Gamma Equulei, Latinized from γ Equulei, is a

double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...

in the northern

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Equuleus. It is located at a distance of around from Earth and is visible to the naked eye with a slightly variable apparent visual magnitude of around 4.7. The star is drifting closer to the Sun with a

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

of −16.5 km/s.

Properties

The primary component of γ Equulei is a chemically peculiar star with a

stellar classification 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 ...

of . It has a spectrum corresponding to an A9

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star, but with unusual abundances of

strontium Strontium is the chemical element with the symbol Sr and atomic number 38. An alkaline earth metal, strontium is a soft silver-white yellowish metallic element that is highly chemically reactive. The metal forms a dark oxide layer when it is ex ...

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hardne ...

, and

europium Europium is a chemical element with the symbol Eu and atomic number 63. Europium is the most reactive lanthanide by far, having to be stored under an inert fluid to protect it from atmospheric oxygen or moisture. Europium is also the softest lanth ...

. Stars with this type of spectral peculiarity are called

Ap star Ap and Bp stars are chemically peculiar stars (hence the "p") of spectral types A and B which show overabundances of some metals, such as strontium, chromium and europium. In addition, larger overabundances are often seen in praseodymium and neodym ...

s. The abundances of some metals are believed to be due to chemical stratification in the slowly-rotating star, unusual for hot main sequence stars. A fairly wide range of spectral types have been published for γ Equulei, ranging from A5 to F1, some of them also indicating unusual abundances of iron in the spectrum. γ Equulei has particularly sharp absorption lines in its spectrum, a sign of very slow rotation. GammaEquLightCurve

γ Equulei undergoes rapid periodic variations in brightness, which places it among the rapidly oscillating Ap (roAp) stars. The apparent magnitude varies between extremes of +4.58 and +4.77. It shows pulsations in several periods near 12 minutes. The strongest pulsation is at 11.7 minutes; others are found at 11.9, 12.2, and 12.4 minutes. These are identified as a series of even and odd p-mode (pressure-induced) pulsations. The surface

magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...

of γ Equulei undergoes slow variation, ranging from +577 G to –1,101 G. Although only 67 years of magnetic field measurements are available, a period of has been fit to the data. This is thought to be the rotation period of γ Equulei. γ Equulei has a magnitude 8.69 companion at an

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

of 1.26

arcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...

References

External links

www.wolframalpha.com/input/?i=gamma+equuleiwww.alcyone.de/SIT/alpcvn/SIT003258
{{DEFAULTSORT:Gamma Equulei Rapidly oscillating Ap stars Equuleus Equulei, Gamma Durchmusterung objects Equulei, 05 201601 104521 8097