The effect of shock waves on the spectra of H II regions and planetary nebulae

Peimbert, M.; Sarmiento, A.; Fierro, Julieta

doi:10.1086/132886

Cited by 49 publications

(61 citation statements)

References 35 publications

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“…Therefore, giant H ii regions in dwarf star-forming galaxies present the highest t 2 values. This may perhaps be related to their complex structure and dynamics due to the action of stellar winds and supernova remnants as it was firstly advocated by Peimbert et al (1991) or even the hardening of the energy distribution of ionizing photons as the central clusters evolve (Perez 1997). Although the simple Peimbert's formalism (Peimbert 1967) may be not completely adequate for such large temperature fluctuations, we consider it is still useful for parameterizing the problem until their existence and nature are definitely proven.…”

Section: Ionic Abundances and Abundance Discrepancymentioning

confidence: 93%

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

Esteban

García‐Rojas

Carigi³

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We present deep echelle spectrophotometry of the brightest emission-line knots of the star-forming galaxies He 2−10, Mkn 1271, NGC 3125, NGC 5408, POX 4, SDSS J1253−0312, Tol 1457−262, Tol 1924−416 and the H ii region Hubble V in the Local Group dwarf irregular galaxy NGC 6822. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100-10420Å range. We determine electron densities and temperatures of the ionized gas from several emission-line intensity ratios for all the objects. We derive the ionic abundances of C 2+ and/or O 2+ from faint pure recombination lines (RLs) in several of the objects, permitting to derive their C/H and C/O ratios. We have explored the chemical evolution at low metallicities analysing the C/O vs. O/H, C/O vs. N/O and C/N vs. O/H relations for Galactic and extragalactic H ii regions and comparing with results for halo stars and DLAs. We find that H ii regions in star-forming dwarf galaxies occupy a different locus in the C/O vs. O/H diagram than those belonging to the inner discs of spiral galaxies, indicating their different chemical evolution histories, and that the bulk of C in the most metal-poor extragalactic H ii regions should have the same origin than in halo stars. The comparison between the C/O ratios in H ii regions and in stars of the Galactic thick and thin discs seems to give arguments to support the merging scenario for the origin of the Galactic thick disc. Finally, we find an apparent coupling between C and N enrichment at the usual metallicities determined for H ii regions and that this coupling breaks in very low-metallicity objects.

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Section: Ionic Abundances and Abundance Discrepancymentioning

confidence: 93%

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

Esteban

García‐Rojas

Carigi³

et al. 2014

Monthly Notices of the Royal Astronomical Society

Self Cite

111

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“…Moreover, departures from a Maxwell-Boltzmann energy distribution of free electrons in nebulae in form of a "kappa-distribution" can mimic the effects of temperature fluctuations on the derived abundances (Nicholls et al 2012) and could explain their ultimate nature. Peimbert et al (1991) explored the effects of shock waves in the spectra of ionised nebulae. They showed that large temperature fluctuations may arise in the presence of shocks with velocities larger than 100 km s −1 .…”

Section: Abundance Discrepancy and Temperature Fluctuationsmentioning

confidence: 99%

The chemical composition of Galactic ring nebulae around massive stars

Esteban

Mesa‐Delgado

Morisset

et al. 2016

Mon. Not. R. Astron. Soc.

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We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C 2+ and O 2+ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O 2+ . The ADFs are larger than the typical ones of normal H ii regions but similar to those found in the ionised gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 M ⊙ seem to reproduce the observed abundance ratios of most of the nebulae.

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“…It is also possible that the [O iii] λ4363 Å emission line is enhanced by shocks and the effect is likely to be stronger in regions with weaker lines (Peimbert et al 1991;Izotov et al 1997a). Consequently, this enhancement would result in the underestimation of the oxygen abundance.…”

Section: Electron Temperature and Electron Number Densitymentioning

confidence: 99%

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

Izotov

Гусева

Fricke

et al. 2009

A&A

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Context. We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W.Aims. Our aim is to derive element abundances in different H ii regions of this unique system of galaxies and to study spatial abundance variations.Methods. The electron temperature T e (O iii) in all H ii regions, except for one, is derived from the [O iii] λ4363/(λ4959+λ5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements.Results. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to 7.32 in different H ii regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ∼1−2 kpc. Good seeing during FORS observations allowed us to extract spectra of four H ii regions in SBS 0335-052W. The oxygen abundance in the brightest region No. 1 of SBS 0335-052W is 7.22 ± 0.07, consistent with previous determinations. Three other H ii regions are much more metal-poor with an unprecedently low oxygen abundance of 12 + log O/H = 7.01 ± 0.07 (region No. 2), 6.98 ± 0.06 (region No. 3), and 6.86 ± 0.14 (region No. 4). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS 0335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H ii regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485 ± 0.0012 and 0.2514 ± 0.0012 for two different sets of He i emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS 0335-052E is lower, while the argon-to-oxygen abundance ratio is higher than those in other low-metallicity galaxies. The Fe/O abundance ratios in different regions of SBS 0335-052E are among the highest for emission-line galaxies implying that iron is almost entirely not depleted onto dust grains despite dust being detected in this galaxy in earlier ISO and Spitzer observations. The N/O abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12 + log O/H < 7.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity.

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The effect of shock waves on the spectra of H II regions and planetary nebulae

Cited by 49 publications

References 35 publications

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

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

The chemical composition of Galactic ring nebulae around massive stars

SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies

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