Canis Minoris Research Articles

Spin-resolved optical CCD spectroscopy and photometry of BG Canis Minoris

We report spin-resolved optical photometry and spectroscopy of the intermediate polar BG Canis Minoris. New 913-s pulsation ephemerides are derived. We find that a cubic fit provides a better description of the O-C values than the hitherto assumed quadratic ephemeris at a confidence level of 97.3 per cent. From the spectroscopy, we find that the violet-to-red (V/R) ratio of the emission lines varies with the 913-s period but not at the alternative period of 847 s detected in the X-ray band. This suggests that 913 s is the most probable spin period of the white dwarf. However, we do find evidence that the emission line intensities and equivalent widths are modulated at 847 s

RAPID OSCILLATIONS IN CATACLYSMIC VARIABLES. IX. BG CANIS MINORIS (=3A 0729+103)

ABSTRACT We report the results of a ten-year photometric program on BG Canis Minoris, a novalike variable distinguished by the presence of a strictly coherent 913 second wave in its light curve. We present long-term ephermides for the orbital clock, which manifests itself through a 3.2 hour light modulation, and the 913 s clock. The former is found to be quite stable, and may originate from partial obscuration of the white dwarf by a bloated bright spot at the outer edge of the disk. The rapid oscillation shows a period decreasing on a timescale of 4 X 105 years, consistent with the idea that a magnetic white dwarf is spinning up under the torques exerted by accreting gas. The P measurement requires M > 7 X 10-10 solar mass/yr; combining the constraints from P and the polarization, we estimate a magnetosphere radius about equal to the corotation radius, with M ~ 10-9 solar mass/yr. Power spectra of the light curves reveal evidence for other high-frequency signals which seem to be related to the 913 s pulse. Features that may be stable in period, though not in amplitude, are found at 1073 ± 8 and 1977 ± 10 s. The former probably arises from reprocessing of the pulsed light in structures which are in prograde orbit around the white dwarf. We find no particularly simple way to understand the other peak, but there is a substantial hint that the true rotation period of the white dwarf is 1827 s, not 913 s.

The magnetic field of the intermediate polar BG Canis Minoris

Observations of the intermediate polar BG CMi show that the circular polarization increases rapidly from the optical toward IR wavelengths. These observations can be understood as the emission from a large magnetic polar cap consisting of hot plasma heated to an accretion shock temperature of 10 keV and an underlying photosphere at 0.01 keV. Reasonable fits to the polarization observations can be obtained with polar fields in the range B = 2-10 MG. Constraints from X-ray observations suggest that the field is likely to be around 4 MG. The polarization in the optical band is mainly due to free-free emission in a magnetic field, while the polarization in the J and H bands is mainly due to cyclotron emission. Dilution by the companion star may allow B up to about 6 MG. Implications of these results for the understanding of the evolution of magnetic cataclysmic variables are discussed. 29 refs.

Detection of the dMe flare star YZ Canis Minoris simultaneously at 20 and 90 centimeter wavelengths

Aperture-synthesis observations of YZ CMi at 20 and 90 cm are reported. The data are presented in extensive graphs and contour maps and discussed in detail. From the 90-cm brightness temperature of about 1000 K it is inferred that the emission is coherent. 19 references.

Narrow-band, slowly varying decimetric radiation from the dwarf M flare star YZ Canis Minoris. II

view Abstract Citations (21) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Narrow-Band, Slowly Varying Decimetric Radiation from the Dwarf M Flare Star YZ Canis Minoris. II. Lang, Kenneth R. ; Willson, Robert F. Abstract The VLA has been used in the spectral-line mode to obtain the frequency spectra of the radiation from the dwarf M star YZ Canis Minoris at frequencies near 1465 MHz. The authors present observations of frequency structure with narrow bandwidths Δν ≈ 30 MHz that persist over 10 minutes of time without evidence for a drift. The fractional bandwidth Δν/ν ≈ 0.02. It is shown that radiation over other 10 minute intervals appears to be broad band with Δν ≥ 50 MHz, but these spectra could represent the time average of many rapid, narrow-band events. The authors interpret the narrow-band, 30 MHz structure in terms of electron-cyclotron maser emission. They also draw attention to certain solar bursts that may require a similar coherent radiation mechanism. Publication: The Astrophysical Journal Pub Date: March 1988 DOI: 10.1086/166091 Bibcode: 1988ApJ...326..300L Keywords: Dwarf Stars; Flare Stars; M Stars; Radio Emission; Stellar Radiation; Circular Polarization; Masers; Narrowband; Wave Generation; Astrophysics full text sources ADS | data products SIMBAD (3)

Flare stars and solar bursts: High resolution in time and frequency

Coronal loops on the Sun and nearby stars are investigated using observations at 20 cm wavelength with high resolution in time and frequency. Observations of the dwarf M star AD Leonis with high time resolution using the Arecibo Observatory have resulted in the discovery of a quasi-periodic train of circularly polarized spikes with a mean periodicity of 32 ± 5 ms and a total duration of 150 ms. The individual spikes had rise times of ≤ 5 ms, leading to an upper limit to the linear size L ≤ 1.5 × 108 cm for the spike emitter. This size is only 0.005 of the estimated radius of AD Leonis. Provided that the emitter is symmetric, it has a brightness temperature of T B ≥ 1016 K, suggesting a coherent burst mechanism such as an electron-cyclotron maser. Coronal oscillations might modulate the maser output, producing the quasi-periodic spikes. Observations at closely spaced wavelengths, or high frequency resolution, using the Very Large Array have revealed narrow-band structure Δv/v ≤ 0.01) in solar bursts and in the slowly-varying radiation of the dwarf M star YZ Canis Minoris. The narrow-band emission cannot be explained by continuum emission processes, but it might be attributed to electron—cyclotron maser radiation. Maser action at the second or first harmonic of the gyrofrequency implies magnetic field strengths of 250 and 500 G, respectively. Thus, observations with high resolution in time and frequency suggest coherent processes in the coronae of the Sun and dwarf M stars. The scientific potential of these discoveries may be best fulfilled by the construction of a solar-stellar synthesis radiotelescope.

Narrow-band, slowly varying decimetric radiation from the dwarf M flare star YZ Canis Minoris

Observations of slowly varying radiation from the dwarf M star YZ Canis Minoris with a maximum flux density of 20 mJy and narrow-band frequency structure at frequencies near 1465 MHz are presented. Possible explanations for this radiation are examined. Thermal gyroresonant radiation would require impossibly large coronal loops and magnetic field strengths. The narrow-band structure cannot be explained by continuum emission processes such as thermal bremsstrahlung, thermal gyroresonant radiation, or nonthermal gyrosynchrotron radiation. Coherent burst mechanisms seem to be required.

Radio wavelength observations of magnetic fields on active dwarf M, RS CVn and magnetic stars

The dwarf M stars YZ Canis Minoris and AD Leonis exhibit narrow-band, slowly varying (hours) microwave emission that cannot be explained by conventional thermal radiation mechanisms. The dwarf M stars AD Leonis and Wolf 424 emit rapid spikes whose high brightness temperatures similarly require a nonthermal radiation process. We attribute them to coherent mechanisms such as an electron-cyclotron maser or coherent plasma radiation. If the electron-cyclotron maser emits at the second or third harmonic of the gyrofrequency, the coronal magnetic field strength H = 250 G or 167 G and constraints on the plasma frequency imply an electron density of N e = 6 × 10 9 cm −3. Coherent plasma radiation requires similar values of electron density but much weaker magnetic fields. Radio spikes from AD Leonis and Wolf 424 have rise times τ R ⩽ 5 ms, indicating a linear size of L ⩽ 1.5 × 10 8 cm, or less than 0.005 of the stellar radius. Although Ap magnetic stars have strong dipole magnetic fields, they exhibit no detectable gyroresonant radiation, suggesting that these stars do not have hot, dense coronae. The binary RS CVn star UX Arietis exhibits variable emission at 6 cm wavelength on time scales ranging from 30 s to more than one hour. The shortest variation implies a linear size much less than that of the halo observed by VLBI techniques, and most probably sizes smaller than those of the component stars. The observed variations might be due to absorption by a thermal plasma located between the stars.

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

ZZ CANIS MINORIS AS A SYMBIOTIC STAR.

ABSTRACT The H-aplha and Na I D-line regions of the M6 giant star ZZ Canis Minoris (ZZ CMi) were observed with the Kitt Peak coude feed telescope and a CCD detector. It is shown that ZZ CMi has similar spectroscopic and photoproperties to the symbiotic star EG And. The data are used to argue for the classification of ZZ CMi as a symbiotic star despite its current listing in the General Catalog of Variable Stars (GCVS) as a semi-regular variable. The infrared magnitudes of ZZ CMi and the known symbiotic stars are compared in a table.

