V923 Aquilae

V923 Aquilae is a variable binary star^[9] system in the equatorial constellation of Aquila. It has the designation HD 183656 from the Henry Draper Catalogue; V932 Aql is the variable star designation. The system is dimly visible to the naked eye with an apparent visual magnitude that fluctuates around 6.06.^[3] It is located at a distance of approximately 890 light years from the Sun based on parallax,^[2] but is drifting closer with a radial velocity of around −26 km/s.^[7]

V923 Aquilae

A photoelectric (yellow) light curve for V923 Aquilae, plotted from data presented by Lynds (1960).[1] The length of a full phase cycle is 0.8518 days.
Observation data Epoch J2000      Equinox J2000
Constellation	Aquila
Right ascension	19h 30m 33.12199s[2]
Declination	+03° 26′ 39.8583″[2]
Apparent magnitude (V)	6.06[3] 5.98 to 6.18[4]
Characteristics
Evolutionary stage	Main sequence[5]
Spectral type	B7III[6]
U−B color index	−0.31[3]
B−V color index	−0.019±0.008[7]
Variable type	Be star[4]
Astrometry
Radial velocity (Rv)	−26.0±7.4[7] km/s
Proper motion (μ)	RA: 11.717[2] mas/yr Dec.: 3.089[2] mas/yr
Parallax (π)	3.6705 ± 0.0607 mas[2]
Distance	890 ± 10 ly (272 ± 5 pc)
Absolute magnitude (MV)	−0.87[7]
Details[5]
Primary
Mass	6.2±0.3 M☉
Luminosity	1517+158 −143 L☉
Surface gravity (log g)	3.64±0.21 cgs
Temperature	16,580±400 K
Rotational velocity (v sin i)	275±17 km/s
Secondary
Mass	~0.5 M☉
Other designations
V923 Aql, BD+03°4043, HD 183656, HIP 95929, HR 7415, SAO 0124704[8]
Database references
SIMBAD	data

This 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".^[10] P. W. Merrill and C. G. Burwell identified it as a shell star in 1949.^[11][12] Merrill and A. L. Lowen showed in 1953 that the shell displayed large radial velocity variations.^[13] 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.^[1]

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 (250 R_☉). They hypothesized that the long-term variation was due to an envelope created by a mass transfer from the secondary component to the primary.^[14] However, the mass transfer concept was later brought into question and remains unverified as of 2004.^[9]

References

1. Lynds, C. R. (March 1960), "The Light-Variations of HD 183656", Astrophysical Journal, 131: 390, Bibcode:1960ApJ...131..390L, doi:10.1086/146842.
2. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
3. Haupt, H. F.; Schroll, A. (1974), "Photoelektrische Photometrie von Shell-Sternen", Astronomy and Astrophysics Supplement Series, 15: 311, Bibcode:1974A&AS...15..311H.
4. Samus', N. N; et al. (2017). "General catalogue of variable stars". Astronomy Reports. GCVS 5.1. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
5. Zorec, J.; et al. (November 2016), "Critical study of the distribution of rotational velocities of Be stars. I. Deconvolution methods, effects due to gravity darkening, macroturbulence, and binarity", Astronomy & Astrophysics, 595: 26, Bibcode:2016A&A...595A.132Z, doi:10.1051/0004-6361/201628760, hdl:11336/37946.
6. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H.
7. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
8. "HD 183656". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-02-21.{{cite web}}: CS1 maint: postscript (link)
9. Arias, M. L.; et al. (April 2004), "The circumstellar environment of the star V923 Aquilae", Astronomy and Astrophysics, 417 (2): 679–688, Bibcode:2004A&A...417..679A, doi:10.1051/0004-6361:20034435, hdl:11336/37035.
10. Harper, W. E. (1937), "The radial velocities of 917 stars", Publications of the Dominion Astrophysical Observatory Victoria, 7: 1–97, Bibcode:1937PDAO....7....1H.
11. Merrill, Paul W.; Burwell, Cora G. (November 1949), "Second Supplement to the Mount Wilson Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines", Astrophysical Journal, 110: 387, Bibcode:1949ApJ...110..387M, doi:10.1086/145215.
12. Bidelman, W. P. (April 1950), "The Spectrum of HR 7415", Publications of the Astronomical Society of the Pacific, 62 (364): 48, Bibcode:1950PASP...62...48B, doi:10.1086/126224, S2CID 119744604.
13. Merrill, Paul W.; Lowen, A. Louise (July 1953), "Intercomparison of Shell Spectra", Astrophysical Journal, 118: 18, Bibcode:1953ApJ...118...18M, doi:10.1086/145723.
14. Koubský, P.; et al. (February 1989), "Properties and Nature of Be Stars. 13. Radial-Velocity Variations of the Shell Star V 923 AQL (HD 183 656) In the Past Sixty Years", Bulletin of the Astronomical Institute of Czechoslovakia, 40: 31, Bibcode:1989BAICz..40...31K.

External links

• HR 7415
• Image V923 Aquilae