Image of the Week

First post-Gaia asteroid occultation success: A feedback from amateur astronomy

   
 

Figure 1. The borders of the predicted occultation path (solid diagonal lines) and their uncertainty margins (dashed lines), superposed on the outlines of New Zealand's main islands. The labelled tick marks are the predicted central occultation times in minutes, counting from September 20, 12:00 UTC. The two smooth arcs are geographic coordinate lines indicating -40 degrees of latitude and +/-180 degrees of longitude, respectively.

 
 

Less than one week after the publication of Gaia Data Release 1 (Gaia DR1), New Zealand amateur astronomer Graeme McKay successfully observed the occultation of a star by an asteroid. Just three weeks earlier, the predicted occultation path lay more than 4 path widths — or hundreds of kilometers — from his location at Blenheim, New Zealand.

On Sep 20, the 60-kilometer minor planet (671) Carnegia was due to pass in front of a 10th-magnitude star with the romantic-sounding designation TYC 6888-01416-1. Predictive calculations by the International Occultation Timing Association (IOTA) said the event should occur along a narrow strip (known as occultation path) of the remote watery solitudes of the Pacific and South Polar Ocean. McKay would probably not have tried any observation that night.

But then two things happened and changed this situation, as reported by IOTA’s Australian activist Dave Herald in a IOTA Yahoo group:

  1. A short-notice improvement of the asteroid's orbital elements by IOTA’s president Steve Preston (USA). This resulted in a lateral shift of the prediction by about 2.6 path widths.
  2. The release of Gaia DR1 on September 14, giving a more precise position of the to-be-occulted star. This shifted the prediction by another 1.4 path widths.

Preston’s September 16 calculation gave a revised occultation path running right over New Zealand’s main islands. It is shown in Fig. 1 (taken from the public prediction page). Accordingly, McKay went to his home observatory in time for the event, started his “C11” telescope (28cm aperture) and “Watec-120N+” video camera and then waited to see what would happen. The star’s brightness recording derived from the resulting video is shown in Fig. 2. A very clear and pretty occultation light curve was the observer’s reward. “I feel privileged to be the first to report a positive occultation result based on the new Gaia data set.” was Graeme McKay’s comment after the observation.

 
   
 

Figure 2. Top: Successful observation by Graeme McKay of the asteroid Carnegia occulting a star. The blue curve shows the brightness of the target star as function of time. The onset and end of the 8-seconds occultation are clearly marked by the two sudden jumps of the blue curve. The other three curves (pink, black and green) show similar curves for three different unrelated stars which are close by on the sky, and which were thus observed by the video camera along with the target star. Such neighbouring stars are routinely used as checks against possible instrumentation malfunctions and terrestrial clouds which could produce fake brightness drops. Bottom: Two original video frames are shown here, the one to the left shows the star during the occultation, the one to the right is taken just after the re-appearance of the star.

 
     

The success means that both the new star position from Gaia and the revised asteroid orbit determination are correct and highly precise. In the future, IOTA’s work on the improvement of asteroid orbits and the determination of diameters and shapes of asteroids will become much more efficient: The missed opportunities — observers sitting on their telescopes in vain — due to imprecise occultation path predictions will become much less frequent.

IOTA is a world-wide amateur-professional organisation devoted to the observation and scientific usage of star occultations by planets, asteroids and the Moon.

Credits: Graeme McKay, Steve Preston, Ulrich Bastian

[Published: 21/10/2016]

 

Image of the Week Archive

2017
24/11: Gaia-GOSA service
27/10: German Gaia stamp in the making
19/10: Hertzsprung-russell diagram using Gaia DR1
05/10: Updated prediction to the Triton occultation campaign
31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
2016
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
2015
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
2014
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
2013
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
2012
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
2011
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
2010
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
 
Please note: Entries from the period 2003-2010 are available in this PDF document.