ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

McDonald, Iain; Zijlstra, A. A.; Lagadec, E.; Sloan, G. C.; Boyer, Martha L.; Matsuura, M.; Smith, Rowan J.; Smith, C. L.; Yates, J.; Loon, Jacco Th. van; Jones, O. C.; Ramstedt, S.; Avison, A.; Justtanont, K.; Olofsson, H.; Blommaert, J. A. D. L.; Goldman, S. R.; Groenewegen, M. A. T.

doi:10.1093/mnras/stv1968

Cited by 16 publications

(7 citation statements)

References 110 publications

(164 reference statements)

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“…Mauron et al (2013) have shown, using dust-scattered light, that there is a steep gradient in the strength of the interstellar radiation field with Galactic radius, and the distribution of OB associations causes substantial local variations. In lower-metallicity and/or extragalactic environments, the interstellar UV field may be very different (e.g., McDonald et al 2015). The results on the circumstellar CO chemistry of Mamon et al (1988) are frequently used in CO line radiative transfer modelling, but recent studies suggest that these may have to be revised (Li et al 2014(Li et al , 2016.…”

Section: Molecular Line Emissionmentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

446

376

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As low-and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newlyformed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angularresolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their windforming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angularresolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building B Susanne Höfner

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Section: Molecular Line Emissionmentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

446

376

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“…Mamon et al 1988). McDonald et al (2015) estimated that the ISRF at V3 was ∼9× stronger than in the Solar Neighbourhood, with a factor ∼3 uncertainty, matching this order-of-magnitude deficit in CO line flux. The same paper presented a model of CO dissociation around V1, which is expected to have an ISRF ∼5× stronger than V3.…”

Section: Observations and Resultsmentioning

confidence: 76%

“…The ISRF: McDonald et al (2015) constrained the mass-loss rate of V3 to be ∼1.2-3.5 × 10 −7 M ⊙ yr −1 . Galactic stars with similar mass-loss rates, luminosity and pulsation properties would (at 4.5 kpc distance) have CO J=3-2 flux densities of nearly 1 Jy km s −1 (Table 1, data from Schöier et al (2013); see also De Beck et al (2010); McDonald et al (2018)).…”

Section: Observations and Resultsmentioning

confidence: 99%

“…Previous observations of AGB stars in 47 Tuc with the Atacama Large Millimeter Array (ALMA) could not detect the CO J=2-1 transition. McDonald et al (2015) argued that was due to rapid photo-dissociation of the CO envelope by a harsh interstellar radiation field (ISRF). McDonald & Zijlstra (2015a) showed this field could be strong enough to ionise any intra-cluster medium (ICM) and boil it off the cluster.…”

Section: Introductionmentioning

confidence: 99%

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Circumstellar CO in metal-poor stellar winds: the highly irradiated globular cluster star 47 Tucanae V3

McDonald

Boyer

Groenewegen

et al. 2019

Monthly Notices of the Royal Astronomical Society: Letters

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We report the first detection of circumstellar CO in a globular cluster. Observations with ALMA have detected the CO J=3-2 and SiO v=1 J=8-7 transitions at 345 and 344 GHz, respectively, around V3 in 47 Tucanae (NGC 104; [Fe/H] = -0.72 dex), a star on the asymptotic giant branch. The CO line is detected at 7σ at a rest velocity v LSR = -40.6 km s −1 and expansion velocity of 3.2 ± ∼0.4 km s −1 . The brighter, asymmetric SiO line may indicate a circumstellar maser. The stellar wind is slow compared to similar Galactic stars, but the dust opacity remains similar to Galactic comparisons. We suggest that the mass-loss rate is set by the levitation of material into the circumstellar environment by pulsations, but that the terminal wind-expansion velocity is determined by radiation pressure on the dust: a pulsationenhanced dust-driven wind. We suggest the metal-poor nature of the star decreases the grain size, slowing the wind and increasing its density and opacity. Metallic alloys at high altitudes above the photosphere could also provide an opacity increase. The CO line is weaker than expected from Galactic AGB stars, but its strength confirms a model that includes CO dissociation by the strong interstellar radiation field present inside globular clusters.

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“…Dust is observed around luminous, metal-poor stars in both nearby dwarf galaxies (e.g. Matsuura et al 2007;Boyer et al 2009aBoyer et al , 2015bSloan et al 2012;McDonald et al 2013;Jones et al 2018;Goldman et al 2019a) and many globular clusters (van Loon et al 2006;Lebzelter et al 2006;McDonald et al 2009;Boyer et al 2009bBoyer et al , 2010Sloan et al 2010;McDonald et al 2011a,c). So far, there has been no clear observational evidence that dust production by oxygen-rich stars 3 is any less efficient at low metallicities Goldman et al 2019b) nor, conversely, any more efficient at super-solar metallicities (van Loon et al 2008).…”

Section: Mass Loss From Metal-poor Starsmentioning

confidence: 99%

Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae

McDonald,

Uttenthaler,

Zijlstra

et al. 2019

Preprint

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We report the first detection of CO J = 3 → 2 around a truly metal-poor evolved star. RU Vulpeculae is modelled to have T eff ≈ 3620 K, L ≈ 3128 ± 516 L ⊙ , log(g) = 0.0 ± 0.2 dex and [Fe/H] = -1.3 to -1.0 dex, and is modelled to have recently undergone a thermal pulse. Its infrared flux has approximately doubled over 35 years. ALMA observations show the 3→2 line is narrow (half-width ∼1.8-3.5 km s −1 ). The 2→1 line is much weaker: it is not confidently detected. Spectral-energy-distribution fitting indicates very little circumstellar absorption, despite its substantial mid-infrared emission. A VISIR mid-infrared spectrum shows features typical of previously observed metal-poor stars, dominated by a substantial infrared excess but with weak silicate and (possibly) Al 2 O 3 emission. A lack of resolved emission, combined with weak 2→1 emission, indicates the dense circumstellar material is truncated at large radii. We suggest that rapid dust condensation is occurring, but with an aspherical geometry (e.g., a disc or clumps) that does not obscure the star. We compare with T UMi, a similar star which is currently losing its dust.

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ALMA reveals sunburn: CO dissociation around AGB stars in the globular cluster 47 Tucanae

Cited by 16 publications

References 110 publications

Mass loss of stars on the asymptotic giant branch

Mass loss of stars on the asymptotic giant branch

Circumstellar CO in metal-poor stellar winds: the highly irradiated globular cluster star 47 Tucanae V3

Circumstellar CO J = 3-2 detected around the evolving metal-poor ([Fe/H] ~ -1.15 dex) AGB star RU Vulpeculae

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