By Celsa Canedo
Variable stars are fascinating. I first learned about them while I was working on my Universe Sampler Observing program. At first, they were just one more item to check off the list. I had to choose two out of four suggested variable stars and make four brightness measurements. Then there was a brief explanation of what variable stars are and how to do such measurements. For more information I was referred to the AAVSO (American Association of Variable Star Observers) website. That was the beginning of a new season for me as an amateur Astronomer.
Variable stars are stars that change brightness for many reasons: it may be an intrinsic variation due expansion, contraction, eruption, etc. It may be due extrinsic variations: eclipses of two or more stars in a system. Studying the variation of brightness in stars adds to the understanding of star formation since most stars are variable in some degree at some point in their lives.
The periods of variation in stars are very revealing of star formation dynamics, it is very important to record this data as accurate as possible to build up a database from where scientists can pull information by decades. AAVSO has a century of data collected in its servers. It is really exciting to know that our visual observations can be part of some Astronomer’s research in this decade or in the next century!
Choose Your Star
Beta Lyrae or β Lyrae, is in the constellation of Lyra, near the star Vega. We know it is just 960 light years from the Sun from the Hipparcos ESA (European Space Agency) astrometry mission, which accurately measured the positions of more than one hundred thousand stars, and other one million stars with less precision. (1)
Beta Lyrae is a multiple star system of six components of apparent magnitude 14.3 or brighter. The components and their spectral class are:
- A, a semi-detached binary system, and a B-type star.
- B, B7V
- C, B2
- D, K3V
- E, G5
- F, G5
The brightest component, Beta Lyrae A, is a triple star system composed by eclipsing binary and a single star. Thanks to the work of CHARA, Center for High Angular Resolution Astronomy, a project based on Georgia State University, we can have great images and data by resolving these star systems. (2)
Eclipsing binaries are systems of two stars that orbit around their center of mass. The orbit is aligned in a way that one star passes in front of the other along our line of sight. This pattern causes brightness to dim when a star is in front of the other.
In Beta Lyrae, material is gravitationally pulled away from one star and accretes, or accumulates, on to the surface of the companion, the smaller star. The system has an orbital period of 13 days. The following animation made with images captured by CHARA, shows the mass donor and a disk surrounding the companion receiving the mass. This effect is referred to as photospheric tidal distortion due to Roche lobe filling.
Light plot for Beta Lyrae, as recorded by AAVSO visual observers
There is so much more to learn about variable stars! You could join a Citizen Scientist project in Zooniverse:
Classify light curves of variable stars identified in the ASAS-SN (All Sky Automated Survey for Super Novae) g-band data.
Have you chosen your star?
- The Hipparcos Space Astrometry Mission, cosmos.esa.int
- CHARA, chara.gsu.edu