The Video Drift Method to Measure Double Stars

1. The Video Drift Method to Measure Double Stars Richard Nugent 33rd IOTA Annual Meeting Las Vegas, Nevada October 17, 2015

2. WHY MEASURE DOUBLE STARS ? • Position angles (θ) and separations (ρ) allow computation of orbits • Orbital periods  Newton’s version Kepler’s 3rd law  Actual separations/distances and stellar masses • Distance  absolute luminosity • H-R Diagram  the basis for the distance scale of the Universe

3. METHODS TO MEASURE DOUBLE STARS Micrometer/Visual Fig. 1 Fig. 2 drift Accuracy ~ ±1°, ± 1″

4. Take image Measure positions of double star and reference stars Perform astrometric (plate) reduction Requires star catalogue With (RA, DEC) of components, compute position angle (PA) and separation (Sep) Accuracy ~ ± 0.3°, ± 0.3″ Photographic/CCD Camera Method (combining multiple exposures)

5. Mann Measuring Engine y x

6. Individual frames are chosen and stacked for a relative astrometric reduction East-West direction is derived from widely spaced frames Calibration doubles required Video Camera Methods

7. Nugent-Iverson Video Drift Method • Video record double stars drifting across the FOV-Motor drive off • Video is analyzed with Limovie* - output is brightness data and standard (x, y) coordinates of components for each video frame • (x, y) coordinates are input into Excel program VidProto calculate PA, SEP, scale factor and other statistical quantities *Limovie written in 2005 by Kazuhisa Miyashita, Japan

8. Data to be sent to CSV File Start End

9. Limovie CSV file

10. Limovie CSV file

11. Meade 14“ LX-200 Collins Image Intensifier Watec 902H camera

13. VidPro – VIdeoDriftPRogramreductiOn

14. VidPro – VIdeoDriftPRogramreductiOn

15. Limovie’s Aperture Rings = (x,y) =photometry

16. Limovie’s Centroid Determination • Brightest pixel in red aperture is identified • All pixels with brightness of at least 50% of max value are assumed to be part of the star image • (x,y) = center of gravity of the top 50% pixels is recorded as the position of the star

17. With Limovie’s (x,y) position output for each star, separation, position angle, scale factor are computed automatically as follows: ρ= { (xp –xs)² + (yp–ys)²}xscale factor θ = tan -1 (xp– xs) (yp– ys) cos  (drift-time) 15.041068 scale factor = (xB –xE)² + (yB–yE)² drift-time = seconds from GPS time of drift endpoints or drift-time =total frames frame rate

18. Correction to Position Angle Camera’s video chip orientation drift angle actual east-west drift

19. Drift angle calculation - method 1 Drift angle calculation - method 1  triangle solution AB -1  = cos AC

20. Drift angle calculation - method 2  least squares y = mx + b drift angle = arctan (m) Accuracy ~ ± 0.02°

21. RESULTS COMPARED TO Washington Double Star Catalog (WDS) ° "

22. For 1,133 doubles measured: PA, average σ = 1.14° Sep, average σ = 0.37″ Closest separation = 3.7″ STATISICAL RESULTS TO DATE

23. WDS 20391-0942 J1400AB, Sep = 3.7″

24. How faint can we go ? • Nugent’s system: • 14″ Meade SCT Watec 902H Ultimate • Collins I3 intensifier • Elevation: 1,705 m • Mag limit: routinely reach +15 in the dry dark skies of west Texas (5 miles from McDonald Observatory) • Iverson’s system: • 14″ Meade SCT Stella Cam 3 (Watec 120N) • Elevation: 92 m • Mag limit: +12 in the humid average skies in east Texas

25. Integrating Video Cameras + + + = Integrating video cameras add (integrate) a predetermined number of frames and then continuously output that image until the next image is available. In simplistic terms, each successive increase in the integration level doubles the exposure time. Using a Stella Cam 3, Iverson can see deeper than magnitude +12, but there are serious problems measuring faint double stars.

26. The Problem • At integration levels greater than 4 frames (0.132 sec.) the target stars are elongated and jump during drift • Limovie is unable to follow these jumps and therefore it has trouble tracking the drifting stars. • Limovie is also unable to accurately resolve the (x,y) coordinates for the primary and secondary stars.

27. A Drift Example with 3-sec Frame Integration

28. The Modified Video Drift Method • Using the Modified Video Drift method Iverson has measured double stars down to magnitude +16.9. • In April 2015 we published a short paper describing the method (JDSO, vol. 11, No. 1)

29. Method consists of 2 Phases: Tracking a) Use integrating video to acquire faint double star. b) Record video for 1-2 minutes – motor drive running c) Stars are stationary in FOV Drifting a) Turn off integration and motor drive (video still b) Video recording rate is back at 30 fps (25 fps PAL) c) Slew telescope east or west until a bright star is visible phase phase recording) at same (or close to) declination as target double d) Continuing, record 3 or 4 drifts as in the regular video drift method

30. Tracking (integrating) the double stars allows the appropriate level of integration to see the double star components • Stars stationary – no skipping/jumping, and Limovie can thus measure their (x, y) coordinates • Drifting – allows drift angle and scale factor to be derived from the same video

31. Modified Drift Video Example

32. Reducing the video data: • Drift phase - place both Limovie aperture rings over the single bright star  Use CSV file into VidPro - computes plate scale/drift angle • When you do this, the position angle/separation results reported by VidPro are meaningless, but the plate scale and drift angle are valid • Tracking phase – Measure with Limovie, insert CSV file into Vidpro. Manually insert drift angle/scale factor into 2nd version of VidPro,

33. VidPro Modifications Manually insert drift angle here Manually insert plate scale here

34. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star)

35. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded

36. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″/ ±0.02°

37. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″, 0.02° • No dark frames, flat/bias frames, no shielding or cooling of video camera

38. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″, 0.02° • No dark frames, flat/bias frames, no shielding or cooling of video camera • Each drift is self calibrating: hardware can be removed and re-installed on telescope without having to worry about re-calibrating

39. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″, 0.02° • No dark frames, flat/bias frames, no shielding or cooling of video camera • Each drift is self calibrating: hardware can be removed and re-installed on telescope without having to worry about re-calibrating • Standard deviations reflect realistic errors in measurements

40. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″, 0.02° • No dark frames, flat/bias frames, no shielding or cooling of video camera • Each drift is self calibrating: hardware can be removed and re-installed on telescope without having to worry about re-calibrating • Standard deviations reflect realistic errors in measurements • No star catalogues, no calibration doubles, no precession needed – PA, SEP are for equator and epoch of date – what you see is what you get

41. Advantages of this Drift Method • Only the component double stars need be visible and measured, no other stars needed (Modified Drift method requires 3rd brighter star) • Each video frame provides PA, SEP which are all averaged. All frames are used – none are discarded • Scale factors/drift angles computed automatically to ±0.03″, 0.02° • No dark frames, flat/bias frames, no shielding or cooling of video camera • Each drift is self calibrating: hardware can be removed and re-installed on telescope without having to worry about re-calibrating • Standard deviations reflect realistic errors in measurements • No star catalogues, no calibration doubles, no precession needed – PA, SEP are for equator and epoch of date – what you see is what you get • Large # of (x,y) data pairs are unprecedented in the data analysis compared to any other double star measurement technique

42. LX-200 Users – No need to turn Scope off for Drift

43. Conclusions • Our drift video method is an alternative method to measure double stars • This drift method produces results for PA and separations with high systematic accuracy • This technique uses a feature of Limovie that was previously overlooked • Web page for VidPro download: • http://www.poyntsource.com/Richard/double_stars_video.htm