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Alnilam

August 29, 2023

Alnilam is the central star of Orion's Belt in the equatorial constellation of Orion. It has the Bayer designation ε Orionis, which is Latinised to Epsilon Orionis and abbreviated Epsilon Ori or ε Ori. This is a massive, blue supergiant star some 2,000 light-years distant. It is estimated to be 832,000 times as luminous as the Sun, and 64.5 times as massive.

Alnilam
Location of Alnilam (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Pronunciation /ælˈnaɪlæm/[1]
Right ascension 05h 36m 12.8s[2]
Declination −01° 12′ 06.9″[2]
Apparent magnitude (V) 1.69[3] (1.64 – 1.74[4])
Characteristics
Spectral type B0 Ia[5]
U−B color index −1.03[3]
B−V color index −0.18[3]
Variable type α Cygni[4]
Astrometry
Radial velocity (Rv)25.9[6] km/s
Proper motion (μ) RA: 1.49[2] mas/yr
Dec.: −1.06[2] mas/yr
Parallax (π)1.65 ± 0.45 mas[2]
Distanceapprox. 2,000 ly
(approx. 600 pc)
Absolute magnitude (MV)−6.89[7]
Details
Mass64.5[8] M☉
Radius42.0[8] R☉
Luminosity832,000[8] L☉
Surface gravity (log g)3.0[8] cgs
Temperature27,000±500[8] K
Rotational velocity (v sin i)40–70[8] km/s
Age5.7[9] Myr
Other designations
Alnilam, ε Ori, 46 Orionis, Orionis, BD−01°969, FK5 210, HD 37128, HIP 26311, HR 1903, SAO 132346, TD1 4963, 參宿二
Database references
SIMBADdata

Observation Edit

 
Alnilam is the middle and brightest of the three stars of Orion's Belt.

It is the 29th-brightest star in the sky (the fourth brightest in Orion) and is a blue supergiant. Together with Mintaka and Alnitak, the three stars make up Orion's Belt, known by many names across many ancient cultures. Alnilam is the middle star.

Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified, for the spectral class B0Ia.[5] Although the spectrum shows variations, particular in the H-alpha absorption lines, this is considered typical for this type of luminous hot supergiant.[8] It is also one of the 58 stars used in celestial navigation. It is at its highest point in the sky around midnight on December 15.

It is slightly variable from magnitude 1.64 to 1.74, with no clear period, and it is classified as an α Cygni variable.[10] Its spectrum also varies, possibly due to unpredictable changes in mass loss from the surface.[8]

Physical characteristics Edit

 
A blue band light curve for Epsilon Orionis, adapted from Krtička and Feldmeier (2018)[11]

Estimates of Alnilam's properties vary. Searle and colleagues, using CMFGEN code to analyse the spectrum in 2008, calculated a luminosity of 537,000 L☉, an effective temperature of 27,500 ± 100 K and a radius of 32.4 ± 0.75 R☉.[7] Analysis of the spectra and age of the members of the Orion OB1 association yields a mass 34.6 times that of the Sun (40.8 M☉ on the main sequence) and an age of 5.7 million years.[9] A more recent detailed analysis of Alnilam across multiple wavelength bands produced very high luminosity, radius, and mass estimates, assuming the distance of 606 parsecs suggested by the Hipparcos new reduction.[2] Adopting the larger parallax from the original Hipparcos reduction gives a distance of 412 parsecs[12] and physical parameters more consistent with earlier publications. The luminosity of 832,000 L☉ and the mass of 64.5 M☉ at 606 parsecs is the highest ever derived for this star.[8]

Alnilam's relatively simple spectrum has made it useful for studying the interstellar medium. Within the next million years, this star may turn into a Wolf-Rayet star and explode as a supernova. It is surrounded by a molecular cloud, NGC 1990, which it illuminates to make a reflection nebula. Its stellar winds may reach up to 2,000 km/s, causing it to lose mass about 20 million times more rapidly than the Sun.[13]

Nomenclature and history Edit

ε Orionis is the star's Bayer designation and 46 Orionis its Flamsteed designation.

The traditional name Alnilam derives from the Arabic النظام al-niẓām 'arrangement/string (of pearls)'. Related spellings are Alnihan and Alnitam:[14] all three variants are evidently mistakes in transliteration or copy errors, the first perhaps due to confusion with النيلم al-nilam 'sapphire'.[15] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] included a table of the first two batches of names approved by the WGSN; which included Alnilam for this star. It is now so entered in the IAU Catalog of Star Names.[18]

Orion's Belt Edit

Main article: Orion's Belt

The three belt stars were collectively known by many names in many cultures. Arabic terms include Al Nijād ('the Belt'), Al Nasak ('the Line'), Al Alkāt ('the Golden Grains or Nuts') and, in modern Arabic, Al Mīzān al H•akk ('the Accurate Scale Beam'). In Chinese mythology, they were also known as the Weighing Beam.[14]

In Chinese, 參宿 (Shēn Sù), meaning Three Stars (asterism), refers to an asterism consisting of Alnilam, Alnitak and Mintaka (Orion's Belt), with Betelgeuse, Bellatrix, Saiph and Rigel later added.[19] Consequently, the Chinese name for Alnilam is 參宿二 (Shēn Sù èr, English: the Second Star of Three Stars).[20] It is one of the western mansions of the White Tiger.

