Chlorine Isotope Ratios in M Giants

Maas, Z. G.; Pilachowski, Catherine A.

doi:10.3847/1538-3881/aac2cf

Cited by 11 publications

(5 citation statements)

References 55 publications

(59 reference statements)

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“…For sources towards which both isotopologues were detected, they found a spread of 35 Cl/ 37 Cl ratios, mostly in the 2.0-2.6 range, with values below 1 for two locations in the W3 star forming region and ∼ 5 for DR21(OH), a region of massive star formation. Maas & Pilachowski (2018) found 35 Cl/ 37 Cl ratios ranging from 1.76 to 3.42 for a sample of six M giants. All of these results point to significant variation in 35 Cl/ 37 Cl across the galaxy.…”

Section: Chlorine Abundance and Isotopic Ratiomentioning

confidence: 93%

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

Danilovich

Sande

Plane

et al. 2021

A&A

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Context. S-type asymptotic giant branch (AGB) stars are thought to be intermediates in the evolution of oxygen- to carbon-rich AGB stars. The chemical compositions of their circumstellar envelopes are also intermediate but have not been studied in as much detail as their carbon- and oxygen-rich counterparts. W Aql is a nearby S-type star, with well-known circumstellar parameters, making it an ideal object for in-depth study of less common molecules. Aims. We aim to determine the abundances of AlCl and AlF from rotational lines, which have been observed for the first time towards an S-type AGB star. In combination with models based on PACS observations, we aim to update our chemical kinetics network based on these results. Methods. We analyse ALMA observations towards W Aql of AlCl in the ground and first two vibrationally excited states and AlF in the ground vibrational state. Using radiative transfer models, we determine the abundances and spatial abundance distributions of Al35Cl, Al37Cl, and AlF. We also model HCl and HF emission and compare these models to PACS spectra to constrain the abundances of these species. Results. AlCl is found in clumps very close to the star, with emission confined within 0′′.1 of the star. AlF emission is more extended, with faint emission extending 0′′.2 to 0′′.6 from the continuum peak. We find peak abundances, relative to H2, of 1.7 × 10−7 for Al35Cl, 7 × 10−8 for Al37Cl, and 1 × 10−7 for AlF. From the PACS spectra, we find abundances of 9.7 × 10−8 and ≤10−8, relative to H2, for HCl and HF, respectively. Conclusions. The AlF abundance exceeds the solar F abundance, indicating that fluorine synthesised in the AGB star has already been dredged up to the surface of the star and ejected into the circumstellar envelope. From our analysis of chemical reactions in the wind, we conclude that AlF may participate in the dust formation process, but we cannot fully explain the rapid depletion of AlCl seen inthe wind.

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Section: Chlorine Abundance and Isotopic Ratiomentioning

confidence: 93%

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

Danilovich

Sande

Plane

et al. 2021

A&A

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“…Combining the results from all the surveys reveals a large range in Cl isotope ratios from 1 < 35 Cl/ 37 Cl < 5 in the ISM. A scatter of 1.76 < 35 Cl/ 37 Cl < 3.42 was also measured in a small sample of six M giants (Maas & Pilachowski 2018). The origin of the Cl isotope ratio scatter is still unknown but may be due to differences in local enrichment or self-enrichment.…”

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confidence: 84%

“…8. The [Cl/Fe] abundances were calculated using the A( 35 Cl) abundances from Table 3 and assuming a 35 Cl/ 37 Cl = 2.66 isotope ratio, the average from the sample of Maas & Pilachowski (2018). Though the Cl isotope ratio may vary in our sample, the uncertainty from the isotope ratio is less significant than the uncertainty from the effective temperature.…”

Section: Evolution In the Galaxymentioning

confidence: 99%

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The Galactic Chemical Evolution of Chlorine

Maas,

Pilachowski

2021

Preprint

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We measured 35 Cl abundances in 52 M giants with metallicities between -0.5 < [Fe/H] < 0.12. Abundances and atmospheric parameters were derived using infrared spectra from CSHELL on the IRTF and from optical echelle spectra. We measured Cl abundances by fitting a H 35 Cl molecular feature at 3.6985 µm with synthetic spectra. We also measured the abundances of O, Ca, Ti, and Fe using atomic absorption lines. We find that the [Cl/Fe] ratio for our stars agrees with chemical evolution models of Cl and the [Cl/Ca] ratio is broadly consistent with the solar ratio over our metallicity range. Both indicate that Cl is primarily made in core-collapse supernovae with some contributions from Type Ia SN. We suggest other potential nucleosynthesis processes, such as the ν-process, are not significant producers of Cl. Finally, we also find our Cl abundances are consistent with H II and planetary nebular abundances at a given oxygen abundance, although there is scatter in the data.

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“…The molecule has been detected in the circumstellar envelope of the carbon rich star IRC+10216, with a molecular abundance with respect to H 2 of 6 × 10 −7 (Cernicharo et al, 2010), in molecular clouds as OMC-1 (Blake et al, 1985;Schilke et al, 1995), Sagittarius B2 (Zmuidzinas et al, 1995), ρ Ophiuci (Federman et al, 1995), and W31C (Monje et al, 2013) . HCl has been used by Maas & Pilachowski (2018) for determining the isotope ratio 35 Cl/ 37 Cl in six M giant stars, finding an average value of 35 Cl 37 Cl = 2.66 ± 0.58. The molecule is expected to be found in low quantities on Jupiter's atmosphere (Teanby et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

ExoMol photodissociation cross sections I: HCl and HF

Pezzella,

Tennyson,

Yurchenko

2022

Preprint

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Photon initiated chemistry, i.e. the interaction of light with chemical species, is a key factor in the evolution of the atmosphere of exoplanets. For planets orbiting stars in UV-rich environments, photodissociation induced by high energy photons dominates the atmosphere composition and dynamics. The rate of photodissociation can be highly dependent on atmospheric temperature, as increased temperature leads to increased population of vibrational excited states and the consequent lowering of the photodissociation threshold. This paper inaugurates a new series of papers presenting computed temperature-dependent photodissociation cross sections with rates generated for different stellar fields. Cross sections calculations are performed by solving the time-independent Schrödinger equation for each electronic state involved in the process. Here photodissociation cross sections for hydrogen chloride and hydrogen fluoride are computed for a grid of 34 temperatures between 0 and 10 000 K. Use of different radiation fields shows that for the Sun and cooler stars the photodissociation rate can increase exponentially for molecular temperatures above 1000 K; conversely the photodissociation rates in UV rich fields instead are almost insensitive to the temperature of the molecule. Furthermore, these rates show extreme sensitivity to the radiation model used for cool stars, suggesting that further work on these may be required. The provision of an ExoMol database of cross sections is discussed.

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Chlorine Isotope Ratios in M Giants

Cited by 11 publications

References 55 publications

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

ATOMIUM: halide molecules around the S-type AGB star W Aquilae

The Galactic Chemical Evolution of Chlorine

ExoMol photodissociation cross sections I: HCl and HF

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