History of our TBG group

(Peter Riepe)


Each November the “Bochumer Herbsttagung der Amateuratsronomen” (BoHeTa) is arranged in the University of Bochum. Organizers are Peter Riepe (VdS e.V., Fachgruppe Astrofotografie) and Ralf-Jürgen Dettmar (professor of the Astronomical Institute of Bochum University). In November 2011 at the 30-th BoHeTa both decided to start a collaboration between amateurs of the VdS and professional astronomers from Bochum, concerning research of stellar streams around prominent galaxies. It was in January 2012, that a new workgroup was established in the Fachgruppe Astrofotografie, called “TBG” (initials of the german expression “Tief Belichtete Galaxien”, meaning “very long exposed galaxies”).

Our aim in the beginning was the detection of new stellar streams. The first targets were galaxies listed by Arpad Miskolczi. But after having got first images we saw, that there can be revealed much more interesting details in the halos of galaxies. The well-known advantage of amateurs is: wide-field photography of galaxies and their neighbourhood with typical modest amateur telescopes and CCD cameras. Amateurs can do this at any time and have no restriction to projects, which have to be applied for by professionals. With this equipment it is possible to reach tidal interaction phenomena between galaxies but also dwarf galaxies of very low surface brightness (LSB). Our used telescopes range from small refractors (4 inch) to reflectors with apertures up to 44 inch. The deepness of the images is depending on sky quality and exposure time. Meanwhile we reach down to magnitudes beyond of 28 mag/arcsec^2, which is deeper than the Sloan Digital Sky Survey (SDSS).

For this reason the TBG aims were redefined in autumn 2013 more generally: detection of LSB phenomena. Our collaboration with professional astronomers was extended. Today we are lucky to have built up intensive contacts with I.D. Karachentsev (professor at Special Astrophysical Observatory, Russia).

The TBG group consists of those amateur astrophotographers listed on the site “team”, coming from german-speaking countries (Austria, Germany, Switzerland). Some have remote controlled telescopes in Spain or the USA. Each TBG member has a special task. Astrophotography is the most important one, but further ongoing work has to be done, e.g. analyzing the images, studying professional literature, getting own photometric results and having discussions with professional astronomers. The framework in group activities is done by Peter Riepe (conceptional work) and Thorsten Zilch (organisation).

To test our capabilities, our first photographic efforts aimed on already known LSB objects. In a second step we decided to establish a new list of targets from the NGC and IC by systematical examination of potential candidates using the Deep Sky Survey (DSS). To identify possible candidates, we applied a heavy contrast enhancement on chosen images. Following this method, we identified some dozens interesting galaxies, showing possible features like stellar streams (read more –>). Due to the limited magnitude of the POSS/DSS we meanwhile compare possible candidates with the SDSS results, whenever possible.

Our first success was the discovery of three new dwarf galaxies in the interacting system NGC 4631/56, obviously embedded in a possible huge stellar stream. This discovery was reported in a preprint by Karachentsev et al. (2014), see “publications” and “latest news“. In the meantime, several new companion galaxies were found also in other extragalactic systems in the Local Volume. At the moment, some of these objects are investigated with the russian 6-m telescope. So dwarf galaxies detected by amateurs can be verified and investigated by professionals in order to increase our knowledge of the Local Universe.


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