EAA Observing Session: 15, February16/02/2025
Astronomy

Session Data

  • Date:  15/02/2025
  • Time:  20:15 – 21:47 UT
  • Seeing: II. Good – Slight
  • Transparency: III. Clear with slight haze
  • Temp: 6 C,
  • Air Pressure: 1014mb
  • Humidity: 90%
  • Dew Point: 4 C
  • Wind Speed: 12mph
  • Average SQM:  magn/arcsec^2

Scope: TMB 80 f/6  Camera: ZWO ASI 183MM. Darks but no Flats

All images are displayed North up and East to the left.

HT37, NGC2175

Located 13.5 degrees North and a little East of Alf Ori in Orion.

At the centre of the Nebula we have the 7.4mag star HD42088. The nebulosity in my image extends out to a radius of about 13 arcmin. My images show this nebula to have patches of dust obscuring the nebulosity , the most prominent of these is a few arcmin to the West of HD42088.

3 arcmin to the East is a bright patch of nebulosity surrounding a couple of stars of differing magnitude. 11 arcmin to the NW is NGC2174. I’m not quite sure why this was regarded a something separate as it doesn’t look as bright as a bright patch 5 arcmins to the East of it.

18 arcmin to the NE is C0607+206, a 6.8mag open cluster containing about 20 stars in the 9.5 to 14.5 mag range and a diameter of 6 arcmins. I have no idea what catalogue C0607+206 comes from, but these numbers are presumably RA and Dec coordinates of a target. If you enter C0607+206 into Simbad, you get a target called Pismis 27 at the 06 10 52.6 +20 37 01 which lands right on top of this small cluster of stars.

Total Integration Time:  495 sec

Collinder 83, NGC2169

Located just over 6 degrees SE of Nu Ori in Orion.

I should have used the larger scope for this target, but I think this view still give a flavour for what is a small compact cluster. While Collinder has linked his entry for CR83 with NGC2169, if you look at his paper he says that the position was taken from the

In the following eight columns the data are given as resulting from a survey of open galactic clusters by
Lundmark, using the Franklin-Adams plates, and by Collinder, using the Franklin-Adams charts. The data
are so arranged that the results of Lundmark are given in the upper lines and the results of Collinder in
the lower lines.

He then gives the size of this cluster at 5×4 arcmins. If you overlay the coordinates for Lund 206 with that of the NGC2169, CR83 is a little smaller and about 2 arcmin to the East of NGC2169.

I guess my point here is that the number of stars within Collinder’s cluster is fewer than that of NGC2169 for the purpose of his catalogue.

Collinder says his star count for this cluster is only 8 stars (Collinder lists Lundmark as counting 20) so we are not looking at those half a dozen brighter stars outside the green circle to the West.

So on this basis, what do see. The brightest star is 4UCAC520-020946 at 8.4mag with the other 9 or so brightest between this and 10.8 mag. I cant say I see an interesting asterism here, but it’s quite pretty and unmistakable as a cluster nonetheless.

Total Integration Time:  240 sec