Is the semi‐regular variable RU Vulpeculae undergoing a helium‐shell flash?

Uttenthaler, S.; Greimel, R.; Templeton, Matthew R.

doi:10.1002/asna.201512296

Cited by 9 publications

(20 citation statements)

References 28 publications

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“…We can therefore simply invert the parallax to provide d = ̟ −1 = 1851 +204 −184 pc. Despite potential issues with both methods, the dis-tances from the pre-decline pulsation period (2070 ± 130 pc; Section 2.1.1; Uttenthaler et al 2016) and parallax (Gaia) agree within uncertainties, confirming RU Vul as a fundamental-mode pulsator (sequence C in, e.g., Wood (2015)). In the following, we adopt a fixed distance of d = 2000 ± 165 pc, based on the combination of pulsation and parallax data, which offer two independent distance estimates.…”

Section: The Distance To Ru Vulmentioning

confidence: 76%

“…Among the literature observations of possible halo giants, one stands out: RU Vulpeculae. Uttenthaler et al (2016) show RU Vul to be an oxygen-rich giant with a metallicity of [Fe/H] ≈ -1.6 dex, and identify that it is undergoing the initial phases of a thermal pulse. RU Vul has a very substantial infrared excess (K s − [22] = 3.295 mag; Cutri et al 2013), making it unusually dusty compared to Galactic (solar-metallicity) stars (K s − [22] ∼ 2 mag for the bulk of stars, i.e.…”

Section: Identifying New Targetsmentioning

confidence: 87%

“…Data from the American Association of Variable Star Observers (AAVSO) 5 from the 1930s onwards shows periodic variability between visual magnitudes of ∼9.0 and ∼11.5. The period begins to decline around 1955 towards today's value of ∼108 days (Richards et al 2012;Uttenthaler et al 2016). A marked brightening of photometric minimum to 10 th magnitude occurred around 1965 (the maximum did not change substantially), upon which the pulsation amplitude decreased to today's V-band semiamplitude of ∼0.39 mag.…”

Section: Discovery Infrared Brightening and Thermal Pulsesmentioning

confidence: 94%

“…1956 (cf., the start of the period decline around 1955) and that, prior to this, RU Vul may have been an unremarkable star in terms of its dust properties (this concept is discussed further in Sections 5.3 and 5.5). Uttenthaler et al (2016) interpret the period decline as the start of a thermal pulse cycle. Here, runaway helium burning shuts off hydrogen burning, causing the star to initially shrink, until the energy from the detonation reaches the stellar surface.…”

Section: Discovery Infrared Brightening and Thermal Pulsesmentioning

confidence: 99%

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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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Section: The Distance To Ru Vulmentioning

confidence: 76%

Section: Identifying New Targetsmentioning

confidence: 87%

Section: Discovery Infrared Brightening and Thermal Pulsesmentioning

confidence: 94%

Section: Discovery Infrared Brightening and Thermal Pulsesmentioning

confidence: 99%

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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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“…For anomalies consistent with the AGB, the variability may be explained by thermal pulsations, where significant mass-losses are expected (Iben 1999;Templeton et al 2005;Rosenfield et al 2014Rosenfield et al , 2016. Thermal pulsating AGB stars have been observed with changing periods, which could lead to a semi-regular light curve (Uttenthaler et al 2016;Neilson et al 2016). We remark that spectroscopic follow-up, specifically to measure carbon and s-process elemental abundances (Stancliffe et al 2004), would be beneficial to confirm whether these anomalies are actually in the thermal pulsating AGB phase.…”

Section: Understanding the Physical Origins Of The Anomaliesmentioning

confidence: 99%

Searching for Anomalies in the ZTF Catalog of Periodic Variable Stars

Chan,

Villar,

Cheung

et al. 2021

Preprint

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Periodic variables illuminate the physical processes of stars throughout their lifetime. Wide-field surveys continue to increase our discovery rates of periodic variable stars. Automated approaches are essential to identify interesting periodic variable stars for multi-wavelength and spectroscopic followup. Here, we present a novel unsupervised machine learning approach to hunt for anomalous periodic variables using phase-folded light curves presented in the Zwicky Transient Facility Catalogue of Periodic Variable Stars by Chen et al. (2020). We use a convolutional variational autoencoder to learn a low dimensional latent representation, and we search for anomalies within this latent dimension via an isolation forest. We identify anomalies with irregular variability. Most of the top anomalies are likely highly variable Red Giants or Asymptotic Giant Branch stars concentrated in the Milky Way galactic disk; a fraction of the identified anomalies are more consistent with Young Stellar Objects. Detailed spectroscopic follow-up observations are encouraged to reveal the nature of these anomalies.

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Meandering periods and asymmetries in light curves of Miras: Observational evidence for low mass-loss rates

Uttenthaler

2023

A&A

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Context. Some Miras (long-period variables in late evolutionary stages) have meandering pulsation periods and light-curve asymmetries, the causes of which are still unclear. Aims. We aim to better understand the origin of meandering periods and light-curve asymmetries by investigating a sample of Miras in the solar neighbourhood. We characterised this group of stars and related their variability characteristics to other stellar parameters. Methods. We analysed observations from several databases to obtain light curves with maximum time span and temporal coverage for a sample of 548 Miras. We determined their pulsation-period evolution over a time span of many decades, searched for changes in the periods, and determined the amplitude of the period change. We also analysed the Fourier spectra with respect to possible secondary frequency maxima. The sample was divided into two groups with respect to the presence of light-curve asymmetries (‘bumps’). Infrared colours and indicators of the third dredge-up were collected to study the mass loss and deep mixing properties of the stars of our sample. Results. Our analysis reveals one new star, T Lyn, with a continuously changing period. The group of Miras with meandering period changes is exclusively made up of M-type stars. The Fourier spectra of the meandering-period Miras have no prominent additional peaks, suggesting that additional pulsation modes are not the cause of the meandering periods. We confirm that light-curve bumps are more common among S and C Miras and show, for the first time, that Miras with such bumps have lower mass-loss rates than those with regular, symmetric light curves. Also, Miras with meandering period changes have relatively little mass loss. Conclusions. We conclude that Miras with strongly changing periods (including meandering periods) or asymmetries in their light curves have relatively low dust mass-loss rates. Meandering period changes and light-curve asymmetries could be connected to He-shell flashes and third dredge-up episodes.

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Is the semi‐regular variable RU Vulpeculae undergoing a helium‐shell flash?

Cited by 9 publications

References 28 publications

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

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

Searching for Anomalies in the ZTF Catalog of Periodic Variable Stars

Meandering periods and asymmetries in light curves of Miras: Observational evidence for low mass-loss rates

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