The six areas of research of CATA have been very active and productive, given rise to 579 (five hundred seventy nine) ISI publications during the reported period. Thus, it is unrealistic to try to summarize in this report all the work and the results obtained in these 4 years of research. Instead in what follows we highlight the most important results in each of the individual areas of research. In particular we emphasize the Key Projects of each area which have become internationally recognized as high-impact large-scale scientific projects associated to CATA.
AREA 1: Birth and Evolution of Structures in the Universe.
P.I.: Leopoldo Infante
The long-term goal of Area 1 is to contribute in the understanding of the nature and evolution of structures in the universe. Faculty members doing research in this Area include Barrientos, Bauer, Bronfman, Cuadra, Galaz, Dunner, Jordán, Lira, López, Minniti, Padilla, Quintana, Reisenegger and Richtler.
This Area emphasizes the study of primeval galaxies, clusters of galaxies and dwarf galaxies, and is carrying out with prominence large surveys of high redshift galaxies, superclusters and clusters of galaxies. It developed from no theory at all to a significant amount of cosmological simulations, galaxy evolution simulations and primordial star formation theory at redshifts greater than 11.
One important objective envisioned in the original project was to prepare the extragalactic community for the ALMA era. At that time there were no extragalactic radio astronomers in our community. Today, after these fours years, we are pleased to say that this objective is being accomplished. Proof of this is the increase in the number of faculty, postdoctoral fellows and students working in projects related to ALMA and the number of extragalactic proposal submitted in cycle 0 to ALMA; 11 out of 34 proposals. These proposals range in topics from studies of the local universe to quasars, AGN, star forming galaxies at z~1-3 to submm emission in the most distant galaxies ever discovered at z>7.
In what follows we highlight three lines of research that are been carried out successfully in Area 1: the MUSYC survey, the QbC project and Cosmo-galaxy simulations. We also mention the latest result, the discovery of the largest and most powerful distant cluster of galaxies ever discovered (El Gordo), which recently received worldwide media attention.
Simulations and theory: Simulations of structure and galaxy formation is one of the major new advances in Area 1, allowing Center members to become competitive in the field. Highlights of this specific area include: a first, physically based, definition of a galaxy supercluster; simulations which show that dark matter merges and that gas accretion into dark matter haloes generate turbulent and supersonic environments, where cooling molecules trigger primordial star formation; simulations of the universe at several different scales, from the large-scale structure, to the physics of galaxy formation, to the dynamics of star forming regions, to the inner pc scales of central supermassive black-holes, both via semi-analytic models and full hydrodynamic simulations.
Quasars behind Clusters (QbC) survey: This survey is aimed at studying the effect of galaxy group and cluster-sized environments on the gaseous content of galaxies at redshifts 0.2 MUSYC (MUltiwavelength Survey by Yale-Chile): The main design of this survey is to study formation and evolution of galaxies and their black holes at redshifts z~3. It includes deep infrared, optical and narrow band imaging and covers four 30x30 square arc-minute fields. Also, Chandra X-ray observations, Spitzer IR imaging and extensive spectroscopy were carried out. The survey has been most successful for studies of Lyman Alpha Emitting galaxies (LAE) at redshift z~3. Center members were able to determine spectral energy distributions of these galaxies, showing that on average these galaxies are quite blue and dust free. On the other hand, given the large volume surveyed, they were able to obtain a large sample of LAEs at z~3.1, which allowed us to make robust estimates of three important physical quantities: the luminosity function, the number density and the clustering length. The latter allowed them to estimate masses and number densities of the dark matter haloes where LAEs reside. They were able to reach the conclusion that these haloes may host galaxies like the Milk Way at present. Furthermore, the use of narrow band data enabled them to extend the survey to lower redshifts of z~2, such that they could constrain the clustering properties and measured the evolution of the luminosity function of LAEs between redshifts 3.1 and 2.1.
EL GORDO: Since 2008 CATA members have been reporting results from their Atacama Cosmology Telescope (ACT) survey collaboration which includes USA and Chile astronomers and physicists. The ACT is a submm radio telescope built to measure the Cosmic Microwave Background radiation (CMB) at high resolution. It is located in Cerro El Toco near the ALMA site in Chile. The Center group has been in charge of detecting clusters of galaxies through the Sunyae-Zeldovic (SZ) imprint in the CMB. Once a cluster is detected they carry out follow up spectroscopic (VLT and Gemini) and imaging (SOAR) observations. A number of clusters have been discovered, normally very massive, at redshifts ranging from 0.3 to 1. One of these clusters, now called “EL Gordo”, is the most massive and powerful distant cluster ever detected. Using X-ray Chandra observations, NIR SOAR imaging and VLT spectroscopy, they estimated its intrinsic mass and luminosity. Its redshift, z=0.87, puts this cluster at an age close to half the age of the universe, 7 billion years. The fact that such a large mass concentration (gravitationally bound and in equilibrium) existed in the early universe puts stringent constraints on current models of dark matter and dark energy cosmology.
AREA 2. Stellar Populations in the Local Universe
P.I.: Doug Geisler
The science cultivated in this Area involves researchers from all 3 institutions, including 14 faculty members (Borissova, Catelan, Costa, Geisler, Gieren, Infante, Jordan, Mendez, Mennickent, Minniti, Pietrzynski, Richtler, Rubio and Zoccali), several postdoctoral fellows and graduate students. The overarching scientific goals of Area 2 are closely aligned with those of Area 1, viz. to study the formation and evolution of structures, in particular galaxies, but using the resolved stars within a galaxy instead of its global, integrated properties as tracers. Obviously, a great deal more information can be gleaned for nearby systems whose individual stars are available to tell us about the details of the secrets of their formation and evolution. The observational techniques are also different. In particular, the main goals are to investigate galaxy (and the Galaxy) formation and evolution, in particular dynamical and chemical evolution. Much of this work is often relegated to the realm of cosmology, the study of the very distant Universe and its nature on very large scales and at very large distances, where only very crude details can be drawn from the limited data. One of the great advantages of this Area is that one can perform ‘near-field’ cosmology and obtain much more detailed and accurate data for nearby galaxies which perfectly complement what can be learned from the distant Universe. Work was divided into 3 main subtopics: globular cluster systems of more distant galaxies, stellar populations in nearby galaxies, and stellar populations in the Galaxy.
