Author name code: sanchez-almeida ADS astronomy entries on 2022-09-14 author:"Sanchez Almeida, Jorge" ------------------------------------------------------------------------ Title: Discovery of Faint Double-peak Hα Emission in the Halo of Low Redshift Galaxies Authors: Sánchez Almeida, J.; Calhau, J.; Muñoz-Tuñón, C.; González-Morán, A. L.; Rodríguez-Espinosa, J. M. Bibcode: 2022ApJ...934..100S Altcode: 2022arXiv220512782S Aimed at the detection of cosmological gas being accreted onto galaxies in the local universe, we examined the Hα emission in the halo of 164 galaxies in the field of view of the Multi-Unit Spectroscopic Explorer Wide survey (MUSE-Wide) with observable Hα (redshift <0.42). An exhaustive screening of the corresponding Hα images led us to select 118 reliable Hα emitting gas clouds. The signals are faint, with a surface brightness of ${10}^{-17.3\pm 0.3}\,\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,{\mathrm{arcsec}}^{-2}$ . Through statistical tests and other arguments, we ruled out that they are created by instrumental artifacts, telluric line residuals, or high-redshift interlopers. Around 38% of the time, the Hα line profile shows a double peak with the drop in intensity at the rest frame of the central galaxy, and with a typical peak-to-peak separation of the order of ±200 km s-1. Most line emission clumps are spatially unresolved. The mass of emitting gas is estimated to be between 1 and 10-3 times the stellar mass of the central galaxy. The signals are not isotropically distributed; their azimuth tends to be aligned with the major axis of the corresponding galaxy. The distances to the central galaxies are not random either. The counts drop at a distance >50 galaxy radii, which roughly corresponds to the virial radius of the central galaxy. We explore several physical scenarios to explain this Hα emission, among which accretion disks around rogue intermediate-mass black holes fit the observations best. Title: The Principle of Maximum Entropy and the Distribution of Mass in Galaxies Authors: Sánchez Almeida, Jorge Bibcode: 2022Univ....8..214S Altcode: 2022arXiv220304150S We do not have a final answer to the question of why galaxies choose a particular internal mass distribution. Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time, and the fact that the mass distribution maximizing the classical Boltzmann–Gibbs entropy is unphysical. These arguments are questionable. In particular, when the Tsallis entropy that describes self-gravitating systems is used to define TE, the mass distributions that result (i.e., the polytropes) are physically sensible. This work spells out this and other arguments for TE and presents the polytropes and their properties. It puts forward empirical evidence for the mass distribution observed in galaxies to be consistent with polytropes. It compares polytropes with Sérsic functions and it shows how the DM halos resulting from cosmological numerical simulations become polytropes when efficient collisions are allowed. It also discusses pathways to thermalization bypassing two-body collisions. It finally outlines future developments including deciphering whether or not DM particles collide efficiently. Title: Polarity-reversal subduction zone initiation triggered by buoyant plateau obstruction Authors: Almeida, J.; Riel, N.; Rosas, F. M.; Duarte, J. C.; Schellart, W. P. Bibcode: 2022E&PSL.57717195A Altcode: Oceanic lithosphere worldwide is younger than ca. 200 Myr, suggesting that it must have been globally recycled by the recurrent formation of new subduction zones since the existence of subduction on Earth. However, postulated subduction zone initiation processes remain difficult to explain in many cases, and the specific geodynamic conditions under which these might occur are still largely unknown. We here use numerical models driven by the internal force balance of a subduction system to better understand the (geo)dynamics governing (intra-oceanic) polarity-reversal subduction zone initiation. This initiation mode assumes that the birth of a new subduction zone could be triggered by buoyant plateau-obstruction of a pre-existent one dipping in the opposite direction. Our work provides a new insight on the key geodynamic conditions governing this type of subduction zone initiation and discusses their general compliance with known natural examples. Title: VizieR Online Data Catalog: MaNGA; parameters of 668 galaxies (Sanchez-Menguiano+, 2020) Authors: Sanchez-Menguiano, L.; Almeida, J. S.; Munoz-Tunon, C.; Sanchez, S. F. Bibcode: 2022yCat..19030052S Altcode: Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an ongoing part of the fourth-generation Sloan Digital Sky Survey (SDSS-IV). The data were collected using the BOSS spectrographs mounted on the Sloan 2.5m telescope at Apache Point Observatory. The field of view (FoV) of the instrument varies from 125 to 325 in diameter for the five different hexagonal configurations displayed by the 17 simultaneous bundles of fibers. The covered wavelength range spans 3600-10300Å, with a nominal resolution of R~2100 at 6000Å.

(1 data file). Title: Physically Motivated Fit to Mass Surface Density Profiles Observed in Galaxies Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio; Plastino, Angel R. Bibcode: 2021ApJ...921..125S Altcode: 2021arXiv210902615S Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ~750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ( $7\lt {\rm{log}}[{M}_{\star }/{{\rm{M}}}_{\odot }]\lt 12$ ). The propol fits are systematically better than Sérsic profiles when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\lesssim 9$ and systematically worse when ${\rm{log}}({M}_{\star }/{{\rm{M}}}_{\odot })\gtrsim 10$ . Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies. Title: The Mass-Metallicity Relation at z 1-2 and Its Dependence on the Star Formation Rate Authors: Henry, Alaina; Rafelski, Marc; Sunnquist, Ben; Pirzkal, Norbert; Pacifici, Camilla; Atek, Hakim; Bagley, Micaela; Baronchelli, Ivano; Barro, Guillermo; Bunker, Andrew J.; Colbert, James; Dai, Y. Sophia; Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Finkelstein, Steven; Kocevski, Dale; Koekemoer, Anton; Malkan, Matthew; Martin, Crystal L.; Mehta, Vihang; Pahl, Anthony; Papovich, Casey; Rutkowski, Michael; Sánchez Almeida, Jorge; Scarlata, Claudia; Snyder, Gregory; Teplitz, Harry Bibcode: 2021ApJ...919..143H Altcode: 2021arXiv210700672H We present a new measurement of the gas-phase mass-metallicity relation (MZR) and its dependence on star formation rates (SFRs) at 1.3 < z < 2.3. Our sample comprises 1056 galaxies with a mean redshift of z = 1.9, identified from the Hubble Space Telescope Wide Field Camera 3 (WFC3) grism spectroscopy in the Cosmic Assembly Near-infrared Deep Extragalactic Survey and the WFC3 Infrared Spectroscopic Parallel Survey. This sample is four times larger than previous metallicity surveys at z ~ 2 and reaches an order of magnitude lower in stellar mass (108 M). Using stacked spectra, we find that the MZR evolves by 0.3 dex relative to z ~ 0.1. Additionally, we identify a subset of 49 galaxies with high signal-to-noise (S/N) spectra and redshifts between 1.3 < z < 1.5, where Hα emission is observed along with [O III] and [O II]. With accurate measurements of SFR in these objects, we confirm the existence of a mass-metallicity-SFR (M-Z-SFR) relation at high redshifts. These galaxies show systematic differences from the local M-Z-SFR relation, which vary depending on the adopted measurement of the local relation. However, it remains difficult to ascertain whether these differences could be due to redshift evolution, as the local M-Z-SFR relation is poorly constrained at the masses and SFRs of our sample. Lastly, we reproduced our sample selection in the IllustrisTNG hydrodynamical simulation, demonstrating that our line flux limit lowers the normalization of the simulated MZR by 0.2 dex. We show that the M-Z-SFR relation in IllustrisTNG has an SFR dependence that is too steep by a factor of around 3. Title: History of the gas fuelling star formation in EAGLE galaxies Authors: Scholz-Díaz, Laura; Sánchez Almeida, Jorge; Dalla Vecchia, Claudio Bibcode: 2021MNRAS.505.4655S Altcode: 2021arXiv210602478S Theory predicts that cosmological gas accretion plays a fundamental role fuelling star formation in galaxies. However, a detailed description of the accretion process to be used when interpreting observations is still lacking. Using the state-of-the-art cosmological hydrodynamical simulation EAGLE, we work out the chemical inhomogeneities arising in the disc of galaxies due to the randomness of the accretion process. In low-mass systems and outskirts of massive galaxies, low metallicity regions are associated with enhanced star-formation, a trend that reverses in the centres of massive galaxies. These predictions agree with the relation between surface density of star formation rate and metallicity observed in the local spiral galaxies from the MaNGA survey. Then, we analyse the origin of the gas that produce stars at two key epochs, z ≃ 0 and z ≃ 2. The main contribution comes from gas already in the galaxy about 1 Gyr before stars are formed, with a share from external gas that is larger at high redshift. The accreted gas may come from major and minor mergers, but also as gravitationally unbound gas and from mergers with dark galaxies (i.e. haloes where more than 95 per cent of the baryon mass is in gas). We give the relative contribution of these sources of gas as a function of stellar mass (8 ≤ log [M/M] ≤ 11). Even at z = 0, some low-mass galaxies form a significant fraction of their total stellar mass during the last Gyr from mergers with dark galaxies. Title: Extreme emission-line galaxies in SDSS - I. Empirical and model-based calibrations of chemical abundances Authors: Pérez-Montero, E.; Amorín, R.; Sánchez Almeida, J.; Vílchez, J. M.; García-Benito, R.; Kehrig, C. Bibcode: 2021MNRAS.504.1237P Altcode: 2021arXiv210310464P; 2021MNRAS.tmp..891P Local star-forming galaxies show properties that are thought to differ from galaxies in the early Universe. Among them, the ionizing stellar populations and the gas geometry make the recipes designed to derive chemical abundances from nebular emission lines to differ from those calibrated in the Local Universe. A sample of 1969 extreme emission-line galaxies (EELGs) at a redshift 0 ≲ z ≲ 0.49, selected from the Sloan Digital Sky Survey (SDSS) to be local analogues of high-redshift galaxies, was used to analyse their most prominent emission lines and to derive total oxygen abundances and nitrogen-to-oxygen ratios following the direct method in the ranges 7.7 < 12 + log(O/H) < 8.6 and -1.8 < log(N/O) < -0.8. They allow us to obtain new empirically calibrated strong-line methods and to evaluate other recipes based on photoionization models that can be later used for a chemical analysis of actively star-forming galaxies in very early stages of galaxy evolution. Our new relations are in agreement with others found for smaller samples of objects at higher redshifts. When compared with other relations calibrated in the local Universe, they differ when the employed strong-line ratio depends on the hardness of the ionizing radiation, such as O32 or Ne3O2, but they do not when the main dependence is on the ionization parameter, such as S23. In the case of strong-line ratios depending on [N II] lines, the derivation of O/H becomes very uncertain due to the very high N/O values derived in this sample, above all in the low-metallicity regime. Finally, we adapt the Bayesian-like code H II-CHI-MISTRY for the conditions found in this kind of galaxies and we prove that it can be used to derive within errors both O/H and N/O, in consistency with the direct method. Title: Numerical simulations of dark matter haloes produce polytropic central cores when reaching thermodynamic equilibrium Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio Bibcode: 2021MNRAS.504.2832S Altcode: 2021arXiv210408055S; 2021MNRAS.tmp.1088S; 2021MNRAS.tmp.1088A Self-gravitating astronomical objects often show a central plateau in the density profile (core) whose physical origin is hotly debated. Cores are theoretically expected in N-body systems of maximum entropy, however, they are not present in the canonical N-body numerical simulations of cold dark matter (CDM). Our work shows that despite this apparent contradiction between theory and numerical simulations, they are fully consistent. Simply put, cores are characteristic of systems in thermodynamic equilibrium, but thermalizing collisions are purposely suppressed in CDM simulations. When collisions are allowed, N-body numerical simulations develop cored density profiles, in perfect agreement with the theoretical expectation. We compare theory and two types of numerical simulations: (1) when DM particles are self-interacting (SIDM) with enough cross-section, then the effective two-body relaxation time-scale becomes shorter than the Hubble time resulting in cored DM haloes. The haloes thus obtained, with masses from dwarf galaxies to galaxy clusters, collapse to a single shape after normalization, and this shape agrees with the polytropic density profile theoretically expected. (2) The inner radii in canonical N-body numerical simulations are always discarded because the use of finite-mass DM particles artificially increases the two-body collision rate. We show that the discarded radii develop cores which are larger than the employed numerical softening and have polytropic shape independently of halo mass. Our work suggests that the presence of cores in simulated (or observed) density profiles can used as evidence for systems in thermodynamic equilibrium. Title: Models source code: CE-QUAL-W2 v3.6, FLake (windows version 1.0), Hostetler and ANN (momentum alg.) - Modeling reservoir surface temperatures for regional and global climate models Authors: Almeida Bibcode: 2021zndo...4803480A Altcode: The source code of the following models: CE-QUAL-W2 V3.6 (Cole and Wells, 2008); FLake model - windows pre-compiled version 1.0 (Mironov et al., 2010); Artificial neural network (Momentum algorithm) and Hostetler model (Hostetler and Bartlein, 1990), was used during the development of the study titled “Modeling reservoir surface temperatures for regional and global climate models: a multi-model study on the inflow and level variation effects”. Title: Evidence for the Accretion of Gas in Star-forming Galaxies: High N/O Abundances in Regions of Anomalously Low Metallicity Authors: Luo, Yuanze; Heckman, Timothy; Hwang, Hsiang-Chih; Rowlands, Kate; Sánchez-Menguiano, Laura; Riffel, Rogério; Bizyaev, Dmitry; Andrews, Brett H.; Fernández-Trincado, José G.; Drory, Niv; Sánchez Almeida, Jorge; Maiolino, Roberto; Lane, Richard R.; Argudo-Fernández, Maria Bibcode: 2021ApJ...908..183L Altcode: 2020arXiv201204073L While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to search for evidence of accretion imprinted in the chemical composition of the interstellar medium. We measure both the O/H and N/O abundance ratios in regions previously identified as having anomalously low values of O/H. We show that the unusual locations of these regions in the N/O versus O/H plane indicate that they have been created through the mixing of disk gas having higher metallicity with accreted gas having lower metallicity. Taken together with previous analysis on these anomalously low-metallicity regions, these results imply that accretion of metal-poor gas can probably sustain star formation in present-day late-type galaxies. Title: VizieR Online Data Catalog: SFR & gas-phase metallicity in MaNGA gal. (Sanchez-Menguiano+, 2019) Authors: Sanchez-Menguiano, L.; Sanchez Almeida, J.; Munoz-Tunon, C.; Sanchez, S. F.; Filho, M.; Hwang, H. -C.; Drory, N. Bibcode: 2021yCat..18820009S Altcode: Mapping Nearby Galaxies at Apache Point Observatory (MaNGA; Bundy+ 2015ApJ...798....7B) is an ongoing survey developed as part of the SDSS-IV project.

The observations are conducted on the basis of an integral field unit (IFU) fiber system feeding the BOSS spectrographs on the Sloan 2.5m telescope at Apache Point Observatory, New Mexico. The field of view (FoV) of the instrument varies from 12.5" to 32.5" in diameter. The spectrographs provide wavelength coverage from 3600 to 10300Å, with a nominal resolution of R~2100 at 6000Å.

In this study, the analyzed sample is extracted from the internal release MaNGA Product Launches 7 (MPL-7) comprising 4688 galaxies.

(1 data file). Title: VizieR Online Data Catalog: 3D shapes of extremely metal-poor galaxies (Putko+, 2019) Authors: Putko, J.; Sanchez Almeida, J.; Munoz-Tunon, C.; Asensio Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M. Bibcode: 2021yCat..18830010P Altcode: The galaxies used in our inference of 3D shape are from Sanchez Almeida+ (2016, J/ApJ/819/110), who mined the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS) in producing the largest published sample (195) of extremely metal-poor galaxies (XMPs) from a single survey.

(1 data file). Title: Direct multielement determination of Cd, Pb, Fe, and Mn in ground coffee samples using energy dispersive X-ray fluorescence spectrometry Authors: Almeida, Jorge S.; Meira, Lucilia A.; Oliveira, Maiara S.; Teixeira, Leonardo S. G. Bibcode: 2021XRS....50....2A Altcode: No abstract at ADS Title: Local and Global Gas Metallicity versus Stellar Age Relation in MaNGA Galaxies Authors: Sánchez-Menguiano, Laura; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Sánchez, Sebastián F. Bibcode: 2020ApJ...903...52S Altcode: 2020arXiv200914211S The search for new global scaling relations linking the physical properties of galaxies has a fundamental interest. Furthermore, their recovery from spatially resolved relations has been in the spotlight of integral field spectroscopy (IFS). In this study, we investigate the existence of global and local relations between stellar age (Age) and gas-phase metallicity (Zg). To this aim, we analyze IFS data for a sample of 736 star-forming disk galaxies from the MaNGA survey. We report a positive correlation between the global Zg and D(4000) (an indicator of stellar age), with a slope that decreases with increasing galaxy mass. Locally, a similar trend is found when analyzing the Zg and D(4000) of the star-forming regions, as well as the residuals resulting from removing the radial gradients of both parameters. The local laws have systematically smaller slopes than the global one. We ascribe this difference to random errors that cause the true slope of the Age-Zg relation to be systematically underestimated when performing a least-squares fitting. The explored relation is intimately linked with the already known relation between gas metallicity and star formation rate at fixed mass, both presenting a common physical origin. Title: The principle of maximum entropy explains the cores observed in the mass distribution of dwarf galaxies Authors: Sánchez Almeida, Jorge; Trujillo, Ignacio; Plastino, Angel Ricardo Bibcode: 2020A&A...642L..14S Altcode: 2020arXiv200908994S Cold dark matter (CDM) simulations predict a central cusp in the mass distribution of galaxies. This prediction is in stark contrast with observations of dwarf galaxies that show a central plateau or "core" in their density distribution. The proposed solutions to this core-cusp problem can be classified into two types. One invokes feedback mechanisms produced by the baryonic component of the galaxies and the other assumes that the properties of the dark matter particle depart from the CDM hypothesis. Here we propose an alternative yet complementary explanation. We argue that cores are unavoidable in the self-gravitating systems of maximum entropy that result from non-extensive statistical mechanics. Their structure follows from the Tsallis entropy, which is attributed to systems with long-range interactions. Strikingly, the mass density profiles predicted by such thermodynamic equilibrium match the observed cores without any adjustment or tuning. Thus, the principle of maximum Tsallis entropy explains the presence of cores in dwarf galaxies. Title: White Paper on MAAT@GTC Authors: Prada, Francisco; Content, Robert; Goobar, Ariel; Izzo, Luca; Pérez, Enrique; Agnello, Adriano; del Burgo, Carlos; Dhillon, Vik; Diego, José M.; Galbany, Lluis; García-Rojas, Jorge; Jones, David; Lawrence, Jon; Martín, Eduardo; Mediavilla, Evencio; Ángeles Pérez García, M.; Sánchez Almeida, Jorge; Acosta Pulido, José A.; López-Sánchez, Angel R.; Arribas, Santiago; Carrera, Francisco J.; Corral, Amalia; Domínguez, Inmaculada; Mateos, Silvia; Martínez Nuñez, Silvia; Villaver, Eva; Rosa Zapatero Osorio, María; Albertus, Conrado; Arrigoni Battaia, Fabrizio; Barrado, David; Bejar, Víctor J. S.; Boffin, Henri M. J.; Bouy, Herve; Burgasser, Adam; Esteban, Cesar; Lodieu, Nicolas; Morales Calderón, María; Pérez Garrido, Antonio; Rodríguez Gil, Pablo; Sagués Carracedo, Ana; Santander García, Miguel; Solano, Enrique; Torres, Manuel A. P.; Wesson, Roger Bibcode: 2020arXiv200701603P Altcode: MAAT is proposed as a visitor mirror-slicer optical system that will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio CANARIAS (GTC) the capability to perform Integral Field Spectroscopy (IFS) over a seeing-limited FoV 14.20''x10'' with a slice width of 0.303''. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6 times as compared to its 0.6'' wide long-slit. All the eleven OSIRIS grisms and volume-phase holographic gratings will be available to provide broad spectral coverage with moderate resolution (R=600 up to 4100) in the 3600 - 10000 Å wavelength range. MAAT unique observing capabilities will broaden its use to the needs of the GTC community to unveil the nature of most striking phenomena in the universe well beyond time-domain astronomy. The GTC equipped with OSIRIS+MAAT will also play a fundamental role in synergy with other facilities, some of them operating on the northern ORM at La Palma. This White Paper presents the different aspects of MAAT@GTC - including scientific and technical specifications, outstanding science cases, and an outline of the instrument concept. Title: Analysis of the galaxy size versus stellar mass relation Authors: Sánchez Almeida, J. Bibcode: 2020MNRAS.495...78S Altcode: 2020arXiv200409433S; 2020MNRAS.tmp.1268S The scatter in the galaxy size versus stellar mass (M) relation gets largely reduced when, rather than the half-mass radius Re, the size at a fixed surface density is used. Here, we address why this happens. We show how a reduction is to be expected because any two galaxies with the same M have at least one radius with identical surface density, where the galaxies have identical size. However, the reason why the scatter is reduced to the observed level is not trivial, and we pin it down to the galaxy surface density profiles approximately following Sersic profiles with their Re and Sersic index (n) anticorrelated (I.e. given M, n increases when Re decreases). Our analytical results describe very well the behaviour of the observed galaxies as portrayed in the NASA Sloan Atlas (NSA), which contains more than half a million local objects with 7 < log (M/M) < 11.5. The comparison with NSA galaxies also allows us to find the optimal values for the mass surface density ( $2.4_{-0.9}^{+1.3}\, M_\odot \, {\rm pc}^{-2}$ ) and surface brightness (r band $24.7\pm 0.5\, {\rm mag\, arcsec^{-2}}$ ) that minimize the scatter, although the actual values depend somehow on the subset of NSA galaxies used for optimization. The physical reason for the existence of optimal values is unknown but, as Trujillo, Chamba & Knapen (2020) point out, they are close to the gas surface density threshold to form stars and thus may trace the physical end of a galaxy. Our NSA-based size-mass relation agrees with theirs on the slope as well as on the magnitude of the scatter. As a by-product of the narrowness of the size-mass relation (only 0.06 dex), we propose to use the size of a galaxy to measure its stellar mass. In terms of observing time, it is not more demanding than the usual photometric techniques and may present practical advantages in particular cases. Title: Triaxiality can Explain the Alleged Dark Matter Deficiency in some Dwarf Galaxies Authors: Sánchez Almeida, J.; Filho, M. Bibcode: 2019RNAAS...3..191S Altcode: 2019arXiv191205268S Dark Matter (DM) is an ingredient essential to the current cosmological concordance model. It provides the gravitational pull needed for the baryons to form galaxies. Therefore, the existence of galaxies without DM is both disquieting and extremely interesting. Guo et al. recently presented "further evidence for a population of DM-deficient dwarf galaxies", however, their analysis bypasses the triaxiality of the dwarf galaxies. We carry out a Monte Carlo simulation showing how triaxiality must be considered to measure dynamical masses from projected axial ratios, calling into question the evidence for a population of DM-deficient dwarf galaxies. Such a population may consist of normal almost face-on HI disks with their inclination overestimated. Title: A contribution of star-forming clumps and accreting satellites to the mass assembly of z ∼ 2 galaxies Authors: Zanella, A.; Le Floc'h, E.; Harrison, C. M.; Daddi, E.; Bernhard, E.; Gobat, R.; Strazzullo, V.; Valentino, F.; Cibinel, A.; Sánchez Almeida, J.; Kohandel, M.; Fensch, J.; Behrendt, M.; Burkert, A.; Onodera, M.; Bournaud, F.; Scholtz, J. Bibcode: 2019MNRAS.489.2792Z Altcode: 2019arXiv190712136Z; 2019MNRAS.tmp.2058Z We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ∼ 1-3. We created continuum and emission line maps and pinpointed residual `blobs' detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M ≳ 109 M) have lifetimes of ∼650 Myr, and the less massive ones (108 < M < 109 M) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies. Title: Inferring the 3D Shapes of Extremely Metal-poor Galaxies from Sets of Projected Shapes Authors: Putko, J.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Asensio Ramos, A.; Elmegreen, B. G.; Elmegreen, D. M. Bibcode: 2019ApJ...883...10P Altcode: 2019arXiv190710496P The three-dimensional (3D) shape of a galaxy inevitably is tied to how it has formed and evolved and to its dark matter halo. Local extremely metal-poor galaxies (XMPs; defined as having an average gas-phase metallicity <0.1 solar) are important objects for understanding galaxy evolution largely because they appear to be caught in the act of accreting gas from the cosmic web, and their 3D shape may reflect this. Here, we report on the 3D shape of XMPs as inferred from their observed projected minor-to-major axial ratios using a hierarchical Bayesian inference model, which determines the likely shape and orientation of each galaxy, while simultaneously inferring the average shape and dispersion. We selected a sample of 149 XMPs and divided it into three subsamples according to physical size and found that (1) the stellar component of XMPs of all sizes tends to be triaxial, with an intermediate axis ≈0.7 times the longest axis and that (2) smaller XMPs tend to be relatively thicker, with the shortest axis going from ≈0.15 times the longest axis for the large galaxies to ≈0.4 for the small galaxies. We provide the inferred 3D shape and inclination of the individual XMPs in electronic format. We show that our results for the intermediate axis are not clouded by a selection effect against face-on XMPs. We discuss how an intermediate axis significantly smaller than the longest axis may be produced by several mechanisms, including lopsided gas accretion, non-axisymmetric star formation, or coupling with an elongated dark matter halo. Large relative thickness may reflect slow rotation, stellar feedback, or recent gas accretion. Title: Characterizing the Local Relation between Star Formation Rate and Gas-phase Metallicity in MaNGA Spiral Galaxies Authors: Sánchez-Menguiano, Laura; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Sánchez, Sebastián F.; Filho, Mercedes; Hwang, Hsiang-Chih; Drory, Niv Bibcode: 2019ApJ...882....9S Altcode: 2019arXiv190403930S The role of gas accretion in galaxy evolution is still a matter of debate. The presence of inflows of metal-poor gas that trigger star formation bursts of low metallicity has been proposed as an explanation for the local anticorrelation between star formation rate (SFR) and gas-phase metallicity (Z g ) found in the literature. In the present study, we show how the anticorrelation is also present as part of a diversified range of behaviors for a sample of more than 700 nearby spiral galaxies from the SDSS-IV MaNGA survey. We have characterized the local relation between SFR and Z g after subtracting the azimuthally averaged radial profiles of both quantities. Of the analyzed galaxies, 60% display an SFR-Z g anticorrelation, with the remaining 40% showing no correlation (19%) or positive correlation (21%). Applying a random forest machine-learning algorithm, we find that the slope of the correlation is mainly determined by the average gas-phase metallicity of the galaxy. Galaxy mass, g - r colors, stellar age, and mass density seem to play a less significant role. This result is supported by the performed second-order polynomial regression analysis. Thus, the local SFR-Z g slope varies with the average metallicity, with the more metal-poor galaxies presenting the lowest slopes (i.e., the strongest SFR-Z g anticorrelations), and reversing the relation for more metal-rich systems. Our results suggest that external gas accretion fuels star formation in metal-poor galaxies, whereas in metal-rich systems, the gas comes from previous star formation episodes. Title: Machine learning in APOGEE. Identification of stellar populations through chemical abundances Authors: Garcia-Dias, Rafael; Allende Prieto, Carlos; Sánchez Almeida, Jorge; Alonso Palicio, Pedro Bibcode: 2019A&A...629A..34G Altcode: 2019arXiv190712796G Context. The vast volume of data generated by modern astronomical surveys offers test beds for the application of machine-learning. In these exploratory applications, it is important to evaluate potential existing tools and determine those that are optimal for extracting scientific knowledge from the available observations.
Aims: We explore the possibility of using unsupervised clustering algorithms to separate stellar populations with distinct chemical patterns.
Methods: Star clusters are likely the most chemically homogeneous populations in the Galaxy, and therefore any practical approach to identifying distinct stellar populations should at least be able to separate clusters from each other. We have applied eight clustering algorithms combined with four dimensionality reduction strategies to automatically distinguish stellar clusters using chemical abundances of 13 elements. Our test-bed sample includes 18 stellar clusters with a total of 453 stars.
Results: We have applied statistical tests showing that some pairs of clusters (e.g., NGC 2458-NGC 2420) are indistinguishable from each other when chemical abundances from the Apache Point Galactic Evolution Experiment (APOGEE) are used. However, for most clusters we are able to automatically assign membership with metric scores similar to previous works. The confusion level of the automatically selected clusters is consistent with statistical tests that demonstrate the impossibility of perfectly distinguishing all the clusters from each other. These statistical tests and confusion levels establish a limit for the prospect of blindly identifying stars born in the same cluster based solely on chemical abundances. Conclusion. We find that some of the algorithms we explored are capable of blindly identify stellar populations with similar ages and chemical distributions in the APOGEE data. Even though we are not able to fully separate the clusters from each other, the main confusion arises from clusters with similar ages. Because some stellar clusters are chemically indistinguishable, our study supports the notion of extending weak chemical tagging that involves families of clusters instead of individual clusters.

The list of stars is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/629/A34 Title: Stellar content, planetary nebulae, and globular clusters of [KKS2000]04 (NGC 1052-DF2) Authors: Ruiz-Lara, T.; Trujillo, I.; Beasley, M. A.; Falcón-Barroso, J.; Vazdekis, A.; Filho, M.; Monelli, M.; Román, J.; Sánchez Almeida, J. Bibcode: 2019MNRAS.486.5670R Altcode: 2019MNRAS.tmp.1193R; 2019arXiv190309163R [KKS2000]04 (NGC 1052-DF2) has become a controversial and well-studied galaxy after the claims suggesting a lack of dark matter and the presence of an anomalously bright globular cluster (GC) system around it. A precise determination of its overall star formation history (SFH) and a better characterization of its GC or planetary nebulae (PNe) systems are crucial aspects to (i) understand its real nature, in particular placing it within the family of ultra diffuse galaxies and (ii) shed light on its possible formation, evolution, and survival in the absence of dark matter. With this purpose we expand on the knowledge of [KKS2000]04 from the analysis of OSIRIS@GTC spectroscopic data. On the one hand, we claim the possible detection of two new PNe and confirm membership of 5 GCs. On the other hand, we find that the stars shaping [KKS2000]04 are intermediate-age to old (90 per cent of its stellar mass older than 5 Gyr, average age of 8.7 ± 0.7 Gyr) and metal-poor ([M/H] ∼ -1.18 ± 0.05), in general agreement with previous results. We do not find any clear hints of significant changes in its stellar content with radius. In addition, the possibility of [KKS2000]04 being a tidal dwarf galaxy with no dark matter is highly disfavoured. Title: VizieR Online Data Catalog: APOGEE stars members of 35 star clusters (Garcia-Dias+, 2019) Authors: Garcia-Dias, R.; Allende Prieto, C.; Sanchez Almeida, J.; Alonso Palicio, P. Bibcode: 2019yCat..36290034G Altcode: Initial list of stars used in the article.

