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HD 172555 is a white-hot A7V star located relatively close by, 95 light years from Earth in the direction of the constellation Pavo.[5] Spectrographic evidence indicates a relatively recent collision between two planet-sized bodies that destroyed the smaller of the two, which had been at least the size of Earth's moon, and severely damaged the larger one, which was at least the size of Mercury. Evidence of the collision was detected by NASA's Spitzer Space Telescope. [6] [2]

HD 172555

An artist's conception of a body about the size of the Moon slamming into a body the size of Mercury. As the bodies hit each other at speeds exceeding 10 km per second (about 22,400 mph), a huge flash of light is emitted, and their rocky surfaces are vaporized and melted, spraying hot matter everywhere.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pavo
Right ascension 18h 45m 26.9011s
Declination −64° 52 16.533
Apparent magnitude (V) 4.8
Characteristics
Spectral type A5 IV/V,[1] A7V (Hipparcos 2007 Catalogue)
Astrometry
Distance95.34 ± 1.86 ly
(29.23 ± 0.57 pc)
Details
Mass2.0[2] M
Luminosity9.5[2] L
Temperature8,000[1] K
Rotational velocity (v sin i)175[3] km/s
Age~12,[2] ~20 [4] Myr
Other designations
CPD−64° 3948, FK5 3489, GC 25604, HIP 92024, SAO 254358
Database references
SIMBADdata

Giant hypervelocity impact debris


HD172555 was first recognized in the 1980s as being unusually bright in the mid-infrared by the IRAS sky survey. Follow-up, ground-based observations by Schütz et al. [7] and the Spitzer Space Telescope, also in 2004,[8] confirmed the unusually strong nature of the infrared spectral emission from this system, much brighter than what would be emitted normally from the star's surface. As part of the Beta Pictoris moving group, HD172555 is coeval with that more famous system, approximately 20 million years old, and is the same kind of white-hot star as Beta Pic, about twice as massive as our Sun and about 9.5 times as luminous. Comparison with current planetary formation theories, and with the very similar Beta Pic system, suggests that HD172555 is in the early stages of terrestrial (rocky) planet formation.


But what makes HD 172555 special is the presence of a large amount of unusual silicaceous material – amorphous silica and SiO gas – not the usual rocky materials, silicates like olivine and pyroxene, which make up much of the Earth as well. The material in the disk was analyzed in 2009 by Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory in Laurel, MD using the infrared spectrometer on board the Spitzer Space Telescope, and the results of the Deep Impact and STARDUST comet missions.[2] Analysis of the atomic and mineral composition, dust temperature, and dust mass show a massive (about a Moon's mass worth) amount of warm (about 340K) material similar to re-frozen lava (obsidian) and flash-frozen magma (tektite) as well as copious amounts of vaporized rock (silicon monoxide or SiO gas) and rubble (large dark pieces of dust) in a region at 5.8+/-0.6 AU from the HD172555 (inside the frost line of that system). The material had to have been created in a hypervelocity impact between two large bodies; relative velocities at impacts less than 10 km/s would not transform the ubiquitous olivine and pyroxene into silica and SiO gas. Giant impacts at this speed typically destroy the incident body, and melt the entire surface of the impactee.

The implications for the detection of abundant amorphous silica and SiO gas are the following:

Follow-up VISNIR observations of the system published in 2020 have shown that the majority of observed fine dust is composed of very fine grains 1-4 micrometers diameter.[10] as expected from a recent hypervelocity impact.[11]

In 2021, a carbon monoxide ring at ~6 AU separation from the star was also found in the system by ALMA, further reinforcing a giant impact scenario for explaining the system's structure. The large amount of CO gas detected would likely have been sourced from the colliding planets' atmospheres. [12]


