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[SII] Observations and what they can tell us. Snippets of possibly useful stuff by Lesa Moore 31 st October 2012. Forbidden lines. Lifetime in excited states Lyman a : 10 -8 s [SII]: 3846 s and 1136 s Forbidden lines appear in low-density gas:

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sii observations and what they can tell us

[SII] Observations and what they can tell us

Snippets of possibly useful stuff by Lesa Moore

31st October 2012

forbidden lines
Forbidden lines
  • Lifetime in excited states
    • Lyman a: 10-8 s
    • [SII]: 3846 s and 1136 s
  • Forbidden lines appear in low-density gas:
    • for transitions that have long lifetimes in excited states [SII], [NII], [OII], [OIII]
    • where there are too few collisions to de-excite collisionally (< a few hundred thousand cc-3)
spectra on the ccd
Spectra on the CCD

OI sky emission at 5577Å

OH sky emission bands

most common emission lines
Most common emission lines
  • “A brief introduction to narrowbanding”
    • http://www.astrosurf.com/brego-sky/A_glimpse_to_the_night_sky/Articles_files/what_is.pdf
targets
Targets
  • Emission nebulae
  • Planetary nebulae
  • Supernova remnants
exercise 3
Exercise 3

In between, ratio describes actual gas density

    • http://web.williams.edu/astronomy/research/PN/nebulae/exercise3.php
  • Ratio of intensities of [SII] lines
    • l6716 to l6731
    • can indicate gas density

Low density: Ratio is statistical weight (how many electrons the level can hold)

High density: Shorter lifetime (6731) makes stronger line

snr in the magellanic clouds
SNR in the Magellanic Clouds
  • http://www.mcsnr.org/about.aspx
  • SNR classification - meet at least two of the following criteria:
    • Diffuse nonthermal radio emission
    • Diffuse thermal X-ray emission
    • High [SII]/Ha ratio (> 0.4) and/or high optical expansion velocity
snr in m31
SNR in M31
  • http://aas.org/archives/BAAS/v25n2/aas182/abshtml/S219.html
  • High [SII]/Ha implies likely SNR
  • Ratio is not very high for many SNRs
  • Complementary test based on a comparison of the Ha flux and the presence or absence of hot, ionizing stars
  • Combined BVRI, Ha, [SII] data has revealed ~200 objects which are candidate SNRs throughout M31 based on this test
optical imaging and spectroscopic observation of the galactic supernova remnant g85 9 0 6
Optical Imaging and Spectroscopic Observation of the GalacticSupernova Remnant G85.9-0.6
  • http://arxiv.org/pdf/0909.2959v1.pdf
  • Images taken with narrow-band interference filters H and [SII] and their continuum.
  • [SII]/Ha ratio image is performed
    • Ratio ~0.42, indicating that the remnant interacts with HII regions.
  • [SII]ll6716/6731 average flux ratio from spectra
    • electron density Ne is obtained to be 395 cm−3.
  • [OIII]/Hb ratio
    • shock velocity has been estimated
    • pre-shock density of nc = 14 cm−3
    • explosion energy of E = 9.2 × 1050 ergs
    • interstellar extinction of E(B−V ) = 0.28
    • neutral hydrogen column density of N(HI) = 1.53 × 1021 cm−2
the final image
The final image
  • The negative if the [SII]/Ha image of G85.9-0.6 (smoothed)
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