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8 Inch Reflector Observations in ORI: Alnitak, lambda, eta, sigma, theta, 52, 42 and STT517

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#1 Nucleophile

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Posted 22 March 2017 - 10:16 PM

Just got in from a quick study of some doubles in Orion with my 8 inch f/5.9 reflector.  I had a 7T6 eyepiece in for most of the time giving a magnification of 171x.

 

First up was Sirius showing the Pup about 40% of the time as a distinct entity out of the glare of the primary.  Encouraged that conditions were beneficial, I moved over to the Trapezium and was pleased to see E and F clear and steady 100% of the time.  This observation allowed me to gauge the seeing as 4 out of 5.

 

Easily split at this magnification were Alinitak [mag: 1.9, 3.7; sep:  2.4"], Eta [mag:  3.6, 4.9; sep:  1.8"], and Meissa [lambda; mag: 3.5, 5.5; sep:  4.5"], which all showed as splendid magnitude contrast doubles with mostly white stars.  Sigma was also a fine sight showing the AB 'primary' along with the fainter C and D components.

 

52 Orionis [mag:  6,6; sep: 1.0"] was clearly resolved (but not split) at this magnification and resembled a snowman with mostly white stars of similar magnitude.

 

I knew this was a night to try to see the companion of 42 Ori [WDS 05354-0450 DA4AB; mag:  4.6, 7.5; sep: 1.2"].  I was first introduced to 42 Ori in pursuit of data to support Sissy Haas' double star research program.  I find this double very challenging for the 8 inch and only resolvable on nights of very good seeing. For this binary I upped the magnification to about 550x using a Pentax 2.5XO along with a Paracorr lens (setting 1).

 

I was encouraged to see the secondary about 50% of the time in the correct pa using a method of alternating averted and direct vision.  The secondary was more or less a light yellow-orange blur vs a distinct orb of light, and probably best described as resolved but not split.  Last month I spent considerable time measuring 42Ori with the 15 inch at f/23.5--perhaps I can find a lucky image to post from these studies.

 

Finally, I managed to star hop over to STT 517AB [WDS 05135+0158; mag:  6.8, 7; sep:  0.7"],  a binary I had made note of on my CDSA vol I edition as a good challenge for the XT8i.  High magnification (550x) was used here as well to afford a very nice pair of close, evenly matched white star that were 'kissing', that is resovled, but not quite split.  I may try to image this one tomorrow night if conditions are favorable.

 

I think I will head back out now to look at LEO.  smile.gif


Edited by Nucleophile, 22 March 2017 - 10:50 PM.

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#2 Nucleophile

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Posted 23 March 2017 - 10:16 PM

42 Orionis is very difficult to image.  I managed to fish out about 5 good frames from about 2400 to make the highly processed composite shown below.  Fortunately, the advent of Reduc and (more recently) Speckle Tool Box (STB) allows one to use interferometric techniques to determine measures instead of relying on lucky imaging.

 

Also shown below is a composite image of 52 Orionis which was measured using the autocorrelation program within Reduc (S4 filter).  [the label under the image says the measures were done using STB, but this is a mistake].  52 Ori is so much easier to image despite being a bit tighter than 42 Ori.

 

Both images were obtained on the same night (22 Feb 2017) at f/23.4 with an ASI 178 MC camera using my 15 inch reflector fitted with a powermater 5x/paracorr train along with an orange filter.

 

          42Ori52Ori.jpg


Edited by Nucleophile, 24 March 2017 - 09:25 AM.

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#3 Nucleophile

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Posted 24 March 2017 - 09:25 AM

...and here are composite pics of Meissa and Alnitak taken on the same night as the previous images under the same conditions.

 

          MeissaAlnitak.jpg

 



#4 Organic Astrochemist

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Posted 24 March 2017 - 11:06 AM

Great report and images.

I also find that 500X to 600X is a great magnification for splitting/resolving tight doubles with the 8". I don't have a paracorr so for the tightest pairs I wait for the stars to drift close to on axis to confirm my result. However usually the coma, while noticeable, doesn't prevent me from resolving the pair.

#5 Nucleophile

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Posted 24 March 2017 - 11:18 AM

And finally, my first ever attempt at imaging the Trapezium (theta orionis).  The E and F stars are visible, albeit underexposed; I had to crank up the gamma a bit to get them to show up.

 

        Trapezium.jpg


Edited by Nucleophile, 24 March 2017 - 11:19 AM.


#6 Nucleophile

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Posted 24 March 2017 - 11:24 AM

Great report and images.

I also find that 500X to 600X is a great magnification for splitting/resolving tight doubles with the 8". I don't have a paracorr so for the tightest pairs I wait for the stars to drift close to on axis to confirm my result. However usually the coma, while noticeable, doesn't prevent me from resolving the pair.

I find the Paracorr gives me a tiny bit of extra resolution on very difficult doubles.  I try to avoid using it with the XT8i most of the time because its mass puts an undue strain on the poor Crayford focuser.  The Moonlite focuser on my Obsessioin has no such issue.



#7 Magnus Ahrling

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Posted 24 March 2017 - 07:52 PM

Nucleophile!

 

Fantastic report and images. I am really impressedsmile.gif

Next winter 42 is prio 1 for me to try.

 

Magnus 57N.



#8 Nucleophile

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Posted 25 March 2017 - 11:33 PM

Last night I observed a few more doubles in Orion through the XT8i--the images through the eyepiece were not as great as the night reported above because the seeing was only a 2.5 out of 5.

 

STT 90AB (mag:  7, 9; sep:  1.8"; WDS 04549+0836):  a single white star at 171x and 240x (Pentax 5XW); no discernible hint of duplicity on this attempt--not sure why; perhaps an image will shed some light on the situation [pun intended].

