Cannibals in the thick disk: the young<i>α</i>-rich stars as evolved blue stragglers

Jofré, P.; Jorissen, A.; Eck, S. Van; Izzard, Robert G.; Masseron, T.; Hawkins, Keith; Gilmore, G.; Paladini, C.; Escorza, A.; Blanco-Cuaresma, S.; Manick, R.

doi:10.1051/0004-6361/201629356

Cited by 93 publications

(89 citation statements)

References 68 publications

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“…Such stars found by Chiappini et al (2015) were primarily in the inner Galactic disk, and they invoked formation at the end of the Galactic bar; although this is inconsistent with KELT-21ʼs current circular orbit and location near the solar circle, as mentioned earlier it could still have formed in the inner Galaxy and experienced radial mixing to move it to its current location, although this would have needed to be rapid in order to move the star several kiloparsecs within the 1.6 Gyr since it formed. The planet orbiting KELT-21 also seems to be at odds with the other proposed explanation for young α-rich stars, namely, that they are blue stragglers formed from stellar mergers (Jofré et al 2016;Yong et al 2016). Such a collision would have destroyed any short-period planet already around one of the stars; KELT-21b would have needed to either form from material thrown off in the collision, or have survived the collision at a larger semimajor axis and only migrated after the collision.…”

Section: Metal Content and Galactic Contextmentioning

confidence: 91%

KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System

Johnson

Rodriguez

Zhou

et al. 2018

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We present the discovery of KELT-21b, a hot Jupiter transiting the V=10.5 A8V star HD 332124. The planet has an orbital period of P=3.6127647±0.0000033 days and a radius of 1.586 0.040 0.039 -+ R J . We set an upper limit on the 1 planetary mass of M 3.91 P < M J at 3s confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spinorbit misalignment of 5.6 1.91.7 . High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1 2 and with a combined contrast of K 6.39 0.06 S D =  with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of ∼0.12 M ☉ , a projected mutual separation of ∼20 au, and a projected separation of ∼500 au from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.

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Section: Metal Content and Galactic Contextmentioning

confidence: 91%

KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System

Johnson

Rodriguez

Zhou

et al. 2018

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“…Their high masses and alpha enhancements imply that they may have formed in the Galactic centre and subsequently migrated into the thick disc (Chiappini et al 2015). However, we already know from radial-velocity monitoring that many of the extra-massive thick-disc stars are plausibly multiple systems (Jofré et al 2016). In this work we test the possibility that these stars originate in multiple stellar systems and their properties arise from binary-star interactions (De Marco & Izzard 2017).…”

Section: Introductionmentioning

confidence: 94%

“…The increase in mass of a star causes it to look younger than it actually is (Sandage 1953;Tout et al 1997). There is every reason to believe that such stellar systems exist in the Galactic thick disc (Jofré et al 2016), however they are more difficult to identify than in stellar clusters because of the lack of a clear turn-off in the Hertzsprung-Russell or colour-magnitude diagram.…”

Section: Introductionmentioning

confidence: 99%

Binary stars in the Galactic thick disc

Izzard

Preece

Jofré

et al. 2017

Monthly Notices of the Royal Astronomical Society

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The combination of asteroseismologically-measured masses with abundances from detailed analyses of stellar atmospheres challenges our fundamental knowledge of stars and our ability to model them. Ancient red-giant stars in the Galactic thick disc are proving to be most troublesome in this regard. They are older than 5 Gyr, a lifetime corresponding to an initial stellar mass of about 1.2 M . So why do the masses of a sizeable fraction of thick-disc stars exceed 1.3 M , with some as massive as 2.3 M ? We answer this question by considering duplicity in the thick-disc stellar population using a binary population-nucleosynthesis model. We examine how mass transfer and merging affect the stellar mass distribution and surface abundances of carbon and nitrogen. We show that a few per cent of thick-disc stars can interact in binary star systems and become more massive than 1.3 M . Of these stars, most are single because they are merged binaries. Some stars more massive than 1.3 M form in binaries by wind mass transfer. We compare our results to a sample of the APOKASC data set and find reasonable agreement except in the number of these thick-disc stars more massive than 1.3 M . This problem is resolved by the use of a logarithmically-flat orbital-period distribution and a large binary fraction.

