Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Classic Rich Field

classic dso equipment eyepieces LP observing observing report refractor sketching
  • Please log in to reply
444 replies to this topic

#51 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 20 February 2017 - 04:01 AM

Cepheus OB-Associations

 

     Looking at the near solar neighbourhood, there are several galactic structures (besides the OB-associations Orion-1 and Perseus 2-3), that I’d like to visit in this context. To name a few close by open clusters inside the 500 pc limit of the Gould Belt: Cr 359, Cr 65, CR 132, Cr 121, Tr 10, Mel 111,  NGC 752. There are also close by in the Orion Spur of our galaxy  some interesting emission nebulae (HII regions) listed in the Sharpless catalog, such as the large supernova shell remnants Gum 12 and 16, of the same type as Bernard’s Loop (Sh 2-276), the Lambda Orionis Ring (Sh 2-264) and the California nebula (Sh 220/NGC 1499).

 

     To proceed with my OB-association survey, I will however now step outside the 0.5 Kpc playpen, and direct my attention towards the major OB-associations in Cepheus, at a distance of ~850 pc (and later on, the more distant “Winter OBs” in Aur, Gem, Mon and CMa) :

 

Cepheus OBs.jpg

 

Cepheus OBs-02.jpg.jpg

*click*  (my annotations)

 

Allan


Edited by AllanDystrup, 20 February 2017 - 04:04 AM.

  • mwedel and BillHarris like this

#52 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 20 February 2017 - 05:45 AM

Cepheus OB-Associations  #2

 

Cepheus-OB-03.jpg

 

Cepheus-OB-04.jpg

 

 

Allan

 

PS: I have to build up the background a little step-by-step and post it piecemeal here, due to CN limitations.
Sorry about that, -- I'll come to my observations in the next post... ;)


Edited by AllanDystrup, 20 February 2017 - 05:58 AM.

  • mwedel and Kimbo_2112 like this

#53 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 20 February 2017 - 10:46 AM

Cepheus OB 2a

 

 

Obs-1:    Time: 2017-02-14, 18:00 UT,  Loc.:56N 12E Denmark, Alleroed,
          Setup: Vixen FL-55S/440mm, 1.5xGPC + Masuyama 2” 32mm
Cep OB2a  Transp.: 3-4/7 (Moon below E horizon), Seeing: 5-6/10, no wind;
          Bortle: Orange, bright suburban (SQM 18.8 NELM 5.3m)

 

Obs-2:    Time: 2017-02-14, 18:30 UT,  Loc.:56N 12E Denmark, Alleroed,
          Setup: Vixen FL-55S/440mm, 1.5xGPC + Masuyama 2” 32mm
Cep OB2b  Transp.: 3-4/7 (Moon below E horizon), Seeing: 5-6/10, no wind;
          Bortle: Orange, bright suburban (SQM 18.8 NELM 5.3m)

 

 

   It’s an early evening in mid February; My observing conditions are still hovering around medium (NELM ~5m) with increasing haze towards the horizon, as it has been the past couple of months, so the DSOs I’d like to visit tonight are a no-go…; but luckily this is a good enough evening for continuing my OB-association project! :)

 

     My goal for tonight is the Cepheus OB-2 association, at a distance ~800 pc. This association contains ~75 bright members, and it is divided into two subgroups:
 

  • the older OB-2a association (7-8 Myr) to the north, with NGC 7160 OC at the center of the large Cepheus Bubble -- a 9° diameter nebula shell from a supernova, showing several HII and star forming regions in the ring. The ~5m type-O6 Lambda Cep is a runaway star, possibly from this association (other sources indicate Cep OB3 as the originating association).
     
  • the younger OB-2b association (3.7 Myr) to the south, with Tr 37 at the center of the HII reflection nebula IC 1396. The beautiful bright 4.2m type-M2 red supergiant Mu Cephei (Herschel’s Garnet Star) is possibly a member of this association.

CEP-OB.jpg

 

 

     At 23x (Masuyama 2” 32mm EP), I can spot ~10 bright, early O/B stars plus many 5m-6m and fainter, more evolved massive stars spread over the 3.2° FoV between the two 4m type-A stars Ksi Cep to the NW, and Nu Cep to the SE.

