Author Topic: Some doubles around Gemini  (Read 670 times)

mccarthymark

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Some doubles around Gemini
« on: March 05, 2017, 10:08:31 AM »
Last week we had three nights of better than average seeing, so I spent the time splitting doubles with my 12.5-inch f/7.  The perimeter of the mirror is masked down to 11.5-inch to deal with a turned edge, so I suppose it is correctly stated as an 11.5-inch f/7.6.  On such nights I focus primarily on very close and fainter doubles, for which I print out AAVSO finder charts since most of them are not plotted in my Cambridge Double Star Atlas.  I stayed at 553x the whole time; here are some of the highlights, which are my observation followed by the confirming data in brackets (A/B magnitudes, separation, position angle) I retrieved from Stelle Doppie afterward:

Propus (means "forefoot") = Eta Geminorum = B 1008: So cool!  Bright orange star with a very close B, ~1.5", just preceding, ~3 delta mag. B is in diffraction but is well separated & has its own bluish white airy disk.   [3.52, 6.15, 1.6" 252°].  06H 14M 52.69S +22° 30' 24.6"

STF 942: Faint near equal brightness stars, well split, PA W-E.  [10.07/10.1, 3.4", 246°] 06H 37M 40.87S +23° 38' 54.2"

BU 100: !! Pretty orange and blue.  4 delta mag, PA to west.  Wide separation ~3".  B is just seen, a very fine point. [7.34/11.1, 3.2, 143°.  Burnham's discovery in 1873 was at 2.5" separation.  Last WDS observation in 1978 -- deserves another measure now] 07H 00M 56.55S +12° 24' 00.4"

HO 342: ! Yellow-orange and blue stars, PA to the east, 1 delta magnitude; tight but well split ~1".  [7.99/8.71, 1.1", 87°] 07H 02M 50.54S +13° 05' 21.7"

WEI 14: A yellow-orange, B blue, 1 delta mag, PA to south.  Nice!  [7.77/8.91, 2.1", 160°]. 07H 12M 48.16S +15° 10' 41.9"

STF 1068: Pumpkin orange pair, near equal magnitude, PA to north.  Well separated ~4".  Nice.  [AB 9.29/.8, 4", 349°] 07H 19M 49.31S +13° 22' 22.4"

STF 1116: Pretty tight white, near equal magnitude, 2-3", PA to east.  Nice pair.  [7.81/8.5, 1.8" 96°] 07H 34M 32.02S +12° 18' 16.9"

STF 981: Very close orange pair, equal magnitude.  Clean split, ~1".  Worth the hop from Tau Geminorum.  [8.72/8.97, 0.95", 292.3°] 06H 55M 28.54S +30° 09' 42.3"

STF 1014: !! Tough find, faint field.  Very faint near equal brightness pair, ~3", PA to the SW.  [9.91/9.93, 2", 219°] 07H 05M 44.95S +26° 08' 25.3"

A 674: B more a blue haze than a point off the yellow A.  I believe I have it, very close and faint.  PA to SE.  [8.21/9.77, 1.1", 125°] 07H 44M 38.11S +31° 06' 50.1"

STF 1147: Very fine 2", equal magnitude blue - white pair, PA to south, ~2".  [9.66/9.68, 2.2", 174°]. 07H 50M 19.69S +24° 31' 55.8"

STF 1126: !! Wow, very close <1" hair-split, near equal brightness; almost overlapping disks.  [6.55/6.96, 0.8", 175°]  07H 40M 06.99S +05° 13' 51.9"

STT 182: Very close, ~1", near equal brightness white.  [7.82/7.93, 0.8", 11°] 07H 52M 42.12S +03° 23' 02.2"

STF 1210: Pretty wide greenish yellow pair, wide separation, 2 delta mag.  [AB 7.25/9.45, 15.5", 113°.  AC is 13.5 mag and 68", not seen] 08H 15M 48.54S +02° 48' 05.0"

STF 1182: White and reddish, 1 delta mag, PA due east.  [7.48/8.76, 4.7", 74°] 08H 05M 24.43S +05° 49' 38.9"

It struck me that I was having trouble detecting any close pair of more than 10th magnitude when it was close to a brighter star.  Examples of my negative sightings are A 2527: 8.58/11.85, 2.2”; BU 579: 7.95/12.3, 1.1"; and AGC 2: 7.76/9.73, 1".  I wonder if it was due to light pollution?  The SQML from my back yard is 18.60.  Maybe it's just bad timing with the seeing?  I used my full aperture through the session, so perhaps a mask would have helped?  I have a 5-inch off-axis mask but I rarely use it since my impression is it dims the stars too much and I lose resolution.  I’m interested to know what others think.
Mark

sgottlieb

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Re: Some doubles around Gemini
« Reply #1 on: March 05, 2017, 06:38:15 PM »
Well done, Mark!  I'm guessing you were just running up against the mag limit of your scope/sky.  Also for some reason I often find the fainter companion of a close unequal, double appears dimmer than its magnitude suggests.

My notes on a several of these pairs are appended at the end, but here are a few more 2" or closer pairs in Gemini you might want to look at another time --

∑899 = ADS 4991
06 22 49.6 +17 34 27
V = 7.4/8.0;  Size 2.2"
18" (1/28/12): tight 2" white pair just cleanly split at 175x in fair seeing.  Crisper view using the 6" mask.

∑932 = ADS 5197
06 34 21.6 +14 45 08
V = 8.1/8.2;  Size 1.7"
18" (1/19/08): well-matched tight pair that at 1.65" that is just resolved at 175x.  Easy at 225x in good seeing.
18" (1/3/04): excellent evenly matched pair of mag 8 stars at 1.7" separation.  Splits at 160x and cleanly resolved at 215x.  Tangent airy discs with 6" mask at this power but easily resolved.

∑1037 = O∑166? = ADS 5871
07 12 49.1 +27 13 30
V = 7.2/7.2;  Size 1.1"

18" (3/10/04): clean split with 6" mask even at 220x!  This is a perfectly matched white pair.  This binary has a period of 119 years and is just past maximum separation (1.1").
18" (1/3/04): very close 1.1" pair of equal mag 7 stars.  Clearly double at 160x but not cleanly split.  Nicely resolved at 300x and with a 6" mask two nearly tangent airy discs are just cleanly resolved at 300x!
18" (3/24/03): very close, evenly matched pair (white/white) at 1.1".  Clean split in good moments at 300x.

∑1070 = ADS 5999
07 21 21.9 +34 01 36
V = 8.6/9.3;  Size 1.7"
18" (1/19/08): tight 1.7" pair but just cleanly resolved using 175x.  At 450x, tiny airy discs were resolved when the seeing was steady.

∑1081 = ADS 6038
07 24 08.9 +21 27 28
V = 7.7/8.5;  Size 1.8"
18" (1/19/08): fairly close 1.8" white pair is resolved at 175x.  Upping the power to 450x gave a wide split with clean star images.
---------------------------------------

Eta Gem = Bu 1008 = ADS 4841
06 14 52.7 +22 30 24
V = 3.3-3.9/6.5;  Size 1.6"
18" (4/10/03): Eta Gem is a challenging mag 3.3-3.9 (variable)/6.5 pair at 1.6" (slowly increasing).  Very large mag contrast with a yellow/orange primary.  Excellent at 300x and easy at 435x in good moments.  Supernova remnant IC 443 is close following.

∑942 = ADS 5258
06 37 40.6 +23 38 53
V = 10.1/10.1;  Size 3.5"
18" (1/28/12): perfectly matched 10th magnitude pair at 175x.  Fairly close (3.5") and nicely split at 175x.  Located 4' NW of mag 6.7 HD 47086.

∑981 = ADS 5570
06 55 28.4 +30 09 45
V = 8.8/9.0;  Size 1.1"
18" (1/19/08): this 1.1" pair was barely resolved at 175x and cleanly split at 225x.  At 450x, tiny airy discs were resolved and well separated.  This binary has a period of 5343 years and is still closing.

18" (3/7/04): very close 1.2" pair but cleanly resolved evenly matched duo.  Used both the 6" mask and at full aperture with a 9mm Ortho (250x).  Current separation at 1.2" is close to minimum.  Closing since discovery in 1831 (3.7").

Ho 342 = ADS 5725
07 02 50.5 +13 05 22
V = 8.0/8.7;  Size 1.2"
18" (1/19/08): very close 1.2" pair cleanly resolved at 300x.  Superb in good seeing at 750x with small airy discs.

∑1014 = ADS 5770
07 05 44.9 +26 08 25
V = 9.9/9.9;  Size 2.0"
18" (1/28/12): excellent perfectly matched 2" pair at 175x.  Cleanly split at this power but very close.

Weisse 14 = ADS 5875
07 12 48.2 +15 10 42
V = 7.8/8.9;  Size 2.1"
18" (1/19/08): this excellent 2" pair was just resolved at 175x and was beautiful at 300x.  Subtle colors.

∑1116 = ADS 6180
07 34 32.0 +12 18 17
V = 7.8/8.6;  Size 1.7"
18" (3/10/04): striking pair at 220x with the 6" mask.  Easily resolved at full aperture at 1.7".

∑1147 = ADS 6394
07 50 19.7 +24 31 56
V = 9.7/9.7;  Size 2.2"
18" (1/28/12): perfectly matched 2" pair just cleanly split at 175x.  Very similar appearance to ∑1014 = 9.9/9.9 at 2.0" observed a little earlier in the evening.