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We present preliminary results of the narrow-band CN observations of comet 8P/Tuttle from early January 2008, realized as part of a project consisting of near-simultaneous spectroscopic monitoring of HCN at millimeter-wavelengths and optical imaging of the coma. The mean-image subtraction method revealed low-contrast CN envelopes. Using the image cross-correlation technique we measured the projected velocity of these shells. For the sunward part we found it to be equal to 0.96 +/- 0.03 km s-1 on January 4 and 1.10 +/- 0.01 km s-1 on January 9, whereas the anti-sunward part reached 0.73 +/- 0.05 and 0.80 +/- 0.02 km s-1, respectively. The periodicity of gas emission was investigated using a repeatability of the shells, their kinematics, and an aperture photometry of the near nucleus region. We found a period of 5.70 +/- 0.07 h (along with multiples), consistent with previous findings by other authors. A toy Monte Carlo model was implemented to reproduce the time-series of the CN images. We show that emission of HCN into a relatively wide cone by a single active region on a rotating nucleus is the most probable scenario. [PUBLICATION ABSTRACT]

RS Oph is a symbiotic recurrent nova containing a massive white dwarf with heavy mass loss during activity. In August 2021, it underwent its seventh optical eruption since the end of the 19th century. The goal of this work is to analyse the structure of the outflows from the outbursting object. Based on broad-band \\(U\\), \\(B\\), \\(V\\), \\(R_{\\rm C}\\), and \\(I_{\\rm C}\\) photometry and high-resolution H\\(\\alpha\\) spectroscopy obtained at days 11--15 of the outburst, we derived some parameters of the system's components and outflows and their changes during our observation. The effective temperature of a warm shell (pseudophotosphere) produced by the ejected material and occulting the hot component of the system was \\(T_{eff}=15000\\pm1000\\) K and the electron temperature of the nebula was \\(T_{e}=17000\\pm3000\\) K throughout the observations. The effective radius of the pseudophotosphere was \\(R_{ eff}=13.3\\pm2.0\\) R\\(_{\\odot}\\) and the emission measure of the nebula \\(EM=(9.50\\pm0.59) \\)10\\(^{61}\\) cm\\(^{-3}\\) for day 11 and \\(R_{eff}=10.3\\pm1.6\\) R\\(_{\\odot}\\) and \\(EM=(5.60\\pm0.35)\\)10\\(^{61}\\) cm\\(^{-3}\\) for day 15. To provide this emission measure, the bolometric luminosity of the outbursting object must exceed its Eddington limit. The mass-loss rate of the outbursting object through its wind is much greater than through its streams. The total rate (from wind + streams) was less than \\((4-5)\\) 10\\(^{-5}\\) (d/1.6kpc)\\(^{3/2}\\) M\\(_{\\odot}\\)yr\\(^{-1}\\). The streams are not highly collimated. Their mean outflowing velocities are \\(\\upsilon_{b}=-3680\\pm60\\) km s\\(^{-1}\\) for the approaching stream and \\(\\upsilon_{r}=3520\\pm50\\) km s\\(^{-1}\\) for the receding one if the orbit inclination is 50\\(^\\circ\\).

Comet 9P/Tempel 1, the target of the Deep Impact mission, has been intensively observed for a long time period before the encounter. Pre-impact ground based monitoring of the comet was an important prerequisite for the success of the first space experiment in which a comet is treated by an artificial impact. It provided the background data needed to disentangle the features caused by the impact from variations caused by the natural activity of the comet. In this paper we present results from the ESO-monitoring of the comet, conducted in the thermal infrared and optical spectral ranges during several months before the Deep Impact encounter with the comet.

