Skip to main content

AG Peg, SA-200 spectroscopy, strong line feature

14 posts / 0 new
Last post
hgeagle
AG Peg, SA-200 spectroscopy, strong line feature

I had some fun last night to take SA-200 spectra of AG Peg.

To calibrate wavelength scale and instrument response I took spectra of Altair and followed the instructions for RSpec given by Tom Fields (thanks, Tom!).

Since the spectrum of AG Peg shows an interesting feature, see below, I tried to upload through SPEC-Obs. Unfortunately that app does not seem to work properly  sad : The help file is not accessible anymore, and without instructions I cannot upload anything. Too bad - what happened to the efforts to create a spectral database in AAVSO?

Well, back to AG Peg: AG Peg appears to have a very strong line feature at about 562-563 nm that I cannot identify. Could it be a red-shifted hydrogen line? Help would be highly appreciated!

I have attached the wavelength and instrument sensitivity corrected spectrum of AG Peg. To demonstrate the correctness of wavelength (and intensity) calibration, I prepared a few slides with copies of RSpec calibration "evolution" spectra, i.e. how I ended up with that AG Peg spectrum based on the calibrations with Altair images and spectra (the latter available in RSpec).

Cheers,

Helmar (AHM)

HQA
HQA's picture
SA200 spectra

Hi Helmar,

The first thing that I would be suspicious of is contamination from the zero-order image of another star in the field.  This is one of the reasons why I had the beta SpecObs created, so others could download your image and check for such issues.  I don't know its status since I retired.

However, there are lots of these bright transient objects, and even fainter ones like V404 Cyg can be observed with the SA200 and a moderate aperture telescope.  I hope more SA200 owners take the time to add a grating exposure along with their photometric imaging on these targets.  Someday there will be a spot where you can upload them for others to use.

Ulisse Munari et al. in ATEL 5258 (2013) indicates that the 1850 outburst took a long time to reach its maximum around 6th magnitude, so we may see AG Peg continue to brighten for a long time to come if it is a similar outburst.  He also indicates that much of the quiescent variability is due to ellipsoidal modulation from the 827-day period.  I'm not sure the BSM photometry supports that; someone should download the quiescent CCD photometry and phase it to see if that is what it looks like.

Arne

hgeagle
Re: Sa200 spectra

Hello Arne,

I was suspicious of contamination, too, but I do not see any on my images that would be strong enough. Thus my wish to upload an image to SpecObs for others to scrutinize...

SpecObs is still there, but there is a particular way to upload images and the help file is not available right now. I hope that the webmaster Will will be able to resurrect?!  

I am attaching the SA200 fits image in the interim. Maybe someone is interested to look at the image? There might be a simple explanation for the "strong line feature" I am seeing (e.g. contamination...).

Thanks,

Helmar (AHM) 

Tonisee
Quicklook

Helmar,

I grabbed your image, made a WCS for it, displayed image in DS9, and loaded UCAC4 catalogue over it. It seems, that just in the middle of stronger 1st order, there is a star. I have no idea yet, how bright it is compared to AG Peg.

At the same time - you have both +1 and -1 orders available, try to extract spectrum from opposite side of zero order spectrum (i.e. star image) and see if there is similar bump to what you got previously.

Best wishes,
Tõnis

hgeagle
Re: Quicklook - AG Peg, SA200

Hi Tõnis,

 

Thank you for your quick response/look! smiley

I have attached the spectrum graph of -1 and +1 order. There are some hot pixels above the spectrum of -1 order in my original images (see marks on graph) that produce an additional spike in the spectrum there (but not in +1 order). I looked carefully in my V-filter images, but cannot find a strong enough star in the area of the +1 order spectrum.

Best,

Helmar (AHM)

Tonisee
Bump as a possible star

Hi Helmar,

now it looks more like a real feature. That star inside +1 order spectrum is ~15.6 magnitude one according to UCAC4 catalog (see attachment). It's interesting for sure. There is some structure visible also in +-2 order (double the resolution ;-)), have you checked if those are similar to +1 spectrum?

Best wishes
Tõnis

hgeagle
Re: Bump as a possible star

Hi Tõnis,

I am afraid I do not have enough signal in 2nd order. Our weather here in NE of US isn't very supportive of new measurements right now...

