共查询到20条相似文献，搜索用时 31 毫秒
1.
F. Bacciotti T.P. Ray D. Coffey J. Eislöffel J. Woitas 《Astrophysics and Space Science》2004,292(1-4):651-658
Many magneto-hydrodynamic (MHD) models have been developed to describe the acceleration and collimation of stellar jets, in the framework of an infall/outflow process. Thanks to high angular resolution instrumentation, such as the one on-board the Hubble Space Telescope (HST), we are finally able to test observationally the proposed ideas. We present the results obtained by us from the first 0”.1 resolution spectra of the initial portion (within 100–200 AU from the source) of the outflows from visible T Tauri stars, taken with the Space Telescope Imaging Spectrograph (STIS). We obtain the jet morphology, kinematics and excitation in different velocity intervals, and we derive the jet mass and momentum fluxes. These results confirm the predictions of magneto-centrifugal models for the jet launch. Recently we have also found indications for rotation in the peripheral regions of several flows. The derived rotational motions appear to be in agreement with the expected extraction of angular momentum from the star/disk system caused by the jet, which in turn allows the star to accrete up to its final mass. Improvements to resolution are expected from observations with STIS in the ultraviolet, and with the forthcoming AMBER spectrometer to be mounted at the VLTI. 相似文献
2.
D. Coffey F. Bacciotti J. Woitas T.P. Ray J. Eislöffel 《Astrophysics and Space Science》2004,292(1-4):553-558
Whether jets from newly forming stars rotate is a fundamental question in star formation research. Theoretical models propose jet rotation as a means of removing angular momentum from the young star and disk system, thus allowing accretion. While widely accepted, this idea has not yet been tested observationally due to the high resolution requirement of examining jets close to their launching point. Previous findings from the Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Owens Valley Radio Observatory (OVRO) give indications of same rotation of the jet and disk respectively, of T Tauri star DG Tau. We report preliminary findings from STIS data for 3 of 8 sources in a current survey to establish conclusively whether protostellar jets rotate. The results were positive, yielding evidence of radial velocity differences about the axis at the base of all three jets of 10–25 km s?1. 相似文献
3.
Francesca Bacciotti Thomas P. Ray Jochen Eislöffel Jens Woitas Josef Solf Reinhard Mundt Christopher J. Davis 《Astrophysics and Space Science》2003,287(1-4):3-13
Collimated jets are believed to be an essential ingredient of the star formation process, and we are now able for the first time to test observationally the theories for their formation and propagation. The major advances achieved in recent years are reviewed, regarding the observed morphology, kinematics and excitation properties of jets, from the parsec-scale `giant outflows' down to the `microjets' from T Tauri stars. High angular resolution images and spectra have provided valuable estimates of jet diameter, space velocity, temperature, ionization fraction, electron and total density, both along and across the flow. We can thus calculate key physical quantites, as the shock excitation parameters, or the mass and momentum fluxes in the flow. The results obtained appear to validate the popular magneto-centrifugal models for jet launching, although some important issues are still under debate, as to the cause of knotty structures, observed wind thermal properties, and the dynamical relationship between jets and molecular outflows. Among the most interesting recent findings, we mention the observed indications for jet rotation, with inferred toroidal velocities consistent with the prescribed angular momentum balance between infall and outflow. 相似文献
4.
赫比格－哈罗天体（ＨＨ天体）包含了有关原恒星吸积和抛射过程的许多重要信息,ＨＨ天体高分辨观测研究取得了一系列新进展：分辨出激波峰面、马赫盘和辐射冷却区;分辨出喷流节点的结构,发现它们大多是内工作面,而不是由Ｋｅｌｖｉｎ－Ｈｅｌｍｈｏｌｔｚ不稳定性所产生的斜激波;发现喷流宽度随到激发源距离的减小仅缓慢减小,对喷流的准直和加速模型提供了限制条件;ＨＨ天体在小尺度上尚有复杂的激发结构。对这些进展进行了评 相似文献
5.
Ultraviolet spectroscopy and imaging of comet Hale-Bopp (C/1995 O1) were obtained from a variety of space platforms from shortly
after the discovery of the comet through perihelion passage. Observations with the International Ultraviolet Explorer (IUE)
and the Hubble Space Telescope (HST) spanned the range of 6.8 to 2.7 AU pre-perihelion, but IUE was decommissioned in September
1996 and HST was precluded from near-perihelion observations because of its solar avoidance constraint. In September 1996,
observations were made by the Extreme Ultraviolet Explorer (EUVE) that showed the presence of soft X-rays offset from the
optical center of the coma and provided a sensitive spectroscopic upper limit to the Ne/O abundance ratio. During the perihelion
period NASA mounted a successful campaign of four sounding rockets that were launched at the White Sands Missile Range, New
Mexico, between March 25 and April 8, 1997. The payloads included long-slit spectroscopy and ultraviolet imaging polarimetry.
