676 replies to this topic

[AllanDystrup]

     Thanks a lot, Matt, for drawing my attention to the Vela area in the early evening sky. This has prompted me to research a little further south in the SCo-CMa blue stream and in the Vela stream. Here's what I've prepared for the Osaka trip:

 

http://sci.esa.int/h...rs-interactive/

*click*

 

The Sco-CMa Blue Stream

     The OB associations and clusters inside this stream are spatially coherent and continous over ~350 pc,and they display an age and distance gradient, that clearly indicates a common origin,

• starting from the old open clusters in puppis (65 Myr NGC 2451A OC and 40 Myr Cr 135, at 400-350 pc),
• then down south through the 50-30 Myr OCs in Vela-Carina (IC 2391, IC 2602 and A-Car OCs, around 200 pc),
• then sequentially passing up through the large 15–20 Myr LCC and UCL associations (100-50 pc),
• to finally reaching the young and close (4 ∼ 11 Myr) USco.

The Vela Blue Stream.

     The OB associations and clusters in the Vela stream are a ~150 pc long and young (< 35 Myr) seperate ”clump” at the old end of the Sco-CMa stream; The Vela stream is at 300-400 pc distance,

• centered on Vela OB2 with the the 5-10 Myr young open cluster Gamma Velorum;
• It also includes the somewhat older (~30 Myr) OCs  : Tr 10  and NGC 2547.

*click*

 

 

     The Omega Cen GC and the Centaurus-A galaxy will be low on the S horizon, and I won't expect any detail in my 10x56 bino, -- but it would certainly be nice just to have a glimpse of these magnificent southern objects!!

 

Allan

Edited by AllanDystrup, 06 March 2017 - 08:37 AM.

[GlennLeDrew]

Allan,

The topmost illustration in your previous post is generated as seen from the direction of the Galactic south pole. Pretty much by convention such maps are presented as seen from Galactic north. In any event, a consistent scheme keeps the reader from having to do mental gymnastics when piecing together a fuller picture.

[AllanDystrup]

Glenn,

 

     Yes, you're spot on with your comment on the orientation of the view of the Sco-Cma and Vela blue streams in my previous post; The "normalized" way of presenting this data would have been as I did in this earlier post : http://www.cloudynig...ield/?p=7723891

 

     But I chose the southern galactic perspective very much on purpose. A great new option with the precision of the Hipparcos data is the posibility to model the data in 3-D, and hence to get a proper spatial understanding of the structures within a good ~100 pc horizon from our solar system :

https://sciencenode....d-star-maps.php
https://youtu.be/TU6RAjABX40
http://stars.chromeexperiments.com

 

     This degree of freedom has made it possible for me to choose a perspective, that matched my specific view of the night sky, and thus made it easy for me to directly correlate the spatial galactic structure with a projection of the structures as seen on my view of the celestial globe (as opposed to a standard N polar galactic projection). I do realize, that this may make it more difficult to mentally "overlay" my map with the traditional standard projections of 2-D maps in most previous scientific work, but I think it is time to move forward and fully exploit the possibilities offered by 3-D modelling.

 

     With the data from Gaia, we will be able to make 3-D models of our galaxy out to a distance of 10 Kpc, all the way to the galactic center, and to measure proper motions up to 20 Kpc. This will make possible new types of data presentation and analysis, that will (i hope) revoultionize our understanding of galactic structures.

 

Allan

Edited by AllanDystrup, 07 March 2017 - 02:23 AM.

[GlennLeDrew]

Allan,

To be sure, the 3-D representation benefits from a good choice of perspective. But if it comes down to a projection where the sight line is more or less parallel to the Galactic polar axis, and the viewpoint is fairly distant, the N and S directions are essentially mirror images of each other. There is no advantage to be realized by one over the other.

 

I gather your intent was to present an image that also somewhat resembles the arrangement in projection on the sky. This is only possible because the spatial arrangement is roughly similarly 'linear'; views of the structure from a variety of positions roughly perpendicular to its long axis would be superficially alike.

