Empirical determination of the lithium 6707.856 Å wavelength in young stars

Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for the 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 complex line comprises two isotope fine-structure doublets. We empirically measured the wavelength of this Li feature in a sample of young stars from the PENELLOPE/VLT programme (using X-shooter, UVES, and ESPRESSO data) as well as HARPS data. For 51 targets, we fit 314 individual spectra using the STAR-MELT package, resulting in … Read more »

The active weak-line T Tauri star LkCa 4 observed with SPIRou and TESS

We report results of a spectropolarimetric and photometric monitoring of the weak-line T Tauri star LkCa 4 within the SPIRou Legacy Survey large programme, based on data collected with SPIRou at the Canada-France-Hawaii Telescope and the TESS space probe between October 2021 and January 2022. We applied Zeeman-Doppler Imaging to our spectropolarimetric and photometric data to recover a surface brightness distribution compatible with TESS photometry, as well as the large-scale magnetic topology of the star. As expected from the difference in wavelength between near-infrared and optical data, the recovered surface brightness distribution is less contrasted than the previously published one … Read more »

The Effelsberg survey of FU Orionis and EX Lupi objects. I. Host environments of FUors and EXors traced by NH3

Context. FU Orionis (FUor) and EX Lupi (EXor) type objects represent two small but rather spectacular groups of low-mass, young, eruptive stars. In both cases, outbursts of several magnitudes are observed, which are attributed to enhanced mass accretion from the circumstellar disc onto the central protostar. Although these objects are well studied at optical and near-infrared wavelengths, their host molecular environments are poorly explored because of the scarcity of systematic molecular line observations.Aims: We aim to carry out the first dedicated survey of the molecular environments of a large sample of FUors and EXors, observing a total of 51 sources, … Read more »

JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

EX Lup is a low-mass pre-main-sequence star that occasionally shows accretion-related outbursts. Here, we present JWST/MIRI medium-resolution spectroscopy obtained for EX Lup 14 yr after its powerful outburst. EX Lup is now in quiescence and displays a Class II spectrum. We detect a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks: H2O, OH, H2, HCN, C2H2, and CO2. The detection of organic molecules demonstrates that they are back after disappearing during the large outburst. Spectral lines from water and OH are for the first time deblended and will provide a much-improved characterization … Read more »

An APEX Study of Molecular Outflows in FUor-type Stars

The FU Orionis-type objects (FUors) are low-mass pre-main-sequence objects that go through a short-lived phase (~100 yr) of increased mass accretion rate (from 10-8 to 10-4 M ⊙ yr-1). These eruptive young stars are in the early stages of stellar evolution and thus still deeply embedded in a massive envelope that feeds material to the circumstellar disk that is then accreted onto the star. Some FUors drive molecular outflows, i.e., low-velocity wide-angle magnetohydrodynamical winds, that inject energy and momentum back to the surrounding envelopes and help clear the material surrounding the young star. Here we present a 12CO (3-2), 13CO (3-2), and 12CO (4-3) survey of 20 … Read more »

Accretion process, magnetic fields, and apsidal motion in the pre-main sequence binary DQ Tau

Classical T Tauri stars (CTTSs) are young stellar objects that accrete materials from their accretion disc influenced by their strong magnetic field. The magnetic pressure truncates the disc at a few stellar radii and forces the material to leave the disc plane and fall onto the stellar surface by following the magnetic field lines. However, this global scheme may be disturbed by the presence of a companion interacting gravitationally with the accreting component. This work is aiming to study the accretion and the magnetic field of the tight eccentric binary DQ Tau, composed of two equal-mass (~ 0.6 M⊙) CTTSs … Read more »

Ly𝛼 Scattering Models Trace Accretion and Outflow Kinematics in T Tauri Systems

T Tauri stars produce broad Lyα emission lines that contribute ~88% of the total UV flux incident on the inner circumstellar disks. Lyα photons are generated at the accretion shocks and in the protostellar chromospheres and must travel through accretion flows, winds, and jets, the protoplanetary disks, and the interstellar medium before reaching the observer. This trajectory produces asymmetric, double-peaked features that carry kinematic and opacity signatures of the disk environments. To understand the link between the evolution of Lyα emission lines and the disks themselves, we model HST-COS spectra from targets included in Data Release 3 of the Hubble … Read more »

The Mass Accretion Rate and Stellar Properties in Class I Protostars

Stars collect most of their mass during the protostellar stage, yet the accretion luminosity and stellar parameters, which are needed to compute the mass accretion rate, are poorly constrained for the youngest sources. The aim of this work is to fill this gap, computing the stellar properties and the accretion rates for a large sample of Class I protostars located in nearby (<500 pc) star-forming regions and analyzing their interplay. We used a self-consistent method to provide accretion and stellar parameters by modeling the spectral energy distribution and using veiling information from near-IR observations when possible. We calculated accretion and … Read more »

A photometric study of the ULLYSES/PENELLOPE T Tauri star sample in Ori OB1 and 𝛔 Ori: the accretion process at the highest time resolution

In order to build up a legacy spectroscopy survey of accreting low-mass pre-main sequence stars, synchronized HST and ESO/VLT observational campaigns, named ULLYSES and PENELLOPE, respectively, were carried out in the Orion star forming region in late 2020. The spectroscopic program was supported by an extensive multi-band photometric monitoring at different ground-based observatories, including our domestic telescopes at Konkoly Observatory, Hungary, as well as by simultaneous TESS observations. Here we report on our ongoing analysis aiming at characterizing the accretion process of the targeted objects based on multi-filter photometry. We observed BVr’i’ light curves with an approximately daily cadence, and … Read more »

Search for far-infrared variability of protoplanetary disks in the Cha I star-forming region

The research of star formation is one of the most popular area of modern astrophysics. Nowadays, we can use ground-based and space-borne observatories to study Young Stellar Objects in different states of their evolution, their time-domain behaviour related to accretion process, and the connection between the stars and their circumstellar environment. The Chamaeleon I molecular cloud complex is one of the most famous star-forming regions, located at a distance of 190 pc. In our study we use photometric data to analyse the multi-wavelength variability of eight T Tauri stars (CR Cha, CT Cha, Glass I, VW Cha, VZ Cha, WW … Read more »