U Pegasi is a binary star system in the constellation of Pegasus, abbreviated U Peg. The pair form an eclipsing binary with a combined peak apparent visual magnitude of 9.23,[4] which is far too faint to be visible to the naked eye. During the primary eclipse the magnitude decreases to 10.07, while the secondary eclipse only drops to magnitude 9.73.[4] This system is located at a distance of approximately 596 light years from the Sun based on parallax measurements, but is drifting closer with a radial velocity of around −28.5 km/s.[4]
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pegasus[2] |
| Right ascension | 23h 57m 58.477s[3] |
| Declination | +15° 57′ 10.09″[3] |
| Apparent magnitude (V) | 9.23 Min I: 10.07 Min II: 9.73[4] |
| Characteristics | |
| Evolutionary stage | main sequence[5] |
| Spectral type | G2 V + G2: V:[5] |
| B−V color index | 0.648±0.033[2] |
| Variable type | W UMa[6] |
| Astrometry | |
| Radial velocity (Rv) | −28.5±4.7[4] km/s |
| Proper motion (μ) | RA: 34.598 mas/yr[3] Dec.: 17.389 mas/yr[3] |
| Parallax (π) | 5.4708 ± 0.0193 mas[3] |
| Distance | 596 ± 2 ly (182.8 ± 0.6 pc) |
| Absolute magnitude (MV) | 3.88[2] |
| Orbit[5] | |
| Period (P) | 8.995 h |
| Eccentricity (e) | 0 (assumed) |
| Inclination (i) | 76.1[7]° |
| Semi-amplitude (K1) (primary) | 77.6±1.1 km/s |
| Semi-amplitude (K2) (secondary) | 246.5±1.4 km/s |
| Details | |
| Primary | |
| Mass | 1.224±0.003[8] M☉ |
| Radius | 1.149±0.009[8] R☉ |
| Luminosity | 1.29[7] L☉ |
| Surface gravity (log g) | 4.32[8] cgs |
| Temperature | 5,860[8] (polar) K |
| Secondary | |
| Mass | 0.379±0.002[8] M☉ |
| Radius | 0.744±0.002[8] R☉ |
| Luminosity | 0.55[7] L☉ |
| Surface gravity (log g) | 4.27[8] cgs |
| Temperature | 5,785±7[8] (polar) K |
| Other designations | |
| Database references | |
| SIMBAD | data |
The variable luminosity of this system was discovered by S. C. Chandler in 1895. He found it to have a continuously varying light curve with a period of 5.192 h.[10] Observing the star photometrically, in 1898 E. C. Pickering and O. Wendell determined a longer period of 8.995 h.[11] H. Shapley published orbital measures for this eclipsing binary in 1913, estimating their relative luminosities and radii.[12] It was determined to be a variable of the W Ursae Majoris type,[13] and in 1945 the orbital period was shown to vary over time.[14]
Properties
editThis is a double-lined spectroscopic binary star system with an orbital period of 8.995 hours.[5] Their orbital separation is just 2.533 R☉.[7] The inclination of the orbital plane is at an angle of 76.1°[7] to the plane of the sky from the Earth, so the components are seen to eclipse each other during an orbit. The deeper eclipse occurs when the cooler secondary overlaps the primary star. They belong to the W sub-class of W UMa eclipsing variables.[15]
The larger member of this system is a G-type main-sequence star with a stellar classification of G2 V.[5] The primary has a larger mass and radius than the Sun, while the secondary component is significantly smaller and less massive.[8] The pair are in over-contact by about 14.9%, which allows a considerable amount of energy transfer between the two stars.[15] As a consequence, the two components show similar effective temperatures and spectral classes. The cooler component displays a significant level of star spot activity that causes the light curve to vary anomalously over time.[15] The system has an X-ray luminosity of 1.449×1030 erg·s−1.[16]
The long term change in the orbital period may be explained by mass transfer between the components,[17] with the matter streaming from the more massive to the less massive star.[8] The overall period change indicates this mass transfer is occurring at an average rate of (3.7±0.3)×10−8 M☉·yr−1. Periodicity in the change rate suggests there may be a third orbiting component in the system with a period of 62 ± 3 years. If so, it would need to have a mass of at least 0.32±0.13 M☉, which is high enough to be a star.[18]
References
edit- ^ Zhai, D. S.; Leung, K. C.; Zhang, R. X. (September 1984). "A new photoelectric investigation of the W UMa system U Pegasi". Astronomy and Astrophysics, Supplement Series. 57: 487–494. Bibcode:1984A&AS...57..487Z. Retrieved 6 October 2024.
