Observation of solar radio emission by the 22-m radio telescope at the Crimean Astrophysical Observatory at 2.25 mm and 8.15 mm wavelengths

The results are given of observation of solar radio emission of the S-component at 8.15 mm-, and 2.25 mm- made with the 22 m radio telescope of the Crimean Astrophysical Observatory. Solar radio images are obtained at both wavelengths. The data are presented of radio emission intensity and brightness temperatures of 10 sources of the S-component as well as the result of a flare observed. The sources of the S-component appear to be opaque at millimetre wavelengths.     

Model calculations of the degree of polarization of solar S-coniponent emission at millimetre waves

Model calculations of the S-component accounting for the emission from uniform sunspot and inhomogeneous plage regions are applied to a prediction of the spectral distribution of the degree of circular polarization at millimetre waves. The results are compared with observations adopted from the literature and a sufficient agreement between model computation and measurement can be slated. However, observations with higher spatial resolution than presently available are needed in order to check the predicted fine structures and to verify details of the applied model.     

Studies of the solar chromosphere from millimetre and sub-millimetre observations

A compilation of brightness temperature data in the millimetre and sub-millimetre wavelength ranges is used to obtain an empirical relation T _B = C ⁿ between brightness temperature and wavelength, valid between 1 mm and 1 cm. An analytically soluble model, giving electron temperatures and densities between 1500 km and 4000 km above the photosphere is derived from this relationship, and eclipse data of Thomas and Athay, of the emission at the head of the Balmer continuum. Although this over-simplified model lacks precision in the height co-ordinate, it allows a scale height of around 1000 km for electrons to be deduced, and supplies a convincing test for the absence of hydrostatic equilibrium throughout the region. A more comprehensive and reliable though still simplified numerical model is then presented, being a modification of previous models accounting only for millimetre data. It shows marked departure from UV derived models in this region, and an explanation for the discrepancy is proposed in terms of thermal inhomogeneities on the scale of the chromospheric supergranulation. The stratified model is then geometrically modified to account for observed centrelimb profiles of the Sun measured throughout the sub-millimetre and millimetre region. The scale of any roughness thus introduced is related to the notable lack of millimetric limb brightening, and observational tests for that scale are suggested here. A qualitative picture of this part of the chromosphere is proposed, consistent with existing observations in the millimetre, visible and UV regions of the spectrum.     

Observational limits to source confusion in the millimetre/submillimetre waveband

The first observations to detect a population of distant galaxies directly in the submillimetre waveband have recently been made using the new Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). The results indicate that a large number of distant galaxies are radiating strongly in this waveband. Here we discuss their significance for source confusion in future millimetre/submillimetre-wave observations of both distant galaxies and cosmic microwave background radiation (CMBR) anisotropies. Earlier estimates of such confusion involved significant extrapolation of the results of observations of galaxies at low redshifts; our new estimates do not, as they are derived from direct observations of distant galaxies in the submillimetre waveband. The results have important consequences for the design and operation of existing and proposed millimetre/submillimetre-wave telescopes: the Planck Surveyor survey will be confusion-limited at frequencies greater than 350 GHz, even in the absence of Galactic dust emission; a 1σ confusion noise limit of about 0.44 mJy beam⁻¹ is expected for the JCMT/SCUBA at a wavelength of 850 μm; and the subarcsecond resolution of large millimetre/submillimetre-wave interferometer arrays will be required in order to execute very deep galaxy surveys.     

