Discovery of post-mass-transfer helium-burning red giants using asteroseismology

Li, Yaguang; Bedding, Timothy R.; Murphy, Simon J.; Stello, Dennis; Chen, Yifan; Huber, Daniel; Joyce, Meridith; Marks, Dion; Zhang, Xianfei; Bi, Shaolan; Colman, Isabel L.; Hayden, Michael R.; Hey, Daniel R.; Li, Gang; Montet, Benjamin T.; Sharma, Sanjib; Wu, Yaqian

doi:10.48550/arxiv.2204.06203

Cited by 3 publications

(19 citation statements)

References 117 publications

(154 reference statements)

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“…While mass loss in some models might explain masses below 0.8 M at the red clump, explaining masses of 0.6 M might require further understanding of mass loss. One of the stars studied here was already reported by Li et al (2022) as a stripped giant from a binary companion, but we find it to be RV constant in this study.…”

Section: Discussioncontrasting

confidence: 45%

“…While some stars might be on the horizontal branch, others have even lower masses. Very recently, Li et al (2022) has reported the existence of these stars in APOKASC, and we discuss them more below and in the next section.…”

Section: Mass Distributions and Evolutionary Stagementioning

confidence: 96%

“…Very recently, Li et al (2022) published the discovery of about 40 red giant stars that have only partially transferred their envelopes; therefore they are not hot sub-luminous stars of spectral type B (sdB) but simply very low mass giant stars. Their study is based on APOKASC, and Y19 is one of the low-mass red giants they uncovered.…”

Section: Under-massive Starsmentioning

confidence: 99%

“…Their study is based on APOKASC, and Y19 is one of the low-mass red giants they uncovered. Li et al (2022) have ran stellar evolutionary models with a progenitor mass of 1.5 M that lost different amounts of mass due to binary stripping. They were unable to reproduce these masses with standard evolution without binary interaction, even when including mass loss in their models.…”

Section: Under-massive Starsmentioning

confidence: 99%

“…Its [N/Fe] abundance is slightly enhanced for its metallicity, and very enhanced for its mass. Li et al (2022) has ran models for this star which include stripping from binary interaction but Y19 is not a binary now. It is possible that its companion, after gaining mass, exploded as a SNIa, fully disrupting the white dwarf.…”

Section: Individual Casesmentioning

confidence: 99%

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Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars

Jofre¹,

Jorissen²,

Aguilera-Gomez³

et al. 2022

Preprint

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Context. Ageing stars for reconstructing the history of the Milky Way remains one of the most difficult tasks in astrophysics. This involves knowing when it is safe to relate the stellar mass with its age and when it is not. The young α−rich (YAR) stars present such a case in which we are still not sure about their ages because they are relatively massive, implying young ages, but their abundances are α−enhanced, which implies old ages. Aims. We report the results from new observations from a long-term radial velocity monitoring campaign complemented with high resolution spectroscopy, as well as new astrometry and seismology of a sample of 41 red giants from the third version of APOKASC (Pinsonneault et al. in prep), which includes YAR stars. The aim is to better characterize the YAR stars in terms of binarity fraction, mass, abundance trends and kinematic properties. Methods. The radial velocities of HERMES, APOGEE and Gaia were combined to determine the binary fraction among YAR stars. In combination with their mass estimate, their evolutionary status, chemical composition and kinematic properties, it allows to better constrain the nature of these objects. Results. We find that the frequency of binaries among over-massive stars is not significantly different than that of the other stars in our sample, but that the most massive YAR stars are indeed single, which has been predicted by population synthesis models. Studying their [C/N], [C/Fe] and [N/Fe] trends with mass, many over-massive stars do not follow the APOKASC stars, favouring the scenario that most of them are product of mass transfer. Our sample further includes two under-massive stars, with sufficiently low masses so that these stars could not have reached the red giant phase without significant mass loss. Both over-massive and under-massive stars might show some anomalous APOGEE abundances such as N, Na, P, K and Cr, although higher resolution optical spectroscopy might be needed to confirm these findings. Conclusions. Considering the significant fraction of stars that are formed in pairs and the variety of ways that make mass transfer possible, the diversity in properties in terms of binarity and chemistry of the over-massive and under-massive stars studied here implies that it is not safe to directly relate the mass of the YAR stars with age and that most of these objects are likely not young.

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Section: Discussioncontrasting

confidence: 45%

Section: Mass Distributions and Evolutionary Stagementioning

confidence: 96%

Section: Under-massive Starsmentioning

confidence: 99%

Section: Under-massive Starsmentioning

confidence: 99%

Section: Individual Casesmentioning

confidence: 99%

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Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars

Jofre¹,

Jorissen²,

Aguilera-Gomez³

et al. 2022

Preprint

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Cannibals in the thick disk

Jofré

Jorissen

Aguilera-Gómez

et al. 2023

A&A

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Context. Determining ages of stars for reconstructing the history of the Milky Way remains one of the most difficult tasks in astrophysics. This involves knowing when it is possible to relate the stellar mass with its age and when it is not. The young α−rich (YAR) stars present such a case in which we are still not sure about their ages because they are relatively massive, implying young ages, but their abundances are α−enhanced, which implies old ages. Aims. We report the results from new observations from a long-term radial-velocity-monitoring campaign complemented with highresolution spectroscopy, as well as new astrometry and seismology of a sample of 41 red giants from the third version of APOKASC, which includes YAR stars. The aim is to better characterize the YAR stars in terms of binarity, mass, abundance trends, and kinematic properties. Methods. The radial velocities of HERMES, APOGEE, and Gaia were combined to determine the binary fraction among YAR stars. In combination with their mass estimate, evolutionary status, chemical composition, and kinematic properties, it allowed us to better constrain the nature of these objects. Results. We found that stars with M < 1M ⊙ were all single, whereas stars with M > 1M ⊙ could be either single or binary. This is in agreement with theoretical predictions of population synthesis models. Studying their [C/N], [C/Fe], and [N/Fe], trends with mass, it became clear that many YAR stars do not follow the APOKASC stars, favoring the scenario that most of them are the product of mass transfer. Our sample further includes two likely undermassive stars, that is to say of such as low mass that they cannot have reached the red clump within the age of the Universe, unless their low mass is the signature of mass loss in previous evolutionary phases. These stars do not show signatures of currently being binaries. Both YAR and undermassive stars might show some anomalous APOGEE abundances for the elements N, Na, P, K, and Cr; although, higher-resolution optical spectroscopy might be needed to confirm these findings. Conclusions. Considering the significant fraction of stars that are formed in pairs and the variety of ways that makes mass transfer possible, the diversity in properties in terms of binarity, and chemistry of the YAR and undermassive stars studied here implies that most of these objects are likely not young.

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Shell helium-burning hot subdwarf B stars as candidates for blue large-amplitude pulsators

Xiong

Casagrande

Chen

et al. 2022

A&A

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Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2-0.4 mag in optical bands, and their rates of period changes are on the order of 10 −7 yr −1 (both positive and negativhe). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around 0.3M ⊙ , or core-helium-burning stars in the range of ∼ 0.7−1.1M ⊙ . In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of ∼ 0.45 − 0.5M ⊙ . Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available.

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Discovery of post-mass-transfer helium-burning red giants using asteroseismology

Cited by 3 publications

References 117 publications

Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars

Cannibals in the thick disk II -- Radial-velocity monitoring of the young alpha-rich stars

Cannibals in the thick disk

Shell helium-burning hot subdwarf B stars as candidates for blue large-amplitude pulsators

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