IN REPORT: Plate Scale and FOV of CCD for Each Telescope using Albireo Stars

Transcription

1 USE ASTROIMAGEJ NOT AIP4WIN To download ALL the public data from Canvas, go to Files, then click the 3 dots next to the Public Data Folder and click Download. It will download all the files at once. 6.1 Measuring the plate scale How does the pixel size relate to angular distance on the sky? Well, we can use two stars with known angular distance (for example, the two stars in Albireo) to determine the pixel, or plate scale of the CCD camera. IN REPORT: Plate Scale and FOV of CCD for Each Telescope using Albireo Stars Think back to the night you went observing, there were at least three telescopes. Two or three of the telescopes took photometric data of Albireo and one took RGB images of the Ring Nebula. Each telescope is a different instrument and will therefore have a different platescale. A plate scale is simply how many arcseconds are in a pixel ( /pixel) for your detector. You are going to be working with two data sets: one from the telescope inside (14 ) that took images of the Ring Nebula (and a few images of Albireo) and the telescopes outside that took lots of photometric images of Albireo. Each data set will have some images of Albireo in anticipation of this part of your analysis. 1. The telescopes have different platescales. You need to measure the X and Y coordinates for BOTH stars in: -14 in- all 3 images of 1 filter (current public data set was taken in clear) -12 in- all 3 images of 1 filter (pick one) So you should have a total of 6 (x,y) coordinates for each telescope. To measure the X, Y coordinates: Open AstroImageJ. You should see a window like this: Click File and open an image OR drag and drop a file to the window shown above. You should see something like this:

2 You can adjust the contrast by moving the two sliders shown in the red box. To get X and Y coordinates, hover over the star and the values will be displayed at the top (shown in the green box in the image above. Include a table of your data in your report. 2. Calculate the distance in pixels between the two stars in EACH image and THEN take the average of all your determinations for each telescope (you should have 2 final values). Show an example of your work in your report. 3. Determine the plate scale for both telescopes (arcsec/pixel) using the known separation of 34.3 arcsec between the two stars. Hint: Check your units. 4. Use the size of your CCD image in pixels (given in Section 4) and the plate scale, to determine the Field of View (FOV) of the detector for both telescopes. Leave it in length x width format. Hint: Check your units. 6.2 Using the Plate Scale IN REPORT: Plate Scale and the Ring Nebula 1. Here, we will align and combine your Ring Nebula images in each filter so that you have three final images (one in each filter). Then, measure the length and the width of the Ring Nebula in pixels for each filter and include your results in a table in your report. (You should have a total of 6 values: three for both the length and the width.). This question is numbered with a 1 because the entirety of aligning and combining the ring nebula images counts as an individual question in the report for part 6.2.

3 6.2.1 Align Images START WITH ONE FILTER. You will align the 3 images in the 1 filter, and then combine these 3 images. a. Open a FITS image, any FITS image. b. Make sure the ImageJ toolbar is on top of the image you just opened, then Open image sequence in new window Select the folder containing your reduced images OR you can drag the folder to the smaller window shown in step 1. c. Check that the number of images is correct and uncheck Use virtual stack

4 d. In your image sequence, click on the align button and read the instructions that pop up. e. Click on a few stars, right click when done to start the alignment process.

5 6.2.2 Combining Aligned Images a. If you didn t flip through your images before, check that they are all aligned. b. Go to Process > Combine Stack Slices into Single Image c. In the pop up window select Sum Slices under Projection Type. Make sure to start at slice 1 d. A new window will open with the combined image. In that window, save that slice by File > Save Image/Slice as FITS. Name the new file RingNebula_B_combined.fits for example. Now you have combined the 3 images for one filter. REPEAT these steps (aligning and combining) for the other two filters. Put ALL of your combined images in one folder. BE SURE TO MEASURE THE LENGTH AND WIDTH OF THE RING NEBULA. Here is a table for your measurements (including calculations from #2 below): Table 1: Ring Nebula size measurements Filter Length (pixels) Width (pixels) Length (arcsec) Width (arcsec) R G B The following (EXCEPT for #7) are calculation and discussion questions that do not require the software and can be done at a later time, but must be included in your report. 2. Using the plate scale you calculated previously (use the one from the 14 telescope which took the M57 data set), estimate the angular size of the Ring Nebula. 3. Assuming a distance of 700 pc, estimate the physical size of the nebula. 4. Compare the size estimates in each filter. Are they the same or different and why?

