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A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER
摘要： We determine the physical parameters of the outer atmosphere of a sample of eight evolved stars, including the red supergiant α Scorpii, the red giant branch stars α Bootis and γ Crucis, the K giant λ Velorum, the normal M giants BK Virginis and SW Virginis, and the Mira star W Hydrae (in two different luminosity phases) by spatially resolving the stars in the individual carbon monoxide (CO) first overtone lines. We used the Astronomical Multi-BEam combineR (AMBER) instrument at the Very Large Telescope Interferometer (VLTI), in high-resolution mode (λ/(cid:5)λ ≈ 12 000) between 2.28 and 2.31 μm in the K band. The maximal angular resolution is 10 mas, obtained using a triplet telescope configuration, with baselines from 7 to 48 m. By using a numerical model of a molecular atmosphere in a spherical shells (MOLsphere), called PAMPERO (an acronym for the ‘physical approach of molecular photospheric ejection at high angular resolution for evolved stars’), we add multiple extended CO layers above the photospheric MARCS model at an adequate spatial resolution. We use the differential visibilities and the spectrum to estimate the size (R) of the CO MOLsphere, its column density (NCO) and temperature (Tmol) distributions along the stellar radius. The combining of the χ 2 minimization and a fine grid approach for uncertainty analysis leads to reasonable NCO and Tmol distributions along the stellar radius of the MOLsphere.
关键词： techniques: high angular resolution,stars: atmospheres,stars: AGB and post-AGB,stars: fundamental parameters,methods: numerical,methods: observational
更新于2025-09-11 14:15:04
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Mode identification based on time-series spectrophotometry for the bright rapid sdB pulsator EC 01541?1409
摘要： We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541?1409 with the aim of identifying the degree index (cid:2) of the larger amplitude modes. This mode identi?cation can be extremely useful in detailed searches for viable asteroseismic models in parameter space, and can be crucial for testing the validity of a solution a posteriori. To achieve it, we exploit the (cid:2)-dependence of the monochromatic amplitude, phase, and velocity-to-amplitude ratio of a mode as a function of wavelength. We use the (cid:2)-sensitive phase lag between the ?ux perturbation and the radial velocity as an additional diagnostic tool. On this basis, we are able to unambiguously identify the dominant 140.5 s pulsation of our target as a radial mode, and the second-highest amplitude periodicity at 145.8 s as an (cid:2) = 2 mode. We further exploit the exceptionally high-sensitivity data that we gathered for the dominant mode to infer modal properties that are usually quite di?cult to estimate in sdB pulsators, namely the physical values of the dimensionless radius, temperature, and surface gravity perturbations.
关键词： stars: oscillations,stars: individual: EC 01541-1409,techniques: imaging spectroscopy,stars: atmospheres,stars: variables: general,asteroseismology
更新于2025-09-10 09:29:36
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Spatially resolved spectroscopy across stellar surfaces
摘要： Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely di?erent stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks. Aims. We observe high-resolution spectral line pro?les across spatially highly resolved stellar surfaces, which are free from the e?ects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic pro?les from 3D models. Methods. During exoplanet transits, successive stellar surface portions become hidden and di?erential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than ～1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identi?ed through simulated observations of synthetic spectral lines. Results. In normal stars, line pro?le ratios between various transit phases may vary by ～0.5%, requiring S /N (cid:38) 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions. For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.
