An Einstein search for X-ray emission from comet Bradfield (1979l)

X-radiation may result from active plasma phenomena in the interactions of comets with the solar wind. We have carried out a limited but sensitive search for soft X-radiation from Comet Bradfield (1979$\text{l}$), on 1980 Feb. 5. No X-radiation was detected at a level (3σ) of 1.7 × 10^?13 erg(cm²sec keV)^?1 in the 0.2 – 4.0 kev range. This corresponds to a limit on the power dissipated in the comet by non-thermal electrons of approximately 10¹⁹ ergs sec^?1, averaged over the 2568-sec exposure to the comet. This energy deposition is near the magnitude suggested by simple theoretical ideas, and further searches of appropriate comets both in soft X-radiation and at radio wavelengths seem warranted.     

A search for millimeter-wave emission from HCN and other molecules in Comet Bradfield (1979l)

Millimeter-wave emission from HCN, CS, CH₃OH, and two unidentified lines (previously observed in Comet Kohoutek (1973 XII)) was sought and not detected from Comet Bradfield (1979l) after perihelion passage. Limits on column densities and production rates are derived. In the case of HCN, the production rate is less than that reported for Comet Kohoutek, even after scaling relative to the observed OH emission from each comet.     

Scanner observations of comet Bradfield (1987 s)

Spectrophotometric observations of the head of comet Bradfield (1987 s) during three nights in 1987 are presented. An estimate of the CN, C₂ and C₃ column densities and production rates have been made.     

Spectrophotometric study of comet Bradfield (1987s)

Spectrophotometric observations of head of comet Bradfield (1987s) during three nights in 1987 are presented. An estimate of the CN, C ₂, and C ₃ column densities and production rates have been made.     

Radio search for pulsed emission from X-ray pulsars

An experiment has been performed at 325 MHz, with a 10 m tracking dish, for the search of pulsed radio emission associated with X-ray pulsars. No evidence of radio pulses has been found in the four sources investigated, although the radio pulsar PSR 0329+54, used as a testing object, has been detected successfully.     

A search for millimeter-wave emission from HCN,CO, and CH3CN in Comet Bradfield (1978c)

Millimeter wavelength emission from the “parent” molecules HCN, CO, and CH₃CN, the latter in both its ground and ν₈ = 1 excited vibrational states, was sought from Comet Bradfield (1978c) during March 1978 after comet perihelion, when the heliocentric distance was between 0.45 and 0.55 AU. No lines were detected, and upper limits on the molecular column densities (averaged over the antenna beam) and production rates, Q are estimated. The upper limits on Q for HCN, CH₃CN (ν₈ = 0), and CH₃CN (ν₈ = 1) are less than the production rates inferred from the millimeter-wave detection of these species in Comet Kohoutek (1973f). The CO upper limit on Q is comparable to that inferred from a detection of Comet West (1975n) in the rocket uv. It seems likely that the total gas production rate of Comet Bradfield (1978c) was relatively low.     

A search for soft X-ray emission from stellar sources

With the soft X-ray detector (0.2–0.284 keV) aboard the Astronomical Netherlands Satellite (ANS) we have searched for X-ray emission from hot star coronae and peculiar stars. On Sirius ( CMa) and Capella ( Aur) X-ray emission has been measured at 6 and 5 level, respectively, above background. In all other cases the search revealed no evidence for soft X-ray emission. Upper limits to the luminosities of about 25 star coronae (main-sequence stars, (sub)giants, and supergiants) and of 4 peculiar stars ( Sco, Lyr, P Cyg, and Car) have been obtained.Paper presented at the COSPAR/IAU Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

CO in the IUE spectrum of Comet Bradfield (1979l)

New identifications are reported of the fourth positive bands and Cameron bands of CO in the IUE satellite spectrum of Comet Bradfield (1979l). Although the predicted band intensities as well as the band identifications in Comet West (1976 VI) support the proposed assignments, VUV cometary spectra of higher resolution are necessary for conformation.     

