracy of Cepheid distance estimates based on optical and near-infrared (NIR) Period-Luminosity (PL) relations. In particular, we plan to discuss the dependence of both slope and zero-point on the metal content using a large sample of extragalactic Cepheids. Moreover, we discuss pros and cons of optical and NIR reddening free Period-Wesenheit relations. We also mention the impact that GAIA will have on the precision of the Cepheid distance scale and the role that E-ELT will play in the identification of Cepheids beyond the Local Volume.
Abstract
Teams from industry, universities and institutes across Europe are contributing to the design and development phase of the European Southern Observatory's project to build the world's biggest optical/infrared telescope. I will outline some of exciting scientific prospects for a fully-adaptive 42m telescope, from studying exoplanets to the furthest galaxies, and then show how some of the technical challenges are being addressed. I will place special emphasis on the work UK teams are doing on instrumentation, detectors and adaptive optics.
Abstract
The SONG SONG (Stellar Observations Network Group) project is a worldwide initiative to design and build a global network of 1m telescopes (6 to 8 nodes) to allow observations with a high duty cycle (> 80%) and near continuous coverage over long time spans (weeks to months). The SONG prototype (first node of the network) is currently under construction and it is expected to be placed at the Observatorio del Teide in mid 2011 on the basis of a bilateral collaborative agreement. The main scientific goals for SONG are to study stars using asteroseismology, and to search for, and characterize, extra-solar planets using microlensing and radial-velocity observations. In order to achieve this, the prototype node will be equipped with a high-resolution spectrograph and a dual-colour lucky-imaging camera. Here we describe the main aspects of the project and the various scientific opportunities that will be offered to the Spanish community.
Abstract
(1) In this talk I will present a recent study of the bar fraction in the Coma Cluster galaxies based on a sample of 190 galaxies selected from the Sloan Digital Sky Survey Data Release 6 and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allows us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 mag (-23 < Mr < -14), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities (-22 < Mr < -17) and masses (109 < M/M? < 1011). This result holds when compared with a sample of bright/massive field galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second-order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks.
(2) The Herschel Space Observatory was launched on 14 May 2009. After a short commissioning and performance verification period, the science demonstration observations started in September 2009. Herschel is carrying out now routine science observations. The three instruments (SPIRE, PACS and HIFI) are working extremely well. The first results of the many Herschel Key Projects were presented at the ESLAB 2010 conference in ESTEC on May 4-7 2010 and will be published in a special issue of Astronomy and Astrophysics. In this talk I will introduce the observing capabilities of Herschel and will review some of the first results in extragalactic astronomy and in particular those of the Herschel Multi-tiered Extragalactic Survey (HerMES).
Abstract
Gamma Dor stars (M = 1.2-2.5 M⊙; spectral type A-F) are very interesting from an asteroseismic point of view. They show gravity modes, which are the only modes that provide information on the deep stellar interior. Observationally they are very challenging targets. Typical pulsation periods are of the order of a day and amplitudes are fairly small (below 0.05 mag; 2 km/s), making it extremely difficult to monitor the periodic variations from the ground. The asteroseismic space missions CoRoT and Kepler are providing uninterrupted time-series from space, with unprecedented accuracy, and hence promise a revolution in the study of gamma Dor stars. I will present results of the seismic analysis of CoRoT and Kepler gamma Dor targets, and the associated ground-based support observations, involving many telescopes at different observatories (including La Palma and Izaña).
Abstract
The main goal of the MASTER-Net project is to produce a unique fast sky survey with all sky observed over a single night down to a limiting magnitude of 21. Such a survey will make it possible to address a number of fundamental problems: search for dark energy via the discovery and photometry of supernovae (including SNIa), search for exoplanets, microlensing effects, discovery of minor bodies in the Solar System, and space-junk monitoring. All MASTER telescopes can be guided by alerts, and we plan to observe prompt optical emission from gamma-ray bursts synchronously in several filters and in several polarization planes.
Abstract
We present a visual determination of the number of bright points (BPs) existing in the quiet Sun, which are structures though to trace intense kG magnetic concentrations. The measurement is based on a 0.1 arcsec angular resolution G-band movie obtained with the Swedish Solar Telescope at the solar disk center. We find 0.97 BPs/Mm2, which is a factor three larger than any previous estimate. It corresponds to 1.2 BPs per solar granule. Depending on the details of the segmentation, the BPs cover between 0.9% and 2.2% of the solar surface. Assuming their field strength to be 1.5 kG, the detected BPs contribute to the solar magnetic flux with an unsigned flux density between 13G and 33G. If network and inter-network regions are counted separately, they contain 2.2 BPs/Mm2 and 0.85 BPs/Mm2, respectively.
IAC
Abstract
We present the new stellar population synthesis models based on the empirical stellar spectral library MILES, which can be regarded nowadays as standard in the field of stellar population studies. The synthetic SEDs cover the whole optical range at resolution 2.3 Å (FWHM). The unprecedented stellar parameter coverage of MILES allowed us to extend our model predictions from intermediate- to very-old age regimes, and the metallicity coverage from super-solar to [M/H] = -2.3. Observed spectra can be studied by means of full spectrum fitting or line-strengths. For the latter we propose a new Line Index System (LIS) to avoid the intrinsic uncertainties associated with the popular Lick/IDS system and provide more appropriate, uniform, spectral resolution. We present a web-page with a suite of on-line tools to facilitate the handling and transformation of the spectra. Online examples with practical applications to work with stellar spectra for a variety of instrumental setups will be shown. Furthermore we will also show examples of how to compute spectra and colors with varying instrumental setup, redshift and velocity dispersion for a suite of Star Formation Histories.
Upcoming talks
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Recent Colloquia
Recent Talks
