Gifts for Astrophysicists: Amateur observations of twinkling stars

As the holidays and the new year approaches, why not make a resolution to give more… data? The economics of science limits what scientists can do on their own. If you’re an amateur astronomer, why not share your data on the twinkling stars?

Why would professional astronomers want data from amateurs? After all enormous mountaintop observatories produce much higher quality data than any amateur could. Amateur astronomy technology, however, is good enough for a lot of research. And amateurs have a strength that the professionals can never match: there are a lot more of us than there are of them. In a world of 7,000,000,000 people only about 10,000 people work as professional astronomers.

One of the longest-standing pro-am collaborations in astronomy is the study of variable stars. The physics of nuclear fusion deep within a star’s core, giant sunspots on its surface, an orbiting companion star, or the star’s own planets can change the star’s brightness as seen from Earth. 

Twinkle, Twinkle (Not So) Little Star

For more than a century professional astronomers have relied on amateurs for observations of the changing light of distant stars. The oldest pro-am astronomy organizations in the world - the British Astronomical Association and the American Association of Variable Star Observers - collect observations of variable stars made by their members. The combined BAA and the AAVSO archives contain over 27 million observations.

An artist's impression of a nova-generating binary star system. The two stars orbit so closely that the white dwarf pulls gas away from its red giant companion. As more gas spirals down to the white dwarf's surface, it becomes dense enough to trigger a thermonuclear explosion.  Credit:  Nasa/CXC/M.Weiss

An artist's impression of a nova-generating binary star system. The two stars orbit so closely that the white dwarf pulls gas away from its red giant companion. As more gas spirals down to the white dwarf's surface, it becomes dense enough to trigger a thermonuclear explosion. Credit: Nasa/CXC/M.Weiss

The Center for Backyard Astrophysics concentrates on a specific class of variable stars: cataclysmic variables. In the binary star systems they study, a white dwarf star’s intense gravity strips gas away from a close-orbiting companion star. The gas forms an accretion disk as it spirals towards the white dwarf’s surface. The complex interaction of the two stars’ orbits, the white dwarf’s rapid spin, the precession of the accretion disk, and other variables cause the brightness of these systems to change dramatically over periods as short as minutes. On much larger timescales the gas piling up on the white dwarf reaches critical mass, triggering a runaway fusion reaction that blasts the gas from the white dwarf. The star goes nova. 

With members scattered all over the world, the CBA can produce round-the-clock observations of very rapid variations in a star’s brightness. They can also produce hundreds of observations over the course of months or years. In both cases the economics of professional astronomy make this kind of research difficult to conduct at the big observatories. The contributions of these amateur astronomers has produced dozens of peer-reviewed papers and advanced astrophysicists’ understanding of the last stages of stellar lifecycles.

The Be Star Spectrum Database collects amateur observations of another class of variable stars  composed of very hot blue stars that periodically eject material from their surfaces. These aren’t like the solar storms emerging from the Sun. These stars spin so fast that they bulge along their equators. For reasons astronomers don’t fully understand something triggers the equatorial gas to fly free from the star and form a thin disk of glowing hot gas. These Be stars - B for the star’s B-class absorption spectra and e for the emission spectra of the gas disk - brighten and dim as the erupts, orbits its star and dissipates.

The Observatoire de Paris-Meudon, France’s leading astronomy center, created the Be Star Spectra Database to collect data from amateurs and professionals alike. Amateur spectroscopy entered its own at the turn of the 21st Century, and now lets amateurs produce low-resolution - but still scientifically useful - data. Prioritized lists of Be stars published on ArasBeam ensures that project’s observers concentrate on the most important stars. Even though the Bess Database now holds over 100,000 observations of more than 2,000 Be stars, that’s only half of the Milky Way’s observable Be stars. Amateurs still have plenty of work to do.

Seeking Out New Worlds

Astronomers collected this light curve in the infrared with the Spitzer Space Telescope. A planet orbiting star HD80606 passes between the star and Earth, blocking some of the star's light in the process (red line). Credit: Nasa/JPL-Caltech/G.Laughlin (UCO/Lick Observatory)

A star’s own planets can make it appear dimmer and brighter in the eyes of observers here on Earth - or at least in their cameras. When an extrasolar planet, or exoplanet, passes between its star and Earth it blocks as much as 1% of its light. Astronomers on Earth can measure that dip and calculate the exoplanet’s size and orbit. That’s how the Kepler Space Telescope has discovered thousands of potential planets. 

Amateurs use the same technique to detect exoplanets using relatively modest equipment. You can even build a planet-hunting rig from a used camera and telephoto lens. Unfortunately, amateurs use such a wide variety of technology and techniques that they can’t contribute to professional exoplanet databases like Nasa’s Exoplanet Archive. Rather than let the growing amount of amateur exoplanet data go to waste, the Czech Astronomical Society created the Exoplanet Transit Database to give the data a permanent home. The CAS also coordinates amateur observations by publishing transit predictions to its Transiting Exoplanets and Candidates website.

[Ed: the CAS brought down their site to change webservers. For more information you can read the CAS’ overview of Tresca and the ETD published in New Astronomy (doi:10.1016/j.newast.2009.09.001, arXiv preprint: 0909.2548)]

Beneath the Shadows of Floating Mountains

The International Occultation Timing Association may do its work in the shadows, but Iota has nothing to do with black magic. When a small object in our own Solar System - an asteroid for example - passes between a star and Earth, it casts a shadow on Earth’s surface. The star seems to disappear when the shadow passes overhead. The time it takes for the star to reappear depends on the size of the asteroid. 

Iota coordinates teams of amateur astronomers who set up their portable telescopes in a line perpendicular to the shadow’s path. Each astronomer will observe a different time for the star’s occultation - some will be at the tip of the asteroid’s shadow while others are beneath the shadow’s equator. Combining all of the observations lets Iota’s coordinators reconstruct the shape of the asteroid - and even detect its moons or rings. 

You can also chip in and help a project that’s looking even further out in the Solar System. The Recon Project is a network of 40 schools and communities that observe occultations of the icy objects beyond Neptune’s orbits. As the project ramps up, amateur astronomers will be able to contribute their observations to help planetary scientists study the most remote objects we know.

Whether the data you collect on a star's variable light comes from the star itself, its planets, or things in our own Solar System, that data can make a difference to scientists' research. So why not give a gift of data and help explore space?