HD 28843, also known as HR 1441 and DZ Eridani, is a star about 550

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 Eridanus. 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 5.70 to 5.84 during its 1.374 day rotation period. It is a member of the μ Tauri Association, a group of young stars within the larger Cassiopeia-Taurus Structure. In 1969 Mercedes Jaschek ''et al.'' determined that HD 28843 is a

helium-weak star Helium-weak stars are chemically peculiar stars which have a weak helium lines for their spectral type. Their helium lines place them in a later (i.e. cooler) spectral type then their hydrogen lines. List of helium-weak stars This is a non-exte ...

, based on its B-V

color index In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the large ...

being bluer (more negative) than would be expected for a star with its

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 ...

. In 1977, Robert Davis reported that the star has an overabundance of

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

. It is classified as a

chemically peculiar star In astrophysics, chemically peculiar stars (CP stars) are stars with distinctly unusual Metallicity, metal abundances, at least in their surface layers. Classification Chemically peculiar stars are common among hot main-sequence (hydrogen-burning) ...

. Henning Jorgensen ''et al.'' reported that HD 28843 was a "suspected variable star" in 1971. The variability of the star was firmly established in 1977 by Holger Pedersen and Bjarne Thomsen, during a

spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wav ...

and photometric study of helium weak and helium strong stars. They determined its period to be days. In 1978 the star was given 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 ...

DZ Eridani. Ermanno Borra ''et al.'' reported in 1983 the detection of the magnetic field of HD 28843, and estimated its strength to be a few hundred

gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...

. Later data from the

International Ultraviolet Explorer International Ultraviolet Explorer (IUE or Explorer 57, formerly SAS-D), was the first space observatory primarily designed to take ultraviolet (UV) electromagnetic spectrum. The satellite was a collaborative project between NASA, the United K ...

implied a field strength of 250 gauss. M. Farthmann ''et al.'' reported in 1994 that high spectral resolution observations of the 4471 Å

spectral line 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 iden ...

of neutral helium can be explained if HD 28843 has two helium-enriched circular "caps" separated by a region with a dramatically lower helium abundance.

References

{{DEFAULTSORT:HD 28843 Eridanus (constellation) 021192 028843 Eridani, DZ SX Arietis variables B-type giants Helium-weak stars