Post Observation Request from David Dunham Subject: Need lightcurve observations of (85) Io Date: Wed, 13 Dec 95 18:31:00 est On December 9th, six chords were timed of an occultation of SAO 111235 by (85) Io. A reasonable size can be determined from these chords, and it seems to be several percent larger than the IRAS diameter. So it is critical that we know what phase of the lightcurve at which the occultation occurred to estimate an overall diameter of the asteroid. (85) Io has a 6.875-hour rotation period and is near opposition at 11th mag., well-placed for observation. Please pass on this message to those who might be able to make photometric observations of the lightcurve during the next few weeks. David Dunham, IOTA _______________________________________________________ Consolidated Reports (Various input about/concerning the same site are group together) Numbered 0 to 16 Updated Dec 15, 9:00 AM PST, jph _________________ _____________________________________ 0) Jim Stamm, Tucson Subject: Io Occultation David, I wasn't going to make an effort at Io because of the twilight problems that you mentioned. After you purged my track, it became a challenge. It was easy to secure PPM 146634 by hopping from Deneb, Capella, and Xi Tau (Aldebaran was behind the house); while fine tuning the setting circles. From here it was 16.7 turns of the dec. knob, and wait 3 minutes and 48 seconds. And here it comes! Slipped in the 120x eyepiece, and began the run at 00:43:00. This was success, because I had the star in a clear steady field, and could add the "negative" observation to whatever the rest obtained. But it gets better! At 00:44:53 +/- 0.5 sec. the bloody thing went out. It returned at 00:45:01.7 +/- 0.2 sec. I was counting the seconds with WWV, and feel absolutely confident in a real event at those times. I was at home (W110.9645, N32.4204, 842m). Thanks for the jump-start! Jim IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object):_________Io________ Star: ____PPM 146634________ Date (U.T.):_____09 Dec. 1995_________ Predicted Time (U.T.):___00:44______ Observer Name:____________Jim Stamm________ Telephone:(520) 575-0830_______ Postal Address:______11781 N. Joi Dr. Tucson, AZ 85737____________________ E-mail Address:______jimstamm@aztec.asu.edu_____ Fax:______________________ TELESCOPE: Aperture:_20 cm_ Focal length:_200 cm__ Type:______SCT________ Eyepiece Power:__120__ Observing site name: ___Tucson, AZ______________ Longitude:_W 110.9645_____________ Latitude:_N 32.4204_________________ Height above sealevel:_842 m_ How determined?:__USGS___________________ Sky Transparency (Circle one, or delete two): Good Star Image Stability ("seeing"; as above): Good Other Conditions: (Wind, Clouds, Lights, etc.):____________________________ EVENT TIMINGS: (All times in Universal Time) Time Source:_____WWV_____ Recording method:_Tape Recorder____________________ Was the Asteroid Visible in you Scope? _______ Approx. Limiting Mag.:______ Universal Time Estimated Accuracy, Remarks h m s Reaction Time, Started Observing: 00:43:___.___ (sec.) ____________________ Star and Object Merged: ___:___:___.___ ____________________ Disappearance: 00:44:53.0.___ __.___ _+/- 1.0 sec._______ Estimated Closest Approach: ___:___:___.___ ____________________ (if no D/R) Reappearance: 00:45:01.7 __.___ _+/- 0.2 sec._______ Star and Object Separated: ___:___:___.___ ____________________ Stopped Observing: 00:48:___.___ ____________________ Was your reaction time applied to the above timings? ___Yes___ If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: _______ List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: _______________________________________________________ Send Jim Stamm E-mail: jimstamm@aztec.asu.edu report to: 11781 North Joi Drive If an occultation is timed, copy to: Tucson, AZ 85737 U.S.A. David_Dunham@jhuapl.edu And Note from Dunham A good chord near the southern limit at track 127S. So the central line might have passed s. of Powell Obs. and the shift from the Flagstaff prediction may have been 0.5 or even 0.6 path widths. David Harvey's position was a little farther s., either at his home? at 131S, or at Steward Obs. at 139S (I would think that might have been too far south considering Stamm's short event). David Addition note from Stamm David, I forgot to include in my report a note about the R. I sent it to Nason, but left it out of "additional remarks": About 1 second before the R I saw something that looked like the target star, but much dimmer. It seemed brighter than Io should be, but when PPM 146634 "snapped" on, I felt the difference in magnitudes was at least 3, so I attributed it to the asteroid. Now that I have heard "double star", I feel that would be a better explanation of what I saw. Jim And response from Dunham Jim, Thanks for the remark. I