Globular Cluster Systems. The Dark Matter Halo of NGC 1399. Central galaxies in galaxy clusters can be key discriminators between competing theories of galaxy formation and dynamics; in particular between the cold dark matter (CDM) paradigm and modified Newtonian dynamics (MOND). However, one requires a very large number of dynamical probes over a wide radial range in the galaxy to definitively discriminate between model predictions. CATA members used globular clusters as tracers of the gravitational potential of NGC 1399, the central galaxy of the nearby Fornax cluster. Using several instruments they obtained velocities of 656 globular clusters out to a galactocentric distance of 80 kpc. This represents the largest sample of dynamical probes so far obtained for any galaxy. They then performed a careful Jeans analysis for a non-rotating isotropic model and compared their results to different dynamical predictions. A generic NFW CDM model fits their data well, while a MOND model requires additional dark matter on the order of the stellar mass in order to get good agreement. This work involved extensive interaction with Area 1 researchers.
Stellar Populations in Nearby Galaxies. Chemical Evolution of the Galactic Bulge. Does the Milky Way possess a ”classic” bulge, formed very rapidly and very early in the history of our Galaxy, or is it instead a ”pseudo-bulge” formed via secular evolution of the disk driven by a bar over an extended time? The answer has important implications for Galaxy formation theories and can be constrained from detailed chemical studies - elemental ratios are sensitive to the previous history of star formation. In particular, the relative abundances of iron and alpha-elements play a key role: the [alpha/Fe] ratio depends on the relative contribution of SNII and SNIa progenitors, and therefore it depends on the timescale of star-formation, as these two processes have very different timescales. Center members obtained high resolution spectra for a large sample of bulge giants and measured alpha and Fe abundances. [alpha/Fe] is found to be higher in bulge stars than in thick disk stars, which were known to be more alpha enhanced than thin disk stars. These results support a scenario in which the bulge formed before and more rapidly than either thin or thick disks, and therefore our bulge is a prototypical old spheroid, with a formation history similar to that of early-type (elliptical) galaxies.
The VVV Survey. The Vista Variables in the Via Lactea Survey (D. Minniti PI) is the public ESO near-IR variability survey scanning the Milky Way bulge and an adjacent section of the disk. The survey will take 1929 hours of observations with the ESO 4-m VISTA telescope during 5 years (2010 - 2014), covering 109 point sources across an area of 520deg2. The final product will be a deep near-IR atlas in five passbands (0.9-2.5 μm) and a catalogue of more than 106 variable point sources. The VVV is the Key Project of Area 2 and is proving to be every bit as much of a goldmine as anticipated. Despite only recently beginning, the Survey has already produced a number of important scientific results and papers. One of the key scientific goals of the VVV is to study star clusters in the Galaxy, including 33 known globular clusters and ~350 known open clusters. Most of these suffer from large and often variable reddening and are thus very poorly studied. The VVV survey will add very substantially to the knowledge of their basic parameters. The VVV is also discovering and studying a wealth of new star clusters. Center members reported (see ESO Press Release 1128) the discovery of ~100 new open star clusters. These are so-called embedded clusters - very young and still surrounded by their cocoons of dust and gas, and thus invisible to optical surveys. But they could not escape the sensitive IR images of the VVV, which penetrate the obscuring interstellar material to reveal the clusters. It has also long been suspected that there are several more globular clusters - much older than open clusters - that are hiding in the obscured and dense regions of the Galactic bulge, and indeed VVV has now found at least 2 new old globular clusters. In addition, very strong synergy has been established with the distance scale work of Area 3. A huge number of RR Lyrae stars, classical population II distance indicators, will be observed in the VVV, allowing extremely accurate distances to be determined to many globular clusters, as well as the bulge and the Sagittarius dwarf galaxy, also allowing us to measure the size of these latter objects.
Multiple Populations in Globular Clusters. Globular clusters, long considered as the prototype of simple stellar populations, have recently been found instead to be more complex, and thus more interesting, than regarded by this traditional wisdom. In particular it has been discovered that the most massive globular clusters have chemical inhomogeneities. In addition, it has been found that a growing number of clusters have an intrinsic spread in the content of their light-elements. The generic phenomenon is labeled multiple populations. These results point toward the fact that globular clusters are not the simple systems previously thought, but had a period of chemical evolution and distinct episodes of star formation at the beginning of their life. This has led to a paradigm shift in our understanding of these key astrophysical objects. The observed spread is probably due to the early evolution of each cluster, when a second generation of stars was born from gas polluted by ejecta of evolved stars of the first generation. Several kinds of polluters have been proposed, including intermediate mass AGB stars and massive main sequence stars. Center members have been involved in a number of investigations to try and shed light on this fascinating phenomenon. They studied stars in NGC1851 belonging to the two RGBs visible in the Stromgren CMD, finding that the double RGB appears to be related to a bimodal distribution of the light and heavy s-element abundances. The cluster also hosts a bimodal SGB, which was theoretically explained with two populations having the same age but different C+N+O content. They proved instead that stars in NGC 1851 share the same C+N+O content. In this case pollution by SNeII appears to have ocurred. On the other hand, for M4 Center members established that the cluster is formed by two stellar populations with distinct patterns of light and light-s elements. These patterns suggest that the second generation was formed by material polluted by ejecta of massive stars (M > 15M). This implies an age difference between the two populations of 10-40 Myrs.
AREA 3. The Extragalactic Distance Scale
P.I.: Wolfgang Gieren
The work in Area 3 has been mainly conducted by four Center scientists (Gieren, Pietrzynski, Mennickent and Minniti), several postdoctoral fellows and students, and a considerable number of international collaborators from the USA and Europe. The main science and Key Project of this Area is the Araucaria Project whose goal was to improve stellar standard candles, and in particular Cepheid variables, to yield distances to nearby galaxies (out to a few Mpc) accurate at the few percent level and this way lay the ground for a truly accurate (<3%) determination of the Hubble constant independent from CMB anisotropy studies. The Araucaria Project is very complementary to the HST Key Project on the Extragalactic Distance Scale by Freedman et al. (2001) and addresses the 3 largest sources of systematic uncertainty in that project which had limited the accuracy of the Hubble constant from the Cepheid approach to 10 percent: reddening of the Cepheids; the little-known metallicity dependence of the Cepheid period-luminosity (PL) relation; and the distance to the fiducial galaxy, the Large Magellanic Cloud (LMC). The strategy adopted to reduce the errors from these sources were a) measure Cepheid distances from near-infrared photometry, reducing the importance of reddening errors quite dramatically; b) select a sample of nearby late-type galaxies exhibiting a broad variety in the (mean) metallicity of their young stellar populations, and looking for systematic effects related to the metallicity; and use a number of different stellar methods to measure the LMC distance and compare the results (this ended up in getting the most accurate results from late-type eclipsing binaries composed of two red giants which we found in the LMC (and SMC) from OGLE 2 and OGLE 3 data; see later in this report). Besides of Cepheids, the Araucaria Project has contributed on the improvement of other stellar techniques of distances measurement, and applied them to nearby galaxies: RR Lyrae stars, red clump giants, TRGB, blue supergiants and eclipsing binaries, with the first 3 methods all calibrated in the near-infrared to minimize effects of reddening and metallicity.
