Giant Herbig-Haro Flow Research Articles

HH 175: a giant Herbig–Haro flow emanating from a multiple protostar

ABSTRACT HH 175 is an isolated Herbig–Haro object seen towards the B35 cloud in the λ Ori region. We use deep Subaru 8 m interference filter images and Spitzer images to show that HH 175 is a terminal shock in a large collimated outflow from the nearby embedded source IRAS 05417+0907. The body of the eastern outflow lobe is hidden by a dense ridge of gas. The western outflow breaks out of the front of the cometary-shaped B35 cloud, carrying cloud fragments along, which are optically visible due to photoionization by the massive λ Ori stars. The total extent of the bipolar outflow is 13.7 arcmin, which at the adopted distance of 415 pc corresponds to a projected dimension of 1.65 pc. The embedded source IRAS 05417+0907 is located on the flow axis approximately midway between the two lobes, and near-infrared images show it to be a multiple system of six sources, with a total luminosity of 31 L⊙. Millimeter maps in CO, 13CO, and C18O show that the B35 cloud is highly structured with multiple cores, of which the one that spawned IRAS 05417+0907 is located at the apex of B35. It is likely that the embedded source is the result of compression by an ionization-shock front driven by the λ Ori OB stars.

The Giant Herbig–Haro Flow HH 212 and Associated Star Formation

The bipolar jet HH 212, among the finest collimated jets known, has so far been detected only in near-infrared H$_2$ emission. Here we present deep optical images that show two of the major bow shocks weakly detected in optical [SII] emission, as expected for a bona fide Herbig-Haro jet. We present widefield H$_2$ images which reveal two more bow shocks located symmetrically around the source and along the main jet axis. Additionally, examination of Spitzer 4.5 $\mu$m images reveals yet another bright bow shock further to the north along the jet axis; no corresponding bow shock is seen to the south. In total, the HH 212 flow has an extent of 1050 arcsec, corresponding to a projected dimension of 2.0 pc. HH 212 thus joins the growing group of parsec-scale Herbig-Haro jets. Proper motion measurements indicate a velocity of about 170 km/sec, highly symmetric around the source, with an uncertainty of $\sim$30 km/sec, suggesting a probable age of the giant HH 212 flow of about 7000 yr. The jet is driven by a deeply embedded source, known as IRAS 05413-0104. We draw attention to a Spitzer near- and mid-infrared source, which we call IRS-B, located only 7 arcsec from the driving source, towards the outskirts of the dense cloud core. Infrared photometry and spectroscopy suggests that IRS-B is a K-type star with a substantial infrared excess, except that for an extinction of A$_V$ = 44 the star would have only a weakinfrared excess, and so in principle it could be a K-giant at a distance of about 2 kpc.

GIANT HERBIG-HARO FLOWS IN L1228: A SECOND LOOK

We present second epoch narrowband H{alpha} and [S II] images of the giant Herbig-Haro flows HH199 and HH200 in the L1228 molecular cloud. Proper motions for several members of the HH200 flow were determined by comparing the new images to similar narrowband images taken 13 years earlier. Based on our measurements, the HH200 flow is inclined by 15 deg. to the plane of the sky and has a steady, fixed outflow axis with P.A. = 49 deg. There is a general nonlinear decline in the proper motions with increasing distance from the source, and it appears that successive eruption episodes have cleared out a relatively free channel through the L1228 cloud. The bright knot HH200B6 is located at the end of the channel along the edge of L1228, and appears to be tracing the location where the outflow erupts from the cloud. We did not detect any proper motions for HH200B6, and suggest that it is the plug of material that has been bored out by the cumulative effects of numerous eruptions along a steady outflow axis. The proper motions combined with the spacing of the HH200 knots along the flow axis are consistent with a velocity variable outflow, whichmore » erupts periodically on timescales of the order of 600 years. The relatively small size of the knots combined with the large proper motions and derived bow-shock speeds would seem to rule out the presence of a less collimated wind component. We also discuss the HH199 flow, which is radically different from HH200. The members of the HH199 flow exhibited large changes in the morphology and emission, and were not suitable for determining proper motions. The HH200 and HH199 flows appear to be the opposite ends of the spectrum of giant HH flows.« less

Multiple Protostars, Jets, and the Origin of Brown Dwarfs

AbstractThe observation that young stars are clustered in few body non-hierarchical multiple systems at very young ages has profound consequences for our understanding of the formation of stars, binaries and the disks and planets that may surround them. In this chapter we review theoretical progress made over the last decade in modeling the break up of these natal clusters and discuss a range of observational predictions that arise from these models, relating to the kinematics, binary statistics and possession of disks of both stars and brown dwarfs. We also argue that one of the most spectacular manifestations of dynamical interactions in young multiple systems should be the formation of giant Herbig-Haro flows, and present observational evidence that may be interpreted in this light.

