THE DETECTION OF INFRARED SiS BANDS IN SPECTRA OF S STARS

Cami, J.; Sloan, G. C.; Markwick-Kemper, A. J.; Zijlstra, A. A.; Bauschlicher, Charles W.; Matsuura, M.; Decin, L.; Hony, S.

doi:10.1088/0004-637x/690/2/l122

Cited by 14 publications

(8 citation statements)

References 34 publications

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“…Previous studies of this sample have already led to the identification of the fundamental ro-vibrational band of SiS at 13 µm and its first overtone at 6.7 µm in absorption (Cami et al 2009) and in emission (Sloan et al 2011). Furthermore, four stars in this sample show the typical hydrocarbon emission features on top of an oxygen-rich photosphere (Smolders et al 2010).…”

Section: Introductionmentioning

confidence: 62%

Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae

Smolders

Verhoelst

Neyskens

et al. 2012

A&A

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We report on the discovery of an infrared emission band in the Spitzer spectrum of the S-type AGB star NP Aurigae that is caused by TiO molecules in the circumstellar environment. We modeled the observed emission to derive the temperature of the TiO molecules (≈600 K), an upper limit on the column density (≈10 17.25 cm −2 ) and a lower limit on the spatial extent of the layer that contains these molecules. (≈4.6 R ). This is the first time that this TiO emission band is observed. A search for similar emission features in the sample of S-type stars yielded two additional candidates. However, owing to the additional dust emission, the identification is less stringent. By comparing the stellar characteristics of NP Aur to those of the other stars in our sample, we find that all stars with TiO emission show large-amplitude pulsations, s-process enrichment, and a low C/O ratio. These characteristics might be necessary requirements for a star to show TiO in emission, but they are not sufficient.

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Section: Introductionmentioning

confidence: 62%

Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae

Smolders

Verhoelst

Neyskens

et al. 2012

A&A

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“…The radiative transfer equation is solved monochromatically using pre-tabulated extinction coefficients as a function of temperature, density, and wavelength. The lookup tables were computed for the same chemical compositions as the RHD simulations using the same extensive atomic and molecular continuum and line opacity data as the latest generation of MARCS models (Gustafsson et al 2008) with the addition -with respect to Table 2 of Gustafsson's paper -of the SiS molecule (Cami et al 2009), which is particularly important for the far-infrared region of the spectrum. While the sources of line opacities used in the RHD simulations of Magic et al (2013) and in OPTIM3D are the same, the data for the continuum opacities are almost the same: Hayek et al (2010) reported that the data used in RHD simulations are mostly identical to those used in the MARCS models, but include additional bound-free data from the Opacity Project and the Iron Project (Trampedach et al, priv.…”

Section: Three-dimensional Radiative Transfermentioning

confidence: 99%

The STAGGER-grid: A grid of 3D stellar atmosphere models

Chiavassa

Casagrande

Collet

et al. 2018

A&A

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Context. The surface structures and dynamics of cool stars are characterised by the presence of convective motions and turbulent flows which shape the emergent spectrum. Aims. We used realistic three-dimensional (3D) radiative hydrodynamical simulations from the STAGGER-grid to calculate synthetic spectra with the radiative transfer code OPTIM3D for stars with different stellar parameters to predict photometric colours and convective velocity shifts. Methods. We calculated spectra from 1000 to 200 000 Å with a constant resolving power of λ∕Δλ = 20 000 and from 8470 and 8710 Å (Gaia Radial Velocity Spectrometer – RVS – spectral range) with a constant resolving power of λ∕Δλ = 300 000. Results. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV (RI)C, SDSS, 2MASS, Gaia, SkyMapper, Strömgren systems, and HST-WFC3. Our synthetic magnitudes are compared with those obtained using 1D hydrostatic models. We showed that 1D versus 3D differences are limited to a small percent except for the narrow filters that span the optical and UV region of the spectrum. In addition, we derived the effect of the convective velocity fields on selected Fe I lines. We found the overall convective shift for 3D simulations with respect to the reference 1D hydrostatic models, revealing line shifts of between −0.235 and +0.361 km s−1. We showed a net correlation of the convective shifts with the effective temperature: lower effective temperatures denote redshifts and higher effective temperatures denote blueshifts. We conclude that the extraction of accurate radial velocities from RVS spectra need an appropriate wavelength correction from convection shifts. Conclusions. The use of realistic 3D hydrodynamical stellar atmosphere simulations has a small but significant impact on the predicted photometry compared with classical 1D hydrostatic models for late-type stars. We make all the spectra publicly available for the community through the POLLUX database.

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“…comm.) as an update after the new energy levels calculated by Ram et al (2010a,b); H 2 O lines were taken from Barber et al (2006); SiO lines were taken from Langhoff & Bauschlicher (1993); MgH lines were taken from Skory et al (2003); OH were taken from Goldman et al (1998), SiS were taken from Cami et al (2009) and OH ones from the HITRAN database (Rothman & Gordon 2009). The atomic lines were taken from the VALD v-0.4.4 database (Kupka et al 2000).…”

Section: Observed Data and Line Listsmentioning

confidence: 99%

Carbon and oxygen isotopic ratios in Arcturus and Aldebaran

Abia

Palmerini

Busso

et al. 2012

A&A

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Context. We re-analyzed the carbon and oxygen isotopic ratios in the atmospheres of the two bright K giants Arcturus (α Boo) and Aldebaran (α Tau). Aims. These stars are in the evolutionary stage following the first dredge-up (FDU). Previous determinations (dating back more than 20 years) of their 16 O/ 18 O ratios showed a rough agreement with FDU expectations; however, the estimated 16 O/ 17 O and 12 C/ 13 C ratios were lower than in the canonical predictions for red giants. Today these anomalies are interpreted as signs of the occurrence of non-convective mixing episodes. We therefore re-investigated this problem to verify whether the observed data can be reproduced in this scenario and if the fairly well determined properties of the two stars can help us in fixing the uncertain parameters that characterize non-convective mixing and in constraining its physical nature. Methods. We used high-resolution infrared spectra from the literature to derive the 12 C/ 13 C and 16 O/ 17 O/ 18 O ratios from CO molecular lines near 5 μm, using the local termodynamic equilibrium (LTE) spectral synthesis method. We made use of the recently published ACE-FTS atlas of the infrared solar spectrum for constructing an updated atomic and molecular line lists in this spectral range. We also reconsidered the determination of the stellar parameters to build the proper atmospheric and evolutionary models. Results. We found that both the C and the O isotopic ratios for the two stars considered actually disagree with pure FDU predictions. This reinforces the idea that non-convective transport episodes occurred in these stars. By reproducing the observed elemental and isotopic abundances with the help of parametric models for the coupled occurrence of nucleosynthesis and mass circulation, we derived constraints on the properties of non-convective mixing, providing information on the so far elusive physics of these phenomena. We find that very slow mixing, like that associated to diffusive processes, is incapable of explaining the observed data, which require a fast transport. Circulation mechanisms with speeds intermediate between those typical of diffusive and convective mixing are necessary. We conclude with a word of caution on the conclusions possible at this stage however, as the parameters for the mass transport are fairly sensitive to the stellar mass and initial composition. At least for α Boo, reducing the uncertainty still remaining on these data would be highly desirable.

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THE DETECTION OF INFRARED SiS BANDS IN SPECTRA OF S STARS

Cited by 14 publications

References 34 publications

Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae

Discovery of a TiO emission band in the infrared spectrum of the S star NP Aurigae

The STAGGER-grid: A grid of 3D stellar atmosphere models

Carbon and oxygen isotopic ratios in Arcturus and Aldebaran

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