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Hernandez-Rojas J.,University La LagunaTenerife | Wales D.J.,University of Cambridge
Chemical Physics | Year: 2014

We investigate the structural predictions obtained using new force fields for rigid water models proposed recently (Nicolini et al., 2013) for (H2O)n clusters. These new force fields are characterized by dispersion damping functions. The putative global minima of these new models up to n<21 are obtained using basin-hopping global optimization technique and compared with previous results for the TIP4P potential and with ab initio calculations. The new models often give different morphologies, and generally exhibit fewer hydrogen bonds, and will require reparameterization if they are to be used for clusters. © 2014 Elsevier B.V. All rights reserved. Source

Calzetti D.,University of Massachusetts Amherst | Lee J.C.,US Space Telescope Science Institute | Lee J.C.,California Institute of Technology | Sabbi E.,US Space Telescope Science Institute | And 54 more authors.
Astronomical Journal | Year: 2015

The Legacy ExtraGalactic UV Survey (LEGUS) is a Cycle 21 Treasury program on the Hubble Space Telescope aimed at the investigation of star formation and its relation with galactic environment in nearby galaxies, from the scales of individual stars to those of ∼kiloparsec-size clustered structures. Five-band imaging from the nearultraviolet to the I band with the Wide-Field Camera 3 (WFC3), plus parallel optical imaging with the Advanced Camera for Surveys (ACS), is being collected for selected pointings of 50 galaxies within the local 12 Mpc. The filters used for the observations with the WFC3 are F275W (λ2704 A˚), F336W(λ3355 A˚), F438W(λ4325 A˚), F555W(λ5308 A˚), and F814W(ë8024 A˚); the parallel observations with the ACS use the filters F435W (λ4328 A˚), F606W(λ5921 A˚), and F814W(λ8057 A˚). The multiband images are yielding accurate recent (≲50 Myr) star formation histories from resolved massive stars and the extinction-corrected ages and masses of star clusters and associations. The extensive inventories of massive stars and clustered systems will be used to investigate the spatial and temporal evolution of star formation within galaxies. This will, in turn, inform theories of galaxy evolution and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of star formation at high redshift. This paper describes the survey, its goals and observational strategy, and the initial scientific results. Because LEGUS will provide a reference survey and a foundation for future observations with the James Webb Space Telescope and with ALMA, a large number of data products are planned for delivery to the community. © 2015. The American Astronomical Society. All rights reserved. Source

Martin N.F.,University of Strasbourg | Martin N.F.,Max Planck Institute for Astronomy | Nidever D.L.,University of Michigan | Besla G.,University of Arizona | And 34 more authors.
Astrophysical Journal Letters | Year: 2015

We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data from the ongoing Survey of the Magellanic Stellar History conducted with the Dark Energy Camera on the Blanco 4 m Telescope. The new satellite is compact (rh = 68 ± 11 pc) and faint (MV = -4.8 ± 0.3), but well within the realm of dwarf galaxies. The stellar distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric distance of 134 ± 10 kpc, Hydra II is located in a region of the Galactic halo that models have suggested may host material from the leading arm of the Magellanic Stream. A comparison with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite of the Magellanic Clouds. © 2015. The American Astronomical Society. All rights reserved. Source

Morales-Luis A.B.,Institute of Astrophysics of Canarias | Morales-Luis A.B.,University La LagunaTenerife | Perez-Montero E.,Institute Astrofisica Of Andalucia Csic | Sanchez Almeida J.,Institute of Astrophysics of Canarias | And 3 more authors.
Astrophysical Journal | Year: 2014

The N2 index ([NII] λ6584/Hα) is used to determine emission line galaxy metallicities at all redshifts, including high redshift, where galaxies tend to be metal-poor. The initial aim of this work was to improve the calibrations used to infer oxygen abundance from N2 by employing updated low-metallicity galaxy databases. We compare N2 and the metallicity determined using the direct method for the set of extremely metal-poor galaxies compiled by Morales-Luis et al. To our surprise, the oxygen abundance presents a tendency to be constant with N2, with a very large scatter. Consequently, we find that the existing N2 calibrators overestimate the oxygen abundance for most low-metallicity galaxies, and can therefore only be used to set upper limits to the true metallicity in low-metallicity galaxies. An explicit expression for this limit is given. In addition, we try to explain the observed scatter using photoionization models. It is mostly due to the different evolutionary state of the H II regions producing the emission lines, but it also arises due to differences in N/O among the galaxies. © 2014. The American Astronomical Society. All rights reserved. Source

Lahoz F.,University La LagunaTenerife | Martin I.R.,University La LagunaTenerife | Urgelles M.,University La LagunaTenerife | Marrero-Alonso J.,University La LagunaTenerife | And 4 more authors.
Laser Physics Letters | Year: 2015

We have demonstrated that chemically modified anticancer drugs can provide random laser (RL) when infiltrated in a biological tissue. A fluorescent biomarker has been covalently bound to tamoxifen, which is one of the most frequently used drugs for breast cancer therapy. The light emitted by the drug-dye composite is scattered in tissue, which acts as a gain medium. Both non-coherent and coherent RL regimes have been observed. Moreover, the analysis of power Fourier transforms of coherent RL spectra indicates that the tissues show a dominant random laser cavity length of about 18 μm, similar to the average size of single cells. These results show that RL could be obtained from other drugs, if properly marked with a fluorescent tag, which could be appealing for new forms of combined opto-chemical therapies. © 2015 Astro Ltd. Source

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