Weltevreden SA
25-10-2015, 07:53 AM
21:20 UT Arp 2 (http://aladin.u-strasbg.fr/java/alapre.pl?-c=Arp+2&button=N%26B) (Huey p.81) is more difficult to track down than to see. It is near M55. Proceed inward on a line bisecting the teapot handle. Arp 2 shows as a tiny triplet of mag 13 – 14 stars in a right triangle. Look carefully at the brightest star and you will detect a soft round glow <2 arcmins in diameter which wavers in and out of view behind the star. This has the canonical round white glow of a faint globular. The fuzzy “star” gives the impression of a core-collapse cluster, but high-rez images don’t show an even brightening from outer to middle. Arp 2 is emaciated in a 180mm scope at 240x. In fact, we are only glimpsing a slightly overdense core in an otherwise loose and much larger Class XI cluster. Look directly at the tiny triplet for a minute or so till the eye has adjusted to the luminosity difference between the field star and the cluster. In time the cluster improves from intermittent glimpses to a steady glow in averted. In deep astrophotos, what the eye sees is only the core of an extended globular whose outer stars are mag 17 on down. If you look it up on WikiSky, you need to type “Cl Arp 2” or you’ll get sent to a blue spiral galaxy in Hercules.
21:50 UT. Terzan 8 (http://aladin.u-strasbg.fr/AladinLite/?target=Cl%2520Terzan%2520%2520%252 0%25208&fov=0.033334&survey=P/DSS2/color) in Sagg (Huey p.118) is very VERY not easy. If you use Aladin Lite, the viewer opens very close-in; back it out quite a bit. WikiSky shows it better, even though the two use the same database. Ter 8 lies in a star-poor region and demands considerable panning during your traipse across imaginary triangles and Trapezium-like quadrilaterals to arrive at the spot where Huey (p.181) and my TriAtlas B (p144) says the cluster is. It looks quite a bit like the Mensa globulars of the LMC, except that they are faint and far away while Terzan 8 is loose and not quite so far away. In a telescope the brightest three stars are mag 14.5 to 15.5. This cluster is so faint that Arp 2 required ten minutes to reveal itself enough for me to call it a confirm. Even then I got only two or three firm glimpses of it per minute over the span of 10 minutes. Scintillation is really important on this one. It didn’t help that the cluster was slipping into the Zodiacal glow by the time I got to it. There is no reddening data for it, but Arp 2 must be significantly reddened because of its 2.3 arcmin diameter but faint red giants.
22:15 UT. ESO 280-6 (http://aladin.u-strasbg.fr/java/alapre.pl?-c=ESO+280-6&button=RGB) in Telescopium (Huey p.68) isn’t marked even on my Torres TriAtlas B set, which usually has EVERYthing. I tracked to its position (TriAtlas B p.173) using Alvin Huey’s “Globular Clusters” observing guide. ESO 280-6 is very close to Epsilon Telescopium, making it an easy track-down. ESO 280-6 is centered between two mag 9-10 field stars, and stands out because it is behind a distinct asterism of <12 mag stars just 2 arcmin apart, which themselves are inside a brighter mag 11.5 pair of stars about 4 arcmin apart. The cluster is a very tiny smudgy spot behind the bottommost mag 11. It looks more like a faint planetary than a cluster. Its appearance is explained by its distance (~160,000 ly) and that it may be an original LMC globular that was tidally stripped by the MW several hundred million years ago. The LMC is chock full of clusters like this; you can always hone your skills on those. ESO 280-6’s integrated visual mag is 12, which normally doesn’t mean a thing. But in this dense, tight cluster the integrated magnitude actually looks like a mag 12 star. In 2000 ESO 280-6 became the 150th MW globular to be discovered. Here’s the paper (http://adsabs.harvard.edu/abs/2000A%26A...361L..57O). Check out the pic on p.2. It’s a very tiny cluster, only 1.4 arcmin. If you subtract the halo it is only 1 arcmin “real” dia. This is probably the least GC-looking cluster in the whole Huey catalog.
Midnight in Capricorn: Pal 12 (http://aladin.u-strasbg.fr/AladinLite/?target=Pal%2012&fov=0.27&survey=P%2FDSS2%2Fcolor) is easy to find, but not easy to see. You can proceed from M30 or by way of Epsilon and 37 Capricornii. When you get into the right area, it’s east to spot the faint right-angle triangle of mag 11.2 to 12.4 stars. They are so cumulatively bright that spotting the faint, oblong smudge of the cluster nearby is more difficult that if the cluster was free-standing. Pal 12 is on a wrenching orbit through the Galactic disc, plunging headlong from far above the disc through a crossing point near the Galactic co-rotation resonance. Such a disc-crossing point is more stressful to a cluster than a plain old gigayear crossing because the Lindblad resonance region exerts a more sharply peaked gaussian tug on the cluster. The Lindblad resonance region has a higher density of stars and lower density of gas,. That means more high-density masses than low-diffuse ones. Think of it as walking across a carpet of pins instead of stones. Pal 12 is pummeled on all sides, which means a larger star-evaporation rate. Pal 12 has been so stressed during its life that has lost roughly 80% to 85% of its original stars.
