A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

Montez, Rodolfo; Ramstedt, S.; Kastner, Joel H.; Vlemmings, Wouter; Sanchez, E.

doi:10.3847/1538-4357/aa704d

Cited by 44 publications

(49 citation statements)

References 41 publications

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“…Mid-IR excess in the spectrum of V CVn (Price et al 2010) and the 9.7 µm silicate feature also favour the existence of a dusty envelope (Olnon et al 1986;Simpson 1991). At the same time the star has quite low colour excess E(B − V ) = 0.04 (Montez et al 2017) which indicates that the envelope is not spherically symmetric.…”

Section: Discussionmentioning

confidence: 93%

The Circumstellar Envelope of the Semiregular Variable Star V CVn

et al. 2019

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V CVn is a semiregular variable star with a V -band amplitude of ≈ 2 mag. This star has an unusually high amplitude of polarimetric variability: up to 6 per cent. It also exhibits a prominent inverse correlation between the flux and the fraction of polarization and a substantial constancy of the angle of polarization. To figure out the nature of these features, we observed the object using the Differential Speckle Polarimetry at three bands centered on 550, 625 and 880 nm using the 2.5-m telescope of Sternberg Astronomical Institute. The observations were conducted on 20 dates distributed over three cycles of pulsation. We detected an asymmetric reflection nebula consisting of three regions and surrounding the star at the typical distance of 35 mas. The components of the nebula change their brightness with the same period as the star, but with significant and different phase shifts. We discuss several hypotheses that could explain this behavior.

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Section: Discussionmentioning

confidence: 93%

The Circumstellar Envelope of the Semiregular Variable Star V CVn

et al. 2019

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“…We observe UV emission not only in lines, but also in the continuum (Montez et al 2017). The nature of this emission is debated: it may be due to a hot companion (Ortiz & Guerrero 2016) or to heating in the chromosphere, perhaps due to dissipation of acoustic waves or to magnetic reconnections in stars with convective surfaces (Schrijver 1995).…”

Section: Continuum Emission and Variabilitymentioning

confidence: 88%

Impact of a companion and of chromospheric emission on the shape of chromosome maps for globular clusters

Martins

Morin

Charbonnel

et al. 2020

A&A

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Context. Globular clusters (GCs) host multiple populations of stars that are well-separated in a photometric diagram -the chromosome map -built from specific Hubble Space Telescope (HST) filters. Stars from different populations feature at various locations on this diagram due to peculiar chemical compositions. Stars of the first population, with field star-like abundances, sometimes show an unexpected extended distribution in the chromosome map. Aims. We aim to investigate the role of binaries and chromospheric emission on HST photometry of globular clusters' stars. We quantify their respective effects on the position of stars in the chromosome map, especially among the first population. Methods. We computed atmosphere models and synthetic spectra for stars of different chemical compositions, based on isochrones produced by stellar evolution calculations with abundance variations representative of first and second populations in globular clusters. From this we built synthetic chromosome maps for a mixture of stars of different chemical compositions. We subsequently replaced a fraction of stars with binaries, or stars with chromospheric emission, using synthetic spectroscopy. We studied how the position of stars is affected in the chromosome map. Results. Binaries can, in principle, explain the extension of the first population in the chromosome map. However, we find that given the binary fraction reported for globular clusters, the density of stars in the extended part is too small. Another difficulty of the binary explanation is that the shape of the distribution of the first population in the chromosome map is different in clusters with similar binary fractions. Also, the decrease of the binary fraction with radius is not mirrored in the shape of the chromosome map. Additionally, we find that the contribution of chromospheric emission lines to the HST photometry is too small to have an observable impact on the shape of the chromosome map. Continuum chromospheric emission has an effect qualitatively similar to binaries. Conclusions. We conclude that binaries do have an impact on the morphology of the chromosome map of globular clusters, but they are unlikely to explain entirely the shape of the extended distribution of the first population stars. Uncertainties in the properties of continuum chromospheric emission of stars in GCs prevent any quantitative conclusion. Therefore, the origin of the extended first population remains unexplained.

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“…This is also a complement, e.g., to searches for UV excesses as a binarity diagnostics (Sahai et al 2008), since there may be other explanations of such an excess (Montez et al 2017).…”

Section: Impacts Of Companions On Cse Morphologymentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

471

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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A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars

Cited by 44 publications

References 41 publications

The Circumstellar Envelope of the Semiregular Variable Star V CVn

The Circumstellar Envelope of the Semiregular Variable Star V CVn

Impact of a companion and of chromospheric emission on the shape of chromosome maps for globular clusters

Mass loss of stars on the asymptotic giant branch

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