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Classic Messier

beginner classic dso observing report observing refractor
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#176 AllanDystrup

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Posted 04 June 2018 - 02:03 AM

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Continued:

M21 Open Cluster  &  M 20  Trifid Nebula

 

    

     For yet more magnification, I now switch to a close up view of the objects using my R2 CCTV for live video (136x @ 0.9° FOV);  The stars in M21 immediately resolves to ~15 brighter members (9-10m), all being hot massive early type-B stars, with an undergrowth of ~50 stars of ~11m and fainter. Just N of the 7.2m center star is a fine ring of faint stars, which makes the cluster look somewhat like a baby octopus in my eyes… A HR-diagram shows the age spread well, with the hot massive stars already evolving off the main sequence, while the cooler medium-size stars are right on the main seq. The cluster also contains a large population of low mass He3->He4 burning pre main seq. stars in the process of settling down on the main sequence, but these are too cool/faint to show up in my telescope. M21 is a relatively close by (4.2 Kly) and young (8 Myr) open cluster, still obscured somewhat by the gas and dust, from which it was created.

    

     I now switch my attention from M21 to M20, the nebulous star below the southern point of the figure “W”. The bright 7.2m star in the center of M20 is actually a multiple star system with six components (HN40/ADS10991). I can detect the tight pair of hot stars: the type O7V HD164492 plus the type B6V HIP88330 (HN40 A-C: 7.5/8.7 Sep 11’ PA 212°). The O-star is the main source of strong UV-radiation that is ionizing the surrounding round cloud of hot H-II hydrogen gas. The ionized nebula is overlaid by three dark lanes of dust (B85), which seem to carve up the H-II cloud into 3 partitions/lobes (thus the name “Trifid” Nebula).

     

    There’s a bright 7.4m star HD164514 north of the ionized part of the Trifid nebula. This is a large star, a type A7I moderately luminous supergiant, but it is not hot enough to ionize the H-II cloud; instead its strong blue light is scattered in the dust component of the outer cocoon, forming a large reflection nebula that entirely surrounds the central ionized H-II cloud.

    

     In the live video at 136x, M20/The Trifid is not stunning at all, but I ascribe this partly to the mediocre observing conditions tonight. By close inspection I am however capable of discerning the three dark lanes of dust and thus the three lobes of the ionized H-II cloud. I can (I think) also *just* glimpse a very faint nebulosity around HD164514, -- a trace of the reflection nebula surrounding the central cloud. M20 is found roughly at the same distance (4 Kly) as M21, but it is much younger, only around 400 thousand years. I’m speculating that in 5 Myr from now, this splendid pair of Messier objects may show up as another “Double Cluster” like h and χ Persei... A little long to wait though, so I decide to call it a night and hit the bunk.

    

R2 M21-M22 BLACK-S.jpg
*click*

 

Allan
 

    
 


Edited by AllanDystrup, 04 June 2018 - 02:11 AM.

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#177 AllanDystrup

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Posted 05 June 2018 - 02:28 AM

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M8, Lagoon Nebula

NGC 6530, 6523

    

    
     We have now entered July (2018-06-02), and the warm spell from May is still going strong. There’s currently a widespread draught across the country with a ban on open fires, as we have already had one large wildfire in the heathlands of Jutland. On the positive side: I don’t have to mow the lawn every week these days… smile.gif 

    

     I’m out again tonight, just past midnight (01h local DST, UT+2), to have a closer look at the open cluster and emission nebula in the M8 area of Sagittarius. Having located the M21 OC and the M20 (Trifid) nebula, it’s easy now to continue from M21 almost 2° straight S in DEC, till I hit upon a “boat” asterism, with a roughly E-W oriented hull of 4 stars (the two westernmost being 9 and 7 Sgr), plus a mast of two stars pointing up NNE.

    

     In my wide field view (CZJ O-25mm, 44x @ 0.9° FOV) I can detect a nebulous mist around the base of the “mast” (9 Sgr), and a string of three ~8m stars embedded in a haze of unresolved fainter cluster members to the E of the nebula. The star cluster is NGC6530 and the nebula is NGC6523, both part of the M8 “Lagoon” star-forming complex.

    

     For a better view, I now boost the magnification to 136x (R2 live video, 0.3° FOV). The NGC6530 OC is seen to contain one bright 7.5m B0V star plus seven hot type B0-1 stars ~9m; The remaining ca. 90 stars in the cluster are fainter than these, and distributed predominantly in the NE-SW direction.  The large gas cloud NGC6503 is illuminated by UV-radiation from several hot type O-stars, primarily the 5.9m type O4V HD164794 (9 Sgr) and the 7.1m HD164816 spectroscopic binary of types O9.5V+B0V. These are marked 9 respectively H on my drawing. The core of the nebulosity is located to the SW of 9 Sgr, around a young 9.5m giant star Herschel 36; the hot radiation from this star has carved out (by photo evaporation) a structure in the dense gas/dust called the “Hourglass Nebula”. On my close-up drawing you can see the bright hourglass structure just E of Herschel 36.

