explanation of the V/R variation. Thereafter, Kato-Okazaki’s theory was widely
accepted in the study of Be stars (Kato 1983; Okazaki 1991, 1996).
Be stars are generally of the luminosity class, III–V, belonging to some evolved
B-type stars. On the other hand, Be and Ae stars, called Herbig Be/Ae stars (Herbig
1960), are pre-main-sequence stars surrounded by MCs. Yoshida Shigeomi, Kogure,
and their group observed the Herbig Be/Ae star MWC 1080 in molecular lines with a
45-m radio telescope and in optical spectral lines at the OAO. They found that the
CO line revealed the bipolar nature of molecular outflow, whereas the
13 CO and CS
observations disclosed a disk structure with a cavity of face-on doughnut-like
structure. The optical spectra exhibited strong emission lines in the Balmer lines
and some metallic lines. The Balmer lines showed prominent P Cygni profiles. From
these profiles the mass-loss rate due to the stellar wind was roughly estimated to be
10
À6 M ☉ year
À1 , and the maximum wind velocity reaches up to 1000 km s
À1 . This
strong wind was supposed to be responsible for the derivation of molecular outflow
and the formation of cavities in molecular disks (Yoshida et al. 1991, 1992).
7.5.3.2 Symbiotic Stars
Symbiotic stars are stars that exhibit combined spectra of early-type and late-type
stars. The nomenclature of symbiotic stars is due to P. W. Merrill (1958) of the
Mt. Wilson Observatory. Initially, symbiotic stars were assumed to be a type of
peculiar star, but it became apparent that they are interacting close binaries composed of an evolved cool giant and an accreting hot component (usually a white
dwarf), both components being surrounded by dense nebulae.
Tamura Shin’ichi of Tohoku University made spectroscopic observations of a
symbiotic star, HBV 475 (V1329 Cygni), at the OAO (Tamura 1977). This star
belongs to a very slow nova (called symbiotic nova) and exhibited a slow explosion
in 1964–1967 with maximum light in 1967. In 1977, when Tamura observed this
star, the spectrum showed a distinct feature in the coexistence of high-excitation and
low-excitation emission lines and their strong variability. The spectra of HBV 475 at
three epochs are illustrated in Fig. 7.24, where the most notable feature was the
appearance of high-excitation emission lines [FeVII], [FeVI], [CaV] and their strong
variations. From the spectral analysis Tamura found that the nebulosity was stratified
into two inner-hotter (electron temperature of around 20,000 K) and outer-warmer
layer (electron temperature of around 6000 K), with a high electron density (higher
than 10
6 cm
À3 ). The temperature of the central star increased from 60,000 K in 1970
to around 100,000 K in 1977. From these results, Tamura argued that symbiotic stars
might be stars in the process of undergoing planetary nebulae formation (Tamura
1977). To test this hypothesis, Tamura (1984) examined the distribution of symbiotic stars and star-like planetary nebulae in the Galaxy. He found that both objects
concentrate near the galactic center with somewhat different degrees of concentration. From these distributions Tamura concluded that there certainly exists a close
relationship between symbiotic stars and stellar-image planetary nebulae (Tamura
1984, 1997).
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7 Postwar Development of Astrophysics, 1946–2000 (Part II: Astrophysics)
accepted in the study of Be stars (Kato 1983; Okazaki 1991, 1996).
Be stars are generally of the luminosity class, III–V, belonging to some evolved
B-type stars. On the other hand, Be and Ae stars, called Herbig Be/Ae stars (Herbig
1960), are pre-main-sequence stars surrounded by MCs. Yoshida Shigeomi, Kogure,
and their group observed the Herbig Be/Ae star MWC 1080 in molecular lines with a
45-m radio telescope and in optical spectral lines at the OAO. They found that the
CO line revealed the bipolar nature of molecular outflow, whereas the
13 CO and CS
observations disclosed a disk structure with a cavity of face-on doughnut-like
structure. The optical spectra exhibited strong emission lines in the Balmer lines
and some metallic lines. The Balmer lines showed prominent P Cygni profiles. From
these profiles the mass-loss rate due to the stellar wind was roughly estimated to be
10
À6 M ☉ year
À1 , and the maximum wind velocity reaches up to 1000 km s
À1 . This
strong wind was supposed to be responsible for the derivation of molecular outflow
and the formation of cavities in molecular disks (Yoshida et al. 1991, 1992).
7.5.3.2 Symbiotic Stars
Symbiotic stars are stars that exhibit combined spectra of early-type and late-type
stars. The nomenclature of symbiotic stars is due to P. W. Merrill (1958) of the
Mt. Wilson Observatory. Initially, symbiotic stars were assumed to be a type of
peculiar star, but it became apparent that they are interacting close binaries composed of an evolved cool giant and an accreting hot component (usually a white
dwarf), both components being surrounded by dense nebulae.
Tamura Shin’ichi of Tohoku University made spectroscopic observations of a
symbiotic star, HBV 475 (V1329 Cygni), at the OAO (Tamura 1977). This star
belongs to a very slow nova (called symbiotic nova) and exhibited a slow explosion
in 1964–1967 with maximum light in 1967. In 1977, when Tamura observed this
star, the spectrum showed a distinct feature in the coexistence of high-excitation and
low-excitation emission lines and their strong variability. The spectra of HBV 475 at
three epochs are illustrated in Fig. 7.24, where the most notable feature was the
appearance of high-excitation emission lines [FeVII], [FeVI], [CaV] and their strong
variations. From the spectral analysis Tamura found that the nebulosity was stratified
into two inner-hotter (electron temperature of around 20,000 K) and outer-warmer
layer (electron temperature of around 6000 K), with a high electron density (higher
than 10
6 cm
À3 ). The temperature of the central star increased from 60,000 K in 1970
to around 100,000 K in 1977. From these results, Tamura argued that symbiotic stars
might be stars in the process of undergoing planetary nebulae formation (Tamura
1977). To test this hypothesis, Tamura (1984) examined the distribution of symbiotic stars and star-like planetary nebulae in the Galaxy. He found that both objects
concentrate near the galactic center with somewhat different degrees of concentration. From these distributions Tamura concluded that there certainly exists a close
relationship between symbiotic stars and stellar-image planetary nebulae (Tamura
1984, 1997).
204
7 Postwar Development of Astrophysics, 1946–2000 (Part II: Astrophysics)