Astronomy:23 Sextantis

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Short description: Variable Star in Constellation Sextans
23 Sextantis
Location of 23 Sex on the map (circled in red)
Observation data
Epoch J2000.0   Equinox (celestial coordinates)
Constellation Sextans[1]
Right ascension  10h 21m 02.01s[2]
Declination +02° 17′ 23.0″[2]
Apparent magnitude (V) 6.64–6.68[3]
Characteristics
Evolutionary stage subgiant / main sequence star
Spectral type B2IV/V[4]
B−V color index −0.094[5]
Variable type β Cep + SPB candidate[3]
Astrometry
Radial velocity (Rv)5±4.4[4] km/s
Proper motion (μ) RA: −8.900[2] mas/yr
Dec.: −0.447[2] mas/yr
Parallax (π)1.1613 ± 0.0659[2] mas
Distance2,800 ± 200 ly
(860 ± 50 pc)
Absolute magnitude (MV)−2.6[6]
Details
Mass7.3[7] M☉
Radius10.0[8] R☉
Luminosity3,990[7] L☉
Surface gravity (log g)4.03[8] cgs
Temperature17,947[7] K
Rotational velocity (v sin i)96.0[9] km/s
Age33[10] Myr
Other designations
23 Sex, RS Sextantis, HD 89688, HIP 50684, HR 4064, SAO 118248[4]
Database references
SIMBADdata

23 Sextantis (also known as RS Sextantis), is a B-type star located in the equatorial constellation Sextans. The star has been identified as a pulsating variable candidate showing characteristics associated with both Beta Cephei variable and 53 Persei variable stars.[3][4] It lies in the faint equatorial constellation Sextans.[3]

Early observations

Early spectroscopic and photometric observations of the star were reported by Sahade, Struve and A. D. Williams in 1956 after the star had been designated the variable star RS Sextantis in the seventh supplement of the General Catalogue of Variable Stars[11]

The authors described the star as having a spectral type of B3 and an absolute magnitude of about −2.0, and noted that earlier photoelectric observations suggested it might belong to the β Canis Majoris (β Cephei) class with a period of roughly four hours.[11]

Spectroscopic observations were obtained at Mount Wilson Observatory, while photometric measurements were carried out at Lick Observatory. The study also reported mean radial velocities of about +5 to +6 km/s from earlier catalogues, although the available photometric data at the time were considered insufficient to establish the star’s variability firmly.[11]

Stellar characteristics

23 Sextantis is spectroscopically classified as a B-type star.[4] Photometric measurements indicate a small variation in brightness between visual magnitudes 6.64 and 6.68.[3] The star has a B−V color index of −0.094.[5]

Astrometric measurements from the Hipparcos mission give a parallax of 1.30 milliarcseconds.[5] The star also shows a small proper motion across the sky.[5]

Variability

Observations have revealed small variations in brightness with an amplitude of only a few hundredths of a magnitude.[3] The measured photometric period of approximately 0.1353 days (about 3.25 hours) places the star among short-period pulsating variables.[3]

Because its observed properties overlap with those of both β Cephei variables and slowly pulsating B-type stars of the 53 Persei class, 23 Sextantis has been described as a possible candidate for either type of pulsating variable star.[3]

Interstellar medium

Spectroscopic studies of the sightline toward 23 Sextantis indicate the presence of intervening interstellar material associated with a molecular cloud.[12] The stellar spectrum exhibits absorption features corresponding to neutral and ionised metals as well as simple molecules, demonstrating that both atomic and molecular gas are present along the line of sight.[12]

Analysis of the Na I profile reveals several distinct velocity components, including a dominant feature near −1.6 km s−1 and additional components extending from approximately −20 to +20 km s−1, consistent with a multi-component interstellar structure.[12]

The absorbing material is associated with a compact molecular cloud identified as DBB 354 at an estimated distance of about 1 kpc.[12] The cloud appears to be both dense and small in scale, with a characteristic size of roughly 0.08 pc and particle densities of several thousand per cubic centimetre.[12]

Infrared observations link this cloud to an IRAS source, suggesting that it may represent a previously unrecognized high-latitude molecular cloud.[12]

Designations

The star appears in several major stellar catalogues. In the Henry Draper Catalogue it is listed as HD 89688, while the Hipparcos catalogue designation is HIP 50684.[5] Additional identifiers include HR 4064 in the Bright Star Catalogue and SAO 118248.[4] Its Flamsteed designation, 23 Sextantis, reflects its approximate ordering by right ascension within the constellation Sextans.[13]

References

  1. ↑ Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A  XHIP record for this object at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 "RS Sex". American Association of Variable Star Observers. https://www.aavso.org/vsx/index.php?view=detail.top&oid=34984. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 "V* 23 Sex – Pulsating variable star". Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=23+Sex. 
  5. ↑ 5.0 5.1 5.2 5.3 5.4 van Leeuwen, F. (2007). "Hipparcos, the New Reduction". VizieR catalogue service. http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-source=I/311/hip2&HIP=50684. 
  6. ↑ Melnik, A. M.; Dambis, A. K. (2020). "Distance scale for high-luminosity stars in OB associations and in field with Gaia DR2. Spurious systematic motions". Astrophysics and Space Science 365 (7): 112. doi:10.1007/s10509-020-03827-0. Bibcode: 2020Ap&SS.365..112M. 
  7. ↑ 7.0 7.1 7.2 Quintana, Alexis L.; Wright, Nicholas J.; Martínez García, Juan (2025). "A census of OB stars within 1 KPC and the star formation and core collapse supernova rates of the Milky Way". Monthly Notices of the Royal Astronomical Society 538 (3): 1367. doi:10.1093/mnras/staf083. Bibcode: 2025MNRAS.538.1367Q. 
  8. ↑ 8.0 8.1 Yu, Jie; Khanna, Shourya; Themessl, Nathalie; Hekker, Saskia; Dréau, Guillaume; Gizon, Laurent; Bi, Shaolan (2023). "Revised Extinctions and Radii for 1.5 Million Stars Observed by APOGEE, GALAH, and RAVE". The Astrophysical Journal Supplement Series 264 (2): 41. doi:10.3847/1538-4365/acabc8. Bibcode: 2023ApJS..264...41Y. 
  9. ↑ Abdurro'uf et al. (2022). "The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data". The Astrophysical Journal Supplement Series 259 (2): 35. doi:10.3847/1538-4365/ac4414. Bibcode: 2022ApJS..259...35A. 
  10. ↑ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 KPC from the Sun". Monthly Notices of the Royal Astronomical Society 410 (1): 190. doi:10.1111/j.1365-2966.2010.17434.x. Bibcode: 2011MNRAS.410..190T. 
  11. ↑ 11.0 11.1 11.2 Sahade, J.; Struve, O.; Williams, A. D. (1956). "Spectroscopic and Photometric Observations of 23 Sextantis". Publications of the Astronomical Society of the Pacific 68 (402): 266. doi:10.1086/126931. Bibcode: 1956PASP...68..266S. 
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 Penprase, B. E. (1993). "Photometric and Spectroscopic Analysis of High Galactic Latitude Molecular Clouds. II. High-Resolution Spectroscopic Observations of Na I, Ca II, Ca I, CH, and CH+". The Astrophysical Journal Supplement Series 88: 433–458. doi:10.1086/191829. Bibcode: 1993ApJS...88..433P. 
  13. ↑ "23 Sextantis". https://theskylive.com/sky/stars/23-sextantis-star. 



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