1. Lee Clement PHYS 2070 Thursday, 7 April, 2011 Image Credit: NASA (Hubble)

2.  Plerionic type remnant of Supernova SN 1054  Filled shell structure powered by pulsar wind (Green)  Located in Taurus  RA: 05h 34m 31.95s Dec: +22° 58’ 54.4” (J2000) (Cutri et al.)  First observed by John Bevis (1731)  Independently rediscovered by Charles Messier (1758)  Distance: 1930 pc (Trimble, 1973)  Angular size: 6’ x 4’ (Dyer)  Magnitude: 8.4 (Dyer) Image Credit: Stellarium

3.  20-21 January, 2011  Conditions ▪ Cold! (-27 C) ▪ Sunset: 17:03 ▪ Moonrise: 18:38 ▪ Waning gibbous with 99% of the visible disc illuminated ▪ Hoped to get data before moon got too high ▪ Cloud: Initially none ▪ Worsened over the course of the evening ▪ Sky glow: Initially some to the North (Winnipeg) ▪ SQM: 19.61 ▪ Worsened as moon rose and clouds rolled in  SQM: 17.15 around 20:45  SQM: 15.63 around 21:30

4.  Series of unfortunate events  Deadbolt on dome side door frozen shut ▪ Possibly inadequate temperature equalization inside dome  Telescope would only focus in one direction ▪ Had to wait for Jennifer ▪ Wire had become disconnected in dome ▪ Rheostat adjustment needed in fuse panel  Dome froze stuck ▪ M1 had drifted past the edge of the aperture ▪ Spent ~30 mins trying to assist dome motor to rotate dome  End result  Not able to start collecting data until 21:20 ▪ Bright moon ▪ Partial cloud cover

5.  30 x 60-sec exposures  Large variations in brightness  Variable clouds  Bright moon

6.  To sample readout noise of the CCD chip  Average of 10 x 0-sec exposures

7.  To correct for thermal noise in the CCD chip  5 x 60-sec exposures with the shutter closed  Master bias subtracted then frames averaged  Interesting feature: periodic noise  Unknown source

8.  To correct for illumination variations, dust, etc.  30 x 60-sec exposures of sky regions near M1  Master bias and master dark subtracted  Normalized to mean value of 1  Median taken  Also exhibits periodic noise  Unknown source

9.  Master bias and master dark subtracted from raw data  Result divided by master flat  Registered images in 3 parts  Brightness variations  Discarded 5 frames

10.  Average of registered calibrated images  Problem:  Persistent gradient from northeast to southwest E N

11.  Used ImageJ’s ‘Subtract Background’ function  Radius: 300.0 px  Create background  Sliding paraboloid  Produced a model of the gradient

12.  Subtracted gradient model from reduced data E N

14.  Nugent (1998) measured the expansion of the Crab Nebula  Scans of 4 high-resolution photographs  Measured the motion of several filaments of the Crab’s structure  Measuring filaments not feasible with GAO data  Too blurry  Needed to look at larger scale features instead  Compared GAO image to POSS I (1951) and POSS II (1991) red filter images

15.  Took the square root of the gradient-subtracted image to enhance contrast around the edges  Vertically flipped to match orientation  Resized POSS I and POSS II images to be a similar scale to GAO image  Also stretched brightness so that only portions visible in GAO image were visible ▪ Some guesswork GAO (2011) POSS I (1951)POSS II (1991) E N E N E N

16.  Made use of the bottom two stars of the southwest trapezoid formation  In Aladin, measured separation on POSS I and POSS II images ▪ Distance: 1.09’ E N 1.09’

17.  Initially intended to measure distance from central pulsar to various features  Problem: Not obvious where the centre is GAO (2011) POSS I (1951)POSS II (1991) E N E N E N ??

18.  Alternative method  Measured distance between two sets of easily distinguishable features  Tried to approximate the major and minor axes GAO (2011)

19. Dataset Julian Date Major “Axis” (arcmin) Minor “Axis” (arcmin) POSS I2433957.9166674.8703.839 POSS II2448546.9583335.0343.914 GAO2455583.6458335.4094.353  All measurements made using line segments in ImageJ

20.  Plotted measured “axis” distances against Julian dates of observations  Calculated slopes of lines of best fit to approximate rate of expansion ▪ Similar for both “axes” ▪ Uniformly expanding

21.  Rate of expansion was found to be 0.5 arcsec/yr  Inconsistent with published value of 0.15 arcsec/yr (Bietenholz)  Extrapolated to point of zero size to determine original date of supernova  Found CE 1405 ± 29 ▪ Inconsistent with result of Nugent (1998): CE 1130 ± 16 ▪ Inconsistent with result of Trimble (1968): CE 1140 ± 15 ▪ Closer to result of Bietenholz (1991): CE 1245 ± 92 ▪ Measured only the synchrotron component  However, known date of supernova is CE 1054 ▪ Confirms result that expansion of the Crab Nebula is accelerating ▪ Exact expansion function unknown (Nugent)

22.  Very limited data set  Low detail of GAO data precluded measuring more than a few features  Random errors would average out with more measurements  Guesswork involved in determining what parts of POSS I and POSS II images were visible in GAO image  Guesswork involved in matching edges of features between images

23.  Despite unfortunate observing conditions, managed to acquire data that shows some large-scale structure of the Crab Nebula  Data not so good for astrometry!  Calculated expansion rate inconsistent with previous results  Calculated date of supernova inconsistent with previous results ▪ Still later than actual date ▪ Confirms acceleration of expansion E N

24. Bietenholz, M. F., Kronberg, P. P., Hogg, D. E. and Wilson, A. S. The Expansion of the Crab Nebula 1991 Cutri, et al. 2MASS All-Sky Catalog of Point Sources 2003 Dyer, Alan. The Messier Catalogue 2010 Green, Dave. G184.6-5.8 2009 Trimble, Virginia. The Distance to the Crab Nebula and NP 0532 1973 Trimble, Virginia. Motions and Structure of the Filamentary Envelope of the Crab Nebula 1968 Images: http://hubblesite.org/gallery/album/pr2005037a/ http://archive.stsci.edu/dss/