Analysis of absorption lines in the high-resolution spectra of five hot post-AGB candidates

Herrero, A.; Parthasarathy, M.; Hubrig, S.; Sarkar, G.; Muneer, S.

doi:10.1093/mnras/staa819

Cited by 8 publications

(3 citation statements)

References 57 publications

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“…Both distance determinations agree within error limits except for Gaia DR2 67 for which the parallax distance is a factor of two larger. We note that similar problems were encountered and discussed, for instance, in spectroscopic analyses of hot WDs (Preval et al 2019) and hot post-AGB stars (Herrero et al 2020). Bertolami & Althaus (2006).…”

Section: Sed Fitting Stellar Radii Luminosities and Distancessupporting

confidence: 54%

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Werner,

Reindl,

Dorsch

et al. 2021

Preprint

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Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of T eff > 70 000 K and a surface gravity of 5.0 < log g < 7.0 are rather rare objects despite recent and ongoing surveys. It is believed that they are the outcome of either single star evolution (late helium-shell flash or late helium-core flash) or binary star evolution (double WD merger). Their study is interesting because the surface elemental abundances reflect the physics of thermonuclear flashes and merger events. Spectroscopically they are divided in three different classes, namely PG1159, O(He), or He-sdO. We present a spectroscopic analysis of five such stars that turned out to have atmospheric parameters in the range T eff = 70 000-80 000 K and log g = 5.2-6.3. The three investigated He-sdOs have a relatively high hydrogen mass fraction (10%) that is unexplained by both single (He core flash) and binary evolution (He-WD merger) scenarios. The O(He) star JL 9 is probably a binary helium-WD merger, but its hydrogen content (6%) is also at odds with merger models. We found that RL 104 is the 'coolest' (T eff = 80 000 K) member of the PG1159 class in a pre-WD stage. Its optical spectrum is remarkable because it exhibits C iv lines involving Rydberg states with principal quantum numbers up to n = 22. Its rather low mass (0.48 +0.03 −0.02 M ⊙ ) is difficult to reconcile with the common evolutionary scenario for PG1159 stars due to it being the outcome of a (very) late He-shell flash. The same mass-problem faces a merger model of a close He-sdO plus CO WD binary that predicts PG1159-like abundances. Perhaps RL 104 originates from a very late He-shell flash in a CO/He WD formed by a merger of two low-mass He-WDs.

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Section: Sed Fitting Stellar Radii Luminosities and Distancessupporting

confidence: 54%

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Werner,

Reindl,

Dorsch

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

Section: Sed Fitting Stellar Radii Luminosities and Distancesmentioning

confidence: 55%

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Werner¹,

Reindl

Dorsch

et al. 2022

A&A

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Hot, compact, hydrogen-deficient pre-white dwarfs (pre-WDs) with effective temperatures of Teff > 70 000 K and a surface gravity of 5.0 < logg < 7.0 are rather rare objects despite recent and ongoing surveys. It is believed that they are the outcome of either single star evolution (late helium-shell flash or late helium-core flash) or binary star evolution (double WD merger). Their study is interesting because the surface elemental abundances reflect the physics of thermonuclear flashes and merger events. Spectroscopically they are divided in three different classes, namely PG1159, O(He), or He-sdO. We present a spectroscopic analysis of five such stars that turned out to have atmospheric parameters in the range Teff = 70 000–80 000 K and logg = 5.2–6.3. The three investigated He-sdOs have a relatively high hydrogen mass fraction (10%) that is unexplained by both single (He core flash) and binary evolution (He-WD merger) scenarios. The O(He) star JL 9 is probably a binary helium-WD merger, but its hydrogen content (6%) is also at odds with merger models. We found that RL 104 is the ‘coolest’ (Teff = 80 000 K) member of the PG1159 class in a pre-WD stage. Its optical spectrum is remarkable because it exhibits C IV lines involving Rydberg states with principal quantum numbers up to n = 22. Its rather low mass (0.48−0.02+0.03 M⊙) is difficult to reconcile with the common evolutionary scenario for PG1159 stars due to it being the outcome of a (very) late He-shell flash. The same mass-problem faces a merger model of a close He-sdO plus CO WD binary that predicts PG1159-like abundances. Perhaps RL 104 originates from a very late He-shell flash in a CO/He WD formed by a merger of two low-mass He-WDs.

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“…References. (1)Kudritzki et al (2014) and references therein, (2) Salvador-Rusiñol et al (2021), (3)Herrero et al (2020).…”

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confidence: 99%

Chemical composition of the young massive cluster NGC 1569-B

Gvozdenko

Larsen

Beasley

et al. 2022

A&A

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Context. The chemical composition of young massive clusters (YMCs) provides stellar population information on their host galaxy. As potential precursors of globular clusters (GCs), their properties can help us understand the origins of GCs and their evolution. Aims. We present a detailed chemical abundance analysis of the YMC NGC 1569-B. The host galaxy, NGC 1569, is a dwarf irregular starburst galaxy at a distance of 3.36±0.20 Mpc. We derive the abundances of the α, Fe-peak, and heavy elements. Methods. We determined the abundance ratios from the analysis of an optical integrated-light (IL) spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope. We considered different red-to-blue supergiant ratios (N RS G /N BS G ), namely: the ratio obtained from a theoretical isochrone (N RS G /N BS G =1.24), the ratio obtained from a resolved colour-magnitude diagram of the YMC (N RS G /N BS G =1.53), and the ratio that minimises the χ 2 when comparing our model spectra with the observations (N RS G /N BS G =1.90). We adopted the latter ratio for our resulting chemical abundances. Results. The derived iron abundance is sub-solar with [Fe/H] = −0.74 ± 0.05. In relation to the scaled solar composition, we find enhanced α-element abundances, [/Fe] = +0.25±0.11, with a particularly high Ti abundance of +0.49±0.05. Other super-solar elements include [Cr/Fe] = +0.50±0.11, [Sc/Fe] = +0.78±0.20, and [Ba/Fe] = +1.28±0.14, while other Fe-peak elements are close to scaled solar abundances: ([Mn/Fe] = −0.22±0.12 and [Ni/Fe] = +0.13±0.11).Conclusions. The composition of NGC 1569-B resembles the stellar populations of the YMC NGC 1705-1, located in a blue compact dwarf galaxy. The two YMCs agree with regard to α-elements and the majority of the Fe-peak elements, except for Sc and Ba, which are extremely super-solar in NGC 1569-B -and higher than in any YMC studied so far. The blue part of the optical spectrum of a young population is still a very challenging wavelength region to analyse using IL spectroscopic studies. This is due to the uncertain contribution to the light from blue supergiant stars, which can be difficult to disentangle from turn-off stars, even when resolved photometry is available. We suggest that the comparison of model fits at different wavelengths offers a route to determining the red-to-blue supergiant ratio from IL spectroscopy.

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Analysis of absorption lines in the high-resolution spectra of five hot post-AGB candidates

Cited by 8 publications

References 57 publications

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Non-local thermodynamic equilibrium spectral analysis of five hot, hydrogen-deficient pre-white dwarfs

Chemical composition of the young massive cluster NGC 1569-B

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