Millimetre continuum observations of southern massive star formation regions – II. SCUBA observations of cold cores and the dust grain emissivity index (β)

We report the results of a submillimetre continuum emission survey targeted towards 78 star formation regions, 72 of which are devoid of methanol maser and UC H  ii  regions, identified in the Swedish ESO Submillimetre Telescope (SEST)/SEST IMaging Bolometer Array (SIMBA) millimetre continuum survey of Hill et al. At least 45 per cent of the latter sources, dubbed 'mm-only', detected in this survey are also devoid of the mid-infrared MSX  emission. The 450- and 850-μm continuum emission was mapped using the Submillimetre Common User Bolometer Array (SCUBA) instrument on the James Clerk Maxwell Telescope (JCMT). Emission is detected towards 97 per cent of the 78 sources targeted as well as towards 28 other SIMBA sources lying in the SCUBA fields.
In total, we have identified 212 cores in this submillimetre survey, including 106 previously known from the SIMBA survey. Of the remaining 106 sources, 53 result from resolving a SIMBA source into multiple submillimetre components, whilst the other 53 sources are submillimetre cores, not seen in the SIMBA. Additionally, we have identified two further mm-only sources in the SIMBA images. Of the total 405 sources identified in the SIMBA survey, 255 are only seen at millimetre wavelengths.
We concatenate the results from four (sub)millimetre continuum surveys of massive star formation, together with the Galactic plane map of Pierce-Price et al. in order to determine the dust grain emissivity index β for each of the sources in the SIMBA source list. We examine the value of β with respect to temperature, as well as for the source classes identified in the SIMBA survey, for variation of this index. Our results indicate that β is typically 2, which is consistent with previous determinations in the literature, but for a considerably larger sample than previous work.     

On the viewing angle dependence of blazar variability

Internal shocks propagating through an ambient radiation field are subject to a radiative drag that, under certain conditions, can significantly affect their dynamics, and consequently the evolution of the beaming cone of emission produced behind the shocks. The resultant change of the Doppler factor combined with opacity effects leads to a strong dependence on the viewing angle of the variability pattern produced by such systems; specifically, the shape of the light curves and the characteristics of correlated emission. One implication is that objects oriented at relatively large viewing angles to the observer should exhibit a higher level of activity at high synchrotron frequencies (above the self-absorption frequency), and also at gamma-ray energies below the threshold energy of pair production, than at lower (radio/millimetre) frequencies.     

Detection of new sources of methanol emission at 95 GHz with the Mopra telescope

A southern hemisphere survey of methanol emission sources has been carried out using the Australia Telescope National Facility Mopra millimetre telescope. 85 sources, the majority of them masers, have been detected in the 8₀−7₁ A⁺ transition of methanol at 95 GHz. Together with a similar northern hemisphere survey, this completes the search for 95-GHz methanol emission from the Galactic plane. The previously found correlation between intensities of methanol emission at 44 and 95 GHz is confirmed here with the larger sample of sources. The results of large velocity gradient statistical equilibrium calculations confirm the classification of these sources as class I methanol masers pumped through collisional excitation.     

85-GHz BIMA observations of the double-hotspot radio galaxy 3C 20

We present 85-GHz observations of the archetypal double-hotspot radio source 3C 20 made with the BIMA millimetre array. The resolution of BIMA allows us to separate the two components of the eastern hotspot. By comparing the BIMA observations with existing VLA data, we show that the spectra of the two hotspot components are very similar, despite the clear differences in their radio structure and their wide separation. We discuss the implications for models of double hotspot formation. Weak emission from the lobes of 3C 20 is detected at 85 GHz, at a level consistent with the predictions of standard spectral ageing models.     

Millimetre/submillimetre-wave emission-line searches for high-redshift galaxies

The redshifted spectral line radiation emitted from both atomic fine-structure and molecular rotational transitions in the interstellar medium (ISM) of high-redshift galaxies can be detected in the centimetre, millimetre and submillimetre wavebands. Here we predict the counts of galaxies detectable in an array of molecular and atomic lines. This calculation requires a reasonable knowledge of both the surface density of these galaxies on the sky, and the physical conditions in their ISM. The surface density is constrained using the results of submillimetre-wave continuum surveys. Follow-up OVRO Millimeter Array observations of two of the galaxies detected in the dust continuum have provided direct measurements of CO rotational line emission at redshifts of 2.56 and 2.81. Based on these direct high-redshift observations and on models of the ISM that are constrained by observations of low-redshift ultraluminous infrared galaxies, we predict the surface density of line-emitting galaxies as a function of line flux density and observing frequency. We incorporate the sensitivities and mapping speeds of existing and future millimetre/submillimetre-wave telescopes and spectrographs, and so assess the prospects for blank-field surveys to detect this line emission from gas-rich high-redshift galaxies.     

