Abstract. High-resolution spectroscopic monitoring of the exceptionally active classical T Tauri star (CTTS) RW Aur A was carried out in three seasons of 1996, 1998 and 1999 with simultaneous B, V photometry. The high quality spectra revealed a multicomponent structure of the spectrum, which includes: 1) a veiled photospheric spectrum of a K1-K4 star, 2) broad emission lines of neutrals and ions, 3) narrow emission lines of He i and He ii, 4) red-shifted accretion features of many lines, 5) shell lines at about the stellar velocity, 6) blue-shifted wind features and 7) forbidden lines. Periodic modulations in many spectral features were found. The photospheric absorption lines show sinusoidal variations in radial velocity with an amplitude of ±6 km s −1 and a period of about 2. d 77. The radial velocities of the narrow emission lines of He vary with the same period but in anti-phase to the photospheric lines. The equivalent widths of the narrow emissions vary with a phase-shift with respect to the velocity curve. The strength of the red-shifted accretion components of Na D and other lines is also modulated with the same period. The broad emission lines of metals vary mostly with the double period of about 5.d 5. One unexpected result is that no correlation was found between the veiling and the brightness, although both parameters varied in wide ranges. This is partly due to a contribution of the shell absorption to the photospheric line profiles, which make them vary in width and depth thus simulating lower veiling. The spectral lines of the accreting gas show two distinct components: one is formed at low velocity at the beginning of the accretion column, and the other at high velocity near the stellar surface. The low velocity components are strong in low excitation lines of neutrals, while the high velocity components are strong in high excitation lines of ions, thus showing the gradients of temperature and density along the accretion column. Most of the observed features can be interpreted in the framework of non-axisymmetric magnetospheric accretion, but the origin of this asymmetry can be explained in different ways. We consider two possible models. The first model suggests that RW Aur A is a binary with a brown dwarf secondary in a nearly circular orbit with a period of 2.d 77. The orbiting secondary generates a moving stream of enhanced accretion from one side of the disk towards the primary. The other model assumes that RW Aur A is a single star with a rotational period of 5.d 5 and with two footpoints of channeled accretion streams within a global magnetosphere which is tilted relative to the rotational axis or otherwise non-axisymmetric. Both models can explain qualitatively and quantitatively most of the observed variations, but there are some details which are less well accounted for.

We survey fluorescent H 2 emission in HST /STIS spectra of the classical T Tauri stars (CTTSs) TW Hya, DF Tau, RU Lupi, T Tau, and DG Tau, and the weak-lined T Tauri star (WTTS) V836 Tau. From each of those sources we detect between 41-209 narrow H 2 emission lines, most of which are pumped by strong Lyα emission. H 2 emission is not detected from the WTTS V410 Tau. The fluorescent H 2 emission appears to be common to circumstellar environments around all CTTSs, but high spectral and spatial resolution STIS observations reveal diverse phenomenon. Blueshifted H 2 emission detected from RU Lupi, T Tau, and DG Tau is consistent with an origin in an outflow. The H 2 emission from TW Hya, DF Tau, and V836 Tau is centered at the radial velocity of the star and is consistent with an origin in a warm disk surface. The H 2 lines from RU Lupi, DF Tau, and T Tau also have excess blueshifted H 2 emission that extends to as much as -100 km s −1 . The strength of this blueshifted component from DF Tau and T Tau depends on the upper level of the transition. In all cases, the small aperture and attenuation of H 2 emission by stellar winds restricts the H 2 emission to be formed close to the star. The Lyα and the H 2 emission blueshifted by 15 km s −1 relative to RU Lupi are extended to the SW by ∼ 0. ′′ 07, although the faster H 2 gas that extends to ∼ 100 km s −1 is not spatially extended. We also find a small reservoir of H 2 emission from TW Hya and DF Tau consistent with an excitation temperature of ∼ 2.5 × 10 4 K.

Abstract.We have collected high-resolution (R ≈ 60 000) VLT-UVES spectrograms of the close T Tauri binary V 4046 Sgr from 3500-6750 Å at different phases of its 2.4 day orbital period. The high quality of these spectra allows us to present an improved ephemeris of the system. To model the photospheric absorption line spectrum we calculate synthetic spectra for the observed phases of the system. These synthetic spectra are used to determine veiling levels, and to extract emission line profiles that are undistorted by photospheric absorption lines. We find that the shapes of the strong emission lines of H and Ca  H & K all vary periodically with phase. A weak veiling continuum is superimposed on the stellar absorption line spectra. The Ca  H & K emission lines are composed of two narrow emission components that closely follow the stellar orbital motion, and we speculate that these lines are formed in global chromospheric networks on the stars. Also the Balmer lines have similar narrow "stellar" components, possibly also chromospheric. However, in addition there are extended wings on each side of the line centers of all H lines, which change dramatically in shape with the orbital phase. We find that the shape and velocity changes of the wing components are consistent with two concentrations of gas moving at high velocity but co-rotating with the stars. These concentrations move with a projected velocity of 80 km s −1 around the center of mass. They are located well inside the edge of the circumbinary disk, and also inside the co-linear Lagrangian points of this binary. With this concept we obtain a very good agreement between calculated and observed line profiles of H8, H9 and H10 as a function of phase. In some recent calculations of mass transfer from circumbinary disks to close binaries in circular motion, accumulations of gas in co-rotation with the stars develop, resulting in structures which are similar to what we have found from our observations. We also investigate the cause of periodic photometric variations observed by others.

