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Short session in CrB

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#1 WRAK

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Posted 02 July 2013 - 02:57 PM

No session without questions it seems. Yesterday clear night but arriving home late - so I preferred to select the 140mm refractor instead of the planned C9.25 to avoid thermal issues. Very good conditions for my location: Moon below horizon, NEML ~3.3mag, Pickering ~7, good transparency. Short session in CrB:

Name ID RA Dec Sep M1 M2

STF1951 HIP 75913, WDS15303+2739 15h 30m 20.3s +27:39:29.8 17.0 7.89 11.88: x40 very faint at 8 o'clock, x75 confirmend. Limit aperture 120mm - one more example how I overestimated the influence of light pollution on TML

STF1941 HIP 75519, WDS15257+2638 15h 25m 42.8s +26:37:40.5 1.4 9.65 9.77: x140 at 5:30, clear separation x200/280 only with averted vision, limit aperture 110mm

STF1936 WDS15211+2702 15h 21m 07.6s +27:02:23.4 19.8 9.92 10.09: x40 at 6:30, limit aperture with averted vision 55mm

STF1932 HIP 74893, WDS15183+2650 15h 18m 20.2s +26:50:24.7 1.6 7.32 7.41: x75 elongation at 2 o'clock, x140 clear separation. Limit aperture 60mm with averted vision - this is about 20% below Dawes. Something is odd here

Beta CrB HIP 75695, JEF1, WDS15278+2906 15h 27m 49.8s +29:06:19.8 0.2 3.68 5.2: Used only as Hop zu STF1937

STF1937 Eta CrB, HIP 75312, WDS15232+3017 15h 23m 12.2s +30:17:17.7 0.6 5.64 5.95: x280 clear elongation 11 to 5 o'clock. Result too good to be true. Eta CrB is a fast moving double, so may be 0.6" is no longer valid

STF1963 HIP 76536, WDS15379+3006 15h 37m 53.7s +30:06:10.4 5.1 8.54 8.85: x40 at 8:30. Limit aperture 45mm

Theta CrB COU610, HIP 76127, WDS15329+3122 15h 32m 55.8s +31:21:32.9 0.8 4.27 6.29: Again nothing

HU746 HIP 76242, WDS15344+3201 15h 34m 26.3s +32:01:01.3 2.1 8.85 11.59: No resolution

STF1959 WDS15347+3446 15h 34m 44.1s +34:43:22.8 2.1 9.79 10.81: x75 at 7 o'clock. Limit aperture 100mm

STF1964 HIP 76563, WDS15382+3615 15h 38m 13.0s +36:14:48.3 14.0 7.85 8.06: The given parameters are these of the main components - resolution x15 at 7:30. Should be a double-double. x140 resolution of the upper star at 11 o'clock with separation 1.6" with +8.07/9.02mag with aperture limit 95mm, no resolution of the lower star.

STF1965 Zeta CrB, HIP 76669, WDS15394+3638 15h 39m 22.7s +36:38:09.0 6.0 4.96 5.91: x40 at 8 o'clock. Limit 25mm

Finally a jump to 90 Her (BU130) 1.6" +5.28/8.76mag: No resolution despite near zenith position.

Remaining questions:
- advertised data of STF1932 correct? Limit aperture of 60mm suggests larger separation
- current separation of STF1937 (Eta CrB) still 0.6"? Observation suggests larger separation
- Theta CrB again - the probability that this one does not show with 140mm aperture at least a pointed elongation seems low, companion must be fainter
- configuration of STF1964 is somewhat unclear to me, especially the position of HU1167 and the advertized data in total. There should also be another 0.1" component with only 1 observation. I found only one photo on the web (http://www.google.at...=1&tx=115&ty=89) suggesting that the companion of the second star is much fainter and that the second star may be even a triple
- 90 Her: Should be despite delta-m of 3.5 rather easy with 140mm, makes curious.

Wilfried

#2 Nucleophile

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Posted 02 July 2013 - 08:01 PM

Great report, Wilfried. And very productive for a "short session".

I saw Eta CrB as extended and then eventually as resolved using the 8 inch.

I will take a peek at 90 HER again tonight with the 8 inch as it has given more trouble than expected lately with a few folks.

I also like the data for STF 1959 for assessing variables in my 8 inch calculator.

CrB is overhead in Dobson's Hole for me once twilight has faded.

I have hundreds of observations with my 15 inch, but only a dozen or so good ones for the 8 inch--I need to fix that. Mining the 15 inch data for meaningful correlations will be a task indeed.

#3 fred1871

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Posted 02 July 2013 - 08:08 PM

Wilfried, Eta CrB has an ephemeris listing (6th orbit catalog) of 0.67" for 2013 and 2014.

I've observed it twice recently, as I mentioned in the "Comparative session..." thread. Both times, 140mm refractor, 400x, clear elongation with suggestions of notching in the best moments. So, yes, the modest increase from 0.6" to 0.67" makes a difference.

I'd think your "clear elongation at 280x" fits with the ephemeris and with what I'm also seeing.

#4 fred1871

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Posted 02 July 2013 - 08:23 PM

Agreed with Mark, a very productive session for a "short" one. And there are some doubles you've looked at that were not on my list; thanks for that. Most interesting is the "double-double" STF 1964 - I'll try that one on the next clear night. I'd think it should be possible with 140mm for both pairs in a dark sky; the current WDS gives AB (m 8.07, 9.87) as 1.2" in PA 079 for 2012, and CD (m 8.06, 9.02) as 1.5" in PA 021 for 2012.

The AB pair is likely to be difficult, closer than CD and bigger delta-m (1.8 compared to 0.96). Your success on CD with 140x makes me hopeful of AB as a "limit" observation with 140mm in good conditions. If not, there's always the 235mm SCT that we both have. :grin:

#5 WRAK

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Posted 03 July 2013 - 07:25 AM

0.67" makes the observed elongation of Eta CrB a bit more plausible.
Regarding STF1964 - the second double is certainly a bit more difficult than the first one, will try again.
Wilfried

#6 WRAK

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Posted 05 July 2013 - 08:21 AM

Reason was to check if I could do it better with a larger aperture compared to last time. Sky a tad darker with NEML +3.5mag (more or less the best I can get at my site) but air somewhat turbulent with seeing Pickering 5-6. The C925 had enough time for temperature adaptation and was equipped with the 225mm iris meaning a base CO of 0.4. Collimation was not checked as I hoped for some stability.
As a starter I visited Izar - with x335 the companion made the impression of a small planet using the third diffraction ring as orbit around the primary. Nice picture but not as beautiful as with the 60mm mask.
Then to the CrB session:
- STF1951: x100 very faint at 9 o'clock. Limit aperture 120mm with surface equivalent 80mm refractor - is this a possible TML value for NEML +3.5mag?
- STF1941: x180 at 6. Limit 150mm = surface equivalent 120mm refractor
- STF1936: x40 at 7. Limit 110mm = surface equivalent to 63mm refractor for TML statistics
- STF1932: x100 at 2. Limit 130mm = surface equivalent to 94mm refractor
- Eta CrB: No resolution but enhanced brightness in the diffraction pattern at the 5 o'clock position. The position would be OK but I suspect rather a collimation problem
- STF1963: x40 at 9. Limit 105mm = surface equivalent to 54mm refractor
- Theta CrB: Again no resolution and again enhanced brightness in the 5 o'clock direction. Would again ~ fit the position but as above
- HU746: x335 at 5, but very faint. Limit 225mm = surface equivalent to 206mm refractor
- STF1959: x180 at 7. Limit 160mm = surface equivalent 133mm refractor
- STF1964: AC x40 at 7:30. CD x100 elongation at 11, x180 clear split. Limit 180mm = surface equivalent to 156mm refractor. No resolution for AB (HU1167) - again collimation issue
- Zeta CrB: x40 at 8. Limit 100mm = surface equivalent to 44mm refractor.
Finally again 90 Her and again no resolution - probably collimation issue and also seeing has gone worse.