Detection of new sources of methanol emission at 107 and 108 GHz with the Mopra telescope

A southern hemisphere survey of methanol emission sources in two millimetre-wave transitions has been carried out using the ATNF Mopra millimetre telescope. 16 emission sources have been detected in the 3₁–4₀ A⁺ transition of methanol at 107 GHz, including six new sources exhibiting class II methanol maser emission features. Combining these results with the similar northern hemisphere survey, a total of eleven 107-GHz methanol masers have been detected. A survey of the methanol emission in the 0₀–1₋₁ E transition at 108 GHz has resulted in the detection of 16 sources; one of them showing maser characteristics. This is the first methanol maser detected at 108 GHz, presumably of class II. The results of large velocity gradient statistical equilibrium calculations confirm the classification of these new sources as class II methanol masers.     

Millimetre and submillimetre τ relations

Relations are presented between the optical depth of the atmosphere  (τ)  in the millimetre and submillimetre windows at 350, 450, 850 and 1250 μm. These relations are derived by an analysis of 849 skydips at 850 μm performed with the submillimetre camera SCUBA at the James Clerk Maxwell Telescope (JCMT) and polynomial fits to over 19 000 measurements of a tipping radiometer operating at 350 μm. The relations allow for an improved calibration of millimetre and submillimetre observations on Mauna Kea, Hawai'i, and for better monitoring of atmospheric conditions.     

Variations in the broad-band spectra of BL Lac objects: millimetre observations of an X-ray-selected sample

Observations at millimetre wavelengths are presented for a representative sample of 22 X-ray-selected BL Lac objects (XBLs). This sample comprises 19 high-energy cut-off BL Lac objects (HBLs), 1 low-energy cut-off BL Lac object (LBL) and 2 'intermediate' sources. Data for LBLs, which are mostly radio-selected BL Lac objects (RBLs), are taken from the literature. It is shown that the radio–millimetre spectral indices of HBLs     are slightly steeper than those of the LBLs     . A correlation exists between α _5–230 and 230 GHz luminosity. While this correlation could be an artefact of comparing two populations of BL Lac objects with intrinsically different radio properties, it is also consistent with the predictions of existing unified schemes that relate BL Lac objects to Fanaroff–Riley class I radio galaxies.
The HBLs have significantly flatter submillimetre–X-ray spectral indices     than the LBLs     although the two intermediate sources also have intermediate values of α _230–X∼−0.9. It is argued that this difference cannot be explained entirely by the viewing-angle hypothesis and requires a difference in physical-source parameters. The α _230–X values for the HBLs are close to the canonical value found for large samples of radio sources and thus suggest that synchrotron radiation is the mechanism that produces the X-ray emission. As suggested by Padovani & Giommi, the inverse-Compton mechanism is likely to dominate in the LBLs requiring the synchrotron spectra of these sources to steepen or cut off at lower frequencies than those of the HBLs.     

Suppression of atmospheric radio emission fluctuations in radio astronomical observations

The fluctuations of radio emission of the atmosphere (for the present only cloudy) are a substantial limiting factor for observations of cosmic radio sources on centimetre and millimetre wavelengths. For suppressing these fluctuations the dual-beam method (differential receiving from two slightly separated direction) is widely used. At the same time works for perfecting this method are going on as well as in searching other possibilities with the principal aim of doing away limitations on sizes of sources under observation. There are considered here these methods with a competitive evaluation of their possibilities for suppressing fluctuation of the atmosphere radio emissions.     