(1 data file). Title: The Fundamental Metallicity Relation Emerges from the Local Anti-correlation between Star Formation Rate and Gas-phase Metallicity that Exists in Disk Galaxies Authors: Sánchez Almeida, J.; Sánchez-Menguiano, L. Bibcode: 2019ApJ...878L...6S Altcode: 2019arXiv190505826S The fundamental metallicity relation (FMR) states that galaxies of the same stellar mass but larger star formation rate (SFR) tend to have smaller gas-phase metallicity (< {Z}g> ). It is thought to be fundamental because it naturally arises from the stochastic feeding of star formation from external metal-poor gas accretion, a process extremely elusive to observe but essential according the cosmological simulations of galaxy formation. In this Letter, we show how the FMR emerges from the local anti-correlation between SFR surface density and Z g recently observed to exist in disk galaxies. We analytically derive the global FMR from the local law, and then show that both relations agree quantitatively when considering the star-forming galaxies of the Mapping Nearby Galaxies at APO (MaNGA) survey. Thus, understanding the FMR becomes equivalent to understanding the origin of the anti-correlation between SFR and metallicity followed by the set of star-forming regions of any typical galaxy. The correspondence between local and global laws is not specific to the FMR, so that a number of local relations should exist that are associated with known global relations. Title: Accretion-Triggered Starbursts in Tadpole Galaxies Authors: Elmegreen, Bruce; Elmegreen, Debra M.; Andersen, Morten; Gallagher, John S.; Kotulla, Ralf; Munoz-Tunon, Casiana; Rafelski, Marc; Sanchez Almeida, Jorge Bibcode: 2019hst..prop15860E Altcode: Gas accretion onto galaxies is believed to drive the average star formation rate. However, there are few observations of this accretion for late-type galaxies, especially impacting the disk or triggering a starburst in the disk. Here we propose optical and Halpha imaging of four metal-poor tadpole galaxies that have local metallicity drops by a factor of 5 in relatively large off-center starburst clumps. The bursts and the unusual metallicities suggest recent accretion of large gas masses. Photometry plus SED modeling will determine the ages, masses, and luminosity distributions of the star clusters and star complexes in the bursts. Halpha will reveal ionization rates along with feedback and possible accretion structures. The sample represents the nearest low-mass galaxies that have high-resolution metallicity variations and single dominant starburst clumps. The results have broad implications for understanding the mass-metallicity relation for galaxies, the formation and feedback of stars and massive clusters in accretion-induced starbursts, and the origin of metal-poor globular clusters in the early universe. Only HST has the combination of angular resolution and sensitivity to carry out this program. Title: A distance of 13 Mpc resolves the claimed anomalies of the galaxy lacking dark matter Authors: Trujillo, Ignacio; Beasley, Michael A.; Borlaff, Alejandro; Carrasco, Eleazar R.; Di Cintio, Arianna; Filho, Mercedes; Monelli, Matteo; Montes, Mireia; Román, Javier; Ruiz-Lara, Tomás; Sánchez Almeida, Jorge; Valls-Gabaud, David; Vazdekis, Alexandre Bibcode: 2019MNRAS.486.1192T Altcode: 2019MNRAS.tmp..733T; 2018arXiv180610141T The claimed detection of a diffuse galaxy lacking dark matter represents a possible challenge to our understanding of the properties of these galaxies and galaxy formation in general. The galaxy, already identified in photographic plates taken in the summer of 1976 at the UK 48-in Schmidt telescope, presents normal distance-independent properties (e.g. colour, velocity dispersion of its globular clusters). However, distance-dependent quantities are at odds with those of other similar galaxies, namely the luminosity function and sizes of its globular clusters, mass-to-light ratio, and dark matter content. Here we carry out a careful analysis of all extant data and show that they consistently indicate a much shorter distance (13 Mpc) than previously indicated (20 Mpc). With this revised distance, the galaxy appears to be a rather ordinary low surface brightness galaxy (Re = 1.4 ± 0.1 kpc; M = 6.0 ± 3.6 × 107 M) with plenty of room for dark matter (the fraction of dark matter inside the half-mass radius is >75 per cent and Mhalo/M>20) corresponding to a minimum halo mass >109 M. At 13 Mpc, the luminosity and structural properties of the globular clusters around the object are the same as those found in other galaxies. Title: Global correlations between the radio continuum, infrared, and CO emissions in dwarf galaxies Authors: Filho, Mercedes E.; Tabatabaei, Fatemeh S.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce G. Bibcode: 2019MNRAS.484..543F Altcode: 2018arXiv181106577F; 2018MNRAS.tmp.3083F Correlations between the radio continuum, infrared, and CO emissions are known to exist for several types of galaxies and across several orders of magnitude. However, the low-mass, low-luminosity, and low-metallicity regime of these correlations is not well known. A sample of metal-rich and metal-poor dwarf galaxies from the literature has been assembled to explore this extreme regime. The results demonstrate that the properties of dwarf galaxies are not simple extensions of those of more massive galaxies; the different correlations reflect different star-forming conditions and different coupling between the star formation and the various quantities. It is found that dwarfs show increasingly weaker CO and infrared emissions for their luminosity, as expected for galaxies with a low dust content, slower reaction rates, and a hard ionizing radiation field. In the higher-luminosity dwarf regime [L_{1.4 GHz} ≳ 10^{27} W, where L_{1.4 GHz} ∼eq 10^{29} W for a Milky Way star formation rate (SFR) of ≃1 M yr-1], the total and non-thermal radio continuum emissions appear to adequately trace the SFR. A breakdown of the dependence of the (H α-based) thermal, non-thermal, and, hence, total radio continuum emission on SFR occurs below L_{1.4 GHz} ∼eq 10^{27} W, resulting in a steepening or downturn of the relations at extreme low luminosity. Below LFIR ≃ 1036 W ≃ 3 × 109 L, the infrared emission ceases to adequately trace the SFR. A lack of a correlation between the magnetic field strength and the SFR in low SFR dwarfs suggests a breakdown of the equipartition assumption. As extremely metal-poor dwarfs mostly populate the low SFR and low-luminosity regime, they stand out in their infrared, radio continuum, and CO properties. Title: Anomalously Low-metallicity Regions in MaNGA Star-forming Galaxies: Accretion Caught in Action? Authors: Hwang, Hsiang-Chih; Barrera-Ballesteros, Jorge K.; Heckman, Timothy M.; Rowlands, Kate; Lin, Lihwai; Rodriguez-Gomez, Vicente; Pan, Hsi-An; Hsieh, Bau-Ching; Sánchez, Sebastian; Bizyaev, Dmitry; Sánchez Almeida, Jorge; Thilker, David A.; Lotz, Jennifer M.; Jones, Amy; Nair, Preethi; Andrews, Brett H.; Drory, Niv Bibcode: 2019ApJ...872..144H Altcode: 2018arXiv181204614H We use data from 1222 late-type star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory survey to identify regions in which the gas-phase metallicity is anomalously low compared to expectations from the tight empirical relation between metallicity and stellar surface mass density at a given stellar mass. We find anomalously low-metallicity (ALM) gas in 10% of the star-forming spaxels and in 25% of the galaxies in the sample. The incidence rate of ALM gas increases strongly with both global and local measures of the specific star formation rate and is higher in lower mass galaxies and in the outer regions of galaxies. The incidence rate is also significantly higher in morphologically disturbed galaxies. We estimate that the lifetimes of the ALM regions are a few hundred Myr. We argue that the ALM gas has been delivered to its present location by a combination of interactions, mergers, and accretion from the halo, and that this infusion of gas stimulates star formation. Given the estimated lifetime and duty cycle of such events, we estimate that the time-averaged accretion rate of ALM gas is similar to the star formation rate in late-type galaxies over the mass range {M}* ∼ {10}9-1010 M . Title: A Headless Tadpole Galaxy: The High Gas-phase Metallicity of the Ultra-diffuse Galaxy UGC 2162 Authors: Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.; Elmegreen, D. M.; Filho, M.; Muñoz-Tuñón, C.; Pérez-Montero, E.; Román, J. Bibcode: 2018ApJ...869...40S Altcode: 2018arXiv181008453S The cosmological numerical simulations tell us that accretion of external metal-poor gas drives star formation (SF) in galaxy disks. One the best pieces of observational evidence supporting this prediction is the existence of low-metallicity star-forming regions in relatively high-metallicity host galaxies. The SF is thought to be fed by metal-poor gas recently accreted. Since the gas accretion is stochastic, there should be galaxies with all the properties of a host but without the low-metallicity starburst. These galaxies have not been identified yet. The exception may be UGC 2162, a nearby ultra-diffuse galaxy (UDG) that combines low surface brightness and relatively high metallicity. We confirm the high metallicity of UGC 2162 (12+{log}({{O}}/{{H}})={8.52}-0.24+0.27) using spectra taken with the 10 m GTC telescope. UGC 2162 has the stellar mass, metallicity, and star formation rate surface density expected for a host galaxy in between outbursts. This fact suggests a physical connection between some UDGs and metal-poor galaxies, which may be the same type of object in a different phase of the SF cycle. UGC 2162 is a high-metallicity outlier of the mass-metallicity relation, a property shared by the few UDGs with known gas-phase metallicity. Title: An unusual transient in the extremely metal-poor Galaxy SDSS J094332.35+332657.6 (Leoncino Dwarf) Authors: Filho, Mercedes E.; Sánchez Almeida, J. Bibcode: 2018MNRAS.478.2541F Altcode: 2018arXiv180411166F; 2018MNRAS.tmp.1073F We have serendipitously discovered that Leoncino Dwarf, an ultrafaint, low-metallicity record-holder dwarf galaxy, may have hosted a transient source, and possibly exhibited a change in morphology, a shift in the centre of brightness, and peak variability of the main (host) source in images taken approximately 40 yr apart; it is highly likely that these phenomena are related. Scenarios involving a Solar System object, a stellar cluster, dust enshrouding, and accretion variability have been considered, and discarded, as the origin of the transient. Although a combination of time-varying strong and weak lensing effects, induced by an intermediate-mass black hole (104-5 × 105 M) moving within the Milky Way halo ( 0.1-4 kpc), can conceivably explain all of the observed variable galaxy properties, it is statistically highly unlikely according to current theoretical predictions, and, therefore, also discarded. A cataclysmic event such as a supernova/hypernova could have occurred, as long as the event was observed towards the later/late-stage descent of the light curve, but this scenario fails to explain the absence of a post-explosion source and/or host H II region in recent optical images. An episode related to the giant eruption of a luminous blue variable star, a stellar merger or a nova, observed at, or near, peak magnitude may explain the transient source and possibly the change in morphology/centre of brightness, but cannot justify the main source peak variability, unless stellar variability is evoked. Title: Extremely metal-poor galaxies: Chemical laboratories of the Early Universe Authors: Pérez-Montero, E.; Sánchez-Almeida, J.; Amorín, R.; Vílchez, J. M.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; García-Benito, R. Bibcode: 2018cagn.conf...49P Altcode: Extremely metal-poor galaxies (XMPs) are objects whose gas-phase metallicity is smaller than one tenth than the solar value, so they are thought to be un-evolved objects and hence to be analogs to the primeval galaxies when they are found in the Local Universe. In this contribution, we review results from several studies of our group to search for XMPs at low- (SDSS) and mid-redshift (zCOSMOS), focused on improving the methods to identify them. Our analysis of the metal content of these objects includes the derivation of abundances of elements with both primary and secondary nucleosynthetic origin. The chemical analysis combined with the use of spatially resolved observations allow us to discriminate true primitive galaxies from other objects rejuvenated by the fall of pristine gas, helping to perform a better analysis of the analogs to the objects in the primitive Universe. Title: First scientific observations with MEGARA at GTC Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Iglesias-Páramo, J.; Cedazo, R.; García-Vargas, M. L.; Arrillaga, X.; Avilés, J. L.; Bouquin, A.; Carbajo, J.; Cardiel, N.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; Esteban San Román, S.; Ferrusca, D.; Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort, B.; López-Orozco, J. A.; Maldonado, M.; Martínez-Delgado, I.; Morales-Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Picazo, P.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Vílchez, J. M.; Zamorano, J.; Aguerri, A. L.; Barrado y Navascues, D.; Berlanas, S. R.; Bertone, E.; Cava, A.; Catalán-Torrecilla, C.; Cenarro, J.; Chávez, M.; Dullo, B. T.; García, M.; García-Rojas, J.; Guichard, J.; González-Delgado, R.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D. H.; Jiménez-Vicente, J.; Kehrig, C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mayya, D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez-Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez Merino, L.; Rodríguez-Muñoz, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez-Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O. Bibcode: 2018SPIE10702E..17G Altcode: On June 25th 2017, the new intermediate-resolution optical IFU and MOS of the 10.4-m GTC had its first light. As part of the tests carried out to verify the performance of the instrument in its two modes (IFU and MOS) and 18 spectral setups (identical number of VPHs with resolutions R=6000-20000 from 0.36 to 1 micron) a number of astronomical objects were observed. These observations show that MEGARA@GTC is called to fill a niche of high-throughput, intermediateresolution IFU and MOS observations of extremely-faint narrow-lined objects. Lyman-α absorbers, star-forming dwarfs or even weak absorptions in stellar spectra in our Galaxy or in the Local Group can now be explored to a new level. Thus, the versatility of MEGARA in terms of observing modes and spectral resolution and coverage will allow GTC to go beyond current observational limits in either depth or precision for all these objects. The results to be presented in this talk clearly demonstrate the potential of MEGARA in this regard. Title: MEGARA, the R=6000-20000 IFU and MOS of GTC Authors: Carrasco, E.; Gil de Paz, A.; Gallego, J.; Iglesias-Páramo, J.; Cedazo, R.; García Vargas, M. L.; Arrillaga, X.; Avilés, J. L.; Bouquin, A.; Carbajo, J.; Cardiel, N.; Carrera, M. A.; Castillo Morales, A.; Castillo-Domínguez, E.; Esteban San Román, S.; Ferrusca, D.; Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort, B.; López Orozco, J. A.; Maldonado, M.; Martínez Delgado, I.; Morales Durán, I.; Mújica, E.; Ortiz, R.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Picazo, P.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Vílchez, J. M.; Zamorano, J.; Aguerri, A. L.; Barrado, D.; Bertone, E.; Cava, A.; Catalán-Torrecilla, C.; Cenarro, J.; Chávez, M.; Dullo, B. T.; Eliche, C.; García, Mi.; García-Rojas, J.; Guichard, J.; González-Delgado, R.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D. H.; Jiménez-Vicente, J.; Kehrig, C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mayya, D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez-Montero, E.; Roca-Fàbrega, S.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rodríguez-Muñoz, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O. Bibcode: 2018SPIE10702E..16C Altcode: MEGARA is the new generation IFU and MOS optical spectrograph built for the 10.4m Gran Telescopio CANARIAS (GTC). The project was developed by a consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The instrument arrived to GTC on March 28th 2017 and was successfully integrated and commissioned at the telescope from May to August 2017. During the on-sky commissioning we demonstrated that MEGARA is a powerful and robust instrument that provides on-sky intermediate-to-high spectral resolutions RFWHM 6,000, 12,000 and 20,000 at an unprecedented efficiency for these resolving powers in both its IFU and MOS modes. The IFU covers 12.5 x 11.3 arcsec2 while the MOS mode allows observing up to 92 objects in a region of 3.5 x 3.5 arcmin2. In this paper we describe the instrument main subsystems, including the Folded-Cassegrain unit, the fiber link, the spectrograph, the cryostat, the detector and the control subsystems, and its performance numbers obtained during commissioning where the fulfillment of the instrument requirements is demonstrated. Title: The Origin of the Relation between Metallicity and Size in Star-forming Galaxies Authors: Sánchez Almeida, J.; Dalla Vecchia, C. Bibcode: 2018ApJ...859..109S Altcode: 2018arXiv180409406S For the same stellar mass, physically smaller star-forming galaxies are also metal richer. What causes the relation remains unclear. The central star-forming galaxies in the EAGLE cosmological numerical simulation reproduce the observed trend. We use them to explore the origin of the relation assuming that the physical mechanism responsible for the anticorrelation between size and gas-phase metallicity is the same in the simulated and the observed galaxies. We consider the three most likely causes: (1) metal-poor gas inflows feeding the star formation (SF) process, (2) metal-rich gas outflows particularly efficient in shallow gravitational potentials, and (3) enhanced efficiency of the SF process in compact galaxies. Outflows (cause 2) and enhanced SF efficiency (cause 3) can be discarded. Metal-poor gas inflows (cause 1) produce the correlation in the simulated galaxies. Galaxies grow in size with time, so those that receive gas later are both metal poorer and larger, giving rise to the observed anticorrelation. As expected within this explanation, larger galaxies have younger stellar populations. We explore the variation with redshift of the relation, which is maintained up to, at least, redshift 8. Title: Local anticorrelation between star formation rate and gas-phase metallicity in disc galaxies Authors: Sánchez Almeida, J.; Caon, N.; Muñoz-Tuñón, C.; Filho, M.; Cerviño, M. Bibcode: 2018MNRAS.476.4765S Altcode: 2018arXiv180208111S; 2018MNRAS.tmp..488S Using a representative sample of 14 star-forming dwarf galaxies in the local Universe, we show the existence of a spaxel-to-spaxel anticorrelation between the index N2 ≡ log ([N II]λ 6583/H α ) and the H α flux. These two quantities are commonly employed as proxies for gas-phase metallicity and star formation rate (SFR), respectively. Thus, the observed N2 to H α relation may reflect the existence of an anticorrelation between the metallicity of the gas forming stars and the SFR it induces. Such an anticorrelation is to be expected if variable external metal-poor gas fuels the star-formation process. Alternatively, it can result from the contamination of the star-forming gas by stellar winds and SNe, provided that intense outflows drive most of the metals out of the star-forming regions. We also explore the possibility that the observed anticorrelation is due to variations in the physical conditions of the emitting gas, other than metallicity. Using alternative methods to compute metallicity, as well as previous observations of H II regions and photoionization models, we conclude that this possibility is unlikely. The radial gradient of metallicity characterizing disc galaxies does not produce the correlation either. Title: NOEMA Observations of a Molecular Cloud in the Low-metallicity Galaxy Kiso 5639 Authors: Elmegreen, Bruce G.; Herrera, Cinthya; Rubio, Monica; Elmegreen, Debra Meloy; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Olmo-García, Amanda Bibcode: 2018ApJ...859L..22E Altcode: 2018arXiv180508253E A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10 m Gran Telescopio Canarias (GTC) and in the emission line of CO(1-0) with the Northern Extended Millimeter Array (NOEMA) mm-wave interferometer. The metallicity was determined to be 12+{log}({{O}}/{{H}})=7.83+/- 0.09, from which we estimate a conversion factor of α CO ∼ 100 M pc-2(K km s-1)-1 and a molecular cloud mass of ∼2.9 × 107 M . This is an enormous concentration of molecular mass at one end of a small galaxy, suggesting a recent accretion. The molecular cloud properties seem normal: the surface density, 120 M pc-2, is comparable to that of a standard giant molecular cloud; the cloud’s virial ratio of ∼1.8 is in the star formation range; and the gas consumption time, 0.5 Gyr, at the present star formation rate is typical for molecular regions. The low metallicity implies that the cloud has an average visual extinction of only 0.8 mag, which is close to the threshold for molecule formation. With such an extinction threshold, molecular clouds in metal-poor regions should have high surface densities and high internal pressures. If high pressure is associated with the formation of massive clusters, then metal-poor galaxies such as dwarfs in the early universe could have been the hosts of metal-poor globular clusters. Title: Cosmic Magnetic Fields Authors: Sánchez Almeida, J.; Martínez González, M. J. Bibcode: 2018cmf..book.....S Altcode: Magnetic fields play an important role in many astrophysical processes. They are difficult to detect and characterize since often their properties have to be inferred through interpreting the polarization of the light. Magnetic fields are also challenging to model and understand. Magnetized plasmas behave following highly non-linear differential equations having no general solution, so that every astrophysical problem represents a special case to be studied independently. Hence, magnetic fields are often an inconvenient subject which is overlooked or simply neglected (the elephant in the room, as they are dubbed in poster of the school). Such difficulty burdens the research on magnetic fields, which has evolved to become a very technical subject, with many small disconnected communities studying specific aspects and details. The school tried to amend the situation by providing a unifying view of the subject. The students had a chance to understand the behavior of magnetic fields in all astrophysical contexts, from cosmology to the Sun, and from starbursts to AGNs. The school was planed to present a balanced yet complete review of our knowledge, with excursions into the unknown to point out present and future lines of research. The subject of Cosmic Magnetic Fields was split into seven different topics: cosmic magnetic field essentials, solar magnetic fields, stellar magnetic fields, the role of magnetic fields on AGN feedback, magnetic fields in galaxies, magnetic fields in galaxy clusters and at larger scales, and primordial magnetic fields and magnetic fields in the early Universe. The corresponding lectures were delivered by seven well known and experienced scientists that have played key roles in the major advances of the field during the last years: F. Cattaneo, P. Judge, O. Kochukhov, R. Keppens, R. Beck, K. Dolag, and F. Finelli. Their lectures were recorded and are freely available at the IAC website: http://iactalks.iac.es/talks/serie/19. Title: Machine learning in APOGEE. Unsupervised spectral classification with K-means Authors: Garcia-Dias, Rafael; Allende Prieto, Carlos; Sánchez Almeida, Jorge; Ordovás-Pascual, Ignacio Bibcode: 2018A&A...612A..98G Altcode: 2018arXiv180107912G Context. The volume of data generated by astronomical surveys is growing rapidly. Traditional analysis techniques in spectroscopy either demand intensive human interaction or are computationally expensive. In this scenario, machine learning, and unsupervised clustering algorithms in particular, offer interesting alternatives. The Apache Point Observatory Galactic Evolution Experiment (APOGEE) offers a vast data set of near-infrared stellar spectra, which is perfect for testing such alternatives.
Aims: Our research applies an unsupervised classification scheme based on K-means to the massive APOGEE data set. We explore whether the data are amenable to classification into discrete classes.
Methods: We apply the K-means algorithm to 153 847 high resolution spectra (R ≈ 22 500). We discuss the main virtues and weaknesses of the algorithm, as well as our choice of parameters.
Results: We show that a classification based on normalised spectra captures the variations in stellar atmospheric parameters, chemical abundances, and rotational velocity, among other factors. The algorithm is able to separate the bulge and halo populations, and distinguish dwarfs, sub-giants, RC, and RGB stars. However, a discrete classification in flux space does not result in a neat organisation in the parameters' space. Furthermore, the lack of obvious groups in flux space causes the results to be fairly sensitive to the initialisation, and disrupts the efficiency of commonly-used methods to select the optimal number of clusters. Our classification is publicly available, including extensive online material associated with the APOGEE Data Release 12 (DR12).
Conclusions: Our description of the APOGEE database can help greatly with the identification of specific types of targets for various applications. We find a lack of obvious groups in flux space, and identify limitations of the K-means algorithm in dealing with this kind of data.

Full Tables B.1-B.4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/A98 Title: The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the Extended Baryon Oscillation Spectroscopic Survey and from the Second Phase of the Apache Point Observatory Galactic Evolution Experiment Authors: Abolfathi, Bela; Aguado, D. S.; Aguilar, Gabriela; Allende Prieto, Carlos; Almeida, Andres; Ananna, Tonima Tasnim; Anders, Friedrich; Anderson, Scott F.; Andrews, Brett H.; Anguiano, Borja; Aragón-Salamanca, Alfonso; Argudo-Fernández, Maria; Armengaud, Eric; Ata, Metin; Aubourg, Eric; Avila-Reese, Vladimir; Badenes, Carles; Bailey, Stephen; Balland, Christophe; Barger, Kathleen A.; Barrera-Ballesteros, Jorge; Bartosz, Curtis; Bastien, Fabienne; Bates, Dominic; Baumgarten, Falk; Bautista, Julian; Beaton, Rachael; Beers, Timothy C.; Belfiore, Francesco; Bender, Chad F.; Bernardi, Mariangela; Bershady, Matthew A.; Beutler, Florian; Bird, Jonathan C.; Bizyaev, Dmitry; Blanc, Guillermo A.; Blanton, Michael R.; Blomqvist, Michael; Bolton, Adam S.; Boquien, Médéric; Borissova, Jura; Bovy, Jo; Bradna Diaz, Christian Andres; Brandt, William Nielsen; Brinkmann, Jonathan; Brownstein, Joel R.; Bundy, Kevin; Burgasser, Adam J.; Burtin, Etienne; Busca, Nicolás G.; Cañas, Caleb I.; Cano-Díaz, Mariana; Cappellari, Michele; Carrera, Ricardo; Casey, Andrew R.; Cervantes Sodi, Bernardo; Chen, Yanping; Cherinka, Brian; Chiappini, Cristina; Choi, Peter Doohyun; Chojnowski, Drew; Chuang, Chia-Hsun; Chung, Haeun; Clerc, Nicolas; Cohen, Roger E.; Comerford, Julia M.; Comparat, Johan; Correa do Nascimento, Janaina; da Costa, Luiz; Cousinou, Marie-Claude; Covey, Kevin; Crane, Jeffrey D.; Cruz-Gonzalez, Irene; Cunha, Katia; da Silva Ilha, Gabriele; Damke, Guillermo J.; Darling, Jeremy; Davidson, James W., Jr.; Dawson, Kyle; de Icaza Lizaola, Miguel Angel C.; de la Macorra, Axel; de la Torre, Sylvain; De Lee, Nathan; de Sainte Agathe, Victoria; Deconto Machado, Alice; Dell'Agli, Flavia; Delubac, Timothée; Diamond-Stanic, Aleksandar M.; Donor, John; Downes, Juan José; Drory, Niv; du Mas des Bourboux, Hélion; Duckworth, Christopher J.; Dwelly, Tom; Dyer, Jamie; Ebelke, Garrett; Davis Eigenbrot, Arthur; Eisenstein, Daniel J.; Elsworth, Yvonne P.; Emsellem, Eric; Eracleous, Michael; Erfanianfar, Ghazaleh; Escoffier, Stephanie; Fan, Xiaohui; Fernández Alvar, Emma; Fernandez-Trincado, J. G.; Fernando Cirolini, Rafael; Feuillet, Diane; Finoguenov, Alexis; Fleming, Scott W.; Font-Ribera, Andreu; Freischlad, Gordon; Frinchaboy, Peter; Fu, Hai; Gómez Maqueo Chew, Yilen; Galbany, Lluís; García Pérez, Ana E.; Garcia-Dias, R.; García-Hernández, D. A.; Garma Oehmichen, Luis Alberto; Gaulme, Patrick; Gelfand, Joseph; Gil-Marín, Héctor; Gillespie, Bruce A.; Goddard, Daniel; González Hernández, Jonay I.; Gonzalez-Perez, Violeta; Grabowski, Kathleen; Green, Paul J.; Grier, Catherine J.; Gueguen, Alain; Guo, Hong; Guy, Julien; Hagen, Alex; Hall, Patrick; Harding, Paul; Hasselquist, Sten; Hawley, Suzanne; Hayes, Christian R.; Hearty, Fred; Hekker, Saskia; Hernandez, Jesus; Hernandez Toledo, Hector; Hogg, David W.; Holley-Bockelmann, Kelly; Holtzman, Jon A.; Hou, Jiamin; Hsieh, Bau-Ching; Hunt, Jason A. S.; Hutchinson, Timothy A.; Hwang, Ho Seong; Jimenez Angel, Camilo Eduardo; Johnson, Jennifer A.; Jones, Amy; Jönsson, Henrik; Jullo, Eric; Khan, Fahim Sakil; Kinemuchi, Karen; Kirkby, David; Kirkpatrick, Charles C., IV; Kitaura, Francisco-Shu; Knapp, Gillian R.; Kneib, Jean-Paul; Kollmeier, Juna A.; Lacerna, Ivan; Lane, Richard R.; Lang, Dustin; Law, David R.; Le Goff, Jean-Marc; Lee, Young-Bae; Li, Hongyu; Li, Cheng; Lian, Jianhui; Liang, Yu; Lima, Marcos; Lin, Lihwai; Long, Dan; Lucatello, Sara; Lundgren, Britt; Mackereth, J. Ted; MacLeod, Chelsea L.; Mahadevan, Suvrath; Maia, Marcio Antonio Geimba; Majewski, Steven; Manchado, Arturo; Maraston, Claudia; Mariappan, Vivek; Marques-Chaves, Rui; Masseron, Thomas; Masters, Karen L.; McDermid, Richard M.; McGreer, Ian D.; Melendez, Matthew; Meneses-Goytia, Sofia; Merloni, Andrea; Merrifield, Michael R.; Meszaros, Szabolcs; Meza, Andres; Minchev, Ivan; Minniti, Dante; Mueller, Eva-Maria; Muller-Sanchez, Francisco; Muna, Demitri; Muñoz, Ricardo R.; Myers, Adam D.; Nair, Preethi; Nandra, Kirpal; Ness, Melissa; Newman, Jeffrey A.; Nichol, Robert C.; Nidever, David L.; Nitschelm, Christian; Noterdaeme, Pasquier; O'Connell, Julia; Oelkers, Ryan James; Oravetz, Audrey; Oravetz, Daniel; Ortíz, Erik Aquino; Osorio, Yeisson; Pace, Zach; Padilla, Nelson; Palanque-Delabrouille, Nathalie; Palicio, Pedro Alonso; Pan, Hsi-An; Pan, Kaike; Parikh, Taniya; Pâris, Isabelle; Park, Changbom; Peirani, Sebastien; Pellejero-Ibanez, Marcos; Penny, Samantha; Percival, Will J.; Perez-Fournon, Ismael; Petitjean, Patrick; Pieri, Matthew M.; Pinsonneault, Marc; Pisani, Alice; Prada, Francisco; Prakash, Abhishek; Queiroz, Anna Bárbara de Andrade; Raddick, M. Jordan; Raichoor, Anand; Barboza Rembold, Sandro; Richstein, Hannah; Riffel, Rogemar A.; Riffel, Rogério; Rix, Hans-Walter; Robin, Annie C.; Rodríguez Torres, Sergio; Román-Zúñiga, Carlos; Ross, Ashley J.; Rossi, Graziano; Ruan, John; Ruggeri, Rossana; Ruiz, Jose; Salvato, Mara; Sánchez, Ariel G.; Sánchez, Sebastián F.; Sanchez Almeida, Jorge; Sánchez-Gallego, José R.; Santana Rojas, Felipe Antonio; Santiago, Basílio Xavier; Schiavon, Ricardo P.; Schimoia, Jaderson S.; Schlafly, Edward; Schlegel, David; Schneider, Donald P.; Schuster, William J.; Schwope, Axel; Seo, Hee-Jong; Serenelli, Aldo; Shen, Shiyin; Shen, Yue; Shetrone, Matthew; Shull, Michael; Silva Aguirre, Víctor; Simon, Joshua D.; Skrutskie, Mike; Slosar, Anže; Smethurst, Rebecca; Smith, Verne; Sobeck, Jennifer; Somers, Garrett; Souter, Barbara J.; Souto, Diogo; Spindler, Ashley; Stark, David V.; Stassun, Keivan; Steinmetz, Matthias; Stello, Dennis; Storchi-Bergmann, Thaisa; Streblyanska, Alina; Stringfellow, Guy S.; Suárez, Genaro; Sun, Jing; Szigeti, Laszlo; Taghizadeh-Popp, Manuchehr; Talbot, Michael S.; Tang, Baitian; Tao, Charling; Tayar, Jamie; Tembe, Mita; Teske, Johanna; Thakar, Aniruddha R.; Thomas, Daniel; Tissera, Patricia; Tojeiro, Rita; Tremonti, Christy; Troup, Nicholas W.; Urry, Meg; Valenzuela, O.; van den Bosch, Remco; Vargas-González, Jaime; Vargas-Magaña, Mariana; Vazquez, Jose Alberto; Villanova, Sandro; Vogt, Nicole; Wake, David; Wang, Yuting; Weaver, Benjamin Alan; Weijmans, Anne-Marie; Weinberg, David H.; Westfall, Kyle B.; Whelan, David G.; Wilcots, Eric; Wild, Vivienne; Williams, Rob A.; Wilson, John; Wood-Vasey, W. M.; Wylezalek, Dominika; Xiao, Ting; Yan, Renbin; Yang, Meng; Ybarra, Jason E.; Yèche, Christophe; Zakamska, Nadia; Zamora, Olga; Zarrouk, Pauline; Zasowski, Gail; Zhang, Kai; Zhao, Cheng; Zhao, Gong-Bo; Zheng, Zheng; Zheng, Zheng; Zhou, Zhi-Min; Zhu, Guangtun; Zinn, Joel C.; Zou, Hu Bibcode: 2018ApJS..235...42A Altcode: 2017arXiv170709322A The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in operation since 2014 July. This paper describes the second data release from this phase, and the 14th from SDSS overall (making this Data Release Fourteen or DR14). This release makes the data taken by SDSS-IV in its first two years of operation (2014-2016 July) public. Like all previous SDSS releases, DR14 is cumulative, including the most recent reductions and calibrations of all data taken by SDSS since the first phase began operations in 2000. New in DR14 is the first public release of data from the extended Baryon Oscillation Spectroscopic Survey; the first data from the second phase of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2), including stellar parameter estimates from an innovative data-driven machine-learning algorithm known as “The Cannon” and almost twice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous release (N = 2812 in total). This paper describes the location and format of the publicly available data from the SDSS-IV surveys. We provide references to the important technical papers describing how these data have been taken (both targeting and observation details) and processed for scientific use. The SDSS web site (www.sdss.org) has been updated for this release and provides links to data downloads, as well as tutorials and examples of data use. SDSS-IV is planning to continue to collect astronomical data until 2020 and will be followed by SDSS-V. Title: VizieR Online Data Catalog: APOGEE full information on classes (Garcia-Dias+, 2018) Authors: Garcia-Dias, R.; Allende Prieto, C.; Sanchez Almeida, J.; Ordovas-Pascual, I. Bibcode: 2018yCat..36120098G Altcode: Data for the classes derived on the paper. The tables provide the star labels, the mean spectra of the classes and the within class standard deviation.

