AR Lacertae is a frequently-studied[7] triple star system in the northern constellation of Lacerta, abbreviated AR Lac. This variable star system is the prototype for "detached systems of the AR Lacertae type".[2] It is dimly visible to the naked eye with a combined peak apparent visual magnitude of 6.08.[2] Based on parallax measurements, AR Lac is located at a distance of 138.6 light years from the Sun. It is drifting closer with a heliocentric radial velocity of −34 km/s.[6]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Lacerta |
| Right ascension | 22h 08m 40.818s[1] |
| Declination | +45° 44′ 32.11″[1] |
| Apparent magnitude (V) | 6.080 Min1 6.770 Min2 6.430[2] |
| Characteristics | |
| Evolutionary stage | Subgiants[3] |
| Spectral type | K0IVe + G2IV[3] + DA(?)[4] |
| B−V color index | 0.567±0.008[5] |
| Variable type | Algol/RS CVn[2] |
| Astrometry | |
| Radial velocity (Rv) | −33.84±0.26[6] km/s |
| Proper motion (μ) | RA: −52.310 mas/yr[1] Dec.: +46.931 mas/yr[1] |
| Parallax (π) | 23.5246 ± 0.0228 mas[1] |
| Distance | 138.6 ± 0.1 ly (42.51 ± 0.04 pc) |
| Absolute bolometric magnitude (Mbol) | 2.75±0.066 |
| Orbit[7] | |
| Period (P) | 1.98395±0.00002 d |
| Semi-major axis (a) | 8.869±0.015 R☉ |
| Eccentricity (e) | 0.00 (adopted) |
| Inclination (i) | 90° (adopted)° |
| Longitude of the node (Ω) | 6.9207±0.0128° |
| Periastron epoch (T) | 2451745.5794 ± 0.0002 HJD |
| Details | |
| Cooler (K0) component | |
| Mass | 1.21±0.077[7] M☉ |
| Radius | 2.61±0.009[7] R☉ |
| Luminosity (bolometric) | 3.55[8] L☉ |
| Surface gravity (log g) | 3.69±0.035[7] cgs |
| Temperature | 5,826±5[7] K |
| Rotational velocity (v sin i) | 73[3] km/s |
| Hotter (G5) component | |
| Mass | 1.17±0.035[7] M☉ |
| Radius | 1.51±0.005[7] R☉ |
| Luminosity (bolometric) | 2.09[8] L☉ |
| Temperature | 5,100±100[7] K |
| Rotational velocity (v sin i) | 46[3] km/s |
| Other designations | |
Observation history
editThe variability of this binary system was discovered by H. R. Leavitt at Harvard College Observatory,[10] and announced in August 1907 by E. C. Pickering.[11][12] Due to an orbital period of nearly two days, the eclipsing binary nature of this system was not recognized until 1929 by L. G. Jacchia.[10] W. E. Harper derived orbital elements in 1933.[12] It has an orbital period of 1.98 days and a brightness variation of 0.06 in visual magnitude.[13]
In 1934, A. B. Wyse published spectral classes of K0 and G5 for the components. The K0 star displayed sharp emission lines of singly ionized calcium.[14] The primary minimum is caused by the larger K0 component eclipsing the hotter G5 star, while the secondary eclipse is an annular eclipse of the K0 component by the smaller companion. The stars displayed periodic light variations indicating ellipticity and reflection. The K0 star also showed evidence of significant limb darkening.[13]
In 1946, F. B. Wood reported the intrinsic variability of the hotter component. This variation only disappeared when the smaller star was being eclipsed. The following year, G. E. Kron hypothesized that this variation was due to the presence of huge light and dark patches on the star. To explain the light variations, these had to cover about 20% of the total visible surface, and they must form, move, and later dissolve. The variation was modulated by the rotation period of the star.[13]
By 1972, AR Lac had been identified as an RS Canum Venaticorum variable (RS CVn), consisting of two subgiant stars in a detached binary system.[15] It was found to be a source for radio emission in 1973.[16] This emission varied over time and the system displayed flare activity.[17] The system was detected as an X-ray source by EXOSAT in 1987. The X-ray source with a temperature of 5–7 million K dropped to a minimum during the primary eclipse, indicating it originated on the hotter star. In contrast, X-ray emission from 15–30 million K plasma was not eclipsed, indicating a source larger than the two stars.[18]
Properties
editThis is a close, double-lined spectroscopic binary star system, which means the spectra of both components are visible and overlap. They have an essentially circular orbit with a period of 1.98395 days and a separation of 8.9 times the radius of the Sun.[7] The orbital plane is inclined at an angle of 90° to the plane of the sky, which is why two eclipses are visible every orbit.[3] As with other RS CVn systems, their rotation periods are tidally locked to their orbital period.[19] The cooler component is the larger and more massive star, which is consistent with its evolutionary state.[7] There is some evidence of extended matter around this star.[3]
Both components display star spots with an activity cycle of about 17 years. Variation in the orbital period of this system has been reported since 1998, which shows a cyclical oscillation over a period of 50.93 years, and a long-term decrease of a day every 470 million years. This orbital variation may be the result of magnetic activity of the two stars.[20][21] Stellar flares radiate at a temperature of 12,000±300 K and expand to 2% of the stellar surface.[19]
In 2022, a co-moving companion to this system was announced, making this a triple star system. It was discovered by the Backyard Worlds: Planet 9 citizen science project. Designated WDJ220838.73+454434.04, this companion is a compact white dwarf star at an angular separation of 21.9″ from the binary pair. At the distance of AR Lac, this is equivalent to a projected separation of about 930 AU. It has a mass of 0.6+0.04
−0.09 M☉ and a radius of 0.0125+0.0014
−0.0012 R☉. The companion has an estimated age of 5.75 Gyr and has been steadily cooling for about the last 1.62 Gyr. As a main sequence star, it had a mass of 1.34+0.46
−0.27 M☉. At the estimated separation, a circular orbit of this companion around the inner binary would have an orbital period of approximately 16,000 years.[4]
References
edit- ^ a b c d Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
- ^ a b c d Samus’, N. N.; et al. (2017), "General catalogue of variable stars", Astronomy Reports, GCVS 5.1, 61: 80–88, doi:10.1134/S1063772917010085. For the data query, see Vizier B/gcvs/gcvs_cat.