In closing, if you try these during November 2015 dark cycle of the 7th to 16th, the Scorpius clusters will be too low. You’ll have to go for the Sagg clusters as soon as it gets to astronomical dark. You’ll need exceptionally transparent skies and no light pollution. Owners of 16-inch glass and larger should have no trouble with them. These clusters are tough and proud of it. You’ll have a right to be just as proud if you get any.
21:50 UT. Terzan 8 (http://aladin.u-strasbg.fr/AladinLite/?target=Cl%2520Terzan%2520%2520%252 0%25208&fov=0.033334&survey=P/DSS2/color) in Sagg (Huey p.118) is very VERY not easy. If you use Aladin Lite, the viewer opens very close-in; back it out quite a bit. WikiSky shows it better, even though the two use the same database. Ter 8 lies in a star-poor region and demands considerable panning during your traipse across imaginary triangles and Trapezium-like quadrilaterals to arrive at the spot where Huey (p.181) and my TriAtlas B (p144) says the cluster is. It looks quite a bit like the Mensa globulars of the LMC, except that they are faint and far away while Terzan 8 is loose and not quite so far away. In a telescope the brightest three stars are mag 14.5 to 15.5. This cluster is so faint that Arp 2 required ten minutes to reveal itself enough for me to call it a confirm. Even then I got only two or three firm glimpses of it per minute over the span of 10 minutes. Scintillation is really important on this one. It didn’t help that the cluster was slipping into the Zodiacal glow by the time I got to it. There is no reddening data for it, but Arp 2 must be significantly reddened because of its 2.3 arcmin diameter but faint red giants.
22:15 UT. ESO 280-6 (http://aladin.u-strasbg.fr/java/alapre.pl?-c=ESO+280-6&button=RGB) in Telescopium (Huey p.68) isn’t marked even on my Torres TriAtlas B set, which usually has EVERYthing. I tracked to its position (TriAtlas B p.173) using Alvin Huey’s “Globular Clusters” observing guide. ESO 280-6 is very close to Epsilon Telescopium, making it an easy track-down. ESO 280-6 is centered between two mag 9-10 field stars, and stands out because it is behind a distinct asterism of <12 mag stars just 2 arcmin apart, which themselves are inside a brighter mag 11.5 pair of stars about 4 arcmin apart. The cluster is a very tiny smudgy spot behind the bottommost mag 11. It looks more like a faint planetary than a cluster. Its appearance is explained by its distance (~160,000 ly) and that it may be an original LMC globular that was tidally stripped by the MW several hundred million years ago. The LMC is chock full of clusters like this; you can always hone your skills on those. ESO 280-6’s integrated visual mag is 12, which normally doesn’t mean a thing. But in this dense, tight cluster the integrated magnitude actually looks like a mag 12 star. In 2000 ESO 280-6 became the 150th MW globular to be discovered. Here’s the paper (http://adsabs.harvard.edu/abs/2000A%26A...361L..57O). Check out the pic on p.2. It’s a very tiny cluster, only 1.4 arcmin. If you subtract the halo it is only 1 arcmin “real” dia. This is probably the least GC-looking cluster in the whole Huey catalog.
Midnight in Capricorn: Pal 12 (http://aladin.u-strasbg.fr/AladinLite/?target=Pal%2012&fov=0.27&survey=P%2FDSS2%2Fcolor) is easy to find, but not easy to see. You can proceed from M30 or by way of Epsilon and 37 Capricornii. When you get into the right area, it’s east to spot the faint right-angle triangle of mag 11.2 to 12.4 stars. They are so cumulatively bright that spotting the faint, oblong smudge of the cluster nearby is more difficult that if the cluster was free-standing. Pal 12 is on a wrenching orbit through the Galactic disc, plunging headlong from far above the disc through a crossing point near the Galactic co-rotation resonance. Such a disc-crossing point is more stressful to a cluster than a plain old gigayear crossing because the Lindblad resonance region exerts a more sharply peaked gaussian tug on the cluster. The Lindblad resonance region has a higher density of stars and lower density of gas,. That means more high-density masses than low-diffuse ones. Think of it as walking across a carpet of pins instead of stones. Pal 12 is pummeled on all sides, which means a larger star-evaporation rate. Pal 12 has been so stressed during its life that has lost roughly 80% to 85% of its original stars.
In closing, if you try these during November 2015 dark cycle of the 7th to 16th, the Scorpius clusters will be too low. You’ll have to go for the Sagg clusters as soon as it gets to astronomical dark. You’ll need exceptionally transparent skies and no light pollution. Owners of 16-inch glass and larger should have no trouble with them. These clusters are tough and proud of it. You’ll have a right to be just as proud if you get any.