Observational 2D model of H2emission from a bow shock in the Orion Molecular Cloud (original) (raw)

Observations of shocked [FeII] and H 2 line profiles in orion bullet wakes

Astrophysics and Space Science, 1995

Recent near-IR imaging of the Orion molecular cloud has revealed a complex of dense bullets, visible as [FeII] emitting HH-objects at the tips of H2 wakes, ejected explosively from the cloud core. Having resolved individual bow-shock structures for the first time in this bright source, we have observed [FeII] 1.644µm velocity profiles of selected bullets and H2 1-0 S(1), 2.122µm velocity profiles for a series of positions along and across the corresponding bow-shock wakes. We present observed profiles for the bullet M42 HH1 and its associated wake and compare with theoretical bow-shock models.

Observations of shocked H2 and [FeII] line profiles in orion bullet wakes

Astrophysics and Space Science, 1995

A b s t r a c t . New observations of H2 velocity profiles in the Orion bullet wakes are extremely difficult to reconcile with existing steady-state shock models. We have obselved [FeII] 1.644tim velocity profiles of selected bullets and It2 1-0 S(1) 2.122/zm velocity profiles for a series of positions along and across the corresponding bow-shock wakes. Integrated [FeII] velocity profiles of the brightest bullets are consistent with theoretical bow shock predictions. Observations of broad, singly-peaked H2 1-0 S(1) profiles in the most clearly resolved bullet wakes challenge our understanding of molecular shocks. It may be necessary to model the effects of instabilities and turbulence in the Orion bullet wakes in order to fit our observations.

H2 excitation imaging of the Orion Molecular Cloud

Astronomy & Astrophysics, 2003

Observations are reported of IR emission in H 2 , around 2 µm in the K-band, obtained with the ESO 3.6 m telescope using the ADONIS adaptive optics system. Data cover a region of the Orion Molecular Cloud north of the Trapezium stars and SW of the Becklin-Neugebauer object. Excellent seeing yielded diffraction limited images in the v = 2−1 S(1) line at 2.247 µm. Excitation temperature images were created by combining these data with similar data for H 2 emission in the v = 1−0 S(1) line reported earlier . Shock models are used to estimate densities in emitting clumps of material. In local zones with high excitation temperatures, post-shock densities are found to be as high as several times 10 8 cm −3 , an order of magnitude denser than our previous estimates. We propose that the nature of these zones is dictated by the combined activity of shocks, which create dense structures, and the powerful radiation field of θ 1 C Ori which photoevaporates the boundaries of these structures.

Shocked molecular hydrogen in the Orion "bullets

1997

The physics of shocked outflows in molecular clouds is one of the fundamental astrophysical processes by which the cycle of s tar formation in our Galaxy is regulated. I outline the basis of our understanding of the star formation process and the violent o u t­ flow always associated with it, the physics of shocks in molecular gas, and the consequent excitation of molecular hydrogen (H2). It is demonstrated th a t molecular hydrogen is the best observational diagnostic of this hot, shocked molecular gas and an introduc­ tion is given to the observational techniques of near-infrared spectroscopy required in its measurement. I describe a detailed observational study of the physics of shocked H2 excitation and dynamics in the nearby massive star forming region of the Orion giant molecular cloud, the brightest source of its type, using the recently upgraded CGS4 near-IR spectrometer at UKIRT. We have demonstrated tha t integrated [Fell] 1.644/im line profiles in the Orion '‘bul­ let...

Observations of spatial and velocity structure in the Orion molecular cloud

Astronomy & Astrophysics, 2007

Observations are reported of H 2 IR emission in the S(1) v = 1−0 line at 2.121 µm in the Orion Molecular Cloud, OMC1, using the GriF instrument on the Canada-France-Hawaii Telescope. GriF uses a combination of adaptive optics and Fabry-Perot interferometry, yielding a spatial resolution of 0.15 to 0.18 and velocity discrimination as high as 1 km s −1. 193 bright H 2 emission regions can be identified in OMC1. The general characteristics of these features are described in terms of radial velocities, brightness and spatial displacement of maxima of velocity and brightness, the latter to yield the orientation of flows in the plane of the sky. Strong spatial correlation between velocity and bright H 2 emission is found and serves to identify many features as shocks. Important results are: (i) velocities of the excited gas illustrate the presence of a zone to the south of BN-IRc2 and Peak 1, and the west of Peak 2, where there is a powerful blue-shifted outflow with an average velocity of −18 km s −1. This is shown to be the NIR counterpart of an outflow previously identified in the radio, originating from either source I or source n. (ii) There is a band of weak radial velocity features (<5 km s −1) in Peak 1. (iii) A small proportion of the flows may represent sites of low mass star formation and one region shows evidence of multiple flows which may indicate multiple low mass star formation within OMC1.

Shocked H2 and Fe+ Dynamics in the Orion Bullets

Monthly Notices of The Royal Astronomical Society, 1999

Observations of H2 velocity profiles in the two most clearly defined Orion bullets are extremely difficult to reconcile with existing steady-state shock models. We have observed [FeII] 1.644um velocity profiles of selected bullets and H2 1-0 S(1) 2.122um velocity profiles for a series of positions along and across the corresponding bow-shaped shock fronts driven into the surrounding molecular cloud. Integrated [FeII] velocity profiles of the brightest bullets are consistent with theoretical bow shock predictions. However, observations of broad, singly-peaked H2 1-0 S(1) profiles at a range of positions within the most clearly resolved bullet wakes are not consistent with molecular shock modelling. A uniform, collisionally broadened background component which pervades the region in both tracers is inconsistent with fluorescence due to the ionizing radiation of the Trapezium stars alone.

