XZ Tau Research Articles

A MULTI-EPOCHHSTSTUDY OF THE HERBIG-HARO FLOW FROM XZ TAURI

We present nine epochs of Hubble Space Telescope optical imaging of the bipolar outflow from the pre–mainsequence binary XZ Tauri. Our data monitor the system from 1995 to 2005 and include emission line images of the flow. The northern lobe appears to be a succession of bubbles, the outermost of which expanded ballistically from 1995 to 1999 but in 2000 began to deform and decelerate along its forward edge. It reached an extent of 6 �� from the binary in 2005. A larger and fainter southern counterbubble was detected for the first time in deep Advanced Camera for Surveys images from 2004. Traces of shocked emission are seen as far as 20 �� south of the binary. The bubble emission nebulosity has a low excitation overall, as traced by the [Sii]/Hα line ratio, requiring a nearly comoving surrounding medium that has been accelerated by previous ejections or stellar winds. Within the broad bubbles there are compact emission knots whose alignments and proper motions indicate that collimated jets are ejected from each binary component. The jet from the southern component, XZ Tau A, is aligned with the outflow axis of the bubbles and has tangential knot velocities of 70–200 km s −1 . Knots in the northern flow are seen to slow and brighten as they approach the forward edge of the outermost bubble. The knots in the jet from the other star, XZ Tau B, have lower velocities of ∼100 km s −1 . To explain the observations of the outer bubble, we propose that the XZ Tau A stellar jet underwent a large velocity pulse circa 1980. This ejection quickly overtook older, slower-moving ejecta very near the star, producing a ∼70 km s −1 shock in a hot (T ∼ 80,000 K), compact “fireball.” The initial thermal pressure of this gas parcel drove the expansion of a spherical bubble. Subsequent cooling caused the bubble to transition to ballistic expansion, followed by slowing of its forward edge by mass loading from the pre-shock medium. Repeated pulses may explain the multiple bubbles seen in the data. Collimated jets continue to flow through the bubble’s interior, and with the fading of the original fireball they are becoming the primary energizing mechanism for the emission line structures. Future evolution of the flow should see the outer bubble structures fade from view, and the emergence of a more typical Herbig–Haro jet/bow shock morphology. We present a preliminary numerical model of a pulsed jet to illustrate this scenario.

Spatially Resolved Molecular Hydrogen Emission in the Inner 200 AU Environments of Classical T Tauri Stars

We present 2.0-2.4 μm integral field spectroscopy at adaptive optics spatial resolution (~0.1 -->'') obtained with the Near-infrared Integral Field Spectrograph (NIFS) at Gemini North Observatory of six classical T Tauri stars: T Tau, DG Tau, XZ Tau, HL Tau, RW Aur, and HV Tau C. In all cases, the -->v = 1–0 S(1) (2.12 μm) emission is detected at spatially extended distances from the central stars. Moreover, HL Tau, T Tau, RW Aur, and HV Tau C have H2 that extends to projected distances of more than ~200 AU from the stars. Integrated over the IFU field, most of the H2 emission is not spatially coincident with the location of continuum flux. Multiple H2 transitions detected in the K-band spectra show that level populations are typical of gas in thermal equilibrium with excitation temperatures in the 1800-2300 K range. Three of the stars have H2 velocity profiles that are centered approximately at the stellar radial velocity, and three show velocity shifts with respect to the system. Each of the stars studied here exhibit H2 morphologies, spatial extents, excitation temperatures, and kinematics that are most consistent with shock-excited emission from the inner regions of the known Herbig-Haro energy flows or from spatially extended wide-angle winds encompassing the outflows rather than predominantly from H2 stimulated quiescently by UV or X-ray emission from the central stars. The data presented in this study highlights the sensitivity of adaptive-optics-fed integral field spectroscopy for spatially resolving emission line structures in the environments of bright young stars.

