Separation Gamma Equ
Posted 04 April 2013 - 04:06 AM
If the WDS data is correct then this pair would be hard to split with 180mm aperture, if the 1.5" from Sissy are correct, then this could be under perfect conditions possible for 120mm aperture.
Gam Equ is below the horizon for me now so I cannot check it myself - for my 140mm refractor this would be the difference between (speaking in terms of Chris Lord's Rule of Thumb according to the implementation in the AstroPlanner software) "unresolvable" and "extremely difficult" (but certainly doable).
Had anybody recently observed Gam Equ or has this possibility now?
Posted 04 April 2013 - 08:23 AM
Conclusion I suggested is that it's moved fairly quickly since the last listed measure and is now too close for mid-size scopes. I'd therefore suggest the claims to split it recently with moderate apertures (eg 180mm) might prove to be spurious resolution.
Essentially what's needed is a new measure, preferably from a large telescope using adaptive optics (speckle is unlikely given the large delta-m). That way we can know what the present level of difficulty is likely to be, and what size telescope might be the minimum now needed for resolution. It's definitely closer than it was.
Posted 04 April 2013 - 01:34 PM
According to the repeatet non split with a 24" scope mentioned in the thread you referred to then even the further reported split with 200mm would be a false positive.
Posted 04 April 2013 - 04:25 PM
I use a go-to mount and SkySafari Pro on my iPad,so location wise I was pretty certain I was looking at the right one. :o
Beautiful pair by the way!
Posted 05 April 2013 - 02:21 AM
The advertised data for doubles in SkySafari amazes me each time I have a look at it. I once sent an inquiry to the SkySafari support for their source but got never an answer. For Gam Equ Sky Safari shows 1.4" +4.71/8.21mag - I have no idea where this data might come from. But this would certainly indicate an easy split with 6" and a good chance with my 5.5".
Posted 05 April 2013 - 03:19 AM
Yes, I don't know where SkySafari gets its data for doubles but they certainly pride themselves in how accurate their satellite, comet and asteroid data is. They claim they are the only software company out there taking into account gravitational perturbations to calculate comet and asteroid positions (to "NASA-like precision")...but that doesn't say much about doubles. Maybe they have gone as long as including orbital data in their doubles and precessing them to accommodate epoch change? - And maybe those orbital models are out?
In any case, I'm pretty sure I was looking at Gamma Equulei and I split it with my 6" refractor last November.
Posted 05 April 2013 - 03:20 AM
Posted 05 April 2013 - 03:44 AM
If that is indeed the separation, it should be easily visible with a 5-6" instrument under good conditions.
What do you think?
Posted 05 April 2013 - 07:02 AM
With 1.25" separation this would be already rather difficult with a 6" scope (Lord rating "XD" = eXceedingly Difficult even with perfect seeing). My current RoT model gives for 1.25" separation 176mm aperture for a 50% split probability - 150mm would then have a chance of about 5% for a split. Your observation report with repeated splits over several nights indicates no difficulties with 150mm so this would speak rather for a 1.5" separation.
Posted 05 April 2013 - 07:11 AM
I found this relatively new (2010) academic paper ( 5 Equ )on the properties of the main star in the 5 Equ system in a search in the Los Alamos Lab online archive. The paper deals mostly with its magnetic properties - as 5 Equ is one of the brightest stars with high frequency magnetic field changes visible in the sky. It lists its current multiple system separation as 1.25" +- 0.04" citing another paper of 2002.
If that is indeed the separation, it should be easily visible with a 5-6" instrument under good conditions.
What do you think?
Roberto, the comment "should be easily visible with a 5-6" instrument under good conditions" gives me the impression you're expecting the pair to be splittable according to the Dawes Limit numbers or nearly so - but if you read through the previous thread I reminded Wilfried of, you'll see that the brightness difference of the A and B stars of Gamma Equulei is 4.0 magnitudes - notice that the figures quoted by the WDS are modern double decimal place magnitudes. They can be expected to be of good accuracy.
