Z Andromedae is a binary star system consisting of a red giant and a white dwarf. It is the prototype of a type of cataclysmic variable star known as symbiotic variable stars or simply Z Andromedae variables. The brightness of those stars vary over time, showing a quiescent, more stable phase and than an active one with a more pronounced variability and stronger brightening and/or dimming.[11]
Binary system
Z Andromedae is a binary star system. The two components have a circular orbit that takes 759 days to complete.[6] The red giant is around twice the mass of the sun and 880 times its luminosity, but its effective temperature is only 2,800 K. The white dwarf is around a thousand times the luminosity of the sun during the quiescent phase, but up to 10 times more luminous during the active phases. Its temperature is as high as 150,000 K when quiescent, but drops below 100,000 K when active.[9] It also spins around its rotation axis every 1682 seconds and displays a strong magnetic field.[10]
The evolved red giant star is losing mass, since radiation pressure overcomes the low gravity on the surface. The outflow of matter is captured by the gravitational field of the white dwarf and falls on its surface in the end. At least during the active phase an accretion disk forms around the white dwarf.[12]
Variability
Light curve of Z Andromedae, showing a typical outburst in 1986 and the abnormally long active period from 2000 onwards
During the quiescent phase, most of the white dwarf luminosity comes from stable hydrogen burning on its surface, and photons emitted this way ionize the wind of the red giant which causes nebular emission. The giant star, however, follows a quasi-periodic activity cycle (similar to the solar cycle) roughly every 7,550 days; when the activity of the star is enhanced, the stellar wind becomes stronger, and in response the white dwarf increases in size and cools, triggering the active phase.[7]
In the quiescent phase, the brightness of Z Andromedae is modulated by the orbital period of the system, and can reach a magnitude of mv = 11.3 at minimum. During the active phase Z Andromedae makes luminosity outbursts and can increase its brightness up to a magnitude of mv = 7.7. Eclipses from the red giant are still visible in this phase. During this phase, a shorter periodicity of 685 days is observed; this could be a beat period between the unknown rotation period of the giant star and the orbital period, which arise from the non-spherical outflow of matter from the atmosphere of the giant star.[8][2][7]
Z Andromedae started an unusually long active phase in September 2000, brightening by several magnitudes multiple times over at least a decade. During the outbursts, irregular brightness variations (up to 0.065 magnitudes) were observed at timescales shorter than a day, interpreted as warping in the accretion disk. If models for this source are correct, it should enter a quiescent phase again in 2020.[12]
Spectrum
Optical
The spectrum of Z Andromedae has been recognised as extremely peculiar since the early 20th century. Early spectra during a bright period, showing only emission lines against a red continuum, were interpreted as a star embedded in dense nebulosity.[13] As the star's brightness faded, the spectrum lost the high excitation "nebular" lines and developed absorption lines with P Cygni profiles. These spectra were readily identified as being due to a hot nova-like star with a cool companion.[14] Emission lines identified included low ionization states of hydrogen and helium with high ionization states of oxygen and iron.[9]
The MK spectral classification is typical of a cool giant, for example M4.5.[3] The exact spectral type has been shown to vary, for example between M5 in 1987 and M3.5 in 1989.[15] Infrared observations gave a combination spectral type of M2III + B1eq. Here the luminosity class of III is for a normal giant star, and the peculiarity codes eq indicate emission lines with P Cygni profiles.[3]
Ultraviolet
Z Andromedae shows also a strong ultraviolet emission, which follows the optical behaviour; absorption lines identified during the quiescent phase becomes emission lines during outbursts. Elements identified in this region of the spectrum are carbon, nitrogen, phosphorus and silicon in their ionized states.[9]
Radio
The radio flux from Z Andromedae at the beginning of outbursts is lower than the usual quiescent level, and has a maximum after the optical one. After the outbursts, radio jets can be seen flowing out of this system, in a direction perpendicular to the orbital plane.[9]
X-ray
Z Andromedae is much fainter in X-ray, and has not been detected when in the quiescent phase. During outbursts, X-ray emission comes from shock-heated plasma, where the kinetic energy of the outflowing material is converted in X-ray radiation. This emission "mimics" a blackbody radiation with a temperature different from the one of the white dwarf, but its real nature can be identified because it shows absorption edges (which shows also the presence of neon) and an excess at high frequencies.[9]
Bipolar jets
Following the 2006 outburst, the hydrogen Balmer emission lines included faint wings at a velocity of ±1,150 km/s. Since extended radio outflows had previously been seen during the long 2000-2002 outbursts, collimated jets along the axis of the system were the most likely explanation for this phenomenon. It is thought that the jets are only present during bright outbursts.[16] The jets were observed again during subsequent outbursts; their velocity is highly variable at the beginning but settles on a constant velocity after roughly 1 month. A single jet can also occur. The jets could be formed by material that cannot accrete on the white dwarf that reaches the Eddington limit.[12]
References
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.
Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
Shenavrin, V. I.; Taranova, O. G.; Nadzhip, A. E. (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.
