Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sunspots appear within active regions, usually in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.
Starspots are stellar phenomena, so-named by analogy with sunspots. Spots as small as sunspots have not been detected on other stars, as they would cause undetectably small fluctuations in brightness. The commonly observed starspots are in general much larger than those on the Sun: up to about 30% of the stellar surface may be covered, corresponding to starspots 100 times larger than those on the Sun.
Differential rotation is seen when different parts of a rotating object move with different angular velocities at different latitudes and/or depths of the body and/or in time. This indicates that the object is not rigid. In fluid objects, such as accretion disks, this leads to shearing. Galaxies and protostars usually show differential rotation; examples in the Solar System include the Sun, Jupiter and Saturn.
An RS Canum Venaticorum variable is a type of variable star. The variable type consists of close binary stars having active chromospheres which can cause large stellar spots. These spots are believed to cause variations in their observed luminosity. Systems can exhibit variations on timescales of years due to variation in the spot surface coverage fraction, as well as periodic variations which are, in general, close to the orbital period of the binary system. Some systems exhibit variations in luminosity due to their being eclipsing binaries. Typical brightness fluctuation is around 0.2 magnitudes. They take their name from the star RS Canum Venaticorum.
Zeta Andromedae is a star system in the constellation Andromeda. It is approximately 189 light-years from Earth.
53 Camelopardalis is a binary star system in the northern circumpolar constellation of Camelopardalis, located 290 light years away from the Sun as determined by parallax measurements. It has the variable star designation AX Camelopardalis; 53 Camelopardalis is the Flamsteed designation. This object is dimly visible to the naked eye as a white hued star with a baseline apparent visual magnitude of +6.02. It is a single-lined spectroscopic binary system with an orbital period of 6.63 years and a high eccentricity of 0.718. The "a sin i" value of the primary is 280 Gm (1.9 AU), where a is the semimajor axis and i is the orbital inclination.
Kappa1 Ceti, Latinized from κ1 Ceti, is a variable yellow dwarf star approximately 30 light-years away in the equatorial constellation of Cetus.
A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.
Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface.
In astrophysics, Zeeman–Doppler imaging is a tomographic technique dedicated to the cartography of stellar magnetic fields, as well as surface brightness or spots and temperature distributions.
FK Comae Berenices is a variable star that varies in apparent magnitude between 8.14 and 8.33 over a period of 2.4 days. It is the prototype for the FK Comae Berenices class of variable stars. The variability of FK Com stars may be caused by large, cool spots on the rotating surfaces of the stars. This star is thought to be the result of a recent binary merger, resulting in a high rate of both spin and magnetic activity.
Ap and Bp stars are chemically peculiar stars of spectral types A and B which show overabundances of some metals, such as strontium, chromium, or europium. In addition, larger overabundances are often seen in praseodymium and neodymium. These stars have a much slower rotation than normal for A- and B-type stars, although some exhibit rotation velocities up to about 100 kilometers per second.
IQ Aurigae is a single, variable star in the northern constellation of Auriga. It is visible to the naked eye as a dim, white-hued star with an apparent visual magnitude that fluctuates around 5.38. The star is located at a distance of about 460 light-years from the Sun based on parallax and is drifting further away with a radial velocity of +28.6 km/s.
XX Trianguli, abbreviated XX Tri, is a variable star in the northern constellation of Triangulum, about 1.5° to the WNW of Beta Trianguli along the constellation border with Andromeda. It is classified as a RS Canum Venaticorum variable and ranges in brightness from magnitude 8.1 down to 8.7, which is too faint to be visible to the naked eye. The system is located at a distance of approximately 642 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −26 km/s.
Phi Phoenicis, Latinized from φ Phoenicis, is a binary star system in the southern constellation of Phoenix. It is faintly visible to the naked eye with an apparent visual magnitude of 5.1. Based upon an annual parallax shift of 10.185 mas as seen from Earth, it is located approximately 320 light years from the Sun. It is moving away with a heliocentric radial velocity of 10.4 km/s.
V1794 Cygni is a single variable star in the northern constellation Cygnus. It has the identifier HD 199178 from the Henry Draper Catalogue; V1794 Cygni is its variable star designation. With an apparent visual magnitude of 7.24, it's too dim to be visible with the naked eye but can be seen with binoculars. V1794 is located at a distance of 367 light-years (113 pc) based on parallax measurements, but is drifting closer to the Sun with a radial velocity of −31 km/s. It lies superimposed over a region of faint nebulosity to the west of the North American Nebula.
HD 283750, also known as V833 Tauri, is a K-type main-sequence star 57 light-years away from the Sun. The star is much younger than the Sun's at 1 billion years. HD 283750 is similar to the Sun in its concentration of heavy elements.
LQ Hydrae is a single variable star in the equatorial constellation of Hydra. It is sometimes identified as Gl 355 from the Gliese Catalogue; LQ Hydrae is the variable star designation, which is abbreviated LQ Hya. The brightness of the star ranges from an apparent visual magnitude of 7.79 down to 7.86, which is too faint to be readily visible to the naked eye. Based on parallax measurements, this star is located at a distance of 59.6 light years from the Sun. It is drifting further away with a radial velocity of 7.6 km/s.
LO Pegasi is a single star in the northern constellation of Pegasus that has been the subject of numerous scientific studies. LO Pegasi, abbreviated LO Peg, is the variable star designation. It is too faint to be viewed with the naked eye, having an apparent visual magnitude that ranges from 9.04 down to 9.27. Based on parallax measurements, LO Peg is located at a distance of 79 light years from the Sun. It is a member of the young AB Doradus moving group, and is drifting closer with a radial velocity of −23 km/s.
HR 1099 is a triple star system in the equatorial constellation of Taurus, positioned 11′ to the north of the star 10 Tauri. This system has the variable star designation V711 Tauri, while HR 1099 is the star's identifier from the Bright Star Catalogue. It ranges in brightness from a combined apparent visual magnitude of 5.71 down to 5.94, which is bright enough to be dimly visible to the naked eye. The distance to this system is 96.6 light years based on parallax measurements, but it is drifting closer with a radial velocity of about −15 km/s.
