A reappraisal of the chemical composition of the Orion nebula based on Very Large Telescope echelle spectrophotometry

Abstract

We present Very Large Telescope (VLT) UVES echelle spectrophotometry of the Orion nebula in the 3100-10 400 Å range. We have measured the intensity of 555 emission lines, many of them corresponding to permitted lines of different heavy-element ions. This is the largest set of spectral emission lines ever obtained for a Galactic or extragalactic H II region. We have derived He + , C 2+ , O + , O 2+ and Ne 2+ abundances from pure recombination lines. This is the first time that O + and Ne 2+ abundances have been obtained from these kinds of lines in the nebula. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. In all cases, ionic abundances obtained from recombination lines are larger than those derived from collisionally excited lines. We have obtained remarkably consistent independent estimations of the temperature fluctuation parameter, t 2 , from different methods, which are also similar to other estimates from the literature. This result strongly suggests that moderate temperature fluctuations (t 2 between 0.02 and 0.03) are present in the Orion nebula. We have compared the chemical composition of the nebula with those of the Sun and other representative objects. The heavy-element abundances in the Orion nebula are only slightly higher than the solar ones, a difference that can be explained by the chemical evolution of the solar neighbourhood.

Carbon and oxygen abundances from recombination lines in low-metallicity star-forming galaxies. Implications for chemical evolution★

“…The different estimations of the amount of C locked up in dust grains in the local interstellar medium show a rather large variation depending on the abundance determination methods applied (see Jenkins 2014). Assuming the quantities complied by Jenkins (2014) we find that the gas+dust C/H ratios in the Orion Nebula would be between 0.09 to 0.26 dex larger than the ionized gas phase values determined by Esteban et al (2004). However, some degree of destruction of C-bearing dust particles is likely to be acting in ionized nebulae and the assumption of depletion factors of the neutral diffuse interstellar medium may not be appropriate for an ionized nebula.…”

“…In this case, there seems to be no discrepancies between the methods for determining the O 2+ abundance used by both research groups. The spectra of some of the sample objects also show permitted lines of other heavy-element ions as N i, N ii, N iii, O i and/or Si ii, but they are produced by fluorescence and can not be used to derive reliable abundance values (see Esteban et al 1998Esteban et al , 2004.…”

The radial abundance gradient of chlorine in the Milky Way

“…We have used intensity ratios of several selected emission lines of spectra of Galactic H ii regions published by Esteban et al (2004Esteban et al ( , 2013 and García-Rojas et al (2004 Esteban et al (2013) and calculated by Copetti et al (2007). The distances are based on kinematical or photometrical methods and have typical uncertainties of less than 1 kpc (e.g.…”

On the production of He, C, and N by low- and intermediate-mass stars: a comparison of observed and model-predicted planetary nebula abundances

“…Open black circles refer to PN located in the MWG disk and taken from our extended sample, red filled circles represent H II regions from Garnett (1995Garnett ( , 1997Garnett ( , 1999, MWG disk stars from Gustafsson et al (1999) are shown with blue filled circles, MWG metal poor halo stars from Akerman et al (2004) are indicated with orange filled diamonds, green open squares and diamonds indicated LMC and SMC PN by Stanghellini et al (2005Stanghellini et al ( , 2009) respectively, and red filled squares correspond to low metallicity dwarf galaxies by Berg et al (2016). The maroon filled triangle and magenta filled diamond represent Orion (Esteban et al 2004) and the Sun (Asplund et al 2009), respectively. of 3rd dredge-up, which elevates C, and hot bottom burning, which does likewise to N. However, explanations of PN abundance patterns based upon progenitor masses is typically not included.…”

“…Open black circles refer to PN located in the MWG disk and taken from our extended sample, filled red squares represent Galactic H II regions from Deharveng et al (2000) and the filled magenta triangle shows the solar position (Asplund et al 2009). The position of Orion (Esteban et al 2004) is indicated. different research groups and evaluate each set of models based upon how well they appear to explain the observed abundances.…”