- ^ a b c 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 c d Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
- ^ a b c d e Gontcharov, G. A. (2006), "Pulkovo compilation of radial velocities for 35495 stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
- ^ a b c d e Lu, W. (November 1985), "A new spectroscopic orbit of the W Ursae Majoris system U Pegasi", Publications of the Astronomical Society of the Pacific, 97: 1086–1091, Bibcode:1985PASP...97.1086L, doi:10.1086/131667, S2CID 122867676.
- ^ Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID 255195566.
- ^ a b c d e Latković, Olivera; et al. (May 2021), "Statistics of 700 Individually Studied W UMa Stars", The Astrophysical Journal Supplement Series, 254 (1), id. 10, arXiv:2103.06693, Bibcode:2021ApJS..254...10L, doi:10.3847/1538-4365/abeb23.
- ^ a b c d e f g h i j Pribulla, T.; Vanko, M. (April 2002), "Photoelectric photometry of eclipsing contact binaries: U Peg, YY CrB, OU Ser and EQ Tau", Contributions of the Astronomical Observatory Skalnate Pleso, 32 (1): 79–98, Bibcode:2002CoSka..32...79P.
- ^ "U Peg", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2024-01-28.
- ^ Chandler, S. C. (November 1895), "On a new variable of peculiar character, 8598 U Pegasi", Astronomical Journal, 15 (358): 181, Bibcode:1895AJ.....15..181C, doi:10.1086/102319.
- ^ Pickering, E. C.; Wendell, O. C. (February 1898), "The variable star U Pegasi", Astrophysical Journal, 7: 141–145, Bibcode:1898ApJ.....7..141P, doi:10.1086/140447.
- ^ Shapley, H. (September 1913), "The orbits of eighty-seven eclipsing binaries---a summary", Astrophysical Journal, 38: 158–174, Bibcode:1913ApJ....38..158S, doi:10.1086/142018.
- ^ Schilt, J. (June 1927), "On the Width of Spectral Lines as a Consequence of Rapid Rotation, in Stars of the W Ursae Majoris Type", Publications of the Astronomical Society of the Pacific, 39 (229): 160, Bibcode:1927PASP...39..160S, doi:10.1086/123698.
- ^ Recillas, Felix; Jones Woodward, Edith (March 1945), "A study of the eclipsing binary U Pegasi, BD +15°4915", Astronomical Journal, 51: 101, Bibcode:1945AJ.....51..101R, doi:10.1086/105834.
- ^ a b c Djurašević, G.; et al. (March 2001), "A photometric study of the W UMa-type system U Pegasi", Astronomy and Astrophysics, 367 (3): 840–847, Bibcode:2001A&A...367..840D, doi:10.1051/0004-6361:20000493.
- ^ Liu, Junhui; et al. (July 2022), "X-ray emission of contact binary variables within 1 kpc", Astronomy & Astrophysics, 663, id. A115, arXiv:2205.13210, Bibcode:2022A&A...663A.115L, doi:10.1051/0004-6361/202142963.
- ^ Zhai, Di-sheng; et al. (June 1985), "A new photometric study of the binary U Pegasi", Acta Astronomica Sinica, 25 (2): 336–347, Bibcode:1985ChA&A...9...98Z, doi:10.1016/0275-1062(85)90002-5.
