S Apodis

Lore & Background

HD 133444 was discovered to be a variable star by Williamina Fleming, who examined images of the star on 58 photographic plates taken from 1889 through 1895. The discovery was announced in 1896. Annie Jump Cannon included the star, with its variable star designation S Apodis, in her 1907 Second Catalogue of Variable Stars. However, its nature as a carbon star was not observed until 1967 by astronomer Brian Warner. In 1973, HD 133444 was listed as a R Coronae Borealis variable. These are extremely hydrogen-deficient supergiants thought to have arisen as the result of the merger of two white dwarfs and fewer than 100 have been discovered as of 2013. A decade later, S Apodis was observed to have a change in its pulsation mode.

S Apodis has a stellar classification of R3, indicating that it is a R-type carbon star. It has a mass of either 0.6 M☉ or 1 M☉, depending on the model. However, it has expanded to an average radius 132 times that of the Sun. It radiates 960 times the luminosity of the Sun from its photosphere at an effective temperature of 4,500–5,115 K, giving it an orange hue. An infrared excess has been detected around the star, indicating the presence of circumstellar dust. The dust has a temperature of 730 K.

Reader's Guide

S Apodis holds significance as a rare R Coronae Borealis variable, a class of extremely hydrogen-deficient supergiants thought to result from the merger of two white dwarfs. As of 2013, fewer than 100 such stars had been discovered, making S Apodis a valuable object for studying stellar evolution and merger products. Its discovery by Williamina Fleming in the late 19th century, using photographic plates from 1889 to 1895, highlights early contributions to variable star astronomy. The star's classification as an R-type carbon star (R3) and its observed change in pulsation mode a decade after 1973 add to its astrophysical interest. The detection of circumstellar dust at 730 K, along with its uncertain mass (0.6 or 1 M☉) and relatively large radius (132 R☉), provides constraints for models of evolved stars. Its heliocentric radial velocity of −75 km/s indicates it is drifting closer to the Solar System, while its distance of about 15,000 light years places it far away. The star's legacy includes its role in the history of variable star cataloging, from Fleming's discovery to Cannon's 1907 catalogue, and its later identification as a carbon star by Brian Warner in 1967.

Did You Know?

• In 1973, it was listed as a R Coronae Borealis variable, a class with fewer than 100 known members as of 2013.
• An infrared excess indicates circumstellar dust with a temperature of 730 K.