The circumstellar structure of lynds 379 IRS1

¹²CO J=2-1 maps of L379 IRS1 show a molecular outflow seen almost end-on while C¹⁸O J=2-1 emission covers a smaller central region, tracing virially bound material deeper within the cloud. Continuum maps at 450, 800 and 1100µm all trace an identical double peaked arc west of IRS1 and VLA NH₃ (1,1) & (2,2) integrated intensity maps reveal the same double-peaked structure. An identical velocity gradient is seen in¹²CO,¹³CO, C¹⁸O and NH₃ (1,1) & (2,2) following the arc-like structure of the continuum emission.     

The structure of circumstellar envelopes

Copious mass loss on the Asymptotic Giant Branch dominates the late stages of stellar evolution. Maps of extended circumstellar envelopes provide a history of mass loss and trace out anisotropic mass loss. This review concentrates on observations of millimeter wavelength molecular line emission, on high resolution maps of maser emission and on observations of submillimeter, millimeter and radio wavelength continuum emission. Radio continuum observations show that AGB stars are larger at radio than at optical wavelengths. The extended chromospheres indicated by these observations extend to distances from the star large enough for dust to form, thereby initiating mass loss. Molecular line maps have found time-variable mass loss for some stars, including detached shells indicating interrupted mass loss and evidence for a rapid increase in the mass loss rate at the end of the AGB phase. Maps of circumstellar envelopes show evidence of flattening, bipolar outflow and angular variations in both the mass loss rate and the outflow velocity. As stars evolve away from the AGB and planetary nebula formation begins, these structures become more pronounced, and fast bipolar molecular winds are observed. The time scales derived from the dynamical times of these winds and from the expansion rates of the central planetary nebulae are very rapid in some cases, about 100 years, in agreement with the predictions of stellar evolution theory.     

The Structure of Young Stellar Jets and Winds Revealed by High Resolution [Fe II] λ1.644μm Line Observations

We present high angular resolution spectra taken along the jets from L1551 IRS 5 and DG Tau obtained with the Subaru Telescope. The position-velocity diagrams of the [Fe II] λ 1.644 μmemission line revealed remarkably similar characteristics for the two sources, showing two distinct velocity components separated from each other in both velocity and space with the entire emission range blueshifted with respect to the stellar velocity. The high velocity component (HVC) has a velocity of –200 ––300 km s^-1 with a narrow line width, while the low velocity component (LVC) is around –100 km s^-1 exhibitinig a broad line width. The HVC is located farther away from the origin and is more extended than the LVC. Our results suggest that the HVC is a well-collimated jet originating from the region close to the star, while the LVC is a widely-opened wind accelerated in the region near the inner edge of the accretion disk.     

A self-consistent model for the S140/L1204 region

Comparison of submillimetre continuum observations of the L1204/S140 complex with previous high resolution CS, NH₃ and CI observations provides evidence that, for the first time, demonstrates the PDR and outflow are intimately linked. The only scenario that is able to explain all of the available molecular and atomic emission line data and our submillimetre continuum data, is one in which the outflow has expanded towards the edge of the molecular cloud and the edge of the blueshifted outflow lobe is now bounded by the expanding HII region. The NH₃ and continuum emission emanate from the inner edge of the outflow lobe, shielded from the external UV field.     

Near—Infrared Imaging Observations of the Orion A—W Star Forming Region

We carried out near-infrared imaging observations of the Ori A-W region using the Italian 1.5m TIRGO infrared telescope at Gornergrat. A group of infrared objects is visible on the K band image, including an IRAS source (IRS 1). From its IRAS flux density the IRAS luminosity is derived to be 45L⊙, which shows that IRS 1 is a low-mass protostar. By superimposing the position of the VLA H2O maser on the K image, we can identify the less evolved object IRS 1 as the excitation source of the H2O maser, within a projected distance of 470AU. This would be evidence that the maser effect is associated with the youngest phase of stellar evolution. The first probable HH object candidate in the Ori A-W region is discovered from the H2 S(1) 1-0 observation. Comparing the position of the H2O maser with the direction of the molecular hydrogen emission in the region, we suggest that the observed H2O maser could be tracing the circumstellar disk of IRS 1.     