 

      Close to the center is a small cluster of stars (~7’ diameter), with a tiny pair of ”eyes” to the NE and a little fuzzy ”tail” down SW. That is the open cluster NGC 7160. I bump up the magnification to 135x (8’ FoV) using R2 live video, and the cluster of ~20 members now strikingly reminds me of a smaller version of the ”Owl” (E.T.) cluster in Cassiopeia. A very nice view! (see detail drawing to the lower right).

 

CEP OB-2a Blabk-S.jpg
*click*

 

Allan


Edited by AllanDystrup, 21 February 2017 - 01:50 AM.

  • HfxObserver, mwedel and Dean Norris like this

#54 mwedel

mwedel

    Goofing off

  • *****
  • Posts: 1180
  • Joined: 16 Dec 2007
  • Loc: Claremont, CA

Posted 20 February 2017 - 11:57 PM

 

PS: I have to build up the background a little step-by-step and post it piecemeal here, due to CN limitations.

Sorry about that, -- I'll come to my observations in the next post... ;)

 

No apology necessary - I like the piece by piece buildup. It lends everything a very deliberate, measured pace that seems to suit the care and attention you put into your sketches. And it gives us time to digest the background info a bit. 

 

Keep 'em coming. This is wonderful stuff, one of the most inspiring threads I've followed in a decade on CN.


  • AllanDystrup likes this

#55 GlennLeDrew

GlennLeDrew

    Hubble

  • *****
  • Posts: 15849
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 21 February 2017 - 07:25 AM

Allan,

It appears as though you are preparing a book on the subject. Even the material presented in this thread amounts to a fine introduction for backyard observers.


  • sparrowhawk, Sarkikos, Dean Norris and 2 others like this

#56 mwedel

mwedel

    Goofing off

  • *****
  • Posts: 1180
  • Joined: 16 Dec 2007
  • Loc: Claremont, CA

Posted 21 February 2017 - 08:26 AM

Allan,

It appears as though you are preparing a book on the subject.

We can hope. I would love to have such a book. It would fill a very valuable and currently empty niche - I have countless books that tell me how to point my telescope at the Orion Nebula, and a few that describe what it is, but none that put it into context like this thread. I would use that book, and I would recommend it to others as a great example of how someone armed with a small telescope and a little determination can observe the physical processes of the galaxy for themselves.


  • Dean Norris, AllanDystrup and Ohmless like this

#57 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 22 February 2017 - 05:51 AM

Glenn, Matt -- sorry, but no book will be emerging from this observation project...

 

     I would very much like to see a book focusing on all the main Milky Way Messiers and Bright NGC's for visual observation with amateur telescopes, but placing them in a structural and evolutionary context, starting from our solar neighborhood and stepwise widening the view to the ever larger structures of interstellar EM/RN and dark nebulae, stellar associations, star clouds, galaxy spurs, arms and halo.

 

     Also a follow up book based on the same concept for deep sky objects, organized by starting with our Local Group, then moving by steps of say ~25Mly to the M81-CVnI-M101 groups, then to CVnII-LeoI, to UMa-Virgo, and further out to the superclusters, along the way outlining the 3D-patterns of groups and clusters, of voids and walls, attractors and streams. Now, wouldn't that be marvelous?

 

     In fact, this is how I try to structure my observations and my notes, in an attempt to build up my mental map of the universe. And if/when I get more time, I may put up my notes in the form of PDFs on a website -- but from there to writing a book is a BIG step. I do have some basic university background from natural sciences in math, physics and chemistry, but not in general astronomy nor astrophysics, so for me it would require a lot of time and effort in collecting, reviewing, selecting, consolidating and presenting the available data in both a technically correct and personally inspiring way.

 

     I started in astronomy at the age of 15yr back in 1965, with a 3" f/12 Unitron bought from money earned in my summer vacations. I learned to navigate the night sky with this refractor in the next years, but then came some decades with love and life, children and work. The 3" Unitron moved to the backseat, but now, after retiring a couple of years ago, my astronomy hobby has been revived. Meanwhile, the clock has been ticking, and I can see the end of the road.The universe is immense, and there is so much to explore, so I simply don't fel I have the time to write books.

