{{Short description|Variable star in the constellation Andromeda}}{{distinguish|Zeta Andromedae}} {{Starbox begin | name = Z Andromedae }} {{Starbox observe | epoch = J2000 | ra = {{RA|23|33|39.95532}}<ref name=GaiaDR3/> | dec = {{DEC|+48|49|05.9749}}<ref name=GaiaDR3/> | appmag_v = 7.7 - 11.3<ref name=gcvs/> | constell = Andromeda }} {{Starbox character | class = M2III + B1eq<ref name=shenavrin/> | b-v = +1.35<ref name=ibvs/> | u-b = −0.49<ref name=ibvs/> | variable = Z And<ref name=gcvs/> }} {{Starbox astrometry | radial_v = −0.59<ref name=rv/> | prop_mo_ra = {{Val|−1.729|0.018}}<ref name=GaiaDR3/> | prop_mo_dec = {{Val|−3.0410|018}}<ref name=GaiaDR3/> | parallax = 0.4866 | p_error = 0.0220 | parallax_footnote=<ref name=GaiaDR3/> | absmag_v = }} {{Starbox orbit | period_unitless = {{nowrap|{{val|759.0|1.9}}<ref name=fekel/> days}} | eccentricity = 0.0<ref name=fekel/> | inclination = {{val|47|12}}<ref name=leibowitz/> | k1 = {{val|6.73|0.22}}<ref name=fekel/> }} {{Starbox detail | component1 = Red giant | mass = 2<ref name=fekel/> | radius = 85<ref name=shenavrin/> | luminosity = 880<ref name=skopal2003/> | temperature = 3,400<ref name=shenavrin/> | metal = | rotation = | component2 = White dwarf | mass2 = 0.75<ref name=fekel/> | temperature2 = 90,000 - 150,000<ref name=sokoloski2006/> | luminosity2 = 1,500 - 9,800<ref name=sokoloski2006/> | radius2 = 0.17 - 0.36<ref name=sokoloski2006/> | rotation2 = 1682.6 ± 0.6 s<ref name=Sokoloski1999/> | age2 = }} {{Starbox catalog | names = MWC 416, HD 221650, HIP 116287, SAO 53146, PPM 64386, AG+48°2087, GCRV 14773, IRAS 23312+4832, HV 193, AN 41.1901, JP11 3636, TYC 3645-2066-1, BD+48°4093, GSC 03645-02066, 2MASS J23333994+4849059, AAVSO 2328+48, 2E 2331.6+4834, PLX 5697, 2E 4735 }} {{Starbox reference | Simbad = HD+221650 | ARICNS = }} {{starbox sources|HIP|CCDM|HR}} {{Starbox end}}
'''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 then an ''active'' one with a more pronounced variability and stronger brightening and/or dimming.<ref name=daviddarling/>
==Binary system== Z Andromedae is a binary star system. The two components have a circular orbit that takes 759 days to complete.<ref name=fekel/> 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.<ref name=sokoloski2006/> It also spins around its rotation axis every 1,682 seconds and displays a strong magnetic field.<ref name=Sokoloski1999/>
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.<ref name=Skopal2018/>
==Variability== thumb|left|Light curve of Z Andromedae, showing a typical outburst in 1986 and the abnormally long active period from 2000 onwards The variability of Z Andromedae was discovered by Williamina Paton Stevens Fleming, and announced in 1901.<ref name="Pickering"/>
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.<ref name=leibowitz/>
In the quiescent phase, the brightness of Z Andromedae is modulated by the orbital period of the system, and can reach a magnitude of m<sub>v</sub> = 11.3 at minimum. During the active phase Z Andromedae makes luminosity outbursts and can increase its brightness up to a magnitude of m<sub>v</sub> = 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.<ref name=skopal2003/><ref name=gcvs/><ref name=leibowitz/>
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.<ref name=Skopal2018/>
==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.<ref name=plaskett/> 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.<ref name=swings/> Emission lines identified included low ionization states of hydrogen and helium with high ionization states of oxygen and iron.<ref name=sokoloski2006/>
The MK spectral classification is typical of a cool giant, for example M4.5.<ref name=shenavrin/> The exact spectral type has been shown to vary, for example between M5 in 1987 and M3.5 in 1989.<ref name=muerset/> 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.<ref name=shenavrin/>
===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.<ref name=sokoloski2006/>
===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.<ref name=sokoloski2006/>
===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 that 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.<ref name=sokoloski2006/>
==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.<ref name=burmeister/> 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.<ref name=Skopal2018/>
==References== {{Reflist|refs=
<ref name=GaiaDR3>{{cite DR3|1941894322438077312}}</ref>
<ref name=muerset>{{cite journal|bibcode=1999A&AS..137..473M|title=Spectral classification of the cool giants in symbiotic systems|journal=Astronomy and Astrophysics Supplement|volume=137|issue=3|pages=473|last1=Mürset|first1=U|last2=Schmid|first2=H. M.|year=1999|doi=10.1051/aas:1999105|doi-access=free}}</ref>
<ref name=swings>{{cite journal|bibcode=1941ApJ....93..356S|title=The Evolution of a Peculiar Stellar Spectrum: Z Andromedae|journal=Astrophysical Journal|volume=93|pages=356|last1=Swings|first1=P|last2=Struve|first2=O|year=1941|doi=10.1086/144272|hdl=2268/72129|url=http://orbi.ulg.ac.be/jspui/handle/2268/74173|hdl-access=free}}{{Dead link|date=March 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
<ref name=plaskett>{{cite journal|bibcode=1928PDAO....4..119P|title=The composite stellar and nebular spectrum of Z Andromedae|journal=Publications of the Dominion Astrophysical Observatory Victoria|volume=4|pages=119|last1=Plaskett|first1=J. S.|year=1928}}</ref>
<ref name=daviddarling>{{cite web|url=http://www.daviddarling.info/encyclopedia/Z/Z_Andromedae_star.html |title=Z Andromedae star |access-date=2018-01-16}}</ref>
<ref name=shenavrin>{{cite journal|bibcode=2011ARep...55...31S|doi = 10.1134/S1063772911010070 |title = Search for and study of hot circumstellar dust envelopes |journal = Astronomy Reports |volume = 55 |issue = 1 |pages = 31–81 |year = 2011 |last1 = Shenavrin |first1 = V. I. |last2 = Taranova |first2 = O. G. |last3 = Nadzhip |first3 = A. E. |s2cid = 122700080 }}</ref>
<ref name="Pickering">{{cite journal |last1=Pickering |first1=E. C. |last2=Colson |first2=H. R. |last3=Fleming |first3=W. P. |last4=Wells |first4=L. D. |title=Sixty-four new variable stars |journal=Astrophysical Journal |date=April 1901 |volume=13 |pages=226–230 |doi=10.1086/140808 |bibcode=1901ApJ....13..226P |url=https://articles.adsabs.harvard.edu/pdf/1901ApJ....13..226P |access-date=12 November 2024}}</ref>
<ref name=rv>{{cite journal|bibcode=2004A&A...424..727P|title=SB9: The ninth catalogue of spectroscopic binary orbits|journal=Astronomy and Astrophysics|volume=424|issue=2|pages=727–732|last1=Pourbaix|first1=D|last2=Tokovinin|first2=A. A.|last3=Batten|first3=A. H.|last4=Fekel|first4=F. C.|last5=Hartkopf|first5=W. I.|last6=Levato|first6=H|last7=Morrell|first7=N. I.|last8=Torres|first8=G|last9=Udry|first9=S|year=2004|doi=10.1051/0004-6361:20041213|arxiv=astro-ph/0406573|s2cid=119387088}}</ref>
<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref>
<ref name=fekel>{{cite journal|bibcode=2000AJ....120.3255F|title=Infrared Spectroscopy of Symbiotic Stars. II. Orbits for Five S-Type Systems with Two-Year Periods|journal=The Astronomical Journal|volume=120|issue=6|pages=3255|last1=Fekel|first1=Francis C|last2=Hinkle|first2=Kenneth H|last3=Joyce|first3=Richard R|last4=Skrutskie|first4=Michael F|year=2000|doi=10.1086/316872|doi-access=free}}</ref>
