Use of Charts.

by Stefano Pesci

This text is a brief introduction to the charts found at the ISN web site. The charts are used by some amateurs in Italy and are now available to world-wide amateurs interested in supernova hunting. Please read carefully this text. Should you have any questions or wish to report errors please contact Stefano Pesci * Why charts for SN hunting * ----------------------------- Back in 1989 when I started hunting for supernovae (SN) there were very few sources that the amateur could use for his search. A reference of the galaxy observed is crucial to determine if any suspect stars are visible or not. So I began to draw my own set of charts using Bob Evans suggestions. A few years later, Bryan & Thompson excellent set of charts became available (published by Cambridge Press). Yet these charts cover only a small sampleof the closest galaxies visible to a northern observer. In supernova hunting success depends also on a large sample of galaxies frequently checked. Today a wide choice of photographic references is available to the amateur. Some of these atlases are collection of prints from Palomar Obs. or Carnegie Institute archives, made by large observatories. CCD atlases have also been published. Yet these sources are not always suitable for SN hunting; most of them show an over-exposed galaxy at its core, or their field of view is too narrow. * How these charts were drawn * ------------------------------- For each galaxy in the list I made a photographic reproduction of the Palomar Sky Survey plate (either blu or red, depending on which showed less over-exposion). The galaxy was then drawn by projection on the chart. The chart then became part of my hunting program and of amateur and friend Piero Mazza. We marked every new chart, and only after at least ten observing session we made the chart available to other amateurs, believing it to be possibly free of errors. The charts down-loadable from ISN are only those that have been used for 4 to 2 years. We have other charts, more recent, that will be available by year end. * What do the charts show * --------------------------- Galaxies are shown as a set of lines, sort of isophotes. The nucleus, if stellar or well condensed is also shown. Stars inside the galaxies or just outside its border are shown to limiting magnitude of about 19. Only the brightest stars are shown in the nearby field. Each chart is labelled with the galaxy name, approximate position, and constellation name (usually top right), the NGC description, the number of Tirion's and Uranometria's chart where the galaxy is shown (bottom). Most of the charts are have south at the top (telescopic view). * Pros and cons of these charts * --------------------------------- These charts are an handy reference for visual hunting with medium to large Newtonian telescopes. If you use a SC telescope you should either flip the chart over or use an image editor and do this digitally on your PC before printing them. They are a complement to Bryan & Thompson set. They cover bright northern galaxies not covered by that source. They are safe to magn. 16.5 (the visual limit of a 20 inch) inside or very close to the galaxy outer border. These charts should not be used for CCD supernova hunting. CCD imaging gives a very deep view of the galaxy and some very faint stars may not be shown on the chart. Beware of possible magnitude difference due to different spectral response of the eye or the CCD. Some very red or blue stars may not be correctly depicted on the chart (dot size not proportional). Star dots on charts are only a approximate representation of their actual brightness. No effort has been made to depict them proportionally. The charts don't have a scale. They usually show a field 10' to 20' across.If you need to know the scale, the best way is to use the galaxy major axis as a reference (this information is available in the NGC catalog). They should not be used to locate a galaxy. If your telescope is not PC assisted you should use a star atlas such as Tirion or Uranometria. * Disclaimer * -------------- These charts can be freely used by any observer interest in SN hunting. They should not be used for profit. Examples of these charts can be used in articles or presentations; author and web site must be mentioned though. Thank you and good hunting!