The Cocoon Nebula and its ionizing star: do stellar and nebular abundances agree?

Abstract

(Abridged) Main sequence massive stars embedded in an HII region should have the same chemical abundances as the surrounding nebular gas+dust. The Cocoon nebula, a close-by Galactic HII region ionized by a narrow line B0.5 V single star (BD+46 3474), is an ideal target to perform a detailed comparison of nebular and stellar abundances in the same Galactic HII region. We investigate the chemical content of O, N and S in the Cocoon nebula from two different points of view: an empirical analysis of the nebular spectrum and a detailed spectroscopic analysis of its ionizing B-type star using state-of-the-art stellar atmosphere modeling. By comparing the stellar and nebular abundances, we aim to indirectly address the long-standing problem of the discrepancy found between abundances obtained from collisionally excited lines (CELs) and optical recombination lines in photoionized nebulae. We collect spatially resolved spectroscopy of the Cocoon nebula and a high resolution optical spectrum of its ionizing star. Standard nebular techniques are used to compute the physical conditions and gaseous abundances of O, N and S. We perform a self-consistent spectroscopic abundance analysis of BD+46 3474 based on the atmosphere code FASTWIND to determine the stellar parameters and Si, O, and N abundances. The Cocoon nebula and its ionizing star, located at a distance of 800+-80 pc, have a very similar chemical composition as the Orion nebula and other B-type stars in the solar vicinity. This result agrees with the high degree of homogeneity of the present-day composition of the solar neighbourhood as derived from the study of the local cold-gas ISM. The comparison of stellar and nebular CELs abundances in the Cocoon nebula indicates that O and N gas+dust nebular values are in better agreement with stellar ones assuming small temperature fluctuations, of the order of those found in the Orion nebula.

Accepted for publication in A&A. 13 pages, 7 tables and 6 figures

References in corpus (14)

• A Unified Representation of Gas-Phase Element Depletions in the Interstellar Medium
• PyNeb: a new tool for analyzing emission lines. I. Code description and validation of results
• Present-day cosmic abundances. A comprehensive study of nearby early B-type stars and implications for stellar and Galactic evolution and interstellar dust models
• Extragalactic chemical abundances: do HII regions and young stars tell the same story? The case of the spiral galaxy NGC 300
• The VLT-FLAMES survey of massive stars: rotation and nitrogen enrichment as the key to understanding massive star evolution
• Resolving the electron temperature discrepancies in HII Regions and Planetary Nebulae: kappa-distributed electrons
• Keck HIRES Spectroscopy of Extragalactic HII Regions: C and O Abundances from Recombination Lines
• On the abundance discrepancy problem in HII regions
• The localized chemical pollution in NGC 5253 revisited: Results from deep echelle spectrophotometry
• Abundance analysis of prime B-type targets for asteroseismology I. Nitrogen excess in slowly-rotating beta Cephei stars
• Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution
• Properties of the ionized gas in HH202. II: Results from echelle spectrophotometry with UVES
• Enrichment of the ISM by metal-rich droplets and the abundance bias in HII regions
• Properties of the ionized gas in HH202. I: Results from integral field spectroscopy with PMAS

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