- ^ a b c d e f Karakuş, O.; Ekmekçi, F. (April 2021), "New Spectral Analysis Results Within the Scope of Extended Matter Research in the AR Lacertae Active Binary System", Revista Mexicana de Astronomía y Astrofísica, 57: 167–179, arXiv:2011.10555, Bibcode:2021RMxAA..57..167K, doi:10.22201/ia.01851101p.2021.57.01.12.
- ^ a b Bickle, Thomas P.; et al. (June 2022), "WDJ220838.73+454434.04: a White Dwarf Companion in the AR Lacertae System", Research Notes of the AAS, 6 (6), id. 127, Bibcode:2022RNAAS...6..127B, doi:10.3847/2515-5172/ac780a.
{{citation}}: CS1 maint: numeric names: authors list (link) - ^ 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.
- ^ a b Karataș, Yüksel; et al. (2004), "Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution", Monthly Notices of the Royal Astronomical Society, 349 (3): 1069–1092, arXiv:astro-ph/0404219, Bibcode:2004MNRAS.349.1069K, doi:10.1111/j.1365-2966.2004.07588.x, S2CID 15290475.
- ^ a b c d e f g h i j k Siviero, A.; et al. (2006), "Period Change, Spot Migration and Orbital Solution for the Eclipsing Binary AR Lac", Baltic Astronomy, 15: 387–394, Bibcode:2006BaltA..15..387S.
- ^ a b Popper, Daniel M. (July 1990), "Orbits of Close Binaries with CA II H and K in Emission. III. Eleven More Systems", Astronomical Journal, 100: 247, Bibcode:1990AJ....100..247P, doi:10.1086/115511.
- ^ "AR Lac". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2024-08-06.
- ^ a b Plavec, M.; et al. (1961), "Period variability in detached systems with undersized subgiants", Bulletin of the Astronomical Institute of Czechoslovakia, 12: 117, Bibcode:1961BAICz..12..117P.
- ^ Pickering, Edward C. (August 1907), "71 new variable stars in Harvard Maps Nos. 9, 12, 21, 48 and 51", Astronomische Nachrichten, 175 (20): 333, Bibcode:1907AN....175..333P, doi:10.1002/asna.19071752006.
- ^ a b Sanford, Roscoe F. (March 1951), "The Spectra and Orbits of AR Lacertae", Astrophysical Journal, 113: 299, Bibcode:1951ApJ...113..299S, doi:10.1086/145398.
- ^ a b c Kron, Gerald E. (October 1947), "The Probable Detecting of Surface Spots on AR Lacertae B", Publications of the Astronomical Society of the Pacific, 59 (350): 261, Bibcode:1947PASP...59..261K, doi:10.1086/125964.
- ^ Wyse, Arthur Bambridge (1934), "A study of the spectra of eclipsing binaries", Lick Observatory Bulletin, 464, Berkeley: University of California Press: 37–52, Bibcode:1934LicOB..17...37W, doi:10.5479/ADS/bib/1934LicOB.17.37W.
- ^ Atkins, H. L.; Hall, D. S. (October 1972), "Infrared excesses in eclipsing binaries of the RS Canum Venaticorum type.", Publications of the Astronomical Society of the Pacific, 84: 638, Bibcode:1972PASP...84..638A, doi:10.1086/129349.
- ^ Hjellming, R. M.; Blankenship, L. C. (June 1973), "Radio Stars AR Lacertae and Cygnus X-2", Nature Physical Science, 243 (127): 81–82, Bibcode:1973NPhS..243...81H, doi:10.1038/physci243081a0.
- ^ Srivastava, R. K. (December 1983), "Flare like Activity in AR Lacertae", Information Bulletin on Variable Stars, 2450 (1), Bibcode:1983IBVS.2450....1S.
- ^ White, N. E.; et al. (1987), Linsky, Jeffrey L.; Stencel, Robert E. (eds.), "The X-ray orbital lightcurve of AR Lac", Cool Stars, Stellar Systems, and the Sun: Proceedings of the Fifth Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun Held in Boulder, Colorado, July 7-11, 1987, Lecture Notes in Physics, vol. 291, pp. 521–524, Bibcode:1987LNP...291..521W, doi:10.1007/3-540-18653-0_191, ISBN 978-3-540-18653-3.
- ^ a b Markus, Ya. S.; Zhilyaev, B. E. (April 2022), Optical Flare Search on the RS CVn-type flare stars AR Lacertae, arXiv:2204.11059, Bibcode:2022arXiv220411059M.
- ^ Lu, Ye; et al. (August 2012), "A Study on the Orbital Period Variation of AR Lacertae", Publications of the Astronomical Society of Japan, 64 (4), id. 84, Bibcode:2012PASJ...64...84L, doi:10.1093/pasj/64.4.84.
- ^ Lanza, A. F.; et al. (April 1998), "Long-term starspot evolution, activity cycle and orbital period variation of AR Lacertae", Astronomy and Astrophysics, 332: 541–560, Bibcode:1998A&A...332..541L.