POST ASYMPTOTIC GIANT BRANCH BIPOLAR REFLECTION NEBULAE: RESULT OF DYNAMICAL EJECTION OR SELECTIVE ILLUMINATION?

ABSTRACT We introduce a new distance determination method using carbon-rich asymptotic giant branch stars (CS) as standard candles and the Large and Small Magellanic Clouds (LMC and SMC) as the fundamental calibrators. We select the samples of CS from the ((J − Ks)0, J0) colour–magnitude diagrams, as, in this combination of filters, CS are bright and easy to identify. We fit the CS J-band luminosity functions using a Lorentzian distribution modified to allow the distribution to be asymmetric. We use the parameters of the best-fitting distribution to determine if the CS luminosity function of a given galaxy resembles that of the LMC or SMC. Based on this resemblance, we use either the LMC or SMC as the calibrator and estimate the distance to the given galaxy using the median J magnitude ($\overline{J}$) of the CS samples. We apply this new method to the two Local Group galaxies NGC 6822 and IC 1613. We find that NGC 6822 has an ‘LMC-like’ CS luminosity function, while IC 1613 is more ‘SMC-like’. Using the values for the median absolute J magnitude for the LMC and SMC found in Paper I we find a distance modulus of μ0 = 23.54 ± 0.03 (stat) for NGC 6822 and μ0 = 24.34 ± 0.05 (stat) for IC 1613.

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Asteroseismology of luminous red giants with Kepler. II. Dependence of mass loss on pulsations and radiation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3970 ◽

2020 ◽

Author(s):

Jie Yu ◽

Saskia Hekker ◽

Timothy R Bedding ◽

Dennis Stello ◽

Daniel Huber ◽

...

Keyword(s):

Mass Loss ◽

Mass Loss Rate ◽

Asymptotic Giant Branch ◽

Red Giants ◽

Asymptotic Giant Branch Stars ◽

Chemical Enrichment ◽

Dust Mass ◽

Red Giant ◽

The Masses ◽

Loss Rates

Abstract Mass loss by red giants is an important process to understand the final stages of stellar evolution and the chemical enrichment of the interstellar medium. Mass-loss rates are thought to be controlled by pulsation-enhanced dust-driven outflows. Here we investigate the relationships between mass loss, pulsations, and radiation, using 3213 luminous Kepler red giants and 135000 ASAS–SN semiregulars and Miras. Mass-loss rates are traced by infrared colours using 2MASS and WISE and by observed-to-model WISE fluxes, and are also estimated using dust mass-loss rates from literature assuming a typical gas-to-dust mass ratio of 400. To specify the pulsations, we extract the period and height of the highest peak in the power spectrum of oscillation. Absolute magnitudes are obtained from the 2MASS Ks band and the Gaia DR2 parallaxes. Our results follow. (i) Substantial mass loss sets in at pulsation periods above ∼60 and ∼100 days, corresponding to Asymptotic-Giant-Branch stars at the base of the period-luminosity sequences C′ and C. (ii) The mass-loss rate starts to rapidly increase in semiregulars for which the luminosity is just above the red-giant-branch tip and gradually plateaus to a level similar to that of Miras. (iii) The mass-loss rates in Miras do not depend on luminosity, consistent with pulsation-enhanced dust-driven winds. (iv) The accumulated mass loss on the Red Giant Branch consistent with asteroseismic predictions reduces the masses of red-clump stars by 6.3%, less than the typical uncertainty on their asteroseismic masses. Thus mass loss is currently not a limitation of stellar age estimates for galactic archaeology studies.

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WD 1856 b: a close giant planet around a white dwarf that could have survived a common envelope phase

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3703 ◽

2020 ◽

Vol 501 (1) ◽

pp. 676-682

Author(s):

F Lagos ◽

M R Schreiber ◽

M Zorotovic ◽

B T Gänsicke ◽

M P Ronco ◽

...

Keyword(s):

White Dwarf ◽

Evolutionary History ◽

Giant Planet ◽

Asymptotic Giant Branch ◽

Orbital Energy ◽

Current Position ◽

Recombination Energy ◽

Additional Energy ◽

Common Envelope ◽

History Of

ABSTRACT The discovery of a giant planet candidate orbiting the white dwarf WD 1856+534 with an orbital period of 1.4 d poses the questions of how the planet reached its current position. We here reconstruct the evolutionary history of the system assuming common envelope evolution as the main mechanism that brought the planet to its current position. We find that common envelope evolution can explain the present configuration if it was initiated when the host star was on the asymptotic giant branch, the separation of the planet at the onset of mass transfer was in the range 1.69–2.35 au, and if in addition to the orbital energy of the surviving planet either recombination energy stored in the envelope or another source of additional energy contributed to expelling the envelope. We also discuss the evolution of the planet prior to and following common envelope evolution. Finally, we find that if the system formed through common envelope evolution, its total age is in agreement with its membership to the Galactic thin disc. We therefore conclude that common envelope evolution is at least as likely as alternative formation scenarios previously suggested such as planet–planet scattering or Kozai–Lidov oscillations.

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Finite Temperature Behavior of Carbon Atom Doped Silicon Clusters: Depressed Thermal Stabilities, Co-existing isomers, Reversible Dynamical Pathways and Fragmentation Channels

New Journal of Chemistry ◽

10.1039/d0nj04515b ◽

2021 ◽

Author(s):

Krati Joshi ◽

Ashakiran Maibam ◽

Sailaja Krishnamurty

Keyword(s):

Silicon Carbide ◽

Carbon Atom ◽

Finite Temperature ◽

Asymptotic Giant Branch ◽

Temperature Behavior ◽

Asymptotic Giant Branch Stars ◽

Silicon Clusters ◽

Thermal Stabilities ◽

Doped Silicon ◽

Giant Branch Stars

Silicon carbide clusters are significant due to their predominant occurrence in meteoric star dust, particularly in carbon rich asymptotic giant branch stars. Of late, they have also been recognized as...