 

     Luckily there are others far more qualified than me to do that job. I do hope they will !

 

Allan


  • Carl Kolchak, mwedel and Kimbo_2112 like this

#58 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 22 February 2017 - 06:06 AM

CEP OB-2b

 

     As previously described, the compressed shell of gas in the Cepheus Bubble was blown out by stellar winds and photoionization from a first generation of massive OB-stars, that have by now gone supernovae and are no longer among us. From the ashes of the supernovae and in compressed fragments of the bubble, second generations of stars were born, most prominent now as seen in the Cepheus OB-2 a and b associations.

 

      The Cepheus OB-2b association is located in a fragment of the MC complex at the S end of the Cepheus Bubble, just SE of the ~4.1m type-M2 Ia Mu Cephei (aka Herschel’s “Garnet Star”). This is a runaway star from OB-2b (peculiar velocity ~80 km/s), and one of the largest and most luminous red supergiants in our Milky Way, -- probably the largest star visible to the naked eye (1260 solar radii ~7AU, or past the orbit of Jupiter, if it were at the center of our solar system). It varies by 3.4-5.1m with a semi-regular pulsation period of more than 2 years (800-1000 days).  It is now on its death bed, scheduled to end soon in a massive cataclysmic supernova explosion that will punch out yet another large bubble with associated new star birth in the interstellar molecular clouds. (https://www.aavso.org/vsots_mucep).

 

     The Cep OB-2b association itself is found embedded in a 3° large emission nebula : IC1396 (Sh 2-131), at the border of the Cepheus Bubble. This giant cloud of gas and dust is lit up by several OB-stars in the young (3 Myr) open cluster TR 37 close to the center.  The main responsible for the ionization is the Trapezium-like massive multiple star system : Struve 2816, consisting of a type O6 binary (HD 206267A-B), with two close by type-B components. Radiation pressure from this hot system is compressing parts of the surrounding MC, creating ionization fronts around globules of gas and dust (such as the close by ”Elephant Trunk”) and triggering new star formation in these, including many small pre main-sequence F-G protostars and young T-Tauri stars.

 

 

     My observation of CEP OB-2b was done on an early evening with thin, high clouds (Cirrostratus undulatus) reducing the transparency. Mu Cep was beautiful with its deep orange-red colour, but the rich Trumpler 37 open cluster in the center of IC 1396 was dimmed to an extent, that I could not detect the looping patterns of faint stars, which can be seen on a dark, clear night.

 

CEP OB-2b Black-S.jpg
*click*

 

 

     At 23x in my rich field view I could however clearly spot the two brightest star systems in the core of TR 37:  Σ2816 and Σ2816, and at higher magnification (138x, using my R2 live video) I was able to resolve Σ2816 in three components plus the close by binary Σ2816 in the same 8’ FoV (lower right box on my drawing).

 

TR-37 Doubles.jpg


    

     My plan was next to look (with my R2 video cam) for the ionization front in the neighbouring “Elephant Trunk” globule (IC1396A,  part of the large Sh 2-131 nebula). I’ve indicated the position on my drawing, but the clouds prevented me from continuing my observation. Maybe some of you have spotted it?   I’ll definitely try for this object again at a later time, but right now Cepheus is relatively low on my N horizon, and on top of that, he is also playing peek-a-boo behind the neighbor’s high conifer trees, so I’ll probably have to wait till a later time this year.

 

 

 

Allan


Edited by AllanDystrup, 22 February 2017 - 06:17 AM.

  • mwedel and ianatcn like this

#59 MP173

MP173

    Viking 1

  • *****
  • Posts: 885
  • Joined: 30 Oct 2015

Posted 22 February 2017 - 10:19 AM

I see that you briefly mentioned CR65 Alan...is this considered a OB?

The iDSA lists this cluster and I observed several doubles in the cluster last week.  Obviously the size of the cluster (in excess of 3 degrees) makes it attractive in binoculars.  

