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beta Cephei1/14/2019We are up all night, observing various stars in the night sky, recording their spectra, using our star charts and coordinates to find them, and taking sometimes very long exposures as some of the stars are fairly dim. After getting a good night’s (day’s?) sleep and then processing the data, we see that indeed something strange is going on.1(Data from http://cfa-www.harvard.edu/~pberlind/atlas/atframes.html) We understand that these stars all have basically the exact same abundances of elements: mostly hydrogen and helium with a sprinkling of other elements. The spectra are similar in some ways – they all have absorption lines, and we can trace the overall blackbodycurve if we go smoothly from the shortest wavelength, over the peak of the spectrum and then back down to the longest wavelength. 01. What is the primary reason why these spectra differ so much from each other?02. What are these spectra telling us about the properties of the atmospheres of the stars? a. b. c.2QuickTime™ and a decompressorare needed to see this picture. QuickTime™ and a decompressorare needed to see this picture.QuickTime™ and a decompressorare needed to see this picture.1/14/201903. List what you observe to be the basic differences among these spectra.04. Focus now on the H alpha line and describe the differences among the spectra.HR 2491 – SIRIUS – A1VmHR 2990 – POLLUX – K0 IIIbHR 3259 – G7.5 V34beta CepheiThe preceding page contains 4 images, all of the same spectrum of beta Cephei observed on 2006-09-23 (according to the image header) at the Dominion Astrophysical Observatory just 17 km north of Victoria, BC. We are now going to take a closer look at these spectra and ask ourselves some questions, questions that will hopefully lead us to some insight as to what steps we need to do to finish processing these spectra so that analysis can begin. The spectrum has been dark-subtracted, flat-fielded, and “flattened” into a 1-D spectrum by summing rows 36 – 42 on the chip.5. Figure A should look familiar – we are simply graphing flux as a function of pixel number (similar to your plotting a line or a column in your photometry). Describe briefly what you see in the spectrum and then state what your first impression was as to why the spectrum had the “curvy-ness.” 6. That “curvey-ness” has been mostly taken out in Figure B. Guess as to how that was done. Also, how has the y-axis been adjusted?Why would this scale be a handy one to use when analyzing spectra?7. In Fig. C, the wavelengths have been added. Magic? How were the wavelengths known? How was a pixel number assigned a wavelength?1/14/20198. Figure D, reproduced here, is a zoom in on part of the spectrum. As you do a quick overview, list some of the notable characteristics of the spectrum.9. What questions should be asked about this spectrum?10. In some parts of the electromagnetic spectra there is a line density of 10,000 per nm (1,000 per Å), making accurate identification nearly impossible if they were noticable lines. However, 9,995 of those lines are grouped into what is called “line-haze” – lines that are so very weak that they only purpose they serve are to slightly depress the continuum. The hydrogen line at 6563 Å is obvious. How will we ever figure out what elements or molecules are forming the other


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UW ASTR 480 - Study Notes

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