Mira
Observation data J2000.0
| ||
---|---|---|
Constellation | Cetus | |
Right ascension | 02h 19m 20.79210s[2] | |
Declination | −02° 58′ 39.4956″[2] | |
Apparent magnitude (V) | 2.0 to 10.1[3] | |
Characteristics | ||
Spectral type | M7 IIIe[4] (M5e-M9e[3]) | |
U−B color index | +0.08[5] | |
B−V color index | +1.53[5] | |
Variable type | Mira[3] | |
Absolute magnitude (MV) | +0.99[7] (variable) | |
Argument of periastron (ω)(secondary) | 258.3° | |
Details | ||
Gyr | ||
LTT 1179, SAO 129825 | ||
Database references | ||
SIMBAD | data |
Mira (.
ο Ceti is a binary stellar system, consisting of a variable red giant (Mira A) along with a white dwarf companion (Mira B). Mira A is a pulsating variable star and was the first non-supernova variable star discovered, with the possible exception of Algol. It is the prototype of the Mira variables.
Nomenclature
ο Ceti (
Observation history
Evidence that the variability of Mira was known in ancient China, Babylon or Greece is at best only circumstantial.[15] What is certain is that the variability of Mira was recorded by the astronomer David Fabricius beginning on August 3, 1596. Observing what he thought was the planet Mercury (later identified as Jupiter), he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21, however, it had increased in brightness by one magnitude, then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on February 16, 1609.[16]
In 1638
There is considerable speculation as to whether Mira had been observed prior to Fabricius. Certainly
Distance and Background Information about Mira
[17]The distance to Mira is uncertain; pre-Hipparcos estimates centered on 220 light-years;[18] while Hipparcos data from the 2007 reduction suggest a distance of 299 light-years, with a margin of error of 11%.[2] The age of Mira is suspected to be about 6 billion years old. Its gaseous material is scattered, as much as one-thousandth as thin as the air around us. Mira is also among the coolest known bright stars of the red giant class, with a temperature ranging from 3,000 to 4,000 degrees Fahrenheit (1,600 to 2,200 degrees Celsius). As with other long-period variables, Mira's deep red color at minimum pales to a lighter orange as the star brightens. Within the next few million years, Mira will discard its outer layers and become a planetary nebula, leaving behind a white dwarf.
Stellar system
This binary star system consists of a red giant (Mira, designated Mira A) undergoing mass loss and a high-temperature white dwarf companion (Mira B) that is accreting mass from the primary. Such an arrangement of stars is known as a symbiotic system and this is the closest such symbiotic pair to the Sun. Examination of this system by the Chandra X-ray Observatory shows a direct mass exchange along a bridge of matter from the primary to the white dwarf. The two stars are currently separated by about 70 astronomical units.[19]
Component A
Mira A is currently an asymptotic giant branch (AGB) star, in the thermally pulsing AGB phase.[20][21] Each pulse lasts a decade or more, and an amount of time on the order of 10,000 years passes between each pulse. With every pulse cycle Mira increases in luminosity and the pulses grow stronger. This is also causing dynamic instability in Mira, resulting in dramatic changes in luminosity and size over shorter, irregular time periods.[22]
The overall shape of Mira A has been observed to change, exhibiting pronounced departures from symmetry. These appear to be caused by bright spots on the surface that evolve their shape on time scales of 3–14 months. Observations of Mira A in the ultraviolet band by the Hubble Space Telescope have shown a plume-like feature pointing toward the companion star.[21]
Variability
Mira A is a variable star, specifically the prototypical Mira variable. The 6,000 to 7,000 known stars of this class[23] are all red giants whose surfaces pulsate in such a way as to increase and decrease in brightness over periods ranging from about 80 to more than 1,000 days.
In the particular case of Mira, its increases in brightness take it up to about magnitude 3.5 on average, placing it among the brighter stars in the Cetus constellation. Individual cycles vary too; well-attested maxima go as high as magnitude 2.0 in brightness and as low as 4.9, a range almost 15 times in brightness, and there are historical suggestions that the real spread may be three times this or more. Minima range much less, and have historically been between 8.6 and 10.1, a factor of four times in luminosity. The total swing in brightness from absolute maximum to absolute minimum (two events which did not occur on the same cycle) is 1,700 times. Mira emits the vast majority of its radiation in the infrared, and its variability in that band is only about two magnitudes. The shape of its light curve is of an increase over about 100 days, and the return to minimum taking twice as long.[24] Contemporary approximate maxima for Mira:[25]
- Oct 21–31, 1999
- Sep 21–30, 2000
- Aug 21–31, 2001
- Jul 21–31, 2002
- Jun 21–30, 2003
- May 21–31, 2004
- Apr 11–20, 2005
- Mar 11–20, 2006
- Feb 1–10, 2007
- Jan 21–31, 2008
- Dec 21–31, 2008
- Nov 21–30, 2009
- Oct 21–31, 2010
- Sep 21–30, 2011
- Aug 27, 2012
- Jul 26, 2013
- May 12, 2014
- Apr 9, 2015
- Mar 6, 2016
- Jan 31, 2017
- Dec 29, 2017
- Nov 26, 2018
- Oct 24, 2019
- Sep 20, 2020
- Aug 18, 2021
- Jul 16, 2022
- Jun 13, 2023
- May 10, 2024
From northern temperate latitudes, Mira is generally not visible between late March and June due to its proximity to the Sun. This means that at times several years can pass without it appearing as a naked-eye object.
The pulsations of Mira variables cause the star to expand and contract, but also to change its temperature. The temperature is highest slightly after the visual maximum, and lowest slightly before minimum. The photosphere, measured at the
In Mira, the highest luminosity occurs close to the time when the star is hottest and smallest. The visual magnitude is determined both by the luminosity and by the proportion of the
The pulsations of Mira have the effect of expanding its photosphere by around 50% compared to a non-pulsating star. In the case of Mira, if it was not pulsating it is modelled to have a radius of only around 240 R☉.[10]
Mass loss
Ultraviolet studies of Mira by NASA's Galaxy Evolution Explorer (GALEX) space telescope have revealed that it sheds a trail of material from the outer envelope, leaving a tail 13 light-years in length, formed over tens of thousands of years.[27][28] It is thought that a hot bow wave of compressed plasma/gas is the cause of the tail; the bow wave is a result of the interaction of the stellar wind from Mira A with gas in interstellar space, through which Mira is moving at an extremely high speed of 130 kilometres per second (290,000 miles per hour).[29] The tail consists of material stripped from the head of the bow wave, which is also visible in ultraviolet observations. Mira's bow shock will eventually evolve into a planetary nebula, the form of which will be considerably affected by the motion through the interstellar medium (ISM).[30] Mira’s tail offers a unique opportunity to study how stars like our sun die and ultimately seed new solar systems. As Mira hurls along, its tail drops off carbon, oxygen and other important elements needed for new stars, planets, and possibly even life to form. This tail material, visible now for the first time, has been shed over the past 30,000 years.
Component B
The companion star is 0.487±0.006
In 2007, observations showed a
References
- ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
- ^ S2CID 18759600.
- ^ Bibcode:1971GCVS3.C......0K.
- doi:10.1086/118589.
- ^ doi:10.1086/113268.
- Bibcode:1967IAUS...30...57E. Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30.
- S2CID 119257644.
- ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Archived from the original on 1 August 2017. Retrieved 22 January 2017.
- ^ doi:10.1086/161527.
- ^ S2CID 17009595.
- S2CID 16131273.
- ISBN 0-486-21079-0.
- ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
- ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
- Bibcode:1996JAVSO..24..129W.
- Bibcode:1997JAVSO..25..115H.
- ^ Burnham, Robert Jr. (1980). Burnham's Celestial Handbook. Vol. 1. New York: Dover Publications Inc. p. 634.
- S2CID 124913393.
- ^ Pogge, Richard (January 21, 2006). "Lecture 16: The Evolution of Low-Mass Stars". Ohio State University. Retrieved 2007-12-11.
- ^ Bibcode:1999IAUS..191..409L.
- ISBN 0-7923-1768-8.
- ^ GCVS: vartype.txt from the GCVS catalogue (statistics at the end of the file indicate 6,006 confirmed and 1,237 probable Mira variables)
- ^ Braune, Werner. "Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne". Archived from the original on 2007-08-10. Retrieved 2007-08-16.
- ^ "SEDS - Mira". Retrieved 2017-11-19.
- S2CID 28966631.
- S2CID 4426573.
- ^ Minkel, JR. (2007). "Shooting Bullet Star Leaves Vast Ultraviolet Wake". Scientific American.
- S2CID 16954556.
- S2CID 29910377.
- S2CID 55554110.
- S2CID 16694.
- S2CID 119247560.
Further reading
- "Mira (Omicron Ceti)". The Encyclopedia of Astrobiology, Astronomy, and Spaceflight. Retrieved June 22, 2006.
- Robert Burnham Jr., Burnham's Celestial Handbook, Vol. 1, (New York: Dover Publications, Inc., 1978), 634.
- James Kaler, The Hundred Greatest Stars, (New York: Copernicus Books, 2002), 121.
External links
- Speeding Bullet Star Leaves Enormous Streak Across Sky at Caltech
- Mira has tail nearly 13 light years in length (BBC)
- Astronomy Picture of the Day:
1998-10-11, 2001-01-21, 2006-07-22, 2007-02-21, 2007-08-17 - SEDS article
- A lightcurve of Mira from the BAV.
- Universe Today, That's Not a Comet, that's a Star
- OMICRON CETI (Mira)
- Winter 2006: Mira revisited