The stellar birthline is a predicted line on the Hertzsprung–Russell diagram

Hertzsprung–Russell diagram

The Hertzsprung–Russell diagram is a scatter graph of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their spectral types or classifications and effective temperatures. Hertzsprung–Russell diagrams are not pictures or maps of the locations of the stars...

 that relates the colour

B-V colour

B-V colour is one of the two colour indices in the UBV photometric system.Astronomers measure the amount of light a star gives off in different colours. Hot stars give off more blue light than red; cool stars give off more red light than blue. Coloured filters are used to measure different...

 and luminosity

Luminosity

Luminosity is a measurement of brightness.-In photometry and color imaging:In photometry, luminosity is sometimes incorrectly used to refer to luminance, which is the density of luminous intensity in a given direction. The SI unit for luminance is candela per square metre.The luminosity function...

 of protostar

Protostar

A protostar is a large mass that forms by contraction out of the gas of a giant molecular cloud in the interstellar medium. The protostellar phase is an early stage in the process of star formation. For a one solar-mass star it lasts about 100,000 years...

s at the end of the initial phase of accretion onto them. Prior to this point, the protostar is deeply embedded in the cloud of dust

Cosmic dust

Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...

 and gas from which it formed, and so radiates only in the far infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

. Once evolutionary effects

Stellar evolution

Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...

 rarefy and disperse this cloud,
the star becomes visible as a pre-main-sequence object. The set of locations on the Hertzsprung–Russell diagram where these newly visible stars reside is called the birthline, and is found to the right of the main sequence

Main sequence

The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

.

The location of the stellar birthline depends on the stellar structure, the accretion

Accretion (astrophysics)

In astrophysics, the term accretion is used for at least two distinct processes.The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc. Accretion discs are common around smaller stars or stellar remnants...

 rate onto the star and geometry of this accretion, i.e. whether or not it is occurring through an accretion disk. This means that the location of the birthline is not uniquely defined.

External links

• http://jila.colorado.edu/~pja/stars02/lecture29.ps – several low-quality plots with the stellar birthline