BI 253 is an O2V star in the

Large Magellanic Cloud The Large Magellanic Cloud (LMC) is a dwarf galaxy and satellite galaxy of the Milky Way. At a distance of around , the LMC is the second- or third-closest galaxy to the Milky Way, after the Sagittarius Dwarf Spheroidal Galaxy, Sagittarius Dwarf ...

and is a primary standard of the O2 type. It is one of the hottest

main-sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color versus brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or dwarf stars, and positions of star ...

stars known and one of the most-massive and most-luminous stars known.

Discovery

BI 253 was first catalogued in 1975 as the 253rd of 272 likely O and early B stars in the

. In 1995, the spectral type was analysed to be O3 V, the earliest type defined at that time. When the classification of the earliest type O stars was refined in 2002, the complete lack of neutral

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

or doubly ionised

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

lines in the spectrum led to BI 253 being placed in a new O2 V class. It was given a ((f^*)) qualifier because of the very weak emission lines of helium and nitrogen. The most recent published data gives a spectral type of O2V-III(n)((f^*)), although it is unclear whether this is due to higher quality spectra or an actual change in the spectrum. BI 253 has been identified as a runaway star because of its relatively isolated position outside the main star-forming areas of

30 Doradus The Tarantula Nebula (also known as 30 Doradus) is a large H II region in the Large Magellanic Cloud (LMC), forming its south-east corner (from Earth's perspective). Discovery The Tarantula Nebula was observed by Nicolas-Louis de Lacaille dur ...

, and because of its high space velocity. It was potentially ejected from the

R136 R136 (formerly known as RMC 136 from the Radcliffe Observatory Magellanic Clouds catalogue) is the central concentration of stars in the NGC 2070 star cluster, which lies at the centre of the Tarantula Nebula in the Large Magellanic Cloud. W ...

cluster about a million years ago.

Properties

BI 253 is one of the hottest, most massive, and most luminous known main sequence stars. The temperature is around 54,000 K, the luminosity over , and the mass of nearly , although its radius is less than . The rotation rate of around is high, but this is common in the youngest and hottest stars, either due to spin-up during stellar formation or merger of a close binary system.

Evolution

BI 253 is still burning hydrogen in its core, but shows enrichment of nitrogen and helium at the surface due to strong rotational and convectional mixing and because of its strong

stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, 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 spheri ...

. It is very close to the expected ZAMS position for an star. It is expected that stars more massive than BI 253 would show a

giant In folklore, giants (from Ancient Greek: ''wiktionary:gigas, gigas'', cognate wiktionary:giga-, giga-) are beings of humanoid appearance, but are at times prodigious in size and strength or bear an otherwise notable appearance. The word ''gia ...

supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...

luminosity class In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...

even on the main sequence.

References

{{DEFAULTSORT:BI 253 Stars in the Large Magellanic Cloud Large Magellanic Cloud Dorado Extragalactic stars O-type main-sequence stars Runaway stars J05373446-6901102 Emission-line stars O-type giants