In Lepus

[Martin Meredith]

Last night was wonderfully clear with no moon and no wind, and ridiculously warm for February (still no darks employed though!). I gave the Berkeleys a break and took advantage of my relatively southern latitude to view a diverse range of objects in constellations I rarely visit: Lepus, Caelum, Columba, Fornax and Eridanus, timing things to catch them while transiting (many are sub-20 degrees above the horizon here). In this thread I'll post some observations in Lepus (which for me was the highlight of the night), starting with the easy to remember NGC 2017.

Immediately south of M42, this is a real jewel of an open cluster that for some reason appears to be barely observed or imaged (I couldn't find any images here). Yes, it is low from many N European latitudes, but here at 43 degrees N it culminates at around 29 degrees above the horizon, so I think ought to be well within reach of UK scopes (just under 19 degrees in my old haunting grounds of Sheffield, for instance). Maybe the glories of Orion draw the eye and mind away from this area. In fact, I only found 6 references to this cluster on SIMBAD. It isn't mentioned in Deep Sky Wonders, and merits a somewhat bland description in the Night Sky Observers' Guide (NSOG) although it rates 4 stars. I can't find it in any of the O'Meara guides either, nor in the Herschel 400 list (presumably because it wasn't discovered by Herschel? Maybe by Dunlop?). It does make it into Burnham's Celestial Handbook (p1100) where it is noted as the multiple star system h3780. In the Webb Society DSO Handbook (vol 7 'Southern Skies') it is listed as an open cluster.

Its cluster status -- as far as I can tell -- remains something of a mystery. NGC 2017 is still listed as an open cluster in the main OC catalogue of Dias et al [1] and is not on their list of 'removed clusters'. Their database lists 56 members and a Trumpler type of 2-1-p-* ('detached with little central concentration; small range in brightness; poor, < 50 stars'). A 2017 paper [2] based on UCAC4 data reports three methods for estimating cluster membership for 1876 clusters, including this one. For NGC 2017 the methods report 30, 19 and 3 members -- quite a discrepancy. It seems likely that the methods don't work so well for sparse clusters. The latest GAIA data appears to suggest that NGC 2017 is not an open cluster [3]. As in Burnhams, the description in NSOG suggests that it may be a multiple star system rather than a true open cluster. In Archinal and Hynes book Star Clusters it is regarded as a possible asterism containing a multiple star system. The WDS catalog lists it as the 10-component multiple star system Burnham 321. Luginbuhl & Skiff's Observing Handbook and Catalog of DSOs also has it an OC and notes that two of the stars are themselves very close doubles (separations 1.5 and 0.6").

Whatever it is, I can only concur with Magda Streicher, who, observing visually with a 12" Schmidt-Cassegrain describes it as "one of the most beautiful stellar groupings I have ever seen" [4]. 

This is one of those objects that certainly comes into its own in EEVA, where colours are readily-apparent. If I ever get round to writing an 'Interesting objects for EEVA-observing' handbook, this will definitely be included! 

This is live-combined LRGB (4 x 15s subs in each of RGB, the rest L) as viewed at the scope. 

More Lepus delights later!

Thanks for looking

Martin

 

[1] https://arxiv.org/pdf/astro-ph/0203351.pdf

[2] https://arxiv.org/abs/1706.05581

[3] https://www.aanda.org/articles/aa/abs/2018/10/aa33476-18/aa33476-18.html

[4] http://articles.adsabs.harvard.edu/pdf/2003MNSSA..62..140S
 

Edited February 15, 2020 by Martin Meredith

[Bill S]

Martin

That's strikingly beautiful. Very well described by Magda Streicher in the article that is your reference [4]. Not impossible for me so perhaps one night.

 

[Mike JW]

Hi Martin,

NGC 2017 is a favourite of mine and an observing mate despite it being so low for us GB.  Just love the group through a big Dob. As 3 of the obvious components are in the WDS  catalogue I have also pointed smaller scopes at the group in my quest for doubles.  Great to see it again. Mike

[Martin Meredith]

Thanks Bill and Mike. Glad to hear it is observable (and being observed) from the UK!

In the northern reaches of Lepus, not far from Orion, is the constellation's only Arp entry. The description is "Elliptical close to and perturbing spiral". In this case, the type SBc spiral (NGC 1888) has a clear tilt at the lower end, and appears to be almost in contact with the type S0 elliptical NGC 1889. They are listed at around 110 M Lyrs with mags 12.8 and 14.1 respectively. The challenge is to spot the 'faint parallel feature on the opposite side from the elliptical", which can be made out in the image as a very narrow hair-like structure. NGC 1888 was 'recently' host to supernova SN2018yu.

