6 Attachment(s)
Observations of the 9 Holmberg dwarfs
Dear DSF
I'm pleased to report visual observations of all 9 Holmberg dwarfs with an 18" telescope. Uwe has made these observations with a 16" telescope, and his observations are largely my inspiration to even attempt something as faint as Holmberg IX with an 18-inch scope. I was pleasantly surprised when it yielded to observation in my 18-inch during this year's Texas Star Party, although it failed to yield in 2012 TSP [reasons are that I a) was much less experienced, b) did not have a tracking platform, c) knew less about mirror collimation etc, d) did not use high-contrast eyepieces.]. I also wish to say that I learned about the existence of these targets from the book "Galaxies and how to observe them", by Dr. Wolfgang Steinicke and Richard Jakiel, published by Springer Verlag -- and I have found this book to have many many wonderful observing programs.
Along with my own reports below, I will also take this opportunity to translate Uwe's reports to English, since I could not find a translation. I have much to learn from Uwe's very clear and precise observation logs, as is evident below. (Also, Uwe, if you find any incorrect translations, please do let me know and I'll fix them. My German is still very poor.)
Uwe's introduction to the catalog, roughly translated
The nine galaxies existing in the Holmberg catalog were detected by Erik Holmberg at the Lund Observatory (Sweden). The galaxies were published in three publications in the years 1950 and 1969. Some of these galaxies are dwarf galaxies. Thus, Holmberg I, II and IX are classified under the M 81 Group, and Holmberg IV under the M 101 Group. As for the others, it is postulated that Holmberg VIII is a companion of the Seyfert galaxy NGC 5033 that lies slightly north of it, and similarly that Holmberg III is related to the IC 342 group.
Visually, the galaxies are difficult to observe due to their low surface brightness. In addition to sufficient aperture, most importantly, good sky conditions are necessary. The most spectacular galaxy of the catalog is certainly Holmberg IX, which lies just a few arcseconds east of M 81. Excluding the very difficult objects I, VII and IX, the rest are definitely within the reach of smaller telescopes.
Holmberg I
Uwe's observation (translated)
16" Newtonian, 150x, fst 6m7
A companion of M 82, about 2.5° NW away. Very weak and only observable with averted vision. Exact finder chart necessary. Only the SE part of the galaxy can be definitely observed. This region is about 2'x1.5', elongated NE-SW, observed as a completely structureless glow.
My observation
18" f/4.5 Obsession, Texas Hill Country (Bortle 2-ish conditions), 2015-01-20
(This observation came after many, many failed attempts at seeing this object)
Started out with a 26mm HD Ortho from University Optics. This has a large exit pupil on my telescope, so it might not have been a very good idea. With an observing hood, I centered the region without knowing the exact position (only roughly where to look).
Repeatedly observed a patch "above" (NE in this context) a pair of stars and to the right (W) of another star. Then went back to the DSS image and validated! Very hard to repeat, extremely faint.
Changed eyepiece to 20mm Pentax XW (~100x) -- it was much easier than in the 26mm. Very faint, feels like a faint Palomar GC.
Holmberg II
Uwe's observation (translated)
16" Newton, 129x, fst 6m7
Big, and already conspiscuous at low magnification. Low surface brightness. Brightest region is 2'x3' in size, and found to the west of the central triangle of stars. East of the triangle is a very weak N-S elongated line, with no individual knots seen. The brighter central region runs towards the north, diffuses out. The object is a member of the M 81 group, lying 8.4° ESE of M 81.
My observation
18" f/4.5 Obsession, Texas Hill country (Bortle 2-ish conditions), 2013-11-02
10mm Delos (~205x): rather easy. Also visible in 31mm Nagler (~66x).
Attachment 1803
Holmberg III
Uwe's observation (translated)
16" Newton, 129x, fst 6m8
Brightening of size 1.5'x2'; Elongated 2:3 SE-NW. Can be held with averted vision. Diffuse. Otherwise structure-less, without any distinct nucleus.
My observation
18" f/4.5 Obsession, Texas Hill Country, 2013-10-08
Certainly existent glow that is very, very faint. Invisible in 31mm Nagler, but seen with considerable effort in 13mm Hyperion. Best view in 10mm Delos. Precise positioning and hood over head were essential! The size of the glow increased with staring. This object was at the edge of visibility, so no attempts were made to try and see the spiral structure.
Attachment 1804
Holmberg IV
Uwe's observation (translated)
16" Newton, 100x, fst 6m7
A companion of M 101, at a distance of about 1.3° WSW. The disturbing 5.7 mag star 86 UMa lies only 13' SW. The galaxy is indeed faint, but can be seen with averted vision as a brightening elongated 3'x1' NE-SW. Holding 86 UMa out of the field of view, the edge contour is well defined. No nucleus or other structure could be made out.
My observation
18" f/4.5 Obsession, Texas hill country, 2014-03-29
At the edge of visibility. Found without using DSS imagery at first. Confirmed precise position against DSS. Then, observed the almost north-south elongation, and later confirmed against DSS imagery. Can hold about 30% of the time. Sensed some mottling.
