HD 21699

HD 21699, also known as HR 1063 and V396 Persei, is a star about 580 light years from the Earth, in the constellation Perseus.[1] 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, whose brightness varies slightly from 5.45 to 5.53 during its 2.4761 day rotation period.[2] It has a remarkable dipole magnetic field which is displaced from the star's center by 0.4 stellar radii, the poles of which appear close to each other on the stellar surface.[11] HD 21699 is a member of the Alpha Persei Cluster.[12]

HD 21699
Location of HD 21699 (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Perseus
Right ascension 03h 32m 08.60842s[1]
Declination +48° 01′ 24.5285″[1]
Apparent magnitude (V) 5.45 - 5.53[2]
Characteristics
Spectral type B8 III[3]
U−B color index −0.61[3]
B−V color index −0.17[3]
Variable type SX Arietis[2]
Astrometry
Radial velocity (Rv)2.6±0.9[4] km/s
Proper motion (μ) RA: 18.314±0.149[1] mas/yr
Dec.: −28.723±0.144[1] mas/yr
Parallax (π)5.6378 ± 0.1539 mas[1]
Distance580 ± 20 ly
(177 ± 5 pc)
Absolute magnitude (MV)−0.982[5]
Details
Mass6.46[5] M☉
Radius3.55[5] R☉
Luminosity708[5] L☉
Surface gravity (log g)4.15[5] cgs
Temperature16,000[5] K
Metallicity [Fe/H]+0.92[6] dex
Rotation2.49246±0.00035 d[7]
Rotational velocity (v sin i)35[8] km/s
Age12±6[9] Myr
Other designations
V396 Per, HR 1063, HIP 16470, SAO 38917[10]
Database references
SIMBADdata

Properties
A light curve for V396 Persei, plotted from TESS data[13]

In 1967, Robert Garrison noted that the U-B color of HD 21699 is significantly bluer (more negative) than the spectral type assigned to it (B8 III) would suggest.[14] Such a discrepancy suggests that the star is helium-weak.[15] The star's helium-weak nature was confirmed by William Morgan et al. in 1971.[3] HD 21699 also has an enhanced silicon abundance.[16]

John Winzer observed HD 21699 during 1971 - 1972 and discovered that it is a variable star. He found it varied by 0.03, 0.04 and 0.05 magnitudes in the visible, blue and ultraviolet photometric bands, respectively. Though he found that the brightness varied periodically, he was unable to unambiguously assign a period to it. It was the first helium-weak star to be found to vary in brightness periodically.[15] In 1974, HD 21699 was assigned the variable star designation V396 Persei.[17] In 1985, John Percy established that the star's variability period is 2.49246±0.00035 days.[7]

Magnetic field

In 1980, Werner Weiss deduced that HD 21699 has a magnetic field, based on a heuristic relationship between photometric colors and a star's surface magnetic field.[18] In 1984, Douglas Brown et al. announced that a magnetic field with a strength of about one kilogauss had been detected from observations of Zeeman splitting of spectral lines.[19] That same year, Brown et al. announced that International Ultraviolet Explorer data showed evidence of a stellar wind flowing from HD 21699, which was constrained to flow from the region of the star's magnetic poles. This "plume" of gas sweeps across the line of sight for an observer on the Earth, as the star rotates.[20]

In 2007, Yu. V. Glagolevskij and G. A. Chuntonov examined the extensive data which had been collected for HD 21699, and concluded that the star has a very peculiar magnetic field. In their model, the field is a dipole, but it is displaced by 0.4±0.1 stellar radii from the star's center. If the dipole were centered within the star, one would expect that the surface magnetic poles would be separated by 180° along a great circle which contained both poles. However, because the dipole is displaced from the star's center, the poles are separated by only 55°. Furthermore, the two magnetic poles lie almost exactly on the star's equator. Their estimate for the field's strength is 21.8±0.2 kilogauss at the poles.[11]