The response of chromospheric emission lines to flares on YZ Canis Minoris

view Abstract Citations (20) References (52) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The response of chromospheric emission lines to flares on YZ Canis Minoris. Worden, S. P. ; Schneeberger, T. J. ; Giampapa, M. S. ; Deluca, E. E. ; Cram, L. E. Abstract Six flares of the dMe star YZ CMi have been observed with simultaneous photometry and high-dispersion, time-resolved spectroscopy.The spectra have temporal resolutions of 3 minutes with spectral resolutions of 0.24 Å. The largest observed flare had a U band amplitude of 1.5 mag. Hα and Hβ line profiles did not broaden during any of the observed flares, although the line center intensity increased by over a factor of 2 during some flares. After the initial increase in intensity, the emission line strength decreases but remains at enhanced levels for hours following U band flares. The Hα flare luminosity and total energy are compared to corresponding properties of solar flares. Publication: The Astrophysical Journal Pub Date: January 1984 DOI: 10.1086/161611 Bibcode: 1984ApJ...276..270W Keywords: Balmer Series; Chromosphere; Emission Spectra; Flare Stars; Stellar Flares; Stellar Spectra; Continuous Spectra; H Alpha Line; Solar Flares; Spectral Line Width; Stellar Luminosity; Ubv Spectra; Astrophysics full text sources ADS | data products SIMBAD (6)

Coordinated X-ray, optical, and radio observations of flaring activity on YZ Canis Minoris

view Abstract Citations (103) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Coordinated X-ray, optical and radio observations of flaring activityon YZ Canis Minoris. Kahler, S. ; Golub, L. ; Harnden, F. R. ; Liller, W. ; Seward, F. ; Vaiana, G. ; Lovell, B. ; Davis, R. J. ; Spencer, R. E. ; Whitehouse, D. R. ; Feldman, P. A. ; Viner, M. R. ; Leslie, B. ; Kahn, S. M. ; Mason, K. O. ; Davis, M. M. ; Crannell, C. J. ; Hobbs, R. W. ; Schneeberger, T. J. ; Worden, S. P. ; Schommer, R. A. ; Vogt, S. S. ; Pettersen, B. R. ; Coleman, G. D. ; Karpen, J. T. ; Giampapa, M. S. ; Hege, E. K. ; Pazzani, V. ; Rodono, M. ; Romeo, G. ; Chugainov, P. F. Abstract The YZ Canis Minoris (Gliese 285), a late-type dwarf star with Balmer emission (dM4.5e), is a member of the UV Ceti class of flare stars. Obtaining good X-ray observations of a dMe star flare is important not only for understanding the physics of flares but also for testing current ideas regarding the similarity between stellar and solar flares. The Einstein X-ray Observatory has made it possible to conduct X-ray observations of dMe stars with unprecedented sensitivity. A description is presented of the results of a program of ground-based optical and radio observations of YZ CMi coordinated with those of the Einstein Observatory. The observations were carried out as part of a coordinated program on October 25, 26, and 27, 1979, when YZ CMi was on the dawn side of the earth. Comprehensive observational data were obtained of an event detected in all three wavelength regions on October 25, 1979. Publication: The Astrophysical Journal Pub Date: January 1982 DOI: 10.1086/159551 Bibcode: 1982ApJ...252..239K Keywords: Dwarf Stars; Flare Stars; Late Stars; Radio Spectra; Stellar Flares; Stellar Spectrophotometry; X Ray Sources; Emission Spectra; Light (Visible Radiation); M Stars; Periodic Variations; Radiant Flux Density; Stellar Spectra; Stellar Temperature; Ultraviolet Spectra; Astronomy full text sources ADS | data products SIMBAD (4)

A spectroscopic flare of YZ Canis Minoris

Observations of a spectroscopic flare in YZ Canis Minoris are reported. Emission lines of Mg I, Fe I, and Fe II were found in the spectral region 5090-5350 A. The intensity of the emission lines declined only slightly over a span of 2 hours. No significant radial-velocity difference was found between the emission and absorption lines. The turbulent velocity dispersion was less than 20 km/s. Upper limits of 7500 and 15,000 gauss can be placed on the longitudinal and transverse magnetic fields. The equal intensities of the Mg I b lines imply that the emitting region was optically thick. The intensity ratios did not change with time.