关键词： line: pro?les,hydrodynamics,stars: atmospheres,planets and satellites: gaseous planets,techniques: spectroscopic,stars: solar-type
更新于2025-09-10 09:29:36
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A new method to compute limb-darkening coefficients for stellar atmosphere models with spherical symmetry: the space missions TESS, Kepler, CoRoT, and MOST
摘要： Aims. One of the biggest problems we can encounter while dealing with the limb-darkening coe?cients for stellar atmospheric models with spherical symmetry is the di?culty of adjusting both the limb and the central parts simultaneously. In particular, the regions near the drop-o?s are not well reproduced for most models, depending on Te?, log g, or wavelength. Even if the law with four terms is used, these disagreements still persist. Here we introduce a new method that considerably improves the description of both the limb and the central parts and that will allow users to test models of stellar atmospheres with spherical symmetry more accurately in environments such as exoplanetary transits, eclipsing binaries, etc. Methods. The method introduced here is simple. Instead of considering all the μ points in the adjustment, as is traditional, we consider only the points until the drop-o? (μcri) of each model. From this point, we impose a condition I(μ)/I(1) = 0. All calculations were performed by adopting the least-squares method. Results. The resulting coe?cients using this new method reproduce the intensity distribution of the PHOENIX spherical models (COND and DRIFT) quite well for the photometric systems of the space missions TESS, Kepler, CoRoT, and MOST. The calculations cover the following ranges of local gravity and e?ective temperatures: 2.5 ≤ log g ≤ 6.0 and 1500 K ≤ T e? ≤ 12 000 K. The new spherical coe?cients can easily be adapted to the most commonly used light curve synthesis codes.
关键词： planetary systems,binaries: eclipsing,stars: atmospheres
更新于2025-09-10 09:29:36
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VLTI/AMBER spectro-interferometry of the late-type supergiants V766 Cen (=HR 5171?A), <i>σ</i> Oph, BM Sco, and HD 206859
摘要： Aims. We add four warmer late-type supergiants to our previous spectro-interferometric studies of red giants and supergiants. Methods. We measure the near-continuum angular diameter, derive fundamental parameters, discuss the evolutionary stage, and study extended atmospheric atomic and molecular layers. Results. V766 Cen (=HR 5171 A) is found to be a high-luminosity (log L/L(cid:12) = 5.8 ± 0.4) source of effective temperature 4290 ± 760 K and radius 1490 ± 540 R(cid:12), located in the Hertzsprung-Russell (HR) diagram close to both the Hayashi limit and Eddington limit; this source is consistent with a 40 M(cid:12) evolutionary track without rotation and current mass 27–36 M(cid:12). V766 Cen exhibits Na i in emission arising from a shell of radius 1.5 RPhot and a photocenter displacement of about 0.1 RPhot. It shows strong extended molecular (CO) layers and a dusty circumstellar background component. The other three sources are found to have lower luminosities of about log L/L(cid:12) = 3.4–3.5, corresponding to 5–9 M(cid:12) evolutionary tracks. They cover effective temperatures of 3900 K to 5300 K and radii of 60–120 R(cid:12). They do not show extended molecular layers as observed for higher luminosity RSGs of our sample. BM Sco shows an unusually strong contribution by an over-resolved circumstellar dust component. Conclusions. V766 Cen is a red supergiant located close to the Hayashi limit instead of a yellow hypergiant already evolving back toward warmer effective temperatures as discussed in the literature. Our observations of the Na i line and the extended molecular layers suggest an optically thick pseudo-photosphere at about 1.5 RPhot at the onset of the wind. The stars σ Oph, BM Sco, and HD 206859 are more likely high-mass red giants instead of RSGs as implied by their luminosity class Ib. This leaves us with an unsampled locus in the HR diagram corresponding to luminosities log L/L(cid:12) ～ 3.8–4.8 or masses 10–13 M(cid:12), possibly corresponding to the mass region where stars explode as (type II-P) supernovae during the red supergiant stage. With V766 Cen, we now confirm that our previously found relation of increasing strength of extended molecular layers with increasing luminosities extends to double our previous luminosities and up to the Eddington limit. This might further point to steadily increasing radiative winds with increasing luminosity.