 

In the case of your graphic, rendering it as seen from the N and rotating it so that Upper Sco is at left and Vela to the right would achieve the same end, but without requiring the mental 'reversal' in order to integrate into the bigger picture.

 

To facilitate visualization, it pays to strive to adhere to projections as seen from a common hemisphere. By convention, this has the viewpoint N of the Galactic disk. And so to the extent possible, oblique views should also be generated as seen from the same side of the disk midplane as for the perpendicular sight lines.

 

Furthermore, and again where it does not conflict with some other requirement, a consistent orientation in azimuth pays dividends. For example, in a series of 'overhead' views focusing on smaller sub-structures, they and the overall big picture are quickly synthesized if Galactic longitude zero points always in the same direction (e.g., downward.)

 

Or if one is striving to relate things to an Earthbound perspective, in all illustrations the Sun could be located toward/at/below bottom center.

 

Just some suggestions to ensure quicker assimilation of information. Especially for those in the audience who don't yet possess our familiarity borne of careful study.

[AllanDystrup]

...

In the case of your graphic, rendering it as seen from the N and rotating it so that Upper Sco is at left and Vela to the right would achieve the same end, but without requiring the mental 'reversal' in order to integrate into the bigger picture.

 

To facilitate visualization, it pays to strive to adhere to projections as seen from a common hemisphere. By convention, this has the viewpoint N of the Galactic disk. And so to the extent possible, oblique views should also be generated as seen from the same side of the disk midplane as for the perpendicular sight lines.

...

Glenn,

 

     I thank you for the clarification, and I totally get your "point og view". I find it valid, and I will try to adhere to it, where I find it an advantage. If not, I will indicate my reason for deviating from the standard.

 

     So for example, here's what you would have preferred with respect to the USco-CMa blue stream (a N.Polar galactic plane rotated view):

 

http://sci.esa.int/h...rs-interactive/
 

 

     It would have worked for sure, but if you compare that to the S.Polar view I presented, you will find a better direct  match with the night sky in the S. Polar view. (take for instance the position of M7 relative to USCo, and the Orion Blue stream relative to Vela;  Also -- due to the N-S extension of the Vela stream perpendicular to the galactic plane, I find that the oblique S. Polar view gives a better representation of this structure).

 

     These are of course details, and as I indicated, I do agree with you in principle, but in practice I find it fun and educational to play with the degrees of freedom. It certainly has helped me get a better understanding of the large spatial structures in our solar neighbourhood, in 3-D and as projected on the night sky.

 

Allan

Edited by AllanDystrup, 08 March 2017 - 02:12 AM.

[GlennLeDrew]

Allan,

Indeed, your 'rectified' second rendering is instantly recognizable and fitting into my own mental map. It's exactly like looking at a globe of the Earth from the outside versus from the inside. (Try looking at a map of any familiar terrain in a mirror, and see how troublesome it is to deal with.)

 

That's why I argue for consistency.

 

While I understand the attraction of an external view that more resembles our own Earth-bound perspective, such can only ever be coincidental and superficial, and rarely enough at that. Better to let an actual sky chart attend to that (as you do provide), and to render the less familiar external 'God's eye' views in as consistent a scheme as possible.

 

By the way, have you tried out the freely available Digital Universe, available through the Hayden Planetarium? The software running it is called Partiview, short for Particle Viewer, and is OpenGL-based. You can edit or create your own databases, which is what I did. Indeed, the package now comes with my own OB Association data, which oddly enough was completely absent initially (but did include such esoteric stuff as neutron stars.) Check it out...

[AllanDystrup]

Blue Streams from Osaka...    

    

     Back from one week in Osaka, Japan. It was early spring, with a comfortable temperature ~15*C/60*F, and the town was just preparing for the "Hanami" festivals (cherry blossom viewing). We had mostly/partly cloudy weather during our stay, with just one night that seemed promising for star gazing.

