The Galactic radial abundance gradients of C, N, O, Ne, S, Cl, and Ar from deep spectra of H ii regions

ABSTRACT We present a reassessment of the radial abundance gradients of C, N, O, Ne, S, Cl, and Ar in the Milky Way using deep spectra of 33 H ii regions gathered from the literature, covering Galactocentric distances from 6 to 17 kpc. The distances of the objects have been revised using Gaia parallaxes. We recalculate the physical conditions and ionic abundances in an homogeneous way using updated atomic data. All the objects have direct determination of the electron temperature, permitting to derive their precise ionic abundances. We analyse and compare different ICF schemes for each element in order to obtain the most confident total abundances. Due to the revised distances, our results do not support previous claims about a possible flattening of the O/H gradient in the inner Galactic disc. We find that the Galactic N/O gradient is rather flat, in contrast to what has been found in other spiral galaxies. The slope of the gradients of some elements is sensitive to the ICF scheme used, especially in the case of Ne. The dispersion around the fit for the gradients of C, N, O, S, Cl, and Ar is of the order of the typical uncertainties in the determination of the abundances, implying the absence of significant inhomogeneities in the chemical composition of the ionized gas phase of the ISM. We find flat gradients of log(S/O) and log(Cl/O) and very shallow or flat ones for log(Ne/O) and log(Ar/O), consistent with a lockstep evolution of Ne, S, Cl, and Ar with respect to O.

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The Nature of Boxy/Peanut Spiral Galaxies: Overview and New Results

Publications of the Astronomical Society of Australia ◽

10.1071/as97146 ◽

1997 ◽

Vol 14 (2) ◽

pp. 146-158 ◽

Cited By ~ 10

Author(s):

M. Bureau ◽

K. C. Freeman

Keyword(s):

Formation Mechanism ◽

Vertical Structure ◽

Near Infrared ◽

Infrared Imaging ◽

Spiral Galaxies ◽

Physical Conditions ◽

Bar Buckling ◽

Line Imaging ◽

Observational Program

AbstractThe formation mechanism of boxy/peanut-shaped bulges in spiral galaxies has been a problem for many years. We briefly review here the possible formation scenarios for boxy/peanut bulges, concentrating on both the bar-buckling and accretion hypotheses, and then describe an observational program aimed at testing those various theories and studying the vertical structure of edge-on bars. Our program includes optical long-slit spectroscopy, Hiline-imaging, near-infrared imaging, and multi-band optical imaging. New spectroscopic results (both optical and Hi) are presented on seven galaxies, including five boxy/peanut-bulge spirals. Based on Kuijken & Merrifield's (1995) idea for detecting edge-on bars, we argue that these observations constitute a strong case in favour of the bar-buckling mechanism for the formation of boxy/peanut-shaped bulges, but they also raise many questions and prompt for more detailed modelling to be made. The implications of the observations concerning the determination of rotation curves and of the physical conditions in bulges are also discussed.

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Effects of the hot stellar component on derived physical parameters of the Carina Nebula

Symposium - International Astronomical Union ◽

10.1017/s0074180900206141 ◽

1999 ◽

Vol 193 ◽

pp. 493-494

Author(s):

Víctor Robledo-Rella ◽

Miriam Peña

Keyword(s):

Physical Parameters ◽

H Ii Regions ◽

Ionized Gas ◽

Physical Conditions ◽

Stellar Component ◽

Carina Nebula

Studies of extragalactic (un-resolved) H II regions, usually rely on assumptions about the underlying stellar absorption to estimate the reddening corrections needed to derive physical conditions of the ionized gas and to infer parameters of the ionizing stars (Robledo-Rella & Firmani 1990). We have addressed the problem of estimating quantitatively the effects of the hot star spectra on derived physical (nebular and stellar) parameters of galactic H II regions.

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Type II Supernova Photospheres and the Distance to Supernova 1987A

International Astronomical Union Colloquium ◽

10.1017/s0252921100094057 ◽

1988 ◽

Vol 108 ◽

pp. 295-304

Author(s):

Manorama Chilukuri ◽

Robert V. Wagoner

Keyword(s):

Time Scales ◽

Direct Determination ◽

Type Ii ◽

Physical Conditions ◽

Supernova 1987A ◽

Spectral Flux ◽

Spectrophotometric Data ◽

Parallel Geometry ◽

The Many

Among the many historic opportunities provided by the recent supernova in the LMC is that to improve our understanding of the physical conditions in the neighborhood of supernova photospheres, even though 1987A was initially characterized by radial and time scales smaller (by a factor 5–10) than “standard” more luminous SNII. Two consequences of this understanding, which we shall focus on in this contribution, are (a) an estimate of the (frequency-dependent) location and thickness of the photosphere and (b) the only direct determination of the distance of the supernova (via the generalized Baade method). We find that the photosphere is sharp enough to allow the use of plane-parallel geometry in the calculation of the emergent continuum spectral flux, if we confine our attention to those epochs (temperature T ~ 5000−6000 K) at which hydrogen is recombining at the photosphere. We also find that the distance to this supernova is 43 ± 4 kpc. The reliability of this determination should improve when accurate spectrophotometric data for dates other than March 1 become available to us.

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THE ADF AND THE t2 FORMALISM IN H II REGIONS BASED ON THE UPPER MASS LIMIT OF THE IMF FOR THE MW

Revista Mexicana de Astronomía y Astrofísica ◽

10.22201/ia.01851101p.2020.56.02.06 ◽

2020 ◽

Vol 56 (2) ◽

pp. 235-244

Author(s):

L. Carigi ◽

A. Peimbert ◽

M. Peimbert ◽

G. Delgado-Inglada

Keyword(s):

Milky Way ◽

Spiral Galaxies ◽

Star Formation Rate ◽

Direct Method ◽

Formation Rate ◽

Mass Function ◽

Initial Mass Function ◽

H Ii Regions ◽

Mass Limit ◽

Better Than

We study in depth the abundance discrepancy problem in H II regions, this time from a different perspective than the usual one: by studying the effect of the upper mass limit (Mup) of the initial mass function (IMF) on the O, C, and He predicted by chemical evolution models for the Milky Way. We use abundances determined with the direct method (DM) and with the temperature independent method (TIM). We compare the predicted abundances at the present time with observations of Orion, M17, and M8 to determine the Mup value of the galactic IMF. From the DM abundances, the models predict an Mup = 25 − 45 M⨀, while from the TIM, CEMs derive an Mup = 70 − 110 M⨀. Spiral galaxies with the stellar mass and star formation rate of the MW are predicted to have an Mup ≈ 100 M⨀. These results support that abundances derived from the TIM are better than those derived from the DM.

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Helium abundances and its radial gradient from the spectra of H ii regions and ring nebulae of the Milky Way

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1705 ◽

2020 ◽

Vol 496 (3) ◽

pp. 2726-2742 ◽

Cited By ~ 1

Author(s):

J E Méndez-Delgado ◽

C Esteban ◽

J García-Rojas ◽

K Z Arellano-Córdova ◽

M Valerdi

Keyword(s):

Milky Way ◽

H Ii Regions ◽

Abundance Gradient ◽

Radial Gradient ◽

Physical Conditions ◽

The Galaxy ◽

Ring Nebulae ◽

Gaia Dr2 ◽

Disc Galaxies ◽

Weakly Dependent

ABSTRACT We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 H ii regions and ring nebulae surrounding massive O-type stars. We revise the Galactocentric distances of the objects considering Gaia DR2 parallaxes (Gaia Collaboration 2018) and determine the physical conditions and the ionic abundance of He+ in a homogeneous way, using between 3 and 10 He i recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ionization correction factor (ICF; He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log(η) < 0.9 are considered. The slope values go from −0.0078 to −0.0044 dex kpc−1, consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O, and N in a sample of ring nebulae around Galactic Wolf–Rayet stars, finding a quite similar He overabundance of about +0.24 ± 0.11 dex in three stellar ejecta ring nebulae.

