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Thread: Object of the Week, February 9, 2014 – “Auner 1” - the cluster and the ghost

  1. #1
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    Object of the Week, February 9, 2014 – “Auner 1” - the cluster and the ghost

    Auner 1 (C 0702-196)

    Canis Major
    RA: 07 04 16
    DEC: -19 45 00

    Type: OC (2 II m)
    Distance: 29000Lj
    Size: 2,5’

    With the beginning of the Palomar Observatory Sky Survey (POSS) in the early 50’s the number of cataloged objects rises tremendously. The plate center with a size of 5,4°x5,4° was of very high quality with only a few plate faults like dust particles or defects on the film emulsion. The only big problem were reflections within the Schmidt optics which produces more or less “ghosts”, especially at a location symmetrically opposite the plate center from a bright star. Behind these bright ghosts all objects were superimposed and no new discoveries were able to find. And this is the story behind the cluster Auner 1. The troublemaker is called “Sirius” which is only 5,5° NW.

    1980 Austrian astronomers around Auner searches more exactly especially in and around these ghosts and found a new cluster on the old POSS1-E plate. The confirmation gave the brand new ESO-B plate which was taken in La Silla. This plate shows no ghost at this position, because for the new plates the telescope was orientated differently.

    Carraro et al classify Auner 1 as an old cluster of 3,25 Gyr. They associate Auner 1 to a very old star population which stand in a line of sight to the more distant population of the “Norma-Cygnus Spiral Arm”.

    For all observers who thought open clusters were boring and too easy for bigger aperture are warned. Even in bigger telescopes a resolution of individual stars are difficult. The brightest stars are around 16mag, most of the cluster members are in the 17mag-19mag range. I know about a successful observation with 8” but even in a 16” telescope the cluster remains difficult to observe. But…

    …"GIVE IT A GO AND LET US KNOW"

    GOOD LUCK AND GREAT VIEWING!

    15'x15' RGB with R=POSS1-E; G,B=POSS1-O
    Abb1.jpg

    15'x15' RGB with R=SERC-J; G,B=AAO SES
    Abb2.jpg
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

  2. #2
    Member Steve Gottlieb's Avatar
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    Excellent choice for OOTW!

    When I first heard of this object and saw the title of the discovery paper was "A ghost image of Sirius as a hiding place for a new star cluster", I assumed this cluster was really close to Sirius. So, I was surprised to find it was quite a distance away (5.5°). Nevertheless, as Uwe stated, this is a pretty tough object!

    This observation was made under somewhat compromised conditions in my 24" (a bonfire was going on up the hill from where I was observing -- Marko, you know what I'm talking about!)

    Auner 1 was just visible at 175x as a small unresolved glow, ~25" diameter. Roughly 1' N is mag 9 PPM 713456, which detracts from viewing, and just to the south is a small group of mag 11.5-13.5 stars. The "glow" of Auner 1 is sandwiched between these stars and the 9th magnitude star. I certainly would never have noticed this glow without knowing it's exact location and even then it was fairly tough, although there appeared to be a few resolved stars around the edges.
    Steve
    24" f/3.7 Starstructure
    18" f/4.3 Starmaster
    Adventures in Deep Space
    Contributing Editor, Sky & Tel

  3. #3
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    Thanks for the input Steve. You confirm it perfectly with 24" that this OC is no easy guy.

    I forgot to write about my own observations:
    4": even under early perfect conditions, nothing is visible with the small aperture
    16": very good transparency, Auner 1 only around 15° over the southern mountains, visible as a very faint glow S of a 9mag star, difficult to hold with averted vision, triangle appearance, southern edge very faint star chain

    Take care when using Guide 8! The star map shows the OC 8' E of the real position, better using a DSS print for searching the OC
    Clear Skies, uwe
    http://www.deepsky-visuell.de
    Germany

    27" f/4,2

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