was obtained by the inclusion of continuous absorption by hydrogen molecules
(Osawa 1956).
3.7.2.2 Photometric Observations of Metallic-Line Stars
Osawa installed a new photoelectric photometer on the 30 cm reflector of the TAO
and carried out three color (UBV) observations of metallic-line stars and found that
these stars indicated considerable ultraviolet deficiency compared to main-sequence
stars (Osawa 1958). The distributions of metallic-line stars on the two-color diagram
(U – B, B – V) are illustrated in Fig. 3.16, where the continuous curve shows the
approximate mean colors of normal main-sequence stars. The U – B color indicates
strong ultraviolet deficiency toward a lower direction in this figure.
3.7.2.3 Spectral Classification
At Yerkes Observatory, Osawa took up the MK spectral classification of early
A-type stars. The MK Spectral Atlas by W. W. Morgan et al. yields the
two-dimensional fine spectra for around 200 normal and peculiar stars over all
spectral types (Morgan et al. 1943). The extension of the spectral classification to
a sufficiently large number of stars was an urgent subject in the 1950s. In particular,
Osawa carried out the MK classification of stars in spectral classes B8 to A2.
Spectral classification near A0 stars is especially difficult because of faint absorption
lines, except Balmer series. Osawa overcame this difficulty with sufficiently deep
observations and determined the MK spectral class for 533 stars in this spectral
region (Osawa 1959).
In 1963 and 1966, Osawa took up the MK classification of faint A-type stars at
the OAO and compared it with the HD classification. He found that MK classifications made by Slettebak for bright stars showed a nearly parallel relation with HD
Fig. 3.16 Colors of
metallic-line stars. Crosses
and dots represent Osawa’s
measurements and Johnson
and Morgan’ observations,
respectively (Osawa 1958)
70
3 Astronomy in Early Showa. I. Tokyo 1926–1945
(Osawa 1956).
3.7.2.2 Photometric Observations of Metallic-Line Stars
Osawa installed a new photoelectric photometer on the 30 cm reflector of the TAO
and carried out three color (UBV) observations of metallic-line stars and found that
these stars indicated considerable ultraviolet deficiency compared to main-sequence
stars (Osawa 1958). The distributions of metallic-line stars on the two-color diagram
(U – B, B – V) are illustrated in Fig. 3.16, where the continuous curve shows the
approximate mean colors of normal main-sequence stars. The U – B color indicates
strong ultraviolet deficiency toward a lower direction in this figure.
3.7.2.3 Spectral Classification
At Yerkes Observatory, Osawa took up the MK spectral classification of early
A-type stars. The MK Spectral Atlas by W. W. Morgan et al. yields the
two-dimensional fine spectra for around 200 normal and peculiar stars over all
spectral types (Morgan et al. 1943). The extension of the spectral classification to
a sufficiently large number of stars was an urgent subject in the 1950s. In particular,
Osawa carried out the MK classification of stars in spectral classes B8 to A2.
Spectral classification near A0 stars is especially difficult because of faint absorption
lines, except Balmer series. Osawa overcame this difficulty with sufficiently deep
observations and determined the MK spectral class for 533 stars in this spectral
region (Osawa 1959).
In 1963 and 1966, Osawa took up the MK classification of faint A-type stars at
the OAO and compared it with the HD classification. He found that MK classifications made by Slettebak for bright stars showed a nearly parallel relation with HD
Fig. 3.16 Colors of
metallic-line stars. Crosses
and dots represent Osawa’s
measurements and Johnson
and Morgan’ observations,
respectively (Osawa 1958)
70
3 Astronomy in Early Showa. I. Tokyo 1926–1945