The mass accretion rate, M sub(acc), is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (Mlow *< or =2.0 M sub(middot ...in circle)) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, L sub(acc), increases with the stellar luminosity, Llow *, with an overall slope of ~1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below Llow *approximate 0.1L sub(middot in circle), where L sub(acc) is always lower than 0.01Llow *. We argue that the L sub(acc)-Llow * slope is not due to observational biases, but is a true property of the Lupus YSOs. The logM sub(acc)- logMlow * correlation shows a statistically significant evidence of a break, with a steeper relation for Mlow *< or =0.2M sub(middot in circle) and a flatter slope for higher masses. The bimodality of the M sub(acc)- Mlow * relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may also lead to disc dispersal on different timescales depending on the stellar mass. The sample studied here more than doubles the number of YSOs with homogeneously and simultaneously determined L sub(acc) and luminosity, L sub(line), of many permitted emission lines. Hence, we also refined the empirical relationships between L sub(acc) and L sub(line) on a more solid statistical basis.
Context. The origin of the observed diversity of planetary system architectures is one of the main topics of exoplanetary research. The detection of a statistically significant sample of planets ...around young stars allows us to study the early stages of planet formation and evolution, but only a handful are known so far. In this regard a considerable contribution is expected from the NASA TESS satellite, which is now performing a survey of ~85% of the sky to search for short-period transiting planets. Aims. In its first month of operation TESS found a planet candidate with an orbital period of 8.14 days around a member of the Tuc-Hor young association (~40 Myr), the G6V main component of the binary system DS Tuc. If confirmed, it would be the first transiting planet around a young star suitable for radial velocity and/or atmospheric characterisation. Our aim is to validate the planetary nature of this companion and to measure its orbital and physical parameters. Methods. We obtained accurate planet parameters by coupling an independent reprocessing of the TESS light curve with improved stellar parameters and the dilution caused by the binary companion; we analysed high-precision archival radial velocities to impose an upper limit of about 0.1 MJup on the planet mass; we finally ruled out the presence of external companions beyond 40 au with adaptive optics images. Results. We confirm the presence of a young giant (R = 0.50 RJup) planet having a non-negligible possibility to be inflated (theoretical mass ≲ 20 M⊕) around DS Tuc A. We discuss the feasibility of mass determination, Rossiter-McLaughlin analysis, and atmosphere characterisation allowed by the brightness of the star.
The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in ...accreting (Class II) young stellar objects. A detailed investigation of the effect of chromospheilc emission on the estimates of mass accretion rate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) K and M-type stars. Our goal is to measure the chromospheric activity of Class III pre main sequence stars to determine its effect on the estimates of the accretion luminosity (Lsubacc) and mass accretion rate (Msubacc) in young stellar objects with disks. Values of Lsubacc < or=10sup -3 obtained in accreting low-mass pre main sequence stars through line luminosity should be treated with caution because the line emission may be dominated by the contribution of chromospheric activity.
We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M⊙, but ...mostly with 0.1 M⊙<M⋆< 0.5 M⊙. Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and in turn the accretion rate (Ṁacc), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (Lline) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ~330 nm to 2500 nm. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring Lacc and Ṁacc yield significantly different results: Hα line profile modelling may underestimate Ṁacc by 0.6 to 0.8 dex with respect to Ṁacc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁacc and other YSOs properties reported in the literature. We derived Ṁacc in the range 2 × 10-12–4 × 10-8 M⊙ yr-1 and conclude that Ṁacc ∝ M⋆1.8(±0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Ṁacc, confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.
OBJECTIVES
Different methods to classify the anatomical configurations of the aorta with bicuspid aortic valve (BAV) have been proposed. We aimed to test them in terms of descriptive power (i.e. ...capability to identify different clusters of patients with unique associations of anatomo-clinical features) and possible prognostic significance.
METHODS
A consecutive echocardiographic series of 696 BAV patients (mean age 48 ± 16 years, male:female ratio 3:1) was analysed. Three possible schemes for classification of the patterns of aortic dimensions were compared. One defined the aortic shape as ‘N’ (ascending < sinuses > sinotubular junction (STJ)), ‘A’ (ascending > sinuses > STJ) or ‘E’ (sinotubular ≥ sinuses), the second as ‘non-dilated’, ‘ascending phenotype’ (dilated, with ascending > sinuses) or ‘root phenotype’ (dilated, with sinuses > ascending) and the third as normal, ‘type I’ (dilated only at the ascending tract), ‘type II’ (dilated at both ascending and sinus levels) or ‘type III’ (dilated only at the sinuses). We evaluated the correlation with valve morphotypes (right-left fusion, right-non-coronary fusion) and patient characteristics. In a smaller longitudinal study (n = 150), the occurrence of fast growth of the aorta (fifth quintile: ≥1 mm/year) during follow-up (5 ± 3 years) in the various phenotypes was assessed.
RESULTS
The three classification methods proved meaningful in terms of association with valve morphotypes: significant associations were found between right-left-coronary BAV and the root phenotype (P < 0.001) and between the right-non-coronary BAV and the shapes A and E (P<0.001) as well as type I aortic configuration (P < 0.001). The aortic shape showed significant association with five of the other tested clinical variables, the phenotype and the type of dilatation with eight. In the longitudinal study, the root phenotype showed the most significant association with fast growth (>1 mm/year) of the ascending diameter (50% root phenotype patients; P = 0.005). The association with the N type was weaker (P = 0.055); no association was found with types from the other classification scheme (P = 0.42).
