IK Pegasi
Observation data Epoch J2000 Equinox J2000 | |
---|---|
Constellation | Pegasus |
Right ascension | 21h 26m 26.66066s[1] |
Declination | +19° 22′ 32.3169″[1] |
Apparent magnitude (V) | 6.08[2] |
Characteristics | |
A | |
Spectral type | A8m:[3] or kA6hA9mF0[4] |
U−B color index | 0.03[5] |
B−V color index | 0.235±0.009[2] |
Variable type | Delta Scuti[3] |
B | |
Spectral type | DA[6] |
Absolute magnitude (MV) | 2.75[2] |
Details | |
A | |
Myr | |
B | |
Mass | 1.15[9] M☉ |
Radius | 0.006[6] R☉ |
Luminosity | 0.12[nb 1] L☉ |
Surface gravity (log g) | 8.95[6] cgs |
Temperature | 35,500[9] K |
B: WD 2124+191, EUVE J2126+193.[10][11] | |
Database references | |
SIMBAD | data |
IK Pegasi (or HR 8210) is a
The primary (IK Pegasi A) is an A-type main-sequence star that displays minor pulsations in luminosity. It is categorized as a Delta Scuti variable star and it has a periodic cycle of luminosity variation that repeats itself about 22.9 times per day.[7] Its companion (IK Pegasi B) is a massive white dwarf—a star that has evolved past the main sequence and is no longer generating energy through nuclear fusion. They orbit each other every 21.7 days with an average separation of about 31 million kilometres, or 19 million miles, or 0.21 astronomical units (AU). This is smaller than the orbit of Mercury around the Sun.
IK Pegasi B is the nearest known supernova progenitor candidate. When the primary begins to evolve into a red giant, it is expected to grow to a radius where the white dwarf can accrete matter from the expanded gaseous envelope. When the white dwarf approaches the Chandrasekhar limit of 1.4 solar masses (M☉),[12] it may explode as a Type Ia supernova.[13]
Observation
This star system was catalogued in the 1862
Examination of the
In 1927, the Canadian astronomer William E. Harper used this technique to measure the period of this single-line spectroscopic binary and determined it to be 21.724 days. He also initially estimated the orbital eccentricity as 0.027. (Later estimates gave an eccentricity of essentially zero, which is the value for a circular orbit.)[13] The velocity amplitude was measured as 41.5 km/s, which is the maximum velocity of the primary component along the line of sight to the Solar System.[17]
The distance to the IK Pegasi system can be measured directly by observing the tiny
The combination of the distance and proper motion of this system can be used to compute the transverse velocity of IK Pegasi as 16.9 km/s.
An attempt was made to photograph the individual components of this binary using the
IK Pegasi A
The Hertzsprung–Russell diagram (HR diagram) is a plot of luminosity versus a color index for a set of stars. IK Pegasi A is currently a main sequence star—a term that is used to describe a nearly linear grouping of core hydrogen-fusing stars based on their position on the HR diagram. However, IK Pegasi A lies in a narrow, nearly vertical band of the HR diagram that is known as the instability strip. Stars in this band oscillate in a coherent manner, resulting in periodic pulsations in the star's luminosity.[22]
The pulsations result from a process called the
Stars within the portion of the instability strip that crosses the main sequence are called
Astronomers define the
The spectrum of A-class stars such as IK Pegasi A show strong
Spectral class-A stars are hotter and more massive than the Sun. But, in consequence, their life span on the main sequence is correspondingly shorter. For a star with a mass similar to IK Pegasi A (1.65 M☉), the expected lifetime on the main sequence is 2–3 × 109 years, which is about half the current age of the Sun.[27]
In terms of mass, the relatively young Altair is the nearest star to the Sun that is a stellar analogue of component A—it has an estimated 1.7 M☉. The binary system as a whole has some similarities to the nearby system of Sirius, which has a class-A primary and a white dwarf companion. However, Sirius A is more massive than IK Pegasi A and the orbit of its companion is much larger, with a semimajor axis of 20 AU.
