arXiv subjects

D. R. Gonçalves

Publications and source records attributed to D. R. Gonçalves.

26 records · Page 2Linked to original sources

arXiv2018

J-PLUS: measuring ${\rm H}α$ emission line fluxes in the nearby universe

In the present paper we aim to validate a methodology designed to extract the Halpha emission line flux from J-PLUS photometric data. J-PLUS is a multi narrow-band filter survey carried out with the 2 deg2 field of view T80Cam camera, mounted on the JAST/T80 telescope in the OAJ, Teruel, Spain. The information of the twelve J-PLUS bands, including the J0660 narrow-band filter located at rest-frame Halpha, is used over 42 deg2 to extract de-reddened and [NII] decontaminated Halpha emission line fluxes of 46 star-forming regions with previous SDSS and/or CALIFA spectroscopic information. The agreement of the inferred J-PLUS photometric Halpha fluxes and those obtained with spectroscopic data is remarkable, with a median comparison ratio R = 1.05 +- 0.25. This demonstrates that it is possible to retrieve reliable Halpha emission line fluxes from J-PLUS photometric data. With an expected area of thousands of square degrees upon completion, the J-PLUS dataset will allow the study of several star formation science cases in the nearby universe, as the spatially resolved star formation rate of nearby galaxies at z < 0.015, and how it is influenced by the environment, morphology or nuclear activity. As an illustrative example, the close pair of interacting galaxies NGC3994 and NGC3995 is analyzed, finding an enhancement of the star formation rate not only in the center, but also in outer parts of the disk of NGC3994.

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arXiv2018

J-PLUS: The Javalambre Photometric Local Universe Survey

J-PLUS is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern hemisphere from the dedicated JAST/T80 telescope at the Observatorio Astrofísico de Javalambre. T80Cam is a 2 sq.deg field-of-view camera mounted on this 83cm-diameter telescope, and is equipped with a unique system of filters spanning the entire optical range. This filter system is a combination of broad, medium and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700-4000Å Balmer break region, H$δ$, Ca H+K, the G-band, the Mgb and Ca triplets) that are key to both characterize stellar types and to deliver a low-resolution photo-spectrum for each pixel of the sky observed. With a typical depth of AB $\sim 21.25$ mag per band, this filter set thus allows for an indiscriminate and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2D photo-spectral information for all resolved galaxies in the local universe, as well as accurate photo-z estimates ($Δ\,z\sim 0.01-0.03$) for moderately bright (up to $r\sim 20$ mag) extragalactic sources. While some narrow band filters are designed for the study of particular emission features ([OII]/$λ$3727, H$α$/$λ$6563) up to $z < 0.015$, they also provide well-defined windows for the analysis of other emission lines at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby universe (Milky Way, 2D IFU-like studies, stellar populations of nearby and moderate redshift galaxies, clusters of galaxies) and at high redshifts (ELGs at $z\approx 0.77, 2.2$ and $4.4$, QSOs, etc). With this paper, we release $\sim 36$ sq.deg of J-PLUS data, containing about $1.5\times 10^5$ stars and $10^5$ galaxies at $r<21$ mag.

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arXiv2017

Observations of the first electromagnetic counterpart to a gravitational wave source by the TOROS collaboration

We present the results of prompt optical follow-up of the electromagnetic counterpart of the gravitational-wave event GW170817 by the Transient Optical Robotic Observatory of the South Collaboration (TOROS). We detected highly significant dimming in the light curves of the counterpart (Delta g=0.17+-0.03 mag, Delta r=0.14+-0.02 mag, Delta i=0.10 +- 0.03 mag) over the course of only 80 minutes of observations obtained ~35 hr after the trigger with the T80-South telescope. A second epoch of observations, obtained ~59 hr after the event with the EABA 1.5m telescope, confirms the fast fading nature of the transient. The observed colors of the counterpart suggest that this event was a "blue kilonova" relatively free of lanthanides.

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arXiv2016

Deciphering the bipolar planetary nebula Abell 14 with 3D ionization and morphological studies

Abell 14 is a poorly studied object despite being considered a born again planetary nebula. We performed a detailed study of its 3D morphology and ionization structure using the SHAPE and MOCASSIN codes. We found that Abell 14 is a highly evolved, bipolar nebula with a kinematical age of $\sim$19,400 yr for a distance of 4 kpc. The high He abundance, and N/O ratio indicate a progenitor of 5 $M_{\odot}$ that has experienced the third dredge-up and hot bottom burning phases. The stellar parameters of the central source reveal a star at a highly evolved stage near to the white dwarf cooling track, being inconsistent with the born again scenario. The nebula shows unexpectedly strong [N I] $λ5200$ and [O I] $λ6300$ emission lines indicating possible shock interactions. Abell 14 appears to be a member of a small group of highly evolved, extreme Type-I PNe. The members of this group lie at the lower-left corner of the PNe regime on the [N II]/H$α$ vs. [S II]/H$α$ diagnostic diagram, where shock--excited regions/objects are also placed. The low luminosity of their central stars, in conjunction with the large physical size of the nebulae, result in a very low photo-ionization rate, which can make any contribution of shock interaction easily perceptible, even for small velocities.

