wimvb Posted March 28, 2020 Share Posted March 28, 2020 (edited) While waiting for my main target to reach its best position, I decided to test my rig on a faint target. UMa I is a dwarf galaxy of the Milky Way, in the constellation Ursa Major. This galaxy was discovered in 2005 by studying images from the Sloan Deep Sky Survey. It is also supposedly the dimmest dwarf galaxy ever found. UMa I is located approximately 330 000 ly from the sun, and has a radius of 11.3 arcminutes. The galaxy consists of very old stars, red giants mostly, created in the early days of the history of the universe. As most other dwarf galaxies surrounding the Milky Way (some 100+ in total), this galaxy is slowly being ripped apart and absorbed. "This object was detected as an overdensity of red, resolved stars in Sloan Digital Sky Survey data. The color-magnitude diagram ofthe Ursa Major dwarf looks remarkably similar to that of Sextans, the lowest surface brightness Milky Way companion known, but with approximately an order of magnitude fewer stars. Deeper follow-up imaging confirms this object has an old and metal-poor stellar population and is ~ 100 kpc away. We roughly estimate MV = -6.75 and r1/2 = 250 pc for this dwarf. Its luminosity is several times fainter than the faintest known Milky Way dwarf. However, its physical size is typical for dSphs. Even though its absolute magnitude and size are presently quite uncertain, Ursa Major is likely the lowest luminosity and lowest surface brightness galaxy yet known." (From B Willman et al. ApJL, 2005, 626(2) L86 - L 88) I couldn't find any amateur images of this galaxy online, understandably. The data for this image was collected 27 March 2020. Setup details are in my signature. Total integration time was only 1 hour (30 x 120 s exposures) using an L filter, calibrated and stacked and annotated in PixInsight. What is in this image: Most of the stars are Milky Way stars in red colour: very few member stars (very faint red giants) of UMa I (only 50 - 60 are catalogued to date) in yellow colour:marked V1 and V5, two RR-Lyrae variables in UMa I in gold colour: two quasars in pink colour: several PCG galaxies at distances up to 500 Mly in gray colour: a galaxy cluster which I haven't been able to identify yet. Simbad reports a cluster ([SPD2011] 47308) in this area that is 6 600 Mly distant, but I very much doubt that this is it. An inverted image, showing the extent of the dwarf galaxy Edited March 28, 2020 by wimvb 10 Link to comment Share on other sites More sharing options...
vlaiv Posted March 28, 2020 Share Posted March 28, 2020 I really enjoy posts like this one. Very interesting and informative. Just to clarify, kit used is BK MN190 DS + ZWO ASI174MM-Cool? 1 Link to comment Share on other sites More sharing options...
Owmuchonomy Posted March 28, 2020 Share Posted March 28, 2020 Excellent post. Do you know the distance (or z) of the two quasars? 1 Link to comment Share on other sites More sharing options...
Waddensky Posted March 28, 2020 Share Posted March 28, 2020 (edited) Wow, that's a subtle one. The labeled image is very informative, thanks! Amazing to imagine how many more of these elusive dwarf galaxies are still to be discovered. I suppose analysis of GAIA data will reveal more members of UMa I? Edited March 28, 2020 by Waddensky Link to comment Share on other sites More sharing options...
wimvb Posted March 28, 2020 Author Share Posted March 28, 2020 1 hour ago, vlaiv said: Just to clarify, kit used is BK MN190 DS + ZWO ASI174MM-Cool? Yes, the 150pds is retired for now. Link to comment Share on other sites More sharing options...
wimvb Posted March 28, 2020 Author Share Posted March 28, 2020 32 minutes ago, Waddensky said: I suppose analysis of GAIA data will reveal more members of UMa I? Vizier & Simbad, so far. I haven't really looked at GAIA yet. 1 Link to comment Share on other sites More sharing options...
Waddensky Posted March 28, 2020 Share Posted March 28, 2020 25 minutes ago, wimvb said: Vizier & Simbad, so far. I haven't really looked at GAIA yet. I understand that. I meant science in general, new datasets like GAIA will provide much more data on the structure and evolution of these dwarf galaxies, I assume. 1 Link to comment Share on other sites More sharing options...
gorann Posted March 28, 2020 Share Posted March 28, 2020 (edited) So a dying galaxy. Very interesting even if it must be the least impressive galaxy around😉 Edited March 28, 2020 by gorann Link to comment Share on other sites More sharing options...
wimvb Posted March 28, 2020 Author Share Posted March 28, 2020 6 minutes ago, gorann said: So a dying galaxy. Very intresting even if it must be the least impressive galaxy around😉 Beauty is in the eyes of the beholder. There is some very interesting physics going on here. 1 Link to comment Share on other sites More sharing options...
wimvb Posted March 29, 2020 Author Share Posted March 29, 2020 19 hours ago, Owmuchonomy said: Excellent post. Do you know the distance (or z) of the two quasars? J103559.74+520235.9: z=0.741221 J103600.4+520218: z=0.66256 Z for QSO's doesn't always translate directly to distance, as is the case with galaxies. I've seen QSO z values in excess of 5. 1 Link to comment Share on other sites More sharing options...
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