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PostPosted: Tue, 27-09-16, 19:00 GMT 
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Thanks to Andrew's great scripting work, we now have a new stars.dat file with almost 2 million Gaia stars for celestia.Sci. First of all, it is of interest how these stars are distributed over the Milky Way neighborhood. For this purpose, I prepared two figures of the Milky Way region around our Sun (marked red as selection):
[Click on image by all means and then hit the browser's fullscreen key (F11?)]
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milky_gaia2.jpg
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or here in a different view:
[Click on image by all means and then hit the browser's fullscreen key (F11?)]
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PostPosted: Tue, 27-09-16, 19:47 GMT 
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One question raised in the thread in the Lounge is whether it is possible to identify the spiral structure of the Milky Way from the Gaia dataset. I have tried to do this by marking the OB stars: massive, short-lived stars that do not live long enough to move very far from their birthplaces, which should be concentrated in the spiral arms. With the dataset as it stands, this is not possible due to a large number of stars that are misidentified as OB-stars based on their B-V colour index. I am working on further updates to the dataset that may help correct this.

Watch this space!


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PostPosted: Tue, 27-09-16, 20:24 GMT 
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ajtribick wrote:
One question raised in the thread in the Lounge is whether it is possible to identify the spiral structure of the Milky Way from the Gaia dataset. I have tried to do this by marking the OB stars: massive, short-lived stars that do not live long enough to move very far from their birthplaces, which should be concentrated in the spiral arms. With the dataset as it stands, this is not possible due to a large number of stars that are misidentified as OB-stars based on their B-V colour index. I am working on further updates to the dataset that may help correct this.

Watch this space!


About two years ago I did quite a lot of research work to infer the MW spiral structure and extent from new kinds of data.
++++++++++++++++++++++++++++++++++
The point was to combine the new data on Massive Young Stellar Objects (MYSOs) and compact / ultra-compact HII regions with a complete set of published ATNF pulsar data, which largely increases the evidence for the arm structure from the RMS = Red MSX Source data alone.
++++++++++++++++++++++++++++++++++

I actually communicated several times with the RMS lead scientist Prof. J.S. Urquhart, who was so kind as to also send me their "hot" numerical data! Chris (ElChristou) helped actively on the graphical side.

Essential Literature:
===============
http://arxiv.org/pdf/1310.4758v1 (published in MNRAS 437, 1791–1807 (2014), link
http://mnras.oxfordjournals.org/content ... l.pdf+html
http://www.ast.leeds.ac.uk/RMS/
http://www.sci-news.com/astronomy/scien ... 01649.html

The RMS reference about MYSOs and compact / ultra-compact HII regions represents the cleanest recent evidence for a four principal arm structure of the MW (Norma, Sagittarius, Perseus and Scutum-Centaurus arms). Moreover, it provides lots of data tracing the so-called Outer arm in the region of present interest (II nd quadrant) (You remember that the Spitzer telescope claimed in 2008 to see only 2 principal arms...)

Here is a summary image from the above RMS paper:
[click on image by all means for a much bigger size!]
Attachment:
rms_MW.jpg
rms_MW.jpg [ 102.47 KiB | Viewed 1048 times ]


Soon more details...
Watch this space... ;-)

The MW template in celestia.Sci takes these new astronomical measurements into account!

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PostPosted: Wed, 28-09-16, 17:37 GMT 
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Perhaps these excerpts from an interview of Prof. Melvin Hoare (Univ. Leeds/UK) make the importance of MYSOs versus YSOs in the tracing task of the MW arms more transparent. Moreover, arguments are given below why Spitzer was missing two MW arms in 2008!

Prof. M. Hoare wrote:
The astronomers behind the new study used several radio telescopes in Australia, USA and China to individually observe about 1650 massive stars that had been identified by the RMS Survey. From their observations, the distances and luminosities of the massive stars were calculated, revealing a distribution across four spiral arms.
...
NASA’s Spitzer Space Telescope, on the other hand, scoured the Galaxy for infrared light emitted by stars. It was announced in 2008 that Spitzer had found about 110 million stars, but only evidence of two spiral arms.

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“Spitzer only sees much cooler, lower mass stars – stars like our Sun – which are much more numerous than the massive stars that we were targeting.”

Massive stars are much less common than their lower mass counterparts because they only live for a short time – about *10 million years*. The shorter lifetimes of massive stars means that they are only found in the arms in which they formed, which could explain the discrepancy in the number of galactic arms that different research teams have claimed.
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Since lower mass stars live much longer than massive stars and thus rotate around our Galaxy many times, they have time enough for spreading out in the MW disc. The gravitational pull in the two stellar arms that Spitzer revealed is enough to pile up the majority of stars in those arms, but not in the other two. However, the gas is compressed enough in all four arms to lead to massive star (MYSO) formation.


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PostPosted: Tue, 29-11-16, 20:40 GMT 
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Apologies for the lack of recent updates.

The generation of the star database now includes information from infrared magnitudes to estimate the properties of the stars with unknown spectral types.

As a result the "infamous" star I posted in the other thread comes out as an F6, which is a lot closer to the actual spectral type (F3V) than the previous estimate of K0. Adding the relevant star names to starnames.dat, it now looks like this...

Attachment:
File comment: View from the vicinity of Boyajian's Star
boyajians_star.jpg
boyajians_star.jpg [ 116.98 KiB | Viewed 852 times ]


The bright star in the background is Deneb.

I can't see any alien megastructures, I guess the light curve must have been caused by something else ;)


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