A search for radio emission from Galactic supersoft X-ray sources

We have made a deep search for radio emission from all the northern hemisphere supersoft X-ray sources using the Very Large Array (VLA) and multi-element radio-linked interferometer network (MERLIN) telescopes, at 5 and 8.4 GHz. Three previously undetected sources, T Pyx, V1974 Cygni and RX J0019.8+2156, were imaged in quiescence using the VLA in order to search for any persistent emission. No radio emission was detected in any of the VLA fields down to a typical 1 σ rms noise of 20 μJy beam⁻¹, however, 17 new point sources were detected in the fields with 5-GHz fluxes between 100 and 1500 μJy, giving an average 100-μJy source density of ∼200 deg⁻², comparable to what was found in the MERLIN Hubble Deep Field survey. The persistent source AG Draconis was observed by MERLIN to provide a confirmation of previous VLA observations and to investigate the source at a higher resolution. The core is resolved at the milliarcsec scale into two components that have a combined flux of ∼1 mJy. It is possible that we are detecting nebulosity, which is becoming resolved out by the higher MERLIN resolution. We have investigated possible causes of radio emission from a wind environment, both directly from the secondary star, and also consequently, of the high X-ray luminosity from the white dwarf. There is an order of magnitude discrepancy between observed and modelled values that can be explained by the uncertainty in fundamental quantities within these systems.     

A search for millimeter wave spectral lines from comet Sugano-Saigusa-Fujikawa (1983e)

The search for radio spectral lines from Comet Sugano-Saigusa-Fujikawa (1983e) was conducted using the 45-m telescope of Nobeyama Radio Observatory. The frequency ranges of 44.0–46.0 and 47.5–49.5 GHz were surveyed down to $\text{ΔT}{}_{\mathrm{<mtext>A</mtext>}}{}^1\text{(}\text{rms}\text{) = 20–30}\text{mK}$, with a beam size of ～35 arc sec. Upper limits have been established for spectral lines of atomic hydrogen, CS, OCS, SO₂, H₂CO, CH₃OH, HCCCCCN, HCOOCH₃, CH₃OCH₃, and CH₃CH₂CN. The J = 5?4 line from HCCCN in the vibrational ground state possibly has been detected but not confirmed. The suggested total amount of HCCCN in the coma is consistent with the possible picture that HCCCN is the main parent molecule of CN.     

Emissions from the head of Comet Bradfield (1978c)

The flux distribution in the head of Comet Bradfield (1978c) during the pre-perihelion period has been obtained in the wavelength range 400–640 nm. The emission fluxes at 474 nm, 516 nm, 564 nm and 589 nm are reported. By use of the observed monochromatic brightness of the Swan band sequences, the number of C₂ molecules in the head of the comet are estimated.     

A search for microwave emission from CH in Comet Kohoutek (1973f)

A search was conducted for the three 9-cm transitions of the ground state Λ-doublet of CH in comet Kohoutek, using the CSIRO 64-m radio telescope and the Onsala Space Observatory's 25.6-m telescope. No lines were detected during the observing periods, and upper limits are given for the corresponding antenna temperatures.     

A search for prompt radio emission from GRBs

The Cambridge Low Frequency Synthesis Telescope (CLFST) is being used to search for prompt radio emission from GRBs at 151 MHz. For this search a special observing mode has recently been developed; the antennas of the CLFST are split into seven groups which are spaced about 30° apart. When triggered by the real-time signals from the BACODINE system the antennas are slewed to the GRB position, with data being sampled at 1.5 or 3-s intervals. The antennas slew at about 10° per minute, so that an appreciable fraction of the sky can be accessed on timescales of a few minutes - any prompt radio emission from a GRB might be delayed by this timescale due to propagation effects.     

An analysis of spectrophotometric observations of comets Austin (1982g) and Bradfield (1980t)

Post-perihelion observed emission fluxes at 388 nm (CN) and 516 nm (C₂) of the coma of comets Austin (1982g) and Bradfield (1980t) are analysed in the framework of the Haser model. Ratios of Haser model CN and C₂ parent production rates with expansion velocity show that each comet behaves normally. For comet Austin (1982g), the Q _CN/v and Q _c2/v values decrease with increase of heliocentric distance of comet. For an assumed %; activity of the total spherical surface area of the nucleus, the water vaporization theory coupled with derived water production rates from the International Ultraviolet Explorer H and OH flux data yields a nuclear diameter of about 6 km for comet Austin (1982g). For comet Bradfield (1980t), the derived nuclear diameter is expected to be of about 1 km. In each comet, the dust mass production rates as well as ratio of dust-to-gas mass production rates decrease with increase of heliocentric distance of comet.     

