We present the results of photometric observations of a dynamically new comet C/2010 S1 (LINEAR), conducted on June 18, 2012. The comet demonstrated a considerable level of physical activity at a heliocentric distance of 6.3AU. The brightness, measured under a phase angle of 8.9 degrees, was equal to 14.55±0.06 and 14.21±0.04 in Vand R-bands, respectively. The brightness distribution over the coma was found to be inversely proportional to the projected onto the sky plane nucleocentric distance, with a slope of approximately −1. Therefore, the calculated Afρ parameter, approximately 8400 cm and 8200 cm for V and R lters, respectively, was used to estimate the dust production rate. Assuming a steady out ow of dust particles from the nucleus, the dust production rate was estimated to be between 20 and 60 kg/s, depending on the assumed value of the grain's albedo. The V R colour index obtained from the near-nucleus region of the coma is in agreement with the solar V R colour index, and does not indicate signi cant reddening of the re ected solar radiation in the spectral region of 540 683 nm.

/pdf/photometry-of-distant-active-comet-c-2010-s1-linear-27c22w3liv.pdf

Photometry of distant active comet C/2010 S1 (LINEAR)

Observations of occultations of stars by asteroids provide useful information about the shape and size of asteroids. Ground-based multisite observations are especially valuable in that regard. To this end, on the joint initiative of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine and Astronomical Observatory of Taras Shevchenko National University of Kyiv, the development of Ukrainian network of stellar occultation observing stations is currently underway. Asteroids vary greatly in size with small asteroids being dominating. Occultations by small asteroids are visible across a rather narrow path. In such a case, it will not be feasible to make use of the entire network. Moreover, it is not always possible to conduct observations using telescopes with the required primary mirror diameter and light-gathering power or those equipped with special high-speed cameras. First of all, it applies to asteroids small in diameter for which the shadow tracks may run far from stationary telescopes. If this is the case, amateur telescopes or movable systems are employed. The aperture of such telescopes does not enable to acquire observations of occultations of faint stars with short exposure times. However, any observations are useful as they may help to determine the limits of asteroid diameter directly using techniques typical for the photometry of stellar occultations. This paper presents the results of observations of the star UCAC4 516-047388 occultation by the asteroid (853) Nansenia on 8 April 2021 performed at the Kryzhanovka observation station of Odessa I.I. Mechnikov National University. This observing station will become a part of the network of stellar occultation observers which is currently being set up. A Schmidt telescope(D = 271.25 mm, F = 440 mm) and Videoscan-415-2001 CCD camera were used to carry out observations. The ICX415AL chip (with the number of effective pixels 782 (H) x 582 (V) and unit cell size of 8.3 μm x 8.3 μm) serves as an interline image sensor for the specified CCD camera. The spectral sensitivity of the CCD camera approximately corresponds to the visible range. The NTP based PC system clock was used for the frame time-stamping. A GPS receiver with a specialised application running in the background was used to set (synchronise) the imaging system computer clock. The exposure duration for the occultation recording was chosen to be 5 seconds in order to acquire an image of the star adequate for photometric measurements, on the one hand, but to minimise the exposure time thus improving temporal resolution, on the other hand. The star UCAC4 516-047388 has a low brightness of 14.2 m which provides another reason for a long exposure time of 5 seconds to be used. This exposure time exceeds the maximum duration of occultation of 2.8 sec. An approach that enables us to draw a conclusion that the occultation has taken place and also to estimate the duration of such a phenomenon is adopted to construe the photometric (light) curve. Our calculations yield the duration of occultation τ = 2.0 ± 1.2 sec, which corresponds to the predicted value within the error. This paper also provides a description of the custom software, designed to process observations of occultations in the form of a series of graphic (image) files, which was employed for the stellar occultation by the asteroid (853) Nansenia. This software application can also be used to process observations of amateurs who will become involved in observing stellar occultations.

Stellar occultation by the asteroid (853) Nansenia on 8 April 2021

The size and shape of the asteroid belongs to its main characteristics. Knowledge of these quantities is necessary to determine the density and albedo of asteroids, as well as to understand the fundamental processes of formation and evolution of the solar system. The most popular method for determining these values for asteroids is the photometric method. However, the accuracy of its determination depends on the asteroid heating model used. There are direct methods for determining the shape – measurements using space missions and ground-based interferometers using the largest telescopes. Such methods give accurate results, but are not applicable for mass determinations. The method of observing the occultations of stars by asteroids is available to a wide range of observers, including amateur astronomers. A community of observers is being formed in Ukraine, who plan to start regular observations of these phenomena. When processing such observations, you need to know the exact position of individual observers and have a detailed occultation ephemeris, which can be found at https://asteroidoccultation.com. It is also necessary to have a good time service, which will allow determining the moments of the beginning and end of the occultation with sufficient accuracy. Detailed ephemeris provides information about the trajectory of the shadow on the Earth’s surface, indicating the exact time the shadow was in the given coordinates. The ephemeris also contains information about the horizontal coordinates of the star for the center of the shadow at the same time points. The ephemeris also gives the coordinates of the edges of the shadow and their errors, which include the errors of the predetermined asteroid diameter and the errors of the parameters of the asteroid’s orbit. The article provides a method for calculating the distance from the observation point to the trajectory of the shadow and a method for calculating the moment of time of the maximum occultation phase for a given observation point. It is possible to combine all independent observations into a single system to determine the diameter and shape of the asteroid knowing these values. This method is planned to be used for processing observations of the Ukrainian community of observers of occultations of stars by asteroids.

pdf/method-of-processing-synchronous-observations-of-star-qe5w94kk.pdf

Method of processing synchronous observations of star occultation by an asteroid from several points

This paper analyzes the influence of diffraction phenomena on measuring the moments of stellar occultations by the moon from television observations. It shows that making the necessary corrections can result in a significant improvement of the accuracy of measuring occultation moments from photometric curves. For bright stars, the accuracy of television observations can be as high as 3 ms.

Diffraction effects in the processing of television observations of stellar occultations by the moon

An electronic version of the catalog of observations of star occultations by the Moon is described. Methods for improving the observation accuracy are analyzed. Some features of the photometric curves of star occultations are described. We demonstrate that the diffraction effects arising in star occultations by the Moon can be detected with the use of television technique.

The Kyiv electronic database of television observations of star occultations by the moon

We performed a series of CCD observations in BVRI bands of a celestial region in cluster M67 (NGC 2682) to study the photometric system of the Kyiv network telescope. The signal recording system consists of a CGE-1400 telescope, Celestron #94175 focal reducer, an automatic turret with a set of UBVRI filters, and a Rolera Mgi CCD camera. The operating field of the system is 10.62′ × 10.62′. CCD images are processed in the MIDAS/ROMAFOT package. The reduction coefficients of the instrumental photometric system relative to Johnson’s BVRI system are determined. The resulted value of the module of distance to cluster M67 V − MV = 9.63m does not contradict the results of other researchers. The mean square errors for one determination of stellar magnitude for different bands are 0.02–0.12m. The errors in determining equatorial coordinates in the TYCHO-2 catalog system are ± 1″.

A study of the photometric system of the Kiev network telescope

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The Kyiv electronic database of television observations of star occultations by the moon

A study of the photometric system of the Kiev network telescope