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What’s Up for Imagers. The Sharpless Catalog January 2011 B. Waddington. It’s Nebula Season. Not many galaxies around….. But plenty of good nebula opportunities Larger targets for shorter focal lengths Interesting structure for longer focal lengths Good narrow-band targets |. - PowerPoint PPT Presentation
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What’s Up for Imagers
The Sharpless Catalog
January 2011
B. Waddington
It’s Nebula Season Not many galaxies around….. <sigh> But plenty of good nebula opportunities
Larger targets for shorter focal lengths Interesting structure for longer focal lengths Good narrow-band targets |
Hunting Nebula Targets Just as the Arp catalog was a good
resource for finding interesting galaxies… The Sharpless catalog is a great resource
for nebulas Amateur contributions have made this
especially easy to do |
Sharpless Catalog Developed by Stewart Sharpless at USNO
in late 1950’s Two increments (SH-1, SH-2)
1953 – 142 objects using Palomar Sky survey plates (Baade & Minkowski)
1957 – Final catalog of 313 objects using National Geographic/Palomar Sky Atlas
“Comprehensive” for Dec > -27° |
Sharpless Catalog Plates taken in both “red” and “blue”; color
used to rule out reflection, planetary nebulas
Catalog included identification of related bright stars
A few “mistakes” – supernova remnants, planetary and reflection nebulas… |
What Was the Point? Map spatial distribution of hydrogen and
regions of star formation in our galaxy A good tool for building a model of Milky
Way spiral arm structure Also used to refine the galactic pole
position |
Quick Review of “HII regions” HII – ionized hydrogen HI – neutral hydrogen H2 – molecular hydrogen A little bonehead physics:
Atomic Emission Spectra - the Origin of Spectral Lines
|
HII Region Behavior Nearby bright OB stars ionize the interstellar
hydrogen Free electrons recombine with protons and
release energy (photons) Electrons “cascade” from higher to lower states,
resulting in well-known emission lines The Balmer series emission lines will be the major
components in an amateur image of an emission nebula |
Sharpless Object Locations
Sharpless RA Values
01020304050607080
Fre
qu
en
cy
Sharpless Object Sizes
Sharpless Object Sizes
020406080
100
Diameter, Arc-minutes
Fre
qu
ency
General Characteristics Wide distribution of sizes, plenty of targets
for all focal lengths Plentiful in Winter and Summer (doh) Good candidates for narrow-band imaging,
especially H-alpha |
Sharpless Catalog Usage Includes many well-known objects – M42,
Rosette, Lagoon, Cone nebulas… But also provides a path to less well-known
but interesting targets “Shopping” is easy with some excellent
amateur sites |
Sharpless Resources Dean Salman (“Mr. Sharpless”) :
http://www.sharplesscatalog.com/ Reiner Vogel’s Sharpless Observing Atlas:
http://www.biophysik.uni-freiburg.de/Reiner/ATM/Sharpless/Sharpless_e.html (Sharpless_Atlas.pdf) |