PV Cephei: Young Star Caught Speeding?

Three independent lines of evidence imply that the young star PV Cep is moving at roughly 20 km s-1 through the interstellar medium. The first and strongest suggestion of motion comes from the geometry of the Herbig-Haro (HH) knots in the giant HH flow associated with PV Cep. Bisectors of lines drawn between pairs of knots at nearly equal distances from PV Cep imply an east-west motion of the source, and a plasmon model fitted to the knot positions gives a good fit of 22 km s-1 motion for the star. The second bit of damning evidence comes from a redshifted trail of molecular gas pointing in the same east-west direction implied by the HH knot geometry. The third exhibit we offer in accusing PV Cep of speeding involves the apparent tilt in the high-velocity molecular jet now emanating from the star. This tilt is best explained if the true, current jet direction is north-south, as it is in Hubble Space Telescope WFPC2 images, and the star is moving, again at roughly 20 km s-1. Tracing the motion of PV Cep backward in time to the nearest cluster from which it might have been ejected, we find that it is very likely to have been thrown out of the massive star-forming cluster NGC 7023, more than 10 pc away. PV Cep and NGC 7023 are at similar distances, and the backward trace of PV Cep's motion is astonishingly well aligned with a dark, previously unexplained rift in NGC 7023. We propose that PV Cep was ejected, at a speed large enough to escape NGC 7023, at least 100,000 yr ago but that it did not enter the molecular cloud in which it now finds itself until more like 35,000 yr ago. Our calculations show that the currently observable molecular outflow associated with PV Cep is about 10,000 yr old, so the flow has had plenty of time to form while in its current molecular cloud. However, the question of what PV Cep was doing and what gas/disk it took along with it in the time it was traveling through the low-density region between NGC 7023 and its current home is an open one. Recent numerical simulations have suggested that condensed objects should be ejected at high velocity before they have finished forming in a cluster. Prior to this work, a handful of pre-main-sequence stars have been shown to be moving at speeds greater than 10 km s-1. To the best of our knowledge, though, the analysis of PV Cep and NGC 7023 described here is the first observational work associating a speeding young star with a distant ancestral cluster. These high-speed ejections from clusters will create a class of rapidly moving young stars in molecular clouds. If these ejections are at all common, their existence confounds both calculations of clouds' star-forming efficiency and theories of star formation that do not allow for stars to move rapidly through a reservoir of star-forming material while they form.

Deep Imaging Surveys of Star-Forming Clouds II. A New Giant Herbig-Haro Flow in L1451

We report the discovery of a new giant Herbig-Haro flow near the L1451 region of the Perseus molecular cloud. The east-west oriented flow contains two known HH objects (HH 280 and HH 317), two new HH objects (HH 492 and HH 493), and is 2.1 pc long. The flow is driven by the Class I protostar IRAS 03235+3004 embedded in a bright-rimmed, sharp-edged cometary cloud facing northeast. The flow source is embedded in a west-facing conical reflection nebula. The cometary cloud appears to have been shaped by O and B stars in the Per OB2 association, including the B0.5 star 40 Per, located along the well-defined symmetry axis of the cloud and with a projected separation of 26 pc. A soft-UV induced photoablation model is proposed to explain the properties of the cometary cloud.

Radio Continuum Jets from Protostellar Objects

We have carried out a deep, 3.6 cm radio continuum survey of young outflow sources using the Very Large Array in its A configuration providing subarcsecond resolution. The eight regions observed are Haro 6-10 and L1527 IRS in Taurus, Haro 5a/6a in OMC 2/3, NGC 2023 MMS, NGC 2264 IRS1, HH 108 IRAS/MMS in Serpens, L1228, and L1251A. In combination with our similar and previously published maps of eight other star-forming regions, we find only one region with a single source, while the other 15 regions have on average 3.9 nearby sources. This supports the view that isolated star formation is rare. We have selected 21 objects, which are all young mostly Class I sources, and find a binary frequency of 33% in the separation range from 05 to 12''. This is within the uncertainties comparable to the observed binary frequency among T Tauri stars in a similar separation range. Seven of the 21 sources drive giant Herbig-Haro flows. Four of these seven are known to have companions (three are triple systems), corresponding to 57%. We discuss these results in relation to the hypothesis that giant Herbig-Haro flows are driven by disintegrating multiple systems.

