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

Thanks Mike. Me too! I have about another 14 to post in the main Berkeley thread at some point. I have about 40 to go but they're mainly in summer constellations (lots in Cygnus) so I will probably take a Berkeley break until then. Yes, I would like to compose a document at some point for these objects. In fact, I've already made such a thing for the GAIA visualisations of these clusters, which have helped enormously in identifying their locations in the first place.What I'd like to do is correct some of the cluster coordinates as quite a few appear to be wrong (by several arc minutes in some cases). I wish I had more time... Martin

Lying way out in the opposite direction to the centre of our galaxy lies the faint open cluster Berkeley 29, believed to be the most distant cluster known (so far!) with a 2018 distance estimate of around 19k parsec (about 63000 light years), based on high-quality GAIA DR2 data [1]. Be 29 can be found in Gemini not too far from Alhena and a degree or so to the S of NGC 2304. The age is a matter of some debate. The estimate I've added to the inverted plot below of just over a billion years comes from the Dias open cluster catalogue, but other estimates [2] place it in the range 3-4 billion years old (a little younger than Messier 67). These images were collected last night prior to moon-rise with Be 29 at a healthy 51 degrees above the horizon. The colour image is 4 x 15s in each of RGB combined with 11 x 15s of L live at the scope in LAB. N is up in this image. No calibration was performed (except hot pixel removal). Ref [2] gives magnitudes (typically 14.5-19.0) and colour indices for some of the cluster members but there appear to be much fainter stars in the background. There are fainter stars I'm not capturing here in this relatively short exposure. This panel compares my shot (left) with the DSS image (centre) and a visualisation from the GAIA DR2 in which I'm plotting down to Gmag 21. Martin [1] http://simbad.u-strasbg.fr/simbad/sim-ref?bibcode=2018A%26A...618A..93C [2] https://www.aanda.org/articles/aa/pdf/2005/03/aa1049.pdf

I don't know the answer but this recent book might be of some help https://www.cambridge.org/es/academic/subjects/physics/computational-science-and-modelling/finding-our-place-solar-system-scientific-story-copernican-revolution Martin

HI Alexandros Although neither of my suggestions is solely about star lore (and I'm interested to see what books others suggest), each of these books does cover the topic. Garfinkle's book is worth having as one of the best star-hopping books out there. Each chapter covers several constellations and starts with some information about mythology (Chinese, Greek, Persian, Roman, etc), and describes how some of the stars in that constellation got their names, etc. Here's a page at random so you get the idea: The Kanas book inevitably covers sky lore, with sections on China, Mesopotamia, Egypt, India and of course classical Greece. Again, its a case of star lore being interwoven with the main text. Here's a page from near the Intro: I read somewhere that Craig Crossen is writing such a book but I've not seen it appear yet. cheers Martin

Thanks Howie. Fortunately, the adding of coords etc is all automatic (if the object is in the database). Martin

Thanks Mike, Michael & Rob. For me the almost the best bit is checking out to see what I can find about these clusters afterwards (even if it turns out their existence is questionable!). Here are 10 more, including Berkeley 64 which some sources regard as non-existent but for which there is a candidate close by, as marked.

That's essentially what I do, actually. I take a set of random points in the image (500), remove the top and bottom 20% percentiles, then do the linear fit. Super-fast and works pretty well most of the time. (29ms or so for Lodestar 580x760 on MAcBook Air c 2015). Example of before/after for a single 15s sub: Another more typical case

On this occasion no calibration was applied (just hot pixel removal). I normally do darks at least (but that part has not yet been re-implemented since I added colour) and will do flats when that aspect is implemented for individual filters. Re flat/QE differences, bear in mind that these views are effectively zoomed in views using a tiny sensor (it's a guide cam after all) so some of the visible artefacts are no doubt due to interpolation, and there is only 1 minute max of each of R G B in all of these shots so plenty of colour noise there too. Also, there is automatic gradient removal being applied which is based on a planar 2D fit -- pretty rough but works well much of the time (but can struggle in strong moonlight). But this is EEVA not AP so nobody minds 😉. The Lodestar is a CCD rather than a CMOS sensor. Martin

