The Best Occultation of a Star by Pluto ever Predicted for North America occurred Sun. March 18 am - Updated 2007 April 11, 18h UT
Several astronomers, amateur and professional, recorded the event from separate locations with a wide spread across the predicted path
The observations at Whipple Observatory in Arizona show that the occultation occurred 4.8 min. late, confirmed by Brian Warner at Palmer Divide Observatory and by others
Bruno Sicardy's first analysis shows that the central line missed the Earth's surface to the north, with the geometrical southern limit crossing Arizona and Oklahoma
The current update adds three observatories that made observations not previously in my list, shown to me today by Leslie Young, but an additional minor update was made 2007 September 26 to specifiy "MIT - Williams College consortium" where just "Williams College" had been specified before. The April 10th update added information about observations made at Kitt Peak, Arizona. The April 4th update added information about observations made from Carson City, NV; and information provided by Jay Pasachoff, from their joint MIT-Williams College consortium, about observations from Mt. Graham, AZ and Magdalena Ridge, NM, with an additional link to information about observations their MIT-Williams group participated in at Mt. Hopkins. On April 2nd, also added was information about the times of the exposures obtained at Moore Observatory, Pasco, Washington. The Mar. 30th update added reduced observations from the Univ. of Oklahoma Observatory. On Mar. 29th I added a plot and information provided by Rick Baldridge, who observed at Oakridge Observatory, California. On Mar. 28, the information for Moore Observatory (Pasco, WA) was updated with a new photometric analysis of the observations, and more information is given for Vail View Observatory. The best occultation of a star by Pluto ever predicted for North America occurred between 10:40 and 11:00 UT Sunday morning, March 18, in northern and possibly central Mexico, the western and central U.S.A., & southwestern Canada. A first summary of the results is below. Extensive pre-event plans and prediction information is here; I have updated the full prediction list there. Sunday morning's occultation of a 15th-magnitude star by Pluto was successfully recorded by several astronomers, amateur and professional, at locations widely separated across the path. The observations are likely to allow a good astrometric determination of the actual occultation path, the location of Pluto's disk relative to the star in the sky plane (and then, an accurate calculation of the actual path of the central line from which a central flash may have occurred), and much information about the current state of Pluto's atmosphere. So far, most of the observations have not been processed to determine the light variations of the star needed for this analysis (a few light curves are available - see below); this should be accomplished in the next week or two. Many thanks to all observers who attempted this faint but important occultation. Before listing and describing the observations and the first results, I give below important messages about reporting and calibrating the Pluto occultation observations: From: David Dunham [dunham@starpower.net] Sent: Thursday, March 22, 2007 12:37 PM To: Dunham, David Cc: Bruno.Sicardy@obspm.fr; layoung@boulder.swri.edu (Leslie Young, SWRI); rpb@mit.edu (Rick Binzel, MIT); jle@mit.edu (Jim Elliot, MIT); hubbard@lpl.arizona.edu (Bill Hubbard, LPL); colkin@lowell.edu (Cathy Olkin, Lowell); buie@lowell.edu (Marc Buie, Lowell) Subject: Reporting observations of the March 18th Pluto occultation; calibration observations useful; other useful events First, I mention those who are most interested in the observations of the recent occultation by Pluto and who will, or will likely, be analyzing them. Then I copy a message from Bruno Sicardy giving information about calibration observations that should be made by successful observers to enhance the results that can be obtained from their observations. At the end (of this Web page), I mention other occultations that would be useful to try to observe. The March 18th occultation by Pluto was successfully observed from over 20 locations. I am copying this message to as many of the successful observers as I can. I'm trying to keep track of all who obtained any possibly useful observations of the Pluto occultation on this Web page; it is mainly just a summary, but some observational data are here; please check it and suggest any changes. Others will be collecting the observations and analyzing them for a formal publication. I think Bruno Sicardy at Paris Observatory (1st Cc: address) will be the main focus for this effort, but others at the SWRI in Colorado; at MIT; at U. of AZ; and at Lowell Observatory (the 1st 7 in the Cc: list) may want to be involved in the effort as well. So once you have your measurements and observations organized, you can "reply all" to this message and attach them (or give a link to a Web site), and that should cover everyone who will want to work with the data. _____________________ Bruno Sicardy writes: Hello Dave, all, I am back to France, and I am catching up with my mails. Thanks for your various accounts on Pluto observations! I would certainly be interested in including various light curves, as they may improve our global fit to Pluto atmospheric models. I will put asap on my page some synthetic light curves, corresponding to various distances to center line (impact parameter), so that you may have a feeling of what to expect. For those who are working on data, here are some important points to remember, if you do not do so yet: - try to provide an as accurate as possible relative flux of the star and Pluto, as recorded the nights before (or after) the event. This allows us to define a zero baseline for the total flux, ie the sum S= Pluto + star during the event. As Pluto is variable from night to night, though, it might be better to use the brighter reference star 45 arcsec W of the occulted star as a reference the night before, to measure the ratio R= star_1/ref, where star_1 is the full stellar flux of the target, and ref is the flux from the reference star. Then one uses that same reference star during the event to extract the stellar flux only: star(t)= S - S_1 + R*ref during the event, where S_1 is the unocculted flux, Pluto + star_1, observed before and after the event. is that any clear??? This has the advantage of getting rid of Pluto variability. Also, by chosing as the reference the brightest star you have in the FOV, you may improve the uncertainties on R, and then on star(t). - please specify to what part of the integration cycle the timing applies: start, middle, end, other. For a several sec cycle, this may change quite a bit the timing of the event. Also, if you do have a GPS time, please specify your timing method, and the error bar you think should be attach to you time. - please specify the coordinates of your station, if not already done. Cheers, Bruno __________ And, regarding calibration, Leslie Young writes: From: Leslie Young [mailto:layoung@boulder.swri.edu] Sent: Friday, March 23, 2007 7:18 PM To: Bruno SICARDY Subject: Pluto event I second Bruno's suggestion that we need to know the normalized lightcurves. With Pluto's atmosphere, you may not reach zero flux at the center. [That seems to be the case for most of the records I've seen, from California to Arizona, Colorado & New Mexico, and south of there; it's clear now that it was a grazing occultation, or nearly so, in those areas - David] If you have a chance, it'll be good to get photometry of the occulted star and a reference starthrough your particular bandpass without the interferrence of Pluto. If you didn't have a reference star, try to get Pluto vs the occulted star. Pluto has a lightcurve and a 6.4-day period, so photometry of Pluto 6 or 7 days later (Sat or Sun AM, or both for interpolation) would be useful in establishing the zero point. [also good then will be Sat. morning, Mar. 31; the Moon will be nearly full then, but red-sensitive systems generally won't be bothered too much by that - David] - Leslie ______________________ Although several others, including myself, were clouded out, the preparations for the event were useful for testing new equipment that might be used for future occultations of faint stars. For example, with help from Bob Sandy, I made last-minute arrangements to use my Collins I3 image intensifier and Astrovid Stellacam II with the 27-inch telescope at Farpoint Observatory near Eskridge, Kansas, about 25 miles southwest of Topeka. During the day before the occultation, Gary Hug made an adaptor for the telescope that would accept the 1.25-inch-diameter cylinder of the front end of my equipment; this would be useful in any case for other equipment that they plan to run with this telescope in the future. In spite of a declination motor that broke when the telescope was first used in the evening, we were able to set the telescope about half a degree from the target star. Then, using Bob Sandy's 9-inch video monitor and a detailed star-charting program on an adjacent computer, we were able to match the video field with the pattern of stars near a 7th-mag. star, and then star hop to Pluto. An hour before the occultation, we were all set, recording the Pluto/target star combination with a good signal to noise ratio with quarter-second integrations. It would have made a nice observation, but fog rolled in about half an hour before the occultation. One of the observers at Farpoint Observatory worked with another computer there to try to record remote observations of the occultation with a remote 14-inch educational telescope in Cloudcroft, NM, but it was too cloudy to obtain any observations there. A summary of the known successful observations is in the table below. This means that the star and Pluto were recorded during the possible occultation time, whether an occultation occurred or not. Click on hot links of the observatory name for reports from the observers with more detail, including the observed light curves. Distance from 2007 predicted March Recording center, 18th Telescope interval km recorded UT ap., type and type Observatory/Observers 1132 occ'n 10:53-56 16" 4s CCD, FITS Moore Obs., WA, Tony George 448 24" IR Somers-Bausch, UCO, Boulder 437 occ'n 10:54-59 12" image inten., visual Mt. Thorodin, CO R. Keen 391 16" Cass. 16s int. DavisObs., Carson City,NV 335 occ'n ctr. 10:55.7 35cm 10s SBIG CCD Palmer Divide, CO B. Warner 310 10:37-11:05 30cm LX200 5s SBIG ST-8 Cloudbait CO Chris Peterson 148 90cm Crossley 25/s Watec Lick, CA Colas,Marchis,Wong 125 10:41-10:53.7 16" f/5Newt 2s Stellacam Oakridge, CA R.Baldridge,Lum 125 CCD Oakridge, CA Chris Kitting 125 10" SCT 4s DSI Pro 2 Oakridge, CA Jim Albers 75 12.5" RC Fremont Pk CA Jurgen Wolf -68 Light curve on Sicardy's Web site below Calvin-Rehoboth, n.w. NM -86 10:41-11:39 20inCDK f6.8 2s LumSKYnyx PintoVyOb CA Andre Paquette -94 61" & 1.3m CCD Flagstaff, AZ Naval S Levine -107 10:34-11:04 42in 3s I-band Anderson Mesa AZ Phil Massey -107 72in IR photometry Anderson Mesa AZ Marc Buie -107 31in (Lowell Obs) Anderson Mesa AZ Bob Millis -167 10:44-10:54 20cmSCT f/5 60s Canon dig. LockwoodVal.CA Steve Edberg -197 14inSCT&LX200 video PC164C BlueBird OK Lucas, Grismore -206 10:20-11:17 0.6m 2.5s, CCD Table Mtn. Obs. CA Jim Young -212 (TAAS) 16" Newt 2s video GNT, Belen NM Steve Welch -212 11" SCT 2s video GNT, Belen NM Bill Wallace -275 2.4m MagdalenaRidge,NM Steven Sousa, Adam McKay -282 ctr. 10:55.1 14" SCT 15s SBIG CCD Etscorn NM Dan Klinglesmith -304 ctr. 10:56:50 0.4m 4s ApogeeCCD U OK, Norman W. Romanishin -345 Mt. Palomar CA -349 16"SCT,FR/3.3 2s, Astrovid Gilbert, AZ Randy Peterson -356 8" 4s DSI Globe AZ Skyway Ob S Gifford -443 8.4m LBTO,MtGraham,AZ Bryce Babcock, John Hill -480 1.5m Kuiper IOTAcam Catalina AZ Widemann,Larson,Jennings -543 2.3m Bok 12/s CCD KittPeak, AZ Sicardy,Harvey -543 10:30-11:10 1.5m McMathPierce main H Kitt Peak, AZ -543 10:30-11:10 0.9m McMathPierce aux. Ks Kitt Peak, AZ -543 10:30-11:10 20in Visitor Center R Kitt Peak, AZ -546 ctr.10:53.7 14" SCT 4s CCD VailView,AZ Peterson,Herrero,Schlottman -585 ctr. 10:53:40 UT 6.5m MMT 2.5 & 4/sCCD MtHopkins AZ McCarthy et al. -591 61cm GrasslandsObs,Sonoita,AZ James McGaha -620 80cm 25/s Watec TenagraAZ Vaubaillon,Schwartz -625 ctr. 10:53.9 UT 14in SCT 3s CCD Hereford AZ Bruce Gary -654 32in Fan Mtn, VA Skrutskie -672 2.1m K & 1.5m CCDs San Pedro Martir,Baja,MX L.Young -744 10:45-11:00 32" 5s R CCD Dark Sky, NC Dan Caton -1064 2 12"SCT, 1 I3, CCDs Big Bend NP, TX M. Kozubal -1203 breaks in clouds 1m image inten. video George Obs. TX Paul Maley -2273? 10:34-11:19 no occ'n 1.5s IOTAcam Ob.Luz,Guanajuato,MX,Beisker The 3 telescopes at Oakridge Observatory, Los Gatos, California, were within 60m of each other. It was clear at all locations during the occultation except at the George Observatory near Needville, west of Houston, where fog/low clouds moved in 20 min. before the occultation, and at Etscorn Observatory, Socorro, NM, where it was partly cloudy with "fast moving clouds" in the region of Pluto. The star/Pluto combination could be recorded only intermittently in breaks in the clouds. Note - we also did that at Farpoint Observatory, switching to half-second integrations, but only once was the brief clearing good enough there to see Pluto; there were other brief breaks where nearby 11th-mag. stars could be seen. The Pinto Valley Observatory (CA) spreadsheet has been updated to correct the previous time error and to give improved and more detailed photometric information. Bruno Sicardy writes: "The timing at MMT (4 mn occultation centered at 10:53:40 UT) indicates a delay of 4-5 mn wrt to my predictions [or 4.8 min. late relative to the combined prediction that Dunham used]. On March 26th, Bruno wrote much more, about his first real anaylsis of the observations: Hello all, thanks for your inputs and mails concerning your Pluto occultation observations. We are starting to look at our data here in Paris In the mean time, I used two light curves, from Calvin-Rehoboth Obs. (NM) by Larry Molnar, and Cloudbait Obs. (CO) by Chris Peterson, to get a first order astrometric solution. My results are posted at the bottom of my Web page at: http://calys.obspm.fr/~sicardy/18_march_07/index.html I used a Pluto astmospheric model as of 2002, knowing that at this stage, this should be enough to give us a satisfactory geometry of the event. I then generated various light curves expected from various sites, it should give a flavor of what to look for and when. Also provided is a post-event map of the shadow on Earth. These are all on my Web site given above. So far, the Moore station in WA is the closest to centrality, but still far enough from centrality to avoid the central flash. The shadow went further north wrt predictions, unfortunately leaving George Obs. (TX) and Guanajuato (Mexico) outside the event. Pluto was about 80 mas away from its DE413 calculated position. This means that we are witnessing a significant degradation of the DE413 Pluto's ephemeris. New solutions should be implemented for more reliable predictions on, say, 1-2 year periods. Cheers, Bruno Unsuccessful attempts have been reported at the following observatories. Distance from predicted center, Location, Observers Reason km for failure 1566 Saskatoon SK U SK Obs R Huziak Below obs. wall 1284 Victoria BC 16" Michael Hoskinson Clouds 200 Oakland CA ChabotObs 20", W. Morgan Fog 143 Foothill Col Obs CA 16" I3 video Fog 133 Eskridge, KS Farpoint Obs, Dunham, Hug, Sandy Low clouds 29 Springville CA Starhome Obs, John Sanford Recording failure -76 St. Louis, MO Wayne Clark Clouds -250 Los Angeles CA Griffith Obs12" SC2, A. Cook Clouds -367 Escondido CA G74 Boulder Knolls Obs. Santore Fog -471 Cloudcroft, NM 14-in. remote [from Farpoint] Clouds -473 Apache Point, NM Clouds -792 Shreveport, LA Terry Atwood Clouds -794 Central Texas Astron. Soc. Obs J. Barton 24" Clouds -808 McDonald Obs Visitors Ctr TX R. Nugent 16" Thin clouds -808 W 711 McDonald Observatory, Fort Davis, TX Clouds -864 Ft McKavett TX Schaeffer 20" Clouds -1808 Baja Cal Sur MX Kerry Coughlin 10" Too faint; thin cirrus? At Saskatoon, SK, R. Huziak reported that it was clear, but a wall blocked the view of Pluto, 14 deg. above the s.e. horizon, as seen from the telescope at the University that he was using; Pluto cleared the wall about 20 min. after the event. R. Nugent made a video recording of the appulse with the 16" telescope at the visitor's center of McDonald Observatory, Ft. Davis, TX, but cirrus clouds moved over the field at the time of the appulse, precluding useful photometry for the shallow event that must have occurred there. Those clouds also spoiled the observations with the larger telescopes on the mountain. So far, I have not received any messages after the occultation reporting what happened at the following locations from which attempts were planned; w or W indicates places that were probably clouded out: Location km 583 A Jelm Mtn WY IR observatory 195 w Holton, KS aprox. Mike Ford 24" -194 * StillwaterOK MendenhallObs 24" -531 w LasCruces NM Rich Richins C11 -2740 A Tonantzintla MX 40" __________________________ Although perhaps not as exciting or important as the occultation by Pluto, we'd also like your help with some brighter useful occultations, when you can, especially of stars by asteroids and by other planets. For example, on the evening of April 26th (April 27 UT, around 2:45 UT), there will be an occultation of 7.4- mag. SAO 76929 by the dark side of Venus (whose 16" disk will be 70% sunlit) visible from central North America, and a similar event with an 8.9-mag. star will occur in the same area the evening of May 19th (Venus then 60% sunlit). Extensive predictions of occultations by asteroids are on Steve Preston's Web site with links to regional maps and other important resources for these events here; a few of these events down to 12th mag. are potentially visible from a given location each month (but of course fewer will actually occur, and mobile observers can greatly increase their chances for success). Also, the International Occultation Timing Association will be holding its annual meeting in Pasco, Washington around July 20; preliminary information about it is here. David Dunham, 2007 April 11, 18h UT Phones home 301-474-4722; office 240-228-5609; cell 301-526-5590 e-mail david.dunham@jhuapl.edu home e-mail: dunham@starpower.net .