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“…Van Eck et al 1998;Shetye et al 2018), blue stragglers (e.g. Bailyn 1995;Mathieu & Geller 2009;Jofré et al 2016), and so on. Binary stars are also the best benchmarks to constrain stellar evolution models because radii and masses of binary-star components can be measured with a precision of a few percent (e.g.…”

Section: Introductionmentioning

confidence: 99%

TheGaia-ESO Survey: detection and characterisation of single-line spectroscopic binaries

Merle

Swaelmen

Eck

et al. 2020

A&A

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Context. Multiple stellar systems play a fundamental role in the formation and evolution of stellar populations in galaxies. Recent and ongoing large ground-based multi-object spectroscopic surveys significantly increase the sample of spectroscopic binaries (SBs) allowing analyses of their statistical properties. Aims. We investigate the repeated spectral observations of the Gaia-ESO Survey internal data release 5 (GES iDR5) to identify and characterise SBs with one visible component (SB1s) in fields covering mainly the discs, the bulge, the CoRot fields, and some stellar clusters and associations. Methods. A statistical χ 2 -test is performed on spectra of the iDR5 subsample of approximately 43 500 stars characterised by at least two observations and a signal-to-noise ratio larger than three. In the GES iDR5, most stars have four observations generally split into two epochs. A careful estimation of the radial velocity (RV) uncertainties is performed. Our sample of RV variables is cleaned from contamination by pulsation-and/or convection-induced variables using Gaia DR2 parallaxes and photometry. Monte-Carlo simulations using the SB9 catalogue of spectroscopic orbits allow to estimate our detection efficiency and to correct the SB1 rate to evaluate the GES SB1 binary fraction and its relation to effective temperature and metallicity. Results. We find 641 (resp., 803) FGK SB1 candidates at the 5σ (resp., 3σ) level. The maximum RV differences range from 2.2 km s −1 at the 5σ confidence level (1.6 km s −1 at 3σ) to 133 km s −1 (in both cases). Among them a quarter of the primaries are giant stars and can be located as far as 10 kpc. The orbital-period distribution is estimated from the RV standard-deviation distribution and reveals that the detected SB1s probe binaries with log P[d] 4. We show that SB1s with dwarf primaries tend to have shorter orbital periods than SB1s with giant primaries. This is consistent with binary interactions removing shorter period systems as the primary ascends the red giant branch. For two systems, tentative orbital solutions with periods of 4 and 6 d are provided. After correcting for detection efficiency, selection biases, and the present-day mass function, we estimate the global GES SB1 fraction to be in the range 7-14% with a typical uncertainty of 4%. A small increase of the SB1 frequency is observed from K-towards F-type stars, in agreement with previous studies. The GES SB1 frequency decreases with metallicity at a rate of (−9 ± 3)% dex −1 in the metallicity range −2.7 ≤[Fe/H]≤ +0.6. This anticorrelation is obtained with a confidence level higher than 93% on a homogeneous sample covering spectral types FGK and a large range of metallicities. When the present-day mass function is accounted for, this rate turns to (−4 ± 2)% dex −1 with a confidence level higher than 88%. In addition we provide the variation of the SB1 fraction with metallicity separately for F, G, and K spectral types, as well as for dwarf and giant primaries.

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Cannibals in the thick disk: the youngα-rich stars as evolved blue stragglers

Cited by 93 publications

References 68 publications

KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System

KELT-21b: A Hot Jupiter Transiting the Rapidly Rotating Metal-poor Late-A Primary of a Likely Hierarchical Triple System

Binary stars in the Galactic thick disc

TheGaia-ESO Survey: detection and characterisation of single-line spectroscopic binaries

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