<ref name=leibowitz>{{cite journal|journal=Mon. Not. R. Astron. Soc.|volume=385|issue=1|pages=445–452|bibcode=2008MNRAS.385..445L|doi=10.1111/j.1365-2966.2008.12847.x |arxiv = 0712.2120 |title=Activity cycle of the giant star of Z Andromedae and its spin period|year=2008|last1=Leibowitz|first1=Elia M|last2=Formiggini|first2=Liliana|doi-access=free |s2cid=88510675}}</ref>
<ref name=sokoloski2006>{{cite journal|bibcode=2006ApJ...636.1002S|arxiv=astro-ph/0509638|title=A ''Combination Nova'' Outburst in Z Andromedae: Nuclear Shell Burning Triggered by a Disk Instability|journal=The Astrophysical Journal|volume=636|issue=2|pages=1002–1019|last1=Sokoloski|first1=J. L.|last2=Kenyon|first2=S. J.|last3=Espey|first3=B. R.|last4=Keyes|first4=Charles D|last5=McCandliss|first5=S. R.|last6=Kong|first6=A. K. H|last7=Aufdenberg|first7=J. P.|last8=Filippenko|first8=A. V.|last9=Li|first9=W|last10=Brocksopp|first10=C|last11=Kaiser|first11=Christian R|last12=Charles|first12=P. A.|last13=Rupen|first13=M. P.|last14=Stone|first14=R. P. S|year=2006|doi=10.1086/498206|s2cid=8941207}}</ref>
<ref name=skopal2003>{{cite journal|journal=Astronomy & Astrophysics|volume=401 |issue=3 |pages=L17–L20 |bibcode=2003A&A...401L..17S |arxiv = astro-ph/0304046 |doi = 10.1051/0004-6361:20030332 |title=Discovery of the eclipse in the symbiotic binary Z Andromedae |year=2003 |last1=Skopal |first1=A |s2cid=13413270 }}</ref>
<ref name=ibvs>{{cite journal|bibcode=1985IBVS.2750....1M|title=UBV Observations of Symbiotic Stars in July and October 1982|journal=Information Bulletin on Variable Stars|volume=2750|pages=1|last1=Martel|first1=M. T.|last2=Gravina|first2=R|year=1985}}</ref>
<ref name=burmeister>{{cite journal|journal=Astronomy & Astrophysics|volume=461 |pages=L5–L8 |bibcode=2007A&A...461L...5B |arxiv = astro-ph/0611475 |doi = 10.1051/0004-6361:20066630 |title= Evidence for bipolar jets from the optical spectra of the prototypical symbiotic star Z Andromedae|year=2006 |last1=Burmeister |first1=M |last2=Leedjärv |first2=L|issue=1 |s2cid=16474465 }}</ref>
<ref name=Skopal2018>{{cite journal|bibcode=2018ApJ...858..120S | title=Repeated Transient Jets from a Warped Disk in the Symbiotic Prototype Z And: A Link to the Long-lasting Active Phase|journal=The Astrophysical Journal|volume=858| issue=2| pages=120|last1=Skopal|first1=A.|last2=Tarasova|first2=T. N.|last3=Wolf|first3=M.|last4=Dubovský|first4=P. A.|last5=Kudzej|first5=I.|year=2018|doi=10.3847/1538-4357/aabc11|arxiv=1805.10908| s2cid=73652665| doi-access=free}}</ref>
<ref name=Sokoloski1999>{{cite journal|journal=The Astrophysical Journal|volume=517|issue=2|pages=919–924|bibcode=1999ApJ...517..919S|doi=10.1086/307234|arxiv = astro-ph/9812294 |title=Discovery of a Magnetic White Dwarf in the Symbiotic Binary Z Andromedae|year=1999|last1=Sokoloski|first1=J. L.|last2=Bildsten|first2=Lars|s2cid=18394589}}</ref>
}}
==Further reading== * {{cite journal|journal=Astronomy & Astrophysics|volume=428 |issue=3 |pages=985–992 |bibcode=2004A&A...428..985T |doi = 10.1051/0004-6361:20041065 |title=Broad-band multicolour observations of the symbiotic binary Z And during quiescence and its activity at the end of 2002|year=2004|last1=Tomov|first1=N. A.|last2=Tomova |first2=M. T. |last3=Taranova |first3=O. G. |doi-access=free }} * {{cite journal|journal=Astronomy Reports|volume=48|bibcode=2004ARep...48..742T|doi=10.1134/1.1800174|issue=9 |pages=742|title=The symbiotic system Z Andromedae during the flare of 2000–2002|year=2004|last1=Taranova|first1=O. G.|last2=Tomov|first2=N. A.|last3=Tomova|first3=M. T.|last4=Shenavrin|first4=V. I.