Search

Ultra-short-period (USP) planets, those with an orbital period less than a day, are a population of rare and extreme worlds that provide an opportunity to study the formation and evolution of small planets in ways that are more difficult for their longer period counterparts. Many of the significant changes a planet experiences occur on timescales of < 100 Myr, so studying planets across these ages is essential to uncovering mechanisms that shape planetary systems. However, active young stars can introduce large-amplitude photometric and spectroscopic variations, making detection and characterization difficult. Luckily, the very short transits of USP planets are separable even from the stellar signal of many rapidly rotating young stars, leading to more complete transit detection of young planets at the shortest periods. I present the development of a specialized pipeline for identification of candidate young transiting planets using TESS 2-minute data, which includes detrending designed to preserve transits in the face of rapid stellar rotation. I tested the pipeline on a set of injected transits, and found it to recover 66% of planets between 1 − 2R⊕ around stars smaller than the Sun. I applied the pipeline to a sample of 6600 young stars from the literature, and identified 51 planet candidates, including a young “twin” of 55 Cnc e and a surprise single-transit candidate with an orbital period likely longer than a month. 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The intrinsic variability of young active stars is one of the main limitations in detection and characterisation of exoplanets with Doppler spectroscopy. Indeed, stellar activity affects the measurement of radial velocity (RV) often preventing the correct detection of the planet, in particular in presence of fast rotation. We present a method to optimize the RVs extraction based on the cross-correlation function (CCF) technique that takes into account the activity of the star modelled by the presence of one or more spots on the stellar disc. We applied our technique to 146 HARPS-N spectra of V830 Tau and to 106 HARPS spectra of DS Tuc A, two young fast rotating stars. We find that the stars are well modelled by applying One or Two-spots model to the CCFs. We verified that the method removes efficiently part of the rotation signal, and that the new RVs show a significantly lower dispersion with respect to the TERRA pipeline dataset for both targets. We also tested the detection sensitivity of the method by direct injection of a planetary signal into the data and we demonstrated that our method improves significantly the detection sensitivity. The “Spots model” provides us also the physical properties of the spots that results modulated by rotation and with filling factor consistent with values as expected from the literature., {"references":["Grankin, K. N. 2013, Astronomy Letters, 39, 251","Donati, J. F., et al. 2015, MNRAS, 453, 3706","Cosentino, R., Lovis, C., Pepe, F., et al. 2014, in SPIE, Vol. 9147","Covino, E., Esposito, M., Barbieri, M., et al. 2013, A&A, 554, A28","Benatti, S., Nardiello, D., Malavolta, L., et al. 2019, A&A, 630, A81","Mayor, M., Pepe, F., Queloz, D., et al. 2003, The Messenger, 114, 20","Gray, D. F. 2018, ApJ, 857, 139","Feroz, F., Hobson, M. P., Cameron, E., & Pettitt, A. N. 2019, The Open Journal of Astrophysics, 2, 10","Damasso, M., Lanza, A. F., Benatti, S., et al. 2020, A&A, 642, A133","Messina, S., Rodonò, M., & Guinan, E. F. 2001, A&A, 366, 215"]}

The latest Gaia data releases (EDR3 and, soon, DR3) have greatly facilitated the identification and investigation of members of nearby young moving groups (NYMGs), here defined as groups of stars of age, {"references":["Kastner J., Allers K., Bowler B. et al. 2019 BAAS 51 294","D. Annie Dickson-Vandervelde et al 2021 AJ 161 87","Murphy S. J., Lawson W. A. and Bessell M. S. 2013 MNRAS 435 1325","Goldman, B., Roser, S., Schilbach, E., Moor, A. C. et al. 2018, ApJ, 868, 32","Burrows et al. 1997, ApJ, 491, 856","Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42","Andrew W. Mann et al. 2022 AJ 163 156"]}

