Jump to content


Photo

My tale of Trapezium F - finally

  • Please log in to reply
50 replies to this topic

#26 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1173
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 05 March 2013 - 03:49 AM

Wow, sounds good. If you ever do a session in UMa could you please try WDS11593+3310 BU919 RA 11h 59m 18s Dec +33:10:01 +5,96/12mag 4,7" - should be a very similar challenge.
Wilfried

#27 nirvanix

nirvanix

    Surveyor 1

  • -----
  • Posts: 1756
  • Joined: 07 Jun 2007
  • Loc: Saskatoon, SK

Posted 05 March 2013 - 11:19 AM

I've found the F member is doable in a 100mm. Actually I think I've viewed it in my 75mm but to be sure I'd have to search my unorganized notes.
Bill


I've tried for F in a 100mm in my light-polluted backyard, but never found it. I suspect that it could be found with that scope in darker skies.

#28 Bonco

Bonco

    Gemini

  • *****
  • Posts: 3450
  • Joined: 17 Apr 2006
  • Loc: Florida

Posted 05 March 2013 - 03:47 PM

Nirvanix,
I too have very light polluted skies. Your main disadvantage compared to my home site is Latitude.
Bill

#29 nirvanix

nirvanix

    Surveyor 1

  • -----
  • Posts: 1756
  • Joined: 07 Jun 2007
  • Loc: Saskatoon, SK

Posted 05 March 2013 - 06:02 PM

Nirvanix,
I too have very light polluted skies. Your main disadvantage compared to my home site is Latitude.
Bill


Well that's a good point Bonco. I forget how good M42 must look for you folks way down there. It's always a bit in the soup for me.

#30 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1173
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 06 March 2013 - 03:50 AM

Light pollution is not such a topic concerning resolution of double stars - it may add a few mm to the required aperture for a split but usually less than 10 even for heavy light pollution. Given stable air without any turbulences (Pickering 7 or better - this certainly excludes altitudes below 35°) and high transparency (no haze or air pollution for example by air traffic) you can more or less ignore light pollution. The exception are very faint companions near the telescope magnitude limit as LP takes some tribute here. This is why I am a bit sceptic about small telescopes below 150mm for resolving F especially given the surface brightness of the M42 nebula adding some haze even in the best of conditions.
Wilfried

#31 Kon Dealer

Kon Dealer

    Viking 1

  • -----
  • Posts: 707
  • Joined: 05 Jan 2011
  • Loc: Cambridge UK

Posted 06 March 2013 - 05:01 AM

Did "E" abd "F" with my 8SE for the first time last night.
I can see "E" quite easily with my 4" 'frac and 6SE.
Never seen "F" in either and they are out alot more than the "8".

#32 HCR32

HCR32

    Messenger

  • -----
  • Posts: 451
  • Joined: 27 Aug 2010
  • Loc: Melbourne Australia

Posted 06 March 2013 - 05:31 AM

I see them no problems with a 6" APO at 125x.

#33 Bonco

Bonco

    Gemini

  • *****
  • Posts: 3450
  • Joined: 17 Apr 2006
  • Loc: Florida

Posted 06 March 2013 - 03:30 PM

Light pollution is not such a topic concerning resolution of double stars - it may add a few mm to the required aperture for a split but usually less than 10 even for heavy light pollution. Given stable air without any turbulences (Pickering 7 or better - this certainly excludes altitudes below 35°) and high transparency (no haze or air pollution for example by air traffic) you can more or less ignore light pollution. The exception are very faint companions near the telescope magnitude limit as LP takes some tribute here. This is why I am a bit sceptic about small telescopes below 150mm for resolving F especially given the surface brightness of the M42 nebula adding some haze even in the best of conditions.
Wilfried