On March 31 and April 1, 1997, simultaneous photometry and polarimetry of comet Hale-Bopp's dust was conducted with the two-channel focal reducer of the Max-Planck-Institute for Aeronomy attached to the 2 m telescope of Pik Terskol Observatory (Northern Caucasus). Interference filters at642 nm and 443 nm selected red and blue narrow-band continuum windows. The observations have been averaged over the one hour of timethe comet could be observed. The polarization maps cover an area of about1 arcmin2 around the nucleus. The values of polarization degree measured close to the nucleus agree very well with observations obtained with aperture polarimetry. They are lower than in the surrounding coma by about 1%. In our field of view the polarization increases along the sun-comet line from the solar to the antisolar side by about 3%. The dust shells are visible in the polarization images. The polarization in the shells is higher by 1 to 2%and this increase is higher in the red than in the blue range. Therefore the ratio of red to blue polarization (≈ 1.2) increases in the shells by ≈ 0.03. In principle, the polarization excess in the shells, the ratio of red/blue polarization and the higher integrated polarization as compared to other comets can be explained by an excess of particles of radius of about 0.1 μm. Such particles, however, are subject to strong radiation pressure and will be pushed back into the tail before they reach the observed location of the shells. Real Rayleigh particles cannot explain the observed increase in the ratio of red/blue polarization. One therefore cannot exclude the possibility that the excess polarization in the shells is caused by fluffy aggregates via effects which are presently not well understood. The colour map shows features not well related to intensity and polarization, perhaps another dust shell of a different particle size.

Since many years cometary ions have been observed by the authors and their coworkers in order to study the comet-solar wind interaction. Comets with water production rates ranging from 10 super(28)(46P/Wirtanen) to 6 10 super(30)molecules s super(-1)(C/1995 O1 Hale-Bopp) have been observed. In this paper we briefly introduce the physics of the comet-solar wind interaction. New observations of comet C/1996 Q1 (Tabur) are presented, where for the first time H sub(2)O super(+)and CO super(+)ions have been recorded exactly simultaneously with a two-channel system. They are compared with previous observations of comets C/1989 X1 (Austin), 46P (Wirtanen) and 109P (Swift-Tuttle). We use a new method of Wegmann et al. (1998), based on the MHD scaling law, to determine the water production of comet Tabur from its H sub(2)O super(+)column density map and obtain a value of 3.3 10 super(28)water molecules s super(-1). Nonstationary phenomena like tail rays and so-called tail disconnections are very briefly reviewed. A movie of plasma envelopes observed in the light of OH super(+)in comet 1995 O1 (Hale-Bopp) is presented on the attached CD-ROM.

Fabry-Pérot interferograms of comet Hale-Bopp were obtained on several nights in March and April 1997. For this purpose we utilized the 2-channel focal reducer of the Max-Planck-Institute for Aeronomy at the 2-m telescope of the Pik Terskol Observatory. Solid Fabry-Pérot etalons of resolving power 30000 were used in both channels of the focal reducer. The main aim of this study is to measure the velocities and abundances of OH+ and H2O+, both ions closely related to the same parent molecule, H2O. In the blue channel interferograms we identified several individual OH+ rotational lines of the A3Πi - X3Σ− (0-0) transition and measured their Doppler shifts. The target emissions in the red channel were the H2O+ lines of the A2A1 − X2B1 (10-0) band. We found that the line of sight velocities, obtained from the Doppler shifted wavelengths of emissions in the comet are higher in sunward direction than in the plasma tail and do not exceed 20 km s–1. The corresponding values, deprojected in antisolar direction, are consistent with predictions by magnetohydrodynamical models of the solar-wind-comet interaction, when one accounts for the extremely high gas production rate of comet Hale-Bopp.

The UBVRI broad band photometric system is widely used in CCD astronomy. There are a lot of sets of standard stars for this photometric system, the Landolt's and Stetson's catalogues being the most precise and reliable. Another photometric system, recently considerably spread in CCD observations is ugriz, which originates from the Sloan Digital Sky Survey (SDSS) and has now many variations based on its 5 broad-band filters. One of the photometric systems based on it is The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). In this paper we compare the BVRI magnitudes in the Stetson catalogue of standard stars with the magnitudes of the corresponding stars in the Pan-STARRS1 (PS1) grizyw catalogue. Transformations between these two systems are presented and discussed. An algorithm for data reduction and calibration is developed and its functionality is demonstrated in the magnitude determination of an asteroid.

