Chlorine Abundances in Cool Stars

Maas, Z. G.; Pilachowski, Catherine A.; Hinkle, Kenneth H.

doi:10.3847/0004-6256/152/6/196

Cited by 14 publications

(24 citation statements)

References 64 publications

(82 reference statements)

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“…Adopting these temperatures, the column densities of Na 37 Cl needed to reproduce the observed Na 37 Cl ( v =0, J =26-25) profile are between ~2×10 14 and 5×10 14 cm −2 , comparable to the column densities of NaCl found in VY CMa and IK Tau (Milam et al 2007). While our crude estimate has large errorbars, this agreement suggests that our order-of-magnitude value is roughly correct, since the 35 Cl/ 37 Cl isotope ratio is known to be low, about two, in intermediate-mass AGB stars (e.g., Maas et al 2016; Highberger et al 2003, and references therein).…”

Section: Discussionsupporting

confidence: 54%

Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH 231.8+4.2

Contreras

Alcolea

Castro-Carrizo

et al. 2018

A&A

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We present continuum and molecular line emission ALMA observations of OH 231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star. The high angular resolution (∼0·″2-0·″3) and sensitivity of our ALMA maps provide the most detailed and accurate description of the overall nebular structure and kinematics of this object to date. We have identified a number of outflow components previously unknown. Species studied in this work include 12CO, 13CO, CS, SO, SO2, QCS, SiO, SiS, H3O+, Na37Cl, and CH3OH. The molecules Na37Cl and CH3OH are first detections in OH 231.8+4.2, with CH3OH being also a first detection in an AGB star. Our ALMA maps bring to light the totally unexpected position of the mass-losing AGB star (QX Pup) relative to the large-scale outflow. QX Pup is enshrouded within a compact (≲60 AU) parcel of dust and gas (clump S) in expansion (Vexp~5-7 km s−1) that is displaced by ∼0·″6 to the south of the dense equatorial region (or waist) where the bipolar lobes join. Our SiO maps disclose a compact bipolar outflow that emerges from QX Pup’s vicinity. This outflow is oriented similarly to the large-scale nebula but the expansion velocities are about ten times lower (Vexp≲35km s−1). We deduce short kinematical ages for the SiO outflow, ranging from ~50-80 yr, in regions within ~150 AU, to ~400-500 yr at the lobe tips (~3500 AU). Adjacent to the SiO outflow, we identify a small-scale hourglass-shaped structure (mini-hourglass) that is probably made of compressed ambient material formed as the SiO outflow penetrates the dense, central regions of the nebula. The lobes and the equatorial waist of the mini-hourglass are both radially expanding with a constant velocity gradient (Vexp ∝ r). The mini-waist is characterized by extremely low velocities, down to ~1 km s−1 at ~150 AU, which tentatively suggest the presence of a stable structure. The spatio-kinematics of the large-scale, high-velocity lobes (HV lobes) and the dense equatorial waist (large waist) known from previous works are now precisely determined, indicating that both were shaped nearly simultaneously about ~800-900 yr ago. We report the discovery of two large (~8″×6″), faint bubble-like structures (fish bowls) surrounding the central parts of the nebula. These are relatively old structures although probably slightly (~100-200 yr) younger than the large waist and the HV lobes. We discuss the series of events that may have resulted in the complex array of nebular components found in OH 231.8+4.2 as well as the properties and locus of the central binary system. The presence of ≲80 yr bipolar ejections indicate that the collimated fast wind engine is still active at the core of this outstanding object.

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Section: Discussionsupporting

confidence: 54%

Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH 231.8+4.2

Contreras

Alcolea

Castro-Carrizo

et al. 2018

A&A

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“…Esteban et al (2015) and Henry et al (2004) found a weak trend towards decreasing Cl abundance with galactic radius, based on data from Hii regions and planetary nebulae (PNe). They also found very similar relations between Cl and O gradients with galactic radius, suggesting that the production of Cl and O are correlated (Maas et al 2016;Maas & Pilachowski 2021) and hence that Cl can be used as a tracer of metallicity. From a study of PNe, Delgado-Inglada et al (2015) found that Cl is a good indicator of metallicity in the progenitors of PNe (i.e., AGB stars).…”

Section: Chlorine Abundance and Isotopic Ratiomentioning

confidence: 80%

“…From a study of PNe, Delgado-Inglada et al (2015) found that Cl is a good indicator of metallicity in the progenitors of PNe (i.e., AGB stars). Hence, the comparison of an AGB Cl abundance with the solar abundance might indicate a higher or lower metallicity of the natal environment of the AGB star, without obfuscation from elements actively synthesised by AGB stars (which 35 Cl is not, based on the investigation of Maas et al 2016). However, the solar abundance of chlorine is very difficult to measure, for reasons discussed in detail by Maas et al (2016).…”

Section: Chlorine Abundance and Isotopic Ratiomentioning

confidence: 99%

“…Halogen-bearing molecules have not been extensively studied in the circumstellar envelopes of many AGB stars. Chlorine has been found to be a tracer of metallicity (Maas et al 2016) and fluorine is thought to be produced in AGB stars and dredged up to the surface of the star (Kobayashi et al 2020). By understanding the total abundance of Cl or F around AGB stars, we can better understand their metallicities or AGB-ages, respectively.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Similar to F, the photospheric Cl abundance can only be estimated from sunspot spectra since the HCl molecule requires cool temperatures; no atomic features of Cl are present in the solar spectrum. Recently, Maas et al (2016) revisited the previous HCl sunspot study of Hall & Noyes (1972) with improved molecular data and observations to obtain a 0.19 dex lower abundance: log Cl = 5.31 ± 0.12. Given the remaining model challenges, especially in finding a suitable model atmosphere for a sunspot of unknown T eff , we argue that the quoted uncertainty is likely overly optimistic, and we instead adopt ±0.20 dex.…”

Section: The Heavy Elements: Copper To Uraniummentioning

confidence: 99%

The chemical make-up of the Sun: A 2020 vision

Asplund

Amarsi

Grevesse

2021

A&A

332

270

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Context. The chemical composition of the Sun is a fundamental yardstick in astronomy, relative to which essentially all cosmic objects are referenced. As such, having accurate knowledge of the solar elemental abundances is crucial for an extremely broad range of topics. Aims. We reassess the solar abundances of all 83 long-lived elements, using highly realistic solar modelling and state-of-the-art spectroscopic analysis techniques coupled with the best available atomic data and observations. Methods. The basis for our solar spectroscopic analysis is a three-dimensional (3D) radiative-hydrodynamical model of the solar surface convection and atmosphere, which reproduces the full arsenal of key observational diagnostics. New complete and comprehensive 3D spectral line formation calculations taking into account of departures from local thermodynamic equilibrium (non-LTE) are presented for Na, Mg, K, Ca, and Fe using comprehensive model atoms with reliable radiative and collisional data. Our newly derived abundances for C, N, and O are based on a 3D non-LTE analysis of permitted and forbidden atomic lines as well as 3D LTE calculations for a total of 879 molecular transitions of CH, C2, CO, NH, CN, and OH. Previous 3D-based calculations for another 50 elements are re-evaluated based on updated atomic data, a stringent selection of lines, improved consideration of blends, and new non-LTE calculations available in the literature. For elements where spectroscopic determinations of the quiet Sun are not possible, the recommended solar abundances are revisited based on complementary methods, including helioseismology (He), solar wind data from the Genesis sample return mission (noble gases), sunspot observations (four elements), and measurements of the most primitive meteorites (15 elements). Results. Our new improved analysis confirms the relatively low solar abundances of C, N, and O obtained in our previous 3D-based studies: log ϵC = 8.46 ± 0.04, log ϵN = 7.83 ± 0.07, and log ϵO = 8.69 ± 0.04. Excellent agreement between all available atomic and molecular indicators is achieved for C and O, but for N the atomic lines imply a lower abundance than for the molecular transitions for unknown reasons. The revised solar abundances for the other elements also typically agree well with our previously recommended values, with only Li, F, Ne, Mg, Cl, Kr, Rb, Rh, Ba, W, Ir, and Pb differing by more than 0.05 dex. The here-advocated present-day photospheric metal mass fraction is only slightly higher than our previous value, mainly due to the revised Ne abundance from Genesis solar wind measurements: Xsurface = 0.7438 ± 0.0054, Ysurface = 0.2423 ± 0.0054, Zsurface = 0.0139 ± 0.0006, and Zsurface/Xsurface = 0.0187 ± 0.0009. Overall, the solar abundances agree well with those of CI chondritic meteorites, but we identify a correlation with condensation temperature such that moderately volatile elements are enhanced by ≈0.04 dex in the CI chondrites and refractory elements possibly depleted by ≈0.02 dex, conflicting with conventional wisdom of the past half-century. Instead, the solar chemical composition more closely resembles that of the fine-grained matrix of CM chondrites with the expected exception of the highly volatile elements. Conclusions. Updated present-day solar photospheric and proto-solar abundances are presented for 83 elements, including for all long-lived isotopes. The so-called solar modelling problem – a persistent discrepancy between helioseismology and solar interior models constructed with a low solar metallicity similar to that advocated here – remains intact with our revised solar abundances, suggesting shortcomings with the computed opacities and/or treatment of mixing below the convection zone in existing standard solar models. The uncovered trend between the solar and CI chondritic abundances with condensation temperature is not yet understood but is likely imprinted by planet formation, especially since a similar trend of opposite sign is observed between the Sun and solar twins.

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Chlorine Abundances in Cool Stars

Cited by 14 publications

References 64 publications

Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH 231.8+4.2

Through the magnifying glass: ALMA acute viewing of the intricate nebular architecture of OH 231.8+4.2

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

The chemical make-up of the Sun: A 2020 vision

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