Krzeminski's Star
Encyclopedia
Krzeminski's Star is a 20.5 solar mass slightly evolved blue supergiant with a radius of 11.8 solar radii and spectral type O6.5II. It is estimate to be 8 kpc distant. Most notably, it is the visible component of the occulting spectroscopic binary system that forms the X-ray pulsar
called Cen X-3.
Despite detailed data from the Uhuru satellite
as to the orbital period of the binary, and the pulsation period in the X-ray band as well as the minimum mass of the occulting star, the optical component remained undiscovered for three years.
This was partly because Cen X-3 lies in the plane of the Galaxy in the direction of the Carina Spiral Arm, and so observations were forced to differentiate among dozens of faint objects. Centaurus X-3 was finally identified with a faint, heavily reddened variable star lying just outside the error box predicted by Uhuru observations. The visible star was later named after its discoverer, Wojtek Krzemiński, and published in the Astrophysical Journal (Krzemiński, W 1974 Astrophys J. 184 271).
There is little doubt as to the correctness of the optical candidate, since it is in apparent agreement with the period and phase of Cen X-3, and exhibits the same similarity in its double wave and amplitude light curve seen in other known massive binary systems. The double wave ellipsoidal light variations are produced by a tidally deformed giant that nearly fills its Roche lobe
. Also, the visible component corresponds to a BO II class star, comparable with the mass derived from X-ray data, consistent with the minimum radius that has been fixed by X-ray eclipse duration.
Using a BO II stellar classification
model, the distance to Cen X-3 is calculated at 8 kpc. A lower limit on the distance can be estimated from the relation between luminosity, effective temperature
and minimum radius of the optical star. Assuming an effective temperature of 30,000 kelvin
s, for a BO type star, and a bolometric correction
of -2.90, the lower limit for the distance is 6.2 kpc.
X-ray pulsar
X-ray pulsars or accretion-powered pulsars are a class of astronomical objects that are X-ray sources displaying strict periodic variations in X-ray intensity...
called Cen X-3.
Despite detailed data from the Uhuru satellite
Uhuru (satellite)
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A , SAS 1, or Explorer 42.The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km...
as to the orbital period of the binary, and the pulsation period in the X-ray band as well as the minimum mass of the occulting star, the optical component remained undiscovered for three years.
This was partly because Cen X-3 lies in the plane of the Galaxy in the direction of the Carina Spiral Arm, and so observations were forced to differentiate among dozens of faint objects. Centaurus X-3 was finally identified with a faint, heavily reddened variable star lying just outside the error box predicted by Uhuru observations. The visible star was later named after its discoverer, Wojtek Krzemiński, and published in the Astrophysical Journal (Krzemiński, W 1974 Astrophys J. 184 271).
There is little doubt as to the correctness of the optical candidate, since it is in apparent agreement with the period and phase of Cen X-3, and exhibits the same similarity in its double wave and amplitude light curve seen in other known massive binary systems. The double wave ellipsoidal light variations are produced by a tidally deformed giant that nearly fills its Roche lobe
Roche lobe
The Roche lobe is the region of space around a star in a binary system within which orbiting material is gravitationally bound to that star. If the star expands past its Roche lobe, then the material can escape the gravitational pull of the star. If the star is in a binary system then the material...
. Also, the visible component corresponds to a BO II class star, comparable with the mass derived from X-ray data, consistent with the minimum radius that has been fixed by X-ray eclipse duration.
Using a BO II stellar classification
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
model, the distance to Cen X-3 is calculated at 8 kpc. A lower limit on the distance can be estimated from the relation between luminosity, effective temperature
Effective temperature
The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation...
and minimum radius of the optical star. Assuming an effective temperature of 30,000 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s, for a BO type star, and a bolometric correction
Bolometric Correction
In astronomy, a bolometric correction is a correction that must be made to the absolute magnitude of an object in order to convert an object's visible magnitude to its bolometric magnitude. Mathematically, such a calculation can be expressed: BC = M_b - M_v\!\,...
of -2.90, the lower limit for the distance is 6.2 kpc.