Martel, M. T.; Gravina, R (1985). "UBV Observations of Symbiotic Stars in July and October 1982". Information Bulletin on Variable Stars. 2750: 1. Bibcode:1985IBVS.2750....1M.
Pourbaix, D; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H; Morrell, N. I.; Torres, G; Udry, S (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
Fekel, Francis C; Hinkle, Kenneth H; Joyce, Richard R; Skrutskie, Michael F (2000). "Infrared Spectroscopy of Symbiotic Stars. II. Orbits for Five S-Type Systems with Two-Year Periods". The Astronomical Journal. 120 (6): 3255. Bibcode:2000AJ....120.3255F. doi:10.1086/316872.
Leibowitz, Elia M; Formiggini, Liliana (2008). "Activity cycle of the giant star of Z Andromedae and its spin period". Mon. Not. R. Astron. Soc. 385 (1): 445–452. arXiv:0712.2120. Bibcode:2008MNRAS.385..445L. doi:10.1111/j.1365-2966.2008.12847.x. S2CID 88510675.
Skopal, A (2003). "Discovery of the eclipse in the symbiotic binary Z Andromedae". Astronomy & Astrophysics. 401 (3): L17–L20. arXiv:astro-ph/0304046. Bibcode:2003A&A...401L..17S. doi:10.1051/0004-6361:20030332. S2CID 13413270.
Sokoloski, J. L.; Kenyon, S. J.; Espey, B. R.; Keyes, Charles D; McCandliss, S. R.; Kong, A. K. H; Aufdenberg, J. P.; Filippenko, A. V.; Li, W; Brocksopp, C; Kaiser, Christian R; Charles, P. A.; Rupen, M. P.; Stone, R. P. S (2006). "A Combination Nova Outburst in Z Andromedae: Nuclear Shell Burning Triggered by a Disk Instability". The Astrophysical Journal. 636 (2): 1002–1019. arXiv:astro-ph/0509638. Bibcode:2006ApJ...636.1002S. doi:10.1086/498206. S2CID 8941207.
Sokoloski, J. L.; Bildsten, Lars (1999). "Discovery of a Magnetic White Dwarf in the Symbiotic Binary Z Andromedae". The Astrophysical Journal. 517 (2): 919–924. arXiv:astro-ph/9812294. Bibcode:1999ApJ...517..919S. doi:10.1086/307234. S2CID 18394589.
"Z Andromedae star". Retrieved 2018-01-16.
Skopal, A.; Tarasova, T. N.; Wolf, M.; Dubovský, P. A.; Kudzej, I. (2018). "Repeated Transient Jets from a Warped Disk in the Symbiotic Prototype Z And: A Link to the Long-lasting Active Phase". The Astrophysical Journal. 858 (2): 120. arXiv:1805.10908. Bibcode:2018ApJ...858..120S. doi:10.3847/1538-4357/aabc11. S2CID 73652665.
Plaskett, J. S. (1928). "The composite stellar and nebular spectrum of Z Andromedae". Publications of the Dominion Astrophysical Observatory Victoria. 4: 119. Bibcode:1928PDAO....4..119P.
Swings, P; Struve, O (1941). "The Evolution of a Peculiar Stellar Spectrum: Z Andromedae". Astrophysical Journal. 93: 356. Bibcode:1941ApJ....93..356S. doi:10.1086/144272.
Mürset, U; Schmid, H. M. (1999). "Spectral classification of the cool giants in symbiotic systems". Astronomy and Astrophysics Supplement. 137 (3): 473. Bibcode:1999A&AS..137..473M. doi:10.1051/aas:1999105.
Burmeister, M; Leedjärv, L (2006). "Evidence for bipolar jets from the optical spectra of the prototypical symbiotic star Z Andromedae". Astronomy & Astrophysics. 461: L5–L8. arXiv:astro-ph/0611475. Bibcode:2007A&A...461L...5B. doi:10.1051/0004-6361:20066630. S2CID 16474465.
Further reading
Tomov, N. A.; Tomova, M. T.; Taranova, O. G. (2004). "Broad-band multicolour observations of the symbiotic binary Z And during quiescence and its activity at the end of 2002". Astronomy & Astrophysics. 428 (3): 985–992. Bibcode:2004A&A...428..985T. doi:10.1051/0004-6361:20041065.
Taranova, O. G.; Tomov, N. A.; Tomova, M. T.; Shenavrin, V. I. (2004). "The symbiotic system Z Andromedae during the flare of 2000–2002". Astronomy Reports. 48 (9): 742. Bibcode:2004ARep...48..742T. doi:10.1134/1.1800174. S2CID 123346371.
Tomov, N. A.; Taranova, O. G.; Tomova, M. T. (2003). "Mass ejection by the symbiotic binary Z And during its 2000–2002 outburst". Astronomy and Astrophysics. 401 (2): 669. Bibcode:2003A&A...401..669T. doi:10.1051/0004-6361:20030140.
