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Harvard University
Astronomy Lab and Clay Telescope
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Eclisping Binary
The goal of this lab is to extract information about the masses, radii and the separation between the members of the double-lined spectroscopic binary NSVS01031772 using both the radial velocity (RV) data provided and the light curve data you will collect using the Clay Telescope atop the Science Center over the next few weeks.
This system is a low-mass binary system. Owing to their low surface brightness, such systems are quite difficult to detect even though they should be numerous. Indeed there is little accurate observational data currently available to constrain the mass-radius relationship for stars less massive that 0.6M, even though these are by far the most numerous stars in the Galaxy! The stellar mass-radius relationship is very important for constraining evolutionary models (e.g. to understand the energy generation rate and therefore the lifetime of the main sequence stars), and is also crucial to infer the masses and radii of planets found to orbit these stars. This means that the data you will collect in this lab are of significant scientific interest!
Here is the original paper which you should read and reference for more information about the system. Your writeup should be in a blog format and should be structured as follows:
Purpose:
State the objective of this lab and its scientific relevance.
Methods:
Outline the steps you follow to estimate the masses, radii and separation between the stars, explaining:
- What is an RV plot and what information can you extract from it? Include a diagram illustrating the relative motion of the stars at various points on the plot. From the provided plot, determine the radial velocity of the center of mass of the system, the maximum radial velocity of each star and the mass ratio of the system.
- What is a light curve and what information can you extract from it? How will you use this information to determine the masses and the radii of the stars?
- Describe your observing strategy, including the instruments you will use, the target and the timeline for the observation. We will combine the results of each lab session to provide a longer time baseline. It is importation that you gather data throughout the duration of your lab, not just during the eclipse.
Observations:
- Let's first slew the telescope to our field: RA, DEC = 13:45:35 +79:23:48
- In the TCS window, goto Telescope -> Movement -> Slew position tab and enter the RA, DEC and EPOCH (2000). Click "apply" and then "start slew".
- The CCD should already be running and cooled. See Telescope User Guide.
- We'll use the R-band filter for this lab, so move the filter to R (In MaximDL > Camera Control Window > Expose tab > filter wheel pulldown).
- It is important to check to make sure we are at the right place, so take a short (~60sec) exposure and using this finder chart check to see that we are at the right field. If you need a refresher on how to take images click here.
- We will use the same reference stars in each lab section so we can combine our data. It is important that all images include these reference stars. If your field doesn't then you should realign the stars accordingly.
- In TCS window, Telescope -> Movement -> Offset/Zenith tab and enter the RA or DEC offset. Only enter one offset at a time and only enter small amounts (< 30). Units are in arcsec.
- Values should be: RA (-) = left, RA (+) = right, DEC (-) = up and DEC (+) = down. To translate, if you want your object to move to the left, enter a -value in the RA box and then "apply" and "start slew".
- Helpful hints: Only move small amounts (<30) and only move one direction left/right or up/down at a time! Be sure to delete the RA offset value before starting to move the DEC value or you will do a double offset!
- Are the images in focus? The focus value for the CCD should be very close to the correct focus but because of temperature changes you may need a slightly different focus. Your stars should be nice and round. They should not be elongated or donut like! You can adust the focus by 10-20 in either direction to find the best optimal focus.
- Now, find the correct exposure time. Hover your mouse over the center of the object star and in the bottom right corner on the MaximDL screen you should see i=xxxx. This is our counts value. The CCD saturates at 65,000 counts. We want to keep our counts ideally 15,000-25,000 counts. Let's say no less than 10,000 and no more than 30,000. Find a good exposure time (also checking that those reference stars don't saturate) and then we'll be ready to start taking images.
- We are now ready to start a sequence of images. See here if unfamiliar. Be sure to create a folder in Ay16 for your section. You can now go to the lab and monitor the images as they come in. Be sure to keep an eye on the weather and the telescope.
- Important information to consider for your writeup:
- Describe the experimental set up and the operation of the dome, telescope, CCD camera and filters. Feel free to use diagrams/illustrations as needed.
- What is The Sky program and why is it useful?
- How does the telescope track its target?
- Describe what astronomical objects you observed.
- Observing your target.
- How did you locate the target on the sky?
- What filter did you use and why?
- How long were your exposures?
- How many exposures did you take?
- Start the time and date over which you took data, weather conditions and any possible sources of error.
Analysis:
You can do a quick-look light curve as the data is coming in and your TF will guide you through this in lab, but for the real analysis we want to do things properly. We will need to flat field our images and make a lightcurve. After all sections have observed an eclipse and created a lightcurve, we will share the data and use a Python Notebook to do the final analysis.
- You will be using AstroImageJ image software to calibrate the images and perform aperture photometry. The software is on the lab computers but you can download it on your computer for free. It runs on Wiindows, Mac, and Linux and the website has instructions for each platform.
- In AstroImageJ, open all your images (File --> Import --> Image Sequence)
- Next, we need to calibrate the files by flat fielding all your images to remove all the dust defects etc. Your TF will cover this in lab but also see AstroImageJ User Guide (Section 6) for more information.
- Now we are ready to do photometry on the data. Again, your TF will guide you through the steps to generate a lightcurve but you can reference the AstroImageJ User Guide (Section 10) for more information.
- Be sure you complete the above steps before leaving lab! Data from each section will be combined for your final analysis.
- Important information to consider for your your writeup:
- What is photometry?
- How did you process your images?
- What is a flat field?
- How did you create a light curve?
- Please include an image of the field and make sure to note the location of the target star and all the reference stars.
Results:
- Include your final light curve. Include a diagram illustrating the relative motion of the stars, and relate this to the RV plot. What is the period of the orbit? What are the durations of the eclipses?
- From these data, calculate the stellar radii and masses, and the separation between the stars. Calculate and include a discussion of the uncertainties in your estimates of these quantities that result from your measurement errors.
- Be sure to include references from any outside sources that you use and cite them properly in your report.