Herbig-Haro Research Articles

Large-Scale Distribution of Herbig-Haro Objects in Taurus

We report our new results on Herbig-Haro (HH) objects in the star forming region of Taurus from a wide-field survey with the 60/90 cm Schmidt telescope of the Beijing Astronomical Observatory. This survey using CCD imaging with a narrow band [SII] filter and an intermediate band [BATC10] filter covered approximately 30 square degrees in Taurus. Besides confirming the known HH Objects in the region, we discovered seven new HH candidates, and groups. Six of these are HH 701A-B, HH 702A-D, HH 703, HH 704A-D, HH 705, HH 706 and the seventh is a group, a new component of HH 319, labeled HH 319B-D. Based on the large-scale distribution of pre-main-sequence (PMS) stars in Taurus, we analyze statistically the most probable distance from the HH objects to each PMS star, from which we estimate the typical timescale of these HH objects to be between (1.3 - 2.0) x 10(4) yrs; and we also obtain the birth rates of HH objects: 0.447+/-0.198 for Class I PMS stars, 0.360+/-0.222 for Class II PMS stars, and -0.148+/-0.234 for Class III PMS stars.

Near-IR [$\ion{Fe}{ii}$] emission diagnostics applied to cold disk winds in young stars

We investigate the emissivity properties of the main near-IR transitions of the Fe+ ion in the conditions prevailing in the inner regions of jets from young stars, based on a simplified 16-level atom model. We present new diagnostic diagrams involving prominent near-IR line ratios that allow us to constrain the electronic density, temperature, and Fe gas phase abundance ratio, independently of the heating process. Comparison with recent near-IR observations of a sample of HH objects indicates gas phase Fe abundances ranging from 15–50% up to 100% of the solar value (depending on the assumed temperature and on the HH object), in agreement with the moderate depletions previously derived from optical line ratios or shock models. Hence, it appears that Fe-bearing dust is efficiently destroyed in stellar jets. We then use our Fe+ emissivity model to predict near-IR [Fe ii] emission maps for self-similar, cold MHD disk wind models. We show that near-IR [Fe ii] lines are stronger than [S ii] λ6731 and [O i] λ6300 in the cool regions ( K) near the wind base, and that observations in [Fe ii] with AMBER on the VLTI could severely constrain the MHD solution and the inner launch radius of the jet. We also compare theoretical predictions with recent observations in the near-IR [Fe ii] lines of the L1551-IRS5 and DG Tau jets. The cold disk wind model reproduces quite well the two velocity components observed at -100 and -300 km s-1, although the high velocity component appears overestimated by a factor of 1.5 in the DG Tau jet. However, the model predicts too little emission at intermediate velocities and insufficient densities. Similar problems were encountered in previous model comparisons in the optical range with jets from T Tauri stars. Denser disk winds with stronger heating at the jet base, which have been invoked for optical jets, also appear needed in younger, embedded Class I jet sources.

The Three-Dimensional Structure of HH 32 from GMOS IFU Spectroscopy

We present new high-resolution spectroscopic observations of the Herbig-Haro object HH 32 from system verification observations made with the GMOS IFU at Gemini North Observatory. The three-dimensional spectral data cover a 87 × 585 spatial field and 4820–7040 A spectral region centered on the HH 32 A knot complex. We show the position-dependent line profiles and radial velocity channel maps of the Hα line, as well as line ratio velocity channel maps of [O III] λ5007/Hα, [O I] λ6300/Hα, [N II] λ6583/Hα, [S II] λλ(6716+6730)/Hα, and [S II] λ6716/λ6730. We find that the line emission and the line ratios vary significantly on spatial scales of ~1'' and over velocities of ~50 km s-1. A 3/2-dimensional bow shock model is qualitatively successful at reproducing the general features of the radial velocity channel maps, but it does not show the same complexity as the data, and it fails to reproduce the line ratios in our high spatial resolution maps. The observations of HH 32 A show two or three superposed bow shocks with separations of ~3'', which we interpret as evidence of a line-of-sight superposition of two or three working surfaces located along the redshifted body of the HH 32 outflow.

