AG Draconis

A blue band light curve for AG Draconis, spanning 123 years, adapted from Gális et al. (2015)[1]
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 16h 01m 41.01257s[2]
Declination +66° 48′ 10.1312″[2]
Apparent magnitude (V) 7.9 - 10.3[3]
Characteristics
Spectral type K3 IIIep[4] + WD[5]
B−V color index 1.425±0.094[6]
Variable type Z And[7]
Astrometry
Radial velocity (Rv)−147.42±0.30[6] km/s
Proper motion (μ) RA: −7.135[2] mas/yr
Dec.: −5.602[2] mas/yr
Parallax (π)0.2101 ± 0.0268 mas[2]
Distanceapprox. 16,000 ly
(approx. 4,800 pc)
Orbit[8]
Period (P)549.73 d
Eccentricity (e)0.06
Periastron epoch (T)2447622.28 JD
Argument of periastron (ω)
(secondary)		359.8°
Semi-amplitude (K1)
(primary)		4.67 km/s
Details[5]
AG Dra A
Mass1.5 M☉
Radius35 R☉
Metallicity [Fe/H]−1.3 dex
AG Dra B
Luminosity~ 103 L☉
Temperature~ 105 K
Other designations
AG Dra, AG+66° 715, BD+67°922, HIP 78512, SAO 16931[9]
Database references
SIMBADdata

AG Draconis is a binary star system in the northern constellation of Draco. It consists of a giant star and a white dwarf that revolve around each other every 550 days.

Discovery

AG Draconis has been catalogued since the start of the 20th century, as BD+67°922. However, its unusual nature did not start to come to light until the middle of the century. It was noted as an emission-line object in 1943,[10] although its nature was not understood.[11] The emission spectrum was serendipitously discovered to be variable by Nancy Grace Roman when she observed the star and found that the spectrum had completely changed since earlier observations.[12] It was given the variable star designation AG Draconis in 1964.[13]

Variability

AG Draconis spends most of its time in a quiescent phase near visual magnitude 9.8, with only small semi-regular variations thought to be due to pulsations of the giant star. At its faintest, it can reach magnitude 10.3.[3] The semi-regular variations have periods of 340 - 370 days. Variations at ultraviolet wavelengths occur with a period of 550 days, which is the orbital period.[5]

Every 12-16 years, outbursts occur and last for several years.[5] The brightness can increase to visual magnitude 7.9,[3] although usually not this bright.[5]

System

The a sin i value for the primary is 50.69 R☉, where a is the semimajor axis and i is the (unknown) orbital inclination.[8] The larger star is thought to be an orange hued giant around 1.5 times as massive as the Sun that has swollen to around 35 times the diameter of the Sun with a spectral type measured at K3IIIep.[5] The smaller star is a compact hot white dwarf around 0.4 times as massive as the Sun, with a surface temperature of around 80,000 K.[14]

References

  1. ↑ Gális, R.; Hric, L.; Smelcer, L. (February 2015). "AG Draconis - a symbiotic mystery". Open European Journal on Variable Stars. 169: 4–9. Bibcode:2015OEJV..169....4G. Retrieved 2 January 2022.
  2. 1 2 3 4 5 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.
  3. 1 2 3 "AG Draconis". Variable Star Index. AAVSO. Retrieved 2020-04-29.
  4. ↑ Shenavrin, V. I.; et al. (2011). "Search for and study of hot circumstellar dust envelopes". Astronomy Reports. 55 (1): 31–81. Bibcode:2011ARep...55...31S. doi:10.1134/S1063772911010070. S2CID 122700080.
  5. 1 2 3 4 5 6 Hric, L.; et al. (September 2014). "Outburst activity of the symbiotic system AG Dra". Monthly Notices of the Royal Astronomical Society. 443 (2): 1103–1112. arXiv:1406.5505. Bibcode:2014MNRAS.443.1103H. doi:10.1093/mnras/stu1162. S2CID 119225658.
  6. 1 2 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.
  7. ↑ Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  8. 1 2 Gális, R.; Hric, L.; Friedjung, M.; Petrík, K. (1999). "Resonances as the general cause of the outbursts in the symbiotic system AG Draconis". Astronomy and Astrophysics. 348: 533. Bibcode:1999A&A...348..533G.
  9. ↑ "AG Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2 September 2018.
  10. ↑ Janssen, Edith M.; Vyssotsky, A. N. (1943). "A Peculiar Emission-Line Object". Publications of the Astronomical Society of the Pacific. 55 (326): 244. Bibcode:1943PASP...55..244J. doi:10.1086/125560. S2CID 122605688.
  11. ↑ Wilson, Ralph E. (1950). "The Spectrum of HD 4174". Publications of the Astronomical Society of the Pacific. 62 (363): 14. Bibcode:1950PASP...62...14W. doi:10.1086/126211. S2CID 120390522.
  12. ↑ Roman, Nancy G. (1953). "The Spectrum of BD+67°922". The Astrophysical Journal. 117: 467. Bibcode:1953ApJ...117..467R. doi:10.1086/145717.
  13. ↑ Robinson, L. J. (1964). "AG Draconis". Information Bulletin on Variable Stars. 73: 1. Bibcode:1964IBVS...73....1R.
  14. ↑ Sion, Edward M.; et al. (2012). "On the Nature of the Hot Component in the Symbiotic, Supersoft X-Ray Binary AG Draconis". The Astronomical Journal. 144 (6): 5. arXiv:1210.1111. Bibcode:2012AJ....144..171S. doi:10.1088/0004-6256/144/6/171. S2CID 118737620. 171.
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