NE Jet Research Articles

AN HST SURVEY OF THE HIGHEST-VELOCITY EJECTA IN CASSIOPEIA A*

ABSTRACT We present Hubble Space Telescope WFC3/IR images of the Cassiopeia A supernova remnant that survey its high-velocity, S-rich debris in the NE jet and SW counterjet regions through [S iii] λλ9069, 9531 and [S ii] λλ10,287–10,370 line emissions. We identify nearly 3400 sulfur emitting knots concentrated in ∼120° wide opposing streams, almost triple the number previously known. The vast majority of these ejecta knots lie at projected distances well out ahead of the remnant’s forward blast wave and main shell ejecta, extending to angular distance of 320 ″ ?> to the NE and 260 ″ ?> to the SW from the center of expansion. Such angular distances imply undecelerated ejecta knot transverse velocities of 15,600 and 12,700 km s−1, respectively, assuming an explosion date ≈ 1670 ?> AD and a distance of 3.4 kpc. Optical spectra of knots near the outermost tip of the NE ejecta stream show strong emission lines of S, Ca, and Ar. We estimate a total mass ∼0.1 M ⊙ ?> and a kinetic energy of at least ∼ 1 × 10 50 ?> erg for S-rich ejecta in the NE jet and SW counterjet. Although their broadness and kinetic energy argue against the Cas A SN being a jet-induced explosion, the jets are kinematically and chemically distinct from the rest of the remnant. This may reflect an origin in a jet-like mechanism that accelerated interior material from a Si-, S-, Ar-, and Ca-rich region near the progenitor’s core up through the mantle and H-, He-, N-, and O-rich outer layers with velocities that greatly exceeded that of the rapidly expanding photosphere.

WIDE-FIELD NEAR-INFRARED IMAGING OF THE L1551 DARK CLOUD

We present wide-field near-infrared images of the densest part of the L1551 dark cloud taken with the narrow-band filters for [Fe II] λ 1.644 μm and H2 v = 1-0 S(1) lines, together with the broadband H and K s filters. Numerous [Fe II] and H2 emission features were detected from the regions around HL/XZ Tau, HH 30, HH 262, L1551 NE, and L1551 IRS 5. Most of the [Fe II] features are compact or jet-like, suggesting that the emission arises from fast shocks occurring in the ejecta of jets. The H2 features are more diffuse and widely distributed in outflow lobes, with none of the H2 features showing the well-collimated emission associated with jets. This implies that the H2 emission originates from slower shocks where the ejecta interacts with ambient material. The outflow structure in the vicinity of the deeply embedded object L1551 NE is revealed, featuring a well-collimated, spatially continuous [Fe II] jet penetrating a fan-shaped infrared reflection nebula. The tangential velocities of knots in the L1551 NE jet are estimated to be 140-190 km s–1 from their proper motions, implying an inclination of 45°-60° for the jet axis. A counter-jet from L1551 IRS 5 is detected for the first time in [Fe II]; this probably corresponds to the northern-most of the two jets on the blueshifted side. The relative brightness of the counter-jet suggests a visual extinction of 20-30 mag. The [Fe II] emissions from collimated jets are relatively strong toward L1551 NE and L1551 IRS 5 compared to those toward HL Tau and HH 30. This implies that the jets from the former objects, which are more embedded, have a higher shock velocity and/or a larger gas density than the latter, more revealed objects. The results presented here show that the near-infrared [Fe II] emission is a useful probe of well-collimated jets from deeply embedded sources, in much the same way that optical [S II] emission is used for relatively revealed objects.

The Shape of Cas A

Based on optical, IR and X-ray studies of Cas A, we propose a geometry for the remnant based on a scenario with significant systematic departures from axial symmetry. In this model, the main axis is oriented in the direction of strong blue-shifted motion at an angle of 110 - 120 degrees East of North and about 40 - 50 degrees to the East of the line of sight. Normal to this axis would be an expanding torus as predicted by jet-induced models. In the proposed geometry, iron-peak elements in the main jet-like flow could appear beyond the portions of the remnant rich in silicon by projection effects, not the effect of mixing. In the context of the proposed geometry, the displacement of the compact object from the kinematic center of the remnant at a position angle of ~169 degrees can be accommodated if the motion of the compact object is near to, but slightly off from, the direction of the main jet axis by of order 30 degrees. In this model, the classical NE jet, the SW counter-jet and other protrusions, particularly the hole in the North, are non-asymmetric flows approximately in the equatorial plane, e.g., out through the perimeter of the expanding torus, rather than being associated with the main jet. We explore the spoke-like flow in the equatorial plane in terms of Rayleigh-Taylor, Richtmyer-Meshkov and Kelvin-Helmholz instabilities and illustrate these instabilities with a jet-induced simulation.

Entrainment Mechanisms for Outflows in the L1551 Star‐forming Region

We present high sensitivity 12/13CO(1-0) molecular line maps covering the full extent of the parsec scale L1551 molecular outflow, including the redshifted east-west (EW) flow. We also present 12CO(3-2) data that extends over a good fraction of the area mapped in the 1-0 transition. We compare the molecular data to widefield, narrow-band optical emission in H$\alpha$. While there are multiple outflows in the L1551 cloud, the main outflow is oriented at 50\arcdeg position angle and appears to be driven by embedded source(s) in the central IRS 5 region. The 3-2 data indicate that there may be molecular emission associated with the L1551 NE jet, within the redshifted lobe of main outflow. We have also better defined the previously known EW flow and believe we have identified its blueshifted counterpart. We further speculate that the origin of the EW outflow lies near HH 102. We use velocity dependent opacity correction to estimate the mass and the energy of the outflow. The resulting mass spectral indices from our analysis, are systematically lower (less steep) than the power law indices obtained towards other outflows in several recent studies that use a similar opacity correction method. We show that systematic errors and biases in the analysis procedures for deriving mass spectra could result in errors in the determination of the power-law indices. The mass spectral indices, the morphological appearance of the position-velocity plots and integrated intensity emission maps of the molecular data, compared with the optical, suggest that jet-driven bow-shock entrainment is the best explanation for the driving mechanism of outflows in L1551. The kinetic energy of the outflows is found to be comparable to the binding energy of the cloud and sufficient to maintain the turbulence in the L1551 cloud.

A Million Second Chandra View of Cassiopeia A

We introduce a million-second observation of the supernova remnant Cassiopeia A with the Chandra X-ray Observatory. The bipolar structure of the Si-rich ejecta (NE jet and SW counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A.

R Aquarii spectra revisited by SUMA

We analyse the optical spectra and the ultraviolet (UV) spectral evolution of the jets and of the H II region inside the R Aquarii binary system using the code SUMA, which accounts for shock and photoionization consistently. The temperature of the hot star is 80 000 K as for a white dwarf. We find that the shock velocity in the NE jet increased between 1983 and 1989. The spectral evolution between 1989 and 1991 of the SW jet indicates that a larger contribution from low-density-velocity matter affects the 1991 spectra. The evolution of the UV spectra from 1980 November 8 to 1991 May 26 in the H II region indicates that the reverse shock is actually a standing shock. The results obtained by modelling the line spectra are cross-checked against the fit of the continuum spectral energy distribution. It is found that a blackbody temperature of 2800 K reproduces the radiation from the red giant. A blackbody emission component corresponding to 1000 K is emitted by dust in the surroundings of the red giant. Model calculations confirm that the radio emission is of thermal origin. We found that the NE jet bulk emission is at a distance of approximately 2 x 10 1 5 cm from the internal system, while the distance of the SW jet bulk is ∼6 x 10 1 4 cm. The distance of the reverse shock from the hot source in the internal region is ≤9 × 10 1 3 cm.

Soft-x-ray emission from small-sized Ne clusters heated by intense, femtosecond laser pulses

Soft-x-ray emission from a cryogenically cooled Ne jet irradiated by intense, 25-fs laser pulses was measured. The Ne spectrum started to drastically change in emitting ions from Ne5+ to Ne7+ below the preexpansion temperature of -120 degrees C. The significant change in the spectrum is attributed to the collisional heating of small-sized Ne clusters formed in the cooled jet. The increase of the laser pulse length from 25 fs to 100 fs resulted in further increase of x-ray emission from Ne7+ states.

Optical and UV Observations of Supernova Remnants

Recent observations of the galactic supernova remnants the Crab Nebula, SN 1006, Cas A, and the Cygnus Loop are reviewed. New studies of the Crab Nebula suggest its progenitor may have had appreciable mass loss in the form of a circumstellar disk resulting in both a bipolar expansion and formation of the synchrotron ‘bays'. Unusually high proper motion knots near to and possibly directed away from the pulsar also have been reported. In the Cas A remnant, a NE jet of ejecta appears to be a plume of mantle material with expansion velocities up to 12000 km s-1 or nearly twice that seen in the main ejecta shell. HST observations of the sdOB star located behind SN 1006 indicate symmetrically expanding Fe II ejecta out to 8100 km s-1. Lastly, deep images of the Cygnus Loop reveal emission structures similar to those seen in 2D & 3D shocked cloud simulations.