关键词： supergiants,stars: individual: BM Sco,stars: atmospheres,stars: individual: V766 Cen,techniques: interferometric,stars: mass-loss
更新于2025-09-09 09:28:46
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Tracking Advanced Planetary Systems (TAPAS) with HARPS-N
摘要： Context. Lithium-rich giant stars are rare objects. For some of them, Li enrichment exceeds the abundance of this element found in solar system meteorites, suggesting that these stars have gone through a Li enhancement process. Aims. We identi?ed a Li-rich giant HD 107028 with A(Li) > 3.3 in a sample of evolved stars observed within the PennState Toru′n Planet Search. In this work we study di?erent enhancement scenarios and we try to identify the one responsible for Li enrichment in HD 107028. Methods. We collected high-resolution spectra with three di?erent instruments, covering di?erent spectral ranges. We determined stellar parameters and abundances of selected elements with both equivalent width measurements and analysis, and spectral synthesis. We also collected multi-epoch high-precision radial velocities in an attempt to detect a companion. Results. Collected data show that HD 107028 is a star at the base of the red giant branch (RGB). Except for high Li abundance, we have not identi?ed any other anomalies in its chemical composition, and there is no indication of a low-mass or stellar companion. We exclude Li production at the luminosity function bump on the RGB as the e?ective temperature and luminosity suggest that the evolutionary state is much earlier than the RGB bump. We also cannot con?rm the Li enhancement by contamination as we do not observe any anomalies that are associated with this scenario. Conclusions. After evaluating various scenarios of Li enhancement we conclude that the Li-overabundance of HD 107028 originates from main-sequence evolution, and may be caused by di?usion processes.
关键词： stars: fundamental parameters,planetary systems,stars: atmospheres,techniques: spectroscopic,stars: individual: HD 107028,stars: late-type
更新于2025-09-04 15:30:14
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The Penn State – Toruń Centre for Astronomy Planet Search stars <i>(Corrigendum)</i>
摘要： Table 2 in our recent paper (Niedzielski et al. 2016) erroneously includes 20 stars that were finally adopted for detailed spectroscopic analysis (including 11 SB1s mentioned in the text) and are listed in Table 1 as well. Consequently, the corrected Table 2 (available in electronic version) contains 33 rather than 53 stars. They are 18 SB2 stars, 14 ones with variable CCFs (possibly SB2) and one with a weak CCF.
关键词： stars: atmospheres,stars: late-type,stars: general,stars: fundamental parameters,errata, addenda
更新于2025-09-04 15:30:14
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Carbon stars in the X-shooter Spectral Library
摘要： In a previous paper, we assembled a collection of medium-resolution spectra of 35 carbon stars, covering optical and near-infrared wavelengths from 400 to 2400 nm. The sample includes stars from the Milky Way and the Magellanic Clouds, with a variety of (J ? Ks) colors and pulsation properties. In the present paper, we compare these observations to a new set of high-resolution synthetic spectra, based on hydrostatic model atmospheres. We ?nd that the broad-band colors and the molecular-band strengths measured by spectrophotometric indices match those of the models when (J ? Ks) is bluer than about 1.6, while the redder stars require either additional reddening or dust emission or both. Using a grid of models to ?t the full observed spectra, we estimate the most likely atmospheric parameters Te?, log(g), [Fe/H] and C/O. These parameters derived independently in the optical and near-infrared are generally consistent when (J ? Ks) < 1.6. The temperatures found based on either wavelength range are typically within ±100 K of each other, and log(g) and [Fe/H] are consistent with the values expected for this sample. The reddest stars ((J ? Ks) > 1.6) are divided into two families, characterized by the presence or absence of an absorption feature at 1.53 μm, generally associated with HCN and C2H2. Stars from the ?rst family begin to be more a?ected by circumstellar extinction. The parameters found using optical or near-infrared wavelengths are still compatible with each other, but the error bars become larger. In stars showing the 1.53 μm feature, which are all large-amplitude variables, the e?ects of pulsation are strong and the spectra are poorly matched with hydrostatic models. For these, atmospheric parameters could not be derived reliably, and dynamical models are needed for proper interpretation.
