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S Aurigae (challenging carbon star)

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#1 LivingNDixie

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Posted 18 March 2013 - 11:34 AM

Hey Everyone!

I was out this past Saturday observing, working on the carbon star list from Astronomical League and came across this star as part of the list. It is a carbon star, variable and is in a pretty crowded field (I was using 22 Pan in my 10in SCT).

However all descriptions I have found for this star say it is really faint, has no color and there is a orange field star that can be mistaken for it.

Last Saturday, I found the orange imposter star quite easily. However finding S Aurigae was very tough, I was about to give up when I saw a little, faint star that was blood red. I was excited and did a sketch and logged the star and moved on. I made a note to look up this star when I got home and see what other observers have seen.

That was when I found one entry on CN of an observer seeing a very faint colorless star. I am seeing a blood red color and it is probably one of darkest red stars I have seen doing this list.

This star varies from around 8 at brightest to around 13.5 at faintest. If I had to guess it is around 12th mag. Also my conditions are rural skies (not super dark) and a several day old Moon was up.

The CSOG guide helped immensely in locating this star, however the pic shows the star near it's brightest, as does wikisky.

If you have a largish scope this little carbon star is worth hunting down right now in my opinion, esp if the color is variable based on how bright it is. I found fainter carbon stars tend to be more red.

S Aurigae
RA 05 27 07
Dec + 34 08 59

#2 Astrodj

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Posted 18 March 2013 - 04:23 PM

Hi Preston,

Thanks for suggesting this one. I agree that when at their faintest carbon stars appear much more red. I was going to check out W Cma tonight (also on the AL carbon star list) so I will see if I can locate S Aur as well.

A look at the AAVSO site shows your mag estimate to be consistent with the latest reports BTW. I printed out a good chart so I won't be fooled by the "imposter". :grin:

#3 LivingNDixie

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Posted 18 March 2013 - 04:30 PM

DJ,
I have never done a magnitude estimate till Saturday, that was my best guess.

Good luck with it, hope you see it. It took me a good 15mins of looking around in the FOV to find it.

Where did you find the charts and estimates on AAVSO?

#4 Astrodj

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Posted 18 March 2013 - 06:23 PM

I'm going to try with the 8" SCT tonight. There's a 6 day old moon in Taurus but that should not interfere too much, I hope.

Here's a link for AAVSO I use. I first like to plot a light curve (the link). Just type in S Aur as the name, set 1200(a good starting point for LPV's), and click plot data.

Once on the light curve page you will notice four links at the top of the plotted light curve.

1. Plot another
2. Search observations
3. Create a chart
4. Search VSX data

#1 Start over.
#2 Gives you the recent observations.
#3 You can create charts.
#4 Data about the star; Mag range, Period, Spectra, etc..

If you make a chart, use the "advanced" portion of the settings area. For your CAT, assuming you are using a diagonal, set the orientation of the chart this way:
North is up, East is on the right.

Set the field of view at 60(seconds of arc, or 1 degree). Or, in your 22mm Pan @f/10, 30 for a 1/2 degree field.

If you want a wider field of view just use multiples of 60.
For a RACI finder change the orientation to North is up, East is left, etc., etc, depending on what scope you are using.

It's a nice tool.

I hope my light pollution does not keep me from finding it tonight! W CMa should be much easier as it is suppose to be quite bright in comparison.

#5 Astrodj

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Posted 19 March 2013 - 12:49 PM

With my handy chart from AAVSO in hand I went hunting for S Aurigae last night, and found it. The chart really helped to confirm the ID in relation to the surrounding star field. I used a 1* FOV chart with stars to magnitude 13, north up and east to the right for the correct orientation in my CAT.

I made a rough(very rough!)sketch so I could check later(which I haven't done yet) to see the limiting magnitude of the 8" SCT for that night. I'll be interested to see the results of that. Using the chart for comparison magnitudes, I felt like S Aur was about 11.5-11.8 mag. I have read that carbon stars, and especially very red ones, are tricky at best to estimate the magnitude visually so take my measurement with the appropriate grains of salt. :thinking:

As for the color, you are so right! An absolutley beautiful gem-like, deep red. I saw the color best at 90x(13.8mm SWA), but 140x(8.8 ES 82*) looked great also. At the higher power I could detect more and fainter surrounding stars while the target star still had very evident color.

I used a 32mm Pl. as my finder eyepiece with the chart. Once I identified S Aur I swithched to the other two eyepieces. The sketch was with the 8.8mm ES.

8" Meade SCT @ f/6.3
13.8mm Meade series 4000 SWA
8.8mm ES 82*

#6 LivingNDixie

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Posted 19 March 2013 - 02:46 PM

DJ,
Sounds like you got it. Glad to hear. I was using a 22 Pan in my 10in f10 SCT. That gives a power of 113X in the scope.

#7 Astrodj

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Posted 19 March 2013 - 02:57 PM

Thanks again for the suggestion. That was a good one!

#8 LivingNDixie

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Posted 19 March 2013 - 03:14 PM

If you like carbon stars, the Astronomical League has a observing program and list for them. I am a huge fan of earning the pins from the Astronomical League!

#9 Rich (RLTYS)

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Posted 20 March 2013 - 08:58 AM

In my 10" refl I got the impression of S Aur being a grayish orange color. An interesting star.

Rich (RLTYS)

#10 LivingNDixie

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Posted 20 March 2013 - 10:13 AM

Rich,
What power were you using and when did you observe it?

#11 Rich (RLTYS)

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Posted 21 March 2013 - 08:59 AM

I observed S Aur while doing the AL Carbon Star Program back in Jan 2011. Used my 10" refl at 76x. I'd estimated S Aur at mag 11.3.

Rich (RLTYS)

#12 ClearSkies.eu

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Posted 27 March 2013 - 10:34 AM

Two observations for this CS in my database, one for 10 March 2007 using an 8" SCT, the other more recently this March 4th using a 12" SCT. In 2007 the star appeared more red to me, at approximately mag. 10. This year it showed a vague orange hue that was evident only when comparing it to field stars.

Preston, great to hear you like the CSOG guides! And nice to read a carbon star observation. A very rewarding object category and lots of fun to observe!






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