    

     I can see two dark “moats” surrounding the bright central castle of nebulosity guarding the Hourglass, like two concentric horse shoes with the opening oriented towards the W. These “channels” are lanes of cold dark dust that obscure emission from the ionized H-II gas. The Lagoon nebula is a site of star formation as revealed by HST in the form of several collapsing protostellar clouds (Bok Globules) and accreting discs (Herbig-Haro objects). The latter of course are too faint to be observed with amateur instruments.

    

     M8 the Lagoon nebula is located at a distance of ~5.2 Kly. The NGC6530 OC is a < 3 Myr young OC, just in front of the Lagoon.

 

     Here's my drawing of the M8 Lagoon area, with a rich field view (44x) and a close up view (136x). For a change, I've taken an iPhone snapshot of the drawing, as I find that a scanning (at least on my printer) does not render the drawing of faint nebulosity very well…

 

M8 Lagoon iPhn5-S.jpg
*click*

 

 

Allan


Edited by AllanDystrup, 05 June 2018 - 03:01 AM.

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#178 AllanDystrup

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Posted 09 June 2018 - 01:54 AM

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M24
the Small Sagittarius Cloud

    

    

     Time to dig into my observation backlog, -- here’s my report from an early morning in late May (2018-05-24, 01:30 Local DST, CEST UT+2).  The target is Messier 24: the small Sagittarius Star Cloud (to distinguish it from the large Sagittarius Star Cloud south of M8, the Lagoon Nebula.  M24 is a view through a 1.5° x 0.5° window, past both our Local spiral arm and the next inner Sagittarius-Carina arm to the innermost Norma spiral arm closest to the galactic bulge. What we see is thus a large number of stars in the Norma Arm at a range of distances from 12 to 16 Kly, half way to the galactic center at 30 Kly. For comparison the Large Sagittarius Star Cloud is much closer, being a bright part of the Sagittarius-Carina arm at a distance of 7-12 Kly.

    

     To locate M24, I use to start from the S tip of the Shield (Gamma Scuti), from where I first drop down 4° due S in DEC to the OC M25, and from there I simply pan another 4° due W in R.A., where I get a wedge shaped asterism of 7-8m stars in the 2.5° FOV of my Masuyama 32mm finder eyepiece. The magnification is 34x in my Vixen FL-80S/640mm refractor, which is perfect for a wide field framing of M24.

    

     Mentally zooming in on M24 from our solar system in the Local Arm, we first encounter the entrance to the tunnel in the form of a darker area at the NW edge of the star cloud. This is two small, compact dark clouds (B92 and B93) located only a few hundred ly away in our own local spiral arm. Looking deeper now into the tunnel, we meet the Wedge of foreground stars in the Sagittarius-Carina spiral arm at around 7.8 Kly. One of these is the double star: Burnham 639 (β639) composed of the 6.4m (HD168021) plus the 7.9m (BD-18 4897C) stars, at 18" Sep. in PA 52° [marked on my drawings]. Looking still deeper, the tunnel is finally filled by the carpet of faint stars in the innermost Norma Arm at ~15 Kly distance.

    

    

     In the 32mm eyepiece at 34x, the Star Cloud is not visible tonight, due to sky glow from nautical twilight, a 70% Moon in the W combined with a slight hazy coating of the celestial dome from thin high cirrus. Though the NELM is actually OK for my suburban backyard tonight at 5.4m, the transparency is lousy at ~3+/7 with no trace of the Milky Way naked eye (M24 is currently at ~12° Alt). Clicking up the magnification to 68x (CZJ O-16) and 108x (CZJ-O10) and slowly sweeping the telescope E <-> W, I start to get a feeling for the location and extent of the star cloud, which is now seen as a very faint carpet of hazy light, with a kind of fine grainy texture from multitudes of stars just below the limit of resolution. Nice! (-- but alas too faint to render in the scanning of my drawing).

    

     I look for the young (200 Myr) open cluster NGC6603 located right in front of the Norma Arm at 12 Kly distance, and I think I spot it as a very  faint smudge above the tip of the wedge of foreground stars. I also look for the smaller OC Cr469 and the two dark clouds B92-93 at the W border of the star cloud, but try as I may, I can’t detect these with glass eyepieces tonight (I've marked them on my rich field drawing anyway, for reference).

    

    

M24-M32 BLACK-S.jpg

*click*

      

TBC
Allan


Edited by AllanDystrup, 09 June 2018 - 02:15 AM.

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#179 AllanDystrup

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Posted 09 June 2018 - 02:05 AM

.

continued:

M24
the Small Sagittarius Cloud

    

         

     Instead I decide to do a sweep @ 136x in live video, using my R2 CCTV.  (I’ve marked the strip for my video sweep on the overview drawing at 34x magnification in the previous post).

