Search results for "stars: variables: T Tauri"
showing 10 items of 10 documents
UV variability and accretion dynamics in the young open cluster NGC 2264
2015
We explore UV and optical variability signatures for several hundred members of NGC 2264 (3 Myr). We performed simultaneous u- and r-band monitoring over two full weeks with CFHT/MegaCam. About 750 young stars are probed; 40% of them are accreting. Statistically distinct variability properties are observed for accreting and non-accreting cluster members. The accretors exhibit a significantly higher level of variability than the non-accretors, especially in the UV. The amount of u-band variability correlates statistically with UV excess in disk-bearing objects, which suggests that accretion and star-disk interaction are the main sources of variability. Cool magnetic spots, several hundred de…
UV And X-Ray Emission from Impacts of Fragmented Accretion Streams on Classical T Tauri Stars
2016
According to the magnetoshperic accretion scenario, during their evo- lution, Classical T Tauri stars accrete material from their circumstellar disk. The accretion process is regulated by the stellar magnetic eld and produces hot and dense post-shocks on the stellar surface as a result of impacts of the downfalling material. The impact regions are expected to strongly radiate in UV and X-rays. Several lines of evidence support the magnetospheric accretion scenario, especially in optical and infrared bands. However several points still remain unclear as, for instance,where the complex-pro le UV lines originate, or whether and how UV and X-ray emission is produced in the same shock region. Th…
Redshifted X-rays from the material accreting onto TW Hya: evidence of a low-latitude accretion spot
2017
High resolution spectroscopy, providing constraints on plasma motions and temperatures, is a powerful means to investigate the structure of accretion streams in CTTS. In particular, the accretion shock region, where the accreting material is heated to temperatures of a few MK as it continues its inward bulk motion, can be probed by X-ray spectroscopy. To attempt to detect for the first time the motion of this X-ray-emitting post-shock material, we searched for a Doppler shift in the deep Chandra/HETGS observation of the CTTS TW Hya. This test should unveil the nature of this X-ray emitting plasma component in CTTS, and constrain the accretion stream geometry. We searched for a Doppler shift…
The Close T Tauri Binary System V4046 Sgr: Rotationally Modulated X-Ray Emission from Accretion Shocks
2012
We report initial results from a quasi-simultaneous X-ray/optical observing campaign targeting V4046 Sgr, a close, synchronous-rotating classical T Tauri star (CTTS) binary in which both components are actively accreting. V4046 Sgr is a strong X-ray source, with the X-rays mainly arising from high-density (n_e ~ 10^(11-12) cm^(-3)) plasma at temperatures of 3-4 MK. Our multiwavelength campaign aims to simultaneously constrain the properties of this X-ray emitting plasma, the large scale magnetic field, and the accretion geometry. In this paper, we present key results obtained via time-resolved X-ray grating spectra, gathered in a 360 ks XMM-Newton observation that covered 2.2 system rotatio…
Effects of radiation in accretion regions of classical T Tauri stars
2019
Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns, in which optically thin and thick plasma components coexist. Thus an accurate description of these impacts requires to account for the effects of absorption and emission of radiation. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock downfalling material. We investigate if a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. We developed a radiation hydrodynamics model describing an accretion column impacting onto the su…
CSI 2264: Simultaneous optical and X-ray variability in pre-main sequence stars. I. Time resolved X-ray spectral analysis during optical dips and acc…
2017
Pre-main sequence stars are variable sources. In stars with disks, this variability is related to the morphology of the inner circumstellar region (<0.1 AU) and that of the photosphere and corona, all impossible to be spatially resolved with present day techniques. This has been the main motivation for the Coordinated Synoptic Investigation of NGC 2264. In this paper, we focus on the stars with disks. We analyze the X-ray spectral properties extracted during optical bursts and dips in order to unveil the nature of these phenomena. We analyze simultaneous CoRoT and Chandra/ACIS-I observations to search for coherent optical and X-ray flux variability in stars with disks. Then, stars are an…
Time Resolved X-Ray Spectral Analysis of Class II YSOs in NGC 2264 During Optical Dips and Bursts
2016
Pre-Main Sequence stars are variable sources. The main mechanisms responsible for their variability are variable extinction, unsteady accretion, and rotational modulation of both hot and dark photospheric spots and X-ray active regions. In stars with disks this variability is thus related to the morphology of the inner circumstellar region (<0.1 AU) and that of photosphere and corona, all impossible to be spatially resolved with present day techniques. This has been the main motivations of the Coordinated Synoptic Investigation of NGC2264, a set of simultaneous observations of NGC2264 with 15 different telescopes. We analyze the X-ray spectral properties of stars with disks extracted du…
Accretion in young stars: measure of the stream velocity of TW Hya from the X-ray Doppler shift
2015
High-resolution X-ray spectra are a unique tool to investigate the accretion process in young stars. In fact X-rays allow to investigate the accretion-shock region, where the infalling material is heated by strong shocks due to the impact with the denser stellar atmosphere. Here we show for the first time that it is possible to constrain the velocity of the accretion stream by measuring the Doppler shift of the emitted X-rays. To this aim we analyzed the deep Chandra/HETGS observation of the accreting young star TW Hya. We selected a sample of emission lines free from significant blends, fitted them with gaussian profiles, computed the radial velocity corresponding to each line, and average…
Effects of radiation in accretion regions of classical T Tauri stars
2019
Context. Models and observations indicate that the impact of matter accreting onto the surface of young stars produces regions at the base of accretion columns where optically thin and thick plasma components coexist. Thus, an accurate description of these impacts is necessary to account for the effects of absorption and emission of radiation. Aims. We study the effects of radiation emerging from shock-heated plasma in impact regions on the structure of the pre-shock down-falling material. We investigate whether a significant absorption of radiation occurs and if it leads to a pre-shock heating of the accreting gas. Methods. We developed a radiation hydrodynamics model describing an accreti…
CSI 2264: Simultaneous optical and X-ray variability in the pre-main sequence stars of NGC 2264
2019
Context. Pre-main sequence stars are variable sources. In diskless stars this variability is mainly due to the rotational modulation of dark photospheric spots and active regions, as in main sequence stars even if associated with a stronger magnetic activity.Aims. We aim at analyzing the simultaneous optical and X-ray variability in these stars to unveil how the activity in the photosphere is connected with that in the corona, to identify the dominant surface magnetic activity, and to correlate our results with stellar properties, such as rotation and mass.Methods. We analyzed the simultaneous optical and X-ray variability in stars without inner disks (e.g., class III objects and stars with…