N. Flores-Fajardo

Publications (5)4.9 Total impact

• Article: Chemical abundances in Orion protoplanetary discs: integral field spectroscopy and photoevaporation models of HST 10

  Y. G. Tsamis, N. Flores-Fajardo, W. J. Henney, J. R. Walsh, A. Mesa-Delgado
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  ABSTRACT: Photoevaporating protoplanetary discs (proplyds) in the vicinity of hot massive stars, such as those found in Orion, are important objects of study for the fields of star formation, early disc evolution, planetary formation, and H II region astrophysics. Their element abundances are largely unknown, unlike those of the main-sequence stars or the host Orion nebula. We present a spectroscopic analysis of the Orion proplyd HST 10, based on integral field observations with the Very Large Telescope/FLAMES fibre array with 0.31" x 0.31" spatial pixels. The proplyd and its vicinity are imaged in a variety of emission lines across a 6.8" x 4.3" area. The reddening, electron density and temperature are mapped out from various line diagnostics. The abundances of helium, and eight heavy elements are measured relative to hydrogen using the direct method based on the [O III] electron temperature. The abundance ratios of O/H and S/H are derived without resort to ionization correction factors. We construct dynamic photoevaporation models of HST 10 with the Cloudy microphysics code that validate the oxygen and sulfur abundances. With the exception of [O I] 6300-A and [S II] 4069-A, the model fit is satisfactory for all spectral lines arising from the proplyd. The models show that the classic ionization correction factor for neon significantly underestimates (0.4 dex) this element's abundance in the low ionization conditions of HST 10. Apart from iron, whose gas-phase abundance is ~0.3 dex lower than in the local Orion nebula, most other elements in the proplyd do not show substantially different gas-phase abundances from the nebula. The abundances of carbon, oxygen and neon in HST 10 are practically the same as those in B-type stars in Orion.
  11/2012;
• Article: Ionized gas diagnostics from protoplanetary discs in the Orion Nebula and the abundance discrepancy problem

  A. Mesa-Delgado, M. Núñez-Díaz, C. Esteban, J. García-Rojas, N. Flores-Fajardo, L. López-Martín, Y. G. Tsamis, W. J. Henney
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  ABSTRACT: We present results from integral field spectroscopy with PMAS. The observed field contains: five protoplanetary discs (also known as proplyds), the high-velocity jet HH 514 and a bowshock. Spatial distribution maps are obtained for different emission line fluxes, the c(H{\beta}) coefficient, electron densities and temperatures, ionic abundances of different ions from collisionally excited lines (CELs), C2+ and O2+ abundances from recombination lines (RLs) and the abundance discrepancy factor of O2+, ADF(O2+). We find that collisional de-excitation has a major influence on the line fluxes in the proplyds. If this is not properly accounted for then physical conditions deduced from commonly used line ratios will be in error, leading to unreliable chemical abundances for these objects. We obtain the intrinsic emission of the proplyds 177-341, 170-337 and 170-334 by a direct subtraction of the background emission, though the last two present some background contamination due to their small sizes. A detailed analysis of 177-341 spectra reveals the presence of high-density gas (3.8\times10^5 cm^-3) in contrast to the typical values observed in the background gas of the nebula (3800 cm^-3). We also explore how the background subtraction could be affected by the possible opacity of the proplyd. We construct a physical model for the proplyd 177-341 finding a good agreement between the predicted and observed line ratios. Finally, we find that the use of reliable physical conditions returns an ADF(O2+) about zero for the intrinsic spectra of 177-341, while the background emission presents the typical ADF(O2+) observed in the Orion Nebula. We conclude that the presence of high-density ionized gas is severely affecting the abundances determined from CELs and, therefore, those from RLs should be considered as a better approximation to the true abundances.
  05/2012;
• Source

  Available from: ArXiv

  Article: Ionization of the diffuse gas in galaxies: Hot low-mass evolved stars at work -- proceedings IAUS284

  N. Flores-Fajardo, C. Morisset, G. Stasinska, L. Binette
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  ABSTRACT: We revisit the question of the ionization of the diffuse medium in late type galaxies, by studying NGC 891. The most important challenge for the models considered so far was the observed increase of [OIII]/Hb, [OII]/Hb, and [NII]/Ha with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic latitude z we look for the models which simultaneously fit the observed values of the [OIII]/Hb, [OII]/Hb, and [NII]/Ha ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.
  11/2011;
• Source

  Available from: ArXiv

  Article: Ionization of the diffuse gas in galaxies: hot low‐mass evolved stars at work

  N. Flores-Fajardo, C. Morisset, G. Stasińska, L. Binette
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  ABSTRACT: We revisit the question of the ionization of the diffuse medium in late-type galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The most important challenge for the models considered so far was the observed increase of [O iii]/Hβ, [O ii]/Hβ and [N ii]/Hα with increasing distance to the galactic plane. We propose a scenario based on the expected population of massive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to explain this observational fact. In the framework of this scenario we construct a finely meshed grid of photoionization models. For each value of the galactic altitude z we look for the models which simultaneously fit the observed values of the [O iii]/Hβ, [O ii]/Hβ and [N ii]/Hα ratios. For each value of z we find a range of solutions which depends on the value of the oxygen abundance. The models which fit the observations indicate a systematic decrease of the electron density with increasing z. They become dominated by the HOLMES with increasing z only when restricting to solar oxygen abundance models, which argues that the metallicity above the galactic plane should be close to solar. They also indicate that N/O increases with increasing z.
  Monthly Notices of the Royal Astronomical Society 08/2011; 415(3):2182 - 2192. · 4.90 Impact Factor
• Source

  Available from: ArXiv

  Article: Photoionized mixing layer models of the diffuse ionized gas

  L. Binette, N. Flores-Fajardo, A. C. Raga, L. Drissen, C. Morisset
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  ABSTRACT: It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated and mixed. The emission spectrum of such layers are compared with observations of Rand (ApJ 462, 712) of the DIG in the edge-on spiral NGC2363. We generate two sequence of models that fit the line ratio correlations between [SII]/H-alpha, [OI]/H-alpha, [NII]/[SII] and [OIII]/H-beta reasonably well. In one sequence of models the hot wind velocity increases while in the other the ionization parameter and layer opacity increases. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.
  02/2009;