Unevenly bright doubles are more difficult than near-even pairs. Once you have 4 magnitudes difference they're much more difficult. It means star A is 40 times as bright as star B.
Note the details I and others gave in discussing the pair in the earlier thread. The separation is now pretty definitely LESS than 1.0". It's very unlikely that a pair with the long-term record of this one will suddenly widen again in a decade, when its behaviour suggests it's moving into the closer part of the orbit and will likely close further, or at least maintain a close separation similar to 2002. I'd think the latter is less likely given the rates of change of angle in various periods.
Also, the lack of recent success in splitting with 16- and 24-inch scopes suggests continuing very close separation, probably closer than in 2002.
We can all try again observing this pair as that section of sky becomes accessible this year.
Sorry to labour some of these points, but I think further discussion does need to take into account the previous discussion and the data presented there.
The observation I quoted from Hartung's book, made back around 1960, was when the pair was likely still about 1.9" (maybe 1.8"?) and he describes it as difficult for 20cm, an 8-inch scope. Hartung was a very experienced observer and generally did very well with doubles in terms of the minimum aperture that would show them. By 2002 the pair was around half the separation of Hartung's c1960 observation.
Quite simply, from the data to hand, and failed splits by experienced observers with 16-inch and 24-inch telescopes (note the details mentioned), it's plain that Gamma Equulei is not going to be easy. Haas listed it for her project because of an older measure that happened to be the most recent in the WDS listing at a particular time. The 2002 measure wasn't published in 2002, so it didn't get into the WDS until after the version Haas used.
What's needed now is
1. a new measure
2. observations by experienced observers with good telescopes of reasonable size under very good seeing conditions
no 1. will give us a good idea of the current state of this binary
no 2. can establish what size scope is needed for splitting a fairly bright 4-magnitude-delta-m pair at very close separation
Posted 05 April 2013 - 08:43 AM
If what I saw was 5 Equ, I observed it over two consecutive nights in late November last year (don't have my notes at hand) and clearly split it the first night and "knew what to look for" the second. After that, the weather took a turn for the worse and it became inaccessible from my backyard.
This is indeed a puzzling double! I look forward to it becoming visible again! I'm happy to stand corrected but would like to have seen it with the 6" Apo
Posted 05 April 2013 - 09:23 AM
My comment on "easily visible in 5-6" apertures" was way out of order and should not have been taken into the context of me dismissing your earlier thread and difficulty in observing it.
I don't agree in not taking into account the separation quoted by the academic paper though. An approved/peer reviewed scientific paper with a quoted separation carries for me a heavier probability of being correct than amateur observations like ours (particularly mine! ). Anecdotal evidence points to the two components coming closer but the rate is at best empirical from what I can read in previous threads. It could well still be in the 1.1-1.2" range.
I get the point about the magnitude differential. I was quite surprised to have been able to split it (if indeed I did so) given I have had more difficulty with other doubles of similar characteristics near that time and since.
Jim Kaler of the University of Illinois has a nice write-up on 5 Equ ( Jim Kaler ) - I think SkySafari uses his descriptions for their planetarium software.
I was trying to find a recent observation in one of the Webb Society Circulars but couldn't. I will have to take a bit more time to do this. I've also been looking for an orbital model but most papers centre around the rotational period of this star (a whopping 70+ years!) and/or its magnetic properties.
As you say the only way of settling this is for us to wait for the Little Horse to rise! As I said to Wilfried, I'm happy to stand corrected if I cannot split it this time around! :o
Posted 05 April 2013 - 12:48 PM
Otherwise, the data in it for stars (such as distance and spectral class) seems to be rather accurate.
Hope you get an answer on the Yahoo group -- a lot of people depend on Sky Safari, so whatever the bug is, it needs to be corrected.
Posted 05 April 2013 - 06:05 PM
The measure referred to in the 2010 paper is quoted from a 2002 paper (Fabricius et al), and we'd need to know what date that measure was made as the double has been changing.
