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

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Presentation on theme: "[SII] Observations and what they can tell us Snippets of possibly useful stuff by Lesa Moore 31 st October 2012."— Presentation transcript:

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

2 2 Forbidden lines Lifetime in excited states Lifetime in excited states Lyman  : s Lyman  : s [SII]: 3846 s and 1136 s [SII]: 3846 s and 1136 s Forbidden lines appear in low-density gas: Forbidden lines appear in low-density gas: for transitions that have long lifetimes in excited states [SII], [NII], [OII], [OIII] 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 ) where there are too few collisions to de-excite collisionally (< a few hundred thousand cc -3 )

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

4 4 Wavelength-Calibrated Galaxy Spectrum

5 5 Most common emission lines “A brief introduction to narrowbanding” “A brief introduction to narrowbanding” urf.com/brego- sky/A_glimpse_to_ the_night_sky/Arti cles_files/what_is. pdf urf.com/brego- sky/A_glimpse_to_ the_night_sky/Arti cles_files/what_is. pdf urf.com/brego- sky/A_glimpse_to_ the_night_sky/Arti cles_files/what_is. pdf urf.com/brego- sky/A_glimpse_to_ the_night_sky/Arti cles_files/what_is. pdf

6 6 Targets Emission nebulae Emission nebulae Planetary nebulae Planetary nebulae Supernova remnants Supernova remnants

7 7 Exercise 3 PN/nebulae/exercise3.php PN/nebulae/exercise3.php PN/nebulae/exercise3.php PN/nebulae/exercise3.php Ratio of intensities of [SII] lines Ratio of intensities of [SII] lines 6716 to to 6731 can indicate gas density 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 In between, ratio describes actual gas density

8 8 SNR in the Magellanic Clouds SNR classification - meet at least two of the following criteria: SNR classification - meet at least two of the following criteria: Diffuse nonthermal radio emission Diffuse nonthermal radio emission Diffuse thermal X-ray emission Diffuse thermal X-ray emission High [SII]/H  ratio (> 0.4) and/or high optical expansion velocity High [SII]/H  ratio (> 0.4) and/or high optical expansion velocity

9 9 SNR in M31 html/S219.html html/S219.html html/S219.html html/S219.html High [SII]/H  implies likely SNR High [SII]/H  implies likely SNR Ratio is not very high for many SNRs Ratio is not very high for many SNRs Complementary test based on a comparison of the H  flux and the presence or absence of hot, ionizing stars Complementary test based on a comparison of the H  flux and the presence or absence of hot, ionizing stars Combined BVRI, H , [SII] data has revealed ~200 objects which are candidate SNRs throughout M31 based on this test Combined BVRI, H , [SII] data has revealed ~200 objects which are candidate SNRs throughout M31 based on this test

10 10 Optical Imaging and Spectroscopic Observation of the Galactic Supernova Remnant G Images taken with narrow-band interference filters H and [SII] and their continuum. Images taken with narrow-band interference filters H and [SII] and their continuum. [SII]/H  ratio image is performed [SII]/H  ratio image is performed Ratio ~0.42, indicating that the remnant interacts with HII regions. Ratio ~0.42, indicating that the remnant interacts with HII regions. [SII] 6716/6731 average flux ratio from spectra [SII] 6716/6731 average flux ratio from spectra electron density N e is obtained to be 395 cm −3. electron density N e is obtained to be 395 cm −3. [OIII]/H  ratio [OIII]/H  ratio shock velocity has been estimated shock velocity has been estimated pre-shock density of n c = 14 cm −3 pre-shock density of n c = 14 cm −3 explosion energy of E = 9.2 × ergs explosion energy of E = 9.2 × ergs interstellar extinction of E(B−V ) = 0.28 interstellar extinction of E(B−V ) = 0.28 neutral hydrogen column density of N(HI) = 1.53 × cm −2 neutral hydrogen column density of N(HI) = 1.53 × cm −2

11 11 Observations

12 12 SNR IMAGES

13 13 The final image The negative if the [SII]/Ha image of G (smoothed) The negative if the [SII]/Ha image of G (smoothed)

14 14 SNR SPECTRA

15 15 Measurements

16 16 Conclusions from image


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