 

     I found an observing spot on the top of a parking building close to our hotel, with a good view towards the south, and I sneaked up there with my 10x56 Zeiss bino, -- in stealth mode, through an opening in the fence, tip toeing (through the tulips...) behind the office of the parking attendant.

 

     The view was disappointing though. Orion was high up, the belt at ~31* altitude, but the NELM was only ca. 2^m (I could just see Kappa Orionis, but almost had to use averted vision for that!), and even with my 10x56 bino, the limiting magnitude was only ~4.5^m, so yes, I could trace the outline of Canis Major, but all fainter stars were drowned out. (Limbo-ing at Bortle 1-2/White, "how low can you go" ...?)

 

     The cause of the low transparancy was a duvet of haze hovering over the Osaka prefecture (2.8 mil citizens), -- as indeed over most of the Kansai metropolitan area (19 mil inhabitants, including Kobe and Kyoto). Osaka is situated in a "bowl" , with Osaka Bay towards the W, bordered by mountains up N, E and S. The haze is obvious when you look from the Osaka suburbs towards the close by mountains to the N, as shown here in the photo from our hotel room in Senri-bampakukoen (Suita, north of downtown Osaka):

 

 

     I think that if you want to look at stars in this region of Japan, you will have to move up in the mountains to get as high as possible above the dome of haze and city lights. I did find what seemed to be a good, dark observing site in the mountains N of Osaka University Minoh Campus, which is reachable by the monorail to Saito-Nichi station. But alas, I had neither the time nor an oportunity to try it out. Maybe some other time.

 

      This means that I'll have to proceed with my astronomy projects (including the classic rich field observations) here from my observation sites N of Copenhagen. I'm a little annoyed that I didn't get a chance to study the SCo-CMa and Vela blue streams from Osaka, and now that we're moving into spring, this study may have to be postponed to next winter. -- Instead it's time to direct my attention to the new OB-associations and DSOs lining up for springtime observation.

 

Allan

Edited by AllanDystrup, 02 April 2017 - 03:50 AM.

[AllanDystrup]

Cygnus Wide Field

    

     It has been a while since I set out on my Milky Way rich field journey with my small classic Vixen FL-55S/440mm refractor. Back in the winter early this year, I started with dipping my toe (refractor) into some of the Gould Belt OB-associations surrounding the local bubble (the Orion, Perseus and Cepheus OBs in the Orion Blue Stream), and I also tried for some OB-associations in the the Sco-CMa and Vela Blue Streams, as seen from Osaka (Japan) -- but the weather was against me.

    
     Now, today it's summer solstice, and we can begin to look forward to the end of nautical twilight (mid July) and to the end of astronomical twilight (mid August), which should allow me to venture a little farther out beyond the Gould Belt OB-associations, to the Cygnus wide-field structures in the local "Orion Spur" arm of the Milky Way.

    
     I hope to be able to travel from the near HII emission nebulae (NA & Pelican and the Veil in the Cygnus Loop) with the close by Cyg OB7 and OB4 associations, past the more distant dust clouds in the Cygnus Rift with the Cyg OB1, OB2 and OB9 groups in the Cygnus X region, to the most remote Cyg OB3 and OB8 associations. There are a lot of interesting nebulae, stellar groups and weird stars to study down our local arm of the galaxy, towards the large Cygnus Star Cloud, -- which should by itself be a great rich field object in my small scope.

    

*click HERE for larger .PDF version*

    

Allan

Edited by AllanDystrup, 23 June 2017 - 05:00 AM.

[AllanDystrup]

 

*click HERE for larger .PDF version*

 

Allan

Edited by AllanDystrup, 23 June 2017 - 04:59 AM.

[C.Hay]

Dear Allan,

 

I only just stumbled across this wonderful thread, otherwise I would have contributed earlier. OB associations have been the focus of my observing for the past three years. I have assembled all the material I could get my hands on - and yet you are clearly a much better researcher than I. You keep unearthing depictions I had not found. I stand in admiration.

