The wavy shape of the light curve of ER Vul resembles those of aW UMa star for adetached binary, indicating that the stars are not in direct contact but are close enough to gravitationally distort their shapes. By 1967, studies showed unexplained fluctuations in the light curve.[12]H. E. Bond in 1970 found calciumH and K lines inemission.[13]D. S. Hall classified the ER Vul system as a short periodRS Canum Venaticorum variable in 1970, based on the spectral type and emission lines.[14] These emission lines suggest some form ofchromospheric activity on the star. Darkstar spots were proposed as an explanation of the intrinsic variability of these types of stars byH. M. Al-Naimiy,[15] and ER Vul was determined to be heavily spotted.[16]
Thecorona of ER Vul was found to be a strongsource of soft X-rays byF. M. Walter andS. Bowyer in 1981.[17][15] The eclipsing nature of the system was confirmed byT. H. Kadouri in 1981, with the primary eclipse being anoccultation.[15] Radio emission was detected with theVLA in 1992, and it was found to be one of the most luminousmain-sequence stars known in that band.[18] Due to gravitational interaction that has forced atidal lock with their close orbit, both stars are rotating rapidly – more than 40 times the rotation rate of the Sun, which is driving theirmagnetic dynamo. They show the "strongest coronal and chromospheric emissions of any main-sequence G-type star".[19]
C. İbanoğlu and associates in 1993 were able to explain the light curve of this system through a combination of "proximity effects, wavelike distortions, mutual eclipses, and short-term light fluctuations".[20] By measuring variations inHydrogen alpha emission,Ö. Çakırlı and associates in 2003 found that cooler secondary component is the moreactive of the pair.[7] However, other observers have observed that the primary is the more active. This changeover may be the result of magnetic interaction between the stars.[8] In 2005,E. Shkolnik and associates discovered a high-velocity stream passing between the stars toward the secondary component. This stream is creating a large active area on the companion.[21]
^abcdefghijkÖzavcı, İ.; et al. (May 2019), "Surface inhomogeneities of the eclipsing binary ER Vul",Contributions of the Astronomical Observatory Skalnaté Pleso,49 (2):278–286,Bibcode:2019CoSka..49..278O.
^Northcott, Ruth J.; Bakos, Gustav A. (February 1967), "Spectroscopic and photometric observations of ER Vulpeculas",Astronomical Journal,72: 89,Bibcode:1967AJ.....72...89N,doi:10.1086/110205.
^Hall, D. S. (1976), Fitch, W. S. (ed.), "The RS CVn Binaries and Binaries with Similar Properties",Multiple Periodic Variable Stars, Proceedings of IAU Colloq. 29, held in Budapest, Hungary, 1–5 September 1975, Astrophysics and Space Science Library, vol. 60, D. Reidel Publishers, p. 287,Bibcode:1976ASSL...60..287H,doi:10.1007/978-94-010-1175-4_15,ISBN978-94-010-1177-8,S2CID120775716.
^Rucinski, S. M. (1979), "Sizes of spots in spotted stars",Acta Astronomica,29:203–209,Bibcode:1979AcA....29..203R.
^Walter, F. M.; Bowyer, S. (April 1981), "On the coronae of rapidly rotating stars. I. The relation between rotation and coronal activity in RS CVn systems.",Astrophysical Journal,245:671–676,Bibcode:1981ApJ...245..671W,doi:10.1086/158842.
^Bradstreet, D. H.; et al. (December 1993), "The Hyperactive Double Suns of the Binary ER Vulpeculae",Bulletin of the American Astronomical Society,25: 1425,Bibcode:1993AAS...183.8504B.
^Ibanoglu, C.; et al. (March 1993), "Photometry of ER Vulpeculae : photometric analysis with the WINK-10 code",Astronomy and Astrophysics,269:310–318,Bibcode:1993A&A...269..310I.
Crăciun, Maria; et al. (April 2015), "Detection of low-level periodic signals through enhanced self-correlation method. The case of ER Vulpeculae",Monthly Notices of the Royal Astronomical Society,448 (3):2066–2076,Bibcode:2015MNRAS.448.2066C,doi:10.1093/mnras/stv108.
Kjurkchieva, D. P.; et al. (June 2003), "Spectroscopic and photometric observations of the short-period RS CVn-type star ER Vulpeculae",Astronomy and Astrophysics,404 (2):611–620,Bibcode:2003A&A...404..611K,doi:10.1051/0004-6361:20030489.
Osten, Rachel A.; et al. (January 2002), "Multiwavelength Observations of Three Short-Period Active Binary Systems: ER Vulpeculae, CC Eridani, and EI Eridani",The Astrophysical Journal Supplement Series,138 (1):99–120,Bibcode:2002ApJS..138...99O,doi:10.1086/323666,S2CID122667001.
Qian, S. B. (2001), Brekke, Pål; et al. (eds.), "Possible Magnetic Activity Cycles of Four Chromospherically Active Binaries: ER Vul, UV Psc, AR Lac and BH Vir",Recent Insights into the Physics of the Sun and Heliosphere: Highlights from SOHO and Other Space Missions, Proceedings of IAU Symposium 203, vol. 203, Astronomical Society of the Pacific, p. 437,Bibcode:2001IAUS..203..437Q,ISBN1-58381-069-2.
Lazaro, C.; Arevalo, M. J. (June 1997), "Time-Resolved Spectroscopy of RS CVn Short-Period Systems. I. CG Cyg, BH Vir, and ER Vul",The Astronomical Journal,113: 2283,Bibcode:1997AJ....113.2283L,doi:10.1086/118439.
