HX Velorum

HX Velorum

HX Velorum is the brightest star in this image of IC 2395.
Observation data
Epoch J2000      Equinox J2000
Constellation Vela
Right ascension 08h 42m 16.19252s[1]
Declination −48° 05′ 56.7481″[1]
Apparent magnitude (V) 5.48 - 5.53[2]
Characteristics
Spectral type B1.5V[3]
U−B color index −0.9[3]
B−V color index −0.17[3]
Variable type ELL[2]
Astrometry
Radial velocity (Rv)27.1±0.7[4] km/s
Proper motion (μ) RA: −3.714±0.128 mas/yr[1]
Dec.: 4.758±0.138 mas/yr[1]
Parallax (π)0.9479±0.1121 mas[1]
Distance2,990±150 ly
(917±45 pc)[4]
Absolute magnitude (MV)−2.32[5]
Orbit[4]
Period (P)1.124480(1) days
Semi-major axis (a)13.6 R☉[a]
Eccentricity (e)0.0
Inclination (i)20.6±0.8°
Semi-amplitude (K1)
(primary)		83.3±0.6 km/s
Semi-amplitude (K2)
(secondary)		131.6±0.6 km/s
Details[4]
Aa
Mass16.30±0.03 M☉
Radius5.66±0.02 R☉
Luminosity29,700±610 L☉
Surface gravity (log g)4.08±0.03 cgs
Temperature25,000±1,300 K
Metallicity = +0.083±0.025
Rotational velocity (v sin i)130±3 km/s
Ab
Mass10.32±0.04 M☉
Radius4.84±0.02 R☉
Luminosity6,170+590
−540 L☉
Surface gravity (log g)4.14±0.04 cgs
Temperature22,000±640 K
Metallicity = +0.083±0.025
Rotational velocity (v sin i)93±6 km/s
Other designations
HD 74455, HR 3462, HIP 42712, SAO 220313[6]
Database references
SIMBADdata

HX Velorum, also known as HR 3462 and HD 74455, is a star in the constellation Vela. It is a 5th magnitude star, so it will be faintly visible to the naked eye of an observer far from city lights. It is a variable star, with its brightness varying slightly from magnitude 5.48 to 5.53 over a period of 1.12 days.[2]

In 1981, Robert Shobbrook announced that HR 3462 is a variable star based on observations made in 1976. He correctly classified it as an ellipsoidal variable, but the period he derived, 0.56205±0.00005 days, was half the actual orbital period because his data did not allow him to distinguish between primary and secondary minima in the light curve.[8] It was given the variable star designation HX Velorum in 1980.[9] In 1983, Christoffel Waelkens and Frédy Rufener published the correct period of variability, 1.124 days.[10]

HX Velorum is a triple star, consisting of a pair (components A, magnitude 5.5, and B, magnitude 8.28) separated by 0.5 arc seconds. Component A is itself a close binary pair (components Aa and Ab).[11][3] The system's brightness variation is caused by the ellipsoidal Aa and Ab components orbiting each other.[3]

HX Velorum is only about 2 arc minutes from the center of IC 2395, so it appears to be within that cluster. However the Gaia DR3 dataset lists the parallax of HX Velorum as 0.9479±0.1121 mas, yielding a distance of 3,400+500
−300 light years, while the distance to IC 2395 has been estimated to be 4,560±200[12] light years, so HX Velorum might be a foreground object rather than a true cluster member. Mark Blackford et al. concluded HX Velorum is a member of the cluster, but that conclusion was based in part on earlier, significantly different distance estimates for both the star and the cluster.[3]

Notes

  1. ^ from a sin i / sin(i), with a sin i = 4.8 R☉ and i = 20.6°.

References

  1. ^ a b c d 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. ^ a b c Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
  3. ^ a b c d e f Blackford, M. G.; Erdem, A.; Sürgit, D.; Özkardeş, B.; Budding, E.; Butland, R.; Demircan, O. (July 2019). "Absolute parameters of young stars: HX Velorum". Monthly Notices of the Royal Astronomical Society. 487 (1): 161–167. Bibcode:2019MNRAS.487..161B. doi:10.1093/mnras/stz1136.
  4. ^ a b c d Cakirli, O.; Hoyman, B.; Ozdarcan, O.; Bilir, S. (2025-09-22). "Selected β Cephei pulsators in eclipsing binaries". arXiv:2509.18277 [astro-ph.EP].
  5. ^ 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. arXiv:2006.14649. Bibcode:2020Ap&SS.365..112M. doi:10.1007/s10509-020-03827-0. S2CID 220128144.
  6. ^ "V* HX Vel -- Double or Multiple Star". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-03-18.
  7. ^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 19 March 2023.
  8. ^ Shobbrook, R. R. (July 1981). "Short period variability of some early B stars". Monthly Notices of the Royal Astronomical Society. 196 (2): 129–134. Bibcode:1981MNRAS.196..129S. doi:10.1093/mnras/196.2.129.
  9. ^ Kholopov, P. N.; Samus, N. N.; Kukarkina, N. P.; Medvedeva, G. I.; Perova, N. B. (February 1981). "65th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 1921: 1. Bibcode:1981IBVS.1921....1K. Retrieved 21 March 2023.
  10. ^ Waelkens, C.; Rufener, F. (May 1983). "An observational study of the influence of close companions on the pulsations of beta Cephei stars". Astronomy and Astrophysics. 121: 45–50. Bibcode:1983A&A...121...45W.
  11. ^ "The Washington Double Star Catalog". The Washington Double Star Catalog. Georgia State University. Retrieved 21 March 2023.
  12. ^ Jaehnig, Karl; Bird, Jonathan; Holley-Bockelmann, Kelly (December 2021). "Membership Lists for 431 Open Clusters in Gaia DR2 Using Extreme Deconvolution Gaussian Mixture Models". The Astrophysical Journal. 923 (1): 129. arXiv:2108.02783. Bibcode:2021ApJ...923..129J. doi:10.3847/1538-4357/ac1d51.
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