Empirical determination of the lithium 6707.856 Å wavelength in young stars
Abstract: Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at ∼6708 Å is commonly used, especially in the case of young stellar objects for which it is one of the strongest absorption lines. However, this is a complex line comprising two isotope fine-structure doublets. We empirically measure the wavelength of this Li feature in a sample of young stars from the PENELLOPE/VLT programme (using X-Shooter, UVES and… Show more
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Cited by 5 publications
References 65 publications
Context. Observing the spatial distribution and excitation processes of atomic and molecular gas in the inner regions (<20 au) of young (<10 Myr) protoplanetary disks helps us to understand the conditions for the formation and evolution of planetary systems. Aims. In the framework of the PENELLOPE and ULLYSES projects, we aim to characterize the atomic and molecular component of protoplanetary disks in a sample of 11 classical T Tauri stars of the Orion OB1 and σ-Orionis associations. Methods. We analyzed the flux-calibrated optical forbidden lines and the fluorescent ultraviolet H2 progressions using spectra acquired with ESPRESSO at VLT, UVES at VLT, and HST-COS. Line morphologies were characterized through Gaussian decomposition. We then focused on the properties of the narrow low-velocity (full width half maximum <40 km s−1 and |υp| < 30 km s−1) component (NLVC) of the [O I] 630 nm line and compared them with those of the UV-H2 lines. Results. We found that the [O I]630 NLVC and the UV-H2 lines are strongly correlated in terms of peak velocities, full width at half maximum values, and luminosity. Assuming that the line width is dominated by Keplerian broadening, the [O I]630 NLVC originates from a disk region between 0.5 and 3.5 au, while that of UV-H2 originates in a region from 0.05 to 1 au. The luminosities of [O I]630 NLVC and UV-H2 correlate with an accretion luminosity with a similar slope, as well as with the luminosity of the C IV154.8, 155 nm doublet. We discuss such correlations in the framework of the currently suggested excitation processes for the [O I]630 NLVC. Conclusions. Our results can be interpreted in a scenario in which the [O I]630 NLVC and UV-H2 have a common disk origin with a partially overlapped radial extension. We also suggest that the excitation of the [O I] NLVC is mainly induced by stellar far-ultraviolet continuum photons, than being of mostly thermal origin. This study demonstrates the potential of contemporaneous wide-band highresolution spectroscopy in linking different tracers of protoplanetary disks.
Context. Observing the spatial distribution and excitation processes of atomic and molecular gas in the inner regions (<20 au) of young (<10 Myr) protoplanetary disks helps us to understand the conditions for the formation and evolution of planetary systems. Aims. In the framework of the PENELLOPE and ULLYSES projects, we aim to characterize the atomic and molecular component of protoplanetary disks in a sample of 11 classical T Tauri stars of the Orion OB1 and σ-Orionis associations. Methods. We analyzed the flux-calibrated optical forbidden lines and the fluorescent ultraviolet H2 progressions using spectra acquired with ESPRESSO at VLT, UVES at VLT, and HST-COS. Line morphologies were characterized through Gaussian decomposition. We then focused on the properties of the narrow low-velocity (full width half maximum <40 km s−1 and |υp| < 30 km s−1) component (NLVC) of the [O I] 630 nm line and compared them with those of the UV-H2 lines. Results. We found that the [O I]630 NLVC and the UV-H2 lines are strongly correlated in terms of peak velocities, full width at half maximum values, and luminosity. Assuming that the line width is dominated by Keplerian broadening, the [O I]630 NLVC originates from a disk region between 0.5 and 3.5 au, while that of UV-H2 originates in a region from 0.05 to 1 au. The luminosities of [O I]630 NLVC and UV-H2 correlate with an accretion luminosity with a similar slope, as well as with the luminosity of the C IV154.8, 155 nm doublet. We discuss such correlations in the framework of the currently suggested excitation processes for the [O I]630 NLVC. Conclusions. Our results can be interpreted in a scenario in which the [O I]630 NLVC and UV-H2 have a common disk origin with a partially overlapped radial extension. We also suggest that the excitation of the [O I] NLVC is mainly induced by stellar far-ultraviolet continuum photons, than being of mostly thermal origin. This study demonstrates the potential of contemporaneous wide-band highresolution spectroscopy in linking different tracers of protoplanetary disks.
