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1.
During past years high angular (<1″) resolution imaging has provided useful information about the propagation of “real” jets. Recently, in addition, the spectrograph Hubble's Space Telescope Imaging spectrograph (STIS) on board the Hubble Space Telescope (HST) has finally allowed us to test the magneto-centrifugal paradigm for the jet launching. I present results from HST/STIS spectra at 0.″1 resolution of small-scale jets from T Tauri stars in their initial 140 AU (1″). The jet morphology, kinematics and excitation in different velocity intervals are derived, from which we calculate mass and momentum fluxes. Even more interestingly, we find indications for rotation around the symmetry axis in the peripheral regions of the flow. The investigated component of the wind appears to originate in the disk at a distance of 0.5-2 AU from the star, and it extracts at least 60% of the inner disk angular momentum. These results confirm for the first time the validity of the magneto-centrifugal approach for the jet launching, and constitute a benchmark to test models and simulations. In the near future, near-infrared (NIR) interferometry with AMBER/VLTI and with the LBTI will permit to observe the jet engine down to 0.1 AU from the source, where the acceleration of the jet takes place.  相似文献   

2.
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.
We report observations of the dwarf star ε Eri (K2 V) made with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope . The high sensitivity of the STIS instrument has allowed us to detect the magnetic dipole transitions of Fe  xii at 1242.00 and 1349.38 Å for the first time in a star other than the Sun. The width of the stronger line at 1242.00 Å has also been measured; such measurements are not possible for the permitted lines of Fe  xii in the extreme-ultraviolet. To within the accuracy of the measurements, the N  v and the Fe  xii lines occur at their rest wavelengths. Electron densities and linewidths have been measured from other transition region lines. Together, these can be used to investigate the non-thermal energy flux in the lower and upper transition regions, which is useful in constraining possible heating processes. The Fe  xii lines are also present in archival STIS spectra of other G/K-type dwarfs.  相似文献   

4.
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   

5.
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   

6.
We present ultraviolet spectra of 62 cataclysmic variables observed with Hubble Space Telescope Space Telescope Imaging Spectrograph & Faint Object Spectrograph (HST STIS FOS) to diagnose cataclysmic variables with enhanced NV/C IV line flux ratios. We concentrated on calculating the line flux ratios of the above mentioned sample. We found that a number of cataclysmic variables reveal enhanced NV/C IV line flux ratios in agreement with the previous studies (de Martino and Gänsicke, 2009, Gänsicke et al., 2003). Also we found that two new systems (U SCO, V1974 CYG) reveal enhanced NV/C IV line flux ratios. Such anomalous line flux ratios confirmed that these CVs went through a phase of thermal timescale mass transfer (TTSMT) and now accrete CNO processed material from a companion stripped of its external layers (Gänsicke et al., 2003, Gänsicke, 2004, de Martino and Gänsicke, 2009).  相似文献   

7.
We use ideal axisymmetric relativistic magnetohydrodynamic simulations to calculate the spin-down of a newly formed millisecond,   B ∼ 1015 G  , magnetar and its interaction with the surrounding stellar envelope during a core-collapse supernova (SN) explosion. The mass, angular momentum and rotational energy lost by the neutron star are determined self-consistently given the thermal properties of the cooling neutron star's atmosphere and the wind's interaction with the surrounding star. The magnetar drives a relativistic magnetized wind into a cavity created by the outgoing SN shock. For high spin-down powers  (∼1051–1052 erg s−1)  , the magnetar wind is superfast at almost all latitudes, while for lower spin-down powers  (∼1050 erg s−1)  , the wind is subfast but still super-Alfvénic. In all cases, the rates at which the neutron star loses mass, angular momentum and energy are very similar to the corresponding free wind values (≲30 per cent differences), in spite of the causal contact between the neutron star and the stellar envelope. In addition, in all cases that we consider, the magnetar drives a collimated  (∼5–10°)  relativistic jet out along the rotation axis of the star. Nearly all of the spin-down power of the neutron star escapes via this polar jet, rather than being transferred to the more spherical SN explosion. The properties of this relativistic jet and its expected late-time evolution in the magnetar model are broadly consistent with observations of long duration gamma-ray bursts (GRBs) and their associated broad-lined Type Ic SN.  相似文献   

8.
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   

9.
Chi Yuan  Patrick Cassen 《Icarus》1985,64(3):435-447
The gravitational collapse of molecular clouds or cloud cores is expected to lead to the formation of stars that begin their lives in a state of rapid rotation. It is known that, in at least some specific cases, rapidly rotating, slf-gravitating bodies are subject to instabilities that cause them to assume ellipsoidal shapes. In this paper we investigate the consequences of such instabilities on the angular momentum evolution of a star in the process of formation from a collapsing cloud, and surrounded by a protostellar disk, with a view toward applications to the formation of the Solar System. We use a specific model of star formation to demonstrate the possibility that such a star would become unstable, that the resulting distortion of the star would generate spiral density waves in the circumstellar disk, and that the torque associated with these waves would regulate the angular momentum of the star as it feeds angular momentum to the disk. We conclude that the angular momentum so transported to the disk would not spread the disk to, say, Solar System dimensions, by the action of the spiral density waves alone. However, a viscous disk could effectively extract stellar angular momentum and attain Solar System size. Our results also indicate that viscous disks could feed mass and angular momentum to a growing protostar in such a manner that distortions of the star would occur before gravitational torques could balance the influx of angular momentum. In other situations (in which the viscosity was small), a gap could be cleared between the disk and star.  相似文献   

10.
We analyzed the spectra of eight T Tauri stars (T Tau, RY Tau, CO Ori, EZ Ori, GW Ori, GX Ori, V1044 Ori, and SU Aur) in the wavelength range from 1200 to 3100 Å taken with the STIS spectrograph from the Hubble Space Telescope. For each star, we found an upper limit on the interstellar extinction A v , which proved to be lower than the values obtained by different authors from optical observations. For T Tau and RY Tau, we found the upper limits on their luminosities, masses, and radii as well as the bolometric luminosity of the excess emission continuum. The latter is most likely associated with mass accretion from a protoplanetary disk. We show that the bulk of the emission continuum is radiated in the infrared. For these stars, we determined the ratio of the flux in the C IV 1550 doublet lines to the excess-continuum flux. This ratio proved to be two orders of magnitude lower than its values predicted by the accretion-shock (AS ) models developed by Lamzin (1998) and Calvet and Gullbring (1998). This result leads us to believe that for T Tau and RY Tau, the emission continuum originates in the accretion disk and/or in the boundary layer rather than in the AS, as has been assumed previously. This implies that in these stars, only a small fraction of the accreted matter passes through the AS, while the bulk of this matter settles in the equatorial plane of the star, passing through the boundary layer.  相似文献   

11.
Hot WDs in binary systems with a less evolved star are particularly invaluable astrophysical probes, the unevolved companion enabling better derivation of distance and age than is usually possible for post-AGB objects, and therefore also of their radius and luminosity. But hot white dwarfs (WD) are elusive at all wavelengths except the UV (Bianchi et al. 2011a). From our GALEX UV source catalogs (Bianchi et al. 2011a,b, 2014, 2017) matched to SDSS, we identified thousands of candidate hot WDs including WDs in binary systems consisting of a hot WD and a companion of spectral type from A to M. The identification and preliminary characterization of the stellar parameters is based on the analysis of the photometric SED from far-UV to z-band.We have observed subsamples of the UV-selected WDs with the Hubble Space Telescope (HST) to better characterize their stellar parameters. We obtained (1) UV spectroscopy with STIS and analyzed the UV spectra together with optical SDSS spectra, and (2) multi-band imaging with WFC3 (\(0.04^{\prime\prime}/\mbox{pixel}\)) to measure angular separation and individual SEDs of the pair’s components in binary systems. In our HST/WFC3 sample of 59 hot-WD binaries with late-type companions, we found that at least a dozen have possibly evolved without exchanging mass. The UV STIS spectroscopy led to the revision of previous results based on optical spectra only, because of the often undetectable or unquantifiable contribution of the hot component to the optical fluxes.  相似文献   

12.
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   

13.
A very well-known property of close binary stars is that they usually rotate slowly than a similar type single star. Massive stars in close binary systems are supposed to experience an exchange of mass and angular momentum via mass transfer and tidal interaction, and thus the evolution of binary stars becomes more complex than that of individual stars. In recent times, it has become clear that a large number of massive stars interact with binary companions before they die. The observation also reveals that in close pairs the rotation tends to be synchronized with the orbital motion and the companions are naturally tempted to invoke tidal friction. We here introduce the effect of tidal angular momentum in the model of wind driven non-conservative mass transfer taking mass accretion rate as uniform with respect to time. To model the angular momentum evolution of a low mass main sequence companion star can be a challenging task. So, to make the present study more interesting, we have considered initial masses of the donor and gainer stars at the proximity of bottom-line main sequence stars and they are taken with lower angular momentum. We have produced a graphical profile of the rate of change of tidal angular momentum and the variation of tidal angular momentum with respect to time under the present consideration.  相似文献   

14.
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   

15.
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   

16.
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   

17.
We present new models for the formation of disc galaxies that improve upon previous models by following the detailed accretion and cooling of the baryonic mass, and by using realistic distributions of specific angular momentum. Under the assumption of detailed angular momentum conservation, the discs that form have density distributions that are more centrally concentrated than an exponential. We examine the influence of star formation, bulge formation, and feedback on the outcome of the surface brightness distributions of the stars. Low angular momentum haloes yield disc galaxies with a significant bulge component and with a stellar disc that is close to exponential, in good agreement with observations. High angular momentum haloes, on the other hand, produce stellar discs that are much more concentrated than an exponential, in clear conflict with observations. At large radii, the models reveal distinct truncation radii in both the stars and the cold gas. The stellar truncation radii result from our implementation of star formation threshold densities, and are in excellent agreement with observations. The truncation radii in the density distribution of the cold gas reflect the maximum specific angular momentum of the gas that has cooled. We find that these truncation radii occur at H  i surface densities of roughly 1 M⊙ pc−2, in conflict with observations. We examine various modifications to our models, including feedback, viscosity, and dark matter haloes with constant-density cores, but show that the models consistently fail to produce bulge less discs with exponential surface brightness profiles. This signals a new problem for the standard model of disc formation: if the baryonic component of the protogalaxies out of which disc galaxies form has the same angular momentum distribution as the dark matter, discs are too compact.  相似文献   

18.
We discuss the rotation of interstellar clouds which are in a stage immediately before star formation. Cloud collisions seem to be the principal cause of the observed rotation of interstellar clouds. The rotational motion of the clouds is strongly influenced by turbulence.Theories dealing with the resolution of the angular momentum problem in star formation are classified into five major groups. We develop the old idea that the angular momentum of an interstellar cloud passes during star formation into the angular momentum of double star systems and/or circumstellar clouds.It is suggested that a rotating gas cloud contracts into a ring-like structure which fragments into self-gravitating subcondensations. By collisions and gas accretion these subcondensations accrete into binary systems surrounded by circumstellar clouds. Using some rough approximations we find analytical expressions for the semi-major axis of the binary system and for the density of the circumstellar clouds as a function of the initial density and of the initial angular velocity of an interstellar cloud. The obtained values are well within the observational limits.  相似文献   

19.
We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). STAGES is a multiwavelength project designed to probe physical drivers of galaxy evolution across a wide range of environments and luminosity. A complex multicluster system at   z ∼ 0.165  has been the subject of an 80-orbit F606W Hubble Space Telescope (HST) /Advanced Camera for Surveys (ACS) mosaic covering the full     span of the supercluster. Extensive multiwavelength observations with XMM–Newton , GALEX, Spitzer , 2dF, Giant Metrewave Radio Telescope and the 17-band COMBO-17 photometric redshift survey complement the HST imaging. Our survey goals include simultaneously linking galaxy morphology with other observables such as age, star formation rate, nuclear activity and stellar mass. In addition, with the multiwavelength data set and new high-resolution mass maps from gravitational lensing, we are able to disentangle the large-scale structure of the system. By examining all aspects of an environment we will be able to evaluate the relative importance of the dark matter haloes, the local galaxy density and the hot X-ray gas in driving galaxy transformation. This paper describes the HST imaging, data reduction and creation of a master catalogue. We perform the Sérsic fitting on the HST images and conduct associated simulations to quantify completeness. In addition, we present the COMBO-17 photometric redshift catalogue and estimates of stellar masses and star formation rates for this field. We define galaxy and cluster sample selection criteria, which will be the basis for forthcoming science analyses, and present a compilation of notable objects in the field. Finally, we describe the further multiwavelength observations and announce public access to the data and catalogues.  相似文献   

20.
Distant Type Ia and II supernovae (SNe) can serve as valuable probes of the history of the cosmic expansion and star formation, and provide important information on their progenitor models. At present, however, there are few observational constraints on the abundance of SNe at high redshifts. A major science driver for the Next Generation Space Telescope is the study of such very distant SNe. In this paper we discuss strategies for finding and counting distant SNe by using repeat imaging of supercritical intermediate redshift clusters whose mass distributions are well constrained via modelling of strongly lensed features. For a variety of different models for the star formation history and supernova progenitors, we estimate the likelihood of detecting lensed SNe as a function of their redshift. In the case of a survey conducted with Hubble Space Telescope ( HST ), we predict a high probability of seeing a supernova in a single return visit with either Wide Field Planetary Camera 2 or Advanced Camera for Surveys, and a much higher probability of detecting examples with     in the lensed case. Most events would represent magnified SNe II at     and a fraction will be more distant examples. We discuss various ways to classify such events using ground-based infrared photometry. We demonstrate an application of the method using the HST archival data and discuss the case of a possible event found in the rich cluster AC 114     .  相似文献   

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