Question

Choose one of the three following topics and write up a brief summary. You can assume solar metal content for the star:

• What is a blue straggler, and what process or processes have been invoked to explain their existence?
• Why are Cepheid and RR Lyrae stars only observed to exist in a narrow range of effective temperatures, and why is the period related to the luminosity?
• Choose a category of stars that experience much higher mass loss than the norm, excluding explosive events, and describe why their mass loss rate is so high.

Answer 1

A blue straggler is a main sequence of stars in an open or globular cluster that is more luminous and bluer than the stars at the main sequence turnoff point for the cluster.

A clue to their origin is that they are only found in dense stellar systems, where distances between stars are extremely small (a fraction of a light year). In these dense environments (for example the cores of globular clusters), collisions between stars are relatively common, and it has long been believed that blue stragglers are the result of the merger of two old, red stars. This merger produces a star with a greater mass (hence bluer in colour), and severely disrupts the two stars involved, mixing hydrogen into the stellar core and giving the star a new lease on life.

We can conclude that it may be formed due to the collision of nearby stars