|s2cid=123346371}} * {{cite journal|journal=Astronomy and Astrophysics|volume=401 |issue=2 |pages=669 |bibcode=2003A&A...401..669T |doi = 10.1051/0004-6361:20030140 |title=Mass ejection by the symbiotic binary Z And during its 2000–2002 outburst |year=2003 |last1=Tomov |first1=N. A. |last2=Taranova |first2=O. G. |last3=Tomova |first3=M. T. |doi-access=free }} * {{cite journal|journal=American Astron. Soc. Meeting|volume=201 |pages=17.12 |bibcode=2002AAS...201.1712S |title=A Radio "Jet" in the Prototypical Symbiotic Star Z Andromedae? |last1=Sokoloski |first1=J. L. |last2=Brocksopp |first2=C |last3=Kaiser |first3=C |last4=Seymour |first4=N |year=2002 }} * {{cite journal|journal=Astronomy Reports|volume=46|issue=12|pages=1022|bibcode=2002ARep...46.1022B|doi=10.1134/1.1529260 |title=Structure of gas flows in Z and in quiescence and during outbursts|year=2002|last1=Bisikalo|first1=D. V.|last2=Boyarchuk|first2=A. A.|last3=Kilpio|first3=E. Yu|last4=Kuznetsov|first4=O. A.|s2cid=121279397}} * {{cite journal|journal=The Astrophysical Journal|volume=507|issue=1|pages=L75–L78|bibcode=1998ApJ...507L..75B|doi=10.1086/311673 |title=Near-simultaneous Observations of Direct and Raman-scattered Linesin the Symbiotic Star Z Andromedae|year=1998|last1=Birriel|first1=Jennifer J|last2=Espey|first2=Brian R|last3=Schulte-Ladbeck|first3=Regina E|doi-access=free}} * {{cite journal|journal=Astronomy & Astrophysics|volume=327 |pages=219 |bibcode=1997A&A...327..219S |title=The polarimetric orbit of Z Andromedae |last1=Schmid |first1=H. M. |last2=Schild |first2=H |year=1997 }} * {{cite journal|journal=Astronomy and Astrophysics|volume=453 |issue=1 |pages=279 |bibcode=2006A&A...453..279S |arxiv = astro-ph/0603718 |doi = 10.1051/0004-6361:20052917 |title=Structure of the hot object in the symbiotic prototype Z Andromedae during its 2000–03 active phase |year=2006 |last1=Skopal |first1=A |last2=Vittone |first2=A. A. |last3=Errico |first3=L |last4=Otsuka |first4=M |last5=Tamura |first5=S |last6=Wolf |first6=M |last7=Elkin |first7=V. G. |s2cid=17416276 }} * {{cite journal|journal= The Astronomer's Telegram|volume=882 |pages=1 |bibcode=2006ATel..882....1S |title=The first detection of the bipolar jets from the symbiotic prototype Z and |last1=Skopal |first1=A |last2=Pribulla |first2=T |year=2006 }} * {{cite journal|journal=Mon. Not. R. Astron. Soc.|volume=376|issue=1|pages=L16–L19|bibcode=2007MNRAS.376L..16T|doi=10.1111/j.1745-3933.2007.00277.x |arxiv = astro-ph/0612502 |title=Bipolar ejection by the symbiotic binary system Z and during its 2006 outburst|year=2007|last1=Tomov|first1=N. A.|last2=Tomova|first2=M. T.|last3=Bisikalo|first3=D. V.|doi-access=free |s2cid=16193674}}
==External links== * [http://aladin.u-strasbg.fr/AladinPreview?-c=23+33+39.9505%2B48+49+05.947&ident=V*+Z+And&submit=Aladin+previewer Image Z Andromedae] * [https://www.aavso.org/apps/vsp/chart/?star=Z+AND&fov=60&maglimit=14.5 AAVSO chart for Z Andromedae] * [https://www.aavso.org/lcg/plot?auid=000-BCR-681&starname=Z%20AND&lastdays=20000&start=&stop=2458136.22329&obscode=&obscode_symbol=2&obstotals=yes&calendar=calendar&forcetics=&pointsize=1&width=800&height=450&mag1=&mag2=&mean=&vmean=&grid=on&visual=on&uband=on&bband=on&v=on AAVSO long-term light curve of Z And]{{Dead link|date=March 2023 |bot=InternetArchiveBot |fix-attempted=yes }} * [http://www.aavso.org/vsots_zand Z Andromedae: The Prototype of the Symbiotic Class] AAVSO
{{Stars of Andromeda}}
221650 Category:Z Andromedae variables Category:Andromeda (constellation) Andromedae, Z Category:M-type giants 116287 Category:Durchmusterung objects 23312+4832 Category:Discoveries by Williamina Fleming