Kinematics and the origin of the internal structures in HL Tau jet (HH 151)

Knotty structures of Herbig-Haro jets are common phenomena, and knowing the origin of these structures is essential for understanding the processes of jet formation. Basically, there are two theoretical approaches: different types of instabilities in stationary flow, and velocity variations in the flow. We investigate the structures with different radial velocities in the knots of the HL Tau jet as well as its unusual behaviour starting from 20 arcsec from the source. Collation of radial velocity data with proper motion measurements of emission structures in the jet of HL Tau makes it possible to understand the origin of these structures and decide on the mechanism for the formation of the knotty structures in Herbig-Haro flows. We present observations obtained with a 6 m telescope (Russia) using the SCORPIO camera with scanning Fabry-Perot interferometer. Two epochs of the observations of the HL/XZ Tau region in Halpha emission (2001 and 2007) allowed us to measure proper motions for high and low radial velocity structures. The structures with low and high radial velocities in the HL Tau jet show the same proper motion. The point where the HL Tau jet bents to the north (it coincides with the trailing edge of so-called knot A) is stationary, i.e. does not have any perceptible proper motion and is visible in Halpha emission only. We conclude that the high- and low- velocity structures in the HL Tau jet represent bow-shocks and Mach disks in the internal working surfaces of episodic outflows. The bend of the jet and the brightness increase starting some distance from the source coincides with the observed stationary deflecting shock. The increase of relative surface brightness of bow-shocks could be the result of the abrupt change of the physical conditions of the ambient medium as well as the interaction of a highly collimated flow and the side wind from XZ Tau.Comment: To be published in Astronomy and Astrophysic

Hypersonic Buckshot: Astrophysical Jets as Heterogeneous Collimated Plasmoids

Herbig-Haro (HH) jets are commonly thought of as homogeneous beams of plasma traveling at hypersonic velocities. Structure within jet beams is often attributed to periodic or ``pulsed'' variations of conditions at the jet source. Simulations based on this scenario result in knots extending across the jet diameter. Observations and recent high energy density laboratory experiments shed new light on structures below this scale and indicate they may be important for understanding the fundamentals of jet dynamics. In this paper we offer an alternative to ``pulsed'' models of protostellar jets. Using direct numerical simulations we explore the possibility that jets are chains of sub-radial clumps propagating through a moving inter-clump medium. Our models explore an idealization of this scenario by injecting small ($r<r_{jet}$), dense ($\rho>\rho_{jet}$) spheres embedded in an otherwise smooth inter-clump jet flow. The spheres are initialized with velocities differing from the jet velocity by $\sim15$%. We find the consequences of shifting from homogeneous to heterogeneous flows are significant as clumps interact with each other and with the inter-clump medium in a variety of ways. Structures which mimic what is expected from pulsed-jet models can form, as can previously unseen ``sub-radial'' behaviors including backward facing bow shocks and off-axis working surfaces. While these small-scale structures have not been seen before in simulation studies, they are found in high resolution jet observations. We discuss implications of our simulations for the interpretation of protostellar jets with regard to characterization of knots by a ``lifetime'' or ``velocity history'' approach as well as linking observed structures with central engines which produce the jets.Comment: 15 pages, 3 figures (1 color), submitted to Ap

First detection of acceleration and deceleration in protostellar Jets? Time variability in the Chamaeleontis II outflows

Context. Kinematical and time variability studies of protostellar jets are fundamental for understanding the dynamics and the physics of these objects. Such studies remain very sporadic, since they require long baselines before they can be accomplished. Alms. We present for the first time a multi-epoch (20 years baseline) kinematical investigation of HH 52, 53, and 54 at optical and near-IR wavelengths, along with medium (optical) and high resolution (NIR) spectroscopic analyses, probing the kinematical and physical time variability conditions of the gas along the flows. Methods. By means of multi-epoch and multi-wavelength narrow-band images, we derived proper motions (PMs), tangential velocities, velocity and flux variability of the knots. Radial velocities and physical parameters of the gas were derived from spectroscopy. Finally, spatial velocities and inclination of the flows were obtained by combining both imaging and spectroscopy. Results. The PM analysis reveals three distinct, partially overlapping outflows. Spatial velocities of the knots vary from 50 km s -1 to 120 km s-1. The inclinations of the three flows are 58 ± 3°, 84 ± 2°, and 67 ± 3° (HH 52, HH 53, and HH 54 flows, respectively). In 20 years, about 60% of the observed knots show some degree of flux variability. Our set of observations apparently indicates acceleration and deceleration in a variety of knots along the jets. For about 20% of the knots, mostly coincident with working surfaces or interacting knots along the flows, a relevant variability in both flux and velocity is observed. We argue that both variabilities are related and that all or part of the kinetic energy lost by the interacting knots is successively radiated. The physical parameters derived from the diagnostics are quite homogeneous along and among the three outflows. The analysis indicates the presence of very light (NH � 103 cm-3), ionised (Te,. � 0.2-0.6), and hot (Te � 14000-26000 K) flows, impacting a denser medium. Several knots are deflected, especially in the HH 52 flow. At least for a couple of them (HH 54 G and GO), the deflection originates from the collision of the two. For the more massive parts of the flow, the deflection is likely the result of the flow collision with a dense cloud or with clumps. Finally, we discuss the possible driving sources of the flows. ©ESO 2009

The H2 velocity structure of inner knots in HH 212: asymmetries and rotation

High-resolution R~50 000 long-slit spectroscopy of the inner knots of the highly symmetrical protostellar outflow HH 212 was obtained in the 1-0 S(1) line of H2 at 2.12 micron with a spatial resolution of ~0.45 arcsec. At the resulting velocity resolution of ~6 km s-1, multiple slit oriented observations of the northern first knot NK1 clearly show double-peaked line profiles consistent with either a radiative bow shock or dual (forward and reverse) shocks. In contrast, the velocity distribution of the southern first knot SK1 remains single-peaked, suggesting a significantly lower jet velocity and possibly a different density variation in the jet pulses in the southern flow compared to the northern flow. Comparison with a semi-empirical analytical model of bow shock emission allows us to constrain parameters such as the bow inclination to the line of sight, the bow shock and jet velocities for each flow. Although a few features are not reproduced by this model, it confirms the presence of several dynamical and kinematical asymmetries between opposite sides of the HH 212 bipolar jet. The position-velocity diagrams of both knots exhibit complex dynamics that are broadly consistent with emission from a bow shock and/or jet shock, which does not exclude jet rotation, although a clear signature of jet rotation in HH 212 is missing. Alternative interpretations of the variation of radial velocity across these knots, such as a variation in the jet orientation, as well as for the velocity asymmetries between the flows, are also considered. The presence of a correlation between flow velocity and collimation in each flow is suggested.Comment: Accepted for publication in Astronomy and Astrophysics, 16 page

Super-paramagnetic clustering of yeast gene expression profiles

High-density DNA arrays, used to monitor gene expression at a genomic scale, have produced vast amounts of information which require the development of efficient computational methods to analyze them. The important first step is to extract the fundamental patterns of gene expression inherent in the data. This paper describes the application of a novel clustering algorithm, Super-Paramagnetic Clustering (SPC) to analysis of gene expression profiles that were generated recently during a study of the yeast cell cycle. SPC was used to organize genes into biologically relevant clusters that are suggestive for their co-regulation. Some of the advantages of SPC are its robustness against noise and initialization, a clear signature of cluster formation and splitting, and an unsupervised self-organized determination of the number of clusters at each resolution. Our analysis revealed interesting correlated behavior of several groups of genes which has not been previously identified

The precession of the HH 111 flow in the infrared

We present Spitzer IRAC images of the HH 111 outflow, that show a wealth of condensations/knots in both jet and counterjet. Studying the positional distribution of these knots, we find very suggestive evidence of a mirror symmetric pattern in the jet/counterjet flow. We model this pattern as the result of an orbital motion of the jet source around a binary companion. From a fit of an analytic, ballistic model to the observed path of the HH 111 system, we find that the motion in a binary with two approx. 1 Msolar stars (one of them being the HH 111 source), in a circular orbit with a separation of approx. 186 AU would produce the mirror symmetric pattern seen in the outflow.Comment: Accepted for publication, ApJLetter

Tomographic reconstruction of the three-dimensional structure of the HH30 jet

The physical parameters of Herbig-Haro jets are usually determined from emission line ratios, obtained from spectroscopy or narrow band imaging, assuming that the emitting region is homogeneous along the line of sight. Under the more general hypothesis of axisymmetry, we apply tomographic reconstruction techniques to the analysis of Herbig-Haro jets. We use data of the HH30 jet taken by Hartigan & Morse (2007) with the Hubble space telescope using the slitless spectroscopy technique. Using a non-parametric Tikhonov regularization technique, we determine the volumetric emission line intensities of the [SII]6716,6731, [OI]6300 and [NII]6583 forbidden emission lines. From our tomographic analysis of the corresponding line ratios, we produce "three-dimensional" images of the physical parameters. The reconstructed density, temperature and ionization fraction present much steeper profiles than those inferred using the assumption of homogeneity. Our technique reveals that the reconstructed jet is much more collimated than the observed one close to the source (a width ~ 5 AU vs. ~ 20 AU at a distance of 10 AU from the star), while they have similar widths at larger distances. In addition, our results show a much more fragmented and irregular jet structure than the classical analysis, suggesting that the the ejection history of the jet from the star-disk system has a shorter timescale component (~ some months) superimposed on a longer, previously observed timescale (of a few years). Finally, we discuss the possible application of the same technique to other stellar jets and planetary nebulae.Comment: 13 pages, 9 figures, accepted by Ap

Authorship Attribution With Few Training Samples

This chapter discusses authorship attribution through a training sample. The focus on authorship attribution discussed in this chapter differs in two ways from the traditional authorship identification problem discussed in the earlier chapters of this book. Firstly, the traditional authorship attribution studies [63, 65] only work in the presence of large training samples from each candidate author, which are typically enough to build a classification model. With authorship attribution, the emphasis is on using a few training samples for each suspect. In some scenarios, no training samples may exist, and the suspects may be asked (usually through court orders) to produce a writing sample for investigation purposes. Secondly, in traditional authorship studies, the goal is to attribute a single anonymous document to its true author. In this chapter, we look at cases where we have more than one anonymous message that needs to be attributed to the true author(s). It is likely that the perpetrator may either create a ghost e-mail account or hack an existing account, and then use it for sending illegitimate messages in order to remain anonymous. To address the aforementioned shortfalls, the authorship attribution problem has been redefined as follows: given a collection of anonymous messages potentially written by a set of suspects {S1, ···, Sn}, a cybercrime investigator first wants to identify the major groups of messages based on stylometric features; intuitively, each message group is written by one suspect. Then s/he wants to identify the author of each anonymous message collection from the given candidate suspects. To address the newly defined authorship attribution problem, the stylometric pattern-based approach of AuthorMinerl (described previously in Sect. 5.4.1) is extended and called AuthorMinerSmall. When applying this approach, the stylometric features are first extracted from the given anonymous message collection Ω

The X-ray puzzle of the L1551 IRS 5 jet

Protostars are actively accreting matter and they drive spectacular, dynamic outflows, which evolve on timescales of years. X-ray emission from these jets has been detected only in a few cases and little is known about its time evolution. We present a new Chandra observation of L1551 IRS 5's jet in the context of all available X-ray data of this object. Specifically, we perform a spatially resolved spectral analysis of the X-ray emission and find that (a) the total X-ray luminosity is constant over almost one decade, (b) the majority of the X-rays appear to be always located close to the driving source, (c) there is a clear trend in the photon energy as a function of the distance to the driving source indicating that the plasma is cooler at larger distances and (d) the X-ray emission is located in a small volume which is unresolved perpendicular to the jet axis by Chandra. A comparison of our X-ray data of the L1551 IRS 5 jet both with models as well as X-ray observations of other protostellar jets shows that a base/standing shock is a likely and plausible explanation for the apparent constancy of the observed X-ray emission. Internal shocks are also consistent with the observed morphology if the supply of jet material by the ejection of new blobs is sufficiently constant. We conclude that the study of the X-ray emission of protostellar jet sources allows us to diagnose the innermost regions close to the acceleration region of the outflows.Comment: A&A accepted, 14 pages, 9 figure

The formation of planetary disks and winds: an ultraviolet view

Planetary systems are angular momentum reservoirs generated during star formation. This accretion process produces very powerful engines able to drive the optical jets and the molecular outflows. A fraction of the engine energy is released into heating thus the temperature of the engine ranges from the 3000K of the inner disk material to the 10MK in the areas where magnetic reconnection occurs. There are important unsolved problems concerning the nature of the engine, its evolution and the impact of the engine in the chemical evolution of the inner disk. Of special relevance is the understanding of the shear layer between the stellar photosphere and the disk; this layer controls a significant fraction of the magnetic field building up and the subsequent dissipative processes ougth to be studied in the UV. This contribution focus on describing the connections between 1 Myr old suns and the Sun and the requirements for new UV instrumentation to address their evolution during this period. Two types of observations are shown to be needed: monitoring programmes and high resolution imaging down to, at least, milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure