<scp>NLTE CNO</scp> abundances in a sample of nine field <scp>RR</scp> Lyr type stars

Andrievsky, S. M.; Коротин, С. А.; Kovtyukh, V. V.; Khrapaty, Sergey V.; Rudyak, Yuri

doi:10.1002/asna.202113955

Cited by 6 publications

(8 citation statements)

References 27 publications

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“…∆7468 is the W7468-weighted mean of ∆7468) suggests that the discrepancy in [N/Fe] of DH Peg may (at least partially) be attributed to the difference in the applied non-LTE correction. 6 In any event, despite the existence of such a partial inconsistency, the consequences of Andrievsky et al (2021) and this investigation are generally in accord with each other. The [Fe/H]-dependent trends of [C/Fe], [N/Fe], and [O/Fe] shown in Fig.…”

Section: Comparison With Previous Studiessupporting

confidence: 61%

“…6 Andrievsky et al (2021) reanalysed Takeda & Sadakane's (1997) equivalent width data of CNO lines for the metal-poor ([Fe/H] ∼ −1.5) horizontal-branch star HD 161817. As seen from Tables 5 and 6 of their paper, their |∆| values for the N i 8683/8686/8706 lines are generally smaller than those of Takeda & Sadakane (1997), just like the case for ∆ 7468 of DH Peg described here.…”

Section: Discussionmentioning

confidence: 99%

“…Very recently, an interesting report following this line has been made by Andrievsky et al (2021). They determined the C, N, and O abundances of nine field RR Lyr stars, and found that the resulting [C/N] ratios tend to decrease towards lower metallicity from [Fe/H] ∼ 0 down to ∼ −2 (cf.…”

Section: Introductionmentioning

confidence: 98%

“…This tendency is almost consistent with the simulation of Lagarde et al (2019), supporting the importance of thermohaline mixing in low-mass giants. However, since Andrievsky et al's (2021) analysis is limited to only 9 stars, their conclusion needs to be confirmed based on a larger sample of RR Lyr stars.…”

Section: Introductionmentioning

confidence: 99%

“…Accordingly, in order to provide an independent followup study after Lagarde et al (2019) and Andrievsky et al (2021), it was decided to newly determine the photospheric abundances of four key elements (C, N, O, and Na) for this sample of RR Lyr variables (covering the metallicity range between [Fe/H] ∼ −2 and ∼ 0), where the main attention is paid to clarifying the trend of [C/N] in terms of metallicity. This is the purpose of this investigation.…”

Section: Introductionmentioning

confidence: 99%

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Surface C, N, O, and Na abundances of RR Lyrae variables implying the nature of internal mixing in low-mass stars

Takeda

2022

Preprint

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Photospheric abundances of C, N, O, and Na were determined by applying the synthetic spectrum-fitting technique to 34 snap-shot high-dispersion spectra of 22 RR Lyr stars covering a metallicity range of −1.8 [Fe/H] 0.0, with an aim of investigating the mixing mechanism in the interior of low-mass giant stars by examining the abundance anomalies of these elements possibly affected by the evolution-induced dredge-up of nuclear burning products. Special attention was paid to check the recent theoretical stellar evolution simulations indicating the importance of thermohaline mixing in low-mass stars (M 1 M ), which is expected to be more significant as the metallicity is lowered. By inspecting the resulting abundances in comparison with those of unevolved metal-poor dwarfs at the same metallicity, the deficiency in C as well as enrichment in N was confirmed (while O is almost unchanged), the extent of peculiarities tending to increase with a decrease in [Fe/H]. Accordingly, the [C/N] ratio turned out to progressively decrease towards lower metallicity from ∼ 0 ([Fe/H] ∼ 0) to ∼ −1 ([Fe/H] ∼ −1.5), which is reasonably consistent with the theoretical prediction in the presence of thermohaline mixing. However, these RR Lyr stars do not show any apparent Na anomaly (i.e., essentially the same [Na/Fe] vs. [Fe/H] trends as those of dwarfs), despite that metallicity-dependent overabundance in Na is theoretically expected for the case of non-canonical mixing. This inconsistency between C/N and Na may suggest a necessity of further improvement in the current theory.

