Search results for "T Tauri"
showing 10 items of 79 documents
XMM-Newton observation of the classical T Tauri star SU Aurigae and the surrounding field
2007
Aims. We investigate the properties of the X-ray emitting plasma of the classical T Tauri star SU Aurigae and of other sources in the field of view. Methods. We use XMM-Newton to obtain a high-resolution RGS spectrum of SU Aur as well as EPIC imaging data and lowresolution spectra of the star and of other X-ray sources in the surrounding field. We reconstruct the emission measure distribution of SU Aur from the RGS spectrum using a line-based method, and we perform multi-temperature fits of the MOS spectra of the strongest sources both for the full observation and for selected time intervals to study their spectral variability. Results. The emission from SU Aur is highly variable, showing t…
The cool Galactic R Coronae Borealis variable DY Persei
2005
Results of first CCD photometry during the recent deep light decline, and high-resolution spectroscopy, are presented for DY Persei. The spectra show variable blueshifted features in the sodium D lines. The C lines are strong whereas neutron- capture elements are not enhanced. The isotopic 13 CN(2, 0) lines relative to 12 CN are of similar strength with those for the carbon star U Hya. All these confirm the RCB nature of DY Per and the existence of ejected clouds. At least two clouds are revealed at −197.3 and −143.0 km s −1 . A star was detected about 0. 4t o the west and 2 . 5 to the north from DY Per. This anonymous companion, with observed colour indices (B − V) = 0.68 and (V − R) � 1…
A comparison between the X-ray variable Sun and solar-like main sequence stars
2003
We analyze the time variations of the solar X-ray luminosity observed with Yohkoh/SXT with the aim to compare the X-ray variability of the Sun with that of the other solar-like main sequence stars as function of the relevant time scales. Since the observational set-up and strategies used to observe the Sun dier from those used for the other stars, we have explored the solar X-ray variability properties starting from the available solar data, trying to reproduce the observational procedures adopted for the stars. We have quantified how the solar variability amplitude increases with the explored time scales and found that solar-cycle variability can contribute at most up to 60% to the spread …
Viewing the Sun as an X-ray star
2003
The Sun is the late-type star we can study with the highest level of detail. In the interpretation of stellar data, therefore, it is often assumed that the physical processes of the coronae of late-type stars are similar to those of the solar corona, i.e. the "solar-stellar analogy". In order to investigate the validity of this assumption, we have started a program to study systematically the Sun as an X-ray star. Our program aims to explore how far the solar model can be applied to other stars. In this paper we review the results obtained from these studies and, in particular, we discuss the variability of a star identical to the Sun during its cycle, the contribution of different coronal …
Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
2013
(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic f…
The Origin of T Tauri X-ray Emission: New Insights from the Chandra Orion Ultradeep Project
2005
We use the data of the Chandra Orion Ultradeep Project (COUP) to study the nearly 600 X-ray sources that can be reliably identified with optically well characterized T Tauri stars (TTS) in the Orion Nebula Cluster. We detect X-ray emission from more than 97% of the optically visible late-type (spectral types F to M) cluster stars. This proofs that there is no ``X-ray quiet'' population of late-type stars with suppressed magnetic activity. All TTS with known rotation periods lie in the saturated or super-saturated regime of the relation between activity and Rossby numbers seen for main-sequence (MS) stars, but the TTS show a much larger scatter in X-ray activity than seen for the MS stars. S…
High Resolution X-ray Spectroscopy of T Tauri Stars in the Taurus-Auriga Complex
2006
Differences have been reported between the X-ray emission of accreting and non-accreting stars. Some observations have suggested that accretion shocks could be responsible for part of the X-ray emission in Classical T Tauri stars (CTTS). We present high-resolution X-ray spectroscopy of nine pre-main sequence stars in order to test the proposed spectroscopic differences between accreting and non-accreting pre-main sequence stars. We use X-ray spectroscopy from the XMM-Newton Reflection Grating Spectrometers and the EPIC instruments. We interpret the spectra using optically thin thermal models with variable abundances, together with an absorption column density. For BP Tau and AB Aur we deriv…
X-ray emission from stellar jets by collision against high-density molecular clouds: an application to HH 248
2015
We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts against a dense molecular cloud. This scenario may be usual for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud by 2D axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig-Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10 MK, consistent with producti…
Study of a sample of faint Be stars in the exofield of CoRoT
2013
International audience; Context. Be stars are probably the most rapid rotators among stars in the main sequence (MS) and, as such, are excellent candidates to study the incidence of the rotation on the characteristics of their non-radial pulsations, as well as on their internal structure. Pulsations are also thought to be possible mechanisms that help the mass ejection needed to build up the circumstellar disks of Be stars.Aims. The purpose of this paper is to identify a number of faint Be stars observed with the CoRoT satellite and to determine their fundamental parameters, which will enable us to study their pulsation properties as a function of the location in the HR diagram and to searc…
Hydrodynamic Modeling of Accretion Shock on CTTSs
2009
High resolution (R ~ 600) X-ray observations of some classical T Tauri stars (CTTSs) (TW Hya, BP Tau, V4046 Sgr, MP Mus and RU Lupi) have shown the presence of X-ray plasma at T ~ 2–3 × 106 K and denser than n e ~ 1011 cm-3 [1, 2, 3, 4, 5], which suggests an origin different from the coronal one (n e ~ 1010 cm_3). Stationary models demonstrated that X-ray emission from CTTSs could also be produced by the accreting material [6]. We address this issue with the aid of a time-dependent hydrodynamic numerical model describing the impact of an accretion stream onto the chromosphere of a CTTS (see [7] for more details). Our simulations include the effects of gravity, radiative losses from opticall…