Gravitational lensing and the Sunyaev–Zel'dovich effect in the millimetre/submillimetre waveband

The intensity of the cosmic microwave background radiation in the fields of clusters of galaxies is modified by inverse Compton scattering in the hot intracluster gas — the Sunyaev–Zel'dovich (SZ) effect. The effect is expected to be most pronounced at a frequency of about 350 GHz (a wavelength of about 800 μm), and has been detected in the centimetre and millimetre wavebands. In the millimetre/submillimetre waveband, the gravitationally lensed images of distant dusty star-forming galaxies in the background of the cluster are predicted to dominate the appearance of clusters on scales of several arcsec, and could confuse observations of the SZ effect at frequencies greater than about 200 GHz (wavelengths shorter than about 1.5 mm). Recent observations by Smail, Ivison &38; Blain confirm that a significant population of confusing sources is present in this waveband. Previous estimates of source confusion in observations of the millimetre/submillimetre-wave SZ effect did not include the effects of lensing by the cluster, and so the accuracy of such measurements could be lower than expected. Source subtraction may be required in order to measure the SZ effect accurately, and a careful analysis of the results of an ensemble of SZ measurements could be used to impose limits to the form of evolution of distant dusty star-forming galaxies.     

Slowly varying component spectrum of the solar radio emission at millimetre wavelengths

This paper deals with the observed data on the solar S-component sources at millimetre wavelengths. The observations were made in 1968 and 1969 using the 22-m radio telescope of the Crimean Astrophysical Observatory at six wavelengths: 2, 4, 6, 8, 13 and 17 mm. The enhanced intensity of the solar active region in comparison with the quiet Sun level varies proportionally to ^–2 if the wavelength is within the range of 2 ÷ 6 mm. In the wavelength band of 6 ÷ 17 mm almost flat spectra of the solar S-component sources is observed. Assuming the bremsstrahlung mechanism of the radio emission for the quiet Sun and the solar active regions an attempt has been made to treat the above presented data. It appears that the most probable explanation of the 2 ÷ 6 mm spectrum is that the S-component sources are opaque. In the 6 ÷ 17 mm wavelength band there are two possibilities: the active region may be either transparent or opaque. But in the last case the source brightness temperature must be proportional to ². Some differences in the spectra of the sources, identified with flocculi and with bipolar sunspot groups, were mentioned. The cold regions (as compared with the quiet Sun) were observed up to = 2 mm and identified with the filaments. However, its visibility falls when the wavelength decreases.     

SCUBA photometry of candidate Vega-like sources

New SCUBA measurements at millimetre wavelengths are presented for a sample of Vega-like stars. Six stars were detected, while sensitive upper limits were obtained for a further 11 sources. Most of the sample selected from a recent catalogue of Vega-like stars have infrared excesses similar to those of the prototype Vega-like stars α Lyr and α PsA. Their IR–submm spectral indices are steep, indicating that the submm emission from the discs is dominated by grains which are smaller than the wavelength of observation and that only small grains exist in those dusty discs. HD 98800 has an IR–submillimetre spectral index of less than two, which suggests that grains have grown to more than 0.3 mm in size. Hipparcos parallax data for HD 42137 and HD 123160 suggest that these two stars are giants rather than dwarfs, similar to the situation previously found for HD 233517. Dust masses, or upper limits, were derived for the sample; these indicate that most of the sources do not have as much dust as Herbig Ae/Be or T Tauri stars, but are likely to have dust masses comparable to those of the prototype Vega-like stars.     