The Star Formation Structure and H2O Supermaser Radiation in Orion KL

The extra fine structure of the active region of H₂O supermaser emission of Orion KL (angular resolution is 0.1 mas) is studied. A central body / accretion disk / bipolar outflow / bullets / envelope is discovered, that corresponds to the earliest stage of the small-mass star formation. The ejector – a compact bright source ≤0.05 AU, T_b ≈ 10¹⁷K. The bipolar outflow, v_ej ≈ 10km/s is a highly-collimated stream with a ration length/diameter～ 60, rotation period is ～ 0.5 yr, precession period ～ 10 yrs, precession angle ～ 33°. Precession forms a conical helix jet. The envelope amplified radio emission by about three orders of magnitude at velocity at v=7.65 km/s.     

A massive, dusty toroid with large grains in the pre-planetary nebula IRAS22036+5306

Using the Submillimeter Array (SMA), we have obtained high angular-resolution (∼1″) interferometric maps of the submillimeter (0.88 mm) continuum and CO J=3–2 line from IRAS 22036+5306 (I 22036), a bipolar pre-planetary nebula (PPN) with knotty jets discovered in our HST SNAPshot survey of young PPNe. In addition, we have obtained supporting lower-resolution (∼10″) 2.6 mm continuum and CO, ¹³CO J=1–0 observations with the Owens Valley Radio Observatory (OVRO) interferometer. We find an unresolved source of submillimeter (and millimeter-wave) continuum emission in I 22036, implying a very substantial mass (0.02–0.04M _⊙) of large (i.e., radius ≳1 mm), cold (≲50 K) dust grains associated with I 22036’s toroidal waist. The CO J=3–2 observations show the presence of a very fast (∼220 km s⁻¹), highly collimated, massive (0.03M _⊙) bipolar outflow with a very large scalar momentum (about 10³⁹ g cm s⁻¹), and the characteristic spatio-kinematic structure of bow-shocks at the tips of this outflow. The fast outflow in I 22036, as in most PPNe, cannot be driven by radiation pressure. The large mass of the torus suggests that it has most likely resulted from common-envelope evolution in a binary, however it remains to be seen whether or not the time-scales required for the growth of grains to millimeter sizes in the torus are commensurate with such a formation scenario. The presence of the torus should facilitate the formation of the accretion disk needed to launch the jet. We also find that the ¹³C/¹²C ratio in I 22036 is very high (0.16), close to the maximum value achieved in equilibrium CNO-nucleosynthesis (0.33). The combination of the high circumstellar mass (i.e., in the torus and an extended dust shell inferred from ISO far-infrared spectra) and the high ¹³C/¹²C ratio in I 22036 provides strong support for this object having evolved from a massive (≳4M _⊙) progenitor in which hot-bottom-burning has occurred.     

MHD simulations of the long-term evolution of a dipolar magnetosphere surrounded by an accretion disk

The evolution of a stellar, initially dipole type magnetosphere interacting with an accretion disk is investigated using numerical ideal MHD simulations. The simulations follow several 1000 Keplerian periods of the inner disk (for animated movies see http://www.aip.de～cfendt).Our model prescribes a Keplerian disk around a rotating star as a fixed boundary condition. The initial magnetic field distribution remains frozen into the star and the disk. The mass flow rate into the corona is fixed for both components. The initial dipole type magnetic field develops into a spherically radial outflow pattern with two main components – a disk wind and a stellar wind – both evolving into a quasi-stationary final state. A neutral field line divides both components, along which small plasmoids are ejected in irregular time intervals. The half opening angle of the stellar wind cone varies from 30° to55° depending on the ratio of the mass flow rates of disk wind and stellar wind. The maximum speed of the outflow is about the Keplerian speed at the inner disk radius. An axial jet forms during the first decades of rotations. However, this feature does not survive on the very long time scale and a pressure driven low velocity flow along the axis evolves. Within a cone of 15° along the axis the formation of knots may be observed if the stellar wind is weak. With the chosen mass flow rates and field strength we see almost no indication for a flow self-collimation. This is due to the weak net poloidal electric current in the magnetosphere which is in difference to typical jet models.     

