Herbig-Haro Research Articles

New Herbig–Haro objects associated with embedded sources

ABSTRACT We continue to present the results of the Byurakan Narrow Band Imaging Survey (BNBIS). The main goal of this survey is to search for Herbig–Haro (HH) objects and jets in Galactic dark clouds. In this work we present the results of the search in the vicinity of infrared sources that are bright in the WISE survey and embedded in the dark clouds. The survey is performed with the 1-m Schmidt telescope of Byurakan Observatory, lately equipped with a new CCD detector, which allows to obtain one square degree images of the sky in various filters. Narrow-band filters were used to obtain H α and [S ii] images, and a medium-width filter was used for the continuum imaging. New HH flows and knots were found near six embedded IR sources, which constitutes a significant proportion of the objects observed. At least two of the newly found HH flows (HH 1226 and HH 1227) lie in isolated dark clouds, thus pointing to active star formation in these regions. Other flows are also located in detached and dense globules or filaments. The length of the HH 1228 flow is about 1 pc; it has also a molecular hydrogen counterpart of the same extension. Coordinates, charts, detailed descriptions and distance estimates are provided. The lower limits of bolometric luminosities of the source stars are typical for low-mass young stellar objects.

Deriving X-Ray Line Profiles for Massive-star Winds from Momentum-conserving Dynamical Working Surface Solutions

We present a general procedure for deriving a line-profile model for massive-star X-ray spectra that captures the dynamics of the wind more directly. The basis of the model is the analytic solution to the problem of variable jets in Herbig–Haro objects given by Cantó et al. In deriving our model, we generalize this jet solution to include flows with a prescribed nonzero acceleration for the context of radiatively driven winds. We provide example line profiles generated from our model for the case of sinusoidal velocity and mass-ejection variations. The example profiles show the expected shape of massive-star X-ray emission lines, as well as interesting but complicated trends with the model parameters. This establishes the possibility that observed X-rays could be a result of temporal variations seeded at the wind base, rather than purely generated intrinsically within the wind volume, and can be described via a quantitative language that connects with the physical attributes of those variations, consistently with the downstream momentum-conserving nature of radiatively cooled shocked radial flows.

The jet of BP Tau

Context. A strong global magnetic field of young low-mass stars and a high accretion rate are the necessary conditions for the formation of collimated outflows (jets) from these objects. But it is still unclear whether these conditions are also sufficient. Aims. We aim to check whether BP Tau, an actively accreting young star with a strong magnetic field, has a jet. Methods. We carried out narrowband [S II] 672 nm imaging and spectroscopic observations of BP Tau and its vicinity. Results. We find that BP Tau is a source of a Herbig-Haro flow (assigned number HH 1181), which includes two HH objects moving from the star in opposite directions and a micro- (counter-) jet of ∼1″ projected length. The flow is oriented along position angle 59 ± 1°.

Discovery of a Candidate Young Stellar Object in a Citizen Science Search for Compact Nebulae

We report the serendipitous discovery of a bipolar nebula in a citizen science search for non-stellar emission line objects using online sky surveys. It is associated with an infrared (IR) source and is situated next to a dark cloud, seen in emission in the far-IR (FIR). Evidence for an extinction gradient across the object has been found, pointing to close-by dust. This supports the notion that the newly found source is a young stellar object (YSO). It shows an enhanced surface brightness in the r-band, which covers the main emission lines typical for Herbig–Haro objects (HHOs). For an estimated distance of 1.7 kpc, an optical to FIR luminosity of ≳18.5 L ⊙ was derived.

HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow

Hubble Space Telescope (HST) images obtained in 2018 are combined with archival HST data taken in 1995 to detect changes and measure proper motions in the HH 80/81 shock complex, which is powered by the fastest known jet driven by a forming star, the massive object IRAS 18162-2048. Some persistent features close to the radio jet axis have proper motions of >1000 km s−1 away from IRAS 18162-2048. About 3–5 pc downstream from the IRAS source and beyond HH 80/81, Hα emission traces the rim of a parsec-scale bubble blown by the jet. Lower speed motions are seen in [S ii] away from the jet axis; these features have a large component of motion at right angles to the jet. We identify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The northeastern counterflow to HH 80/81 exhibits an extended but faint complex of 2.12 μm H2 shocks. The inner portion of the outflow is traced by dim 1.64 μm [Fe ii] emission. The full extent of this outflow is at least 1500″ (∼10 pc in projection at a distance of 1.4 kpc). We speculate about the conditions responsible for the production of the ultrafast jet and the absence of prominent large-scale molecular outflow lobes.

Modeling of thermal and non-thermal radio emission from HH80-81 jet

Protostellar jets are one of the primary signposts of star formation. A handful of protostellar objects exhibit radio emission from ionized jets, of which a few display negative spectral indices, indicating the presence of synchrotron emission. In this study, we characterize the radio spectra of HH80-81 jet with the help of a numerical model that we have developed earlier, which takes into account both thermal free–free and non-thermal synchrotron emission mechanisms. For modeling the HH80-81 jet, we consider jet emission towards the central region close to the driving source along with two Herbig-Haro objects, HH80 and HH81. We have obtained the best-fit parameters for each of these sources by fitting the model to radio observational data corresponding to two frequency windows taken across two epochs. Considering an electron number density in the range of $$10^3$$ – $$10^5$$ cm $$^{-3}$$ , we obtained the thickness of the jet edges and fraction of relativistic electrons that contribute to non-thermal emission in the range of $$0.01^{\circ }$$ – $$0.1^{\circ }$$ and $$10^{-7}$$ – $$10^{-4}$$ , respectively. For the best-fit parameter sets, the model spectral indices lie in the range of − 0.15 to $$+$$ 0.11 within the observed frequency windows.

REFRACTION OF A HERBIG-HARO JET TRAVELLING THROUGH A SHEAR LAYER

We study the problem of a radiative Herbig-Haro (HH) jet which travels through a slip surface into a region of side-streaming environment. The interaction with the streaming environment produces an oblique shock that deflects the jet beam. A simple, analytic model for this shock gives the jet deflection as a function of the incidence angle and the environment-to-jet ram pressure ratio. We find that in the case of higher environmental ram pressure, for a high enough incidence angle, the jet stalls and does not penetrate substantially into the streaming environment. We present 3D gas dynamic simulations illustrating the jet deflection and stalling regimes. Possible applications to HH jets showing sudden deflections in their propagation are discussed.

Analysis of line intensity ratio for optical transitions of 3d6 levels and plasma screening effect on atomic structure of Fe III ion

Iron emission lines are observed from most classes of astronomical objects through a wide spectral range from infrared to X-ray. For a useful analysis of these lines, accurate atomic data for neutral iron and its ions is required. In this work, we have done calculations of energy levels and radiative data of Fe III by using the relativistic configuration interaction method with the implementation of the flexible atomic code (FAC). We have calculated emission-line intensity ratios for optical transitions among the fine-structure levels of the 3d6 configuration at temperature 104 K and density ne=104cm−3. We have also compared our results with the observed spectra of Herbig-Haro objects HH 202 of Orion Nebula, Planetary Nebula, and NGC 2392, post-asymptotic giant branch star (PAGB) HD341617. We have also discussed various discrepancies between the observed spectra from these nebulae and our calculations. The atomic structure of plasma-embedded Fe III is also analyzed using flexible atomic code (FAC). The graphical study shows that transition wavelengths, oscillator strengths, and transition rates are very sensitive to the plasma environment in the density range 1021cm−3 to 5×1022cm−3 and spectral lines associated to Δn = 0 transitions for Fe III ion are blueshifted. We have also studied the dependence of emission line intensity ratios on plasma density and temperature. We believe that our presented results are useful in spectroscopic analysis and examination of astrophysical and laboratory plasma.

