Sky brightness from Dome A

Transcription

1 Sky brightness from Dome A Preliminary results from the HRCAM all-sky camera Authors: & Michael Ashley Date: Meeting:

2 Collaborators University of NSW Michael C. B. Ashley Daniel M. Luong-Van John W. V. Storey Macquarie University / AAO Jon S. Lawrence University of Western Sydney Nick Tothill Nanjing Institute of Optics & Technology, China Purple Mountain Observatory, China Chinese Centre for Antarctic Astronomy, China Tianjin Normal University, China Polar Research Institute of China National Astronomical Observatories, China Texas A&M University, USA Xiangqun Cui LongLong Feng Xuefei Gong Zhongwen Hu Zhaohui Shang Lifan Wang Huigen Yang Ji Yang Xu Zhou Zhenxi Zhu

3 Outline 1. Motivation 2. Instrumentation 3. Reduction & calibration 4. Preliminary results (incl. pretty pictures!)

4 Scientific motivation 1. Site characterisation in optical (B, V, R) Sky brightness? Extinction? Auroral distribution? Auroral intensity? N/A N/A N/A N/A

5 Scientific motivation 1. AST3-#2 and AST3-#3 Growing interest worldwide in AST3-#1 data ('I' band) AST3-#2 and #3 will observe in 'G' and 'R' bands

6 Instrumentation 1. Consumer grade Canon DSLR + fisheye lens Canon 50 D Sigma 4.5 mm f/ megapixel digital SLR 1.6x crop sensor 14 bit RAW data format All sky coverage

7 Instrumentation 2. Installed on PLATO (Dome A) in January Returned in 2012 lens flush with top (no cover) reflective cover shields snow low emissivity > heated easily operates down to -80 C

8 Instrumentation 3. HRCAM clones throughout Antarctica HRCAM-2 Dome F 2011 HRCAM-3 Ridge A 2012 HRCAM Dome A 2010

9 Instrumentation 4. Control Controlled via USB & linux gphoto2 command Exposure times (set automatically) from 1/2000th to 120 seconds Sensitivity set to ISO px2 (20 kb) JPEG thumbnails returned via Iridium satellite

10 Instrumentation 5. Complementary instruments HRCAM All sky, Canon RGB 240 / px Gattini Bessel BVR 150 / px Nigel Spectroscopic CSTAR i-band 15 / px

11 Instrumentation 6. Stats for 2010 Number of images (total): 35,679 Number of images ( night time ): 16,894

12 Instrumentation 6. Stats for 2010 Number of images (total): 35,679 Number of images ( night time ): 16,894

13 Reduction 1. Bayer colour filter array e.g., 10 Mpixel image: 2.5 Mpixels red 5.0 Mpixels green 2.5 Mpixels blue Credit: Wikipedia user CBurnett

14 Reduction 2. Conversion from native Canon RAW (.CR2) format to FITS

15 Reduction 3. Collapse the 4 separate colour channels

16 Reduction 4. Flat field? Cauwerts et al. (2012)

17 Photometric calibration 1. Astrometry Most standard astrometry routines fail for wide fields of view. Need to account for radial distortion of the fish-eye lens.

18 Calibration 2. Image scale Altitude Azimuth

19 Calibration 3. Photometry Aperture photometry on: ~7000 images ~800 stars per image Extinction: Use typical Mauna Kea value Assumed constant throughout year RMS ~ 0.3 mag

20 Calibration 3. Photometry

21 Results 1. Sample images 14th June, :04 UT 13th June, :19 UT 16th June, :49 UT

22 Results 1. Sample images - unwrapped

23 Results 1. Sample images - unwrapped

24 Results 1. Sample images - unwrapped

25 Results 1. Sample images v. bright aurora 3rd August, :34 UT

26 Results 1. Sample images v. bright aurora

27 Results 1. Sample images v. bright aurora Dark winter night - no moon - no aurora Dark winter night - no moon - strong aurora

28 Results 2. Sky brightness

29 Results 3. Sky brightness - aurora distribution

30 Results 4. Transparency variations

31 Results 4. Transparency variations 65% < 0.5 mag 90% < 1.0 mag 99% < 2.0 mag etc

32 Results 5. Consistency with auroral intensity data Nigel spectroscopic data (Sims et al. 2012) shows maximum intensity typically occur at: 04:00 Local 23:00 UT 22:00 Magnetic (at ZENITH)

33 Results 5. Consistency with auroral intensity data eyeballing 1,500 images

34 Results 5. Consistency with auroral intensity data

35 Future work 1. Disentangle vignetting and extinction 2. Use precise and accurate reference magnitudes 3. Transparency as function of position > clouds, fog etc 4. Sky brightness as function of position, temporal variation 5. Aurora intensity, distribution 6. Coherently compile data for ~17,000 all-sky images 7. Publish

36 Timelapse 2100 images Spans ~3 weeks (11th June to 3rd July, 2010) Images taken every 15 minutes 120 s, f/2.8, ISO 400 Playback speed 24 fps Look for: - aurora! - twilight glow - moon rise - 22 degree diamond-dust halo