Sokoloski, J. L.; Brocksopp, C; Kaiser, C; Seymour, N (2002). "A Radio "Jet" in the Prototypical Symbiotic Star Z Andromedae?". American Astron. Soc. Meeting. 201: 17.12. Bibcode:2002AAS...201.1712S.
Bisikalo, D. V.; Boyarchuk, A. A.; Kilpio, E. Yu; Kuznetsov, O. A. (2002). "Structure of gas flows in Z and in quiescence and during outbursts". Astronomy Reports. 46 (12): 1022. Bibcode:2002ARep...46.1022B. doi:10.1134/1.1529260. S2CID 121279397.
Birriel, Jennifer J; Espey, Brian R; Schulte-Ladbeck, Regina E (1998). "Near-simultaneous Observations of Direct and Raman-scattered Linesin the Symbiotic Star Z Andromedae". The Astrophysical Journal. 507 (1): L75–L78. Bibcode:1998ApJ...507L..75B. doi:10.1086/311673.
Schmid, H. M.; Schild, H (1997). "The polarimetric orbit of Z Andromedae". Astronomy & Astrophysics. 327: 219. Bibcode:1997A&A...327..219S.
Skopal, A; Vittone, A. A.; Errico, L; Otsuka, M; Tamura, S; Wolf, M; Elkin, V. G. (2006). "Structure of the hot object in the symbiotic prototype Z Andromedae during its 2000–03 active phase". Astronomy and Astrophysics. 453 (1): 279. arXiv:astro-ph/0603718. Bibcode:2006A&A...453..279S. doi:10.1051/0004-6361:20052917. S2CID 17416276.
Skopal, A; Pribulla, T (2006). "The first detection of the bipolar jets from the symbiotic prototype Z and". The Astronomer's Telegram. 882: 1. Bibcode:2006ATel..882....1S.
Tomov, N. A.; Tomova, M. T.; Bisikalo, D. V. (2007). "Bipolar ejection by the symbiotic binary system Z and during its 2006 outburst". Mon. Not. R. Astron. Soc. 376 (1): L16–L19. arXiv:astro-ph/0612502. Bibcode:2007MNRAS.376L..16T. doi:10.1111/j.1745-3933.2007.00277.x. S2CID 16193674.
External links
Image Z Andromedae
AAVSO chart for Z Andromedae
AAVSO long-term light curve of Z And
Z Andromedae: The Prototype of the Symbiotic Class AAVSO
vte
Constellation of Andromeda
Adhil Andromeda in Chinese astronomy List of Andromeda's satellite galaxies List of stars in Andromeda
Stars
Bayer
α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ σ τ υ φ χ ψ ω
Flamsteed
2 3 4 5 6 7 8 9 10 11 12 13 14 15 18 22 23 26 28 32 36 39 41 44 45 47 49 51 55 56 58 59 60 62 63 64 65 66
Variable
R T U W Z RT RU RV RX SU SW TU TW WZ XZ AB AC AD AE AR BM BX CC CN DS DX EG ET EU FF GP GR GY HN KK KX KZ LL LP LQ OP OS OU PX QR QV QX V385 V455 V529 V807
HD
3 166 895 1185 1606 2421 2767 2942 3322 3346 4778 5608 5789/5788 6114 7853 8673 10307 13931 14622 16004 16028 16175 217811 220105 221246 221776 222109 222155 222399 223229 224365 224801 225218
Other
3XMM J004232.1+411314 6 Persei ADS 48 Groombridge 34 HAT-P-6 HAT-P-16 HAT-P-19 HAT-P-28 HR 178 HR 8768 M31-RV KELT-1 NGC 44 NGC 82 NGC 84 NGC 91 NGC 162 NGC 464 PA-99-N2 Ross 248 WASP-1 WISE 0146+4234 WISE J0005+3737 WISE J004945.61+215120.0
Exoplanets
14 Andromedae b Upsilon Andromedae b c d e Gliese 15 Ab HD 13931 b HD 16175 b HAT-P-6b HAT-P-32b WASP-1b WASP-33b
Star clusters
Mayall II NGC 206 NGC 272 NGC 752 NGC 956 NGC 7686
Nebulae
NGC 7662
Galaxies
NGC
5 13 19 21 27 39 43 48 49 51 67 68 69 70 71 72 74 76 79 80 81 83 85 86 90 93 94 96 97 108 109 112 140 149 160 169 181 183 184 214 218 226 228 229 233 243 252 258 260 262 280 304 317 389 393 404 425 431 477 512 513 523 528 531 536 668 679 687 700 703 704 705 708 709 710 712 714 717 732 753 759 891 1000 7640 7836
Numbered
I II III IV V VIII IX X XI XVIII XIX XXI
Other
3C 66A 3C 66B Andromeda Galaxy Donatiello I Messier 32 Messier 110
Galaxy clusters
Abell 262 NGC 68 group
Astronomical events
GRB 101225A SN 1885A
Category Category
Hellenica World - Scientific Library
Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License
