Observings of occultations of stars by asteroids
Observings of occultations of stars by asteroids
This rather young direction in an astronomical science, in fact an opportunity precisely enough to predict occultations, has arisen more recently with the advent of exact astrometric catalogues.
It is necessary to note that important fact, that, observing occultations, the simple amateur can bring invaluable advantage for a science. And it needs only a small telescope and a stop watch, the majority of the stars published in lists of occultations, is brighter 11m. The received results, under condition of if an occultation observed some person in various points, can give value of diameter and even the form of an asteroid with accuracy which is inaccessible to the most powerful telescopes! Moreover, at the certain share of luck it is possible to open the satellite of an asteroid! But also it yet everything, at attentive tracking a course of an occultation is possible to open a duality of the star, and even to estimate its true diameter!
Someone can will think, that it only loud phrases, but are not present, examples to that read further under the text. I began the first observings of occultations in the spring 2002 and firstly they had irregular character. At the best I got out once a month to lead similar observings. Nevertheless, the success has not kept itself waiting for a long time. On 15 December 2002 I managed to register an occultation of a star the satellite of Saturn the Tethys, the similar event first in a history! And though it was not an asteroid, nevertheless, difficultly to describe feelings which you test when the star instantly dies away on your eyes, and then again flashes, and the reason thus marks, that you managed to see passage on a background of a disk far star of the satellite other planet located on distance of one and a half billions of kilometers. And still for a long time after observings does not leave feeling of moral satisfaction, that you managed to see unique historical event, and in fact each similar occultation, be the satellite of a planet or an asteroid, on the it is unique.
The most significant results...
2004
(828)Lindemannia 30.01.2004 - The first successful observing of an occultation on the basis of own calculations (V.Nevski)
(1135)Colchis 12.09.2003 - The first successful observing of an occultation of star by asteroid in the Vitebsk observatory.
(402)Chloe 01.09.2003 - The first successful observing an occultation of star by asteroid from territory of Belarus (S.Shurpakov)
(420)Bertholda 26.08.2003 - 77 positive timings!
SATELLITE of Saturn: Tethys 15.12.2002 - The first successful observing of an occultation of star by satellite of other planet from territory of Belarus (V.Nevski)
The strip of an occultation stars UCAC39840122 (brightness 12.7m) by asteroid (828) Lindemannia (prospective diameter 53km) passed through average of Russia, Belarus and Baltic. The data while preliminary, but, most likely, that behind an occultation, except for me, S.Shurpakov (Belarus) watched only, but to him has not carried with weather.
This first successful observing of an occultation which has been predicted on the basis of own calculations. I conducted observing over a course of an occultation in a personal observatory. As the tool, it was used 30cm a reflector of Newton with magnification 180х. The registered moments of the beginning and the end of an occultation accordingly: 20h 17m 39.29s and 20h 17m 40.23s on World time. Duration of an occultation has made 0.94secs.!
Conditions for observings this occultation were good enough. Weather stood excellent with an easy frost and very transparent sky. In spite of the fact that in 56 degrees from a star the Moon in 1-st quarter settled down, it at all did not prevent observing - a star it was visible distinctly.
The strip of an occultation has passed practically in exact conformity with predicted, and only the moment of time was for some seconds later. On a map my point of observing is marked red.
I conducted observing over a course of an occultation in the observatory. As the tool, it was used 30cm a reflector of Newton with magnification 180х. The registered moments of the beginning and the end of an occultation accordingly: 23h45m52.45s and 23h45m56.25s on World time. Duration of an occultation - 3.80secs. Unfortunately, other observers did not manage to register the fact of an occultation of star by asteroid. Conditions for observings this occultation were, to put it mildly, are far from ideal, the star weak, and all in 10 degrees from it has settled down almost full Moon which eclipsed all the shine even in an observatory. As much as possible to lower influence of a moonlight, it was necessary to be covered with a dark coverlet. Together with me participation in observings was accepted by Anton Gorokhov, planned, that he will watch an occultation in 150mm the Maksutov (180х), but because of a moonlight a star it was not visible in this telescope.The strip of an occultation an stars TYC0617-00997-1 (brightness 11.8m, spectral class F) by asteroid (1135) Colchis (brightness 13.7m, prospective diameter 52km) passed through average of Russia, Belarus and further on the north of Europe. Behind an occultation, except for me, watched only S.Shurpakov (Belarus) and C. Hills (Great Britain).
The valid strip of an occultation was displaced approximately on 30km to the north from predicted, such the conclusion follows that Shurpakov could not register an occultation though was within the limits of a path of a shadow while my point of observing (on a map it is marked red) settled down outside of a path, hardly to the north. The width of a path was 70km. During observing an occultation I could note hardly perceptible effect - the star at the moment of contact faded and inflamed not instantly, and smoothly. Duration of this process made about 0.1 - 0.2secs. Most likely, it is connected by that I observed an occultation of a star edge of an asteroid, it is visible on the circuit.
Line in the top part of figure - a course of an eclipse of a star. Under condition of the round form of an asteroid, the corner of an eclipse made about 20 degrees. Unfortunately, still there is no detailed information on an asteroid, therefore there is no opportunity more precisely to simulate this process. Speed of movement of an asteroid made 0.005"/sec and if it has really covered a star under a corner in 20 degrees it is possible to estimate approximately its diameter - 0.0003 angular seconds. Exclusive accuracy for amateur observings! A linear diameter while I can not calculate, as the distance up to a star is not known.
The predicted path of an occultation
Observing an occultation of star TYC1310-02435-1 by the satellite of Saturn Tethys of 15 desember 2002
The initial data on an occultation allowed very favorable forecast. Vitebsk got almost in the maximal duration of an eclipse with practically absolute probability. The beginning of an occultation should take place at 21:01 on local time.
At 21:00, with some share of risk to miss an occultation, I have started a stop watch, but all has passed successfully. The first contact has taken place on 25secs after predicted time. But has surprised not it. Expected maximal duration of an occultation should make 39.5secs, in a result this value appeared on 1sec more predicted!
In calculations of duration of an occultation the data from "Voyager" according to which diameter of the Tethys have accepted 1060км were used. Actually diameter of the satellite on 20-30км is more?
Unfortunately, this event could observe 8 more person and so it has turned out, that to Vitebsk the maximal duration of the phenomenon was came, and it enables to determine diameter of object. Preliminary results have really confirmed the received data. Diameter of the Tethys turned out 1085km. The map with chords of observers and a path of an occultation for Europe below is resulted, (asterisks mark points of observings).
The subsequent thorough studying of the observant data, has a little specified value of diameter and, eventually, the world community has stopped on value 1074км. In more detail about results.
So the first discovery in this direction of work of an observatory has been made, we shall be hopes, what not the last. Now in my plans to give it is more than attention to these observings.
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