Pascual Ramírez, Sergio

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First Name
Last Name
Pascual Ramírez
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Física de la Tierra y Astrofísica
Astronomía y Astrofísica
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Now showing 1 - 10 of 45
  • Publication
    Results of the verification of the NIR MOS EMIR
    (SPIE, the international society for optics and photonics, 2014) Garzón, F.; Castro Rodríguez, N.; Insausti, M.; López Martín, L.; Hammersley, Peter; Barreto, M.; Fernández Sánchez, Paloma; Joven, E.; López, P.; Mato, A.; Moreno, H.; Nuñez, M.; Patrón, J.; Rasilla, J. L.; Redondo, P.; Rosich, J.; Pascual Ramírez, Sergio; Grange, R.
    EMIR is one of the first common user instruments for the GTC, the 10 meter telescope operating at the Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain). EMIR is being built by a Consortium of Spanish and French institutes led by the Instituto de Astrofisica de Canarias (IAC). EMIR is primarily designed to be operated as a MOS in the K band, but offers a wide range of observing modes, including imaging and spectroscopy, both long slit and multiobject, in the wavelength range 0.9 to 2.5 μm. This contribution reports on the results achieved so far during the verification phase at the IAC prior to its shipment to the GTC for being commissioned, which is due by mid 2015. After a long period of design and fabrication, EMIR finally entered into its integration phase by mid 2013. Soon after this, the verification phase at the IAC was initiated aimed at configuring and tuning the EMIR functions, mostly the instrument control system, which includes a sophisticated on line data reduction pipeline, and demonstrating the fulfillment of the top level requirements. We have designed an ambitious verification plan structured along the three kind of detectors at hand: the MUX and the engineering and scientific grade arrays. The EMIR subsystems are being integrated as they are needed for the purposes of the verification plan. In the first stage, using the MUX, the full optical system, but with a single dispersive element out of the three which form the EMIR suite, the two large wheels mounting the filters and the pseudo-grisms, plus the detector translation unit holding the MUX, were mounted. This stage was mainly devoted to learn about the capabilities of the instrument, define different settings for its basic operation modes and test the accuracy, repeatability and reliability of the mechanisms. In the second stage, using the engineering Hawaii2 FPA, the full set of pseudo-grisms and band filters are mounted, which means that the instrument is fully assembled except for the cold slit unit, a robotic reconfigurable multislit mask system capable of forming multislit pattern of 55 different slitlets in the EMIR focal plane. This paper will briefly describe the principal units and features of the EMIR instrument as the main results of the verification performed so far are discussed. The development and fabrication of EMIR is funded by GRANTECAN and the Plan Nacional de Astronomia y Astrofisica (National Plan for Astronomy and Astrophysics, Spain).
  • Publication
    Stars and brown dwarfs in the σ Orionis cluster (Research Note) III. OSIRIS/GTC low-resolution spectroscopy of variable sources
    (EDP Sciencies, 2012-10) Caballero, J. A.; Cabrera Lavers, A.; García Álvarez, D; Pascual Ramírez, Sergio
    Context. Although many studies have been performed so far, there are still dozens of low-mass stars and brown dwarfs in the young σ Orionis open cluster without detailed spectroscopic characterisation. Aims. We look for unknown strong accretors and disc hosts that were undetected in previous surveys. Methods. We collected low-resolution spectroscopy (R ~ 700) of ten low-mass stars and brown dwarfs in σ Orionis with OSIRIS at the Gran Telescopio Canarias under very poor weather conditions. These objects display variability in the optical, infrared, Hα, and/or X-rays on time scales of hours to years. We complemented our spectra with optical and near-/mid-infrared photometry. Results. For seven targets, we detected lithium in absorption, identified Hα, the calcium doublet, and forbidden lines in emission, and/or determined spectral types for the first time. We characterise in detail a faint, T Tauri-like brown dwarf with an 18 h-period variability in the optical and a large Hα equivalent width of –125  ±  15 Å, as well as two M1-type, X-ray-flaring, low-mass stars, one with a warm disc and forbidden emission lines, the other with a previously unknown cold disc with a large inner hole. Conclusions. New unrevealed strong accretors and disc hosts, even below the substellar limit, await discovery among the list of known σ Orionis stars and brown dwarfs that are variable in the optical and have no detailed spectroscopic characterisation yet.