GIARPS High-resolution Observations of T Tauri stars (GHOsT)
This paper aims to revisit the kinematical and physical properties of the warm ($T 5000-10\ 000 K) atomic gas in the inner disk ($<5$ au) region of classical T Tauri stars (CTTs) and relate them to the properties of the outer dusty disk resolved with ALMA. We also want to define constraints for the mass-loss in the inner atomic winds and jets to assess their role in the evolution and dispersal of planet-forming disks. We used the high resolution (R=115,000, sim 2.6 spectra of 36 CTTs observed as part of the GIARPS High-resolution Observations of T Tauri stars (GHOsT) project and analysed the profile and luminosity of the brightest optical forbidden lines, namely and We decomposed the line profiles into different velocity components, and concentrated our analysis mostly on the so-called narrow low-velocity component (NLVC). We find that about 40 $<!PCT!>$ of sources display a NLVC peak velocity (V$_p$) compatible with the stellar velocity. These include the transitional disks (TD) and typically show a single low velocity component (LVC), lower mass accretion rates, and the absence of a jet. They therefore might represent later evolutionary stages where the emission from the disk is dominant with respect to the wind contribution. No difference in kinematical properties was instead found between sources with full disks and disks with substructures as resolved by ALMA. The profiles peaking at the stellar velocity are well fitted by a simple Keplerian disk model, where the emission line region extends from sim 0.01 au up to several tens of au in some cases. The emission is detected inside the sub-millimetre dust cavities of all the TDs. No correlation is found between kep $, derived from the line half width at half maximum (HWHM), and the size of the dust cavity. We see an anti-correlation between the 557/630 nm ratio and kep $, which suggests that the emitting region expands as the gas dominating the emission cools and becomes less dense. We confirmed previous findings that the line ratios observed in the LVC, if compared with a thermal single temperature and density model, imply $n_e and $T_e 5000 - 10\,000 K, and additionally constrained the ionisation fraction in the NLVC to be $x_e < 0.1$. We however discuss the limits of applying this diagnostic to winds that are not spatially resolved. The emission from the disk should be considered as an important contribution to the forbidden line emission in CTTs. Also, the clearing of warm atomic gas from the upper disk layers does not seem to follow the dispersal of the bulk of molecular gas and dust during late disk evolution. For the outflow component, we estimated the mass-loss for both the disk winds and jets. We conclude that without better knowledge of the wind geometry and spatial extent, and given the limitation of the diagnostics, the mass-loss rates in the wind traced by the blue shifted LVC cannot be constrained better than a factor of 100, with a spanning between sim 0.01 and more than 1. When compared with synthetic images of X-ray photoevaporation models, the estimated represents a lower limit to the total mass-loss rate of the model, indicating that is likely not the best tracer to probe mass-loss in low-velocity winds.
The physical mechanism leading to the formation of the blue loop in the Hertzsprung-Russell (HR) diagram is not satisfactorily explained by the evolutionary track of single stars. Rapid rotation and low metallicity drastically modify the internal structures and surface compositions of stars. Therefore, they provide a very significant pattern to investigate the evolutionary properties of the blue loop. In this paper, we mainly explore how rapid rotation and low metallicity have an important impact on the occurrence and extension of the blue loop. To this end, we implemented the rotating stellar evolution model, including the angular momentum transportation and chemical element mixing. We incorporated several initial rotational velocities and two characteristic metallicities in various models to explore the blue loop extension. The blue loop can occur when the hydrogen burning shell merges with the hydrogen--helium abundance discontinuity. We find that the blue loop extension strongly depends on the amplitude and gradient of the hydrogen--helium discontinuity. The hydrogen--helium discontinuity is created by the intermediate convective region or the convective dredge-up. A steeper hydrogen gradient in association with a greater amplitude of the hydrogen abundance discontinuity may favour a hotter star. Both the low metallicity and rapid rotation tend to restrain the development of the outer convective envelope and thus disfavour the occurrence and extension of the blue loop. There are three main reasons for this occurrence. Firstly, the helium core and its core potential can be enlarged by rotational mixing or low metallicity. Secondly, rapid rotation reduces the convective dredge-up depth in the star with $ Z=0.014$ and the mass extension of the intermediate convective region in the star with $ Z=0.0008$. Both of these phenomena lead to a reduction of the amplitude of the hydrogen abundance gradient. Thirdly, strong rotational mixing in the model (i.e. $ ini =350$ Km/s) with $ Z=0.0008$ reduces the energy generation rate from the hydrogen burning shell. Without bending towards higher effective temperature in the HR diagram, the additional helium brought near the H-burning shell associated with the larger He core can cause the star to expand towards becoming a red giant star directly after the core hydrogen burning. Rapid rotation and low metallicity tend to produce surface enrichment of the ratio of nitrogen to carbon and reduce the $ C$ left in the core; this has an important influence on the stellar compactness of the supernovae progenitor.
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