Most investigations of star-forming regions (SFRs) focus on their cores, where disks, jets, outflows and nebular clouds are commonplace. However, searches around the peripheries of stellar nurseries are almost non-existent, yet ought to contain additional young members, informing us about cloud dynamics and the dissolution of SFRs. “It’s a fishing trip” -- who’s going to offer that kind of observing time, right? Welcome to HYPERS*, a HST project which obtained 100 cycles of mostly optical photometry around the outskirts of SFRs by using the vacant second observing facility whilst the primary mission targeted a known nebulous region. Observations, completed in February 2022 consist of ~30 SFRs at distances 100-1000pc, size-scales 5-50 pc and populations of a few to a few thousand. Early results show: (1) dozens of emission disk candidates and a few potential jets; (2) many resolved multiple systems as close as ~0.05" that could not be detected without HST's powerful angular resolution; (3) large, previously unreported, cavities in the molecular clouds around the Eagle nebula. Our cross-match with several astronomical surveys indicates that we have lots of new stuff in there!

Accretion is one of the defining characteristics of young stars. For the late-type ones, accretion is channelled by the stellar magnetic field. Magnetospheric accretion thus connects the protoplanetary disk to the young star and opens a gap in the innermost disk, which can affect planet migration. While direct mapping cannot access these regions, emission (and absorption) lines in young stars trace their winds, accretion-related structures, spots, and sometimes, the innermost disk. Young stars are rich in emission (and absorption) lines, related to their winds, accretion, hot spots, and innermost gaseous disk. Optical, near-UV, and near-IR lines include a large number of species with various excitation potentials that can provide information on the temperature, density, and velocity of hot and tiny structures. Combining the velocity information with repeated, time-resolved data, we can reconstruct scales of a few stellar radii. With time-resolved spectroscopy covering several rotational and disk orbital periods, we can obtain a detailed view of the structure and variability of accretion columns and spots and information on the presence and launching points of stellar/disk winds in young stars. Data acquired over months-to-year can reveal the long-term stability of the accretion process and related structures. Understanding these processes and how they affect the observed spectra can also help us to identify (or rule out) the presence of young and newly-formed planets and stellar companions that may be perturbing the disk. Highly variable and outbursting sources provide a further point: with the temperature varying during outbursts, we can spectroscopically access an even larger region of the stellar surroundings and even the disk. In this poster we present the results for stars with different spectral types and behaviours, and show the application of the STAR-MELT code we created in Dundee for this type of analysis (see also poster by J. Campbell-White), exploring what we can learn from "reading between their (spectral) lines". We explore the location of the accretion post-shock regions and accretion column footprints and unveil stable (often, for years) and unstable accretion in different types of stars and the presence of infall and non-axisymmetric winds. We further discuss how this can help us to unveil why wild and variable stars are so wild., STAR-MELT code is publicly available at https://github.com/justyncw/STAR_MELT, {"references":["Campbell-White, J., et al. (2021), MNRAS, 507, 3331","Sicilia-Aguilar, A. et al. (2020), A&A, 643, 29","Sicilia-Aguilar, A., et al. (2020), A&A, 633, 37","Sicilia-Aguilar, A., et al. (2015), A&A, 580, 82"]}

In earlier type Herbig Ae/Be stars the accretion mechanisms are not yet well understood because their magnetic fields are too weak to sustain magnetospheric accretion. These are the first steps in my study of time variability of accretion-related lines in young intermediate-mass stars, using the STAR-MELT code, combined with long- and short-cadence spectroscopic data. The targets chosen for study are promising sources as they have well-known protoplanetary discs, and evidence of extinction by circumstellar material. Emission and absorption lines with broad and narrow components, including metallic ones, are detected in these stars in a similar way to what is found in their lower-mass counterparts, and the STAR- MELT Python code assists in quantifying any variability found. By measuring the variability in velocity and relative intensity for different lines we aim to trace the structure of accretion columns and distinguish between different accretion mechanisms as they evolve over time.

In this project we employ tools such as dynamic time warping (DTW) and variography for detailed time series study of TTS light curves. The main goal is to be able to classify the light curves, identify recurring patterns that might unveil potential planetary signatures that are hidden behind obvious signals in the data (e.g periodic modulations due to spots or dips, bursting events, etc..).