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Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽

10.3390/universe7070233 ◽

2021 ◽

Vol 7 (7) ◽

pp. 233

Author(s):

Ambra Nanni ◽

Sergio Cristallo ◽

Jacco Th. van Loon ◽

Martin A. T. Groenewegen

Keyword(s):

Wind Speed ◽

Galactic Halo ◽

Magellanic Clouds ◽

Asymptotic Giant Branch ◽

Agb Stars ◽

Circumstellar Envelopes ◽

Chemical Enrichment ◽

Wide Range ◽

The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

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New models for the rapid evolution of the central star of the Stingray Nebula

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab890 ◽

2021 ◽

Author(s):

T M Lawlor

Keyword(s):

Mass Loss ◽

Stellar Evolution ◽

Planetary Nebula ◽

Rapid Evolution ◽

Central Star ◽

Asymptotic Giant Branch ◽

Initial Mass ◽

Thermal Pulse ◽

The Past ◽

New Models

Abstract We present stellar evolution calculations from the Asymptotic Giant Branch (AGB) to the Planetary Nebula (PN) phase for models of initial mass 1.2 M⊙ and 2.0 M⊙ that experience a Late Thermal Pulse (LTP), a helium shell flash that occurs following the AGB and causes a rapid looping evolution between the AGB and PN phase. We use these models to make comparisons to the central star of the Stingray Nebula, V839 Ara (SAO 244567). The central star has been observed to be rapidly evolving (heating) over the last 50 to 60 years and rapidly dimming over the past 20–30 years. It has been reported to belong to the youngest known planetary nebula, now rapidly fading in brightness. In this paper we show that the observed timescales, sudden dimming, and increasing Log(g), can all be explained by LTP models of a specific variety. We provide a possible explanation for the nebular ionization, the 1980’s sudden mass loss episode, the sudden decline in mass loss, and the nebular recombination and fading.

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Rubidium in Barium Stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3888 ◽

2020 ◽

Author(s):

M P Roriz ◽

M Lugaro ◽

C B Pereira ◽

N A Drake ◽

S Junqueira ◽

...

Keyword(s):

Neutron Source ◽

Slow Neutron ◽

Asymptotic Giant Branch ◽

Neutron Density ◽

Data Sets ◽

Agb Stars ◽

Branching Points ◽

Theoretical Predictions ◽

Low Mass ◽

Chemically Peculiar Stars

Abstract Barium (Ba) stars are chemically peculiar stars that display in their atmospheres the signature of the slow neutron-capture (the s-process) mechanism that occurs in asymptotic giant branch (AGB) stars, a main contributor to the cosmic abundances. The observed chemical peculiarity in these objects is not due to self-enrichment, but to mass transfer between the components of a binary system. The atmospheres of Ba stars are therefore excellent astrophysical laboratories providing strong constraints for the nucleosynthesis of the s-process in AGB stars. In particular, rubidium (Rb) is a key element for the s-process diagnostic because it is sensitive to the neutron density and therefore its abundance can reveal the main neutron source for the s-process in AGB stars. We present Rb abundances for a large sample of 180 Ba stars from high resolution spectra (R = 48000), and we compare the observed [Rb/Zr] ratios with theoretical predictions from AGB s-process nucleosynthesis models. The target Ba stars in this study display [Rb/Zr] <0, showing that Rb was not efficiently produced by the activation of branching points. Model predictions from the Monash and FRUITY data sets of low-mass (≲ 4 M⊙) AGB stars are able to cover the Rb abundances observed in the target Ba stars. These observations indicate that the 13C(α,n)16O reaction is the main neutron source of the s-process in the low-mass AGB companions of the observed Ba stars. We have not found in the present study candidate companion for IR/OH massive AGB stars.

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Are extreme asymptotic giant branch stars post-common envelope binaries?

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slaa204 ◽

2021 ◽

Vol 502 (1) ◽

pp. L35-L39

Author(s):

F Dell’Agli ◽

E Marini ◽

F D’Antona ◽

P Ventura ◽

M A T Groenewegen ◽

...

Keyword(s):

Large Fraction ◽

Carbon Star ◽

Large Magellanic Cloud ◽

Asymptotic Giant Branch ◽

Theoretical Modelling ◽

Binary Interaction ◽

Spectral Energy ◽

Small Subset ◽

Stellar Radius ◽

Common Envelope

ABSTRACT Modelling dust formation in single stars evolving through the carbon-star stage of the asymptotic giant branch (AGB) reproduces well the mid-infrared colours and magnitudes of most of the C-rich sources in the Large Magellanic Cloud (LMC), apart from a small subset of extremely red objects (EROs). An analysis of the spectral energy distributions of EROs suggests the presence of large quantities of dust, which demand gas densities in the outflow significantly higher than expected from theoretical modelling. We propose that binary interaction mechanisms that involve common envelope (CE) evolution could be a possible explanation for these peculiar stars; the CE phase is favoured by the rapid growth of the stellar radius occurring after C/O overcomes unity. Our modelling of the dust provides results consistent with the observations for mass-loss rates $\dot{M} \sim 5\times 10^{-4}\,{\rm M}_{\odot }$ yr−1, a lower limit to the rapid loss of the envelope experienced in the CE phase. We propose that EROs could possibly hide binaries with orbital periods of about days and are likely to be responsible for a large fraction of the dust production rate in galaxies.

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