 

With my co-author Rene Merting I have produced an observer's guide which, to my knowledge, is the only one that makes a serious attempt to present all the visually rewarding associations observable from 50°N. By "visually rewarding" I mean associations that contain at least two observable deep-sky objects in addition to individual stars. That excludes, for instance, Lac OB1.

 

I estimate there are about 25 of these from 50°N. We have profiled 17 of them in our Observer's Atlas, which is available free for download, in German, here:

https://www.freunde-...t/projekt-bafk/

The other half dozen are in progress.

 

In addition, we are assembling fuller presentations of OB associations on our website here:

https://www.freunde-...nassoziationen/

We have covered 8 associations there; others will follow. These contain nice illustrations that may benefit viewers regardless of whether they understand German.

 

I would be pleased if you could find these presentations helpful. Be that as it may, please keep up the good work on this great thread of yours!

 

Best regards, Christopher Hay

[vkhastro1]

Christopher,

I checked out your Observer's Atlas @ https://www.freunde-...t/projekt-bafk/

A very impressive catalogue with extensive observing info.

I downloaded the PDF (German language).

Tried using several German to English translation methods on my IPad without success.

Does anyone know how to perform this iPad translation to English?

 

Gary

[AllanDystrup]

Dear Christopher,

  

Thank you for the positive comments on my observation logs of OB associations!

  

     I have not been able to find much coherent and systematic information and presentation on wide field astronomy with a cosmologic structural and evolutionary perspective; This is a shame, as I often miss the broader context when observing isolated NGC/IC objects out there in the universe.

 

     There is however quite a lot of scientific data available on wide field astronomy in technical research papers and articles, and much can be studied and downloaded for free on the internet. This does require an effort in locating and piecing together the jigsaw puzzles of information in different wavelengths (X-ray, radio, IR, optical), kinematics, astrophysics etc. -- but I currently have the time and I find the task interesting (though I would have preferred if the topic had already been covered in a book by someone with an astrophysics background).

 

     I've had a look at your and Rene's https://www.freunde-der-nacht.net/ website, and I like the idea of compiling lists for each constellation of all visually interesting objects, including WR-stars, Be, BI and Bica groups plus wider field B and Sh nebulae and OB associations -- well done! (I read German, and I like your presentation). I especially applaud your project for describing the OB associations including photographic maps -- this is much along the same line of research, that I'm persueing as preparation for my observation of these objects.

 

     So I'll follow the development of your website with great interest. Also, of course, I hope you will contribute to this thread with new information and updates, that may help us all get a better grip on understanding and observing the fascinating wide field objects in our own galaxy.

 

Thanks and best regards,
Allan

Edited by AllanDystrup, 27 June 2017 - 02:01 PM.

[C.Hay]

Dear Allan,

 

Thank you for your comments about our website and various projects. I am delighted that you evidently share my interest in observing our galaxy in a structural and evolutionary perspective.

 

One of my main sources, by the way, is the Handbook of Star Forming Regions (2008, ed. Bo Reipurth). The table of contents of Vol. 1 is here: http://www.aspmonogr...e_of_contents/4

This is not made for observers, but does occasionally provide actual maps of the boundaries of associations - a rare thing! It also provides "normal" photos of many objects in visual wavelengths, which helps to link the text to the visual appearance of objects in the sky. The book is expensive, but many of the individual chapters can be found as free PDF downloads in the Web.

I notice you have used some of its Figures, but I thought I'd point the book out for others here.

 

I look forward to contributing to this thread wherever I can.

 

Best regards, Christopher

[AllanDystrup]

    

Cygnus Wide Field -- continued
    

     The summer of 2017 has been exceptionally poor here in Denmark, from an amateur astronomical point of view : cool, mostly overcast and lots of rainy nights. The "white nights" in June-July up here at 56° North, with perpetual nautical/astronomical twilight of course has just added to the challenges of night sky observation. There is however darkness at the end of the tunnel, as we are now entering August, where dark nights will start to return again, with the sun now sailing >18° below the horizon on it’s journey through the underworld.