IK Pegasi B
The companion star is a dense white dwarf star. This category of stellar object has reached the end of its evolutionary life span and is no longer generating energy through nuclear fusion. Instead, under normal circumstances, a white dwarf will steadily radiate away its excess energy, mainly stored heat, growing cooler and dimmer over the course of many billions of years.[28]
Evolution
Nearly all small and intermediate-mass stars (below about 8~9 M☉) will end up as white dwarfs once they have exhausted their supply of
As the hydrogen fuel at the core of the progenitor of IK Pegasi B was consumed, it evolved into a
The outer envelope of a red giant or AGB star can expand to several hundred times the radius of the Sun, occupying a radius of about 5 × 108 km (3 AU) in the case of the pulsating AGB star Mira.[34] This is well beyond the current average separation between the two stars in IK Pegasi, so during this time period the two stars shared a common envelope. As a result, the outer atmosphere of IK Pegasi A may have received an isotope enhancement.[9]
Some time after an inert oxygen-carbon (or oxygen-magnesium-neon) core formed, thermonuclear fusion began to occur along two shells concentric with the core region; hydrogen was burned along the outermost shell, while helium fusion took place around the inert core. However, this double-shell phase is unstable, so it produced thermal pulses that caused large-scale mass ejections from the star's outer envelope.[35] This ejected material formed an immense cloud of material called a planetary nebula. All but a small fraction of the hydrogen envelope was driven away from the star, leaving behind a white dwarf remnant composed primarily of the inert core.[36]
Composition and structure
The interior of IK Pegasi B may be composed wholly of carbon and oxygen; alternatively, if its progenitor underwent
At an estimated 1.15 M☉, IK Pegasi B is considered to be a high-mass white dwarf.[nb 3] Although its radius has not been observed directly, it can be estimated from known theoretical relationships between the mass and radius of white dwarfs,[39] giving a value of about 0.60% of the Sun's radius.[6] (A different source gives a value of 0.72%, so there remains some uncertainty in this result.)[7] Thus this star packs a mass greater than the Sun into a volume roughly the size of the Earth, giving an indication of this object's extreme density.[nb 4]
The massive, compact nature of a white dwarf produces a strong
The effective surface temperature of IK Pegasi B is estimated to be about 35,500 ± 1,500 K,[9] making it a strong source of ultraviolet radiation.[6][nb 6] Under normal conditions this white dwarf would continue to cool for more than a billion years, while its radius would remain essentially unchanged.[40]
Future evolution
In a 1993 paper, David Wonnacott, Barry J. Kellett and David J. Stickland identified this system as a candidate to evolve into a Type Ia supernova or a cataclysmic variable.[13] At a distance of 150 light years, this makes it the nearest known candidate supernova progenitor to the Earth. However, in the time it will take for the system to evolve to a state where a supernova could occur, it will have moved a considerable distance from Earth but may still pose a threat.
