[Weltevreden SA (Dana)]

06/05/2013:

Thanks, Gary. I should've double-checked on WikiSky re the coordinates. I don't have ArgoNavis, my equip't is very limited. I've confirmed both objects on five separate nights in the recent dark-moon cycle, and HP1 once last year. The seeing/transparency minimum criterion I use for validating an HP 1 sighting is whether I can resolve 15-20 stars at the limit of seeing in nearby NGC 6256 Sco using a 180mm Mak. The 15 to 20 don't appear all in one glimpse but rather shimmer individually in and out of the dim glow, perhaps 8 to 10 at any one moment.

If the air passes that test, HP 1's whitish core glow is easily detected 1/2 the time on my 150 Mak 'finder', about 75% of the time in a 180mm, and 80% of the time using the 200mm. It's a very seeing-dependent object, located using a small circlet of 13 - 14 mag stars in a prolate circle reminiscent of the Pisces circlet. The cluster requires magnification, 225x to 300x. HP 1 has an exceptionally concentrated core, luminosity half-light radius at 1.5 arcmins with total photometrically verified diameter 8.1 arcmins dia. This is an odd core concentration for a post-core-collapse cluster. It points to recombinant binary formation from very close encounters in the core during the full-collapse phase.

HP 1 has received a bit of recent attention in the professional papers due to its location as the nearest GC to the bulge center and number of stars in the blue horizontal branch pointing to a 2nd generation origin. Hence it is unusually metals-rich >12 Gyr old cluster, [Fe/H] -1.61 and high Mg - Al ratios. A number of its 2nd gen stars evolved using the Na-Mg-Al process subsequent to the C-N-O cycle; the higher metals content ends in very thin stellar envelopes with 20,000 K surface temps on the far left end of the HB blue branch. Astronomer's can’t quite figure out why this happened. It appears to be an Na-rich, Mg-poor cluster, hence the recent interest. HP 1 also is unusual in acquiring bulge stars through tidal truncation on its front end as it plows through the bulge medium ~64 kms faster than the mean bulge rotational velocity at that radius, while losing trailing stars back into the bulge at about the same rate. IOW, it remains at ≈ constant mass while accreting and evaporating at the same time. Only a few stars every 10,000 years, but has GC specialists examining other resident bulge GCs to see if the behaviour is common. At that velocity is must acquire and lose stars through the LaGrange L1 and L2 points, much like the Jupiter Trojans. If you're into all thus stuff, ask and I can send you the links to the papers.

Ton 2 is also a bulge GC, and relatively nearby HP 1. Visually in my equip't it is the most difficult log I've ever entered as confirmed. Never more than a vague whitish glow with 3 or 4 foreground stars at my 200mm's seeing limit of vm14.5 to 15.3. The test I use is whether nearby NGC 6380 can be seen in the 150mm scope as a cometary glow despite the distraction of a 10.4 mag foreground star. If the 200mm scope can detect hints of granularity in 6380, then the air is good enough to tackle Ton 2. 'Tackle' is a relative word here. There's a whitish quickening at about 2 arcmins dia about 20% of the time. Luckily, the cluster is placed near the vertex of an easily tracked isosceles triangle of 12.75 - 13.25 mag field stars, so keeping the eye directly on it for long periods is easy.

I've devised a last-resort method to confirm objects like this using star counts in four adjacent fields applied to a mathematical formula based on the RMS function used in optical wavefront testing. IYI, The method takes an hour or more of star counting and number crunching, but it is more quantitative than the term 'hesitant glow'. If you are interested in trying the method, look the Wiki article on RMS, and adapt the first long root-square formula. Substitute 'log2.51x, + log2.51y . . . log2.51n’ etc, for the RMS ‘x, y . . . n’ terms. If you calculate the left side of the equation using log2.51 you get a numerically exact solution. I find that to be unsupportable when adjacent field counts number only three or four stars of similar magnitude to the cluster's brightest star. So I do not multiply the left side by the log2.51, which then becomes a probability function. For me that is more reliable.

In the literature, Ton 2 has received about as much attention as it has in enthusiast circles like our own. Next to nil, in other words. Too bad. It's like the long-lost cousin you finally located on Google, wrote, and received a 'deceased' notice in reply.

Cheers and thanks for the data . . .
=Dana in S Africa