 

     On July 30. the sky cleared up unexpectedly past midnight, and so I decided to resume my rich field observation project, which was put on hold somewhere in the Cygnus Superbubble after I returned from Osaka in April. My first stop in the Cygnus wide field area will be the Cygnus OB-2 association.

         

         
The Cygnus-X region of the CSB

    

     Cyg OB-2 is is embedded within the wider region of intense star formation and associated very strong emissions in IR and radio wavelengths: Cygnus X.  This region contains the largest molecular cloud (3M Mass _solar) and the largest number of massive protostars within 2 Kpc from the sun.

    

         

*click*

    

    

*click*
         

    

*click*

     

Allan  -- to-be-continued...

 

Edited by AllanDystrup, 31 July 2017 - 04:58 AM.

[AllanDystrup]

     Bright stars in the Cygnus OB2 Association

    

     For the wide field view of the Cyg OB-2 stellar association, I chose my ATC  K-32mm eyepiece, yielding 73x @ 0.66dg FOV.

    

     Of the central "Trapetzium" group, 3 components are immediately visible:

• Schulte OB2 #8AB (O6 If + O5.5 III plus O6.5 III), two giant type O stars, where A is itself double (not resolved)
• Schulte OB2 #8C (O5 If) hot supergiant
• Schulte OB2 #8D (O8.5 V + O9 V) upper main series type O binary

      

     In the field of view, around the central "Trapetzium" of Cyg OB-2, are scattered :

• Schulte OB2 #5 (O7 Ianfp + O fpe / WN9) Beta LYR eclipsing variable
• Schulte OB2 #7 (O3 If) supergiant, one of the hottest known stars in the Milky Way : 50 K Kelvin!
• Schulte OB2 #9 (O5.5 I + O3.5 III) massive binary with x-ray/radio shock waves from stellar wind collision
• Schulte OB2 #12 (B3.5 Ia), LBV hypergiant  pt. the visually brightest and most intrinsically luminous star known star in the Milky Way (M_bol -12.2, Mass_sol 110x)

     

     Well, it may not look of much when seen through the eyepiece, but it is just a jaw dropping view, when you know what you are looking at ... If that is not enough, you can take a hike -- and have a look at :

• NML Cygni (semiregular V1489)  located on the SE outskirts of Cyg OB2 (not included in my drawing). This is a red hypergiant, and one of the largest and most luminous (M_bol −9.0m)  cool stars currently known with a radius about 1183 x the Sun. Unfortunately its m_v is down at ~16.6^m, so it is beyond the reach of my 4" refractor.

 

*click*

 

Allan

Edited by AllanDystrup, 01 August 2017 - 04:12 AM.

[AllanDystrup]

     For a closer look at Cyg OB-2, I now switch to live video using my R2 ccd/lcd yielding ~215x mag at 0.17dg FOV.

    

     The AB of the OB-2 "Trapetzium" is now cleanly split in two components, and the central region of OB-2 including #7, #8 and #9 is nicely presented in the ~10' field of view :

 

    

*click*

 

Allan

[deSitter]

These are awesome reports! It's too bad the handboxes on go-to mounts don't have lectures like this, instead of simple lists of DSOs.

 

-drl

[GlennLeDrew]

Allan,

Being outside the Gould Belt system, I've not investigated in such depth these associations. Thanks for the inspiration!

 

Out of curiosity. Given the high degree of (variable) extinction, have you looked up the B-V color indices for the stars you're reporting on? Such O-types are intrinsically bluish, with B-V_0 of about -0.34. It would be interesting to know how much they're reddened and dimmed. For example, an intrinsc B-V_0 -0.34 star that appears to have a B-V 0.6 has a color excess E(B-V) 0.94. This equates to a visual extinction A_v = 0.94 * 3.1 = 2.91; a dimming by almost 3 magnitudes. (While not universally applicable due to differing dust grain composition and size, a value of 3.1 for total to selective absorption w.r.t. to B-V is a good enough first order assumption.)

 

Such perspectives further enhance appreciation of what we see.

 

I've said it before; you're well on your way to putting a book together. Thanks again for the detailed and inspirational work!

[AllanDystrup]

     Thank you guys, for your kind words

 

     Glenn -- you have yourself to thank for my Rich Field Ramblings, as they are in no small way inspired by your very own writings! -- And yes, I did wonder about the dimming of the Schulte #stars, that I described above, -- but I had no quantitative handle on the stellar extinction, so thank you for providing that calculation!

 

     More on that below, but first a little more info on the Cygnus OB-associations; Cygnus OB4 has poorly determined properties, and OB 5-6  are thought to be artificial associations due to projection and selection effects (click for larger images...):

 

 

     As can be seen in the illustrations above, CYG OB-2 is "hiding" behind the IMC of the Cygnus Rift and the Cygnus-X region,--  thus the extreme dimming of the giant newborn stars. I learned something new today (thanks again Glenn! ), so I calculated the visual extinction of the stars in CYG OB2, that I have observed. The extinction ranges from 4.2 up to a mind blowing 10.7 magnitudes. -- A funny thing is, when observing the association using my colour camera in live video, sometimes - depending on the camera settings and the seeing - some stars (like OB2#8B and OB2#9) seemed to have an orange tinge, which I thought was weird given their hot O-type spectrum. I now think this can be ascribed to the reddening factor...

 

 

Allan

Edited by AllanDystrup, 01 August 2017 - 03:58 AM.

[GlennLeDrew]

Allan,

The final step when dealing with notable extinction is to indicate how bright a star (or cluster) would appear were it not for extinction. But of course that's mostly just a curiosity, not a crucial parameter. For instance, it puts things into some perspective whenever I bear in mind that the Double Cluster could have been as much as 1.5 magnitudes (a factor of four) brighter if we happened to have a fortuitous, clear 'window' to peer through over the 6-7kly along the line of sight to Per OB1.

[AllanDystrup]

.         

Cygnus OB-3

    
     It’s just past midnight local time (UT+2) in mid August, up here at 56°N in Denmark. I now have a window from 00:¹⁵ – 02:¹⁵ with full darkness, wedged between astronomical dusk/dawn. “Full darkness?” --  ahh well, in my suburban backyard with a 89% waning gibbous moon hanging up at 16° altitude in Aquarius towards the SE, my NELM is currently down at 4.9^m, and furthermore there’s a lot of  humidity in the air (97%), with a high haze reducing the transparency to ~3/7, -- and going downhill. So definitely not a night for DSO, but luckily I have my Rich Field project with some OB-associations waiting for me in Cygnus!

    

 

*click*

    

*click*

    

     I start with taking stock of NGC 6891 at the center of CYG OB3. As this is a fairly concentrated part of the association, a “rich field view” in this context means using my 25mm CZJ ortho eyepiece, which on my Vixen 4” refractor yields 93x @ 24” FOV. WOW…, this is a brilliant view, with the 10 brightest stars being 3 of type B1, 5 of type B0 plus 2 superhot luminous type O stars (HD 190918 and HD 192864). The bright stars are furthermore arranged in groups with a triple (ADS 13374) plus a double (ADS 13376) to the north and another pair to the south in the field. The triple is easily resolved into its AB-D-F components, as are the double into the A-D members.

    

    

To-be-continued...

Allan

 

 

 

 

[AllanDystrup]

.    

