Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER★

Cruzalèbes, P.; Jorissen, A.; Rabbia, Yves; Sacuto, Stéphane; Chiavassa, A.; Pasquato, Ester; Plez, B.; Eriksson, Karl‐Erik; Spang, A.; Chesneau, O.

doi:10.1093/mnras/stt1037

Cited by 30 publications

(36 citation statements)

References 103 publications

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“…The literature values can vary (see e.g. Dehaes et al 2011;Cruzalèbes et al 2013;Jönsson et al 2014), but will not influence our conclusions. We use the sets of evolutionary tracks from Bertelli et al (2008Bertelli et al ( , 2009) who use isochrones from Girardi et al (2000).…”

Section: Stellar Parametersmentioning

confidence: 97%

Systematic trend of water vapour absorption in red giant atmospheres revealed by high resolution TEXES 12 μm spectra

Ryde

Lambert

Farzone

et al. 2014

A&A

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Context. The structures of the outer atmospheres of red giants are very complex. Recent interpretations of a range of different observations have led to contradictory views of these regions. It is clear, however, that classical model photospheres are inadequate to describe the nature of the outer atmospheres. The notion of large optically thick molecular spheres around the stars (MOLspheres) has been invoked in order to explain spectro-interferometric observations and low-and high-resolution spectra. On the other hand high-resolution spectra in the mid-IR do not easily fit into this picture because they rule out any large sphere of water vapour in LTE surrounding red giants. Aims. In order to approach a unified scenario for these outer regions of red giants, more empirical evidence from different diagnostics are needed. Our aim here is to investigate high-resolution, mid-IR spectra for a range of red giants, spanning spectral types from early K to mid M. We want to study how the pure rotational lines of water vapour change with effective temperature, and whether we can find common properties that can put new constraints on the modelling of these regions, so that we can gain new insights. Methods. We have recorded mid-IR spectra at 12.2−12.4 μm at high spectral resolution of ten well-studied bright red giants, with TEXES mounted on the IRTF on Mauna Kea. These stars span effective temperatures from 3450 K to 4850 K. Results. We find that all red giants in our study cooler than 4300 K, spanning a wide range of effective temperatures (down to 3450 K), show water absorption lines stronger than expected and none are detected in emission, in line with what has been previously observed for a few stars. The strengths of the lines vary smoothly with spectral type. We identify several spectral features in the wavelength region that are undoubtedly formed in the photosphere. From a study of water-line ratios of the stars, we find that the excitation temperatures, in the line-forming regions, are several hundred Kelvin lower than expected from a classical photospheric model. Conclusions. All stars in our sample show several photospheric features in their 12 μm spectra, which can be modelled with a classical model photosphere. However, in all stars showing water-vapour lines (stars cooler than ∼4300 K), the water lines are found to be much deeper than expected. The line ratios of these pure-rotational lines reveal low excitation temperatures. This could either be due to lower temperatures than expected in the outer regions of the photospheres caused by for example extra cooling, or due to non-LTE level populations, affecting the source function and line opacities, but this needs further investigation. We have demonstrated that these diagnostically interesting water lines are a general feature of red giants across spectral types, and we argue for a general explanation of their formation rather than explanations requiring specific properties, such as dust. Since the water lines are neither weak (filled in by emission) ...

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Section: Stellar Parametersmentioning

confidence: 97%

Systematic trend of water vapour absorption in red giant atmospheres revealed by high resolution TEXES 12 μm spectra

Ryde

Lambert

Farzone

et al. 2014

A&A

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“…at a few mas distance. Most recently, Cruzalèbes et al (2013) presented evidence that there is a departure from centrosymmetry based on VLTI/AMBER data. On the other hand, MIDI interferometry carried out by Klotz et al (2013) was found to be consistent with a spherical structure of the star and its circumstellar envelope.…”

Section: The Targetmentioning

confidence: 99%

The complex environment of the bright carbon star TX Piscium as probed by spectro-astrometry