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arXiv2015

Evidence for a [WR] or WEL-type binary nucleus in the bipolar planetary nebula Vy 1-2

We present high-dispersion spectroscopic data of the compact planetary nebula Vy 1-2, where high expansion velocities up to 100 km/s are found in the Ha, [N II] and [O III] emission lines. HST images reveal a bipolar structure. Vy 1-2 displays a bright ring-like structure with a size of 2.4"x3.2" and two faint bipolar lobes in the west-east direction. A faint pair of knots is also found, located almost symmetrically on opposite sides of the nebula at PA=305 degrees. Furthermore, deep low-dispersion spectra are also presented and several emission lines are detected for the first time in this nebula, such as the doublet [Cl III] 5517, 5537 A, [K IV] 6101 A, C II 6461 A, the doublet C IV 5801, 5812 A. By comparison with the solar abundances, we find enhanced N, depleted C and solar O. The central star must have experienced the hot bottom burning (CN-cycle) during the 2nd dredge-up phase, implying a progenitor star of higher than 3 solar masses. The very low C/O and N/O abundance ratios suggest a likely post-common envelope close binary system. A simple spherically symmetric geometry with either a blackbody or a H-deficient stellar atmosphere model is not able to reproduce the ionisation structure of Vy 1-2. The effective temperature and luminosity of its central star indicate a young nebula located at a distance of ~9.7 kpc with an age of ~3500 years. The detection of stellar emission lines, C II 6461 A, the doublet C IV λλ 5801, 5812 A and O III 5592 A, emitted from a H-deficient star, indicates the presence of a late-type Wolf-Rayet or a WEL type central star.

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arXiv2014

Planetary nebulae: the universal mass-metallicity relation for Local Group dwarf galaxies and the chemistry of NGC 205

Here we study 16 planetary nebulae (PNe) in the dwarf irregular galaxy NGC 205 by using GMOS@Gemini spectra to derive their physical and chemical parameters. The chemical patterns and evolutionary tracks for 14 of our PNe suggest that there are no type I PNe among them. These PNe have an average oxygen abundance of 12+log(O/H)=8.08$\pm$0.28, progenitor masses of 2-2.5M$_{\odot}$ and thus were born ~1.0-1.7Gyr ago. Our results are in good agreement with previous PN studies in NGC 205. The present 12+log(O/H) is combined with our previous works and with the literature to study the PN metallicity trends of the Local Group (LG) dwarf galaxies, in an effort to establish the PN luminosity- and mass-metallicity relations (LZR and MZR) for the LG dwarf irregulars (dIrrs) and dwarf spheroidals (dSphs). Previous attempts to obtain such relations failed to provide correct conclusions because were based on limited samples (Richer & McCall 1995; Gonçcalves et al. 2007). As far as we are able to compare stellar with nebular metallicities, our MZR is in very good agreement with the slope of the MZR recently obtained for LG dwarf galaxies using spectroscopic stellar metallicities (Kirby et al. 2013). Actually, we found that both dIrr and dSph galaxies follow the same MZR, at variance with the differences claimed in the past. Moreover our MZR is also consistent with the global MZR of star-forming galaxies, which span a wider stellar mass range ($\sim10^6$ - $\sim10^{11}$M$\odot$).

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arXiv2013

Spatially resolved physical and chemical properties of the planetary nebula NGC 3242

Optical integral-field spectroscopy was used to investigate the planetary nebula NGC 3242. We analysed the main morphological components of this source, including its knots, but not the halo. In addition to revealing the properties ofthe physical and chemical nature of this nebula, we also provided reliable spatially resolved constraints that can be used for future photoionisation modelling of the nebula. The latter is ultimately necessary to obtain a fully self-consistent 3D picture of the physical and chemical properties of the object. The observations were obtained with the VIMOS instrument attached to VLT-UT3. Maps and values for specific morphological zones for the detected emission-lines were obtained and analysed with routines developed by the authors to derive physical and chemical conditions of the ionised gas in a 2D fashion. We obtained spatially resolved maps and mean values of the electron densities, temperatures, and chemical abundances, for specific morphological structures in NGC 3242. These results show the pixel-to-pixel variations of the the small- and large-scale structures of the source. These diagnostic maps provide information free from the biases introduced by traditional single long-slit observations. In general, our results are consistent with a uniform abundance distribution for the object, whether we look at abundance maps or integrated fluxes from specified morphological structures. The results indicate that special care should be taken with the calibration of the data and that only data with extremely good signal-to-noise ratio and spectral coverage should be used to ensure the detection of possible spatial variations.

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arXiv2010

Physico-chemical spectroscopic mapping of the planetary nebula NGC 40 and the 2D_NEB, a new 2D algorithm to study ionised nebulae

In this paper we present an analysis of the physical and chemical conditions of the planetary nebula NGC 40 through spatially-resolved spectroscopic maps. We also introduce a new algorithm --2D_NEB-- based on the well-established IRAF nebular package, which was developed to enable the use of the spectroscopic maps to easily estimate the astrophysical quantities of ionised nebulae. The 2D_NEB was benchmarked, and we clearly show that it works properly, since it compares nicely with the IRAF nebular software. Using this software, we derive the maps of several physical parameters of NGC 40. From these maps, we conclude that Te[NII] shows only a slight temperature variation from region to region, with its values constrained between ~8,000 K and ~9,500 K. Electron densities, on the other hand, have a much more prominent spatial variation, as Ne[SII] values vary from ~1,000 cm^(-3) to ~3,000 cm^(-3). Maps of the chemical abundances also show significant variations. From the big picture of our work, we strongly suggest that analysis with spatial resolution be mandatory for more complete study of the physical and chemical properties of planetary nebulae.

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