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 the
se 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 of accretion tracers such as H$alpha$ and therefore planetary companions could be detected with spectro-astrometry in the same way as it has been used to detect stellar companions to young stars. A probable planetary-mass companion was recently detected in the disk of LkCa 15. Therefore, it is an ideal target for this pilot study. We studied several key accretion lines in the wavelength range 300 nm to 2.2 $mu$m with spectro-astrometry. While no spectro-astrometric signal is measured for any emission lines the accuracy achieved in the technique is used to place an upper limit on the contribution of the planet to the flux of the H$alpha$, Pa$gamma$, and Pa$beta$ lines. The derived upper limits on the flux allows an upper limit of the mass accretion rate, log($dot{M}_{acc}$) = -8.9 to -9.3 for the mass of the companion between 6 M$_{Jup}$ and 15 M$_{Jup}$, respectively, to be estimated (with some assumptions).
As the number of observed brown dwarf outflows is growing it is important to investigate how these outflows compare to the well studied jets from young stellar objects. A key point of comparison is the relationship between outflow and accretion activ
ity and in particular the ratio between the mass outflow and accretion rates ($dot{M}_{out}$/$dot{M}_{acc}$). The brown dwarf candidate ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric study of brown dwarfs, to be driving an asymmetric outflow with the blue-shifted lobe having a position angle of $sim$ 20$^{circ}$. The aim here is to further investigate the properties of ISO-ChaI 217, the morphology and kinematics of its outflow, and to better constrain ($dot{M}_{out}$/$dot{M}_{acc}$). The outflow is spatially resolved in the $[SII]lambda lambda 6716,6731$ lines and is detected out to $sim$ 1farcs6 in the blue-shifted lobe and ~ 1 in the red-shifted lobe. The asymmetry between the two lobes is confirmed although the velocity asymmetry is less pronounced with respect to our previous study. Using thirteen different accretion tracers we measure log($dot{M}_{acc}$) [M$_{sun}$/yr]= -10.6 $pm$ 0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI 217 outflow $dot{M}_{out}$ was derived for a range of values of A$_{v}$, up to a value of A$_{v}$ = 2.5 mag estimated for the source extinction. The logarithm of the mass outflow ($dot{M}_{out}$) was estimated in the range -11.7 to -11.1 for both jets combined. Thus $dot{M}_{out}$/$dot{M}_{acc}$ [Msun/yr] lies below the maximum value predicted by magneto-centrifugal jet launching models. Finally, both model fitting of the Balmer decrements and spectro-astrometric analysis of the H$alpha$ line show that the bulk of the H I emission comes from the accretion flow.
We present broad-band mid-resolution X-Shooter/VLT spectra for four brown dwarfs of the TW Hya association. Our targets comprise substellar analogs representing the different evolutionary phases in young stellar evolution: For the two diskless brown
dwarfs, TWA-26 and TWA-29, we determine the stellar parameters and we study their chromospheric emission line spectrum. For the two accreting brown dwarfs, TWA-27 and TWA-28, we estimate the mass accretion rates from empirical correlations between emission line luminosities and the accretion luminosity.
We report first results on the large-scale distribution of the ROSAT All-Sky Survey (RASS) X-ray sources in a 5000 deg^2 field centered on Orion. Our final aim is to study the properties of different widespread populations in the Orion Complex close
to the Gould Belt (GB) in order to trace the star formation history in the solar neighbourhood.
In this letter we characterise IRAS12556-7731 as the first lithium-rich M-type giant. Based on its late spectral type and high lithium content, and because of its proximity in angular distance to the ChamaeleonII star-forming region, the star was mis
classified as a young low-mass star in a previous work. Based on HARPS data, synthetic spectral modelling, and proper motions, we derive the astrophysical parameters and kinematics of the star and discuss its evolutionary status. This solar-mass red giant (Teff=3460+/-60K and log(g)=0.6+/-0.2) is characterised by a relatively fast rotation (v sin(i)~8km/s), slightly subsolar metallicity and a high-lithium abundance, A(Li)=2.4+/-0.2dex. We discuss IRAS12556-7731 within the context of other known lithium-rich K-type giants. Because it is close to the tip of the red giant branch, IRAS12556-7731 is the coolest lithium-rich giant known so far, and it is among the least massive and most luminous giants where enhancement of lithium has been detected. Among several possible explanations, we cannot preclude the possibility that the lithium enhancement and rapid rotation of the star were triggered by the engulfment of a brown dwarf or a planet.