High Resolution Observations of Herbig-Haro Flows

Observational techniques with high angular and high spectral resolution have become available in recent years and have had a major impact on the study of Herbig-Haro outflows from very young stars. We discuss new results obtained using WFPC2, ACS and STIS onboard the Hubble Space Telescope, as well as spectroscopic data obtained at the Keck telescope and with the Integral Field Unit at the Gemini telescope. We also discuss centimeter radio continuum maps from the Very Large Array and their importance in testing scenarios for the formation of giant Herbig-Haro flows.

The Great PV Cephei Outflow: A Case Study in Outflow‐Cloud Interaction

We present a set of detailed molecular-line maps of the region associated with the giant Herbig-Haro flow HH 315 from the young star PV Cephei, aimed at studying the outflow-cloud interaction. Our study clearly shows that the HH 315 flow is affecting the kinematics of its surrounding medium and has been able to redistribute considerable amounts of the surrounding medium-density (~103 cm-3) gas in its star-forming core as well at parsec-scale distances from the source. The single-dish observations include a map of the outflow in the 12CO (2-1) line, with a beam size of 27'', and more extended maps of the outflow region in the 12CO (1-0) and 13CO (1-0) lines, with 45'' and 47'' beam sizes, respectively. A companion paper published in this issue presents higher resolution (IRAM 30 m) observations and discusses their implications. The giant molecular outflow HH 315 is a highly asymmetric bipolar flow with a projected linear extent of about 2 pc. Our results indicate that the two outflow lobes are each interacting with the ambient medium in different ways. The southern (redshifted) lobe, with a mass of 1.8 M☉, interacts with a dense ambient medium, very close to the young stellar outflow source, and its kinetic energy is comparable to both the turbulent and gravitational binding energy of its host cloud (of order 1044 ergs). In addition, we find evidence that the southern lobe is responsible for the creation of a cavity in the 13CO emission. In contrast, the northern (mainly blueshifted) outflow lobe, with a total mass of 4.8 M☉, extends farther from PV Cep and interacts with ambient gas much less dense than the southern lobe. There is very little 13CO emission north of the outflow source, and the only prominent 13CO emission is a shell-like structure coincident with the outer edge of the northern lobe, about 1.2 pc northwest of PV Cep. It appears that the northern lobe of the HH 315 outflow has been able to push aside a substantial fraction of the gas in the area, piling it in a dense shell-like structure at its edges. In addition, we find that about 50% of the gas in the region of the northern lobe has been put into motion by the outflow and that the northern outflow lobe is responsible for a velocity gradient in the ambient gas.

Bow Shocks, Wiggling Jets, and Wide‐Angle Winds: A High‐Resolution Study of the Entrainment Mechanism of the PV Cephei Molecular (CO) Outflow

We present a new set of high-resolution molecular-line maps of the gas immediately surrounding various Herbig-Haro (HH) knots of the giant HH flow HH 315 from the young star PV Cephei. The observations, aimed at studying the entrainment mechanism of the 2.6 pc-long HH 315 flow, include IRAM 30 m maps of the 12CO (2-1), 12CO (1-0), and 13CO (1-0) lines, with beam sizes of 11'', 21'', and 22'', respectively. We compare the morphology and the kinematics of the outflow gas, as well as the temperature and momentum distribution of the molecular outflow, with those predicted by different entrainment models. With our detailed study we are able to conclude that jet bow shock entrainment by an episodic stellar wind, with a time-varying axis, produces most of the high-velocity molecular outflow observed far from the source. In addition, near PV Cep we find evidence for a poorly collimated, wide-angle molecular outflow and a collimated, wiggling jet-like molecular outflow. We propose that the poorly collimated component is entrained by a wide-angle wind and the collimated component is entrained by a variable jet with internal working surfaces. If this picture is true, then a stellar wind model that allows for the coexistence of a wide-angle component and a collimated (jetlike) stellar wind component is needed to explain the observed properties of the PV Cep outflow. The wiggling axis of the redshifted molecular outflow lobe indicates that the outflow ejection axis is changing over time. We find that the timescale of the axis variation shown by the molecular outflow lobe is about a factor of 10 less than that shown by the large-scale optical HH knots.

