Small-spatial-scale variations of nebular properties and the abundance discrepancy in three Galactic H ii regions★

Mesa‐Delgado, A.; Esteban, C.

doi:10.1111/j.1365-2966.2010.16664.x

Cited by 16 publications

(17 citation statements)

References 63 publications

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“…4. Mesa-Delgado & Esteban (2010) found C/H ratios between 8.6 to 9.0 dex in several zones of NGC 7635, indicating an abnormally high abundance of this element. However, the comparison of the C/H ratios included in Table 12 indicates that the values we determine from our new observations are consistent with those expected from the abundance gradient.…”

Section: Ngc 7635mentioning

confidence: 92%

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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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Section: Ngc 7635mentioning

confidence: 92%

“…4 -show larger values of n e . Rodríguez (1999), Moore et al (2002b) and Mesa-Delgado & Esteban (2010) Table 3. continued Figure 4), so the determination is highly confident.…”

Section: Physical Conditionsmentioning

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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“…It is also evidenced by the presence of dense (≈ 10 3 − 10 4 cm −3 ; e.g. Mesa-Delgado & Esteban 2010;Moore et al 2002a;Esteban et al 2016) bright-rimmed structures around the Bubble Nebula (one of which is even penetrated into the bubble; e.g. Moore et al 2002a), whose "elephant trunk" morphology is typical of H ii regions expanding into dense molecular clouds (e.g.…”

Section: Bubble Nebula and Bd+60 • 2522mentioning

confidence: 99%

Thermal emission from bow shocks I: 2D Hydrodynamic Models of the Bubble Nebula

Green,

Mackey,

Haworth

et al. 2019

Preprint

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The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60 • 2522. The small dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We have run 2D hydrodynamic simulations to model the interaction of the central star's wind with the interstellar medium (ISM). The models cover a range of possible ISM number densities of n = 50 − 200 cm −3 and stellar velocities of v * = 20 − 40 km s −1 . Synthetic Hα and 24 µm emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had v * ≈ 20 km s −1 into an ISM with n ∼ 100 cm −3 , at an angle of 60 • with respect to the line of sight. Synthetic maps of soft (0.3 − 2 keV) and hard (2 − 10 keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have luminosity ∼ 10 32 − 10 33 erg s −1 . The hard X-rays are fainter, luminosity ∼ 10 30 − 10 31 erg s −1 , and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths, and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique, it could be just a favourably oriented very dense bow shock. The dense ISM surrounding BD+60 • 2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission.

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“…From intermediate and high resolution spectroscopy, several works have found that the ADF(O 2+ ) is always between 0.1 and 0.3 dex in Galactic and extragalactic H ii regions (see e.g. Esteban et al 2002;Tsamis et al 2003;Esteban et al 2004;López-Sánchez et al 2007;Mesa-Delgado et al 2008;Esteban et al 2009;Mesa-Delgado & Esteban 2010). García-Rojas & Esteban ( 2007) argued that the AD problem in H ii regions seems to be consistent with the predictions of the temperature fluctuation paradigm proposed by Peimbert (1967) and parametrized by the mean square of the spatial variations of temperature, the so-called t 2 parameter.…”

Section: Abundance Discrepancy Problemmentioning

confidence: 99%

Integral field spectroscopy of selected areas of the Bright bar and Orion-S cloud in the Orion nebula★

Mesa‐Delgado

Núñez-Díaz

Esteban

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present integral field spectroscopy of two selected zones in the Orion nebula obtained with the Potsdam Multi‐Aperture Spectrophotometer, covering the optical spectral range from 3500 to 7200 Å and with a spatial resolution of 1 arcsec. The observed zones are located on the prominent Bright bar and on the brightest area at the north‐east of the Orion south cloud, both containing remarkable ionization fronts. We obtain maps of emission‐line fluxes and ratios, electron density and temperatures, and chemical abundances. We study the ionization structure and morphology of both fields, whose ionization fronts show different inclination angles with respect to the plane of the sky. We find that the maps of electron density, O+/H+ and O/H ratios show a rather similar structure. We interpret this as produced by the strong dependence on density of the [O ii] lines used to derive the O+ abundance, and that our nominal values of electron density – derived from the [S ii] line ratio – may be slightly higher than the appropriate value for the O+ zone. We measure the faint recombination lines of O ii in the field at the north‐east of the Orion south cloud, allowing us to explore the so‐called abundance discrepancy problem. We find a rather constant abundance discrepancy across the field and a mean value similar to that determined in other areas of the Orion nebula, indicating that the particular physical conditions of this ionization front do not contribute to this discrepancy.

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Small-spatial-scale variations of nebular properties and the abundance discrepancy in three Galactic H ii regions★

Cited by 16 publications

References 63 publications

The chemical composition of Galactic ring nebulae around massive stars

The chemical composition of Galactic ring nebulae around massive stars

Thermal emission from bow shocks I: 2D Hydrodynamic Models of the Bubble Nebula

Integral field spectroscopy of selected areas of the Bright bar and Orion-S cloud in the Orion nebula★

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