BONITO, Rosaria

Eislöffel, J

Favata, F.

MICELI, Marco

Orlando, S

PERES, Giovanni

Eislöffel, J

Archivio istituzionale della ricerca - Università di Palermo

The 16th Cambridge Workshop on Cool Stars, Stellar Systems and the SunASP Conference Series, Vol. 448, Electronic EditionChristopher M. Johns-Krull, Matthew K. Browning, and Andrew A. West, eds.c©2011 Astronomical Society of the PacificGeneration of Knots in a Randomly Pulsed Protostellar Jet:Synthesis of the X-ray EmissionR. Bonito,1,2 S. Orlando,2 M. Miceli,1,2 J. Eislo¨ffel,3 G. Peres,1,2 and F.Favata41Dip. Scienze Fisiche ed Astronomiche, Sez. Astronomia, Universita` diPalermo, P.zza del Parlamento 1, 90134 Palermo, Italy2INAF – Osservatorio Astronomico di Palermo, P.zza del Parlamento 1, 90134Palermo, Italy3Thu¨ringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany4European Space Agency Community Coordination and Planning Office 8-10rue Mario Nikis F-75738 Paris cedex 15 FranceAbstract. X-rays from protostellar jets have been discovered first in HH 2 and HH154 and are now considered as a general feature of jets. HH 154 is among the beststudied X-ray emitting jet: up to now it is the only jet whose X-ray source propermotion has been measured. By observing this jet in X-rays, a complex morphologyof the detected source has been revealed. Here we discuss the results of modelinga randomly ejected pulsed jet traveling into an initially homogeneous medium. Ourmodel allows us to directly compare the model predictions and the observations.1. IntroductionX-rays from shocks in protostellar jets have been discovered taking advantage of bothChandra and XMM/Newton X-ray telescopes, with data collected in 2000 by Pravdoet al. (2001) in HH 2 and by Favata et al. (2002) in HH 154. The detected X-rayemission is now considered as a possible general feature of jets, as reviewed by Bonitoet al. (2010a) (see Table 1 for a summary of the physical properties observed in all theX-ray emitting jets discovered so far). HH 154 is among the best studied X-ray emittingjet, being observed with both XMM/Newton (Favata et al. 2002) and Chandra (Ballyet al. 2003) and being the first and so far only jet whose X-ray source proper motion hasbeen measured (Favata et al. 2006). The X-ray luminosity of jets has been studied firstanalytically by Raga et al. (2002) and through detailed numerical model by our group(Bonito et al. 2004, 2007, 2010b,a). Bonito et al. (2007) performed for the first time awide exploration of the parameter space describing the jet/ambient physical parametersand synthesized the X-ray emission to reproduce the observations of protostellar jets.The observations of Favata et al. (2006) showed a complex morphology of the X-raymoving source detected in HH 154. Here we present the synthesis of the X-ray emissionderived from the model of a randomly ejected pulsed jet ramming through an initiallyhomogeneous ambient medium and the comparison between the model predictions andthe observations.E-559E-560 Bonito et al.2. The ModelThe knotty morphology observed in the X-ray source of HH 154 (Favata et al. 2006)suggests a pulsed jet propagating through the ambient medium. To reproduce the ob-servations, we performed detailed numerical simulations of a randomly ejected pulsedjet using the FLASH code (Fryxell et al. 2000). In our model the protostellar jet con-sists of several bullets, each described as an impulse lasting 0.5 yr, ejected along the jetaxis with random values of the velocity. We take into account the main physical effectsdescribing the jet/ambient interaction, i.e. fluid dynamics and energetics include thethermal conduction and the radiative losses. We performed an exploration of the ejec-tion rate parameter by considering three ejection rates corresponding to time intervalsbetween two consecutive blobs: dt = 0.5, 2, and 8 yr.In Fig. 1 we show a cut along the jet axis of the density distribution of the pulsed jetmodel for the dt = 0.5 yr case (see also Bonito et al. 2010b). The red line superimposedon the figure indicates the initial jet density: the initially homogeneous ambient mediumbecomes quickly inhomogeneous due to blobs interactions.Figure 1. Example of a cut along the jet axis of the density distribution of one ofour pulsed jet model.We also investigated the effects due to the presence of the thermal conduction. InFig. 