In the Cepheid work, CATA members performed as a first step wide-field optical searches for Cepheids in the Araucaria target galaxies, which included all Local Group irregulars and 4 spiral galaxies in the Sculptor Group (NGC 55, 247, 300 and 7793). The ground-breaking initial work was conducted in NGC 300 where they found 117 classical Cepheid variables with periods between 5-115 days. In a follow-up study they obtained near-IR photometry at the ESO VLT for a subsample of these Cepheids and developed a multi-wavelength VIJK technique to determine the distance to NGC 300 with a total error of 3%, unprecedentedly small. This technique was later applied to all other Araucaria target galaxies and yielded in all cases Cepheid distances accurate to better than 5%. Since the project involved a huge observational effort, members applied for and were granted numerous semestral programs at the ESO Paranal and La Silla observatories, and at Las Campanas Observatory (Magellan, Warsaw 1.3-m imaging telescope used for the OGLE Project). Most of the wide-field imaging surveys for Cepheids and the other stellar candles were conducted with the Warsaw telescope in which members were allocated observing time in many nights, to allow proper phase coverage of the variables and making the Cepheid work possible.
Comparing the observed Cepheid PL relations in all target galaxies of the Araucaria Project led to the conclusion that the slope of the PL relation is universal, that is metallicity-independent, in the broad range from -0.3 dex (LMC) to -1.0 dex (WLM). This result was extended to solar metallicity (which is important because most HST KP galaxies have ~solar metallicity in their central regions) by another project undertaken by our group: the application of the Baade-Wesselink-type Infrared Surface Brightness (IRSB) Technique for Cepheids to Milky Way and Magellanic Cloud Cepheids. This technique establishes Cepheid angular diameters from their measured (V-K) colors using a surface brightness-color calibration obtained from VLTI interferometry of nearby Cepheids, and combines these with their radius variations obtained from integrating their observed radial velocity curves. The largest source of systematic error in the method comes from the p-factor needed to transform the observed radial velocities of a Cepheid into the pulsational velocity at its surface. To determine the “p-factor law” this Center group did theoretical work using theoretical Cepheid atmospheres, and provided an improved empirical calibration by applying the IRSB technique for the first time to Cepheids in the LMC; using the constraint that individual LMC Cepheid distances cannot depend on their pulsation period (they are all very nearly at the same distance!), together with the HST FGS parallaxes measured by Benedict et al (2007) for ten nearby Milky Way Cepheids which basically set the zero point of the method, they found that the Cepheid PL relations in Milky Way and LMC do show exactly the same slopes, particularly in the near-IR J and K bands, and that there is also no significant metallicity effect on the zero points.
As a conclusion, the work on the Cepheid PL relation from both the Araucaria Project approach, and the IRSB technique has yielded, as a very firm result, that the Cepheid PL relations in the near-infrared J and K bands are truly universal, unaffected by the metallities of the observed Cepheid samples. The IRSB distances to 36 LMC Cepheids have further yieldes an accurate LMC barycenter distance of 18.45 mag, with a 5% systematic error and in line with our first analyzed late-type eclipsing binary system (see next section).
Center members discovered from OGLE 2 data the first 8 eclipsing binaries in the LMC composed of two red giants, bright enough for measuring accurate orbital radial velocity curves with 4-8-m class telescopes. These systems have an enormous potential for accurate distance determinations, and for precision measurements of the masses and radii of their component stars. Observationally, they are difficult targets because of their very long orbital periods, typically 100-500 days. The first analyzed system yielded indeed a distance accurate to 2.7%. From OGLE 3 images they detected 16 additional systems which are all being observed with high-resolution spectroscopy. Once the 10-15 best LMC systems have been fully analyzed by the Center group, with individual distances accurate in the 2-3% range, they expect to determine the LMC barycenter distance to 2%. This will mean a breakthrough in comparison to the HST Key Project´s assumed LMC distance of 18.50 which was uncertain to 10% at the time.
As part of the LMC eclipsing binary programme, members were lucky enough to detect the first ever two classical Cepheids in eclipsing systems with a stable red giant star as a companion in both cases. This allowed them to solve the famous “Cepheid mass discrepancy problem” in favour of the pulsation mass, given that the Cepheid dynamical masses could be measured to 1%. The result was published in Nature (also see ESO Press Release 1046, 2010). Due to this result and the disappearance of the annoying mass problem, Cepheids are now an even more reliable tool for calibrating the first rungs of the distance ladder.
Through the collaboration in the Araucaria Project with the University of Hawaii group, Center members achieved to set up a completely new, and first spectroscopic stellar method to measure precision distances out to at least 10 Mpc with blue supergiant stars. The accuracy is very competitive (5% with 10 blue supergiants in a given galaxy), has the advantage of yielding individual metallicities and reddenings as a byproduct, and uses the brightest normal stars in the Universe.
AREA 4. Star Formation
P.I.: Guido Garay.
The main scientific goal of this area is to understand and characterize the formation process of low and high mass stars that takes place within dense molecular cores. Faculty members doing research in this Area include Bronfman, Casassus, Escala, Garay, Mardones, May and Rubio, several postdoctoral fellows and more than 15 thesis students.
The Key Project in this Area, entitled Studies of massive star forming regions in the southern hemisphere, has been designed to specifically undertake a thorough study of the formation process of high-mass stars within massive dense cores, in particular to determine the gas kinematics prior to and during the onset of the gravitational contraction. The first part of this Key Project, already completed, consisted of a survey of 1.2 mm dust continuum emission towards a large sample of luminous massive star forming regions, made using SEST/SIMBA. This survey allowed Center members to determine the physical characteristics of the molecular cores harboring high-mass YSOs. They showed that the formation of massive stars takes place in molecular structures with distinct physical parameters, namely sizes of ~0.4 pc, dust temperatures of ~30 K, masses of ~2000 Msun, column densities of ~3x1023 cm-2, and densities of ~4x105 cm-3. The observed radial intensity profiles of these massive and dense cores are well fitted with power-law intensity profiles, indicating that they are centrally condensed. They also found that the ultra-compact H II regions detected towards these objects are usually projected at their peak position, suggesting that massive stars are formed at the center of the centrally condensed massive and dense cores.