 

I have often wondered about the CR and MEL open clusters.  These always seem to be larger in size and not condensed with stars, was curious as if these were "random" stars aligned or actual groupings.

 

Interesting discussion.

 

Ed


  • AllanDystrup likes this

#60 GlennLeDrew

GlennLeDrew

    Hubble

  • *****
  • Posts: 15849
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 22 February 2017 - 10:57 AM

A number of the Collinder objects are either spurious or contain just a few possibly related stars. They were assessed before good quality proper motion  (p.m.) data could at all reliably discriminate on membership. Indeed, even the Hipparcos mission p.m. data are often inconclusive for the more distant candidates, where errors are of order the motion and/or are too large to confidently constrain peculiar velocity to smaller than the required 1-2 km/s limit for a coeval group.

 

Furthermore, refinements in our understanding of the mass-luminosity relation for the more massive stars (which the O and B types are), has altered older values for spectroscopic parallax.

 

It's worth mentioning that the large angular size of a number of Cr groupings, when the likely distance derived from spectroscopic parallax is considered, are likely too large to be gravitationally bound. For those, if indeed they are real 'clusterings', would qualify as disrupted clusters or unbound associations.

 

In and near the band of the milky way, numerous clumpings of early type stars (mostly B, for the O-types are pretty uncommon) are certainly chance projections of unrelated stars. If we include the A-types, which are far more numerous than the B stars, chance projection becomes even more likely.

 

The GAIA mission data will be a boon to settling the status for many poorly studies 'clusters.'


  • AllanDystrup likes this

#61 GlennLeDrew

GlennLeDrew

    Hubble

  • *****
  • Posts: 15849
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 22 February 2017 - 01:36 PM

Allan,

In your star chart in post #53, the Cep flare molecular clouds, which are delineated with a dashed ellipse in NW Cepheus, are some 5 degrees farther north than shown. In part due to the large size of this cloud complex, I use it as a naked-eye indicator of sky clarity/darkness. They become apparent when at least 40 degrees above the horizon and when the zenithal sky glow is 21.3 MPSAS (which is not spectacularly dark.)

 

I independently 'discovered' these clouds back in the early '90s when reviewing my own wide angle milky way photos. I was fascinated to see dark clouds extending so far from the galactic equator, out to 20 or so degrees latitude. Immediately after seeing their photographic aspect I looked for them on the next dark night. Lo and behold! Not at all so difficult to see with no optical aid. My 2.3X41 "Owl Eyes" 'opera glass', with its 28 degree FoV, brings this structure out very nicely indeed.

 

Here's one image I found with a Google Search which shows the flare clouds fairly nicely.

 

https://www.flickr.c...oc/16795349376/

 

There is a broken series of clouds running from LeGentil 3 (the big dark cloud between IC 1396 and the N. Am. nebula) up to the denser part in NE Cep. The latter, corresponding to your plotted portion, has a notable curvature in its large-scale aspect, which is evident to the unaided eye.


Edited by GlennLeDrew, 22 February 2017 - 01:47 PM.

  • AllanDystrup likes this

#62 Larry Mc

Larry Mc

    Mariner 2

  • -----
  • Posts: 201
  • Joined: 29 Sep 2008
  • Loc: Pittsburgh, PA.

Posted 22 February 2017 - 07:42 PM

hi Allan,

This continues to be a great thread on observing OB Associations with your sketches, and lots of interesting info from Glenn. Here's my contribution to the Cepheus discussion, a sketch I made back in September 1993 of Cep OB2-A made with my little 80mm f4 University Optics 'Super-finder' using a 24mm Konig eyepiece & amici prism:

My description was "18 stars counter, two bright triangles with fainter stars interspersed".

 

Attached Thumbnails

  • OBCCEPHS.GIF
  • Cepob2s.gif

  • AllanDystrup likes this

#63 Larry Mc

Larry Mc

    Mariner 2

  • -----
  • Posts: 201
  • Joined: 29 Sep 2008
  • Loc: Pittsburgh, PA.

