Ads
related to: cepheids and pulsating temperature sensor
Search results
Results From The WOW.Com Content Network
Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months. Classical Cepheids are Population I variable stars which are 4–20 times more massive than the Sun, [ 24 ] and up to 100,000 times more luminous. [ 25 ]
Classical Cepheids are also known as Population I Cepheids, Type I Cepheids, and Delta Cepheid variables. There exists a well-defined relationship between a classical Cepheid variable's luminosity and pulsation period, [ 1 ] [ 2 ] securing Cepheids as viable standard candles for establishing the galactic and extragalactic distance scales .
In astronomy, a period-luminosity relation is a relationship linking the luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables, sometimes called the Leavitt Law.
Like all variables on the Cepheid instability strip, pulsations are caused by the κ-mechanism, when the opacity of ionised helium varies with its temperature. RR Lyraes are old, relatively low mass, Population II stars, in common with W Virginis and BL Herculis variables, the type II Cepheids.
For the regular variables (Cepheids, RR Lyrae, etc.) numerical stellar modeling and linear stability analysis show that κ is at most of the order of a couple of percent for the relevant, excited pulsation modes. On the other hand, the same type of analysis shows that for the high L/M models κ is considerably larger (30% or higher).
Type II Cepheids are not as well known as their type I counterparts, with only a couple of naked eye examples. In this list, the period quoted for RV Tauri variables is the interval between successive deep minima, hence twice the comparable period for the other sub-types.