International Supernovae Network

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  G A L A X Y - " l i g h t " 
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            (1996)
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     a.cidadao@mail.telepac.pt

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Welcome to GALAXY-"light", a project that is expected to produce a continuously growing atlas of "thumbnail" CCD galaxy images and that was specially conceived to be useful in amateur supernova surveys. The project's title, GALAXY-"light", can be easily explained. First of all, the atlas will ONLY include galaxies. Obviously, its images do collect galaxy's "light" and, hopefully, will help me and/or someone else to recognise the "light" of explosive newcomers. In addition, it was conceived as a "lightweight" project (e.g. composed of SMALL images obtained with SHORT exposures), not intended to compete with or replace the on-line, CD-ROM or printed editions of the excellent "PRO"-atlases that are presently available. As a matter of fact, I use and I do recommend such atlases. They were at least crucial to interpret my "first" image of a given galaxy. All GALAXY-"light" images are obtained by ANTONIO JOSE CIDADAO, a Portuguese amateur living in Oeiras, member of APAA (Portuguese Association of Amateur Astronomers, one of the founders of the "Astro-Port" mailing list, and also subscriber of "AUDE", "MAPUG" and "SBIGUSER" mailing-lists. GALAXY-"light" is thus a personal project, with all the resulting advantages (homogeneous set of images, obtained from the same site, with the same telescope, CCD camera, integration time, scale and orientation, and subjected to the same processing routine) and disadvantages (new images will be added less rapidly, galaxy coverage will be only that typical of a North hemisphere location). I use the atlas in my own supernova survey (GALAXY-"light" does contain the most up-to-date results of the survey itself) which just started systematically in 96/04/28. However, I also decided to put GALAXY-"light" in the Net so that everybody could benefit from its images, either in their own surveys (visual, photographic or with CCDs), or just to have access to an "additional" library of galaxy images obtained under conditions that are typical to most amateurs. In fact, one of the things I noticed when I started looking for galaxy images on-line was that, if one excludes the most bright and/or "photogenic" galaxies, most of the remaining targets are often neglected. Furthermore, a high percentage of the images that are available has overexposed nuclei, a fact that difficults its use in supernova-"hunting" projects. As expected from a supernova survey, GALAXY-"light" will be under permanent (re)construction. My first priority will be to obtain images of new objects (as quickly as possible for an amateur that loves his hobby but has "also" other important things to do in life). In a second phase (namely when galaxies are revisited) I will always replace the existing images for new ones when these are of better quality. This will happen frequently since images will be obtained whenever possible and/or wise, namely in less than optimal sky transparency or stability and even when the moon is present.

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     IMAGE SPECIFICATIONS

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Thanks to CCDs, GALAXY-"light" images are obtained from a "light"-polluted urban site (Oeiras, Portugal, from my "roof-top" observatory) and with a "lightweight" aperture telescope (10" f/10 MEADE LX200, converted to f/6.3 with a wide-field adapter), thus in conditions that are typical to a large number of amateurs. All images are obtained at the same scale (1 pixel = 5.9 arcsec) and orientation (North = up; West = right), and represent the full sensor area of the CCD camera used (if we exclude minor area losses due to the corrections during the "track & accumulate" routine). All images are obtained with a SBIG's ST6 CCD camera (low "anti-blooming gate" setting), operating at - 30ºC and in LOW RESOLUTION mode (34.5 x 54 micron pixels). All images have a total integration time of 5 MINUTES, resulting from the sum of ten 30 second exposures using the SBIG's "track & accumulate" routine. A "master" dark frame (average of twenty 30 second dark exposures obtained at -30ºC, in low resolution mode, previously obtained and uploaded to the camera when necessary) is used for all images. All images are subjected to "flat-field" correction, logarithmic processed (in order to show details close to the galaxy's nucleus) and then exported as standard 8-bit TIFF files. TIFF files are inverted to produce negative images, and the rectangular pixels are corrected by interpolation (originating 34.5 x 34.5 micron pixels). Images are then subjected to an unsharp-mask, to a size reduction to 75% of the original (originating 42 x 42 micron pixels), and to a second unsharp-mask. The GALAXY-"light" logotype is then added to each image (M100 "icon" plus the text GALAXY-"light"), as well as the object's identification and my e-mail address. For objects larger that the ST6's field-of-view, several images are obtained and labelled a, b, c, ....

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              NOTES: 

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Although the GALAXY-"light" is project only composed of "GIF" images, I do keep all its originals in SBIG's ST6 format. If someone ever wants to have access to any of those originals in order to retrieve details potentially lost during the 16- to 8-bit conversion, please do not hesitate to contact me.


Antonio Jose Cidadao
Rua D. Antonio Luis de Menezes, No9, 3A,
S. Juliao da Barra, Oeiras,
2780 Oeiras - PORTUGAL
phone: +351-1-4412192
e-mail: a.cidadao@mail.telepac.pt