Switching Back to Standard Time

Just a quick reminder that all of our RECON teams outside of Arizona will be going off Daylight Savings this Sunday morning, November 6, at 2AM local time. In addition to giving participants an extra hour of sleep, turning clocks back will place the majority of our teams 8 hours behind Universal Time (UT) from now through March.

RECON teams should take care in converting UT times to local times:

  • Our Arizona teams remain on Mountain Standard Time = 7 hours behind UT
  • All other teams fall back onto Pacific Standard Time = 8 hours behind UT

All times listed on the Event Detail Page for 08FC76 are provided in UT and need to be adjusted for the correct time zone for each site. The event will be centered around 11:55 UT on November 23, 2016. Using the offsets above, this converts to:

  • 4:55 AM MST on the morning of November 23
  • 3:55 AM PST on the morning of November 23

All RECON Teams are reminded to complete the RECON Campaign Signup Form as soon as possible so that we can ensure telescope coverage for this Thanksgiving campaign!

 

Occultation of TYC 5780-01169-1 by (19) Fortuna

On 2016, August 13 at 06:30 UT, main belt asteroid (19) Fortuna occulted the star TYC 5780-01169-1 in the constellation Aquarius. Four RECON teams and two other observers recorded the event. A total of five teams actually observed an occultation and one team observed a miss. Observing a miss can be just as important as observing an occultation because misses help define the size of the asteroid. For a more comprehensive overview about the data analysis process for main belt asteroid occultations, see Tony George’s blog post from January, 2016.

Here is the path for the event, which passed over the northern part of the RECON network. Even if you don’t have access to the Occult Watcher program, occultation announcements and maps such as this can be found at the asteroid occultation website.

Map of 19 Fortuna's shadow path

Map of 19 Fortuna’s shadow path

Here are light curves from the three RECON teams that recorded an occultation. Note that the horizontal and vertical scales on each of these light curves are different.

Manson light curve of 19 Fortuna

RECON Manson, Jared Mumley

Ellensburg light curve of 19 Fortuna

RECON Ellensburg, Megan Rivard and Bruce Palmquist

The Dalles light curve of 19 Fortuna

RECON The Dalles, Bryan Dean

Occultation scientists, such as every member of RECON, can use these light curves to determine the disappearance and reappearance time of the occulted star. IOTA, the International Occultation Timing Association, uses these disappearance and reappearance times, along with the location of the observers to estimate the outline of the asteroid.

Each of the chords in the plot below shows when and where the target star is visible. When the asteroid occults the star, there is a gap in the cord equivalent to the amount of time the star disappeared. When all of the chords and gaps are combined, you can start to see the size and shape of the asteroid. The gray area shows a model of the asteroid’s shape based on existing data. Notice how chord 1 fits the model almost exactly while chord 4, measured by RECON Ellensburg, starts and stops inside the predicted shape of the asteroid model. This could indicate a slight error in Ellensburg’s timing. But it could also mean that the actual shape of the asteroid is a little narrower along that line than predicted. Less likely but still possible, there are deep indentations in those portions of the asteroid. Chord 7, measured by RECON The Dalles, has a very small gap indicating that just the tip of the asteroid occulted the star.

Shape of 19 Fortuna according to current models

Click on the image above for a higher resolution view of the plot.

Main belt asteroid occultations are a great way to train new RECON participants in occultation science. One of the main reasons for this is that you can often see the target star and the asteroid. So even if your site does not record an occultation, you can still observe the dynamic nature of the Solar System by watching the asteroid move towards and then away from the target star.

Credits: We give a big “Thank You” to Tony George for generating and extracting precise timing information from our light curves.

Lassen Dark Sky Festival

This past summer 12 RECON team members participated in the 4th annual Lassen Dark Sky Festival in August of 2015. Members helped conduct stargazing and discussions about astronomy with over 4,500 visitors.  Since 2012, thousands of spectators visit Lassen national park every year to celebrate special astronomical events including the annular eclipse, the transit of Venus and the Lassen Dark Sky Festival.

Visitors can participate in various activities throughout the festival:

Lassen National Park is a sanctuary of natural darkness and offers spectacular views of the night sky.

Check out our RECON Team members at the Lassen Festival.

Check out more pictures of the Lassen Dark Sky Festival here.

Here are future events dates at Lassen National Park:
August 12-14, 2016 -100th Anniversary of National Park Service and Lassen Festival
August 11-13, 2017  One week before the total solar eclipse
August 3-5, 2018  James Webb Space Telescope launches in October

Documentation of occultation of 2UCAC 39956822 by (86) Aegle

The last positive occultation captured in North America in 2015 was the occultation of the star 2UCAC 39956822 by the asteroid (96) Aegle.  Overall, there were 8 observers who observed the event.  There were 7 positive observations and one miss observation.  Three of the positives were recorded by RECON team members, Chris Patrick, Steve Bock, and Tony George.  This blog will document the data contributed by the RECON members.

Here is the path map for the event.  You can see the path crosses through central Arizona and southern Nevada, where three RECON members are located.  Other observers in Arizona and central California were also able to observe the event.

Light Curve Analysis

All videos were uploaded via DropBox to an IOTA repository.  DropBox is a tool used by IOTA for capturing and exchanging video files.  Each of the video files were then analyzed by Tony George using Limovie.  Limovie is a tool for commonly used by IOTA for video light curve analysis.  Here are the three light curves that were captured by RECON members:

Chris Patrick

(96) Aegle 2015-12-30 Chris Patrick.ROTE.sqWave

Steve Bock

Aegle 20151229 Mt Potosi PSF TG.ROTE.blockint.detrended.sqWave

Tony George

(96) Aegle 2015-12-30.ROTE.detrended.sqWave

These three light curves have some interesting characteristics that should be noted.

The Chris Patrick light curve is very erratic and during the event, a very flat and uniform bottom.  These are characteristics of the camera settings, which did not match the standard RECON guidelines.  Whenever observing asteroidal occultations, RECON guidelines should be used for camera settings unless otherwise directed by the campaign organizer.

The Steve Bock light curve looks very ‘skimpy’.  Again, this is the result of camera settings, most significantly, the degree of sense-up that was set.  Steve used a sense-up of 64x.  This integrates 32 frames which means that each block of 32 video frames looks essentially the same.  Integration also cuts down on the amount of variation between individual frames and blocks of integrated frames. A sense-up of 64x is a common RECON guideline for TNO occultation observations, however it may be too much integration for use in brighter asteroid occultations.

When compared to Tony George’s light curve, you can see the degree to which a high sense-up can affect the look of the light curve.  Tony used a sense-up of 2x.  This integrates two video fields into one frame, so there are 30 frames per second that are all independent of adjacent frames.

While Tony’s light curve might not look good, it actually is the best of the three light curves for determining the correct D (disappearance) and R (reappearance) times from the video.  That is because integration (sense-up) averages the video data and the D or R might occur somewhere within the integration block and the actual time must be estimated from the brightness value of the block of frames.  With Tony’s video, the times can be derived to times less than 1-frame accuracy.

Occultation Disappearance and Reapperance Analysis

Once each video file was analyzed in Limovie, a data file is created in a comma separated variable format (csv).  That csv file can be analyzed by different software applications to search for hard-to-find occultations, however this occultation was easy to see.  The software programs can also be used on easy-to-see occultations, particularly those with video integration, so that more accurate estimates of the D and R times can be derived.  Tony George used the program R-OTE (R-code Occultation Timing Extractor) to analyze all three light curves.  The D and R times were determined and provided to the observers so they could send in their reports on a standard Excel spreadsheet provided by IOTA.  For those that have OccultWatcher on their computers, the Excel form is easily available through a reporting app in OccultWatcher.

Asteroid Profile Analysis

Once the various observation D and R times are sent to IOTA  for analysis, a powerful program called Occult4 is used to combine the times and geographic coordinates to determine the size and shape of the asteroid.  For each observer, a chord across the earth is developed indicating where and when the star was visible.  Where the star disappears, there is a gap in the chord equivalent to the length of time of the disappearance.  When multiple chords are combined, the gaps in the chords trace out the size and shape of the asteroid.  Here is the profile developed for the (96) Aegle event:

20151230_AegleProfileUpdated

Note:  Click on the above image to get a high-resolution view of the plot

The chords of observations by the various observers are shown in different colors.  The chords of the three RECON observers are Chord 1: Chris Patrick; Chord 2: Steve Bock; and, Chord 5: Tony George.  You can see from this plot the rough outline of the size and shape of the asteroid.  Superimposed on the plot of the chords is the ellipse of best fit to the openings in the chords.  The size of the asteroid as determined by this analysis is and ellipse with major axis of 169.6 km and minor axis of 163.0 km.  This is one of the best observations ever obtained of the asteroid (96) Aegle.  While this is only one snapshot of the asteroid on the date of the observation, future observations can determine the size and shape from other perspectives and hence the volume and density of the asteroid can also be determined from amateur astronomer observations.  This type of data is very helpful to astronomers and space scientists as they continue to characterize the main belt asteroids and try and made decisions on asteroids to visit on future space flights.

RECON Observations Were Critical to Getting Size and Shape of (96) Aegle

The determination of the size and shape of an asteroid by occultations requires a good spread of observers across the path.  In the case of the (96) Aegle event, the two Chords collected by RECON members Chris Patrick and Steve Bock were critical in setting the northern limb of the asteroid.  Without those two chords, the true size and shape of (96) Aegle could not be determined from the other chords.  This shows that occultation astronomy is a team sport.  It takes a variety of observations to get the size and shape of an asteroid.

Opportunity to Participate in Future Main Belt Asteroid Events

While not a focus of the RECON project, RECON members can participate in the observation of main belt asteroids to sharpen their skill in doing occultations.  The probability of getting a positive with a main belt asteroid event is higher for those within the path, since the orbits of main belt asteroids are better known than TNO’s.  In the future, Tony George will be sending out alerts for main belt asteroid occultations predicted to cross the observing sites of RECON members.  Typically, for a large main belt asteroid, the path may go over 3 or 4 RECON observers in the network.  Watch for postings of favorable main belt asteroid events on the tnorecon email list.  With luck, we will see your groups chord on a future profile plot.