N70 - A mass-loss bubble within a massive collapsing H I cloud

Dopita, Michael A.; Ford, V. L.; McGregor, Peter; Mathewson, D. S.; Wilson, I. R.

doi:10.1086/159352

Cited by 14 publications

(21 citation statements)

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“…It is a typical mass for giant molecular clouds from which associations can be formed. A similar result was found by Dopita et al (1981) for shell N70 (diameter » 120pc) in the LMC.…”

Section: On the Nature Of The Giant Envelope Around Stellar Assosupporting

confidence: 88%

Large-Scale Bubble Structure of the Interstellar Medium (ISM) and Properties of the Local Spiral Arm (LSA)

Бочкарев

1984

International Astronomical Union Colloquium

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Bubbles are very common structure units in the Galaxy and galaxies. Collection of radio, optical, infrared and x-ray observations of the Cyg superbubble (CSB) region of the sky show that the CSB is not a single bubble object. Between 50 to 75 percent of its x-ray emission can be ascribed to discrete sources. The other 25 to 50% x-ray emission, probably originates from bubbles around 8 OB associations of the region. All bubbles located within the spiral structure of Galaxy, M31 and M33 have diameter ≲ 300pc.The large distance of stellar association from the galactic plane (GP) combined with picture of the gas distribution within the LSA shows that a Reyleigh-Taylor instability in the LSA can develop and give use to the formation of compact steller clusters, such as the Cyg OB2 association. Development stages of the Reyleigh-Taylor instability, some peculiarities of the dust distribution and departures of the local structure from the galactic grand design suggest the absence of a spiral Shockwave in the LSA.

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“…It is a typical mass for giant molecular clouds from which associations can be formed. A similar result was found by Dopita et al (1981) for shell N70 (diameter » 120pc) in the LMC.…”

Section: On the Nature Of The Giant Envelope Around Stellar Assosupporting

confidence: 88%

Large-Scale Bubble Structure of the Interstellar Medium (ISM) and Properties of the Local Spiral Arm (LSA)

Бочкарев

1984

International Astronomical Union Colloquium

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“…Thus, the nebular emission-line properties might be comparable to DEM L323, except now varying the parameter of morphology. Dopita et al (1981) found that the nebular emission is largely consistent with photoionization as the dominant excitation mechanism, rather than shocks. However, Lasker (1977) and Skelton et al (1999) suggest a limited contribution by shock heating to resolve discrepancies that are apparent in the lower-ionization species.…”

Section: Photoionization Modelsmentioning

confidence: 85%

Calibration of Nebular Emission‐Line Diagnostics. I. Stellar Effective Temperatures

Oey

Dopita

Shields

et al. 2000

ASTROPHYS J SUPPL S

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We present a detailed comparison of optical H ii region spectra to photoionization models based on modern stellar atmosphere models. We examine both spatially resolved and integrated emission-line spectra of the H ii regions DEM L323, DEM L243, DEM L199, and DEM L301 in the Large Magellanic Cloud. The published spectral classifications of the dominant stars range from O7 to WN3, and morphologies range from Strömgren sphere to shell structure. Two of the objects include SNR contamination. The overall agreement with the predictions is generally within 0.2 dex for major diagnostic line ratios. An apparent pattern in the remaining discrepancies is that the predicted electron temperature is ∼ 1000 K hotter than observed. [Ne III] intensities are also slightly overpredicted, which may or may not be related. We model the shock emission for the SNR-contaminated objects, and find excellent agreement with the observations for composite shock and photoionized spectra. DEM L301's emission apparently results from both shocks and density-bounded photoionization. The existence of contaminating shocks can be difficult to ascertain in the spatially integrated spectra.Our analysis of the complex DEM L199 allows a nebular emission-line test of unprecedented detail for WR atmospheres. Surprisingly, we find no nebular He II λ4686 emission, despite the fact that both of the dominant WN3 stars should be hot enough to fully ionize He I in their atmospheres. The nebular diagnostics are again in excellent agreement with the data, for stellar models not producing He + -ionizing photons. The optical diagnostics are furthermore quite insensitive to the ionizing energy distribution for these early WR stars.We confirm that the η ′ emission-line parameter is not as useful as hoped for determining the ionizing stellar effective temperature, T ⋆ . Both empirically and theoretically, we find that it is insensitive for T ⋆ ∼ > 40 kK, and that it also varies spatially. The shock-contaminated objects show that η ′ will also yield a spuriously high T ⋆ in the presence of shocks. It is furthermore sensitive to shell morphology. We suggest [Ne III]/Hβ as an additional probe of T ⋆ . Although it is abundance-dependent, [Ne III]/Hβ has higher sensitivity to T ⋆ , is independent of morphology, and is insensitive to shocks in our objects. These observations should be useful data points for a first empirical calibration of nebular diagnostics of T ⋆ , which we attempt for LMC metallicity.

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“…To correct for this effect, post-observation "spectral flat fields" were made using images of the Orion nebula that were taken with fixed-wavelength interference filters (Walter et al 1992) Reddening corrections were determined based on Oey's spectroscopy and photometry of stars in LH 114 (the association inside N70); her median E(B − V )=0.06 (Oey 1996a) was used with reddening coefficients from Mathis (1990) (R V = 3.1) to determine the interstellar reddening and extinction (0.2 magnitudes in V ). When comparing line ratios, it is worth noting that Dopita et al (1981) used A V = 0.6 magnitudes, which over-corrects in the blue.…”

Section: Reductionsmentioning

confidence: 99%

“…This, of course, assumes that the motions observed in N70 are in fact due to expansion, which Dopita et al (1981) contests. Kinematics of N70 have been observed by Dopita et al (1981), Rosado et al (1981), Blades et al (1980), Georgelin et al (1983), and Lasker (1977), yielding velocity dispersions of order 40 km s −1 but differing conclusions regarding the overall velocity field.…”

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confidence: 99%

Emission‐Line Properties of the Large Magellanic Cloud Bubble N70

Skelton

Waller

Gelderman

et al. 1999

PUBL ASTRON SOC PAC

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We present a spectrophotometric imaging study of the emission bubble N70 (DEM 301) in the Large Magellanic Cloud. N70 is approximately 100 pc in size with a nearly circular shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova shock waves from the central population of high-mass stars (the OB association LH 114). We have obtained narrow-band images (FWHM ∼6Å) of N70 in the light of Hαλ6563, [N II]λ6584, [S II]λλ6717,6731, and [O III]λ5007, along with the corresponding red and green continua. The resulting line fluxes and flux ratios are used to derive ionization rates, nebular densities, volume filling fractions, and excitation indices. The photoionizing luminosity inferred from the embedded stellar population is more than adequate to account for the observed hydrogen ionization rate. We compare the emission-line photometry with that derived from similar imaging of the Orion nebula and with data collected from the literature on other emission-line regions in the LMC. Compared to the Orion nebula, N70 shows much higher [S II]/Hα intensity ratios which increase smoothly with radius -from < 0.3 near the center to > 1.0 towards the outer filamentary shell. The measured intensity ratios in N70 more closely match the range of excitation spanned by giant and supergiant H II shells and by some of the supernova remnants observed in the LMC. The contending ionization and excitation processes in the interior and outer shell of N70 are evaluated in terms of the available data. EUV photons probably contribute most of the inner nebula's ionization, whereas a combination of photoionization plus collisional ionization and excitation of sulfur atoms by low-velocity shocks seems to best fit the emission-line luminosities and intensity ratios observed in the outer shell. -4 -Considerations of the radiative and mechanical energetics that are involved may indicate the need for one or two supernova explosions having occurred during the last ∼ Myr.

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N70 - A mass-loss bubble within a massive collapsing H I cloud

Cited by 14 publications

References 0 publications

Large-Scale Bubble Structure of the Interstellar Medium (ISM) and Properties of the Local Spiral Arm (LSA)

Large-Scale Bubble Structure of the Interstellar Medium (ISM) and Properties of the Local Spiral Arm (LSA)

Calibration of Nebular Emission‐Line Diagnostics. I. Stellar Effective Temperatures

Emission‐Line Properties of the Large Magellanic Cloud Bubble N70

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