[Nev] Imaging of the Cygnus Loop

Abstract

We present continuum-subtracted images of a 20@ ] 20@ region of the eastern Cygnus Loop (NGC 6995) in the 3425 forbidden line of Ne V. The images reveal bright linear Ðlaments which are associ-A ated with, but not positionally coincident with, bright features seen in Ha, [O III], and other narrowband images. In some areas, the [Ne V] Ðlaments deÐne the edge of X-rayÈemitting regions. The Ðlaments exhibit a peak surface brightness of 1.2 ] 10~4 photons cm~2 s~1 arcsec~2 at the top of the atmosphere in images with typical detection limits of D10~5 photons cm~2 s~1 arcsec~2. We present arguments that these structures are produced by radiative shock waves and discuss implications for the shock velocities and the three-dimensional structure of this section of the Cygnus Loop. We place limits on the importance of thermal conductionÈdriven evaporation as a contribution to the mass of X-rayÈemitting gas. Lack of evidence of [Ne V] emission resulting from thermal evaporation may have signiÐcance for supernova remnants and interstellar medium models that rely heavily on the importance of thermal evaporation. 5 ] 104 K) and the high-temperature regime imaged in X-rays (T º 106 K). The ionization potential of Ne IV is 97.11 eV, so the concentration of Ne V peaks at a temperature of D3 ] 105 K in collisionally ionized equilibrium plasmas. While there are alternative plasma diagnostics in this temperature regime (e.g., O VI, N V), only the forbidden Ne V lines at jj3345.8, 3425.9, corresponding to the 2p2 3PÈ2p2 1D transition, are observable at ground-based optical telescopes ; all other bright emission features formed near this temperature are well shortward of the atmospheric cuto † near 3000 or in the thermal infrared and thus are A the exclusive province of exoatmospheric telescopes. The j3425.9 feature (henceforth integerized to j3425) is preferred for narrowband imaging, since the transition probability is 2.7 times that of j3345.8 transition (Giles 1979 ;Nussbaumer & Rusca 1979 Rowlands et al. (1989) have obtained spectra at the 24.28 km Ðne-structure transition of Ne V in PNs from the Kuiper Airborne Observatory. A key advantage of observing in the [Ne V] j3425 line is that this wavelength is detectable with blue-optimized, backside-illuminated charge-coupled devices (CCDs) on ground-based telescopes of moderate aperture with standard reÑective coatings (aluminum) and ultraviolet (UV) transmissive refractive elements (fused silica or calcium Ñuoride). The images we present in this paper are the Ðrst continuum-subtracted astronomical images in [Ne V] j3425.While photoionized plasmas are characterized by highionization states and low temperatures, collisionally ionized plasma, as exempliÐed by SNR shocks, may have quite high temperatures. The requisite temperatures for strong Ne V concentrations occur behind shock with velocities 190È250 km s~1. For faster shocks, [Ne V] images "" connect ÏÏ hightemperature X-ray images to images of cooler plasmas in the postshock regions of the Ñow (Fig. 1). The morphology exhi...

Far Ultraviolet Spectroscopic Explorer and Hopkins Ultraviolet Telescope Observations of Radiative Shocks in the Cygnus Loop

“…However, work such as the [Ne v] 3425 imaging by Szentgyorgyi et al (2000) and the results presented here demonstrate clearly a partial decoupling between the bright regions of optical emission and the bright UV emission. This partial decoupling causes significant uncertainty in interpretation (see also Danforth et al 2001).…”

SPITZERIRS OBSERVATIONS OF THE XA REGION IN THE CYGNUS LOOP SUPERNOVA REMNANT

“…The value for E B−V obtained from the optical spectrum differs from the usual value for the Cygnus Loop ( §4.2). As a check, we extracted the flux in the [Ne V] 3425Å line in the region of the Spitzer SH aperture from the image presented by Szentgyorgyi et al (2000) and compared it with the [Ne V] 14.33 µm flux, and the ratio agrees with the theoretical value and E B−V = 0.08.…”

“…The reddening-corrected [Ne V] λ3425 intensities were not scaled, because the flux was extracted from the region corresponding to the SH aperture. The uncertainty in the placement of the aperture on the image gives a 7% uncertainty, and Szentgyorgyi et al (2000) quote a photometric uncertainty of 30%. Finally, we normalized the relative fluxes to Hβ = 100, for comparison with the models.…”

The High‐Excitation Planetary Nebula NGC 246: Optical and Near‐Ultraviolet Observations and Two‐dimensional Numerical Models

“…While it is possible for shock heating or hot gas in a thermal conduction boundary layer to contribute to the [Ne v] emission (Weaver et al 1977;Szentgyorgyi et al 2000), the photoionizing flux from the central star is large enough that collisional ionization is not needed unless the density is very high. We therefore consider pure photoionization models.…”