Chapter 10:Characterizing the Stars
Chapter 10:Characterizing the Stars 41087 - AST 115 - A
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This 3 page Bundle was uploaded by Ashley Notetaker on Sunday November 1, 2015. The Bundle belongs to 41087 - AST 115 - A at Missouri State University taught by Robert S Patterson in Fall 2015. Since its upload, it has received 24 views. For similar materials see Basic Astronomy in Physics 2 at Missouri State University.
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Date Created: 11/01/15
Chapter 10 Characterizing Stars Measuring Distance to Stars Surveying Basic method of measuring stars based on phenomenon of parallax Stellar parallax The apparent shift in position of a nearby star as we change our advantage point while the Earth orbits the Sun d 1 Stellar parallax angle or d 1p Stellar parallax angle must b in arc seconds d must be in parasec 1 parasec 326 ly Max distance using stallar parallax From Earth d min about 01 parasec d Max about 100 parasec Brightness of the Star Magnitudes Brightest stars seen from Earth runs backwards like golf 1 Brightest 6 Dimmest A difference between 61 5 magnitude ratio of 100 0 amp negative 5 for objects brighter than 1 magnitude 6 for objects too faint to see w naked eye Ex Sun 265 Full moon 12 Jupiter 25 Vega 0 Polaris 2 Definitions Apparent Magnitude m Brightness of a star current distance from Earth Absolute Magnitude M Brightness of a star seen from a standard distance of 10 parasec Sirius is the brightest star from Earth Alpha Sentari is the closest star to Earth Distance Modules mM Apparent Magnitude m minus Absolute Magnitude M A measure of the distance to a star The more the star the further away it is More About Magnitudes The magnitudes above are known as visual magnitudes Visual magnitudes bc special filters were used to limit what part of the spectrum contributes to brightness Originally yellow glass filters were used but any color can be used Yellow was used bc it was similar to what human eyes see Temp of star color Redder the star the cooler it is U Ultraviolet B Blue V Visual Color Index The difference between Blue amp Visual BV magnitude of a star It is used to determine a stars temp More cooler Inverse Square Law of Electromagnetic Radiation How much E passes through a unit area at a distance from the source Gets dimmer the further away proportional to brightness 1dquot2 For a given detector eye CCD etc the brightness is the energy received per unit area Stellar Spectra Spectrum of star tells star chem makeup and temp The darkness or quotstrengthquot of spectral lines tells temp Each element shows diff strength over the normal temp range 2500 K 50000 K Spectral Classification Astronomers sort stellar spectra using capital letters in order AO Later learned that surface temp determines the appearance of the spectrum Redundant classes were deleted leaving 7 classes Hottest Coolest OBAFGKM Oh Be A Fine Girl Kiss Me Decimal subdivision are used Ex F7 F8 G0 G1 The classes quotLquot and quotTquot have been added to the sequence for objects w very low surface temps Brown Dwarfs Spectral classification is done by comparing unknown spectra to standard ones The spectral class for the Sun G2 Types of Stars HR Diagram An important tool used by astronomers to study properties amp how they change over time The underlying physical properties of HR diagram are luminosity and surface temp Binary Stars Discovered by Herschel who showed that these stars are gravitationally bound to each other Multiple star systems can have 2 stars all are referred to as binary Optical Double Not binary just 2 stars aligned by chance Recent estimates show that 23 of stars exist as single But slightly more than 12 are binary all stars in binary system are counted that is why s don t match up Categories of Binaries VASE VVisual 2 stars orbiting a common gravitational center AAstrometric Presence of 2ncl star shown by wavy proper motion 5 Spectroscopic Presence of 2 stars is shown by double andor moving spectral lines E Eclipsing 2 Stars get in each other s way bc the place of their orbit is in our line of sight Categories are not mutually exclusive
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