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

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en

cy

Sharpless Object Sizes

Sharpless Object Sizes

020406080

100

Diameter, Arc-minutes

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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) |