Spectral and photometric variability of the “runaway” star HD 214930

The paper contains the analysis of spectral and photometric variability of the “runaway” star HD 214930. The previously reported period of 4.7 day of the star’s radial velocity variability is confirmed. Optical photometric variability of the star has not been detected.     

Major prospects of exoplanet astronomy with the World Space Observatory–UltraViolet mission

The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory–UltraViolet (WSO–UV). In its characteristics, the WSO–UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO–UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO–UV.     

Spectral and photometric evolution of the symbiotic nova HM Sagittae in 1986–2002

We present the results of our photometric and spectroscopic observations of the symbiotic nova HM Sge in 1994–2002. After its outburst in 1975, the star was shown to fade in the U, B, V bands at a rate of about \(0\mathop m\limits_. 05\) per year. The behavior of the B-V and U-B color indices reflects the variations of emission lines and, in part, the fading of the erupted component. We have studied the evolution of the emission spectrum in the range from Hδ to λ7751 Å over the period 1986–2002. The absolute fluxes in the hydrogen lines decreased by half, the ionization of the gaseous envelope continued to increase, and the Raman O VI lines appeared and strengthened. The significant (threefold) decrease in the ratio of the auroral and nebular O III lines is interpreted as a drop in the electron temperature of the envelope as its density decreased by a factor of about 1.5. We have measured the absolute intensity of the near-infrared continuum up to 10 000 Å and show that the infrared continuum follows the pulsations of the Mira star in the system HM Sge. We conclude that the dust envelope around the cool component became noticeably transparent in the 1990s.     

Spectral Broadening of the 3463 å Line in a Zirconium Plasma Generated by Laser Irradiation

In a vacuum chamber a plasma is produced by shining a pulsed Nitrogen laser, 20 mJ and 20 ns (Nordstrom, 1995), focused in an area of 0.1 mm² over a high purity polycrystalline Zirconium surface. This is accomplished by an optical system coupled to a monochromator, with a 0.1 Å resolution power, by detecting the visible and ultraviolet radiation for Zr I and Zr II. For the transition a₂ H_4.5 y² G_3.5 ⁰, measurements are performed at different distances with respect to the impact area, to determine the Doppler and Stark effects dependence on the laser fluency (J/cm²). The Zr II ions velocity is determined in order to estimate the Doppler broadening effect in the fitting of the Voigt profile for the spectral line studied. These measurements are performed in a shoot to shoot way.     

Time dependent studies of the aurora—I. Ion density and composition

Ion densities and composition are investigated in a time varying model aurora. There is a time lag between turning on the source of ionization and the resulting increase in ion densities that depends on the species and the height level in the ionsophere, so that altitude profiles of auroral electron densities evolve with time. Characteristic buildup times for the ionization are a few seconds at the altitude of maximum energy deposition, increasing to tens of seconds above and below this level. A wide range of composition ratios, n(NO⁺/n(O₂⁺ and n(NO⁺/n(O⁺), can be expected, depending on the time an observation is made during buildup or decay of ionization. The concentrations of atomic nitrogen and nitric oxide increase as a result of auroral ionization, but the associated characteristic times are long compared to the average duration of ‘auroral event’. Thus, intermittent auroral bombardment could result in a gradual buildup of these minor neutral constituents in the auroral atmosphere. Variations in the electron density during pulsating, fluctuating or coruscating aurora lag the source function variations by a few seconds in a typical aurora.     

Studying the errors in the estimation of the variation of energy by the “patched-conics” model in the three-dimensional swing-by

The swing-by maneuver is a technique used to change the energy of a spacecraft by using a close approach in a celestial body. This procedure was used many times in real missions. Usually, the first approach to design this type of mission is based on the “patched-conics” model, which splits the maneuver into three “two-body dynamics.” This approach causes an error in the estimation of the energy variations, which depends on the geometry of the maneuver and the system of primaries considered. Therefore, the goal of the present paper is to study the errors caused by this approximation. The comparison of the results are made with the trajectories obtained using the more realistic restricted three-body problem, assumed here to be the “real values” for the maneuver. The results shown here describe the effects of each parameter involved in the swing-by. Some examples using bodies in the solar system are used in this part of the paper. The study is then generalized to cover different mass parameters, and its influence is analyzed to give an idea of the amount of the error expected for a given system of primaries. The results presented here may help in estimating errors in the preliminary mission analysis using the “patched-conics” approach.     

The Violet Opacity in the Red Peculiar Stars – III. Spectral analysis of the SC star GP Ori

Medium-resolution (1.5-2.5 Å) spectrum has been obtained for SC star GP Ori in a wide range of wavelengths from 3730 to 6250 Å. It is characterised mainly by strong atomic lines, as well as moderately strong bands of the CN violet system and CH (0,0) and (0,1) bands at 4315 and 4890 Å. Weak bands of C₂, C₃, and ZrO molecules are observed, however, no evidence is found for the presence of either SiC₂ (Merrill-Sanford bands) or YO. The most prominent atomic lines along with the NaID12 are those of CaII (K,H), CaI at 4227 Å, SrI at 4607 Å, SrII at 4077 and 4215 Å, and BaII at 4554 Å. H seems to be in emission.     