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The Extreme Outer Regions of Disk Galaxies: Star Formation and Metal Abundances

International Astronomical Union Colloquium ◽

10.1017/s0252921100054312 ◽

1999 ◽

Vol 171 ◽

pp. 196-203

Author(s):

Annette Ferguson ◽

Rosemary Wyse ◽

Jay Gallagher

Keyword(s):

Star Formation ◽

Gas Phase ◽

Massive Star ◽

Spiral Galaxies ◽

Disk Galaxies ◽

Physical Conditions ◽

First Results ◽

Disk Evolution ◽

Metal Abundances ◽

Optical Radius

AbstractThe extreme outer regions of disk galaxies, lying at or beyond the classical optical radius defined by R25, present an opportunity to study star formation and chemical evolution under unique physical conditions, possibly reminscent of those which existed during the early stages of disk evolution. We present here some of the first results from a large study to measure star formation rates and metallicities in the extreme outer limits of a sample of nearby spiral galaxies. Despite their low gas column densities, massive star formation is often observed in these outer parts, but at an azimuthally–averaged rate much lower than that seen in the inner disk. Gas-phase O/H abundances of roughly 10% solar characterize the gas at 1.5–2 R25. The implications of our results for star formation ‘laws’ and models of disk evolution are discussed.

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Properties of H ɪɪ Regions Along Galactic Bars

International Astronomical Union Colloquium ◽

10.1017/s0252921100049435 ◽

1996 ◽

Vol 157 ◽

pp. 70-75

Author(s):

P. Martin

Keyword(s):

Star Formation ◽

Spiral Galaxies ◽

H Ii Regions ◽

Electron Densities ◽

Physical Conditions ◽

General Properties

AbstractA study of general properties of H ɪɪ regions along the bars of 11 spiral galaxies is presented. From Hα imaging, distributions, morphology and star formation rates are established. Physical conditions derived from spectrophotometry reveal that strong shocks are absent in H ɪɪ regions along bars and electron densities appear to be normal. Abundance distributions indicate that mixing of the ISM is taking place along bars.

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A method for the direct determination of the rate constants for radical-radical interactions in the gas phase II. The rate constant for the recombination of methyl radicals

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1957.0209 ◽

1957 ◽

Vol 243 (1232) ◽

pp. 130-142 ◽

Cited By ~ 5

Keyword(s):

Gas Phase ◽

Rate Constant ◽

Room Temperature ◽

Direct Determination ◽

Theoretical Interpretation ◽

Methyl Radicals ◽

Gas Phase Reactions ◽

A Value ◽

Acetone Vapour

The technique outlined in part I of this paper has been employed to study the photosensitized decomposition of acetone vapour. A theoretical interpretation of the non-stationary state applied to non-chain photochemical gas phase reactions with second-order termination has been given and the effects of non-homogeneous absorption of radiation have been considered. A value has been obtained for the rate constant for the recombination of methyl radicals in the gas phase at room temperature.

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Direct determination of the kinetics of oxygen diffusion to the photocytes of a bioluminescent elaterid larva, measurement of gas- and aqueous-phase diffusional barriers and modelling of oxygen supply

Journal of Experimental Biology ◽

10.1242/jeb.203.16.2479 ◽

2000 ◽

Vol 203 (16) ◽

pp. 2479-2484 ◽

Cited By ~ 2

Author(s):

G.S. Timmins ◽

E.J. Bechara ◽

H.M. Swartz

Keyword(s):

Gas Phase ◽

Aqueous Phase ◽

Oxygen Diffusion ◽

Time Course ◽

Oxygen Supply ◽

Direct Determination ◽

Tracheal System ◽

Significant Mechanism ◽

Fluid Levels

We describe the development and use of a direct kinetic technique to determine the time taken for oxygen to diffuse from the external environment into the light-producing cells (photocytes) in the prothorax of bioluminescent larvae of Pyrearinus termitilluminans. This was achieved by measuring the time course of the pseudoflash induced through sequential anoxia followed by normoxia. We have also determined the separate times taken for this oxygen diffusion in gaseous and tissue (predominantly aqueous) phases by using helium and nitrogen as the carrier gas. Of the total time taken for diffusion, that in the gas phase required 613+/−136 ms (mean +/− s.e. m., N=5) whilst that in the aqueous phase required 1313+/−187 ms. These values imply pathlengths of diffusion in the gaseous and aqueous phases of 4.80×10(−)(3)+/−0.53×10(−)(3) and 8. 89×10(−)(5)+/−0.61×10(−)(5)m, respectively. In addition, the pathlength of gas-phase diffusion was used to derive a parameter relating to the tortuosity of the tracheal system. These values, together with those obtained upon bioluminescent oxygen consumption, have been used to model oxygen supply to the photocyte. From these studies, it would also appear that the modulation of tracheolar fluid levels might be a significant mechanism of control of tissue oxygen levels in at least some insects.

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