L1551NE-Discovery of a Binary Companion

L1551NE is a very young (class 0 or I) low-mass protostar located close to the well-studied L1551 IRS 5. Here we present evidence, from 1.3 mm continuum interferometric observations at approximately 1&arcsec; resolution, for a binary companion to L1551NE. The companion, whose 1.3 mm flux density is approximately 13 that of the primary component, is located 1&farcs;43 ( approximately 230 AU at 160 pc) to the southeast. The millimeter-wave emission from the primary component may have been just barely resolved, with a deconvolved size of approximately 0&farcm;82x0&farcm;70 ( approximately 131x112 AU). The companion emission was unresolved (<100 AU). The pair is embedded within a flattened circumbinary envelope of size approximately 5&farcm;4x2&farcm;3 ( approximately 860x370 AU). The masses of the three components (i.e., from the circumstellar material of the primary star and its companion and the envelope) are approximately 0.044, 0.014, and 0.023 M middle dot in circle, respectively.     

The stellar-disk electric (short) circuit: observational predictions for a YSO jet flow

We discuss the star-disk electric circuit for a young stellar object (YSO) and calculate the expected torques on the star and the disk. We obtain the same disk magnetic field and star-disk torques as given by standard magnetohydrodynamic (MHD) analysis. We show how a short circuit in the star-disk electric circuit may produce a magnetically-driven jet flow from the inner edge of a disk surrounding a young star. An unsteady bipolar jet flow is produced that flows perpendicular to the disk plane. Jet speeds of order hundreds of kilometers per second are possible, while the outflow mass loss rate is proportional to the mass accretion rate and is a function of the disk inner radius relative to the disk co-rotation radius.     

Two jets from the Orion nebula (M42) 'proplyds': kinematics, morphologies and origins

A spatially unresolved velocity feature, with an approaching radial velocity of  ≈100 km s⁻¹  with respect to the systemic radial velocity, in a position–velocity array of [O  iii ] 5007-Å line profiles is identified as the kinematical counterpart of a jet from the proplyd LV 5 (158–323) in the core of the Orion nebula. The only candidate in Hubble Space Telescope ( HST ) imagery for this jet appears to be a displaced, ionized knot. Also an elongated jet projects from the proplyd GMR 15 (161–307). Its receding radial velocity difference appears at  ≈80 km s⁻¹  in the same position–velocity array.
A 'standard' model for jets from young, low-mass stars invokes an accelerating, continuous flow outwards with an opening angle of a few degrees. Here an alternative explanation is suggested which may apply to some, if not all, of the proplyd jets. In this, a 'bullet' of dense material is ejected which ploughs through dense circumstellar ambient gas. The decelerating tail of material ablated from the surface of the bullet would be indistinguishable from a continuously emitted jet in current observations.     

Evolution of the structure of the H<Subscript>2</Subscript>O supermaser outburst region in Orion KL

During the period 1979–1999, we investigated the hyperfine structure of the H₂O supermaser region located in the core of the molecular cloud OMC-1 in Orion KL. The angular resolution is 0.1 mas, which corresponds to 0.045 AU. The detected structure, which consists of a central object, an accretion disk, a bipolar outflow, and an envelope, corresponds to the initial formation stage of a low-mass star. The accretion disk is at the stage of separation into groups of concentric rings. The bipolar outflow is a neutral, highly collimated jet of accreted material that includes H₂O molecules and dust grains in the icy envelope. The injector is a bright compact source with a size <0.05 AU and a brightness temperature T_b≈10¹⁷ K. The velocity of the bipolar outflow is v≈10 km s^?1. The rotation velocity of the jet is v_rot≈1.5 km s^?1. The jet has the shape of a conical helix due to the precession of the rotation axis. Occasionally, dense blobs (comet-shaped bullets) are ejected. The envelope amplifies the radio emission from the structures in a ～0.5 km s^?1 maser window band with velocities v≈7.65 km s^?1 by more than two orders of magnitude.     

On the jet of a young star RWAurA and related problems

Having compared images of a jet of the young star RWAurA obtained with an interval of 21.3 yr, we have found that the outermost knots of the jet have emerged approximately 350 years ago. We come up with arguments that the jet itself has appeared at the same time, and intensive accretion onto the star has begun due to rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RWAur B. More precisely suppose that intensification of accretion is a response to changing conditions in the outer-disk regions which has followed after the sound wave, generated by these changes, has passed the disk in the radial direction. In our opinion difference in the parameters of blue and red lobes of the RWAurA jet is a result of the asymmetric distribution of the circumstellar matter above and below the disk due to companion’s passage. It was found from the analysis of the RWAur historical light curve that deep and long-term (Δt > 150 days) light attenuations of RWAurA observed after 2010 had no precedents in the previous 110 years.We also associate the change in the character of photometric variability of the star with the rearrangement of the structure of inner (r < 1 AU) regions of its protoplanetary disk, and discuss why these changes have begun only 350 years after the beginning of the active accretion phase.     

