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Garcia-Vargas M.L.,FRACTAL SLNE | Molla M.,CIEMAT | Martin-Manjon M.L.,Autonomous University of Madrid
Monthly Notices of the Royal Astronomical Society | Year: 2013

This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of single stellar populations resulting from our POPSTAR code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, Hα and Hβ luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z=0.0001-0.05) and age (0.1 Myr to 20 Gyr).We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated starforming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of POPSTAR spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as theHa radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Martin-Manjon M.L.,Autonomous University of Madrid | Garcia-Vargas M.L.,FRACTAL SLNE | Garcia-Vargas M.L.,Institute of Astrophysics of Canarias | Molla M.,CIEMAT | Diaz A.I.,Autonomous University of Madrid
Monthly Notices of the Royal Astronomical Society | Year: 2010

This is the second paper of a series reporting the results from the popstar evolutionary synthesis models. Here, we present synthetic emission-line spectra of H ii regions photoionized by young star clusters, for seven values of cluster masses and for ages between 0.1 and 5.2 Myr. The ionizing spectral energy distributions (SEDs) are those obtained by the popstar code for six different metallicities, with a very low-metallicity set,Z = 0.0001, not included in previous similar works. We assume that the radius of the H ii region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster. In this way, the ionization parameter is eliminated as free argument, since now its value is obtained from the cluster physical properties (mass, age and metallicity) and from the gaseous medium characteristics (density and abundances). We discuss our results and compare them with those from previous models and also with a large data set of giant H ii regions for which abundances have been derived in a homogeneous manner. The values of the [O iii] lines (at λλ 4363, 4959, 5007 Å) in the lowest metallicity nebulae are found to be very weak and similar to those coming from very high-metallicity regions (solar or oversolar). Thus, the sole use of the oxygen lines is not enough to distinguish between very low and very high metallicity regions. In these cases, we emphasize the need of the additional support of alternative metallicity tracers, like the [S iii] lines in the near-infrared. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Sanchez-Janssen R.,European Southern Observatory | Amorin R.,Institute Astrofisica Of Andalucia Csic | Garcia-Vargas M.,FRACTAL SLNE | Gomes J.M.,University of Porto | And 10 more authors.
Astronomy and Astrophysics | Year: 2013

Context. Even though they are by far the most abundant of all galaxy types, the detailed properties of dwarf galaxies are still only poorly characterised-especially because of the observational challenge that their intrinsic faintness and weak clustering properties represent. Aims. AVOCADO aims at establishing firm conclusions on the formation and evolution of dwarf galaxies by constructing and analysing a homogeneous, multiwavelength dataset for a statistically significant sample of approximately 6500 nearby dwarfs (Mi-5 log h100 >-18 mag). The sample is selected to lie within the 20 < D < 60 h100 -1 Mpc volume covered by the SDSS-DR7 footprint, and is thus volume-limited for Mi-5 log h100 <-16 mag dwarfs-but includes ≈1500 fainter systems. We will investigate the roles of mass and environment in determining the current properties of the different dwarf morphological types-including their structure, their star formation activity, their chemical enrichment history, and a breakdown of their stellar, dust, and gas content. Methods. We present the sample selection criteria and describe the suite of analysis tools, some of them developed in the framework of the Virtual Observatory. We use optical spectra and UV-to-NIR imaging of the dwarf sample to derive star formation rates, stellar masses, ages, and metallicities-which are supplemented with structural parameters that are used to classify them morphologically. This unique dataset, coupled with a detailed characterisation of each dwarf's environment, allows for a fully comprehensive investigation of their origins and enables us to track the (potential) evolutionary paths between the different dwarf types. Results. We characterise the local environment of all dwarfs in our sample, paying special attention to trends with current star formation activity. We find that virtually all quiescent dwarfs are located in the vicinity (projected distances ≤ 1.5 h100 -1 Mpc) of a≥ L* companions, consistent with recent results. While star-forming dwarfs are preferentially found at separations of the order of 1 h100 -1 Mpc, there appears to be a tail towards low separations (≤ 100 h100 -1 kpc) in the distribution of projected distances. We speculate that, modulo projection effects, this probably represents a genuine population of late-type dwarfs caught upon first infall about their host and before environmental quenching has fully operated. In this context, these results suggest that internal mechanisms-such as gas exhaustion via star formation or feedback effects-are not sufficient to completely cease the star formation activity in dwarf galaxies, and that becoming the satellite of a massive central galaxy appears to be a necessary condition to create a quiescent dwarf. © 2013 ESO. Source

Castillo-Dominguez E.,National Institute of Astrophysics, Optics and Electronics | Ferrusca Rodriguez D.,National Institute of Astrophysics, Optics and Electronics | Tulloch S.,FRACTAL SLNE | Velazquez M.,National Institute of Astrophysics, Optics and Electronics | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the new integral field unit (IFU) and multi-object spectrograph (MOS) instrument for the GTC. The spectrograph subsystems include the pseudo-slit, the shutter, the collimator with a focusing mechanism, pupil elements on a volume phase holographic grating (VPH) wheel and the camera joined to the cryostat through the last lens, with a CCD detector inside. In this paper we describe the full preliminary design of the cryostat which will harbor the CCD detector for the spectrograph. The selected cryogenic device is an LN2 open-cycle cryostat which has been designed by the "Astronomical Instrumentation Lab for Millimeter Wavelengths" at INAOE. A complete description of the cryostat main body and CCD head is presented as well as all the vacuum and temperature sub-systems to operate it. The CCD is surrounded by a radiation shield to improve its performance and is placed in a custom made mechanical mounting which will allow physical adjustments for alignment with the spectrograph camera. The 4k x 4k pixel CCD231 is our selection for the cryogenically cooled detector of MEGARA. The characteristics of this CCD, the internal cryostat cabling and CCD controller hardware are discussed. Finally, static structural finite element modeling and thermal analysis results are shown to validate the cryostat model. © 2012 SPIE. Source

Tulloch S.,FRACTAL SLNE | Gil De Paz A.,Complutense University of Madrid | Gallego J.,Complutense University of Madrid | Zamorano J.,Complutense University of Madrid | Tapia C.,Complutense University of Madrid
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

A CCD test-bench has been built at the Universidad Complutense's LICA laboratory. It is initially intended for commissioning of the MEGARA1 (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) instrument but can be considered as a general purpose scientific CCD test-bench. The test-bench uses an incandescent broad-band light source in combination with a monochromator and two filter wheels to provide programmable narrow-band illumination across the visible band. Light from the monochromator can be directed to an integrating sphere for flat-field measurements or sent via a small aperture directly onto the CCD under test for high accuracy diode-mode quantum efficiency measurements. Point spread function measurements can also be performed by interposing additional optics between sphere and the CCD under test. The whole system is under LabView control via a clickable GUI. Automated measurement scans of quantum efficiency can be performed requiring only that the user replace the CCD under test with a calibrated photodiode after each measurement run. A 20cm diameter cryostat with a 10cm window and Brooks Polycold PCC closed-cycle cooler also form part of the test-bench. This cryostat is large enough to accommodate almost all scientific CCD formats has initially been used to house an E2V CCD230 in order to fully prove the test-bench functionality. This device is read-out using an Astronomical Research Camera controller connected to the UKATC's UCAM data acquisition system. © 2012 SPIE. Source

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