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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


    Observations
    Observations Galactic


    Snr images
    SNR IMAGES Galactic


    The final image
    The final image Galactic

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


    Snr spectra
    SNR SPECTRA Galactic


    Measurements
    Measurements Galactic



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