Sky & Telescope - May 2021 - 24

One-hit Wonders

M AY 2 0 2 1 * S K Y & T E L E S C O P E

NGC 4618 HST: ESA / HUBBLE / N ASA / I. K A R ACHEN TSE V; NGC 4214 HST: N ASA / ESA / HUBBLE HERITAG E TE A M / STSCI / AUR A / ESA / R. O'CONNELL / WFC3 SCIEN TIFIC OV ERSIG H T
CO M MIT TEE; SK E TCH: SCOT T H A RRINGTON; K ISO 5639 HST: N ASA / ESA / D. ELMEG REEN / B. ELMEG REEN / J. A LMEIDA , C. M UNOZ-T UNON / M. FILHO / J. MENDE Z-A BREU / J.
G A LL AG HER / M. R A FELSK I / D. CE V ERINO; DSS: POSS-II / STSCI / CA LTECH / PA LO M A R OBSERVATORY (2)

Star magnitudes

that's offset to the north and strongly
13h 00m
12h 30m
12h 00m
11h 30m
11h 00m
elongated northeast to southwest. With
M63
averted vision, the hazy glow of the
3
4618 β
M94
galaxy's disk extends nearly halfway to
4
+40°
the 11th-magnitude star. Images show
5
6
this is due to the galaxy's bright arm,
α
7
6
which is evident in the eyepiece as a
8
URSA MAJOR
broad curve that's slightly brighter than
4244
C
A
N
E
S
V
E
N
A
T
I
C
I
the disk. The arm appears attached
4214
to the northeast end of the core and
+35°
4861
sweeps counterclockwise before disappearing on the galaxy's western side.
ν
Upon closer inspection, I can glimpse
Kiso 5639
an extended diffuse spot on the arm's
3788
3786
ξ
outside edge as it swings closest to that
62
+30°
11th-magnitude star.
In the Hubble Space Telescope (HST)
image on page 25, this knot - which
carries the designation IC 3668 - is well resolved into indiin the same direction for another 3.4° will bring you to the
vidual stars. What I'm seeing, then, is an older H II/SFR in
dwarf starburst galaxy NGC 4214 and safely past the clutches
which the nebula has mostly dissipated, revealing a wealth
of the much more arresting edge-on galaxy NGC 4244.
of hot, massive O- and B-type stars. In my scope it appears
NGC 4214 is the only galaxy on our tour that I've seen in
distinctly nonstellar.
my 7×35 binoculars. At 73× in my 10-inch, my ﬁ rst impresLying just 3.5° south-southeast of 3rd-magnitude Alpha
sion is that of a 2.5′ × 2′ soft disk that has an intensely
(α) CVn is another tadpole galaxy. This one is an even
bright but irregular central band running northwest to
more amazing enigma for the visual observer! At 73× in
southeast. Inside this band is a strongly condensed core
my 10-inch, NGC 4861 is visible 15′ southwest of a pair of
that shines at about magnitude 13.5. There is a scattering of
ﬁve 14th- and 15th-magnitude stars to the galaxy's north7th-magnitude stars that are 4.8′ apart and aligned nearly
ern and eastern edges, along with an 11.8-magnitude star
north-south. The galaxy is easy to overlook, appearing only
only 4.5′ to the southeast. At 153× the shape of its bright,
as a dim streak spanning a 2.5′ gap between two stars of
elongated center vaguely reminds me of a shrimp. It appears
roughly 13th magnitude. Upon closer inspection at 264×,
even more irregular along its length - it bulges to the
the dimmer (I estimate magnitude 13.3) and more southnortheast, and a small bright section of about magnitude 14
ern of the two stars begins to appear nonstellar. It's hard to
is seemingly detached from its southeastern end. At 264×,
believe until you've seen the HST image (page 22), but this
its center appears mottled while the detached section forms
" star " is actually a highly luminous and compact H II/SFR
an arc that bulges west. By adding a UHC ﬁ lter, the whole
knot known as Markarian 59.
length of the central bar responds favorably, revealing an
Surprisingly, Mrk 59's true nature was suspected as early
emission component.
as 1855, just 70 years after William Herschel discovered the
As seen in the HST image on page 25, NGC 4214 has a
host galaxy. That's when R. J. Mitchell, an assistant observing
confusing jumble of H II complexes and knots running down
with the 72-inch reﬂector of William Parsons, the third Earl
its middle. Professional astronomers label the large central
of Rosse, recorded " . . . [NGC 4861] has a plain star in north
extremity and either a star or what looks more like a bright lit- H II complex NGC 4214-I and the smaller detached complex NGC 4214-II. They further break NGC 4214-I into two
tle knot involved in south end. " It wasn't until 1974, however,
substructures (I-A and I-B). Region I-A is the H II region in
that Mrk 59 was identiﬁed as a super-giant H II region. It's
which a massive, young super star cluster has evacuated the
now one of the largest known at some 8,000 light-years across
gas at its center. Known as I-As, it lies among a rich spray of
and has an ultra-luminous X-ray source associated with it.
O-type stars and contains several hundred O-type and WolfI've looked for NGC 4861 in my 5.1-inch and found its
Rayet stars of its own. My big surprise came when I realized
dim streak just barely detectable at 59×. But I've seen Mrk 59
that I-As is the condensed core I saw!
in my 10-inch with a 75-mm off-axis mask. If you want to
Smaller NGC 4214-II consists of about half a dozen H II
see the H II/SFR but are having trouble making out its host
knots involved with three massive OB associations, which are
galaxy, try blinking the ﬁeld with either an O III or UHC
ﬁlter. Mrk 59, like Mrk 71, is among the few extragalactic H II a little older than the ones in NGC 4214-I. If you have the
opportunity to observe this galaxy with a large telescope, look
regions that respond well to ﬁlters.
for two super star clusters of roughly 16th and 17th magniStaying in Canes Venatici, return to Beta CVn and drop
tudes just north of its core.
2.8° south-southwest to 5th-magnitude 6 CVn. Continuing

Sky & Telescope - May 2021

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