A New Video Method to Measure Double Stars

1. A New Video Method to Measure Double Stars 28thAnnual IOTA Meeting December 4, 2010Richard Nugent

2. WHY MEASURE DOUBLE STARS ? • Position angle (θ) and separation (ρ) allow computation of orbits • Orbital periods  Kepler’s 3rd law  Actual separations/distance • Distance  absolute luminosity, masses, radii • Absolute quantities is the basis for the distance scale of the Universe

3. drift CURRENT METHODS TO MEASURE DOUBLE STARS Micrometer/Visual Fig. 1 Fig. 2

4. Take CCD image Measure positions of double star and reference stars Perform astrometric reduction With (RA, DEC) of components, compute position angle (PA) and separation (Sep) CCD Camera Method

5. Individual frames are chosen and stacked for an astrometric reduction East-West direction is derived from drift from two widely spaced frames Video Camera Methods

6. New Video Methods • Both methods use “LiMovie” software written by Kazuhisa Miyashita and • require GPS time insertion • 1) Artificial occultations - Uses LiMovie custom version to create an • artificial occultation • Details here: http://weblore.com/richard/double_stars.htm

9. 2) X-Y Video Drift across the Field of View • LiMovie Basics • LiMovie calculates brightness of stars for individual frames using for up to 3 • adjustable apertures = 3 individual stars • Apertures can remain fixed or drift to follows stars • Results are exported for all frames to Excel CSV file for analysis: brightness • levels, noise filtering, diffraction, FFT, etc.

10. LiMovie’s grid size is 635 x 475 pixels, origin is upper left corner of FOV

11. At 30 frames/sec recording rate, a 1-2 minute video can produce 1,000’s of (x,y) data pairs to analyze.

12. With LiMovie’s (x,y) position output for each star, separation and position angle are computed as follows: (user must determine quadrant)

13. Camera/telescope orientation drift angle actual east-west drift Drift does not have to be perfectly aligned East-West, a drift angle is easily calculated using least squares:

15. 3-D contour plots

16. RESULTS WDS X,Y WDS X-Y Star Sep Sep Diff PA PA Diff Observer Notes --------------------------------------------------------------------------------------------------------------------------------- 61 Cygni 31.1 31.1 0.0 152 153.1 1.1 RN Questar WDS 2346-1841 6.9 6.5 0.4 136 127.4 8.6 RN Questar STF 2280 14.2 14.2 0.0 182.9 183 0.1 RN Questar 15 AQL 40.5 39.7 1.8 209 209.7 0.7 RN Questar SF 2848 10.8 10.8 0.0 56 56.4 0.4 RN Questar WDS 2353+1155 19.3 19.2 0.1 282 281.5 0.5 RN Questar WDS 0013+2659 18.0 19.0 1.0 224 224.8 0.8 RN Questar WDS 0128+0758 69.1 67.8 1.3 100 105 5.0 RN Meade 14” WDS 0153+1918 7.5 7.3 0.2 356 358 2.0 RN Meade 14” WDS 0203-0020 43.0 42.6 0.4 194 196 2.0 RN Meade 14” WDS 0213-0224 16.6 16.7 0.1 234 235.7 1.7 RN Meade 14” WDS 0218+4017 11.4 10.9 0.5 294 284.7 9.3 RN Meade 14” WDS 0227+1034 73.6 73.2 0.4 32 31.5 0.5 RN Meade 14” WDS 0230+0504 27.1 26.5 0.6 328 310.7 17.3 RN Meade 14” - Video very noisy/bad seeing WDS 0231+0106 13.8 13.4 0.4 220 219.9 0.1 RN Meade 14” WDS 0243-2017 19.7 19.0 0.7 164 157.8 6.2 RN Meade 14” WDS 0257-0034 8.9 8.6 0.3 192 195.8 3.8 RN Meade 14” WDS 0302+0005 8.0 7.8 0.2 139 147.2 8.2 RN Meade 14” WDS data 10 yrs old WDS 0303-0205 8.9 8.7 0.2 223 222.6 0.4 RN Meade 14” WDS 0319-1834 8.4 6.9 1.5 120 124 4 RN Meade 14” star images merged WDS 0345-1320 19.8 20.0 0.2 324 324.5 0.5 RN Meade 14” stars out of focus

17. Potential Sources of Error • Precession/proper motion – can usually be neglected for data < 10 yrs compared to WDS positions • Abberations and distortions of your optical system – can be neglected since the effect should be identical for both components • f/10, f/6.3, f/3.3 – Use the least amount of glass between the stars and your video camera • Gnomonic projection - can be neglected for small (< 100) separations • Seeing/turbulence effects – are averaged out for the large numbers of video frames and effect both components simultaneously

18. Other Considerations • Scale factor – must be re-computed for each run. Slight instrument/ flexture changes and differential refraction. • The scale factor should be computed for each star and averaged • Watec 902H – f/10 Meade 14 LX-200 = 0.6/pixel • f/14 Questar 3.5, = 2.0/pixel • LiMovie’s CSV (x,y) output is the “Tracking (x,y)” data: • Doubles with large magnitude differences > 3 or very faint companions cause LiMovie’s apertures to jump around too much  use linked tracking

19. From Kazuhisa Miyashita: In operation, LiMovie examines the value of each Pixel in a StarTracking (aperture) circle set by the ‘radius’ setting, before doing photometry. Any pixel with a value of at least 50% of the maximum value in that is assumed to be part of the "star image", and the centre of gravity of the pixels is recorded as a centre of the star. When you set the "StarTracking Radius" small, the centre of gravity can be decided more accurately. However, when the movement of the star grows, LiMovie cannot track the star because the searched range becomes smaller than the movement. The StarTracking radius needs to be set to accommodate the movement of the star. In general, it should be set to be the same as Aperture, or 1-3 pixels larger than the Aperture radius."

20. LX-200 Users – No need to turn Scope off for Drift = motor drive OFF = motor drive sidereal rate

21. Conclusions • X-Y drift video method produces excellent results for PA and separations • This technique uses a feature of LiMovie that was previously overlooked • Large # of (x,y) data pairs is unprecedented in the data analysis compared to any other double star measurement technique • Occultation observers now have a new pastime in between occultations • Web page : http://weblore.com/richard/double_stars_video.htm