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Investigations With an 8 Inch Reflector. Part I: Canis Major, Canis Minor, Lepus, and Monoceros

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#1 Nucleophile

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Posted 03 June 2019 - 02:23 PM

tl:dr version:  I researched and then observed some challenging double stars with an 8 inch reflector; have you observed any of these?

 

This report is the first installment of a series of observational investigations I have made using an 8 inch f/5.9 reflecting telescope.  The goals of this project are threefold:

 

1) empirically develop a predictive resolution calculator for this instrument via construction of a Treanor plot built from observations of carefully selected binaries,

2) investigate angular separation and delta magnitude discrepancies within the WDS through observational and/or photographic examination, and

3) provide a vetted list of double star candidates for other observers wishing to perform their own investigations.

 

Methods
All observations were conducted with an 8 inch f/5.9 Orion XT8i reflecting telescope atop an equatorial tracking platform.  Most observations were made at moderate to high power with an optical train consisting of a Paracorr Type 1 lens (setting 4), a Televue 5x Powermate, and Televue plossl eyepieces (20mm:  345x, exit pupil = 0.6 mm; 15mm:  460x, exit pupil = 0.45 mm; or 11mm:  627x, exit pupil = 0.33 mm.)  A few binaries with larger delta magnitude values were observed at lower powers (173x or 230x) by swapping out the 5x Powermate for a 2.5x Powermate.

 

Double star candidates were selected by visual examination of lists generated from the WDS database using the search engine Stelle Doppie.  Generally, systems containing stars brighter than visual magnitude 10 and a separation greater than 0.56 arcsesconds were screened and sorted by constellation.  For each system the following was also conducted:  a) examination of the speckle data contained within 4th Catalog of Interferometric data; b) examination of any data provided by the Gaia satellite through the DR2 release.

 

Where necessary, independent measures will be obtained using a 15 inch reflecting telescope equipped with an ASI290MM CMOS camera operating at f/13.  Data will be processed using Speckle Tool Box (STB) to generate separation and position angle data.  The bispectrum feature of STB may allow a measure of delta magnitude in some instances.

 

Observations were made on nights of seeing graded as good or better (≥ 3 out of 5; Danjon scale).  Observational descriptors mostly included:  single star, elongated (or pointy), resolved (meaning two discs visible), and split (dark space seen between discs.)  Particular interest was given to objects sitting on the border of elongated and resolved—these are termed ‘limit objects’ and will be the basis for construction of the resolution calculator if the separation value is deemed accurate.

 

To be considered a vetted double star candidate, Tycho satellite green channel (530 nm) magnitude data must be available (and this is what is listed.)  For each system, the separation data was scrutinized and the most accurate value was inferred by assessing the following:  last precise, orbital data (if available), speckle interferometry historical record, the author’s own measures, and/or Gaia DR2 data (if available.)  When two or more sources of separation data converged and followed the historical trend, the information was considered ‘solid’.  In many instances, the separation data was scant, inconsistent, or old; in these cases, the objects require additional measures before the observational data can be used for construction of the resolution calculator.

 

Canis Major

Hu 1240 (06200-1741) mags 8.90/9.68; pa = 239°; sep = 0.632”, 2016 (scant data)
345x:  elongated only; below resolution limit; separation re-measure desired

 

I 765 (06592-2123) mags 9.15/9.72; pa = 317°; sep = 0.586”, 1993 (data is old)
345x:  very faint pair; pushes past elongated to resolved 20% of time with secondary seen as smaller; suspect separation is greater than 0.586”—re-measure desired

 

Hu 112 (07018-1118) mags 7.03/7.70; pa = 197°; sep = 0.62”, 2014 (solid data)
345x:  pointy in correct pa;
460x:  snowman shape, but not resolved; just below resolution limit; will get a re-measure of separation as this is an important data point

 

SEE 79 (07263-2810) mags 8.75/8.87; pa = 305°; sep = 0.721”, 2015.5 (Gaia DR2, solid data)
552x (Pentax XO 2.5/Paracorr Type 1, setting 1):  pushes past resolved to split 50% of time, stars are two even points of light

 

Bu 568 (06238-1947) mags 6.85/8.18; pa = 185°; sep = 0.849”, 2017 (solid data)
460x:  mostly pointy, but 20% of time small secondary disc seen touching primary; just above resolution limit; surprisingly difficult—will get a re-measure of separation

 

Bu 324AB (06497-2405) mags 6.56/7.93; pa = 210°; sep = 1.797”, 2015.5 (Gaia DR2, solid data)
345x:  easily split; secondary a bit whiter and smaller than primary

 

Bu 328AB (07067-1118) mags 5.70/6.91; pa = 111°; sep = 0.58”, 2003 (data is old)
345x:  single star;
460x:  diffraction ring brightens to show distinct secondary as resolved 20% of time;
627x:  persistent blur in correct pa sharpens to resolved secondary 40% of time; just above resolution limit; separation re-measure desired

 

