Bonding with Periodic Variable Stars
Measuring the Pulse of Distant Suns
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Introduction
If you look up into the night sky, the stars you see may appear static and eternal but in reality, there is a lot happening. Many of them vary in brightness over time — some gently, others dramatically — for a variety of physical reasons. These are known as variable stars. By studying how their brightness changes, astronomers uncover clues about stellar structure, composition, and evolution.
In this project, you will help your PI set up a simple telescope-based system to observe a periodic variable star across its pulsation period and construct its light curve — a graph showing how brightness changes with time.
This project brings together observation, instrumentation, data analysis, and computational modelling to give you a taste of how astrophysicists extract meaning from starlight.
Project Details
In this project, you are expected to observe and image a periodic variable star across its pulsation period, and plot its light curve. Therefore you must,
- Choose a periodic variable star.
- Image it multiple times in its variability cycle using a telescope.
- Extract the star’s magnitude using AstroImageJ (AJI).
- Plot the data and fit a light curve using Python.
By the end of this project, you should be able to:
- Collect observational astronomy data with appropriate calibration frames (light, dark, and flat).
- Create and refine a data processing pipeline from image acquisition to photometric analysis.
- Apply basic principles of differential photometry and signal analysis.
- Demonstrate familiarity with the operation of the telescope and associated software.
- Present your experimental pipeline during the viva, including your images, calibration frames, analysis, and final light curve.
- Maintain a clear group logbook that documents data collection, calibration, analysis steps, and key reflections or decisions.
Equipment & Resources
- Celestron NexStar 6SE Telescope
- Celestron Mount and Tripod for NexStar 6SE
- ZWO ASI Camera (model to be confirmed) with data cable
- Celestron Battery Pack with power cable
- Eyepieces (optional)
- Red-dot Finder (optional)
- Laptop for data capture and analysis
| Software | Purpose | |
|---|---|---|
| Stellarium Desktop | Star selection and observation planning | Link |
| ZWO ASI Drivers | Connects camera to laptop (May not be required if you already have the drivers installed) |
Link |
| SharpCap | Image acquisition software (You are free to use any other astrophotography software) |
Link |
| DeepSkyStacker | Image stacking and calibration (You are free to use any other stacking software) |
Link |
| AstroImageJ | Magnitude calculation and photometry | Link |
| Resource | Purpose / Description | |
|---|---|---|
| SPS Telescope Manual | Instructions on setting up and operating the telescope. | Link |
| AstroImageJ Tutorials | Introductory tutorials for using AstroImageJ to analyse and extract magnitudes from astronomical images. | Video 1 Video 2 |
| MeteoBlue | Check weather forecasts, cloud cover, and atmospheric seeing conditions before planning observations. | Link |
| AAVSO | Access light curves of variable stars and create customised observation charts with reference stars. | Link |
| Astrometry.net | Apply World Coordinate System (WCS) calibration to images in AstroImageJ. A free account is required to use this service. | Link |
Which star to choose?
Different variables stars have different pulsation periods and different average brightness too. Choose a star with a pulsation period you can observe in the time frame of the project, and one which is bright enough to be observed in the telescope properly.
You may use Stellarium for this.
How to take proper pictures of the stars?
While the manuals in the references provides information on how to setup the telescope and capture frames, there are three types of frames you must capture: light, dark, and flat.
- Light frames are the standard images you take using the telescope after focusing it and adjusting the camera’s settings (gain, exposure, etc). More information is present in the manual.
- Dark frames are the images you capture after covering the aperture of the telescope. For Celestron NexStar 6SE, you can just place its cap on the aperture and capture the darks.
- Flat frames are arguably the hardest to capture, and are obtained by uniformly illuminating the whole field-of-view of the telescope. You can consider putting a white paper or a white T-shirt on the aperture and lighting it using a white light source, pointing the telescope at a white board, etc.
While Darks and Flats do not concern first time astrophotographers, they are required for this project to obtain good data.
Quick tips on AstroImageJ (AJI)
This software is quite similar to ImageJ, but specialised for astronomy. To extract the magnitudes, the following steps can be taken (note that these are non-exhaustive and you should do your own research if necessary. The video links in the resources section are a good starting point):
Apply World Coordinate System (WCS) on all the images through plate-solving in AJI. Use the American Association of Variable Star Observers’ (AAVSO) observer resources to create a observation chart for your chosen variable star. This also allows you to choose the reference stars against which your main star’s magnitude is created. Using multiple aperture photometry, calculate the magnitude of your chosen variable stars against the reference stars.
What Are Periodic Variable Stars?
A periodic variable star is one whose brightness changes cyclically over time. This category includes:
- Cepheid variables — stars whose intrinsic brightness varies as they expand and contract.
- Eclipsing binaries — two-star systems whose orbits cause periodic dips in observed brightness.
Studying these stars allows astronomers to understand stellar structure and even measure distances in the universe.
- Cepheid variables — stars whose intrinsic brightness varies as they expand and contract.
What Is a Light Curve? A light curve is a plot of a star’s brightness (magnitude) versus time or phase, showing how its brightness varies. Analysing this curve allows us to infer the star’s pulsation period and physical properties.
References
Carroll, B. W., & Ostlie, D. A. (2017). An Introduction to Modern Astrophysics (2nd ed.). Cambridge University Press.