分类： 天文学 >> 天文学 提交时间： 2023-02-19
Nicole Arulanantham
Max Gronke
Eleonora Fiorellino
Jorge Filipe Gameiro
Antonio Frasca
Joel Green
Seok-Jun Chang
Rik A. B. Claes
Catherine C. Espaillat
Kevin France
Gregory J. Herczeg
Carlo F. Manara
Laura Venuti
Péter Ábrahám
Richard Alexander
Jerome Bouvier
Justyn Campbell-White
Jochen Eislöffel
William J. Fischer
Ágnes Kóspál
摘要： T Tauri stars produce broad Lyman-alpha emission lines that contribute $\sim$88% of the total UV flux incident on the inner circumstellar disks. Lyman-alpha 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 Lyman-alpha emission lines and the disks themselves, we model HST-COS spectra from targets included in Data Release 3 of the Hubble UV Legacy Library of Young Stars as Essential Standards (ULLYSES) program. We find that resonant scattering in a simple spherical expanding shell is able to reproduce the high velocity emission line wings, providing estimates of the average velocities within the bulk intervening H I. The model velocities are significantly correlated with the K band veiling, indicating a turnover from Lyman-alpha profiles absorbed by outflowing winds to emission lines suppressed by accretion flows as the hot inner disk is depleted. Just 30% of targets in our sample have profiles with red-shifted absorption from accretion flows, many of which have resolved dust gaps. At this stage, Lyman-alpha photons may no longer intersect with disk winds along the path to the observer. Our results point to a significant evolution of Lyman-alpha irradiation within the gas disks over time, which may lead to chemical differences that are observable with ALMA and JWST.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yapeng Zhang
Christian Ginski
Jane Huang
Alice Zurlo
Hervé Beust
Jaehan Bae
Myriam Benisty
Antonio Garufi
Michiel R. Hogerheijde
Rob G. van Holstein
Matthew Kenworthy
Maud Langlois
Carlo F. Manara
Paola Pinilla
Christian Rab
Álvaro Ribas
Giovanni P. Rosotti
Jonathan Williams
摘要： Circumstellar disks do not evolve in isolation, as about half of solar-type stars were born in binary or multiple systems. Resolving disks in binary systems provides the opportunity to examine the influence of stellar companions on the outcomes of planet formation. We aim to investigate and compare disks in stellar multiple systems with near-infrared scattered-light imaging as part of the Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS) program. We used polarimetric differential imaging with SPHERE/IRDIS at the VLT to search for scattered light from the circumstellar disks in three multiple systems, CHX 22, S CrA, and HP Cha. We performed astrometric and orbit analyses for the stellar companions using archival HST, VLT/NACO, and SPHERE data. Combined with the age and orbital constraints, the observed disk structures provide insights into the evolutionary history and the impact of the stellar companions. The small grains in CHX 22 form a tail-like structure surrounding the close binary, which likely results from a close encounter and capture of a cloudlet. S CrA shows intricate structures (tentative ringed and spiral features) in the circumprimary disk as a possible consequence of perturbations by companions. The circumsecondary disk is truncated and connected to the primary disk via a streamer, suggesting tidal interactions. In HP Cha, the primary disk is less disturbed and features a tenuous streamer, through which the material flows towards the companions. The comparison of the three systems spans a wide range of binary separation (50 - 500 au) and illustrates the decreasing influence on disk structures with the distance of companions. This agrees with the statistical analysis of exoplanet population in binaries, that planet formation is likely obstructed around close binary systems, while it is not suppressed in wide binaries.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jane Huang
Christian Ginski
Myriam Benisty
Bin Ren
Alexander J. Bohn
Élodie Choquet
Karin I. Öberg
Álvaro Ribas
Jaehan Bae
Edwin A. Bergin
Til Birnstiel
Yann Boehler
Stefano Facchini
Daniel Harsono
Michiel Hogerheijde
Feng Long
Carlo F. Manara
François Ménard
Paola Pinilla
Christophe Pinte
摘要： While protoplanetary disks are often treated as isolated systems in planet formation models, observations increasingly suggest that vigorous interactions between Class II disks and their environments are not rare. DO Tau is a T Tauri star that has previously been hypothesized to have undergone a close encounter with the HV Tau system. As part of the DESTINYS ESO Large Programme, we present new VLT/SPHERE polarimetric observations of DO Tau and combine them with archival HST scattered light images and ALMA observations of CO isotopologues and CS to map a network of complex structures. The SPHERE and ALMA observations show that the circumstellar disk is connected to arms extending out to several hundred au. HST and ALMA also reveal stream-like structures northeast of DO Tau, some of which are at least several thousand au long. These streams appear not to be gravitationally bound to DO Tau, and comparisons with previous Herschel far-IR observations suggest that the streams are part of a bridge-like structure connecting DO Tau and HV Tau. We also detect a fainter redshifted counterpart to a previously known blueshifted CO outflow. While some of DO Tau's complex structures could be attributed to a recent disk-disk encounter, they might be explained alternatively by interactions with remnant material from the star formation process. These panchromatic observations of DO Tau highlight the need to contextualize the evolution of Class II disks by examining processes occurring over a wide range of size scales.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Justyn Campbell-White
Carlo F. Manara
Aurora Sicilia-Aguilar
Antonio Frasca
Louise D. Nielsen
P. Christian Schneider
Brunella Nisini
Amelia Bayo
Barbara Ercolano
Péter Ábrahám
Rik Claes
Min Fang
Davide Fedele
Jorge Filipe Gameiro
Manuele Gangi
Ágnes Kóspál
Karina Maucó
Monika G. Petr-Gotzens
Elisabetta Rigliaco
Connor Robinson
摘要： Absorption features in stellar atmospheres are often used to calibrate photocentric velocities for kinematic analysis of further spectral lines. The Li feature at $\sim$ 6708 {\AA} 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 ESPRESSO data) as well as HARPS data. For 51 targets, we fit 314 individual spectra using the STAR-MELT package, resulting in 241 accurately fitted Li features, given the automated goodness-of-fit threshold. We find the mean air wavelength to be 6707.856 {\AA}, with a standard error of 0.002 {\AA} (0.09 km/s) and a weighted standard deviation of 0.026 {\AA} (1.16 km/s). The observed spread in measured positions spans 0.145 {\AA}, or 6.5 km/s, which is up to a factor of six higher than typically reported velocity errors for high-resolution studies. We also find a correlation between the effective temperature of the star and the wavelength of the central absorption. We discuss how exclusively using this Li feature as a reference for photocentric velocity in young stars could potentially be introducing a systematic positive offset in wavelength to measurements of further spectral lines. If outflow tracing forbidden lines, such as [O i] 6300 {\AA}, are actually more blueshifted than previously thought, this then favours a disk wind as the origin for such emission in young stars.
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