CYG OB3 -- continued

    

    

 

*click*

    

      I now zoom in on the N group of OB stars, switching to my 10mm ortho (for 233x @ 0.17° FOV). The brightest star in NGC 6871 is the AB member of ADS 13374 : a spectroscopic binary of a O9.5 Ib supergiant in tight orbit with a WN4.5 Wolf-Rayet star. (I plan to return to this WR-star later, for possibly studying it using my low-res spectroscope). The F-member is a type B0.7 Iab supergiant, whereas the D is a “normal” type B3 V main sequence star. Here’s the positional data for the NGC 6871 OB multiple systems:
 

ADS 13374

          AB-D : PA 301°, Sep 11.0”, M1 6.8, M2 9.5,  optical
          AB-F : PA    28°, Sep 34.7”, M1 6.8, M2 7.3,

    

ADS 13376
           D    :   HD  27634    M 7.89   B0.2 IIc
           A    :   BD+35 956   M 8.72   B0.5 Vne

 

     Sweeping the telescope now ½° to the NW, I find another bright member of CYG OB3: the double ADS 13312, also known as ∑2624. The intrinsically most luminous star in CYG OB3 is the close AB binary of ADS 11312: a O4 If supergiant with a bolometric abs. mag. of -10.2 in close orbit with a O9.5 giant. The positional data for the system is:

 

ADS 13312    
         AB  :   PA 175°,  Sep 1.9”, M1 7.1, M2 6.6, Spec O4 If, binary, close 366x

    

    

To-be-continued...

Allan

Edited by AllanDystrup, 13 August 2017 - 01:47 AM.

[AllanDystrup]

.

CYG OB3 -- continued

 

     

*click*

     

     Finally I switch to my small R2 cam for live video of these interesting OB3 multiple systems. The view at 215x with 5s integration and 30dB gain is beautiful, showing significantly more faint stars, -- but no further resolving of the components. The AB pair of ADS13312 is close to the resolving limit of my 4” telescope, and at times during the observation the pair do show signs of elongation in roughly the expected direction, but certainly no split of the components. It should surrender to higher mag. (~366x) and better transparency.

    

    

To-be-continued...

Allan

[AllanDystrup]

.

 

CYG OB3, X-1

 

     It’s now 02^AM, and the sky – “her face at first just ghostly, turned a whiter shade of pale” due to increased high haze, but I want to close the observation of CYG OB3 with what is possibly the most interesting object in this association: Cygnus X-1. This object was discovered back in 1964 as the brightest X-ray source in Cygnus, and its location (~½° NE of Eta Cyg) coincides with the 6 kly (1.9 kpc) distant type O9.7Iab star: HDE226868 (~9^m).

 

     As blue supergiants don’t radiate strong X-rays by themselves, a closer look at HDE 226868 did indeed reveal a massive spectroscopic companion: Cyg X-1, i.e. we’re looking at a tight (1/5 the Sun-Earth distance) binary system, with an orbiting period only 5.6 dy. An analysis of the spectrum and orbits showed HDE226868 to be of 30x M_sol and 400K L_sol, while its companion Cyg X-1 is a tiny, optically invisible, yet extremely compact object (~15x M_sol), -- way too small to be a normal or even a neutron star. It has to be a black hole with a Schwarzschild radius out to the event horizon of only ~44km!

    

*click*

    

    

     HDE 226868 (aka variable V1357 Cyg) is being tidally distorted by Cyg X-1 into a teardrop shape, causing its brightness to vary by 0.06^m in each orbit.  As the gravity of Cyg X-1 sucks material from HDE 226868’s outer stellar atmosphere into an accretion disk,  this matter is heated to millions of degrees, generating the observed X-rays, as it spirals into the black hole. A pair of jets perpendicular to the accretion disk are carrying part of the energy of the infalling material away into interstellar space, where it (at close to light speed) collides with the interstellar matter generating a visible bow shock to the NW of HDE 226868. The jet has been imaged in radio waves, and the bow shock can be detected in amateur astro photographies.

    

*click*
 

    

  Allan

Edited by AllanDystrup, 13 August 2017 - 04:53 AM.

[AllanDystrup]

.

CYG OB3  X-1

 

 

     Here's my wide field obs. of CYG X-1 at low mag (93x); I've indicated the position of the bow shock from the black hole's relativistic jet on the drawing (It can of course only be seen on photographs of the area).

 

*click*

 

Allan

Edited by AllanDystrup, 13 August 2017 - 04:55 AM.