We characterize the physical properties of T Chamaeleontis, a transitional T Tauri star showing UX Ori-type variability, and of its associated disc, and probe possible effects of disc clearing processes. Different spectral diagnostics are examined, based on a rich collection of optical high- and low-resolution spectra. We determine radial and projected rotational velocities, and measure equivalent widths of the Li I (6708 A) line and of the most prominent emission lines (e.g. Ha, Hb and [OI] 6300A); we analyse shape changes of photospheric lines via bisector-method, while variability in Ha and Hb is inspected through line-profile correlation matrices. The strength of the Ha and Hb emission is highly variable and well correlated with that of the [OI] lines, as well as with Av variations of over three magnitudes. Variations up to nearly 10 km/s in the radial velocity of the star are measured on analogous time-scale, but with no apparent periodicity. SED modelling confirms the existence of a gap in the disc. Variable circumstellar extinction is pointed out as responsible for the conspicuous variations observed in the stellar continuum flux and for concomitant changes in the emission features by contrast effect. Clumpy structures, incorporating large dust grains and orbiting the star within a few tenths of AU, obscure episodically the star and, eventually, part of the inner circumstellar zone, while the bulk of the hydrogen lines emitting zone and outer low-density wind region traced by the [OI] remain unaffected. Coherently with this scenario, the detected radial velocity changes are also explainable in terms of clumpy materials transiting and partially obscuring the star.
Protoplanetary discs are the birthplace for planets. Studying protoplanetary discs is the key to constraining theories of planet formation. By observing dust and gas in associations at different ages we can study the evolution of these discs, their clearing timescales, and their physical and geometrical properties. The stellar association Eta Cha is peculiar; some members still retain detectable amounts of gas in their discs at the late age of 7 Myr, making it one of the most interesting young stellar associations in the solar neighbourhood. We characterise the properties of dust and gas in pr…
New data from the Herschel Space Observatory are broadening our understanding of the physics and evolution of the outer regions of protoplanetary disks in star forming regions. In particular they prove to be useful to identify transitional disk candidates. The goals of this work are to complement the detections of disks and the identification of transitional disk candidates in the Lupus clouds with data from the Herschel Gould Belt Survey. We extracted photometry at 70, 100, 160, 250, 350 and 500 $μ$m of all spectroscopically confirmed Class II members previously identified in the Lupus region…
Although advances in exoplanet detection techniques have seen an increase in discoveries, observing a planet in the earliest stages of formation still remains a difficult task. Here four epochs of spectra of the transitional disk object T Cha are analysed to determine whether spectro-astrometry can be used to detect a signal from its proposed protoplanet, T Cha b. The unique properties of T Cha are also further constrained. Hα and [O I]λ 6300, the most prominent lines, were analysed using spectro-astrometry. Hα being a direct accretion tracer is the target for the T Cha b detection while [O I]…
We present \emph{Herschel} PACS observations of 8 Classical T Tauri Stars in the $\sim 7-10$ Myr old OB1a and the $\sim 4-5$ Myr old OB1b Orion sub-asscociations. Detailed modeling of the broadband spectral energy distributions, particularly the strong silicate emission at 10 $μ$m, shows that these objects are (pre)transitional disks with some amount of small optically thin dust inside their cavities, ranging from $\sim 4$ AU to $\sim 90$ AU in size. We analyzed \emph{Spitzer} IRS spectra for two objects in the sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the presence …
We carried out optical high-resolution spectroscopy of T Tauri stars using the Subaru Telescope. Using archived data from the Keck Telescope and the Very Large Telescope, we detected forbidden lines of [S II] at 4069 A, in addition to those of [O I] at 5577 A and 6300 A, for 13 T Tauri stars. We consider that low-velocity components of these forbidden lines emanate from the wind associated with T Tauri stars. Using two flux ratios of the three lines, we simultaneously determined the hydrogen density and temperature of the winds. The winds of T Tauri stars have a hydrogen density of $2.5 \times…
Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in high-resolution optical spectra of 39 young stellar objects.We found that the equivalent widths of the emission lines decrease with stellar evolution. It has been often claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere. However, we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity. Instead, we found that the objects with high mass accretion rates had stronger Ca II emission lines. This…