We present far-ultraviolet spectra of the classical T Tauri star RU Lupi covering the 912-1710Å spectral range, as observed by the HST /STIS and FUSE satellites. We use these spectra, which are rich in emission and absorption lines, to probe both the accreting and outflowing gas. Absorption in the Lyα profile constrains the extinction to A V ∼ 0.07 mag, which we confirm with other diagnostics. We estimate a mass accretion rate of (5 ± 2) × 10 −8 M ⊙ yr −1 using the optical-NUV accretion continuum. The accreting gas is also detected in bright, broad lines of C IV, Si IV, and N V, which all show complex structures across the line profile. Many other emission lines, including those of H 2 and Fe II, are pumped by Lyα. RU Lupi's spectrum varies significantly in the FUV; our STIS observations occurred when RU Lupi was brighter than several other observations in the FUV, possibly due to a high mass accretion rate.

We have obtained three long-slit, far-UV spectra of the pre-main-sequence system T Tauri. These Hubble Space Telescope STIS spectra show a strong and variable on-source spectrum composed of both fluoresced H 2 and stellar chromospheric lines. Extended H 2 emission is seen up to 10 00 from the T Tau system. The on-source and extended H 2 are both pumped by H i Ly. The on-source H 2 is pumped by the red wing of a broad, self-absorbed Ly line, while the progressions seen in the extended gas are pumped from near line center. This suggests that the extended H 2 is pumped locally and not by the stellar Ly line. The H 2 to the north and west coincides with the evacuated cavity bounded by the optical reflection nebulosity; to the south the extended H 2 coincides with the HH 255 outflow from the embedded infrared companion T Tau S. The spatial profile of the extended gas shows a prominent dip coincident with the position of T Tau S. This may be absorption by a disk associated with T Tau S. There is no evidence for absorption by a disk surrounding T Tau N large enough to obscure T Tau S.

Context. Molecular oxygen, O 2 , has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O 2 emission. Aims. The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods. The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O 2 . Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs. Results. We detect a spectral line at v LSR = +3.5 km s −1 with ∆v FWHM = 1.5 km s −1 , parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O 2 (N J = 1 1 −1 0 ) transition at 118 750.343 MHz. Conclusions. The abundance of molecular oxygen, relative to H 2 , is 5 × 10 −8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.

Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ∼3 mag in the V band and went into a long-lasting minimum. In 2010 the star underwent a similar fading, although less pronounced. These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds. Aims. We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention of gathering more information on the occulting body and the cause of the phenomenon. Methods. We collected spectra of the two components of RW Aur. The photometry was performed before and during the minimum. Results. The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading. However, blue-shifted absorption components related to the stellar wind increased in strength in certain resonance lines, and the profiles and strengths but not the fluxes of forbidden lines became drastically different. Conclusions. The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind or jet further out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk into the line of sight through the interaction with an enhanced wind.

Young close binaries open central gaps in the surrounding circumbinary accretion disc, but the stellar components may still gain mass from gas crossing through the gap. It is not well understood how this process operates and how the stellar components are affected by such inflows. Our main goal is to investigate how gas accretion takes place and evolves in close T Tauri binary systems. In particular, we model the accretion flows around two close T Tauri binaries, V4046 Sgr and DQ Tau, both showing periodic changes in emission lines, although their orbital characteristics are very different. In order to derive the density and velocity maps of the circumbinary material, we employ two‐dimensional hydrodynamic simulations with a locally isothermal equation of state. The flow patterns become quasi‐stable after a few orbits in the frame corotating with the system. Gas flows across the circumbinary gap through the corotating Lagrangian points, and local circumstellar discs develop around both components. Spiral density patterns develop in the circumbinary disc that transport angular momentum efficiently. Mass is preferentially channelled towards the primary and its circumstellar disc is more massive than the disc around the secondary. We also compare the derived density distribution to observed line profile variability. The line profile variability tracing the gas flows in the central cavity shows clear similarities with the corresponding observed line profile variability in V4046 Sgr, but only when the local circumstellar disc emission was excluded. Closer to the stars normal magnetospheric accretion may dominate, while further out the dynamic accretion process outlined here dominates. Periodic changes in the accretion rates on to the stars can explain the outbursts of line emission observed in eccentric systems such as DQ Tau.