Sigma Sculptoris
A binary star in Sculptor, faintly visible to the naked eye.
σ Sculptoris, commonly written as Sigma Sculptoris, is a binary system located in the southern constellation Sculptor. With an apparent visual magnitude of +5.54, it is just bright enough to be seen without a telescope. Parallax measurements place it roughly 232 light-years from Earth.
The primary star is an A-type star, classified as A1/A2 IV in older catalogs, though more recent studies assign it a spectral type of A2V and describe it as a somewhat evolved main-sequence star. Earlier suspicions that it might be an Ap or Am star, or an Alpha² Canum Venaticorum variable, were not confirmed by observations in 2018. This star has about 1.95 times the Sun’s mass and roughly twice its radius. It rotates at a projected speed of 82 km/s and is estimated to be 560 million years old. Its photosphere radiates 25.7 times the Sun’s luminosity at an effective temperature of 8,470 K.
The secondary star is much smaller, with only 72% of the Sun’s mass and a brightness 5.7 magnitudes fainter than the primary.
The designation Sigma Sculptoris has not always belonged to this star. It was originally assigned by Lacaille when he created the constellation Sculptor. Later, when Bode formed his own constellation Machina Electrica, he took roughly half of Sculptor along with parts of Fornax, including this star, which he renamed Zeta Machinae Electricae. Bode instead used the name Sigma Sculptoris for the star HD 220929 (HR 8914). After the International Astronomical Union retired Machina Electrica, all stars were returned to their original constellations.
- Apparent visual magnitude
- +5.54
- Distance
- 232 light years
- Spectral type (primary)
- A1/A2 IV (also given as A2V)
- Mass (primary)
- 1.95 solar masses
- Radius (primary)
- 2 times solar
- Projected rotational velocity
- 82 km/s
- Age
- 560 million years
Lore & Background
The main component is an A-type star with a stellar classification of A1/A2 IV, although many modern papers use a spectral class of A2V and describe Sigma Sculptoris as a somewhat evolved main sequence star. It was suspected to be an Ap or Am star, and an Alpha2 Canum Venaticorum variable, but no chemical peculiarity or variability was found in 2018. The star has an estimated 1.95 the mass of the Sun and around two times the Sun's radius. It is spinning with a projected rotational velocity of 82 km/s and is about 560 million years old. Sigma Sculptoris radiates 25.7 times the solar luminosity from its photosphere at an effective temperature of 8,470 K. The secondary is a relatively small star with 72% the mass of the Sun, 5.7 magnitudes fainter than the primary.
Reader's Guide
The designation Sigma Sculptoris has not always been allocated to this star. It was given this designation by Lacaille when he created Sculptor. When Bode created his own constellation Machina Electrica, he took about half of Sculptor and parts of Fornax, including this star, which he designated Zeta Machinae Electricae. Bode used Sigma Sculptoris for HD 220929 (HR 8914) instead. After Machina Electrica was deemed obsolete by the IAU, the stars were returned to their original constellations. This history illustrates how star designations can shift with the creation and dissolution of constellations. The star's suspected variability and chemical peculiarity were not confirmed, leaving its classification as a stable A-type binary. Its legacy lies in its role as a faint but persistent marker in the southern sky, and as a case study in the evolution of constellation boundaries and nomenclature.
Did You Know?
- Sigma Sculptoris was once designated Zeta Machinae Electricae in Bode's now-obsolete constellation Machina Electrica.
- The secondary star has 72% the mass of the Sun and is 5.7 magnitudes fainter than the primary.
- Bode used the designation Sigma Sculptoris for a different star, HD 220929 (HR 8914).
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