Ниже приводится ряд сообщений из рассылки PLANOCCULT. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- От: Michael Schmid Кому: Planoccult mailing list Написано: 14 сентября 2006 г., 23:22:12 Тема: [PLANOCCULT] Target star for 144 Vibilia (Sept. 19): double --====----====----====----====---- Hi Occultation specialists: As remarked in a side-note by Steve Preston on www.asteroidoccultation.com, the target star for the occultation by 144 Vibilia on Sept 19 is double. Nevertheless, it might be a promising event for people equipped with a camera (bright star) and thus worthwile calculating the paths for the two components. The only reference that SIMBAD gives for the star, the list of double stars by P. Couteau in Astron. Astrophys., Suppl. Ser., 79, 385-389 (1989) gives a PA of 234.7° and separation of 0.35" for year 1988.996. Based on only one night of observation with a filar micrometer at the 74 cm telescope on Pic du Midi, these values are probably not extremely accurate (the author says, +/- 15% for typical separation measurements with this telescope, +/- 1° for P.A.) Nevertheless, could maybe someone calculate the occultation path under the assumption that these values have not changed, or try to find newer data? Also, I think that a word of caution should be added to the plots of the ground paths (on various sites, e.g. EAON, asteroidoccultation.com) since the error margins given suggest much more accuracy than actually true for a double star; also the magnitude drop will be much less than stated there. Michael =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- От: Steve Preston Кому: Написано: 15 сентября 2006 г., 00:50:59 Тема: [PLANOCCULT] Target star for 144 Vibilia (Sept. 19): double --====----====----====----====---- > Also, I think that a word of caution should be added to the plots of > the ground paths (on various sites, e.g. EAON, asteroidoccultation.com) > since the error margins given suggest much more accuracy than actually > true for a double star; also the magnitude drop will be much less than > stated there. Yes, I agree that the "caution" for multiple stars could be more prominent in the posting on asteroidoccultation.com. Currently, the note in the comments section is the only "warning" that there might be an issue. I decided to leave the uncertainty data alone in these cases because this provides more flexibility for the observer. Although the uncertainty should be greatly increased in many cases, in some cases it makes sense to leave the uncertainty as calculated. If the target star is the larger of a pair widely separated stars with no noticeable motion, the uncertainty estimate is probably good. If the stars are 0.5" apart with apparent motion, the uncertainty estimate is not accurate. To save myself the time of trying to determine the best way to treat each double star situation, I merely note that the star is double and leave it to the observer (or postings on Planoccult) to research the particulars of a specific event. I will put it on my "todo" list that I should make a more prominent notation in the event web page for double stars. Ideally the notation would be link to a small help page explaining the issue. Steve =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- От: jlx@meteores.net Кому: planoccult@AULA.COM Написано: 15 сентября 2006 г., 16:16:32 Тема: [PLANOCCULT] Double star COU581 occulted by Vibilia on next Sep.18-19. Файлы: VIBIL_AB.GIF --====----====----====----====---- >From J.Lecacheux. I- 144 VIBILIA (diam. 178 km or 142 km, depending from the source) will occult a V= 9.7 star on Tuesday Sep.19 at 01:32-34 UT. As the track will cross Europe diagonally from the Iberian peninsula to Russia, with no moon in the sky, this event should have appeared as very favourable to many [planoccult] aficionados. Unfortunately the target star is BINARY, as it was pointed out first by Steve Preston in his update, with components almost equal and 'a ~ 0".4 separation'. It results two main consequences : 1/ Steve's path shall split into two parallel paths; 2/ The drop depth will be limited to ~0.75 magnitude only. The first consequence is a good new for our occultation community, as a broader set of countries will be concerned; but the second one is a bad new for visual observers, as with a 0.75 mag. drop you can get secure result only by doing some camera recording. II- I have searched some informations about this binary star. It is known as COU 581, discovered by the French astronomer P.Couteau. Only three visual measurements seem exist : Date Separation P.A. Observer Refractor ---------------------------------------------------------- 1970.96 0".33 231.2 P.Couteau Nice 50-cm 1977.09 0".34 240.4 W.D.Heintz 60-cm Sproul 1988.996 0".35 234.7 P.Couteau Nice 76-cm. It looks like no new measurement was made since almost 18 years ! Performing a linear fit would yield 0".37 and P.A.