Ultraviolet Temporal Variability of the Peculiar Star R Aquarii

view Abstract Citations (17) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet Temporal Variability of the Peculiar Star R Aquarii Meier, S. R. ; Kafatos, M. Abstract This paper is a comprehensive study of all far-UV spectra obtained with the International Ultraviolet Explorer (IUE) satellite of the symbiotic star R Aquarii (R Aqr) covering a 13 yr period between 1979 and 1992. We have analyzed the ultraviolet emission for the compact H II region and the NE and SW extended "jetlike" filamentary structures. The results of our ultraviolet analysis indicate that the H II region and features A, B, and D of the NE jet are increasing in intensity, while the SW counterjet, feature A', has declined in intensity. We have found much stronger evidence that the high ionization lines of N V λλ1238, 1240 and He II λ1640 in the H II region and NE jet have steadily increased over the entire period of lUE observations. This result could indicate that the ionized region is increasing in excitation. We have found that the observations of the NE jet are consistent with a decreasing electron temperature and increasing line-emitting region, which suggest that the strengthening of emission-line fluxes may be a result of an expanding emitting volume in a post-shocked region. Low-resolution absolute line intensities and wavelengths for the most prominent emission lines in the λλ1200-3200 wavelength range have been tabulated. In addition, we present plots of the total ultraviolet flux (λλ200-3200) and absolute line intensities as a function of time to discern the temporal variability of R Aqr. These plots indicate that the far-UV emission from the NE jet is not variable on a ∼1.5 yr timescale as suggested by Kafatos, Michalitsianos, & Hollis. Moreover, we find that the variations in the far-UV emission in R Aqr are not coupled to the 386 day pulsation period of the Mira. Finally, successive ionization levels of carbon, nitrogen, oxygen, and silicon of the NE jet are compared with each other to probe the nature of the ionization source in the NE jet. High- and low-resolution ultraviolet spectra were used to calculate the properties of the emission nebula and hot component. We determined electron densities of ne = 4 × 105 cm-3 (H II region) and ne = 6 × 104 cm-3 NE jet), electron temperatures of Te ∼ 20,000K (H II region) and a high value of Te ≥ 26,000 K between 1982 May and 1983 December, to a low value of T < 18,000 K from observations during the period of 1986 December and 1989 June (NE jet), and also line-emitting regions of L = 6.3 × 1014 cm (H II region) and L = 1.5 × 1015 cm (NE jet). The He II λ1640 modified Zanstra method yielded an effective temperature of T* =61,000 K for the hot component. Estimates of the number of ionizing photons beyond the Lyman limit, blackbody parameters, and possible accretion disk parameters for the hot component are also given. Publication: The Astrophysical Journal Pub Date: September 1995 DOI: 10.1086/176225 Bibcode: 1995ApJ...451..359M Keywords: ISM: H II REGIONS; ISM: JETS AND OUTFLOWS; STARS: BINARIES: SYMBIOTIC; STARS: INDIVIDUAL CONSTELLATION NAME: R AQUARII; STARS: PECULIAR; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (1) MAST (1)

Hubble Space Telescope imaging of Eta Carinae

We present new high spatial resolution observations of the material around η Carinae obtained with the Hubble Space Telescope Wide Field/Planetary Camera. The star η Carinae is one of the most massive and luminous stars in our Galaxy, and has been episodically expelling significant quantities of gas over the last few centuries. The morphology of the bright central nebulosity (the homunculus) indicates that it is a thin shell with very well defined edges, and is clumpy on 0.2 (~10^(16)cm) scales. An extension to the northeast of the star {NN/NS using Walborn's [ApJL, 204, L17 ( 1976)] nomenclature} appears to be a stellar jet and its associated bow shock. The bow shock is notable for an intriguing series of parallel linear features across its face. The S ridge and the W arc appear to be part of a of emission located to the SW and behind the star. Together, the NE jet and the SW cap suggest that the symmetry axis for the system runs NE-SW rather than SE-NW, as previously supposed. Overall, the data indicate that the material around the star may represent an oblate shell with polar blowouts, rather than a bipolar flow.