关键词： stars: carbon,stars: atmospheres,infrared: stars
更新于2025-09-04 15:30:14
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CRIRES-POP: a library of high resolution spectra in the near-infrared
摘要： Context. High resolution stellar spectral atlases are valuable resources to astronomy. They are rare in the 1?5 μm region for historical reasons, but once available, high resolution atlases in this part of the spectrum will aid the study of a wide range of astrophysical phenomena. Aims. The aim of the CRIRES-POP project is to produce a high resolution near-infrared spectral library of stars across the H-R diagram. The aim of this paper is to present the fully reduced spectrum of the K giant 10 Leo that will form the basis of the first atlas within the CRIRES-POP library, to provide a full description of the data reduction processes involved, and to provide an update on the CRIRES-POP project. Methods. All CRIRES-POP targets were observed with almost 200 different observational settings of CRIRES on the ESO Very Large Telescope, resulting in a basically complete coverage of its spectral range as accessible from the ground. We reduced the spectra of 10 Leo with the CRIRES pipeline, corrected the wavelength solution and removed telluric absorption with Molecfit, then resampled the spectra to a common wavelength scale, shifted them to rest wavelengths, flux normalised, and median combined them into one final data product. Results. We present the fully reduced, high resolution, near-infrared spectrum of 10 Leo. This is also the first complete spectrum from the CRIRES instrument. The spectrum is available online. Conclusions. The first CRIRES-POP spectrum has exceeded our quality expectations and will form the centre of a state-of-the-art stellar atlas. This first CRIRES-POP atlas will soon be available, and further atlases will follow. All CRIRES-POP data products will be freely and publicly available online.
关键词： infrared: stars,atlases,atmospheric effects,stars: atmospheres,techniques: spectroscopic,stars: late-type
更新于2025-09-04 15:30:14
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A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars
摘要： Aims. Hot subdwarf stars represent a poorly understood late phase of stellar evolution. While binary evolution plays an important role for the formation of B-type subdwarfs (sdB), the origin of the helium dominated subclass of O-type subdwarfs (He-sdO) is still unknown. We search for chemical signatures of their genesis by means of quantitative spectral analyses of high-quality visual and ultraviolet spectra. Methods. Four prototypical He-sdO stars, one belonging to the nitrogen-rich and three to the C-rich subclass, were selected for which archival far-ultraviolet spectra from the FUSE satellite as well as high-resolution visual and UVA spectra taken with the ESO-UVES/FEROS spectrographs are available. Using Tlusty200/Synspec49 to compute line blanketed- non-local thermodynamic equilibrium (NLTE) model atmospheres and synthetic spectra, atmospheric parameters and the abundances patterns have been derived. The ?nal models included H, He, C, N, O, Ne, Mg, Al, Si, P, S, Fe, and Ni represented by the most detailed model atoms available. Because of the enrichment of either nitrogen or carbon, it turned out, that models including these elements at the appropriate high abundance provide su?ciently accurate approximations to the temperature strati?cation of full models. Results. No indications for binarity were found, neither radial velocity variations nor photometric evidence for the presence of a companion could be detected. All stars have helium-dominated atmospheres almost free of hydrogen and temperatures between 42 000 K and 47 000 K while their surface gravities lie between log g = 5.4 and 5.7. The abundance pattern of CD–31?4800 displays the signatures of CNO burning, while heavier elements are subsolar by about 0.4 dex, except for Ne and Si which are close to solar. The abundance patterns of the C-rich He-sdOs are more complex. A slightly subsolar metallicity is accompanied by N-enrichment and O-de?ciency, less pronounced than in CD–31?4800. Neon is mildly to strongly enriched, up to a factor of ten with respect to the sun in LS IV +10? 9. The nickel-to-iron ratio is signi?cantly super-solar. Using spectral energy distributions and Gaia parallaxes the masses of the stars were determined. They are found to scatter around the canonical mass for the core helium ?ash, although the uncertainties are large. Conclusions. The abundance pattern observed for CD–31?4800 is consistent with predictions of models for slow (cold) mergers of pairs of equal mass helium WDs except for the low oxygen abundance observed. Models for composite mergers were considered for the C-rich stars, but predict abundance pattern dissimilar to those determined. [CW83] 0904?02, though, may be a candidate for a composite He-WD merger, as it rotates and appears to be more massive than the other program stars. New evolutionary models for the hot ?asher scenario predict abundance patterns similar to those determined for the C-rich stars. Hence, C-rich He-sdO may well result from late He ?ashes with deep-mixing episodes.
关键词： stars: evolution,subdwarfs,stars: atmospheres,stars: abundances
更新于2025-09-04 15:30:14