Star UV Ceti Research Articles

Laboratory astrophysics: Investigation of planetary and astrophysical maser emission

This paper describes a model for cyclotron maser emission applicable to planetary auroral radio emission, the stars UV Ceti and CU Virginus, blazar jets and astrophysical shocks. These emissions may be attributed to energetic electrons moving into convergent magnetic fields that are typically found in association with dipole like planetary magnetospheres or shocks. It is found that magnetic compression leads to the formation of a velocity distribution having a horseshoe shape as a result of conservation of the electron magnetic moment. Under certain plasma conditions where the local electron plasma frequency ω pe is much less than the cyclotron frequency ω ce the distribution is found to be unstable to maser type radiation emission. We have established a laboratory-based facility that has verified many of the details of our original theoretical description and agrees well with numerical simulations. The experiment has demonstrated that the horseshoe distribution produces cyclotron emission at a frequency just below the local electron cyclotron frequency, with polarisation close to X-mode and propagating nearly perpendicularly to the electron beam motion. We discuss recent developments in the theory and simulation of the instability including addressing radiation escape problems, and relate these to the laboratory, space, and astrophysical observations. The experiments showed strong narrow band EM emissions at frequencies just below the cold-plasma cyclotron frequency as predicted by the theory. Measurements of the conversion efficiency, mode and spectral content were in close agreement with the predictions of numerical simulations undertaken using a particle-in-cell code and also with satellite observations confirming the horseshoe maser as an important emission mechanism in geophysical/astrophysical plasmas. In each case we address how the radiation can escape the plasma without suffering strong absorption at the second harmonic layer.

Variation in the flare activity of the star UV Ceti

This is an analysis of the dependence of the flare activity of the well known flare star UV Ceti on the linear distance between the components of this binary system. It is shown that its flaring activity clearly depends on the mutual distance of the components, while this kind of variability is not seen in isolated flare stars.

Search for extrasolar planets around radio‐emitting stars by very long baseline interferometry astrometry

A planet orbiting a radio‐emitting star can be indirectly detected by high‐precision very long baseline interferometry (VLBI) astrometry through the reflex orbit of the star. We have observed the radio‐emitting star σ2 CrB at 15 epochs over 7.5 years by VLBI and fitted its five astrometric parameters to the measured VLBI coordinates. The postfit coordinate residuals have an rms scatter of 0.33 milliarcsecond (mas) when all 15 epochs are used. However, when only the seven epochs at which the star was in its radio quiescent regime are used, the postfit rms drops to 0.20 mas, indicating that the radio centroid is more stable than during outbursts. The systematic errors in these VLBI astrometric observations are estimated to be 0.1 mas only. The larger rms scatter found (0.20 mas) might be caused by either a random jitter of the radio source or a planetary perturbation that is not sampled sufficiently to be recognized by visual inspection of the postfit position residuals. This will be tested by more frequent VLBI observations of this star in the future. Finally, the theoretical (signal‐to‐noise ratio‐limited) astrometric precision of VLBI observations of radio‐emitting stars is ∼10 μarc sec and corresponds to an interesting limit to search for giant planets around stars up to 200 pc and even for an Earth‐like planet but around the nearest radio‐emitting star UV Ceti.

Simultaneous Optical and ROSAT Soft X-Ray Observations of Impulsive Bursts on the Flare Star UV Ceti

Two small flares on the nearby flare star UV Ceti were simultaneously observed with ground-based, highspeed optical multicolor photometry and in soft X-rays using the ROSAT Observatory. Optically, each flare showed a brief (∼12 s duration) impulsive event. The second flare also showed a gradual phase lasting about 5 minutes. Upon closely examining the soft X-ray timing data, it was found that for both flares a soft X-ray burst followed the optical spike by about 30 s. The gradual phase of the second flare was accompanied by a rising and falling X-ray flux, as has been observed in numerous previous flares, but our timing data appear to show soft X-ray bursts continuing during this phase as well. These impulsive X-ray bursts may be the low energy tails of hard X-ray emission from particle beams

Dynamic spectrum of a radio flare on UV Ceti

The dMe flare star UV Ceti (L726-8B) was observed at four frequencies simultaneously in the 1385-1652 MHz band using the Very Large Array. A flare lasting 10 minutes was observed with 6.67 s time resolution 'Dynamic spectrum'-type images in the Stokes parameters I and V show considerable complexity in the frequency-time domain; some features show a positive frequency drift with time, while others are more complex, involving both positive and negative frequency drifts. The positive drift features would be consistent with disturbances traveling downward in the star's corona.

Microwave emission from late-type dwarf stars UV Ceti and YZ Canis Minoris

Microwave emission from late-type dwarf stars UV Ceti and YZ Canis Minoris

Variable mid-latitude X-ray source 3U0042+32

THE faint high latitude X-ray sources are a mixed population of galactic and extragalactic objects. Identified extragalactic X-ray sources include clusters of galaxies, Seyfert and other active galaxies, quasars, and nearby normal galaxies1,2. Identified galactic sources with ∣bII∣ > 20° include several X-ray binaries, two in globular clusters—M15 (ref. 1) and NGC1851 (ref. 3)—the hot white dwarf HZ43 (ref. 4), the dwarf binary AM Her (ref. 5) and the flare star UV Ceti (ref. 6). The high-latitude sources generally lie in fields of low obscuration and density of objects so that the prospects for their identification with optical or other counterparts are relatively good, given position measurements of moderate accuracy. We report here a precise celestial location (1′ error radius) for one such X-ray source, 3U0042+32 (ref. 1), that is situated at mid-galactic latitude (bII ∼ −30°). A study of the error box for this source indicates that it may be a distant galactic binary system similar to Her X-1.

Model for a flare on the star UV Ceti

ON October 11, 1972 a large flare occurred on the star UV Ceti. It was observed simultaneously at photoelectric frequencies and at the radio frequency of 408 MHz (ref. 1). These observations provide enough information to describe a reasonably good model of the outer layers of the star, and of the overall mechanics of the flare.

Large flare on the red dwarf star UV Ceti

ATTEMPTS to measure radio emission occurring simultaneously with the sporadic optical flares on the red dwarf dMe type stars have been hindered by the rarity of large flares. Apart from one case of a flare with an unusually long duration and a peak magnitude of 1.7 (ref. 1) the correlation so far established has been limited to flares of about 1 mag or less2,3. On October 11, 1972 we were able to obtain simultaneous radio and optical recordings of an unusually large flare on the star UV Ceti (L726–8AB), during which the apparent magnitude of the star increased by more than 4.55 mag.

Optical and Radio Observations of the Flare Star UV Ceti in Australasia During September?October 1967

This paper presents the results of a joint radio-optional programme of observations in Australasia on the flare star UV Ceti during an observing period in September October 1967 organized by Commission 27 of the International Astronomical Union.

Observation of a Solar Type Radio Burst from a Flare Star

During observations of the star UV Ceti in Oct. 1963, radioemission was recorded on two frequencies that appears to have a different relationship with the visible flare. A pronounced time lag between the maximum of the optical flare and the maxima of the radioflares, and the time difference between the radio maxima on the two frequencies was compared with frequency drift type solar radio bursts A comparison of the major features of the UV Ceti flare with the mean values for the drift type solar bursts is tabulated. Available evidence both in regard to temporal relationships and spectra suggests that the flare on UV Ceti is analogous to the large solar noise storms or Type I bursts, whereas the other represents a much rarer type of event analogous to frequency drift solar bursts. (P.C.H)