6 5. Discuss the possible errors in your measurements and possible underlying assumptions that may cause your estimate to misrepresent the actual dimensions of the nebula. 6. Research the Ring Nebula. What kind of nebula is it? How did it originate? What causes the color variations observed? 7. Make a composite 3-color image (RGB) of the nebula (see Section 6.2.3). Describe the appearance of the Nebula Creating an RGB Color Image of the Ring Nebula Now that you ve created the 3 final combined images in each filter, you need to align them with each other by repeating the process above in 6.2.1, repeated here: a. Open your 3 combined images (1 R, 1 B, 1 G) by going to File Open image sequence in new window Select the folder containing your reduced images OR you can drag the folder to the smaller window shown in step 1. b. Check that the number of images is correct and uncheck Use virtual stack. In your image sequence, click on the align button and read the instructions that pop up. c. Click on a few stars, right click when done to start the alignment process. d. Go to Image > Stacks > Stack to Images e. Go to Image > Color > Merge Channels) f. Change the files to match with the specified color. Make sure create composite is selected. Press OK.

7 g. Go to Scale and select fixed brightness & contrast per image slice h. Go to Color > Make Composite Image. This will bring up a window that lets you only display one color at a time. i. Start with only selecting Channel 1 and MAKE SURE THE SCROLL BAR IS ALL THE WAY TO THE LEFT. Shift the scale/contrast bar to the right so that the background level is NOT bright/looks black, but the stars are still bright. REPEAT for the other channels, moving the scroll bar each time you switch filters.

8 j. When you are satisfied with the colors, go to File > Save Image Display as PNG or JPG to save your final color image.

9 6.3 Photometry Photometry (best done in B, V, and I filters) refers to the measurement with which we determine the apparent magnitude of an object. In this project, we are going to observe a binary star or a cluster and find out the magnitude of each star of it. In order to do photometry, we are also going to need to observe another star, of which the magnitude is known (i.e., the standard star ). Note that the instructions here describe a simplified version of the actual process of photometry that astronomers use, as our version skips several key steps (i.e., flat-fielding, airmass correction, etc.). Nevertheless, the fundamentals of photometry are all covered, and the accuracy is still acceptable (<0.2 mag) if everything is done correctly. IN REPORT: Photometry of Albireo Stars 1. Determine and record in a table, the observed magnitudes of the two stars in Albireo and calibration star (Gamma Lyrae) in each of three images in each of the the B, V and I filters by performing aperture photometry (see Section 6.3.1) Aperture Photometry As you are doing the photometry, fill out these tables: Table 2: Gamma Lyrae Photometry Filter Source - Sky Flux (Counts) Exp time (s) M_ins (mag) (see eqn below) Offset (mag) Avg offset +- std dev B V I

10 Table 3: Albireo Photometry - star a is the one in the upper left/smaller one; star b is the lower right/bigger one < REPLACE THIS with how you designated your stars. Filter Source - Sky Flux (Counts) Exp time (s) m_ins (mag) (see eqn below) m_final= m_ins+avg_offset Avg m_final +- std dev B a1 a b1 a2 b2 b a3 b3 V a1 b1 a2 b2 a3 b3 I a1 b1 a2 b2 a3 b3 a. Open an image of Gamma Lyrae/Sulafat b. Alt-click on the star to open Seeing Profile. Check that the radii are okay. Click Save Aperture a the bottom

11 c. Change to Single Aperture photometry by clicking this button d. Click on the star again. This will bring up a measurements table. Record the Source-Sky value under the corresponding column in the table above. e. Repeat these measurements for all stars in all filters. f. Calculate the magnitude for each star in each filter using this formula: m_instrumental = -2.5*log10(flux/exposure time)

12 IN REPORT: Photometry of Albireo Stars (cont.) 2. Using the given standard star magnitudes, determine and record in a table the zero-point offset: zero-point offset = m_standard - m_instrumental Where the m_standard for Gamma Lyrae in the various filters are B = 3.20, V = 3.25, and I = Determine and record the average and standard deviation of the zero-point offset for each filter and put these values in the table above. 3. Determine and record in the next table the final calibrated magnitudes or apparent magnitude of the Albireo stars for each observation using the zero-point offset calculated in step 3. m_final = m_instrumental + offset Continue to fill out the table for each star, taking averages when shown in the table. For this part of the analysis, refer to Chapter 13 of our textbook. 4. Calculate the B-V and V-I colors for each star. (This is just m_b - m_v). 5. Research to find the actual magnitudes and compare your values for magnitudes and colors with the actual values. If your values differed from the published values, you should discuss why they differ (i.e. what are your sources of error) and you can either use the correct values for the remainder of the project or you can re-analyze your data, correcting your procedure to get more reasonable values. Please specify what you do. 6. Assuming a distance of 118 pc to Albireo, determine the absolute V magnitude, M_v of each star. 7. Using the Stellar photometry data tables on the Class Website, construct a color magnitude diagram. Plot Mv vs B-V for the stars. Place the Albireo stars on this diagram with special symbols. 8. Using the B-V colors, estimate the surface temperature for each star. 9. Using your color-magnitude plot estimate the luminosity class for each star. 10. Are your results consistent with the stars being a true binary system (i.e. did the stars form at the same time)? Why or Why not? Check the rubric below to make sure that you have answered all of the questions.

