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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 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

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  1. [SII] Observations and what they can tell us Snippets of possibly useful stuff by Lesa Moore 31st October 2012

  2. 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)

  3. Spectra on the CCD OI sky emission at 5577Å OH sky emission bands

  4. Wavelength-Calibrated Galaxy Spectrum

  5. 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

  6. Targets • Emission nebulae • Planetary nebulae • Supernova remnants

  7. 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

  8. 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

  9. 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

  10. 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

  11. Observations

  12. SNR IMAGES

  13. The final image • The negative if the [SII]/Ha image of G85.9-0.6 (smoothed)

  14. SNR SPECTRA

  15. Measurements

  16. Conclusions from image

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