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Spectrum of Campbell's hydrogen star with SA 100

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#1 mwr

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Posted 06 July 2019 - 07:49 AM

Any suggestions for the element that causes the emmission line at approx. 6720 A (perhaps [SII] of the nebula)?

The other assigments I've made are based on data from: Grosdidier et al.  Astron. Astrophys. 364, 597-612 (2000)

 

Campbell's Hydrogen Star/ PK 64+ 5.1 / BD+30 3639

 


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#2 descott12

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Posted 06 July 2019 - 09:07 AM

That is an awesome spectrum with so many sharp peaks.

A few questions:

 

1. What scope/camera did you capture it with?  I see it was a color camera.

2. I am assuming that that is a raw spectrum as it has a very flat baseline. Do you have  a version that is corrected for your instrument response?

3. How did you capture it? I am learning to use RSpec but I haven't tried stacking multiple captures. I see that you used 10 x 180 seconds.  How exactly did you do that?

 

Thanks in advance



#3 mwr

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Posted 06 July 2019 - 10:06 AM

That is an awesome spectrum with so many sharp peaks.

A few questions:

 

1. What scope/camera did you capture it with?  I see it was a color camera.

2. I am assuming that that is a raw spectrum as it has a very flat baseline. Do you have  a version that is corrected for your instrument response?

3. How did you capture it? I am learning to use RSpec but I haven't tried stacking multiple captures. I see that you used 10 x 180 seconds.  How exactly did you do that?

 

Thanks in advance

It is a rather poor spectrum with a low signal to noise ratio. All "sharp peaks" can be attributed to background noise. Only the broad peaks are real emmission lines from either the central Wolf-Rayet star or the surrounding nebula.

 

1. I used an old Canon EOS 450 Da and a cheap Vixen VMC 110L (Maksutov Cassegrain at f/9.4) with the Star Analyser 100 at a distance of 14 cm to the camera sensor.

2. The spectrum is indeed a raw spectrum without flat or dark correction. 

3. I'm usually also using RSpec but in this case the signal to noise ratio was too low. I have stacked 10x 3 minute subframes" by hand" with Fitswork (Deep Sky Stacker couldn't handle the very noisy image files) and did a Gaussian denoising. Subsequently, I have extracted a pixel line of the spectrum (luminance channel) and imported the corresponding pixel map to Microsoft Excel. Calibration was done by linear regression using H alpha and H beta lines as reference points. 



#4 robin_astro

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Posted 06 July 2019 - 02:49 PM

Any suggestions for the element that causes the emmission line at approx. 6720 A (perhaps [SII] of the nebula)?

The other assigments I've made are based on data from: Grosdidier et al.  Astron. Astrophys. 364, 597-612 (2000)

 

Nice spectrum!

 

There are several possibilities for the line at ~6720A.  It could be a blend but mainly CIII. (6727-6773).  See 

 

An atlas of optical spectrophotometry of Wolf-Rayet carbon and oxygen stars
Authors:
Torres, Ana V.; Massey, Philip

http://adsabs.harvar...ApJS...65..459T

 

Cheers

Robin


Edited by robin_astro, 06 July 2019 - 02:51 PM.

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#5 robin_astro

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Posted 06 July 2019 - 03:20 PM

 

3. How did you capture it? I am learning to use RSpec but I haven't tried stacking multiple captures. I see that you used 10 x 180 seconds.  How exactly did you do that?

 

Don't forget you can capture and pre process your image (convert to mono, dark subtract, align, stack) outside RSpec using another capture/image processing software, just like normal astro-imaging and then pass the pre processed fits image back to RSpec (or use another specialist spectrum processing program) to do the rest of the reduction/calibration. (sky background subtraction, binning, wavelength calibration, instrument response/atmospheric extinction correction)

 

Cheers

Robin



#6 descott12

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Posted 06 July 2019 - 03:24 PM

Don't forget you can capture and pre process your image (convert to mono, dark subtract, align, stack) outside RSpec using another capture/image processing software, just like normal astro-imaging and then pass the pre processed fits image back to RSpec (or use another specialist spectrum processing program) to do the rest of the reduction/calibration. (sky background subtraction, binning, wavelength calibration, instrument response/atmospheric extinction correction)

 

Cheers

Robin

Hey Robin,

Thanks for the tip. I use SharpCap for planetary stuff and EAA. I wonder how it would do with stacking a spectrum? I will give it a try...so few clear nights to do everything!



#7 The Ardent

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Posted 06 July 2019 - 03:45 PM

When observing this I have not seen any nebula with a higher surface brightness in H-alpha.

The central star disappears when filter is added- I’m guessing the star is poor emitter at red and longer wavelengths, and/or the nebula is not transparent in h-alpha.

#8 catalogman

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Posted 06 July 2019 - 04:14 PM

Any suggestions for the element that causes the emmission line at approx. 6720 A (perhaps [SII] of the nebula)?

The other assigments I've made are based on data from: Grosdidier et al.  Astron. Astrophys. 364, 597-612 (2000)

 

This article identifies [SII] at 6724 A:

 

http://articles.adsa...AJ....113.2147H

 

--catalogman


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#9 robin_astro

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Posted 06 July 2019 - 05:33 PM

This article identifies [SII] at 6724 A:

 

http://articles.adsa...AJ....113.2147H

 

--catalogman

Possibly but this refers to the halo region. At this resolution and with the line broadening in the WR star spectrum we cannot fully resolve this region of the spectrum.  The spectrum is that of a late WR star ~WC8 superimposed on Balmer emission (and probably other lines) from the surrounding nebula. CIII from the WR star wind is already prominent at other wavelengths in the spectrum so will be present in this area too.  Here for example is the spectrum of a WC8 star from the Torres/Massey catalogue referenced above (fig10). The feature in question is clear in this spectrum and the spectral components are identified there. The detailed wavelengths are also listed in the paper (tables 3-6)

 

Cheers

Robin 

WC8_spectrum.png


Edited by robin_astro, 06 July 2019 - 05:34 PM.