Comment on “superrotation of the upper atmosphere by global deposition of meteoroids”

The hypothesis that superrotation of the Earth's atmosphere results from meteoroid influx is untenable. Meteor observations are not of sufficient precision to substantiate direct rotation when the meteoroid influx is treated macroscopically. Detailed dynamic studies argue against any possible direct rotation.     

The Lyman-alpha Solar Telescope(LST) for the ASO-S mission——Ⅱ. design of LST

As one of the three payloads for the Advanced Space-based Solar Observatory(ASO-S) mission,the Lyman-alpha(Lyα) Solar Telescope(LST) is composed of three instruments: a Solar Corona Imager(SCI), a Lyα Solar Disk Imager(SDI) and a full-disk White-light Solar Telescope(WST). When working in-orbit, LST will simultaneously perform high-resolution imaging observations of all regions from the solar disk to the inner corona up to 2.5 R_⊙(R_⊙ stands for the mean solar radius) with a spatial resolution of 4.8′′and 1.2′′for coronal and disk observations, respectively, and a temporal resolution of 30 – 120 s and 1 – 120 s for coronal and disk observations, respectively. The maximum exposure time can be up to20 s due to precise pointing and image stabilization function. Among the three telescopes of LST, SCI is a dual-waveband coronagraph simultaneously and independently observing the inner corona in the HI Lyα(121.6±10 nm) line and white light(WL)(700±40 nm) wavebands by using a narrowband Lyα beam splitter and has a field of view(FOV) from 1.1 to 2.5 R_⊙. The stray-light suppression level can attain10~(-6) B_⊙(B_⊙ is the mean brightness of the solar disk) at 1.1 R_⊙ and ≤5×10~(-8) B_⊙ at 2.5 R_⊙. SDI and WST are solar disk imagers working in the Lyα line and 360.0 nm wavebands, respectively, which adopt an off-axis two-mirror reflective structure with an FOV up to 1.2 R_⊙, covering the inner coronal edge area and relating to coronal imaging. We present the up-to-date design for the LST payload.     

Multi-frequency survey of background radiations of the Universe. The “Cosmological Gene” project. First results

The results of the first stage of the “Cosmological Gene” project of the Russian Academy of Sciences are reported. These results consist in the accumulation of multi-frequency data in 31 frequency channels in the wavelength interval 1–55 cm with maximum achievable statistical sensitivity limited by the noise of background radio sources at all wavelengths exceeding 1.38 cm. The survey region is determined by constraints 00 ^h < RA < 24 ^h and 40°30′ < DEC < 42°30′. The scientific goals of the project are refined in view of recent proposals to use cosmological background radiation data for the development of a unified physical theory. Experimental data obtained with the RATAN-600 radio telescope are used to refine the contribution of the main “screens” located between the observer and the formation epoch of cosmic background radiation (z = 1100). Experimental data for synchrotron radiation and free-free noise on scales that are of interest for the anisotropy of cosmic microwave background are reported as well as the contribution of these noise components in millimeter-wave experiments to be performed in the nearest years. The role of dipole radio emission of fullerene-type dust nanostructures is shown to be small. The most precise estimates of the role of background radio sources with inverted spectra are given and these sources are shown to create no serious interference in experiments. The average spectral indices of the weakest sources of the NVSS and FIRST catalogs are estimated. The “saturation” data for all wavelengths allowed a constraint to be imposed on the Sunyaev-Zeldovich noise (the SZ noise) at all wavelengths, and made it possible to obtain independent estimates of the average sky temperature from sources, substantially weaker than those listed in the NVSS catalog. These estimates are inconsistent with the existence of powerful extragalactic synchrotron background associated with radio sources. Appreciable “quadrupole” anisotropy in is detected in the distribution of the spectral index of the synchrotron radiation of the Galaxy, and this anisotropy should be taken into account when estimating the polarization of the cosmic microwave background on small l. All the results are compared to the results obtained by foreign researchers in recent years.     

High Spectral Resolution Observation of Decimetric Radio Spikes Emitted by Solar Flares – First Results of the Phoenix-3 Spectrometer

A new multichannel spectrometer, Phoenix-3, is in operation having capabilities to observe solar flare radio emissions in the 0.1?–?5 GHz range at an unprecedented spectral resolution of 61.0 kHz with high sensitivity. The present setup for routine observations allows measuring circular polarization, but requires a data compression to 4096 frequency channels in the 1?–?5 GHz range and to a temporal resolution of 200 ms. First results are presented by means of a well observed event that included narrowband spikes at 350?–?850 MHz. Spike bandwidths are found to have a power?–?law distribution, dropping off below a value of 2 MHz for full width at half maximum (FWHM). The narrowest spikes have a FWHM bandwidth less than 0.3 MHz or 0.04% of the central frequency. The smallest half-power increase occurs within 0.104 MHz at 443.5 MHz, which is close to the predicted natural width of maser emission. The spectrum of spikes is found to be asymmetric, having an enhanced low-frequency tail. The distribution of the total spike flux is approximately an exponential.