As a byproduct of the 1.2 mm dust continuum emission survey, Center members discovered the first few luminous objects without counterparts at mid-infrared (Midcourse Space Experiment [MSX]) and far-infrared (IRAS) wavelengths. These clouds have sizes of 0.2-0.3 pc, masses of typically 1000 Msun, densities of ~2×105 cm-3, and dust temperatures < 17 K. They concluded that these objects correspond to massive, dense and cold cores in very early stages of evolution, prior to the formation of a central massive object and that will eventually collapse to form high-mass stars.
Soon after the ASTE and APEX telescopes became operationally, CATA members started the second part of the Key project. This consisted in a galactic survey of the dust continuum emission at 850 microns. Center members joined forces with the European ATLASGAL team to carry out a survey of the whole Galactic plane using LABOCA, allowing them locate in an unbiased way the cold and dense massive molecular cores wherein massive starts will eventually form.
Follow up work is being done using a variety of instruments available in order to: (a) investigate the dynamic interaction between embedded massive protostars and their parent cores; (b) Study the spatial distribution of massive protostars within GMCs and across the inner galaxy; and (c) Investigate the origin of jets and molecular outflows. One of the major astronomical results of the last two decades has been the discovery that star formation is accompanied by energetic, collimated mass outflow. The driving mechanism is however unknown and requires study on scales as close to the star as possible. Center members made an unbiased search of ionized jets, using ATCA, towards high-mass YSOs candidates. They found that the phenomena of highly collimated stellar wind is also present in the most luminous massive protostars yet known, and concluded that the lifetime of this phase in high-mass YSOs last for only 3x104 yrs. They also studied the characteristics of high velocity molecular gas towards massive young stellar objects and investigated whether or not the ionized jets have enough momentum to drive the bipolar molecular outflows.
Center members are also carrying out studies of Infrared Dark Clouds, namely cold, dense molecular clouds seen as extinction features against the bright Galactic infrared background. They have mapped the emission in several molecular lines, using MOPRA, toward a large number of filamentary IRDCs in order to better characterize the various stages of high-mass star formation as well as the timescales and physical conditions during the collapse into proto-stellar cores. In addition, Center members are part of a large international project (MALT90) to make maps in 16 molecular lines near 90 GHz, using MOPRA, of 3,000 dense cores in the galactic plane. These molecular lines will probe the physical conditions, chemical state, and evolutionary state of 3,000 dense molecular cores in a wide range of evolutionary states (from pre-stellar cores, to proto-stellar cores, and on to H II regions).
Finally, Center members are building up data on the topic of the gas content in proto-planetary disks, and also on signs for on-going planet accretion. Molecular lines were observed with APEX towards a dozen of high mass star forming cores showing kinematical signatures for the presence of a rotating disk. The aim is to search for enhanced abundance of certain molecular species based on the prediction from chemical models of disks. This will provide reliable candidates to spatially resolve a disk surrounding a high mass star with the ALMA telescope.
In summary, CATA members have been able to study and characterize the long-sought onset of massive star formation within cores. The Key project of this Area turned out to be a strong pathfinder for ALMA studies. Center members are now ready to begin use ALMA to study the density structure and kinematics of massive protostellar envelopes, inner disks and winds at sub-arcsecond resolution, yielding detailed information on massive star forming cores at scales of 10 – 100 AU.
AREA 5. Extrasolar Planets and Brown Dwarfs
P. I.: D. Minniti
More than ten researchers were involved in the successful development of this new area of research. Faculty members include: Borissova, Geisler, Gieren, Jordan, Kurtev, Mendez, Minniti, Pietrzynski, Rojo, Ruiz and Zoccali.
Undoubtedly the biggest success in research of Area 5 has been the creation of large key programmes, which reach far beyond the normal scientific activities. These large key programmes developed slowly at the beginning, but already started to bring fruits after only a few years of operation, and the future looks most promising. The large programmes in line with the scientific goals of Area 5 are:
(1) ESO Large Programme 666 on Extrasolar Planets at the ESO VLT. This, the Key Project of the Area, has produced a considerable number of newly discovered objects for which the main physical parameters were determined. These data are allowing to test the different planetary models of atmospheres, of internal structure, and of evolution, of objects at the bottom of the main sequence and beyond.
(2) The HAT-South Planet Search Programme at Las Campanas Observatory. This is a global network of small, custom made telescopes that were installed during 2009 in Australia (Siding Springs), Namibia (HESS site) and Chile (Las Campanas), and that is providing 24-hr monitoring of selected fields to discover transiting exoplanets more efficiently than ever before. Euler/CORALIE and duPont/Echelle runs to confirm transiting exoplanet candidates from HATnet.
(3) The Magellan Planet Search Programme at Las Campanas Observatory. This radial velocity search for planets made a dozen new discoveries. Center members are now finishing up a study of the HK chromospheric activity of a large sample of stars and improving the precision of M-dwarf radial velocity observations, which resulted in the discovery of the super-Earth in the habitable zone of GJ667c;
(4) The Calan-Hertfordshire Extrasolar Planet Search (CHEPS) survey with HARPS and CORALIE. Even though the project is still very much in its infancy, discoveries and orbits have been published for three exoplanets and a brown dwarf, or extreme Jupiter-like planet. The target selection was done using FEROS, with two publications of chromospheric activities, kinematics, rotational velocities, and metallicities for a sample of over 950 nearby, Sun-like stars.
Another initiative involves perfecting new techniques to measure exoplanetary atmospheres and proto-planetary disks. A first attempt involves using high-resolution IR spectrographs, available to the Chilean community, to attempt detecting the Doppler wobble of the exo-atmospheric molecular lines. These studies will be complemented later with ALMA, to ultimately gain new knowledge of planetary “weather”, the structure of atmospheric wind and the variations in chemical constituents. Studies of proto-planetary disks will also be carried out using the recently available IR facilities. Future ALMA observations will provide definite answers regarding their formation and evolution.
Among other on going research projects we mention:
Planet search around bright giant stars in the southern hemisphere using the FEROS and FECH spectrographs;
Search for proto-BDs in Barnard 30. A few candidates have been already detected with APEX;
Search for cool Brown Dwarfs (UCDs) using VVV. Center members developed a set of automatic procedures for identification, reduced proper motion and photometric classification of the UCD population using VVV catalogs. As a result a candidate list from late-M to T-Y spectral types was built. A massive campaign for spectral follow up on VLT, Magellan, SOAR and du Pont telescopes is in course;
Spectral synthesis analysis of main sequence and subgiant stars using FEROS optical spectroscopy. Center members are applying a new method for abundance analysis of Sun-like stars to a large sample of stars to analyse them for future planet search and also for analysis of abundance trends in the galaxy;
Search for wide brown dwarf binaries to white dwarfs and subgiant stars. As part of this effort, Center members discovered the first white dwarf - T-dwarf binary system.
AREA 6. Supernovae and Dark Energy.
P. I.: M. Hamuy
The long-term goals of Area 6 are twofold: (1) The determination of extragalactic distances using supernovae, and (2) the understanding of the physics of supernovae and of dark energy. Faculty members doing research in this Area include: Clocchiatti, Hamuy, Gieren, Maza, and Pignata. The activities performed during the reported period along these two lines are summarized below.
Since the beginning of our activities on 2008, CATA members have carried out a complete study of nearby supernovae (SN) in order to understand the origin of the dark energy of the Universe and its properties. With this in mind, the SN group carried out (1) a nearby supernovae search (z<0.03) in the southern hemisphere with four of the six robotic PROMPT telescopes in Cerro Tololo, which are available for them to use, and (2) a follow-up program, in close collaboration with the Carnegie Supernova Project, to establish a database with hundreds of nearby supernovae (z<0.07) of both thermonuclear and gravitational core collapse nature in optical and infrared (IR) wavelengths.
The first step along this research line consists in discovering supernovae. With this purpose Center members are carrying out a systematic search of several hundred galaxies using four of the six PROMPT robotic telescopes at Cerro Tololo. This project, which involves the participation of several undergraduate students, has secured more than 1120 hours of observation each year. Every night, several hundred galaxies are observed, the images are downloaded to our computers in Santiago, and an automatic search pipeline is triggered. During 2008-2012 the search project, dubbed CHASE, discovered 150 nearby supernovae. The supernovae discovered by CHASE are all nearby and generally young supernovae (cz < 25000 km s-1).
The second step in this research line is obtaining photometric and spectrometric follow-up data for the discovered supernovae by CHASE (and additional equatorial or southern supernovae found at other observatories). This project was done in collaboration with the Carnegie Supernova Program that used 280 nights every year, between 2004-2009, in the 1 and 2.5m telescopes in the Las Campanas Observatory, in the north of Chile, to study supernovae with redshifts less than 0.07. The collaboration with CSP observed a total of 129 Type Ia supernovae, in the ugriYJHK filters and with optical spectrographs. So far, Center members have analyzed the first batch of 35 supernovae. Based on the light curves, they were able to derive parameters which are used in distance determinations, such as the time and magnitude at maximum light, and the decline rate, Δm15(B). Furthermore, they built a set of template light curves which are of general use for fitting Type Ia supernova data from any source. Using the light-curve parameters, we calibrated intrinsic colors at maximum light and thus derived color excesses. The availability of optical-NIR colors allowed them to study the properties of the reddening law in the host galaxies, which is a fundamental step in controlling possible systematic errors involved in the measurement of distances with Type Ia supernovae. They found that the group of supernovae which suffered small or moderate reddening favored a low value of the total-to-selective absorption coefficient of Rv=3.2 which is typical for the Galaxy, whereas the two supernovae in the sample with highest reddening yielded significantly lower values (Rv~1.5). They studied in detail the cases of these two supernovae by comparing with alternative models of reddening by dust in a dense circumstellar shell. One of the main goals of the work was to calibrate Type Ia supernovae as distance indicators. For this purpose they fit the absolute magnitudes at maximum light in each of the ten photometric bands as a function of Δm15(B) and of the color at maximum or, alternatively, the color excess. The results for all bands showed dispersions of ~0.10-0.15 mag in the calibration of the absolute magnitudes (i.e., a precision of ~6% in the distance.) We noticed a strong correlation among the residuals of the fits in all bands, especially in the optical. These correlations allowed them, by combining results from different bands, to estimate that the precision in the measurement of the absolute magnitude of a Type Ia supernova can be as low as ~0.06 mag (~3% in distance.) Regarding the reddening law, the fits yielded low values of Rv~1-2 in all cases, contrary to what was found through the analysis of color excesses as described above. This discrepancy suggests that, apart from the effect of reddening, there is an intrinsic color dispersion which is correlated with luminosity but not with decline rate.
CATA members also performed a study on distance determinations using the Standardized Candle Method for Type II plateau supernovae, using a sample of 37 objects with BVRI photometry and optical spectroscopy obtained by them between 1986 and 2003. Using these data they implemented a procedure to fit analytic functions to the light curves, color and expansion velocity curves. Then they demonstrated that the V-I color toward the end of the plateau phase can be used as a good indicator of host-galaxy dust reddening and we recovered the luminosity-velocity relation previously published in the literature. Using this relation and assuming a standard reddening law they obtained Hubble diagrams with a dispersion of 0.4 mag in BVI. Leaving Rv as a free parameter it was found that the dispersion decreased to 0.25-0.30 mag, which implies that these objects can deliver distances with a precision of 12-14%. The resulting value for Rv was 1.4, which suggests a non-standard extinction law along the line of sight toward these supernovae.
In 2010, researchers of Area 6 began a new collaboration with the Araucaria Project group at U. de Concepción with the purpose of calibrating the luminosities of nearby supernova using Cepheid distances. The first result, published in 2010, is a paper reporting the distance modulus to NGC 7793 of 27.68 ± 0.05 mag (internal error) ± 0.08 mag (systematic error), which is the host galaxy to SN 2008bk. This Cepheid distance will allow them to calibrate the optical/near-infrared light curves obtained by us during the first two years of the evolution of SN 2008bk, a very interesting object similar to the sub-luminous Type II P SN 1999br.
2. TECHNOLOGICAL INNOVATION
CATA has supported several initiatives of its members at the different Associated Institutions concerning technological innovation. In what follows we provide in detail the work and progress made during this period in the three main technological initiatives.
AREA 7: Astronomical Instrumentation
P.I.: Leonardo Bronfman
ALMA BAND 1 PROTOTYPE RECEIVER CONSTRUCTION
The foundational project of CATA in Astronomical Instrumentation is to develop an ALMA Band 1 receiver prototype and study the feasibility of producing 66 operational receivers for the ALMA Project, the largest array telescope in the world, consisting of 66 antennas, each housing 10 low-noise receivers in different bands between 31 and 950 GHz. The Band 1 receiver, covering the 31.3 - 45 GHz range, is being developed at the Millimeter-Wave Laboratory of the Astronomy Department, in collaboration with the Electrical Engineering Department, both at the Universidad de Chile. The Band 1 receiver is a dual polarization Single Sideband SSB receiver. The noise temperature is aimed to be 17 K over the central part of the band. The IF output covers from 4 to 12 GHz with a power variation less than 6 dB. The RF signal is coupled into the receiver by a horn and a lens. Two filters prevent IR radiation to heat the optics. After the horn the signal is split, by an OMT, into two signals with perpendicular linear polarizations, each processed by separate receiver chains driven by the same LO. In the first stage the signal is amplified by a cryogenic LNA, with 30-35 dB of gain. A compact isolator between the LNA and the down-conversion system permits a relaxed specification for the output return loss of the amplifier. Before the mixer a high pass filter cancels the image frequency, having in this way an upper sideband (USB) conversion scheme. The down conversion process is carried out by a commercial Schottky mixer. Finally, the IF signal is amplified by an LNA at room temperature
In 2008 Dr. Patricio Mena, formerly at SRON, was hired by the Electrical Engineering Department as Assistant Professor, and became involved in the project. Two major pieces of equipment were purchased to set up the Millimeter-wave Laboratory at the National Astronomical Observatory in Cerro Calán; a high sensitivity Vector Network Analyzer and a high-precision Computer Numerically Controlled (CNC) Drilling and Milling Machine. A preliminary design of the receiver was produced, and electromagnetic modeling of several parts was carried out. A mechanical technician, José Pizarro, was hired and trained. A preliminary physical layout of the receiver was completed in 2009 and the key components specified. Construction of key optic components was carried out in the laboratory machine-shop, including the receiver feed horn and the Ortho Mode Transducer (OMT). A beam scanner for measuring the horn pattern was built and implemented. A first Low Noise Amplifier (LNA), based on commercial GaAs chips was designed, built, and tested at the laboratory.
Cryogenic capabilities were set up in 2010. A NAOJ Cryostat (for ALMA cartridges testing) was set to work, and a CBI Cryostat was modified for component testing. The horn was successfully characterized using our beam scanner; the OMT design was improved; a series of LNAs based on MMIC was produced improving our knowledge of the fabrication process. The optical design was completed and an analysis of the different alternatives was done in collaboration with HIA. For the design of the complete receiver, the internal dimensions of the main components were defined, allowing a detailed design of the receiver.
Status of the Receiver Prototype.
OMT: The OMT was designed following a model by H. Asayama which has been successfully used in ALMA bands 4, 5 and 8 receivers. After several iterations an improved and final version was obtained. The measurements for transmissions and reflections corroborate that this design achieves ALMA specs regarding cross-polarization and crosstalk. We fabricated a second version of the OMT to test reproducibility of fabrication. Both OMTs present similar performance.
Horn: We designed a spline-line corrugated horn and constructed using a split-block technique. The near-field beam-pattern setup has been improved and used to obtain a final test of the horn. These results were published in our first ISI article.
Lens: A theoretical analysis of the quasi optical beam propagation between the secondary mirror, lens, filters and horn was completed. A first version of the lens was designed at the lab; then machined at the University of Koln; and finally tested successfully at the lab. A second version will incorporate an antireflection pattern in its design, and measurements are underway to refine the models.
Amplification and down conversion
LNA: Preliminary calculations indicate that the optics will have a contribution of around 7K above the noise temperature of the receiver. Considering this, the specification for the LNA is a noise temperature of 17 K over 80% of the band. This noise specification is comparable with the state of the art Q Band LNAs, but Band 1 has a wider bandwidth (36% instead of 20 % of the central frequency). A review of the specifications for Band 1 and some proposed technologies were presented in international meetings. We have finalized our initial project, packaging commercial MMICs amplifiers, with 3 amplifiers characterized. Gold plating of the final unit was achieved in association with local industry. To reach the specifications of ALMA Band 1, we have focused on the design of hybrid amplifiers based on InP transistors (obtained from JPL-CalTech), which promise to achieve state-of-the-art performance. While a lot of effort has been done to realize this design, more work is required to achieve this implementation. The main hinder is the construction of the waveguide-to-stripline transitions, as both the technology and the materials for these frequencies are novel in Chile. We have learned several lessons and are implementing them in a second version of the amplifier packaging. The new version will use a different substrate material for the waveguide-to-stripline transitions, namely Si instead of Cuflon, that has already been ordered to a US company.
Isolators: The use of isolators is indispensable. We identified a company that provided four isolators, optimized for low-temperature operation. These isolators have been characterized in the component test set-up, giving acceptable results.
Mixers: A commercial mixer has already been purchased and tested. While its performance is marginal for the project, it can be used in the first prototype. In the meanwhile we have identified other commercial options that will be purchased and tested next year.
Lens and Horn: The horn and lens were mounted and tested in our beam-pattern setup. The results validate the original design, the only remaining issue being the antireflection pattern.
Mechanical and Electrical Assembly: The first mechanical design is completed (Fig. 4). The support structure (namely the ALMA blank cartridge) has been built in collaboration with a local company. The commercial elements, like DC bias connectors, RF feed-through connectors, and temperature sensors, have been purchased; the electrostatic discharge protection (ESD) card is being designed and will be built at DIE; and the full assembly will begin in Q1 2012.
Cartridge Optical/Cryogenic Test Setup
The ALMA cryostat purchased from NAOJ is performing to specifications in the lab. An adapter to incorporate the lens in the cryostat was designed in house and built by a local company. The cryostat, adapter and lens were successfully assembled, and no vacuum leaks were found. The heat filters at the different cryogenic shields have been already procured and will be mounted soon. An engineer was hired to implement the optical/cryogenic test setup to characterize the receiver mounted in the NAOJ cryostat. Fully compatible control electronics were purchased from NRAO, allowing measurement to be performed in an ALMA compatible environment.
The goal for 2012 is to mount the first receiver and test its performance in the laboratory. This will require finalizing all the described sub projects. The LNA design is the only component that might need more time to achieve the ALMA specifications. The first receiver will be tested preliminary using the already built MMIC amplifiers, to test the complete receiver and its components. The work on LNA will continue during next year and probably beyond, as it is still an open field of research.
In summary, the prototype development is well underway. During this year, we aim to have a receiver cold cartridge assembly (CCA) unit operating at the laboratory, with its optical and electrical properties characterized with an in-house cryogenic set-up. The process is requiring lots of research, laboratory development, and mastering of several technologies that are new in the country. We have been particularly successful in the development of the receiver optics, presently up to ALMA standards, and our anechoic chamber is a unique facility in the country. The design of the cartridge is ready. Several parts, including the blank cartridge assembly (support structure) are built, while mounting and wiring is ongoing. The cryogenic test set up to characterize the receiver at cold temperature is designed and an engineer is working in its implementation.
One of the most important technologies, low noise amplifiers, is still developing world wide to meet the specifications from ALMA. Our strategy is to characterize and pack high performance transistors from CALTECH –JPL into an amplifier at the laboratory. We have preliminary packed commercial components, and realized that it requires mastering intermediate techniques, each with specific timescales, which could indeed be improved with the addition of new equipment.
Based on the work already executed, we should be able to study the feasibility of producing the full suit of receivers in Chile. Crucial for this is to evaluate what has to be outsourced to local industry and whether it is possible for industry to meet the challenge. The Continuity plan for CATA should therefore contain the description of the prototype plus a feasibility study for production, including the interaction with technology providers and local industry. An important goal for the second period of Basal would be the transfer of technology.
While the design of our prototype is ready according to ALMA specs; the CCA is under construction and should be ready by 2012; and a state-of-the-art LNA construction should materialize via our collaboration with Yebes, the astronomical requirements for the receiver are being re discussed by the ALMA community to raise the upper limit of the Band 1 up to 50 GHz. While not fully decided, inclusion of such frequency extension in our design would certainly increase our ability to be considered as a suitable provider. Two years of development are estimated to accommodate the extension. This is also about the time needed to build the WCA (warm cartridge assembly), with the goal of producing a fully operational ALMA receiver by the end of 2014, and be ready for pre-production of more units. It is roughly the time scale for maturing of the ALMA development plan, and to start planning construction of a full suite of Band 1 receivers.
AREA 8: High performance computing
P.I.: Alejandro Clocchiatti
The Computing Lab (CL) of the Center for Astro-Engineering (AIUC) at Campus San Joaquin of Pontificia Universidad Catolica de Chile (PUC) started as a concept by the turn of the century. This was motivated in part by the projects of wide angle survey telescopes that were going to be installed in Chile, with the promise of delivering very massive amounts of data, and in part by the need of theoretical astrophysicists who require massive computational power to model a given survey, or the evolution of astrophysical objects. The concept started to become a reality with the approval of CONICYT Basal project CATA in December 2007, which invested 30% of its funds for large capital investment in the computer for the CL. This document is a description of the advancement of the project, the difficulties and successes within the period. In what follows, we will call the computer by its designated name: Geryon.
Putting Geryon to work involved several steps which involved identifying the appropriate machine, to buy it, to construct a computer room, install the machine, test operating and qeue systems, install the software suites, and to try and test-bench the computer. The first applications envisioned were both observational and theoretical, and the new computer immediately allowed us to enter scientific grade development and number crunching locally, experiment with queues and, finally, open the system to the whole community.
Putting the CL to work consisted on using Geryon to run software built by several consecutive generations of researchers, with contributions from our own people, taking advantage of the capabilities of the computer, and using this to motivate the connection between observational and computational astrophysicists with computer science specialists, and to develop new software for theoretical and observational research. This required, in addition to the computer, a focus on hiring Computer Scientists with interest in Astronomical applications and establishing the necessary collaborations.
As a result, the CL has already acted as a consultant for the computing industry in Chile. The experience developed by the engineers and technicians that set up Geryon has been required by other public and private institutions that were following our steps. Therefore, in addition to providing a unique computing service to the astronomical community, the CL has contributed to capacity building within the Chilean academia and industry.
First steps: Purchase and Installation of Geryon
This computer was the first piece of equipment in its price category acquired for Chilean astronomy. Following the guidelines for the grant, we opened a call for bids in October 2008 after we were transferred the funds. To do this we defined the profile of the system we required. A strategic decision was to stay with the hardware we had in our pre-Geryon machine (with 24 Quad Core Intel Xeon 2.0 GHz processors). We proposed to purchase 96 CPUs, each 4 cores, each core with 1GB of RAM, for a total of 384 GB of RAM, 13 TB of iSCSI disk, three 10 KVA UPSs, Gigabit Ethernet equipment and a 19" rack. To facilitate the bidding, and give room for more companies to enter the call, we divided the purchase in three packages that could be proposed for independently:
CPU's, network equipment, casing, cables and accessories.
3x10 KVA UPSs.
iSCSI Disk of 13 TB.
We received the equipment in March 2009, which was installed by April 2009 in a temporary computer room. In May we started trials on the base of an open source Linux OS with 64-bit architecture. Pretty soon the machine was equipped with the required tools: Intel FORTRAN and C compilers, a Distributed Resource Management suite, and the Sun Grid Engine. In June, Geryon started operations. At the time, it was the most powerful machine for exclusive astrophysical use in Latin-America.
The new building for the AIUC and the CL was finished in February of 2010. Additional funding from the Departamento de Astronomia y Astrofisica of PUC allowed us to purchase a professional grade AC system and an additional power transformer to warrant a safe power supply for the machine. Geryon was fully installed in its definite place by April 2010. The event was celebrated with a workshop “Supercomputer Techniques in Astrophysics,” which brought many specialists from around the world to our campus.
During the following months the system was tested thouroughly, and several small grants from different researchers were joined to achieve the expansion of the memory to the necessary 1TB of RAM for a total of 2Gb per core. The computer power of the system was 2 TFLOPS.
By the second semester of 2010 we announced the opening of the system to the whole Chilean astronomical community. A protocol was established to access the resource and from this point, the prospective users submit their requests for time according with instructions available on the web, and using a downloadable LaTeX form. For runs that require more than 6000 core hours per month, a local TAC evaluates the request within 10 working days. These jobs are scheduled in special blocks during the nights and weekends whereas smaller jobs are run freely in the remaining cores. Geryon has been continuously upgraded. Different projects and users contributed in a coordinated way different pieces of hardware. The system now has a front-end of 64 bits, a hard drive of 4 TB for users and their accounts, 40 TB of iSCSI disks, and ~ 60 TB of other disks for special projects.
In summary, CATA was successful in establishing the CL area as a community resource. The CL now hosts Geryon and some other independent (smaller) machines which are ran by the same technical team. Several lines of science have already been developed with Geryon. Many of them fall within the original lines of the project, and new ones arised as the result of new scientific drives which are now possible thanks to the available computing power. Four students have already gotten their Ph.D. with work based mainly, or significantly, on Geryon. All of them accepted postdoctoral positions abroad. At present, several students at different levels are intensively using Geryon.
Given that the computing power of new computers already outrun the individual CPUs in Geryon, we put in a grant proposal to purchase a major piece of equipment in November 2011, which was awarded by the end of the year. With these funds we will be able to buy a new system which will represent a 10 fold increase with respect to our present capabilities. A challenge for Chilean astronomers is to be able to use the first world instrumentation we have access to, and this means matching resources for analysis and modeling. CATA CL is a proof that we can do it.