= 238 at today's date, but this is unsignificant from a stastistical point of view, as the visual accuracy was ± 0".05, at best. So one might simply assume for both 1980 and 2006 the mean values 0".34 and 235 degrees. However from dynamical considerations, a bigger uncertainty arises, as explained below. The two magnitudes are V= 10.4 and V= 10.5. I presume that we have a couple of quasi-solar G0V stars at ~150 parsecs. So their apparent separation on the sky was 50 or 55 AU (Astron. Units) near 1980. How much has it become today ? Luyten (1930) published a formula predicting at confidence level 67 % the orbital period of a visual binary star of which are known its separation, parallax and total mass : log(P) = 1.460*log(d) -0.487*log(M) + 0.168 ± 0.4 (P in years, d in AU, M in solar masses) By applying that here, taking M= 2.1 solar masses, we get P= 3.3 (+5.0,-2.0) centuries, i.e. between 1.3 and 8.3 centuries. So COU 581 may have covered between 3 % and 20 % of its complete orbit since 1980. Sure that the separation and the P.A. should have changed a bit !... As the P.A. did not vary by more than some degrees between 1970 and 1988 (only +3.5 degrees if we rely on Couteau), either the orbital period is long (1.3 century -or so- then being excluded), or we see the orbit roughly side-on. Finally by doing some numerical tests with side-on orbits, I have concluded that the current separation probaby lies anywhere between 0".2 and 0".5, and the current P.A. between 230 and 245 degrees. III- In order to test the above rough estimations, I also planned new measurements of the couple with the 1-meter Pic-du-Midi, using a 0".1 pixel and a severe image selection, which often allows us to reach an Airy-like quality. Alas the weather was bad along all this week. So very likely this project will fail. As I cannot obtain new values, I resign myself to assume the parameters 0".37 and 238 degrees from my initial linear fit, and in consequence to claim very large uncertainties. Then it is easy to compute that the two center lines will be separated in the Bessel plane by 310 (+200,-180) km, or on the ground by 375 (+240,-215 km). The "A" path from the main star will be located southeasterly, and the "B" path from the companion northwesterly. Let us look at the modified version of Steve's map here attached. VIBIL_AB.GIF Every path (A: pink, B: blue) is 173 km wide (measured on the ground or a roadmap), like in the original version. For example : starting from the original center line of Steve, if we want to join the new center line of the B (blue) path, we have to travel 375/2= 187.5 km to the NW. Remark the tremendous expansion of the error limits. The lateral uncertainty (1 sigma) was 0.22*173= 38 km (really a tiny value) on the original version. So Steve drew the NW limit 38 km outside the NW edge of the shadow path. Now the NW limit is pushed at 38 + 200/2 ~ 140 km outside the new NW edge. So it lies at 140 + 173/2 + 187.5 ~ 414 km NW from the original center line, almost reaching Paris, Berlin or Gdansk. Finally we may conclude that the European observers have to watch the VIBILIA event within a 800km-wide band, almost five times broader than Steve's original occultation path. This includes the whole Spain and Portugal, 70 % of France, the south half of Germany and the north half of Italy, the whole Switzerland, Austria, Slovenia, Croatia, Czech Republic, Slovakia and Hungary, 80 % of Poland, the north 25% of Romania, the whole Belarus and the south half of Lithuania, north 60 % of Ukraine, and finally an important part of west Russia (sorry if I fortuitously forgot any country). People staying within the gray strip between A and B have nearly equal chances to catch B ~11 seconds early (by reference to the times of Steve's update), or A ~11 seconds late, or... nothing. Clear sky to everyone. PS : Succesful chords would provide a fourth measurement of COU 581 ! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- От: jlx@meteores.net Кому: planoccult@AULA.COM, stevepr@acm.org, schmid@iap.tuwien.ac.at, frappa@euraster.net, apexoccult@versateladsl.be Написано: 16 сентября 2006 г., 00:03:54 Тема: [PLANOCCULT] COU581 and Vibilia : ERRATUM and remark. Файлы: VIBIL2AB.gif --====----====----====----====---- >From J.Lecacheux. Sorry. I made a mistake (a stupid scale error) when I prepared the vibil_ab.gif map attached to my precedent message. Please discard it, and consider instead the here attached vibil2ab.gif new version. (Note: the old version would be nearly correct if the A-B separation were 0".30 instead of 0".37). I take advantage of the present erratum to add a remark : I wrote in my precedent message : > People staying within the gray strip between A and B have nearly > equal chances to catch B ~11 seconds early (by reference to the > times of Steve's update), or A ~11 seconds late, or... nothing. Actually it may exist a fourth possibility in the limit case of a small A-B separation (rho < 0".25) plus a large P.A. (near 245 deg.) Such a combination is not very probable, but is not impossible. Then people located near Steve's nominal center line could observe two successive grazing occultations : first the B star would briefly disappear behind the southern limb of Vibilia; then the A star would produce a second occultation, now behind the northern limb, about 15 seconds later . :-)) =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- От: David Dunham Кому: jlx@meteores.net Написано: 16 сентября 2006 г., 01:32:43 Тема: [PLANOCCULT] Double star COU581 occulted by Vibilia on next Sep.18-19. --====----====----====----====---- Jean and Steve, When you spot double star issues like this for asteroidal occultations that could be well-observed, please also copy Brian Mason at USNO (last Cc: address). As keeper of the WDS, he may have newer information, and with some warning, could also schedule new speckle interferometric or other observations. David