TZ Cassiopeaie (TZ Cas, HIP 117763, SAO 20912) is a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...

in the constellation Cassiopeia with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

of around +9 to +10. It is approximately 8,400

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away from Earth. The star is a

red supergiant star Red supergiants (RSGs) are stars with a supergiant luminosity class (Stellar classification#Yerkes spectral classification, Yerkes class I) of spectral classification, spectral type K or M. They are the List of largest stars, largest stars in the ...

with a spectral type of M3 and a

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

below .

TZ Cassiopeiae was reported as being variable by

Williamina Fleming (15 May 1857 – 21 May 1911) was a Scottish-American astronomer. She was a single mother, hired by the director of the Harvard College Observatory to help in the photographic classification of stellar spectra. She helped develop a common d ...

and published posthumously in 1911. It is a slow irregular

with a possible period of 3,100 days. It is over 90,000 times the

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

of the Sun, and it is 767 times larger than the Sun. It is a member of the Cas OB5

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more stars. The stars share a common origin, but have become gravitationally u ...

, together with the nearby red supergiant

PZ Cassiopeiae PZ Cassiopeiae is a red supergiant star located in the constellation of Cassiopeia (constellation), Cassiopeia, and a semi-regular variable star. Characteristics PZ Cassiopeiae is a luminous red supergiant star, one of the List of larg ...

. The initial mass of TZ Cassiopeiae has been estimated from its position relative to theoretical

stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is cons ...

ary tracks to be around . TZ Cas is losing mass through a powerful

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

at two millionths of a solar mass each year. It is unclear whether this is sufficient to cause the star to lose its atmosphere and become a blue supergiant before the core exhausts its fuel and collapses as a supernova. Either as a red or blue supergiant, or a

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

, it will inevitably end its life violently in a supernova explosion when the core collapse occurs.

References

{{Stars of Cassiopeia Cassiopeia (constellation) Slow irregular variables M-type supergiants Cassiopeiae, TZ 117763 BD+60 2634 J23525623+6100083