#10 robin_astro

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Posted 06 July 2019 - 05:48 PM

When observing this I have not seen any nebula with a higher surface brightness in H-alpha.

The central star disappears when filter is added- I’m guessing the star is poor emitter at red and longer wavelengths, and/or the nebula is not transparent in h-alpha.

The central (Wolf Rayet) star is indeed extremely hot but we do not actually see the star surface itself, only the dense stellar wind excited by UV radiation from the star. The continuum spectrum of the wind is relatively flat in the optical and dominated by  broad emission lines, (C,He,O, though not Hydrogen as that has already  been used up or expelled into the surrounding region)

 

(Note the spectrum from the catalogue is a log scale plotted in magnitude for the Y scale so exaggerates the strength of the continuum.)

 

Robin


Edited by robin_astro, 06 July 2019 - 05:56 PM.


#11 mwr

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Posted 07 July 2019 - 02:49 AM

Nice spectrum!

 

There are several possibilities for the line at ~6720A.  It could be a blend but mainly CIII. (6727-6773).  See 

 

An atlas of optical spectrophotometry of Wolf-Rayet carbon and oxygen stars
Authors:
Torres, Ana V.; Massey, Philip

http://adsabs.harvar...ApJS...65..459T

 

Cheers

Robin

 

 

This article identifies [SII] at 6724 A:

 

http://articles.adsa...AJ....113.2147H

 

--catalogman

Many thanks for sharing these articles I wasn't aware of.

 

Planetary nebula with Wolf-Rayet type central stars are really highly interesting objects even for low resolution spectroscopy with the SA 100. I was able to get a spectrum of the central WR star and the surrounding nebula of NGC 40 (bow tie nubula):

 

NGC 40 Bow-Tie Nebula with central Wolf-Rayet carbon star
 
Has been somebody able to get a spectrum of the follwing planetary nebula with central WC stars ?
 
NGC 6751 (glowing eye nebula in Aquila)
NGC 1501 (camel's eye nebula in Camelopardalis)
 
Would it be worth to start a "spectroscopy challenge" on these objects? 


#12 mwr

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Posted 10 July 2019 - 11:30 AM

This article identifies [SII] at 6724 A:

 

http://articles.adsa...AJ....113.2147H

 

--catalogman

Finally I've found an excellent APLY 600 spectrum of this object on the following webpage: 

 

http://www.krannich-...e/spekt_pn.html

 

In the reference list on this webpage a publication that contains the correct assignment can be found: 

 

Auroral and nebular emission lines of SII in the optical spectra of planetary nebulae, 1996 MNRAS,281,1073

 

So I think it's indeed SII 



#13 robin_astro

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Posted 22 July 2019 - 09:14 AM

There is a very high resolution (R=42000) spectrum in the ELODIE archive

http://atlas.obs-hp.fr/elodie/

If we zoom into this region we can see the feature in question is a blend of  wide CIII lines from the WR star with narrow [S II] lines from the nebula at 6716, 6730 A. 

 

HD184738_ELODIE.png

 

All these lines blend into one feature in the much lower resolution Star Analyser spectrum. 

 

Note how the nebular lines in the ELODIE spectrum are doubled due to the expansion velocity of the nebula (we see light coming from the front and back of the transparent expanding shell).  From the the difference in wavelength of the two peaks, the expansion velocity works out to be around 20km/s

 

Cheers

Robin

 

(EDIT:corrected Si to S)


Edited by robin_astro, 22 July 2019 - 09:31 AM.

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#14 robin_astro

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Posted 22 July 2019 - 02:46 PM

Similarly if we zoom in on the H alpha region we find that the line near H alpha in the Star Analyser spectrum is in fact a blend of 3 narrow lines from the nebula ( [NII] at 6548,6583A and  H alpha at 6563A )

 

HD184738_ELODIE_Ha_region.png

 

 

 


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#15 robin_astro

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Posted 24 July 2019 - 12:34 PM

I had a quick look  at this region last night (20 min exposure) using my LHIRES with a 1200 l/mm grating (R=5500)

 

hd184738_20190723_935_Leadbeater.png

 

The [NII], H alpha and [SII] lines from the nebula dominate but expanding the Y scale also reveals He I (?), both in the nebula and in the WR star wind along with other broad WR star features.

 

Cheers

Robin


Edited by robin_astro, 24 July 2019 - 12:36 PM.

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#16 mwr

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Posted 25 July 2019 - 10:37 AM

I had a quick look  at this region last night (20 min exposure) using my LHIRES with a 1200 l/mm grating (R=5500)

 

attachicon.gif hd184738_20190723_935_Leadbeater.png

 

The [NII], H alpha and [SII] lines from the nebula dominate but expanding the Y scale also reveals He I (?), both in the nebula and in the WR star wind along with other broad WR star features.

 

Cheers

Robin

Impressive! That's beautiful science!

According to Aller (RASC J. Vol. 71 (2) 67; Table II) the broad line at approx. 6678 A can be, indeed, attributed to He of the central WR star:

6678.15 He I (major)

6683.2 He II (minor)




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