Iota1 Scorpii

For other stars with this Bayer designation, see ι Scorpii

Iota¹ Scorpii, Latinized from ι¹ Scorpii, is a star in the southern constellation of Scorpius. With an apparent visual magnitude of 3.03,^[2] this star can be seen with the naked eye. It is sometimes called by the proper name Apollyon.^[10] Parallax measurements place it at a distance of roughly 1,930 light-years (590 parsecs) from Earth, with a 9% margin of error.^[1] At the estimated distance, the apparent magnitude is diminished by 0.66 magnitudes due to interveining gas and dust between Earth and the star.^[5]

ι¹ Scorpii

Location of ι1 Scorpii (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
Right ascension	17h 47m 35.08113s[1]
Declination	−40° 07′ 37.1893″[1]
Apparent magnitude (V)	3.03[2]
Characteristics
Spectral type	F2 Ia[3]
U−B color index	+0.26[2]
B−V color index	+0.51[2]
Astrometry
Radial velocity (Rv)	−26.00[4] km/s
Proper motion (μ)	RA: +0.01[1] mas/yr Dec.: −6.24[1] mas/yr
Parallax (π)	1.69 ± 0.15 mas[1]
Distance	1,900 ± 200 ly (590 ± 50 pc)
Absolute magnitude (MV)	−6.51±0.19[5]
Details
Mass	12.11±0.66[6] M☉
Radius	120.3[7] R☉
Luminosity	35,070[6] L☉
Surface gravity (log g)	0.5 to 1.0[8] cgs
Temperature	6,910 or 7,103[8] K
Metallicity [Fe/H]	−0.13 to −0.11[8] dex
Age	17.0 ± 0.5[9] Myr
Other designations
ι1 Sco, CD−40° 11838, FK5 666, HD 161471, HIP 87073, HR 6615, SAO 228420
Database references
SIMBAD	data

This star has a stellar classification of F2 Ia,^[3] with the 'Ia' luminosity class indicating this is a supergiant more luminous than typical supergiants. It has about 12 times the Sun's mass^[11] and is 35,000 times more luminous.^[6] The limb-darkened angular diameter of Iota¹ Scorpii is estimated at 1.896±0.213 mas.^[12] At the estimated distance, this corresponds to a physical radius of 120.3 R_☉.^[7] The effective temperature of the photosphere is 6,910 or 7,103 K,^[8] which gives it a yellow-white hue typical of an F-type star.^[13]

Iota¹ Scorpii has a 10th magnitude companion at an angular separation of 37.5 arcseconds, which, at the distance of this star, gives it a projected separation of 20,000 Astronomical Units (AU). As the relative separation of the two stars along the line of sight to the Earth is not known, however, this distance represents only a minimum value for their separation.^[14]

References

1. van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
2. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
3. Houk, Nancy (1978), "Michigan catalogue of two-dimensional spectral types for the HD stars", Ann Arbor: Dept. Of Astronomy, 2, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H
4. De Bruijne, J. H. J.; Eilers, A.-C. (2012). "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project". Astronomy & Astrophysics. 546: A61. arXiv:1208.3048. Bibcode:2012A&A...546A..61D. doi:10.1051/0004-6361/201219219. S2CID 59451347.
5. R., Neuhäuser; G., Torres; M., Mugrauer; L., Neuhäuser, D.; J., Chapman; D., Luge; Matteo, Cosci (2022). "Colour evolution of Betelgeuse and Antares over two millennia, derived from historical records, as a new constraint on mass and age". Monthly Notices of the Royal Astronomical Society (in Italian). 516 (1). doi:10.1093/mnra (inactive 1 November 2024). hdl:10278/5003332. ISSN 0035-8711.{{cite journal}}: CS1 maint: DOI inactive as of November 2024 (link) CS1 maint: multiple names: authors list (link)
6. Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (2010-04-01). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten. 331 (4): 349. arXiv:1003.2335. Bibcode:2010AN....331..349H. doi:10.1002/asna.200911355. ISSN 0004-6337.
7. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3 ed.), Birkhäuser, ISBN 978-3-540-29692-8. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(590\cdot 1.896\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 240.61\cdot R_{\bigodot }\end{aligned}}}$

8. Luck, R. Earle (2014). "Parameters and Abundances in Luminous Stars". The Astronomical Journal. 147 (6): 137. Bibcode:2014AJ....147..137L. doi:10.1088/0004-6256/147/6/137.
9. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873
10. Moore, Patrick (2010), The Sky at Night, Patrick Moore's Practical Astronomy, Springer, p. 97, ISBN 978-1-4419-6408-3
11. Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten, 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355, S2CID 111387483
12. Cruzalèbes, P.; Petrov, R. G.; Robbe-Dubois, S.; Varga, J.; Burtscher, L.; Allouche, F.; Berio, P.; Hofmann, K. -H.; Hron, J.; Jaffe, W.; Lagarde, S.; Lopez, B.; Matter, A.; Meilland, A.; Meisenheimer, K. (2019-12-01). "A catalogue of stellar diameters and fluxes for mid-infrared interferometry". Monthly Notices of the Royal Astronomical Society. 490 (3): 3158–3176. arXiv:1910.00542. Bibcode:2019MNRAS.490.3158C. doi:10.1093/mnras/stz2803. ISSN 0035-8711.
13. "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
14. Kaler, James B., "Iota-1 Scorpii", Stars, University of Illinois, retrieved 2012-01-12