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Latest Website Update [19 Jan 2015] >> DSO 166 >> Observations of STF 644 >> January Double Star of the Month >> January Picture of the Month - David Davies >> January 2015 Galaxy of the Month

The Deep Sky Observer (DSO) issue 166 is out now.

January 2015 - Galaxy of the Month

NGC 2749 in Cancer

NGC2749 - Image Courtesy the Sloan Sky Survey

This image was provided by the Sloan Sky Survey, and this finder chart should help you locate these galaxies.

The constellation of Cancer is often overlooked except as a stepping stone between the two richer constellations, in terms of deep sky objects, of Gemini and Leo and if it is considered at all it is for the two open clusters M44 and M67.

The constellation does however have its fair smattering of faint galaxies. Indeed there are over 100 galaxies catalogued in the NGC alone and whilst those hidden amongst the stars of M44 have often been mentioned there is a nice group around NGC 2749.

NGC 2749 itself is a 12th magnitude elliptical galaxy (E2) discovered by d’Arrest in 1862 and is perhaps the brightest of the group. NGC 2745 and 2747 were discovered by Marth along with NGC 2751 and 2752. Remember though that Marth was using Lassell’s 40” speculum metal reflector from Malta so these galaxies are going to be a challenge. Oddly the other galaxy in the field NGC 2744 was discovered by William Herschel so how he missed 2749 must be a mystery as it is a brighter galaxy.

The group is listed as number 202 in the WBL catalogue of poor galaxy clusters with a total of 5 galaxies counted as part of the cluster. These are NGC 2745, 2749, 2747, 2751 and 2752. The group would appear to be at about 192 million light years from us. Interestingly 2744 was not counted by WBL to be part of the group despite showing obvious signs of interaction. With the exception of NGC 2749 all the other galaxies in the group appear to be either spirals or lenticular (2745).

Although the WBL catalogue does not include NGC 2744 within the group more recent papers suggest that in fact NGC 2749 and NGC 2744 are an interacting pair. Here NGC 2749 is classified as a low luminosity AGN (LLAGN). Fundamentally this is not that dissimilar to the activity (or lack of it) we see from the centre of our own galaxy.

The faintness of these galaxies suggests that probably a 30cm telescope will be needed to see NGC 2749 and probably 40cm to find the others, although they will require a dark sky. There seem to be few images of this group so they may also make an interesting target for imagers. The classic references such as NSOG and L&S do not make much mention of the galaxies in this area apart from NGC 2479.

Owen Brazell - Galaxy Section Director

January 2015 - Double Star of the Month

STF 644 in Auriga (05 10 18.81 +37 18 06.7) is a pair noted for the contrasting colours of its components. The spectral types of the two stars are respectively B2II and K3 and when W. H. van den Bos observed the pair with the Lick observatory 12-inch refractor in 1962 he noted the colours were white and reddish. E. J. Hartung noticed this colour disparity too - he found orange amd white with 10.5-cm aperture adding if merely elongated the appearance of the ellipse is striking with one end orange and the other white. Sissy Haas on the other hand with 125-mm at x200 found both stars to be yellow-white.

This is a close pair which has remained virtually motionless since it was discovered by F. G .W. Struve. The magnitudes are 7.0 and 6.8 with the orange component being slightly brighter visually. G. van Biesbroeck added a distant mag 10.5, K3 dwarf at 192 degs, 72". To find STF 644 look about 1.5 degree south of mu Aurigae. It is the preceding of two mag 6 stars - the other being the unequal wide pair SEI 105 (6.5, 11, 27 degs, 35"), about 1 degree following.

HJ 3683 (04 40 17.72 -58 56 39.5). Very fine noted John Herschel from South Africa in 1836 when he first laid eyes on this pair of stars and gave them both magnitude 8. The WDS catalogue says they are 7.3 and 7.5 but the main interest lies in the nature of the apparent orbit of this 326 year binary. The high inclination means that motion is restricted to a narrow range of position angles and so mainly manifests itself in separation, whilst the very high eccentricity (0.95) means that the maximum separation is 4".3 whilst the minimum is only 0".03 which, given the Hipparcos parallax of 32.77 mas, indicates that the two stars are only 3.7 AU apart at periastron but 144 AU apart at apastron. When at their nearest separation the position angle changes by 1 degree per day, almost 5 times faster than that managed by the two components of gamma Virginis at periastron.

The pair is currently at 3".7 and so is an easy object for the small telescope. Gould with 175-mm calls both stars yellow and the pair can be found about three degrees south and slightly following alpha Doradus.

Bob Argyle - Double Star Section Director

Object of the Season (Winter 2014/15)

NGC 4449 in Canes Venatici

Irregular galaxy NGC 4449 in Canes Venatici will be announced in DSO 166, and the results will be published in DSO 168.