- ^ Tvardovskyi, D. E.; et al. (2017), "Effects of the Mass Transfer and Presence of the Third Components in Close Binary Stellar Systems", Odessa Astronomical Publications, 30: 135–139, arXiv:1711.04831, Bibcode:2017OAP....30..135T, doi:10.18524/1810-4215.2017.30.115463.
Further reading
edit- Vaccaro, T. R.; et al. (December 2010), Prša, Andrej; Zejda, Miloslav (eds.), "Distance to U Pegasi by the DDE Algorithm", Binaries - Key to Comprehension of the Universe. Proceedings of a conference held June 8–12, 2009 in Brno, Czech Republic, vol. 435, San Francisco: Astronomical Society of the Pacific, p. 89, arXiv:0908.2137, Bibcode:2010ASPC..435...89V.
{{citation}}: CS1 maint: date and year (link) - Edalat, M. T.; Taheri, M. (December 2001), "The Photometric Observations and the Light Curve Analysis of U Pegasi", Astrophysics and Space Science, 278 (4): 375–384, doi:10.1023/A:1013195114799, S2CID 118363795.
- Maupome, L.; et al. (October 1991), "Photoelectric observations of W UMa stars: U Pegasi and AB Andromedae.", Revista Mexicana de Astronomía y Astrofísica, 22: 235, Bibcode:1991RMxAA..22..235M.
- Zhai, Di-Sheng; Zhang, Xiao-Yu (March 1989), "Analysis of the variations in the light curve of U Pegasi and starspot activity", Chinese Astronomy and Astrophysics, 13 (1): 97–104, Bibcode:1989ChA&A..13...97Z, doi:10.1016/0275-1062(89)90064-7.
- Zhai, Di-sheng; Lu, Wen-xian (September 1988), "A combined solution of the light curve and velocity curve of U pegasi", Acta Astronomica Sinica, 29 (3): 9–15, Bibcode:1988ChA&A..12..223Z, doi:10.1016/0275-1062(88)90051-3.
- Zhai, Disheng; et al. (1988), "Simultaneous light and velocity curve solution and probable starspot activities for the W Uma system U Pegasi", Vistas in Astronomy, 31 (1): 349, Bibcode:1988VA.....31..349Z, doi:10.1016/0083-6656(88)90225-5, S2CID 122565520.
- Lafta, S. J.; Grainger, J. F. (April 1986), "A Photoelectric Study of the W-Ursae System U-Pegasi", Astrophysics and Space Science, 121 (1): 61–81, Bibcode:1986Ap&SS.121...61L, doi:10.1007/BF00648263, S2CID 120267326.
- Rovithis, P.; Rovithis-Livaniou, H. (October 1982), "Photoelectric observations of the eclipsing binary U Pegasi", Astrophysics and Space Science, 87 (1–2): 287–295, Bibcode:1982Ap&SS..87..287R, doi:10.1007/BF00648924, S2CID 122296476.
- Russo, G.; et al. (February 1982), "Determination of parameters of W UMa system. II : TW Cet, S Ant, U Peg, ER Ori.", Astronomy and Astrophysics, Supplement Series, 47: 211–216, Bibcode:1982A&AS...47..211R.
- Rigterink, P. V. (May 1972), "A new analysis of the eclipsing binary, U Pegasi", Astronomical Journal, 77: 319–329, Bibcode:1972AJ.....77..319R, doi:10.1086/111286.
- Binnendijk, L. (March 1960), "The light variation and orbital elements of U Pegasi", Astronomical Journal, 65: 88–96, Bibcode:1960AJ.....65...88B, doi:10.1086/108194.
- Huruhata, Masaaki (August 1952), "Flaring Phenomena in U Pegasi", Publications of the Astronomical Society of the Pacific, 64 (379): 200, Bibcode:1952PASP...64..200H, doi:10.1086/126463, S2CID 122860173.
- Lafara, Robert (January 1952), "A Photoelectric Study of U Pegasi in Two Colors", Astrophysical Journal, 115: 14, Bibcode:1952ApJ...115...14L, doi:10.1086/145504.