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Mira variable

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Type of variable star

Mira, the prototype of the Mira variables

Mira variables/ˈmaɪrə/ (named for the prototype starMira) are a class ofpulsating stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than onemagnitude ininfrared and 2.5 magnitude at visual wavelengths.^[1] They arered giants in the very late stages ofstellar evolution, on theasymptotic giant branch (AGB), that will expel their outer envelopes asplanetary nebulae and becomewhite dwarfs within a few million years.

Mira variables are stars massive enough that they have undergonehelium fusion in their cores but are less than twosolar masses,^[2] stars that have already lost about half their initial mass.^{[citation needed]} However, they can be thousands of times moreluminous than theSun due to their very large distended envelopes. They are pulsating due to the entire star expanding and contracting. This produces a change in temperature along with radius, both of which factors cause the variation inluminosity. The pulsation depends on the mass and radius of the star and there is a well-definedrelationship between period and luminosity (and colour).^[3]^[4] The very large visual amplitudes are not due to large luminosity changes, but due to a shifting of energy output between infra-red and visual wavelengths as the stars change temperature during their pulsations.^[5]

Early models of Mira stars assumed that the star remained spherically symmetric during this process (largely to keep the computer modelling simple, rather than for physical reasons). A recent survey of Mira variable stars found that 75% of the Mira stars which could be resolved using theIOTA telescope are not spherically symmetric,^[6] a result which is consistent with previous images of individual Mira stars,^[7]^[8]^[9] so there is now pressure to do realistic three-dimensional modelling of Mira stars on supercomputers.^[10]

Mira variables may be oxygen-rich or carbon-rich. Carbon-rich stars such asR Leporis arise from a narrow set of conditions that override the normal tendency forAGB stars to maintain a surplus of oxygen over carbon at their surfaces due todredge-ups.^[11] Pulsating AGB stars such as Mira variables undergo fusion in alternating hydrogen and helium shells, which produces periodic deep convection known asdredge-ups. These dredge-ups bring carbon from the helium burning shell to the surface and would result in a carbon star. However, in stars above about 4 M_☉, hot bottom burning occurs. This is when the lower regions of the convective region are hot enough for significantCNO cycle fusion to take place which destroys much of the carbon before it can be transported to the surface. Thus more massive AGB stars do not become carbon-rich.^[12]

Mira variables are rapidly losing mass and this material often formsdust shrouds around the star. In some cases conditions are suitable for the formation of naturalmasers.^[13]

A small subset of Mira variables appear to change their period over time: the period increases or decreases by a substantial amount (up to a factor of three) over the course of several decades to a few centuries. This is believed to be caused bythermal pulses, where thehelium shell reignites the outerhydrogen shell. This changes the structure of the star, which manifests itself as a change in period. This process is predicted to happen to all Mira variables, but the relatively short duration of thermal pulses (a few thousand years at most) over theasymptotic giant branch lifetime of the star (less than a million years), means we only see it in a few of the several thousand Mira stars known, possibly inR Hydrae.^[14] Most Mira variables do exhibit slight cycle-to-cycle changes in period, probably caused by nonlinear behaviour in the stellar envelope including deviations from spherical symmetry.^[15]^[16]

Mira variables are popular targets foramateur astronomers interested invariable star observations, because of their dramatic changes in brightness. Some Mira variables (includingMira itself) have reliable observations stretching back well over a century.^[17]

List

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The following list contains selected Mira variables. Unless otherwise noted, the given magnitudes are in theV-band, and distances are from theGaia DR2 star catalogue.^[18]

Star	Brightest magnitude	Dimmest magnitude	Period (in days)	Distance (inparsecs)	Reference
Mira	2.0	10.1	332	92+12 −9^[19]	[1]
Chi Cygni	3.3	14.2	408	180+45 −30	[2]
R Hydrae	3.5	10.9	380	224+56 −37	[3]
R Carinae	3.9	10.5	307	387+81 −57	[4]
R Leonis	4.4	11.3	310	71+5 −4	[5]
S Carinae	4.5	9.9	149	497+22 −20	[6]
R Cassiopeiae	4.7	13.5	430	187+9 −8	[7]
R Horologii	4.7	14.3	408	313+40 −32	[8]
U Orionis	4.8	13.0	377	216+19 −16	[9]
RR Scorpii	5.0	12.4	281	277+18 −16	[10]
R Serpentis	5.2	14.4	356	285+26 −22	[11]
T Cephei	5.2	11.3	388	176+13 −12	[12]
R Aquarii	5.2	12.4	387	320+31 −26	[13]
R Centauri	5.3	11.8	502	385+159 −87^[19]	[14]
RR Sagittarii	5.4	14	336	386+48 −38	[15]
R Trianguli	5.4	12.6	267	933+353 −201	[16]
S Sculptoris	5.5	13.6	367	1078+1137 −366	[17]
R Aquilae	5.5	12.0	271	238+27 −22	[18]
R Leporis	5.5	11.7	445	419+15 −14	[19]
W Hydrae	5.6	9.6	390	164+25 −19	[20]
R Andromedae	5.8	15.2	409	242+30 −24	[21]
S Coronae Borealis	5.8	14.1	360	431+60 −47	[22]
U Cygni	5.9	12.1	463	767+34 −31	[23]
X Ophiuchi	5.9	8.6	338	215+15 −13	[24]
RS Scorpii	6.0	13.0	319	709+306 −164	[25]
RT Sagittarii	6.0	14.1	306	575+48 −41	[26]
RU Sagittarii	6.0	13.8	240	1592+1009 −445	[27]
RT Cygni	6.0	13.1	190	888+47 −43	[28]
R Geminorum	6.0	14.0	370	1514+1055 −441	[29]
S Gruis	6.0	15.0	402	671+109 −82	[30]
V Monocerotis	6.0	13.9	341	426+50 −41	[31]
R Cancri	6.1	11.9	357	226+32 −25	[32]
R Virginis	6.1	12.1	146	530+28 −25	[33]
R Cygni	6.1	14.4	426	674+47 −41	[34]
R Boötis	6.2	13.1	223	702+60 −52	[35]
T Normae	6.2	13.6	244	1116+168 −129	[36]
R Leonis Minoris	6.3	13.2	372	347+653 −137^[19]	[37]
S Virginis	6.3	13.2	375	729+273 −156	[38]
R Reticuli	6.4	14.2	281	1553+350 −241	[39]
S Herculis	6.4	13.8	304	477+27 −24	[40]
U Herculis	6.4	13.4	404	572+53 −45	[41]
R Octantis	6.4	13.2	407	504+46 −39	[42]
S Pictoris	6.5	14.0	422	574+74 −59	[43]
R Ursae Majoris	6.5	13.7	302	489+54 −44	[44]
R Canum Venaticorum	6.5	12.9	329	661+65 −54	[45]
R Normae	6.5	12.8	496	581+10000 −360^[19]	[46]
T Ursae Majoris	6.6	13.5	257	1337+218 −164	[47]
R Aurigae	6.7	13.9	458	227+21 −17	[48]
RU Herculis	6.7	14.3	486	511+53 −44	[49]
R Draconis	6.7	13.2	246	662+58 −49	[50]
V Coronae Borealis	6.9	12.6	358	843+43 −39	[51]
T Cassiopeiae	6.9	13.0	445	374+37 −31	[52]
R Pegasi	6.9	13.8	378	353+35 −29	[53]
V Cassiopeiae	6.9	13.4	229	298+15 −14	[54]
T Pavonis	7.0	14.4	244	1606+340 −239	[55]
RS Virginis	7.0	14.6	354	616+81 −64	[56]
Z Cygni	7.1	14.7	264	654+36 −33	[57]
S Orionis	7.2	13.1	434	538+120 −83	[58]
T Draconis	7.2	13.5	422	783+48 −43	[59]
UV Aurigae	7.3	10.9	394	1107+83 −72	[60]
W Aquilae	7.3	14.3	490	321+22 −20	[61]
S Cephei	7.4	12.9	487	531+23 −21	[62]
R Fornacis	7.5	13.0	386	633+44 −38	[63]
RZ Pegasi	7.6	13.6	437	1117+88 −76	[64]
RT Aquilae	7.6	14.5	327	352+24 −21	[65]
V Cygni	7.7	13.9	421	458+36 −31	[66]
RR Aquilae	7.8	14.5	395	318+33 −28	[67]
S Boötis	7.8	13.8	271	2589+552 −387	[68]
WX Cygni	8.8	13.2	410	1126+86 −75	[69]
W Draconis	8.9	15.4	279	6057+4469 −1805	[70]
R Capricorni^[20]	8.9	14.9	343	1407+178 −142	[71]
UX Cygni	9.0	17.0	569	5669+10000 −2760	[72]
LL Pegasi	9.6 K	11.6 K	696	1300^[21]	[73]
TY Cassiopeiae	10.1	19.0	645	1328+502 −286	[74]
IK Tauri	10.8	16.5	470	285+36 −29	[75]
CW Leonis	11.0 R	14.8 R	640	95+22 −15^[22]	[76]
TX Camelopardalis	11.6 B	17.7 B	557	333+42 −33	[77]
LP Andromedae	15.1	17.3	614	400+68 −51	[78]

References

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^Mattei, Janet Akyuz (1997)."1997JAVSO..25...57M Page 57".Journal of the American Association of Variable Star Observers (Jaavso).25 (2): 57.Bibcode:1997JAVSO..25...57M. Retrieved2023-02-23.
^Ireland, M.J.; Scholz, M.; Tuthill, P.G.; Wood, P.R. (December 2004)."Pulsation of M-type Mira variables with moderately different mass: search for observable mass effects".Monthly Notices of the Royal Astronomical Society.355 (2):444–450.arXiv:astro-ph/0408540.Bibcode:2004MNRAS.355..444I.doi:10.1111/j.1365-2966.2004.08336.x.S2CID 12395165.
^Glass, I.S.; Lloyd Evans, T. (1981). "A period-luminosity relation for Mira variables in the Large Magellanic Cloud".Nature.291 (5813). Macmillan:303–4.Bibcode:1981Natur.291..303G.doi:10.1038/291303a0.S2CID 4262929.
^Bedding, Timothy R.; Zijlstra, Albert A. (1998). "Hipparcos Period-Luminosity Relations for Mira and Semiregular variables".The Astrophysical Journal.506 (1):L47 –L50.arXiv:astro-ph/9808173.Bibcode:1998ApJ...506L..47B.doi:10.1086/311632.S2CID 14529151.
^Smith, Beverly J.; Leisawitz, David; Castelaz, Michael W.; Luttermoser, Donald (2002). "Infrared Light Curves of Mira Variable Stars fromCOBE DIRBE Data".The Astronomical Journal.123 (2): 948.arXiv:astro-ph/0111151.Bibcode:2002AJ....123..948S.doi:10.1086/338647.S2CID 16934459.
^Ragland, S.; Traub, W. A.; Berger, J.-P.; Danchi, W. C.; Monnier, J. D.; Willson, L. A.; Carleton, N. P.; Lacasse, M. G.; Millan-Gabet, R.; Pedretti, E.; Schloerb, F. P.; Cotton, W. D.; Townes, C. H.; Brewer, M.; Haguenauer, P.; Kern, P.; Labeye, P.; Malbet, F.; Malin, D.; Pearlman, M.; Perraut, K.; Souccar, K.; Wallace, G. (2006). "First Surface-resolved Results with the Infrared Optical Telescope Array Imaging Interferometer: Detection of Asymmetries in Asymptotic Giant Branch Stars".The Astrophysical Journal.652 (1):650–660.arXiv:astro-ph/0607156.Bibcode:2006ApJ...652..650R.doi:10.1086/507453.S2CID 30825403.
^Haniff, C. A.; Ghez, A. M.; Gorham, P. W.; Kulkarni, S. R.; Matthews, K.; Neugebauer, G. (1992)."Optical aperture synthetic images of the photosphere and molecular atmosphere of Mira"(PDF).Astronomical Journal.103: 1662.Bibcode:1992AJ....103.1662H.doi:10.1086/116182.
^Karovska, M.; Nisenson, P.; Papaliolios, C.; Boyle, R. P. (1991)."Asymmetries in the atmosphere of Mira".Astrophysical Journal.374: L51.Bibcode:1991ApJ...374L..51K.doi:10.1086/186069.
^Tuthill, P. G.; Haniff, C. A.; Baldwin, J. E. (1999)."Surface imaging of long-period variable stars".Monthly Notices of the Royal Astronomical Society.306 (2): 353.Bibcode:1999MNRAS.306..353T.doi:10.1046/j.1365-8711.1999.02512.x.
^Freytag, B.; Höfner, S. (2008)."Three-dimensional simulations of the atmosphere of an AGB star".Astronomy and Astrophysics.483 (2): 571.Bibcode:2008A&A...483..571F.doi:10.1051/0004-6361:20078096.
^Feast, Michael W.; Whitelock, Patricia A.; Menzies, John W. (2006)."Carbon-rich Mira variables: Kinematics and absolute magnitudes".Monthly Notices of the Royal Astronomical Society.369 (2):791–797.arXiv:astro-ph/0603506.Bibcode:2006MNRAS.369..791F.doi:10.1111/j.1365-2966.2006.10324.x.S2CID 12805849.
^Stancliffe, Richard J.; Izzard, Robert G.; Tout, Christopher A. (2004)."Third dredge-up in low-mass stars: Solving the Large Magellanic Cloud carbon star mystery".Monthly Notices of the Royal Astronomical Society: Letters.356 (1):L1 –L5.arXiv:astro-ph/0410227.Bibcode:2005MNRAS.356L...1S.doi:10.1111/j.1745-3933.2005.08491.x.S2CID 17425157.
^Wittkowski, M.; Boboltz, D. A.; Ohnaka, K.; Driebe, T.; Scholz, M. (2007). "The Mira variable S Orionis: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs".Astronomy and Astrophysics.470 (1):191–210.arXiv:0705.4614.Bibcode:2007A&A...470..191W.doi:10.1051/0004-6361:20077168.S2CID 14200520.
^Zijlstra, A. A.; Bedding, T. R.; Mattei, J. A. (2002)."The evolution of the Mira variable R Hydrae".Monthly Notices of the Royal Astronomical Society.334 (3): 498.arXiv:astro-ph/0203328.Bibcode:2002MNRAS.334..498Z.doi:10.1046/j.1365-8711.2002.05467.x.S2CID 16663228.
^Templeton, M. R.; Mattei, J. A.; Willson, L. A. (2005). "Secular Evolution in Mira Variable Pulsations".The Astronomical Journal.130 (2):776–788.arXiv:astro-ph/0504527.Bibcode:2005AJ....130..776T.doi:10.1086/431740.S2CID 359940.
^Zijlstra, Albert A.; Bedding, Timothy R. (2002). "Period Evolution in Mira Variables".Journal of the American Association of Variable Star Observers.31 (1): 2.Bibcode:2002JAVSO..31....2Z.
^Mattei, Janet Akyuz (1997). "Introducing Mira Variables".The Journal of the American Association of Variable Star Observers.25 (2): 57.Bibcode:1997JAVSO..25...57M.
^Gaia Collaboration (2018),Gaia DR2, VizieR, retrieved20 April 2019
^^a ^b ^c ^dvan Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction".Astronomy and Astrophysics.474 (2):653–664.arXiv:0708.1752.Bibcode:2007A&A...474..653V.doi:10.1051/0004-6361:20078357.S2CID 18759600.
^Discovered in 1848 by Hind.Patrick Moore and Robin Rees (2011).Patrick Moore's Data Book of Astronomy (second ed.). Cambridge University Press. p. 323.ISBN 978-1139495226.
^Lombaert, R.; De Vries, B. L.; De Koter, A.; Decin, L.; Min, M.; Smolders, K.; Mutschke, H.; Waters, L. B. F. M. (2012). "Observational evidence for composite grains in an AGB outflow. MgS in the extreme carbon star LL Pegasi".Astronomy & Astrophysics.544: L18.arXiv:1207.1606.Bibcode:2012A&A...544L..18L.doi:10.1051/0004-6361/201219782.S2CID 119022145.
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External links

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OGLE Atlas of Variable Star Light Curves - Mira Variables

Variable stars

Pulsating

Cepheids and cepheid-like	Type I(Classical cepheids,Delta Scuti) Type II(BL Herculis,W Virginis,RV Tauri) RR Lyrae Rapidly oscillating Ap SX Phoenicis
Blue-white with early spectra	Alpha Cygni Beta Cephei Slowly pulsating B-type PV Telescopii Blue large-amplitude pulsator
Long-period	Mira Semiregular Slow irregular
Other	Gamma Doradus Solar-like oscillations White dwarf

Eruptive

Protostar andPMS	Herbig Ae/Be Orion FU Orionis T Tauri
Giants and supergiants	Luminous blue variable R Coronae Borealis(DY Persei) Yellow hypergiant
Eruptive binary	Double periodic FS Canis Majoris RS Canum Venaticorum
Other	Flare Gamma Cassiopeiae Lambda Eridani Wolf–Rayet