Masers, Lasers and the Interstellar Medium

This paper discusses recent results obtained by myself and my colleagues in three domains of astrophysics: interstellar supersonic turbulence, circumstellar disks, and natural masers and lasers. S.A. Kaplan, S.B. Pikelner, and I.S. Shklovskii were among those who, 30-40 years ago, laid the foundation of these domains.H2O masers become an effective probe of supersonic turbulence associated with mass outflow from very young stars. They demonstrate a very low (1) fractal dimension of the spatial set on which turbulence dissipates its kinetic energy, and, thereby, a strong intermittency of the turbulence. They also indicate that supersonic turbulence, like incompressible turbulence, has an inner scale, on which the bulk of turbulent energy dissipates in low-Mach, random shocks. H2O masers themselves find thereby a new pumping source in these random shocks.Masers in hydrogen recombination lines, discovered 8 years ago, originate in a circumstellar disk surrounding a massive star MWC 349A. They give a possibility to investigate kinematics and structure of the disk. Far-infrared nydrogen recombination lines, recently detected in MWC349A from the Kuiper Airborn Observatory, proved to be amplified as well. They are the first known natural amplifiers of electromagnetic waves in the laser wavelength domain. Analysis of their radiation, along with the radiation in other recombination lines, gives a possible key to understanding the lack of optical lasers in the Universe.     

Near-ir spectroscopy and the photospheres of embedded ysos

We present a study of weak near-IR absorption lines in 44 low luminosity YSOs. Using a spectral resolution of 1000 most Class II sources show CO overtone absorption bands of varying strength in the K window, whether they have optical counterparts or not. Class I sources tend to show featureless 2µm continua even though a S/N > 100 was achieved. High resolution (R=17000) echelle spectra were also obtained for a sub-sample of YSOs. Most show an unresolved¹²CO(2-0) bandhead, which when combined with inferred CO excitation temperatures and optical depths clearly points to a photospheric rather than a disk origin for the bands. They also show that embedded Class IIs are not rapidly rotating.We find an excellent correlation between increasing near-IR colour excess and decreasing band strength and interpret this in a straightforward way as due to veiling of the stellar photosphere by circumstellar dust emission at 1000-1200 K, probably from a disk. A veiling correction was applied and intrinsic indices obtained for many YSOs. The results provide confirmation that Class II sources are equivalent to T Tauri stars.     

BIMA and JCMT Spectropolarimetric Observations of the CO J = 2 − 1 Line Towards Orion KL/IRc2

We present results of JCMT and BIMA CO J = 2 ? 1 polarization observations towards the Orion KL/IRc2 high mass star forming region. The linear polarization fraction of the JCMT CO J = 2 ? 1 spectra presents a clear decrease towards the center of the line, as expected, due to the increase of the optical depth. The position angle remains constant along the spectral line, except at the line center, where the highest optical depth and lower fractional polarization are measured. The combined BIMA and JCMT maps of the redshifted and blueshifted CO emission show a uniform polarization pattern that does not coincide with previous dust continuum observations at similar angular resolution. This suggests that the CO and dust are tracing different spatial components along the line of sight.     

On the MHD Acceleration of Astrophysical Jets

We present a 2.5D magnetohydrodynamic (MHD) simulation of the acceleration of a collimated jet from a magnetized accretion disk. We employ a MHD Adaptive Mesh Refinement (AMR) code (FLASH—University of Chicago). Thanks to this tool we can follow the evolution of the system for many dynamical timescales with a high-spatial resolution. Assuming an initial condition in which a Keplerian disk, thus with no accretion motions, is threaded by a uniform poloidal magnetic field, we show how both the accretion flow and the acceleration of the outflow occur, and we present in detail which are the forces responsible for the jet launching and collimation. Our simulation also shows how the collimating forces due to the self-generated toroidal magnetic field can produce some peculiar knotty features.     