At some point in the future, IK Pegasi A will consume the hydrogen fuel at its core and start to evolve away from the main sequence to form a red giant. The envelope of a red giant can grow to significant dimensions, extending up to a hundred times its previous radius (or larger). Once IK Pegasi A expands to the point where its outer envelope overflows the Roche lobe of its companion, a gaseous accretion disk will form around the white dwarf. This gas, composed primarily of hydrogen and helium, will then accrete onto the surface of the companion. This mass transfer between the stars will also cause their mutual orbit to shrink.[41]
On the surface of the white dwarf, the accreted gas will become compressed and heated. At some point the accumulated gas can reach the conditions necessary for hydrogen fusion to occur, producing a runaway reaction that will drive a portion of the gas from the surface. This would result in a (recurrent) nova explosion—a cataclysmic variable star—and the luminosity of the white dwarf would rapidly increase by several magnitudes for a period of several days or months.[42] An example of such a star system is RS Ophiuchi, a binary system consisting of a red giant and a white dwarf companion. RS Ophiuchi has flared into a (recurrent) nova on at least six occasions, each time accreting the critical mass of hydrogen needed to produce a runaway explosion.[43][44]
It is possible that IK Pegasi B will follow a similar pattern.[43] In order to accumulate mass, however, only a portion of the accreted gas can be ejected, so that with each cycle the white dwarf would steadily increase in mass. Thus, even should it behave as a recurring nova, IK Pegasus B could continue to accumulate a growing envelope.[45]
An alternate model that allows the white dwarf to steadily accumulate mass without erupting as a nova is called the close-binary
Should the white dwarf's mass approach the Chandrasekhar limit of 1.4 M☉ it will no longer be supported by electron degeneracy pressure and it will undergo a collapse. For a core primarily composed of oxygen, neon and magnesium, the collapsing white dwarf is likely to form a neutron star. In this case, only a fraction of star's mass will be ejected as a result.[48] If the core is instead made of carbon-oxygen, however, increasing pressure and temperature will initiate carbon fusion in the center prior to attainment of the Chandrasekhar limit. The dramatic result is a runaway nuclear fusion reaction that consumes a substantial fraction of the star within a short time. This will be sufficient to unbind the star in a cataclysmic, Type Ia supernova explosion.[49]
Such a supernova event may pose some threat to life on the Earth. It is thought that the white dwarf, IK Pegasi B, is unlikely to detonate as a supernova for 1.9 billion years.[50] As shown previously, the space velocity of this star relative to the Sun is 20.4 km/s (12.7 mi/s). This is equivalent to moving a distance of one light year every 14,700 years. After 5 million years, for example, this star will be separated from the Sun by more than 500 light years. A Type Ia supernova within a thousand parsecs (3,300 light-years) is thought to be able to affect the Earth,[51] but it must be closer than about 10 parsecs (around thirty light-years) to cause a major harm to the terrestrial biosphere.[50]
Following a supernova explosion, the remnant of the donor star (IK Pegasus A) would continue with the final velocity it possessed when it was a member of a close orbiting binary system. The resulting relative velocity could be as high as 100–200 km/s (62–124 mi/s), which would place it among the
See also
Notes
- ^ Based upon:
Krimm, Hans (August 19, 1997). "Luminosity, Radius and Temperature". Hampden-Sydney College. Archived from the original on May 8, 2003. Retrieved 2007-05-16. - ^ The net proper motion is given by:
- mas/y.
- Vt = μ • 4.74 d (pc) = 16.9 km.
Majewski, Steven R. (2006). "Stellar Motions". University of Virginia. Archived from the original on 2012-01-25. Retrieved 2007-05-14. - doi:10.1086/305489. of all white dwarfs have at least one solar mass.
- ^ R* = 0.006 • (6.96 × 108) ≈ 4,200 km.
- ^ The surface gravity of the Earth is 9.780 m/s2, or 978.0 cm/s2 in cgs units. Thus:
- ^ From Wien's displacement law, the peak emission of a black body at this temperature would be at a wavelength of:
- nm
References
- ^ .
- ^ S2CID 119257644.
- ^ hdl:2152/34842
- Bibcode:2014yCat....1.2023S.
- ^ a b "HD 12139". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-11-13. — Note: some results were queried via the "Display all measurements" function on the web page.
- ^
- ^
- ^
- ^ doi:10.1086/133242
- ^ doi:10.1086/305926, retrieved 2010-01-05
- doi:10.1086/305496
- S2CID 16408991.
- ^
- Bibcode:1908AnHar..50....1P
- ISBN 978-0-12-373980-3
- ^ Staff, Spectroscopic Binaries, University of Tennessee, retrieved 2007-06-09
- Bibcode:1928PDAO....4..171H
- Bibcode:1997A&A...323L..49P
- Bibcode:1953GCRV..C......0W
- ISBN 1-58381-058-7
- ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 30 November 2022.
