M13 CEPHEID VARIABLE STAR - V2 ELVIRA CRUZ-CRUZ UC COSMOS ASTROPHYSICS 24 JULY 2015

M13 “THE GREAT GLOBULAR CLUSTER IN HERCULES”  Star Cluster -Located in the constellation Hercules -Found between the two brightest stars: Vega and Arcturus -Considered to be one of the oldest clusters

VARIABLE STARS  Stars whose brightness changes periodically  Classified into subcategories  Most common- RR Lyrae and Cepheids How do we know?  If the absolute magnitude of the star is altered in any way seen here from Earth.

VARIABLE STARS Changes in star luminosity and/or in the star’s mass The light variations that occur in different variable stars allow for the classification of variable stars into several categories. The change in brightness of these stars ranges from.001 of a magnitude to 20 magnitudes depending on the type of variable star. Intrinsic Variables:  The stars luminosity changes due to pulsations, eruptions, or through swelling and shrinking occurring in the star. Extrinsic Variables:  Changes in brightness happen in the star because of it being eclipsed by another star or planet.

RR LYRAE VARIABLE STARS Pulsating variable stars Has a short pulsation period (.05 to 1.2 days), from.3 to 2 magnitudes Class A white giant stars Pulsations are radial, which means that the stars remain in a spherical shape Older and less massive than Cepheids Considered a Standard Candle

CEPHEID VARIABLE STARS Very luminous stars (500 to 300,000 times greater than the sun) Pulsating variables- pulsate with in a short period of time; have a specific pattern Pulsating period from 1 to 70 days Light variations from 0.1 to 2 magnitudes High luminosity Part of F spectral class at its max and G to K at its minimum The longer the period, the more luminous the star. Example:

WHY IS THIS IMPORTANT? Provides information of stellar properties  Mass  Radius  Luminosity  Temperature  Internal and external structures  Composition  Evolution Edwin Hubble:  He discovered with the variable star, Cepheid Variable Star V1, that the Milky Way was not the whole universe, but only a part of it; due to the fact that V1 was located in a different galaxy (M31-V1).

CALCULATING DISTANCE (V2) (FOR A CEPHEID STAR)

LIGHT CURVES The period and apparent magnitude of the star can be seen by generating a light curve. Period- Luminosity relationship founded by Henrietta Leavitt Period- Luminosity Relationship: Longer period= more luminous star

CALCULATIONS Period : m= 13.0 M= Distance= 5.6 kpc

WORKS CITED Chandra. Chandra X-Ray Observatory. 9 March July Commonwealth Scientific and Industrial Research Organisation. Australia Telescope National Facility July "Google Images." Google Images. Web. 30 July Google Search. Web. 30 July Vzy-ICh2ImgRM#imgrc=bukJPk05wjDp3M%3A "Light Curve of a Cepheid Variable - Google Search." Light Curve of a Cepheid Variable Space.com Staff. Types of Variable Stars: Cepheid, Pulsating and Cataclysmic. 28 January July Swineburne Cosmos: Distance Modulus. n.d. Swineburne University of Technology. 25 july Types of Variables. Ed. BSJ. 18 June July