What is MOST?
The MOST (Microvariability & Oscillations of STars) space mission is the first satellite designed to specifically conduct asteroseismic observations of stars (Walker et al. 2003; Matthews 2007). Equipped with a 15 cm Rumak-Maksutov telescope feeding a CCD photometer through a custom broadband optical filter (350–700 nm), MOST can collect rapid high-precision photometry of bright stars with nearly uninterrupted coverage for up to 2 months.
The data collected from the telescope is being used to study the oldest stars in the solar neighborhood, the atmospheres of planets orbiting other stars, the properties of rapidly rotating stars, and the interior structure of Sun-like stars. The telescope is capable of detecting brightness variations comparable to that of moving your eye just one-half a millimeter closer or farther away from a streetlight located one km away. Although scientists predict that the light given off by many different types of stars fluctuate, the light fluctuations have never been observed because they are so small. The fluctuations are not the twinkling of stars that are caused by turbulence in the atmosphere of the earth but are true variations in the light output of the star caused by sound waves trapped inside the star.
The MOST instrument is a uniquely Canadian product. Funded by the Canadian Space Agency, the instrument was developed by the University of British Columbia Physics and Astronomy Department. The satellite's pointing system, an extremely critical component of the light weight, hence, easily jostled telescope, was developed by Dynacon Enterprises in Ontario. The communication system was designed by the University of Toronto, Institute for Aerospace Studies, and additional design work on the instrument was carried out by the Center for Research in Earth and Space Technology and Spectral Applied Research both also located in Ontario.
Jaymie Matthews and the MOST satellite enclosure and, still to be installed, telescope components.
The MOST Science Team are responsible for analyzing the data obtained from the MOST satellite.
Left to Right: Tony Moffat, Werner Weiss, David Guenther, Jaymie Matthews (front), Gordon Walker, Dimitar Sasselov, Slavek Rucinski (front), Rainer Kuschnig.
First Results: The Story of Procyon
MOST observed Procyon, a bright star believed to exhibit detectable periodic variability (oscillations). After careful analysis the MOST Science Team concluded that if Procyon was variable it was below the ability to detect.
As reported in Nature.
As reported by the popular press.
Response from community
The response from the scientific community was immediate and not altogether complimentary. Indeed, many in the scientific community called the Science Team incompetent for not being able to see variability in Procyon.
"MOST Science team made exaggerated claims about their instrument’s capabilities, their data reduction was inadequate, and their data are heavily contaminated with stray light not granulation noise."
Our response to the community's response
The MOST instrument was used successfully to observe oscillations on other stars.
MOST reobserved Procyon two more times with improved sensitivity. No oscillations were detected.
The MOST Science Team collaborated with the Yale Convection Group (Demarque) to model the convective outer layers of Procyon where the oscillations are created. They discovered that the behavior of convection in Procyon's outer layers is different from what was expected. And that this meant that the oscillations would be difficult to see as luminosity variations (via MOST), but would be accessible to radial velocity measurements (ground based observations).
Simulation of Procyon's surface convection. Side view. Dark cool plumes fall from above, while hotter material rises from below.
Stars similar to Procyon were observed by CoRoT and Kepler (two bigger more sensitive space telescopes like MOST), confirming the results discovered by the MOST Science Team for Procyon.
MOST's Other Contributions
Older stars evolved off of the main-sequence. New result: they exhibit nonradial oscillations.
Young stars, just recently formed. New result: exhibit nonradial oscillations.
A type stars with strong magnetic fields, near instability strip and near main-sequence convective envelope edge. Discovered: new roAp stars and rich oscillation spectrum.
Massive, O type stars, undergoing heavy mass loss from strong stellar winds. Discovered: rich oscillation spectrum revealing physical phenomena.
Stars with spots similar to the Sun's sunspots except much larger. New result: multiple spots reveal differential rotation.
Observe the change in in a star's brightness as a planet passes in front of the star: Discovered: properties of the eclipsing planet's atmosphere.
For more information on MOST visit the MOST web site.