3. FORMATION OF HUMAN RESOURCES
3.1 Graduate students
CATA is strongly and continuously supporting the formation of human resources in astrophysics in all of the Astronomy programs in the country. During the last four years the number of graduate astronomy students at the three institutions associated to the Center experienced a considerable growth. In the four year of operation (2011) there were fourty nine (49) Ph.D. students in astronomy and thirty three (33) students in Master's in Astrophysics programs, with a total of 82 graduate students. Most of the graduate students have taken advantage of the Center by being granted funds in order to participate in observing runs at the International Observatories in Chile and/or to attend international meetings. In addition the Center has given full fellowships to more than sixty of the graduate students.
The Key projects are having a big impact on the graduate programs since they broadened the range of thesis topics and giving the students the possibility of engaging in first-class frontier research. In fact more than fifty percent of the graduate and undergraduate students have worked or are working in individual science projects associated with Key Projects. During the four years of operation twenty three (23) students obtained Ph.D. degrees and thirty four (34) students obtained Master degrees. Most of the later continued their high learning education at top North-American and European universities. In addition, a few dozen students obtained their undergraduates diploma (Licenciaturas).
In order to educate the new generation of astronomers, CATA continuously supported the delivery, at their associated Universities, of Mini-courses with the goal of training graduate students on specific topics. The Mini-courses consisted of five to ten lectures given in a period of 2-3 weeks, in order to allow the presence of invited lecturers from abroad, and were open to all graduate students of the different astronomy programs in the country.
3.2 Postdoctoral Fellows
The Center provided the funds and visibility necessary to attract young scientists from all over the world. Most of the postdoctoral positions were selected through international competitions, and we hired postdoctoral fellows from Argentina, Australia, Brazil, Bulgaria, Germany, Italy, Mexico, Poland, United Kingdom and USA. With the presence of these postdocs the CATA has gathered a real international team working at Chilean institutions. Postdoctoral fellows have been central to the success of the Key projects of the Center, which required lots of manpower in the experimental and analytical work.
3.3 Human Resources devoted to Research
CATA has allowed a substantial increase in the number of researchers and engineers working at all three Associated Universities. Fourteen (14) new researchers -- ten astronomers and four engineers -- have been hired with the Center support and received continuous support for their scientific activities. In the following we give the names of the new researchers, the year of incorporation to the Center, their areas of research and the University in which they were hired (UCH: Universidad de Chile, PUC: Pontificia Universidad Catolica, UdC: Universidad de Concepcion) :
Escala, Andrés 2008 Theoretical Astrophysics, Black Hole Mergers, Star formation UCH
Jordán, Andrés 2008 Early-type galaxies and their globular cluster systems PUC
Mena, Patricio 2008 Electrical Engineer UCH
Vanzi, Leonardo 2008 Engineer PUC
Altamirano, Pablo 2009 Engineer UCH
Bauer, Franz 2009 AGN Demographics; Super-Massive Black Holes PUC
Cuadra, Jorge 2009 Theoretical Astrophysics., Gas dynamics, Massive Black Holes PUC
Demarco, Ricardo 2009 Galaxy formation, Cluster of galaxies UdC
Dünner, Rolando 2010 Formation and evolution of super-clusters of galaxies PUC
Fellhauer, Michael 2009 Numerical simulations of stellar dynamics in galaxies UdC
Bustos, Ricardo 2010 Enginner UdC
Puzia, Thomas 2010 Star clusters, galaxy formation and chemical evolution PUC
Muñoz, Ricardo 2011 Evolution of dwarf galaxies and Galaxy interactions UCH
Treister, Ezequiel 2011 Active Galactic Nuclei UdC
The new faculty positions were made through international competitions, which attracted a large number of outstanding candidates from all over the world willing to come to Chile.
In addition, the Center supported selected researchers at other Universities in Chile in order to increase the scientific collaboration with their new astronomy groups. The Center provided them with funds for travel and expansion of human resources, in particular for the hiring of postdoctoral fellows with research interests close to those of the Key projects. S. Sharma and R. Muñoz were hired at Universidad de Valparaiso and G. Gunthardt and M. Soto were hired at Universidad de La Serena. The researchers from other Universities that became associated to the Center are:
Rodolfo Barba, Universidad de La Serena
Jura Borissova, Universidad de Valparaiso
Veronica Motta, Universidad de Valparaíso
Giuliano Pignata, Universidad Andres Bello
Matthias Schrieber Universidad de Valparaiso
4. NATIONAL AND INTERNATIONAL COLLABORATION
In this section we briefly specify the activities conducted by CATA during the 4 years of operation that contributed to the networking at National and International levels, and at Institutional and personal levels.
Collaboration among Center members of the three participating institutions have taken place in all the areas of research, amply fulfilling one the scientific goals of the Center. The Center Key Projects, which were implemented to foster collaborations between researchers of the different astronomy sites within the country, developed quite successfully. They received considerable amounts of telescope time, allowing Center members to carry out scientific projects that were beyond the scope of small research groups. The most emblematic Key Projects with respect to collaborations, involving more than 10 researchers from the three associated Universities, are the MUltiwavelength Survey by Yale-Chile (MUSYC) and the Vista Variables in the Via Lactea Survey (VVV).
Thirty percent of the refereed papers that were published during the ten year period have two or more Center members as co-authors. The scientific collaborations between Center members increased continuously in time and have produced results of considerable impact. The degree of collaborations, measured from published ISI papers, increased from nine eight (98) during the first year of operation to a value of two hundred and fourteen (214) during the fourth year of operation, indicating that joint work has more than double during the period.
In particular, there are numerous collaborative contributions between researchers of Areas 2 and 3, including the work on chemical abundances of Milky Way Cepheids which helped to measure the metallicity gradient in the MW disk, the first determination of the element abundance gradient in the disk of a spiral galaxy beyond the Milky Way using blue supergiant stars in NGC 300, and the first empirical demonstration of strong population effects in red clump stars in optical bands. Another example of synergy, involving researchers of Areas 3 and 6, is the Cepheid distance determination to the Sculptor Group spiral galaxy NGC 7793 which hosted SN 2008bk. The synergy was also strong between researchers of Area 5 and researchers of Area 2 and Area 3, with common publications taking advantage of similar techniques (e.g. precision photometry, optical spectroscopy). Another example of synergy is the on going project of characterisation of extrasolar planetary transit candidates, involving scientists from the three associated Universities.
The Center also invited world experts on different astrophysical topics. The contribution of the visiting scientists has been remarkable, supplying the expertise needed for an expansion and broadening of the areas of research cultivated at the Center, and providing the theoretical support needed in the young Ph.D. programs. They usually give concentrated courses, during periods of 3 to 6 weeks.