Bu 753 (06287-3222) mags 7.60/5.86; pa = 43°; sep = 1.177”, 2015.5 (Gaia DR2, solid data)
345x:  easily split, secondary is much smaller; Gaia DR2 indicates the presence of a third star:  a mag 5.9 component separated from A by ~0.52” and possessing a similar proper motion as B; WDS note:  Bu 753 is variable; will get an image to see if there are indeed three stars

 

Bu 18 (06167-12) mags 7.06/8.42; pa = 286°; sep = 1.872”, 2017 (solid data)
345x:  split without difficulty, averted vision helps visualize fainter secondary

 

Canis Minor

A 2866 (07267+0424) mags 9.34/10.04; pa = 138°; sep = 0.671”, 2015.5 (Gaia DR2, solid data)
preliminary evidence indicates this is a limit object; unfortunately, details of observing notes are lost; will need to re-examine next season

 

Lepus

Bu 884 (05030-1226) mags 8.98/9.44; pa = 12°; sep = 0.6”, 1991 (data is old)
345x:  at most object is pointy or elongated past being a single star; definitely below the resolution limit (too faint and too tight); re-measure of separation needed

 

B 1951 (05467-2101) mags 8.54/9.48; pa = 243°; sep = 0.62”, 1991 (data is old)
as yet unobserved; requires separation re-measure

 

A 3018 (05457-1447) mags 9.43/9.39; pa = 303°; sep = 0.707”, 2017 vs 0.909”, Gaia DR2 (significant separation discrepancy)
as yet unobserved; requires separation re-measure

 

Hu 106 (06093-1141) mags 9.44/9.98; pa = 332°; sep = 0.74”, 1991 (data is old)
345x:  viewed for a long time; was an extended rod the vast majority of the time with possible resolution to two discs <10% of the time; right at resolution limit; requires re-measure of separation

 

Bu 314AB (04590-1623) mags 5.92/7.50; pa = 315°; sep = 0.73”, 4th Int. Cat. estimate
460x:  resolved to a dot from a blur of light about 20% of time;
627x:  similar to 460x observation but separation a bit wider when seeing allows; this object is at the limit of resolution, requires a re-measure of separation

 

Bu 320AB Nihal (05282-2046) mags 2.90/7.50; pa = 8°; sep = 2.670” (2015.5, Gaia DR2, data is solid)
230x:  very difficult because low in sky, secondary flickers into view as a tiny dot in correct pa 25% of time; at resolution limit

 

Monoceros

Bu 98 (06327-0520) mags 8.37/8.31; pa = 152°; sep = 0.58”, 2002 (data is old, scant)
460x:  elongated only, never resolved;
627x:  10% of time moves past elongated to show two stars of uneven magnitude just touching and (possibly resolved?); at or just below resolution limit; requires re-measure of separation

 

RST 3489 (07044-1027) mags 7.40/8.45; pa = 299°; sep = 0.65”, 4th Int. Cat. estimate (scant data)
460x:  brightening of diffraction ring in correct pa;
627x:  persistent brightening of diffraction ring that resolves to very small secondary 20% of time; at limit of resolution; requires re-measure of separation

 

STF 1157 (07546-0248) mags 7.93/7.89; pa = 173°; sep = 0.647”, 2017 (scant data)
460x:  elongated only, never resolved;
627x:  resolves to two discs touching about 25% of time aided by averted vision; just above resolution limit; requires re-measure to solidify separation value

 

Bu 327AB (06585-0301) mags 7.80/8.15; pa = 102°; sep = 0.7”, 1997 (data is old)
345x:  just split to two even light yellow stars; requires re-measure of separation

 

A 1062 (06596-0823) mags 8.42/9.24; pa = 140°; sep = 0.68”, 4th Int. Cat. estimate (scant data)
340x:  seen as resolved 25% of time, secondary is much smaller;
460x:  moves past resolved to split about 40% of time; a bit above resolution limit; requires re-measure of separation

 

Ho 245AB (07387-0127) mags 7.92/8.70; pa = 186°; sep = 0.668”, 2015.5 (Gaia DR2; solid data)
345x:  brightening of diffraction ring that sharpens to very small secondary just split from primary 50% of time; significant delta magnitude discrepancy between Tycho (0.78) and Gaia (0.18); observation suggests delta mag is greater than 0.18; requires re-measure of delta mag

 

A 539 (08019-0333) mags 8.80/9.54; pa = 21°; sep = 0.746”, 2015.5 (Gaia DR2, solid data)
460x:  pointy/snowman that possibly resolves to two discs <10% of time;
627x:  elongated only; never resolved; just below resolution limit

 

AC 3 (06117-0440) mags 6.34/8.15; pa = 9°; sep = 0.64”, 4th Int. Cat. estimate (scant data)
460x:  just pointy;
627x:  persistently elongated but never resolved; just below resolution limit; requires re-measure of separation

 

 

**That is it for now for this installment.  I will update this thread with additional observations and separation re-measure data as I acquire it.

I would be interested in hearing of other’s observations of these binaries using objectives in the 5 to 10 inch range.**


Edited by Nucleophile, 03 June 2019 - 02:25 PM.

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#2 Astrojensen

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Posted 03 June 2019 - 03:28 PM

Stellar work, if I may say so.

 

 

Clear skies!
Thomas, Denmark



#3 Organic Astrochemist

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Posted 03 June 2019 - 05:30 PM

Excellent work.
I’m not surprised at the success that 627X afforded you. I think you might find a combination of faint magnitude and moderate separation that is resolved at less magnification but not at 627X, but in general it would be my goto magnification for tight doubles (if seeing supports it).

I found Dubhe quite challenging. I also invite you to try Procyon (next year). I’m sure I split it fleetingly on very rare occasions (but I’m not sure anyone believes me).

#4 Nucleophile

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Posted 03 June 2019 - 06:31 PM

I don't think I have ever observed Procyon--it's on my list now.  That is some delta mag there!

 

I remember Dubhe giving me fits with the 15"--but now I feel emboldened to try it with the 8"

 

"I’m sure I split it fleetingly on very rare occasions (but I’m not sure anyone believes me)."--I know the feeling!



#5 rugby

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Posted 05 June 2019 - 12:00 PM

Nucleophile:  Can you please explain to me the use of a Paracorr and a barlow together



#6 Nucleophile

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Posted 05 June 2019 - 12:38 PM

sure thing;

 

The paracorr tightens all the images no matter the magnification employed--this is important for the type of observing and imaging I do.  I pretty much always use it with my reflectors for this effect vs the standard use which is reducing coma away from the center of the FOV.

 

The powermate is different from a barlow and, in my hands, it is a magic means of increasing magnification while maintaining snap focus--I happened on the powermate/plossl combo by accident, but it is now my standard setup for double stars (in lieu of Pentax eyepieces.)

 

This is just what works best for me. grin.gif



#7 rugby

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Posted 05 June 2019 - 08:18 PM

I am going to try the technique used by nucleophile. I have a paracorr and a siebert 1.75 barlow. However I dont own a plossl.



#8 Nucleophile

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Posted 05 June 2019 - 08:21 PM

I am going to try the technique used by nucleophile. I have a paracorr and a siebert 1.75 barlow. However I dont own a plossl.

try an eyepiece used for planetary if you have one....



#9 Nucleophile

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Posted 07 June 2019 - 08:46 AM

I found Dubhe quite challenging. I also invite you to try Procyon (next year). I’m sure I split it fleetingly on very rare occasions (but I’m not sure anyone believes me).

Regarding Dubhe:  last night we were treated to clear skies all night and 4 out of 5 seeing (especially early on.)  I took the opportunity to examine Dubhe with the 8" reflector.

 

After some experimentation,  I found the 11mm  plossl (627x) with an orange filter screwed onto it gave the best image.  I am fairly certain I saw the secondary as a small bump sitting on the primary about 10% of the time.  The rest of the time that area was either a brightening of the first diffraction ring or a smear of light.  I was surprised by how many diffraction rings I could see around the very bright primary-- a testament to the very good seeing!

 

I remember the image of Dubhe I assembled a few years back with the 15" reflector when the secondary was a bit closer:

 

https://tinyurl.com/DubheObs2016

 

What I saw last night looked similar except that there was no space between the primary and the secondary.  Dubhe has a separation of 0.80" right now based on the grade 2 orbit.

 

I will definitely revisit Dubhe in the coming days--it is likely more the case of learning how to see the secondary vs being able to see it at all.


Edited by Nucleophile, 07 June 2019 - 08:47 AM.

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#10 Organic Astrochemist

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Posted 08 June 2019 - 01:05 PM

I will definitely revisit Dubhe in the coming days--it is likely more the case of learning how to see the secondary vs being able to see it at all.


This is so true. There is an equipment component: I think the paracorr is a good idea (I could always see lots of coma without it), I’ve never used colored filters but I bet they could help, of course one needs enough aperture. But I think there is also an observational technique component: if you look straight at the primary, I think you will never split Sirius (more so for Procyon). I think something similar may be at work with doubles like Dubhe, where the primary shows many diffraction rings and the secondary sits on top of one.
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#11 Nucleophile

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Posted 11 June 2019 - 09:34 PM

I had an even better view tonight at a notch lower in power (460x): again, I employed the orange filter and this time when the secondary presented, it was sharp enough of an image to be seen as split.  Again, learning how to see it...



#12 jmillsbss

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Posted 21 June 2019 - 09:59 AM

tl:dr version:  I researched and then observed some challenging double stars with an 8 inch reflector; have you observed any of these?

 

This report is the first installment of a series of observational investigations I have made using an 8 inch f/5.9 reflecting telescope.  The goals of this project are threefold:

 

1) empirically develop a predictive resolution calculator for this instrument via construction of a Treanor plot built from observations of carefully selected binaries,

2) investigate angular separation and delta magnitude discrepancies within the WDS through observational and/or photographic examination, and

3) provide a vetted list of double star candidates for other observers wishing to perform their own investigations.

 

Methods
All observations were conducted with an 8 inch f/5.9 Orion XT8i reflecting telescope atop an equatorial tracking platform.  Most observations were made at moderate to high power with an optical train consisting of a Paracorr Type 1 lens (setting 4), a Televue 5x Powermate, and Televue plossl eyepieces (20mm:  345x, exit pupil = 0.6 mm; 15mm:  460x, exit pupil = 0.45 mm; or 11mm:  627x, exit pupil = 0.33 mm.)  A few binaries with larger delta magnitude values were observed at lower powers (173x or 230x) by swapping out the 5x Powermate for a 2.5x Powermate.

 

Double star candidates were selected by visual examination of lists generated from the WDS database using the search engine Stelle Doppie.  Generally, systems containing stars brighter than visual magnitude 10 and a separation greater than 0.56 arcsesconds were screened and sorted by constellation.  For each system the following was also conducted:  a) examination of the speckle data contained within 4th Catalog of Interferometric data; b) examination of any data provided by the Gaia satellite through the DR2 release.

 

Where necessary, independent measures will be obtained using a 15 inch reflecting telescope equipped with an ASI290MM CMOS camera operating at f/13.  Data will be processed using Speckle Tool Box (STB) to generate separation and position angle data.  The bispectrum feature of STB may allow a measure of delta magnitude in some instances.

 

Observations were made on nights of seeing graded as good or better (≥ 3 out of 5; Danjon scale).  Observational descriptors mostly included:  single star, elongated (or pointy), resolved (meaning two discs visible), and split (dark space seen between discs.)  Particular interest was given to objects sitting on the border of elongated and resolved—these are termed ‘limit objects’ and will be the basis for construction of the resolution calculator if the separation value is deemed accurate.

 

To be considered a vetted double star candidate, Tycho satellite green channel (530 nm) magnitude data must be available (and this is what is listed.)  For each system, the separation data was scrutinized and the most accurate value was inferred by assessing the following:  last precise, orbital data (if available), speckle interferometry historical record, the author’s own measures, and/or Gaia DR2 data (if available.)  When two or more sources of separation data converged and followed the historical trend, the information was considered ‘solid’.  In many instances, the separation data was scant, inconsistent, or old; in these cases, the objects require additional measures before the observational data can be used for construction of the resolution calculator.

 

Canis Major

Hu 1240 (06200-1741) mags 8.90/9.68; pa = 239°; sep = 0.632”, 2016 (scant data)
345x:  elongated only; below resolution limit; separation re-measure desired

 

I 765 (06592-2123) mags 9.15/9.72; pa = 317°; sep = 0.586”, 1993 (data is old)
345x:  very faint pair; pushes past elongated to resolved 20% of time with secondary seen as smaller; suspect separation is greater than 0.586”—re-measure desired

 

Hu 112 (07018-1118) mags 7.03/7.70; pa = 197°; sep = 0.62”, 2014 (solid data)
345x:  pointy in correct pa;
460x:  snowman shape, but not resolved; just below resolution limit; will get a re-measure of separation as this is an important data point

 

SEE 79 (07263-2810) mags 8.75/8.87; pa = 305°; sep = 0.721”, 2015.5 (Gaia DR2, solid data)
552x (Pentax XO 2.5/Paracorr Type 1, setting 1):  pushes past resolved to split 50% of time, stars are two even points of light

 

Bu 568 (06238-1947) mags 6.85/8.18; pa = 185°; sep = 0.849”, 2017 (solid data)
460x:  mostly pointy, but 20% of time small secondary disc seen touching primary; just above resolution limit; surprisingly difficult—will get a re-measure of separation

 

Bu 324AB (06497-2405) mags 6.56/7.93; pa = 210°; sep = 1.797”, 2015.5 (Gaia DR2, solid data)
345x:  easily split; secondary a bit whiter and smaller than primary

 

Bu 328AB (07067-1118) mags 5.70/6.91; pa = 111°; sep = 0.58”, 2003 (data is old)
345x:  single star;
460x:  diffraction ring brightens to show distinct secondary as resolved 20% of time;
627x:  persistent blur in correct pa sharpens to resolved secondary 40% of time; just above resolution limit; separation re-measure desired

 

Bu 753 (06287-3222) mags 7.60/5.86; pa = 43°; sep = 1.177”, 2015.5 (Gaia DR2, solid data)
345x:  easily split, secondary is much smaller; Gaia DR2 indicates the presence of a third star:  a mag 5.9 component separated from A by ~0.52” and possessing a similar proper motion as B; WDS note:  Bu 753 is variable; will get an image to see if there are indeed three stars

 

Bu 18 (06167-12) mags 7.06/8.42; pa = 286°; sep = 1.872”, 2017 (solid data)
345x:  split without difficulty, averted vision helps visualize fainter secondary

 

Canis Minor

A 2866 (07267+0424) mags 9.34/10.04; pa = 138°; sep = 0.671”, 2015.5 (Gaia DR2, solid data)
preliminary evidence indicates this is a limit object; unfortunately, details of observing notes are lost; will need to re-examine next season

 

Lepus

Bu 884 (05030-1226) mags 8.98/9.44; pa = 12°; sep = 0.6”, 1991 (data is old)
345x:  at most object is pointy or elongated past being a single star; definitely below the resolution limit (too faint and too tight); re-measure of separation needed

 

B 1951 (05467-2101) mags 8.54/9.48; pa = 243°; sep = 0.62”, 1991 (data is old)
as yet unobserved; requires separation re-measure

 

A 3018 (05457-1447) mags 9.43/9.39; pa = 303°; sep = 0.707”, 2017 vs 0.909”, Gaia DR2 (significant separation discrepancy)
as yet unobserved; requires separation re-measure

 

Hu 106 (06093-1141) mags 9.44/9.98; pa = 332°; sep = 0.74”, 1991 (data is old)
345x:  viewed for a long time; was an extended rod the vast majority of the time with possible resolution to two discs <10% of the time; right at resolution limit; requires re-measure of separation

 

Bu 314AB (04590-1623) mags 5.92/7.50; pa = 315°; sep = 0.73”, 4th Int. Cat. estimate
460x:  resolved to a dot from a blur of light about 20% of time;
627x:  similar to 460x observation but separation a bit wider when seeing allows; this object is at the limit of resolution, requires a re-measure of separation

 

Bu 320AB Nihal (05282-2046) mags 2.90/7.50; pa = 8°; sep = 2.670” (2015.5, Gaia DR2, data is solid)
230x:  very difficult because low in sky, secondary flickers into view as a tiny dot in correct pa 25% of time; at resolution limit

 

Monoceros

Bu 98 (06327-0520) mags 8.37/8.31; pa = 152°; sep = 0.58”, 2002 (data is old, scant)
460x:  elongated only, never resolved;
627x:  10% of time moves past elongated to show two stars of uneven magnitude just touching and (possibly resolved?); at or just below resolution limit; requires re-measure of separation

 

RST 3489 (07044-1027) mags 7.40/8.45; pa = 299°; sep = 0.65”, 4th Int. Cat. estimate (scant data)
460x:  brightening of diffraction ring in correct pa;
627x:  persistent brightening of diffraction ring that resolves to very small secondary 20% of time; at limit of resolution; requires re-measure of separation

 

STF 1157 (07546-0248) mags 7.93/7.89; pa = 173°; sep = 0.647”, 2017 (scant data)
460x:  elongated only, never resolved;
627x:  resolves to two discs touching about 25% of time aided by averted vision; just above resolution limit; requires re-measure to solidify separation value

 

Bu 327AB (06585-0301) mags 7.80/8.15; pa = 102°; sep = 0.7”, 1997 (data is old)
345x:  just split to two even light yellow stars; requires re-measure of separation

 

A 1062 (06596-0823) mags 8.42/9.24; pa = 140°; sep = 0.68”, 4th Int. Cat. estimate (scant data)
340x:  seen as resolved 25% of time, secondary is much smaller;
460x:  moves past resolved to split about 40% of time; a bit above resolution limit; requires re-measure of separation

 

Ho 245AB (07387-0127) mags 7.92/8.70; pa = 186°; sep = 0.668”, 2015.5 (Gaia DR2; solid data)
345x:  brightening of diffraction ring that sharpens to very small secondary just split from primary 50% of time; significant delta magnitude discrepancy between Tycho (0.78) and Gaia (0.18); observation suggests delta mag is greater than 0.18; requires re-measure of delta mag

 

A 539 (08019-0333) mags 8.80/9.54; pa = 21°; sep = 0.746”, 2015.5 (Gaia DR2, solid data)
460x:  pointy/snowman that possibly resolves to two discs <10% of time;
627x:  elongated only; never resolved; just below resolution limit

 

AC 3 (06117-0440) mags 6.34/8.15; pa = 9°; sep = 0.64”, 4th Int. Cat. estimate (scant data)
460x:  just pointy;
627x:  persistently elongated but never resolved; just below resolution limit; requires re-measure of separation

 

 

**That is it for now for this installment.  I will update this thread with additional observations and separation re-measure data as I acquire it.

I would be interested in hearing of other’s observations of these binaries using objectives in the 5 to 10 inch range.**

How in the WORLD are you using anything at 672x?  My visual struggles to go over 250x.  I had the same sort of seeing last night, according to a couple of apps, and have all Explore Scientific oculars and focal extenders.  5x on an 11mm ep?   Is it because you're using a plossl and not a multiple element ep?  I'm well collimated, with decent seeing, in a bortle 4.5-5 zone, with very good ep's in a 10" Orion.  I don't know how I'm going wrong!



#13 Nucleophile

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Posted 21 June 2019 - 10:34 AM

How in the WORLD are you using anything at 672x?  My visual struggles to go over 250x.  I had the same sort of seeing last night, according to a couple of apps, and have all Explore Scientific oculars and focal extenders.  5x on an 11mm ep?   Is it because you're using a plossl and not a multiple element ep?  I'm well collimated, with decent seeing, in a bortle 4.5-5 zone, with very good ep's in a 10" Orion.  I don't know how I'm going wrong!

I cant use that mag (627x not 672x) every night; but I do get a lot of 4/5 nights here (Danjon scale). I think a few other things are at play here:

 

a.  I lucked out with an excellent mirror in my XT8i

b.  the TV plossl EPs are an upgrade in the image over even the Pentax EPs, especially when used with a powermate

c.  my eye is well-trained to make a composite picture out of fleeting moments of clarity

d.  despite being in suburbia, my skies are nearly a green zone (especially after 11 pm)

e.  in depends on your visual target; for double stars, you can get away with high power to assemble useful observational data which might otherwise not be available for DSOs or planets

 

I should add that for the entire time I have owned this instrument (purchased in 2009), I have routinely been able to use 340x and beyond to get sharp views of planets, DSOs, and double stars--again, I think the two most important factors are the instrument and my locale.

 

Just curious:  do you do a star test to assess seeing/collimation?


Edited by Nucleophile, 21 June 2019 - 10:57 AM.


#14 jmillsbss

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Posted 21 June 2019 - 04:21 PM

Just curious:  do you do a star test to assess seeing/collimation?

I've not really been at it long enough to perform a star test that would yield any useful information.  I have done a few star tests, according to a couple of online resources as guides.  Best I could understand, my optics, at least to me, appear to be of a good quality.  I had similar images infocus as well as out.

 

I'm not involved with anyone or any astronomy groups.  Sorta just a solitary exercise, which is cool but that's got a pretty big learning curve.

 

I probably don't have very dark skies, at least not as dark as I think I do.  But I'll be out there again tonight if possible, and see what I can see!



#15 Nucleophile

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Posted 21 June 2019 - 04:36 PM

I've not really been at it long enough to perform a star test that would yield any useful information.  I have done a few star tests, according to a couple of online resources as guides.  Best I could understand, my optics, at least to me, appear to be of a good quality.  I had similar images infocus as well as out.

 

I'm not involved with anyone or any astronomy groups.  Sorta just a solitary exercise, which is cool but that's got a pretty big learning curve.

 

I probably don't have very dark skies, at least not as dark as I think I do.  But I'll be out there again tonight if possible, and see what I can see!

Check out this website (scroll almost all the way to the bottom) to see an animation of what the Danjon seeing scale looks like through the eyepiece:

 

https://www.handprin...2.html#variants

 

 

The star test is best done (according to Suiter's book) using an eyepiece that matches your focal ratio whilst viewing a bright mag 1 or 2 star.  Defocus the star inward so that about 3 diffraction rings are visible and see what you can to determine your local seeing.  As a bonus, if the pattern is not perfectly symmetrical, it means the collimation needs a tweak or two.  I always do a final collimation of my large reflector based on what the star test tells me.

 

And you are never alone when out looking at the stars--you have the rest of us as company!   smile.gif


Edited by Nucleophile, 21 June 2019 - 04:41 PM.


#16 fred1871

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Posted 13 July 2019 - 03:29 AM

Okay, notes on a few of the Canis Major pairs. Generally I don't have observations for the 9th magnitude and below 1-arcsecond pairs. These I regard, from occasional attempts on them, as being tests of eyesight and observing conditions rather than telescope, when we're looking at 20cm (8-inch). If I had a C14 or similar I might pursue them, the extra light gives the eye better resolution; as stars become dimmer, visual acuity for separating them drops off. So I do observe 8th mag pairs below 1-arcsecond, with the Mewlon 210 or C9.25. Occasionally on moonless nights and with good seeing, with the 14cm refractor. Long ago, with C14 access, I found various 9th mag pairs not too difficult, around 0.6".

 

Here are the pairs I found my notes for.

 

HU 112 in CMa - where did you find the 2014 measure? - Tycho in 1991 had 0.62", same as your 2014 (solid data) measure.... but the better measure for 1991 was Hipparcos at 0.654", much the same as Hartkopf 1989 at 0.646". Separation on this one is not very variable in recent times so around 0.65" may be fine.
     Only observation for this one I can find in my records is old, 1998, with 18cm refractor - at 330x elongated and in best moments touching discs. Separation at the time was Dawes Limit for 18cm. No surprise.

BU 568 in CMa. Another 18cm observation from 1998. Around 0.83" at the time, and again not one that's changing quickly. With the 18cm at 180x seen as a figure-8 (overlapping discs); 330x showed it looking barely split in the steadiest moments.

BU 328 CMa.  For this one my observations straddle the 7"/8" position. With a C14 at 240x, double but not a clean split due to not good seeing. With 14cm refractor on a good night, an elongated image at 400x. Roughly 0.50", a little closer than this, has been my best for elongation with that scope ; I'll be trying for slightly better when weather allows. Again, separation of the pair not much changing over recent years.



#17 Nucleophile

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Posted 16 July 2019 - 06:56 AM

Fred:

 

I picked a cutoff of about mag 10.3 for the secondary for the reasons you listed.  However, for the purposes of my study, I am interested in determining what factor faintness plays in resolution of doubles--in many cases, this can be simply modeled by adding a value to the calculator value.

 

RE:  HU 112, the 2014 value is the last precise listed by Stelle Doppie (attempted to confirm this from the WDS itself but having trouble [again] with the site).  I believe my thinking was this should be considered solid because the last precise matched the last speckle--but there is a real paucity of recent speckle data, so  a better determination should have been 'not solid'. Indeed, it is slow, but I would like to re-measure this one.  The fact that I could not split this one speaks to 0.62" vs 0.65"--but we shall see.  The mag 7ish stars make this one rather brighter than many I have looked at and (just like faintness), this can play a role in the ability to resolve the pair.

 

RE:  BU 328AB, I feel I should not be able to resolve this one if the listed values of separation of 0.58"  and delta mag of 1.2 is correct -- this one is very interesting and warrants further study.  It may be a slow mover but last speckle in 2003 doesnt sit well with me.

 

I appreciate your thoughtful comments will try to address the others in the other post.  School has started back up again so this will likely occur piecemeal going forward.



#18 fred1871

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Posted 16 July 2019 - 08:59 PM

Okay, a few thoughts. I've looked through the long series of interferometer measures (mainly speckle) from 1976 to 2003 - using McAlister (lots), Hipparcos and Hartkopf as the best of them it's clear enough there's no definite sign of separation change over the period. Choose somewhere around 0.565" to 0.570" as the separation. That, by the way, is pretty much a Dawes Limit point for an 8-inch aperture. No doubt the brightness difference makes the pair tougher. I'm a little puzzled by the comment

460x:  diffraction ring brightens to show distinct secondary as resolved 20% of time;

because with an 8-inch the diffraction ring is centred about 0.9" from the primary, not a little under 0.6".

 

Regarding another comment:

the last precise matched the last speckle

is unsurprising if the last speckle was the last measure. The term "last precise" is in fact very misleading - it's simply the most recent published measure recorded into the WDS. It rather too often is not precise at all. For example, a micrometer measure with the known vagaries of that technique won't be as precise (or accurate) as a speckle measure on a large scope by someone who is expert in speckle measures. The last measure for HU 112 is not listed in the Interferometer catalogue, and therefore is likely a micrometer or perhaps lucky imaging. Without knowing the origin of the measure it's not possible to assess it (whodunnit and with what technique on what telescope).

 

On the matter of faint doubles that are close. The telescope does not have less resolution because the stars are dimmer. You can confirm that with lucky imaging of fainter pairs under good seeing conditions. This can be muddled a bit because of longer exposure times for fainter stars, so seeing intrudes more, but the essential point is there. Imaging largely overcomes the limits of the eye as things get dimmer. The biggest difference with faint versus fairly bright pairs is that the human eye loses resolution capability as the light gets dimmer; fainter pairs are harder to see at the same separation as brighter pairs because of reduced resolution capability with less light. So, effectively, what you're doing with the fainter close pairs is testing your eye's capability when there's less light available.



#19 Nucleophile

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Posted 17 July 2019 - 06:52 AM

 

> indicates my comments follow

 

 I'm a little puzzled by the comment

460x:  diffraction ring brightens to show distinct secondary as resolved 20% of time;

because with an 8-inch the diffraction ring is centred about 0.9" from the primary, not a little under 0.6".

 

>At that power the ring was likely less than a stable optical entity; I didn't say it was right on the ring itself and perhaps it was inside of it a bit.  One thing I have learned after 20 +years of conducting scientific research (chemistry and astronomy) is to trust my observational data made at the time of recording; i.e, that is what I saw and that is what I wrote.  Also, I am in no way dismissing the veracity of the historical speckle information.  Since I have the ability to independently verify the data I will do so.

 

Regarding another comment:

the last precise matched the last speckle

is unsurprising if the last speckle was the last measure. The term "last precise" is in fact very misleading - it's simply the most recent published measure recorded into the WDS. It rather too often is not precise at all. For example, a micrometer measure with the known vagaries of that technique won't be as precise (or accurate) as a speckle measure on a large scope by someone who is expert in speckle measures. The last measure for HU 112 is not listed in the Interferometer catalogue, and therefore is likely a micrometer or perhaps lucky imaging. Without knowing the origin of the measure it's not possible to assess it (whodunnit and with what technique on what telescope).

 

>Plenty of times I have found non-speckle, 'recent measures' to be valid based on my own measures and I take these at face value until such time as I have observational or imaging information that conflicts with the measure.

 

So, effectively, what you're doing with the fainter close pairs is testing your eye's capability when there's less light available.

>That is exactly correct and  I am keen to see if this additional information (which I call Limiting mag - mag 2 or LM-m2) can be folded into the mathematical model (along with the separation and delta mag) to generate an Opik-based resolution equation.  As Bruce MacEvoy states on his site, a  model is most instructive when it focuses less on prediction and more on discovering errors or anomalies with the current data [already I have seen evidence affirming this].  I will add in closing that 'brightness' also factors into the equation--very bright pairs near the Dawes limit can also present an added level of challenge.  I have seen with both of my reflectors there is a sweet spot in magnitude where the Dawes limit is most approachable (and it is not necessarily mag 7 btw).


Edited by Nucleophile, 17 July 2019 - 07:00 AM.


#20 fred1871

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Posted 17 July 2019 - 09:14 PM

 

 

> indicates my comments follow

 

 I'm a little puzzled by the comment

460x:  diffraction ring brightens to show distinct secondary as resolved 20% of time;

because with an 8-inch the diffraction ring is centred about 0.9" from the primary, not a little under 0.6".

 

>At that power the ring was likely less than a stable optical entity; I didn't say it was right on the ring itself and perhaps it was inside of it a bit.  One thing I have learned after 20 +years of conducting scientific research (chemistry and astronomy) is to trust my observational data made at the time of recording; i.e, that is what I saw and that is what I wrote.  Also, I am in no way dismissing the veracity of the historical speckle information.  Since I have the ability to independently verify the data I will do so.

 

Regarding another comment:

the last precise matched the last speckle

is unsurprising if the last speckle was the last measure. The term "last precise" is in fact very misleading - it's simply the most recent published measure recorded into the WDS. It rather too often is not precise at all. For example, a micrometer measure with the known vagaries of that technique won't be as precise (or accurate) as a speckle measure on a large scope by someone who is expert in speckle measures. The last measure for HU 112 is not listed in the Interferometer catalogue, and therefore is likely a micrometer or perhaps lucky imaging. Without knowing the origin of the measure it's not possible to assess it (whodunnit and with what technique on what telescope).

 

>Plenty of times I have found non-speckle, 'recent measures' to be valid based on my own measures and I take these at face value until such time as I have observational or imaging information that conflicts with the measure.

 

So, effectively, what you're doing with the fainter close pairs is testing your eye's capability when there's less light available.

>That is exactly correct and  I am keen to see if this additional information (which I call Limiting mag - mag 2 or LM-m2) can be folded into the mathematical model (along with the separation and delta mag) to generate an Opik-based resolution equation.  As Bruce MacEvoy states on his site, a  model is most instructive when it focuses less on prediction and more on discovering errors or anomalies with the current data [already I have seen evidence affirming this].  I will add in closing that 'brightness' also factors into the equation--very bright pairs near the Dawes limit can also present an added level of challenge.  I have seen with both of my reflectors there is a sweet spot in magnitude where the Dawes limit is most approachable (and it is not necessarily mag 7 btw).

 

No issue regarding trusting your observational data. I can see how the original description can be read differently, either the way I did (creating a puzzle) or what now appears to be a different descriptive intention.

 

Plenty of times I have found non-speckle, 'recent measures' to be valid based on my own measures.... 

I wasn't dismissing "recent measures" as such - rather, pointing to the uncertain quality of what is described as a "recent measure" - some of these are highly accurate, others not - that's the issue. One can't tell merely by noting that something is the most recent measure. Which is why I pointed to the need for evaluation of these.

 

Best of luck on an Opik-based resolution criterion. If it's about the fainter close pairs, it will be an equation that depends to a significant degree on your perceptual abilities as an individual. And those abilities vary greatly from one person to another. Also, the type as well as degree of perceptual ability is not uniform - some people see fainter, but not sharper; some see sharper but not fainter; some are very good at both; some are mediocre or poor at both.

 

Of course, you could get a number of other observers trying the same objects, and see what results from that. It can be a mixed result. We saw that a few years ago with the work done by Napier Munn and his group of observers, discussed on CN back in the day (the original article is in the JDSO v4 no 4 (2008). The ongoing Sissy Haas project has turned up quite a variety of observing results from many observers; analysing these will be interesting when it happens.

 

One aspect of that project is the observations of the (now deleted) Gamma Equulei, originally listed as the result of what turned out to be a wrong measure (it was the "latest precise" at one time). Several folk got false positives observing the star, claiming resolution. A newly made speckle measure showed the earlier last measure to be wrong. None of the false positive observers should be treated as other than honestly reporting what they believed they saw. But the real numbers showed the impossibility of resolution while using modest apertures. This binary had been closing for some time; the wrong measure suggested it was widening again.

 

Several of us had already analysed the old measures list, and found that the measure that turned out to be wrong was a non-fit for the trend lines. The new speckle measure showed as clearly a good fit for the older measures trend, and some of those measures were not especially old. That double had simply fallen into the neglected list in more recent times, otherwise the wrong measure would earlier have shown up. (Incidentally, a wrong measure is sometimes merely a typo; sometimes a mistake in copying measures from A to the listing of B; less often, the wrong star measured....of course, it can also be a measuring error.).



#21 Nucleophile

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Posted 17 July 2019 - 10:59 PM


 

Best of luck on an Opik-based resolution criterion. If it's about the fainter close pairs, it will be an equation that depends to a significant degree on your perceptual abilities as an individual. And those abilities vary greatly from one person to another. i

I never claimed the developed criterion was to be generalized for any other observers.  It is necessarily for myself, with my instrument, in my locale.  The fainter (and brighter) pairs play an important role.

 

Of course, I am always interested in hearing of others observations--they are instructive for myriad reasons.


Edited by Nucleophile, 17 July 2019 - 11:00 PM.



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