Hron

Uttenthaler

Aringer

et al. 2015

A&A

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Context. Stars on the asymptotic giant branch (AGB) show broad evidence of inhomogeneous atmospheres and circumstellar envelopes. These have been studied by a variety of methods on various angular scales. In this paper we explore the envelope of the well-studied carbon star TX Psc by the technique of spectro-astrometry. Aims. We explore the potential of this method for detecting asymmetries around AGB stars. Methods. We obtained CRIRES observations of several CO ∆v = 1 lines near 4.6 µm and HCN lines near 3 µm in 2010 and 2013. These were then searched for spectro-astrometric signatures. For the interpretation of the results, we used simple simulated observations. Results. Several lines show significant photocentre shifts with a clear dependence on position angle. In all cases, tilde-shaped signatures are found where the positive and negative shifts (at PA 0• ) are associated with blue and weaker red components of the lines. The shifts can be modelled with a bright blob 70 mas to 210 mas south of the star with a flux of several percent of the photospheric flux. We estimate a lower limit of the blob temperature of 1000 K. The blob may be related to a mass ejection as found for AGB stars or red supergiants. We also consider the scenario of a companion object. Conclusions. Although there is clear spectro-astrometric evidence of a rather prominent structure near TX Psc, it does not seem to relate to the other evidence of asymmetries, so no definite explanation can be given. Our data thus underline the very complex structure of the environment of this star, but further observations that sample the angular scales out to a few hundred milli-arcseconds are needed to get a clearer picture.

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“…The investigation of AGB stars using a combination of different techniques has been increasing over the last few years, while, to date, only a few interferometric observations of carbon stars have been directly compared with model atmospheres (Ohnaka et al 2007;Paladini et al 2011;Cruzalèbes et al 2013;Klotz et al 2013;van Belle et al 2013). From those, only very few have made use of time-dependent self-consistent dynamic models (Sacuto et al 2011;Rau et al 2015).…”

Section: Introductionmentioning

confidence: 99%

The adventure of carbon stars

Rau

Hron

Paladini

et al. 2017

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Context. Modeling stellar atmospheres is a complex and intriguing task in modern astronomy. A systematic comparison of models with multi-technique observations is the only efficient way to constrain the models. Aims. We intend to perform self-consistent modeling of the atmospheres of six carbon-rich AGB stars (R Lep, R Vol, Y Pav, AQ Sgr, U Hya, and X TrA) with the aim of enlarging the knowledge of the dynamic processes occurring in their atmospheres. Methods. We used VLTI/MIDI interferometric observations, in combination with spectro-photometric data, and compared them with self-consistent, dynamic model atmospheres. Results. We found that the models can reproduce spectral energy distribution (SED) data well at wavelengths longer than 1 µm, and the interferometric observations between 8 µm and 10 µm. Discrepancies observed at wavelengths shorter than 1 µm in the SED, and longer than 10 µm in the visibilities, could be due to a combination of data-and model-related effects. The models best fitting the Miras are significantly extended, and have a prominent shell-like structure. On the contrary, the models best fitting the non-Miras are more compact, showing lower average mass loss. The mass loss is of episodic or multi-periodic nature but causes the visual amplitudes to be notably larger than the observed ones. A number of stellar parameters were derived from the model fitting: T Ross , L Ross , M, C/O, andṀ. Our findings agree well with literature values within the uncertainties. T Ross , and L Ross are also in good agreement with the temperature derived from the angular diameter T (θ (V−K) ) and the bolometric luminosity from the SED fitting L bol , except for AQ Sgr. The possible reasons are discussed in the text. Finally, θ Ross and θ (V−K) agree with one another better for the Miras than for the nonMiras targets, which is probably connected to the episodic nature of the latter models. We also located the stars in the H-R diagram, comparing them with evolutionary tracks. We found that the main derived properties (L, T eff , C/O ratios and stellar masses) from the model fitting are in good agreement with TP-AGB evolutionary calculations for carbon stars carried out with the COLIBRI code.

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Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER★

Cited by 30 publications

References 103 publications

Systematic trend of water vapour absorption in red giant atmospheres revealed by high resolution TEXES 12 μm spectra

Systematic trend of water vapour absorption in red giant atmospheres revealed by high resolution TEXES 12 μm spectra

The complex environment of the bright carbon star TX Piscium as probed by spectro-astrometry

The adventure of carbon stars

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