The Orion nebula (M42) Herbig–Haro object, HH 201, within the tip of a molecular finger

The most prominent Herbig-Haro (HH) object, HH 201, in the Orion nebula is investigated using optical spectroscopy along with optical and infrared images. An infrared Subaru H 2 ν = 1-0 S(1) image of the region surrounding the optical line emission of HH 201 has yielded the discovery of a faint H 2 finger associated with HH 201. The H 2 finger is seen to share a common width and orientation with the optical line emission. Therefore, it is unlikely that the association is caused by a chance superposition along the line of sight. The finger is found to precede the optical line emission, which is inconsistent with this H 2 emission being produced within a bowshock. The origin of this finger is discussed in the context of the current understanding of HH objects and the Orion molecular fingers. Multi-epoch HST [S II] 6716- arid 6731-A images are used to measure the proper motions of the various knots present in the filamentary structure of HH 201. Tangential velocities of between 40 and 178 km s - 1 are found. Two new knots with associated proper motions are found in the wake of HH 201 and the general structure of the tangential flow is shown by means of a multi-epoch difference image. [S II] 6716- and 6731-A spectra taken with the RGO spectrograph are used to spectroscopically resolve the velocity profile of HH 201 into distinct components with radial velocities of between -267 and -9 km s - 1 . Using the [S II] 6716- and 6731-A line ratios, the local electron density of gas at the various velocities is found to be between 830 and 12 200 cm - 3 . Combining radial and tangential velocities, the angle between the direction of motion and the line of sight is found to be approximately 30°. Assuming that the emission knots and velocity components correspond to condensations in a bowshock, a shock velocity at the head of HH 201 of 295 km s - 1 is established. Using this combination of optical and infrared data, the morphology and kinematics of HH 201 and its immediate environs are elucidated.

Irradiated Jets and Outflows in the Pelican Nebula

We report the discovery of new Herbig-Haro objects in the Pelican Nebula (IC 4050). HH 555 is a bipolar jet emerging from the tip of a major elephant trunk protruding into the Pelican Nebula from the adjacent molecular cloud. Both beams of HH 555 bend toward the west, indicating deflection by a side wind. A chain of three nearly equally spaced bow shocks, HH 563, HH 564, and HH 565, trace a bent flow bursting out of the southern rim of the Pelican molecular cloud, possibly driven by the moderate-luminosity Class I protostar IRAS 20489+4406. Object HH 570 is a highly collimated jet emerging from a compact cloud located about 15' southeast of the Pelican molecular cloud. A parallel outflow, possibly driven by IRAS 20496+4354, powers the bright bow shock HH 569. These observations demonstrate that vigorous star formation is still occurring within the clouds that surround the evolved North America/Pelican Nebula complex.

Jets and Herbig-Haro Objects in the Ophiuchi Embedded Cluster

We present results from a near-infrared 2.12 μm survey covering a large portion of the ρ Ophiuchi cloud (three regions of ~20' × 20' each, on average) in an effort to improve the detection of embedded molecular hydrogen emission objects in the cloud. We complement these observations with deep optical [S II] images of six areas of 10' × 10' each. We recovered all previously known optical jets/Herbig-Haro (HH) objects as well as H2 outflows in the region and report the detection of four new HH objects and 13 near-infrared knots. We provide coordinates and describe the morphology of these knots, several of which are identified as belonging to the same flow on the basis of morphological and proximity arguments. We discuss likely exciting sources. A unique association of the driving star is not always possible, as several young stars lie in close proximity to these knots.

Blowout from IC 1396N: The Emergence of Herbig-Haro Flows from a Cloud Core

We have identified a major Herbig-Haro flow, HH 777, that is bursting out of the IC 1396N cometary cloud core. Near- and mid-infrared images reveal a very red object embedded in the center of the core, located on the symmetry axis of the large HH 777 flow, suggesting that this is likely the driving source. The projected separation of the working surface from the source is 0.6 pc. Additionally, 0.4 pc to the east of the source and on the flow axis, there is a faint, previously known HH object (HH 594) that may be part of the counterflow. It thus appears that we are seeing a blowout of a parsec-scale flow into the surrounding H II region. We study numerical simulations of a jet breaking out of a neutral cloud into a photoionized medium, and we reproduce the main features of the HH 777 flow.