CONCLUSIONS
When tested on a large population, three previously suggested phenotypic classifications of the BAV aorta proved to categorize patients into significantly different clusters, but only the classification system distinguishing between ascending phenotype and root phenotype showed a potential prognostic value. Phenotypic class of the aorta could be a factor to integrate in future comprehensive models for risk stratification of BAV aortopathy.
Disks around T Tauri stars are known to lose mass, as best shown by the profiles of the forbidden emission lines of low-ionization species. At least two separate kinematic components have been ...identified, one characterized by velocity shifts of tens to hundreds of km s super(-1) (HVC) and one with a much lower velocity of a few km s super(-1) (LVC). The HVC are convincingly associated to the emission of jets, but the origin of the LVC is still unknown. In this paper we analyze the forbidden line spectrum of a sample of 44 mostly low-mass young stars in Lupus and sigma Ori observed with the X-shooter ESO spectrometer. We detect forbidden line emission of OI, OII, S II, N I, and N II, and characterize the line profiles as LVC, blueshifted HVC, and redshifted HVC. We focus our study on the LVC. We show that there is a good correlation between line luminosity and both L sub(star) and the accretion luminosity (or the mass accretion rate) over a large interval of values (L sub(star) ~ 10 super(-2)-1 L sub(middot in circle); L sub(acc) ~ 10 super(-5)-10 super(-1) L sub(middot in circle); M sub(acc) ~ 10 super(-11)-10 super(-7) M sub(middot in circle)/yr). The lines show the presence of a slow wind (V sub(peak) < 20 km s super(-1)) that is dense (n sub(H) > 10 super(8) cm super(-3) ), warm (T ~ 5000-10 000 K), mostly neutral. We estimate the mass of the emitting gas and provide a value for the maximum volume it occupies. Both quantities increase steeply with the stellar mass, from ~10 super(-12) M sub(middot in circle) and ~0.01 AU super(3) for M sub(star) ~ 0.1 M sub(middot in circle), to ~3 x 10 super(-10) M sub(middot in circle) and ~1 AU super(3) for M sub(star) ~ 1 M sub(middot in circle), respectively. These results provide quite stringent constraints to wind models in low-mass young stars, that need to be explored further.
Abstract
We present stellar parameters and abundances of 11 elements (Li, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni and Zn) of 13 F6-K2 main-sequence stars in the young groups AB Doradus, Carina Near and ...Ursa Major. The exoplanet-host star ι Horologii is also analysed.
The three young associations have lithium abundance consistent with their age. All other elements show solar abundances. The three groups are characterized by a small scatter in all abundances, with mean Fe/H values of 0.10 (σ = 0.03), 0.08 (σ = 0.05) and 0.01 (σ = 0.03) dex for AB Doradus, Carina Near and Ursa Major, respectively. The distribution of elemental abundances appears congruent with the chemical pattern of the Galactic thin disc in the solar vicinity, as found for other young groups. This means that the metallicity distribution of nearby young stars, targets of direct-imaging planet-search surveys, is different from that of old, field solar-type stars, i.e. the typical targets of radial velocity surveys.
The young planet-host star ι Horologii shows a lithium abundance lower than that found for the young association members. It is found to have a slightly super-solar iron abundance (Fe/H = 0.16 ± 0.09), while all X/Fe ratios are similar to the solar values. Its elemental abundances are close to those of the Hyades cluster derived from the literature, which seems to reinforce the idea of a possible common origin with the primordial cluster.
Young, close stars are ideal targets for searching planets using the direct imaging technique. We have conducted a large program with NaCo at the VLT to search for planets and brown dwarfs in wide ...orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. Several stars are confirmed or proposed here to be members of close young moving groups. Eight spectroscopic binaries are identified.
Objectives This study sought to identify risk factors for rapid growth of the ascending aorta in patients with bicuspid aortic valve (BAV) disease, taking into account its phenotypic variability. ...Background Phenotypic heterogeneity of BAV-related aortopathy has recently been widely recognized. However, few studies have addressed the determinants of aortic growth so far, not distinguishing among morphological phenotypes. Methods Serial retrospective data on 133 adult outpatients with BAV undergoing echocardiographic follow-up were analyzed to search for factors associated with aortic diameter growth over time and with rapid aortic growth (fifth quintile of growth rate distribution), focusing on the impact of different valve morphotypes (i.e., cusp fusion pattern: right-left coronary RL and right-noncoronary RN) and previously defined aortic phenotypes (nondilated aorta, ascending dilation, root dilation). Results The RL pattern was present in 69% of patients with BAV and RN in 31%. At baseline, an ascending dilation phenotype was observed in 57% of patients and a root phenotype in 13.5%. No patient with RN-BAV had a root dilation phenotype at either baseline or last examination. Follow-up time averaged 4.0 ± 2.7 years (535 patient-years). The mean growth rate was 0.3 mm/year at the sinuses and 0.6 mm/year at the ascending level. Aortic regurgitation predicted an increase in ascending diameter over time (odds ratio OR: 2.3; p = 0.03). Root phenotype at presentation, not absolute baseline diameter, was an independent predictor of fast progression (>0.9 mm/year) for the ascending tract (OR: 14; p = 0.001). Fast growth was rarely seen in patients with the RL morphotype and ascending phenotype (6% at the root and 10% at the ascending level). Conclusions In patients with BAV, the root phenotype (aortic dilation predominantly at the sinuses, with normal or less dilated ascending tract) may be a marker of more severe aortopathy, warranting closer surveillance and earlier treatment. The more common ascending phenotype proved to be a more stable disease entity, generally with slower progression.
PDF
