4 Attachment(s)
Object of the Week, September 15, 2019 – NGC 6717/Palomar 9 - the forgotten globular cluster
Palomar 9
= NGC 6717, ESO 523-14
Type: Globular Cluster
Class: VIII
RA: 18h 55m 06.2s
Dec: -22° 42' 01"
Constellation: Sgr
Size: 5.4'
Mag: 8.4V
Brightest Star: 15.0V Skiff (14.0V Archinal)
Distance (Galactic center): 7800 l.y.
Distance (sun): 23000 l.y.
The history of the obscure sounding Globular Cluster began simple - with the discovery of William Herschel in 1784. He described the object as "...nebulosity" but saw similar to his son John stars in it.
The confusion began 1901 when Bigourdan published his results with the 12,4-inch refractor of Paris Observatory and wrote: "nebulous star mag 13, situated near NGC 6717 in PA 35° [NE], d = 15"" Did he saw the knot in the NE as a individual object or simply the same object NGC 6717? He got an IC entry and the number 4802.
But what type of object was NGC 6717? 1931 Collinder accepted NGC 6717 rightly as a globular star cluster. But the story was not over.
Unfortunately (or not) George O. Abell missed the entry and cataloged this star cluster under number "9" in his compilation of 15 "Globular Clusters...discovered on the National Geographic Society-Palomar Observatory Sky Survey" in 1955.
Physical the metal-poor cluster lies near the Galactic center in the bulge. Astronomers observed a very concentrated structure and suspect a so called "post-core-collapse morphology".
In the telescope NGC 6717 is in my mind one of only a few clusters which are worth a visit for nearly all apertures. In small apertures to see the cluster at all and in big telescopes to resolve as many stars as possible. I visited the cluster often and got results from 4-inch to 27-inch, see my Palomar project.
DSS red 10'x10'
Attachment 3640
PanSTARRS 4'x4'
Attachment 3641
HST
Attachment 3642
sketch: 16", 515x, NELM 7m0+ (Austria, 47°N)
Attachment 3643
But now it is your turn.
Give it a go and let us know!
