A comprehensive study of NGC 2345, a young open cluster with a low metallicity

Alonso-Santiago, J.; Negueruela, I.; Marco, A.; Tabernero, H. M.; González-Fernández, C.; Castro, N.

doi:10.1051/0004-6361/201936109

Cited by 27 publications

(22 citation statements)

References 86 publications

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“…The age of every cluster has been taken from the WEBDA database. ( * ) Ages derived by our group in this paper (for NGC 6649, NGC 6664 and Be 55) or in previous works(Alonso-Santiago et al 2017, 2019b, for NGC 6067 and NGC 2345. ( * * ) According toCantat-Gaudin et al (2018), Cepheids QZ Nor (NGC 6067) and RU Sct(Trumpler 35) are not considered cluster members and, therefore, to maintain homogeneity, they have not been taken into account in this table.…”

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confidence: 73%

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Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55

Alonso-Santiago

Negueruela

Marco

et al. 2020

A&A

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Classical Cepheids in open clusters play an important role in benchmarking stellar evolution models, in addition to anchoring the cosmic distance scale and invariably securing the Hubble constant. Three pertinent clusters hosting classical Cepheids and red (super)giants are: NGC 6649, NGC 6664, and Berkeley 55. These clusters form the basis of analysis to assess newly acquired spectra (≈50), archival photometry, and Gaia DR2 data. Importantly, for the first time chemical abundances were determined for the evolved members of NGC 6649 and NGC 6664. We find that they are slightly metal-poor relative to the mean Galactic gradient. Also, an overabundance of Ba is observed. These two clusters likely belong to the thin disc and the latter finding supports the “s-enhanced” scenario of D’Orazi et al. (2009). NGC 6664 and Berkeley 55 exhibit radial velocities consistent with Galactic rotation, while NGC 6649 displays a peculiar velocity. The resulting age estimates for the clusters (≈70 Ma) imply masses of ≈6 M⊙ for the (super)giant demographic. Lastly, the observed yellow-to-red (super)giant ratio is lower than expected and the overall differences that are relative to the models reflect the outstanding theoretical uncertainties.

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confidence: 73%

“…In this age range, open clusters containing a similar number of (super)giants are rare (see Table 15) and also significantly more massive. Representative examples of this kind of clusters are NGC 6067 (Alonso-Santiago et al 2017), Be 51 (Negueruela et al 2018), and NGC 2345(Alonso-Santiago et al 2019b.…”

Section: Cluster Parametersmentioning

confidence: 99%

Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55

Alonso-Santiago

Negueruela

Marco

et al. 2020

A&A

Self Cite

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“…SteParSyn has been used to infer stellar atmospheric parameters using atomic features (see e.g. Lohr et al 2018;Negueruela et al 2018;Tabernero et al 2018;Alonso-Santiago et al 2019). Unfortunately, the optical spectrum of VX Sgr is dominated by molecular absorptions.…”

Section: Stellar Atmospheric Parametersmentioning

confidence: 99%

The nature of VX Sagitarii

Tabernero

Dorda

Negueruela

et al. 2021

A&A

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Aims. We present a spectroscopic analysis of the extremely luminous red star VX Sgr based on high-resolution observations combined with AAVSO light curve data. Given the puzzling characteristics of VX Sgr, we explore three scenarios for its nature: a massive red supergiant (RSG) or red hypergiant (RHG), a Thorne Żytkow object, and an extreme asymptotic giant branch (AGB) star. Methods. Sampling more than one whole cycle of photometric variability, we derive stellar atmospheric parameters by using state-of-the-art PHOENIX atmospheric models. We compare them to optical and near-infrared spectral types. We report on some key features due to neutral elemental atomic species such as Li I, Ca I, and Rb I. Results. We provide new insights into its luminosity, its evolutionary stage, and its pulsation period. Based on all the data, there are two strong reasons to believe that VX Sgr is some sort of extreme AGB star. Firstly, it has Mira-like behaviour during active phases. VX Sgr shows light variation with amplitude that is much larger than any known RSG and clearly larger than all RHGs. In addition, it displays Balmer line emission and, as shown here for the first time, line doubling of its metallic spectrum at maximum light, both characteristics typical of Miras. Secondly, unlike any known RSG or RHG, VX Sgr displays strong Rb I lines. In addition to the photospheric lines that are sometimes seen, it always shows circumstellar components whose expansion velocity is compatible with that of the OH masers in the envelope, demonstrating a continuous enrichment of the outer atmosphere with s-process elements, a behaviour that can only be explained by a third dredge-up during the thermal pulse phase.

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“…It has already been employed in many astrophysical contexts, including the study of stars in open clusters 6, but for the TiO γ and bands. (Lohr et al 2018;Alonso-Santiago et al 2019), stars in galaxies of the Local Group (Tabernero et al 2018), and exoplanet host stars (Borsa et al 2021;Demangeon et al 2021).…”

Section: Steparsynmentioning

confidence: 99%

The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn

Marfil,

Tabernero,

Montes

et al. 2021

Preprint

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We determined effective temperatures, surface gravities, and metallicities for a sample of 343 M dwarfs observed with CARMENES, the double-channel, high-resolution spectrograph installed at the 3.5 m telescope at Calar Alto Observatory. We employed SteParSyn, a Bayesian spectral synthesis implementation particularly designed to infer the stellar atmospheric parameters of late-type stars following a Markov chain Monte Carlo approach. We made use of the BT-Settl model atmospheres and the radiative transfer code turbospectrum to compute a grid of synthetic spectra around 75 magnetically insensitive Fe i and Ti i lines plus the TiO γ and bands. To avoid any potential degeneracy in the parameter space, we imposed Bayesian priors on T eff and log g based on the comprehensive, multi-band photometric data available for the sample. We find that this methodology is suitable down to M7.0 V, where refractory metals such as Ti are expected to condense in the stellar photospheres. The derived T eff , log g, and [Fe/H] range from 3000 to 4200 K, 4.5 to 5.3 dex, and −0.7 to 0.2 dex, respectively. Although our T eff scale is in good agreement with the literature, we report large discrepancies in the [Fe/H] scales, which might arise from the different methodologies and sets of lines considered. However, our [Fe/H] is in agreement with the metallicity distribution of FGK-type stars in the solar neighbourhood and correlates well with the kinematic membership of the targets in the Galactic populations. Lastly, excellent agreement in T eff is found for M dwarfs with interferometric angular diameter measurements, as well as in the [Fe/H] between the components in the wide physical FGK+M and M+M systems included in our sample.

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A comprehensive study of NGC 2345, a young open cluster with a low metallicity

Cited by 27 publications

References 86 publications

Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55

Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55

The nature of VX Sagitarii

The CARMENES search for exoplanets around M dwarfs. Stellar atmospheric parameters of target stars with SteParSyn

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