- ^
- ^ For an explanation of the star colors, see: "The Colour of Stars". Australia Telescope Outreach and Education. December 21, 2004. Archived from the original on March 18, 2012. Retrieved 2007-09-26.
- ^ Templeton, Matthew (2004), Variable Star of the Season: Delta Scuti and the Delta Scuti variables, AAVSO, retrieved 2021-05-06
- ISBN 978-981-270-777-2
- Bibcode:1994AAS...184.0607M
- ^ Anonymous (2005), Stellar Lifetimes, Georgia State University, retrieved 2007-02-26
- ^ Staff (August 29, 2006), White Dwarfs & Planetary Nebulas, Harvard-Smithsonian Center for Astrophysics, retrieved 2007-06-09
- S2CID 59065632
- ^ Seligman, Courtney (2007), The Mass-Luminosity Diagram and the Lifetime of Main-Sequence Stars, retrieved 2007-05-14
- ^ Staff (August 29, 2006), Stellar Evolution - Cycles of Formation and Destruction, Harvard-Smithsonian Center for Astrophysics, retrieved 2006-08-10
- ^ Richmond, Michael (October 5, 2006), Late stages of evolution for low-mass stars, Rochester Institute of Technology, retrieved 2007-06-07
- ^ Darling, David, Carbon burning, The Internet Encyclopedia of Science, retrieved 2007-08-15
- ^ Savage, D.; Jones, T.; Villard, Ray; Watzke, M. (August 6, 1997), Hubble Separates Stars in the Mira Binary System, HubbleSite News Center, retrieved 2007-03-01
- S2CID 2884928
- doi:10.1086/191565
- S2CID 11890376
- , retrieved 2021-05-06
- ^ Estimating Stellar Parameters from Energy Equipartition, ScienceBits, retrieved 2007-05-15
- ^ Imamura, James N. (February 24, 1995), Cooling of White Dwarfs, University of Oregon, archived from the original on May 2, 2007, retrieved 2007-05-19
- PMID 28163653
- ^ Malatesta, K.; Davis, K. (May 2001), Variable Star Of The Month: A Historical Look at Novae (PDF), AAVSO, retrieved 2021-05-06
- ^ a b Malatesta, Kerri (May 2000), Variable Star Of The Month—May, 2000: RS Ophiuchi, AAVSO, retrieved 2021-05-06
- ^ Hendrix, Susan (July 20, 2007), Scientists see Storm Before the Storm in Future Supernova, NASA, retrieved 2007-05-25
- Bibcode:2000A&A...362.1046L
- Bibcode:2002ASPC..261..252L
- Bibcode:1997astro.ph..1199D
- ^ Fryer, C. L.; New, K. C. B. (January 24, 2006), "2.1 Collapse scenario", Gravitational Waves from Gravitational Collapse, Max-Planck-Gesellschaft, archived from the original on March 27, 2011, retrieved 2007-06-07
- ^ Staff (August 29, 2006), Stellar Evolution - Cycles of Formation and Destruction, Harvard-Smithsonian Center for Astrophysics, retrieved 2006-08-10
- ^ S2CID 119803426
- ^ Richmond, Michael (April 8, 2005), Will a Nearby Supernova Endanger Life on Earth?, archived from the original (TXT) on March 6, 2007, retrieved 2006-03-30—see section 4.
- S2CID 16653531
- S2CID 17251956
- ^ Staff (September 7, 2006), Introduction to Supernova Remnants, NASA/Goddard, retrieved 2007-05-20
External links
- Davies, Ben (2006), Supernova events, retrieved 2007-06-01
- Richmond, Michael (April 8, 2005), Will a Nearby Supernova Endanger Life on Earth?, The Amateur Sky Survey, archived from the original on March 6, 2007, retrieved 2007-06-07
- Tzekova, Svetlana Yordanova (2004), IK Pegasi (HR 8210), ESO (European Organisation for Astronomical Research in the Southern Hemisphere), archived from the original on 2012-05-20, retrieved 2007-09-30