13 AST 3018 Observing Project Summary/Rubric: (number/staple) = 195 pts Your reports should include the following: 1. (18 pts) Log Book a. (5 pts) Description of telescope set up and observing procedure- DO NOT COPY INSTRUCTIONS b. (3 pts) RA and Dec of each object observed c. (5 pts per log book) Date, time, filter, integration time of each observation for each object. Also, report on the weather conditions during the observations Part c should already be on the logbooks you got from observing. You can attach an image of the logbook, or create a table. Be sure to include BOTH logbooks from EACH telescope you are doing data analysis for (1 for Albireo, 1 for Ring Nebula) For each sub-project in Parts 2-4 below, please follow these organizational requirements (15 pts per sub-project, 3 pts each for A-E): A. Introduction a. State the goal of the section- what are you trying to do and why it is important B. Description of Data Analysis for each section in Parts 2-4 a. Summarize the tools you used in the AIP4WIN software to analyze your data- DO NOT JUST COPY THE MANUAL INSTRUCTIONS b. Include any calculations done (equations used, numbers put in, and final answer) - EXPLAIN how and why C. Description of Results a. Include figures such as picture of final images, plots (i.e. section 4 part h) b. Include table of results (i.e. magnitudes, sizes, etc.) D. Conclusions and Summary of Findings a. Summarize your results and discuss their significance b. Include answers to the analysis questions posed E. Clarity a. Easy to follow work b. Work explained - If you use an equation, state the equation, where it comes from and why you are using it and what numbers you plugged in c. Neat tables d. Clean writeup 2. Plate Scale and FOV of CCD for Each Telescope using Albireo Stars (20 pt + 15 organizational pts) a. (6pts) Measure the X and Y pixel coordinates for the two stars in three images in one filter of Albireo from the two telescopes: one set of three images from the photometric filter data sets and one set of three images from the RGB filters used to take data for the Ring Nebula. b. (8 pts) Determine the distance in pixels between the two stars in each image and take the average of all three of your determinations for both telescopes.

14 c. (2 pts) Determine the plate scale (arcsec/pixel) using the known separation of 34.3 arcsec between the two stars for both telescopes. d. (4 pts) Use the size of your CCD image in pixels and the plate scale to determine the Field of View (FOV) of the detector for both telescopes. 3. Size of the Ring Nebula (40 pts + 15 organizational pts) a. (6 pts) Measure the longest and shortest dimensions of the Ring Nebula in pixels for each aligned image in each filter (3 images, 6 values). b. (2 pts) Using the plate scale you calculated in Part 1 (make sure you use the correct corresponding telescope), estimate the angular size of the Ring Nebula. c. (4 pts) Assuming a distance of 700 pc, estimate the physical size of the nebula (eqn (1pt) and calculation (1 pt a filter)) d. (6 pts) Compare the size estimates in each filter. Are they the same or different and why? e. (6 pts) Discuss the possible errors in your measurements and possible underlying assumptions that may cause your estimate to misrepresent the actual dimensions of the nebula. f. (6 pts) Research the Ring Nebula. What kind of nebula is it? How did it originate? What causes the color variations observed? Include references (2 pts) g. (10 pt) Make a composite 3-color image (RGB) of the nebula. Describe the appearance of the Nebula. 4. Photometry of Albireo Stars (70 pts + 15 organizational pts) Photometry (38 pts): a. (24 pts) Determine and record in a table, the observed magnitudes of the two stars in Albireo (8 pts each = 16pts) and calibration star (8 pts) in each of the B, V and I images by performing aperture photometry. b. (8 pts) Determine and record in a table the zero-point calibration offset by comparing the observed magnitude of your calibrator star to its standard value. c. (6 pts) Determine and record in a table the final calibrated magnitudes or apparent magnitude, m of the Albireo stars for each filter using the zero-point offset calculated in step b. For this part of the analysis refer to Chapter 13 of our textbook (32 pts): d. (4 pts) Calculate the B-V and V-I colors for each star (1 pt per calculation per star) e. (3 pts) Assuming a distance of 118 pc to Albireo, determine the absolute V magnitude, M of each star (1 pt eqn and 1 pt per calculation per star). f. (8 pts) Using the Stellar photometry data tables on the Class Website, construct a color-magnitude (or H-R) diagram. Plot M vs B-V for the stars (6 pts). Place the Albireo stars on this diagram with special symbols (2 pts). CHECK YOUR AXES!!! g. (3 pts) Using the B-V colors, estimate the surface temperature for each star (1 pt eqn and 1 pt per calculation per star). h. (4 pts) Using your color-magnitude plot, estimate the luminosity class for each star. (If you re not sure what this is exactly, look in your book or Google it. This is different than the spectral type.) i. (10 pts) Are your results consistent with the stars being a true binary system (i.e. did the stars form at the same time)? Why or Why not?