  • Publication
    Robust isoclinic calculation for automatic analysis of photoelastic fringe patterns
    (SPIE--The International Society for Optical Engineering, 2008) Quiroga Mellado, Juan Antonio; Pascual Ramírez, Sergio; Villa Hernández, José de Jesús
    There are two main steps in the analysis of photoelastic fringe patterns: the isoclinics and isochromatics computation. For the isochromatic computation there exist several possibilities but one of the best, from the point of view of reliability and automatization, is the phase shift technique. However all phase shift isochromatic algorithms need a good estimation of the isoclinic direction angle that is a challenging task in presence of low birrefringence, isotropic points and monochromatic illumination. In this work we discuss the application of a novel isoclinic direction calculation method based in a phase shifting technique and a fast direction estimation regularized filter. Experimental results show that the proposed method together with a standard phase shifting isochromatic estimation is a good option for the automatic analysis of photoelastic fringe patterns under different illumination conditions, load levels and sample complexity, making possible further processing steps as full-field stress separation.
  • Publication
    Making observations with GTC/MEGARA easier: the MEGARA observing preparation software suite
    (Universidad Nacional Autónoma Mexico, Inst. de Astronomía, 2013) Eliche Moral, María del Carmen; Pascual Ramírez, Sergio; Gruel, N.; Castillo Morales, África; Carrasco, E.; Gallego Maestro, Jesús; García Vargas, M. L.; Gil de Paz, Armando; Marino, Raffaella Anna; Morales, I.; Pérez Calpena, A.; Sánchez, F. M.; Vílchez, J. M.; Villar, V.; Zamorano Calvo, Jaime
    MEGARA (Multi-Espectrografo en GTC de Alta Resolucion para Astronomia) is an optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) designed for the GTC 10.4 m telescope in La Palma. Its relatively complex layout makes necessary a set of tools to facilitate the observation preparation to the user. The MEGARA Observing Preparation Software Suite (MOPSS) consists on three software components designed to assist observers to optimally plan their observations with GTC/MEGARA: the Exposure Time Calculator, the Image Simulator, and the Fiber MOS Positioning tool. We describe these software tools and the status of their prototypes up to the date.
  • Publication
    Data reduction pipeline for emir, the near-IR multi-object spectrograph for GTC
    (Universidad Nacional Autónoma México, Instituto Astronomía, 2007) Pascual Ramírez, Sergio; Gallego Maestro, Jesús; Cardiel López, Nicolás
    EMIR (Balcells et al. 2000) is a near-infrared wide-field camera and multi-object spectrograph being built for the GTC. The Data Reduction Pipeline (DRP) will be optimized for handling and reducing near-infrared data acquired with EMIR.
  • Publication
    MEGARA-IFU detection of extended He II λ4686 nebular emission in the central region of NGC1569 and its ionization budget
    (Oxford Univ. Press, 2020-10) Gil de Paz, Armando; Gallego Maestro, Jesús; Castillo Morales, África; Pascual Ramírez, Sergio
    We here report the detection of extended He ii λ4686 nebular emission in the central region of NGC 1569 using the integral field spectrograph MEGARA at the 10.4-m Gran Telescopio Canarias. The observations cover a Field of View (FoV) of 12.5 arcsec×11.3 arcsec at seeing-limited spatial resolution of ∼15 pc and at a spectral resolution of R=6000 in the wavelength range 4330–5200 Å. The emission extends over a semi-circular arc of ∼40 pc width and ∼150 pc diameter around the super star cluster A (SSC-A). The A_(V) derived using Balmer decrement varies from the Galactic value of 1.6 mag to a maximum of ∼4.5 mag, with a mean value of 2.65±0.60 mag. We infer 124±11 Wolf-Rayet (WR) stars in SSC-A using the He ii λ4686 broad feature and A_(V)=2.3 mag. The He+ ionizing photon rate from these WR stars is sufficient to explain the luminosity of the He ii nebula. The observationally-determined total He+ and H0 ionizing photon rates, their ratio, and the observed number of WR stars in SSC-A are all consistent with the predictions of simple stellar population models at an age of 4.0±0.5 Myr, and mass of (5.5±0.5)×105 Mꙩ.Our observations reinforce the absence of WR stars in SSC-B, the second most massive cluster in the FoV. None of the other locations in our FoV where He ii λ4686 emission has been reported from narrow-band imaging observations contain WR stars.
  • Publication
    Evolution of the energy consumed by street lighting in Spain estimated with DMSP-OLS data
    (Pergamon-Elsevier Science Ltd., 2014-05) Sánchez de Miguel, Alejandro; Zamorano Calvo, Jaime; Gómez Castaño, José; Pascual Ramírez, Sergio
    We present the results of the analysis of satellite imagery to study light pollution in Spain. Both calibrated and non-calibrated DMSP-OLS images were used. We describe the method to scale the non-calibrated DMSP-OLS images which allows us to use differential photometry techniques in order to study the evolution of the light pollution. Population data and DMSP-OLS satellite calibrated images for the year 2006 were compared to test the reliability of official statistics in public lighting consumption. We found a relationship between the population and the energy consumption which is valid for several regions. Finally the true evolution of the electricity consumption for street lighting in Spain from 1992 to 2010 was derived; it has been doubled in the last 18 years in most of the provinces. (C) 2013 Elsevier Ltd. All rights reserved,
  • Publication
    MEGARA-GTC stellar spectral library: I
    (Oxford University Press., 2020-03) García Vargas, M. L.; Carrasco, E.; Mollá, M.; Gil de Paz, Armando; Berlanas, S.R.; Cardiel López, Nicolás; Gómez Álvarez, P.; Gallego Maestro, Jesús; Iglesias Páramo, J.; Cedazo, R.; Pascual Ramírez, Sergio; Castillo Morales, África; Pérez Calpena, A.; Martínez Delgado, I.
