QZ Carinae
QZ Carinae is a multiple star system in the constellation Carina. It is the brightest member of the loose open cluster Collinder 228 and one of the brightest stars in the Carina Nebula. The apparent magnitude is variable from +6.16 to +6.49 with a period of 6 days.
Description
Hierarchy of components in the QZ Carinae system, omitting the distant B and C components
QZ Carinae is approximately 2,300 parsecs from Earth in the Carina Nebula star-forming region.
QZ Carinae is a complex multiple star system made up of perhaps nine individual stars. Four massive luminous stars dominate the light output of the system. They form a quadruple system of two spectroscopic binaries: Aa and eclipsing binary Ac.
The A1/A2 and B1/B2 pairs take no more than 25 years to orbit each other, while the A pair completes an orbit around each other every 20.7 days and the B pair every 6.0 days. The system is bright at x-ray wavelengths primarily due to colliding stellar winds in the two close pairs. Pair A1/A2 contributes the bulk of the x-ray luminosity.
In 2014, a survey looking for companions of O-type stars reported resolving the Aa/Ac pair at a separation of. It also reported the long-known companions Ab, B and C at 1, 7.3, and respectively, as well as a faint component E at. Detailed examination of the vicinity of QZ Carinae for faint companions revealed 19 individual sources close to QC Carinae, but most are likely to be unrelated. Components Ab and E are considered very likely to be physically associated with the QZ Carinae system, as well as a new component Ad at. A 2022 paper described the system as containing nine components, including the widely-separated B and C, the very close Ab and Ad, and component E which they refer to as D.
Components
QZ Carinae A1 is a blue supergiant of spectral type O9.7I with around 70 times the Sun's mass that has expanded to 22 times the Sun's radius. With a surface temperature of, it is around 400,000 times as luminous as the Sun. Its partner A2 is a blue-white main sequence star of spectral type B2V with around 9 times the Sun's mass and 3 times its radius. With a surface temperature of, it is around 1,260 times as luminous as the Sun.QZ Carinae B1 is a hot blue giant that is expanding and cooling away from the main sequence. It is of spectral type O8III with around 25 times the Sun's mass and 14 times its radius. With a surface temperature of, it is around 200,000 times as luminous as the Sun. Partner B2 is a hot main sequence star of spectral type O9V with around 33 times the Sun's mass and 8 times its radius. With a surface temperature of, it is around 50,000 times as luminous as the Sun. Star B1 is less massive than B2 and is assumed to have undergone significant mass loss or mass transfer to B2. Together, all four stars have a combined mass 137 times that of the Sun.
The properties of the fainter component stars are difficult to determine, with orbits not well known, and even colours or spectral types difficult to determine for faint stars very close to the bright central pairings. Component Ad appears to be an A-type main sequence star with an effective temperature of, about twice the mass of the Sun, and 18 times as luminous. Component Ab is the most massive star outside the central four, around 10 to, but its other physical properties can only be guessed. The properties of component E are even more uncertain, but the most likely model is a star. An alternative model, a pre-main sequence star is considered less likely as it conflicts with the expected ages of the other stars in the system.