How do we use RR Lyrae to measure distances? RS Boötis Rachel Zheng UC Davis COSMOS Cluster 4 Astrophysics 2015

What Are Variable Stars? ●Stars whose brightness fluctuates as seen from Earth ●Extrinsic Variability: apparent changes in brightness o Ex: transit of an extrasolar planet, stellar rotation ●Intrinsic Variability: changes in the actual luminosity of the star o Ex: pulsating, eruptions

Variable Stars ●What causes pulsation? o When the star is fully expanded, gravity is stronger than the pressure in the star o Star starts contracting, becomes opaque, trapping the photons o The trapped photons create a lot of heat and pressure, so the star starts expanding again, releasing the photons o Cycle starts over again

Variable Stars ●Standard Candle o An object with a known luminosity o Can be used to measure distances to stars farther away from us

RR Lyrae Variable ●short period ( days) ● magnitude ●usually class A white stars ●found in globular clusters ●low mass Compared to Cepheids: ●dimmer and smaller than Cepheids ●shorter period ●higher frequency

RS Boötis ●A type of pulsating RR Lyrae star ●Located in the constellation Boötis ●Subclass RRab o most common type o steep rises in brightness

How do we calculate the distance to RS Boötis?

Data Reduction ●Received data of RS Boo in the blue filter ●Data from 7 days, 4/28/12 - 5/14/12 ●Imported pictures into CCDSoft ●Data Reduction: o Dark Current o Flat Field

The Arduous Process - ÷ = ÷ YAY!!

Light Curve ●Astrometry ●Pre-analyze ●Picked reference stars C and K ●Generated light curve ●Saved graph as a text file

Folding the Light Curve ●Loaded data from text file into IPython ●Plotted the apparent magnitude as a function of time ●How do you find the period? o φ = t - t o / p ●Found the period was.3773 days, or 9 hours

Calculations ●Apparent Magnitude = ●Absolute Magnitude = 0.75 o How do we calculate M? ●Distance Modulus: o m − M = −5 + 5 log 10 d ●distance = parsecs

Results My Results ●Period = days ●m = V ●M = 0.75 ± 0.1 V ●d = ± parsecs Actual Measurements ●Period = days ●m = V

What is the Importance? ●Research on variable stars provides information about stellar properties that can then be used to understand other stars o help understand the future evolution of our own star ●Variable stars play a major role in determining distances to other objects such as galaxies and other stars

Works Cited "RR Lyrae Variable." Wikipedia. Wikimedia Foundation, n.d. Web. 29 July "TYC " TYC Simbad. N.p., n.d. Web. 29 July "Pulsating Variable Stars." Australia Telescope National Facility. N.p., n.d. Web. 29 July "Interstellar Medium and the Milky Way." Interstellar Medium and the Milky Way. N.p., n.d. Web. 29 July "VSX : Detail for RS Boo." VSX : Detail for RS Boo. N.p., n.d. Web. 29 July Bisque, Matthew L. CCDSoft. Vers Computer software. Software Bisque, Windows 7, 99.2 MB, download. IPython. Pylab Mode. Computer software. Python Software Foundation, Windows 7, 20.7 MB, download. Ben Cain.

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