The Episodic, Precessing Giant Molecular Outflow from IRAS 04239+2436 (HH 300)

We present the first set of detailed molecular line maps of the region associated with the giant Herbig-Haro flow HH 300, from the young star IRAS 04239+2436. Our results indicate that the red lobe of the HH 300 flow is depositing a fair amount of momentum and kinetic energy over a notable volume of its host dark cloud. This makes HH 300 a key player in the evolution and fate of its parent cloud. The redshifted molecular outflow lobe of HH 300 is 1.1 pc long and 0.3 pc wide, and has a very clumpy structure. The density, velocity, and momentum distributions in the outflow indicate that the observed clumps arise from the prompt entrainment of ambient gas. Bow shock-shaped structures are associated with the clumps, and we hypothesize that the shocks are produced by different mass ejection episodes. Lines drawn from IRAS 04239+2436 to each of these clumps have different orientations on the plane of the sky, and we conclude that HH 300 is a precessing and episodic outflow. The observations include a map of the red lobe in the 12CO(2-1) line, with a beam size of 27'', and more extended maps of the outflow region in the 12CO(1-0) and 13CO(1-0) lines, with 45'' and 47'' beam sizes, respectively. We obtain a steep power-law mass spectrum for HH 300, which we believe is best explained by the evolution of the outflow mass kinematics. In addition, our 13CO observations show that the HH 300 flow has been able to redistribute (in space and velocity) considerable amounts of its surrounding medium-density gas.

Herbig-Haro Objects HH 434–436: Part of a Giant Flow Driven by the Central Source A/B of IRAS 04325+2402?

While carrying out a wide-field survey of nearby star-forming regions for Herbig-Haro (HH) objects we discovered three Herbig-Haro objects, HH 434-436, in a similar to2' x 2' (0.08 x 0.08 pc) region near L1536. HH 434 consists of three knots. HH 435 shows a bow shock shape, and HH 436 is an elongated patch. Spectroscopic observations indicate that the excitation levels of HH 434-436 are different : HH 436 has a high excitation level, while 434A has an intermediate, and 435 has a low excitation level. The overall morphology of HH 434-436 shows a bow shock shape and suggests that HH 434-436 may be a single bow shock fragmented into separate knots. Near-infrared observations of the region in the JHK' broad bands and H-2 upsilon = 1-0 S(1) narrow band were also carried out, but no embedded source was detected. The overall bow shock of HH 434-436 points back toward an embedded multiple system, IRAS 04325+2402. Moreover, from Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer 3 observations HH 434-436 are located on the expected outflow axis of the central source A/B of this multiple system. On the basis of these facts we propose that HH 434-436 may be driven by the central source A/B of IRAS 04325+2402; therefore, they are probably part of a giant HH flow, which has a scale of 2.4 pc, although the possibility that HH 434-436 are three distinct flows cannot be completely ruled out.

Outflows from Newborn Multiple Stars

Analysis of a sample of giant Herbig-Haro flow sources shows that 79%–86% are binaries or higher order multiples. This represents the youngest sample of stars studied so far for binarity. A stellar dynamics jet hypothesis is proposed in which the dynamical decay of triple or multiple systems leads to giant outflow activity. Close triple approaches will cause serious perturbations and probably direct collisions among individual circumstellar disks, with a consequent burst of outflow activity, which can produce giant HH bow shocks. As one component is ejected, the two remaining stars and their small truncated disks form a closer bound pair with high eccentricity. Gas streams from a circumbinary disk feed the stars and this as well as other dynamical effects cause the binary orbit to shrink. As the stellar components gradually spiral towards each other, accretion and outflow becomes cyclic, modulated on an orbital time scale. The resulting HH flows can be read as a fossil record of the evolution of orbital motions of the newly formed binary as it shrinks from a typical separation of 100 AU or more to 10 AU or less. After a triple disintegration event, both components (star and close binary) leave their nascent envelope, and while one component becomes visible as a T Tauri star, the other will be obscured for a while by the envelope and will appear as a bright near-infrared object, thus explaining the socalled IRC binaries which are infrequently found in star forming regions.

