LESSON 6 GROUP LAB

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Central Texas College *

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Apr 3, 2024

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Lesson 6 Lab - Variable Star Photometry ( TREVINO - WRIGHT ) Question 1: The light variation from a variable star is shown in the figure to the right. A.) Identify the type of variable star and explain your criteria for classifying it as such, B.) estimate the period of the variable star, and C.) estimate its pulsation amplitude. Answer 1: A.) This is an RRab Lyrae star due to its asymmetric amplitude light curve. B.) The period is about 11.5 hours, which tends to be towards the large end of the RR Lyrae range. C.) The amplitude is about 10.3 magnitudes Question 2: The light curve for a variable star is shown in the figure to the right. A.) Identify the type of variable star and explain your criteria for classifying it as such, B.) estimate the depth of the primary (deeper) eclipse, and C.) describe what you can conclude about the period of the variable from looking at the light curve. Answer 2: A.) This is a binary star system where two stars are gravitationally bound and eclipse each other. This means that it is an extrinsic variable system. B.) The depth of the primary eclipse is about 4.19 magnitudes C.) I can not conclude anything about the period from this curve.
Question 3: A CCD has the greatest possible pixel value of 4095. What is the bit level of this CCD? Answer 3: The bit level of this CCD would be 12 Question 4: A star is being observed with an 8-bit CCD that has a central pixel value of 82 counts when the exposure time is 10 seconds. What would the central pixel value be if the exposure time were 25 seconds? Explain your reasoning. Answer 4: The central pixel value is 205 counts at the exposure time of 25 seconds. Question 5: A 12-bit CCD collects light from a star over a 10-second exposure and obtains a central pixel value of 1068. What is the longest exposure that could be taken of this star and still avoid saturation? Explain your reasoning. Answer 5: The longest exposure is about 38 seconds since the detector is linear and will saturate at 4095 counts. Question 6: Enter the o ff sets you obtained for Star-field 2 and Star-field 3 in the table below. x offset y offset starfield 2 -35 29 starfield 3 -14 -20
Question 7: The star-fields of the blink comparator contain 5 variable stars. Create di ff erent blinking sequences in the simulator to identify the variables and record the x and y locations of the variables on this star field. One variable star has already been located for you. Note that the coordinates do not need to be exact, you just need to be able to find the stars again in the next simulator. Question 8: Hypothetically, suppose that you add a long series of observations all taken one day apart to the blinking queue. Would you be able to detect large-amplitude variable stars with periods of a.) 1.0 days, b.) 0.5 days, or c.) 0.75 days? Answer 8: You could detect the stars with a period of 0.75 days but not 0.5 or 1 day. Question 9: What is the range of pixel values inside the inner circle for this star? (Find the maximum and minimum values.) Question 10: Determine the background sky brightness average counts per pixel for the star at x = 359, y=129. ( Give your answer to two decimal places. ) Answer 10: 2334.49 x coordinate y coordinate Variable #1 64 114 Variable #2 124 260 Variable #3 131 201 Variable #4 309 177 Variable #5 331 22 Pixel Values Minimum 1633 Maximum 31495
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Question 11: What are the radii of the inner disc and outer ring used to define the apertures? *Answer 11: Inner disc radius: 261411 Outer ring radius: 275469.5 Question 12: Use the simulator to determine the di ff erential magnitudes for the following pairs of stars . Question 13 : Find a star (give its x and y coordinates) that is 0.63 magnitudes fainter than the star at x = 29, y = 157. Answer 13: X Coordinate: 301 Y Coordinate: 185 Question 14: Identify two constant stars in the star field and form di ff erential magnitudes for them. Explain how you know that they are constant stars and not variables. Answer 14: Star A: x=82 y=66 ( Photometry Simulator ) Star B: x= 113 y=186 ( Photometry Simulator ) Magnitude Di ff erence = 0.89 ( Photometry Simulator ) / 0.08 ( Variable Star Photometry Analyzer ) Constant stars have a steady brightness, remaining relatively unchanged over time. They serve as dependable reference points for measuring distances in astronomy. In contrast, variable stars experience fluctuations in brightness due to factors like pulsations, eclipses in binary systems, or eruptive events. X coord Y coord X coord Y coord M1-M2 170 52 41 72 -0.10 41 72 170 52 0.10 170 52 113 186 0.45 348 33 279 262 0.42
Question 15: Analyze the observations for each of the other four variable stars in this field. You should determine the period, light curve amplitude, and the type of variable. You should clearly discuss what factors led you to classify the variable star in the manner you did (which may involve a process of elimination). VARIABLE #2 VARIABLE #3 VARIABLE #4 VARIABLE #5 x=124 y=260 Period: Amplitude: x=131 y=201 Period: Amplitude: x=309 y=177 Period: Amplitude: x=331 y=22 Period: Amplitude:
Question 16: Based on your experiences with the Blink Comparator Simulator and the Variable Star Photometry Analyzer, how do you think variable stars are detected today? Answer 16: Variable stars are detected using modern methods such as photometric surveys and spectroscopy. Photometric surveys involve telescopes taking repeated images of the sky to detect stars that vary in brightness over time. Spectroscopy analyzes the light from stars spread into colors, detecting changes in brightness, temperature, and composition. These methods are more e cient than older techniques like the Blink Comparator Simulator and the Variable Star Photometry Analyzer. They enable astronomers to study various types of variable stars in detail, including eclipsing binaries & pulsating variables.
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