 

STT 98 (mag:  5.8, 6.7; sep:  0.9"; WDS 05079+0830):  a single yellowish-white star at 171x; resolved 50% of the time from merely extended to two yellowish stars at 340x (Pentax 3.5XW) with the secondary clearly smaller than the primary; a challenging system for the XT8i that begs revisiting and/or imaging.

 

32 Orionis (mag:  4.4, 5.8; sep:  1.3"; WDS 05308+0557:  extended only at 171x; resolved to two discs at 240x, secondary is yellow and primary is white; very nice, will get a picture with measurements soon if I can.

 

STF 726 (mag:  7.9, 8.6; sep:  1.1"; WDS 05309+1015):  a faint tight pair for the XT8i; 240x:  mostly a single white star; 340x:  at most, slightly extended; this one is very challenging due to faintness--will revisit on a night of better seeing.  This binary would be ridiculously easy for the 15 inch as mag 8 is the Goldilocks sweet spot for that instrument.

 

Tau Orionis (an interesting quadruple not far from Rigel; H V 25 = AB; BC = Bu188; mag:  3.6, 11, 10.9, 10.9; sep AB = 33"; AD= 35"; CD = 3.8"):  171x shows BC as a single faint star with direct vision and puts D in a favorable spot for an averted view detection.  In Jan of 2016 I logged a split of the BC pair at 569x using the 15 inch reflector and obtained the following lucky image of the system using my Nikon:

 

         TauOrionis.JPG

 

The DSLR image shows C quite a bit fainter than B; I will re-image using the ASI 178 camera and use the DeltaMag function of Reduc to see what information that yields.


Edited by Nucleophile, 26 March 2017 - 09:18 AM.

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#9 Nucleophile

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Posted 30 March 2017 - 06:40 PM

Last night I was able to re-image Tau Orionis with the ASI 178MC at f/9.  Again, the image shows the C component much dimmer than the B star.  From a composite image I used Reduc to assess delta mag for the D-B pair as 0.5 and 1.1 for the B-C pair.  Assuming the listed value of the D component is in the correct ballpark (11ish), this puts the magnitude of the C component above 12 and at odds with the WDS listed value.

 

         TauOrionis_2017.jpg


Edited by Nucleophile, 30 March 2017 - 06:41 PM.


#10 fred1871

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Posted 30 March 2017 - 08:45 PM

Mark, looking at your first photo of the Tau Orionis stars using the Nikon, and then getting what data I could via Simbad, I reached a similar conclusion.

 

Simbad gives mags for D, as 10.9 (V) and 10.75 ®.

For B and C only R magnitudes were listed, 11.58 and 12.56. In Red that gives a Delta-m of ~1.0. Not much different than your assessment using Reduc.

 

If we go with that for V as well (despite not knowing spectral types), and assume as we both have done that D is 0.5 mag brighter than B, then the B and C magnitudes are 11.4 and 12.4. Or 12.5 for C via Reduc. That's obviously a better fit for the first photo. And a useful first step to correction for the WDS.

 

Incidentally, based on how these images show on my computer screen, the Nikon is doing better than the ASI camera. Of course, it could be due to different exposure times - 1 sec versus 4 fps. If you've stacked the images for the AVI camera how does the total exposure time compare? Overall, how do you evaluate the respective sensitivity and resolution of the two cameras? 


Edited by fred1871, 30 March 2017 - 09:06 PM.


#11 Nucleophile

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Posted 30 March 2017 - 09:53 PM

Hi Fred,

 

The pictures posted from my ASI camera are enough removed from the raw data due to processing to eliminate some signal; the ASI actually does a much better job at detecting faint stars than the Nikon.  What I see on the screen right after capture always has more signal than the composites I post.

 

This was sort of a one-off attempt to get some data through holes in the clouds on a night of rapidly degrading seeing; a subsequent try would have me ramp up the integration time to say 300ms or so (and possibly up the gain as well) to get more signal for 'C".  The image posted was a stack of 22 frames.

 

The faintness of C at about 250ms also lead me to conclude the magnitude was about 12.5



#12 ssmith

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Posted 30 March 2017 - 10:25 PM

Fred, Mark -

 

I photographed Tau Ori  back in January.  Attached is a cropped unprocessed .jpg photo.  I extracted the green channel from the raw file, converted it to Fits format, plate solved and ran it through Astrometrica.  The magnitudes derrived from Astrometrica are shown on the photo.

Attached Thumbnails

  • Tau Ori 120mm 1-27-17 148.jpg

Edited by ssmith, 30 March 2017 - 10:26 PM.

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#13 fred1871

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Posted 31 March 2017 - 12:56 AM

Very nice photo Steve - as usual with your images. smile.gif

 

Is this another of the DSLR shots? ISO listing suggests it is.

What camera? - as the sensors vary from one brand to another, and even one camera model to another within a brand.



#14 Nucleophile

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Posted 31 March 2017 - 05:18 AM

Steve:  can you refresh my memory as to the software you use for plate solving?  Thanks.



#15 ssmith

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Posted 31 March 2017 - 07:29 AM

Fred, Mark -

The camera is an Olympus E-PL5 (micro 4/3 format).

For plate solving I use the on-line site @ astrometry.net.
Astrometrica also allows you to manually plate solve a given photo.

I have many more photos of Tau Ori not only from this particular session
But also from 2016 & 2014 as well. Perhaps over the weekend I can refine
the magnitude values.

#16 Nucleophile

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Posted 31 March 2017 - 06:25 PM

Thanks for the information, Steve.




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