Posted 22 February 2017 - 08:04 PM

hi all,

Regarding the Collinder Clusters, back in June of 2014, I wrapped up an observing project, capturing all of the possible 348 objects (out of 471 total) that are visible from my Pittsburgh, PA latitude of +40.

(in addition to my backyard observatory site, the project also includes observations from Cherry Springs State Park and Calhoun Park in WV). Here's a link to the webpage: http://www.stellar-j...linder-tour.htm

While I have a number of sketches made for Collinder Clusters, most of these objects were observed after I had transitioned to StellaCam deep-sky video cameras. A number of CR objects are quite large, for CR65, I ended up using an Orion 50mm 'guider' to video-capture that particular large, sparse cluster. It would be a suitable visual object for small rich-field telescopes.

Here's the pic: (StellaCam-II @ 8 seconds)

Attached Thumbnails

  • cr65-09052013.jpg

  • Dave Mitsky and AllanDystrup like this

#64 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 23 February 2017 - 08:05 AM

Ed,

     OB associations are unbound moving groups of young, giant hot stars. The classification is done by astrometric analysis of parallax data, where the kinematics of the groups (the "perspective" from earth) allow this. Beyond ~500 pc, the paralaxes are of limited use.
 

     CR 65 does not have any type-O stars, but it does contain some of type-B, and as the distance to these is ~310 pc, it is possible to determine their parallaxes. On the basis of Hipparcos data, a recent 3D map of the OB stars within 500 pc from the sun shows 3 major "blue streams" of the massive young stars in Sco to CMa (incl CR 135), Vela (incl Tr10), and Orion. These streams are what shows up as the Gould Belt in 2D projection.

 

     Between the Orion stream and the Taurus MCs is a more dispersed OB stream (proposeded named as the "Taurion" part of the Cas-Tau OB-association), that includes some of the bright type-B stars in CR 65 (such as 113,115 and 116 Tauri). Collinder 65 thus does not seem to be an evolutionary or kinematic entity, but rather a chance alignment (asterism) in our night sky. As Glenn has well described, it is indeed another "spurious" Collinder object.
__________

Glenn,

     Yes, you're right, thank you for the correction! The denser part of the Cepheus Flare molecular cloud complex seems to be centered around 21h30m, +71 dg, above the line connecting 16 Cep and Bet Cep, and as can be seen from the photo you linked to, the structure bends from here well up NE and down SW. Alas, my suburban night skies have never allowed me to see this. I will have to travel to darker skies!

 

__________

Larry,

     Thanks for sharing your OB-observarions! You have captured a 2*45' FoV NE of (and including) Nu Cep, -- the center of Cep OB-2, and right between the OB-2a and OB-2b sketches I made. Nice :)

 

     Your collection of Stellacam images of clusters and DSOs is a treasure chest, and I very much enjoy browsing them and comparing them with my own visual and electronic observations.

 

 

Allan


Edited by AllanDystrup, 23 February 2017 - 08:19 AM.


#65 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 23 February 2017 - 09:04 AM

CEP OB-6

  

  The Cepheus OB-6 association was described relatively recently in 1997, based on new data from Hipparcos. At a mean distance of ~270 pc it is considerably closer than the CEP OB 2-3-4 associations (~800 pc), and can thus be considered part of the Gould Belt formations.  It is a moving group of ~20 stars showing a modest concentration. The earliest spectral type is B5  (suggesting an age of ~50 Myr), and the brightest members are the 3.4m type-K1 supergiant Zeta Cep plus the ~4m  Delta Cep

 

     Delta Cepheus is a wide double star, already split in the A (4.1m—5.2m type F5-G3) and the C (6m type B8, Sep 40.6” @ PA 191°) components at 23x in my rich field view (the B component is a faint 13m type-G0 star with sep. 21" @ PA 284°).

 

      Delta Cep A is of course the prototype of pulsating Cepheid stars, -- yellow (super)giants varying in brightless like a clockwork from 1-135 days, and showing a strict relation between the variation period and their absolute magnitude. As the period of Delta Ceph A is 5.3 days, corresponding to an abs. magnitude of -2.9m, its distance can be calculated to 1030 ly (~ 300 pc).

