1 / 24

Observation of the Crab Nebula

Lee Clement PHYS 2070 Thursday, 7 April, 2011. Observation of the Crab Nebula. Image Credit: NASA (Hubble). M1: The Crab Nebula. Plerionic type remnant of Supernova SN 1054 Filled shell structure powered by pulsar wind (Green) Located in Taurus

gilles
Download Presentation

Observation of the Crab Nebula

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lee Clement PHYS 2070 Thursday, 7 April, 2011 Observation of the Crab Nebula Image Credit: NASA (Hubble)

  2. M1: The Crab Nebula • 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. GAO Data Collection • 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. Data Collection Challenges • 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. Raw Data • 30 x 60-sec exposures • Large variations in brightness • Variable clouds • Bright moon

  6. Calibration Frames: Master Bias • To sample readout noise of the CCD chip • Average of 10 x 0-sec exposures

  7. Calibration Frames: Master Dark • 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. Calibration Frames: Master Flat • 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. Image Registration • 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. Reduced Data • Average of registered calibrated images • Problem: • Persistent gradient from northeast to southwest E N

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

  12. Gradient Removal • Subtracted gradient model from reduced data E N

  13. Measurement of Expansion Rate

  14. Expansion Rate • 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. Expansion Rate N N N • 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 E E E GAO (2011) POSS I (1951) POSS II (1991)

  16. Calibration of Image Scale N • 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 1.09’

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

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

  19. Measurements • All measurements made using line segments in ImageJ

  20. Analysis • 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. Results • 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. Sources of Error • 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. Summary • 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. References 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/

More Related