The other bright galaxy to the upper-left of Arp 123 is entry 534 from the Flat Galaxy Catalog, a mag 15 S0-a type which, intriguingly, is at a similar distance to the Arp pair. 

At the top left is another edge-on, a mag 16.4 galaxy PGC 147414.

 

Martin

 

Edited February 16, 2020 by Martin Meredith

[Martin Meredith]

Of course, the best-known object in Lepus is the constellation's only Messier object, M79. This globular cluster was long the subject of age estimates that put it beyond the accepted age of our galaxy, but the estimate seems to have stabilised recently at around 12 billion years.

I was observing this for quite a while -- such a long exposure is not really required, as there is only 1 minute in each of RGB (4 x 15s subs each). As you can see, there is a lot of information in a single 15s luminosity capture even at just above 20 degrees above the horizon:

but the colour version really brings out the contrast between the blue-white nucleus and the band of yellow-orange stars that appear to encircle the cluster like a scarf.

 

I find log stretch works really well with globulars for some reason (I normally use arcsinh except for inverted displays where I use  x/(x+c) stretch). There are a few galaxies in this image too, the brightest being around mag 16.

Martin

 

[Mike JW]

Hi Martin,

You did well to get the thin line for Arp 123. I wish I had your knowledge to do the colour thing - a whole new dimension. I cannot compare to mine because I have had a computer disaster - all 330 of my Arp images on the laptop and the two back up copies held elsewhere  have all been corrupted and lost!!!!!!!!!!! Gutted to say the least.

What is a log stretch? and x/(x+c) stretch.

Mike

[Martin Meredith]

Hi Mike

Noooooooo! On the plus side, it gives you the perfect excuse to start again.

The log stretch is compressing the original intensity values in the image by taking their log, so faint areas are boosted relative to bright areas. The x / (x+c) stretch is something I came up with that does an even more extreme compression (I use it habitually when I invert the image, for instance). Here, x is the intensity of each pixel, and c is a constant value, which can be chosen to vary the degree of compression. I call it 'hyper' stretch on the Jocular interface because I haven't yet found the correct name for what is a very simple function to map the image brightness.

I hope you manage to somehow recover your drives but I imagine you've tried all the usual approaches. In my only experience of a computer failure I was still able to extract the hard drive and recover stuff.

Martin 

 

[Mike JW]

Hi Martin,

Arp images well and truly lost. A long story and yes they may well lurk somewhere but way out of my knowledge to see if they still exist. However as you say a great excuse to do it all over again, this time with much more camera experience. I shall of course pick them up again as I peruse the VV galaxies.

Mike

[Mike JW]

Hi Martin,

I have just managed to grab an hour before cloud arrived, so I pointed the C11 at NGC  2017. A lovely sight. It has been awhile since I looked at it visually. Hint of colour seen.

I then put the camera in and took a shot of NGC 2017 - not posting it - it lacks the sparkle your image does.

Next I took a look at Arp 123. I had to use 3 sec subs because of the wind. Also looking through thin cloud at times. No sign of the thin line.

Mike

 

[RobertI]

Nice work Martin, I love your capture of NGC2017, worthy of the imaging forum! An interesting looking cluster, I'll try and track this down. I'm mostly doing visual at the moment with a newly acquired 150PL which is fun, especially on doubles. But I shall return to EAA soon, probably when the council fixes the nearby streelight and my garden is illuminated once more - thank heavens for EAA!

On 17/02/2020 at 14:21, Mike JW said:

all 330 of my Arp images on the laptop and the two back up copies held elsewhere  have all been corrupted and lost!!!!!!!!!!!

That's really gutting Mike, so sorry to hear that. Could you recover some images from your posts on SGL?

[Mike JW]

Hi Rob,

Good idea to recover the images from SGL.

I enjoy doubles and will sometimes do doubles at the start of a session then switch to  EAA and then finish on doubles/clusters.

I can supply lists of Cambridge 2nd Edition Doubles for all the northern constellations. These are true doubles/multiples. In excel spreadsheet form. Just ask if you would like some or all of the lists. Anyone reading this - just ask - happy to share.

Mike