See also



References


  1. Wyatt, M. C.; Smith, R.; Su, K. Y. L.; et al. (July 2007), "Steady State Evolution of Debris Disks around A Stars", The Astrophysical Journal, 663 (1): 365–382, arXiv:astro-ph/0703608, Bibcode:2007ApJ...663..365W, doi:10.1086/518404, S2CID 18883195
  2. Lisse, C.M.; Chen, C.H.; Wyatt, M.C.; et al. (2009), "Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the ~12 Myr HD172555 System", Astrophysical Journal, 701 (2): 2019–2032, arXiv:2011.13168, Bibcode:2009ApJ...701.2019L, doi:10.1088/0004-637X/701/2/2019, S2CID 56108044
  3. Song, Inseok; Caillault, J.-P.; Barrado y Navascués, David; et al. (February 2001), "Ages of A-Type Vega-like Stars from uvbyβ Photometry", The Astrophysical Journal, 546 (1): 352–357, arXiv:astro-ph/0010102, Bibcode:2001ApJ...546..352S, doi:10.1086/318269, S2CID 18154947
  4. Mamajek, Eric E.; Bell, Cameron P. M. (2014). "On the age of the beta Pictoris moving group". Monthly Notices of the Royal Astronomical Society. 445 (3): 2169–2180. arXiv:1409.2737. Bibcode:2014MNRAS.445.2169M. doi:10.1093/mnras/stu1894.
  5. When worlds collide Discover magazine, August 10, 2009
  6. Hot Dust Evinces a Violent Planetary Collision Around a Nearby Star Physics Today, October 2009
  7. Schütz, O.; Meeus, G.; Sterzik, M. F. (10 Sep 2004). "Mid-IR observations of circumstellar disks. II. Vega-type stars and a post-main sequence object". Astronomy & Astrophysics. 431: 175–182. arXiv:0904.4278. Bibcode:2005A&A...431..175S. doi:10.1051/0004-6361:20041490.
  8. Chen, C. H.; Sargent, B. A; Bohac, C.; et al. (2006). "Spitzer IRS Spectroscopy of IRAS-discovered Debris Disks". Astrophysical Journal. 166 (1): 351–377. arXiv:astro-ph/0605277. Bibcode:2006ApJS..166..351C. doi:10.1086/505751. S2CID 14042387.
  9. L., Schafer; B., Fegley (2009), "Chemistry of Silicate Atmospheres of Evaporating Super-Earths", Astrophysical Journal, 703 (2): L113–L117, arXiv:0906.1204, Bibcode:2009ApJ...703L.113S, doi:10.1088/0004-637X/703/2/L113, S2CID 28361321
  10. Marshall, Jonathan P.; Cotton, Daniel V.; Scicluna, Peter; Bailey, Jeremy; Kedziora-Chudczer, Lucyna; Bott, Kimberly (2020), "Polarimetric and radiative transfer modelling of HD 172555", Monthly Notices of the Royal Astronomical Society, 499 (4): 5915–5931, arXiv:2011.13168, doi:10.1093/mnras/staa3195
  11. Johnson, B.C.; Lisse, C.M.; Chen, C.H.; et al. (2012), "A Self-Consistent Model Of The Circumstellar Debris Created By A Giant Hypervelocity Impact in the HD172555 System", Astrophysical Journal, 761 (1): 45, arXiv:1210.6258, Bibcode:2012ApJ...761...45J, doi:10.1088/0004-637X/761/1/45, S2CID 119215296
  12. Schneiderman, Tajana; Matrà, Luca; Jackson, Alan P.; Kennedy, Grant M.; Kral, Quentin; Marino, Sebastián; Öberg, Karin I.; Su, Kate Y. L.; Wilner, David J.; Wyatt, Mark C. (2021), "Carbon monoxide gas produced by a giant impact in the inner region of a young system", Nature, 598 (7881): 425–428, arXiv:2110.15377, Bibcode:2021Natur.598..425S, doi:10.1038/s41586-021-03872-x, PMID 34671135, S2CID 239050652



Further reading



На других языках


[de] HD 172555

HD 172555 ist ein Stern der Spektralklasse A5 V, der etwas mehr als 90 Lichtjahre von der Erde in der Richtung des Sternbildes Pfau liegt.[6]
- [en] HD 172555

[es] HD 172555

HD 172555 (HR 7012)[1] es una estrella situada en la constelación del Pavo de magnitud aparente +4,78. Se encuentra a 93 años luz del Sistema Solar y es miembro de la Asociación estelar de Beta Pictoris.[2]

[ru] HD 172555

HD 172555 — звезда в созвездии Павлина. Находится на расстоянии около 95 св. лет от Солнца.



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