Disintegrating Multiple Systems in Early Stellar Evolution

An analysis of the multiplicity of 14 sources driving giant Herbig-Haro flows has revealed an observed binary frequency between 79% and 86%, of which half are higher order multiples. These sources represent the hitherto youngest sample of stars examined for binarity. I postulate that the dynamical decay of triple or multiple systems leads to strong outflow activity. It is well known that a large fraction of nonhierarchical triple systems rapidly break up and eject the lightest member. At the same time a closer binary in a highly eccentric orbit is formed. Massive disk truncation results, accompanied by large-scale accretion, with a consequent burst of outflow activity, which produces the observed giant HH bow shocks. Some of the material culled from the individual circumstellar disks may settle into a circumbinary disk around the newly bound stellar pair. The small remaining and truncated circumstellar disks are fed from the circumbinary disk through gas streams, and this as well as other dynamical effects cause the binary orbit to shrink. Gas streams together with disk interactions at periastron drive cyclic accretion modulated on an orbital timescale. As the stellar components gradually spiral toward each other, the increasingly frequent mass-loss events form chains of HH objects until eventually the binary has a semimajor axis of only 9–12 AU, at which point the closely spaced shocked ejecta appear as a finely collimated jet. Thus, such HH flows can be read as a fossil record of the evolution of orbital motions of a binary, newly formed in a triple disintegration event, as it shrinks from a typical separation of 100 AU or more to 10 AU or less. When the triple system disintegrates and a single star is ejected, the newly formed binary recoils, and as a result both components (star and close binary) leave their nascent envelope. While one component becomes visible as a T Tauri star, the other will be obscured for a while by the envelope and will appear as a bright near-infrared object. For typical parameters, this geometry persists for only 5000 yr or so. If the ejected star does not escape, cyclic motion of a hierarchical triple begins. This explains the so-called IRC binaries that are infrequently found in star-forming regions. The standard model of early stellar evolution states that young stars gradually and smoothly make the transitions from Class 0 through Class I and II objects to eventually become Class III objects. In contrast, stars born in multiple systems can abruptly transit from a Class 0 or I object to a visible T Tauri star. The main accretion phase may be terminated by the stochastic process of triple decay. Depending on the moment of triple disintegration, the ejected objects can range from stellar embryos, which will emerge as very low mass stars or even brown dwarfs, to essentially fully built-up stars. In this picture, the initial mass function toward its low-mass end has an important stochastic component that can only be described by the half-life of the decay processes. Because the ejected stars can take only limited circumstellar material with them, they will soon lose their classical T Tauri characteristics and join the halo of weak-line T Tauri stars that surround star-forming clouds. Differences in ejection may explain why two apparently similar T Tauri stars of about the same age can have major differences in the size of their circumstellar disks.

A Giant Herbig-Haro Flow from a Massive Young Star in G192.16−3.82

We report the discovery of a 10 pc–long Herbig-Haro (HH) flow powered by a moderately massive young star associated with the compact H II region G192.16-3.82. At a distance of 2 kpc, the luminosity of G192.16-3.82 is about 3000 L⊙. The HH 396/397 complex consists of a network of filamentary emission-line objects tracing a pair of collimated and limb-brightened outflow lobes that emerge from an opaque cloud core. The Hα- and [S II]-bright nebulosity has a large area covering factor, extending well beyond the mapped extent of the associated high-velocity molecular outflow. The HH 396/397 complex contains some shocks with a surface brightness comparable to HH 168 in Cepheus A, placing these among the brightest known HH objects. Furthermore, a large fraction of a 1' by 18' region surrounding G192.16-3.82 is laced with lower surface brightness emission-line features, making HH 396/397 one of the most spatially extended HH complexes studied so far. The dynamical age of this outflow is in the range 104 to 105 yr. We discuss plausible evolutionary scenarios for outflows powered by high-mass protostars and argue that the G192.16-3.82 outflow complex is relatively evolved. Despite being very elongated, this HH flow is most likely powered by a moderately collimated wind, rather than a highly collimated jet.

A Giant Herbig-Haro Flow from Haro 6-10

We report the discovery of a parsec-scale Herbig-Haro flow emanating from the young binary system Haro 6-10 in Taurus. The flow extends for about 39' (1.6 pc) at a position angle of about 222° and contains part of the previously known HH 184. The apparent ends of the flow are defined by the newly discovered HH 410 and HH 411, which are located 24' southwest and 15' northeast, respectively, from Haro 6-10. We suggest that the giant HH flow is most likely driven by the infrared companion to the T-Tauri primary in Haro 6-10; however, the T-Tauri component also appears to be driving a relatively weak and much smaller outflow with a north-south orientation. The two flows appear to undergo synchronized episodes of increased mass ejection, which may be due to enhanced gravitational interactions between the binary components during periastron. We also report the discovery of a new HH jet, HH 414, which is driven by IRAS 04264+2433. HH 414 points directly toward an associated bow shock, HH 413; the HH 413/414 flow crosses the axis of the HH 410/411 flow at a large angle.