In spite of a 97% illuminated moon which gave the sky a milky washed out look and killed off all but the brightest stars visually, I continued looking at faint open clusters in Cassiopeia. Although gradients were sometimes a struggle to suppress, it never ceases to amaze me how much is visible using EEVA techniques under such conditions (and indeed how much colour can be extracted). Here are a few captures live at the scope. N is up, all were composed of 15s L, R, G, B subs, live-combined in LAB colour. NGC 436. This is apparently a young cluster similar in age to Alpha Persei, full of blueish stars, and very different from the other clusters I observed. Berkeley 64. I'm not sure of the current status of this cluster as it is not mentioned in a recent (2018) GAIA-based survey of likely clusters , so it might be a chance grouping. Earlier data give an age of 1 billion years and a distance of 12-13000 light years. There is in fact little to see at the listed coordinates, but I can see a potential cluster nearby, and centred in my image. (The listed position is well to the right of centre, near the red star). There is still quite a lot of work to be done finding correct coordinates for some of these less-visited clusters. Having plotted all the GAIA data for the Berkeleys, it seems that 10-20% are not in the catalogued position! Berkeley 2. This one seems more definite with 93 members (as of the 2018 study), a distance of 22000 light years and an age of around 800 million years. When this was building up on the screen the most notable features were the 2 arcs of stars rather like the Antennae galaxy tails, merging at the orange star in the centre of the cluster (the bright foreground stars are not part of the cluster). The most enjoyable sight for me was Berkeley 8, both for the cluster itself and the field of foreground stars is is embedded in. Some of those foreground stars form a beautiful curve and display a remarkable range of colours which inspired me to look up their types. Unfortunately, very little data appears to be available on a cursory search. Having observed 37 Berkeley clusters in the last week, I'm beginning to notice some common visual elements (although they are probably ilusory!). Many of them possess arcs of faint stars. For Berkeley 8, these arcs emanate from the centre like the legs of a malnourished starfish (although I count 6 of them). Berkeley 8 is a very old cluster, estimated to be 3.2 billion years old, rich in members (252), but relatively close (for a Berkeley) at around 11,600 light years. cheers Martin

That's a good one too. And I note they've used a synthetic English voice this time! Martin

Nice work. I checked on Simbad and the Gaia G mags are 13.5 and 13.6, so good guess! 'Saturn' itself has Gmag 10.5. Tonight is predicted to be clear and in spite of the moon I'll see if I observe some of the remaining Bs in CAS... Martin

It might have been mentioned before on SGL but I just came across this rather mind-expanding video showing a visualisation of where we, and our neighbours, fit into the overall universal scheme of things. I've often wondered where the great walls, voids, attractors fit and this really helps to understand their size and location. http://irfu.cea.fr/cosmography Here's the abstract of the accompanying paper: "The large scale structure of the universe is a complex web of clusters, filaments, and voids. Its properties are informed by galaxy redshift surveys and measurements of peculiar velocities. Wiener Filter reconstructions recover three-dimensional velocity and total density fields. The richness of the elements of our neighborhood are revealed with sophisticated visualization tools. A key component of this paper is an accompanying movie. The ability to translate and zoom helps the viewer fol- low structures in three dimensions and grasp the relationships between features on different scales while retaining a sense of orientation. The ability to dissolve between scenes provides a technique for comparing different information, for example, the observed distribution of galaxies, smoothed repre- sentations of the distribution accounting for selection effects, observed peculiar velocities, smoothed and modeled representations of those velocities, and inferred underlying density fields. The agreement between the large scale structure seen in redshift surveys and that inferred from reconstructions based on the radial peculiar velocities of galaxies strongly supports the standard model of cosmology where structure forms from gravitational instabilities and galaxies form at the bottom of potential wells." Martin

Six more from last night under an 85% illuminated moon, 2 in Lacerta, 4 in Cepheus. Be 93 likely non-existent (according to 2018 data), and certainly looks to be absent!

Hi Mike Thanks for that ID. It was too much to hope for a physical grouping. I think the same goes for V674 Cep (I couldn't spot it in the WDS list). Martin

With the moon up and about I continued to focus on open clusters and managed to observe a further 6 Berkeley clusters (2 in Lacerta and 4 in Cepheus) this evening until my mount battery gave up for the night. One of these clusters in particular I found fascinating for reasons other than the cluster itself. This is Berkeley 95 in Cepheus. For once, the 3' cluster is easily spotted and quite well resolved in the middle of the shot with what seems to be a characteristic signature (no doubt illusory) of some Berkeleys, namely a pair of near-circular arcs of stars --a good-looking cluster as these faint ones go. However, the attention is drawn to the bright red star above the cluster. This is the mag 8.65 red supergiant variable V674 Cep, type M3Iab, with a colour index of 3.88 (GAIA blue-red index is even higher, at 4.5). Its mag 14.2 yellow 'companion' (I'm not sure if it is a real companion) is just about visible peeping out at around 11 o'clock. This must be amongst the brightest/reddest stars visible and I wonder how it would appear in binoculars or a small scope. But what I really like about this field is the 'false saturn' that is evident at 8 o'clock. This triplet is aligned in such a way that the two fainter 'wings' are just offset to give the tilted Saturn-like impression. I see a lot of star fields doing EEVA and this is the first time I've come across a jewel like this. Again, something to look out for in a medium-sized scope perhaps? cheers Martin

