The Properties of Stars•Luminosity- Another word for Brightness•Temperature•Mass
Brightness•Apparent brightness•Absolute brightness – Luminosity•Inverse square law
Stellar Mass•To directly determine mass, we need anorbiting object!•Binary Star Systems–Visual Binary–Eclipsing Binary–Spectroscopic Binary
Temperature•Color – continuous spectrum – where is thepeak of the emitted radiation?•Spectral lines – stars of differenttemperatures contain different elements,molecules, etc.
Temperature•Wien’s Law:The hotter the object, the bluer the radiation itemits, and the more total energy is emitted.
Temperature•The level of heat determines what sorts elements will be prominentin the star’s spectrum–For example only the hottest stars can ionize helium–Only the coolest stars can have molecules
Spectral Type Classification SystemOBAFGKMOhBeAFineGirl/Guy,KissMe!50,000 K3,000 KTemperature(L)
Stellar Evolution•Stars are like people in that they are born, grow up,mature, and die.•Astar’smassdetermines what life path it will take.•We will divide all stars into three groups:–Low Mass(0.08 Mh< M < 2 Mh)–Intermediate Mass (2 Mh< M < 8 Mh)–High Mass (M > 8 Mh)
Stellar Evolution•The life of any star can be described as a battlebetween two forces:–Gravityvs.Pressure•Gravity always wants to collapse the star.•Pressure holds up the star.–the type of star is defined by what provides thepressure
The Birth of Stars•Stars are born deep inmolecular clouds.–cold (10 – 30 K) dense nebulae–so cold that H2can exist•A cold cloud can fragment–gravity overcomes thermalpressure in dense regions–these regions (cores) becomemore dense and compactdark molecular cloud inScorpius