Coordinated X-ray, optical, and radio observations of YZ Canis Minoris

We report coordinated X-ray, optical, and radio observations of the flare star YZ CMi, including the first occasion on which such a star has been monitored in all three spectral regions simultaneously. Thirty-one minor optical flares and 11 radio events were recorded. No major optical flares greater than 3 magnitudes were observed during the program. Although no flare- related X-ray emission was observed, the measured upper limits in this band enable meaningful comparisons with published flare-star models. Three of the five models predicting the relative X-ray to optical or radio flare luminosities are in serious disagreement with the observations. For the largest optical flare with coincident X-ray co1verage, the 3 a upper limit on X-ray emission in the 0.15-0.8 keV band is about 9 x 1028 ergs 5 - , corresponding to a ratio of X-ray to B-band luminosity of <0.3. Based on the present results, the fraction of the galactic component of the diffuse soft X-ray background contributed by UV Ceti-type flare stars is <9 x H, where H is the mean density of interstellar hydrogen within a few hundred parsecs of the Sun. Subject headings: radio sources: variable - stars: flare - stars: individual - X-rays: bursts

Simultaneous radio and optical observations of UV Ceti-type flare stars

The UV Ceti-type stars, YZ Canis Minoris, AD Leonis, and Wolf 424 AB, were monitored for 57.8 hours from January 15 to February 22, 1974, using the 1000-foot (305-m) radio telescope at Arecibo, Puerto Rico, and the 91-cm or 76-cm reflector at McDonald Observatory. Radio observations were made at frequencies of 430, 318, and 196 MHz, and optical monitoring was done in the Johnson U or B band, the Stromgren u band, or white light. During the period of simultaneous observations, 62 optical flares were detected. A total of 13 RF flares were independently identified, of which 10 reached maximum flux within 10 min of the peak time of an optical flare. Using times of optical-flare events as reference data, an additional 15 cases of radio enhancements associated with optical flares are identified. The most probable delay interval between the optical-flare maximum and 318-MHz radio peak was found to be 0 to 5 min, with the optical flare occurring first. Aside from this statistical delay of peak occurrence and a general tendency for radio and optical flares to be associated, no systematic correlations of optical and radio amplitudes or morphology were found. The possible consequences of the radio emission's being due to a coherent process are discussed.

Short-Duration Radio Flares of UV Ceti Stars

view Abstract Citations (32) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Short-Duration Radio Flares of UV Ceti Stars Spangler, Steven R. ; Shawhan, Stanley D. ; Rankin, John M. Abstract The UV Ceti-type stars YZ Canis Minoris, AD Leonis, Woll 424, and V371 Orionis were monitored with the Arecibo radio telescope at meter wavelengths. A total of 26 flares were recorded on YZ CMi, AD Leo, and Wolf 424. The observed flares had shorter durations and smaller amplitudes than those previously reported in the literature. Rates of radio-flare detection are similar to those found optically. Subject headings: flare stars - radio sources, variable Publication: The Astrophysical Journal Pub Date: June 1974 DOI: 10.1086/181523 Bibcode: 1974ApJ...190L.129S full text sources ADS | data products SIMBAD (6)

Large Flare on YZ Canis Minoris

Visual and photoelectric recordings of the outburst from the star YZ Canis Minoris, reported from the Cerro Tololo Interamerican Observatory.

Observation of Prolonged Radio Emission from a Red Dwarf Star

A remarkable outburst from a red dwarf flare star (YZ Canis Minoris) has been observed by radio and optical telescopes. This article is an account of the radio observations, and is followed by articles on the optical measurements, and on the coronal structure of YZ Canis Minoris.

Outer Layers of the Red Dwarf Star YZ CMi

A discussion of the structure of the corona around YZ Canis Minoris, based on the observations by Lovell and Kunkel.

FLARES OF V 1216 SAGITTARII

The flare star V 1216 Sagittarii (Ross 154, a = lSMT^, 8 = 23°52' (1966), vis. mag. 10.5, dM4.5e) was observed photoelectrically at the Boyden Observatory for 114 hours from June 26 until July 26, 1966. The purpose of this series of observations was, first, to provide optical coverage for radio observations at Jodrell Bank and, second, to search for recently suspected recurrences of certain time lapses between flares noted in another flare star, YZ Canis Minoris (Andrews 1966). The instruments used were the 16-inch Nishimura and 60-inch Rockefeller reflectors, both equipped with E.M.I. 6256A photomultipliers and standard UBV filters. Ten possible flares were recorded, one of which was a major optical event ( Fig. 1 ) . Details of the photoelectric coverage are given in Table I where interruptions to monitoring of more than 5 minutes are indicated. Suspected flares are listed in Table II. Exceptionally good weather conditions during a 12-night period allowed observations capable of detecting flares of 0.1 magnitude in blue for more than 90 hours, which represents optical coverage of the star for one-third of that total day-and-night period. Simultaneous photographic confirmation of the major flare of July 15 was obtained with the aid of a telephone link to the 36/42/62 cm Hamburg Schmidt telescope at Boyden. Information on simultaneous radio events is not yet available.