Fine Structure of the Core of the Blazar OJ 287-I

The fine structure of the active region, the bulge, of the blazar OJ 287 has been investigated with a resolution of 20 μas (0.1 pc) at a wavelength of 7 mm, the epochs of 2007–2017. The structure and kinematics correspond to a vortex nature. The surrounding matter, the plasma, is transferred to the center along two arms from opposite directions. The emerging excess angular momentum is carried away along the rotation axis by bipolar outflows, rotating coaxial tubes, in a direction X ≈ ?120? in the plane of the sky as it is accumulated. The central high-velocity bipolar outflow has a helical shape. The diameters of the low-velocity flows are ø1 ≈ 0.3 and ø2 ≈ 0.65 mas, or 1.4 and 3 pc, respectively. Ring currents whose tangential directions are observed as parallel chains of components are excited in the flow walls. The peak brightness temperature of the nozzle reaches Tb ≈ 1012?1013 K. A “disk” with a diameter ø ≈ 0.5 mas (≈2.2 pc) is observed by the absorption of synchrotron radiation. The disk is inclined to the plane of the sky at an angle of 60? in the jet direction. The fragments are seen from a distance of ～0.2 mas outside the absorption zone. The jet sizes exceed considerably the counterjet ones. An enhanced supply of plasma from the northern arm gives rise to an independent vortex 0.2 mas away from the central one in the NW direction. As in the first case, the helical central bipolar outflow is surrounded by a low-velocity component ø ≈ 0.28 mas in diameter with built-in ring currents. The jet is ejected in the direction X = ?50? in the plane of the sky. The jet orientation changes, X = ?130? at a distance of 1 mas. A high activity of the central and two side nozzles spaced 0.22 mas apart in the direction X = ?40? is occasionally observed simultaneously. The active region of the blazar is observed through an ionized medium, a screen, whose influence is significant even at a wavelength of 7 mm. The absorption and refraction of the transmitted emission in the screen affect the apparent brightness relative to the positions of the fragments.     

The physical conditions in the BHR71 outflows

Highly-collimated outflows are believed to be the earliest stage in outflow evolution, so their study is essential for understanding the processes driving outflows. The BHR71 Bok globule is known to harbour such a highly-collimated outflow, which is powered by a protostar belonging to a protobinary system. Using the APEX telescope on Chajnantor, we mapped the BHR71 highly-collimated outflow in CO(3-2), and observed several bright points of the outflow in the molecular transitions CO(4-3), CO(7-6), ¹³CO(3-2), C¹⁸O(3-2), CH₃OH(7-6) and H₂CO(4-3). We use an LVG code to characterise the temperature enhancements in these regions. These observations are particularly interesting for investigating the interaction of collimated outflows with the ambient molecular cloud. In our CO(3-2) map, the second outflow driven by IRS2, which is the second source of the binary system, is completely revealed and shown to be bipolar. We also measure temperature enhancements in the lobes. The CO and methanol LVG modelling points to temperatures between 30 and 50 K in the two lobes. The methanol emission in the southern lobe bright knot is barely resolved with the APEX single-dish. ALMA will thus be a central tool to study the shock chemistry in these regions.     

Ejector and bipolar outflow of the radio galaxy M87

The superfine structure of the jet formation region in the radio galaxy M87 has been investigated. An accretion disk and high- and low-velocity jet and counterjet components have been identified. The high-velocity bipolar outflow is ejected from the central disk region, a nozzle 4 mpc in diameter, while the low-velocity one is ejected from a ring 60 mpc in diameter and 14 mpc in width. The low-velocity plasma flow is a hollow tube with a built-in helix. The observed helical structure of the high-velocity jet is determined by precession. The components of the structure, its disk and bipolar outflow, suggest solid-body rotation. Ring currents and aligned magnetic fields are generated in them under the action of an external magnetic field. The bipolar outflows are ejected coaxially but in opposite directions—along and opposite to the disk field. As a result, the jet flow accelerates, while the counterjet one decelerates. This causes the extent of the region of radiative cooling of the ejected relativistic electrons in the counterjet to decrease and maintains their “afterglow” at large distances in the jet. The high collimation of the rotating flows is determined by their interaction with the environment.