<scp>NLTE</scp> C and O abundances in <scp>RR</scp> lyrae stars

Andrievsky, S. M.; Wallerstein, George; Коротин, С. А.; Kovtyukh, V. V.; Khrapaty, Sergii V.; Rydyak, Yuri; Huang, W.

doi:10.1002/asna.202013831

Cited by 5 publications

(16 citation statements)

References 37 publications

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“…In our previous paper (Andrievsky et al 2020), we reported about decreased/or near-to-normal carbon abundance in a sample of 21 field RR Lyrae stars. We made a conclusion that no additional carbon is expected to be brought to the stellar surface after the He flash in the RR Lyrae core.…”

Section: Resultsmentioning

confidence: 90%

“…Microturbulent velocity was derived by avoiding dependence between iron abundance from individual Fe I lines and their equivalent widths. Finally, the gravity value was found by keeping equal mean iron abundances from Fe Andrievsky et al (2020). In Figures 1 and 2, we graphically show the procedure of T eff and V t determination for KX Lyr and RX Eri, and sensitivity of the adopted T eff and V t values to variations within ±150 K and ±0.2 km s −1 .…”

Section: Abundance Analysismentioning

confidence: 99%

“…The corresponding mean values of iron abundance from Fe I and Fe II lines give the final [Fe/H] value for a given star. Error analysis was made in the same way as it was described in Andrievsky et al (2020). In Figures 1 and 2, we graphically show the procedure of T eff and V t determination for KX Lyr and RX Eri, and sensitivity of the adopted T eff and V t values to variations within ±150 K and ±0.2 km s −1 .…”

Section: Abundance Analysismentioning

confidence: 99%

“…Atomic models of carbon and oxygen, which were used to derive NLTE abundances of these elements in our program stars, are described in detail in several papers, see, for instance, Andrievsky et al (2020) for reference. In that paper, we also give the lists of analyzed carbon and oxygen lines, and a description of how we applied spectral synthesis to match the observed profiles of selected lines of the studied ions.…”

Section: Carbon and Oxygen Nlte Abundancesmentioning

confidence: 99%

“…In our recent paper (Andrievsky et al 2020), we reported on the results of the determination of C and O NLTE abundances in a sample of 21 RR Lyrae stars from the Galactic field. In all stars studied, carbon showed underabundance comparing to the solar (C/H), while oxygen was found to be overabundant.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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For the first time, a direct non-local thermodynamic equilibrium (NLTE) analysis of carbon and nitrogen lines in the spectra of nine RR Lyrae stars was carried out. We have determined the abundances of these elements together with oxygen, and have shown that the nitrogen content is increased in metallicity-deficient program stars. We conclude that this is a sign of the first dredge up, which occurred at the previous stage of the red giant branch, and brought material processed in an incomplete carbon, nitrogen, oxygen (CNO) cycle to the surface of the star. This effect is significantly enhanced by thermohaline (extra-) mixing, which is more effective for metal-poor RR Lyrae stars. This is clearly seen in the plot showing that C/N ration in our sample of stars gradually decreases as metallicity decreases from about −0.2 to −2. Oxygen abundance depends on metallicity in a similar way to what we see in the Population II stars.

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Section: Resultsmentioning

confidence: 90%

Section: Abundance Analysismentioning

confidence: 99%

Section: Abundance Analysismentioning

confidence: 99%

Section: Carbon and Oxygen Nlte Abundancesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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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A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood

Matsunaga

Itane

Hattori

et al. 2022

ApJ

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Metal-deficient stars are important tracers for understanding the early formation of the Galaxy. Recent large-scale surveys with both photometric and spectroscopic data have reported an increasing number of metal-deficient stars whose kinematic features are consistent with those of the disk stellar populations. We report the discovery of an RR Lyrae variable (hereafter RRL) that is located within the thick disk and has an orbit consistent with the thick-disk kinematics. Our target RRL (HD 331986) is located at around 1 kpc from the Sun and, with V ≃ 11.3, is among the ∼130 brightest RRLs known so far. However, this object has scarcely been studied because it is in the midplane of the Galaxy, at a Galactic latitude around –1°. Its near-infrared spectrum (0.91–1.32 μm) shows no absorption line except hydrogen lines of the Paschen series, suggesting [Fe/H] ≲ –2.5. It is the most metal-deficient RRL, at least among RRLs whose orbits are consistent with the disk kinematics, although we cannot determine to which of the disk and the halo it belongs. This unique RRL would provide us with essential clues for studying the early formation of stars in the inner Galaxy with further investigations, including high-resolution optical spectroscopy.

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NLTE C and O abundances in RR lyrae stars

Cited by 5 publications

References 37 publications

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

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

The Baade-Wesselink projection factor of RR Lyrae stars

A Very Metal-poor RR Lyrae Star with a Disk Orbit Found in the Solar Neighborhood

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