    MEGARA (Multi Espectrografo en GTC de Alta Resolucion para Astronomia) is an optical (3650-9750 Å), fibre-fed, medium-high spectral resolution (R = 6000, 12 000 and 20 000) instrument for the Gran Telescopio CANARIAS (GTC) 10.4-m telescope, commissioned in the summer of 2017, and currently in operation. The scientific exploitation of MEGARA requires a stellar spectra library to interpret galaxy data and to estimate the contribution of the stellar populations. In this paper, we introduce the MEGARA-GTC spectral library, detailing the rationale behind the building of this catalogue. We present the spectra of 97 stars (21 individual stars and 56 members of the globular cluster M15, which are both subsamples taken during the commissioning runs, and 20 stars from our ongoing GTC Open-Time programme). The spectra have R = 20 000 in the HR-R and HR-I set-ups, centred at 6563 and 8633 Å, respectively. We describe the procedures to reduce and analyse the data. Then, we determine the best-fitting theoretical models to each spectrum through a χ^(2) minimization technique, to derive the stellar physical parameters, and we discuss the results. We have also measured some absorption lines and indices. Finally, we introduce our project to complete the library and the data base in order to make the spectra available to the community.
  • Publication
    First scientific observations with MEGARA at GTC
    (Spie-Int Soc Optical Engineering, 2018) Gil de Paz, Armando; Gallego Maestro, Jesús; Bouquin, A.; Carbajo, J.; Cardiel López, Nicolás; Castillo Morales, África; Esteban San Román, Segundo; López Orozco, José Antonioi; Pascual Ramírez, Sergio; Picazo, P.; Sánchez Penim, Ainhoa; Zamorano Calvo, Jaime; Catalán Torrecilla, Cristina; Dullo, Bililign; Pérez González, P.G.
    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 & 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, intermediate resolution IFU & 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.
  • Publication
    Near-IR narrow-band imaging with CIRCE at the Gran Telescopio Canarias: Searching for Ly alpha-emitters at z similar to 9.3
    (EDP Sciencies, 2022-03-16) Cabello González, Cristina; Gallego Maestro, Jesús; Cardiel López, Nicolás; Pascual Ramírez, Sergio; Guzmán, R.; Herrero, A.; Manrique, A.; Marín Franch, A.; Mas Hesse, J. M.; Rodriguez Espinosa, J. M.; Salvador Solé, E.
    Context. Identifying very high-redshift galaxies is crucial for understanding the formation and evolution of galaxies. However, many questions still remain, and the uncertainty on the epoch of reionization is large. In this approach, some models allow a double-reionization scenario, although the number of confirmed detections at very high z is still too low to serve as observational proof. Aims. The main goal of this project is studying whether we can search for Lyman-alpha emitters (LAEs) at z similar to 9 using a narrow-band (NB) filter that was specifically designed by our team and was built for this experiment. Methods. We used the NB technique to select candidates by measuring the flux excess due to the Ly alpha emission. The observations were taken with an NB filter (full width at half minimum of 11 nm and central wavelength lambda(c)1.257 mu m) and the CIRCE near-infrared camera for the Gran Telescopio Canarias. We describe a data reduction procedure that was especially optimized to minimize instrumental effects. With a total exposure time of 18.3 h, the final NB image covers an area of similar to 6.7 arcmin(2), which corresponds to a comoving volume of 1.1 x 10(3) Mpc(3) at =9.3. Results. We pushed the source detection to its limit, which allows us to analyze an initial sample of 97 objects. We detail the different criteria we applied to select the candidates. The criteria included visual verifications in different photometric bands. None of the objects resembled a reliable LAE, however, and we found no robust candidate down to an emission-line flux of 2.9 x 10(-16) erg s(-1) cm(-2), which corresponds to a Ly alpha luminosity limit of 3 x 10(44) erg s(-1). We derive an upper limit on the Ly alpha luminosity function at similar to 9 that agrees well with previous constraints. We conclude that deeper and wider surveys are needed to study the LAE population at the cosmic dawn.