Sky and Telescope - December 2015 - 51

Sue French

Sue French welcomes your comments at scfrench@nycap.rr.com.

A
C

As shown by his sketches, Michael Vlasov easily resolved the triple
star Iota Cassiopeiae with an 8-inch f/5 Newtonian reﬂector at 125×.
3h 00m

2h 30m

2h 00m

1h 30m

+68°

ι
CASSIOPEIA

+66°

+64°

Stock 5
Tr 3
HDW 2

Star magnitudes

the bright primary (A) appears white, and there's a much
dimmer, orange companion (C) to its east-southeast.
Boosting the magniﬁcation to 117×, a brighter, yellowwhite companion (B) pops out close southwest of the
primary. These colors correspond fairly well with their
spectral types of A5 (A), F5 (B), and K3 (C).
Contrast illusions often play havoc with an observer's
perception of color, especially with tightly grouped stars
such as these. In his 1844 Bedford Catalogue, Admiral
William Henry Smyth described the A, B, and C components as pale yellow, lilac, and ﬁne blue, respectively.
Swedish astronomer Nils Christoﬀer Dunér saw the C
component as pink. Try detecting the hues of these stars
for yourself using two tricks to help you see colors better.
Slightly defocus the stars to give them a little dimension,
and increase the apparent separation of the stars with
high powers to lessen color-contrast eﬀects.
In the June 2006 Astronomical Journal, Julian
Christou and Jack Drummond published a remarkable
infrared image of Iota Cassiopeiae taken with the Lick
Observatory adaptive optics system. (Adaptive optics
improve a telescope's resolution by making rapid adjustments to a deformable mirror to compensate for image
blurring caused by atmospheric turbulence.) Iota's
image shows close, faint companions to both the A and
C components, the latter previously unknown. Further
measurements are needed to determine whether C and
its apparent companion form a true pair.
Another delightful group of stars is found in the
guise of Stock 5, an open cluster located 1.3°° northeast
of Epsilon (ε) Cassiopeiae. Through my 130-mm scope at
48×, its four brightest suns form a misshapen kite ﬂying
east-southeast. The kite's bottom is marked by 5.6-magnitude 53 Cassiopeiae, which appears yellow-white. The
northern star of the kite's crossbar seems creamy white
to me, and the southern one looks orange. About 20 faint
stars ﬁ ll out this 24′ group. Stock 5 looks more clusterlike at 63×, boasting a total of 45 stars. Most are concentrated in the vicinity of the kite, and the rest are loosely
scattered north of it.
Stock 5 lies about 3,600 light-years away from us, and
its stars have an average age of 50 million years. There
are roughly 180 probable cluster members within a 24′
diameter, but 53 Cassiopeiae and the bright, orange star
HD 12399 aren't among them.
My Deep-Sky Wonders column for January 2011
included the open cluster Trumpler 3 in far eastern
Cassiopeiae. It's visible in my 9×50 ﬁnder as a patch of
fog harboring 5 stars, while the 130-mm refractor at 37×
displays 30 fairly bright to faint stars loosely ﬂung across
nearly 18′. An orange gem adorns the southeastern quadrant. At the time, I twice attempted to observe nearby

+62°

3
4
5
6
7
8

In Royal Favor
Object

Type

Mag(v)

Size/Sep

Dec.

4.6, 6.9, 9.1

2.9″, 7.1″

02h 29.1m +67° 24′

Iota (ι) Cas

Triple star

Stock 5

Open cluster

24′

02h 04.4m +64° 23′

Trumpler 3

Open cluster

7.0

15′

03h 12.0m +63° 11′

HDW 2

Planetary nebula

5.7′

03h 11.0m +62° 48′

Psi (ψ) Cas Triple star

4.7, 9.2, 10.0 20″ (AC), 2.3″ (CD) 01h 25.9m +68° 08′

Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller
than the cataloged value and varies according to the aperture and magniﬁcation of the viewing
instrument. Right ascension and declination are for equinox 2000.0.

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Sky and Telescope - December 2015

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