Herbig-Haro jets in 3D: the HL/XZ Tauri region

Context. Jets and outflows from young stellar objects (YSOs) can be identified and traced through the distribution and structure of shocked emission-line features. To understand the formation of these regions requires kinematic data at high spectral resolution and with full spatial coverage. Aims. In this work, we investigate the environment of HL/XZ Tau, which contains a compact and very active nest of YSOs. We explore the kinematic properties of the close association of jets in this region and study the interaction of jets with the ambient medium, as well as the outflows with each other. Methods. We present scanning Fabry-Perot interferometry of the HL/XZ Tau region in Ha and [S II] 6716 angstrom emission. We also measure the proper motions of the knots in the outflows, as derived from images obtained in 1997 and 2001, to achieve the full 3D kinematic picture. Results. Radial velocities of the HL Tau jet indicate a fast spine of low excitation surrounded by a slower sheared sheath of higher excitation. Proper motions range from 200-220 km s(-1) in the HL Tau jet and are aligned within 10 degrees of the jet spine. In combination, the proper motions and radial velocities indicate that three outflows in this region may be interacting with each other. Evidence of an outflow associated with LkH alpha 358 is found, and we suggest it is a source of Herbig-Haro (HH) knots that lie to the southeast of HL Tau and HH 265. Conclusions. We conclude that the southern lobe of the XZ Tau wind disrupts the eastern lobe of the collimated outflow from LkHa 358. The jet emerging from HL Tau is deflected by the northern lobe of the wind from XZ Tau. We propose several probable explanations for the unusual structure of the HL Tau jet. It is plausible that the shocks in the jet spine are maintained by the ram pressure of a low-density crosswind from XZ Tau. The crosswind interacts to form a sheath of entrained gas.

X-ray and optical bursts and flares in YSOs: results from a 5-day XMM-Newton monitoring campaign of L1551

We present the results of a five-day monitoring campaign with XMM-Newton of six X-ray bright young stellar objects (YSOs) in the star-forming complex L1551 in Taurus. All stars present significant variability on the five-day time scale. Modulation of the light curve on time scales comparable with the star's rotational period appeared to be present in the case of one weak-lined T Tauri star. Significant spectral variations between the 2000 and the 2004 observations were detected in the (unresolved) classical T Tauri binary system XZ Tau: a hot plasma component which was present in the X-ray spectrum in 2000 had significantly weakened in 2004. As XZ Tau N was undergoing a strong optical outburst in 2000, which had terminated since then, we speculate on the possible relationship between episodic, burst accretion, and X-ray heating. The transition object HL Tau underwent a strong flare with a complex temperature evolution, which is indicative of an event confined within a very large magnetic structure (few stellar radii), similar to the ones found in YSOs in the Orion Nebula Cluster.

An XMM-Newton-based X-ray survey of pre-main sequence stellar emission in the L1551 star-forming complex

We present a study of the X-ray sources present in the nearby L1551 star forming region, based on a deep XMM-Newton observation complemented with Chandra data for the brightest sources. Most known pre-main sequence stars in the region have been detected, most of them with sufficient statistics to allow a detailed study of the temporal and spectral characteristics of their X-ray emission. Significant temporal (and spectral) variability on both short and long time scales is visible for most of the stars. In particular XZ Tau shows large-amplitude variations on time scales of several hours with large changes in the intervening absorption, suggestive of the X-ray emission being eclipsed by the accretion stream (and thus of the X-ray emission being partly or totally accretion-induced). The coronal metal abundance of the WTTS sources is clustered around , while the CTTS sources span almost two orders of magnitudes in coronal Z, even though the photospheric abundance of all stars in the L1551 is likely to be very similar. Some individual elements (notably Ne) appear to be systematically enhanced with respect to Fe in the WTTS stars. The significant differences between the spectral and temporal characteristics of the CTTS and WTTS populations suggest that a different emission mechanism is (at least partly) responsible for the X-ray emission of the two types of stars.

A Spectroscopic Survey of Subarcsecond Binaries in the Taurus‐Auriga Dark Cloud with theHubble Space Telescope

We report the results of a spectroscopic survey of 20 close T Tauri binaries in the Taurus-Auriga dark cloud where the separations between primaries and their secondaries are less than the typical size of a circumstellar disk around a young star. Analysis of low-resolution and medium-resolution STIS spectra yields the stellar luminosities, reddenings, ages, masses, mass accretion rates, IR excesses, and emission line luminosities for each star in each pair. We examine the ability of IR color excesses, H-alpha equivalent widths, [O I] emission, and veiling to distinguish between weak emission and classical T Tauri stars. Four pairs have one cTTs and one wTTs; the cTTs is the primary in three of these systems. This frequency of mixed pairs among the close T Tauri binaries is similar to the frequency of mixed pairs in wider young binaries. Extinctions within pairs are usually similar; however, the secondary is more heavily reddened than the primary in some systems, where it may be viewed through the primary's disk. Mass accretion rates of primaries and secondaries are strongly correlated, and H-alpha luminosities, IR excesses, and ages also correlate within pairs. Primaries tend to have somewhat larger accretion rates than their secondaries do, and are typically slightly older than their secondaries according to three different sets of modern pre-main-sequence evolutionary tracks. Age differences for XZ Tau and FS Tau, systems embedded in reflection nebulae, are striking; the secondary in each pair is less massive but more luminous than the primary. The stellar masses of the UY Aur and GG Tau binaries measured from their rotating molecular disks are about 30% larger than the masses inferred from the spectra and evolutionary tracks.

High‐Resolution, Wide‐Field Imaging of the HL Tauri Environment in13CO (1–0)

We present a high-resolution image of the region near HL Tau in 13CO (1-0) over a region of 3' made with the BIMA array, supplemented by data from the NRAO 12 m telescope to include emission structures with low spatial frequencies. We find evidence for a shell of dimensions ~2' × 15 (~0.08 × 0.06 pc), with XZ Tau being the closest known source to its center. The 13CO map is consistent with an expanding bubble that has blown out on the far side from earth. Portions of the bubble wall are seen in optical scattered light. HL Tau is situated in the bubble wall; the evacuated region corresponds to the truncation in the reflection nebula northeast of HL Tau. Although it is thought that a remnant protostellar envelope is still infalling onto HL Tau, the existence of the expanding bubble makes it difficult to interpret the geometry and kinematics of the HL Tau circumstellar material. Our results demonstrate the importance of including low-spatial frequency emission for the interpretation of interferometer maps.

Spatial and kinematic properties of the forbidden emission line region of T Tauri stars

We have carried out a long-slit spectroscopic survey for 38 T Tauri stars (TTSs) to study the spatial and kinematic properties of their forbidden emission line (FEL) regions. With these observations we hope to pro- vide more insight into the complex physical structure of the outflows from young stars on the smallest spatial scales observable by long-slit spectroscopy. Due to the dieren- tial nature of the observational method, information on the spatial properties (oset from the stellar continuum and spatial width) on sub-arcsec (sub-seeing) scales can be obtained. For most TTSs the (OI) 6300, 6363, (NII) 6583 and (SII) 6716, 6731 lines have been investigated at a typical spatial resolution of 1:5 00 and a velocity res- olution of 20 50 km s 1 . A sub-sample of 9 closeby stars (Haro 6-10, XZ Tau, UZ Tau E, HN Tau, DO Tau, DP Tau, UY Aur, RW Aur and V536 Aql) has been ex- tensively studied and the direction of their outflows has been approximately determined by taking spectra at sev- eral slit position angles, if not known from emission-line CCD imaging. The spatial and kinematic properties of the FEL regions of these 9 TTSs are described in detail. Together with 3 additional stars discussed in the litera- ture, a sample of 12 stars provides the basis for the follow- ing main results of our survey: The so-called high-velocity component (HVC) of the FELs (or gas of high velocity which presumably represents in many cases a HVC be- ing blended with emission of lower velocity) is generally spatially more extended than the so-called low-velocity component (LVC, or gas near the stellar velocity). In the (SII) 6731 line the centroid of the high-velocity gas is lo- cated typically at distances of 0:6 00 from the TTS while for the low-velocity gas this value is smaller on average by more than a factor of 3. Comparing the spatial properties of the high-velocity gas among the investigated FELs, it turns out that the largest spatial width and the largest oset of the centroid from the star is usually observed in the (NII) 6583 line, while the emission region is most compact in the (OI) 6300 line. In (OI) the centroid of the

Hubble Space TelescopeWFPC Images of Emission Nebulosity near XZ Tauri

XZ Tauri is a M3 V T Tauri star with a pre-main-sequence binary companion detected by infrared speckle interferometry at a projected separation of 03 (about 40 AU). Previous ground-based observations of the system have shown bipolar emission nebulosity, including a possible jet knot. Images obtained with the Wide Field and Planetary Camera 2 on the Hubble Space Telescope show an elongated, filled bubble of emission nebulosity extending over 4'' to the north of the system which contains two or three compact knots. The source of the nebulosity is undetermined. For the first time, the components are separated in visible light, and the southern component (XZ Tau S) dominates the integrated light of the system. The reverse has been found to be true in the near-infrared. Thus we confirm that XZ Tauri belongs to the small class of young binaries with cool infrared companions.

A close association of five jet and outflow sources in the HL Tauri region

view Abstract Citations (79) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Close Association of Five Jet and Outflow Sources in the HL Tauri Region Mundt, Reinhard ; Ray, Thomas P. ; Buehrke, Thomas Abstract The discovery of a high degree of outflow activity in the HL Tau/HH 30 region, with five out of six known young stars showing outflows within a region of 0.05 x 0.1 pc, is reported. CCD images reveal not only hitherto unseen features in the known bipolar jets associated with the HH 30 star and VLA 1-HL Tau source, but also show jets emanating directly from HL Tau and a source southeast of XZ Tau. Elongated Herbig-Harolike emission is also found centered on XZ Tau. If these outflows are somehow caused by mass accretion, this high degree of activity may be due to mutual gravitational disturbances (and subsequent mass infall) increasing the degree and duration of the outflow over that expected for an'isolated star'. Publication: The Astrophysical Journal Pub Date: October 1988 DOI: 10.1086/185283 Bibcode: 1988ApJ...333L..69M Keywords: Charge Coupled Devices; Early Stars; Pre-Main Sequence Stars; Stellar Coronas; Stellar Mass Ejection; Taurus Constellation; Emission Spectra; Herbig-Haro Objects; Image Processing; Line Spectra; Very Large Array (Vla); Astrophysics; NEBULAE: GENERAL; STARS: MASS LOSS; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (13)

Narrow-band imaging and velocity maps of young stellar objects - Initial results

The first trials of a new technique, designed to map low-excitation ionized gas surrounding young stellar objects, are reported. The region surrounding the T Tau stars HL Tau and XZ Tau, that near HH 101, and that near IRS 5 in L1551 have been imaged through a narrow-band (4.7 A FWHM) forbidden S II filter; three-phase CCD chip was used as the detector. By tilting the narrow-band filter, it is possible to vary the wavelength of peak transmission and thus to detect high-velocity radial flows as well as map the morphology of the excited gas near these young stars. Evidence of an apparently helical outflow is found for HH 101. Redshifted gas appears to extend southward from HL Tau toward HH 30; a blueshifted jet extends northeastward of HL Tau. A series of forbidden S II knots is seen to extend along a jet directed southwestward from the infrared source IRS 5; the knot chain appears to delineate a blueshifted outflow that decelerates as it recedes from IRS 5.

Observations of the J=1-0 and J=2-1 Lines of 12CO in L1551: Evidence for Anisotropic Mass Loss

Observations of the J=1-0 lines of 12CO have been made to determine the extent and nature of the broad secondary velocity feature in L1551 (S239) first detected by Knapp et al. (1976). L1551 is associated with an extended Herbig-Haro object, HH102 (Strom et al. 1974), and two compact HH objects, HH28 and HH29 (Herbig 1974). Two nearby stars, HL Tau and XZ Tau, show extreme T-Tauri characteristics. The broad CO velocity component is seen toward HH102. Strom et al. (1976) have detected an infrared source near the HH objects which has a luminosity and infrared colors consistent with a late B star reddened by roughly 20 magnitudes of visual extinction (Snell 1979). The infrared source lies in the direction of the core of L1551, which has a density of 105 cm-3 (Loren et al. 1979; Snell 1979). The infrared source is likely to be embedded in this dense core.