(3 data files). Title: The Shape of Extremely Metal-Poor Galaxies Authors: Putko, Joseph; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Elmegreen, Bruce; Elmegreen, Debra Bibcode: 2018AAS...23134002P Altcode: This work is the first study on the 3D shape of starbursting extremely metal-poor galaxies (XMPs; a galaxy is said to be an XMP if its ionized gas-phase metallicity is less than 1/10 the solar value). A few hundred XMPs have been identified in the local universe primarily through mining the spectroscopic catalog of the Sloan Digital Sky Survey (SDSS), and follow-up observations have shown that metallicity drops significantly at the starburst (compared to the quiescent component of the galaxy). As the timescale for gas mixing is short, the metal-poor gas triggering the starburst must have been accreted recently. This is strong observational evidence for the cold flow accretion predicted by cosmological models of galaxy formation, and, in this respect, XMPs seem to be the best local analogs of the very first galaxies.The ellipsoidal shape of a class of galaxies can be inferred from the observed axial ratio (q) distribution (q = minor axis/major axis) of a large sample of randomly-oriented galaxies. Fitting ellipses to 200 XMPs using r-band SDSS images, we observe that the axial ratio distribution falls off at q < ~0.4 and q > ~0.8, and we determine that these falloffs are not due to biases in the data. The falloff at low axial ratio indicates that the XMPs are thick for their size, and the falloff at high axial ratio suggests the vast majority of XMPs are triaxial. We also observe that smaller XMPs are thicker in proportion to their size, and it is expected that for decreasing galaxy size the ratio of random to rotational motions increases, which correlates with increasing relative thickness. The XMPs are low-redshift dwarf galaxies dominated by dark matter, and our results are compatible with simulations that have shown dark matter halos to be triaxial, with triaxial stellar distributions for low-mass galaxies and with triaxiality increasing over time. We will offer precise constraints on the 3D shape of XMPs via Bayesian analysis of our observed axial ratio distribution.This work has been supported by the La Caixa Foundation and the Estallidos Spanish Ministry of Science and Innovation grant. Title: Gas accretion from the cosmic web feeding disk galaxies Authors: Sánchez Almeida, J.; Olmo-García, A.; Elmegreen, B. G.; Muñoz-Tuñón, C.; Elmegreen, D. M.; Filho, M. E.; Pérez-Montero, E.; Amorín, R. Bibcode: 2017IAUS..321..208S Altcode: Disk galaxies in cosmological numerical simulations grow by accreting gas from the cosmic web. This gas reaches the external disk, and then spirals in dragged along by tidal forces and/or disk instabilities. The importance of gas infall is as clear from numerical simulations as it is obscure to observations. Extremely metal poor (XMP) galaxies seem to be the best example we have of the gas accretion process at work. They have large off-center starbursts which show significant metallicity drop compared with the host galaxy. This observation is naturally explained as a gas accretion event caught in the act. We present preliminary results of the kinematical properties of the metal poor starbursts in XMPs, which suggest that the starbursts are kinematically decoupled entities within the host galaxy. Title: Circumgalactic gas absorption in extremely metal-poor dwarf dalaxies Authors: Filho, M. E.; Sánchez Almeida, J.; Muñoz Tuñón, C. Bibcode: 2017IAUS..321..287F Altcode: Accretion of metal-poor gas via cold accretion flows has been recently proposed as a means to trigger/sustain star formation in extremely metal-poor dwarf galaxies (XMPs), a scenario in agreement with theoretical predictions. We report on the tentative detection of CaII absorption used to trace the conditions of the gas clouds in the halo of the XMP UGCA 20. Title: On the Dearth of Ultra-faint Extremely Metal-poor Galaxies Authors: Sánchez Almeida, J.; Filho, M. E.; Dalla Vecchia, C.; Skillman, E. D. Bibcode: 2017ApJ...835..159S Altcode: 2016arXiv161200273S Local extremely metal-poor galaxies (XMPs) are of particular astrophysical interest since they allow us to look into physical processes characteristic of the early universe, from the assembly of galaxy disks to the formation of stars in conditions of low metallicity. Given the luminosity-metallicity relationship, all galaxies fainter than Mr ≃ -13 are expected to be XMPs. Therefore, XMPs should be common in galaxy surveys. However, they are not common, because several observational biases hamper their detection. This work compares the number of faint XMPs in the SDSS-DR7 spectroscopic survey with the expected number, given the known biases and the observed galaxy luminosity function (LF). The faint end of the LF is poorly constrained observationally, but it determines the expected number of XMPs. Surprisingly, the number of observed faint XMPs (∼10) is overpredicted by our calculation, unless the upturn in the faint end of the LF is not present in the model. The lack of an upturn can be naturally understood if most XMPs are central galaxies in their low-mass dark matter halos, which are highly depleted in baryons due to interaction with the cosmic ultraviolet background and to other physical processes. Our result also suggests that the upturn toward low luminosity of the observed galaxy LF is due to satellite galaxies. Title: The Nearest Ultra Diffuse Galaxy: UGC 2162 Authors: Trujillo, Ignacio; Roman, Javier; Filho, Mercedes; Sánchez Almeida, Jorge Bibcode: 2017ApJ...836..191T Altcode: 2017arXiv170103804T We describe the structural, stellar population and gas properties of the nearest ultra diffuse galaxy discovered so far: UGC 2162 (z = 0.00392 {R}e,g=1.7(+/- 0.2) kpc; {μ }g(0) = 24.4 ± 0.1 mag arcsec-2 g-I = 0.33 ± 0.02). This galaxy, located at a distance of 12.3(±1.7) Mpc, is a member of the M77 group. UGC 2162 has a stellar mass of ∼ 2{(}-1+2) × 107 {M} and is embedded within a cloud of HI gas ∼10 times more massive: ∼1.9(±0.6) × 108 {M}. Using the width of its HI line as a dynamical proxy, the enclosed mass within the inner R ∼ 5 kpc is ∼4.6(±0.8) × 109 {M} (I.e., M/L ∼ 200). The estimated virial mass from the cumulative mass curve is ∼8(±2)×1010 M . Ultra-deep imaging from the IAC Stripe82 Legacy Project show that the galaxy is irregular and has many star-forming knots, with a gas-phase metallicity around one-third of the solar value. Its estimated star-formation rate is ∼0.01 {M} yr-1. This SFR would double the stellar mass of the object in ∼2 Gyr. If the object were to stop forming stars at this moment, after a passive evolution, its surface brightness would become extremely faint: {μ }g(0) ∼ 27 mag arcsec-2 and its size would remain large {R}e,g ∼ 1.8 kpc. Such faintness would make it almost undetectable to most present-day surveys. This suggests that there could be an important population of {M}\star ∼ 107 {M} “dark galaxies” in rich environments (depleted of HI gas) waiting to be discovered by current and future ultra-deep surveys. Title: Evidence of a White-Light Flare on 10 September 1886 Authors: Vaquero, J. M.; Vázquez, M.; Sánchez Almeida, J. Bibcode: 2017SoPh..292...33V Altcode: 2017arXiv170105910V We present evidence of the occurrence of a white-light flare on 10 September 1886. It represents the third such rare event reported in the history of astronomy. The flare was mentioned by Valderrama (L'Astronomie5, 388, 1886). In this article we have used the original logbook of the observer, J. Valderrama y Aguilar, an amateur astronomer who lived in Madrid and Santa Cruz de Tenerife at that time. Title: Gas Accretion and Star Formation Rates Authors: Sánchez Almeida, Jorge Bibcode: 2017ASSL..430...67S Altcode: 2016arXiv161200776S Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star formation are analyzed, specifically, the short gas-consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the α-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas. Title: Kinematics of Extremely Metal-poor Galaxies: Evidence for Stellar Feedback Authors: Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero, E.; Méndez-Abreu, J. Bibcode: 2017ApJ...834..181O Altcode: 2016arXiv161107426O The extremely metal-poor (XMP) galaxies analyzed in a previous paper have large star-forming regions with a metallicity lower than the rest of the galaxy. Such a chemical inhomogeneity reveals the external origin of the metal-poor gas fueling star formation, possibly indicating accretion from the cosmic web. This paper studies the kinematic properties of the ionized gas in these galaxies. Most XMPs have a rotation velocity around a few tens of km s-1. The star-forming regions appear to move coherently. The velocity is constant within each region, and the velocity dispersion sometimes increases within the star-forming clump toward the galaxy midpoint, suggesting inspiral motion toward the galaxy center. Other regions present a local maximum in velocity dispersion at their center, suggesting a moderate global expansion. The Hα line wings show a number of faint emission features with amplitudes around a few per cent of the main Hα component, and wavelength shifts between 100 and 400 km s-1. The components are often paired, so that red and blue emission features with similar amplitudes and shifts appear simultaneously. Assuming the faint emission to be produced by expanding shell-like structures, the inferred mass loading factor (mass loss rate divided by star formation rate) exceeds 10. Since the expansion velocity far exceeds the rotational and turbulent velocities, the gas may eventually escape from the galaxy disk. The observed motions involve energies consistent with the kinetic energy released by individual core-collapse supernovae. Alternative explanations for the faint emission have been considered and discarded. Title: MEGARA, the Next Generation Optical MOS and IFU for GTC Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias, J.; Sánchez, F.; Vílchez, J.; García Vargas, M.; Andrés, P.; Arrillaga, X.; Avilés, J.; Bonache, J.; Carrera, M.; Castillo, A.; Castillo, E.; Cedazo, R.; Dormido, J.; Eliche Moral, C.; Esteban, S.; Ferrusca, D.; González, E.; Lefort, B.; López, J.; Maldonado, M.; Marino, R.; Martínez, I.; Morales, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez, A.; Sánchez, A.; Sánchez, E.; Tolloch, S.; Velázquez, M.; Zamorano, J.; Aguerri, A.; Barrado, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, A.; Chávez, M.; García, M.; González Delgado, R.; Guichard, J.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D.; Jiménez, J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya, D.; Méndez Abreu, J.; Mollá, M.; Muñoz Tuñón, C.; Peimbert, M.; Pérez González, P.; Pérez Montero, E.; Rodríguez, M.; Rodríguez Espinosa, J. M.; Rodríguez, L.; Rosa, D.; Sánchez Almeida, J.; Sánchez Contreras, C.; Sánchez Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón Díaz; S.; Tenorio Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O.; Villar, V. Bibcode: 2016ASPC..507..103G Altcode: MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the new optical spectrograph for the 10.4 m Gran Telescopio CANARIAS (GTC). Once installed at GTC by the end of 2016, MEGARA will provide both Integral Field Unit and Multi-Object Spectroscopy capabilities covering a field-of-view of 12.5×11.3 arcsec2 and 3.5×3.5 arcmin2, respectively. The MEGARA spectrograph will yield spectral resolutions in the range R=6,000-18,700 across the entire optical window with superb image quality and throughput, thanks to the use of state-of-the-art optical fibers, pupil elements (VPHs) and CCD detector. In this contribution we provide a brief description of the status of the instrument construction and of the science that our Science Team is aiming to pursue with MEGARA, with special emphasis on potential synergies with the future Multi-Object Spectrograph for the William Herschel Telescope (WHT), WEAVE. Title: Gas accretion from the cosmic web in the local Universe Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón, C.; Elmegreen, D. M. Bibcode: 2016IAUS..308..390S Altcode: Numerical simulations predict that gas accretion from the cosmic web drives star formation in disks galaxies. The process is important in low mass haloes (< 1012 M), therefore, in the early universe when galaxies were low mass, but also in dwarf galaxies of the local universe. The gas that falls in is predicted to be tenuous, patchy, partly ionized, multi-temperature, and large-scale; therefore, hard to show in a single observation. One of the most compelling cases for gas accretion at work in the local universe comes from the extremely metal poor (XMP) galaxies. They show metallicity inhomogeneities associated with star-forming regions, so that large starbursts have lower metallicity than the underlying galaxy. Here we put forward the case for gas accretion from the web posed by XMP galaxies. Two other observational results are discussed too, namely, the fact that the gas consumption time-scale is shorter than most stellar ages, and the systematic morphological distortions of the HI around galaxies. Title: MEGARA, the new intermediate-resolution optical IFU and MOS for GTC: getting ready for the telescope Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Iglesias-Páramo, J.; Cedazo, R.; García Vargas, M. L.; Arrillaga, X.; Avilés, J. L.; Cardiel, N.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; de la Cruz García, J. M.; Esteban San Román, S.; Ferrusca, D.; Gómez-Álvarez, P.; Izazaga-Pérez, R.; Lefort, B.; López-Orozco, J. A.; Maldonado, M.; Martínez-Delgado, I.; Morales Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Picazo, P.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Vílchez, J. M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues, D.; Bertone, E.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.; García-Rojas, J.; Guichard, J.; González-Delgado, R.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D. H.; Jiménez-Vicente, J.; Kehrig, C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mayya, Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rodríguez-Muñoz, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez Moreno, F. M.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O. Bibcode: 2016SPIE.9908E..1KG Altcode: MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is an optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) designed for the GTC 10.4m telescope in La Palma that is being built by a Consortium led by UCM (Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). The instrument is currently finishing AIV and will be sent to GTC on November 2016 for its on-sky commissioning on April 2017. The MEGARA IFU fiber bundle (LCB) covers 12.5x11.3 arcsec2 with a spaxel size of 0.62 arcsec while the MEGARA MOS mode allows observing up to 92 objects in a region of 3.5x3.5 arcmin2 around the IFU. The IFU and MOS modes of MEGARA will provide identical intermediate-to-high spectral resolutions (RFWHM 6,000, 12,000 and 18,700, respectively for the low-, mid- and high-resolution Volume Phase Holographic gratings) in the range 3700-9800ÅÅ. An x-y mechanism placed at the pseudo-slit position allows (1) exchanging between the two observing modes and (2) focusing the spectrograph for each VPH setup. The spectrograph is a collimator-camera system that has a total of 11 VPHs simultaneously available (out of the 18 VPHs designed and being built) that are placed in the pupil by means of a wheel and an insertion mechanism. The custom-made cryostat hosts a 4kx4k 15-μm CCD. The unique characteristics of MEGARA in terms of throughput and versatility and the unsurpassed collecting are of GTC make of this instrument the most efficient tool to date to analyze astrophysical objects at intermediate spectral resolutions. In these proceedings we present a summary of the instrument characteristics and the results from the AIV phase. All subsystems have been successfully integrated and the system-level AIV phase is progressing as expected. Title: Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639 Authors: Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Mendez-Abreu, Jairo; Gallagher, John S.; Rafelski, Marc; Filho, Mercedes; Ceverino, Daniel Bibcode: 2016ApJ...825..145E Altcode: 2016arXiv160502822E The tadpole galaxy Kiso 5639 has a slowly rotating disk with a drop in metallicity at its star-forming head, suggesting that star formation was triggered by the accretion of metal-poor gas. We present multi-wavelength Hubble Space Telescope Wide Field Camera 3 images of UV through I band plus Hα to search for peripheral emission and determine the properties of various regions. The head has a mass in young stars of ∼ {10}6 {M} and an ionization rate of 6.4× {10}51 s-1, equivalent to ∼2100 O9-type stars. There are four older star-forming regions in the tail, and an underlying disk with a photometric age of ∼1 Gyr. The mass distribution function of 61 star clusters is a power law with a slope of -1.73 ± 0.51. Fourteen young clusters in the head are more massive than {10}4 {M}, suggesting a clustering fraction of 30%-45%. Wispy filaments of Hα emission and young stars extend away from the galaxy. Shells and holes in the head H II region could be from winds and supernovae. Gravity from the disk should limit the expansion of the H II region, although hot gas might escape through the holes. The star formation surface density determined from Hα in the head is compared to that expected from likely pre-existing and accreted gas. Unless the surface density of the accreted gas is a factor of ∼3 or more larger than what was in the galaxy before, the star formation rate has to exceed the usual Kennicutt-Schmidt rate by a factor of ≥slant 5. Title: Starbursts and Galaxy Evolution: results from COSMOS survey. Authors: Muñoz-Tuñón, C.; Hinojosa Goñi, R.; Jairo Méndez Abreu, J.; Sánchez Alméida, J. Bibcode: 2016ilgp.confE..64M Altcode: The search for starbursts galaxies in COSMOS database by a tailored procedure that uses the photometry from SUBARU, results in 220 targets at z<0.5. The typical mass of the starburst is 10^8 and its distribution is similar to that of the quiescent galaxies in the survey at the same redshift range. From the detailed analysis of the galaxies images using the HST, the star forming clumps are characterized. The galaxies are of three different kinds, Snot, Snot and diffuse light and multiple knots. The mass of the knots are typically one order of magnitude below that of the host galaxy and the clumps in multiple knot galaxies are bigger the closer they are to the center. The sSFR however does not change with the particular position of the burst in their host galaxy, which suggests a similar process independently of their location. This result applies also to the galaxies at the largest z range (0.9). Our interpretation is that the star formation is happening at all possible locations on the galaxy discs, possibly from gas accreted from the halo or the IGM, with clumps which grow as they spiral and get to the centermost regions. Our previous work on nearby SF -tadpole galaxies of similar mass reported metallicity drops coinciding with the location of the burst what we have interpreted as SF driven by cold flows. Our results in COSMOS would be consistent with a similar interpretation and a scenario in which medium mass disks are growing by gas accretion that show up as scattered starbursts knots. Title: The Role of Galaxy Morphology in the Mass-Metallicity-SFR Relation Authors: Rafelski, Marc; Elmegreen, Bruce; Elmegreen, Debra M.; Gardner, Jonathan P.; Henry, Alaina L.; Munoz-Tunon, Casiana; Sanchez Almeida, Jorge; Straughn, Amber Bibcode: 2016hst..prop14580R Altcode: The mass-metallicity-SFR (M-Z-SFR) relation for galaxies gives insight into the accretion and outflow of gas. Heightened accretion should increase disk turbulence and the corresponding Jeans mass for gravitational instabilities, making star-formation clumpy, and it should also trigger star formation directly in large clumps where infalling clouds impact the disk. It follows that if the most irregular and clumpy galaxies are the most actively accreting, then they should be low-Z outliers in the M-Z-SFR relation. We propose to investigate for the first time whether any relationship exists between position on the M-Z-SFR relation and clumpy morphology. We will use WFC3/IR grism observations from several large surveys in the CANDELS fields to measure metallicities of intermediate redshift (1.3 Title: VizieR Online Data Catalog: Extremely metal-poor galaxies in SDSS. II. (Sanchez Almeida+ 2016) Authors: Sanchez Almeida, J.; Perez-Montero, E.; Morales-Luis, A. B.; Munoz-Tunon, C.; Garcia-Benito, R.; Nuza, S. E.; Kitaura, F. S. Bibcode: 2016yCat..18190110S Altcode: First, we search for XMP candidates using the algorithm k-means (Sanchez Almeida et al. 2010ApJ...714..487S; Ordovas-Pascual & Sanchez Almeida 2014A&A...565A..53O). It leads to 1281 candidates. Then, we use the SDSS-DR7 spectra of the candidates to measure their integrated metallicity, which narrows down the list to 196 XMPs. We also include a second list (Table 2) with 332 potential XMPs that are selected under less restrictive noise constraints.

