HD 21699, also known as HR 1063 and V396 Persei, is a star about 580

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from the Earth, in the constellation

Perseus In Greek mythology, Perseus (Help:IPA/English, /ˈpɜːrsiəs, -sjuːs/; Greek language, Greek: Περσεύς, Romanization of Greek, translit. Perseús) is the legendary founder of Mycenae and of the Perseid dynasty. He was, alongside Cadmus ...

. It is a 5th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

star, so it will be faintly visible to the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

of an observer far from

city lights ''City Lights'' is a 1931 American silent romantic comedy film written, produced, directed by, and starring Charlie Chaplin. The story follows the misadventures of Chaplin's Tramp as he falls in love with a blind girl (Virginia Cherrill) and ...

. It is a variable star, whose brightness varies slightly from 5.45 to 5.53 during its 2.4761 day rotation period. 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. HD 21699 is a member of the

Alpha Persei Cluster The Alpha Persei Cluster, also known as Melotte 20 or Collinder 39, is an open cluster of stars in the northern constellation of Perseus. To the naked eye, the cluster consists of several blue-hued spectral type B stars. The most luminous member ...

Properties

In 1967, Robert Garrison noted that the U-B

color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...

of HD 21699 is significantly bluer (more negative) than the

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

assigned to it (B8 III) would suggest. Such a discrepancy suggests that the star is helium-weak. The star's helium-weak nature was confirmed by William Morgan ''et al.'' in 1971. HD 21699 also has an enhanced silicon abundance. 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. In 1974, HD 21699 was assigned the

variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...

V396 Persei. In 1985, John Percy established that the star's variability period is days.

Magnetic field

In 1980, Werner Weiss deduced that HD 21699 has a magnetic field, based on a

heuristic A heuristic (; ), or heuristic technique, is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, ...

relationship between photometric colors and a star's surface magnetic field. In 1984, Douglas Brown ''et al.'' announced that a magnetic field with a strength of about one

kilogauss The gauss, symbol (sometimes Gs), is a unit of measurement of magnetic induction, also known as ''magnetic flux density''. The unit is part of the Gaussian system of units, which inherited it from the older CGS-EMU system. It was named after th ...

had been detected from observations of

Zeeman splitting The Zeeman effect (; ) is the effect of splitting of a spectral line into several components in the presence of a static magnetic field. It is named after the Dutch physicist Pieter Zeeman, who discovered it in 1896 and received a Nobel prize ...

spectral lines A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to ident ...

. That same year, Brown ''et al.'' announced that

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data showed evidence of a

stellar wind A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. D ...

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. 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 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 kilogauss at the poles.

References

{{DEFAULTSORT:HD 21699 Perseus (constellation) 16470 21699 Persei, V396 SX Arietis variables