At the risk of the title of this thread not quite representing its contents (these are no longer in MON), I've decided to post some additional Berkeleys here rather than generate a new thread for each session. These are all in the Cepheus/Cassiopeia region from 2 nights ago. Forecast is good for tonight too so I may continue on this quest in spite of the bright moon. Each plot shows the most recent data I could find on age/distance/number of members. I'm querying age data on some of them as it seems very much at odds with the others, but it might be correct. As you can see, the majority of these would be quite hard to spot! I'm very much relying on the GAIA data to help here. The Berkeleys are rather faint Martin

Thanks Mike. I agree, it is always good to see some details of the objects themselves (as opposed to the kit used to observe them). Before you turn the dob on to the Berkeleys, it is worth checking out the latest information on cluster parameters and existence in this Vizier table: https://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/A%2BA/618/A93 based on a 2018 article. There are 88 Berkeleys listed which I think suggests the rest were regarded as non-detected (and possibly not real?). Amongst those not listed that I show above is Berkeley 26, and looking at my inverted figure it is easy to see that this might not be more than a chance grouping. The table also gives updated membership numbers and distance estimates which I think can be considered as better estimates than the figures I quote on the plots. Generally, N is quite a bit higher. Martin

Another clear Monday night (why can't it be clear at the weekend?!) was too good an opportunity to continue my observation of Berkeley open clusters, this time in the Cassiopeia region. I may post some of the dozen I observed later, although frankly, like many Berkeleys, in some cases it was pretty hard to spot anything exciting, especially with a bright moon around. As in the last session I compensated for the faint Berkeleys by starting and ending with 3 more in-your-face (NGC) open clusters, which I'm posting here. The other reason for the post is to sing the praises of the latest GAIA data release (DR2) for the excellent magnitude reach and colour data it contains. For each of the 3 NGC clusters I'm showing GAIA data for comparison purposes. These reach down to magnitude 21 and are all 40' wide fields. The shots all use StarlightLive as a capture engine (including control of the electronic filterwheel), and Jocular for everything else. They were all 15s subs in L, R, G, B, live combined in LAB with adjustment of color stretch and saturation only (plus the usual L controls). No darks nor other calibration was done as I'm using an experimental version of the software and that aspect is currently not yet integrated. All shots have N at top to make comparison with the GAIA data easier. Usual kit: 8" f/4 Quattro Newt, Lodestar X2 mono camera, alt-az mounted using AzEQ6 mount. First up is NGC 559. According to https://academic.oup.com/mnras/article/437/1/804/2907736, "NGC 559 is a moderately populated and heavily reddened intermediate-age open cluster, classified as type I2m by Trumpler (1930) and II2m by Ruprecht (1966). It is located in the direction of the second Galactic quadrant in the vicinity of the Perseus and Local arms ... " My shot shows many red stars, possibly a little more saturated than the GAIA data (which could perhaps usually have its saturation increased). The aforementioned article identified the 22 most likely cluster members, and it is notable that all of them have B-V colour indices in the range 0.63-1.73, suggesting orange-red colours. Next, something quite different. NGC 743 is a sparse but fairly bright cluster of blue-white stars, with a formation that looks to me like a flock of migrating birds, or maybe a curved letter tau. I found very little information online about this cluster, although it is mentioned here https://iopscience.iop.org/article/10.3847/1538-3881/aaa45b which suggests a much large diameter -- 1 degree -- than my data. This means it is possible the cluster extends outside the zone shown in the GAIA plot also. Finally, here is NGC 609. This is for me the best-looking of the three, with two squashed circlets (a pair of ear-rings, maybe?) containing nearly all reddish stars. The only paper I can find dealing explicitly with this cluster dates back to 1971. http://articles.adsabs.harvard.edu/pdf/1971AJ.....76..467L argues that it is similar to M11. Things have moved on since that time: it is interesting that it is described as "a conglomeration of very faint stars; a few of the brightest, of about mag 14, are discernable in a diffuse gray patch". As in NGC 559 the colour indices in this paper are at the redder end, with values up to 2.35. Most of those with index > 2 are very close to mag 15. The GAIA data go much deeper. For a better comparison I produced an inverted grayscale image which I think indicates captures down to around mag 19 or so but no deeper. My stars are rather eggy (it was rather gusty) so most likely any further depth was limited by smearing the fainter captures into the background. (the odd appearance on my GAIA plot comes from processing artefacts when saving as .png, I suspect, resulting from the way I have mapped size/colour at the very faint end of the magnitude range -- this mapping is still a work in progress). Thanks for looking Martin