Discovery of a New Molecular Bubble–Outflow Structure in the Taurus B18 Cloud

Star formation can produce bubbles and outflows, as a result of stellar feedback. Outflows and bubbles inject momentum and energy into the surrounding interstellar medium, and so are related to the overall energy balance of the molecular cloud. Molecular bubbles can be resolved by higher-resolution radio telescopes to quantify the effect of star formation on molecular clouds. We report here the identification of a new molecular bubble with an outflow, and a Herbig–Haro object, HH 319, located at the bubble center. Multiwavelength data have been utilized to study its spatial structure, energy injection, and dynamical timescale. This bubble has a kinetic energy of 5.8 × 1043 erg within the smallest radius of a bubble in Taurus, 0.077 pc. The bubble formed ∼70,000 yr ago. According to the proper-motion velocities of protostars from Gaia EDR3, the T Tauri binary stars (FY Tau and FZ Tau) at the southwest edge of the bubble may have produced the outflow–bubble structure. This is an unusual new structure found in low- and intermediate-mass star formation regions. Only a bubble in Orion A, driven by V380 Ori, has a similar structure. The bubble–outflow structure provides additional observational evidence for the theory of stellar wind from T Tauri stars. It enhances our understanding of how stellar feedback acts on molecular clouds.

Deep diving off the ‘Cosmic Cliffs’: previously hidden outflows in NGC 3324 revealed by JWST

ABSTRACT We present a detailed analysis of the protostellar outflow activity in the massive star-forming region NGC 3324, as revealed by new Early Release Observations (EROs) from the James Webb Space Telescope (JWST). Emission from numerous outflows is revealed in narrow-band images of hydrogen Paschen α (Paα) and molecular hydrogen. In particular, we report the discovery of 24 previously unknown outflows based on their H2 emission. We find three candidate driving sources for these H2 flows in published catalogues of young stellar objects (YSOs), and we identify 15 infrared point sources in the new JWST images as potential driving protostars. We also identify several Herbig–Haro (HH) objects in Paα images from JWST; most are confirmed as jets based on their proper motions measured in a comparison with previous Hubble Space Telescope (HST) Hα images. This confirmed all previous HST-identified HH jets and candidate jets, and revealed seven new HH objects. The unprecedented capabilities of JWST allow the direct comparison of atomic and molecular outflow components at comparable angular resolution. Future observations will allow quantitative analysis of the excitation, mass-loss rates, and velocities of these new flows. As a relatively modest region of massive star formation (larger than Orion but smaller than starburst clusters), NGC 3324 offers a preview of what star formation studies with JWST may provide.

NIR spectroscopic survey of protostellar jets in the star-forming region IC 1396N

Context. The bright-rimmed cloud IC 1396N, associated with an intermediate-mass star-forming region, hosts a number of CO, molecular hydrogen, and Herbig-Haro (HHs) outflows powered by a set of millimetre compact sources. Aims. The aim of this work is to characterise the kinematics and physical conditions of the H2 emission features spread throughout the IC 1396N region. The features appear as chains of knots with a jet-like morphology and trace different H2 outflows. We also obtain further information about (and an identification of) the driving sources. Methods. Low-resolution, long-slit near-infrared spectra were acquired with the NICS camera at the TNG telescope, using grisms KB (R ~ 1200), HK, and JH (R ~ 500). Several slit pointings and position angles were used throughout the IC 1396N region in order to sample a number of the H2 knots that were previously detected in deep H2 2.12 μm images. Results. The knots exhibit rich ro–vibrational spectra of H2, consistent with shock-excited excitation, from which radial velocities and relevant physical conditions of the IC 1396N H2 outflows were derived. These also allowed estimating extinction ranges towards several features. [Fe ii] emission was only detected towards a few knots that also display unusually high H2 1–0 S(3)/S(1) flux ratios. The obtained radial velocities confirm that most of the outflows are close to the plane of the sky. Nearby knots in the same chain often display different radial velocities, both blue–shifted and red–shifted, which we interpret as due to ubiquitous jet precession in the driving sources or the development of oblique shocks. One of the chains (strand A, i.e. knots A1 to A15) appears as a set of features trailing a leading bow-shock structure consistent with the results of 3D magneto-hydrodynamical models. The sides of the leading bow shock (A15) exhibit different radial velocities. We discuss possible explanations. Our data cannot confirm whether strands A and B have both originated in the intermediate mass young stellar object [BGE2002] BIMA 2 because a simple model of a precessing jet cannot account for their locations. Conclusions. Near-infrared spectroscopy has confirmed that most of the H2 ro-vibrational emission in IC 1396N is shock-excited rather than uv-excited in photon-dominated regions. It has shown a complex kinematical structure in most strands of emitting knots as well.

Hydrodynamic instabilities in a highly radiative environment

In this paper, we present the effects of a radiative shock (RS) on the morphology of jet-like objects subjected to hydrodynamic instabilities. To this end, we used an experimental platform developed to create RSs on high energy laser facilities such as LULI2000 and GEKKO XII. Here, we employed modulated targets to initiate Richtmyer–Meshkov and Rayleigh–Taylor instability (RTI) growth in the presence of an RS. The RS is obtained by generating a strong shock in a dense pusher that expands into a low-density xenon gas. With our design, only a limited RTI growth occurs in the absence of radiative effects. A strongly radiative shock has opposite effects on RTI growth. While its deceleration enhances the instability growth, the produced radiations tend to stabilize the interfaces. Our indirect experimental observations suggest a lower instability growth despite the interface deceleration. In addition, the jets, produced during the experiment, are relevant to astrophysical structures such as Herbig–Haro objects or other radiatively cooling jets.

Orbital parameters and activity of ZZ Tau – a low-mass young binary with circumbinary disc

ABSTRACT We present the results of our new observations of the young binary ZZ Tau with a circumbinary disc. The system was found to consist of two coeval (age < 2 Myr) classical T Tauri stars with the total mass 0.86 ± 0.09 M⊙, orbital period 46.8 ± 0.8 yr, semimajor axis 88.2 ± 2.1 mas, eccentricity 0.58 ± 0.02, and the orbital inclination 123${_{.}^{\circ}}$8 ± 1${_{.}^{\circ}}$0. The accretion rate of ZZ Tau A and ZZ Tau B is approximately 7 × 10−10 and 2 × 10−10 M⊙ yr−1, respectively. No correlation was found between the long-term photometric variability of ZZ Tau and orbital position of its components. The periodic light variations with P = 4.171 ± 0.002 d were observed in the BVRI bands presumably connected with an accretion (hot) spot on the surface of the primary (ZZ Tau A). At the same time, no periodicity was observed in the U band nor in the emission line profile variations probably, due to the significant contribution of ZZ Tau B’s emission, which dominates shortward of λ ≈ 0.4 $\mu$m. We argue that the extinction in the direction to the primary is noticeably larger than that to the secondary. It appeared that the rotation axis of the primary is inclined to the line of sight by ≈31° ± 4°. We also concluded that ZZ Tau is the source of a CO molecular outflow; however, ZZ Tau IRS rather than ZZ Tau is the source of the Herbig–Haro object HH393.

