V923 Aquilae
A spectroscopic binary with a shell star and variable brightness.
V923 Aquilae is a binary star system in the constellation Aquila, just barely visible to the naked eye at an apparent magnitude of about 6.06. It lies roughly 890 light-years from the Sun and is moving closer at a radial velocity of roughly −26 km/s. The system was first recognized as a likely spectroscopic binary in 1937, when W. E. Harper noted its spectrum showed “narrow intense lines of peculiar spectrum.” In 1949, P. W. Merrill and C. G. Burwell classified it as a shell star, and Merrill and A. L. Lowen found in 1953 that the shell’s radial velocity varied widely. A 1960 photometric study by C. R. Lynds revealed brightness changes with an amplitude exceeding 0.1 magnitude and a characteristic period of 0.85 days, though the variation is not strictly periodic over long spans. A more detailed 1989 study by P. Koubský and colleagues, using long-term radial velocity data, confirmed it as a spectroscopic binary with an orbital period of 214.75 days, plus a superimposed long-term cyclical variation of changing amplitude and period. The model suggests a primary star of spectral type B5–7e and a low-mass secondary, separated by about 250 times the Sun’s radius. The long-term variation was initially attributed to an envelope from mass transfer from the secondary to the primary, but this idea has since been questioned and remains unverified as of 2004.
- Designations
- HD 183656, V923 Aql
- Apparent visual magnitude
- 6.06 (fluctuating)
- Distance
- approximately 890 light years
- Radial velocity
- approximately −26 km/s
- Orbital period
- 214.75 days
- Spectral type primary
- B5–7e
- Separation
- 250 R☉
Lore & Background
The system was first identified as a likely spectroscopic binary by W. E. Harper in 1937, who noted it showed 'narrow intense lines of peculiar spectrum'. P. W. Merrill and C. G. Burwell identified it as a shell star in 1949. Merrill and A. L. Lowen showed in 1953 that the shell displayed large radial velocity variations. A photometric study by C. R. Lynds in 1960 showed the system varied in brightness with an amplitude of more than 0.1 in magnitude and a characteristic period of 0.85 days, although it does not behave periodically over long time intervals.
A more thorough investigation by P. Koubský and associates in 1989 using long-term radial velocity measurements determined this is a spectroscopic binary with an orbital period of 214.75 days. There is also an overlaying long-term cyclical variation of changing amplitude and period. The modelled binary system shows a primary with a class of around B5–7e and a low mass secondary separated by around 250 times the radius of the Sun. They hypothesized that the long-term variation was due to an envelope created by a mass transfer from the secondary component to the primary. However, the mass transfer concept was later brought into question and remains unverified as of 2004.
Reader's Guide
V923 Aquilae holds significance as a spectroscopic binary system that has been studied for nearly a century, revealing complex variability. Its identification as a shell star in 1949 and the subsequent detection of large radial velocity variations in the shell contributed to understanding of such stars. The 1960 photometric study established a short-term brightness variation with a 0.85-day period, though its non-periodic behavior over long intervals indicates instability. The 1989 investigation by Koubský and associates provided a detailed orbital model with a 214.75-day period and a primary of spectral type B5–7e, while also identifying a long-term cyclical variation of changing amplitude and period. The hypothesis that mass transfer from the secondary to the primary creates an envelope driving the long-term variation remains unverified as of 2004, leaving an open question about the system's evolution. This uncertainty underscores the ongoing need for observation and analysis of such binary systems.
Did You Know?
- The binary components are separated by about 250 times the radius of the Sun.
- The mass transfer hypothesis for the long-term variation remains unverified as of 2004.
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