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Download Computer Modeling the Line of Sight Column Densities of Polars
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Computer Modeling the Line of Sight Column Densities of Polars Mentor: Dr. Jennifer Cash Student: Scott Swindell Outline ● ● ● Description of Polars – Evolution of stars – white dwarf and main sequence star – Cataclysmic Variables Column Density (CD) – What do we see in observations of Polars – Why do we want to model the CD How do we model the Column Densities – SPH – Know the behaviour of the stream – IDL ● What's Next ● Why do we care ● Acknowledgments White Dwarf and Main Sequence Stars White Dwarf Main Sequence When a star that has exhausted its nuclear fuel and has stopped all fusion processes. It then begins to expand and looses all of its outer gas until only the very hot core remains. The radius of the core is generally around 1/100th the radius of the sun. A star that has entered its “adult” phase. It is characterized by its nuclear fusion. Our Sun is in its main sequence phase of life. Cataclysmic Variables ● ● ● Binary Star made of White Dwarf and a Main Sequence Star. The more massive White Dwarf gravitationally pulls plasma from the Main Sequence Star. The plasma whirlpools around the White Dwarf in an accretion disc. Polars Polars are a type of CV that has a strong magnetic field around 100 million times earths magnetic field. The plasma is not allowed to form an accretion disc because it follows the magnetic field lines. The stream takes a more direct path toward the white dwarf. The high speeds of the impacting particles creates a hot spot Polars The accretion stream • • • • • L1 Point: material is pulled off main sequence star Coupling Region: Primary force acting on stream changes from gravitational to magnetism Ballistic Stream: material flow is directed by gravity L1 Stream : smaller stream that was coupled at the L1 point and therefore is under magnetic influence Hot Spot: Point of impact of the stream on the white dwarf produces EUV’s and Soft x-rays L1 L1 Stream Balli stic S tream Coupling Region Hot Spot Why do we care ● The Magnetic Field – ● Polars have one of the most powerful magnetic fields in the universe The Plasma Stream – This a great chance to study thin plasmas in extreme magnetic fields Observations of Polars The Flux varies dramatically with time but repeats the variations making a pattern. This tells scientists that the source of flux is being eclipsed by something. Observers can usually tell if the main sequence star is eclipsing the white dwarf. It is more difficult to determine when the stream is eclipsing the source of radiation. Observations of Polars L1 Stream eclipse Stream Eclipse Secondary Star Eclipse Self Eclipse Modeling Polars Fortran Interactive Data Language (IDL) •Older Language • High level code •Designed for fast calculations • Easier to use than older languages •Write, Compile, Run • GUI tools Very strict syntax • Command line interaction • Ideal for visualization of Data Modeling Polars Smooth Particle Hydrodynamics • It is difficult to model fluids and gasses. • Computer modelers need a method of representing all the particles without actually accounting for each atom • SPH models groups of particles as one unit which makes computation much easier • The graph is a 1 dimensional density verses radius for an individual unit in an SPH model Modeling Polars Dr Cash created Fortran code to model the forces within the stream This code gives the position density and velocity of each SPH particle Internals Structure Ballistic: The rotational and gravitational forces in the stream Thermal : The pressure and density gradients Magnetic: Ions following the magnetic field lines of the white dwarf Modeling Polars I wrote IDL code to extract the column densities of the modeled Polar • Reads in the data from Dr. Cash’s Code • Finds the axes of the cube • Rotates the axes for a given line of sight. • Extracts density information Modeling Polars Modeling Polars Modeling Polars • What were really interested in is the column density between us and the hot spot • Instead of calculating all the column densities of the system we just calculate it for the position of the white dwarf. • We do this for many phases Whats Next Further refinement of code and data Compare analysis with observation Acknowledgments ● ● ● Dr. Jennifer Cash, Dr. Donald Walter, Ms Irene Scott, Mr. Joe Bartolini, Dr. Payne, Dr. Smith All Uria students This work has been supported in part by NASA/MUSPIN (NNG04GD62G) NASA's Science Mission (NNG04GD62G) and NASA URC through a subgrant from Tennessee State University (NCCW0085).
