The Structure of the Atmosphere in Clear Weather by C. J. P. Cave

Blair, William R.

doi:10.1086/141998

Cited by 20 publications

(36 citation statements)

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“…It is worth noting as well that the UV emission-line ratios in NGC 6500 are quite unlike those seen in supernova remnants. Spectra of shock-excited filaments in the Cygnus Loop and of Puppis A with shock velocities of ∼ 170 km s −1 show C IV > He II Blair et al 1995), while in NGC 6500 our upper limit on C IV is a factor of 2 weaker than the strength of He II.…”

Section: Emission-line Diagnosticscontrasting

confidence: 55%

Ultraviolet Emission from the Liner Nucleus of NGC 6500

Barth¹,

Reichert²,

Ho³

et al. 1997

The Astronomical Journal

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As a step towards clarifying the ionization mechanism of LINERs, we have used the Hubble Space Telescope Faint Object Spectrograph to obtain an ultraviolet spectrum of the nucleus of NGC 6500. This is the first time that such a spectrum has been taken of a "LINER 2" nucleus-that is, a LINER lacking broad permitted emission lines like those in Type 1 Seyfert nuclei. Compared with more luminous Seyfert nuclei, the ultraviolet emission-line spectrum of NGC 6500 is remarkable for its low-excitation character: C III] λ1909, C II] λ2326, and Mg II λ2800 are the strongest collisionallyexcited lines in the spectrum, and C IV λ1549 is not detected. We use the emissionline fluxes to test the hypothesis, advanced by Dopita & Sutherland (1995), that the narrow-line regions of LINERs are primarily excited by fast (150-500 km s −1 ) shocks, rather than photoionized by a central continuum source. The fast shock models are a poor match to the observed spectrum, as they predict much stronger emission than is observed for high-excitation lines such as C IV λ1549. Photoionization by an obscured nonstellar continuum source, or possibly ionization by slower (∼ 100 km s −1 ) shocks, are more likely explanations for the emission-line ratios. The origin of the ultraviolet continuum is unclear; its overall spectral shape is reasonably well matched by spectral evolution models for single-burst populations with ages in the range 70-100 Myr, but no definite stellar absorption features due to young stars are present. Alternately, the ultraviolet continuum (or some fraction of it) may be scattered radiation from a hidden active nucleus. We tentatively detect a broad He II λ4686 emission feature, which may be due to Wolf-Rayet stars, although the ultraviolet spectrum does not show any clear Wolf-Rayet signatures. We also find that NGC 6500 is weakly detected in an archival

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Section: Emission-line Diagnosticscontrasting

confidence: 55%

Ultraviolet Emission from the Liner Nucleus of NGC 6500

Barth¹,

Reichert²,

Ho³

et al. 1997

The Astronomical Journal

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“…Likewise, Mg I] 4571Å is predicted to be about half the strength of Hα yet is not seen in either 79C or 80K. Large differences between observed and predicted Mg II intensities are a problem common in young, O-rich SNRs (Blair et al 1994;Sutherland & Dopita 1995) and may simply be indicating an incorrect assumed Mg abundance. However, large differences exist for other UV lines, such as C II] 2324,2325 which is about twice the predicted strength, and this difference grows somewhat larger if internal SN dust extinction is considered.…”

