25 Sextantis

25 Sextantis (HD 90044; HR 4082; 43 G. Sextantis), or simply 25 Sex, is a star located in the equatorial constellation Sextans; it also bears the variable star designation SS Sextantis (SS Sex). With an average apparent magnitude of 5.97,^[2] 25 Sex is barely visible to the naked eye, even under ideal conditions. Gaia DR3 parallax measurements imply a distance of 345 light-years,^[1] and it is currently drifting away with a heliocentric radial velocity of approximately 23 km/s.^[6] At its current distance, 25 Sex's average brightness is diminished by an interstellar extinction of 0.17 magnitudes and it has an absolute magnitude of +0.86.^[7]

A light curve for SS Sextantis, plotted from TESS data.^[14] The 4.37 day rotation period is shown in red.

25 Sextantis

Location of 25 Sex on the map (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Sextans
Right ascension	10h 23m 26.47823s[1]
Declination	−04° 04′ 26.5182″[1]
Apparent magnitude (V)	5.97[2] (5.94 - 5.98)[3]
Characteristics
Evolutionary stage	main sequence star[4]
Spectral type	B9p Si(CrSr)[5]
U−B color index	−0.17[2]
B−V color index	−0.10[2]
Variable type	α2 CVn[3]
Astrometry
Radial velocity (Rv)	23.0±3.4[6] km/s
Proper motion (μ)	RA: −50.818 mas/yr[1] Dec.: +4.114 mas/yr[1]
Parallax (π)	9.4414 ± 0.0598 mas[1]
Distance	345 ± 2 ly (105.9 ± 0.7 pc)
Absolute magnitude (MV)	+0.86[7]
Details
Mass	2.48±0.07[4] M☉
Radius	2.22±0.11[8] R☉
Luminosity	45.7+13.2 −10.2[9] L☉
Surface gravity (log g)	4.14[10] cgs
Temperature	11,500[11] K
Metallicity [Fe/H]	−0.19[10] dex
Rotational velocity (v sin i)	24±3[9] km/s
Age	309+54 −80[4] Myr
Other designations
25 Sex, 43 G. Sextantis[12], SS Sextantis, BD−03°2911, FK5 388, GC 14268, HD 90044, HIP 50885, HR 4082, SAO 137533, TIC 1712781[13]
Database references
SIMBAD	data

The star was first discovered to be variable in 1980 by French astronomers P. Renson & J. Manfroid. They observed a 4.37 day period for 25 Sex and a flucation of 0.03 magnitudes in optical light.^[15] The next year, it was confirmed to be variable and it was given the variable star designation SS Sextantis.^[16] J. Manfroid and G. Mathys refined the period of 25 Sextantis to be slightly longer than previously measured; the period of SS Sextantis was measured at 4.39 days but with a larger uncertainty.^[17] In 1993, D. A. Bohlender and colleagues measured the magnetic field of the star and found that it varied between 650 and 1,200 gauss, although with some uncertainty about the variation.^[18] Subsequent observations provide a much wider range between 1 and -1,000 gauss.^[19]

25 Sex has a stellar classification of B9pSi(CrSr),^[5] indicating that it is a Bp star with abundance of silicon, chromium, and strontium in its spectrum. It has 2.48 times the mass of the Sun^[4] and 2.22 times the radius of the Sun.^[8] It radiates 45.7 times the luminosity of the Sun^[9] from its photosphere at an effective temperature of roughly 11,500 K,^[11] giving it a bluish-white hue when viewed in the night sky. 25 Sex is metal deficient with an iron abundance 64.6% of the Sun's^[10] and it is estimated to be 309 million years old.^[4] At that age, it has completed 56% of its main sequence lifetime.^[4] Like many chemically peculiar stars it spins modestly—having a projected rotational velocity of 24 km/s.^[9]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR Online Data Catalog. 2237. Bibcode:2002yCat.2237....0D.
3. Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. eISSN 1562-6881. ISSN 1063-7729. S2CID 125853869.
4. Kochukhov, O.; Bagnulo, S. (10 April 2006). "Evolutionary state of magnetic chemically peculiar stars". Astronomy and Astrophysics. 450 (2): 763–775. arXiv:astro-ph/0601461. Bibcode:2006A&A...450..763K. doi:10.1051/0004-6361:20054596. eISSN 1432-0746. ISSN 0004-6361. S2CID 18596834.
5. Cowley, A.; Cowley, C.; Jaschek, M.; Jaschek, C. (April 1969). "A study of the bright stars. I. A catalogue of spectral classifications". The Astronomical Journal. 74: 375. Bibcode:1969AJ.....74..375C. doi:10.1086/110819. ISSN 0004-6256. S2CID 121555804.
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. eISSN 1562-6873. ISSN 1063-7737. S2CID 119231169.
7. Anderson, E.; Francis, Ch. (May 2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331–346. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015. eISSN 1562-6873. ISSN 1063-7737. S2CID 119257644.
8. Kervella, P.; Thévenin, F.; Di Folco, E.; Ségransan, D. (April 8, 2004). "The angular sizes of dwarf stars and subgiants: Surface brightness relations calibrated by interferometry". Astronomy & Astrophysics. 426 (1): 297–307. arXiv:astro-ph/0404180. Bibcode:2004A&A...426..297K. doi:10.1051/0004-6361:20035930. eISSN 1432-0746. ISSN 0004-6361. S2CID 6077801.
9. Netopil, Martin; Paunzen, Ernst; Hümmerich, Stefan; Bernhard, Klaus (17 March 2017). "An investigation of the rotational properties of magnetic chemically peculiar stars". Monthly Notices of the Royal Astronomical Society. 468 (3): 2745–2756. arXiv:1703.05218. Bibcode:2017MNRAS.468.2745N. doi:10.1093/mnras/stx674. eISSN 1365-2966. ISSN 0035-8711. S2CID 119215348.
10. Anders, F.; et al. (August 2019). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia DR2 stars brighter than G = 18". Astronomy & Astrophysics. 628: A94. arXiv:1904.11302. Bibcode:2019A&A...628A..94A. doi:10.1051/0004-6361/201935765. eISSN 1432-0746. ISSN 0004-6361. S2CID 131780028.
11. Floquet, M. (August 1981). "Effective temperature of AP stars". Astronomy and Astrophysics. 101: 176–183. Bibcode:1981A&A...101..176F. ISSN 0004-6361.
12. Gould, Benjamin Apthorp (1878). "Uranometria Argentina : brillantez y posicion de las estrellas fijas, hasta la septima magnitud, comprendidas dentro de cien grados del polo austral : con atlas". Resultados del Observatorio Nacional Argentino. 1. Bibcode:1879RNAO....1.....G.
13. "25 Sextantis". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved February 2, 2024.
14. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 4 July 2024.
15. Manfroid, J.; Renson, P. (July 1980). "Nouvelle Recherche de Periodes D'etoiles Ap Observees a l'ESO-V". Information Bulletin on Variable Stars. 1824: 1. Bibcode:1980IBVS.1824....1M. ISSN 0374-0676.
16. Kholopov, P. N.; Samus', N. N.; Kukarkina, N. P.; Medvedeva, G. I.; Perova, N. B. (November 1981). "66th Name-List of Variable Stars". Information Bulletin on Variable Stars. 2042: 1. Bibcode:1981IBVS.2042....1K. ISSN 0374-0676.
17. Manfroid, J.; Mathys, G. (March 1985). "New period determinations for variable CP stars". Astronomy and Astrophysics Supplement Series. 59: 429–432. Bibcode:1985A&AS...59..429M. ISSN 0365-0138.
18. Bohlender, D. A.; Landstreet, J. D.; Thompson, Ian B. (March 1993). "A study of magnetic fields in AP SI and He weak stars". Astronomy and Astrophysics. 269: 355–376. Bibcode:1993A&A...269..355B. ISSN 0004-6361.
19. Leone, F.; Catanzaro, G. (2001). "Spectropolarimetric measurements of the mean longitudinal magnetic field of chemically peculiar stars: II. Phase relating the magnetic and luminosity variabilities". Astronomy & Astrophysics. 365 (2): 118–127. Bibcode:2001A&A...365..118L. doi:10.1051/0004-6361:20000450. ISSN 0004-6361.