Result: Did not much better as with the 140mm refractor with the exception of HU746 as seeing was somewhat worse and collimation was neglected - will not do this again. Regarding limit apertures: Will have to check if the calculation of the surface equivalent refractor diameter is of any use.
Wilfried

#7 R Botero

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Posted 07 July 2014 - 04:08 AM

Hello All

After a long hiatus (a few moths only really... ;)) without a mount and not much time to observe, I wheeled out my TEC MC250 last night for collimation and star testing. Tried Eta CrB after achieving collimation using a webcam and got a nice split at PA 180-190. I believe the current reported separation is 0.7 or thereabouts so I was pleased with my result given the conditions last night were not the best.
I still need to tweak my 10" TEC a bit more to achieve perfect focus with binoviewers so will test this beautiful pair again when it clears.
Cheers

Roberto

#8 WRAK

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Posted 07 July 2014 - 04:30 AM

Nice to hear from you again.
Wilfried

#9 R Botero

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Posted 07 July 2014 - 05:51 AM

Cheers Wilfried - it's good to be back :cool:. I've been lurking in the background without much to add but plenty to read! ;)

Roberto

#10 WRAK

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Posted 08 August 2014 - 10:29 AM

Weather is currently not very cooperative so I was pleased to have an unexpected clear sky last night. Did not exactly repeat the session mentioned above but visited again Eta CrB 0.7" +5.64/5.95mag with my 140mm refractor. With a magnification of x420 I got a very distinctive rod at 11:30 (later checked for correct position). Applied then central obstuction of 0.1 and got for fractions of seconds hints of a split despite the 3/4 moon making the sky really light grey.

Tried later on also Theta CrB 0.8" +4.27/6.29mag but got nothing.

Most of the time in this session I used for experiments regarding influence of CO size on limit aperture for resolution.

 

A1369 4.1" +10.66/11.46mag. With 140mm and magnification of x70 hint at 9 o'clock, x140 then clearly 8:30. With x200 limit aperture with averted vision 135mm. No change with with CO 0.1. With CO 0.15 then 140mm - should have continued here to the point of non resolution but missed this opportunity.

 

STF1963 5.1" +8.54/8.85.mag. Resolution with 140mm and magnification of x75 at 8 o'clock. With x140 limit aperture 50mm. Same with CO 0.28, with CO 0.38 limit aperture 55mm and with CO 0.47 limit aperture 65mm.

 

STF1959 – 2.1"DS +9.79/10.81mag. With 140mm and magnification of x200 resolution at 7 o'clock. Limit aperture 128mm. With CO 0.21 limit aperture 133mm and with CO 0.25 limit aperture 140mm.

I hope with some more observations of this kind I will be able to find a statistical significant relationsship between CO size and limit aperture with respect to the other parameters of the objects.

 

Wilfried

 



#11 WRAK

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Posted 09 August 2014 - 05:17 PM

Two clear nights in a row - nice. Repeate/continue CrB session. Seeing slightly worse than last night. Eta CrB hints of rod 11:30 but with jumping image and not very clear.

Yet really nice double-double in CrB is STF1964:

AC – 14.7" +8.07/8.07mag. Resolution with 140mm and magnification of x18 at 7:30, with x75 limit aperture 25mm

CD – 1.5" +8.07/9.02mag. This is the northern star of the AC pair. With 140mm and magnification of x140 resolution at 11 o'clock, with x280 limit aperture 105mm

AB (also designation HU1167) – 1.2" +8.07/9.87mag. With 140mm and magnification x200 resolution at 1 o'clock. Limit aperture stays with140mm.

Wilfried



#12 WRAK

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Posted 25 August 2014 - 04:05 PM

CrB is already a bit low in the sky for me but last night I got the probably last opportunity this season or another session in this constellation. Seeing was for my location rather fair and I got some very good results with for example a distinctive elongation/rod for Gamma CrB - 0.6" +4.04/5.6mag with 140mm aperture. On the other side I got rather disappointing results like a non resolution of STF2022 - 2.2" +6.54/10.03mag with the same aperture (last year I got here a resolution as well). An explanation might be thin veil clouds passing quickly my field of view changing thus seeing conditions also quickly. Such veil clouds were present during the day but in the night I could not see them against the grey sky in my location due to light pollution. First time I made such an experience.

Wilfried

PS: Did also an interesting experiment regarding influence of CO size for telescope magnitude limit. The faintest star I could see with 140mm and zero CO near Alpha CrB was UCAC4 listed with +12.25mag. The next faintest star had +12.65mag - so TML had to be somewhere in between. I tried then different CO values with 0.25, 0.35 and 0.4 but got each time the same result meaning basically that CO size plays despite the reduction of the photons sampling surface a rather modest role regarding TML. Might not be such a surprise but I like things to be verified by experiment results








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