 

     Starting at the top of the Wedge and sweeping W across the M24 Star Cloud at 136x, it’s evident that the E part of the field is much more densely populated with stars, while at the W end we hit the wall of the viewing tunnel in the form of the interstellar dark dust clouds B92-93 in our Local Arm. The double star β639 in the Wedge is now easily separated, and ca. 10’ N of it, the OC N6603 is also partly resolved. At the W end, B92-B93 are seen as evident vacant areas, while the small OC Cr469 is located  below B93, and resolved with some effort to a handful of stars in a small hazy knot.

    

         

M24-R2 BLACK-S.jpg

*click*

         

Allan


Edited by AllanDystrup, 09 June 2018 - 02:40 AM.


#180 AllanDystrup

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Posted 10 June 2018 - 02:06 AM

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M25 (IC4725)

    

    

     Next up from my Messier backlog this early summer is the open cluster M25, -- an observation record from 2018-05-24, 01h:00m  Local DST (CEST, UT+2). As described in the previous post on M24, the observing conditions this night were below medium, mostly due to sky glow from Nordic nautical twilight combined with thin high cirrus (Trsp.: 3-4/7, Seeing 8/10, NELM 5.5m, Moon 69% at 19° Alt.). Now, this is no show stopper for hunting down OCs, though low magnification / rich field views will of course be somewhat degraded (as can be seen in my drawing).

    

     M25 is easy to locate, even at the reduced transparency tonight: from the tail of The Eagle, down S through The Shield to the base star Gamma Scutii. From γ Sct, it’s 4° due S in DEC, and M25 is in the center of the FOV of my Mas 32mm finder eyepiece (34x @ 2½°).

 

     At this rich field view, M25 is seen just below a line bending E of one 6m plus two 7m stars, the easternmost a tight double. Below the two ~7m stars, M25 is seen as a central 7m star (U Sgr aka HD170764, a pulsating 6.3-7.1m 6.75 day δ Cephei var) in a triangle of three ~8m stars, with a loose assembly of ca. 10 fainter ~9m stars scattered S of U Sgr.

    

     Changing to live video at 136x (R2 CCTV, 0.3° FOV), the cluster now spreads out with U Sgr in the center, above a scattering of 9-10m stars towards the SW. These fainter stars are distributed in a tight knot W of U Sgr plus two lines of stars oriented E-W below the central knot.

    

     M25 is a young (95 Myr) OC in ~2 Kly distance (known precisely due to the Cepheid cluster member: U Sgr). It is located in the gap between our own Local Orion-Cygnus spiral arm, and the next, inner Sagittarius-Carina arm. There are several hot blue (type late B) stars in the cluster, for instance in the knot W of U Sgr. The V* U Sgr itself is a type G1 Ib orange “less luminous” supergiant, and though I looked for the color of the star, I was not able to see it that night.

    

    

M25 BLACK-S.jpg
*click*

         

     Allan 


Edited by AllanDystrup, 10 June 2018 - 07:00 AM.


#181 AllanDystrup

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Posted 15 June 2018 - 12:48 PM

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Messier M22 & M28 GC
NGC6656 & NGC6626

    

    

     It’s a good hour past midnight in the start of June (2018-06-02, 01:30 Local DST, CEST UT+2). It’s a calm and mild early summer morning in Nordic nautical dawn, with a 90% rising Moon at 7% Alt. in Sagittarius, still hiding below the roof ridge of my neighbor’s house towards the S. There’s a thin high haze, which - combined with the light of the Moon - results in some sky glow with a NELM of 5.3m (SQM 18.5) towards zenith, but considerably reduced transparency towards the horizon, where my targets for tonight are hiding. Let’s see if I can catch the Messier globular clusters M22 and M28 from this bright suburban sky.

    

    

     Both these globs are easily found when starting from the tip of the “Teapot”: Kaus Borealis (λ Sgr). I start with M22, which is located 2½ due NE of λ Sgr. Placing Kaus B. to the SW just outside the 2½° FOV of my Mas 32mm EP (34x), I get a triangle of 6-7m stars (including 24 and 25 Sgr) to the NE in the FOV, and I can now just glimpse M22 right at the NE border of the field. Centering M22 in the view, it shows up as a diffuse glow with a slightly brighter core area, a little oval in the E-W direction. I can’t resolve any stars in the glob in this wide field view tonight; -- this is pretty much as Messier saw the cluster back in 1764.

    

     Switching to live video at 136x (R2 CCTV, 0.3° FOV), M22 explodes into a swarm of 11-15m stars, with the brightest ones well resolved across the face of the cluster. The brightest stars are arranged in ~7 chains sprawling out from the center, primarily in the SW direction, all seen on a hazy background of fainter unresolved stars. This makes the cluster look somewhat compressed to the NE, an overall oval shape with a darker NE-SW oriented “lane” between two of the arms in the W part of the cluster

    

     M22 (aka “The Great Sagittarius Cluster”) is the closest, brightest and largest GC on the N celestial hemisphere. M22 features two stellar mass black holes in binary systems (VLA 1 & 2), >78 variable stars, a planetary nebula (GJJC1) and 6 large planet like objects (brown dwarfs or rogue Jupiters). I look for the PN  - position marked by a small circle on my close up drawing -- but I'm not able to spot it; It is after all a 3” diameter 15m object lying just 1’ S of the cluster center.

    

    

  M22-BLACK-S.jpg
*click*

 

Allan    


Edited by AllanDystrup, 15 June 2018 - 01:27 PM.

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#182 AllanDystrup

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Posted 15 June 2018 - 01:21 PM

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Continued
Messier M22 & M28 GC
NGC6656 & NGC6626

    

    

          Having finished my observation of M22, I now return to Kaus Borealis (λ Sgr) for starting my star hop to the next target: the M28 Globular Cluster.  Comparing the two globs: M22 and M28, both close to Lambda Sgr, they are roughly of the same age (12 Gyr) and absolute size (diam. ~100 Ly), but M22 is close to our solar system and loose, whereas M28 is far away at the galactic bulge, dense and more concentrated. As a consequence M22 seems bright and large on the night sky, whereas M28 - as seen from Earth - is almost 2m fainter and only 1/3 the size of M22.

    

     M28 is located NW of Kaus Borealis, almost 1° ~ 2/3 the way in the direction of the 6m star HD168574. Placing Kaus B. in the SE “corner” of my Mas.32mm finder eyepiece (34x @ 2½°), I get HD168574 to the W in the field, and M28 close to the center. The glob can *just* be glimpsed visually as a very small and faint glow of diffuse light.

    

     At higher magnification using the R2 CCTV for live video (136x @ 0.3°), the GC is seen as a hazy patch of light, obviously elongated in the NE-SW direction, with a peppering of brighter ~12-13m stars across the unresolved haze.  Due to the cluster's close proximity to the Milky Way center, it is experiencing a strong tidal interaction, which is the cause of its asymmetric shape.

    

 

M28-BLACK-S.jpg

*click*

    

    

     At this point of time (02:45) the Moon is steadily climbing up over the rooftop of the neighboring house, and the globular is heading precariously for a collision with my neighbor’s TV antenna and chimney, -- so I have to terminate the observation. I thus don’t get a chance to observe the two chains of stars stretching up N from the cluster like a pair of antennae. It has however been a good astronomy night in spite of the not quite favorable observing conditions.

    

     The two GCs close to λ Sgr / Kaus Borealis (M22 and M28) are interesting for a comparative study, much like the two GCs close to α Sco / Antares (M4 and M80). Here’s the basic data for M22 and M28; comparing my drawings of the pair of objects (which are done at the exact same magnifications) illustrates quite well (I think) how different two - in several ways physically identical - open clusters can show up at our night sky, depending on their closeness to the galactic center.

    

Messier   NGC   Mag    Dist(Kly)    Mass     Diam     Class
                      Earth Gal.C.  Ksun    ’   Ly
-------------------------------------------------------------
M22      6656   5.2    10    16     300     32’ 100    VII
M28      6626   6.9    18     8     500     13’  70     IV

    

 

Allan


Edited by AllanDystrup, 15 June 2018 - 01:33 PM.


#183 AllanDystrup

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Posted 10 July 2018 - 02:17 AM

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Messier 75 Global Cluster
NGC 6864 - A Gaia Sausage GC

    

    

     It’s an early morning (02:00 Loc. DST, UT+2 CEST) in the start of July (2018-07-09). I’m out in my suburban backyard in Nordic nautical twilight, with only an hour to sunrise and civil dawn; The sky glow is considerable with a SQM of 18.5 (NELM 5.3), but the 25dy / 22% waning moon is still just below the E horizon, and the temperature is a very comfortable 14°C with a low humidity (75%, dew pt. 10°C), so all is GO for adding another globular cluster to my “Messier Kill List”.

    

     Including the target for tonight: Messier M75, my M body count with the small Vixen refractors will now be 102, with 8 Messiers to go, all the remaining objects at or below -20° altitude (M83, 62, 6, 7, 69, 70, 54, 55), and thus hard for me to bag from my backyard @ 56° N latitude. I will be giving these a try next year, but after M75 I plan to concentrate on rich field nebula observation for a while, using low power filtered equipment.

    

    

     To locate M75 in this twilight sky, I start my sweep from Altair in the Eagle, then down SE to Theta Aql. From here I pan due S ~12° till I hit the nice group of stars around the double Alpha Capricorni, then continue 6° S to the tip of a small arrow asterism (Rho-Pi-Omi-Sig Cap) The arrow points roughly to a small dipper shaped asterism of 6-7m stars, with M75 hanging just below the handle of the dipper.

    

      I take some time to try spotting the GC in my Mas-32mm finder eyepiece on the small 55mm Vixen refractor (23x @ 3.6° FOV) – I have the location spot on, but the GC is very difficult to see in these adverse conditions; -- after some time I think I do catch glimpses with averted vision of a very faint small hazy fuzzy spot: M75.