I have documented observations of F with my 4 inch f/5. It is very doable in the right conditions. I've observered it many times in a 10 inch but I've also not been able to see it or E in the bigger scope. It's fickle. I checked my notes concerning my 75mm. Notes reflect positive observations of E but questionable views of F. So I won't say the 75mm viewed F, but I can guarantee you the 4 inch has revealed it.
Bill

#34 cpsTN

cpsTN

    Mercury-Atlas

  • ****-
  • Posts: 2502
  • Joined: 26 Apr 2007
  • Loc: Rutherford Co, TN

Posted 07 March 2013 - 07:58 AM

That's great. With the seeing we have here in Middle Tennessee, I have to work a little to see star E and have never seen star F. ...and that is with the 12" dob. I included a diagram to help people.

Attached Files



#35 bhuloka

bhuloka

    Vostok 1

  • -----
  • Posts: 124
  • Joined: 06 Mar 2012
  • Loc: Maryland, USA

Posted 07 March 2013 - 09:11 AM

Last November, under better-than-average seeing, red zone, I set up my 8" edge HD and my 16" Hubble optics dob, as a test of the 16" mirror, since I knew the 8" was very good. The 8" showed F star faintly and only intermittently. The 16" showed it clearly and steadily, very easy. So aperture does play a big role here. BTW, I used a variety of magnifications.

On other days, when seeing was not as good, neither scope revealed F. E was usually there in the 16" even under mediocre seeing. Light pollution didn't seem to be a major factor.

#36 nirvanix

nirvanix

    Surveyor 1

  • -----
  • Posts: 1756
  • Joined: 07 Jun 2007
  • Loc: Saskatoon, SK

Posted 07 March 2013 - 10:06 AM

I find in my backyard the theoretical limiting magnitude of my scopes cannot be reached - I'm assuming it's light pollution. E and F are magnitude 11 which is a stretch for my 4" refractor in the city. In fact I find the 10" dob can only reach about magnitude 12 from the yard. Under good seeing, it's not the separation of the doubles that presents the problem with the trapezium. I've split tougher doubles that are brighter using the 4" in town, Porrima for example.

#37 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1173
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 07 March 2013 - 04:21 PM

Surprise - after a cloudy day a clear sky in the evening. NEML about +3mag and Pickering 6-7. M42 about 33° altitude so I gave STF748 AE and CF a try with a 140mm refractor. With x140 magnification I could barely make out the faint spot of E with a magnitude of +11.1mag but I could not resolve F with +11.5mag. This is my telescope magnitude limit with this degree of light pollution (without it would be about +13.4mag). Now and then there was a flicker in the diffraction pattern in the right position but then - there were also flickers in wrong positions, so no resolution.
Wilfried

#38 azure1961p

azure1961p

    Voyager 1

  • *****
  • Posts: 10432
  • Joined: 17 Jan 2009
  • Loc: USA

Posted 08 March 2013 - 07:45 AM

That's great. With the seeing we have here in Middle Tennessee, I have to work a little to see star E and have never seen star F. ...and that is with the 12" dob. I included a diagram to help people.


Charles,

F can be a frustrating object for me in common seeing in winter from Connecticut. I will say though , if you haven't done it, running a small 5" DC fan rated 12v off a boxy 6v flashlight battery purrs along with no vibration for me and significantly less flaring in star patterns. My 5" is the typical computer type DC fan of the variety like the more common 3 or 4" had at RadioShack. I wouldn't rule out running two 4" DC fans behind that large a glass.

If you already are doing something similar than its probably seeing/collimation related.

In 7/10 its nicely shown for me, but in 3-4 its basically invisible and 5/10 barely there.

Pete

#39 nirvanix

nirvanix

    Surveyor 1

  • -----
  • Posts: 1756
  • Joined: 07 Jun 2007
  • Loc: Saskatoon, SK

Posted 08 March 2013 - 11:06 AM

Good idea Pete. Right now I have a little 50mm fan at the back of my 10" dob and I don't run it during observing because of vibration. The 120mm fan will move much more air and do it with less vibration.

