UV UV Ceti stars

- These are K Ve-M Ve stars sometimes displaying flare activity with amplitudes of from several tenths of a magnitude up to 6"' in V. The amplitude is considerably greater in the ultraviolet spectral region. Maximum light is attained in several seconds or dozens of seconds after the beginning of a flare; the star returns to its normal brightness in several minutes or dozens of minutes. UVN (subtype) - Flaring Orion variables of spectral types Ke-Me. These are phenomenologically almost identical to

'-Dorado, the Swordfish, was formed by Johann Bayer in 1603 and appears in his Uranometria (star catalog).

UV Cet variables observed in the solar neighborhood. In addition to being related to nebulae, they are normally characterized by being of earlier spectral type and greater luminosity, with slower development of flares. They are possibly a specific subgroup of INB variables with irregular variations superimposed by flares. GCVS

UV Ceti variables, also known as flare stars, are late-type dwarf stars that undergo a sudden brightening at irregular time intervals. Their spectral type is K or M, but most are M[e] stars, that is they show emission lines in their spectrum. During a flare, the increase in the brightness of the star can be more than 6™0. Interestingly, the amplitude of the flares increases with decreasing wavelength, that is, it is stronger in the U band than in the V band.

The time intervals between consecutive flares can be very different but they are usually between several hours and several days. Of course, exceptions occur. These flares are, in principle, the same kind of phenomenon as solar flares, but with much higher energies involved (Figure 3.6).

Observers making observation of UV Ceti stars should be prepared to conduct lengthy observations with the intent of catching a short flare or perhaps, several flares, over the course of an evening. Since the

Figure 3.6. Artist's conception of a UV Ce type variable star showing a bright Hare erupting on the surface Copyright: Gerry A. Goo<

flares can reach maximum within several seconds, vigilance and patience will be required of the observer. Precise timing as well as precise determination of the brightness of the flare will be expected if your data is to have value.

Observation

-X- Bright stars g Small amplitudes A Mixed periods <3> CCD or PEP

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