This system was discovered to be adouble star byF. G. W. Struve in 1822, with the components A and B having anangular separation of5.4″. (The separation was measured at6.7″ in 2016.)[16]R. E. Wilson in 1953 determined that the brighter member of this pair, component A, has a variable radial velocity. In 1963,O. C. Wilson noted that the same component shows very highemission cores in the calciumH and Kabsorption lines.[17] Follow-up observations by O. C. Wilson in 1964 showed that thehydrogen–α line of component A is fully in emission and it displays moderate broadening due to rotation. He found astellar classification of K3 V for component B, matching an ordinaryK-type main-sequence star.[18]
Observations during 1974–1975 demonstrated that component A is aspectroscopic binary star system of theRS Canum Venaticorum variable class. Given its average magnitude of around 5.9, it is one of the brighter known variables of this type.[20] Noeclipses were observed, but anorbital period of 2.838 days was determined. Most of the emission was found to be coming from the more massive member of this pair.[21]Radio emission from the binary was detected byF. N. Owen in 1976.[22] It was shown to be asoft X-ray source in 1978 using theHEAO 1 satellite.[23]
In 1980, significant variations were found in some spectral features related to surface temperature, suggesting the presence ofstarspots.[25]Doppler imaging confirmed these starspots are associated with the K subgiant. (It was the first cool star to have its surface Doppler imaged.[26]) The evidence suggests that the spots first appear at low latitude then migrated toward the poles.[20] These spots are much larger than they are on the Sun.[5] About 70% of all spots have been observed at latitudes higher than 50°, particularly around the polar region.[9][24] A polar spot has persisted for at least twenty years.[5]
The baseline apparent magnitudes of the two stars, after subtracting the effects of starspots, is 5.80 and 7.20.[5] Long term monitoring indicates the subgiant has two activity cycles, similar to the 11-yearsolar cycle. A5.3±0.1 year cycle is associated with symmetrical flip-flopping of the spotted area between hemispheres. The longer 15–16 year cycle is a periodic variation in the total spot area. The global magnetic field of the star may beprecessing with respect to theaxis of rotation.[26]
^Strassmeier, K. G.; Bartus, J. (February 2000), "Doppler imaging of stellar surface structure. XII. Rapid spot changes on the RS CVn binary V711 Tauri = HR 1099",Astronomy and Astrophysics,354:537–550,Bibcode:2000A&A...354..537S.
^abcDonati, J. -F.; et al. (November 2003), "Dynamo processes and activity cycles of the active stars AB Doradus, LQ Hydrae and HR 1099",Monthly Notices of the Royal Astronomical Society,345 (4):1145–1186,Bibcode:2003MNRAS.345.1145D,doi:10.1046/j.1365-2966.2003.07031.x.
^Sinnott, Roger W.; Perryman, Michael A. C. (1997),Millennium Star Atlas, vol. 1, Sky Publishing Corporation and the European Space Agency, p. 260,ISBN0-933346-84-0.
^Wilson, O. C. (October 1963), "A Probable Correlation Between Chromospheric Activity and Age in Main-Sequence Stars",Astrophysical Journal,138: 832,Bibcode:1963ApJ...138..832W,doi:10.1086/147689.
^abVogt, S. S.; Penrod, G. D. (September 1983), "Doppler imaging of spotted stars : application to the RS Canum Venaticorum star HR 1099",Publications of the Astronomical Society of the Pacific,95:565–576,Bibcode:1983PASP...95..565V,doi:10.1086/131208,S2CID123206530.
^Ramsey, L. W.; Nations, H. L. (August 1980), "HR 1099 and the starspot hypothesis for RS CVn binaries",Astrophysical Journal,239:L121 –L124,Bibcode:1980ApJ...239L.121R,doi:10.1086/183306.
Ayres, Thomas R.; et al. (March 2001), "Chandra, EUVE, HST, and VLA Multiwavelength Campaign on HR 1099: Instrumental Capabilities, Data Reduction, and Initial Results",Astrophysical Journal,549 (1):554–577,Bibcode:2001ApJ...549..554A,doi:10.1086/319051,S2CID15938906.
Brinkman, A. C.; et al. (January 2001), "First light measurements with the XMM-Newton reflection grating spectrometers: Evidence for an inverse first ionisation potential effect and anomalous Ne abundance in the Coronae of HR 1099",Astronomy and Astrophysics,365:L324 –L328,arXiv:astro-ph/0011018,Bibcode:2001A&A...365L.324B,doi:10.1051/0004-6361:20000047,S2CID15848464.
Trigilio, C.; et al. (February 1993), "VLBI observations of a strong radio flare in HR 1099",Monthly Notices of the Royal Astronomical Society,260 (4):903–907,Bibcode:1993MNRAS.260..903T,doi:10.1093/mnras/260.4.903.
Donati, J. -F.; et al. (November 1992), "Photospheric imaging of the RS CVn system HR 1099.",Astronomy and Astrophysics,265:682–700,Bibcode:1992A&A...265..682D.
Donati, J. -F.; et al. (June 1990), "Detection of a magnetic region of HR 1099",Astronomy and Astrophysics,232:L1 –L4,Bibcode:1990A&A...232L...1D.
Rodono, M.; et al. (April 1987), "Rotational modulation and flares on RS CVn and BY DRA stars. III. IUEobserations of V711 Tau = (HR 1099), II Peg and AR Lac",Astronomy and Astrophysics,176:267–284,Bibcode:1987A&A...176..267R.
Lestrade, J. F.; et al. (July 1984), "Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099",Astrophysical Journal,282:L23 –L26,Bibcode:1984ApJ...282L..23L,doi:10.1086/184296.
Fekel, F. C. Jr. (May 1983), "Spectroscopy of V711 Tauri (= HR 1099) : fundamental properties and evidence for starspots",Astrophysical Journal,268:274–281,Bibcode:1983ApJ...268..274F,doi:10.1086/160952.
Brown, R. L.; Crane, P. C. (December 1978), "On the rapidly variable circular polarization of HR 1099 at radio frequencies",Astronomical Journal,83:1504–1509,Bibcode:1978AJ.....83.1504B,doi:10.1086/112352.
Feldman, P. A.; et al. (December 1978), "Discovery of a strong radio flaring from HR 1099",Astronomical Journal,83:1471–1484,Bibcode:1978AJ.....83.1471F,doi:10.1086/112346.
Bopp, B. W.; Talcott, J. C. (December 1978), "Survey of Halpha emission in V711 Tau (HR 1099) and related Ca II emission binaries",Astronomical Journal,83:1517–1521,Bibcode:1978AJ.....83.1517B,doi:10.1086/112355.
Gibson, D. M.; et al. (December 1978), "VLA observations of HR 1099 during the 1977 international campaign",Astronomical Journal,83:1495–1498,Bibcode:1978AJ.....83.1495G,doi:10.1086/112350.
Weiler, E. J.; et al. (August 1980), "Coordinated ultraviolet, optical, and radio observations of HR 1099 and UX Arietis",Astrophysical Journal,239:L121 –L124,Bibcode:1980ApJ...239L.121R,doi:10.1086/183306.
Owen, F. N.; et al. (November 1976), "The detection of radio emission from the RS CVn binary HR 1099",Astrophysical Journal,210:L27 –L30,Bibcode:1976ApJ...210L..27O,doi:10.1086/182295.
