Determination of the stellar parameters of C-rich hydrostatic stars from spectro-interferometric observations

Paladini, C.; Belle, Gerald van; Aringer, B.; Hron, J.; Reegen, P.; Davis, C. J.; Lebzelter, T.

doi:10.1051/0004-6361/201116538

Cited by 14 publications

(18 citation statements)

References 65 publications

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“…This result is consistent with the similar observations of the RSG VY CMa by Wittkowski et al (2012) and the results shown by Lançon et al (2007). The satisfactory fit to stellar spectra, together with an unsatisfactory fit to interferometric visibilities, illustrates the importance of interferometric observations in addition to spectral observations to fully constrain and test stellar model atmospheres, as noted previously by, e.g., Wittkowski et al (2006) and Paladini et al (2011). In a future work, it may be possible to extend PHOENIX model atmospheres farther out, for instance by attaching a slow wind to the atmosphere, or by considering NLTE in the molecular lines or 3D structures.…”

Section: Atmospheric Structuresupporting

confidence: 80%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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Aims. We present the atmospheric structure and the fundamental properties of the red supergiants (RSGs) AH Sco, UY Sct, and KW Sgr based on VLTI/AMBER observations. Methods. We carried out spectro-interferometric observations of AH Sco, UY Sct, and KW Sgr in the near-infrared K band (1.92-2.47 μm) with the VLTI/AMBER instrument with spatial and spectral resolutions of 3 milliarcsec and 1500, respectively, and compared the data to a new grid of hydrostatic PHOENIX model atmospheres.Results. In our visibility data, we observe molecular layers of water and CO in extended atmospheres. For a uniform disk modeling, we observe size increases at the water band centered at 1.9 μm of 10% to 25% and at the CO bandheads at 2.3-2.5 μm of 20%-35% with respect to the near-continuum bandpass at around 2.20 μm. Our near-infrared spectra of AH Sco, UY Sct, and KW Sgr are well reproduced by the PHOENIX model atmospheres. The continuum visibility values are consistent with a limb-darkened disk as predicted by the PHOENIX models. However, the model visibilities do not predict the large observed extensions of the molecular layers. Comparing the continuum visibility values to PHOENIX models, we estimate the Rosseland-mean photospheric angular diameters of AH Sco, UY Sct, and KW Sgr to be 5.81 ± 0.15 mas, 5.48 ± 0.10 mas, and 3.91 ± 0.25 mas, respectively. Together with the distance and the spectro-photometry, we calculate radii of 1411 ± 124 R for AH Sco, 1708 ± 192 R for UY Sct, and 1009 ± 142 R for KW Sgr and effective temperatures of 3682 ± 190 K for AH Sco, 3365 ± 134 K for UY Sct, and 3720 ± 183 K for KW Sgr. Conclusions. AH Sco, UY Sct, and KW Sgr exhibit extended atmospheric layers of H 2 O and CO. The PHOENIX atmosphere models predict the spectra and the continuum visibility values, but cannot reproduce the large extensions of the molecular layers. This indicates that the opacities of the molecular bands are included, but that the model atmospheres are too compact compared to the observations. The observed extended layers may be levitated by processes such as pulsation or convection, which are not included in the hydrostatic atmospheric models. The location of the targets in the HR-diagram is confirmed to be close to, and possibly slightly to the right of, the Hayashi limit of recent evolutionary tracks corresponding to masses between about 20 M and 40 M .

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Section: Atmospheric Structuresupporting

confidence: 80%

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Arroyo-Torres

Wittkowski²,

Marcaide

et al. 2013

A&A

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“…4.2.1 and 4.2.2 low-resolution spectroscopic observations are compared with synthetic spectra of hydrostatic models to fix the fundamental stellar parameters C/O ratio and T eff . The overall energy distribution as well as the bands of the molecules that are present from 2.3−6 μm put strong constraints on these parameters (Jørgensen et al 2000;Loidl et al 2001;P11).…”

Section: Approach 2: Hydrostatic Modelsmentioning

confidence: 99%

“…To get precise estimates of T eff , additional model atmospheres were produced that resulted in a grid spacing of ΔT = 10 K. All the main molecular opacities typical of C-stars were included: CO (Goorvitch & Chackerian 1994), C 2 (Querci et al 1974), HCN (Harris et al 2006), CN (Jørgensen 1997) in the form of line lists, and C 2 H 2 and C 3 (Jorgensen et al 1989) as OS data. CS is not included due to the lack of line lists and OS data.…”

Section: Hydrostatic Modelsmentioning

confidence: 99%

“…It is demonstrated that the combined use of spectroscopic and interferometric observing techniques can efficiently help ascertain stellar parameters (e.g. Wittkowski et al 2001Wittkowski et al , 2008Wittkowski et al , 2011Neilson & Lester 2008;Paladini et al 2011;Sacuto et al 2011a;Martí-Vidal et al 2011). At the same time these observations provide constraints for existing model atmospheres: e.g.…”

Section: Introductionmentioning

confidence: 99%

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Catching the fish – Constraining stellar parameters for TX Piscium using spectro-interferometric observations

Klotz

Paladini

Hron

et al. 2013

A&A

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Context. Stellar parameter determination is a challenging task when dealing with galactic giant stars. The combination of different investigation techniques has proven to be a promising approach. Aims. We analyse archive spectra obtained with the Short Wavelength Spectrometer (SWS) onboard ISO, and new interferometric observations from the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The aim of this work is to determine stellar parameters using spectroscopy and interferometry. Methods. The observations are used to constrain the model atmosphere, and eventually the stellar evolutionary model in the region where the tracks map the beginning of the carbon star sequence. Two different approaches are used to determine stellar parameters: (i) the "classic" interferometric approach where the effective temperature is fixed by using the angular diameter in the N-band (from interferometry) and the apparent bolometric magnitude; (ii) parameters are obtained by fitting a grid of state-of-the-art hydrostatic models to spectroscopic and interferometric observations. Results. We find good agreement between the parameters of the two methods. The effective temperature and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star just recently, which means that the star is still in a "quiet" phase compared to the subsequent strong-wind regime. This agrees with the C/O ratio being only slightly greater than one.

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“…On the other hand, to date only a few interferometric observations of carbon stars have been compared with model atmospheres (Sacuto et al 2011;Paladini et al 2011;Cruzalèbes et al 2013;Klotz et al 2013;van Belle et al 2013).…”

Section: Introductionmentioning

confidence: 99%

Modelling the atmosphere of the carbon-rich Mira RU Virginis

Rau

Paladini

Hron

et al. 2015

A&A

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Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir with hydrostatic and dynamic models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kinds of observations (photometry, spectroscopy, interferometry) is essential for shedding light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit the ISO spectrum well in the wavelength range λ = [2.9, 25.0] µm. Nevertheless, a discrepancy is noticeable both in the SED (visible) and in the interferometric visibilities (shape and level), which is a possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres, as well as in the observations. The presence of a companion star and/or a disk or a decrease in mass loss within the past few hundred years cannot be excluded, but these explanations are considered unlikely.

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Determination of the stellar parameters of C-rich hydrostatic stars from spectro-interferometric observations

Cited by 14 publications

References 65 publications

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii

Catching the fish – Constraining stellar parameters for TX Piscium using spectro-interferometric observations

Modelling the atmosphere of the carbon-rich Mira RU Virginis

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