don't think it was stellar duplicity, which I have considerable doubts about; even if it were, what you saw should have been visible during the whole occultation, not just a small part of it. None of the central occultation observers with dark skies reported any step events. Since you were so near the southern limit, it very well could have been the star almost reappearing in a valley on the asteroid; the diffraction (or stellar diameter) "toe" of the lightcurve would be a few hundred meters, I think. Such "flashes" were seen near the limits of the Pallas and Nemausa occultations in 1983. David ________________________________________ 1) Guy Nason, Ontario IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object):___85 Io_____________ Star:__SAO 111235_____ Date (U.T.):_1995-12-10______________ Predicted Time (U.T.):_00:41______ Observer Name:_Guy Nason______________ Telephone:_(416) 222-4814______ Postal Address:_5 Abbotsford Rd., North York, ON, M2N 2P6, Canada_ E-mail Address:___Guy_Nason@tvo.org_______ Fax:_____________________ TELESCOPE: Aperture:_25cm__ Focal length:125cm_ Type:_Newtonian_____ Eyepiece Power:_119x___ Observing site name: Hwys 9 & 400, Ontario Longitude:_79d 36' 51".7 West Latitude:_44d 01' 27".0 North Height above sealevel:_225M +/-5M How determined?:1:50,000 Cdn topo. Sky Transparency (Circle one, or delete two): Fair Star Image Stability ("seeing"; as above): Good Other Conditions: (Wind, Clouds, Lights, etc.):_Hazy Cold (-17C)__ EVENT TIMINGS: (All times in Universal Time) Time Source:_WWV (5MH)_ Recording method:_Audio Cassette Recorder__ Was the Asteroid Visible in you Scope? No___ Approx. Limiting Mag.:4.5 Universal Time Estimated Accuracy, Remarks h m s Reaction Time, Started Observing: 00:36:00 (sec.) ____________________ Star and Object Merged: ___:___:___.___ N/A_________________ Disappearance: 00:40:50.8 0.4 0.05 sec. Estimated Closest Approach: N/A (if no D/R) Reappearance: 00:41:09.7 0.4 0.05 sec. Star and Object Separated: N/A Stopped Observing: 00:47:00 Was your reaction time applied to the above timings? _yes____ If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: _N/A___ List all Interruptions in Observing: Reason From 00:45:27 to 00:45:29 Intruding car headlights From ___:___:___ to ___:___:___ __________________________________ Additional comments: Sudden drop and rise in magnitude: no stepped or gradual changes observed. Asteroid was visible only during the occultation; steady and constant near the limit of visibility (much fainter than field star to narth and east of target). Good morning, David and Jim! Just a quick note to give some additional details of the 85 Io/SAO111235 occultation not included on the report form e-mailed yesterday. Four of us attempted to observe the event. Brian Cheaney was totally clouded out about 50kms. south of my position. Robert Chapman lost the star behind clouds about 5 minutes before the predicted time and regained it 2 minutes after the show ended. He was in his backyard observatory about 30 kms. east and 10 kms. north of me. Frank Dempsey was successful. I don't have his detailed report yet, but he told me he observed a 20.5 second disappearance from his location perhaps 50 kms. southeast of mine. I'll pass along his report form as soon as I get it. Once I know his exact location, I'll try to determine both his track and mine vis a vis your track data message of 12/08. I observed the occultation, but not before a 150 km. chase of a hole in the clouds. I had originally planned to head to Huntsville (track 3N), but a "severe snow squall warning" for the lea of Georgian Bay convinced me to stay stay well to the south. So I drove as far north and west as I dared, watched the clouds move south-eastward and retraced my path to a place I hoped (yes!) would stay clear long enough to do the job. But, man, it was cold! minus17C and windy. So my poor 25 cm. Newtonian telescope didn't have enough time to become temperature stabilized, limiting my magnification to 119x (10.5 mm eyepiece). With a hazy sky limiting the Mv to about 4.5, I was unable to see the asteroid except during the occultation itself. (Bob Chapman had no trouble seeing it in his 20cm. SCT as it moved away from the star a few minutes after the event.) I don't know how many asteroidal occultations you've seen, but this is my first. After so many unsuccessful attempts (either clouded out or observed misses) over the last few years this was a great thrill! I was afraid this would be another disappointment, especially after seeing a pair of beautiful sundogs just before sunset. I've come to hate sundogs, so often precursors to cloudy failure (most recently in PA 2 weeks ago), but this time they were the vanguard of success. And a pair of moondogs escorted me home shortly afterward! David, did you get to Kansas City? How did others fare? Frank and I are planning to give a talk at the next RASC Toronto Centre meeting on 10 Jan. Any info you can give us on observations elsewhere will be very much appreciated and we'll include them in the presentation. I was very excited and relieved to learn that Frank (a very experienced variable star observer) had also recorded a duration longer than the expected maximum of 17 seconds. I had 2 tape recorders running and both tapes played back a corrected time of 18.9 seconds. So we must have been near the centreline of the path and, if so, then the path may have shifted southward from the latest predictions. I might have missed it entirely if not for the bad weather in Huntsville. Am I correct in surmising that the asteroid must be at least 189kms. wide, given Frank's 20.5 second duration? 157 kms (predicted diameter) X 20.5 secs. (observed dur.) = 189.3 kms. 17 secs. (predicted duration) Can't wait for the next one. Guy __________________________ 2) Tom Martinez, Cleveland MO I have succesfully observed the occultation of SAO 111235 by asteriod 85 Io on December 9. Bob Sandy contacted me that morning about the event and asked if I could observe and time the event. He tells me that you were also observing from somewhere near St. Joseph, MO. I have given the tape of my observation to Bob. I found your e-mail address via the Internet at the IOTA Web page. You are asking for help in this endevour and I would like to offer my services. I have been doing graze and occultation observations for Bob off and on over the last 16 years, but I have never done an asteriod occultation. It was very exciting. I understand video is a good way to do more accurate observations. I have access to a video camera that is 1 lux and have taped the moon and the planets. Are there other cameras that would be better suited? Tom Martinez (martinez@sound.net) 45 Lone Pine Drive Cleveland, MO 64734 I just read the report from Jimstamm@aztec.asu.edu and the time for Bob Sandy at Powell Observatory. I was about 10 miles north east of Bob in Cleveland, MO Lat - N38.68, W94.59 and my brief review of my tape was an occultation of about 17 to 18 seconds. Bob will get you a more accurate time. Tom Martinez Note: Cleveland, MO, is about 10 miles northeast of Powell Obs., so Tom's chord will be almost the same as Bob Sandy's. David IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: SAO 111235 Date (U.T.): Dec. 10, 1995 Predicted Time (U.T.): 00:43.2 Observer Name: Tom Martinez Telephone: (816) 658-3959 Postal Address: 45 Lone Pine Drive; Cleveland, MO 64734 E-mail Address: Martinex@sound.net Fax: TELESCOPE: Aperture: 8 " Focal length: 2000mm Type: Sch-Cas Eyepiece Power: 82 Observing site name: Residence Longitude: W 94 35 53.6 Latitude: 38 40 01.8 Height above sealevel: 298 m How determined?: USGS Sky Transparency (Circle one, or delete two): (Good) Fair Poor Star Image Stability ("seeing"; as above): Good (Fair) Poor Other Conditions: (Wind, Clouds, Lights, etc.) EVENT TIMINGS: (All times in Universal Time) Time Source: WWV Recording method: Radio, recorder, voice Was the Asteroid Visible in your Scope? Yes Approx. Limiting Mag.: Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: 00:40:55.0 ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: 00:42:55.9 1.0 +/-0.5 sec. Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: 00:43:14.6 0.5 +/-0.2 sec. Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: 00:44:20.s ____________________ Was your reaction time applied to the above timings? No If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: N/A!! List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: _________________________________________________________ 3) Dean Armstrong, Chicago Subject: Re: 85 Io occultation Clouded out here in Chicago- Ryerson Astronomical Society From: "Dean W. Armstrong" ___________________________________________________________ 4) Frank Dempsey , Greenwood, Ontario Subject: asteroid 85 Io occultation report Asteroid: 85 Io PPM 146634 Star: SAO 111235 Date: 1995 Dec 10 Predicted Time: UTC 00:41 Observer Name: Frank Dempsey Telephone: 905-420-4236 Postal Address: 1152 Tanzer Court, Pickering, Ontario, Canada L1W 3S6 E-Mail Address: fjd@idirect.com Fax: None Telescope: Aperture: 15 cm (6 in) Focal Length: 150 cm (60 in) Type: Newtonian Reflector Eyepiece Power: 60 Observing Site Name: Greenwood Longitude: W. 79=B0 04' 35.3" (79.0598056=B0 ) Latitude: N 43=B0 56' 13.8" (43.9371667=B0 ) Height above sealevel: 160 m How Determined: Canadian Topographic map Sky Transparency: Fair Star Image Stability: Good Other Conditions: Strong wind, moonlight Event Timings: Time Source: WWV Recording method: Stopwatch method Was the asteroid visible in scope: no Approx limiting magnitude: 12 Started Observing: UTC 00:39:30 Star and Object Merged: not observed Disappearance: UTC 00:40:47.1 Estimated Reaction Time: 0.3s Reappearance: UTC 00:41:07.6 Estimated Reaction Time: 0.3s Star and Object Separated: Not observed Stopped Observing: UTC 00:47:00.0 Was reaction time applied to the above timings: Yes List interruptions in observing: None Additional comments: None ______________________________________________________ 5) Marin Gaskell, From: gaskell@unlinfo.unl.edu (martin gaskell) Subject: 85 Io how was the 85 Io event? I know that my friends Dave Scherping and Eric Hubl both saw it by going about a hour south of here. Eric told me that the event was quite late (about 3 minutes he thought), lasted quite a bit longer than predicted and was preceded by a flickering (seen by both of them; 6" and 20" 'scopes). Doubtless you'll be hearing this from them. They are all psyched up to try another occultation now! Unfortunately my observation is probably of no use as I think I had stopped looking after about 2 1/2 minutes after the predicted time. If necessary I can probably get a more precise time range off the tape. I'd be very interested to hear how the event went at other stations. It would be a relief to know that the path had NOT passed over N.E. Lincoln, else I'm going to be kicking myself for a LONG time for not having watched long enough! I don't know whether this is a known technique, but my technique, in the absence of a WWV signal was to tape a ticking quartz alarm clock to the the microphone of my tape recorder and record the US naval observatory clock before starting. Had I seen anything I would also have recorded the USNO at the end as well. I hadn't heard anybody suggest recording a ticking clock. Sincerely Yours, Martin Gaskell ________________________________________________________ 6) David Harvey, Tucson From: comsoft@primenet.com (David Harvey) Subject: 85 Io Occultation Seen from Tucson I observed the 85 Io occultation of SAO 111235 on 12/10 with an automated C-14 and Axiom Research AX-2 CCD camera. The event was seen - however only a bracketing time can be gleaned from the data since images were obtained at 5 sec intervals. Do you want me to file a report? Dave Harvey IOTA email: comsoft@primenet.com And Subsequent reply from David Dunham Subject: 85 Io Occultation Seen from Tucson David, Thanks for your observation. Based on the reports I received from tracks north of you, I thought that Tucson would be too far south to get this event, but I guess not - yours would be a very valuable chord near the southern limit. Anything that you can provide to contrain the time will be useful - too bad you couldn't get any finer timing. A visual timing would have been better, but I guess with the twilight, you had to integrate in order to have a useable signal. David Dunham _____________________________________________ 7) Robert Sandy, Lewisburg, KS An 18.4-second occultation was timed visually by Robert Sandy at the Kansas City A. S.'s 30-in. telescope at Lewisburg, KS, at track 54S, so the path apparently shifted about 0.4 path widths south from the update from Lowell. IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: SAO 111235 Date (U.T.): Dec. 10, 1995 Predicted Time (U.T.): 00:43.2 Observer Name: Robert Sandy Telephone: (816) 795-8116 Postal Address: 4901 S. Valley View; Blue Springs, MO 64015 E-mail Address: Fax: TELESCOPE: Aperture: 30" Focal length: 150" Type: Newtonian Eyepiece Power: 69 Observing site name: Louisberg, KS Longitude: W 94 41 59.0 Latitude: 38 38 46.0 Height above sealevel: 325 m How determined?: USGS Sky Transparency (Circle one, or delete two): (Good) Fair Poor Star Image Stability ("seeing"; as above): (Good) Fair Poor Other Conditions: (Wind, Clouds, Lights, etc.) EVENT TIMINGS: (All times in Universal Time) Time Source: WWV Recording method: Radio, recorder, voice, SW Was the Asteroid Visible in your Scope? Yes Approx. Limiting Mag.: Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: 00:41:00.0 ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: 00:42:57.2 0.6 +/-0.5 sec. Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: 00:43:15.6 0.5 +/-0.3 sec. Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: 00:45:15.6 ____________________ Was your reaction time applied to the above timings? No If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: N/A!! List all Interruptions in Observing: Reason From 00:44:55 to 00:45:00 __________________________________ From ___:___:___ to ___:___:___ __________________________________ ______________________________________________ 8) David Dunham, St Joseph I was at 23N and had no occultation) and Albuquerque areas; Wichita, KS; Phoenix & Casa Grande, AZ (but in very bright twilight there); Socorro, NM; Urbana-Champaign, IL; and areas farther east that were probably clouded out, including much of southern Michigan, Toronto, Montreal, and Tromso (& Skibotn), Norway. David Larry, Thanks for the shift you derived. I printed your map, and am thoroughly disgusted - it shows the northern limit passing right through St. Joseph, MO, and I was 17 miles north of there. By the way, was the miss at Anderson Mesa observed? Two hours before the event at a parking lot in St. Joseph, I finished the calculation from the Australian astrometry indicating a 2 path widths shift to the south from the Flagstaff prediction. At that time, I also calculated that the equivalent path for Anderson Mesa was about 14 miles north of from where I decided to observe from (I would have gone a few miles farther north if I hadn't known that). I decided to stick with the original plan to get coverage reasonably far on the north side of the path. But I should have instead gone halfway between the Anderson Mesa line and one passing through Topeka, where it looked pretty certain that observations would be made (unfortunately, they got their video systems going too late, a couple of minutes after the event). If I had done that, I would have been south of St. Joseph and might have obtained a valuable northern-limit chord. Next time, I will give at least some consideration to all of the observations. Anyway, at least more chords (6 so far, although we don't yet have all of the data) were observed for this event than for any other asteroidal occultation since 1991, and we look forward to updates for future events. David 9) Erik Hubl, Lincoln NE As promised, here is my report from the occultation Saturday night. It appears our results were not accurate based on other reports. It is most baffleing and somewhat disheartening. However, as you say a negative observation at 0:43:00 is additional confirmation of the more southerly track. Both of us thought we did see something....We were having local seeing problems because our scopes were still warm from the car. (The stars would become like fuzzy balls). We arrived at the site at 0:20:00, had my 6" newtonian and Dave's 20" Dobsonian set up and collimated in record time and found the star by 0:37:00. We started recording at 0:42:00. We were both pretty quiet until 0:45:41 when I said "hey is it dimming?" at 0:45:52 I said "yes it is" and Dave said "yes" at 0:46:14 I said "now its bright again" and Dave also acknowledged it. We are absolutely certain we had the correct star. In fact at 1:16:00 we saw the very faint asteroid next to the star. Our last view of it was at 2:15:00 and it had moved quite a bit. By then the moon was already 20+ minutes up. Oh well, next time we will be better prepared (and not as rushed). PS. Could you please share with us the data obtained from this event. There is much we have to learn about these events and want to participate more in the future. Thanks Erik IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object):_______85_IO_______ Star:________SAO111235______ Date (U.T.):____DECEMBER 10, 1995_____ Predicted Time (U.T.):___0:43:00____ Observer Name:____ERIK J. HUBL_____________ Telephone:___(402) 488-1698____ Postal Address:____________624 SOUTH 51ST LINCOLN, NE 68510________________ E-mail Address:____ehubl@mars.ci.lincoln.ne.us__ Fax:______________________ TELESCOPE: Aperture:__6"___ Focal length:___8__ Type:__RV-6 NEWTONIAN____ Eyepiece Power:___76x___ Observing site name: ____BLUE RAPIDS__________ Longitude:________96d 38m__________ Latitude:______39d 41m_____________ Height above sealevel:_350m est.__ How determined?:__Rand McNally______ Sky Transparency (Circle one, or delete two): Good Star Image Stability ("seeing"; as above): Poor Other Conditions: (Wind, Clouds, Lights, etc.):____TEMPERATURE WAS 3 F_____ EVENT TIMINGS: (All times in Universal Time) Time Source:_____WWV_____ Recording method:___SMALL TAPE RECORDER__________ Was the Asteroid Visible in you Scope? __YES__ Approx. Limiting Mag.:___13_ Universal Time Estimated Accuracy, Remarks h m s Reaction Time, Started Observing: __0:37_:___.___ (sec.) ____________________ Star and Object Merged: __0:45_:41_.___ __LIGHT FLUTTER?____ Disappearance: __0:45_:52_.___ _2.___ _STAR DIMMED BY HALF Estimated Closest Approach: ___:___:___.___ ____________________ (if no D/R) Reappearance: __0:46_:14_.___ _1.___ __BOTH ACKNOWLEDGED_ Star and Object Separated: __1:16_:00_.___ __FIRST SAW IN 20"__ Stopped Observing: __2:15_:00_.___ ____________________ Was your reaction time applied to the above timings? ____NO___ If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: _______ List all Interruptions in Observing: Reason From __0:55_:___ to __1:16_:___ _DURING THIS TIME WE WERE ONLY____ From ___:___:___ to ___:___:___ ______VIEWING OCCASIONALLY________ Additional comments: ___IT WAS FUN, WE'LL DO BETTER NEXT TIME_____ Send Jim Stamm E-mail: jimstamm@aztec.asu.edu report to: 11781 North Joi Drive If an occultation is timed, copy to: Tucson, AZ 85737 U.S.A. David_Dunham@jhuapl.edu 10) Larry Wasserman, Marc Buie, Anderson Mesa Negative Observation at Anderson Mesa, track 37N Observed from 00:37:00 to 00:54:00. David - I've finally extracted the lightcurve from the 31" here in Flagstaff. Our conditions weren't the best, strong twilight, close to the horizon, and clouds all conspired against us. Nonetheless, we do have a trace that should be of some use. As expected, there are no obvious occultation dips in our data but we would have easily seen the occultation had it occurred. Our data covers 0:37:01 to 0:51:57 UT at 0.160 seconds per integration. The signal to noise we have is about 30 so I can safely say that there were no secondary occultations greater than 10% (3-sigma limit). Smoothing the data won't help push this limit down thanks to the clouds. In any case, it looks like enough chords were observed to pin down the actual track and size. It looks like our transit telescope measurement technique works pretty well though we really need to understand the errors a bit more. The sigma we quoted isn't too bad. Keep an eye on my WWW page. As soon as I get a chance I will post Larry's latest plot of the track and chord plots so that everyone can see where they were. Marc 11) Phil McCausland, St. Johns NF, Canada Good day! I'm writing to report observations obtained for the Dec. 9-10 occultation of SAO 111235 by minor planet (85) Io. Observations were made between 21:01-21:18 local time (Newfoundland), or 00:31-00:48 UT, from the back porch of my house near downtown St. John's. This observing site has position 47deg 33' 40" N, 52deg 43' 22" W, at an elevation of 85+/-3m above mean sea level. I regret to say that this is not a complete record of the event, as there were some clouds, particularly during the most critical predicted occultation time. Nevertheless, these observations may be of some value in a negative sense for constraining other occultation related events. Also, I did observe what may be an occultation event around 00:42 UT, about 1-2 minutes after the predicted occultation time for eastern Nfld. This is my first serious try at an occultation observation, although I have been observing and plotting for hobby the paths of many of the brighter minor planets for the last 8 years or so. I'm also a variable star observer. For this occultation I used 11X80 mounted binoculars (4.5 degree field of view) , and recorded on cassette tape simultaneously my vocal observations and the NRC time signal broadcast at 3330 kHz on station CHU. That time signal indicates that UT1 is behind the UTC time signal by 4/10 of a second. The following is a brief transcription of my observations; the cassette tape can be sent to you if needed. -------- SAO 111235 was positively observed during the following periods: 00:38:18.5 - 00:38:33.0 UT 00:39:04.0 - 00:39:06.0 UT (yes, a 2 second clear patch...!) 00:41:54.0 - 00:41:56.5 UT * 00:42:11.3 - 00:43:57.5 UT * (possible event within, more below) 00:44:13.5 - 00:44:29.0 UT 00:47:04.0 - 00:47:29.0 UT 00:47:31.5 - 00:47:36.0 UT These times include estimation of reaction time, and with one exception are given rounded to the half-second, both to reflect the accuracy of vocal recording and to allow for the variable time it took for the star to emerge fully from behind cloud. I'd take the accuracy of this report to be +/- 1/2 second for all but the * observation, which proved more memorable. During the marked * period, a possible occultation or graze was observed. Specifically, the star emerged from behind cloud at 00:42:11.3 UT and was seen clearly for several seconds until 00:42:17.5 (estimated) when it seemed to disappear. I was surprised and did not vocalize this observation until ~1.5 seconds later at 00:42:19.0 (recorded, certain time within 0.1 s). I still could not see it 5-6 s later at 00:42:23.5 (+/-0.1), *while still being able to see surrounding nearby guide stars of similar magnitude*. It reappeared at 0:42:28.3 UT, just as I was going to say "I don't see it," again. The star's disappearance was sudden and its reappearance was noticable, taking perhaps a third of a second to come up to full brightness. In short, the times of this odd event were: 00:42:17.5 (+/- 0.5s) UT: SAO 111235 disappearance 00:42:19.0 (+/- 0.1s) UT: vocal record of disappearance 00:42:23.5 (+/- 0.1s) UT: continued disappearance 00:42:28.3 (+/- 0.1s) UT: completion of reappearance Totalling about a 10s disappearance. I am uncertain about the celestial nature of this possible occultation, the star may simply have been selectively blocked out by a thin wisp of cloud! However, I didn't see cloud during the 10s period, and I could usually see grey clouds passing through my 4.5 degree view (boy, could I ever!). Also, I could see the field guide stars during the star's disappearance... Generally, during the observation period seeing was steady, limiting magnitude was about 4 to 4.5 (mostly due to waning gibbous moon to the east), and I could confidently see stars down to magnitude 9.1 in the 11X80 mounted binoculars. Several other people also made an effort in other locations in St. John's to observe this occultation, provided with a time check from the shortwave time signal. Unfortunately, observer Garry Dymond was clouded out shortly after finding the star before the predicted occultation time and setting his Celestron C-8 to track it! I haven't yet been in contact with observers Eric and Marlene Young. We'll try the next one! I hope this proves to be of some help. Cheers! -pjam (Phil McCausland) Additional Note from Dunham, re: above observation St. John's was well south of the observed occultation path, so this is a secondary extinction. Too bad nobody nearby could confirm or deny it with a larger instrument. If it is celestial, the path would have passed a little south of the south coast of Nova Scotia, over the Washington, DC area (large storm was still over this area), a little south of Nashville and Memphis, TN, and near Nacogdoches and a little north of Austin, TX. The duration is almost half that of the main event and occurred about 4.5 minutes after the closest approach of the main occultation shadow to them. If it were a satellite of Io, it should be possible to observe directly with a distance greater than 1" and intensity some 0.2 that of Io; such an object should have changed the astrometry noticeably such that the main event should have been farther from the prediction (if so, main the main event should have been earlier and farther north than it was). So I am rather dubious of a celestial explanation. David 12) David Harvey, Tucson Station IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object):_________Io________ Star: ____PPM 146634________ Date (U.T.):_____10 Dec. 1995_________ Predicted Time (U.T.):___00:44______ Observer Name:____________David Harvey________ Telephone:(520) 621-3648_______ Postal Address:____1552 West Chapala Drive Tucson Arizona 85704____________ E-mail Address:______comsoft@primenet.com_____ Fax:____(520) 621-1532_____ TELESCOPE: Aperture:_35 cm_ Focal length:_385 cm__ Type:______SCT________ Eyepiece Power:__CCD direct__ Observing site name: CBA /Tucson Station Longitude:_W 111.0000_____________ Latitude:_N 32.34272217_________________ Height above sealevel:_750 m_ How determined?:__USGS___________________ Sky Transparency (Circle one, or delete two): Good Star Image Stability ("seeing"; as above): Fair Other Conditions: (Wind, Clouds, Lights,etc.):____Strong Twilight________ EVENT TIMINGS: (All times in Universal Time) Time Source:_____WWV_____ Recording method:_CCD Image header ____________ Was the Asteroid Visible in your Scope? __Yes__ Approx. Limiting Mag.:__11.5_ Universal Time Estimated Accuracy, Remarks h m s Reaction Time, Started Observing: 00:43:30._ (sec.) ____________________ Star and Object Merged: ___:___:___.___ ____________________ Disappearance: After 00:44:52.9 + 5.0 sec._______ Estimated Closest Approach: ___:___:___.___ ____________________ (if no D/R) Reappearance: Before 00:45:03.4 - 5.0 sec._______ Star and Object Separated: ___:___:___.___ ____________________ Stopped Observing: 00:49:___.___ ____________________ Was your reaction time applied to the above timings? ___Yes___ If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: _______ List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: _____Observations were made with an automated patrol Telescope that took 0.5 sec exposures every 5 seconds. The star was visible at 00:44:52.9, invisible at 00:44:58.1, and visible again at 00:45:03.4 UT. 13) Benny Roberts, Jackson MS, No Event Observed IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: SAO 111235 Date (U.T.): Dec. 10, 1995 (?) Predicted Time (U.T.): 00:42 Observer Name: Benny Roberts Telephone: 601-373-6244 Postal Address: 4607 Ironwood Lane; Jackson, MS 39212 E-mail Address: BENNYHIKER@aol.com Fax: TELESCOPE: Aperture: 13 in. Focal length: 59 in. Type: Newtonian Eyepiece Power: 52 Observing site name: Jackson, MS Longitude: W 90 17 52.4 Latitude: N 32 15 17.8 Height above sealevel: 360 ft. How determined?: USGS Topo Sky Transparency (Circle one, or delete two): (Good) Fair Poor Star Image Stability ("seeing"; as above): (Good) Fair Poor Other Conditions: (Wind, Clouds, Lights, etc.): None EVENT TIMINGS: (All times in Universal Time) Time Source: Recording method: Was the Asteroid Visible in your Scope? No Approx. Limiting Mag.: 13 Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: 00:39:30.0 ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: hh:mm:ss.s __.___ ____________________ Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: hh:mm:ss.s __.___ ____________________ Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: 00:47:00.0 ____________________ Was your reaction time applied to the above timings? If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: NO EVENTS OBSERVED, E-MAILED MESSAGE TO DUNHAM Information copied to report form from other correspondence. (by Jim Stamm) 14) Doug Kniffen, Warrenton MO IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: SAO 111235 Date (U.T.): Dec. 09, 1995 Predicted Time (U.T.): 00:43 Observer Name: Doug Kniffen Telephone: Postal Address: 2861 Hwy U; Warrentin, MO 63383 E-mail Address: Fax: TELESCOPE: Aperture: Focal length: Type: Eyepiece Power: Observing site name: Warrenton? Longitude: W 91 13 14 Latitude: N 38 43 30 Height above sealevel: How determined?: Sky Transparency (Circle one, or delete two): Good Fair Poor Star Image Stability ("seeing"; as above): Good Fair Poor Other Conditions: (Wind, Clouds, Lights, etc.): EVENT TIMINGS: (All times in Universal Time) Time Source: Recording method: Was the Asteroid Visible in your Scope? Approx. Limiting Mag.: Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: hh:mm:ss.s ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: 00:42:42.5 __.___ ____________________ Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: 00:42:55.2 __.___ ____________________ Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: hh:mm:ss.s ____________________ Was your reaction time applied to the above timings? If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: Flicker (bumps?) at beginning. R was definite. Information copied to report form from other correspondence. (by Jim Stamm) 15) Timothy Wilson Jefferson City MO IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: SAO 111235 Date (U.T.): Dec. 10, 1995 Predicted Time (U.T.): Observer Name: Timothy G. Wilson Telephone: Postal Address: RR6 413 Bald Hill Rd.; Jefferson City, MO 65101 E-mail Address: Fax: TELESCOPE: Aperture: 90 mm Focal length: Type: Mak-Cas Eyepiece Power: 50 Observing site name: Longitude: W 92 08 Latitude: N 38 31 Height above sealevel: How determined?: Sky Transparency (Circle one, or delete two): Good Fair Poor Star Image Stability ("seeing"; as above): Good Fair Poor Other Conditions: (Wind, Clouds, Lights, etc.) EVENT TIMINGS: (All times in Universal Time) Time Source: Recording method: Was the Asteroid Visible in your Scope? Approx. Limiting Mag.: Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: hh:mm:ss.s ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: hh:mm:ss.s __.___ ____________________ Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: hh:mm:ss.s __.___ ____________________ Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: hh:mm:ss.s ____________________ Was your reaction time applied to the above timings? If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ From ___:___:___ to ___:___:___ __________________________________ Additional comments: Used a stopwatch to get a 16.07 occultation - uncorrected for reflex. Information copied to report form from other correspondence. (by Jim Stamm) 16) Robert Bolster, Franconia, VA IOTA ASTEROIDAL OCCULTATION REPORT FORM Asteroid (or other object): (85) Io Star: PPM 146634 Date (U.T.): Dec. 10, 1995 Predicted Time (U.T.): 00:42 Observer Name: Robert N. Bolster Telephone: (703) 960-9126 Postal Address: 6007 Ridge View Dr.; Alexandria, VA 22310-2055 E-mail Address: Bob.Bolster@f118.n109.z1.fidonet.org Fax: TELESCOPE: Aperture: 4 in. Focal length: 154 in. Type: Sch-Cas Eyepiece Power: 125 Observing site name: Franconia, VA Longitude: W 77 06 21.1 Latitude: N 38 47 14.0 Height above sealevel: 189 ft. How determined?: Topo Sky Transparency (Circle one, or delete two): (Good) Fair Poor Star Image Stability ("seeing"; as above): Good (Fair) Poor Other Conditions: (Wind, Clouds, Lights, etc.) EVENT TIMINGS: (All times in Universal Time) Time Source: WWV Recording method: Tape recorder Was the Asteroid Visible in your Scope? No Approx. Limiting Mag.: Universal Time Accuracy, Remarks Reaction Time-sec. Started Observing: 00:36:20.s ____________________ Star and Object Merged: hh:mm:ss.s ____________________ Disappearance: hh:mm:ss.s __.___ ____________________ Estimated Closest Approach: hh:mm:ss.s ____________________ (if no D/R) Reappearance: hh:mm:ss.s __.___ ____________________ Star and Object Separated: hh:mm:ss.s ____________________ Stopped Observing: 00:45:40.s ____________________ Was your reaction time applied to the above timings? If you could tell, did the object pass NORTH, SOUTH, EAST, or WEST of the star (cicle one, or delete three)? If possible, estimate the distance of closest approach in arc seconds: List all Interruptions in Observing: Reason From ___:___:___ to ___:___:___ __________________________________ Additional comments: