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.
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.
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
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
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
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.