Search results for "T Tauri"
showing 10 items of 79 documents
DR Tauri: Temporal variability of the brightness distribution in the potential planet-forming region
2015
We investigate the variability of the brightness distribution and the changing density structure of the protoplanetary disk around DR Tau, a classical T Tauri star. DR Tau is known for its peculiar variations from the ultraviolet (UV) to the mid-infrared (MIR). Our goal is to constrain the temporal variation of the disk structure based on photometric and MIR interferometric data. We observed DR Tau with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) at three epochs separated by about nine years, two months, respectively. We fit the spectral energy distribution and the MIR visibilities with radiative transfer simulations. We are able to r…
Convection in the Surface Layers of Neutron Stars
1997
During some phases of a neutron star's evolution, the temperature gradient in the surface layers, calculated assuming only radiative and conductive transport, may exceed the adiabatic gradient. This superadiabatic gradient is the necessary (but not sufficient) condition for convective instability. The present paper examines the sufficiency condition for the onset of convection in neutron stars in the presence of a strong magnetic field. It is shown that the large fields typically found in neutron stars—about 1011 to 1013 G—stabilize the atmosphere against convection. Convective instability can arise only in neutron stars with very weak magnetic fields, ≤108-109 G. Convective motions in such…
X-ray emission from MP Muscae: an old classical T Tauri star
2007
We study the properties of X-ray emitting plasma of MP Mus, an old classical T Tauri star. We aim at checking whether an accretion process produces the observed X-ray emission and at deriving the accretion parameters and the characteristics of the shock-heated plasma. We compare the properties of MP Mus with those of younger classical T Tauri stars to test whether age is related to the properties of the X-ray emission plasma. XMM-Newton X-ray spectra allows us to measure plasma temperatures, abundances, and electron density. In particular the density of cool plasma probes whether X-ray emission is produced by plasma heated in the accretion process. X-ray emission from MP Mus originates from…
The enigmatic young brown dwarf binary FU Tau: accretion and activity
2010
FU Tau belongs to a rare class of young, wide brown dwarf binaries. We have resolved the system in a Chandra X-ray observation and detected only the primary, FU Tau A. Hard X-ray emission, presumably from a corona, is present but, unexpectedly, we detect also a strong and unusually soft component from FU Tau A. Its X-ray properties, so far unique among brown dwarfs, are very similar to those of the T Tauri star TW Hya. The analogy with TW Hya suggests that the dominating soft X-ray component can be explained by emission from accretion shocks. However, the typical free-fall velocities of a brown dwarf are too low for an interpretation of the observed X-ray temperature as post-shock region. O…
XMM-Newton spectroscopy of the metal depleted T Tauri star TWA 5
2005
We present results of X-ray spectroscopy for TWA 5, a member of the young TW Hydrae association, observed with XMM-Newton. TWA~5 is a multiple system which shows Halpha emission, a signature typical of classical T Tauri stars, but no infrared excess. From the analysis of the RGS and EPIC spectra, we have derived the emission measure distribution vs. temperature of the X-ray emitting plasma, its abundances, and the electron density. The characteristic temperature and density of the plasma suggest a corona similar to that of weak-line T Tauri stars and active late-type main sequence stars. TWA 5 also shows a low iron abundance (~0.1 times the solar photospheric one) and a pattern of increasin…
The rich young cluster NGC 6530: a combined X-ray-optical-infrared study
2006
We present a combined X-ray, optical, and IR (2MASS) study of NGC 6530, complementing our previous studies of this cluster. We consider different indicators of IR excesses, which can be taken as an indicator of circumstellar disks and therefore of pre-main-sequence status. We used reddening-free indices to ensure that our results are unaffected by highly irregular, differential reddening. More than the study of the JHK bands alone (33 IR-excess stars found), we found it useful to compare various optical and IR colors, finding overall 333 stars with optical-IR excess. In the field of the previously studied Chandra ACIS-I observation, we found 196 stars with optical-IR excess, of which 120 ha…
Structure of X-ray emitting jets close to the launching site: from embedded to disk-bearing sources
2018
Several observations of stellar jets show evidence of X-ray emitting shocks close to the launching site. In some cases, the shocked features appear to be stationary, also for YSOs at different stages of evolution. We study the case of HH 154, the jet originating from the embedded binary Class 0/I protostar IRS 5, and the case of the jet associated to DG Tau, a more evolved Class II disk-bearing source or Classical T Tauri star (CTTS), both located in the Taurus star-forming region. We aim at investigating the effect of perturbations in X-ray emitting stationary shocks in stellar jets; the stability and detectability in X-rays of these shocks; and explore the differences in jets from Class 0…
Activity and Rotation in the Young Cluster h Per
2013
We study the stellar rotation-activity relation in the crucial age at which stars reach the fastest rotation. To this aim we have analyzed data of the young cluster h Per, very rich and compact, located at 2300 pc, that at an age of 13 Myr should be mainly composed of stars that have ended their contraction phase and that have not lost significant angular momentum viamagnetic breaking. To constrain the activity level of h Per members we have analyzed a deep Chandra/ACIS-I observation. Rotational periods of h Per members have been derived by Moraux et al. (2013) in the framework of the MONITOR project (Aigrain et al. 2007; Irwin et al. 2007). In the Chandra observation we have detected 1010 …
FLAMES Observations of the Star Forming Region NGC 6530
2006
Context. Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. Aims. We select cluster members using different membership criteria, to study the properties of pre-main sequence stars with or without circumstellar disks. Methods. We use intermediate resolution spectra including the Li I 6707.8 $\AA$ line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined …
XMM-Newton survey of two upper Scorpius regions
2006
We study X-ray emission from young stars by analyzing deep XMM-Newton observations of two regions of the Upper Scorpius association, having an age of 5 Myr. Based on near infrared and optical photometry we identify 22 Upper Scorpius photometric members among the 224 detected X-ray sources. We derive coronal properties of Upper Scorpius stars by performing X-ray spectral and timing analysis. The study of four strong and isolated stellar flares allows us to derive the length of the flaring loops. Among the 22 Upper Scorpius stars, 13 are identified as Upper Scorpius photometric members for the first time. The sample includes 7 weak-line T Tauri stars and 1 classical T Tauri star, while the na…