The data I used was the complete data set obtained from the US Naval Observatory last year, and which included the 2002 measure. Unfortunately, that 2002 figure appears to be the most recent currently available. That's why I'm hoping for a new measure, preferably with a very large scope and adaptive optics to ensure high accuracy.
Posted 05 April 2013 - 10:26 PM
PA for 1867 was 277; for 2002, 258. So 265 is fairly late (rate of change is faster later) but definitely earlier than 2002 by some years.
I'm away from home this weekend so I don't have all my data files with me, to provide a basis for a more detailed commentary.
Looking at the WDS online today, the 2002 measure is still the most recent. Annoyingly, the wide C and D stars were re-measured in 2011, but not AB. Does this suggest AB was too close for whatever was used for C and D? Without the full data files and their sources that's only a hypothetical possibility.
Posted 06 April 2013 - 01:24 AM
Welcome to the world of astronomical data catalogs, where everything is precise to 18 digits, and every source is in complete disagreement with every other source :-)
FWIW, the star catalogs we use are listed here:
Our basic stellar database is NASA SkyMap + Hipparcos + Tycho, plus GSC 1.3 in the Pro version.
For those stars in the above catalogs which have listings in the WDS, we've done our best to include separations, positions angles, etc. from the latest WDS. We do not include the complete WDS, altho I will proably do this in version 4, next year.
For the roughly 2000 stars in WDS which have published orbits - and nearly all of them are included in SkySafari, since these are well-observed stars with entries in Tycho/Hipparcos - SkySafari uses the published orbit to compute angular separation and position angle "live". You can use Sirius or Alpha Centauri as an example. Their PA/Separation will change as the years go by. You can also animate the motion year-over-year and watch the components move in the sky chart.
That's about the best we can do for now. There will not be any major rewrites of the database until SkySafari 4, next year.
Posted 06 April 2013 - 04:01 AM
Posted 06 April 2013 - 08:02 AM
Incidentally - "For the roughly 2000 stars in WDS which have published orbits - and nearly all of them are included in SkySafari, since these are well-observed stars with entries in Tycho/Hipparcos - SkySafari uses the published orbit to compute angular separation and position angle "live"."
I hope this will NOT include binaries with grade 5 orbits - as orbits so graded in the 6th orbit catalog are generally far too preliminary - uncertain - to be useful for ephemerides. Some grade 5 orbits are best treated as "premature".
Posted 06 April 2013 - 09:27 AM
This possibility intrigues me greatly. Imagine having this resource available at the telescope while observing. And for making observing lists!
As for the statistics/data we already know that there is some variation in the published numbers as we have seen in the case of Gamma Equ. Sky Safari can only put one set of Sep. and PA for each double so, no matter which one they choose, they will be "wrong". I'd rather not criticize them for this.
The 'live orbits' is an excellent resource. (even for grade 5 orbits if we don't try to go more than 10 or so years into the future by which time Sky Safari will have better orbital elements as they come available...)
Posted 06 April 2013 - 01:40 PM
But I've run into more than a few cases where the separation and distance info in Sky Safari is just plain way off.
For example, here's one I just came across:
Tau Ursae Majoris -- Sky Safari shows a separation of 0.0" with a PA of 311 degrees. It's actually a triple star, with the WDS showing AB at 52.80" and 37 degrees (2003) and AC at 102.60" at six degrees (1991).
I wish now I had made a list of others, but I've just quit using it as a double star reference. Otherwise, it's really a great little tool.
At any rate, the best advice until this kind of thing is corrected is to stay with the WDS or StelleDoppie sites.
Posted 06 April 2013 - 05:41 PM
Posted 06 April 2013 - 11:36 PM
I rely on the WDS almost exclusively -- it's the ultimate source for any other program, anyway.
Posted 07 April 2013 - 01:39 AM
Posted 07 April 2013 - 04:49 AM