Engineering topics

Nassiopoulos, G. E.

Publications and source records attributed to Nassiopoulos, G. E..

3 records

NASA NTRS1988

Periodic modulation of the atmosphere of Alpha Orionis

Alpha Orionis (Betelgeuse; M2 Iab) was monitored with IUE since 1984. Discovery of a 420-day periodic modulation of the flux in the optical and ultraviolet continua, and in the Mg II h and k line emission cores suggests that periodic photospheric pulsations were present from 1984 to 1986. This behavior continues through 1987. However, the general flux level of the ultraviolet continuum and the Mg II lines is decreasing, and the amplitude of the variation may be reduced. These decreases may be the emerging signature of an additional longer period. The density sensitive C II diagnostic, 2325.4/2328.1, indicates the chromospheric densities range between log N(sub e) (cm-3) = 8.7 and 9.5, but periodicities are not evident.

Dupree, A. K.↗

NASA NTRS1987

The interstellar medium toward SN 1987A

High-resolution spectra of SN 1987A obtained with the IUE satellite show absorption features from the disk and halo of the Galaxy and the LMC. A rich variety of elements and ionization states is found, including allowed resonance lines of abundant elements with ionization states ranging from C I and O I to Al III, Si IV, and C IV. The Si IV and C IV absorption at LMC velocities is unusually strong toward the supernova as compared to most other stars in the LMC and SMC. The origin of these lines is discussed.

Dupree, A. K.↗

NASA NTRS1987

Periodic photospheric and chromospheric modulation in Alpha Orionis (Betelgeuse)

The bright cool supergiant Alpha Orionis has been monitored spectroscopically and photometrically over the past three years (1984-1986) in the optical and the ultraviolet wavelength regions. A 420-day periodic modulation of the flux is observed in the optical and ultaviolet continua, and in the Mg II line emission cores. Periodic photospheric pulsations are the most likely explanation of these observations. This identification is based on the large amplitude of the variation, the correlation of the continuum and chromospheric fluxes, and the length of the observed period. Pulsation may heat and extend the atmosphere of Alpha Ori and initiate the mass flow from the star.

Dupree, A. K.↗