A wealth of models to explain the early evolution of planetary systems have emerged following the discovery of nearly 5000 unexpectedly diverse exoplanets. Validating these theories requires knowledge of planetary properties at all stages of a system’s life and is best informed by giant planets, more accessible to current detections methods and excellent tracers of formation history. Currently, the early days (< 500 Myr) of planets orbiting Sun-like stars is greatly under sampled and it is essential to increase the pool of young giant planets. In this talk, we present HIP 67522 b and TOI 4562 b and show how these two young giant planets, discovered by the TESS mission, contribute to our understanding of early planet evolution. HIP 67522 b is the youngest Jupiter sized planet showing a well-aligned orbit with its star spin axis and TOI 4562 b is a 200 Myr old, long period and highly eccentric Jupiter like planet. By placing both planets in the broader context of young gas giants, including additional very recent discoveries, we will demonstrate the necessity to shift our focus to younger stars and the associated need to overcome the barrier imposed by stellar activity., {"references":["Heitzmann, A. et al. (2021), ApJ, 922, L1","Heitzmann, A. et al. (2022), arXiv, 2208.10854"]}

V magistrskem delu je raziskana kemijska homogenost Orionovega kompleksa molekularnih oblakov na podlagi meritev zastopanosti kisika v posameznih zvezdah. Najprej so predstavljene osnove zvezdne spektroskopije. Opisana sta spekter črnega telesa in formacija absorpcijskih črt. Podrobneje je opisan teoretični Voightov profil absorpcijskih črt z upoštevanjem tlačne in termične razširitve, opisani pa so tudi premiki in razširitve črt, ki izvirajo iz zvezdne dinamike. Predstavljena je tehnika Echelle spektroskopije, HR in Kielov diagram ter spektralna klasifikacija zvezd na podlagi podobnosti v njihovih spektrih. Sledi opis procesov življenja zvezd -- od njihove formacije iz molekularnih oblakov in obdobja na glavni veji, do razvoja v orjakinje ter smrti zvezd in obogatitve okoliškega prostora z elementi nukleosinteze. Predstavljene so tudi glavne fizične in kemijske značilnosti Orionovega kompleksa. V praktičnem delu naloge so uporabljena spektroskopska opazovanja 30 zvezd iz območij molekularnih oblakov v Orionu in Samorogu v območju valovnih dolžin od 395 do 680,nm. V glavnem so to vroče zvezde glavne veje, nekaj pa je tudi orjakinj. Opisan je postopek obdelave surovih spektrov v programu IRAF, za katere sem nato z uporabo programa iSpec določil vrednosti radialne hitrosti, atmosferskih parametrov (efektivna temperatura, gravitacijski pospešek na površju, mikro- in makroturbulenčna hitrost, projekcija rotacijske hitrosti in koeficient robne zatemnitve) in zastopanosti kisika. Zastopanosti kisika sem določil pod predpostavko kemijske homogenosti kompleksa v kovinskosti in zastopanosti $alpha$ elementov -- pričakoval sem torej enakomerno zastopanost kisika v različnih spektralnih tipih zvezd. Območji sta glede na zastopanosti kisika v zvezdah homogeni. Določena absolutna zastopanost kisika v opazovanih zvezdah znaša $A$(O)$=(8,33 pm 0,49),$dex, določena relativna zastopanost glede na železo pa [O/Fe]$=(-0,26pm0,49),$dex. Povprečna velikost napake določene zastopanosti kisika vseh zvezd je enaka $0,54,$dex. Raziskani so tudi vplivi posameznih parametrov na končne določene zastopanosti kisika. Med vsemi parametri na končno napako najbolj vplivata natančnost določitve efektivne temperature in gravitacijskega pospeška na površju. The Master’s thesis explores the chemical homogeneity of the stars of the Orion Molecular Complex, based on measurements of Oxygen abundance in individual stars. Stellar spectroscopy is introduced, followed by the description of a blackbody spectrum and the formation of absorption lines. Theoretical Voigt profile of absorption lines is described in detail by taking pressure and thermal broadening into account. Doppler shift and rotational broadening of lines that originate from the star dynamics are described as well. Furthermore, the Echelle Spectroscopy technique, HR and Kiel diagram, and the spectral classification of stars, based on similarities in their spectra, are presented. The process of the stellar life is described from the formation in molecular clouds and the main sequence phase, to the evolution into giants and finally deaths that enrich the surrounding environment with the elements of stellar nucleosynthesis. Theoretical part is concluded with the presentation of physical and chemical features of the Orion Complex. In practical part, spectroscopical observations of 30 stars from the molecular cloud areas in Orion and Monoceros, covering the area of wavelengths from 395 to 680 nm, have been used. Mainly, these are hot main sequence stars, including a few giants. It is described how raw spectra have been processed in IRAF programme and how iSpec programme has been used to determine the radial velocities, atmospheric parameters (effective temperature, gravitational acceleration on the surface, micro- and macro-turbulence velocities, the projection of the rotational velocity and the limb darkening coefficient) and most importantly, the Oxygen abundances of observed stars. Oxygen abundance have been determined under the assumption that Orion complex is chemically homogeneous in metallicities and abundances of $alpha$ elements – therefore, the Oxygen abundance should not vary between different spectral types. Considering Oxygen abundance, the Orion Complex is proven homogenous. The determined absolute Oxygen abundance in the observed stars is $A$(O)$=(8,33pm0,49),$dex, while the determined abundance, relative to iron is [O/Fe]$=(-0,26pm0,49),$dex. The average spread of determined Oxygen abundances of all stars is equal to 0,54,dex. Lastly, the relations between the determined Oxygen abundances and uncertainties of individual parameters have been researched. Among all the parameters, what affects the Oxygen abundances the most, is the accuracy of determining the effective temperature and the gravitational acceleration on the surface.

