STEPARSYN: A Bayesian code to infer stellar atmospheric parameters using spectral synthesis

Tabernero, H. M.; Marfil, E.; Montes, D.; Hernández, J. I. González

doi:10.1051/0004-6361/202141763

Cited by 34 publications

(28 citation statements)

References 113 publications

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“…In contrast to some of the lines used in other works, such as K I (Passegger et al 2018(Passegger et al , 2019Rajpurohit et al 2018b), non-LTE effects are negligible for Fe I and Ti I lines (Olander et al 2021). We followed Tabernero et al (2021) to define the wavelength regions around the observed Fe I and Ti I line profiles in the template spectra to be compared with the synthetic grid (i.e. the line masks).…”

Section: Selection Of Spectral Features and Line Masksmentioning

confidence: 99%

“…Next, we adjusted the line profiles assuming an initial width of 3σ around their centre, avoiding adjacent spectral features. For targets with sin i > 4 km s −1 where the Gaussian approximation may no longer accurately reproduce the line profiles, we also broadened these line regions to account for rotation following the expression (Tabernero et al 2021):…”

Section: Selection Of Spectral Features and Line Masksmentioning

confidence: 99%

“…As discussed in Tabernero et al (2021), the STEPARSYN code allows the synthetic grid to be sequentially convolved on the fly (i.e. prior to the comparison with the observed spectra) to account for both the stellar rotation and the instrumental profile as the main sources of spectral broadening.…”

Section: Synthetic Gridmentioning

confidence: 99%

“…STEPARSYN is a Bayesian code written in Python 3 designed to map the probability distributions of the stellar atmospheric parameters (T eff , log g, [Fe/H], and sin i) from a given observed spectrum following an Markov chain Monte Carlo approach (Tabernero et al 2021). It has already been employed in many astrophysical contexts, including the study of stars in open clusters (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%

“…In this work we derived the stellar atmospheric parameters (T eff , log g, and [Fe/H]) for a sample of 343 M dwarfs observed with CARMENES (i.e. 5200-17 100 Å at R ∼ 90 000) by means of the STEPARSYN code (Tabernero et al 2021), a Bayesian implementation of the spectral synthesis technique. This approach relied on the comparison of a synthetic grid against 75 magnetically insensitive Ti I and Fe I absorption lines along with the TiO γ and bands.…”

Section: Introductionmentioning

confidence: 99%

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The CARMENES search for exoplanets around M dwarfs

Marfil

Tabernero

Montes

et al. 2021

A&A

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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 ϵ bands. To avoid any potential degeneracy in the parameter space, we imposed Bayesian priors on Teff and logg 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 Teff, logg, 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 Teff 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 Teff 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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Section: Selection Of Spectral Features and Line Masksmentioning

confidence: 99%

Section: Selection Of Spectral Features and Line Masksmentioning

confidence: 99%

Section: Synthetic Gridmentioning

confidence: 99%

Section: Steparsynmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The CARMENES search for exoplanets around M dwarfs

Marfil

Tabernero

Montes

et al. 2021

A&A

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Metallicities in M dwarfs: Investigating different determination techniques

Passegger

Bello-García

Ordieres-Meré

et al. 2022

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Deriving metallicities for solar-like stars follows well-established methods, but for cooler stars such as M dwarfs, the determination is much more complicated due to forests of molecular lines that are present. Several methods have been developed in recent years to determine accurate stellar parameters for these cool stars (Teff ≲ 4000 K). However, significant differences can be found at times when comparing metallicities for the same star derived using different methods. In this work, we determine the effective temperatures, surface gravities, and metallicities of 18 well-studied M dwarfs observed with the CARMENES high-resolution spectrograph following different approaches, including synthetic spectral fitting, analysis of pseudo-equivalent widths, and machine learning. We analyzed the discrepancies in the derived stellar parameters, including metallicity, in several analysis runs. Our goal is to minimize these discrepancies and find stellar parameters that are more consistent with the literature values. We attempted to achieve this consistency by standardizing the most commonly used components, such as wavelength ranges, synthetic model spectra, continuum normalization methods, and stellar parameters. We conclude that although such modifications work quite well for hotter main-sequence stars, they do not improve the consistency in stellar parameters for M dwarfs, leading to mean deviations of around 50–200 K in temperature and 0.1–0.3 dex in metallicity. In particular, M dwarfs are much more complex and a standardization of the aforementioned components cannot be considered as a straightforward recipe for bringing consistency to the derived parameters. Further in-depth investigations of the employed methods would be necessary in order to identify and correct for the discrepancies that remain.

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A tentative detection of He I in the atmosphere of GJ 1214 b

Orell-Miquel

Murgas

Πάλλη

et al. 2022

A&A

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The He I λ10833 Å triplet is a powerful tool for characterising the upper atmosphere of exoplanets and tracing possible mass loss. Here, we analysed one transit of GJ 1214 b observed with the CARMENES high-resolution spectrograph to study its atmosphere via transmission spectroscopy around the He I triplet. Although previous studies using lower resolution instruments have reported non-detections of He I in the atmosphere of GJ 1214 b, we report here the first potential detection. We reconcile the conflicting results arguing that previous transit observations did not present good opportunities for the detection of He I, due to telluric H2O absorption and OH emission contamination. We simulated those earlier observations, and show evidence that the planetary signal was contaminated. From our single non-telluric-contaminated transit, we determined an excess absorption of 2.10−0.50+0.45% (4.6 σ) with a full width at half maximum (FWHM) of 1.30−0.25+0.30 Å. The detection of He I is statistically significant at the 4.6 σ level, but repeatability of the detection could not be confirmed due to the availability of only one transit. By applying a hydrodynamical model and assuming an H/He composition of 98/2, we found that GJ 1214 b would undergo hydrodynamic escape in the photon-limited regime, losing its primary atmosphere with a mass-loss rate of (1.5–18) × 1010 g s−1 and an outflow temperature in the range of 2900–4400 K. Further high-resolution follow-up observations of GJ 1214 b are needed to confirm and fully characterise the detection of an extended atmosphere surrounding GJ 1214 b. If confirmed, this would be strong evidence that this planet has a primordial atmosphere accreted from the original planetary nebula. Despite previous intensive observations from space- and ground-based observatories, our He I excess absorption is the first tentative detection of a chemical species in the atmosphere of this benchmark sub-Neptune planet.

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STEPARSYN: A Bayesian code to infer stellar atmospheric parameters using spectral synthesis

Cited by 34 publications

References 113 publications

The CARMENES search for exoplanets around M dwarfs

The CARMENES search for exoplanets around M dwarfs

Metallicities in M dwarfs: Investigating different determination techniques

A tentative detection of He I in the atmosphere of GJ 1214 b

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STEPARSYN: A Bayesian code to infer stellar atmospheric parameters using spectral synthesis

Cited by 34 publications

References 113 publications

The CARMENES search for exoplanets around M dwarfs

The CARMENES search for exoplanets around M dwarfs

Metallicities in M dwarfs: Investigating different determination techniques

A tentative detection of He I in the atmosphere of GJ 1214 b

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Product

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A tentative detection of He I in the atmosphere of GJ 1214 b