In addition, Hale-Bopp was observed near perihelion by ultraviolet instruments on orbiting spacecraft that were designed for
solar or terrestrial observations. Observations with HST, using the Space Telescope Imaging Spectrograph (STIS), installed
during the February 1997 servicing mission, resumed in August 1997. Intercomparison of the ultraviolet observations and comparison
with the results on gas composition and activity from ground-based visible, infrared and radio observations may permit the
resolution of many discrepant results present in the literature.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
C. Dougados S. Cabrit J. Ferreira N. Pesenti P. Garcia D. O'Brien 《Astrophysics and Space Science》2004,292(1-4):643-650
We discuss in this contribution constraints on the origin of mass-loss from young stars brought by recent observations at high angular resolution (0.1″ = 14 AU) of the inner regions of winds from T Tauri stars. Jet widths and collimation scales, the large extent of the velocity profile as well as the detection of rotation signatures agree with predictions from magneto-centrifugal disk wind ejection models. However dynamically cold disk wind solutions predict too large terminal velocities and too low jet densities and ionisation fractions, suggesting that thermal gradients (originating in an accretion heated disk corona for example) may play an important role in accelerating the flow. 相似文献
7.
Jeffrey L. Linsky 《Astrophysics and Space Science》2011,335(1):177-185
Our understanding of the important physical processes operating in the diffuse interstellar medium (ISM) has advanced in recent
years from the analysis of high-resolution ultraviolet (UV) spectra obtained with the Hubble Space Telescope (HST) and the
Far-Ultraviolet Spectrograph Explorer (FUSE) and from high-fidelity simulations of the kinematics and energetics of the ISM.
Nevertheless, much remains to be learned from observations with the Space Telescope Imaging Spectrograph (STIS) instrument
on HST and spectrographs on the World Space Observatory (WSO). I will describe several major unanswered questions and suggest
how future UV observations can answer these questions. I will also summarize the instrument requirements needed for a future
UV spectroscopic mission and recommend how to achieve a successful mission. 相似文献
8.
Catherine Dougados Sylvie Cabrit Jonathan Ferreira Nicholas Pesenti Paulo Garcia Darren O'brien 《Astrophysics and Space Science》2004,293(1-2):45-52
We discuss in this contribution constraints on the origin of mass-loss from young stars brought by recent observations at high angular resolution (0.1″ = 14 AU) of the inner regions of winds from T Tauri stars. Jet widths and collimation scales, the large extent of the velocity profile as well as the detection of rotation signatures agree with predictions from extended (R e ≥ 1 AU) magneto-centrifugal disk wind ejection models. Detected poloidal and toroidal velocities imply large ejection efficiencies (ξ ? 0.05, λ ? 10), suggesting that thermal gradients (originating in an accretion heated disk corona for example) play an important role in accelerating the flow. 相似文献
9.
The auroras on Jupiter and Saturn can be studied with a high sensitivity and resolution by the Hubble Space Telescope ( HST ) ultraviolet (UV) and far-ultraviolet Space Telescope Imaging Spectrograph (STIS) and Advanced Camera for Surveys (ACS) instruments. We present results of automatic detection and segmentation of Jupiter's auroral emissions as observed by the HST ACS instrument with the VOronoi Image SEgmentation (VOISE). VOISE is a dynamic algorithm for partitioning the underlying pixel grid of an image into regions according to a prescribed homogeneity criterion. The algorithm consists of an iterative procedure that dynamically constructs a tessellation of the image plane based on a Voronoi diagram, until the intensity of the underlying image within each region is classified as homogeneous. The computed tessellations allow the extraction of quantitative information about the auroral features, such as mean intensity, latitudinal and longitudinal extents and length-scales. These outputs thus represent a more automated and objective method of characterizing auroral emissions than manual inspection. 相似文献
10.
Francesca Bacciotti Leonardo Testi Alessandro Marconi Paulo J.V. Garcia Thomas P. Ray Jochen Eislöffel Catherine Dougados 《Astrophysics and Space Science》2003,286(1-2):157-162
The interplay between accretion and ejection in the environment of young stellar objects (YSOs) is believed to be a crucial
element in the star formation process. Since most of the properties of the models are set up in the first few AUs from the
source (below the so-called Alfvèn surface), to validate and constrain the models observationally we need very high angular
resolution. With HST (resolution ∼ 0.'1, i.e. about 14 AU in Taurus)we have been able to access the external border of the
acceleration region, for jets in the Taurus-Auriga cloud. Here we see an onion-like kinematic structure in the first 200 AU
of the flow, and indications for rotation around the symmetry axis for the resolved low/moderate velocity component. We have
now planned observations with AMBER on the VLTI to investigate at 1 mas resolution (in J) the core of the central engine,
down to 0.1 AU from the source. Here we describe a joint project by several Institutes in the AMBER consortium dedicated to
the study of the morphology and detailed kinematics of a few selected targets. On one hand we will use the large UV coverage
of the ATs to explore at medium spectral resolution the structure of the flow. On the other hand the large collection area
of the UTs combined with the high resolution mode (R=10000) of AMBER will allow us to search for interesting kinematic features,
among which signatures of rotation around the axis, that would constitute an important validation of the proposed models for
the jet launching.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
The combination of accretion disks and supersonic jets is used to model many active astrophysical objects, viz., young stars, relativistic stars, and active galactic nuclei. However, existing theories on the physical processes by which these structures transfer angular momentum and energy from disks to jets through viscous or magnetic torques are still relatively approximate. Global stationary solutions do not permit understanding the formation and stability of these structures; and global numerical simulations that include both the disk and jet physics are often limited to relatively short time scales and astrophysically out-of-range values of viscosity and resistivity parameters that are instead crucial to defining the coupling of the inflow/outflow dynamics. Along these lines we discuss self-consistent time-dependent simulations of the launching of supersonic jets by magnetized accretion disks, using high resolution numerical techniques. We shall concentrate on the effects of the disk physical parameters, and discuss under which conditions steady state solutions of the type proposed in the self-similar models of Blandford and Payne can be reached and maintained in a self-consistent nonlinear stationary state. 相似文献
12.
Juan P. Madrid William B. Sparks D. E. Harris Eric S. Perlman Duccio Macchetto John Biretta 《Astrophysics and Space Science》2007,311(1-3):329-333
Near-ultraviolet imaging with HST offers the best possible spatial resolution currently available for optical/UV astronomical
imaging. The giant elliptical galaxy M87 hosts one of the most spectacular, best studied and nearest (d=16 Mpc) galactic-scale relativistic (synchrotron emitting plasma) jets. We have extracted from the HST archive all 220 nm
images of the jet of M87, taken with the STIS MAMA camera and co-added them to provide the deepest image ever at this wavelength.
The combination of highest spatial resolution and long integration time, 42500 seconds, reveals a wealth of complex structure,
knots, filaments and shocks. We compare this image with deep X-ray observations obtained with the Chandra X-ray telescope. 相似文献
13.
L. Fossati D. Bisikalo H. Lammer B. Shustov M. Sachkov 《Astrophysics and Space Science》2014,354(1):9-19
The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory–UltraViolet (WSO–UV). In its characteristics, the WSO–UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO–UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO–UV. 相似文献
14.
The Space Telescope Imaging Spectrograph (STIS) on HST provides the first ultraviolet data that are of sufficient spectral and temporal resolution to generate Doppler tomograms of X‐ray binaries.We show both optical and ultraviolet maps constructed for the intermediate mass system Hercules X‐1/HZ Her and the massive wind‐fed system SMC X‐1/SK160. We have used the maps and corresponding lightcurves as diagnostics with which to test the validity of published models for Hercules X‐1. We find that although the models are mostly able to explain the light curves they are not consistent with the full phase maps. We present simulations of Doppler maps of X‐ray lines that will be possible with the spectral and temporal resolution and substantial effective area of the next major X‐ray mission, Con‐X. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
15.
High angular resolution spectroscopy obtained with the Hubble Space Telescope (HST) has revealed a remarkable population of galaxies hosting dwarf Seyfert nuclei with an unusually large broad-line region (BLR). These objects are remarkable for two reasons. Firstly, the size of the BLR can, in some cases, rival those seen in the most luminous quasars. Secondly, the size of the BLR is not correlated with the central continuum luminosity, an observation that distinguishes them from their reverberating counterparts. Collectively, these early results suggest that non-reverberating dwarf Seyferts are a heterogeneous group, and not simply scaled versions of each other. Careful inspection reveals broad H Balmer emission lines with single peaks, double peaks, and a combination of the two, suggesting that the broad emission lines are produced in kinematically distinct regions centered on the black hole (BH). Because the gravitational field strength is already known for these objects, by virtue of knowing their BH mass, the relationship between velocity and radius may be established, given a kinematic model for the BLR gas. In this way, one can determine the inner and outer radii of the BLRs by modeling the shape of their broad emission line profiles. In the present contribution, high quality spectra obtained with the Space Telescope Imaging Spectrograph (STIS) are used to constrain the size of the BLR in the dwarf Seyfert nuclei of M81, NGC 3998, NGC 4203, NGC 3227, NGC 4051 and NGC 3516. 相似文献
16.
D. J. Ampleford S. V. Lebedev A. Ciardi S. N. Bland S. C. Bott G. N. Hall N. Naz C. A. Jennings M. Sherlock J. P. Chittenden A. Frank E. Blackman 《Astrophysics and Space Science》2007,307(1-3):51-56
Collimated flows ejected from young stars are believed to play a vital role in the star formation process by extracting angular
momentum from the accretion disk. We discuss the first experiments to simulate rotating radiatively cooled, hypersonic jets
in the laboratory. A modification of the conical wire array $z$-pinch is used to introduce angular momentum into convergent
flows of plasma, a jet-forming standing shock and into the jet itself. The rotation of the jet is evident in laser imaging
through the presence of discrete filaments which trace the rotational history of the jet. The presence of angular momentum
results in a hollow density profile in both the standing conical shock and the jet. 相似文献
17.
18.
J. Meaburn M. F. Graham M. P. Redman 《Monthly notices of the Royal Astronomical Society》2002,337(1):327-331
A spatially unresolved velocity feature, with an approaching radial velocity of ≈100 km s−1 with respect to the systemic radial velocity, in a position–velocity array of [O iii ] 5007-Å line profiles is identified as the kinematical counterpart of a jet from the proplyd LV 5 (158–323) in the core of the Orion nebula. The only candidate in Hubble Space Telescope ( HST ) imagery for this jet appears to be a displaced, ionized knot. Also an elongated jet projects from the proplyd GMR 15 (161–307). Its receding radial velocity difference appears at ≈80 km s−1 in the same position–velocity array.
A 'standard' model for jets from young, low-mass stars invokes an accelerating, continuous flow outwards with an opening angle of a few degrees. Here an alternative explanation is suggested which may apply to some, if not all, of the proplyd jets. In this, a 'bullet' of dense material is ejected which ploughs through dense circumstellar ambient gas. The decelerating tail of material ablated from the surface of the bullet would be indistinguishable from a continuously emitted jet in current observations. 相似文献
A 'standard' model for jets from young, low-mass stars invokes an accelerating, continuous flow outwards with an opening angle of a few degrees. Here an alternative explanation is suggested which may apply to some, if not all, of the proplyd jets. In this, a 'bullet' of dense material is ejected which ploughs through dense circumstellar ambient gas. The decelerating tail of material ablated from the surface of the bullet would be indistinguishable from a continuously emitted jet in current observations. 相似文献
19.
Comparisons of the northern and southern far ultraviolet (UV) auroral emissions of Jupiter from the Hubble Space Telescope (HST) or any other ultraviolet imager have mostly been made so far on a statistical basis or were not obtained with high sensitivity and resolution. Such observations are important to discriminate between different mechanisms responsible for the electron acceleration of the different components of the aurora such as the satellite footprints, the «main oval» or the polar emissions. The field of view of the ACS and STIS cameras on board HST is not wide enough to provide images of the full jovian disk. We thus compare the morphology of the north and south aurora observed 55 min apart and we point out similarities and differences. On one occasion HST pointed successively the two polar regions and auroral images were seen separated by only 3 min. This makes it possible to compare the emission structure and the emitted FUV power of corresponding regions. We find that most morphological features identified in one hemisphere have a conjugate counterpart in the other hemisphere. However, the power associated with conjugate regions of the main oval, diffuse or discrete equatoward emission observed quasi-simultaneously may be different in the two hemispheres. It is not directly nor inversely proportional to the strength of the B-field as one might expect for diffuse precipitation or field-aligned acceleration with equal ionospheric electron density in both hemispheres. Finally, the lack of symmetry of some polar emissions suggests that some of them could be located on open magnetic field lines. 相似文献
20.
The Cosmic Origins Spectrograph (COS) is an ultraviolet spectrograph scheduled for installation in the Hubble Space Telescope (HST) during HST Servicing Mission 4, currently planned to occur in August 2008. COS was designed to maximize sensitivity to faint point sources, and will provide limiting sensitivities at moderate spectral resolutions (R～20,000) that are a factor of 2 to >10 times better than those provided by previous ultraviolet spectrographs on HST. Here, we present an overview of the some of the science areas that will be addressed by COS observations and provide a summary of the capabilities of COS and the expected on-orbit performance. 相似文献