Spatial distribution of bright stars

[selden]

This Addon displays the positions of 69 O, 7101 B, and 3366 M stars in the Hipparcos catalog. It can be used with Celestia v1.3.0 or later.


http://www.lns.cornell.edu/~seb/celestia/hip-obm-stars.zip (264KB, 10Mar04)

The intent of this Addon was to find out if there is any obvious indication of the local galactic arm in the distribution of stellar positions. Since there were very few O stars in the sample, type B stars were presumed to be the best tracers of regions of recent stellar formation. Type M stars were included just to see what the difference in their distribution might be.


What? I should tell you what happens??

[Cham]

I'm not sure to understand, Selden. I tried this addon and many of the stars in the addon was already there in my version of Celestia. For example, I now have two HIP 112078, two HIP 109789, etc, and the info isn't exactly the same. In the case of HIP 112078, I get one star with a Radius of 83.99 Rsun, and near it, there's another star with the same name but with a Radius of 14685.02 Rsun. I don't understand.

[marc]

Hi Selden, you might like to have another look at my mysql addon.
You can perform all sorts of queries on the star database that can mark, delete and change stars.
There is even code which will write new stars.dat and starnames.dat after you have made changes to the database.

For instance to do something similar to the above you could use any of the following queries.

show only these stars.
LOAD STARS WHERE spectralClass='O' OR spectralClass='B';

delete all the other stars and make a custom stars.dat (reload after in standard celestia)
DELETE FROM stars WHERE spectralClass!='O' AND spectralClass!='B';
TO DAT FILE;

or even highlight a certain class of star
UPDATE star SET absoluteMagnitude=absoluteMagnitude-5
WHERE CONCAT(spectralClass,luminosityClass,spectralSubClass ) = 'M9V';

There are a lot more examples in the documentation. Though to get the most out of it you may need to learn a little SQL.

Here is what is available in the star table. Ignore the breathable and seed columns, they are for the system generator.

Code: Select all

describe star;
+---------------------+---------------------------------------------------------------------+------+-----+-------------+-------+
| Field               | Type                                                                | Null | Key | Default     | Extra |
| 0                   | 1                                                                   | 2    | 3   | 4           | 5     |
+---------------------+---------------------------------------------------------------------+------+-----+-------------+-------+
| hip                 | int(11) unsigned                                                    |      | PRI | 0           |       |
| hd                  | int(11) unsigned                                                    | YES  |     | NULL        |       |
| RA                  | float                                                               |      |     | 0           |       |
| declination         | float                                                               |      |     | 0           |       |
| distFromSol         | float                                                               |      |     | 0           |       |
| absoluteMagnitude   | float                                                               |      |     | 0           |       |
| starType            | enum('Normal Star','White Dwarf','Neutron Star','Black Hole')       |      |     | Normal Star |       |
| spectralClass       | enum('O','B','A','F','G','K','M','R','S','N','WC','WN','?','L','T') |      |     | ?           |       |
| spectralSubClass    | tinyint(4) unsigned                                                 |      |     | 0           |       |
| luminosityClass     | enum('Ia0','Ia','Ib','II','III','IV','V','VI')                      |      |     | Ia0         |       |
| parallax            | float                                                               |      |     | 0           |       |
| parallaxError       | tinyint(4)                                                          |      |     | 0           |       |
| mass                | float                                                               |      |     | 0           |       |
| bolometricMagnitude | float                                                               |      |     | 0           |       |
| radius              | float                                                               |      |     | 0           |       |
| rotationPeriod      | float                                                               | YES  |     | NULL        |       |
| temperature         | float                                                               | YES  |     | NULL        |       |
| systemType          | enum('Single','Binary','Ternary','Quaternary')                      | YES  |     | NULL        |       |
| breathable          | tinyint(4)                                                          |      |     | 0           |       |
| seed                | int(10) unsigned                                                    | YES  |     | NULL        |       |
+---------------------+---------------------------------------------------------------------+------+-----+-------------+-------+
20 rows returned
(0.39 seconds)


regards. Marc.

[selden]

Chan,

The addon is a selected list of stars that are in the Hipparcos catalog. I didn't change the numbering. All of them are duplicates of stars already in Celestia. As a result, there should be two of every one of those stars after you've installed the Addon.

I used the RA, Dec and parallax values that are in the Hipparcos catalog, so their positions should be exactly the same as are in Celestia. I'm not sure where the position errors are coming from. We had a long discussion of this some months ago, but I'm beginning to think that indeed the positions do need to be precessed from the nominal Hipparcos date to J2000. It should be a relatively small effect, though.

Since I arbitrarily set the brightness of all of them to be -13, Celestia calculates an unrealistically large radius for all of the stars that are included in the addon. That's a side-effect that's irrelevant to the question being studied:

Does the distribution of the positions of type B stars reveal any structure that might be related to the position of the sun in the local spiral arm of the Milky Way?

