HD 21699
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  | |
| 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] |
| Distance | 580 ± 20 ly (177 ± 5 pc) |
| Absolute magnitude (MV) | −0.982[5] |
| Details | |
| Mass | 6.46[5] M☉ |
| Radius | 3.55[5] R☉ |
| Luminosity | 708[5] L☉ |
| Surface gravity (log g) | 4.15[5] cgs |
| Temperature | 16,000[5] K |
| Metallicity [Fe/H] | +0.92[6] dex |
| Rotation | 2.49246±0.00035 d[7] |
| Rotational velocity (v sin i) | 35[8] km/s |
| Age | 12±6[9] Myr |
| Other designations | |
| V396 Per, HR 1063, HIP 16470, SAO 38917[10] | |
| Database references | |
| SIMBAD | data |
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. This 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]
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]
