Variability and evolution in various classes of post‐AGB stars

Şahìn, T.; Jeffery, C. S.

doi:10.1002/asna.200710808

Cited by 2 publications

(2 citation statements)

References 27 publications

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“…The found velocity variability based on the Fe II emission (2) can be considered an indication on the possible binarity of the star. Note here the results of Şahin and Jeffery [60], who, having analyzed the variability of photometric data for V534 Lyr did not find an explicit period and assumed that the variations can be short-period. There are currently no reliable photometric and spectral data required for the study and determination of the variability parameters of brightness and spectrum.…”

Section: Discussionmentioning

confidence: 86%

On the Evolutionary State of High-Latitude Variable V534 Lyr

2018

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Based on the high resolution spectral monitoring conducted at the 6-m BTA telescope, we study the optical spectrum of the high-latitude variable V534 Lyr. Heliocentric radial velocities V r corresponding to the positions of all metal absorption components, as well as the Na I D and Hα lines were measured during all the observational dates. The analysis of the velocity field examining the lines of various nature revealed a low-amplitude variability of V r based on the lines with a high excitation potential, which are formed in deep layers of the stellar atmosphere, and allowed to estimate the systemic velocity of V sys ≈ −125 km s −1 (V lsr ≈ −105 km s −1 ). The distance estimate of d ≈ 6 kpc for the star leads us to its absolute magnitude of M V ≈ −5. m 3, what corresponds to the MK spectral classification. The previously undetected for this star spectral phenomenon was revealed: at certain times a splitting of the profiles of low-excited absorptions is observed, reaching ∆V r = 20-50 km s −1 . A combination of the parameters: reduced metallicity [Met/H] ⊙ = −0.28, increased nitrogen abundance [N/Fe] = +1.10, large spatial velocity, high luminosity, a strong variability of the emission-absorption profiles of H I lines, splitting of metal absorptions at different times of observations and the variability of the velocity field in the atmosphere allow us to classify V534 Lyr as a pulsating star near the HB and belonging to the thick disk of our Galaxy.

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Section: Discussionmentioning

confidence: 86%

On the Evolutionary State of High-Latitude Variable V534 Lyr

2018

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“…They can often be ascribed to eclipses, trivial episodes of obscuration (e.g., by dusty wind material), or to pulsations (cf. Şahin & Jeffery 2007;Hrivnak et al 2022). These cases do not require any activation of an additional energy source.…”

Section: Nature Of the Photometric Risementioning

confidence: 99%

A radical transition in the post-main-sequence system U Equulei

Kamiński,

Schmidt,

Djupvik

et al. 2024

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U Equ is an unusual maser-hosting infrared source discovered in the 1990s. It was tentatively classified as a post-asymptotic giant branch (post-AGB) star with a unique optical spectrum displaying rare emission and absorption features from molecular gas at a temperature of about 500\,K. In 2022, we serendipitously discovered that its optical spectrum had drastically changed since the last observations in the 1990s. We aim to characterize the drastic change in the spectrum and analyze the photometric behavior of the object since 1989. Optical high-resolution spectra of U\,Equ from the Southern African Large Telescope were supplemented by archival data and near-infrared photometry from the Nordic Optical Telescope. New spectral line observations with the Effelsberg 100\,m radio telescope and Atacam Large Millimeter Array are presented. Radiative transfer modeling of multiple epoch spectral energy distributions was performed. No circumstellar molecular features are present in the contemporary optical spectra of U\,Equ. Nonphotospheric absorption and emission from neutral and ionized species dominate the current spectrum. Some of the observed features indicate an outflow with a projected terminal velocity of 215\ Broad H K lines of Ca II indicate a photosphere of spectral type F or similar. For the first time, we find SiO $J=$1--0 varv =1 maser emission in U\,Equ. Our collected photometric measurements show that the source has monotonically increased its optical and near-infrared fluxes since about the beginning of this century and continues to do so. The current rise in the optical regime is about 1 mag. Spectral energy distributions at different epochs show dusty circumstellar material that is very likely arranged in a highly inclined disk. Adopting a distance of 4\,kpc, informed by the Gaia parallax of U\,Equ, we find that the source luminosity is about 10$^4$ sun $. This luminosity has likely increased by a factor of a few in the last decades, which is most probably related to the drastic change in the optical circumstellar spectrum of the object. The object has changed considerably in the past three decades, either due to geometrical reconfiguration of the circumstellar medium, evolutionary changes in the central star, or owing to an accretion event that started very recently in the system. Observationally, U\,Equ appears to resemble category\,0 of disk-hosting post-AGB stars reported previously, especially the post-common-envelope binary HD\,101584. It is uncertain whether the drastic spectral change and the associated optical and mid-infrared rise in brightness witnessed in U\,Equ are common in post-AGB stars, but this radical change may be related to the real-time onset of the evolution of the system into a planetary nebula. We find that the post-AGB star V576\,Car has undergone a similar transformation as U\,Equ in the past few decades, which means that the phenomenon is not extremely rare.

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Variability and evolution in various classes of post‐AGB stars

Cited by 2 publications

References 27 publications

On the Evolutionary State of High-Latitude Variable V534 Lyr

On the Evolutionary State of High-Latitude Variable V534 Lyr

A radical transition in the post-main-sequence system U Equulei

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