2 we compare the 2D distribution of the temperature of the model with thermalconduction after 90 yr (right panel) and the pure radiative case after 350 yr (left panel).As discussed in Bonito et al. (2010b), the thermal conduction plays a crucial role indamping out hydrodynamic instabilities in the cocoon contributing to the jet braking.Knots in a Pulsed Jet: the X-ray Emission E-561Figure 2. Comparison between models either with (right panel) or without (leftpanel) the thermal conduction.Figure 3. X-ray image (left panel) and density distribution (right panel) derivedfrom the model.3. ResultsIn the pulsed jet model the interactions between blobs, ejected at different epochs andwith different speed, lead to the generation of internal shocks. Fig. 3 shows the gener-E-562 Bonito et al.ation of a knotty structure both in the density distribution and in the synthesized X-rayimage. The derived knotty structure reproduces a multi-structures morphology consis-tent with the observations.The X-ray morphology derived from the pulsed jet model shows several structureswithin the jet: interacting knots, forward, reverse, and steady shocks. As shown in Fig.4, reverse shocks powered by freshly ejected plasma blobs may explain the formationof apparently stationary shocks as detected at the base of the X-ray emitting jets.Figure 4. Sequence of four X-ray maps synthesized from the model over a timebaseline of 3 yr and with a frequency of 1 yr, at the base of the jet (see Bonito et al.2010a).The comparison between our model results and the observations allow us to con-strain the ejection rate and to derive predictions on the physical parameters of thejet/ambient system for all the X-ray emitting jets discovered so far. We derive thatthe most energetic case is the one with ejection rate corresponding to dt = 0.5 yr andleads to the highest luminosity and temperature: the higher dt, the lower LX and TX .Figure 7 in Bonito et al. (2010a) shows that HH jets with X-ray emission at the base ofthe jet have properties (LX and best-fit temperature) that nicely agree with our results.In particular, there is a good agreement for the nearest X-ray emitting jets: HH 154is well described by a pulsed jet with dt = 2 yr, while DG Tau (the weakest X-ray-emitting jet; see Table 1 in Bonito et al. 2010a) is consistent with a jet with low ejectionrate (i.e. the case with the lowest luminosities derived).In general, our model provides the first attempt to describe the characteristics ofalmost all the X-ray-emitting HH jets detected so far. We also derived detailed predic-tions on the future X-ray observations of HH 154, as discussed in detail in Bonito et al.(2010a).Acknowledgments. We acknowledge support by the Marie Curie Fellowship Con-tract No. MTKD-CT-2005-029768. The software used in this work was in part devel-oped by the DOE-supported ASC/Alliances Center for Astrophysical ThermonuclearKnots in a Pulsed Jet: the X-ray Emission E-563Flashes at the University of Chicago. The calculations were performed on the clusteron the SCAN facility on the INAF-OAPa and at CINECA (Bologna, Italy).ReferencesBally, J., Feigelson, E., & Reipurth, B. 2003, ApJ, 584, 843Bonito, R., Orlando, S., Miceli, M., Eislo¨ffel, J., Peres, G., & Favata, F. 2010a, A&A, 517, A68Bonito, R., Orlando, S., Peres, G., Eislo¨ffel, J., Miceli, M., & Favata, F. 2010b, A&A, 511, A42Bonito, R., Orlando, S., Peres, G., Favata, F., & Rosner, R. 2004, A&A, 424, L1— 2007, A&A, 462, 645Favata, F., Bonito, R., Micela, G., Fridlund, M., Orlando, S., Sciortino, S., & Peres, G. 2006,A&A, 450, L17Favata, F., Fridlund, C. V. M., Micela, G., Sciortino, S., & Kaas, A. A. 2002, A&A, 386, 204Fryxell, B., Olson, K., Ricker, P., Timmes, F. X., Zingale, M., Lamb, D. Q., MacNeice, P.,Rosner, R., Truran, J. W., & Tufo, H. 2000, ApJS, 131, 273Pravdo, S. H., Feigelson, E. D., Garmire, G., Maeda, Y., Tsuboi, Y., & Bally, J. 2001, Nat, 413,708Raga, A. C., Noriega-Crespo, A., & Vela´zquez, P. F. 2002, ApJ, 576, L149

Generation of Knots in a Randomly Pulsed Protostellar Jet: Synthesis of the X-ray Emission

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Generation of Knots in a Randomly Pulsed Protostellar Jet: Synthesis of the X-ray Emission

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