High precision astrometryat the≈10 uas level is now routinelyachieved from the ground with theVery Long BaseIine Interferometry (VLBI)technique.The milli-arcsecond (mas) angular resolution of VLBI instruments allows to resolvebinary systemswere angular separations can be as small as a few mas.In addition, high precision astrometry allows searching forunseen companions, by the detection of the astrometric signature or“wobble”due to the gravitational pull of the companion.We have used astrometry at radio wavelengths to search for giant planets around very low mass stars, which are difficult to find by other techniques. In this contribution, we present the properties of low-mass young binariesand oftwo giant planets discovered withthis technique.

Current theories predict that very young giant planets have large radii and very low densities before they slowly contract to reach their final size after several hundred million years. Open stellar clusters and young moving groups of stars offer a unique opportunity to study exoplanets at their infant stages because of the well-constrained ages. The extreme stellar activity of young stars makes measuring the masses of their planets a very challenging task. Planet-induced radial velocity signals are typically smaller in amplitude and at lower frequencies than stellar-induced signals. These situations place very demanding requirements for RV observation campaigns and puts us in a worst-case scenario for the standard methods of stellar activity modelling. With an estimated age of 20 million years, V1298 Tau is one of the youngest solar-type stars known to host transiting planets; it harbours a system composed of four planets, two Neptune-sized, one Saturn-sized and one Jupiter-sized. Using more than 200 radial velocity measurements, condensed into a 4-month period, we were able to measure the radial velocity amplitude induced by the planet V1298 Tau b, and to pick up a second signal that was suspected to be linked to V1298 Tau e. The analysis required the combination of radial velocities, ground-based photometry contemporary to the RV campaign, and K2 photometry. The result obtained indicated that V1298 Tau might have contracted much faster than predicted by theoretical models, highlighting the importance of attempting these difficult cases.

We present SOFIA+ALMA continuum and spectral-line polarisation data on the massive molecular cloud BYF 73, revealing important details about the magnetic field morphology, gas structures, and energetics in this unusual massive star formation laboratory. The 154$\mu$m HAWC+ polarisation map finds a highly organised magnetic field in the densest, inner 0.55$\times$0.40 pc portion of the cloud, compared to an unremarkable morphology in the cloud's outer layers. The 3mm continuum ALMA polarisation data reveal several more structures in the inner domain, including a pc-long, $\sim$500 M$_{\odot}$ "Streamer" around the central massive protostellar object MIR 2, with magnetic fields mostly parallel to the east-west Streamer but oriented north-south across MIR 2. The magnetic field orientation changes from mostly parallel to the column density structures to mostly perpendicular, at thresholds $N_{\rm crit}$ = 6.6$\times$10$^{26}$ m$^{-2}$, $n_{\rm crit}$ = 2.5$\times$10$^{11}$ m$^{-3}$, and $B_{\rm crit}$ = 42$\pm$7 nT. ALMA also mapped Goldreich-Kylafis polarisation in $^{12}$CO across the cloud, which traces in both total intensity and polarised flux, a powerful bipolar outflow from MIR 2 that interacts strongly with the Streamer. The magnetic field is also strongly aligned along the outflow direction; energetically, it may dominate the outflow near MIR 2, comprising rare evidence for a magnetocentrifugal origin to such outflows. A portion of the Streamer may be in Keplerian rotation around MIR 2, implying a gravitating mass 1350$\pm$50 M$_{\odot}$ for the protostar+disk+envelope; alternatively, these kinematics can be explained by gas in free fall towards a 950$\pm$35 M$_{\odot}$ object. The high accretion rate onto MIR 2 apparently occurs through the Streamer/disk, and could account for $\sim$33% of MIR 2's total luminosity via gravitational energy release., Comment: 33 pages, 32 figures, accepted by ApJ. Line-Integral Convolution (LIC) images and movie versions of Figures 3b, 7, and 29 are available at https://gemelli.spacescience.org/~pbarnes/research/champ/papers/

Current theories predict that very young giant planets have large radii and very low densities before they slowly contract to reach their final size after several hundred million years. Open stellar clusters and young moving groups of stars offer a unique opportunity to study exoplanets at their infant stages because of the well-constrained ages. The extreme stellar activity of young stars makes measuring the masses of their planets a very challenging task. Planet-induced radial velocity signals are typically smaller in amplitude and at lower frequencies than stellar-induced signals. These situations place very demanding requirements for RV observation campaigns and puts us in a worst-case scenario for the standard methods of stellar activity modelling. With an estimated age of 20 million years, V1298 Tau is one of the youngest solar-type stars known to host transiting planets; it harbours a system composed of four planets, two Neptune-sized, one Saturn-sized and one Jupiter-sized. Using more than 200 radial velocity measurements, condensed into a 4-month period, we were able to measure the radial velocity amplitude induced by the planet V1298 Tau b, and to pick up a second signal that was suspected to be linked to V1298 Tau e. The analysis required the combination of radial velocities, ground-based photometry contemporary to the RV campaign, and K2 photometry. The result obtained indicated that V1298 Tau might have contracted much faster than predicted by theoretical models, highlighting the importance of attempting these difficult cases.

In this thesis, I present the results of a number of studies using high-resolution observations from world-class telescopes. The aim of these studies is to investigate protostellar jets and their role in star formation. In a case study of the bipolar jet from the T Tauri star DO Tau, we observe significant asymmetries in the morphology and kinematics of the jet and counterjet. The collimation of the jet supports the idea that magnetic fields collimate the jet, rather than pressure from the infalling envelope. If magnetic fields are responsible for jet collimation, then they may also drive jet launching. By measuring the radial velocities across the jet, we can calculate an upper limit on the jet launching radii. Our results support an X-wind or narrow disk wind model. Jet axis wiggling is also observed and is consistent with jet precession, which may be caused by an unseen companion in the disk or by launching the disk wind. In a study of four Class 0/I jets (HH 1, HH 34, HH 46 and HH 111) using high-resolution HST images, we were able to detect the inner knots of the red-shifted lobes in all four sources in more detail than previous studies. We compare these images to archival data to measure the proper motions in each jet. Jet axis wiggling is observed in three of these sources and the wiggling pattern in the HH 111 jet is consistent with jet precession and the presence of a companion in the disk. We also measure the extinction in each jet, which is quite high close to the star but decreases further out along each jet. Extinction measurements are important in the interpretation of emission line ratios, which reveal plasma conditions along the jet and hence the mass and momentum transfer. These two case studies illustrate the power of high resolution observations in differentiating between models of jet launching, and also reveal that protostellar jet trajectories could be a useful tool in identifying newly forming substellar companions close to the star. Finally, a survey of over 100 stars was conducted using high-resolution X-Shooter spectra. This study examines He I line profiles which vary between the two star forming regions examined in the sample, suggesting a trend with age. We also find that the maximum absorption velocity appears to be correlated with the source inclination and with the accretion rates of the sources. Our study confirms the results of past works (Edwards et al., 2006; Kwan et al., 2007; Fischer et al., 2008) and supports the idea that these winds are accretion powered. This survey gives context to our two case studies, by examining the link between accretion and ejection. High resolution observations are critical to advance understanding of the role of protostellar jets in star formation, as illustrated by the contribution of this thesis. The recently launched JWST facility marks the start of an era which will see exciting progress in this field, as its near-IR instruments peer deep into the embedded accretion-ejection engine. 2022-06-30 JG: Signatures removed or redacted from PDF

We present the results of BVRcIc CCD photometric observations of the classical T Tauri stars AS 205 (V866 Sco), V1082 Cyg and the HAeBe star AS 310 obtained in 2016-2022. Photometric variations of the star AS 310 with a large amplitude were reliably established for the first time, they are possibly due to binarity or multiplicity of the star. The scale of the star's activity differs from a year to year. Parameters of the upgraded photometric system, currently at use at the Shamahy Observatory, are described., Представлены результаты ПЗС-фотометрии в системе BVRcIc для классических звездтипа T Тельца AS 205 (V866 Sco), V1082 Cyg и звезды типа AeBe Хербига AS 310, полученные в 2016 2022 гг. Фотометрическая переменность звезды AS 310 с большой амплитудой уверенно выявлена впервые, она может быть связана с двойственностью звезды или с ее принадлежностью к кратной системе. Масштабы активности звезды меняются от года к году. Описаны параметры усовершенствованной фотометрической системы, используемой в настоящее время на Шамахинской обсерватории.

Studying planetary systems in their infancy is essential to understand of the origin of gas giant exoplanets found to closely orbit their host stars. Tied with the study of young stars is the challenge of stellar activity, arising from their fast rotation and strong magnetic fields. This cocktail yields a wealth of phenomena able to mask signatures from orbiting planets, greatly hampering our capacity to detect them. In this Ph. D. project, we first assessed our chances to detect non-transiting gas giants in close orbit around young and very active stars, using legacy data from a non-stabilised spectrograph. We performed an injection and recovery study using Doppler Imaging and Gaussian Processes as stellar activity mitigation strategies. We were able to recover planets down to 4 times below the stellar noise and conclude that both a robust statistical framework and high quality datasets are crucial. We then precisely measured, despite the stellar activity, the spin–orbit alignment for the youngest Jupiter-sized planet known to transit, the 17 Myr old HIP 67522 b, and showed that its origin pathway is unlikely to be the commonly invoked high eccentricity migration. Finally, we conducted a 2-year radial velocity follow up yielding the discovery of TOI- 4562 b, identified in Transiting Exoplanet Survey Satellite data. TOI-4562 b is a highly eccentric (e = 0.77±0.03), 225 day period, 300±190 Myr old Jupiter analogue. We strongly suspect the presence of a companion that could be at the origin of TOI-4562 b eccentricity. We hope to reveal the 3D architecture of this system with on-going observing campaigns. This work paves the way for further characterisation of young short-orbit gas giants, key to constrain models explaining their formation and evolution.

Young stars represent important laboratories for studying stellar and planet formation. Furthermore, low-mass stars are not only the most common product of star formation, but also provide appealing conditions for the direct imaging of exoplanets. Determining youth in solar-type stars and low-mass stars can be challenging. I have examined young stars and the planet formation processes that occur around them from several different perspectives. First, I examined one of the most commonly-used age determination methods for solar-type stars - chromospheric activity. I compiled a large (~2,800 star) sample of stars with known chromospheric activity levels, calculated their ages, and searched for evidence of an infrared excess (indicative of a circumstellar debris disk) using data from the Wide Field Infrared Survey Explorer (WISE). I found that, while the distribution of stars with a strong infrared excess peaks at young ages, there are a significant number of debris disks occurring at much later ages. I present 74 newly discovered debris disks. Following this work, I examined dust production mechanisms in debris disks by performing an in-depth analysis of 24 stars observed with the Herschel Space Observatory. I present 7 newly resolved stars, and characterize the dust formation mechanisms in 15 stars with confirmed infrared excesses. In addition, I identify four stars as potential targets for follow-up observations to search for previously unseen planets. Finally, I analyzed over 450 optical spectra of low-mass stars to identify young, nearby stars as targets for direct imaging observations. As a part of this project, I also identify 60 stars as bonafide members of nearby moving groups, 39 of which are presented for the first time. I also identify 41 stars with signatures of youth, but that do not appear to belong to any one particular moving group. I discovered 36 spectroscopic binaries, 30 of which are newly presented here. I used the UCAC4 catalog to search for wide binary companions to stars in my sample, and discovered 35 stars in common proper motion pairs, 32 of which are presented here for the first time. I also used my measurements of Li to re-calculate lithium depletion boundary ages for three nearby moving groups (beta Pic, Tuc Hor, and AB Dor). In an effort to characterize youth indicators in low-mass stars, I investigated the magnetic activity of stars in my sample using NUV, X-Ray, and H-alpha emission. I identify a new late-type (M4.9) debris disk host that shows some signatures of active accretion. This newly discovered debris disk host joins a very small population of late-type stars with dusty debris disks.

Stellar associations can be discerned as over-densities of sources not only in the physical space but also, more importantly, in the velocity space. The common motion of their members, gradually eroded by thegalactic tidal field, is partially reminiscent of the initial kinematic structure. Using recent data from GaiaEDR3, combined with radial velocities from GALAH and APOGEE, we traced back the present positions ofstars belonging to Upper Scorpius, a subgroup of the Scorpius-Centaurus association. A significant part of these stars (the "clustered" population) appears composed of many smaller entities, which were in amore compact configuration in the past. The presence of a kinematic duality is reflected into an age spreadbetween this younger clustered population and an older diffuse population, in turn confirmed by a differentfraction of disc-bearing stars. Star formation in the region appears to have lasted more than 10 Myr and tohave proceeded in small groups that, after a few Myr, dissolve in the field of the older population but retain for some time memory of their initial structure. The consequences of our results will be discussed here, and a comparison with stellar ages inferred through isochrone fitting will shed light on the timescale of gas removal.

High-resolution infrared observations allow us to probe regions close to young stars, normally obscured by the surrounding envelope. While a young star is actively accreting material from the disk onto the star, jets and outflows remove mass from the system. The connection between accretion and ejection is relevant for the final star and disk mass, and therefore has implications for planet formation. We probe this connection between the two processes using X-Shooter spectra of the infrared He I 1 micron line in a large sample of young stars in the Lupus and Upper Scorpius star forming regions. The He I line traces both accretion and ejection in the innermost regions close to the star, therefore allowing us to connect the accretion and ejection properties of the system to stellar properties and to the evolutionary stage of the star., Presented at "STAR FORMATION: FROM CLOUDS TO DISCS - A Tribute to the Career of Lee Hartmann" in Malahide, Dublin on October 18-21 2021

We present results of the large-scale magnetic topology and photospheric brightness distribution of the young star DK Tau using data from ESPaDOnS, a spectropolarimeter at the CFHT. We analyzed 18 spectra collected in 2010 and 2012, each set spanning over one rotation cycle. When using the literature's value of 21° for the inclination (of DK Tau's rotation axis), based on the inclination of the outer disk, we find several inconsistencies. Using the star's rotational properties, we derive an inclination of the stellar rotation axis of 51° and used this value for the magnetic mapping. We find that DK Tau’s rotation axis is likely to be misaligned compared to its outer disk axis by 30°., {"references":["Donati, J. F., Semel, M., Carter, B. D., Rees, D. E., & Collier Cameron, A. 1997, MNRAS, 291, 658","Donati, J. F. & Brown, S. F. 1997, A&A, 326, 1135","Folsom, C. P., Bouvier, J., Petit, P., et al. 2018, MNRAS, 474, 4956","Rota et al. submitted to A&A","Roggero, N., Bouvier, J., Rebull, L. M., & Cody, A. M. 2021, A&A, 651, A44"]}