See also Edit

References Edit

  1. ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
  2. ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy & Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  3. ^ a b c Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  4. ^ a b Ruban, E. V.; Alekseeva, G. A.; Arkharov, A. A.; Hagen-Thorn, E. I.; Galkin, V. D.; Nikanorova, I. N.; Novikov, V. V.; Pakhomov, V. P.; Puzakova, T. Yu. (September 2006). "Spectrophotometric observations of variable stars". Astronomy Letters. 32 (9): 604–607. Bibcode:2006AstL...32..604R. doi:10.1134/S1063773706090052. S2CID 121747360.
  5. ^ a b Morgan, W. W.; Keenan, Philip C.; Kellman, Edith (1943). "An Atlas of Stellar Spectra" (PDF). Astrophysical Monographs. 152 (3849): 147. Bibcode:1943Natur.152..147.. doi:10.1038/152147a0. S2CID 4109100.
  6. ^ Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  7. ^ a b Searle, S. C.; Prinja, R. K.; Massa, D.; Ryans, R. (2008). "Quantitative studies of the optical and UV spectra of Galactic early B supergiants. I. Fundamental parameters". Astronomy and Astrophysics. 481 (3): 777–97. arXiv:0801.4289. Bibcode:2008A&A...481..777S. doi:10.1051/0004-6361:20077125. S2CID 1552752.
  8. ^ a b c d e f g h i Puebla, R.E.; Hillier, D.J.; Zsargó, J.; Cohen, D.H.; Leutenegger, M.A. (2015). "X-ray, UV and optical analysis of supergiants: ϵ Ori". Monthly Notices of the Royal Astronomical Society. 456 (3): 2907–2936. arXiv:1511.09365. Bibcode:2016MNRAS.456.2907P. doi:10.1093/mnras/stv2783. S2CID 7887625.
  9. ^ a b Voss, R.; Diehl, R.; Vink, J. S.; Hartmann, D. H. (2010). "Probing the evolving massive star population in Orion with kinematic and radioactive tracers". Astronomy and Astrophysics. 520: 10. arXiv:1005.3827. Bibcode:2010A&A...520A..51V. doi:10.1051/0004-6361/201014408. S2CID 38599952. A51.
  10. ^ "GCVS Query forms". www.sai.msu.su. Retrieved 2019-01-12.
  11. ^ Krtička, J.; Feldmeier, A. (September 2018). "Light variations due to the line-driven wind instability and wind blanketing in O stars" (PDF). Astronomy & Astrophysics. 617: A121. arXiv:1807.09407. Bibcode:2018A&A...617A.121K. doi:10.1051/0004-6361/201731614. S2CID 119388848. Retrieved 11 August 2022.
  12. ^ Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F.; Grenon, M.; Grewing, M.; Van Leeuwen, F.; Van Der Marel, H.; Mignard, F.; Murray, C. A.; Le Poole, R. S.; Schrijver, H.; Turon, C.; Arenou, F.; Froeschlé, M.; Petersen, C. S. (1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49. Bibcode:1997A&A...323L..49P.
  13. ^ Crowther, P. A.; Lennon, D. J.; Walborn, N. R. (January 2006). "Physical parameters and wind properties of galactic early B supergiants". Astronomy & Astrophysics. 446 (1): 279–293. arXiv:astro-ph/0509436. Bibcode:2006A&A...446..279C. doi:10.1051/0004-6361:20053685. S2CID 18815761.
  14. ^ a b Allen, Richard Hinckley (1936). Star-names and their meanings. pp. 314–315.
  15. ^ Knobel, E. B. (September 1909). "The name of epsilon Orionis". The Observatory. 32: 357. Bibcode:1909Obs....32..357K.
  16. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  17. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016.
  18. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016.
  19. ^ (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  20. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 25 日

External links Edit

  • NASA Astronomy Picture of the Day: Image of Alnilam (29 September 2009)

August 29, 2023
alnilam, central, star, orion, belt, equatorial, constellation, orion, bayer, designation, orionis, which, latinised, epsilon, orionis, abbreviated, epsilon, this, massive, blue, supergiant, star, some, light, years, distant, estimated, times, luminous, times,. Alnilam is the central star of Orion s Belt in the equatorial constellation of Orion It has the Bayer designation e Orionis which is Latinised to Epsilon Orionis and abbreviated Epsilon Ori or e Ori This is a massive blue supergiant star some 2 000 light years distant It is estimated to be 832 000 times as luminous as the Sun and 64 5 times as massive AlnilamLocation of Alnilam circled Observation dataEpoch J2000 Equinox J2000Constellation OrionPronunciation ae l ˈ n aɪ l ae m 1 Right ascension 05h 36m 12 8s 2 Declination 01 12 06 9 2 Apparent magnitude V 1 69 3 1 64 1 74 4 CharacteristicsSpectral type B0 Ia 5 U B color index 1 03 3 B V color index 0 18 3 Variable type a Cygni 4 AstrometryRadial velocity Rv 25 9 6 km sProper motion m RA 1 49 2 mas yr Dec 1 06 2 mas yrParallax p 1 65 0 45 mas 2 Distanceapprox 2 000 ly approx 600 pc Absolute magnitude MV 6 89 7 DetailsMass64 5 8 M Radius42 0 8 R Luminosity832 000 8 L Surface gravity log g 3 0 8 cgsTemperature27 000 500 8 KRotational velocity v sin i 40 70 8 km sAge5 7 9 MyrOther designationsAlnilam e Ori 46 Orionis Orionis BD 01 969 FK5 210 HD 37128 HIP 26311 HR 1903 SAO 132346 TD1 4963 參宿二Database referencesSIMBADdata Contents 1 Observation 2 Physical characteristics 3 Nomenclature and history 3 1 Orion s Belt 4 See also 5 References 6 External linksObservation Edit Alnilam is the middle and brightest of the three stars of Orion s Belt It is the 29th brightest star in the sky the fourth brightest in Orion and is a blue supergiant Together with Mintaka and Alnitak the three stars make up Orion s Belt known by many names across many ancient cultures Alnilam is the middle star Since 1943 the spectrum of this star has served as one of the stable anchor points by which other stars are classified for the spectral class B0Ia 5 Although the spectrum shows variations particular in the H alpha absorption lines this is considered typical for this type of luminous hot supergiant 8 It is also one of the 58 stars used in celestial navigation It is at its highest point in the sky around midnight on December 15 It is slightly variable from magnitude 1 64 to 1 74 with no clear period and it is classified as an a Cygni variable 10 Its spectrum also varies possibly due to unpredictable changes in mass loss from the surface 8 Physical characteristics Edit A blue band light curve for Epsilon Orionis adapted from Krticka and Feldmeier 2018 11 Estimates of Alnilam s properties vary Searle and colleagues using CMFGEN code to analyse the spectrum in 2008 calculated a luminosity of 537 000 L an effective temperature of 27 500 100 K and a radius of 32 4 0 75 R 7 Analysis of the spectra and age of the members of the Orion OB1 association yields a mass 34 6 times that of the Sun 40 8 M on the main sequence and an age of 5 7 million years 9 A more recent detailed analysis of Alnilam across multiple wavelength bands produced very high luminosity radius and mass estimates assuming the distance of 606 parsecs suggested by the Hipparcos new reduction 2 Adopting the larger parallax from the original Hipparcos reduction gives a distance of 412 parsecs 12 and physical parameters more consistent with earlier publications The luminosity of 832 000 L and the mass of 64 5 M at 606 parsecs is the highest ever derived for this star 8 Alnilam s relatively simple spectrum has made it useful for studying the interstellar medium Within the next million years this star may turn into a Wolf Rayet star and explode as a supernova It is surrounded by a molecular cloud NGC 1990 which it illuminates to make a reflection nebula Its stellar winds may reach up to 2 000 km s causing it to lose mass about 20 million times more rapidly than the Sun 13 Nomenclature and history Edite Orionis is the star s Bayer designation and 46 Orionis its Flamsteed designation The traditional name Alnilam derives from the Arabic النظام al niẓam arrangement string of pearls Related spellings are Alnihan and Alnitam 14 all three variants are evidently mistakes in transliteration or copy errors the first perhaps due to confusion with النيلم al nilam sapphire 15 In 2016 the International Astronomical Union organized a Working Group on Star Names WGSN 16 to catalog and standardize proper names for stars The WGSN s first bulletin of July 2016 17 included a table of the first two batches of names approved by the WGSN which included Alnilam for this star It is now so entered in the IAU Catalog of Star Names 18 Orion s Belt Edit Main article Orion s Belt The three belt stars were collectively known by many names in many cultures Arabic terms include Al Nijad the Belt Al Nasak the Line Al Alkat the Golden Grains or Nuts and in modern Arabic Al Mizan al H akk the Accurate Scale Beam In Chinese mythology they were also known as the Weighing Beam 14 In Chinese 參宿 Shen Su meaning Three Stars asterism refers to an asterism consisting of Alnilam Alnitak and Mintaka Orion s Belt with Betelgeuse Bellatrix Saiph and Rigel later added 19 Consequently the Chinese name for Alnilam is 參宿二 Shen Su er English the Second Star of Three Stars 20 It is one of the western mansions of the White Tiger See also EditList of most massive starsReferences Edit Kunitzsch Paul Smart Tim 2006 A Dictionary of Modern star Names A Short Guide to 254 Star Names and Their Derivations 2nd rev ed Cambridge Massachusetts Sky Pub ISBN 978 1 931559 44 7 a b c d e f van Leeuwen F November 2007 Validation of the new Hipparcos reduction Astronomy amp Astrophysics 474 2 653 664 arXiv 0708 1752 Bibcode 2007A amp A 474 653V doi 10 1051 0004 6361 20078357 S2CID 18759600 a b c Ducati J R 2002 VizieR Online Data Catalog Catalogue of Stellar Photometry in Johnson s 11 color system CDS ADC Collection of Electronic Catalogues 2237 Bibcode 2002yCat 2237 0D a b Ruban E V Alekseeva G A Arkharov A A Hagen Thorn E I Galkin V D Nikanorova I N Novikov V V Pakhomov V P Puzakova T Yu September 2006 Spectrophotometric observations of variable stars Astronomy Letters 32 9 604 607 Bibcode 2006AstL 32 604R doi 10 1134 S1063773706090052 S2CID 121747360 a b Morgan W W Keenan Philip C Kellman Edith 1943 An Atlas of Stellar Spectra PDF Astrophysical Monographs 152 3849 147 Bibcode 1943Natur 152 147 doi 10 1038 152147a0 S2CID 4109100 Gontcharov G A November 2006 Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system Astronomy Letters 32 11 759 771 arXiv 1606 08053 Bibcode 2006AstL 32 759G doi 10 1134 S1063773706110065 S2CID 119231169 a b Searle S C Prinja R K Massa D Ryans R 2008 Quantitative studies of the optical and UV spectra of Galactic early B supergiants I Fundamental parameters Astronomy and Astrophysics 481 3 777 97 arXiv 0801 4289 Bibcode 2008A amp A 481 777S doi 10 1051 0004 6361 20077125 S2CID 1552752 a b c d e f g h i Puebla R E Hillier D J Zsargo J Cohen D H Leutenegger M A 2015 X ray UV and optical analysis of supergiants ϵ Ori Monthly Notices of the Royal Astronomical Society 456 3 2907 2936 arXiv 1511 09365 Bibcode 2016MNRAS 456 2907P doi 10 1093 mnras stv2783 S2CID 7887625 a b Voss R Diehl R Vink J S Hartmann D H 2010 Probing the evolving massive star population in Orion with kinematic and radioactive tracers Astronomy and Astrophysics 520 10 arXiv 1005 3827 Bibcode 2010A amp A 520A 51V doi 10 1051 0004 6361 201014408 S2CID 38599952 A51 GCVS Query forms www sai msu su Retrieved 2019 01 12 Krticka J Feldmeier A September 2018 Light variations due to the line driven wind instability and wind blanketing in O stars PDF Astronomy amp Astrophysics 617 A121 arXiv 1807 09407 Bibcode 2018A amp A 617A 121K doi 10 1051 0004 6361 201731614 S2CID 119388848 Retrieved 11 August 2022 Perryman M A C Lindegren L Kovalevsky J Hoeg E Bastian U Bernacca P L Creze M Donati F Grenon M Grewing M Van Leeuwen F Van Der Marel H Mignard F Murray C A Le Poole R S Schrijver H Turon C Arenou F Froeschle M Petersen C S 1997 The HIPPARCOS Catalogue Astronomy and Astrophysics 323 L49 Bibcode 1997A amp A 323L 49P Crowther P A Lennon D J Walborn N R January 2006 Physical parameters and wind properties of galactic early B supergiants Astronomy amp Astrophysics 446 1 279 293 arXiv astro ph 0509436 Bibcode 2006A amp A 446 279C doi 10 1051 0004 6361 20053685 S2CID 18815761 a b Allen Richard Hinckley 1936 Star names and their meanings pp 314 315 Knobel E B September 1909 The name of epsilon Orionis The Observatory 32 357 Bibcode 1909Obs 32 357K 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 IAU Catalog of Star Names Retrieved 28 July 2016 in Chinese 中國星座神話 written by 陳久金 Published by 台灣書房出版有限公司 2005 ISBN 978 986 7332 25 7 in Chinese AEEA Activities of Exhibition and Education in Astronomy 天文教育資訊網 2006 年 5 月 25 日External links EditNASA Astronomy Picture of the Day Image of Alnilam 29 September 2009 Portals Astronomy Stars Outer space Retrieved from https en wikipedia org w index php title Alnilam amp oldid 1168591349, 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