Astronomers study stars by looking at the different colors of light they emit - colors they capture and analyze using spectroscopy. Now a team led by Université de Montréal's Étienne Artigau has developed a technique that uses a star's spectrum to chart variations in its temperature to the nearest tenth of a degree Celsius, over a range of time scales. "By tracking a star's temperature, we can learn a lot about it, such as its rotation period, its stellar activity, its magnetic field," explained Artigau, an astrophysicist at UdeM's Trottier Institute for Research on Exoplanets (IREx). "Such detailed knowledge is also essential for finding and studying a star's planets." In an article accepted for publication in The Astronomical Journal and currently available on the arXiv preprint server, Artigau and his team demonstrate the technique's effectiveness and versatility using observations of four very different stars made with the Canada-France-Hawaii Telescope in Hawaii and the European Southern Observatory (ESO) 3.6-m telescope in La Silla, Chile. The scientists first turned their attention to stellar spectra to improve exoplanet detection using radial velocity. This method measures slight oscillations in a star generated by the gravitational pull of an orbiting planet. The greater the oscillations, the larger the planet. But it's hard to detect very small oscillations and therefore low-mass planets. To overcome this problem, Artigau and his team developed a technique exploiting the radial velocity method that analyzes a star's full spectrum and not just a few portions, as previously done with this method. This makes it possible to detect planets as small as the Earth orbiting around small stars. Artigau then came up with the idea of using a similar strategy to detect not only variations in a star's oscillations but also in its temperature. Temperature measurements are critical in the search for exoplanets, which are mostly... |