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. 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. Morgan, W. W.; Hiltner, W. A.; Garrison, R. F. (April 1971). "The H-R diagram of the Alpha Persei cluster". Astronomical Journal. 76: 242–245. Bibcode:1971AJ.....76..242M. doi:10.1086/111111. Retrieved 5 March 2023.
  4. 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. Retrieved 6 March 2023.
  5. Glagolevskij, Yu. V.; Leushin, V. V; Chuntonov, G. A.; Shulyak, D. (January 2006). "The atmospheres of helium-deficient Bp stars". Astronomy Letters. 32 (1): 54–68. Bibcode:2006AstL...32...54G. doi:10.1134/S1063773706010087. S2CID 120225963. Retrieved 5 March 2023.
  6. Ghazaryan, S.; et al. (August 2019). "Statistical analysis of roAp, He-weak, and He-rich stars". Monthly Notices of the Royal Astronomical Society. 487 (4): 5922–5931. arXiv:1906.06984. Bibcode:2019MNRAS.487.5922G. doi:10.1093/mnras/stz1678. S2CID 189928323.
  7. Percy, J. R. (September 1985). "The period of the helium-weak variable star HR 1063". Publications of the Astronomical Society of the Pacific. 97: 856–857. Bibcode:1985PASP...97..856P. doi:10.1086/131615. S2CID 120356941. Retrieved 5 March 2023.
  8. Freire Ferrero, R.; et al. (February 2012). "High Ionization Species in the Nearby Interstellar Medium from an Exhaustive Analysis of the IUE INES Database". The Astronomical Journal. 143 (2): 38. Bibcode:2012AJ....143...28F. doi:10.1088/0004-6256/143/2/28. 28.
  9. Wolff, Sidney C. (December 1990). "Luminosities, Masses, and Ages of B-Type Stars". Astronomical Journal. 100: 1994. Bibcode:1990AJ....100.1994W. doi:10.1086/115654. Retrieved 6 March 2023.
  10. "HD 21699 -- Rotating Variable". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-03-03.
  11. Glagolevskij, Yu. V.; Chuntonov, G. A. (July 2007). "Composite model for the magnetic field of HD 21699". Astrophysics. 50 (3): 362–371. Bibcode:2007Ap.....50..362G. doi:10.1007/s10511-007-0035-5. S2CID 120563093. Retrieved 5 March 2023.
  12. Molnar, M. R.; Stephens, T. C.; Mallama, A. D. (July 1978). "OAO 2 observations of the Alpha Persei cluster". Astrophysical Journal. 223: 185–191. Bibcode:1978ApJ...223..185M. doi:10.1086/156249. Retrieved 5 March 2023.
  13. "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 4 March 2023.
  14. Garrison, R. F. (March 1967). "Some Characteristics of the B and A Stars in the Upper Scorpius Complex". Astrophysical Journal. 147: 1003–1016. Bibcode:1967ApJ...147.1003G. doi:10.1086/149090. S2CID 121615150. Retrieved 5 March 2023.
  15. Winzer, J. E. (January 1974). "Photometric variations of the helium-weak star HR 1063". Astronomical Journal. 79: 45–46. Bibcode:1974AJ.....79...45W. doi:10.1086/111528. Retrieved 5 March 2023.
  16. Molnar, Michael R. (July 1972). "The Helium-Weak Stars". Astrophysical Journal. 175: 453. Bibcode:1972ApJ...175..453M. doi:10.1086/151570. Retrieved 5 March 2023.
  17. Kukarkin, B. V.; Kholopov, P. N.; Kukarkina, N. P.; Perova, N. B. (January 1975). "60th Name-List of Variable Stars" (PDF). Information Bulletin on Variable Stars. 961. Bibcode:1975IBVS..961....1K. Retrieved 5 March 2023.
  18. Weiss, W. W. (September 1980). "Is There a Magnetic Field - Period Relation for the Hotter Ap Stars?" (PDF). Information Bulletin on Variable Stars. 1841. Bibcode:1980IBVS.1841....1W. Retrieved 6 March 2023.
  19. Brown, D. N.; Shore, S. N.; Barker, P. K.; Sonneborn, G. (December 1984). "Magnetospheres and winds in the helium weak stars: observations of C IV in upper main sequence CP stars". NASA Conference Publication. 2349: 487–490. Bibcode:1984NASCP2349..487B. Retrieved 6 March 2023.
  20. Brown, D. N.; Shore, S. N.; Bolton, C. T.; Hulbert, S. J.; Sonneborn, G. (December 1984). "Ultraviolet and optical spectroscopy and polarimetry of the helium weak star HD 21699: evidence for a magnetically controlled stellar wind". NASA Conference Publication. 2349. Bibcode:1984NASCP2349..483B. Retrieved 6 March 2023.
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