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WANTED: search access to a) Spectra b) Space Velocity

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#1 silv

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Posted 10 January 2019 - 02:19 AM

Hi Folks, 

 

does one of you guys know databases where I can search for a star's name and get space velocity and spectrum?

 

whenever a beautiful asterism enters my eye piece looking like a precious diamond necklace or an abandoned construction site of a highway, my imagination is triggered, and while looking at it, I make up a story of why this string of stars came into being right THERE where it is. It's one of my special enjoyments in our hobby. 

The Coathanger, Collinder 399, fitting wonderfully into 12.5x magnification eyepiece,  was my first such discovery. Doesn't it look like a short section of a highway with an access loop? As if aliens had planned a bigger highway network and begun construction there - but then ran out of money? 

 

Usually, these diamonds on a necklace aren't actually related to each other but only asterisms, I assume. 

But some of them might all have been born in the same nursery far, far away. 

Reading about "moving groups" of stars on Wikipedia https://en.wikipedia...inematic_groups as well as in some scientific papers, I think the details to determine "real" from "fake" necklaces are

 

a) Spectra - if they look the same-ish, the stars have the same metallicity and that's one possible indication for their shared same origin

 

b) Space velocity. If the stars move with the same speed in 3D space, it could indicate a common point of origin.

From Wikipedia again "The components of space velocity in the Milky Way's Galactic coordinate system are usually designated U, V, and W, given in km/s, with U positive in the direction of the Galactic Center, V positive in the direction of galactic rotation, and W positive in the direction of the North Galactic Pole.[3] The peculiar motion of the Sun with respect to the LSR is[4]

(U, V, W) = (11.1, 12.24, 7.25) km/s,
with statistical uncertainty (+0.69−0.75, +0.47−0.47, +0.37−0.36) km/s"

https://en.wikipedia...Space_velocity 

 

 

 

Now I am looking for a data source where I can look up those details for each star, spectrum and space velocity. 

I installed GaiaSky which is a visual 3D interpretation of the GAIA DataRelease2. https://zah.uni-heidelberg.de/?id=660 (Freeware running on Windows, Mac and Linux) 

 But the graphical user interface doesn't include fields for the information I require. I assume, I would have to add more fields manually to the GUI and then feed information by loading further catalogs. I don't know yet if this is possible. 

 

Or - does one of you guys know databases where I can search a star's name and get space velocity and spectrum? 

 

Thanks a million smile.gif

Annette


Edited by silv, 10 January 2019 - 02:38 AM.


#2 silv

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Posted 10 January 2019 - 02:34 AM

GaiaSky is rather great. It enables us to drive through our galaxy (and other galaxies if we load more catalogs, I assume) and look at everything from different angles in 3D. 

 

I only have an old  MacbookPro from 2011. It's so old it doesn't fulfil the hardware requirements for any 3D cruising application. Not even GAIA Sky's. 

But where other programs fail installation procedure, Gaia Sky succeeds. And it works quite beautifully, too! Instantaneous reaction to mouse manipulation, no lagging.  The default setting to let the program decide which performance parameters to choose according to the hardware apparently works wonders. I am very happy!

I haven't fully understood how to use it yet. 

Even with the "Large" catalog of 15GB it doesn't know the searchable object Collinder 399, the Coathanger. I would really like to cruise around that abandoned highway section, see what it looks like from a different POV. Maybe a "very large" catalog includes this object - but I'd have to run that from an SMB network drive for lack of free space on my internal drive. Not sure if GAIASky catalog data is supposed to run from network drives. Am in the process of testing that... 

 

Or...

I'd have to learn to navigate properly so I can locate Coathanger in the 3D display... haven't figured out yet how that works. But it would work, I am sure.    


Edited by silv, 10 January 2019 - 02:37 AM.


#3 rekokich

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Posted 10 January 2019 - 03:04 AM

www.sky-map.org
allows you to search star fields and star names. Images are from the Palomar Deep Sky Survey 2.
For example, search for 75 Cyg

http://simbad.u-stra.../simbad/sim-fid
allows you to search for celestial objects by identifier.
For example, search for 75 Cyg, and you receive the spectral class and physical properties.

See this article on stellar spectroscopy. Stars of common origin and similar metallicity may have entirely different spectra based on their mass and surface temperature.
https://www.cloudyni...ctroscopy-r3006

Rudy



#4 robin_astro

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Posted 10 January 2019 - 11:34 AM

Probably the most complete source for spectral classifications is Brian Skiff's catalogue here

http://vizier.u-stra...eR?-source=B/mk

 

Metallicity does affect the spectrum (mainly the strength of the metal lines) but the largest differences are due to temperature. Surface gravity (mass and diameter) also significantly affects the spectrum.  

 

If you want to know what the actual spectrum of a specific star looks like then you can find very high resolution spectra of many stars in the ELODIE archive

http://atlas.obs-hp.fr/elodie/

and similarly a list of southern hemisphere stars of different types from UVES 

http://www.eso.org/s...rs_uptonow.html

 

For amateur spectra there is the BAA database

https://britastro.org/specdb/

or the ARAS database

http://www.astrosurf...se/DataBase.htm

 

 

You can get the radial velocity from SIMBAD  but note this is just the component of the velocity towards or away from us (negative means it is coming towards us), not the actual velocity relative to us so you cannot backtrack to say they come from the same point

 

Robin


Edited by robin_astro, 10 January 2019 - 11:52 AM.

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#5 robin_astro

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Posted 10 January 2019 - 11:45 AM

You might also be interested in this exercise where the colour (which is related to temperature and spectral type) for stars in clusters  are plotted against brightness.  (This is called a Hertzprung Russel Diagram and is a common exercise for students as it shows how stars which formed at the same time, have different temperatures (and hence different spectra) and evolve at different rates and in different ways depending on their mass.

 

http://www.atnf.csir...leiadesact.html

or perhaps better

https://web.njit.edu.../Lecture17.html

 

for example

 

Robin


Edited by robin_astro, 10 January 2019 - 11:50 AM.

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#6 silv

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Posted 11 January 2019 - 05:21 AM

Thank you, Rudy. 

 

And thank you Robin. From your information and links, I was able to figure out how the databases work, as in: how I can find and then view the plot of a recorded spectrum. Tricky to use, these tools are at first, when you don't have a clue what you're looking at or looking for, exactly.  

 

The stars of my diamond necklace, Corona Australis, and the abandoned highway construction site, Collinder 399, haven't been plotted, yet.  But that's not sooo important to me. Their missing spectra serves as a kind, little nudge: "do it yourself, Annette, and add your data to the crowd's at https://britastro.org/specdb/data.php ". 

Costly, though not out of reach for a saving goal, I reckon. 

In the meantime, I'll make use of your suggestions and read about how mass and other factors play into spectra. It's all fascinating, especially since I have this story in my head as a motivator. 

 

If, in the future,  I find information or databases regarding the space velocity U, V, W I might add it here in case other lay people are interested. 

 

For the known "moving group R CrA " , that's "around" the area of Corona Australis, the common space velocity is 

 

(U, V, W) = (−3.8 ± 1.2, −14.3 ± 1.7, −8.3 ± 2.0) km/s

 

as per https://arxiv.org/ab...o-ph/0105292v1 

 

I assume, the investigated stars aren't members of the asterism C-A, but unfortunately, the authors don't list the stars' names. Surely, such information re U, V, W, once computed, is not kept a secret and lost -  but enters some form of database?  

 

In any case, how U, V, W are determined/computed stays a fascinating but scary question. Maybe I'll be brave enough to pursue it even though it sounds like a lot of maths and formulae. Having the story in my head helps as a motivator here, as well. 

 

Thanks Annette


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#7 robin_astro

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Posted 12 January 2019 - 07:41 AM

Hi Annette,

 

Their missing spectra serves as a kind, little nudge: "do it yourself, Annette, and add your data to the crowd's at https://britastro.org/specdb/data.php ". 

Costly, though not out of reach for a saving goal, I reckon. 

 

If you do decide to take the plunge and have a go at spectroscopy then there are several other active spectroscopists besides me on this forum who can be found here in the Observational Astrophysics section.

https://www.cloudyni...l-astrophysics/

Amateur spectroscopy has advanced considerably in the past 5-10 years and there is a lot that the amateur can do in this area these days

 

Cheers

Robin




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