The Intriguing Giant Bow Shocks near HH 131

The Astronomical Journal, 2005

Using the High Dispersion Spectrograph (HDS) at the Subaru Telescope, echelle spectra of two giant arcs, i.e. nebulosities Cw and L (hereafter Nebu. Cw and L, or simply Cw and L) associated with HH 131 in Orion are presented. Typical emission lines of Herbig-Haro (HH) objects have been detected towards Nebu. Cw with the broadband filter KV 408. With the low dispersion spectrograph at the National Astronomical Observatories (NAO) 2.16 m telescope, spectra of Nebu. C, L and K are obtained, which also show strong [S II]λλ 6717/6731, Hα and [N II]6583 emission lines. Position-velocity distributions of Cw and L are analyzed from the long-slit spectra observed with the HDS Hα narrowband filter. The fastest radial velocity of Cw is V r ∼-18.0 km s −1 . When the flow at L goes to the south, it slows down. The fastest radial velocity of L has been observed of -45.0 km s −1 and the slowest value is about -18.3 km s −1 , the radial velocity gradient is about 200 km s −1 pc −1 . The similarity of the fastest radial velocity of Cw to the slowest value of L and their positional connection indicate that they are physically associated. There is a tendency for the entire flow to become less excited and less ionized when going further to the south (i.e., from Nebu. K, L to C), where the most extended (and presumably evolved) objects are seen. The electron densities of all the observed nebulosities are low (n e ∼10 2 cm −3 ). Double kinematic signatures have been found in Cw from its [N II]6583 profiles while the observed Hα profiles of Cw are almost symmetric. Bow shock models appear to agree with the observed position-velocity diagrams of the [N II] spectra better than Hα spectra, and a bow shock with its wing, apex and postshock has been -2possibly revealed near Cw from the [N II] emission. With the suggestion that these arcs are HH shocks possibly ejected out of the Orion A molecular cloud by an uncertain source, their spectra show low to intermediate excitation from their diagnostic line ratios.

The CHESS survey of the L1157-B1 bow-shock: high and low excitation water vapor

Astronomy & Astrophysics, 2014

Context. Molecular outflows powered by young protostars strongly affect the kinematics and chemistry of the natal molecular cloud through strong shocks resulting in substantial modifications of the abundance of several species. In particular, water is a powerful tracer of shocked material due its sensitivity to both physical conditions and chemical processes. Aims. As part of the "Chemical Herschel Surveys of Star forming regions" (CHESS) guaranteed time key program, we aim at investigating the physical and chemical conditions of H 2 O in the brightest shock region B1 of the L1157 molecular outflow. Methods. We observed several ortho-and para-H 2 O transitions using HIFI and PACS instruments on board Herschel toward L1157-B1, providing a detailed picture of the kinematics and spatial distribution of the gas. We performed a Large Velocity Gradient (LVG) analysis to derive the physical conditions of H 2 O shocked material, and ultimately obtain its abundance. Results. We detected 13 H 2 O lines with both instruments probing a wide range of excitation conditions. This is the largest data set of water lines observed in a protostellar shock that provide both the kinematics and the spatial information of the emitting gas. PACS maps reveal that H 2 O traces weak and extended emission associated with the outflow identified also with HIFI in the o-H 2 O line at 556.9 GHz, and a compact (∼10 ′′ ) bright, higher-excitation region. The LVG analysis of H 2 O lines in the bow-shock show the presence of two gas components with different excitation conditions: a warm (T kin ≃200-300 K) and dense (n(H 2 )≃(1-3)×10 6 cm −3 ) component with an assumed extent of 10 ′′ and a compact (∼2 ′′ -5 ′′ ) and hot, tenuous (T kin ≃900-1400 K, n(H 2 )≃10 3−4 cm −3 ) gas component, which is needed to account for the line fluxes of high E u transitions. The fractional abundance of the warm and hot H 2 O gas components is estimated to be (0.7-2)×10 −6 and (1-3)×10 −4 , respectively. Finally, we identified an additional component in absorption in the HIFI spectra of H 2 O lines connecting with the ground state level. This absorption probably arises from the photodesorption of icy mantles of a water-enriched layer at the edges of the cloud, driven by the external UV illumination of the interstellar radiation field.

Herschel HIFI Observations of O2 toward Orion: Special Conditions for Shock Enhanced Emission

The Astrophysical Journal, 2014

We report observations of molecular oxygen (O2) rotational transitions at 487 GHz, 774 GHz, and 1121 GHz toward Orion Peak A. The O2 lines at 487 GHz and 774 GHz are detected at velocities of 10-12 km s-1 with line widths ~3 km s-1 however, the transition at 1121 GHz is not detected. The observed line characteristics, combined with the results of earlier observations, suggest that the region responsible for the O2 emission is sime9'' (6 × 1016 cm) in size, and is located close to the H 2 Peak 1 position (where vibrationally excited H2 emission peaks), and not at Peak A, 23'' away. The peak O2 column density is sime1.1 × 1018 cm-2. The line velocity is close to that of the 621 GHz water maser emission found in this portion of the Orion Molecular Cloud, and having a shock with velocity vector lying nearly in the plane of the sky is consistent with producing maximum maser gain along the line of sight. The enhanced O2 abundance compared to that generally found in dense interstellar clouds can be explained by passage of a low-velocity C shock through a clump with preshock density 2 × 104 cm-3, if a reasonable flux of UV radiation is present. The postshock O2 can explain the emission from the source if its line-of-sight dimension is sime10 times larger than its size on the plane of the sky. The special geometry and conditions required may explain why O2 emission has not been detected in the cores of other massive star-forming molecular clouds.