Cheers,

Helmar (AHM)

 

WBY
WBY's picture
WN6 + M3III

VSX lists this pair as WN6 + M3III. There don't seem to be strong lines where you would expect for a WN6. The most prominent emission line should be should be HeII at about 4686. This doesn't look anything like a WN6 to me.  Any ideas what is going on?

Brad Walter

HQA
HQA's picture
calibration

Looking at the original FITS image, I agree that this is likely to be a real spectral feature.  Looking at the higher-resolution spectra on the ARAS site, I'm wondering if the wavelength calibration is wrong, and the emission line is actually Halpha.  Altair doesn't match up all that well, but I don't know what should be expected with a diffraction grating.  Such fun!

Arne

hgeagle
Mystery solved - one fool goes back into his corner...

Hello Arne et al.,

Regarding wavelength calibration - you are saying "Altair doesn't match up all that well...":

I think it actually matches up  very well - regarding the Balmer lines - (I assume you are referring to my earlier spectral comparison between SA200 and reference spectra). I did a 3rd order wavelength calibration on the Altair spectrum, and then applied the same wavelength calibration to AG Peg.  At least I thought I did.

Also I agree to Arne's remarks regarding Halpha. So back to the drawing board:

I made graphs from raw data without wavelength calibration and overlayed Altair and AG Peg spectra (intensity vs. pixel no.): Perfect alignment of Halpha on the pixel scale, see attachment. I also placed the wavelength calibrated Altair spectrum from RSpec underneath: Good alignment of Halpha - Hdelta...

I guess I do not understand RSpec's wavelength calibration (I thought one does it well once, then one can just shift the wavelength zero point to the 0-order peak of the star and apply the same calibration fit). But that obviously did not work - my AG Peg wavelength scale got assigned badly, hm...

So, my apologies and thanks for all who looked into this!   At least I got you thinking smiley...

As usual: Arne is almost right, it all "depends", and I will go back into my corner now...

 

Cheers,

Helmar (AHM)

 

 

Lew Cook
Lew Cook's picture
Does the bump disappear?

If you rotate the camera a little, does it affect the "bump"?

Lew

WBY
WBY's picture
AG Pegassi Comparison Spectra

Aha, so it is the Hα emission line. 

Attached are Four spectra of AG Pegassi that I found in an on-line search of refereed papers (two are in the same figure). It is interesting and expected for an eclipsing system with stars of much different spectral classes that  the spectrum is quite dependent on the orbital phase at the the time of observation as can be seen in Fig 2 of the chemical abundance paper. Am I interpreting correctly from this figure that the absence of the FeII emission at phase 0.56 implies that the hot star is fully eclipsed by the the much larger M3III star?

Brad Walter

hgeagle
Re: AG Pegassi Comparison Spectra

Hello Brad,

Thanks for posting these paper excerpts! I struggled a little to find spectra of AG Peg in the visible...

I think I can handle the wavelength calibration a little better. So, starting from wavelength and instrument response calibrations using Altair images, I think I succeeded to apply those to AG Peg.

Then I used the visible part of the spectrum from Fig. 1 of the first paper you posted (after copying, cropping and changing the transparency of the remaining image) and overlaid it with the "RSpec-massaged" AG Peg spectrum.

I want to share this comparison with you, since I find it quite impressive, i.e. what can be done with an SA-200 grating and an 8 inch telescope in a backyard these days  smiley.

What do you think?

Cheers,

Helmar (AHM)

 

 

 

WBY
WBY's picture
AG Pegasi Spectrum Comparison to Paper

Very impressive. I am becoming aware of the capabilities of the SA200. I recently purchased one for our 610mm aperture  5490mm FL club telescope and have been playing around with it trying to get a spectrum of ASASSN-15lf. 

Try the following URL for all kinds of spectra photometry theory  and orbital dynamics re AG Pegasi:

http://adsabs.harvard.edu/cgi-bin/nph-abs_connect?bibcode=2003MNRAS.339....

You will have to piece it together without breaks or spaces in your browser address window or go to 

http://adsabs.harvard.edu/abs/2003MNRAS.339..125C

and click on the similar articles link. That will take you to the same place. There are a whole bunch of papers, some of them landmark papers, on this star. 

Brad Walter WBY

Log in to post comments
AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484