Task: Text Categorization
Input (English): Subclasses of this type of object are named for Delta Scuti and W Virginis. Doubly ionized helium converts to singly ionized helium in the atmosphere of these stars as they expand and contract, creating its characteristic "shark fin" light curve. Henrietta Leavitt used large populations of these stars in the Magellanic Clouds to develop a (*) period-Luminosity relation for them, and Edwin Hubble used this relationship to calibrate his namesake constant of universe expansion. For 10 points, name this class of intrinsic variable stars used as standard candles .
Output (English): Science