High Spectral Resolution H2Measurements of Herbig-Haro Objects 38, 46/47, and 120

We report high spectral resolution (R 20,000) measurements of the H2 1–0 S(1) line in Herbig-Haro objects 38, 46/47, and 120. The long-slit spectra reveal complex velocity structure with evidence for bow-shock structures, as well as prompt entrainment and shock heating of ambient molecular gas. Individual knots within HH 38 show distinct double-peaked velocity structure, consistent with that expected from spatially unresolved bow shocks. A portion of the HH 47A bow shock is resolved in our measurements, and the kinematics of the H2 trace closely that found for Hα emission. The evidence indicates that the preshock medium for HH 47A that formed in the wake of a previous ejection contains molecular clumps. The HH 46C jet A feature in the HH 46/47 counterflow is suggestive of a bow shock emerging from near the base of the flow, with H2 emission arising from ambient cloud material excited in the oblique flanks of the bow shock. HH 46F is situated downstream at the boundary between the ovoid cavity and the ambient cloud material, and represents either entrainment by a stellar wind that fills the cavity or entrainment in the far wing of a giant bow shock. For HH 120, the H2 velocity results also corroborate those found from atomic emission, and there is substantial evidence that the preshock medium is inhomogeneous, producing clumps of H2 emission on the wings of a bow shock that has an apex at HH 120A.

Adaptive Optics Spectroscopy of the [Feii] Outflow from DG Tauri

We present results of the velocity-resolved spectroscopy of the [Fe ii] � 1.644 lm emission line along the optical jet emanating from DG Tau. The slit spectrum, obtained with the Subaru Telescope adaptive optics system at an angular resolution of 0>16, shows strong, entirely blueshifted emission on the southwest side of the star. A faint, redshifted counterfeature was also detected on the northeast side with emission within 0>7 of the star being occulted by the circumstellar disk. The blueshifted emission has two distinct radial velocity components. The low-velocity component (LVC) has a peak radial velocity of �� 100 km s � 1 with a FWHM line width of � 100 km s � 1 , and it peaks at 0>2–0>5 from the star. The high-velocity component (HVC) peaks at 0>6–0>8 away from the star, showing a peak radial velocity of �� 220 km s � 1 with a line width of � 50 km s � 1 . These characteristics are remarkably similar to the [Fe ii] outflow from L1551 IRS 5, although the linear scales of the HVCs and LVCs are different for the two objects. We conclude, as an analogy to the case of L1551 IRS 5, that the HVC is a well-collimated jet launched from the region close to the star and that the LVC is a disk wind with a wide opening angle. Detailed comparison of emission parameters between the two sources, however, suggests that part of the LVC emission from DG Tau arises from the gas entrained and accelerated by the HVC, if we assume continuous steady state outflows. The presence of two distinct emission components clearly separated in space and velocity may favor theoretical models with two outflows: one is the LVC magnetohydrodynamically driven near the inner edge of an accretion disk, and the other is the HVC driven by the reconnection of dipolar stellar magnetic fields anchored to the disk. Subject headings: ISM: Herbig-Haro objects — ISM: individual (DG Tauri, HH 158) — ISM: jets and outflows — stars: formation — stars: pre–main-sequence — techniques: high angular resolution

XMM-Newtonstudy of the star forming region NGC 1333

We analyze the data of a deep XMM-Newton X-ray imaging observation of the NGC 1333 star forming region. The observation covered a period of about 14 hours and has a total MOS-equivalent exposure time of 235 ksec. In addition to 46 bright X-ray sources revealed by source detection routines, we find weak X-ray emission at the positions of 40 X-ray sources detected originally in a recent Chandra observation of NGC 1333. The XMM-Newton count rates of most sources agree well with their countrates in the Chandra data; about 80% of the sources vary by a factor of less than 3 between the two X-ray observations which are separated by 18 month. The X-ray lightcurves of several sources reveal large flares with parameters typical for X-ray active young stellar objects. We also construct and analyze the X-ray spectra of the stronger sources and derive plasma temperatures between ~0.7 keV and ~3 keV for the T Tauri stars in NGC 1333, and higher temperatures up to ~12 keV for flaring sources and deeply embedded young stellar objects. We consider in detail the X-ray properties of the optically invisible infrared source SVS 16, which showed a large X-ray flare during our observation. Its X-ray spectrum confirms that the hydrogen column density towards SVS 16 is much lower than expected from the extinction determined from near-IR spectroscopy and photometry. The reason for this inconsistency remains unclear. Finally, we search for, but do not detect any X-ray emission from HH 7-11 or one of the other Herbig-Haro objects in NGC 1333. Also, none of the class 0 protostars in the region is detected in X-rays.