Section: Observed Vs Predicted Late-time Sne Ii-l Emissionmentioning

confidence: 95%

Late-Time Optical and Ultraviolet Spectra of SN 1979C and SN 1980K

Fesen

Gerardy

Filippenko

et al. 1999

The Astronomical Journal

112

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A low-dispersion Keck I spectrum of SN 1980K taken in August 1995 yr after explosion) and a November 1997 MDM spectrum (t = 17.0 yr) show broad 5500 km s −1 emission lines of Hα, [O I] 6300,6364Å, and [O II] 7319,7330Å. Weaker but similarly broad lines detected include [Fe II] 7155Å, [S II] 4068,4072Å, and a blend of [Fe II] lines at 5050-5400Å. The presence of strong [S II] 4068,4072Å emission but a lack of [S II] 6716,6731Å emission suggests electron densities of 10 5−6 cm −3 . From the 1997 spectra, we estimate an Hα flux of 1.3 ± 0.2 × 10 −15 erg cm −2 s −1 indicating a 25% decline from 1987-1992 levels during the period 1994 to 1997, possibly related to a reported decrease in its nonthermal radio emission. A May 1993 MMT spectrum of SN 1979C (t = 14.0 yr) shows a somewhat different spectrum from that of SN 1980K. Broad, 6000 km s −1 emission lines are also seen but with weaker Hα, stronger [O III] 4959,5007Å, more highly clumped [O I] and [O II] line profiles, no detectable [Fe II] 7155Å emission, and a faint but very broad emission feature near 5750Å. A 1997 HST Faint Object Spectrograph, near-UV spectrum (2200 -4500Å) shows strong lines of C II] 2324,2325Å, [O II] 2470Å, and Mg II 2796,2803 A along with weak [Ne III] 3969Å, [S II] 4068,4072Å and [O III] 4363Å emissions.The UV emission lines show a double-peak profile with the blueward peak substantially stronger than the red, suggesting dust extinction within the expanding ejecta (E[B-V] = 0.11 − 0.16 mag). The lack of detectable [O II] 3726,3729Å emission together with [O III] (4959+5007)/4363 ≃ 4 imply electron densities 10 6−7 cm −3 .These new SNe II-L spectra show general agreement with the lines expected in a circumstellar interaction model, but the specific models that are available show several differences with the observations. High electron densities (10 5−7 cm −3 ) result in stronger collisional de-excitation than assumed in the models, thereby explaining the absence of 1 several moderate to strong predicted lines such as [O II] 3726,3729Å, [N II] 6548,6583 A, and [S II] 6716,6731Å. Interaction models are needed that are specifically suited to these supernovae. We review the overall observed range of late-time SNe II-L properties and briefly discuss their properties relative to young, ejecta dominated Galactic SNRs.

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“…The flux detected in the broad F336W filter is dominated by near-UV starlight scattered by dust grains in the Homunculus, but there is also a minor contribution from emission lines of low-ionization metals. In the Outer Ejecta, there is no strong contribution from high ionization lines like Ne iii or Ne v as in some supernova remnants (Sutherland & Dopita 1995;Blair et al 2000). Referring to the archival HST FOS UV spectrum of the S Condensation (see Dufour et al 1999), the strongest emission line in the F336W bandpass is [N i] λ3466.…”

Section: F336w and F658nmentioning

confidence: 99%

Ultraviolet Mg ii emission from fast neutral ejecta around Eta Carinae

Smith

Morse²

2019

Monthly Notices of the Royal Astronomical Society

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We present the first images of the nebula around η Carinae obtained with the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST), including an ultraviolet (UV) image in the F280N filter that traces Mg ii emission, plus contemporaneous imaging in the F336W, F658N, and F126N filters that trace near-UV continuum, [N ii], and [Fe ii], respectively. The F336W and F658N images are consistent with previous images in these filters, and F126N shows that for the most part, [Fe ii] λ12567 traces clumpy shocked gas seen in [N ii]. The F280N image, however, reveals Mg ii emission from structures that have not been seen in any previous line or continuum images of η Carinae. This image shows diffuse Mg ii emission immediately outside the bipolar Homunculus nebula in all directions, but with the strongest emission concentrated over the poles. The diffuse structure with prominent radial streaks, plus an anticorrelation with ionized tracers of clumpy shocked gas, leads us to suggest that this is primarily Mg ii resonant scattering from unshocked, neutral atomic gas. We discuss the implied structure and geometry of the Mg ii emission, and its relation to the Homunculus lobes and various other complex nebular structures. An order of magnitude estimate of the neutral gas mass traced by Mg ii is 0.02 M ⊙ , with a corresponding kinetic energy around 10 47 erg. This may provide important constraints on polar mass loss in the early phases of the Great Eruption. We argue that the Mg ii line may be an excellent tracer of significant reservoirs of freely expanding, unshocked, and otherwise invisible neutral atomic gas in a variety of stellar outflows.

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The Structure of the Atmosphere in Clear Weather by C. J. P. Cave

Cited by 20 publications

References 0 publications

Ultraviolet Emission from the Liner Nucleus of NGC 6500

Ultraviolet Emission from the Liner Nucleus of NGC 6500

Late-Time Optical and Ultraviolet Spectra of SN 1979C and SN 1980K

Ultraviolet Mg ii emission from fast neutral ejecta around Eta Carinae

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