(2 data files). Title: Gas inflow and metallicity drops in star-forming galaxies Authors: Ceverino, Daniel; Sánchez Almeida, Jorge; Muñoz Tuñón, Casiana; Dekel, Avishai; Elmegreen, Bruce G.; Elmegreen, Debra M.; Primack, Joel Bibcode: 2016MNRAS.457.2605C Altcode: 2015arXiv150902051C Gas inflow feeds galaxies with low-metallicity gas from the cosmic web, sustaining star formation across the Hubble time. We make a connection between these inflows and metallicity inhomogeneities in star-forming galaxies, by using synthetic narrow-band images of the Hα emission line from zoom-in AMR cosmological simulations of galaxies with stellar masses of M* ≃ 109 M at redshifts z = 2-7. In ∼50 per cent of the cases at redshifts lower than 4, the gas inflow gives rise to star-forming, Hα-bright, off-centre clumps. Most of these clumps have gas metallicities, weighted by Hα luminosity, lower than the metallicity in the surrounding interstellar medium by ∼0.3 dex, consistent with observations of chemical inhomogeneities at high and low redshifts. Due to metal mixing by shear and turbulence, these metallicity drops are dissolved in a few disc dynamical times. Therefore, they can be considered as evidence for rapid gas accretion coming from cosmological inflow of pristine gas. Title: The fate of high-redshift massive compact galaxies Authors: de la Rosa, Ignacio G.; La Barbera, Francesco; Ferreras, Ignacio; Sánchez Almeida, Jorge; Dalla Vecchia, Claudio; Martínez-Valpuesta, Inma; Stringer, Martin Bibcode: 2016MNRAS.457.1916D Altcode: 2016arXiv160103920D Massive high-redshift quiescent compact galaxies (nicknamed red nuggets) have been traditionally connected to present-day elliptical galaxies, often overlooking the relationships that they may have with other galaxy types. We use large bulge-disc decomposition catalogues based on the Sloan Digital Sky Survey to check the hypothesis that red nuggets have survived as compact cores embedded inside the haloes or discs of present-day massive galaxies. In this study, we designate a compact core as the bulge component that satisfies a prescribed compactness criterion. Photometric and dynamic mass-size and mass-density relations are used to show that, in the inner regions of galaxies at z ∼ 0.1, there are abundant compact cores matching the peculiar properties of the red nuggets, an abundance comparable to that of red nuggets at z ∼ 1.5. Furthermore, the morphology distribution of the present-day galaxies hosting compact cores is used to demonstrate that, in addition to the standard channel connecting red nuggets with elliptical galaxies, a comparable fraction of red nuggets might have ended up embedded in discs. This result generalizes the inside-out formation scenario; present-day massive galaxies can begin as dense spheroidal cores (red nuggets), around which either a spheroidal halo or a disc is formed later. Title: The Kennicutt-Schmidt Relation in Extremely Metal-Poor Dwarf Galaxies Authors: Filho, M. E.; Sánchez Almeida, J.; Amorín, R.; Muñoz-Tuñón, C.; Elmegreen, B. G.; Elmegreen, D. M. Bibcode: 2016ApJ...820..109F Altcode: 2016arXiv160204772F The Kennicutt-Schmidt (KS) relation between the gas mass and star formation rate (SFR) describes the star formation regulation in disk galaxies. It is a function of gas metallicity, but the low-metallicity regime of the KS diagram is poorly sampled. We have analyzed data for a representative set of extremely metal-poor galaxies (XMPs), as well as auxiliary data, and compared these to empirical and theoretical predictions. The majority of the XMPs possess high specific SFRs, similar to high-redshift star-forming galaxies. On the KS plot, the XMP H I data occupy the same region as dwarfs and extend the relation for low surface brightness galaxies. Considering the H I gas alone, a considerable fraction of the XMPs already fall off the KS law. Significant quantities of “dark” H2 mass (I.e., not traced by CO) would imply that XMPs possess low star formation efficiencies (SFEgas). Low SFEgas in XMPs may be the result of the metal-poor nature of the H I gas. Alternatively, the H I reservoir may be largely inert, the star formation being dominated by cosmological accretion. Time lags between gas accretion and star formation may also reduce the apparent SFEgas, as may galaxy winds, which can expel most of the gas into the intergalactic medium. Hence, on global scales, XMPs could be H I-dominated, high-specific-SFR (≳10-10 yr-1), low-SFEgas (≲10-9 yr-1) systems, in which the total H I mass is likely not a good predictor of the total H2 mass, nor of the SFR. Title: Search for Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey. (II). High Electron Temperature Objects Authors: Sánchez Almeida, J.; Pérez-Montero, E.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; García-Benito, R.; Nuza, S. E.; Kitaura, F. S. Bibcode: 2016ApJ...819..110S Altcode: 2016arXiv160101631S Extremely metal-poor (XMP) galaxies are defined to have a gas-phase metallicity smaller than a tenth of the solar value (12+{log}[{{O/H}}]< 7.69). They are uncommon, chemically and possibly dynamically primitive, with physical conditions characteristic of earlier phases of the universe. We search for new XMPs in the Sloan Digital Sky Survey (SDSS) in a work that complements Paper I. This time, high electron temperature objects are selected; metals are a main coolant of the gas, so metal-poor objects contain high-temperature gas. Using the algorithm k-means, we classify 788,677 spectra to select 1281 galaxies that have particularly intense [O III]λ4363 with respect to [O III]λ5007, which is a proxy for high electron temperature. The metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 XMPs. A less restrictive noise constraint provides a larger set with 332 candidates. Both lists are provided in electronic format. The selected XMP sample has a mean stellar mass around {10}8 {M}, with the dust mass ∼ {10}3{M} for typical star-forming regions. In agreement with previous findings, XMPs show a tendency to be tadpole-like or cometary. Their underlying stellar continuum corresponds to a fairly young stellar population (< 1 {{Gyr}}), although young and aged stellar populations coexist at the low-metallicity starbursts. About 10% of the XMPs show large N/O. Based on their location in constrained cosmological numerical simulations, XMPs have a strong tendency to appear in voids and to avoid galaxy clusters. The puzzling 2%-solar low-metallicity threshold exhibited by XMPs remains. Title: Evidence of Cosmic Accretion in Local Tadpole Galaxies Authors: Elmegreen, Debra M.; Elmegreen, Bruce; Sanchez Almeida, Jorge; Munoz-Tunon, Casiana; Rafelski, Marc; Gallagher, John S.; Mendez-Abreu, Jairo; Amorin, R.; Filho, M.; Ascasibar, Y.; Papaderos, P.; Vilchez, J.; Perez-Montero, E. Bibcode: 2016AAS...22711101E Altcode: Star formation in galaxies over cosmic time may be driven by gas accretion from the cosmic web. Spectra of local extremely metal-poor galaxies (XMPs), obtained using the Gran Telescopio Canarias, show oxygen abundances that decrease by a factor of 5 to 10 in the main star-forming regions compared with the disks in 9 of 10 observed galaxies. The results suggest that the galaxies have accreted metal-poor gas in the starburst regions. Tadpole galaxies, which have a main star-forming head and a tail, are common at high redshift but rare locally. Local tadpoles tend to be XMPs. We present multiband HST WFC3 observations of Kiso 5639, one of the tadpole XMPs in our GTC sample. There are faint extended H alpha filaments, and dense star clusters in the midst of a powerful starburst. The clusters, with log masses of 4 to 5, are reminiscent of those found in other dwarf irregular galaxies where impacting gas streams have been suggested. Title: Localized Starbursts in Dwarf Galaxies Produced by the Impact of Low-metallicity Cosmic Gas Clouds Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón, C.; Elmegreen, D. M.; Pérez-Montero, E.; Amorín, R.; Filho, M. E.; Ascasibar, Y.; Papaderos, P.; Vílchez, J. M. Bibcode: 2015ApJ...810L..15S Altcode: 2015arXiv150900180S Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter halos. Although these predictions are unambiguous, the observational support has been indirect so far. Here, we report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local universe, taking the form of localized starbursts associated with gas having low metallicity. Detailed abundance analyses based on Gran Telescopio Canarias optical spectra of 10 XMPs show that the galaxy hosts have metallicities around 60% solar, on average, while the large star-forming regions that dominate their integrated light have low metallicities of some 6% solar. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr), the observed metallicity inhomogeneities are only possible if the metal-poor gas fell onto the disk recently. We analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. If this interpretation is correct, XMPs trace the cosmic web gas in their surroundings, making them probes to examine its properties. Title: Gas accretion from halos to disks: observations, curiosities, and problems Authors: Elmegreen, Bruce G.; Hunter, Deidre A.; Ashley, Trisha; Nidever, David; Johnson, Megan; Simpson, Caroline; Pokrel, Nau Raj; Sanchez Almeida, Jorge; Munoz-Tunon, Casiana; Elmegreen, Debra; Mendez-Abreu, Jairo; Belen Morales-Luis, Ana Bibcode: 2015IAUGA..2251098E Altcode: Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GCT. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a recent study of their far-outer regions sees no need for, or evidence of, continuing gas buildup. Title: Gas accretion from the cosmic web in the local Universe Authors: Sánchez Almeida, J.; Elmegreen, B. G.; Muñoz-Tuñón, C.; Elmegreen, D. M. Bibcode: 2015hsa8.conf..335S Altcode: Numerical simulations predict that gas accretion from the cosmic web drives star formation in disks galaxies. The process is more important in low mass haloes, therefore, when galaxies were low mass in the early universe, but also in dwarf galaxies of the local universe. The central role played by cosmic gas infall is as clear from numerical simulations as it is obscure to observations. The gas that falls in is predicted to be tenuous, patchy, partly ionized, multi-temperature, low-metallicity, and large-scale; thus, hard to show in a single observation. One of the most compelling cases for gas accretion at work in the local universe comes from the extremely metal poor (XMP) galaxies. They show metallicity inhomogeneities associated with star-forming regions, so that large starbursts have lower metallicity that then underlying galaxy. This and other evidence suggest that local XMP are primitive disks sustained by cosmic web gas accretion. In the contribution we described the case posed by XMP galaxies to support the existence of cosmological gas accretion. Title: MEGARA, the new IFU and MOS for the GTC Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias-Páramo, J.; Sánchez Moreno, F. M.; Vílchez, J. M.; García Vargas, M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; Cedazo, R.; Eliche-Moral, M. C.; Ferrusca, D.; González-Guardia, E.; Lefort, B.; Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Guzmán, R.; Herrero, A.; Huélamo, N., Hughes, D.; Jiménez-Vicente, J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya, Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S. F.; Sarajedini, A.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O.; Villar, V. Bibcode: 2015hsa8.conf..804G Altcode: MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is the future intermediate-resolution optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) of the 10.4m GTC telescope. The instrument can be used to observe either a contiguous (100% filling factor) field-of-view of 12.5×11.3 arcsec^{2} or 92 objects anywhere in a 3.5×3.5 arcmin^{2} field patrolled by robotic actuactors attached to optical-fiber minibundles, respectively in its IFU and MOS modes. The MEGARA Consortium is led by the Universidad Complutense de Madrid (UCM, Spain) and also includes the Instituto Nacional de Astrofísica, óptica y Electrónica (INAOE, Mexico), the Instituto de Astrofísica de Andalucía (IAA-CSIC, Spain) and the Universidad Politécnica de Madrid (UPM, Spain). The instrument passed its Critical Design Review (CDR) on late 2014 and is currently in construction phase with a planned date for the start of operations at GTC on early 2017. In this paper we summarize the main characteristics of the instrument and the status of the project. Title: Extremely Metal-poor Galaxies: The Environment Authors: Filho, M. E.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Nuza, S. E.; Kitaura, F.; Heß, S. Bibcode: 2015ApJ...802...82F Altcode: 2015arXiv150106709F We have analyzed bibliographical observational data and theoretical predictions, in order to probe the environment in which extremely metal-poor dwarf galaxies (XMPs) reside. We have assessed the H i component and its relation to the optical galaxy, the cosmic web type (voids, sheets, filaments and knots), the overdensity parameter and analyzed the nearest galaxy neighbors. The aim is to understand the role of interactions and cosmological accretion flows in the XMP observational properties, particularly the triggering and feeding of the star formation. We find that XMPs behave similarly to Blue Compact Dwarfs; they preferably populate low-density environments in the local universe: ∼60% occupy underdense regions, and ∼75% reside in voids and sheets. This is more extreme than the distribution of irregular galaxies, and in contrast to those regions preferred by elliptical galaxies (knots and filaments). We further find results consistent with previous observations; while the environment does determine the fraction of a certain galaxy type, it does not determine the overall observational properties. With the exception of five documented cases (four sources with companions and one recent merger), XMPs do not generally show signatures of major mergers and interactions; we find only one XMP with a companion galaxy within a distance of 100 kpc, and the H i gas in XMPs is typically well-behaved, demonstrating asymmetries mostly in the outskirts. We conclude that metal-poor accretion flows may be driving the XMP evolution. Such cosmological accretion could explain all the major XMP observational properties: isolation, lack of interaction/merger signatures, asymmetric optical morphology, large amounts of unsettled, metal-poor H i gas, metallicity inhomogeneities, and large specific star formation. Title: On the Use of the Index N2 to Derive the Metallicity in Metal-poor Galaxies Authors: Morales-Luis, A. B.; Pérez-Montero, E.; Sánchez Almeida, J.; Muñoz-Tuñón, C. Bibcode: 2014ApJ...797...81M Altcode: 2014arXiv1410.2850M The N2 index ([N II] 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. Title: Star Formation in Tadpole Galaxies Authors: Muñoz-Tuñon, Casiana; Sanchez Almeida, Jorge; Elmegreen, Debra M.; Elmegreen, Bruce G. Bibcode: 2014mbhe.conf...96M Altcode: No abstract at ADS Title: Does Cold-Flow Accretion Drive Star-Formation in the Local Universe? Authors: Sánchez Almeida, J.; Muñoz, C.; Elmegreen, D.; Elmegreen, B. G.; Méndez-Abreu, J. Bibcode: 2014mysc.conf...99S Altcode: Numerical simulations of galaxy formation predict direct gas accretion from the cosmic web to be the main mode of disk galaxy formation. However, observational evidence of the process are so far scarce and indirect. This write up should be regarded as a progress report listing several of our works which, in the long term, aim at finding evidence for or against pristine gas accretion as a driver of star formation in the local Universe. Here we motivate the interest of the study, and then refer the reader to the actual papers for further details. Title: Chemical Evolution of Super Star Clusters in a Positive Star Formation Feedback Scenario Authors: Mollá, M.; Sánchez Almeida, J.; Terlevich, R.; Tenorio-Tagle, G.; Silich, S.; Muñoz-Tuñón, C. Bibcode: 2014mysc.conf...79M Altcode: No abstract at ADS Title: Star formation sustained by gas accretion Authors: Sánchez Almeida, Jorge; Elmegreen, Bruce G.; Muñoz-Tuñón, Casiana; Elmegreen, Debra Meloy Bibcode: 2014A&ARv..22...71S Altcode: 2014arXiv1405.3178S Numerical simulations predict that metal-poor gas accretion from the cosmic web fuels the formation of disk galaxies. This paper discusses how cosmic gas accretion controls star formation, and summarizes the physical properties expected for the cosmic gas accreted by galaxies. The paper also collects observational evidence for gas accretion sustaining star formation. It reviews evidence inferred from neutral and ionized hydrogen, as well as from stars. A number of properties characterizing large samples of star-forming galaxies can be explained by metal-poor gas accretion, in particular, the relationship among stellar mass, metallicity, and star-formation rate (the so-called fundamental metallicity relationship). They are put forward and analyzed. Theory predicts gas accretion to be particularly important at high redshift, so indications based on distant objects are reviewed, including the global star-formation history of the universe, and the gas around galaxies as inferred from absorption features in the spectra of background sources. Title: MEGARA: a new generation optical spectrograph for GTC Authors: Gil de Paz, A.; Gallego, J.; Carrasco, E.; Iglesias-Páramo, J.; Cedazo, R.; Vílchez, J. M.; García-Vargas, M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; Eliche-Moral, M. C.; Ferrusca, D.; González-Guardia, E.; Lefort, B.; Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales Durán, I.; Mujica, E.; Páez, G.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Tulloch, S.; Velázquez, M.; Zamorano, J.; Aguerri, A. L.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Gúzman, R.; Herrero, A.; Huélamo, N.; Hughes, D.; Jiménez-Vicente, J.; Kehrig, C.; Márquez, I.; Masegosa, J.; Mayya, Y. D.; Méndez-Abreu, J.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa-González, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez Moreno, F. M.; Sánchez, S. F.; Sarajedini, A.; Serena, F.; Silich, S.; Simón-Díaz, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Torres-Peimbert, S.; Trujillo, I.; Tsamis, Y.; Vega, O.; Villar, V. Bibcode: 2014SPIE.9147E..0OG Altcode: MEGARA (Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía) is an optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) designed for the GTC 10.4m telescope in La Palma. MEGARA offers two IFU fiber bundles, one covering 12.5x11.3 arcsec2 with a spaxel size of 0.62 arcsec (Large Compact Bundle; LCB) and another one covering 8.5x6.7 arcsec2 with a spaxel size of 0.42 arcsec (Small Compact Bundle; SCB). The MEGARA MOS mode will allow observing up to 100 objects in a region of 3.5x3.5 arcmin2 around the two IFU bundles. Both the LCB IFU and MOS capabilities of MEGARA will provide intermediate-to-high spectral resolutions (RFWHM~6,000, 12,000 and 18,700, respectively for the low-, mid- and high-resolution Volume Phase Holographic gratings) in the range 3650-9700ÅÅ. These values become RFWHM~7,000, 13,500, and 21,500 when the SCB is used. A mechanism placed at the pseudo-slit position allows exchanging the three observing modes and also acts as focusing mechanism. The spectrograph is a collimator-camera system that has a total of 11 VPHs simultaneously available (out of the 18 VPHs designed and being built) that are placed in the pupil by means of a wheel and an insertion mechanism. The custom-made cryostat hosts an E2V231-84 4kx4k CCD. The UCM (Spain) leads the MEGARA Consortium that also includes INAOE (Mexico), IAA-CSIC (Spain), and UPM (Spain). MEGARA is being developed under a contract between GRANTECAN and UCM. The detailed design, construction and AIV phases are now funded and the instrument should be delivered to GTC before the end of 2016. Title: A fast version of the k-means classification algorithm for astronomical applications Authors: Ordovás-Pascual, I.; Sánchez Almeida, J. Bibcode: 2014A&A...565A..53O Altcode: 2014arXiv1404.3097O Context. K-means is a clustering algorithm that has been used to classify large datasets in astronomical databases. It is an unsupervised method, able to cope very different types of problems.
Aims: We check whether a variant of the algorithm called single pass k-means can be used as a fast alternative to the traditional k-means.
Methods: The execution time of the two algorithms are compared when classifying subsets drawn from the SDSS-DR7 catalog of galaxy spectra.
Results: Single-pass k-means turn out to be between 20% and 40% faster than k-means and provide statistically equivalent classifications. This conclusion can be scaled up to other larger databases because the execution time of both algorithms increases linearly with the number of objects.
Conclusions: Single-pass k-means can be safely used as a fast alternative to k-means. Title: Star Formation in Tadpole Galaxies Authors: Munoz-Tunon, Casiana; Sanchez Almeida, Jorge; Elmegreen, Debra M.; Elmegreen, Bruce G. Bibcode: 2014arXiv1404.5170M Altcode: Tadpole Galaxies look like a star forming head with a tail structure to the side. They are also named cometaries. In a series of recent works we have discovered a number of issues that lead us to consider them extremely interesting targets. First, from images, they are disks with a lopsided starburst. This result is firmly established with long slit spectroscopy in a nearby representative sample. They rotate with the head following the rotation pattern but displaced from the rotation center. Moreover, in a search for extremely metal poor (XMP) galaxies, we identified tadpoles as the dominant shapes in the sample- nearly 80% of the local XMP galaxies have a tadpole morphology. In addition, the spatially resolved analysis of the metallicity shows the remarkable result that there is a metallicity drop right at the position of the head. This is contrary to what intuition would say and difficult to explain if star formation has happened from gas processed in the disk. The result could however be understood if the star formation is driven by pristine gas falling into the galaxy disk. If confirmed, we could be unveiling, for the first time, cool flows in action in our nearby world. The tadpole class is relatively frequent at high redshift - 10% of resolvable galaxies in the Hubble UDF but less than 1% in the local Universe. They are systems that could track cool flows and test models of galaxy formation. Title: Metallicity Inhomogeneities in Local Star-forming Galaxies as a Sign of Recent Metal-poor Gas Accretion Authors: Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; Elmegreen, D. M.; Elmegreen, B. G.; Méndez-Abreu, J. Bibcode: 2014ApJ...783...45S Altcode: 2014arXiv1401.1985S We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show sime0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the same unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpreted as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well. Title: Extremely metal-poor galaxies: The H I content Authors: Filho, M. E.; Winkel, B.; Sánchez Almeida, J.; Aguerri, J. A.; Amorín, R.; Ascasibar, Y.; Elmegreen, B. G.; Elmegreen, D. M.; Gomes, J. M.; Humphrey, A.; Lagos, P.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; Papaderos, P.; Vílchez, J. M. Bibcode: 2013A&A...558A..18F Altcode: 2013arXiv1307.4899F Context. Extremely metal-poor (XMP) galaxies are chemically, and possibly dynamically, primordial objects in the local Universe.
Aims: Our objective is to characterize the H i content of the XMP galaxies as a class, using as a reference the list of 140 known local XMPs compiled by Morales-Luis et al. (2011).
Methods: We have observed 29 XMPs, which had not been observed before at 21 cm, using the Effelsberg radio telescope. This information was complemented with H i data published in literature for a further 53 XMPs. In addition, optical data from the literature provided morphologies, stellar masses, star-formation rates and metallicities.
Results: Effelsberg H i integrated flux densities are between 1 and 15 Jy km s-1, while line widths are between 20 and 120 km s-1. H i integrated flux densities and line widths from literature are in the range 0.1-200 Jy km s-1 and 15-150 km s-1, respectively. Of the 10 new Effelsberg detections, two sources show an asymmetric double-horn profile, while the remaining sources show either asymmetric (seven sources) or symmetric (one source) single-peak 21 cm line profiles. An asymmetry in the H i line profile is systematically accompanied by an asymmetry in the optical morphology. Typically, the g-band stellar mass-to-light ratios are ~0.1, whereas the H i gas mass-to-light ratios may be up to two orders of magnitude larger. Moreover, H i gas-to-stellar mass ratios fall typically between 10 and 20, denoting that XMPs are extremely gas-rich. We find an anti-correlation between the H i gas mass-to-light ratio and the luminosity, whereby fainter XMPs are more gas-rich than brighter XMPs, suggesting that brighter sources have converted a larger fraction of their H i gas into stars. The dynamical masses inferred from the H i line widths imply that the stellar mass does not exceed 5% of the dynamical mass, while the H i mass constitutes between 20 and 60% of the dynamical mass. Furthermore, the dark matter mass fraction spans a wide range, but can account, in some cases, for over 65% of the dynamical mass. XMPs are found to be outliers of the mass - and luminosity - metallicity relation, whereby they lack metals for their estimated dynamical mass and luminosity, suggesting the presence of pristine gas. However, they generally follow the luminosity - and baryonic mass Tully-Fisher relation, indicating that the H i gas is partly virialized and contains some rotational support. 60% of the XMP sources show a small velocity offset (10-40 km s-1) between the H i gas and the stellar/nebular component, implying that, in these sources, the H i gas is not tightly coupled to the stars and ionized gas. The effective yields provided by oxygen are often larger than the standard theoretical yields, suggesting that the observed H i gas is relatively metal-free. 80% of the XMP sources present asymmetric optical morphology - 60 XMPs show cometary structure, 11 show two bright star-forming knots and 18 show multiple star-forming regions. Star-formation rates are found to be similar to those typically found in BCDs. However, specific star-formation rates are high, with timescales to double their stellar mass, at the current rate, of typically less than 1 Gyr.
Conclusions: XMP galaxies are among the most gas-rich objects in the local Universe. The observed H i component suggests kinematical disruption and hints at a primordial composition.

Full Fig. 1, Tables 3-5 are available in electronic form at http://www.aanda.orgReduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/558/A18 Title: VizieR Online Data Catalog: HI spectra of extremely metal-poor (XMP) galaxies (Filho+, 2013) Authors: Filho, M. E.; Winkel, B.; Sanchez Almeida, J.; Aguerri, J. A.; Amorin, R.; Ascasibar, Y.; Elmegreen, B. G.; Elmegreen, D. M.; Gomes, J. M.; Humphrey, A.; Lagos, P.; Morales-Luis, A. B.; Munoz-Tunon, C.; Papaderos, P.; Vilchez, J. M. Bibcode: 2013yCat..35580018F Altcode: 2013yCat..35589018F The HI spectra, in FITS format, of the XMP galaxies observed with Effelsberg.

(5 data files). Title: Massive Clumps in Local Galaxies: Comparisons with High-redshift Clumps Authors: Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Dewberry, J.; Putko, J.; Teich, Y.; Popinchalk, M. Bibcode: 2013ApJ...774...86E Altcode: 2013arXiv1308.0306E Local UV-bright galaxies in the Kiso survey include clumpy systems with kiloparsec-size star complexes that resemble clumpy young galaxies in surveys at high redshift. We compare clump masses and underlying disks in several dozen galaxies from each of these surveys to the star complexes and disks of normal spirals. Photometry and spectroscopy for the Kiso and spiral sample come from the Sloan Digital Sky Survey. We find that the largest Kiso clumpy galaxies resemble Ultra Deep Field (UDF) clumpies in terms of the star formation rates, clump masses, and clump surface densities. Clump masses and surface densities in normal spirals are smaller. If the clump masses are proportional to the turbulent Jeans mass in the interstellar medium, then for the most luminous galaxies in the sequence of normal:Kiso:UDF, the turbulent speeds and surface densities increase in the proportions 1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe B-band absolute magnitude. For the least luminous galaxies in the overlapping magnitude range, the turbulent speed and surface density trends are 1.0:2.7:7.4 and 1.0:1.4:3.0, respectively. We also find that while all three types have radially decreasing disk intensities when measured with ellipse-fit azimuthal averages, the average profiles are more irregular for UDF clumpies (which are viewed in their restframe UV) than for Kiso galaxies (viewed at g-band), and major axis intensity scans are even more irregular for the UDF than Kiso galaxies. Local clumpy galaxies in the Kiso survey appear to be intermediate between UDF clumpies and normal spirals. Title: A Virtual Observatory Census to Address Dwarfs Origins (AVOCADO). I. Science goals, sample selection, and analysis tools Authors: Sánchez-Janssen, R.; Amorín, R.; García-Vargas, M.; Gomes, J. M.; Huertas-Company, M.; Jiménez-Esteban, F.; Mollá, M.; Papaderos, P.; Pérez-Montero, E.; Rodrigo, C.; Sánchez Almeida, J.; Solano, E. Bibcode: 2013A&A...554A..20S Altcode: 2013arXiv1301.5320S 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 ≳ 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. Title: Outliers of the ASK classification as targets for GTC serendipity Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C. Bibcode: 2013RMxAC..42..111S Altcode: We classified the ∼10^6 galaxy spectra in SDSS/DR7 (Abazajian et al. 2009) into only 17 major classes (ASK classification; Sánchez Almeida et al. 2010). The algorithm provides the goodness of the classification for each individual spectrum and, therefore, a straightforward way to identify those targets which do not fit in the ASK classes. A significant part of these outliers turn out to be failures of the automatic reduction pipelines. However, a fraction of them represents genuine unusual objects which deserve detailed follow up work to assess their nature. These targets provide a unique opportunity for GTC to carry out serendipitous discoveries. This contribution summarizes the main properties of the outliers. Title: MEGARA: The future IFU and MOS of the 10.4 m GTC Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Vílchez, J. M.; Sánchez, F. M.; García-Vargas, M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.; Castillo, E.; Cedazo, R.; Eliche-Moral, M. C.; Ferrusca, D.; González, E.; Maldonado, M.; Marino, R. A.; Martínez, I.; Morales Durán, I.; Mújica, E.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Serena, F.; Tulloch, S. M.; Villar, V.; Zamorano, J.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, A. J.; Chávez, M.; García, M.; Guichard, J.; Guzmán, R.; Herrero, A.; Huélamo, N.; Hughes, D.; Iglesias, J.; Jiménez-Vicente, J.; Aguerri, J. A. L.; Mayya, Y. D.; Méndez-Abreu, J. M.; Mollá, M.; Muñoz-Tuñón, C.; Torres-Peimbert, S.; Peimbert, M.; Pérez-González, P. G.; Pérez-Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa-González, D.; Sánchez Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, P.; Sánchez, S.; Sarajedini, A.; Silich, S.; Simón, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Trujillo, I.; Tsamis, Y.; Vega, O. Bibcode: 2013RMxAC..42...90G Altcode: In these proceedings we summarize the characteristics and current status of MEGARA, the future optical IFU and MOS for the 10.4 m GTC. MEGARA is being built by a Consortium led by the UCM (Spain) that also includes the INAOE (Mexico), the IAA-CSIC (Spain) and the UPM (Spain). The MEGARA IFU offers two different bundles, one called LCB with a field-of-view of 14×12 arcsec^2 and a spaxel size of 0.685 arcsec yielding spectral resolutions between R=6000-19000 and another one called SCB covering 10×8 arcsec^2 with 0.48 arcsec spaxels and resolutions R=8000-25000. The MOS component allows observing up to 100 targets in 3.5×3.5 arcmin^2. In September 2010 MEGARA was selected as the next optical spectrograph for GTC. Its PDR is scheduled for March 2012 with First Light on 2015. Title: Oxygen abundance from strong-line methods at extremely low metallicities Authors: Morales-Luis, A. B.; Sánchez Almeida, J.; Pérez Montero, E.; Muñoz-Tuñon, C.; Aguerri, J. A. L.; Vilchez, J. M.; Terlevich, E.; Terlevich, R. Bibcode: 2013hsa7.conf..294M Altcode: The determination of oxygen abundance in nebulae requires measuring a significant number of emission lines distributed along a wide spectral range. The required measurements are hard to obtain at high redshift, where sources are very faint, and where the accessible spectral range is limited. These difficulties are often overcome using empirical relationships between the oxygen abundance and the fluxes in a small number of strong lines. The so-called strong-line methods are often the only practical alternative for metallicity estimate at high redshift. In this sense, the low metallicities range is particularly important since high redshift objects are primitive and so of low metallic content. One of the most widely used relationships links the oxygen with the ratio between [NII]6583 and Hα. This relationship shows a large scatter at low metallicity. In an effort to bring down the errors, we re-calibrated the relationship using a large sample of extremely metal-poor galaxies. The SDSS spectra of the galaxies were all analyzed in the same way to minimize systematic errors. To our surprise, the decrease of scatter reveals that the ratio [N{II}]6583 to Hα seems to be independent of metallicity at low oxygen abundance (12+log[{O}/{H}] < 7.6). This result casts doubts on the metallicities of high-redshift objects based on the relationship. We explain how the re-calibration was carried (including the sample selection and the abundance determinations). In addition, we try explain what produces the lack of correlation. Title: Study of the AGN population at intermediate redshifts in the SHARDS survey Authors: Hernán-Caballero, A.; Alonso-Herrero, A.,; Pérez-González, P. G.; Cava, A.; Barro, G.; Balcells, M.; Cardiel, N.; Cenarro, J.; Cepa, J.; Charlot, S.; Cimatti, A.; Conselice, C. J.; Daddi, E.; Donley, J.; Elbaz, D.; Ferreras, I.; Gallego, J.; Gobat, R.; Guzmán, R.; Renzini, A.; Rieke, G.; Rodríguez-Espinosa, J. M.; Tresse, L.; Trujillo, I.; Villar, V.; Zamorano, J.; de Diego, J. A. López-Aguerri, J. A.; Masegosa, J.; Muñoz Tuñon, C.; Prieto, M.; Sánchez Almeida, J. Bibcode: 2013hsa7.conf..442H Altcode: We present the first results of a program aimed to study the stellar populations of moderate luminosity X-ray selected Active Galactic Nuclei (AGN) at intermediate redshifts. We use observations taken as part of the Survey for High-z Absorption Red and Dead Sources (SHARDS) with the optical instrument OSIRIS on the 10.4m Gran Telescopio Canarias (GTC). SHARDS is an on-going ESO/GTC Large Programme that is observing the GOODS-North cosmological field with 24 medium-band filters (22 of 17nm and 3 of 25nm) in the spectral range 500-950nm. Although SHARDS was originally designed to select and study the properties of high-z massive and passively evolving galaxies, it can also provide very valuable information about AGN at intermediate redshifts. We show that the SHARDS observations provide sufficiently high spectral resolution (R∼50) to detect broad absorption stellar features (e.g., the 4000Å{} break) as well as emission lines and to estimate accurate photometric redshifts. Together with the SHARDS observations we use the wealth of multi-wavelength data from the UV to radio available for this cosmological field to study the stellar populations and star formation histories of AGN at z∼0.5-1.2. Title: Local Tadpole Galaxies: Dynamics and Metallicity Authors: Sánchez Almeida, J.; Muñoz-Tuñón, C.; Elmegreen, D. M.; Elmegreen, B. G.; Méndez-Abreu, J. Bibcode: 2013ApJ...767...74S Altcode: 2013arXiv1302.4352S Tadpole galaxies, with a bright peripheral clump on a faint tail, are morphological types unusual in the nearby universe but very common early on. Low mass local tadpoles were identified and studied photometrically in a previous work, which we complete here analyzing their chemical and dynamical properties. We measure Hα velocity curves of seven local tadpoles, representing 50% of the initial sample. Five of them show evidence for rotation (~70%), and a sixth target hints at it. Often the center of rotation is spatially offset with respect to the tadpole head (three out of five cases). The size and velocity dispersion of the heads are typical of giant H II regions, and three of them yield dynamical masses in fair agreement with their stellar masses as inferred from photometry. In four cases the velocity dispersion at the head is reduced with respect to its immediate surroundings. The oxygen metallicity estimated from [N II] λ6583/Hα often shows significant spatial variations across the galaxies (~0.5 dex), being smallest at the head and larger elsewhere. The resulting chemical abundance gradients are opposite to the ones observed in local spirals, but agrees with disk galaxies at high redshift. We interpret the metallicity variation as a sign of external gas accretion (cold-flows) onto the head of the tadpole. The galaxies are low-metallicity outliers of the mass-metallicity relationship. In particular, two of the tadpole heads are extremely metal poor, with a metallicity smaller than a tenth of the solar value. These two targets are also very young (ages smaller than 5 Myr). All these results combined are consistent with the local tadpole galaxies being disks in early stages of assembling, with their star formation sustained by accretion of external metal-poor gas. Title: Automated Unsupervised Classification of the Sloan Digital Sky Survey Stellar Spectra using k-means Clustering Authors: Sánchez Almeida, J.; Allende Prieto, C. Bibcode: 2013ApJ...763...50S Altcode: 2012arXiv1211.5321S Large spectroscopic surveys require automated methods of analysis. This paper explores the use of k-means clustering as a tool for automated unsupervised classification of massive stellar spectral catalogs. The classification criteria are defined by the data and the algorithm, with no prior physical framework. We work with a representative set of stellar spectra associated with the Sloan Digital Sky Survey (SDSS) SEGUE and SEGUE-2 programs, which consists of 173,390 spectra from 3800 to 9200 Å sampled on 3849 wavelengths. We classify the original spectra as well as the spectra with the continuum removed. The second set only contains spectral lines, and it is less dependent on uncertainties of the flux calibration. The classification of the spectra with continuum renders 16 major classes. Roughly speaking, stars are split according to their colors, with enough finesse to distinguish dwarfs from giants of the same effective temperature, but with difficulties to separate stars with different metallicities. There are classes corresponding to particular MK types, intrinsically blue stars, dust-reddened, stellar systems, and also classes collecting faulty spectra. Overall, there is no one-to-one correspondence between the classes we derive and the MK types. The classification of spectra without continuum renders 13 classes, the color separation is not so sharp, but it distinguishes stars of the same effective temperature and different metallicities. Some classes thus obtained present a fairly small range of physical parameters (200 K in effective temperature, 0.25 dex in surface gravity, and 0.35 dex in metallicity), so that the classification can be used to estimate the main physical parameters of some stars at a minimum computational cost. We also analyze the outliers of the classification. Most of them turn out to be failures of the reduction pipeline, but there are also high redshift QSOs, multiple stellar systems, dust-reddened stars, galaxies, and, finally, odd spectra whose nature we have not deciphered. The template spectra representative of the classes are publicly available in the online journal and at ftp://stars:kmeans@ftp.iac.es. Title: The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey Authors: Ahn, Christopher P.; Alexandroff, Rachael; Allende Prieto, Carlos; Anderson, Scott F.; Anderton, Timothy; Andrews, Brett H.; Aubourg, Éric; Bailey, Stephen; Balbinot, Eduardo; Barnes, Rory; Bautista, Julian; Beers, Timothy C.; Beifiori, Alessandra; Berlind, Andreas A.; Bhardwaj, Vaishali; Bizyaev, Dmitry; Blake, Cullen H.; Blanton, Michael R.; Blomqvist, Michael; Bochanski, John J.; Bolton, Adam S.; Borde, Arnaud; Bovy, Jo; Brandt, W. N.; Brinkmann, J.; Brown, Peter J.; Brownstein, Joel R.; Bundy, Kevin; Busca, N. G.; Carithers, William; Carnero, Aurelio R.; Carr, Michael A.; Casetti-Dinescu, Dana I.; Chen, Yanmei; Chiappini, Cristina; Comparat, Johan; Connolly, Natalia; Crepp, Justin R.; Cristiani, Stefano; Croft, Rupert A. C.; Cuesta, Antonio J.; da Costa, Luiz N.; Davenport, James R. A.; Dawson, Kyle S.; de Putter, Roland; De Lee, Nathan; Delubac, Timothée; Dhital, Saurav; Ealet, Anne; Ebelke, Garrett L.; Edmondson, Edward M.; Eisenstein, Daniel J.; Escoffier, S.; Esposito, Massimiliano; Evans, Michael L.; Fan, Xiaohui; Femenía Castellá, Bruno; Fernández Alvar, Emma; Ferreira, Leticia D.; Filiz Ak, N.; Finley, Hayley; Fleming, Scott W.; Font-Ribera, Andreu; Frinchaboy, Peter M.; García-Hernández, D. A.; García Pérez, A. E.; Ge, Jian; Génova-Santos, R.; Gillespie, Bruce A.; Girardi, Léo; González Hernández, Jonay I.; Grebel, Eva K.; Gunn, James E.; Guo, Hong; Haggard, Daryl; Hamilton, Jean-Christophe; Harris, David W.; Hawley, Suzanne L.; Hearty, Frederick R.; Ho, Shirley; Hogg, David W.; Holtzman, Jon A.; Honscheid, Klaus; Huehnerhoff, J.; Ivans, Inese I.; Ivezić, Željko; Jacobson, Heather R.; Jiang, Linhua; Johansson, Jonas; Johnson, Jennifer A.; Kauffmann, Guinevere; Kirkby, David; Kirkpatrick, Jessica A.; Klaene, Mark A.; Knapp, Gillian R.; Kneib, Jean-Paul; Le Goff, Jean-Marc; Leauthaud, Alexie; Lee, Khee-Gan; Lee, Young Sun; Long, Daniel C.; Loomis, Craig P.; Lucatello, Sara; Lundgren, Britt; Lupton, Robert H.; Ma, Bo; Ma, Zhibo; MacDonald, Nicholas; Mack, Claude E.; Mahadevan, Suvrath; Maia, Marcio A. G.; Majewski, Steven R.; Makler, Martin; Malanushenko, Elena; Malanushenko, Viktor; Manchado, A.; Mandelbaum, Rachel; Manera, Marc; Maraston, Claudia; Margala, Daniel; Martell, Sarah L.; McBride, Cameron K.; McGreer, Ian D.; McMahon, Richard G.; Ménard, Brice; Meszaros, Sz.; Miralda-Escudé, Jordi; Montero-Dorta, Antonio D.; Montesano, Francesco; Morrison, Heather L.; Muna, Demitri; Munn, Jeffrey A.; Murayama, Hitoshi; Myers, Adam D.; Neto, A. F.; Nguyen, Duy Cuong; Nichol, Robert C.; Nidever, David L.; Noterdaeme, Pasquier; Nuza, Sebastián E.; Ogando, Ricardo L. C.; Olmstead, Matthew D.; Oravetz, Daniel J.; Owen, Russell; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan, Kaike; Parejko, John K.; Parihar, Prachi; Pâris, Isabelle; Pattarakijwanich, Petchara; Pepper, Joshua; Percival, Will J.; Pérez-Fournon, Ismael; Pérez-Ràfols, Ignasi; Petitjean, Patrick; Pforr, Janine; Pieri, Matthew M.; Pinsonneault, Marc H.; Porto de Mello, G. F.; Prada, Francisco; Price-Whelan, Adrian M.; Raddick, M. Jordan; Rebolo, Rafael; Rich, James; Richards, Gordon T.; Robin, Annie C.; Rocha-Pinto, Helio J.; Rockosi, Constance M.; Roe, Natalie A.; Ross, Ashley J.; Ross, Nicholas P.; Rossi, Graziano; Rubiño-Martin, J. A.; Samushia, Lado; Sanchez Almeida, J.; Sánchez, Ariel G.; Santiago, Basílio; Sayres, Conor; Schlegel, David J.; Schlesinger, Katharine J.; Schmidt, Sarah J.; Schneider, Donald P.; Schultheis, Mathias; Schwope, Axel D.; Scóccola, C. G.; Seljak, Uros; Sheldon, Erin; Shen, Yue; Shu, Yiping; Simmerer, Jennifer; Simmons, Audrey E.; Skibba, Ramin A.; Skrutskie, M. F.; Slosar, A.; Sobreira, Flavia; Sobeck, Jennifer S.; Stassun, Keivan G.; Steele, Oliver; Steinmetz, Matthias; Strauss, Michael A.; Streblyanska, Alina; Suzuki, Nao; Swanson, Molly E. C.; Tal, Tomer; Thakar, Aniruddha R.; Thomas, Daniel; Thompson, Benjamin A.; Tinker, Jeremy L.; Tojeiro, Rita; Tremonti, Christy A.; Vargas Magaña, M.; Verde, Licia; Viel, Matteo; Vikas, Shailendra K.; Vogt, Nicole P.; Wake, David A.; Wang, Ji; Weaver, Benjamin A.; Weinberg, David H.; Weiner, Benjamin J.; West, Andrew A.; White, Martin; Wilson, John C.; Wisniewski, John P.; Wood-Vasey, W. M.; Yanny, Brian; Yèche, Christophe; York, Donald G.; Zamora, O.; Zasowski, Gail; Zehavi, Idit; Zhao, Gong-Bo; Zheng, Zheng; Zhu, Guangtun; Zinn, Joel C. Bibcode: 2012ApJS..203...21A Altcode: 2012arXiv1207.7137S The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z ~ 0.52), 102,100 new quasar spectra (median z ~ 2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T eff < 5000 K and in metallicity estimates for stars with [Fe/H] > -0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SEGUE-2. The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the APOGEE along with another year of data from BOSS, followed by the final SDSS-III data release in 2014 December. Title: MEGARA: the future optical IFU and multi-object spectrograph for the 10.4m GTC telescope Authors: Gil de Paz, A.; Carrasco, E.; Gallego, J.; Sánchez, F. M.; Vílchez Medina, J. M.; García-Vargas, M. L.; Arrillaga, X.; Carrera, M. A.; Castillo-Morales, A.; Castillo-Domínguez, E.; Cedazo, R.; Eliche-Moral, C.; Ferrusca, D.; González-Guardia, E.; Maldonado, M.; Marino, R. A.; Martínez-Delgado, I.; Morales Durán, I.; Mújica, E.; Pascual, S.; Pérez-Calpena, A.; Sánchez-Penim, A.; Sánchez-Blanco, E.; Serena, F.; Tulloch, S.; Villar, V.; Zamorano, J.; Barrado y Naváscues, D.; Bertone, E.; Cardiel, N.; Cava, A.; Cenarro, J.; Chávez, M.; García, M.; Guichard, J.; Gúzman, R.; Herrero, A.; Huélamo, N.; Hughes, D.; Iglesias, J.; Jiménez-Vicente, J.; Aguerri, A. L.; Mayya, D.; Méndez-Abreu, J. M.; Mollá, M.; Muñoz-Tuñón, C.; Peimbert, S.; Peimbert, M.; Pérez-González, P. G.; Pérez Montero, E.; Rodríguez, M.; Rodríguez-Espinosa, J. M.; Rodríguez-Merino, L.; Rosa, D.; Sánchez-Almeida, J.; Sánchez Contreras, C.; Sánchez-Blázquez, Patricia; Sánchez, S.; Sarajedini, A.; Silich, S.; Simón, S.; Tenorio-Tagle, G.; Terlevich, E.; Terlevich, R.; Trujillo, I.; Tsamis, Y.; Vega, O. Bibcode: 2012SPIE.8446E..4QG Altcode: In these proceedings we give a summary of the characteristics and current status of the MEGARA instrument, the future optical IFU and MOS for the 10.4-m Gran Telescopio Canarias (GTC). MEGARA is being built by a Consortium of public research institutions led by the Universidad Complutense de Madrid (UCM, Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The MEGARA IFU includes two different fiber bundles, one called LCB (Large Compact Bundle) with a field-of-view of 12.5×11.3 arcsec2 and a spaxel size of 0.62 arcsec yielding spectral resolutions between R=6,800-17,000 and another one called SCB (Small Compact Bundle) covering 8.5×6.7 arcsec2 with hexagonally-shaped and packed 0.42-arcsec spaxels and resolutions R=8,000-20,000. The MOS component allows observing up to 100 targets in 3.5×3.5 arcmin2. Both the IFU bundles and the set of 100 robotic positioners of the MOS will be placed at one of the GTC Folded-Cass foci while the spectrographs (one in the case of the MEGARA-Basic concept) will be placed at the Nasmyth platform. On March 2012 MEGARA passed the Preliminary Design Review and its first light is expected to take place at the end of 2015. Title: Qualitative Interpretation of Galaxy Spectra Authors: Sánchez Almeida, J.; Terlevich, R.; Terlevich, E.; Cid Fernandes, R.; Morales-Luis, A. B. Bibcode: 2012ApJ...756..163S Altcode: 2012arXiv1207.3928S We describe a simple step-by-step guide to qualitative interpretation of galaxy spectra. Rather than an alternative to existing automated tools, it is put forward as an instrument for quick-look analysis and for gaining physical insight when interpreting the outputs provided by automated tools. Though the recipe is for general application, it was developed for understanding the nature of the Automatic Spectroscopic K-means-based (ASK) template spectra. They resulted from the classification of all the galaxy spectra in the Sloan Digital Sky Survey data release 7, thus being a comprehensive representation of the galaxy spectra in the local universe. Using the recipe, we give a description of the properties of the gas and the stars that characterize the ASK classes, from those corresponding to passively evolving galaxies, to H II galaxies undergoing a galaxy-wide starburst. The qualitative analysis is found to be in excellent agreement with quantitative analyses of the same spectra. We compare the mean ages of the stellar populations with those inferred using the code STARLIGHT. We also examine the estimated gas-phase metallicity with the metallicities obtained using electron-temperature-based methods. A number of byproducts follow from the analysis. There is a tight correlation between the age of the stellar population and the metallicity of the gas, which is stronger than the correlations between galaxy mass and stellar age, and galaxy mass and gas metallicity. The galaxy spectra are known to follow a one-dimensional sequence, and we identify the luminosity-weighted mean stellar age as the affine parameter that describes the sequence. All ASK classes happen to have a significant fraction of old stars, although spectrum-wise they are outshined by the youngest populations. Old stars are metal-rich or metal-poor depending on whether they reside in passive galaxies or in star-forming galaxies. Title: Flux-Calibrated Emission-Line Imaging of Extended Sources Using GTC/OSIRIS Tunable Filters Authors: Mayya, Y. D.; Rosa González, D.; Vega, O.; Méndez-Abreu, J.; Terlevich, R.; Terlevich, E.; Bertone, E.; Rodríguez-Merino, L. H.; Muñoz-Tuñón, C.; Rodríguez-Espinosa, J. M.; Sánchez Almeida, J.; Aguerri, J. A. L. Bibcode: 2012PASP..124..895M Altcode: 2012arXiv1203.1842M We investigate the utility of the tunable filters (TFs) for obtaining flux-calibrated emission-line maps of extended objects such as galactic nebulae and nearby galaxies using the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS) at the 10.4-m Gran Telescopio Canarias (GTC). Despite the relatively large field of view (FoV) of OSIRIS (8 × 8), the change in wavelength across the field (∼80 Å) and the long tail of the TF spectral response function are hindrances for obtaining accurate flux-calibrated emission-line maps of extended sources. The purpose of this article is to demonstrate that emission-line maps useful for diagnostics of nebulae can be generated over the entire FoV of OSIRIS if we make use of theoretically well-understood characteristics of TFs. We have successfully generated the flux-calibrated images of the nearby large late-type spiral galaxy M101 in the emission lines of Hα, [N II]λ6583, [S II]λ6716 and [S II]λ6731. We find that the present uncertainty in setting the central wavelength of TFs (∼1 Å) is the biggest source of error in the emission-line fluxes. By comparing the Hα fluxes of H II regions in our images with the fluxes derived from Hα images obtained using narrow-band filters, we estimate an error of ∼11% in our fluxes. The flux-calibration of the images was carried out by fitting the Sloan Digital Sky Survey (SDSS) griz magnitudes of in-frame stars with the stellar spectra from the SDSS spectral database. This method resulted in an accuracy of 3% in flux-calibration of any narrow-band image, which is as good as, if not better than, what has been feasible using the observations of spectrophotometric standard stars. Thus time-consuming calibration images need not be taken. A user-friendly script under the IRAF environment was developed and is available on request.

Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. Title: Stokes V Asymmetries in the Quiet Sun Authors: Viticchié, B.; Sanchez Almeida, J.; Moro, D. D.; Berrilli, F. Bibcode: 2012ASPC..455..271V Altcode: Stokes profiles emerging from the magnetized quiet photosphere and observed by the Solar Optical Telescope (SOT) spectropolarimeter (SP) aboard the Hinode satellite present a large variety of complex shapes. These are indicative of unresolved magnetic structures and/or gradients along the line of sight that have been overlooked in the inversion analyses performed so far. The interpretation of the complex shapes of SOT/SP Stokes V profiles for the understanding of the quiet Sun magnetism must be seriously considered in the near future. In fact, Stokes V profiles significantly deviating from an antisymmetric shape are rather common in the quiet Sun and, in particular, in intranetwork (IN) regions. Here we present the results of the analysis of the shapes of SOT/SP Stokes V profiles performed through a k-means classification. Such an analysis aims at defining different profile classes representative of SOT/SP polarization measurements. We found that about 35 classes can be defined from quiet Sun measurements. Among these, two main subsets can be recognized: network profiles and IN profiles. Approximately 34% of quiet Sun profiles present important asymmetries. From such results, it follows that new inversion techniques able to reproduce line asymmetries must be considered in future analyses of Hinode SOT/SP measurements. The number of line shapes to be reproduced by such analyses is finite and small. Title: Local Tadpole Galaxies Authors: Elmegreen, Debra Meloy; Elmegreen, Bruce G.; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Putko, Joseph; Dewberry, Janosz Bibcode: 2012ApJ...750...95E Altcode: 2012arXiv1203.2486E Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use Sloan Digital Sky Survey data to determine the ages, masses, and surface densities of the heads and tails in 14 local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with rest-frame galaxy luminosity, ranging from ~105 M at galaxy absolute magnitude U = -13 mag to 109 M at U = -20 mag. The corresponding head surface density increases from several M pc-2 locally to 10-100 M pc-2 at high redshift, and the star formation rate (SFR) per unit area in the head increases from ~0.01 M yr-1 kpc-2 locally to ~1 M yr-1 kpc-2 at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological SFRs, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far-outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size. Title: Dissecting the morphological and spectroscopic properties of galaxies in the local Universe. I. Elliptical galaxies Authors: Aguerri, J. A. L.; Huertas-Company, M.; Sánchez Almeida, J.; Muñoz-Tuñón, C. Bibcode: 2012A&A...540A.136A Altcode: 2012arXiv1201.2409A
Aims: We revisit the scaling relations and star-forming histories of local elliptical galaxies using a novel selection method applied to the Sloan Digital Sky Survey DR7.
Methods: We combine two probability-based automated spectroscopic and morphological classifications of ~600 000 galaxies with z < 0.25 to isolate true elliptical galaxies. Our sample selection method does not introduce artificial cuts into the parameters describing the galaxy but instead associates every object with a weight measuring the probability of being in a given spectro-morphological class. Thus, the sample minimizes the selection biases.
Results: We show that morphologically defined ellipticals are basically distributed into three spectral classes, which dominate at different stellar masses. The bulk of the population (~50%) is formed by a well-defined class of galaxies with old stellar populations that formed their stars at very early epochs in a short episode of star formation. They dominate the scaling relations of elliptical galaxies known from previous works and represent the canonical elliptical class. At the low mass end, we find a population of ellipticals with relatively large shapes and smaller velocity dispersions at fixed stellar mass, which seem to have experienced a more recent episode of star formation probably triggered by gas-rich minor mergers. The high mass end tends to be dominated by a third spectral class that is slightly more metal rich and hosts more efficient stellar formation than the reference class. This third class contributes to the curvature in the mass-size relation at high masses reported in previous works. Our method is therefore able to isolate the typical spectra of elliptical galaxies following different evolutionary pathways.

Appendix A is available in electronic form at http://www.aanda.org Title: VizieR Online Data Catalog: ASK spectroscopic sequence of galaxies (Ascasibar+, 2011) Authors: Ascasibar, Y.; Sanchez Almeida, J. Bibcode: 2012yCat..74152417A Altcode: We identify a spectroscopic sequence of galaxies, analogous to the Hubble sequence of morphological types, based on the Automatic Spectroscopic K-means-based (ASK) classification. Considering galaxy spectra as multidimensional vectors, the majority of the spectral classes are distributed along a well-defined curve going from the earliest to the latest types, suggesting that the optical spectra of normal galaxies can be described in terms of a single affine parameter. Optically bright active galaxies, however, appear as an independent, roughly orthogonal branch that intersects the main sequence exactly at the transition between early and late types.

(1 data file). Title: Center-to-limb variation of the area covered by magnetic bright points in the quiet Sun Authors: Bonet, J. A.; Cabello, I.; Sánchez Almeida, J. Bibcode: 2012A&A...539A...6B Altcode: 2011arXiv1112.2513B Context. The quiet Sun magnetic fields produce ubiquitous bright points (BPs) that cover a significant fraction of the solar surface. Their contribution to the total solar irradiance (TSI) is so-far unknown.
Aims: We aim at measuring the center-to-limb variation (CLV) of the fraction of solar surface covered by quiet Sun magnetic bright points. The fraction is referred to as the fraction of covered surface (FCS).
Methods: We count the area covered by BPs in G-band images obtained at various heliocentric angles with the 1-m Swedish Solar Telescope on La Palma. We restore the images to bring them close to the diffraction limit of the instrument (~0'.1).
Results: The FCS is largest at the disk center (≃1%), and then drops down to become ≃0.2% at μ ≃ 0.3 (where μ is the cosine of the heliocentric angle). The relationship has a large scatter, which we evaluate by comparing different subfields within our FOVs. We develop a toy-model to describe the observed CLV, which considers the BPs as depressions in the mean solar photosphere characterized by a depth, a width, and a spread in the inclinations. Although the model is poorly constrained by observations, it shows the BPs to be shallow structures (depth < width) with a large range of inclinations. We also estimate how different parts of the solar disk may contribute to the TSI variations, finding that 90% is contributed by BPs with μ > 0.5, and half of it is due to BPs with μ > 0.8. Title: Local Tadpole Galaxies Authors: Elmegreen, Debra M.; Elmegreen, B. G.; Sanchez Almeida, J.; Muñoz-Tuñón, C.; Putko, J.; Dewberry, J. Bibcode: 2012AAS...21924409E Altcode: Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. The origin of this asymmetric structure is not known, although suggestions range from ram pressure to mergers. We use SDSS data to determine the ages, masses, surface densities, and star formation rates of the heads and tails in 13 local tadpoles identified from Kiso and Michigan surveys and compare them to tadpoles previously surveyed in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with restframe galaxy luminosity, ranging from 105 Mo at galaxy U = -13 mag to 109 Mo at U = -20 mag. The young star surface density in the head is relatively small for local tadpoles, 1 Mo pc-2, but much larger for high redshift tadpoles, 10 - 100 Mo pc-2. The star formation rate per unit area increases with increasing redshift by 2 orders of magnitude from z=0 to 3.

J. Putko was supported through NSF REU grant AST-1005024, and J. Dewberry through the Vassar URSI program. Title: The Distribution of Galaxies in Spectral Space Authors: Ascasibar, Y.; Sánchez Almeida, J. Bibcode: 2012adm..book...63A Altcode: Considering Galaxy spectra as multidimensional vectors, we use the k-means algorithm and the minimum spanning tree to show that the data in the Sloan Digital Sky Survey do not fill the entire space but are confined to a manifold with very low dimensionality. More precisely, all the spectra can be described in terms of only two degrees of freedom: one discrete parameter labelling the Galaxy as "normal" or "active," and one continuous affine parameter describing its position along the corresponding sequence. Title: Systematic Search for Extremely Metal-poor Galaxies in the Sloan Digital Sky Survey Authors: Morales-Luis, A. B.; Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C. Bibcode: 2011ApJ...743...77M Altcode: 2011arXiv1109.0235M We carry out a systematic search for extremely metal-poor (XMP) galaxies in the spectroscopic sample of Sloan Digital Sky Survey (SDSS) data release 7 (DR7). The XMP candidates are found by classifying all the galaxies according to the form of their spectra in a region 80 Å wide around Hα. Due to the data size, the method requires an automatic classification algorithm. We use k-means. Our systematic search renders 32 galaxies having negligible [N II] lines, as expected in XMP galaxy spectra. Twenty-one of them have been previously identified as XMP galaxies in the literature—the remaining 11 are new. This was established after a thorough bibliographic search that yielded only some 130 galaxies known to have an oxygen metallicity 10 times smaller than the Sun (explicitly, with 12 + log (O/H) <= 7.65). XMP galaxies are rare; they represent 0.01% of the galaxies with emission lines in SDSS/DR7. Although the final metallicity estimate of all candidates remains pending, strong-line empirical calibrations indicate a metallicity about one-tenth solar, with the oxygen metallicity of the 21 known targets being 12 + log (O/H) ~= 7.61 ± 0.19. Since the SDSS catalog is limited in apparent magnitude, we have been able to estimate the volume number density of XMP galaxies in the local universe, which turns out to be (1.32 ± 0.23) × 10-4 Mpc-3. The XMP galaxies constitute 0.1% of the galaxies in the local volume, or ~0.2% considering only emission-line galaxies. All but four of our candidates are blue compact dwarf galaxies, and 24 of them have either cometary shape or are formed by chained knots. Title: Wavelength Calibration for OSIRIS/GTC Tunable Filters Authors: Méndez-Abreu, J.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Rodríguez-Espinosa, J. M.; Aguerri, J. A. L.; Rosa González, D.; Mayya, Y. D.; Vega, O.; Terlevich, R.; Terlevich, E.; Bertone, E.; Rodríguez-Merino, L. H. Bibcode: 2011PASP..123.1107M Altcode: 2011arXiv1107.4000M OSIRIS (Optical System for Imaging and low Resolution Integrated Spectroscopy) is the first light instrument of the Gran Telescopio Canarias (GTC). It provides a flexible and competitive tunable filter (TF). Since it is based on a Fabry-Perot interferometer working in a collimated beam, the TF transmission wavelength depends on the position of the target with respect to the optical axis. This effect is nonnegligible and must be accounted for in the data reduction. Our article establishes a wavelength calibration for OSIRIS TF with the accuracy required for spectrophotometric measurements using the full field of view (FOV) of the instrument. The variation of the transmission wavelength λ(R) across the FOV is well described by , where λ(0) is the central wavelength, R represents the physical distance from the optical axis, and f2 = 185.70 ± 0.17 mm is the effective focal length of the camera lens. This new empirical calibration yields an accuracy better than 1 Å across the entire OSIRIS FOV (∼8 × 8), provided that the position of the optical axis is known within 45 μm (≡1.5 binned pixels). We suggest a calibration protocol to grant such precision over long periods, upon realignment of OSIRIS optics, and in different wavelength ranges. This calibration differs from the calibration in the OSIRIS manual, which nonetheless provides an accuracy ≲1 Å for R ≲ 2.

This work is based on observations made with the GTC operated on the island of La Palma by Grantecan in the Spanish Observatorio del Roque de los Muchachos. Title: Do galaxies form a spectroscopic sequence? Authors: Ascasibar, Y.; Sánchez Almeida, J. Bibcode: 2011MNRAS.415.2417A Altcode: 2011arXiv1104.1388A; 2011MNRAS.tmp..956A We identify a spectroscopic sequence of galaxies, analogous to the Hubble sequence of morphological types, based on the Automatic Spectroscopic K-means-based (ASK) classification. Considering galaxy spectra as multidimensional vectors, the majority of the spectral classes are distributed along a well-defined curve going from the earliest to the latest types, suggesting that the optical spectra of normal galaxies can be described in terms of a single affine parameter. Optically bright active galaxies, however, appear as an independent, roughly orthogonal branch that intersects the main sequence exactly at the transition between early and late types. Title: Relationship between Hubble Type and Spectroscopic Class in Local Galaxies Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.; Huertas-Company, M. Bibcode: 2011ApJ...735..125S Altcode: 2011arXiv1104.4864S We compare the Hubble type and the spectroscopic class of the galaxies with spectra in the Sloan Digital Sky Survey Data Release 7. As has long been known, elliptical galaxies tend to be red whereas spiral galaxies tend to be blue; however, this relationship presents a large scatter, which we measure and quantify in detail for the first time. We compare the Automatic Spectroscopic K-means-based classification (ASK) with most of the commonly used morphological classifications. Despite the degree of subjectivity involved in morphological classifications, all of them provide consistent results. Given a spectral class, the morphological type wavers with a standard deviation between 2 and 3 T types, and the same large dispersion characterizes the variability of spectral classes given a morphological type. The distributions of Hubble types for each ASK class are very skewed—they present long tails that extend to late morphological types in the red galaxies and to early morphological types in the blue spectroscopic classes. The scatter is not produced by problems with the classification and it remains when particular subsets are considered—low and high galaxy masses, low and high density environments, barred and non-barred galaxies, edge-on galaxies, small and large galaxies, or when a volume-limited sample is considered. A considerable fraction of red galaxies are spirals (40%-60%), but they never present very late Hubble types (Sd or later). Even though red spectra are not associated with ellipticals, most ellipticals do have red spectra: 97% of the ellipticals in the morphological catalog by Nair & Abraham used here for reference belong to ASK 0, 2, or 3; only 3% of the ellipticals are blue. The galaxies in the green valley class (ASK 5) are mostly spirals, and the active galactic nuclei class (ASK 6) presents a large scatter of Hubble types from E to Sd. We investigate variations with redshift using a volume-limited subsample mainly formed by luminous red galaxies. From redshift 0.25 to the present, the galaxies redden from ASK 2 to ASK 0, as expected from the passive evolution of their stellar populations. Two of the ASK classes (1 and 4) gather edge-on spirals, and they may be useful in studies requiring knowledge of the intrinsic shape of a galaxy (e.g., weak-lensing calibration). Title: Asymmetries of the Stokes V profiles observed by HINODE SOT/SP in the quiet Sun Authors: Viticchié, B.; Sánchez Almeida, J. Bibcode: 2011A&A...530A..14V Altcode: 2011arXiv1103.1987V
Aims: A recent analysis of polarization measurements of HINODE SOT/SP in the quiet Sun pointed out very complex shapes of Stokes V profiles. Here we present the first classification of the SOT/SP circular polarization measurements with the aim of highlighting exhaustively the whole variety of Stokes V shapes emerging from the quiet Sun.
Methods: k-means is used to classify HINODE SOT/SP Stokes V profiles observed in the quiet Sun network and internetwork (IN). We analyze a 302 × 162 arcsec2 field-of-view (FOV) that can be considered a complete sample of quiet Sun measurements performed at the disk center with 0.32 arcsec angular resolution and 10-3 polarimetric sensitivity. This classification allows us to divide the whole dataset into classes, with each class represented by a cluster profile, i.e., the average of the profiles in the class.
Results: The set of 35 cluster profiles derived from the analysis completely characterizes the SOT/SP quiet Sun measurements. The separation between network and IN profile shapes is evident - classes in the network are not present in the IN, and vice versa. Asymmetric profiles are approximately 93% of the total number of profiles. Among these, about 34% of the profiles are strongly asymmetric, and they can be divided into three families: blue-lobe, red-lobe, and Q-like profiles. The blue-lobe profiles tend to be associated with upflows (granules), whereas the red-lobe and Q-like ones appear in downflows (intergranular lanes).
Conclusions: These profiles need to be interpreted considering model atmospheres different from a uniformly magnetized Milne-Eddington (ME) atmosphere, i.e., characterized by gradients and/or discontinuities in the magnetic field and velocity along the line-of-sight (LOS). We propose the use of cluster profiles as a standard archive to test inversion codes, and to check the validity and/or completeness of synthetic profiles produced by MHD simulations. Title: Relationship between Hubble type and spectroscopic class in local galaxies Authors: Sánchez Almeida, J. Bibcode: 2011iac..talk..282S Altcode: 2011iac..talk..218S No abstract at ADS Title: The Magnetic Fields of the Quiet Sun Authors: Sánchez Almeida, J.; Martínez González, M. Bibcode: 2011ASPC..437..451S Altcode: 2011arXiv1105.0387S This work reviews our understanding of the magnetic fields observed in the quiet Sun. The subject has undergone a major change during the last decade (quiet revolution), and it will remain changing since the techniques of diagnostic employed so far are known to be severely biased. Keeping these caveats in mind, our work covers the main observational properties of the quiet Sun magnetic fields: magnetic field strengths, unsigned magnetic flux densities, magnetic field inclinations, as well as the temporal evolution on short time-scales (loop emergence), and long time-scales (solar cycle). We also summarize the main theoretical ideas put forward to explain the origin of the quiet Sun magnetism. A final prospective section points out various areas of solar physics where the quiet Sun magnetism may have an important physical role to play (chromospheric and coronal structure, solar wind acceleration, and solar elemental abundances). Title: MISMA Interpretation of Stokes V Asymmetries Measured by HINODE in Internetwork and Network Regions Authors: Viticchiè, B.; Sánchez Almeida, J.; Del Moro, D.; Berrilli, F. Bibcode: 2011ASPC..437..127V Altcode: Stokes profiles observed in the quiet photosphere by HINODE SOT/SP present very complex shapes. These are indicative of unresolved magnetic structures and/or gradients along the line of sight in HINODE's pixels which have linear dimension of ∼0.15". We present the first interpretation of the Stokes profile asymmetries measured in the 630 nm Fe I lines by SOT/SP in both quiet Sun internetwork (IN) and network. The inversion is carried out under the hypothesis of MIcro-Structured Magnetized Atmosphere (MISMA) which can account for sub-pixel structuring of magnetic fields. The MISMA code is able to reproduce the observed asymmetries in a very satisfactory way. Moreover, 25% of inverted profiles present asymmetries that are interpreted as produced by regions in which mixed polarities are present. kG field strengths are found in both network and internetwork regions. In the internetwork both kG fields and hG fields are found. Our analysis constrains the magnetic field of only 4.5% of the analyzed photosphere. The rest of the plasma can be thought to be filled by weak fields not contributing to the detected polarization signals. Title: Interpretation of HINODE SOT/SP asymmetric Stokes profiles observed in the quiet Sun network and internetwork Authors: Viticchié, B.; Sánchez Almeida, J.; Del Moro, D.; Berrilli, F. Bibcode: 2011A&A...526A..60V Altcode: 2010arXiv1009.6065V Stokes profiles emerging from the magnetized solar photosphere and observed by SOT/SP aboard the HINODE satellite exhibit a variety of complex shapes. These are indicative of unresolved magnetic structures that have been overlooked in the inversion analyses performed so far. Here we present the first interpretation of the Stokes profile asymmetries measured in the ion{Fe}{i} 630 nm lines by SOT/SP, in both quiet Sun internetwork (IN) and network regions. The inversion is carried out based on the hypothesis of MIcro-Structured Magnetized Atmosphere (MISMA), where the unresolved structure is assumed to be optically thin. We analyze a 29.52 arcsec × 31.70 arcsec subfield carefully selected to be representative of the properties of a 302 arcsec × 162 arcsec quiet Sun field-of-view (FOV) at the disk center. The inversion code is able to reproduce the observed asymmetries in a very satisfactory way, including 35% of the inverted profiles with large asymmetries. The inversion code interprets 25% of inverted profiles as emerging from pixels in which both positive and negative polarities coexist. These pixels are located in either frontiers between opposite polarity patches or very quiet regions. The kG field strengths are found at the base of the photosphere in both network and IN regions; in the case of the latter, both kG fields and hG fields are admixed. When considering the magnetic properties of the mid photosphere, most kG fields do not exist, and the statistics is dominated by hG fields. According to the magnetic filling factors derived from the inversion, we constrain the magnetic field of only 4.5% of the analyzed photosphere (and this percentage reduces to 1.3% when considering all pixels, including those with low polarization that have not been analyzed). The properties of the rest of the plasma imply that weak fields do not contribute to the detected polarization signals. The average flux densities derived in the full subfield and IN regions are higher than those derived from the same dataset by Milne-Eddington (ME) inversion. We detect large asymmetries in the HINODE SOT/SP polarization profiles. These are not negligible in quiet Sun data. The MISMA inversion code reproduces them in a satisfactory way, and provides a statistical description of the magnetized IN and network which partly differs and complements the results obtained so far. The importance of having a complete interpretation of the line profile shapes is therefore clearly evident. Title: Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample: a publicly available Bayesian automated classification Authors: Huertas-Company, M.; Aguerri, J. A. L.; Bernardi, M.; Mei, S.; Sánchez Almeida, J. Bibcode: 2011A&A...525A.157H Altcode: 2010arXiv1010.3018H We present an automated morphological classification in 4 types (E, S0, Sab, Scd) of ~700 000 galaxies from the SDSS DR7 spectroscopic sample based on support vector machines. The main new property of the classification is that we associate a probability to each galaxy of being in the four morphological classes instead of assigning a single class. The classification is therefore better adapted to nature where we expect a continuous transition between different morphological types. The algorithm is trained with a visual classification and then compared to several independent visual classifications including the Galaxy Zoo first-release catalog. We find a very good correlation between the automated classification and classical visual ones. The compiled catalog is intended for use in different applications and is therefore freely available through a dedicated webpage* and soon from the CasJobs database.