 

     The strong stellar wind from Delta Cep creates a bow shock where it collides with the surrounding interstellar medium; The shock wave is ionized by the hot B8 C-companion in the system :

Delta Cep.jpg

 

 

     In the drawing of my rich field view, I was able to spot 12 of the 20 probable members of Cep OB6; I have indicated these stars of the moving group with a small line (like a comet tail) on my drawing.

 

     Most of the remaining members of OB6 are primarily  located to the E and N of my drawing (7 stars), while one star is outside the field to the SW.  This illustrates the difficulty of catching large structures like stellar associations, extended nebulae and star clouds in one field of view, even using a rich field telescope (without panning). A good pair of binoculars is a nice supplement to the RFT for providing even more context, and I would like to also have a night vision device in my tool box, -- had they not been so darn expensive.

 

CEP OB-6 Black-S.jpg

*click*

 

Allan



#66 GlennLeDrew

GlennLeDrew

    Hubble

  • *****
  • Posts: 15849
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 23 February 2017 - 12:56 PM

Allan,

I'm given to understand that the spectral type cut-off where sufficient UV is present to ionize at least hydrogen is about B2.5. A B8 star should be quite incapable of inducing any sensible ionization. Is this how shock for delta Cep revealed in the IR, as are those for a number of other cool stars emitting significant winds? If so, we are seeing the signature of warmed dust.


  • AllanDystrup likes this

#67 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 23 February 2017 - 02:10 PM

Glenn, thanks again !

And yes, you're quite right, -- with the B8 companion of Delta Cephei it's not UV radiation causing ionization of the bow shock in the ISM, but rather, as you describe, intense heat from the C-companion, that causes dust in the shock wave to emit radiation in the IR part of the spectrum.

 

Pardon me, I'm learning as I go (and happy to be put on the right track, when I am derailed)... :)

 

Allan


Edited by AllanDystrup, 23 February 2017 - 02:21 PM.


#68 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 24 February 2017 - 09:00 AM

A 3D view of our solar neighbourhood OB stars.

 

 

     I've been playing a little with the hipparcos data for OB stars, as presented in the interactive 3D map developed by Bouy & Alves in their recent article (both are warmly recommended).

 

 

     Here's a view I found useful. I've marked the 3 major "blue streams" of OB-stars, they identified in their analysis :
 

  1. The Scorpius to Canis major stream (Sco-CMa), 350 pc long with age >65 Myr
  2. The Vela stream (Vel),150 pc long and age >35 Myr
  3. The Orion stream, 300 pc long and age >20 Myr

OB-Cosmography-2S.jpg

*click*

 

     Several smaller OB-associations and clusters emerge naturally within these streams (Per OB3, Sco OB2, Vela OB2, Vela OB5, Tr 10, Pleiades, Hyades etc).

 

     The blue streams (esp. the old Sco-Cma stream) show an age sequence indicating a line of star formation propagation :

 

OB-Cosmography-1S.jpg

*click*

 

     Furthermore the streams seems to be flanked by young associations as well as remnant clouds. I've tentatively marked the location of two new young proposed associations bordering on the outer edge of the Orion stream:

  • Monorion OB, 15 B stars
  • Taurion OB, 26 B stars, age 10-40 Myr

 

     This study indicates, that the Gould Belt - as it can be traced on sky images above (Fig. 4) - is an artefact of the 2D projection, and not a solid physical reality. This also seems evident, when you play with the interactive 3D-map of the OB-stars.

 

 

Allan

 

 



 

 


  • mwedel, Ohmless and Millennium like this

#69 GlennLeDrew

GlennLeDrew

    Hubble

  • *****
  • Posts: 15849
  • Joined: 17 Jun 2008
  • Loc: Ottawa, Ontario, Canada

Posted 24 February 2017 - 11:05 AM

Extended structures of age several tens of millions of years will not necessarily take on such a neat arrangement as the schematically represented Gould Belt ellipse commonly drawn. Variations in density of the ISM will differentially retard the propagation of gas fronts and shocks. And star formation will not necessarily tidily propagate in an organized, expanding ring. The result is expected to be a certain degree of 'raggedness' in the distribution of gas clouds and stellar associations.

 

I myself am not so quick to discount the Gould Belt as a kinematic structure just because of the seeming disarray evident in the locations of its purported constituent sub-groups. The organization and magnitude of the peculiar velocity vectors, especially with respect to the center of the system, would be more telling characteristics than the spatial arrangement by itself. The GAIA data should be a boon here...


  • AllanDystrup likes this

#70 Organic Astrochemist

Organic Astrochemist

    Viking 1

  • *****
  • Posts: 886
  • Joined: 10 Jan 2015

Posted 24 February 2017 - 11:37 PM

Great thread Allan.

 

I've got a couple of observations from more Southerly skies (I might see a bit further South if I took the telescope to the beach).

 

I was pretty intrigued by that Sco-CMa stream, but I couldn't see IC 2602 or IC 2391. Collinder 135 fit nicely in the one degree FOV at 100X. The color contrast of the B stars with the K-type supergiant (a former B-type cluster member) was striking. I could see NGC2451A completely with the 2 degree FOV of my 30 mm eyepiece at 40X (The view also included NGC 2451B, which also contains an K-type bright giant).

 

But things really got interesting with the Vela blue stream. Trumpler 10 was quite sparse, even at 200X, but NGC 2547 had many bright stars. I found some early B stars in the newly proposed Vela OB5 and I assume that some of the B stars around gamma Velorum were members of the Vela OB2 association. But the star of show was gamma Velorum. This is a Wolf Rayet star, an evolved B-type star. It has blown away its outer atmosphere of hydrogen and reveals strong emission lines of helium and carbon. The star is so far South for me that I have to put my telescope at the side of my house on my front lawn to get over my neighbor's house behind me. Rather than trying to take an image of the spectrum of gamma Velorum, I observed it visually with my R-spec star analyzer 100. Because the star is so bright (1.78 m) I cranked up the magnification of the spectrum to 500X. Like little beads on the beautiful color spectrum, I could easily see three emissions of ionized carbon at 465 nm and 570 nm and helium at 588 nm (I had to check these values later). The first was blue, the second was yellow and the third was orange. It looked a little bit like this image . It was the best visual image I have seen with the star analyzer, which is better suited to imaging. Wikipedia calls gamma Velorum the "spectral gem of the southern skies" with good reason.

 

I really like how iconoclastic papers like the one you cited appear frequently in astronomy. The fact that they did not observe a Gould Belt, that there is no mechanism to form a belt, that they observe streams nearby and in other galaxies and they have a mechanism to explain the formation of streams looks to me like they are overturning and old paradigm.



#71 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 04 March 2017 - 05:24 AM

Orion Blue Stream

Monorion, MON OB1, OB2, NGC 2232

 

     Some further notes...
 

MON-01.jpg

*click*
 

      I’m realizing, that  to better understand the creation, evolution and spatial distribution of OB associations, I will benefit from also looking at ”both ends of the age spectrum” , ie.

  • at one end: the ISM (interstellar molecular clouds), from structures like large clouds, bubbles and rings, to smaller HII-regions and dark nebulae, and their embeddet young stellar objects (YSO: HH-globules and pre main sequence / PMS stars like T-tauri)
     
  • at the other end: the nearby moving clusters, such as the Pleiades, Hyades, Praesepe, Coma Berenices and the Sco-UMa clusters

 

    There is a progressive dissolution from YSO born in the ínterstellar molecular clouds, over tightly bound clusters in galactic nebula, to loose open clusters surrounded by expanding OB associations, and finally to wide moving groups and completely unbound OB associations, scattering to galactic disc field stars. Many processes  contribute to this disruption, among others: stellar wind, radiation and galactic tidal forces.  

 

     "It’s complicated”, as the saying goes... wink.gif 

 

 

MON-02.jpg
*click*

 

MON-03.jpg

The proposed Monorion OB association with NGC 2232, plus the Monoceros OB1 and OB2 associations.
*click*

 

 

Allan


Edited by AllanDystrup, 04 March 2017 - 05:45 AM.

  • mwedel likes this

#72 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 04 March 2017 - 08:31 AM

     The weather in Denmark this winter has been relatively mild, which implies overcast and rainy, with a lot of haze and fog. And that, combined with a week of being down with the flu, means I've only had one chance for a quick observation of NGC 2232, -- I'll return to that later.

 

     I read the post from Organic Astrochemist with great interest, partly because it's a fine observation report, but also because the objects in the Vela and the Sco-CMa Blue Streams are totally or mostly impossible to observe from my 56* N Danish latitude. Oh, I'd love to have a closer look at the gamma Velorum WR star! (I also have an R-spec SA-100 grating).

 

     Now, the last week of March, I'll be flying to Osaka for a 7 day visit to my youngest son and his wife (who are both on a 1 year exchange study in Japanese at Osaka University); I do hope I'll get a night or two under the stars, and with a latitude of 43*41' 34*41' (thanks for the correction, Gary waytogo.gif), I will be able to have a look at the US and UCL parts of the Scorpius OB2 association. I also have made up a list of southern Messiers, that I hope to bag, -- but as I'm only planning on packing my Zeiss 10x56 Bino, some of these will be challenging, and will also depend on finding a good observing site with a reasonable view of the S horizon.

 

We'll see...

CS / Allan


Edited by AllanDystrup, 05 March 2017 - 05:44 AM.

  • mwedel likes this

#73 vkhastro1

vkhastro1

    Apollo

  • *****
  • Posts: 1201
  • Joined: 21 Aug 2005
  • Loc: Vankleek Hill, Ontario, Canada

Posted 04 March 2017 - 04:12 PM

Hi Allan,

 

Just a little correction on your last post #72 concerning Osaka's latitude.

It is 34*41' N.

 

FYI  love your articles - already photocopied all your OB Association charts on 8.5" x 11" paper and placed in plastic glycene sleeves in a 3 ring binder ready for observing. Just waiting for our present cold spell ( clear and very cold -30*C wind chill) to end.

 

Gary


  • AllanDystrup likes this

#74 AllanDystrup

AllanDystrup

    Apollo

  • *****
  • topic starter
  • Posts: 1491
  • Joined: 27 Sep 2012
  • Loc: Denmark

Posted 05 March 2017 - 05:31 AM

Hi Gary,

 

     First, thank you for the kind feed back, -- I'm glad to find a few that share the same interests as me in astronomy, and who find my notes of use for planning their own explorations of the universe smile.gif.

 

     And then of course, you are quite right with respect to the latitude of Osaka!! Thank you for the correction.waytogo.gif

 

     Here's an overview of the Scorpius-Centaurus part of the Sco-CMa Blue Stream, as I hope to be able to view it from Osaka later this month :

 

Sco-Cen (Sco OB2) association - OSAKA overview.png
*click*

 

Allan


Edited by AllanDystrup, 05 March 2017 - 05:39 AM.


#75 mwedel

mwedel

    Goofing off

  • *****
  • Posts: 1180
  • Joined: 16 Dec 2007
  • Loc: Claremont, CA

Posted 05 March 2017 - 05:04 PM

     Now, the last week of March, I'll be flying to Osaka for a 7 day visit to my youngest son and his wife (who are both on a 1 year exchange study in Japanese at Osaka University); I do hope I'll get a night or two under the stars, and with a latitude of 43*41' 34*41' (thanks for the correction, Gary waytogo.gif), I will be able to have a look at the US and UCL parts of the Scorpius OB2 association. I also have made up a list of southern Messiers, that I hope to bag, -- but as I'm only planning on packing my Zeiss 10x56 Bino, some of these will be challenging, and will also depend on finding a good observing site with a reasonable view of the S horizon.

You'll be very close to my latitude, just on the other side of the Pacific. If you do get a spot with a good southern horizon, Vela is wonderful in the early evening, Scorpius is good before dawn, and Omega Centauri and Centaurus A are fun to look at just after midnight - although a little farther afield than your titular interest.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: classic, dso, equipment, eyepieces, LP, observing, observing report, refractor, sketching



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics