Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly 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 starspots 100 times larger than those on the Sun.
This section needs expansion. You can help by adding to it. (August 2008)
To detect and measure the extent of starspots one uses several types of methods.
For rapidly rotating stars – Doppler imaging and Zeeman-Doppler imaging.[1] With the Zeeman-Doppler imaging technique the direction of the magnetic field on 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 than 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.
Observed starspots have a temperature which is in general 500–2000 kelvins cooler than the stellar photosphere. This temperature difference could give rise to a brightness variation up to 0.6 magnitudes between 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).
Lifetimes
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.[6]
For large spots the sizes depend on the differential rotation of 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.[6]
Activity cycles
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.
Maunder minimum
Some stars may have longer cycles, possibly analogous to the Maunder minima for the Sun which lasted 70 years, for example some Maunder minimum candidates are 51 Pegasi b,[7] HD 4915[8] and HD 166620.[9][10]
Flip-flop cycles
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.
^Cameron 2008. Eclipse movies show spots on two imaged binaries
^Parks J, et al. (24 May 2021). "Interferometric Imaging of λ Andromedae: Evidence of Starspots and Rotation". The Astrophysical Journal. 913 (1): 54. Bibcode:2021ApJ...913...54P. doi:10.3847/1538-4357/abb670. S2CID 235286160.
^Konchady T (23 June 2021). "Searching for Spots with Interferometry". AASnova.
^Sanchis-Ojeda, Roberto; Winn, Joshua N.; Marcy, Geoffrey W.; et al. (2013). "Kepler-63b: A Giant Planet in a Polar Orbit Around a Young Sun-like Star". The Astrophysical Journal. 775 (1): 54. arXiv:1307.8128. Bibcode:2013ApJ...775...54S. doi:10.1088/0004-637X/775/1/54. ISSN 0004-637X. S2CID 36615256.
^Poppenhäger, K.; Robrade, J.; Schmitt, J. H. M. M.; Hall, J. C. (2009-12-01). "51 Pegasi – a planet-bearing Maunder minimum candidate". Astronomy & Astrophysics. 508 (3): 1417–1421. doi:10.1051/0004-6361/200912945. ISSN 0004-6361. S2CID 118626420.
^Shah, Shivani P.; Wright, Jason T.; Isaacson, Howard; Howard, Andrew; Curtis, Jason L. (2018-08-16). "HD 4915: A Maunder Minimum Candidate". The Astrophysical Journal. 863 (2): L26. arXiv:1801.09650. doi:10.3847/2041-8213/aad40c. ISSN 2041-8213. S2CID 119358595.
^Baum, Anna C.; Wright, Jason T.; Luhn, Jacob K.; Isaacson, Howard (2022-04-01). "Five Decades of Chromospheric Activity in 59 Sun-like Stars and New Maunder Minimum Candidate HD 166620". The Astronomical Journal. 163 (4): 183. arXiv:2203.13376. doi:10.3847/1538-3881/ac5683. ISSN 0004-6256. S2CID 247613714.
^"Astronomers see star enter a 'Maunder Minimum' for the first time". Physics World. 2022-04-05. Retrieved 2022-04-06.
References
Cameron, Andrew Collier. "Mapping starspots and magnetic fields on cool stars". University of St Andrews. Retrieved 2008-08-28. (explains how Doppler imaging works)
Berdyugina, Svetlana V. (2005). "Starspots: A Key to the Stellar Dynamo". Living Reviews in Solar Physics. Institute of Astronomy ETHZ, Max Planck Society. 2 (8): 8. Bibcode:2005LRSP....2....8B. doi:10.12942/lrsp-2005-8. S2CID 54791515. Retrieved 2008-08-28.
K. G. Strassmeier (1997), Aktive Sterne. Laboratorien der solaren Astrophysik, Springer, ISBN3-211-83005-7
Further reading
Strassmeir, Klaus G. (September 2009). "Starspots". The Astronomy and Astrophysics Review. 17 (3): 251–308. Bibcode:2009A&ARv..17..251S. doi:10.1007/s00159-009-0020-6.
January 09, 2023
starspot, stellar, phenomena, named, analogy, with, sunspots, spots, small, sunspots, have, been, detected, other, stars, they, would, cause, undetectably, small, fluctuations, brightness, commonly, observed, starspots, general, much, larger, than, those, abou. Starspots are stellar phenomena so named by analogy with sunspots Spots as small as sunspots have not been detected on other stars as they would cause undetectably small fluctuations in brightness The commonly 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 starspots 100 times larger than those on the Sun Contents 1 Detection and measurements 2 Temperature 3 Lifetimes 4 Activity cycles 4 1 Maunder minimum 4 2 Flip flop cycles 5 Notes 6 References 7 Further readingDetection and measurements EditThis section needs expansion You can help by adding to it August 2008 To detect and measure the extent of starspots one uses several types of methods For rapidly rotating stars Doppler imaging and Zeeman Doppler imaging 1 With the Zeeman Doppler imaging technique the direction of the magnetic field on 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 than 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 mapping produces images and maps of spots on both stars 2 For giant binary stars Very long baseline interferometry 3 4 For stars with transiting extrasolar planets Light curve variations 5 Temperature EditObserved starspots have a temperature which is in general 500 2000 kelvins cooler than the stellar photosphere This temperature difference could give rise to a brightness variation up to 0 6 magnitudes between 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 Lifetimes EditThe lifetime for a starspot depends on its size For small spots the lifetime is proportional to their size similar to spots on the Sun 6 For large spots the sizes depend on the differential rotation of 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 6 Activity cycles EditThe 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 Maunder minimum Edit Some stars may have longer cycles possibly analogous to the Maunder minima for the Sun which lasted 70 years for example some Maunder minimum candidates are 51 Pegasi b 7 HD 4915 8 and HD 166620 9 10 Flip flop cycles Edit 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 Notes Edit Cameron 2008 Cameron 2008 Eclipse movies show spots on two imaged binaries Parks J et al 24 May 2021 Interferometric Imaging of l Andromedae Evidence of Starspots and Rotation The Astrophysical Journal 913 1 54 Bibcode 2021ApJ 913 54P doi 10 3847 1538 4357 abb670 S2CID 235286160 Konchady T 23 June 2021 Searching for Spots with Interferometry AASnova Sanchis Ojeda Roberto Winn Joshua N Marcy Geoffrey W et al 2013 Kepler 63b A Giant Planet in a Polar Orbit Around a Young Sun like Star The Astrophysical Journal 775 1 54 arXiv 1307 8128 Bibcode 2013ApJ 775 54S doi 10 1088 0004 637X 775 1 54 ISSN 0004 637X S2CID 36615256 a b Berdyugina 5 3 Lifetimes Poppenhager K Robrade J Schmitt J H M M Hall J C 2009 12 01 51 Pegasi a planet bearing Maunder minimum candidate Astronomy amp Astrophysics 508 3 1417 1421 doi 10 1051 0004 6361 200912945 ISSN 0004 6361 S2CID 118626420 Shah Shivani P Wright Jason T Isaacson Howard Howard Andrew Curtis Jason L 2018 08 16 HD 4915 A Maunder Minimum Candidate The Astrophysical Journal 863 2 L26 arXiv 1801 09650 doi 10 3847 2041 8213 aad40c ISSN 2041 8213 S2CID 119358595 Baum Anna C Wright Jason T Luhn Jacob K Isaacson Howard 2022 04 01 Five Decades of Chromospheric Activity in 59 Sun like Stars and New Maunder Minimum Candidate HD 166620 The Astronomical Journal 163 4 183 arXiv 2203 13376 doi 10 3847 1538 3881 ac5683 ISSN 0004 6256 S2CID 247613714 Astronomers see star enter a Maunder Minimum for the first time Physics World 2022 04 05 Retrieved 2022 04 06 References EditCameron Andrew Collier Mapping starspots and magnetic fields on cool stars University of St Andrews Retrieved 2008 08 28 explains how Doppler imaging works Berdyugina Svetlana V 2005 Starspots A Key to the Stellar Dynamo Living Reviews in Solar Physics Institute of Astronomy ETHZ Max Planck Society 2 8 8 Bibcode 2005LRSP 2 8B doi 10 12942 lrsp 2005 8 S2CID 54791515 Retrieved 2008 08 28 K G Strassmeier 1997 Aktive Sterne Laboratorien der solaren Astrophysik Springer ISBN 3 211 83005 7Further reading EditStrassmeir Klaus G September 2009 Starspots The Astronomy and Astrophysics Review 17 3 251 308 Bibcode 2009A amp ARv 17 251S doi 10 1007 s00159 009 0020 6 Retrieved from https en wikipedia org w index php title Starspot amp oldid 1126114084, wikipedia, wiki, book, books, library,