NGC4449 - Image Courtesy of Hubble Space Telescope (HST) Please click on the image for a high resolution version taken by the Hubble Space Telescope (HST).

Position (2000)
12 28 11.0 +44 05 33 (CVn)
Visual magnitude
9.4 mag
Type
IBm
Size
5.5' x 3.6'
Distance
12.5 Mio. ly
Other Designations
I 213, h 1281, GC 3002, UGC 7592, CGCG 216-5, MCG 7-26-9, PGC 40973

Wolfgang Steinicke - Nebulae and Clusters Section Director

January 2015 - Picture of the Month

Sh2-155 The Cave Nebula in Cepheus

Our images this month are courtesy of David Davies from Cambridge in the UK. They provide an interesting comparison of the difference aperture can make when imaging nebulae. Please click on either image for the high resolution version. For more images from David please visit his Flickr Photostream.

I've been collecting data for an image of the Cave Nebula over four nights during December (5, 7, 13 15) and it has been a chapter of carelessness and frustration. I ended up binning hours of data after discovering it was slightly out of focus or was captured with the wrong filters. In the end I did some work on what I could rescue and the attached image is the result.

I set off trying to image the Cave in narrow-band but soon discovered that although the main cup-shaped nebula is rated as reasonably bright (integrated magnitude 7) it covers around 15 arc minutes of sky and is quite faint. The surrounding nebulosity comprising emission, reflection and dark nebulae is much fainter. Hydrogen-alpha emission can be acquired fairly readily but oxygen III and sulphur II emissions are very faint indeed. I decided to cut my losses and abandoned my acquisition of oxygen and sulphur, changed the filter wheel to RGB and acquired around an hour of each.

I was interested to see the Cave in its context and chose to image it with my ED120 refractor plus a reducer/flattener to give a field of view of 81 x 61 arc minutes. The attached image is a crop to approximately 60 x 60 arc minutes.

The Cave Nebula (Sh2-155) with an Equinox ED120 - Image Courtesy of David Davies

The image is Hydrogen-alpha, RGB; four hours of hydrogen-alpha in 20 minute subs; 132 minutes of RGB in 8-minute subs; all binned 1 x 1. Processing was in Pixinsight with a final touch-up in Photoshop.

  • Telescope is Skywatcher Equinox ED120 with a Skywatcher X0.85 reducer/flattener.
  • Camera is a QSI 583 wsg with Astrodon LRGB and 3 nm narrow band filters and Lodestar guide camera.
  • Mount is a Skywatcher NEQ6 controlled via EQMOD.
  • Image capture was with Nebulosity and Scopefocus for automatic focusing.

I was curious to see what my 10-inch Newtonian would make of it so here is the Cave again but this time captured with a 10-inch Newtonian. The faster optics and longer exposures have yielded a deeper image.

The Cave Nebula (Sh2-155) with a 10 inch newtonian - Image Courtesy of David Davies

A hydrogen-alpha RGB image captured on the nights of 19 and 24 December 2014 from Cambridge, UK. Two hours each of RGB in 10-minute subs plus one hour of hydrogen-alpha in 20-minute subs.

  • Telescope is a 10-inch Newtonian plus Televue Paracorr at F/4.5.
  • Camera is a QSI 583 wsg with a Lodestar camera as off-axis guider.
  • Mount is a Skywatcher NEQ6.
  • Image processing with PixInsight and Photoshop.

Deep-Sky Observer (DSO) No 153 - Free Sample

DSO153 Cover

This free journal is DSO 153 from 2010. You can download it as a PDF file onto your computer by right clicking the link below and choosing either 'Save Target As' or 'Save Link As'...

Download DSO 153 (2MB PDF file)

The Brightest Planetary Nebulae Observing Atlas - 2nd Edition

Massimo Zecchin has just completed the 2nd Edition of an atlas of planetary nebulae observed with small apertures and from suburban locations, entitled: "The Brightest Planetary Nebulae Observing Atlas".

Massimo has kindly made the atlas is freely available in two versions, Black (for display) and White (printer friendly with the images in negative).

The Brightest Planetary Nebulae Observing Atlas (2nd Ed) Black - Courtesy of Massimo Zecchin The Brightest Planetary Nebulae Observing Atlas (2nd Ed) White - Courtesy of Massimo Zecchin

The 2nd Edition contains:

  • Six additional objects.
  • Data of visual magnitude, central star magnitude and object size from the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (SEC catalogue) and in a few cases from the Saguaro Astronomy Club database (SAC catalogue).
  • Calculated surficial brightness for any object (in magnitude per square arcsec).
  • Six additionaltables showing the objects sorted by magnitude, surficial brightness, size, central star mag, constellation and declination.
  • A general position map.

Either version of the atlas can be downloaded as a PDF file onto your computer by right clicking the respective image above and choosing either Save Target As or Save Link As...

Please note that the Black version is 14MB and the White version 10MB