The impact of the Herbig--Haro object HH2 on local dust and gas

We present results from a study of molecular gas and dust in the vicinity of the Herbig Haro object HH2. Emission from the sub-mm continuum, 12CO and HCO+ was mapped with angular resolutions ranging from 14 arcsec to 5 arcsec (or 0.01pc at the distance of HH2). The continuum shows an extended dust clump of mass 3.8Msun and temperature 22K, located downstream of the bright optical HH knots. However, a compact emission peak lies within ~0.01pc of the low-excitation H2-prominent shocks, with a luminosity consistent with local heating by the outflow. The HCO+ emission shows two velocity components: firstly, ambient-velocity gas lying in a region roughly corresponding to the dust clump, with abundance enhanced by a factor of a few close to the H2-prominent knots. Secondly a component of high-velocity emission (20 km/s linewidth), found mainly in a collimated jet linking the low-excitation HH objects. In this high-velocity jet, the line wings show an abundance ratio HCO+/CO proportional to v^2, with an HCO+ enhancement compared with ambient gas of up to 10^3 at the most extreme velocities. Such high abundances are consistent with models of shock chemistry in turbulent mixing layers at the interaction boundaries of jets. Extrapolating this effect to low velocities suggests that the more modest HCO+ enhancement in the clump gas could be caused by low velocity shocks. A UV precursor may not, therefore be necessary to explain the elevated HCO+ abundance in this gas.

The Enigmatic HH 255

ABSTRACTTo gain insight into the nature of the peculiar Herbig‐Haro object HH 255 (also called Burnham's nebula), we use previously published observations to derive information about the emission‐line fluxes as a function of position within HH 255 and compare them with the well‐studied and relatively well behaved bow shock HH 1. There are some qualitative similarities in the Hα and [O iii] λ5007 lines in both objects. However, in contrast to the expectation of the standard bow‐shock model, the fluxes of the [O i] λ6300, [S ii] λ6731, and [N ii] λ6583 lines are essentially constant along the axis of the flow, while the electron density decreases, over a large distance within HH 255. We also explore the possibility that HH 255 represents the emission behind a standing or quasi‐stationary shock. The shock faces upwind, and we suggest, using theoretical arguments, that it may be associated with the collimation of the southern outflow from T Tauri. Using a simplified magnetohydrodynamic simulation to illustrate the basic concept, we demonstrate that the existence of such a shock at the north edge of HH 255 could indeed explain its unusual kinematic and ionization properties. Whether or not such a shock can explain the detailed emission‐line stratification remains an open question.

Herbig-Haro Objects in the Monoceros OB1 Molecular Cloud

We carried out a wide-field [S II]-emission imaging of the Monoceros OB1 molecular cloud (NGC 2264) to investigate the star formation and outflow activity of the region. Our narrowband [S II] imaging covers an area of sky of similar to2 deg(2), including the entire Mon OB1 cloud. In the northern part of the cloud two new Herbig-Haro (HH) objects, HH 572 and HH 575, are discovered. All four of the previously known HH objects, HH 124, 125, 225, and 226, are also detected in our imaging. Low-dispersion spectroscopic observations of HH 572A, 575B, and 575C1 further confirmed the HH-object nature of these objects. Molecular hydrogen v = 1-0 S(1) narrowband imaging revealed a bright H-2 emission knot in each of the HH 572 and HH 575 regions. By comparing the results of our optical [S II] emission survey with those of the CO molecular outflow survey, it is found that the occurrence frequency of HH objects is similar to that of CO outflows in the Mon OB1 cloud. However, HH objects and CO outflows display different spatial distributions.

The molecular condensations ahead of Herbig-Haro objects

Clumps of enhanced molecular emission are present close to a number of Herbig-Haro (HH) objects. These enhancements may be the consequence of an active photochemistry driven by the UV radiation originating from the shock front of the HH object. On the basis of this picture and as a follow up to a molecular line survey toward the quiescent molecular clump ahead of the HH object, HH 2 (Girart et al. 2002), we present a detailed time and depth dependent chemical model of the observed clump. Despite several difficulties in matching the observations, we constrain some of the physical and chemical parameters of the clump ahead of HH 2. In particular, we find that the clump is best described by more than one density component with a peak density of 3 × 105 cm-3 and a visual extinction of ≤3.5 mag; its lifetime can not be much higher than 100 years and the impinging radiation is enhanced with respect to the ambient one by probably no more than 3 orders of magnitude. Our models also indicate that carbon-bearing species should not completely hydrogenate as methane when freezing out on grains during the formation of the clump.

