The Carbon Star T-Lyrae

June 11, 2020

T Lyra in Lyra Constellarion EPOD

Photographer: Dario Giannobile
Summary Author: Dario Giannobile 

The image above showing the constellation Lyra with the intensely colored star, T Lyrae, was taken from near my home in Syracuse, Sicily, Italy. That the stars have color is appreciated by any amateur astronomer. A star’s color is directly related to its surface temperature. Like a piece of iron that’s gradually heated, the color goes from dark red to yellow and to dazzling white. An orange-red star has a temperature of about 3,500 C, a yellow one, like the Sun, about 5,500 C and blue stars approximately 30,000 C.

In order to classify the color of the stars, and therefore obtain their temperature, a scale was introduced in the 1950s made by measuring the apparent brightness in different photometric bands. This scale is called B-V. The more positive the value of a star, the colder and redder the star. For instance, Betelgeuse has a B-V value of 1.85.

The sky is full of small cold, red gems that have highly positive indices, such as the very red star T Lyrae. Its color index is 5.46! Spectroscopic analysis of T Lyrae and similar stars show the marked signature of carbon, and for this reason, they’re referred to as carbon stars. Note that all carbon stars exhibit changes in brightness.