Full catalog is only available in electronic form at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/525/A157 or via http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html Title: The Sun, the Solar Wind, and the Heliosphere Authors: Miralles, Mari Paz; Sánchez Almeida, Jorge Bibcode: 2011sswh.book.....M Altcode: No abstract at ADS Title: The Sun, the Solar Wind, and the Heliosphere Authors: Miralles, M. P.; Sánchez Almeida, J. Bibcode: 2011sswh.book....3M Altcode: We describe the aims and contents of the book entitled "The Sun, the Solar Wind, and the Heliosphere". This is a volume in the IAGA Special Book Series dedicated to the science covered by IAGA Division IV, Solar Wind and Interplanetary Field. The book features review articles on topics from the interior of the Sun to the outermost regions of the heliosphere. In addition, we highlight some of the results presented during the Division IV symposia at the 11th Scientific Assembly of IAGA in Sopron, Hungary, which was planned simultaneously with this book. Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows in the Sun Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios, J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.; Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M. Bibcode: 2010ApJ...723L.139B Altcode: 2010arXiv1009.1992B We characterize the observational properties of the convectively driven vortex flows recently discovered on the quiet Sun, using magnetograms, Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE telescope. By visual inspection of time series, we find some 3.1 × 10-3 vortices Mm-2 minute-1, which is a factor of ~1.7 larger than previous estimates. The mean duration of the individual events turns out to be 7.9 minutes, with a standard deviation of 3.2 minutes. In addition, we find several events appearing at the same locations along the duration of the time series (31.6 minutes). Such recurrent vortices show up in the proper motion flow field map averaged over the time series. The typical vertical vorticities are lsim6 × 10-3 s-1, which corresponds to a period of rotation of some 35 minutes. The vortices show a preferred counterclockwise sense of rotation, which we conjecture may have to do with the preferred vorticity impinged by the solar differential rotation. Title: VizieR Online Data Catalog: SDSS automated morphology classification (Huertas-Company+, 2011) Authors: Huertas-Company, M.; Aguerri, J. A. L.; Bernardi, M.; Mei, S.; Sanchez Almeida, J. Bibcode: 2010yCat..35250157H Altcode: 2010yCat..35259157H We used all the SDSS DR7 spectroscopic sample as the starting base. Then, the selection of objects was based on Sanchez Almeida et al. (2010ApJ...714..487A) who performed an unsupervised automated classification of all the SDSS spectra. Basically, we chose galaxies with redshift below 0.25, and with good photometric data and clean spectra, meaning objects not too close to the edges, not saturated, or not properly deblended. The final catalog contains 698420 objects for which we estimate the morphology (also available at http://gepicom04.obspm.fr/sdssmorphology/Morphology2010.html ).

(3 data files). Title: Automatic unsupervised spectral classification of all SDSS/DR7 galaxies Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.; de Vicente, A. Bibcode: 2010ada..confE...3S Altcode: No abstract at ADS Title: Safe and Secure Virtualization: Answers for IMA next Generation and Beyond Authors: Almeida, J.; Vatrinet, F. Bibcode: 2010ESASP.682E..56A Altcode: This paper presents some of the challenges the aerospace industry is facing for the future and explains why and how a safe and secured virtualization technology can help solving these challenges Efforts around the next generation of IMA have already started, like the European FP7 funded project SCARLETT or the IDEE5 project and many avionics players and working groupware focused on how the new technologies like SMP capabilities introduced in latest CPU architectures, can help increasing system performances in future avionics system. We present PikeOS, a separation micro-kernel, which applies the state-of-the-art techniques and widely recognized standards such as ARINC 653 and MILS in order to guarantee safety and security properties, and still improve overall performance. Title: Automatic unsupervised classification of all Sloan Digital Sky Survey Data Release 7 galaxy spectra Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.; de Vicente, A. Bibcode: 2010iac..talk...25S Altcode: 2010iac..talk..164S No abstract at ADS Title: Magnetic Bright Points in the Quiet Sun Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchié, B.; Del Moro, D. Bibcode: 2010ApJ...715L..26S Altcode: 2010arXiv1004.1885S 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 0farcs1 angular resolution G-band movie obtained with the Swedish Solar Telescope at the solar disk center. We find 0.97 BPs Mm-2, which is a factor 3 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 13 G and 33 G. If network and inter-network regions are counted separately, they contain 2.2 BPs Mm-2 and 0.85 BPs Mm-2, respectively. Title: Magnetic bright points in the quiet Sun Authors: Sánchez Almeida, J.; Bonet, J. A.; Viticchie, B.; Del Moro, D. Bibcode: 2010iac..talk...95S Altcode: 2010iac..talk..157S No abstract at ADS Title: Automatic Unsupervised Classification of All Sloan Digital Sky Survey Data Release 7 Galaxy Spectra Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.; de Vicente, A. Bibcode: 2010ApJ...714..487S Altcode: 2010arXiv1003.3186S 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. Title: A Topology for the Penumbral Magnetic Fields Authors: Sánchez Almeida, J. Bibcode: 2010ASSP...19..210S Altcode: 2009arXiv0902.4532S; 2010mcia.conf..210S We describe a scenario for the topology of the magnetic field in penumbrae that accounts for recent observations showing upflows, downflows, and reverse magnetic polarities. According to our conjecture, short narrow magnetic loops fill the penumbral photosphere. Flows along these arched field lines are responsible for both the Evershed effect and the convective transport. This scenario seems to be qualitatively consistent with most existing observations, including the dark cores in penumbral filaments reported by Scharmer et al. Each bright filament with dark core would be a system of two paired convective rolls with the dark core tracing the common lane where the plasma sinks down. The magnetic loops would have a hot footpoint in one of the bright filament and a cold footpoint in the dark core. The scenario fits in most of our theoretical prejudices (siphon flows along field lines, presence of overturning convection, drag of field lines by downdrafts, etc). If the conjecture turns out to be correct, the mild upward and downward velocities observed in penumbrae must increase upon improving the resolution. This and other observational tests to support or disprove the scenario are put forward. Title: On the origin of reverse polarity patches found by Hinode in sunspot penumbrae Authors: Sánchez Almeida, J.; Ichimoto, K. Bibcode: 2009A&A...508..963S Altcode: 2009arXiv0909.3232S Context: The topology of penumbral magnetic fields is poorly known. The satellite Hinode has recently revealed penumbral structures of a magnetic polarity that is opposite to the main sunspot polarity. They may be direct confirmation that magnetic field lines and mass flows return to the solar interior throughout the penumbra, a configuration previously inferred from interpretation of observed Stokes profile asymmetries.
Aims: We try to point out the relationship between the reverse polarity features found by Hinode, and the model Micro-Structured Magnetic Atmospheres (MISMAs) proposed for sunspots.
Methods: The work is based on synthesis and inversion of sunspot Stokes profiles.
Results: Existing model MISMAs produce strongly redshifted reverse polarity structures as found by Hinode. Ad hoc model MISMAs also explain the asymmetric Stokes profiles observed by Hinode. The same modeling may be consistent with magnetograms of dark cored penumbral filaments if the dark cores are associated with the reverse polarity. This hypothetical relationship can only be identified in the far red wings of the spectral lines.
Conclusions: The reverse polarity patches may result from aligned magnetic field lines and mass flows that bend over and return to the solar interior throughout the penumbra. Title: Mn I Lines with Hyperfine Structure Synthesized in Realistic Quiet-Sun Atmospheres Authors: Viticchié, B.; Sánchez Almeida, J.; Landi Degl'Innocenti, E.; Berrilli, F. Bibcode: 2009ASPC..405..319V Altcode: We present the first synthesis of Mn I lines in realistic multi-component magnetized quiet Sun atmospheres, including variation of magnetic field strength, magnetic field direction, plasma velocity, and coupling between magnetic field and thermodynamics. All synthesized Mn I lines weaken for strong magnetic fields. A detailed analysis of the Mn I λ5538 line shows that the Weak Field Approximation (WFA) breaks down at 400~G, and that kG magnetic fields produce Stokes V profiles with amplitudes up to two orders of magnitude smaller than those predicted by the WFA. Consequently, the polarization emerging from an atmosphere in which weak (hG) and strong (kG) fields coexist is biased towards the hG field polarization. When including velocity gradients, profiles showing important asymmetries are produced, and these profiles cannot be obtained using single-component magnetized model atmospheres. We synthesize Mn I lines presenting very different hyperfine structure (HFS) patterns, and all of them reproduce the observed Stokes I profiles in a really satisfactory way. Title: Search for Blue Compact Dwarf Galaxies During Quiescence. II. Metallicities of Gas and Stars, Ages, and Star Formation Rates Authors: Sánchez Almeida, J.; Aguerri, J. A. L.; Muñoz-Tuñón, C.; Vazdekis, A. Bibcode: 2009ApJ...698.1497S Altcode: 2009arXiv0904.2150S We examine the metallicity and age of a large set of Sloan Digital Sky Survey/Data Release 6 galaxies that may be blue compact dwarf (BCD) galaxies during quiescence (QBCDs). The individual spectra are first classified and then averaged to reduce noise. The metallicity inferred from emission lines (tracing ionized gas) exceeds by ~0.35 dex the metallicity inferred from absorption lines (tracing stars). Such a small difference is significant according to our error budget estimate. The same procedure was applied to a reference sample of BCDs, and in this case the two metallicities agree, being also consistent with the stellar metallicity in QBCDs. Chemical evolution models indicate that the gas metallicity of QBCDs is too high to be representative of the galaxy as a whole, but it can represent a small fraction of the galactic gas, self-enriched by previous starbursts. The luminosity-weighted stellar age of QBCDs spans the whole range between 1 and 10 Gyr, whereas it is always smaller than 1 Gyr for BCDs. Our stellar ages and metallicities rely on a single stellar population spectrum fitting procedure, which we have specifically developed for this work using the stellar library MILES. Title: Safe and Secure Partitioning with Pikeos: Towards Integrated Modular Avionics in Space Authors: Almeida, J.; Prochazka, M. Bibcode: 2009ESASP.669E..27A Altcode: This paper presents our approach to logical partitioning of spacecraft onboard software. We present PikeOS, a separation micro-kernel which applies the state-of-the- art techniques and widely recognised standards such as ARINC 653 and MILS in order to guarantee safety and security properties of partitions executing software with different criticality and confidentiality. We provide an overview of our approach, also used in the Securely Partitioning Spacecraft Computing Resources project, an ESA TRP contract, which shifts spacecraft onboard software development towards the Integrated Modular Avionics concept with relevance for dual-use military and civil missions. Title: The dynamic magnetic quiet Sun: physical mechanisms and UV signature Authors: Sánchez Almeida, J. Bibcode: 2009Ap&SS.320..121S Altcode: 2008Ap&SS.tmp..156S The changes in the Sun occurring at human time-scales can be pinned down to the presence of magnetic fields. These fields determine the structure of the outer solar atmosphere and, therefore, they are responsible for all the energetic part of the solar spectrum, including the UV. Our understanding of the magnetic fields existing at the base of the atmosphere has changed during the last years. The new spectro-polarimeters reveal an ubiquitous magnetic field, present even in the quiet regions. They are widespread and of complex topology, containing far more (unsigned) magnetic flux and magnetic energy that all traditional manifestations of solar activity. These so-called quiet Sun magnetic fields are the subject of the contribution. I summarize their main observational properties, as well as the models put forward to explain them. According to the common wisdom, they may be generated by a turbulent dynamo driven by convective motions. Their true physical role is not understood yet, but it may be consequential both for the Sun (e.g., in determining the structure of the quiet corona), and for other astronomical objects (e.g., if a turbulent dynamo operates in the Sun, the same mechanism provides a very efficient mean of creating surface magnetic fields in all stars with convective envelopes). I discuss the impact of the quiet Sun fields on the transition region and corona, trying to point out the UV signatures of those fields. Title: MISMA inversion of HINODE SOT/SP data. Preliminary results Authors: Viticchiè, B.; Berrilli, F.; Sánchez Almeida, J.; Orozco Suárez, D. Bibcode: 2009MmSAI..80..255V Altcode: We analyze full Stokes observations of a quiet Sun region at disk center taken with the spectropolarimeter of the Solar Optical Telescope aboard the HINODE satellite. We present the preliminary results derived from the MISMA inversion of the observed Stokes I and V profiles. The complete analysis has as a final goal the definition of probability density function for the statistical description of the quiet Sun magnetic field vector for a direct comparison with recently published results. Title: A topology for the penumbral magnetic fields Authors: Sanchez Almeida, J. Bibcode: 2008arXiv0811.4319S Altcode: We describe a scenario for the sunspot magnetic field topology that may account for recent observations of upflows and downflows in penumbrae. According to our conjecture, short narrow magnetic loops fill the penumbral volume. Flows along these field lines are responsible for both the Evershed effect and the convective transport. This scenario seems to be qualitatively consistent with most existing observations, including the dark cores in penumbral filaments reported by Scharmer et al. Each bright filament with dark core would be a system of two paired convective rolls with the dark core tracing the lane where the plasma sinks down. The magnetic loops would have a hot footpoint in one of the bright filament and a cold footpoint in the dark core. The scenario also fits in most of our theoretical prejudices (siphon flows along field lines, presence of overturning convection, drag of field lines by downdrafts, etc). If the conjecture turns out to be correct, the mild upward and downward velocities observed in penumbrae must increase upon improvement of the current spatial resolution. This and other observational tests to support or disprove the proposed scenario are put forward. Title: Convectively Driven Vortex Flows in the Sun Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello, I.; Domingo, V. Bibcode: 2008ApJ...687L.131B Altcode: 2008arXiv0809.3885B We have discovered small whirlpools in the Sun, with a size similar to terrestrial hurricanes (lesssim0.5 Mm). The theory of solar convection predicts them, but they had remained elusive so far. The vortex flows are created at the downdrafts where the plasma returns to the solar interior after cooling down, and we detect them because some magnetic bright points (BPs) follow a logarithmic spiral on their way to being engulfed by a downdraft. Our disk-center observations show 0.9 × 10-2 vortexes per Mm2, with a lifetime of the order of 5 minutes, and with no preferred sense of rotation. They are not evenly spread out over the surface, but they seem to trace the supergranulation and the mesogranulation. These observed properties are strongly biased by our type of measurement, unable to detect vortexes except when they are engulfing magnetic BPs. Title: Convectively driven vortex flows in the Sun Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Cabello, I.; Domingo, V. Bibcode: 2008iac..talk..143B Altcode: 2008iac..talk...26B No abstract at ADS Title: MISMA inversion of HINODE SOT/SP and IBIS data: Preliminary Results Authors: Viticchiè, B.; Berrilli, F.; Sanchez Almeida, J.; Del Moro, D. Bibcode: 2008ESPM...12.2.33V Altcode: We present the preliminary results derived from the MISMA inversion of Stokes I and V profiles of FeI 630.1nm FeI 630.2nm lines observed with:

1. SOT/SP instrument aboard the HINODE satellite.

2. IBIS in spectropolarimetric mode imaging, supported by simultaneous white light and G-band images, for blind deconvolution reconstruction.

The complete analysis has as a final goal the comparison of the results obtained from the analysis of the two datasets for a reliable statistical description of the quiet Sun through the definition of a probability density function. Title: Search for Blue Compact Dwarf Galaxies During Quiescence Authors: Sánchez Almeida, J.; Muñoz-Tuñón, C.; Amorín, R.; Aguerri, J. A.; Sánchez-Janssen, R.; Tenorio-Tagle, G. Bibcode: 2008ApJ...685..194S Altcode: 2008arXiv0805.3298S Blue compact dwarf (BCD) galaxies are metal-poor systems going through a major starburst that cannot last for long. We have identified galaxies which may be BCDs during quiescence (QBCD), i.e., before the characteristic starburst sets in or when it has faded away. These QBCD galaxies are assumed to be like the BCD host galaxies. The SDSS DR6 database provides ~21,500 QBCD candidates. We also select from SDSS DR6 a complete sample of BCD galaxies to serve as reference. The properties of these two galaxy sets have been computed and compared. The QBCD candidates are 30 times more abundant than the BCDs, with their luminosity functions being very similar except for the scaling factor and the expected luminosity dimming associated with the end of the starburst. QBCDs are redder than BCDs, and they have larger H II region-based oxygen abundance. QBCDs also have lower surface brightness. The BCD candidates turn out to be the QBCD candidates with the largest specific star formation rate (actually, with the largest Hα equivalent width). One out of every three dwarf galaxies in the local universe may be a QBCD. The properties of the selected BCDs and QBCDs are consistent with a single sequence in galactic evolution, which the quiescent phase lasting 30 times longer than the starburst phase. The resulting time-averaged star formation rate is low enough to allow this cadence of BCD-QBCD phases during the Hubble time. Title: Quiet-Sun Magnetic Field Measurements Based on Lines with Hyperfine Structure Authors: Sánchez Almeida, J.; Viticchié, B.; Landi Degl'Innocenti, E.; Berrilli, F. Bibcode: 2008ApJ...675..906S Altcode: 2007arXiv0710.5393S The Zeeman pattern of Mn I lines is sensitive to hyperfine structure (HFS), and because of this, they respond to hectogauss magnetic field strengths differently than the lines commonly used in solar magnetometry. This peculiarity has been employed to measure magnetic field strengths in quiet-Sun regions, assuming the magnetic field to be constant over a resolution element. This assumption is clearly insufficient, biasing the measurements. The diagnostic potential of Mn I lines can be fully exploited only after one understands the sense and magnitude of such bias. We present the first syntheses of Mn I lines in realistic quiet-Sun model atmospheres. The Mn I lines weaken with increasing field strength. In particular, kilogauss magnetic concentrations produce Mn I λ5538 circular polarization signals (Stokes V) that can be up to 2 orders of magnitude smaller than what the weak magnetic field approximation predicts. The polarization emerging from an atmosphere having weak and strong fields is biased toward the weak fields, and HFS features characteristic of weak fields show up even when the magnetic flux and energy are dominated by kilogauss fields. For the HFS feature of Mn I λ5538 to disappear, the filling factor of kilogauss fields has to be larger than the filling factor of subkilogauss fields. Since the Mn I lines are usually weak, Stokes V depends on magnetic field inclination according to the simple cosine law. Atmospheres with unresolved velocities produce very asymmetric line profiles, which cannot be reproduced by simple one-component model atmospheres. Using the HFS constants available in the literature, we reproduce the observed line profiles of nine lines with varied HFS patterns. Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and 6302 Å Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.; Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J. Bibcode: 2008ApJ...674..596S Altcode: The reliability of quiet-Sun magnetic field diagnostics based on the Fe I lines at 6302 Å has been questioned by recent work. Here we present the results of a thorough study of high-resolution multiline observations taken with the new spectropolarimeter SPINOR, comprising the 5250 and 6302 Å spectral domains. The observations were analyzed using several inversion algorithms, including Milne-Eddington, LTE with 1 and 2 components, and MISMA codes. We find that the line-ratio technique applied to the 5250 Å lines is not sufficiently reliable to provide a direct magnetic diagnostic in the presence of thermal fluctuations and variable line broadening. In general, one needs to resort to inversion algorithms, ideally with realistic magnetohydrodynamic constrains. When this is done, the 5250 Å lines do not seem to provide any significant advantage over those at 6302 Å. In fact, our results point toward a better performance with the latter (in the presence of turbulent line broadening). In any case, for very weak flux concentrations, neither spectral region alone provides sufficient constraints to fully disentangle the intrinsic field strengths. Instead, we advocate for a combined analysis of both spectral ranges, which yields a better determination of the quiet-Sun magnetic properties. Finally, we propose the use of two other Fe I lines (at 4122 and 9000 Å) with identical line opacities that seem to work much better than the others. Title: Small magnetic structures in the photosphere, radiative properties Authors: Palacios, Judith; Domingo, Vicente; Cabello, Iballa; Bonet, José Antonio; Sánchez Almeida, Jorge Bibcode: 2008cosp...37.2331P Altcode: 2008cosp.meet.2331P The three dimensional structure of small magnetic field features in the photosphere, their dynamic behavior and their radiative properties are studied. We analyze data obtained in simultaneous observations made on Sept 29 and 30, 2007 with the HINODE spacecraft and the Swedish Solar Telescope (SST) in La Palma in different wavelengths, such as CaII (396.85 nm) and CN (388.35 nm) and other with Hinode data; and Gband (430.56 nm) with SST. Tha analysis is completed with high resolution Gband and Gcontinuum (436.39 nm) images from SST obtained on 2005 and 2006. Magnetograms have been obtained from both observatories. SST images have been processed with MOMFB code. Ribbon-like structures and "flowers" are studied in detail. Comparisons with solar atmospheric models are presented. Title: de Sitter Relativity and Quantum Physics Authors: Aldrovandi, R.; Almeida, J. P. Beltrán; Mayor, C. S. O.; Pereira, J. G. Bibcode: 2007AIPC..962..175A Altcode: 2007arXiv0710.0610A In the presence of a cosmological constant, interpreted as a purely geometric entity, absence of matter is represented by a de Sitter spacetime. As a consequence, ordinary Poincaré special relativity is no longer valid and must be replaced by a de Sitter special relativity. By considering the kinematics of a spinless particle in a de Sitter spacetime, we study the geodesics of this spacetime, the ensuing definitions of canonical momenta, and explore possible implications for quantum mechanics. Title: Search for photospheric footpoints of quiet Sun transition region loops Authors: Sánchez Almeida, J.; Teriaca, L.; Sütterlin, P.; Spadaro, D.; Schühle, U.; Rutten, R. J. Bibcode: 2007A&A...475.1101S Altcode: 2007arXiv0709.3451S Context: The footpoints of quiet Sun Transition Region (TR) loops do not seem to coincide with the photospheric magnetic structures appearing in traditional low-sensitivity magnetograms.
Aims: We look for the so-far unidentified photospheric footpoints of TR loops using G-band bright points (BPs) as proxies for photospheric magnetic field concentrations.
Methods: We compare TR measurements with SoHO/SUMER and photospheric magnetic field observations obtained with the Dutch Open Telescope.
Results: Photospheric BPs are associated with bright TR structures, but they seem to avoid the brightest parts of the structure. BPs appear in regions that are globally redshifted, but they avoid extreme velocities. TR explosive events are not clearly associated with BPs.
Conclusions: The observations are not inconsistent with the BPs being footpoints of TR loops, although we have not succeeded to uniquely identify particular BPs with specific TR loops. Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J. Bibcode: 2007arXiv0710.1099S Altcode: The reliability of quiet Sun magnetic field diagnostics based on the \ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We present here the results of a thorough study of high-resolution multi-line observations taken with the new spectro-polarimeter SPINOR, comprising the 5250 and 6302 Åspectral domains. The observations were analyzed using several inversion algorithms, including Milne-Eddington, LTE with 1 and 2 components, and MISMA codes. We find that the line-ratio technique applied to the 5250 Ålines is not sufficiently reliable to provide a direct magnetic diagnostic in the presence of thermal fluctuations and variable line broadening. In general, one needs to resort to inversion algorithms, ideally with realistic magneto-hydrodynamical constrains. When this is done, the 5250 Ålines do not seem to provide any significant advantage over those at 6302 Å. In fact, our results point towards a better performance with the latter (in the presence of turbulent line broadening). In any case, for very weak flux concentrations, neither spectral region alone provides sufficient constraints to fully disentangle the intrinsic field strengths. Instead, we advocate for a combined analysis of both spectral ranges, which yields a better determination of the quiet Sun magnetic properties. Finally, we propose the use of two other \ion{Fe}{1} lines (at 4122 and 9000 Å) with identical line opacities that seem to work much better than the others. Title: The Evershed Effect Observed with 0.2" Angular Resolution Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez Cerdeña, I. Bibcode: 2007ApJ...658.1357S Altcode: 2006astro.ph.11523S We present an analysis of the Evershed effect observed with a resolution of 0.2". Using the new Swedish 1 m Solar Telescope and its Littrow spectrograph, we scan a significant part of a sunspot penumbra. Spectra of the nonmagnetic line Fe I λ7090.4 allows us to measure Doppler shifts without magnetic contamination. The observed line profiles are asymmetric. The Doppler shift depends on the part of the line used for measuring, indicating that the velocity structure of penumbrae remains unresolved, even with our angular resolution. The observed line profiles are properly reproduced if two components with velocities between zero and several km s-1 coexist in the resolution elements. Using Doppler shifts at fixed line depths, we find a local correlation between upflows and bright structures and between downflows and dark structures. This association is not specific to the outer penumbra, but it also occurs in the inner penumbra. The existence of such a correlation was originally reported in 1969 by Beckers and Schröter, and it is suggestive of energy transport by convection in penumbrae. Title: A Simple Model for the Distribution of Quiet-Sun Magnetic Field Strengths Authors: Sánchez Almeida, J. Bibcode: 2007ApJ...657.1150S Altcode: 2006astro.ph.11711S We derive a first-order linear differential equation describing the shape of the probability density function (PDF) of magnetic field strengths in the quiet Sun. The modeling is very schematic. It considers convective motions which continuously supply and withdraw magnetic structures. In addition, a magnetic amplification mechanism increases the field strength up to a threshold that cannot be exceeded. These three basic ingredients provide PDFs in good agreement with the PDFs produced by realistic numerical simulations of magnetoconvection, as well as with quiet-Sun PDFs inferred from observations. In particular, the distribution is approximately lognormal, and it produces an excess of magnetic fields (i.e., a hump in the distribution) right before the maximum field strength. The success of this simple model may indicate that only a few basic ingredients shape the quiet-Sun PDF. Our approach provides a concise parametric representation of the PDF, as required to develop automatic methods of diagnostics. Title: The Micro-Structure of a Sunspot Penumbra Authors: Sánchez Almeida, J. Bibcode: 2006ASPC..358...13S Altcode: The spectral lines observed in penumbrae are asymmetrical, revealing the existence of spatially unresolved structures. We infer their physical properties by fitting Stokes spectra of Fe I 6301.5 Å and Fe I 6302.5 Å with model atmospheres having two magnetic components interleaved along the line-of-sight (LOS). Combining ten thousand fits, we set up a semi-empirical model sunspot, whose two components present very different magnetic-field inclinations. The major component, which contains most of the mass, is more vertical than the minor component, which is inclined below the horizontal plane throughout the penumbra. Magnetic field lines and mass flows are parallel, consequently both upflows and downflows are present everywhere in the penumbra. Major and minor components have very different velocities (several 102 m s-1 vs. 10 km s-1), but they transport the same mass per unit time. The similarity between the vertical mass flow and the magnetic flux of the two components suggests that field lines emerging as major component may return to the photosphere as minor component. If so, the observed magnetic field strength difference between components leads to a siphon flow whose magnitude and direction agree with the Evershed flow.

Several tests support the internal consistency of the retrieved model sunspot, in particular, the magnetic field vector B does not violate the div B=0 condition.

A detailed description of the techniques and results presented in this meeting is given by tet{s1 SA05}. Title: Proper Motions in Sunspot Penumbrae: Signs of Convection Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J. Bibcode: 2006ASPC..358...80B Altcode: Proper motions in penumbra have been measured using local correlation tracking techniques in a high spatial resolution series of images (∼0.12 arcsec). Assuming these motions to trace true plasma motions, we have detected converging flows that arrange the plasma in long narrow filaments mostly placed along dark penumbral filaments. These converging flows suggest downflows in the filaments of ∼ 200 m s-1. We interpret the association between downflows and dark features as a sign of convection that, once several observational biases are considered, could transport enough energy to balance the radiative losses of penumbra. Title: The Evershed Effect with 0.2 arcsec Angular Resolution Authors: Márquez, I.; Bonet, J. A.; Sánchez Almeida, J.; Domínguez Cerdeña, I. Bibcode: 2006ASPC..358...96M Altcode: We present a preliminary analysis of penumbral spectra observed with unprecedented angular resolution (0.2 arcsec) using the new Swedish 1-m Solar Telescope. The use of a non-magnetic line allows us to measure Doppler shifts without magnetic contamination.

The observed Doppler shifts depend on the part of the line used for measuring, indicating that the velocity structure of penumbrae remains unresolved even with our resolution.

We find a correlation between upflows and bright filaments. This association is not specific of the outer penumbra but it also occurs in the inner penumbra.

The existence of such correlation was originally reported by tet{m1 BS69},

and it is suggestive of energy transport by convection in penumbrae. Title: Magnetic Fields of the Quiet Sun: Distribution of Field Strengths Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ASPC..358...48D Altcode: The quiet Sun photospheric plasma has a variety of magnetic field strengths going from zero to 1800 G. The empirical characterization of these field strengths requires a probability density function (PDF), i.e., a function P(B) describing the fraction of quiet Sun occupied by each field strength B. We present a method to combine magnetic field strength measurements based on the Zeeman effect and the Hanle effect in order to estimate the true P(B). The application of the method to real observations renders a set of possible PDFs, which outline the general characteristics of the quiet Sun magnetic fields. Their most probable field strength differs from zero. The magnetic energy density is a significant fraction of the kinetic energy of the granular motions at the base of the photosphere (larger than 15 or larger than 2×103 erg cm-3). The unsigned flux density (or mean magnetic field strength) has to be between 130 G and 190 G. A significant part of the unsigned flux (between 10% and 40%) and of the magnetic energy (between 40% and 80%) are provided by the field strengths larger than 1 kG which, however, occupy only a small fraction of the surface (between 1% and 4%).

The quiet Sun photosphere has far more unsigned magnetic flux and magnetic energy than the active regions and the network together. Title: Quiet-Sun Magnetic Fields: Simultaneous Inversion of Visible and IR Spectro-Polarimetric Observations Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ASPC..358...88D Altcode: We studied the quiet-Sun magnetic fields interpreting spectro-polarimetric observations of infrared and visible spectral lines. Magnetic field strengths and filling factors were inferred by the simultaneous inversion of Stokes profiles of the Fe I lines at 6301.5, 6302.5, 15648, and 15653 Å under the MISMA hypothesis. They cover a solar intra-network region at disk center. We analyzed Stokes profiles with signals above noise in both spectral ranges, which correspond to 40% of the field of view. Most of these 2280 profiles could only be inverted with a model including 3 magnetic components with very different field strengths, which indicates the co-existence of kG and sub-kG fields. We measured a total unsigned magnetic flux density of 9.6 G over the whole field of view. For half of the pixels the magnetic field has opposite polarities within the resolution element. We computed the probability density function of finding each magnetic field strength. It has an important contribution of kG field strengths, which concentrates most of the magnetic flux and energy. This kG contribution has a preferred magnetic polarity while the weak fields are balanced. Title: Quiet Sun Magnetic Fields from Simultaneous Inversions of Visible and Infrared Spectropolarimetric Observations Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ApJ...646.1421D Altcode: 2006astro.ph..4381D We study the quiet Sun magnetic fields using spectropolarimetric observations of the infrared and visible Fe I lines at 6301.5, 6302.5, 15648, and 15653 Å. Magnetic field strengths and filling factors are inferred by the simultaneous fit of the observed Stokes profiles under the MISMA hypothesis. The observations cover an intranetwork region at the solar disk center. We analyze 2280 Stokes profiles whose polarization signals are above noise in the two spectral ranges, which correspond to 40% of the field of view. Most of these profiles can be reproduced only with a model atmosphere including three magnetic components with very different field strengths, which indicates the coexistence of kG and sub-kG fields in our 1.5" resolution elements. We measure an unsigned magnetic flux density of 9.6 G considering the full field of view. Half of the pixels present magnetic fields with mixed polarities in the resolution element. The fraction of mixed polarities increases as the polarization weakens. We compute the probability density function of finding each magnetic field strength. It has a significant contribution of kG field strengths, which concentrates most of the observed magnetic flux and energy. This kG contribution has a preferred magnetic polarity, while the polarity of the weak fields is balanced. Title: Magnetic flux in the inter-network quiet Sun from comparison with numerical simulations Authors: Sánchez Almeida, J. Bibcode: 2006A&A...450.1199S Altcode: 2005astro.ph.12395S Khomenko et al. estimate the mean magnetic field strength of the quiet Sun to be 20 G. The figure is smaller than several existing estimates, and it comes from the comparison between observed Zeeman polarization signals and synthetic signals from numerical simulations of magneto-convection. The numerical simulations require an artificially large magnetic diffusivity, which smears out magnetic structures smaller than the grid scale. Assuming a turbulent cascade for the unresolved artificially smeared magnetic fields, we find that their unsigned magnetic flux is at least as important as that explicitly shown in the simulation. The unresolved fields do not produce Zeeman polarization but contribute to the unsigned flux. Since they are not considered by Khomenko et al., their mean magnetic field strength has to be regarded as a lower limit. This kind of bias is not specific of a particular numerical simulation or a spectral line. It is to be expected when observed quiet Sun Zeeman signals are compared with synthetic signals from simulations. Title: High-Resolution Proper Motions in a Sunspot Penumbra Authors: Márquez, I.; Sánchez Almeida, J.; Bonet, J. A. Bibcode: 2006ApJ...638..553M Altcode: 2005astro.ph.10220M Local correlation tracking techniques are used to measure proper motions in a series of high angular resolution (~0.1") penumbra images. If these motions trace true plasma motions, then we have detected converging flows that arrange the plasma in long narrow filaments cospatial with dark penumbral filaments. Assuming that these flows are stationary, the vertical stratification of the atmosphere and the conservation of mass suggest downflows in the filaments on the order of 200 m s-1. The association between downflows and dark features may be a sign of convection, as it happens with the nonmagnetic granulation. Insufficient spatial resolution may explain why the estimated vertical velocities are not fast enough to supply the radiative losses of penumbrae. Title: The Distribution of Quiet Sun Magnetic Field Strengths from 0 to 1800 G Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2006ApJ...636..496D Altcode: 2005astro.ph..9243D; 2006ApJ...636..496C The quiet-Sun photospheric plasma has a variety of magnetic field strengths going from zero to 1800 G. The empirical characterization of these field strengths requires a probability density function (PDF), i.e., a function P(B) describing the fraction of quiet Sun occupied by each field strength B. We show how to combine magnetic field strength measurements based on the Zeeman effect and the Hanle effect to estimate an unbiased P(B). The application of the method to real observations renders a set of possible PDFs, which outline the general characteristics of the quiet-Sun magnetic fields. Their most probable field strength differs from zero. The magnetic energy density is a significant fraction of the kinetic energy of the granular motions at the base of the photosphere (larger than 15% or larger than 2×103 ergs cm-3). The unsigned flux density (or mean magnetic field strength) has to be between 130 and 190 G. A significant part of the unsigned flux (between 10% and 50%) and of the magnetic energy (between 45% and 85%) are provided by the field strengths larger than 500 G, which, however, occupy only a small fraction of the surface (between 1% and 10%). The fraction of kG fields in the quiet Sun is even smaller, but they are important for a number of reasons. The kG fields still trace a significant fraction of the total magnetic energy, they reach the high photosphere, and they appear in unpolarized light images. The quiet-Sun photosphere has far more unsigned magnetic flux and magnetic energy than the active regions and the network combined. Title: On the Sr I λ4607 Å Hanle depolarization signals in the quiet Sun Authors: Sánchez Almeida, J. Bibcode: 2005A&A...438..727S Altcode: 2005astro.ph..4339S The Hanle depolarization signals of Sr i λ4607 Å have been used to estimate the unsigned magnetic flux and magnetic energy existing in the quiet Sun photosphere. However, the Sr i λ4607 Å Hanle signals are not sensitive to the unsigned flux and energy. They only bear information on the fraction of photosphere occupied by magnetic field strengths smaller than the Hanle saturation, which do not contribute to the unsigned flux and energy. We deduce an approximate expression for the relationship between magnetic fill factor and Hanle signal. When applied to existing Hanle depolarization measurements, it indicates that only 40% of the quiet Sun is filled by magnetic fields with a strength smaller than 60 G. The remaining 60% of the surface has field strengths above this limit. Such constraint will be needed to determine the distribution of magnetic field strengths existing in the quiet Sun. Title: Quiet sun magnetic fields vs. polar faculae - local vs. global dynamo? Authors: Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2005AN....326..205O Altcode: Quiet Sun magnetic fields in the internetwork are almost ubiquitous. Simultaneous observations in infra-red and visible lines and high spatial resolution (< 0.5'') data in visible lines show that their field strengths range from below few hundred Gauss to kilo-Gauss. Most of the flux is contained in small-scale, strong-field features located mainly in intergranular lanes. The average unsigned flux density exceeds 20 Gauss. The new detections are confirmed by recent quiet Sun observations in the G band. The generation of the strong fields in the internetwork, which may be due to a local dynamo, poses a challenging problem. - Polar faculae (PFe) are small-scale magnetic features at the polar caps of the Sun. They take part in the solar cycle and are thus likely to be rooted deeply in the solar interior. They are the result of the global dynamo at the solar poles. PFe also possess kilo-Gauss magnetic fields which have the same polarity as the global magnetic field. The rôle of quiet Sun magnetic field structures and of PFe for the dynamics of the corona and for the solar wind are addressed. Title: Physical Properties of the Solar Magnetic Photosphere under the MISMA Hypothesis. III. Sunspot at Disk Center Authors: Sánchez Almeida, J. Bibcode: 2005ApJ...622.1292S Altcode: 2004astro.ph.12217S; 2004astro.ph.12217A Small-scale fluctuations of magnetic field and velocity may be responsible for the Stokes asymmetries observed in all photospheric magnetic structures (the microstructured magnetic atmosphere [MISMA] hypothesis). We support the hypothesis by showing that atmospheres with optically thin microstructure reproduce the polarization of Fe I λλ6301.5 and 6302.5 observed in a sunspot. Ten thousand spectra were fitted by model MISMAs with two magnetic components interleaved along the line of sight. Combining all the fits, we set up a semiempirical model sunspot characterized by two components with very different magnetic field inclinations. The major component, which contains most of the mass, is more vertical than the minor component. The field lines of the minor component are inclined below the horizontal plane throughout the penumbra. Magnetic field lines and mass flows are parallel; consequently, both upflows and downflows are present everywhere on the penumbra. Major and minor components have very different velocities (several hundred meters per second for the major component versus 10 km s-1 for the minor component), but the mass transported per unit time is similar. The similarity between the vertical mass flow and the magnetic flux of the two components suggests that field lines emerging as major components may return to the photosphere as minor components. If so, the observed magnetic field strength difference between components leads to a siphon flow whose magnitude and direction agree with the inferred Evershed flow. Several tests support the internal consistency of the retrieved model sunspot. The magnetic field vector B does not violate the ∇B=0 condition. The model sunspot reproduces the net circular polarization of the observed lines plus the abnormal behavior of Fe I λ15648. The use of only one magnetic component to interpret the spectra leads to inferring upflows in the inner penumbra and downflows in the outer penumbra, in agreement with previous findings. Title: Counting Publications in Astronomy Authors: Corral, L. J.; Sanchez Almeida, J. Bibcode: 2005coas.conf...14C Altcode: No abstract at ADS Title: Simultaneous Visible and IR spectropolarimetry of the quiet Sun Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2005ASSL..320..175D Altcode: 2005ASSL..320..175C; 2005smp..conf..175D This work presents the first quiet Sun spectropolarimetric observations carried out in the visible and the infrared (IR) simultaneously. The Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed co-spatially, and at the same time (with a time lag of only 1 minute), with high sensitive spectropolarimeters operated in two different telescopes (VTT and THEMIS at the Observatorio del Teide). We find Stokes V profiles above noise in 30% of the observed area, showing intrinsic magnetic fields of kG (traced by visible lines) co-existing with sub-kG fields (traced by infrared lines). We also found V profiles with opposite polarity in the visible and the IR in 25% of the pixels under study (8% of the area). Title: The Magnetism of the Very Quiet Sun Authors: Sánchez Almeida, J. Bibcode: 2004ASPC..325..115S Altcode: 2004astro.ph..4053S; 2004astro.ph..4053A When the polarimetric sensitivity and the angular resolution exceed a threshold, magnetic fields show up almost everywhere on the solar surface. Here I revise the observational properties of the weakest polarization signals, which appear in the InterNetwork (IN) regions. We already have some information on the magnetic field strengths and inclinations, mass motions, lifetimes, magnetic fluxes, magnetic energies, etc. Since the IN covers a substantial faction of the solar surface, it may account for most of the unsigned magnetic flux and energy existing on the solar surface at any given time. This fact makes IN fields potentially important to understand the global magnetic properties of the Sun (e.g. the structure of the quiet solar corona, an issue briefly addressed here). The spectropolarimeters on board of SolarB have the resolution and sensitivity to routinely detect these IN fields. Title: Bright Points in the Internetwork Quiet Sun Authors: Sánchez Almeida, J.; Márquez, I.; Bonet, J. A.; Domínguez Cerdeña, I.; Muller, R. Bibcode: 2004ApJ...609L..91S Altcode: 2004astro.ph..5515S; 2004astro.ph..5515A High-resolution G-band images of the interior of a supergranulation cell show ubiquitous bright points (BPs; some 0.3 BPs per Mm2). They are located in intergranular lanes and often form chains of elongated blobs whose smallest dimension is at the resolution limit (135 km on the Sun). Most of them live for a few minutes, having peak intensities from 0.8 to 1.8 times the mean photospheric intensity. These BPs are probably tracing intense magnetic concentrations, whose existence has been inferred in spectropolarimetric measurements. Our finding provides a new convenient tool for the study of the internetwork magnetism, so far restricted to the interpretation of weak polarimetric signals. Title: Analysis of simultaneous visible and infrared spectropolarimetric observations of quiet Sun. Authors: Dominguez Cerdena, I.; Sanchez Almeida, J.; Kneer, F. Bibcode: 2004ANS...325...94D Altcode: 2004ANS...325a..94D; 2004ANS...325..P23D No abstract at ADS Title: Inter-Network magnetic fields observed during the minimum of the solar cycle Authors: Sánchez Almeida, J. Bibcode: 2003A&A...411..615S Altcode: 2003astro.ph.10164S; 2003astro.ph.10164A We analyze a time series of high angular resolution magnetograms of quiet Sun Inter-Network (IN) magnetic fields. These magnetograms have a spatial resolution better than 0\farcs5, a noise of some 20 G, and they have been obtained at the disk center during the minimum of the solar cycle. The IN regions show a typical unsigned flux density of the order of 15 G. Signals occur, preferentially, in the intergranular lanes, and the strongest signals trace a network with a scale similar to the mesogranulation. All these features are consistent with the IN magnetograms by \citet{dom03a,dom03b}, obtained during the maximum of the solar cycle. Consequently, the unsigned magnetic flux of the structures that give rise to the IN polarization signals does not seem to undergo large variations during the solar cycle. Title: Simultaneous Visible and Infrared Spectropolarimetry of a Solar Internetwork Region Authors: Sánchez Almeida, J.; Domínguez Cerdeña, I.; Kneer, F. Bibcode: 2003ApJ...597L.177S Altcode: 2003astro.ph..9727A; 2003astro.ph..9727S We present the first simultaneous infrared (IR) and visible spectropolarimetric observations of a solar internetwork region. The Fe I lines at 6301.5, 6302.5, 15648, and 15652 Å were observed, with a lag of only 1 minute, using highly sensitive spectropolarimeters operated in two different telescopes (Vacuum Tower Telescope and THEMIS at the Observatorio del Teide). Some 30% of the observed region shows IR and visible Stokes V signals above noise. These polarization signals indicate the presence of kilogauss (kG) magnetic field strengths (traced by the visible lines) coexisting with sub-kG fields (traced by the infrared lines). In addition, one-quarter of the pixels with signal have visible and IR Stokes V profiles with opposite polarity. We estimate the probability density function of finding each longitudinal magnetic field strength in the region. It has a tail of kG field strengths that accounts for most of the (unsigned) magnetic flux of the region. Title: Quiet Sun Magnetic Fields Authors: Sánchez Almeida, J. Bibcode: 2003AIPC..679..293S Altcode: The seemingly un-magnetized part of the solar surface is not really un-magnetized. It is occupied by magnetic structures producing low polarization which, therefore, escape detection in traditional measurements. Since most of the solar surface belongs to this category, the quiet Sun magnetic fields can easily carry most of the magnetic flux and energy existing in the photosphere at any given time. Consequently, they are a potentially important ingredient of the solar magnetism. Most of the physical properties of the quiet Sun are still uncertain (distribution of field strengths, area coverage, influence on higher atmospheric layers, etc.).It is clear, however, that the topology of the field is complex, with field lines of very different properties coexisting in each resolution element. This fact hampers the detection of the quiet Sun magnetic fields. I argue that the best present measurements detect, at most, 30 % of the existing magnetic flux. Then the quiet Sun contains at least as much magnetic flux as all active regions and the network during the solar maximum. Title: Magnetic Fields in the Quiet Sun: Observational Discrepancies and Unresolved Structure Authors: Socas-Navarro, H.; Sánchez Almeida, J. Bibcode: 2003ApJ...593..581S Altcode: Observations of magnetically sensitive lines in the visible and the infrared yield apparently contradictory values for the intrinsic field strength in the internetwork quiet Sun. It is shown that this discrepancy can be understood if one assumes that the magnetic field is not homogeneous over the resolution element. The difference between visible and infrared measurements may be used to set constrains on the subpixel distribution of field strengths. We suggest a specific probability density function that seems to satisfy the existing observational constraints. Title: Inter-network magnetic fields observed with sub-arcsec resolution Authors: Domínguez Cerdeña, I.; Sánchez Almeida, J.; Kneer, F. Bibcode: 2003A&A...407..741D Altcode: 2003astro.ph..6329C; 2003astro.ph..6329D We analyze a time sequence of Inter-Network (IN) magnetograms observed at the solar disk center. Speckle reconstruction techniques provide a good spatial resolution (0\farcs5 cutoff frequency) yet maintaining a fair sensitivity (some 20 G). Patches with signal above noise cover 60% of the observed area, most of which corresponds to intergranular lanes. The large surface covered by signal renders a mean unsigned magnetic flux density between 17 G and 21 G (1 G equiv 1 Mx cm-2). The difference depends on the spectral line used to generate the magnetograms (łinetwo or łineone ). Such systematic difference can be understood if the magnetic structures producing the polarization have intrinsic field strengths exceeding 1 kG, and consequently, occupying only a very small fraction of the surface (some 2%). We observe both, magnetic signals changing in time scales smaller than 1 min, and a persistent pattern lasting longer than the duration of the sequence (17 min). The pattern resembles a network with a spatial scale between 5 and 10 arcsec, which we identify as the mesogranulation. The strong dependence of the polarization signals on spatial resolution and sensitivity suggests that much quiet Sun magnetic flux still remains undetected. Title: Polarization of Photospheric Lines from Turbulent Dynamo Simulations Authors: Sánchez Almeida, J.; Emonet, T.; Cattaneo, F. Bibcode: 2003ApJ...585..536S Altcode: 2002astro.ph.11175S; 2002astro.ph.11175A We employ the magnetic and velocity fields from turbulent dynamo simulations to synthesize the polarization of a typical photospheric line. The synthetic Stokes profiles have properties in common with those observed in the quiet Sun. The simulated magnetograms present a level of signal similar to that of the Inter-Network regions. Asymmetric Stokes V profiles with two, three, and more lobes appear in a natural way. The intensity profiles are broadened by the magnetic fields in fair agreement with observational limits. Furthermore, the Hanle depolarization signals of the Sr I λ4607 Å line turn out to be within the solar values. Differences between synthetic and observed polarized spectra can also be found. There is a shortage of Stokes V asymmetries, which we attribute to a deficit of structuring in the magnetic and velocity fields from the simulations as compared to the Sun. This deficit may reflect the fact that the Reynolds numbers of the numerical data are still far from solar values. We consider the possibility that intense and tangled magnetic fields, like those in the simulations, exist in the Sun. This scenario has several important consequences. For example, less than 10% of the existing unsigned magnetic flux would be detected in present magnetograms. The existing flux would exceed by far that carried by active regions during the maximum of the solar cycle. Detecting these magnetic fields would involve improving the angular resolution, the techniques to interpret the polarization signals, and to a lesser extent, the polarimetric sensitivity. Title: Quiet-Sun Magnetic Fields at High Spatial Resolution Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003ApJ...582L..55D Altcode: 2002astro.ph.11454C; 2002astro.ph.11454D We present spectropolarimetric observations of internetwork magnetic fields at the solar disk center. A Fabry-Pérot spectrometer was used to scan the two Fe I lines at 6301.5 and 6302.5 Å. High spatial resolution (0.5") magnetograms were obtained after speckle reconstruction. The patches with magnetic fields above noise cover approximately 45% of the observed area. Such large coverage renders a mean unsigned magnetic flux density of some 20 G (or 20 Mx cm-2), which exceeds all previous measurements. Magnetic signals occur predominantly in intergranular spaces. The systematic difference between the flux densities measured in the two iron lines leads to the conclusion that, typically, we detect structures with intrinsic field strengths larger than 1 kG occupying only 2% of the surface. Title: High Resolution 2D Spectro-polarimetric Observations of Polar Faculae and Quiet Sun in Two Iron Lines Authors: Domínguez Cerdeña, I.; Okunev, O.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003ASPC..307..370D Altcode: No abstract at ADS Title: Na I D1 Stokes V Asymmetries and Velocity Structure Around Sunspots Authors: Eibe, M. T.; Sánchez Almeida, J.; Mein, P.; Aulanier, G.; Malherbe, J. M. Bibcode: 2003ASPC..307..374E Altcode: No abstract at ADS Title: The Polarized Spectrum Emerging from Fast Dynamo Simulations Authors: Sánchez Almeida, J.; Emonet, T.; Cattaneo, F. Bibcode: 2003ASPC..307..293S Altcode: No abstract at ADS Title: Solar Polarization Authors: Trujillo-Bueno, Javier; Sanchez Almeida, Jorge Bibcode: 2003ASPC..307.....T Altcode: 2003sopo.conf.....T No abstract at ADS Title: High resolution 2D spectro-polarimetric observations of the quiet Sun in two iron lines Authors: Domínguez Cerdeña, I.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2003AN....324..327D Altcode: No abstract at ADS Title: Magnetic Properties of Photospheric Regions with Very Low Magnetic Flux Authors: Socas-Navarro, H.; Sánchez Almeida, J. Bibcode: 2002ApJ...565.1323S Altcode: 2001astro.ph.10025S The magnetic properties of the quiet Sun are investigated using a novel inversion code, FATIMA, based on the Principal Component Analysis of the observed Stokes profiles. The stability and relatively low noise sensitivity of this inversion procedure allows for the systematic inversion of large data sets with a very weak polarization signal. Its application to quiet-Sun observations of network and internetwork regions reveals that a significant fraction of the quiet-Sun contains kilogauss fields (usually with very small filling factors) and confirms that the pixels with weak polarization account for most of the magnetic flux. Mixed polarities in the resolution element are also found to occur more likely as the polarization weakens. Title: Results from the Thermal Vacuum Tests of the Chinese-Brazilian Earth Resources Satellite - CBERS FM2 Authors: Almeida, J. S.; Garcia, E. C.; Santos, M. B.; Fu, P. Z. Bibcode: 2002iaf..confE.478A Altcode: This paper details the approach adopted and applied on the thermal vacuum tests campaign of the CBERS Flight Model #2 spacecraft, successfully performed at the Integration and Tests Laboratory - LIT, National Institute for Space Research - INPE, in São José dos Campos, SP, from September 7th to 28th, 2001. Measuring approximately 1.8 x 2.0 x 2.2m, weighting 1,500kg and carrying three cameras as the main payload, this spacecraft is scheduled to be launched in China and it will be orbiting the Earth at 778km as part of its remote sensing mission profile. Exploring the capabilities of LIT's 3m x 3m thermal vacuum chamber in terms of appropriately selecting and adjusting its cold shroud temperatures and also some low cost heat input/sink techniques, the spacecraft was adequately disjoined at its service and payload model interface in such a way that each part could physically fit inside the T/V chamber one at a time. Assuring all the necessary functional and test cabling interconnection between the two models through the chamber walls for the proper spacecraft electrical operations as an integrated system, specific thermal test techniques were applied in order to obtain the required hot and cold acceptance levels of temperature at the spacecraft subsystems and structural surfaces, as a consequence of the simulated thermal conditioning from the distinct orbital configurations. These thermal simulation techniques consisted of a combination of skin-heaters, the thermal vacuum chamber main shrouds and dedicated LN2 cold plates, effectively leading to reliable and very satisfactory testing methodology results. Taking more than 350 hours and having 67 people directly involved, including teams from both Brazil and China, this test can be considered as a very important accomplishment in terms of distinct technique of spacecraft testing and also in terms of the satisfactory working relationship between two quite different cultures. Title: Thermal Relaxation of Very Small Solar Magnetic Structures in Intergranules: A Process That Produces Kilogauss Magnetic Field Strengths Authors: Sánchez Almeida, J. Bibcode: 2001ApJ...556..928S Altcode: 2001astro.ph..3415A; 2001astro.ph..3415S The equilibrium configuration of very small magnetic flux tubes in an intergranular environment automatically produces kilogauss magnetic field strengths. We argue that such a process takes place in the Sun and complements the convective collapse (CC), which is traditionally invoked to explain the formation of kilogauss magnetic concentrations in the solar photosphere. In particular, it can concentrate the very weak magnetic fluxes revealed by the new IR spectropolarimeters, for which the operation of the CC may have difficulty. As part of the argument, we show the existence of solar magnetic features of very weak fluxes yet concentrated magnetic fields (some 3×1016 Mx and 1500 G). Title: G-Band Spectral Synthesis in Solar Magnetic Concentrations Authors: Sánchez Almeida, J.; Asensio Ramos, A.; Trujillo Bueno, J.; Cernicharo, J. Bibcode: 2001ApJ...555..978S Altcode: 2001astro.ph..3006A; 2001astro.ph..3006S Narrowband imaging in the G band is commonly used to trace the small magnetic field concentrations of the Sun, although the mechanism that makes them bright has remained unclear. We carry out LTE syntheses of the G band in an assorted set of semiempirical model magnetic concentrations. The syntheses include all CH lines as well as the main atomic lines within the bandpass. The model atmospheres produce bright G-band spectra having many properties in common with the observed G-band bright points. In particular, the contrast referring to the quiet Sun is about twice the contrast in continuum wavelengths. The agreement with observations does not depend on the specificities of the model atmosphere; rather, it holds from single flux tubes to microstructured magnetic atmospheres. However, the agreement requires that the real G-band bright points are not spatially resolved, even in the best observations. Since the predicted G-band intensities exceed by far the observed values, we foresee a notable increase of contrast of the G-band images upon improvement of the angular resolution. According to the LTE modeling, the G-band spectrum emerges from the deep photosphere that produces the continuum. Our syntheses also predict solar magnetic concentrations showing up in continuum images but not in the G band. Finally, we have examined the importance of the CH photodissociation in setting the amount of G-band absorption. It turns out to play a minor role. Title: Spectral signature of uncombed penumbral magnetic fields. Comment Authors: Sánchez Almeida, J. Bibcode: 2001A&A...369..643S Altcode: The conservation of magnetic flux demands a magnetic field fine structure as small as 15 km to explain the net circular polarization observed in penumbrae (Sánchez Almeida \cite{san98a}). A recent work by Martínez Pillet (\cite{mar00}) claims that modeling penumbrae as a collection of fluxtubes 100 km wide suffices. We identify several shortcomings of such modeling so that it is presently unclear whether it really contradicts the former conclusion. Title: The Micro-Structure of the Solar Magnetic Fields Authors: Sánchez Almeida, J. Bibcode: 2001ASPC..248...55S Altcode: 2001mfah.conf...55S No abstract at ADS Title: Ghost Magnetic Structures in the Sun and Solar-type Stars (CD-ROM Directory: contribs/sanchez) Authors: Sánchez Almeida, J. Bibcode: 2001ASPC..223..145S Altcode: 2001csss...11..145S No abstract at ADS Title: Elusive Magnetic Structures in the Sun and Solar-Type Stars Authors: Sánchez Almeida, J. Bibcode: 2000ApJ...544.1135S Altcode: The magnetic structures of the Sun are very inhomogeneous, with irregularities smaller than the smallest sizes that we resolve from Earth. Such irregularities are not properly accounted for by standard magnetic field diagnostic techniques. We have identified a quantitatively important bias that has remained unnoticed hitherto. Intense magnetic fields embedded in inhomogeneous magnetic structures produce little light and easily escape detection. These elusive magnetic fields, which cheat standard observing techniques, seem to be common. We estimate that they carry at least half of the solar magnetic flux. Should the bias be so severe, it would cast doubts on the present interpretation of many solar magnetic phenomena. Since magnetic field measurements in solar-type stars reproduce solar methods, they are liable to the same systematic errors. Title: Physical Properties of the Solar Magnetic Photosphere under the MISMA Hypothesis. II. Network and Internetwork Fields at the Disk Center Authors: Sánchez Almeida, J.; Lites, B. W. Bibcode: 2000ApJ...532.1215S Altcode: This paper is the second in a series that models photospheric magnetic structures in terms of atmospheres having optically thin fluctuations of magnetic field and thermodynamic state (the MISMA hypothesis). We apply an inversion procedure to the polarization of Fe I λ6301.5 and Fe I λ6302.5 observed in network and internetwork regions with the Advanced Stokes Polarimeter. Some 5200 independent spectra, comprising mildly asymmetric to very abnormal Stokes profiles, were reproduced by a single type of model atmosphere. It has three components, two that are magnetized and one that is not. A large fraction among the field strengths we measure are in the kG regime, but simulations suggest that the polarization of the observed Fe I lines weakens below detectable levels for fields substantially smaller than the observed ones. Synthesis of Stokes profiles of the IR Fe I λ15648.5 line in MISMAs reveals the opposite behavior, i.e., an increase of polarization for sub-kG fields. The highly transparent MISMAs inferred from observations are significantly brighter in the continuum than an unmagnetized atmosphere. The mass of the magnetic structures tends to be at rest, although a minor fraction undergoes strong downflows. Downflows are also present in the nonmagnetic environment. A significant number of fitted Stokes profiles require opposite magnetic polarities within the same resolution element. The occurrence of mixed polarities increases with weakening degree of polarization, such that 25% of the weakest signals require mixed polarity. The weak polarization signals account for most of the total (unsigned) magnetic flux of the observed region. By extrapolation, this indicates that a significant fraction of photospheric magnetic flux remains undetected. The MISMA framework provides a unified and physically consistent scenario for interpretation of quiet Sun magnetism. Moreover, it is the only one available at present that is able to fit the abnormal Stokes profiles as revealed by the new generation of sensitive Stokes polarimeters. Title: Radiative Transfer in Weakly Polarizing Media Authors: Sánchez Almeida, J.; Trujillo Bueno, J. Bibcode: 1999ApJ...526.1013S Altcode: We study radiative transfer through a weakly polarizing medium, i.e., a medium in which the degree of polarization of the absorbed, retarded, and emitted light is always weak. In this case, the general radiative transfer equation for the Stokes parameters yields very simple formal solutions. The intensity does not depend on the polarization, and the other Stokes parameters are uncoupled from each other. It is shown how this simplified radiative transfer equation holds in many realistic cases relevant for solar and stellar magnetometry. It can be applied whenever the weak magnetic field approximation works, i.e., for weakly split lines. In addition, it handles weak spectral lines, structures with complex magnetic topology, chromospheric lines formed under non-LTE conditions, etc. The merits of the approximation, which we call the weakly polarizing medium (WPM) approximation, are illustrated by means of several LTE and non-LTE line syntheses in realistic solar model atmospheres. The WPM approximation should be useful in planning and understanding measurements based on polarization. It simplifies the relationship between the observed polarization and the physical structure that one tries to retrieve. The approximation may also be used in numerical problems requiring extensive polarized radiative transfer (inversion codes, syntheses of stellar spectra, self-consistent multilevel non-LTE Zeeman line transfer with atomic polarization, etc.). Title: The profuse optically-thin irregularities of the photospheric magnetic fields Authors: Sánchez Almeida, J. Bibcode: 1999AIPC..471...55S Altcode: 1999sowi.conf...55S The highly irregular nature of most photospheric magnetic fields is analyzed here, trying to emphasize the connection between photospheric fluctuations and those existing in the solar wind. It is discussed how the magnetic flux conservation in sunspots demands penumbrae pervaded by kilometer-wide irregularities. The diagnosis of this type of tiny scales requires special tools having degrees of freedom for optically-thin magnetic irregularities. One of such tools is introduced here, to be subsequently applied to the quiet Sun. It turns out to reproduce the observed Zeeman induced polarization, despite the fact that the polarization is frequently very abnormal. The kind of irregular atmosphere that the inversion technique favors seems to provide a consistent picture of the quiet Sun magnetism. Title: The Spectrum of Intensity Fluctuations Across Penumbral Filaments Authors: Sánchez Almeida, J.; Bonet, J. Bibcode: 1999ASPC..183...87S Altcode: 1999hrsp.conf...87S No abstract at ADS Title: LPSP & TIP: Full Stokes Polarimeters for the Canary Islands Observatories Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.; González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.; Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D. Bibcode: 1999ASPC..183..264M Altcode: 1999hrsp.conf..264M No abstract at ADS Title: Influence of Unresolved Optically-Thin Irregularities on Quiet Sun Magnetic Field Determinations Authors: Sánchez Almeida, J. Bibcode: 1999AGAb...15Q..10S Altcode: 1999AGM....15..A10S Observations and theory both point out that the magnetic photosphere is not smooth but irregular at optically-thin scales. The relevance of these irregularities for a proper magnetic field diagnostics depends upon the not yet known structure of the magnetic field fluctuations (and, of course, on the purpose of our determination). Sánchez Almeida & Lites (1999) analyze quiet Sun network and internetwork Stokes profiles allowing for optically thin fluctuations (i.e., they use MIcro-Structured Magnetic Atmospheres). The retrieved semi-empirical quiet Sun model atmospheres present several conspicuous counter-intuitive properties. If these models contain the essentials of the real Sun then standard quiet Sun magnetic field determinations are seriously biased. This contribution presents and discusses some of these unexpected properties: the IR Fe i 15648 Å line is rather insensitive to strong kG fields; large magnetic field strengths can easily escape detection; unresolved mixed polarities seems to be the rule when dealing with most of the solar surface, that is to say, when measuring the signals that may be carrying most of the solar magnetic flux, etc. The conclusion to be drawn from these results is that accounting for optically-thin fluctuations does matter for a proper quiet Sun magnetic field diagnostics. Title: The current status of the MISMA hypothesis Authors: Sánchez Almeida, J. Bibcode: 1999ASSL..243..251S Altcode: 1999sopo.conf..251S No abstract at ADS Title: The Spectrum of Fluctuations across Penumbral Filaments Authors: Sánchez Almeida, J.; Bonet, J. A. Bibcode: 1998ApJ...505.1010S Altcode: We estimate the typical spectrum of spatial fluctuations of intensity due to the penumbral filaments. High angular resolution continuum images are used (cut-off frequencies equivalent to 0.28" wavelength of about 5257 Å). The amplitude of the observed spectra follows the modulation transfer function of our optical system. In other words, the spectrum of real penumbral fluctuations seems to be flat up to the higher observable spatial frequency. We expect it to continue far beyond the artificial instrumental cutoff, which implies that the structure of the penumbra remains unresolved to the present solar observations. Title: Optically Thin Irregularities in the Penumbrae of Sunspots Authors: Sánchez Almeida, J. Bibcode: 1998ApJ...497..967S Altcode: Different estimates of the vertical gradient of magnetic field inclination in penumbrae disagree by 2 orders of magnitude. This disagreement may be resolved if measuring with typical angular resolutions implies averaging hundreds of independent fibrils whose residual variation, upon spatial averaging, gives rise to the observed large-scale structures. The small-scale gradients show up in estimates based on the broadband circular polarization, whereas significant bias affects other methods. From the comparison of these two types of measurements, one can infer the typical sizes of the penumbral irregularities. They turn out to be between 1 and 15 km wide, depending on details of the calculation. This result supports the kind of highly irregular atmosphere that Sánchez Almeida and coworkers proposed to represent the solar magnetic photosphere. Title: The Unresolved Structure of Photospheric Magnetic Fields: Truths, Troubles and Tricks (Invited review) Authors: Sánchez Almeida, J. Bibcode: 1998ASPC..155...54S Altcode: 1998sasp.conf...54S No abstract at ADS Title: Physical Properties of the Solar Magnetic Photosphere under the MISMA Hypothesis. I. Description of the Inversion Procedure Authors: Sánchez Almeida, J. Bibcode: 1997ApJ...491..993S Altcode: The paper describes an automatic inversion code to recover microstructured magnetic atmospheres (MISMAs) by fitting Stokes profiles. These solar model atmospheres incorporate small-scale fluctuations of the magnetic field vector, the velocity, the temperature, etc., which seems to be an intrinsic property of the magnetic photosphere. The model MISMAs considered for inversion have several distinct components. Each one of them is made of slender flux tubes, so that the whole vertical stratification of the MISMA is reconstructed from a finite set of parameters. The inversion code has been thoroughly tested using both synthetic and real observations. In particular, it successfully reproduces line profiles and model atmospheres corresponding to the quiet Sun and plage regions. As a by-product, we introduce a new error estimate for nonlinear least-squares minimizations. Title: Chromospheric polarity reversals on sunspots. Are they consistent with weak line emission? Authors: Sanchez Almeida, J. Bibcode: 1997A&A...324..763S Altcode: Photospheric and chromospheric solar magnetograms sometimes show opposite polarity. This intriguing phenomenon is associated with the emergence of magnetic flux and with nearby, but not necessarily superposed, flaring activity. Despite the fact that there may be different explanations, it is shown here that the observed reversals are consistent with weak flare-like line emission all over the reversed polarity regions. Although this emission does not show up as a flare in filtergrams, it exhibits itself as a polarity reversal of the chromospheric magnetograms. If this interpretation were correct, the reversal would not correspond to a real flip of the magnetic field direction from the photosphere to the chromosphere. It would be an artifact due to radiative transfer effects. Observations to support or discard this hypothesis are briefly pointed out. Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing Projects Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.; Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven, E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum, L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I. Bibcode: 1997ASPC..118..366S Altcode: 1997fasp.conf..366S The IAC is currently developing two similar polarimeters, one for optical wavelengths and one for near infra-red wavelengths (1.5 mu m). Both instruments will provide spectra of the four Stokes parameters over 2D solar regions. The visible spectro-polarimeter will be operated at the Swedish Tower (La Palma), and it is being developed in collaboration with the Royal Swedish Academy of Sciences. We intend to take advantage of the excellent seeing conditions at this telescope, while maintaining high polarimetric precision. The IR polarimeter is being designed for the German VTT (Tenerife) which has better angular resolution in the near infra-red. This report describes the goals and technical solutions. It also briefs on the current status of the projects. Title: Heights of formation for measurements of atmospheric parameters. Authors: Sanchez Almeida, J.; Ruiz Cobo, B.; del Toro Iniesta, J. C. Bibcode: 1996A&A...314..295S Altcode: We argue that heights of formation (HOFs) should not be assigned to spectral lines since a single line my sample very different layers of the atmosphere, depending on the physical parameter of interest and the technique employed to determine it. HOFs should be assigned to specific measurements. General expressions to compute these HOFs for measurements are derived. The equations are subsequently used to show, in representative solar measurements, the uncertainties produced by assigning HOFs to lines. Only weak lines can probe a single height of the atmosphere. Title: Line Asymmetries and the Microstructure of Photospheric Magnetic Fields Authors: Sanchez Almeida, J.; Landi Degl'Innocenti, E.; Martinez Pillet, V.; Lites, B. W. Bibcode: 1996ApJ...466..537S Altcode: A systematic structuring of magnetic fields over scales much smaller than the mean free path of photospheric photons may be responsible for the observed asymmetrical Stokes profiles. We explore this possibility by deriving the radiative transfer equation for microstructured magnetic atmospheres (the MISMA approximation). This equation is subsequently employed to show that very schematic MISMA scenarios for the penumbrae of sunspots, plage and network regions, and internetwork regions produce Stokes profiles that have the observed asymmetries. The details of these model atmospheres are of secondary importance, but the ease of generating the type of observed asymmetries with MISMAs is significant, so the existence of MISMAs deserves serious consideration. Should such microstructures exist, the techniques currently employed to infer properties of the solar photosphere need to be revised. MISMAs are also of concern for the physics of the photosphere itself. These two topics are briefly discussed. Title: Micro-structured magnetic atmospheres Authors: Sánchez Almeida, J.; Landi Degl'innogenti, E. Bibcode: 1996SoPh..164..203S Altcode: Asymmetrical Stokes profiles are produced if the photospheric magnetic and velocity fields are structured on scales smaller than the mean-free-path of the photons. Here we put forward a compact analytical expression for the radiative transfer equation in this case. Explicitly, micro-variations of the magnetic field strength and the velocity are considered. The existence of micro-structures might have serious implications on the techniques currently used to measure solar magnetic fields. For example, we show the failure of the relationship employed to calibrate magnetographs. Title: Two-dimensional, high spatial resolution, solar spectroscopy using a Correlation Tracker. II. Maps of spectral quantities. Authors: Collados, M.; Rodriguez Hidalgo, I.; Ballesteros, E.; Ruiz Cobo, B.; Sanchez Almeida, J.; del Toro Iniesta, J. C. Bibcode: 1996A&AS..115..367C Altcode: In this paper we illustrate some of the capabilities of the Correlation Tracker prototype developed at the Instituto de Astrofisica de Canarias used for two-dimensional, high spatial resolution, solar spectroscopy. Slit spectra have been taken, using the Correlation Tracker as a stabilizer (minimizing image motion during exposures) and as an accurate positioning device (allowing to precisely locate the entrance slit of the spectrograph at adjacent positions on the solar disc). Spectral information is obtained from several solar regions of different sizes. Granules (including some exploding ones) and intergranules are clearly resolved. Several sub-arcsecond structures are undoubtedly distinguished as well. The two-dimensional variation of several spectral quantities in the solar atmosphere is shown, demonstrating the power of this technique and its future possibilities. Title: Empirical granular/intergranular average model atmospheres. Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.; Collados, M.; Sánchez Almeida, J. Bibcode: 1996joso.proc..162R Altcode: No abstract at ADS Title: Empirical model of an average solar granule Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Rodriguez Hidalgo, I.; Collados, M.; Sanchez Almeida, J. Bibcode: 1996ASPC..109..155R Altcode: 1996csss....9..155R No abstract at ADS Title: A proposal for a low instrumental polarization coude telescope. II. The German Gregory-Coude Telescope at the Observatorio del Teide. Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Kneer, F. Bibcode: 1995A&AS..113..359S Altcode: We have put into practice the technique to minimize the instrumental polarization (IP) of coude telescopes proposed by Martinez Pillet & Sanchez Almeida (1991): a λ/2-plate inserted into the optical path, with the proper orientation, cancels the IP. The compensation of the Gregory-Coude Telescope at the Observatorio del Teide turns out to fulfil theoretical expectations. Empirical tests at 630nm demonstrate that its IP decreases by a factor ~4. We show that the residual IP is not intrinsic to the method but it is due to the limited precision of the retarder presently used. In addition, observations indicate that the insertion of the λ/2-plate does not noticeably deteriorate the optical quality of the whole telescope. In short, this work proves the practical soundness of the λ/2-plate technique to reduce IP. Title: Uncertainties in the determination of the Stokes parameters due to photon noise. Authors: Sanchez Almeida, J. Bibcode: 1995A&AS..109..417S Altcode: We derive inequalities which restrict the precision of the Stokes parameters imposed by photon noise. The signal-to-noise ratio of the measured Stokes parameters is never better than the square root of the number of detected photons. In case of weakly polarized sources (i.e., most astronomical sources), such an inequality imposes no practical limit and it should be replaced by the intensity-to-noise ratio, which approximately follows the same square root law. Besides these general results, we also find relationships between the errors of the Stokes parameters which apply to particular (although fairly common) analyzers. The equations are presented in a device-independent fashion, so that they can be used to tell, in an absolute sense, whether photon noise allows the measurement of small polarimetric signals. Title: Lithium at High Redshifts Authors: Sánchez Almeida, J.; Rebolo, R. Bibcode: 1995lea..conf...85S Altcode: No abstract at ADS Title: Li, Na, K and Hα in a Sunspot Authors: Barrado Y Navascués, D.; de Castro, E.; García López, R. J.; Sánchez Almeida, J.; Montesinos, B. Bibcode: 1995IAUS..176P.123B Altcode: No abstract at ADS Title: Instrumental polarization in the focal plane of telescopes. II. Effects induced by seeing. Authors: Sanchez Almeida, J. Bibcode: 1994A&A...292..713S Altcode: This work quantifies the influence of the terrestrial atmosphere on the instrumental polarization (IP) of telescopes. Our numerical simulations show that seeing mostly induces a random crosstalk between Stokes parameters. The main contamination affects the linear polarization signals and is due to mixing with intensity. In general, circular polarization signals are less corrupted by atmospheric effects. We have analyzed the IP considering the imaging mirrors and the entrance window of a particular instrument, namely the Large Earth-based Solar Telescope (LEST). Crosstalks up to 2x10^-2^ (window) and up to 2x10^-3^ (mirrors) occur in short-exposure images. This level of IP is largely reduced by increasing the exposure time or the pixel size. Means for extrapolating the IP of LEST to other instruments are provided. Using them, the dependence of the seeing-induced IP on wavelength, telescope size etc. is briefly examined. Title: The Inclination of Network Magnetic Fields Authors: Sanchez Almeida, J.; Martinez Pillet, V. Bibcode: 1994ApJ...424.1014S Altcode: We have observed the linear polarization of 21 bright grains of the photospheric network close to the disk center. The linear polarization of Fe I 6302.5 A was always lower than 1.9 x 10-3 (referred to continuum intensity). This level of linear polarization implies a very small magnetic field inclination with respect to the vertical, which we estimate below 10 deg. Our finding is in apparent disagreement with previous studies which claim large inclinations; however, it fulfills theoretical expectations. Plage regions close to sunspots might show inclination, but isolated network elements do not. Title: Spectral lines unaffected by instrumental polarization. II. Selected lines of astrophysical interest Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D. Bibcode: 1994A&AS..103..293V Altcode: Lines with no linear polarization induced by Zeeman effect are unaffected by instrumental polarization. We compile 86 such electric dipole lines with differing temperature and magnetic field sensitivities. In addition, we list 420 spectral lines which produce negligible linear polarization. In most cases, this second set can also be regarded as lines unaffected by instrumental polarization. Title: Instrumental polarization. Authors: Sánchez Almeida, J. Bibcode: 1994imfm.conf..106S Altcode: The techniques employed to overcome the instrumental polarization (IP) of solar observations are revised. Special attention is paid to the method used by the new generation of IP-free telescopes (LEST & THEMIS). The specific polarimetric errors of spectrographs and telescopes are discussed. Title: The inclination of magnetic fields in small-scale flux concentrations Authors: Sánchez Almeida, J.; Martínez Pillet, V. Bibcode: 1994smf..conf..316S Altcode: No abstract at ADS Title: Spectral lines insensitive to instrumental polarization Authors: Vela Villahoz, E.; Sánchez Almeida, J. Bibcode: 1994smf..conf..340V Altcode: No abstract at ADS Title: Instrumental polarization of telescopes: a laboratory test of the diffraction model Authors: Sánchez Almeida, J.; Martínez Pillet, V. Bibcode: 1994smf..conf..343S Altcode: No abstract at ADS Title: Spectral lines unaffected by instrumental polarization. 1: Theory Authors: Sanchez Almeida, J.; Vela Villahoz, E. Bibcode: 1993A&A...280..688S Altcode: We propose a new approach to minimize the instrumental polarization (IP) of current polarimetric observations. It is shown how the instrumental polarization can be deduced and removed, by using lines with no intrinsic linear polarization. Notably, no specific understanding of the polarizing properties of our optical setup is required. For the technique to be of practical application, lines unaffected by IP presenting various temperature, magnetic field, etc. sensitivities must be identified. We work out the atomic levels involved in electric dipole transitions which create no linear polarization, from the Zeeman effect. Title: VizieR Online Data Catalog: Lines unaffected by polarization (Vela Villahoz+ 1994) Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D. Bibcode: 1993yCat..41030293V Altcode: Not Available (2 data files). Title: Polarizing properties of grazing-incidence X-ray mirrors - Comment Authors: Sanchez Almeida, J.; Martinez Pillet, V. Bibcode: 1993ApOpt..32.4231S Altcode: We show that grazing-incidence telescopes, like those used for X-ray imaging, present negligible instrumental polarization. This property does not depend on the number of reflections the telescope employs to lead light from the entrance pupil to the focal plane. The result applies to the various mirrors of the advanced X-ray astrophysics facility satellite. In this particular case we have quantified the residual instrumental polarization to be between 10 exp -3 and 5 x 10 exp -5, depending on the size of the resolution elements. Title: A multiline method to determine stellar magnetic fields Authors: Ripodas, P.; Collados, M.; Sanchez Almeida, J.; Garcia Lopez, R. J. Bibcode: 1993ASPC...40..196R Altcode: 1993IAUCo.137..196R; 1993ist..proc..196R No abstract at ADS Title: Asymmetric Stokes Q, U and V Line Profiles Observed in Sunspots Authors: Sanchez Almeida, J.; Lites, B. W. Bibcode: 1993ASPC...46..177S Altcode: 1993mvfs.conf..177S; 1993IAUCo.141..177S No abstract at ADS Title: Atomic orientation in chromospheric lines. Authors: Trujillo Bueno, J.; Martínez Pillet, V.; Sánchez Almeida, J.; Landi Degl'Innocenti, E. Bibcode: 1993ASPC...46..526T Altcode: 1993ASPC...46..526B; 1993mvfs.conf..526T; 1993IAUCo.141..526T Observations of the Stokes I and V profiles of the Ca II H and K lines in solar magnetic regions are presented. Least-squares fits of dI/dλ to V are obtained and the wavelength variation of the residuals, i.e. V-kdI/dλ, calculated. The authors find significant symmetric residuals in umbrae, which are in agreement with the effect on the V profiles due to atomic orientation, i.e. with the existence of an unequal population of the Zeeman sublevels with M > 0 with respect to those with M < 0. Title: High Angular Resolution Stokes V Spectra in Penumbrae Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Lites, J. T. Buenol B. W. Bibcode: 1993ASPC...46..192S Altcode: 1993mvfs.conf..192S; 1993IAUCo.141..192S No abstract at ADS Title: Observation and Interpretation of the Asymmetric Stokes Q, U, and V Line Profiles in Sunspots Authors: Sanchez Almeida, J.; Lites, B. W. Bibcode: 1992ApJ...398..359S Altcode: We present a first approach to systematic characterization and interpretation of observed asymmetries of Stokes profiles as a function of spatial position within sunspots. Spatial maps of the full Stokes profiles of Fe I 6302.5 A gathered in large sunspots using the HAO Stokes II instrument reveal asymmetries that vary systematically across large sunspots observed during 1980. We use the inversion technique by Landolfi to extract the velocity gradients along the line of sight (LOS) which give rise to these asymmetries. The gradients derived from full Stokes profiles are in agreement with previous characterizations of the Evershed flow derived from Stokes I profiles alone (i.e., a flow increasing with depth in the atmosphere). By coupling this semiempirical gradient of velocity with a magnetic field inclination varying along the LOS, the synthesized profiles are able to mimic basic observed features of the broad-band circular polarization present in our data and observed previously by others. This characterization has magnetic field lines which become progressively more horizontal with depth in the penumbra. Title: Observations of the microwave background on a scale of 8 deg. I - The observing system Authors: Davies, R. D.; Watson, R. A.; Daintree, E. J.; Hopkins, J.; Lasenby, A. N.; Sanchez Almeida, J.; Beckman, J. E.; Rebolo, R. Bibcode: 1992MNRAS.258..605D Altcode: A sensitive observing system for observing the cosmic microwave background on an angular scale of 8 deg is described. This angular scale is appropriate for studies of intrinsic fluctuations in the CMB generated by gravitational potential fluctuations (the Sachs-Wolfe effect). The beam-switching system employs low-noise and broadband cryogenically cooled receivers. A major improvement in the stability of the system has resulted from triple-beam operation which removes the effect of atmospheric water vapour and ambient temperature changes to a level of several millikelvin on a single scan. The evaluation and assessment of this system operating at an elevation of 2400 m on Tenerife is described. Results for an RA circle at Dec. = 40 deg are shown; these reach a sensitivity of better than 100 micro-K in an 8.4 deg beam. Title: Instrumental polarization in the focal plane of telescopes Authors: Sanchez Almeida, J.; Martinez Pillet, V. Bibcode: 1992A&A...260..543S Altcode: We present a technique to model the instrumental polarization in the focal plane of a telescope. It takes into account that different rays of an incoming beam suffer different variation of the original polarization in their paths through the system. It also considers that the net effect depends on the way in which the different rays interfere with each other. We show that the Mueller matrix which describes this instrumental polarization greatly simplifies if the polarimetric measurements have poor spatial resolution. The Mueller matrices corresponding to a pair of academic cases are worked out: a diffraction limited telescope when the source lies on its axis and an axisymmetric mirror with the source off the axis. We discuss the consequences of these mathematical results on real telescopes (e.g. LEST). Finally, we briefly consider the seeing-induced instrumental polarization. Title: Radiative transfer for polarized light: Equivalence between Stokes parameters and coherency matrix formalisms Authors: Sanchez Almeida, J. Bibcode: 1992SoPh..137....1S Altcode: 1992SoPh..137....1A Two formal solutions of the radiative transfer equation for polarized light have been proposed. One uses the Stokes parameters to describe the polarization, while the other uses the coherency matrix. It is shown in the present work that they are equivalent. Both can be used to compute response and contribution functions for the Stokes parameters and both require the solution of systems of differential equations with similar numbers of independent variables. New equations to solve the radiative transfer problem using the Stokes parameters formalism are presented. In addition, a computer code which synthesizes the Stokes profiles by means of these equations is described. Title: A proposal for a low instrumental polarization coude telescope Authors: Martinez Pillet, V.; Sanchez Almeida, J. Bibcode: 1991A&A...252..861M Altcode: 1991A&A...252..861P A technique for obtaining an ideal two-mirror coude system with no instrumental polarization is described. A half-wave plate positioned between the two mirrors with the proper orientation produces the desired effect. The level of spurious polarization is limited by the characteristics of the retarder and the similarity of the mirrors. The telescope design and accuracy are discussed. Title: Spectrograph distortion in sunspot line profiles Authors: Pillet, V. Martínez; Almeida, J. Sánchez Bibcode: 1991SoPh..134..403P Altcode: We show empirically how the effect of the instrumental polarization of the spectrograph can distort the shape of the intensity profiles in sunspots. In order to avoid the problems an analysis of the polarization of the light should be performed at the entrance slit of the spectrograph. Title: Spectrograph distortion in sunspot line profiles Authors: Martinez Pillet, V.; Sanchez Almeida, J. Bibcode: 1991SoPh..134..403M Altcode: We show empirically how the effect of the instrumental polarization of the spectrograph can distort the shape of the intensity profiles in sunspots. In order to avoid the problems an analysis of the polarization of the light should be performed at the entrance slit of the spectrograph. Title: The instrumental polarization of a Gregory-Coudé telescope Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Wittmann, A. D. Bibcode: 1991SoPh..134....1A Altcode: We calculate a theoretical model of the polarization properties of a Gregory-Coudé telescope to predict the behaviour of the German Gregory-Coudé Telescope installed at the Observatorio del Teide (Spain). Measurements of the real effects produced by this telescope acting upon light of known polarization are compared with the model. We estimate an uncertainty in its predictions of about 10%, which is produced by the uncertainties of the (complex) refractive index of the metallic layers covering the mirrors. The paper concludes by briefly considering the way in which the plain telescope changes the Stokes' profiles. Title: Performance of the IAC Stokes I and V analyzer. Authors: Sánchez Almeida, J.; Martínez Pillet, V. Bibcode: 1991sopo.work..191S Altcode: The chromatic behaviour of the IAC analyzer, commonly used at the German Vacuum Gregory-Coude telesope at the Spanish Observatorio del Teide (Canary Islands), is investigated. It is shown that, through careful alignment of the optical components, a nearly perfect circular analysis can be obtained at wavelengths of 4000 Å and 6000 Å. For other visible regions the crosstalk between linear and circular polarization can be always made lower than 10%. Title: Magnetic Flux Determination in Late-Type Dwarfs Authors: Rípodas, P.; Sánchez Almeida, J.; García López, R. J.; Collados, M. Bibcode: 1991LNP...380..417R Altcode: 1991IAUCo.130..417R; 1991sacs.coll..417R We present a very preliminary and simplified analysis designed to measure photospheric magnetic fields in late-type stars, using the FeI 5247.06 Å and 5250.22 Å lines. We show how the use of the equivalent widths of the lines and differences in their depth can give a rapid estimation of the magnetic flux. Title: A New Technique to Measure Magnetic Field Strength in Active Stars Authors: Sánchez Almeida, J.; García López, R. J. Bibcode: 1991LNP...380..414S Altcode: 1991IAUCo.130..414S; 1991sacs.coll..414S We explore the use of the flux difference between the lines Fe 15250 Å and Fe 15247 Å as a technique to measure photospheric magnetic fields in late-type stars. The technique developed takes into account all the LTE physics of the problem, assuming a radial and homogeneous magnetic field distribution over the stellar surface. Some test calculations, in order to prove the feasibility of the method, are shown. Title: Numerical Test of a New V-Profile Inversion Technique Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J. Bibcode: 1990Ap&SS.170..113R Altcode: The diagnostic method proposed by Landi Degl'Innocenti and Landolfi (1982), based on the observation of circular polarization, has been generalized to derive the thermodynamic properties of unresolved magnetic elements in the solar atmosphere. The final aim is to derive the height dependence of several parameters of the flux tube atmosphere (such as temperature, magnetic field and velocity distributions, macroturbulence and filling factor). We have used a perturbation method based on the concept of response functions for the Stokes profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti (1977). We present here the preliminary results of invertingV-profiles by an iterative standard least-squares technique, which allows to find the magnetic 1-D atmosphere consistent with simulated data. Title: Facular points and small-scale magnetic elements Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Martinez Pillet, V.; Ruiz Cobo, B. Bibcode: 1990Ap&SS.170....9D Altcode: We present spectroscopic observations, with high spatial resolution, of Ca ii K bright points very near the disc centre. Magnetic concentrations have been detected in these network (facular) points by only using intensity profiles of the well-known pair of lines Fe i5250.22 Å and 5247.06 Å. No brightening of these structures with respect to the quiet photosphere can be ascertained within an accuracy threshold of 1.2%. Title: Velocity Fields Associated with the Magnetic Component of Solar Faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1990Ap&SS.170...31S Altcode: The StokesV asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the StokesV profile around its zero-crossing point. We find that the empirical curves of growth for theV zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeidaet al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations. The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae. Title: Are small-scale magnetic concentrations spatially coincident with bright facular points? Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Martinez Pillet, V.; Ruiz Cobo, B. Bibcode: 1990A&A...233..570D Altcode: The usually assumed identification of small-scale magnetic concentrations with bright facular or network points on the photosphere is observationally checked by using high spatial resolution spectra of Ca II K bright points very near the disk center. The detection of spatially unresolved magnetic structures is made via a new differential analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22 A; these concentrations are present in the central part of a line weakening zone, which is of some 2 arcsec wide. No continuum intensity enhancement with respect to the quiet photosphere can be ascertained of these structures, within an accuracy threshold of 1.2 percent. In spite of this, magnetic concentrations brighter than the quiet photosphere are compatible with the observations, but if so, they must be narrower than 0.2 arcsec. Title: Spectropolarimetry of solar faculae - High spatial resolution results Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Semel, M. Bibcode: 1990A&A...227..591D Altcode: A new method to measure the magnetic field strength of small-scale solar magnetic concentrations is presented. It is based on the center of gravity method (Semel, 1967), is independent of radiative transfer calculations and only observable parameters are needed. This method also provides parameters like filling factor (area fraction occupied by the tubes), continuum intensity contrast between flux tubes and their surroundings, in a two-component model scheme. The method is applied to spectropolarimetric high spatial resolution data. Local variations of the above parameters inside single faculae are found. This result suggests some indications about flux tube evolution. A comparison with low spatial resolution results is also made. Title: On the generation of the net circular polarization observed in solar faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1989A&A...222..311S Altcode: The net circular polarization observed in solar faculae (Stenflo et al., 1984) follows a law expected from the combination of velocity and magnetic field gradients in the photosphere. To show this, the theoretical curve of growth (net circular polarization produced by a single line versus its absorption coefficient) predicted by this mechanism is developed. An empirical curve of growth with more than 80 Fe I lines is also constructed. The agreement between theory and observation seems to point toward this mechanism as responsible for circular polarization in faculae at the disk center. Title: Les facules solaires ou comment observer l'invisible. Authors: Sanchez Almeida, J.; Collados, M.; Del Toro Iniesta, J. C. Bibcode: 1989Rech...20..810S Altcode: 1989Rech...20..810A No abstract at ADS Title: An explanation for the Stokes V asymmetry in solar faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1988A&A...201L..37S Altcode: The asymmetry in the Stokes V profile observed in solar faculae can be explained by assuming that the magnetic field increases with height while downflow speed decreases. The MHD compatibility of such solution is briefly discussed together with an observational test for that possibility. Title: Magnetic field strength in solar flux tubes - A model atmosphere independent determination Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.; Solanki, S. K. Bibcode: 1988A&A...196..266S Altcode: The "line ratio method" (Stenflo, 1973) has been extensively used in the past to carry out measurements of the magnetic field strength in spatially unresolved magnetic flux concentrations. The authors present here a new variant of this technique, which is particularly simple as it does not depend on any radiative transfer calculations and thus the assumption of a model atmosphere is not required. General properties of the transfer equation lead to a relationship between the circular polarization generated by two lines which are identical except for their Landé factors. This can be used to directly determine the field strength from the measured line profiles. In order to test the method the authors have applied it to experimental data. A comparison with the traditional line ratio method is shown. Title: Estudio de la componente magnética de fáculas y red fotosférica Title: Estudio de la componente magnética de fáculas y red fotosférica Title: Study of the magnetic component of faculae and the photospheric network; Authors: Sánchez Almeida, Jorge Bibcode: 1988PhDT.......280S Altcode: No abstract at ADS Title: Sensitive measurement of fluctuations in the cosmic microwave background Authors: Davies, R. D.; Lasenby, A. N.; Watson, R. A.; Daintree, E. J.; Hopkins, J.; Beckman, J.; Sanchez Almeida, J.; Rebolo, R. Bibcode: 1987Natur.326..462D Altcode: Extensive high sensitivity observations of the cosmic microwave background have been made on an angular scale of 8° covering a substantial fraction of the northern sky. An observed anisotropy in the sky emission at a level of δT/T = 3.7×l0-5 has been detected (T is temperature). This level should strictly be interpreted as an upper limit to the cosmic microwave background fluctuations. It is possibly the direct imprint of density perturbations in the early Universe. Title: Continuum intensity and magnetic flux of solar fluxtubes. Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.; Sánchez Almeida, J. Bibcode: 1987PAICz..66..265D Altcode: 1987eram....1..265D The continuum contrast between fluxtubes and their quiet background, and the magnetic flux carried by these magnetic elements, have been determined at different points of a solar facula, in the frame of a two-component model from spectropolarimetric observations of 1arcsec spatial resolution. Local spatial variations of these two parameters have been obtained. Title: Isotopic neon cross sections for a study of neutron balance and temperature during s-process nucleosynthesis Authors: Almeida, J.; Kaeppeler, F. Bibcode: 1983ApJ...265..417A Altcode: The neutron source of the s-process is believed to be the 22Ne(α, n) reaction, taking place in the He-burning shell of a pulsating red giant. Such a periodic neutron irradiation leads to an exponential distribution of neutron fluences for the seed nuclei, which can be deduced from the observed solar system abundances. Using this empirically determined distribution of neutron fluences and the abundances and the experimental cross sections of the elements present in the He shell, the number of neutrons captured by each nuclear species during the s-process has been calculated. The authors have measured the capture cross sections of the three stable neon isotopes in the energy range 5-400 keV; the total cross sections were also measured, between 5 and 800 keV. It is concluded that the traditional s-process treatment of the neutron balance yields strong evidence in favor of the 22Ne(α,n) reaction as the effective neutron source to build most s-process abundances. Title: Neutron capture cross sections of 20,21,22Ne between 5 and 400 keV and the neutron balance in s-process nucleosynthesis. Authors: Almeida, J.; Kappeler, F. Bibcode: 1983ndst.conf..948A Altcode: No abstract at ADS