Scientific recording of sunspots started with Galileo in 1609. Since Hale (1908) we know that sunspots are strong concentrations of magnetic field of up to 4000 gauss. They could be formed by subsurface magnetic flux tubes piercing the surface. Meanwhile, numerical simulations by many different groups suggest that strong magnetic fields could be generated in the bulk of the convection zone. This would mean that sufficiently strong magnetic fields may be generated not far from the surface. However, at the surface the magnetic field appears to be strongly concentrated into only a few isolated spots – in stark contrast to the more diffuse magnetic field beneath the surface. This is still a mystery. Continua a leggere Sunspot formation: theory, simulations and observations→
A “brown dwarf” star that appears to be the coldest of its kind — as frosty as Earth’s North Pole — has been discovered by a Penn State University astronomer using NASA’s Wide-field Infrared Survey Explorer (WISE) and Spitzer Space Telescopes. Images from the space telescopes also pinpointed the object’s distance at 7.2 light-years away, making it the fourth closest system to our Sun.
Since the Sun is the closest star to Earth, it has been extensively studied in a variety of ways. Despite considerable efforts by astronomers, we do not know yet how typical a star the Sun is. Except for the youngest stars, the true rotation of those similar to the Sun is unknown, and there are few studies of mature solar twins or of more evolved ones. The mass, the amount of matter, and chemical composition of a star are the main characteristics that determine its evolution. Studying stars with the same mass and composition as the Sun, the so-called “solar twins”, can give us more information about our own Sun; solar twins of various ages offer snapshots of the Sun’s evolution at different phases. The satellite CoRoT has provided precise space-based data from which it is possible to determine the rotation periods of stars. The current team selected the best solar twin candidates within a range of rotation periods to study the evolution of the Sun’s rotation period in detail. Because solar twins are faint, the team initially used the High Dispersion Spectrograph (HDS) on the Subaru Telescope to observe three of their solar twin candidates. The large size of the Subaru Telescope and the capability of HDS to precisely spread out the stellar light into many constituent colors allowed them to study the stars’ characteristics in detail. A meticulous analysis of the data showed that one of the solar twin candidates was truly a star with a mass and chemical composition similar to that of the Sun. The finding was even more precious, because the star is at a more evolved stage and can serve as an indicator of the future of the Sun.
Determining the age of a star is probably one of its most difficult aspects to ascertain, but high quality spectra shed light on stellar ages. CoRoT Sol 1 is about two billion years older than the Sun, but its rotation period is about the same as the Sun’s. Subaru Telescope’s HDS spectra of CoRoT Sol 1 show that its overall chemical composition is similar to that of the Sun, but its detailed abundance pattern shows some differences, like most nearby solar twins. For example, the abundance of lithium (Li), an element that decreases with age, is less than that of the Sun. Team leader Dr. Jose Dias do Nascimento commented on the significance of CoRoT Sol 1’s age for understanding the Sun’s future: “In two billion years’ time, about the solar twin’s actual age, the Sun’s radiation may increase and make the Earth’s surface so hot that liquid water can no longer exist there in its natural state“. In contrast to other solar twins that are relatively bright, CoRoT Sol 1, which is located in the constellation Unicorn (Monoceros), is more than 200 times fainter than the brightest solar twin known. The large 8.2 m mirror of the Subaru Telescope and the precision of its high dispersion spectrograph made it possible to conduct this detailed study of the spectra of such a faint star. The team plans to use the Subaru Telescope to continue its research on how typical a star the Sun is. They intend to describe its rotation evolution by finding solar twins representing a broad range of stellar ages and then placing the Sun within this context.
In the last 50 years, helioseismology has made significant contributions to the knowledge of the Sun’s interior physics and has led the way to asteroseismology. We have now reached an era where more sophisticated questions are being asked to understand the subtle properties of the Sun and other stars due to the synoptic and high-resolution observations available from BISON, GONG and space missions such as SOHO, SDO, CoRot and Kepler. On this occasion, a workshop on the theme of “Fifty Years of Seismology of the Sun and Stars” is being organized to discuss the advances, reflect on the progress that has been made, and address new challenges. We plan to bring together helio- and asteroseismologists, theorists and observers in a journey that will take us from the interior of the Sun and its magnetism towards the structure of distant stars and activity cycles.
Solar ALMA workshop – The Atacama Large Millimeter/submillimeter Array (ALMA), an international partnership of Europe, North America and East Asia in cooperation with the Republic of Chile, is the largest astronomical project in existence. Continua a leggere Solar ALMA workshop→