Photoionized Herbig–Haro objects in the Orion Nebula through deep high-spectral resolution spectroscopy – III. HH 514

ABSTRACT We analyse the physical conditions and chemical composition of the photoionized Herbig–Haro object HH 514, which emerges from the protoplanetary disc (proplyd) 170-337 in the core of the Orion Nebula. We use high-spectral resolution spectroscopy from Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope and IFU-spectra from MEGARA at the Gran Telescopio de Canarias. We observe two components of HH 514, the jet base and a knot, with $n_{\rm e}= (2.3 \pm 0.1) \times 10^5 \rm{cm}^{-3}$ and $n_{\rm e}= (7 \pm 1) \times 10^4 \rm{ cm}^{-3}$, respectively, both with Te ≈ 9000 K. We show that the chemical composition of HH 514 is consistent with that of the Orion Nebula, except for Fe, Ni, and S, which show higher abundances. The enhanced abundances of Fe and Ni observed in HH objects compared with the general interstellar medium are usually interpreted as destruction of dust grains. The observed sulphur overabundance (more than two times solar) is challenging to explain since the proplyd photoevaporation flow from the same disc shows normal sulphur abundance. If the aforementioned S-overabundance is due to dust destruction, the formation of sulfides and/or other S-bearing dust reservoirs may be linked to planet formation processes in proplyds, which filter large sulfide dust grains during the accretion of matter from the disc to the central star. We also show that published kinematics of molecular emission close to the central star are not consistent with either a disc perpendicular to the optical jet, or with an outflow that is aligned with it.

Probing the origin of 4FGL J0822.8–4207: cosmic ray illumination from the SNR Puppis A and the Herbig–Haro object HH219

ABSTRACT 4FGL J0822.8–4207 is a point source found in the 4FGL-DR2 catalogue by the gamma-ray observatory Fermi-LAT and has no known association. We carry out X-ray observations of 4FGL J0822.8–4207 to help understand its nature. We explore two scenarios for the origin of 4FGL J0822.8–4207 . In the first case, we study the possibility that cosmic rays from the supernova remnant (SNR) Puppis A, seen nearby in the sky, reach the dense gas at the location of the source and produce the gamma-rays through inelastic proton–proton collisions. We apply a standard model for particle diffusion in the interstellar medium and derive the required physical parameters. We find that this scenario for the gamma-rays is possible if the gas is located at a distance that is not higher than ∼40 pc from Puppis A, unless the SNR is older than 7 kyr or the diffusion coefficient is higher than typical Galactic values, and relatively low-energy cosmic rays are currently escaping from the SNR. In the second scenario, we consider the protostellar jet HH219 as the origin of the GeV source and find the very interesting possibility that particles could be accelerated up to energies of at least several TeV in HH219. This would make this system the first known of its kind to produce gamma-ray emission extending up to hundreds of GeV without any apparent cut-off and an excellent laboratory to study the process of particle acceleration.

High-resolution Hα imaging of the northern Galactic plane and the IGAPS image database

The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys IPHAS and UVEX based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. It captures the entire northern Galactic plane within the Galactic coordinate range |b|< 5° and 30° < ℓ < 215°. From the beginning, the incorporation of narrow-band Hα imaging has been a unique and distinctive feature of this effort. Alongside a focused discussion of the nature and application of the Hα data, we present the IGAPS world-accessible database of images for all five survey filters, i, r, g, URGO, and narrow-band Hα, observed on a pixel scale of 0.33 arcsec and at an effective (median) angular resolution of 1.1−1.3 arcsec. The background, noise, and sensitivity characteristics of the narrow-band Hα filter images are outlined. Typical noise levels in this band correspond to a surface brightness at full ∼1 arcsec resolution of around 2 × 10−16 erg cm−2 s−1 arcsec−2. Illustrative applications of the Hα data to planetary nebulae and Herbig-Haro objects are outlined and, as part of a discussion of the mosaicking technique, we present a very large background-subtracted narrow-band mosaic of the supernova remnant Simeis 147. Finally, we lay out a method that exploits the database via an automated selection of bright ionised diffuse interstellar emission targets for the coming generation of wide-field massive-multiplex spectrographs. Two examples of the diffuse Hα map output from this selection process are presented and compared with previously published data.

Extinction Correction and the [Fe ii] 1.26 μm/1.64 μm Intensity Ratio

Abstract From imaging observations of [Fe ii] emission in Herbig–Haro objects, I find a lower limit to the zero-extinction [Fe ii] 1.26 μm/1.64 μm intensity ratio of 2.6 and argue that this lower limit must be close to the true zero-extinction intensity ratio. My extinction determinations using this zero-extinction value yields results on well-studied HH objects consistent with results from other ionic-line spectra, whereas using nearly all theoretical values of [Fe ii] 1.26 μm/1.64 μm in the literature gives rise to unphysical results.

Photoionized Herbig–Haro Objects in the Orion Nebula through Deep High Spectral Resolution Spectroscopy. II. HH 204

Abstract We analyze the physical conditions, chemical composition, and other properties of the photoionized Herbig–Haro (HH) object HH 204 through Very Large Telescope echelle spectroscopy and Hubble Space Telescope imaging. We kinematically isolate the high-velocity emission of HH 204 from the emission of the background nebula and study the subarcsecond distribution of physical conditions and ionic abundances across the HH object. We find that low- and intermediate-ionization emission arises exclusively from gas at photoionization equilibrium temperatures, whereas the weak high-ionization emission from HH 204 shows a significant contribution from higher-temperature shock-excited gas. We separately derive the ionic abundances of HH 204, the emission of the Orion Nebula, and the fainter diffuse blue layer. In HH 204, the O+ abundance determined from collisional excited lines matches the one based on recombination lines, while the O2+ abundance is very low, so that the oxygen abundance discrepancy is zero. The ionic abundances of Ni and Fe in HH 204 have similar ionization and depletion patterns, with total abundances that are a factor of 3.5 higher than in the rest of the Orion Nebula due to dust destruction in the bow shock. We show that a failure to resolve the kinematic components in our spectra would lead to significant error in the determination of chemical abundances (for instance, a 40% underestimate of O), mainly due to incorrect estimation of the electron density.

Numerical Models of Externally Irradiated Herbig–Haro Objects

Abstract We use 3D radiation–hydrodynamic simulations to study the effects of an external photoionization source on the structure of a Herbig–Haro (HH) jet launched from a young stellar object. Different ionizing photon rates are considered as well as a time-dependent ejection velocity and density. From our numerical results, synthetic Hα emission maps are computed in order to study how the external ionizing source affects the observed morphology of the jet and counterjet. We find that, as expected, the outflow has jet/counterjet and side-to-side asymmetries (with brighter Hα emission toward the external photoionizing source). We find that, for a variable ejection velocity, jet morphologies similar to different observed externally irradiated jets can be straightforwardly obtained. Models of jets with a variable ejection density (and constant outflow velocity) produce morphologies that are not seen in observed HH jets and are, therefore, not justified by the presently available observations.

Variability of Disk Emission in Pre-main Sequence and Related Stars. V. Occultation Events from the Innermost Disk Region of the Herbig Ae Star HD 163296

Abstract HD 163296 is a Herbig Ae star that underwent a dramatic ∼0.8 magnitude drop in brightness in the V photometric band in 2001 and a brightening in the near-IR in 2002. Because the star possesses Herbig–Haro objects traveling in outflowing bipolar jets, it was suggested that the drop in brightness was due to a clump of dust entrained in a disk wind, blocking the line of sight toward the star. In order to quantify this hypothesis, we investigated the brightness drop at visible wavelengths and the brightening at near-IR wavelengths of HD 163296 using the Monte Carlo Radiative Transfer Code, HOCHUNK3D. We created three models to understand the events. Model 1 describes the quiescent state of the system. Model 2 describes the change in structure that led to the drop in brightness in 2001. Model 3 describes the structure needed to produce the observed 2002 brightening of the near-IR wavelengths. Models 2 and 3 utilize a combination of a disk wind and central bipolar flow. By introducing a filled bipolar cavity in Models 2 and 3, we were able to successfully simulate a jet-like structure for the star with a disk wind and created the drop and subsequent increase in brightness of the system. On the other hand, when the bipolar cavity is not filled, Model 1 replicates the quiescent state of the system.