We present a detailed study of the disk around the intermediate mass star SO 411, aiming to explain the spectral energy distribution of this star. We show that this is a transitional disk truncated at $\sim$11 au, with $\sim$0.03 lunar masses of optically thin dust inside the cavity. Gas also flows through the cavity, since we find that the disk is still accreting mass onto the star, at a rate of $\sim 5x10^{-9}$ Msun/yr. Until now, SO 411 has been thought to belong to the $\sim$3 Myr old {$σ$} Orionis cluster. However, we analyzed the second Gaia Data Release in combination with kinematic dat…
Planet formation is one explanation for the partial clearing of dust observed in the disks of some T Tauri stars. Indeed studies using state-of-the-art high angular resolution techniques have very recently begun to observe planetary companions in these so-called transitional disks. The goal of this work is to use spectra of the transitional disk object LkCa 15 obtained with X-Shooter on the Very Large Telescope to investigate the possibility of using spectro-astrometry to detect planetary companions to T Tauri stars. It is argued that an accreting planet should contribute to the total emission…
The results of a spectroscopic survey of H alpha emission line stars associated with fourteen bright rimmed clouds are presented. Slit-less optical spectroscopy was carried out with the Inter University Centre for Astronomy and Astrophysics (IUCAA) 2m telescope and IUCAA Faint Object Spectrograph and Camera (IFOSC). H alpha emission line was detected from 173 objects. Among them 85 objects have a strong H alpha emission line with its equivalent width larger than 10 A. Those are classical T Tauri stars. 52 objects have a weak H alpha emission line with its equivalent width less than 10 A and do…
The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-$μ$m size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations c…
(Abridged) The detection of forming planets in disks around young stars remains elusive, and state-of-the-art observational techniques provide somewhat ambiguous results. It has been reported that the pre-transitional T Tauri star LkCa 15 could host three planets; candidate planet b is in the process of formation, as inferred from its H$α$ emission. However, a more recent work casts doubts on the planetary nature of the previous detections. We have observed LkCa 15 with ISIS/WHT. The spectrograph's slit was oriented towards the last reported position of LkCa 15 b (parallel direction) and 90deg…
We investigate the circumstellar disc fraction as determined from L-band excess observations of the young, massive Arches and Quintuplet clusters residing in the central molecular zone of the Milky Way. The Quintuplet cluster was searched for L-band excess sources for the first time. We find a total of 26 excess sources in the Quintuplet cluster and 21 in the Arches cluster, of which 13 are new detections. With the aid of proper motion membership samples, the disc fraction of the Quintuplet cluster was derived for the first time to be 4.0 +/- 0.7%. There is no evidence for a radially varying d…
Variability is a defining characteristic of young low-mass stars that are still accreting material from their primordial protoplanetary disk. Here we present the largest \textit{HST} variability study of Classical T Tauri stars (CTTS) to date. For 5 of these objects, we obtained a total of 25 spectra with the Space Telescope Imaging Spectrograph (STIS). Mass accretion rates and the fraction of the star covered by accretion columns (i.e., filling factors) were inferred using 1D NLTE physical models whose parameters were fit within a Bayesian framework. On week long timescales, typical changes i…
We present the largest survey of spectrally resolved mid-infrared water emission to date, with spectra for 11 disks obtained with the Michelle and TEXES spectrographs on Gemini North. Water emission is detected in 6 of 8 disks around classical T Tauri stars. Water emission is not detected in the transitional disks SR 24 N and SR 24 S, in spite of SR 24 S having pre-transitional disk properties like DoAr 44, which does show water emission (Salyk et al. 2015). With R~100,000, the TEXES water spectra have the highest spectral resolution possible at this time, and allow for detailed lineshape anal…
Investigating the molecular gas in the inner regions of protoplanetary disks provides insight into how the molecular disk environment changes during the transition from primordial to debris disk systems. We conduct a small survey of molecular hydrogen (H$_2$) fluorescent emission, using 14 well-studied Classical T Tauri stars at two distinct dust disk evolutionary stages, to explore how the structure of the inner molecular disk changes as the optically thick warm dust dissipates. We simulate the observed HI-Lyman $α$-pumped H$_2$ disk fluorescence by creating a 2D radiative transfer model that…