Gunn, A. G.; Doyle, J. G. (February 1997), "Environments of active close binaries. I. ER Vulpeculae",Astronomy and Astrophysics,318:60–72,Bibcode:1997A&A...318...60G.
Oláh, K.; Kövári, Zs. (1997), "Spot temperatures in binaries with two active components: By Dra and Er Vul",Astronomical and Astrophysical Transactions,13 (4):295–299,Bibcode:1997A&AT...13..295O,doi:10.1080/10556799708202971.
Edalati, M. T.; Zeinali, F. (December 1995), "The Photometric Observations of ER Vulpeculae: Photometric Analysis with the W-D Code",Astrophysics and Space Science,234 (2):271–280,Bibcode:1995Ap&SS.234..271E,doi:10.1007/BF00627672,S2CID119974452.
Zeinali, F.; et al. (May 1995), "Photoelectric Observations of the Eclipsing Variable ER Vulpeculae",Information Bulletin on Variable Stars,4190: 1,Bibcode:1995IBVS.4190....1Z.
Olah, K.; et al. (November 1994), "The active close binary system ER Vulpeculae",Astronomy and Astrophysics,291:110–120,Bibcode:1994A&A...291..110O.
Eryurt, D.; et al. (December 1991), "The Light Curve of ER Vulpeculae",Information Bulletin on Variable Stars,3692: 1,Bibcode:1991IBVS.3692....1E.
Guinan, E. F.; et al. (September 1991), "Simultaneous IUE and Ground-Based Observations of ER Vul Over Two Orbits",Bulletin of the American Astronomical Society,23: 1412,Bibcode:1991BAAS...23.1412G.
Rucinski, S. M. (August 1991), "The radio light curve of ER Vulpeculae",Journal of the Royal Astronomical Society of Canada,85: 184,Bibcode:1991JRASC..85..184R.
Bradstreet, D. H.; Guinan, E. F. (August 1991), Marsden, B. G. (ed.), "ER Vulpeculae",IAU Circular, vol. 5329, p. 1,Bibcode:1991IAUC.5329....1B.
Heckert, P. A.; Zeilik, M. (July 1991), "1988 and 1989 BV Photometry of ER Vul",Information Bulletin on Variable Stars,3636: 1,Bibcode:1991IBVS.3636....1H.
Fernández-Figueroa, M. J.; et al. (1991), Tuominen, I.; et al. (eds.), "CAII H and K Spectroscopy of ER-Vulpeculae",The Sun and Cool Stars. Activity, Magnetism, Dynamos. Proceedings of Colloquium No. 130 of the International Astronomical Union, held in Helsinki, Finland, July 17–20, 1990, vol. 380, no. 130, Berlin, Germany; New York, NY: Springer-Verlag, p. 483,Bibcode:1991LNP...380..483F,doi:10.1007/3-540-53955-7_185,ISBN3-540-53955-7.
Hill, G.; et al. (November 1990), "Studies of late-type binaries. IV. The physical parameters of ER Vulpeculae",Astronomy and Astrophysics,238: 145,Bibcode:1990A&A...238..145H.
Mennella, V. (August 1990), "Time-scale variability of the light curves of ER Vulpeculae.",Astronomy and Astrophysics,234: 203,Bibcode:1990A&A...234..203M.
Akan, M. C.; et al. (August 1987), "B, V Photometry of ER Vulpeculae",Information Bulletin on Variable Stars,3059: 1,Bibcode:1987IBVS.3059....1A.
White, N. E.; et al. (August 1987), "An EXOSAT observation of 1.5 orbital cycles of the 0.7 day short-period RS CVn system ER Vul",Monthly Notices of the Royal Astronomical Society,227 (3):545–551,Bibcode:1987MNRAS.227..545W,doi:10.1093/mnras/227.3.545.
Arevalo, M. J.; Fuensalida, J. J. (December 1985), "1984 UBVR Light Curves of ER Vul",Information Bulletin on Variable Stars,2831: 1,Bibcode:1985IBVS.2831....1A.
Ibanoglu, C.; Akan, M. C.; Evren, S.; Tunca, Z. (August 1985), "Photoelectric Observations of ER Vulpeculae",Information Bulletin on Variable Stars,2782: 1,Bibcode:1985IBVS.2782....1I.
Barden, S. C. (March 1984), "The Hα Nature of the Short Period RS CVn Systems HD86590, σαCr B, ER Vul and UV Psc.",Bulletin of the American Astronomical Society,16: 473,Bibcode:1984BAAS...16..473B.
Zeilik, M.; et al. (November 1982), "1982 Photometry of ER Vul",Information Bulletin on Variable Stars,2221: 1,Bibcode:1982IBVS.2221....1Z.
McLean, B. J. (November 1982), "A spectroscopic investigation of the eclipsing variable ER Vul",Monthly Notices of the Royal Astronomical Society,201:421–427,Bibcode:1982MNRAS.201..421M,doi:10.1093/mnras/201.2.421.
Kadouri, T. H. (December 1981), "BVR Photoelectric Observations of ER Vul June, July, 1981",Information Bulletin on Variable Stars,2057: 1,Bibcode:1981IBVS.2057....1K.
Al-Naimiy, H. M. K. (January 1981), "Photometric observations and light curve analysis of the peculiar system ER Vul",Astronomy and Astrophysics Supplement Series,43:85–90,Bibcode:1981A&AS...43...85A.
Al-Naimiy, H. M. (October 1978), "Observation of the Peculiar Eclipsing Variable ER Vulpeculae",Information Bulletin on Variable Stars,1481: 1,Bibcode:1978IBVS.1481....1A.