Chemistry ahead of Herbig-Haro objects

There is now compelling evidence that dark molecular clouds are clumpy. Much of the clumpiness is unresolved by single-dish telescopes but is apparent in the data from array telescopes. Molecular clumps may also be observed close to Herbig-Haro (HH) objects. These clumps are easily observable because they are ‘illuminated’ due to the UV radiation from the shock front of the HH jet. A detailed observational and theoretical study of one HH clump has been performed and it indicates that this clump must be transient and has a similar density and temperature to those clumps detected in the cloud interior. Thus, HH clumps may be used as an independent method of determining physical parameters of the clumpiness of molecular clouds.

New T-Association in the Cyg OB7 Region

Observations in a new region of size 6x11 min2 situated nearly in the center of the Cyg OB7 stellar association are reported. A new T-association, a group of new Herbig-Haro objects, and a single trapezium type stellar system are found within this region.

HH 111 STIS Observations and their Analysis using Analytical and Numerical Models

The internal structure of stellar jets arising from young stellar objects is characterized by a series of ‘knots’ or condensations which have highly supersonic proper motions. These structures, we believe, are the result of a variable ejection from the source, which leads to the formation of internal working surfaces or small bowshock within the jet beam. In this paper we present a long-slit spectrum of Herbig-Haro object HH 111 obtained with STIS and an interpretation of this observation in terms of an ejection velocity variability model.

Clumpiness in Star Forming Regions

In this article, some aspects of the clumpy nature of molecular clouds are reviewed. In particular the observational evidence for small-scale structures both in low and high mass star forming regions will be discussed. I will review some examples of `clumpiness' such as: i) the molecular clumps ahead of HH objects and how the study of the physical and chemical nature of these clumps is important for the understanding of the clumpiness of the Interstellar Medium; and ii)hot cores and their use as a tool to study the early phases of massive star formation.

Near and Mid-infrared images of the massive star forming complex G9.62+0.19

A near- and mid-infrared study of the star formation complex G9.62+0.19 is presented. It includes photometrically calibrated images through wide-band JHK and narrow-band Bry, H 2 and 12.5 μm filters. These were taken at Las Campanas, La Silla and OAN-San Pedro Martir. We found evidence of two embedded young clusters of O-B5 stars associated with the radio components B and C, one compact and one ultracompact HII region. The data suggest the presence of a third, more dispersed cluster of more luminous infrared stars at the southern edge of the cloud complex. A large fraction of the star members of each cluster exhibit significant infrared excess. We confirm the detection of a very red near- and mid-infrared source immersed in the molecular hot core (component F). An H 2 shocked gas knot, probably an obscured Herbig-Haro object, was found associated to the blue-shifted lobe of the high-velocity molecular outflow in this core. The properties of the individual sources are discussed in detail.

The Precession of the Giant HH 34 Outflow: A Possible Jet Deceleration Mechanism

The giant jets represent a fundamental trace of the historical evolution of the outflow activity over timescales of ~104 yr, i.e., a timescale comparable to the accretion time of the outflow sources in their main protostellar phase. The study of such huge jets provides the possibility of retrieving important elements related to the life of the outflow sources. In this paper, we study the role of precession (combined with jet velocity variability and the resulting enhanced interaction with the surrounding environment) as a deceleration mechanism for giant jets, using a numerical approach. This thesis was proposed for the first time by Devine et al., but it could not be numerically explored until now, because it is intrinsically difficult to reproduce, at the same time, the large range of scales from ~100 AU up to a few parsecs. In the present paper, we obtain predictions of Hα intensity maps and position-velocity diagrams from three-dimensional simulations of the giant HH 34 jet (including an appropriate ejection velocity time variability and a precession of the outflow axis), and we compare them with previously published observations of this object. Our simulations represent a step forward from previous numerical studies of HH objects, in that the use of a seven-level, binary adaptive grid has allowed us to compute models that appropriately cover all relevant scales of a giant jet, from the ~100 AU jet radius close to the source to the ~1 pc length of the outflow. A good qualitative and quantitative agreement is found between the model predictions and the observations, indicating that a precession of the jet axis can indeed be the probable cause of the deceleration of the giant jets. Moreover, we show that a critical parameter for obtaining a better or worse agreement with the observations is the ratio ρj/ρa between the jet and the environmental densities. The implications of this result in the context of the current star formation models are discussed.