Aims. We aim to investigate how polarimetric observations can improve our understanding of the nature and diversity of M/X-type asteroids. Methods. Polarimetric observations of the selected M/X-type asteroids were carried out at the Tohoku 0.6-m telescope at Haleakala Observatory, Hawaii (simultaneously in BVR filters), the 2-m telescope of the Bulgarian National Astronomical Observatory in Rozhen (in R filter), and the 2.15-m telescope of the Complejo Astronómico El Leoncito (CASLEO), Argentina (in V filter). We analysed the polarimetric characteristics of M/X-type asteroids along with the available data obtained by other techniques. Results. New polarimetric observations of 22 M/X-type asteroids combined with published observations provide a data set of 41 asteroids for which the depth of a negative polarisation branch and/or inversion angle were determined. We found that the depth of the negative polarisation branch tends to increase with decreasing steepness of the near-infrared spectra. Asteroids with a deeper negative polarisation branch tend to have a higher radar circular polarisation ratio. We show that, based on the relationship of the depth of the negative polarisation branch and inversion angle, two main sub-types can be distinguished among M-type asteroids. We suggest that these groups may be related to different surface compositions similar to (1) irons and stony-irons and (2) enstatite and iron-rich carbonaceous chondrites.

We report spectroscopic observations of the \\(H\\alpha\\) emission line of the recurrent nova RS~Oph obtained between 12 and 23 August 2021 during the recent outburst. On the basis of the sharp P~Cyg profile superimposed onto the strong H-alpha emission, we estimate that the outflowing velocity of the material surrounding RS Oph is in the range 32 km/s < V_{out} < 68 km/s. The new GAIA distance indicates that the red giant should be probably classified in between II and III luminosity class. The spectra are available upon request from the authors and on Zenodo.

The rotation state of small asteroids is affected by the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, which is a net torque caused by solar radiation directly reflected and thermally reemitted from the surface. Due to this effect, the rotation period slowly changes, which can be most easily measured in light curves because the shift in the rotation phase accumulates over time quadratically. We collected archived light curves and carried out new photometric observations for asteroids (10115) 1992 SK, (1620) Geographos, and (1685) Toro. We applied the method of light curve inversion to fit observations with a convex shape model. The YORP effect was modeled as a linear change of the rotation frequency \\(\\upsilon \\equiv \\mathrm{d}\\omega / \\mathrm{d}t\\) and optimized together with other spin and shape parameters. We detected the acceleration \\(\\upsilon = (8.3 \\pm 0.6) \\times 10^{-8}\\,\\mathrm{rad}\\,\\mathrm{d}^{-2}\\) of the rotation for asteroid (10115) 1992 SK. This observed value agrees well with the theoretical value of YORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we obtained \\(\\upsilon = (3.3 \\pm 0.3) \\times 10^{-9}\\,\\mathrm{rad}\\,\\mathrm{d}^{-2}\\), which confirms an earlier tentative YORP detection. For (1620) Geographos, we confirmed the previously detected YORP acceleration and derived an updated value of \\(\\upsilon\\) with a smaller uncertainty. We also included the effect of solar precession into our inversion algorithm, and we show that there are hints of this effect in Geographos' data. The detected change of the spin rate of (10115) 1992 SK has increased the total number of asteroids with YORP detection to ten. In all ten cases, the \\(\\mathrm{d}\\omega / \\mathrm{d}t\\) value is positive, so the rotation of these asteroids is accelerated. It is unlikely to be just a statistical fluke, but it is probably a real feature that needs to be explained.