Chin.Astron.Astrophys. 2 (1985) 322-323 Act.Astrophys.Sin. 2 (1985) 188-191

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HISTORICAL RECORDS OF OUTBURST OF R AQUARII

LI Jing Beijing Observatory, Academia Sinica

ABSTRACT The expansion of the nebulosity surrounding R Aqr suggests the star undergoing an outburst some 550 -1100 years ago. It is pointed out here that the record of a "guest star" in the year 1073 A.D. contained in the "History of Korea" is possibly a description of the outburst event of this pecular variable star.

R Aqr is a variable star discovered by Harding in 1811, [l]. It was the 16th variable star discovered in the history of variable stars. In the "General Catalogue of Variable Stars", R Aqr is classified as a Mira star, with maximum magnitude 5.8 and minimum magnitude 11.5, and period 386.92 days. In the 40's, Hubble confirmed the characteristics of symbiotic stars in its spectrum [2]. Its spectral type is gM7e+ Pet. Baade [3] measured the velocity of expansion of its surrounding nebulosity. According to its parallox (n=0'.'0025) and its present average rate of expansion of 50- lOOkm/s, we can infer that some 550- 1100 years ago, an outburst took place, [4]. Photographic data taken by Henbig between 1970 and 1977 with the 3-metre telescope of

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the Lock Observatory, [S], revealed new nebulous structures in its vicinity. In 1980, Wallerstein et al. [6] observed an optical jet coming out of the central star. Combined optical, VLA radio and IUE ultraviolet observations in 1982 [7] revealed a composite emission nebula in the periphery ofthe symbiotic system. At a distance of about 200 arcsec from the central star, there was a compact, double radio source along the direction of the jet. Moreover, there was a weak radio source at a mere distance of 3 arcsec from R Aqr and its jet. This triple system spans about 7 arcsec, [S]. The ultraviolet region of the jet is a strong continuum spectrum, very different from the flat spectrum of the central star. At present, R Aqr is regarded

R Aquarii in History 323

as the second SS4~3phe~omenon, and is the first star with an observed optical jet.

I believe that R Aqr underwent a nova explosion with a maximum brightness not less than magnitude 4 and should have been visible to the naked eye and included in historical records of heavenly phenomena. In the “History of Korea”, there are two entries of guest stars appearing in the vicinity of R Aqr. One says: “Korea (King) Wenzong, Year 27, Month 8, Day Ding-thou, a guest star is seen south of (the lunar mansion) Dong-Bi” [9, lo]. This should be i.nterpreted as : Y&I 1073 October 9, a nova appeared south of y Pegasi”. The 1950 position of R Aqr is Right Ascension 23h41m 14.2s and Declination -1S033’42”, which is precisely south of y Peg. The other entry reads : “Korea (King) Ruizong, Year 8, Month 7, Day Xin-si, a star bursts (“bo”) in (the lunar mansion) Ying-shin. Our understanding of this record is: “On 1113 August 15, a not very bright new star appeared in the segian of o and B Peg. The mean right ascension of Ying-shi is close to that of R Aor”.

judging from these two records, I am inclined to identify the guest star of 1073 as a historical record of the nova outburst of R Aqr. The time interval between the year 1073 and the present is some 900 years, which is good agreement with the time of explosion deduced from the expansion rate of the surrounding nebulosity,

The word **bo” often referred to a comet. Chapter 18 of “Kai-yuan Zhan +Iing” (“Kai- yuan Canon of Prognostication”) quotes the ancient astronomer Shi Shen as saying that comets have four names, bo, fou, saa and hui, referring to different shapes. I think the bo star of 1113 probably referred to a faint comet.

It should be mentioned that Kafatos et al. [8] identified R Aqr as the remnant of an explosion in A.D, 930 141. This was based on records in “Mingyue Ji?’ and “Yidai Yao Ji”, reproduced in “Riben Tianwen. Shiliao” t5 apanese Historical Material on Astronomy”) s The “Yidai Yao Ji” record reads: i%eign Yanchang, Year 8, after Month 5, before Month 3, a guest star enters (the asterism) Ytllin, begins to move westwards in Yalin”. As judged by the words “enter” and ‘move westwards”, this event of A.D. 930 should be considered as referring to a comet, and not a nova.

ACKNOWLEDG~~E~ I thank XI Ze-zong, BO Shu- ren and LIU Yin-xi of the Institute of History of Natural Sciences for usful discussion, and for calling attention to the Japanese record referred to in the text.

REFERENCES

XI Ze-zong and I30 Shu-ren Act. ast~n. Sin. I.3 (1965) 1 T’Zhoneeuo Tianwenzui Shi” (f2History of Chinese Astr~nom~~~) , Kexue Chubanshe (X981) 255.