28 april 2021

I can't remember a night when there was good enough seeing to push the limits of the 20-inch.... Last night was predicted to be good seeing, which is sometimes good enough to reach the limits, and I held out hope. The first pair seen was STF 1356, which was very nicely split with the 7-inch mask, so I thought just maybe I could go further. I vacillated between the 20-inch, apodising screen, and 7-inch mask. Some nice stars but I'm falling behind in my short period project and haven't nabbed one of those in months. High clouds started to build at 11pm so I ended there.

STF1356 AB: 178; 445x: Ome Leo. Elongated at 205x, but nice clear disks with diffraction rings at 445x, plenty of room in the split, <1", slight magnitude difference, white stars. Physical with a 117.97-year period, it is nearing apastron where it will sit for the next two decades. I should sketch it for posterity...
09h 28m 27.41s +09° 03' 24.4" P.A. 114.60 sep 0.9 mag 5.69,7.28 Sp F9IV dist. 33.17 pc (108.2 l.y.)



STF1372 AB: 508; 445-1334x: With apodising mask.  All I have is an elongation with PA WSE, which seems to be where B is.  A is canary yellow at low power, light yellow-orange with high power, and there is definite elongation.  Physical with a 371-year period, it is slowly coming off apastron.  My PA estimate was correct!  Current separation 0.321"
09h 37m 07.57s +16° 13' 33.3" P.A. 253.00 sep 0.4 mag 8.50,8.60 Sp F8 dist. 147.06 pc (479.71 l.y.)

HU 722 AB: 178; 445x: Notched elongation best I can get.  
09h 06m 39.07s +50° 37' 36.5" P.A. 244.00 sep 0.5 mag 9.16,9.10 Sp G5 dist. 126.42 pc (412.38 l.y.)

STFB 7 AB: 178; 205x: Light yellow-white A and very wide 4 delta mag B.  WDS is saying this is physical based on the proper motion.  Unfortunately there is no parallax data in Gaia, and I would highly doubt these two are gravitationally bound given their separation.

11h 47m 59.23s +20° 13' 08.2" P.A. 355.00 sep 74.9 mag 4.59,9.03 Sp A7V dist. 71.33 pc (232.68 l.y.)

STF1540 AB: 178; 205x: Light orange-yellow A and light blue B, >1 delta mag, very wide.  Physical with 32,000-year period.  Running this through the Plot Tool with EDR3 data, it confirms it is physical, only 18 parsecs / 58 light years away (which is why it has such a high proper motion) and 520 AU separation.  
11h 26m 45.32s +03° 00' 47.2" P.A. 146.00 sep 28.6 mag 6.55,7.50 Sp G7V dist. 17.75 pc (57.9 l.y.)

STF1547 AB: 178; 205x: Very light yellow and 2 delta, very wide B.  Physical, with a 3453-year period, it is also close-by at 23.33 pc.  I wonder if these were / are part of a cluster?
11h 31m 44.94s +14° 21' 52.2" P.A. 332.10 sep 15.3 mag 6.33,9.14 Sp G0V+G5 dist. 23.33 pc (76.1 l.y.)

STF1670 AB: 178; 205x:  Porrima.  Bright near equal, dull white, well split about 4".  Physical with a 169-year period, I missed my chance to witness the rapid periastron a few years ago :-(

12h 41m 39.60s -01° 26' 57.9" P.A. 357.50 sep 2.9 mag 3.48,3.53 Sp F0V+F0V dist. 11.68 pc (38.1 l.y.)

STF1560 AB: 178; 205x: Nice dull yellow-white and 3 delta mag, well separated bluish B around 5".  Physical (90% on the Harshaw scale).
11h 38m 24.07s -02° 26' 09.3" P.A. 279.00 sep 4.9 mag 6.42,9.43 Sp G9III dist. 116.69 pc (380.64 l.y.)

STF1568 AB: 178; 205x: White, very slight magnitude difference, wide.  Physical.  
11h 43m 16.61s +00° 45' 40.1" P.A. 43.00 sep 9.2 mag 10.36,10.48 Sp F5 dist. 231.48 pc (755.09 l.y.)

STF1593 AB: 178; 205x: Very finely split near equal white stars, quite a nice pair.  Very likely physical, 55% overlap and 250 AU separation
12h 03m 31.79s -02° 26' 49.0" P.A. 15.00 sep 1.2 mag 8.70,8.57 Sp F0 dist. 246.91 pc (805.42 l.y.)

STF1580 AB: 178; 205x: Near equal white, well split.  WDS says parallax indicates physical, but in the Plot Tool with the error included, there is -3% overlap -- again the max and min distance of the two stars are within fractions, so it does not give a parallax error.  So maybe physical, maybe not.
11h 55m 29.73s +03° 32' 36.0" P.A. 262.00 sep 8.7 mag 9.34,10.01 Sp A9V

STF1571 AB: 178; 205x: Faint pair, white, well separated.  Maybe physical; 28% parallax overlap, 2355 AU separation

11h 46m 22.32s +09° 04' 28.3" P.A. 298.00 sep 9.8 mag 9.94,11.50 Sp F8 dist. 195.31 pc (637.1 l.y.)