A model for X-ray emission from loop prominences

A study is made of X-ray line emission observed during the developing stages of a set of post-flare loop prominences. The time behaviour of the line emission can be described by a model consisting of two flux tubes containing plasma heated impulsively at the flash phase; the plasma cools by radiation and by conduction to the chromosphere. These ideas are extended to the possible formation of H prominences from low-lying hot loops.     

A new orbit for comet C/1858 L1 (Donati)

A new orbit for comet C/1858 L1 (Donati), based on 1036 observations in α and 971 in σ made between 7 June 1858 and 5 March 1859, is calculated using iteratively reweighted least squares. Residuals were weighted by the Welsch weighting function. The orbit represents a high eccentricity ellipse, e = 0.996265, with large semi‐major axis, a = 154.8612 AU, and long period, P = 1927.22 yr. The residuals are relatively random, a 10.7% chance of being random, but with a slight indication of possible nongravitational forces influencing the motion. The comet will not return until the year 3759, when it will pass 0.8442 AU from the Earth. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A search for electron cyclotron maser emission from compact binaries

Unipolar induction (UI) is a fundamental physical process, which occurs when a conducting body transverses a magnetic field. It has been suggested that UI is operating in RX J0806+15 and RX J1914+24, which are believed to be ultracompact binaries with orbital periods of 5.4 and 9.6 min, respectively. The UI model predicts that those two sources may be electron cyclotron maser sources at radio wavelengths. Other systems in which UI has been predicted to occur are short period extrasolar terrestrial planets with conducting cores. If UI is present, circularly polarized radio emission is predicted to be emitted. We have searched for this predicted radio emission from short period binaries using the Very Large Array (VLA) and Australian Telescope Compact Array (ATCA). In one epoch, we find evidence for a radio source, coincident in position with the optical position of RX J0806+15. Although we cannot completely exclude that this is a chance alignment between the position of RX J0806+15 and an artefact in the data reduction process, the fact that it was detected at a significance level of 5.8σ and found to be transient suggests that it is more likely that RX J0806+15 is a transient radio source. We find an upper limit on the degree of circular polarization to be ∼50 per cent. The inferred brightness temperature exceeds 10¹⁸ K, which is too high for any known incoherent process, but is consistent with maser emission and UI being the driving mechanism. We did not detect radio emission from ES Cet, RX J1914+24 or Gliese 876.     

A new model for X-ray emission from NGC 4151

We present an analysis of the reported spectral features of NGC 4151 in X-rays. It is shown that the origin of X-rays from the source is inconsistent with a single production mechanism. We suggest a new two-component model in which soft X-rays arise from the black-body emission of a tiny hot nucleus withT2×10⁷ K and the hard X-ray photons are generated in an extended region by inverse Compton scattering of electrons with the infrared photons.     

Thermal emission from the dust coma of comet bowell and a model for the grains

We present 2.2-, 10-, and 20-μm photometry of Comet Bowell (1982 I) taken on 24 June 1982 when the comet was at 3.5 AU postperihelion. From these and earlier thermal emission measurements we conclude that the OH production in 1981 was probably supplied by large dirty-ice grains in the coma, as proposed by A'Hearn et al. (1984). The temperature of the grains must have been 140–155°K. Amorphous ice and the phase change from amorphous to cubic ice may have supplied much of the energy for sublimation. The much lower OH production in 1982 could have arisen from icy grains or from the nucleus. There is no evidence for an extremely low geometric albedo of the grains (<1%); in fact, much of the scattered light may have come froman additional component of cold icy grains.     

Evolution of C/2006 M4 (SWAN) comet tails

We studied variations in the structure of plasma and dust tails of the C/2006 M4 (SWAN) comet during a long observation period (September–December 2006). We found sizes of grains ejected by the comet from the synchronic-syndynamic analysis of comet images. We calculated solar wind speed for high heliographic latitudes from calculations of the aberration angle of the comet plasma tail. Rapid changes in the calculated values of the solar wind speed are caused by its variable transversal component.