Massive star formation in galaxies: radiative transfer models of the UV to millimetre emission of starburst galaxies

We present illustrative models for the UV to millimetre emission of starburst galaxies which are treated as an ensemble of optically thick giant molecular clouds (GMCs) centrally illuminated by recently formed stars. The models follow the evolution of the GMCs owing to the ionization-induced expansion of the H  ii regions and the evolution of the stellar population within the GMC according to the Bruzual & Charlot stellar population synthesis models. The effect of transiently heated dust grains/PAHs on the radiative transfer, as well as multiple scattering, is taken into account.
The expansion of the H  ii regions and the formation of a narrow neutral shell naturally explain why the emission from PAHs dominates over that from hot dust in the near- to mid-infrared, an emerging characteristic of the infrared spectra of starburst galaxies.
The models allow us to relate the observed properties of a galaxy to its age and star formation history. We find that exponentially decaying 10⁷–10⁸ yr old bursts can explain the IRAS colours of starburst galaxies. The models are also shown to account satisfactorily for the multiwavelength data on the prototypical starburst galaxy M82 and NGC 6090, a starburst galaxy recently observed by ISO . In M82 we find evidence for two bursts separated by 10⁷ yr. In NGC 6090 we find that at least part of the far-infrared excess may be due to the age of the burst (6.4×10⁷ yr). We also make predictions about the evolution of the luminosity of starbursts at different wavelengths which indicate that far-infrared surveys may preferentially detect older starbursts than mid-infrared surveys.     

Coronal sources at meter and optical wavelengths during the declining phase of the solar cycle

We present observations of the corona at 169 MHz with the Nançay Radioheliograph during the summer of 1984. We compare synoptic maps of the metric radio emission on the solar disk with synoptic charts of the K-corona as well as of the green and the red lines. Local sources of radio emission are not located near regions of enhanced green or red line emission which, in turn, are in general above chromospheric faculae. Thus the radio emissions located in the surroundings of faculae are apparently related to different loop systems, with lower density. The comparison of the radio data with the K-corona showed one radio source associated with enhanced emission both at 1.3 and at 1.7 R , apparently a streamer. Other radio sources did not show any clear associations, but were nevertheless located within the coronal plasma sheet, delineated by the large-scale K-corona emission. Moreover the large-scale structure of the corona at 169 MHz was quite similar to the coronal plasma sheet observed at 1.3 R above the limb. The extent of the radio emission in latitude is very similar to that of the K-corona, while the coronal line emission is more concentrated near the solar equator.     

Effect of changes in magnitudes of QSOs in their redshift distribution

Strong emission lines may change the brightness of QSOs and hence their observed magnitudes. Since different lines will affect the magnitudes by entering a particular filter at different redshifts, this effect may alter the number of QSOs at a particular redshift and hence the redshift distribution. The present analysis shows that the influence of the emission lines on the U and B magnitudes are significantly correlated to the redshift distribution. It is concluded that the changes in observed magnitudes of QSOs caused by the emission lines have significant effects on the present redshift distribution.     

Stellarv sini and optical emission line widths in Be stars

I re-investigate empirical correlations between line widths of photospheric absorption lines — as a measure of the stellar projected rotational velocityv sini- and of circumstellar emission lines in Be stars. The degree of this correlation is a measure for the kinematic, i.e., rotational, contribution to the total emission line broadening.From the literature and from additional data, I have collected a sample of photoelectric measurements of Balmer and Feii emission lines of the 115 brightest Be stars in the sky, most of them observed several times during the past decade. I investigate the following emission line widths parameters: full width at half maximum, total width at the base, and double-peak separation. I find from the FWHM that the basic origin of emission line broadening in Be stars is undoubtedly rotational, the correlations withv sini being best for weaker emission lines while H shows considerable scatter. Total width at the base is uncorrelated withv sini except for the Feii lines. Peak separation is found to be a function both ofv sini and of equivalent width. The latter dependence can straightforwardly be understood by the fact that within Huang's disk model peak separation, normalized tov sini, is governed by the outer envelope radius.I conclude that observational evidence leaves no doubt that Be star envelopes as visible in optical emission lines are rotationally supported and have axisymmetric geometry.Partly based on observations obtained at the European Southern Observatory, La Silla, Chile.