    

     Upping the magnification now to 94x in 0.4° FOV (Live video with my R2 ccd/lcd), the GC is evidently seen, though it looks mostly like a fuzzy star: a very tight core in a faint outer halo. There is no real resolution of the cluster, though in fleeting moments I can detect a mottled texture of groups of stars in the core and in tiny extensions N and W out into the halo.

    

     M75 is the second farthest globular cluster in the Messier Catalog: 68 Kly distance from Earth, corresponding to 40 Kly beyond the Galactic center. It is a compact cluster (Shapley Class I) with a condensed center that harbors 26 blue stragglers. The member stars are faint due to the great distance: all are >14.6m, and the average magnitude of the 25 brightest stars is down at 17.1m.  Though the visual appearance of M75 is unimpressive, the history of the glob is fascinating, as it - together with 7 other GCs - belongs to the “Gaia Sausage”: an elongated population of globs and stars which are the shredded remains of the massive “Sausage Dwarf Galaxy” that was cannibalized by our Milky Way ca. 10 Byr ago (https://arxiv.org/abs/1805.00453).

    

M75 GC - BLACK-S.jpg
*click*

    

    

-- Allan


Edited by AllanDystrup, 10 July 2018 - 02:52 AM.

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#184 Organic Astrochemist

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Posted 10 July 2018 - 03:03 PM

Dear Allan,
Great catch on the Gaia Sausage GC’s. Although quite South for you they are bright and i have seen most of them:
NGC 1851, M79, M75, M56, M2, and NGC 2298. I haven’t seen NGC 2808 and NGC 5286.
The upper panel in figure 3 is interesting. It suggests that these clusters have unusually high eccentricity, especially for clusters that were considered as old halo GC. For this group of GC, the eccentricity may constitute an important property that is discernable visually. I think I’ll try to observe them again, contrasting them to nice round bulge/disc GC’s.

Edited by Organic Astrochemist, 10 July 2018 - 07:45 PM.

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#185 AllanDystrup

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Posted 11 July 2018 - 04:03 AM

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     Yes indeed, Organic Astrochemist  waytogo.gif  -- the Gaia Sausage GCs I'm able to observe from up here @ 56° N latitude all show up as rather elliptic/skewed with tidal "starfish" arms out into the halo, as can be seen in my drawings below (all taken from my observation reports in this thread) :

     

Gaia Sausage GCs.png

M79: https://www.cloudyni...sier/?p=8334449

M75: https://www.cloudyni...sier/?p=8693332
M56: https://www.cloudyni...sier/?p=7349252
M02: https://www.cloudyni...sier/?p=8131537

    

    

     Unfortunately the remailing 4 (6?) Gaia Sausage GCs are too far down south (< -35° Altitude) to be observable from Denmark; Could have been a real fun observation project though!

 

-- Allan


Edited by AllanDystrup, 11 July 2018 - 04:09 AM.

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#186 starblue

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Posted 11 July 2018 - 10:50 PM

It suggests that these clusters have unusually high eccentricity, especially for clusters that were considered as old halo GC. For this group of GC, the eccentricity may constitute an important property that is discernable visually. I think I’ll try to observe them again, contrasting them to nice round bulge/disc GC’s.

I don't understand this statement about the eccentricity, which concerns the orbits of the globulars (look at Table 1 of the PDF). How is observing them going to tell you anything about the orbits?


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#187 AllanDystrup

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Posted 12 July 2018 - 12:58 AM

starblue,

 

     The way I understand it is that the capture and subsequent high eccentricity of the Gaia Sausage Globs (GSG) subject them to great tidal forces due to periodic close encounters with the galactic bulge. The 4 Messier GSGs do exhibit abnormal elongation and tidal star streams, and I'd be interested in knowing, if this is the case too for the remaining 4 (+2?) GSGs. And can we observe this visually?

 

-- Allan


Edited by AllanDystrup, 12 July 2018 - 01:03 AM.


#188 starblue

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Posted 12 July 2018 - 12:17 PM

That seems plausible, but it's not a direct conclusion of the article. I searched for every reference to "eccentricity" in the article and every one referred to *orbital* eccentricity, not the distribution of stars inside a spherical volume.


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#189 Organic Astrochemist

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Posted 12 July 2018 - 08:15 PM

There may be many reasons why globular clusters deviate from sphereical symmetry, presenting instead an elongated, triaxial ellipsoidal appearance. This may include their history of formation and evolution.

Given Allan’s description of M75, I wondered if the eccentric orbits of these Gaia Sausage GC’s might afford them a more elongated appearance.

Personally, I often find the elongated appearance difficult to observe. I also think that what can be visually observed of GC often doesn’t reveal very much about their structure or history. I wonder, for this group of GC, if things might be different?
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#190 AllanDystrup

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Posted 01 December 2018 - 10:15 AM

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M1, The Crab Nebula -- revisited.

 

     

    

     M1 is a supernova remnant (SNR) from the collapse of a giant star >10x the solar mass. The remains show up as a nebula surrounding a small (~15km radius) fast spinning (30x/s) neutron star with an extremely strong magnetic field.  As electrons are accelerated through this magnetic field they emit synchrotron radiation jets along the rotational axis. The nebula shows :

• A faint skin surrounding it ([OIII])
• An outer web of ejecta filaments expelled by the SN explosion, (Hydrogen at the right temperature to emit Hα)
• An inner synchrotron emission nebula (ionized H)

__________

 

 

     It’s an evening in late November (2018-11-27, 21:30 CEST, UT+1); the 73%/20dy Moon is low at the E horizon (7° Alt. in Cancer), so it is well out of the way for my observation tonight. The humidity is high (92%) and with a temp. of -3°C (DewPt -4°C), there’s already a thin glazing forming on the dew-shields of my refractors – but the lenses are clear! Both transparency (5-6/7) and seeing (8/10) are above medium and the LP is fine for my suburban backyard (SQM 19.0 / NELM 5.6), so all is GO for throwing the moorings…

 

     I’ve previously studied M1, the Crab SNR in Taurus, with glass only -- see https://www.cloudyni...sier/?p=7078483.  Back then I wrote of the view in my Vixen FL-80S/640mm with an ATC K-40mm EP for 19x @ 2.2° FOV:

 

   “The nebula is faint, but obvious with peripheral vision (I can not hold the nebula with direct vision). It is diffuse, with no brighter core (as in many galaxies). It is rather large (ca.3’ diameter) in the 19x wide field eyepiece; It seems “woolly”, like a dust bunny, with no evident outer boundary or internal structure, but obviously elongated in the NW-SE direction”

 

M1-B.jpg

*click*

    

    

     I’d now like to repeat the observation of the Crab, but this time using night vision on my small 60/360mm finder scope. I start with an overview in 6nm Hα of the area at 6½x (5° FOV). I love the wide bright view on my small finder scope. M1 is easily seen with direct vision, and now shows up as round-ish nebula with a brighter central NE-SW oriented bar.

 

    

M1-6nm-B.jpg

M1-6nm-W.jpg

*click*

 

     Upping the magnification to 25x (1.3° FOV), and now switching to a 12nm Hα filter I start to see some interesting details in the Crab. I can see the Y-shaped central SN ejecta filament in the web from the supernova explosion, shining brightly in Hα. The filament is oriented NE-SW, following the orientation of the magnetic field generated by the pulsar. I can also detect traces of the fainter, branching parts in the outer web of filaments, -- consistent with what shows up on long exposure photography of the object. That is nice!

    

M1-12nm-B.jpg

M1-12nm-W.jpg

*click*

 

   -- Allan


Edited by AllanDystrup, 01 December 2018 - 10:19 AM.

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#191 AllanDystrup

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Posted 15 March 2019 - 03:02 AM

.

M68 (NGC 4590)
Globular Cluster

 

 

    I have this spring (2019) embarked on a wide-field galaxy survey, -- but I also have some objects left on my Messier “Kill List”, that I’d like to bump off if possible. The remaining 9 objects on my list to bag with my small classic refractors are however the most southern as seen here from 56N in Denmark, and thus also the most difficult to catch.

    
     Tonight (2019-03-12, 01:15) the globular cluster M68 (Dec -26⁰51’) is close to culmination at +7⁰18’ Alt, so this is as good as it gets from my backyard just N. of Copenhagen. Corvus has just cleared the roof of our neighbor towards the S, so I point my 4” refractor at β Corvi, pan E a good 1⁰ to a triangle of ~8m stars, then continue due S in RA a good 3⁰, till I get a line of three 5-6m stars in the S part of the FOV.

    
     The LP tonight is ~NELM 5.8m at zenith, but I’m now aiming close to the horizon right through the dust and light dome of our suburb, where there are absolutely no stars visible naked eye. I have however a 41mm EP on my 4” refractor for 16x in a 5½⁰ field, so I can clearly spot the line of three ~5½m stars, and I can also glimpse a small group of fainter stars almost ½⁰ to the NE of the northernmost star in the line.

 

     From star maps I know the exact location of M68, so with some patience and averted eyesight I do manage to glimpse M68 as a very faint hazy spot, just SW of the star FI Hydrae (a type M4 Mira variable 15 – 8.9m with a period of 326 days). I take a snapshot at short exposure and low ISO to properly reflect how the object looks through the glass of my small refractor:

    

    

M68-Obs.jpg
*click*

    

    
     Messier had some difficulty observing M68 too, with his small 3½” achromatic refractors, even from his more southern latitude of ~49⁰ N; He saw M68 as a “nebula without stars below Corvus and Hydra; it is very faint, very difficult to see with the refractors”. I can confirm that smile.gif.  Herschel had more success with his 20-foot (~19” aperture) reflector from 51⁰ N latitude, where he saw M68 as very pale, but “beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together”.

    
     M68 is in the outer halo, opposite the galactic center and far away from the plane of the Milky Way, in an eccentric orbit that takes 500 Myr pr. revolution. It is one of the most metal-poor globular clusters known, probably captured from a satellite galaxy, which was swallowed in the past by the strong tidal field of our Milky Way.

    

     -- Allan


Edited by AllanDystrup, 15 March 2019 - 04:43 AM.

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#192 dUbeni

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Posted 17 March 2019 - 10:48 AM

Hi AllanDystrup

For an unknown reason I miss a sketch on the latest post smile.gif 

 

CS

Bernardo 



#193 AllanDystrup

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Posted 23 March 2019 - 07:05 AM

.

     Ahh well, -- yes Bernardo, you're quite right wink.gif. It has been some time since I sketched the night sky, -- mostly because I have recently used my image intensifier monocular to study the ionized hydrogen clouds around OB-associations in our Milky Way disc, and it's just so much easier to take an iPhone snapshot of the view instead of sketching the very intricate and detailed features of these objects. Also, for my current wide field galaxy observations, I'm starting to use iPhone snaps to document the views. So there...

    

 

Messier 83
The Southern Pinwheel

    
     It’s a good hour past midnight in the middle of March (2019-03-19, 01:30 CEST, UT+1), and I’m out with my small 60/360mm finder scope for a wide field view of M83 (NGC 5236), the Southern Pinwheel galaxy. M83 is a type SAB face-on spiral with three arms wrapped tightly around an elliptic nucleus featuring a weak stellar bar.

   

M83-CenA.jpg
*click*

    

    
     The conditions for DSO this early morning are actually quite bad: a 93% moon is blazing right above Regulus in Leo, and there’s a mediocre 3-4/7 transparency due to condensing humidity in the atmosphere, accompanied by a few low, drifting Stratus Fractus clouds.

    

     Since M83 is at only ~4⁰ altitude right now as seen here from 56⁰ on the outskirts of Copenhagen (culminating dues S in ½h at 4⁰20’), all the stars below 10⁰ towards the horizon are drowned out by sky glow, and I have a hard time star hopping to the galaxy. With a 610nm red longpass filter and my night vision monocular behind the 55mm Plössl eyepiece, I do manage to pan from γ Hya, 5⁰ SE to a line of ~6m stars curving south, and less than 1⁰ E from the end of this line I finally identify the location of M83.

    

M83-Obs.jpg
*click*

    
     One thing is identifying the location though, another is actually spotting the galaxy... After prolonged observation with shielded and averted eyesight, I do manage to catch a very faint undifferentiated hazy glow at the location of M83, so I count it as a positive observation of the object. I take an iPhone snapshot of the view, and later I confirm the observation on a zoom-in of this image. -- I do hope to get a more detailed view of M83 under better observing conditions in the near future though.

 

     -- Allan

PS: I'd love to see a sketch of this galaxy from a more southern location, say Portugal for instance. Anyone? grin.gif


Edited by AllanDystrup, 24 March 2019 - 01:47 AM.

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#194 WyattDavis

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Posted 30 April 2019 - 10:29 AM

 

Virgo Cluster
3: "The Triangle", South

M99 - M98

    

    
     It’s a calm, relatively balm spring evening in early May, 2330 local time. The Moon is below the horizon, and the transparency and seeing are good (NELM 5.4m), so toninght I will continue my hunt for Messier galaxies in the Virgo cluster, this time focusing on M98-M99-M100, forming ”The Triangle” to the NW of the center of the galaxy cluster.

 

 

     Starting at Denebola (Beta LEO), I first scan (naked eye) due E ca 6°, where I find 6 Coma Berenices. Centering my 8x50 finder scope on 6 COM, I now see a T-shaped asterism of 6-7m stars in the field of view, with 6 COM at the right end of the upper bar in the ”T”. I use this asterism to locate the 3 Messier galaxies in ”The Triangle” part of the Virgo Cluster :

  • off the left (E) upper end of the ”T” is M100,
  • off the right (W) upper end is M98, and
  • midway in the downstroke of the ”T” is M99.

 

attachicon.gif VirgoCluster-Triangle BlackL-Crop-Small.jpg

 

 

     M99 is the brightest of the three galaxies, so I start with this one, which I can just glimpse at 27x in my ATC K-40 finder EP. 
 

     I keep the field of my drawing as seen with the K-40mm eye piece (ie. 1.5° FOV), but for the galaxy observation I increase the magnification, first to 44x (0.9° FOV) : M99 is now seen as a weak, round nebulosity without any specific orientation or structure. It does get more dense towards the center, but shows no stellar core. Clicking the magnification up to 68x (0.6° FOV), I suspect a mottled core, and a weak NE-SW assymetry of the galaxy. One more click to 108x (0.5° FOV), and I can definitely see a mottled core, -- and even suspect fainter, outer sprawling arms! (says my notes... maybe I was carried away by the nice view).

 

 

     Continuing my observation of M-galaxies in the S part of ”The Triangle” in the Virgo Cluster, I now shift my attention from M99 to M98. I first return to the 1.5° field of my K-40mm EP, and center it on 6 COM in the ”T” asterism. This should give me M99 in the W part of the field; -- but I am not able to spot the galaxy at this 27x magnification.
 

     I keep the field for my drawing at 1.5° though (which allows me to draw M98 on the same observation sheet as M99), but I increase the magnification to 44x (CZJ O-25 @ 0.9° FOV). I can now catch glimpses of the faint nebulosity of M99 with averted vision : it is seen as a hazy streak of diffuse light with a NW-SE orientation, but with no brighter center or texture (no core, no mottling). It is difficult to observe, as I can catch no more details by shifting the field or increasing the magnification to 68x (O-16mm).

 

attachicon.gif Triangle-S M99-M98 BlackL-Crop-Small.jpg

 

 

Link tofull  ->Obs. Report<-

 

Allan

 

Hi Allan - thanks for this reference. The "T-asterism" is proving to be a very useful reference point in Coma/Virgo!


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#195 AllanDystrup

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Posted 01 May 2019 - 03:53 AM

.

Thank you, Wyatt!

    

    

     These are the star patterns I normally use to navigate the Virgo Cluster for Messier galaxies:

 

     The :

  • Rho Virginis Lambda (the anchor)
  • The Wall: from the Bar, the Kite, the Axe to the Arrow
  • The Hook (N. of the Wall; -- beware, some faint white walkers up there...)
  • The T

Virgo Cluster Asterisms.jpg
*click*

 

     -- Allan

 

 


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#196 antariksha

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Posted 26 June 2019 - 12:52 PM

Allan, this is a great work and wonderful documentation.

I am curious know about-

- how much time do you spend observing a particular object? ( must be few hours)

- Do you keep changing Eye pieces or prefer to consistently view in the same?

- In case, for some reason, the sketch has to go over multiple nights, how do you go about it? ( It is like a long break in between and you have to resume the next night.

 

thanks



#197 AllanDystrup

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Posted 27 June 2019 - 02:14 AM

.

Antariksha, -- Thank you for the thumbs up on my Messier observing reports smile.gif .

    

  •      An average observing session for me is ~2½h length, and in this time frame I some times manage to observe 2 objects, but mostly only 1. My observations are done from my suburban NELM ~5 backyard at 56N latitude in Denmark. I sit down with my 3" classic Vixen refractor (FL-80S/640) on a manual motor driven Zeiss Ib EQ Mount, and observe visually, recording my observation in sketches made at the telescope:
    https://www.cloudyni...sier/?p=7229835
    https://www.cloudyni...ield/?p=7689779

         For wide field objects I may need two observation sessions to complete the observation. After that, I'll need at least an hour next day to clean up the drawing and add celestial coordinates to verify the observation. Then some extra time to write up the obs. report and add additional astrophysical information and illustrations.

        
  •      For the Messiers observations, I have been using mostly:
    - for star hopping: my 8x50 finder plus my Zeiss 8x30 and 10x56 Binos 
       (https://www.cloudyni...sier/?p=7212087)
    - For low power: a Masuyama or ATC 32mm EP (34x/2½dg FOV)
    - For medium power: CZJ O25 & O16mm orthoscopics (44x/0.9dg & 68x/0.6dg FOV)
    - For high power: a R2 ccd/lcd live video session (110x/0.3dg FOV)
        
         I normally make a small sketch of the finder view, and then choose a suitable medium power eyepiece that frames the object best, and stay with that for the sketch. Most often that is the CZJ O16 68x view.
        
         For many Messiers I have also done a high-power sketch, mostly using live video at the telescope (R2 110x/0.3dg FOV). This tool often made the difference between glimpsing the target as a faint fuzzy spot from my LP suburban backyard, and actually being able to see and study the details of the object.

     
  •      For observations requiring more than one night, I almost always have needed two consecutive nights to finish my drawing; On a couple of occasions where I was not able to do that, I preferred starting over the observation with a new fresh drawing.
        

     I've now observed most of the Messiers using this setup, excluding only 7 objects, all between -30 and -40 dg latitude. I expect I will be able to catch M62, M54 and M55, while the remaining 4 (M6-7 and M69-70) will be out of reach from my 56dg N. We'll see...
    

     After this Messier sweep, I have considered doing a follow up study of the "Best Messiers", using my larger 4" Zeiss refractor with glass EP, supplemented by EAA for high res views. That could be interesting for comparison.

    

     -- Allan


Edited by AllanDystrup, 27 June 2019 - 02:38 AM.

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#198 antariksha

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Posted 28 June 2019 - 12:22 PM

Allan, it was really interesting to read the above post and response to me. I read it twice!!.

This gives me a fresh perspective about " how to observe DSOs" and of course sketching those objects later.

Thanks


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