Attachment 1805
Holmberg V
Uwe's observation (translated)
16" Newton, 129x, fst 6m8
Galaxy nearly round with a 1.5' diameter. Concentrated towards the center. Difficult to hold with averted vision.
My observation
18" f/4.5 Obsession, Texas hill country, 2014-03-29
Rather easy object, much easier than Holmberg IV. Didn't need DSS image reference at all to find! Couldn't discern any structure. Sensed elongation, confirmed against DSS image. 7mm Nagler gave nice view but still no spiral arms; however, it felt mottled.
Attachment 1806
Holmberg VI
Uwe's observation (translated)
16" Newton, 100x, fst 6m9
Despite poor seeing 5° above the horizon, could be easily held with indirect vision as a round, 1' diameter-sized galaxy. The edge diffuses out. The galaxy is concentrated towards the center. 13' NNE of NGC 1325.
My observation
18" f/4.5 Obsession, Okie-Tex Star Party 2015
Easiest of the Holmberg galaxies. Dim NGC galaxy in Eridanus. 14mm Pentax shows hints of mottling and direction of "bar". Otherwise, just a faint round patch.
Holmberg VII
Uwe's observation (translated)
16" Newton, 100x, fst 6m9
A difficult Holmberg galaxy, could be found only with exact finder chart. Difficult to hold with averted vision. A mild 3:2 NW-SE elongation can be observed. The galaxy is otherwise completely structure-less and not concentrated. 12' SE of NGC 4532.
My observation
18" f/4.5 Obsession, Texas Hill Country, 2015-03-23
Holmberg VII is probably the third faintest of the 9. However, it was much easier than the (blue POSS II) DSS image made one believe. It was easy to galaxy-hop from M 49 to Holmberg VII. There is a bright star and nice edge on galaxy NGC 4532 near the galaxy. The galaxy was sensed even without knowing the exact position once I brought it into the field. It appeared quite big in a 10mm Delos (206x). It was pretty big and very low surface brightness. Still, much easier than some of the Palomar globulars.
Attachment 1807
Holmberg VIII
Uwe's observation (translated)
16" Newton, 129x, fst 6m9
An easy Holmberg. At 129x, seen with direct vision as a 1.5' round brightening. No concentration towards the center. Edges diffuse outwards. Possible companion of the Seyfert galaxy NGC 5033, being only 23' S away.
My observation
18" f/4.5 Obsession, Texas Hill Country, 2015-03-23
Holmberg VIII was much more easier than Holmberg VII. Just moved south of NGC 5033 and as the telescope moved, a faint patch was seen. Held steadily thereafter. Exact position confirmed against DSS images. Irregular shape sensed. Asymmetric shape vaguely sensed multiple times at 14mm Pentax (~146x)/ 10mm Delos (~206x).
(Caricature of the asymmetric shape referred to is below)
Attachment 1808
Holmberg IX
Uwe's observations (translated)
16" Newton, 180x, fst 6m+
Found without knowing the exact position by searching the arms of M 81. Sits in a faint trapezium and slightly E-W elongated. Can be held with indirect vision.
16" Newton, 225x, fst 6m7
Indeed very difficult with a 16", but unambiguously visible. 2:3 elongation, structure-less.
24" Newton, 192x, fst 6m7
With 24", can be easily seen and held with averted vision with intermediate exit pupil. 2:3 SE-NW elongated. Sits in a faint trapezium of 14mag stars. Also in the field of view is the eastern spiral arm of M 81, which lies only 6' west.
27" Newton, 172x, fst 6m5+
Continuously held with averted vision, nearly conspiscuous. Without any structure.
My observations
(Negative observation with 18" f/4.5 at Texas Star Party 2012; probably because of lack of experience, lack of tracking, poor quality eyepieces, and lack of knowhow on how to collimate correctly)
Observation with Josh Wright's (skyraider) 25" Obsession at Texas Star Party 2012:
We could hold it for less than 50% of the time with averted vision. I had the best observation at 380x. No regular boundary was visible. Brightness was held at 3 different locations at different instants, possibly indicating the extent of the object. Could hold the entire blob only occasionally.
Observation with my 18" f/4.5 at Texas Star Party 2015:
Very faint, but definitely observable. Of 20mm Pentax, 14mm Pentax, 10mm Delos (~205x), 16mm Ortho (~128x), the ortho delivered the best performance on this. 10mm Delos view was second best.
The patch was sensed a bit more away from M81 than suggested by the POSSII blue plate, i.e. a difference between 7:30 and 8 o' clock orientations from the star near it. The galaxy was easier to see than the fainter two stars in the triangle that flanks it.
My sincere thanks to Uwe Glahn for the motivation to try Holmberg IX with an 18", Josh Wright for letting me observe through his 25", Dr. Wolfgang Steinicke and Richard Jakiel for their wonderful book which suggested this observing program.
Clear Skies
Regards
Akarsh