#40 fred1871

fred1871

    Viking 1

  • -----
  • Posts: 897
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 08 March 2013 - 08:49 PM

My experience with E and F is similar to many others' experience - E is much easier to see than F, and is less likely to disappear when seeing gets unsteady.

Nights I've seen both with 140mm refractor there's a big difference in the look of E and F - E pretty easy, F a tiny pinpoint of light.

These days, with both AE and CF being a little wider than the earliest measures, the AE and CF separations are near enough identical - 4.6" for AE, 4.5" for CF. Not enough to account for the difference.

The big factor is the magnitudes of A and C - A is listed at 6.55, C at 5.06. So you're looking at an 11th magnitude star not far from a much brighter one in each case - but C is ~4 times as bright as A. That by itself makes a big difference. Comparisons with brighter, closer, near-even pairs (such as Porrima) are meaningless - there's a totally different factor set involved.

The other thing that might make a small difference is the brightness level of the nebulous background - is it the same, to the eye, in both cases? I don't know, but in marginal cases a difference could affect visibility.

For smaller telescopes a further factor is that m11.5 is closer to the magnitude limit than m11.1 - especially when the other factors (above) are also in play.

So I'm surprised when F is seen with less than about 100mm aperture - even at 100mm it's doing very well. I'd expect it to take very good conditions and very good eyesight with 70-80mm telescopes. Exceptional in fact. It doesn't mean it can't happen, but it won't be the standard experience, as the many and varied comments in this thread show.

#41 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20514
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 08 March 2013 - 10:34 PM

That's odd. I'd figure the spot size would be just as small in a 10" or 12" Dob, and I've never had any trouble with E or F in such scopes. In fact, I find it pretty easy in any scope down to 4" so long as it has decent optics and seeing cooperates. :shrug:

Regards,

Jim

#42 jrbarnett

jrbarnett

    Eyepiece Hooligan

  • *****
  • Posts: 20514
  • Joined: 28 Feb 2006
  • Loc: Petaluma, CA

Posted 08 March 2013 - 11:09 PM

"So aperture does play a big role here."

Not really. None of these are particularly tight splits, so resolution is irrelevant. The issue with targets like Sirius B and Trapezium E and F is suppression of glare and stray light control. Quality and effectiveness of baffling, not aperture, are key with these targets. A high quality small scope (3" to 4") will have little problem with any of these targets. Heck, a good 80mm handles Sirius B at a mere 70x. Trapezium E and F are easy in a quality 4-incher at just over 100x. Often a larger scopes, and also an obstructed scope, have considerably more difficulty with these targets due to reduced contrast, increased scatter and excessive brightness and glare. Seeing is important too, and larger scopes suffer worse under poorer seeing - another indication that aperture may be the OPPOSITE of what is required on these targets on some nights.

Perhaps the Hubble just has considerably better contrast than the 8" SCT? 8" SCT have monster COs and even with (impossibly) perfect optics, can't achieve diffraction limited system performance. I'll bet that 16-incher has a much smaller CO than the C8, and accordingly a higher potential system Strehl and less scatter. :thinking:

Regards,

Jim

#43 azure1961p

azure1961p

    Voyager 1

  • *****
  • Posts: 10432
  • Joined: 17 Jan 2009
  • Loc: USA

Posted 09 March 2013 - 12:03 AM

Good idea Pete. Right now I have a little 50mm fan at the back of my 10" dob and I don't run it during observing because of vibration. The 120mm fan will move much more air and do it with less vibration.


Lol well if the 50mm is shaking your system the 125mm will too. I don't know why I've been so lucky with the lack of vibration . The tube is 6' long so that's a dampening effect I guess. Try lower voltage to bring the shakes down. I will say I don't run any fan at its rated voltage - its too much power to say nothing of the noise. Try different rubber bands .

Good luck Nirv.

Pete

#44 buddyjesus

buddyjesus

    Vanguard

  • *****
  • Posts: 2236
  • Joined: 07 Jul 2010
  • Loc: Davison, Michigan

Posted 09 March 2013 - 03:04 AM

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.

#45 Bonco

Bonco

    Gemini

  • *****
  • Posts: 3450
  • Joined: 17 Apr 2006
  • Loc: Florida

Posted 09 March 2013 - 04:03 PM

Fred from Australia is spot on. Good explanation.
Thanks, Bill

#46 Bonco

Bonco

    Gemini

  • *****
  • Posts: 3450
  • Joined: 17 Apr 2006
  • Loc: Florida

Posted 09 March 2013 - 04:09 PM

Today spent some time in my darkened basement with an artificial star so I could rotate my crown to find the point of least astigmatism in my achromat.

Tonight was above average seeing for Michigan. I used a 9mm K eyepiece in my 4" scope. E was usually there and definitely confirmed with less than one minute of observation. CF sure looked elongated, but after ten minutes of staring I was without definitive separation let alone confirmation.

I know this is brought up every year but it is bothering me more this year than in the past. Who gave the stars the wrong lettering? Isn't the brightest one supposed to be the A? ugh. Always some exception to the rule.


I'm not sure CF would ever look elongated. Because of the magnitude difference you must have sufficient magnification to create black space between the stars. Best wishes, Bill

#47 buddyjesus

buddyjesus

    Vanguard

  • *****
  • Posts: 2236
  • Joined: 07 Jul 2010
  • Loc: Davison, Michigan

Posted 09 March 2013 - 04:38 PM

i can definitely say I didn't see black space. I wasn't fully convinced about elongation either since I couldn't even pick a most likely position angle.

#48 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1173
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 10 March 2013 - 04:35 AM

If +11.6mag STF748F would be a single star without nebula you would be able under else perfect conditions so resolve it with a 60mm scope as the TML for 60mm is theoretical +11.6mag.
Given that F is near glaring C and within a nebula then under not so perfect conditions (Pickering 7, NEML 4.5, M42 below 45° altitude, some haze ...) I think it also impossible to resolve it with a 100mm scope with a theoretical TML of +12.7mag as the TML-loss due to these conditions is certainly larger than 1.2mag.
With some more light pollution as it usual near or on the fringe of big cities means NEML about +3mag even a 140mm scope will no longer resolve a +11.6mag star regardless if double or not and certainly not in competition with a glaring primary.
Wilfried

#49 fred1871

fred1871

    Viking 1

  • -----
  • Posts: 897
  • Joined: 22 Mar 2009
  • Loc: Australia

Posted 10 March 2013 - 06:36 AM

Wilfried, I think you're right about 60mm telescopes. But NEML isn't as bad as 3.0 on the fringe of every city, even large ones. It varies a lot.

From a suburban area with 2 million city population, where I was observing some years ago, I could see mag 4.5 normally on moonless nights. Another example - outer suburb, local population 400,000, NELM 5.0-5.5 on moonless nights.

Worst case from my recent experience - in outer parts of Sydney I can see mag 4-4.5 stars from some locations (moonless). Sydney area, 4+ million. Now there are areas of (suburban) Sydney that are overlit, so NELM of 3.0 would apply there.

But there's no universal level of light pollution in cities. I'm sure other people will make the same point. Obviously, you're in a difficult location for light pollution. What's your local population total? High, I'd expect, given your NELM figure often being around 3. That makes Trapezium F very difficult even with 140mm.

#50 WRAK

WRAK

    Apollo

  • -----
  • Posts: 1173
  • Joined: 18 Feb 2012
  • Loc: Vienna, Austria, Europe

Posted 10 March 2013 - 07:12 AM

Fred, I am located in the southern part of Vienna/Austria and my average NEML is about +3mag (on very transparent nights 3.5 and on hazy ones about 2.5).
Wilfried






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics