Chemistry in the dIrr galaxy Leo A

Abstract

We present chemical abundance determinations of two H II regions in the dIrr galaxy Leo A, from GTC OSIRIS long-slit spectra. Both H II regions are of low excitation and seem to be ionised by stars later than O8V spectral type. In one of the H II regions we used the direct method: O${}^{+2}$ ionic abundance was calculated using an electronic temperature determined from the [O III] $\lambda \lambda$4363/5007 line ratio; ionic abundances of O${}^{+}$, N${}^{+}$, and S${}^{+}$ were calculated using a temperature derived from a parameterised formula. O, N and S total abundances were calculated using Ionisation Correction Factors from the literature for each element. Chemical abundances using strong-line methods were also determined, with similar results. For the second H II region, no electron temperature was determined thus the direct method cannot be used. We computed photoionisation structure models for both H II regions in order to determine their chemical composition from the best-fitted models. It is confirmed that Leo A in a very low metallicity galaxy, with 12+log(O/H)=7.4$\pm$0.2, log(N/O)=$-$1.6, and log(S/O)=$-$1.1. Emission lines of the only PN detected in Leo A were reanalysed and a photoionisation model was computed. This PN shows 12+log(O/H) very similar to the ones of the H II regions and a low N abundance, although its log(N/O) ratio is much larger than the values of the H II regions. Its central star seems to have had an initial mass lower than 2 M${}_{\odot }$.

arXiv commentAccepted in MNRAS

References in corpus (21)

• The observed properties of dwarf galaxies in and around the Local Group
• A Grid of NLTE Line-Blanketed Model Atmospheres of O-type Stars
• Updated stellar yields from Asymptotic Giant Branch models
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
• A grid of synthetic ionizing spectra for very hot compact stars from NLTE model atmospheres
• Leo A: A Late-Blooming Survivor of the Epoch of Reionization in the Local Group
• Evolution and nucleosynthesis of asymptotic giant branch stellar models of low metallicity
• Ionization Correction Factors for Planetary Nebulae: I- Using optical spectra
• The ACS LCID Project: On the origin of dwarf galaxy types: a manifestation of the halo assembly bias?
• Leo P: An Unquenched Very Low-Mass Galaxy
• Electron impact excitation of OII fine-structure levels
• Collision Strengths for [O III] Optical and Infrared Lines
• WFPC2 Observations of Leo A: A Predominantly Young Galaxy within the Local Group
• Variable Stars in Leo A: RR Lyraes, Short-period Cepheids, and Implications on Stellar Content
• Oxygen and Nitrogen in Leo A and GR 8
• Spectral Analysis of the Stromlo-APM Survey I. Spectral Properties of Galaxies
• Revisiting the radial abundance gradients of nitrogen and oxygen of the Milky Way
• The ACS LCID Project. VIII. The short-period Cepheids of Leo A
• Chemical behavior of the Dwarf Irregular Galaxy NGC 6822. Its PN and HII region abundances
• The oxygen abundance gradient in M81 and the robustness of abundance determinations in H II regions

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• A Panchromatic Study of Massive Stars in the Extremely Metal-Poor Local Group Dwarf Galaxy Leo A
• Star clusters in the dwarf irregular galaxy Leo A
• The ionization structure and chemical history in isolated H ii regions of dwarf galaxies with VIMOS/IFU II. The Leo A galaxy