Far-Ultraviolet Spectra of Six Stars in Orion.

Abstract

view Abstract Citations (20) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Ultraviolet Spectra of Six Stars in Orion. Morton, Donald C. Abstract An Aerobee rocket carried two ultraviolet objective spectrographs to 186 km on the morning of 13 October 1965 and pointed them towards Orionis within 1 ~. The cameras and stabilization system were similar to those used to obtain spectra of stars in Scorpius in June 1965. This time one of the f/2 Schmidt cameras had a lithium fluoride corrector, while the other used calcium fluoride as be- fore. An unexpected shock during re-entry severed the mirror and film cassettes from the calcium fluoride camera so that films from only the lithium fluoride one were recovered. Development of these films showed ultraviolet spectra of the six OB stars in Orion listed below with their wavelength ranges. Spec- Wavelength Star V B-V trum range Velocity 1 Ori2.20 -0.21 09.511 1200 to 1415A -1400 km sec~ Ori 1.70 -0.19 BOla 1220 1595 -1900 ~On 2.05 09.51b 1200 1740 -1900 ~ Ori3.35 -0.19 BO.5V 1220 1400 (weak) Ori 2.77 -0.25 09111 1235 2100 -3000: Ori 2.04 -0.18 BO.51a 1630 2795 An exposure of 180 sec gave the best spectra, wiil~ a resolution of about 3 A, somewhat poorer than the 1 A obtained on the previous flight. Nevertheless, many absorption lines and a few emission lines are definitely visible in the spectra. Zero-order images of other stars on the same film permit an absolute calibration of wavelengths within 1 A. Emission lines of Si IV at 1402.7 A and C IV at 1549.5 A are identified in ~ and E. Strong absorption lines of both components of the Si IV doublet and the unresolved C IV doublet are found in ~, E, and t shifted to shorter wavelengths by several angstroms. The Si IV doublet is also present in ~, shifted in a similar way. The velocities corresponding to these shifts are indicated in the table. The value for is uncertain because of poor lines and a lack of unshifted features for checking the wavelength scale. These displaced absorption features must be formed by gas escaping from the stars at high velocities indicating a significant mass loss from these early type giants and supergiants. Rough limits on the rate of mass loss can be obtained by assuming that 4~e broadening of the lines 15 entirely by either Maxwellian Doppler velocities or radiation damping. For the widths of the lines in ~ Orionis the Doppler model gives ~10-~ M0 yr-1 while damping gives ~10-~ M0 yr-'. Absorption lines about 8 A wide are also visible at 1216 A in ~ and 8, and are attributed to Lyman-~ absorption by interstellar hydrogen atoms. Assuming broadening by radiation damping, the width corresponds to ~lO~~ atoms Cm-- 1n il~e line of sight. Publication: The Astronomical Journal Pub Date: 1966 DOI: 10.1086/110137 Bibcode: 1966AJ.....71S.172M full text sources ADS | data products SIMBAD (6)