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• Mira_variable abstract "Mira variables /ˈmaɪrə/, named after the prototype star Mira, are a class of pulsating variable stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelengths. They are red giants in the very late stages of stellar evolution, on the asymptotic giant branch, that will expel their outer envelopes as planetary nebulae and become white dwarfs within a few million years.Mira variables are stars massive enough that they have undergone helium fusion in their core but are less than two solar masses, stars that have already lost about half their initial mass. However, they can be thousands of times more luminous than the Sun 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 in luminosity. The pulsation depends on the mass and radius of the star and there is a well-defined relationship between period and luminosity (and colour). 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.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 the IOTA telescope are not spherically symmetric, a result which is consistent with previous images of individual Mira stars, so there is now pressure to do realistic three-dimensional modelling of Mira stars on supercomputers.Mira variables may be oxygen-rich or carbon-rich. Carbon-rich stars such as R Leporis arise from a narrow set of conditions that override the normal tendency for AGB stars to maintain a surplus of oxygen over carbon at their surfaces due to dredge-ups. Pulsating AGB stars such as Mira variables undergo fusion in alternating hydrogen and helium shells, which produces periodic deep convection known as dredge-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 significant CN 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.Mira variables are rapidly losing mass and this material often forms dust shrouds around the star. In some cases conditions are suitable for the formation of natural masers.A small subset of Miras 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 by thermal pulses, where the helium shell reignites the outer hydrogen 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 the asymptotic 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 in R Hydrae. 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.Mira variables are popular targets for amateur astronomers interested in variable star observations, because of their dramatic changes in brightness. Some Mira variables (including Mira itself) have reliable observations stretching back well over a century.".
• Mira_variable thumbnail A_Wide-field_view_of_the_sky_around_a_field_studied_in_the_MASSIV_survey.jpg?width=300.
• Mira_variable wikiPageID "204539".
• Mira_variable wikiPageLength "15372".
• Mira_variable wikiPageOutDegree "123".
• Mira_variable wikiPageRevisionID "697600121".
• Mira_variable wikiPageWikiLink AFGL_2290.
• Mira_variable wikiPageWikiLink Amateur_astronomy.
• Mira_variable wikiPageWikiLink Apparent_magnitude.
• Mira_variable wikiPageWikiLink Astrophysical_maser.
• Mira_variable wikiPageWikiLink Asymptotic_giant_branch.
• Mira_variable wikiPageWikiLink CIT_13.
• Mira_variable wikiPageWikiLink CNO_cycle.
• Mira_variable wikiPageWikiLink Capricornus.
• Mira_variable wikiPageWikiLink Category:Mira_variables.
• Mira_variable wikiPageWikiLink Chi_Cygni.
• Mira_variable wikiPageWikiLink Dredge-up.
• Mira_variable wikiPageWikiLink Dust.
• Mira_variable wikiPageWikiLink Helium.
• Mira_variable wikiPageWikiLink Hydrogen.
• Mira_variable wikiPageWikiLink IK_Tauri.
• Mira_variable wikiPageWikiLink IRAS_23166+1655.
• Mira_variable wikiPageWikiLink IRC_+10216.
• Mira_variable wikiPageWikiLink IRC_-10529.
• Mira_variable wikiPageWikiLink Infrared.
• Mira_variable wikiPageWikiLink Infrared_Optical_Telescope_Array.
• Mira_variable wikiPageWikiLink LP_Andromedae.
• Mira_variable wikiPageWikiLink Long-period_variable_star.
• Mira_variable wikiPageWikiLink Luminosity.
• Mira_variable wikiPageWikiLink Mira.
• Mira_variable wikiPageWikiLink NV_Aurigae.
• Mira_variable wikiPageWikiLink OH_127.8+00.
• Mira_variable wikiPageWikiLink OH_231.8+4.2.
• Mira_variable wikiPageWikiLink OH_26.5+0.6.
• Mira_variable wikiPageWikiLink OH_32.8-0.3.
• Mira_variable wikiPageWikiLink Parsec.
• Mira_variable wikiPageWikiLink Planetary_nebula.
• Mira_variable wikiPageWikiLink RR_Aquilae.
• Mira_variable wikiPageWikiLink RR_Sagittarii.
• Mira_variable wikiPageWikiLink RR_Scorpii.
• Mira_variable wikiPageWikiLink RS_Scorpii.
• Mira_variable wikiPageWikiLink RS_Virginis.
• Mira_variable wikiPageWikiLink RT_Aquilae.
• Mira_variable wikiPageWikiLink RT_Cygni.
• Mira_variable wikiPageWikiLink RT_Sagittarii.
• Mira_variable wikiPageWikiLink RU_Herculis.
• Mira_variable wikiPageWikiLink RU_Sagittarii.
• Mira_variable wikiPageWikiLink RZ_Pegasi.
• Mira_variable wikiPageWikiLink R_Andromedae.
• Mira_variable wikiPageWikiLink R_Aquarii.
• Mira_variable wikiPageWikiLink R_Aquilae.
• Mira_variable wikiPageWikiLink R_Aurigae.
• Mira_variable wikiPageWikiLink R_Boötis.
• Mira_variable wikiPageWikiLink R_Cancri.
• Mira_variable wikiPageWikiLink R_Canum_Venaticorum.
• Mira_variable wikiPageWikiLink R_Carinae.
• Mira_variable wikiPageWikiLink R_Cassiopeiae.
• Mira_variable wikiPageWikiLink R_Centauri.
• Mira_variable wikiPageWikiLink R_Cygni.
• Mira_variable wikiPageWikiLink R_Draconis.
• Mira_variable wikiPageWikiLink R_Fornacis.
• Mira_variable wikiPageWikiLink R_Geminorum.
• Mira_variable wikiPageWikiLink R_Horologii.
• Mira_variable wikiPageWikiLink R_Hydrae.
• Mira_variable wikiPageWikiLink R_Leonis.
• Mira_variable wikiPageWikiLink R_Leonis_Minoris.
• Mira_variable wikiPageWikiLink R_Leporis.
• Mira_variable wikiPageWikiLink R_Normae.
• Mira_variable wikiPageWikiLink R_Octantis.
• Mira_variable wikiPageWikiLink R_Pegasi.
• Mira_variable wikiPageWikiLink R_Reticuli.
• Mira_variable wikiPageWikiLink R_Serpentis.
• Mira_variable wikiPageWikiLink R_Trianguli.
• Mira_variable wikiPageWikiLink R_Ursae_Majoris.
• Mira_variable wikiPageWikiLink R_Virginis.
• Mira_variable wikiPageWikiLink Red_giant.
• Mira_variable wikiPageWikiLink S_Boötis.
• Mira_variable wikiPageWikiLink S_Carinae.
• Mira_variable wikiPageWikiLink S_Cephei.
• Mira_variable wikiPageWikiLink S_Coronae_Borealis.
• Mira_variable wikiPageWikiLink S_Gruis.
• Mira_variable wikiPageWikiLink S_Herculis.
• Mira_variable wikiPageWikiLink S_Orionis.
• Mira_variable wikiPageWikiLink S_Pictoris.
• Mira_variable wikiPageWikiLink S_Sculptoris.
• Mira_variable wikiPageWikiLink S_Virginis.
• Mira_variable wikiPageWikiLink Semiregular_variable_star.
• Mira_variable wikiPageWikiLink Solar_mass.
• Mira_variable wikiPageWikiLink Southern_Crab_Nebula.
• Mira_variable wikiPageWikiLink Stellar_evolution.
• Mira_variable wikiPageWikiLink Sun.
• Mira_variable wikiPageWikiLink TX_Camelopardalis.
• Mira_variable wikiPageWikiLink TY_Cassiopeiae.
• Mira_variable wikiPageWikiLink T_Cassiopeiae.
• Mira_variable wikiPageWikiLink T_Cephei.
• Mira_variable wikiPageWikiLink T_Draconis.
• Mira_variable wikiPageWikiLink T_Normae.
• Mira_variable wikiPageWikiLink T_Ursae_Majoris.
• Mira_variable wikiPageWikiLink UV_Aurigae.
• Mira_variable wikiPageWikiLink UX_Cygni.

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