Physics and Chemistry of Circumstellar Dust Shells

Gail, H. P.; Sedlmayr, E.

doi:10.1017/cbo9780511985607

Cited by 283 publications

(457 citation statements)

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“…These two choices should span most of parameter space. Our standard model assumes that amorphous silicate grains condense first, followed by metallic iron that forms on top of the amorphous silicates, along the lines suggested by Gail & Sedlmayr (1999). Therefore metallic iron and amorphous silicates are in thermal contact and have the same temperature in our calculations.…”

Section: Dust Opacitiesmentioning

confidence: 97%

“…Dust condensation theory suggests that the density is critical in the formation of crystalline silicates (Tielens et al 1998;Gail & Sedlmayr 1999;Sogawa & Kozasa 1999), but this has still not been verified by observations. Secondly, how much crystalline silicate material is deposited by AGB stars to the diffuse ISM?…”

Section: Introductionmentioning

confidence: 96%

“…Theoretical studies predict that the formation of crystalline silicate dust is dependent on the gas density (Tielens et al 1998;Gail & Sedlmayr 1999;Sogawa & Kozasa 1999). Higher densities are more favorable for the formation of crystals than low densities.…”

Section: Introductionmentioning

confidence: 99%

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Determining the forsterite abundance of the dust around asymptotic giant branch stars

Vries

Min

Waters

et al. 2010

A&A

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Aims. We present a diagnostic tool to determine the abundance of the crystalline silicate forsterite in AGB stars surrounded by a thick shell of silicate dust. Using six infrared spectra of high mass-loss oxygen rich AGB stars we obtain the forsterite abundance of their dust shells. Methods. We use a monte carlo radiative transfer code to calculate infrared spectra of dust enshrouded AGB stars. We vary the dust composition, mass-loss rate and outer radius. We focus on the strength of the 11.3 and the 33.6 μm forsterite bands, that probe the most recent (11.3 μm) and older (33.6 μm) mass-loss history of the star. Simple diagnostic diagrams are derived, allowing direct comparison to observed band strengths. Results. Our analysis shows that the 11.3 μm forsterite band is a robust indicator for the forsterite abundance of the current mass-loss period for AGB stars with an optically thick dust shell. The 33.6 μm band of forsterite is sensitive to changes in the density and the geometry of the emitting dust shell, and so a less robust indicator. Applying our method to six high mass-loss rate AGB stars shows that AGB stars can have forsterite abundances of 12% by mass and higher, which is more than the previously found maximum abundance of 5%.

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Section: Dust Opacitiesmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 96%

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Determining the forsterite abundance of the dust around asymptotic giant branch stars

Vries

Min

Waters

et al. 2010

A&A

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“…Nava et al (2006), except in the case of SMC N88A for which we used the value obtained by Testor et al (2003). Contrary to what happens with C and O, N is expected not being a major constituent of dust, due to its inclusion in the highly stable gas form of N2 (Gail & Sedlmayr 1986;Jenkins 2014). In the case of Figure 11 we recommend to subtract ∼0.1 dex to the log(N/O) values of H ii regions to correct for dust depletion in O.…”

Section: The C/o Vs N/o Relationmentioning

confidence: 99%

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

111

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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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“…5, source #6 is located in a hole of the 5.8 μm emission (see zoom of the region in the figure). It is well known that the exciting star(s) of an HII region generates a cavity of dust and gas because of the action of the radiation pressure on the dust grains (Gail & Sedlmayr 1979), which suggests that source #6 is the more likely exciting-star candidate of G35.6. On the other hand, using the same assumptions as for R1, we found that based on the radio continuum flux at 1.4 GHz in R2, the exciting stars of NVSS 185938+020012 would be later than an O9.5V star.…”

Section: Exciting Starsmentioning

confidence: 99%

The HII region G35.673-00.847: another case of triggered star formation?

Paron

Petriella

Ortega

2010

A&A

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Aims. As part of a systematic study that we are performing to increase the observational evidence of triggered star formation in the surroundings of HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly studied source. Methods. Using data from the large-scale surveys Two Micron All Sky Survey, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL, Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky Survey (NVSS), we performed a multiwavelength study of G35.673-00.847 and its surroundings. Results. The mid-IR emission shows that G35.673-00.847 has an almost semi-ring like shape with a cut towards the galactic west. The radius of this semi-ring is about 1. 5 (∼1.6 pc, at the distance of ∼3.7 kpc). The distance was estimated from an HI absorption study and the analysis of the molecular gas. We find a molecular shell composed of several clumps distributed around the HII region, suggesting that its expansion is collecting the surrounding material. We identify several YSO candidates across the molecular shell. Finally, comparing the HII region dynamical age and the fragmentation time of the molecular shell, we discard the so-called collect and collapse as being the mechanism responsible for the YSO formation, suggesting that other processes such as radiative-driven implosion and/or small-scale Jeans gravitational instabilities operate.

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Physics and Chemistry of Circumstellar Dust Shells

Cited by 283 publications

References 0 publications

Determining the forsterite abundance of the dust around asymptotic giant branch stars

Determining the forsterite abundance of the dust around asymptotic giant branch stars

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

The HII region G35.673-00.847: another case of triggered star formation?

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