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Seyfert galaxy core of Messier 77 with SA-200

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#1 mwr

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Posted 31 December 2019 - 08:09 AM

Messier 77 is a Seyfert galaxy with an active core that shows emission lines. Encouraged by the bright and star like core that is visible in the image which I took last year, I have tried to obtain a low resolution spectrum of this object with the slitless SA-200 setup:

 

Folie1.JPG

 

The H alpha Balmer line and the forebidden [O III] line are indeed visible as emission lines on a broad continuum:

 

Folie2.JPG

 

The emmission lines should show a redshift (H alpha approx. 24 Angstrom). What would be the best method to measure this redshift with my slitless low resolution setup (if possible at all)?? 


Edited by mwr, 31 December 2019 - 10:46 AM.

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#2 dcornelis

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Posted 31 December 2019 - 09:24 AM

Impressive result, what about calibrating against a bright nearby star?



#3 mwr

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Posted 31 December 2019 - 10:36 AM

Impressive result, what about calibrating against a bright nearby star?

Thanks for the hint! However, the brightest star in the captured field is a M 2 class star without a visible H alpha line (only some broad TiO bands are visible):

 

m77_komplett.jpg



#4 robin_astro

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Posted 31 December 2019 - 12:01 PM

Provided nothing has changed (ie the focal length of the lens for objective grating setups or the distance of the grating to the sensor for non objective setups) you can just take a hot (A/B) reference star with the same setup (even, neater, perhaps, gamma Cas for example would give you a nice H alpha emission line at zero redshift) and wavelength calibrate using that (or simply just measure the ratio of the distance of the H alpha line from the zero order for the galaxy and your reference star which will give you the redshift z directly)

http://www.threehill...o/spectra_3.htm

 

Cheers

Robin


Edited by robin_astro, 31 December 2019 - 12:17 PM.

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#5 robin_astro

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Posted 31 December 2019 - 12:09 PM

It could be tough to detect though at this dispersion. According to NED the redshift is only ~1000km/s (z~0.004) so less than 0.5% increase in the length of the spectrum

https://ned.ipac.cal...wmap=4&corr_z=1

 

Robin



#6 mwr

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Posted 31 December 2019 - 02:57 PM

It could be tough to detect though at this dispersion. According to NED the redshift is only ~1000km/s (z~0.004) so less than 0.5% increase in the length of the spectrum

https://ned.ipac.cal...wmap=4&corr_z=1

 

Robin

I have measured with the same setup during the same session (yesterday night) also the planetary nebula NGC 7662 showing an H alpha emission line (https://www.cloudyni...-blue-snowball/).

A comparison with M77 shows a very small, barely detectable shift (approx. 20 A). This is probably rather non significant taking into account the low resolution of my setup.

 

M77_vs_NGC7662_ppt.jpg

 

 

I will see if it is reproducible next year...


Edited by mwr, 01 January 2020 - 08:48 AM.


#7 descott12

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Posted 07 January 2020 - 08:12 PM

Hello all,

I have never tried to capture the spectrum from non-star object so I figured I would give it a try using my SA-100. 

Still figure out how to stack so this was from a single 9 second exposure.  This was pretty dim and more noise than signal but I was happy to get something at all.

As you can see I have two prominent emissions at around 4500 and 6000 A. But they don't really match anything. They are about the same distance apart as the two peaks in the originally posted spectrum so I think they are the same??

Any ideas?

Also, the original spectrum had Ha at about 4400 A. Was that an incorrect labeling on the a axis?

 

Attached Thumbnails

  • M77-full_spectrum.png


#8 robin_astro

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Posted 07 January 2020 - 09:02 PM

Hi Dave,

 

A great result. The M77 core appears almost stellar so forms a good spectrum even with the Star Analyser. I would say the emission lines are [OIII] and H alpha but your dispersion used to calibrate the wavelength  is out by  about 10% for some reason so the wavelengths are about 10%  low.  (The wavelength scale on the original spectrum at the top of the thread is in uncalibrated, in pixels I think)

 

Cheers

Robin



#9 descott12

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Posted 07 January 2020 - 09:06 PM

Hi Dave,

 

A great result. The M77 core appears almost stellar so forms a good spectrum even with the Star Analyser. I would say the emission lines are [OIII] and H alpha but your dispersion used to calibrate the wavelength  is out by  about 10% for some reason so the wavelengths are about 10%  low.  (The wavelength scale on the original spectrum at the top of the thread is in uncalibrated, in pixels I think)

 

Cheers

Robin

Thanks Robin. Hmmm... I will have to see why the calibration was off.

Ah yes, they were pixels, not wavelength.



#10 mwr

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Posted 08 January 2020 - 04:17 AM


  (The wavelength scale on the original spectrum at the top of the thread is in uncalibrated, in pixels I think)

 

The x-axis is indeed scaled in pixels. I did not label the axes. Bad practice.... (however, the 2nd spectrum in this thread is calibrated https://www.cloudyni...200/?p=9877900)

 


Still figure out how to stack so this was from a single 9 second exposure.

 

Great sensitivity! I had to stack ten 300 second exposures to get the original spectrum which is still quite noisy (f/9.4 and DSLR).
 


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#11 descott12

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Posted 08 January 2020 - 06:40 PM

Here is my spectrum again with the x-axis correctly calibrated. The data is the same but somehow I messed up the calibration up in RSpec. The H alpha line is where it should be.

 

Attached Thumbnails

  • M77.png



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