[selden]

Marc,

I created this addon because I know a lot of people don't have your SQL addon installed.

I've considered using the SQL addon several times, but the description on the Web page seems to imply that it's only for Celestia v1.3.0. Is that's not the case, you might want to add a statement about it. Since I'm running 1.3.2p5, I'd rather not take the risk of trashing it and having to spend time restoring things, or of setting up a "sandbox" just to test the compatibility.

Also, I have no experience in writing SQL queries, so that's another language to learn. Fortran IF statements, on the other hand, I grok quite well

[Cham]

Thanks for the explanation, Selden.

I feel a bit unsafe, because of the discrepencies in stars position. Most of my double stars are displaced a bit from the original one. I understand there are uncertainties in star postion, but to what extent is the stars.dat reliable ? I would feel very unconfortable with arbitrary distributions in distances from Sol.

This brings me to another question. There are some stars cluster addons, like the M4 cluster. There is a huge pack of stars in this one. Are their position reliable, in the cluster ? Or maybe their distance from Sol were choosed arbitrarily by the addon author, just to make a beautifull addon ?

There is another stars cluster addon (I can't remember which one), related to some nebula (I think it's the Crab nebula or the Rose nebula). All stars in this addon are placed on a perfect imaginary plane, located at about 7000 ly from Sol. Their angular position is surely reliable, but their distance aren't because of that plane correlation. Do we know their actual distance ? In this case, I suppose the distance is very hard to mesure, because of the nebula presence.

[selden]

Thanks for the explanation, Selden.

I feel a bit unsafe, because of the discrepencies in stars position. Most of my double stars are displaced a bit from the original one. I understand there are uncertainties in star postion, but to what extent is the stars.dat reliable ? I would feel very unconfortable with arbitrary distributions in distances from Sol.

I'm not quite sure what "discrepancies" you're feeling uncomfortable with.
A quick check of a few stars seems to indicate that their positions are different only in their distances from the Earth, and that they differ by only a small fraction of the total distance, typically less than 1 part in 10,000 (less than 0.1 LY out of 1,000). This is easily explained by minor differences in how the distances were calculated (I used single precision and Fortran, not double precision and C++). Remember, the uncertainty in Hipparcos' measurements of the distances to the stars is much worse than that -- often light years even for the relatively nearby ones, and hundreds of light years for the more distant ones.

This brings me to another question. There are some stars cluster addons, like the M4 cluster. There is a huge pack of stars in this one. Are their position reliable, in the cluster ? Or maybe their distance from Sol were choosed arbitrarily by the addon author, just to make a beautifull addon ?

Sorry: I have not the slightest idea. You'll have to provide the details of where you got the Addon. I don't know them all by heart
The WebDA database of open clusters often can be used to get RA and Dec values for many cluster members, but even so, the precision of the values may be worse than you seem to be expecting. Often astronomers can guestimate the distance to a cluster, but individual distances of the members is very unreliable.

There is another stars cluster addon (I can't remember which one), related to some nebula (I think it's the Crab nebula or the Rose nebula). All stars in this addon are placed on a perfect imaginary plane, located at about 7000 ly from Sol. Their angular position is surely reliable, but their distance aren't because of that plane correlation. Do we know their actual distance ? In this case, I suppose the distance is very hard to mesure, because of the nebula presence.

Right. For example, the absolute luminosities of the stars are very hard to determine: the amount of attenuating gas is different between us and each of the stars.

[maxim]

Cham,

The M4 Cluster was AFAIK originally published by Rassilon, and was generated using his star system generator. Thus the individual members should be completely random.

Marc,

I really like your Celestia SQL Engine, but I still don't unterstand, why it isn't yet part of the standard distribution or at least pluggable to it. I would for example appreciate script access to the SQL Interface for stunning shows of dependencies that selden currently has to assemble by boring handwork. Furthermore SELECT Statements can be shared like cel:URLS and SQL Server could share their data via network.

Well, hopefully looking into the future...

maxim

[marc]

Selden, the addon should work with the new version but I cannot gaurentee anything as I haven't tested it. (ill put this on the web page) Its not really an addon as such as it has its own executable, config and datafiles. If you want to do a fake installation you can create a dummy celestia.exe in any folder then install the addon to it, so you can look at the files.

Or if you have the bandwidth 0.2.0 installs to its own directory and is independent of celestia.


Thanks Maxim. Whether it gets added or not is up to the developers, and how many people really want it. Adding it permanently would require many more hours of work, and I'd rather spend my time on MH. It will also add a new (and quite large) dependency to Celestia. The installer would be larger and the start up time would be slightly slower. Also to do it properly stars.dat would need to be discarded which might cause an uproar.