Long baseline interferometric observations of long period variable stars

Recent observations of long-period variable stars at spatial resolutions from approximately 1 arcsec to several milli-arcsecs have provided new insights into pulsation, dust formation, and mass-loss of AGB stars. These insights have come from long baseline interferometric observations obtained across a wide range of wavelengths, from the optical, through the infrared, to wavelengths as long as several millimeters. The present status and recent results from long baseline interferometry, particularly at optical and infrared wavelengths, are discussed. Such results include diameters and limb-darkening, surface features, mode of pulsation, location of SiO masers, inner radii of dust shells, physical conditions in the dust formation zone and of the inner regions of the dust shells. The results are interpreted in terms of present models of dust formation and mass-loss.     

The Temperature-Dependent Spectrum of Methane Ice I between 0.7 and 5 μm and Opportunities for Near-Infrared Remote Thermometry

New infrared absorption coefficient spectra of pure methane ice I were measured at temperatures between 30 and 90 K, over wavelengths from 0.7 to 5 μm, along with spectra of methane ice II at 20 K and liquid methane at 93 K. The spectra were derived from transmission measurements through monocrystalline samples grown in a series of closed cells having interior dimensions ranging from 100 μm to 1 cm. The thicker samples permitted measurement of extremely weak absorption bands, with absorption coefficients as small as 0.003 cm⁻¹. We report 14 new absorption bands, which we tentatively assign to specific vibrational transitions. Two of the new bands are attributed to CH₃D. Measurements of the weaker CH₄ bands are particularly needed for interpreting spectral observations of Pluto and Triton, where a number of weak CH₄-ice absorption bands have been observed. The data presented in this paper complement studies of spectral transmission by thin films of methane ice, which are most suitable for measuring the stronger absorption bands. Temperature-dependent spectral features revealed by the new data offer the opportunity to determine CH₄-ice temperatures remotely, via near-infrared reflectance spectroscopy. This approach could prove particularly valuable for future spacecraft exploration of Pluto.     

Temporal trends of solar EUV and UV full-disk fluxes

Several progressions in the temporal characteristics of full-disk solar UV and EUV fluxes have been identified that raise many questions about the solar physics involved. The collective effect of numerous enhancements smaller than scaled plages contribute significantly to the solar cycle variations, especially for emissions from the cooler portions of the corona and the chromosphere. Active-region remnants are suggested to have a strong role even in solar-rotation induced variations late in an episode of major activity. Although cool coronal EUV emissions are long lasting, the persistence of the solar-rotation induced variations is even greater at photospheric UV wavelengths. Gyroresonance and possibly nonthermal radio emission at centimeter wavelengths are suggested to be particularly important during the first solar rotation of an episode of major activity.     

Temporal trends of solar EUV and UV full-disk fluxes

Several progressions in the temporal characteristics of full-disk solar UV and EUV fluxes have been identified that raise many questions about the solar physics involved. The collective effect of numerous enhancements smaller than scaled plages contribute significantly to the solar cycle variations, especially for emissions from the cooler portions of the corona and the chromosphere. Active-region remnants are suggested to have a strong role even in solar-rotation induced variations late in an episode of major activity. Although cool coronal EUV emissions are long lasting, the persistence of the solar-rotation induced variations is even greater at photospheric UV wavelengths. Gyroresonance and possibly nonthermal radio emission at centimeter wavelengths are suggested to be particularly important during the first solar rotation of an episode of major activity.     

The radio and infrared spectrum of DR 21

The radio and infrared spectrum of DR 21 is established over a wide range of frequencies (from 10² to 10⁸ MHz). Two physical processes, free-free emission from the ionized hydrogen at radio wavelengths and reradiation at infrared wavelengths of the original stellar ultraviolet radiation by dust grains have to be considered in the explanation of the derived spectrum. Physical parameters of the object deduced from its radio emission are also presented.     

