Sky & Telescope - September 2019 - 59

HD 179124

S26

HD 179104

HD 179493

SS 433
HD 179596

t SS 433 The object that kicked off microquasar research, SS 433 is located some 10½′ north of HD 179285
and about 16′ southeast of 7th-magnitude HD 179104.

p P13 AND S26 IN NGC 7793 The supernova remnant
S26 lies on the northeastern edge of NGC 7793, which
is where you'll find the extragalactic microquasar in our
sample, P13.

POSS-II / CA LTECH / STSCI / PA LO M A R OBSERVATORY (2)

HD 179285

telescope. The donor star in SS 433 is
a supergiant, while consensus leans
toward a neutron star for the compact
object. The pair orbits each other every
13.1 days. The jets precess like a spinning top over a period of around 163
days, producing a distinctive corkscrew
pattern - the National Radio Astronomy Laboratory has made a "movie"
that spans some 42 days of observation
highlighting this effect: see https://
is.gd/ss433movie. In November 2003 I
located SS 433 using my 25-inch reﬂector and saw it as a stellar point with no
detail. I estimated it to be magnitude
14.5 and a little fainter than a parallelogram of stars 1.5′ to its northwest.
With the help of an O III ﬁ lter, I managed to spot two of its eastern fragments in my 32-inch.
So is that the end of the story? Not
quite. As often happens, once a new type
of object is identiﬁed, scientists know
what to look for and so they can extend
their reach into more exotic locales. Several years ago, preparing for the OkieTex Star Party, I was researching targets
and came across P13 in NGC 7793, a
galaxy in central Sculptor a little less
than 5° south-southeast of Delta Scl. I
can see moderate detail with my 32-inch
reﬂector of this 9.3-magnitude spiral

(type SA) at the relatively close distance
of 12 million light-years, with a very
open structure and a size of 9.1′ × 6.6′.
A 1997 extensive survey of the galaxy
identiﬁed multiple supernovae remnant
candidates. Follow-up X-ray and radio
observations showed that one of these,
S26, contained both a point source and
extended features, and was later identiﬁed to be a microquasar. P13 is considered to be the long-sought extragalactic
analog to SS 433, but on a much bigger
scale, spanning some 1,000 × 500 lightyears. Although P13 itself is too faint to
see, I easily spotted S26 as a 19th-magnitude stellaring on the northeastern
edge of NGC 7793 in a 9-mm eyepiece

at 361× at the Okie-Tex Star Party in
late September 2016. Three of my fellow
observers conﬁrmed the sighting.
For those who love the complexity
and interconnectedness of the night
sky, understanding the history of
microquasars, then pursuing and successfully observing them may evoke the
Japanese term yugen: a nearly ineffable,
deep emotional response to the mystery
and beauty of the Universe.
¢ DAVE TOSTESON has been an observer for more than 30 years. When
he's not working as a family physician in
Minnesota, he keeps busy by traveling to
regional star parties and solar eclipses.

Microquasars
Object

Donor
Companion

Spectral
Type

Mag(v)

Orbital
Period (d)

RA

Dec.

Cygnus X-1

HD 226868

O9.7I

8.9

5.6

19h 58.4m

+35° 12′

LS 5039

V479 Sct

ON6.5V

11.3

3.9

18h 26.3m

-14° 51′

Scorpius X-1

V818 Sco

Oev E

12.2

0.8

16h 19.9m

-15° 38′

-

B9III

13.7

2.8

18h 19.4m

-25° 24′

19h

11.8m

+04° 59′

23h 58.0m

-32° 33′

V4641 Sgr
SS 433
P13

V1343 Aql

A7Ib

14.2

13.1

-

B9I

20.5

64

Right ascension and declination are for equinox 2000.0.

sk yandtele scope.com * S E P TE M B E R 2 019

59
https://www.is.gd/ss433movie https://www.is.gd/ss433movie http://www.skyandtelescope.com
Sky & Telescope - September 2019

Table of Contents for the Digital Edition of Sky & Telescope - September 2019