Nebulosity also supports manual stacking by selecting the same 2 stars per sub. Martin

Very interesting thread! To follow on from Vlaivs earlier comment about colour temperature, I've been recently looking at the colour data in GAIA data release 2 in order to compare against some of my images, and coincidentally downloaded data in the M36 region yesterday. Here's a plot with colour indices mapped to temperature and then to RGB values (using this technique: https://stackoverflow.com/a/45497817). I've enlarged the stars a little so the colours show up better. The image needs to be rotated 90 degree clockwise to line up with Alacant's image. This is down to GAIA mag 17 although the data is available down to around mag 21-22 (but the colour data is not reliable I believe past mag 19). Martin

The GAIA data release also contains parallax data to allow an estimation of distance and hence cluster membership. This is a histogram of distance data in the region of NGC 2301 from which it is clear that the cluster is somewhere around 3000 light years distant (the pre-GAIA distance was given as 2838, which looks about right). Also, by subtracting the general background distribution of stellar distance on which the peak is superimposed, one can estimate the number of likely members, which I'd say is roughly 350 from eyeballing the plot. This is similar to the 355 in the pre-GAIA database. Similar things can be done with proper motions. There's some interesting work to be done with the GAIA data. Only a few weeks ago a new stellar cluster was discovered by a more sophisticated form of analysis, looking for very blue stars at a similar distance: https://www.cosmos.esa.int/web/gaia/iow_20200109 cheers Martin

I've been looking at the GAIA second data release which has extensive colour data (https://www.cosmos.esa.int/web/gaia/iow_20180316). I downloaded stellar data in the region of NGC 2301 and created this plot with a little python. I'm using a colour index based on the difference between the B filter and the G filter, then some code from here https://stackoverflow.com/questions/21977786/star-b-v-color-index-to-apparent-rgb-color#22630970 that converts to temperature and thence to RGB values. I'm plotting all stars down to GAIA G-magnitude 18, which is about as deep as my image (possibly the image is a little deeper). If I get time I'd love to create similar figures for other open clusters, and go somewhat deeper (to mag 21 say). Compare this to my image below and they are reasonably close.(Note there are a few missing stars in the GAIA data...)

In addition to the Berkeley clusters, I book-ended my recent session with a couple of much brighter open clusters. The first is NGC 2304 in Gemini. I can't find a lot of information about this but came across this image and report by the sadly-missed RickJ from CloudyNights, who says it much better than I can (and has nice round stars compared to my undersampled exemplars) in this link: https://www.cloudynights.com/topic/608639-ngc-2304-another-rarely-imaged-open-cluster/ The cluster has a large number of blue stars of very even magnitudes. [The image was constructed from 4R, 2G and 4B subs and 9Ls added at the end. The only colour controls I use are saturation, colour stretch (power stretch) and fractional colour binning. No histograms. I see some greenish stars in here so still some work to do I think.] The other cluster, NGC 2301, is numerically-close but very different (indeed, in a different constellation). Apparently it is known as the Great Bird Cluster. Turning it upside down it does indeed look like an enormous bird in flight. This contains a range of star colours/types (although it may be that not all are cluster members). I don't have colour data for all of them but Aladin reports a B-V value of 1.2 for the orange star at the centre, while the two orange-red stars at bottom left have values of around 1.6. The very red star to the east of the cluster seems to have a colour index of 2.6 according to GAIA if I'm interpreting the R-P value correctly. The red star just north of the cluster centre has B-V of 1.9, consistent with the image. This cluster contains quite a few variable stars as described in this paper, so could be an interesting object to study on multiple occasions (it is a beautiful cluster so well worth returning to!). There are 11 pulsating variables with various periods, including those short enough to see changes within a session (although with quite small delta magnitudes). Subs were 3R, 4G, 3B, 3L Unfortunately this was at the end of a cold session so I didn't spend as long on it as I should have, but I am enjoying re-loading it into Jocular and re-observing it now! Cheers Martin

Great stuff! SHK 92 is just outside the field of view (closer then SHK 87). Times like this one needs a larger sensor... Martin