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Section: Comparison With Previous Studiessupporting

confidence: 61%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Surface C, N, O, and Na abundances of RR Lyrae variables implying the nature of internal mixing in low-mass stars

Takeda

2022

Preprint

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Toward more accurate RR Lyrae metallicities

Kovacs,

Jurcsik

2023

A&A

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By using a large sample of fundamental mode RR Lyrae stars with published spectroscopic iron abundances and gravities, we point out the importance of correcting these abundances by using more accurate temporal gravities. For the 197 stars with multiple spectra, overall we find [Fe/H] standard deviations of 0.167 (as published), 0.145 (shifted by data source zero points), and 0.121 (both zero point shifted and corrected for the static gravity). These improvements are significant at the ~2σ level at each correction step, leading to a clearly significant improvement after both corrections are applied. The higher quality of the gravity-corrected metallicities is also strongly supported by the tighter correlation with the metallicities predicted from the period and Fourier phase, φ31. This work highlights the need for using some external estimates of the temporal gravity in the chemical abundance analysis, rather than relying on a full-fetched spectrum fit that leads to large correlated errors in the estimated parameters.

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The Baade-Wesselink projection factor of RR Lyrae stars

Bras,

Kervella,

Trahin

et al. 2024

A&A

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The application of the parallax of pulsation (PoP) technique to determine the distances of pulsating stars implies the use of a scaling parameter, namely the projection factor ($p$-factor), which is required to transform disc-integrated radial velocities (RVs) into photospheric expansion velocities. The value of this parameter is poorly known and is still debated. Most present applications of the PoP technique assume a constant $p$-factor. However, it may actually depend on the physical parameters of each star, as past studies designed to calibrate the $p$-factor (predominantly for Cepheids) led to a broad range of individual values. We aim to calibrate the $p$-factors of a sample of RR Lyrae stars (RRLs) in order to compare them with classical Cepheids (CCs). Due to their higher surface gravity, RRLs have more compact atmospheres, and therefore provide a valuable comparison with their supergiant siblings. We determined the $p$-factor of 17 RRLs by modelling their pulsation using the SPIPS code. The models are constrained using Gaia DR3 parallaxes, photometry, and new RVs that we collected with the OHP/SOPHIE spectrograph. We carefully examine the different steps of the PoP technique, in particular the method used to determine the RV from spectra using the classical approach based on the cross-correlation function (CCF). The method employed to extract the RV from the CCF has a strong impact on the $p$-factor, that is, of up to 10<!PCT!>. However, this choice of method results in a global scaling of the $p$-factor, and only marginally affects the scatter of $p$ within the sample for a given method. Over our RRL sample, we find a mean value of $p = 1.248 0.022$ for RVs derived using a Gaussian fit of the CCF. There is no evidence for a different value of the $p$-factor of RRLs, although its distribution for RRLs appears significantly less scattered ($ 7<!PCT!>$) than that for CCs ($ 12<!PCT!>$). The $p$-factor does not appear to depend in a simple way on fundamental stellar parameters (pulsation period, radius, metallicity, amplitude of the RV curve). We argue that large-amplitude dynamical phenomena occurring in the atmospheres of RRLs (and CCs) during their pulsation affect the relative velocity of the spectral line-forming regions compared to the velocity of the photosphere.

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NLTE CNO abundances in a sample of nine field RR Lyr type stars

Cited by 6 publications

References 27 publications

Surface C, N, O, and Na abundances of RR Lyrae variables implying the nature of internal mixing in low-mass stars

Surface C, N, O, and Na abundances of RR Lyrae variables implying the nature of internal mixing in low-mass stars

Toward more accurate RR Lyrae metallicities

The Baade-Wesselink projection factor of RR Lyrae stars

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