05.06.2013 Views

The Caldwell Objects

The Caldwell Objects

The Caldwell Objects

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

evealed a significant blue-straggler population<br />

in NGC 6101. It was found that these stars are<br />

more centrally concentrated than the cluster's<br />

similarly bright subgiants. This indicates that<br />

NGC 6101's blue stragglers have larger masses<br />

than their ostensible counterparts, supporting the<br />

theory that they either are binary systems or have<br />

been formed by the merging of stars. Fifteen<br />

variable stars have been discovered in the region<br />

of NGC 6101. Eleven of these appear to be RR<br />

Lyrae stars, one of the types of variables used to<br />

size up our galaxy.<br />

To find NGC 6101 start with magnitude-1.9<br />

Atria, Alpha (α) Trianguli Australis. <strong>The</strong> cluster<br />

lies 3½° to the southwest of it. If that's too far a<br />

jump, first locate 5th-magnitude Zeta (ζ)<br />

Trianguli Australis 2° to the southwest of Atria;<br />

the globular is another 2° south of Zeta Trianguli<br />

Australis. NGC 6101 can be seen in binoculars.<br />

Look for a tight triangle of 7th- to 8th-magnitude<br />

stars whose westernmost, 7th-magnitude<br />

member appears double. <strong>The</strong> cluster should be<br />

just south of the triangle and will<br />

107<br />

appear as a dim glow with a slight central condensation.<br />

It's best to have some magnification<br />

handy if you want to confirm your sighting.<br />

With an 8-inch telescope sited in Wellington,<br />

New Zealand, I saw the cluster as a moderately<br />

bright sphere surrounded by a dim gray halo.<br />

<strong>The</strong> roughly 3'-wide core is fractured into three<br />

parts. <strong>The</strong> innermost section is an uneven wedge<br />

of suns. A dark lane separates this mass from a<br />

tiny cap of stars to the northwest (Dunlop's "very<br />

small" nebula?), while a chevron of starlight to<br />

the south appears to have calved off the core.<br />

Through Auckland Observatory's 20-inch Zeiss<br />

reflector, the core of NGC 6101 looks herniated. A<br />

splash of 13th- to 15th-mag-nitude suns crosses<br />

the cluster's entire face, as if some disgruntled<br />

artist shook a wet paint brush at it. <strong>The</strong> drawing<br />

here is a composite of all these views. Through<br />

his 12-inch telescope, Ernst Hartung discerned a<br />

"rather faint but very rich globular cluster...<br />

irregularly round, rising broadly to the centre,<br />

about 3' across with rays of faint stars emerging."<br />

<strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong> 425

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!