203 research outputs found
Analysis of historical meteor and meteor shower records: Korea, China, and Japan
We have compiled and analyzed historical Korean meteor and meteor shower
records in three Korean official history books, Samguksagi which covers the
three Kingdoms period (57 B.C -- A.D. 935), Goryeosa of Goryeo dynasty (A.D.
918 -- 1392), and Joseonwangjosillok of Joseon dynasty (A.D. 1392 -- 1910). We
have found 3861 meteor and 31 meteor shower records. We have confirmed the
peaks of Perseids and an excess due to the mixture of Orionids, north-Taurids,
or Leonids through the Monte-Carlo test. The peaks persist from the period of
Goryeo dynasty to that of Joseon dynasty, for almost one thousand years. Korean
records show a decrease of Perseids activity and an increase of
Orionids/north-Taurids/Leonids activity. We have also analyzed seasonal
variation of sporadic meteors from Korean records. We confirm the seasonal
variation of sporadic meteors from the records of Joseon dynasty with the
maximum number of events being roughly 1.7 times the minimum. The Korean
records are compared with Chinese and Japanese records for the same periods.
Major features in Chinese meteor shower records are quite consistent with those
of Korean records, particularly for the last millennium. Japanese records also
show Perseids feature and Orionids/north-Taurids/Leonids feature, although they
are less prominent compared to those of Korean or Chinese records.Comment: 29 pages, 7 figures. To appear in Icaru
Do happy people lead better?
Leaders with more positive moods at work are more likely to be viewed by employees as transformational, argue Sirkwoo Jin, Myeong-Gu Seo and Debra L. Shapir
The Stream-Stream Collision after the Tidal Disruption of a Star Around a Massive Black Hole
A star can be tidally disrupted around a massive black hole. It has been
known that the debris forms a precessing stream, which may collide with itself.
The stream collision is a key process determining the subsequent evolution of
the stellar debris: if the orbital energy is efficiently dissipated, the debris
will eventually form a circular disk (or torus). In this paper, we have
numerically studied such stream collision resulting from the encounter between
a 10^6 Msun black hole and a 1 Msun normal star with a pericenter radius of 100
Rsun. A simple treatment for radiative cooling has been adopted for both
optically thick and thin regions. We have found that approximately 10 to 15% of
the initial kinetic energy of the streams is converted into thermal energy
during the collision. The angular momentum of the incoming stream is increased
by a factor of 2 to 3, and such increase, together with the decrease in kinetic
energy, significantly helps the circularization process. Initial luminosity
burst due to the collision may reach as high as 10^41 erg/sec in 10^4 sec,
after which the luminosity increases again (but slowly this time) to a steady
value of a few 10^40 erg/sec in a few times of 10^5 sec. The radiation from the
system is expected to be close to Planckian with effective temperature of
\~10^5K.Comment: 19 pages including 12 figures; Accepted for publication in Ap
Korean Nova Records in A.D. 1073 and A.D. 1074: R Aquarii
R Aqr is known to be a symbiotic binary system with an associated extended
emission nebula, possibly produced by a historic outburst. To find the
associated historic records, we searched for and compiled all 'Guest Star' and
'Peculiar Star' records in three Korean 'official' history books that cover
almost two thousand years, Samguksagi, Goryeosa, Joseonwangjosillok. In
addition to the record of A.D. 1073, previously noted by Li (1985), we have
found in Goryeosa another candidate record of A.D. 1074, which has the same
positional description as that of A.D. 1073 with an additional brightness
description. We examined various aspects of the two records and conclude that
they both are likely to be the records of outburst of R Aqr. This means that
there were two successive outbursts in A.D. 1073 and in A.D. 1074, separated by
approximately one year. Based on these records, we estimate the distance to R
Aqr to be 273 pc if the expansion of the nebula has been at a constant rate.
The brightness record of A.D. 1074 corresponds to the absolute magnitude at
outburst of M_(outburst) = -6.2 mag. ~ -5.2 mag. at this distance. The two
Korean records associated with R Aqr may provide astronomically meaningful
constraints to the outburst model of R Aqr and the formative process of its
nebulosity.Comment: 10 pages, 2 figures, 1 appendix. To appear in Astronomy and
Astrophysic
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