Starspots are equivalent to sunspots but located on other stars. Spots the size of sunspots are very hard to detect since they are too small to cause fluctuations in brightness. Observed starspots are in general much larger than those on the
Sun, up to about 30 % of the stellar surface may be covered, corresponding to sizes 100 times greater than those on the Sun.
Detection and Measurements
To detect and measure the extent of starspots one uses several types of methods.
*For rapidly rotating stars -
Doppler imagingand Zeeman-Doppler imaging. [Cameron] :With the Zeeman-Doppler imaging technique the direction of the magnetic fieldon stars can be determined since spectral lines are split according to the Zeeman effect, revealing the direction and magnitude of the field.
*For slowly rotating stars - Line Depth Ratio (LDR).:Here one measures two different spectral lines, one sensitive to temperature and one which is not. Since starspots have a lower temperature then their surroundings the temperature-sensitive line changes its depth. From the difference between these two lines the temperature and size of the spot can be calculated, with a temperature accuracy of 10K.
*For eclipsing binary stars -
Eclipse mappingproduces images and maps of spots on both stars. [Cameron [http://star-www.st-and.ac.uk/~acc4/coolpages/movies.html Eclipse movies] show spots on two imaged binaries]
Observed starspots have a temperature which is in general 500-2000
Kelvincooler then the stellar photosphere. This temperature difference could give rise to a brightness variation up to 0.6 magnitudesbetween the spot and the surrounding surface.There also seems to be a relation between the spot temperature and the temperature for the stellar photosphere, indicating that starspots behave similarly for different types of stars (observed in G-K dwarfs)
The lifetime for a starspot depends on its size.
*For small spots the lifetime is proportional to their size, similar to spots on the Sun.Berdyugina [http://solarphysics.livingreviews.org/Articles/lrsp-2005-8/articlesu22.html#x30-270005.3 5.3 Lifetimes] ]
*For large spots the sizes depend on the
differential rotationof the star, but there are some indications that large spots which give rise to light variations can survive for many years even in stars with differential rotation.
The distribution of starspots across the stellar surface varies analogous to the solar case, but differs for different types of stars, e.g., depending on whether the star is a binary or not. The same type of activity cycles that are found for the Sun can be seen for other stars, corresponding to the solar (2 times) 11-year cycle. Some stars have longer cycles, possibly analogous to the Maunder minima for the Sun.
Another activity cycle is the so called flip-flop cycle, which implies that the activity on either hemisphere shifts from one side to the other. The same phenomena can be seen on the Sun, with periods of 3.8 and 3.65 years for the northern and southern hemispheres. Flip-flop phenomena are observed for both binary RS CVn stars and single stars although the extent of the cycles are different between binary and singular stars.
*cite web |last=Cameron |first=Andrew Collier |publisher=
University of St Andrews|title=Mapping starspots and magnetic fields on cool stars |url=http://star-www.st-and.ac.uk/~acc4/coolpages/imaging.html |accessdate=2008-08-28 (explains how Doppler imaging works)
*cite journal |last=Berdyugina |first=Svetlana V. |year=2005 |publisher=Institute of Astronomy ETHZ,
Max Planck Society|title=Starspots: A Key to the Stellar Dynamo |url=http://www.livingreviews.org/lrsp-2005-8 |journal=Living Reviews in Solar Physics |volume=2 |issue=8 |accessdate=2008-08-28
* K.G.Strassmeier (1997), [http://cdsads.u-strasbg.fr/abs/1997akst.book.....S “Aktive sterne. Laboratorien der solaren Astrophysik”] , Springer, ISBN # 3-211-83005-7
Wikimedia Foundation. 2010.
Look at other dictionaries:
starspot — noun The equivalent of a sunspot on another star … Wiktionary
starspot — starˈspot noun An area of relative darkness on the surface of a star • • • Main Entry: ↑star … Useful english dictionary
Sunspot — A sunspot is a region on the Sun s surface (photosphere) that is marked by intense magnetic activity, which inhibits convection, forming areas of reduced surface temperature. They can be visible from Earth without the aid of a telescope. Although … Wikipedia
Star — For other uses, see Star (disambiguation) … Wikipedia
T Tauri star — Drawing of a T Tauri star with a circumstellar accretion disc … Wikipedia
12 Ophiuchi — Starbox begin name=12 Ophiuchi Starbox observe epoch=J2000 ra=RA|16|36|21.4493 dec=DEC| 02|19|28.501 appmag v=5.76 constell=Ophiuchus Starbox character class=K2 V b v=0.82 u b=0.50 variable=BY Draconis Starbox astrometry radial v= 15.4 prop mo ra … Wikipedia
Stellar magnetic field — A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a main sequence (hydrogen burning) star. This motion is created through convection, which is a form of energy transport involving the physical… … Wikipedia
BY Draconis — Starbox begin name=BY Draconis AB Starbox observe epoch=J2000 ra=RA|18|33|55.7728cite web url=http://simbad.u strasbg.fr/simbad/sim id?protocol=html Ident=BY+Dra title=SIBMAD query result: V* BY Dra Variable of BY Dra type publisher=Centre de… … Wikipedia
Portal:Star — Shortcut: P:STR The Star Portal Wikipedia portals: Culture Geography Health History … Wikipedia
Apparent magnitude — Asteroid 65 Cybele and 2 stars with their magnitudes labeled The apparent magnitude (m) of a celestial body is a measure of its brightness as seen by an observer on Earth, normalized to the value it would have in the absence of the atmosphere.… … Wikipedia