Radio observations of active galactic nuclei with mm-VLBI

Over the past few decades, our knowledge of jets produced by active galactic nuclei (AGN) has greatly progressed thanks to the development of very-long-baseline interferometry (VLBI). Nevertheless, the crucial mechanisms involved in the formation of the plasma flow, as well as those driving its exceptional radiative output up to TeV energies, remain to be clarified. Most likely, these physical processes take place at short separations from the supermassive black hole, on scales which are inaccessible to VLBI observations at centimeter wavelengths. Due to their high synchrotron opacity, the dense and highly magnetized regions in the vicinity of the central engine can only be penetrated when observing at shorter wavelengths, in the millimeter and sub-millimeter regimes. While this was recognized already in the early days of VLBI, it was not until the very recent years that sensitive VLBI imaging at high frequencies has become possible. Ongoing technical development and wide band observing now provide adequate imaging fidelity to carry out more detailed analyses. In this article, we overview some open questions concerning the physics of AGN jets, and we discuss the impact of mm-VLBI studies. Among the rich set of results produced so far in this frequency regime, we particularly focus on studies performed at 43 GHz (7 mm) and at 86 GHz (3 mm). Some of the first findings at 230 GHz (1 mm) obtained with the Event Horizon Telescope are also presented.     

The icy Galilean satellites: ultraviolet phase curve analysis

Ultraviolet disk-integrated solar phase curves of the icy galilean satellites Europa, Ganymede, and Callisto are presented, using combined data sets from the International Ultraviolet Explorer (IUE), Hubble Space Telescope (HST), and the Galileo Ultraviolet Spectrometer. Global, disk-integrated solar phase curves for all three satellites, in addition to disk-integrated solar phase curves for Europa's leading, trailing, jovian, and anti-jovian hemispheres, are modeled using Hapke's equations for 7 broadband UV wavelengths between 260 and 320 nm. The sparse coverage in solar phase angle, particularly for Ganymede and Callisto, and the noise in the data sets poorly constrain some of the photometric parameter values in the model. However, the results are sufficient for forming a preliminary relationship between the effects of particle bombardment on icy surfaces and photometric scattering properties at ultraviolet wavelengths. Callisto exhibits a large UV opposition surge and a surface comprised of relatively low-backward scattering particles. Europa's surface displays a dichotomy between the jovian and anti-jovian hemispheres (the anti-jovian hemisphere is more backward scattering), while a less pronounced hemispherical variation was detected between the leading and trailing hemispheres. Europa's surface, with the exception of the trailing hemisphere region, appears to have become less backscattering between the late-1970s-early-1980s and the mid-1990s. These results are commensurate with the bombardment history of these surfaces by magnetospheric charged particles.     

The magnitude and albedo of Mars

A comprehensive set of magnitudes obtained between 1954 and 2006 are analyzed. The martian brightness and its variations are characterized empirically at UBVRI wavelengths. Geometrical factors including phase angle, orbital longitude and rotation angle are distinguished from geophysical factors including dust storms and changing albedo features. The phase function indicates a brightness surge near opposition at all wavelengths except possibly in the U band. The color indices reveal increased reddening with phase angle. No significant brightness difference between morning and evening hemisphere observations is indicated with the possible exception of the I band. There is no conclusive evidence for inter-annual brightness variation during the years from 1991 to 2006 when abundant photometry is available. Major dust storms caused brightness excesses that were strongest in the R band at an average of 0.15 mag more luminous than the empirical model for dust-free conditions. The storm of 2001 produced a rapid increase at the onset followed by a slower decline, while the 2003–2004 event show a more gradual increase. The return to normal brightness was linear in magnitude for both storms. Brightness excesses at longer wavelengths were about 0.20 to 0.25 mags at the peak of the 2001 storm. The observed geometric albedo of Mars is 0.059±0.001 in U, 0.089±0.001 in B, 0.170±0.002 in V, 0.289±0.003 in R, and 0.330±0.003 in I. The corresponding albedo values for all five colors exceed those recorded in the literature, with larger percentage increases at shorter wavelengths.     

分光仪PSP0的偏振器设计与实验

本文介绍人光仪ＰＳＰ０ 的偏振器设计和实验结果。偏振器设计为旋转半滤片加固定偏振片的系统,但在选用偏振器件方面提出了两种方案。对于低价设计的实验结果表明,偏振器可在４３０７８０ｎｍ 波长范围内工作,能够实现ＰＳＰ０ 在其最佳工作波长的偏振测量。     

Optical, infrared and millimetre-wave properties of Vega-like systems – IV. Observations of a new sample of candidate Vega-like sources

Photometric observations at optical and near-infrared wavelengths are presented for members of a new sample of candidate Vega-like systems, or main sequence stars with excess infrared emission due to circumstellar dust. The observations are combined with IRAS fluxes to define the spectral energy distributions of the sources. Most of the sources show only photospheric emission at near-IR wavelengths, indicating a lack of hot (∼1000 K) dust. Mid-infrared spectra are presented for four sources from the sample. One of them, HD 150193, shows strong silicate emission, while another, HD 176363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon materials. Detailed comparisons of the optical and IRAS positions suggest that in some cases the IRAS source is not physically associated with the visible star. Alternative associations are suggested for several of these sources. Fractional excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured previously for other Vega-like sources.     

Solar Large-Scale Emitting Chains: Evidence of Reality and Some Properties

A phenomenon of large-scale solar activity – relatively weak extended emitting chains with a characteristic length comparable with the solar disk radius or even diameter – were detected recently on the modified heliograms in the microwave (Nobeyama radioheliograph), soft X-ray (Yohkoh/SXT), EUV (SOHO/EIT, TRACE), and some other ranges. In this paper, some examples of the chains are presented to draw attention to their existence. Evidence on the reality of the chains is given, particularly based on the following factors: (a) the coincidence of the chains with other large-scale structures, particularly with boundaries of some coronal holes; (b) the similarity and identity of the clearly distinguishable chain-like structures on the various spacecraft and ground-based heliograms at different wavelengths, and (c) intensity changes of the chains of long duration ranging from a few tens of hours to several days. Some features of the long-lived and transient chains, including their relations to long-duration events (LDEs) and coronal mass ejections (CMEs), are outlined briefly. Based on the observed properties of the chains it is suggested that at least some of the chains are visible manifestations of separators or quasi-separatrix layers formed between different interacting large-scale magnetic flux systems in the evolving global magnetic solar atmosphere. In this paper, some images and movies illustrating the chains are presented also on the accompanying CD-ROM. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005226502908     

New progress on the Fresnel imager for UV space astronomy

We propose a next generation space instrument: the Fresnel imager, a large aperture and lightweight focusing device for UV astrophysics. This paper presents the laboratory setup used to validate the Fresnel imager at UV at wavelengths around 260 nm, and the results obtained. The validation of this optical concept in the visible domain has been previously published, with the first results on sky objects. In this paper we present new optical tests in the UV, of diffractive focusing and chromatic correction at wavelengths around 260 nm. The results show images free from chromatic aberration, thanks to a chromatic corrector scheme similar to the one used in the visible. To complete these tests and reach real astrophysical UV sources, we propose a short space mission featuring a Fresnel imager prototype placed on the international space station: during the mission this small aperture instrument would be aimed at UV sources such as bright stars and solar system objects, to assess at relatively low cost the limits in contrast and resolution of diffractive focusing in space conditions, on real UV astrophysical objects. At wavelengths from 100 to 300 nm, covering Lyman-α, we expect some scientific return from this mission, but the main goal is to increase the TRL, improving the chances of success for a later proposal featuring a full fledged Fresnel imager 10 meters in aperture or more, that would explore new domains of UV astrophysics at very high angular resolution and very high contrast.     

Parametric determination of the inclination of Keplerian circumstellar discs from spectropolarimetric profiles of scattered lines

Polarimetric line profiles arising from the Doppler redistribution of monochromatic stellar line radiation, Thomson scattered in a Keplerian rotating circumstellar disc are presented. It is shown that analysis of the scattered line profiles at different wavelengths which, due to Doppler redistribution, sample different disc regions allows the disc inclination to be determined.     

The influence of autoionizing states on absorption cross sections for atomic oxygen

Multi-channel expressions, in the dipole approximation, are used to calculate absorption cross sections for the ejection of an outer subshell electron from atomic oxygen. Autoionization levels have been included and the resulting resonances in the cross section are characterized by the dispersion formula. Averaged absorption cross sections are presented for wavelengths 911-754 Å and 705-675 Å.     

Theoretical visibility curves of late type stars

Theoretical visibility curves are presented for one carbon and one oxygen star. We aim to show the importance of measurements at wavelengths across the band.     

Raman instrument calibration for astromaterials and analysis of Mars return samples

The study of astromaterials generally involves the distribution of limited sample to many laboratories for analysis. Maximum scientific yield for a sample occurs when the data and results from different studies are examined as a collective. This collective examination of results will be particularly important for upcoming sample return missions including Mars sample return and OSIRIS-REx. When comparing results across laboratories, instrument calibration is of key importance. For Raman data, this includes the calibration of all three Raman band parameters: peak wavenumber position, bandwidth, and intensity. Although wavenumber is routinely calibrated, bandwidth and intensity are not; though they are commonly compared across studies. In addition, Raman instrument calibration is time dependent. An understanding of the time dependence of instrument calibration is important for proper calibration. Here, we use a mixture of well-established and recently developed calibration techniques to propose a standard method of calibrating Raman astromaterial data across laboratories to maximize the scientific value of the data.     

Maps of Titan's surface from 1 to 2.5 μm

We have acquired resolved images of Titan with the adaptive optics systems PUEO/KIR at the CFHT (Hawaii) and NAOS/CONICA at the VLT (Chile). We report here on images and maps (when data at several orbital phases are available) of Titan's surface from observations taken during the last 4 years (2001-2004) in all the methane windows between 1 and 2.5 μm (namely, at 1.08, 1.28, 1.6, and 2 μm). We present the only complete maps of Titan currently available at 1.3 μm, a spectral window where Titan appears particularly bright in spectroscopy, with a resolution of about 200 km at best on the ground. Our surface maps show the bright and dark regions sharing Titan's landscape with as much detail as possible from the ground and with high contrast in most cases. From the information gathered by comparing the maps at different wavelengths we derive constraints on the ground's composition. Our results could complete/optimize the return of the Cassini-Huygens mission.     

Dust models confronted with observations

We critically discuss the two major models for interstellar dust grains developed by Greenberg and Mathis and their co-workers. So far, knowledge about the dust has been obtained mainly from extinction and polarization measurements in the UV, visual and near IR. Analysis of dust emission at longer wavelengths generally requires an evaluation of the radiative transfer. Such a procedure is necessary to assess optical grain properties at long wavelengths and also to interpret the emission from the different kinds of IR objects. The 10 m silicate resonance and the submm dust absorptivity are presented as two examples. We then briefly summarize the implications which follow from the existence of extremely small dust grains.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

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.     

VLBA multi-frequency monitoring of SS433

We present results of VLBA observations of SS433 at two epochs at 5, 8.4, and 15 GHz. The AU-scale region of the source is resolved and shows the familiar quasi-symmetric core-jet structures. But at another epoch, the maps show bright knots ejected a few days before the observation, while the core-complex disappeared. The bright jet components are completely depolarised with fractional polarization less than 0.5%. We also present the first VLBI image of SS433 at 22 GHz.