Typical star inside a planetary nebula

[Cham]

I need to know the typical AppMag and SpectralType of the star at the center of most planetary nebula. Is it a White Dwarf ?

What is the typical AppMag and SpectralType of a White Dwarf ?

[selden]

The stars in the centers of planetary nebulae are the cores of stars that used to be red giants but which have blown off their upper layers, forming the nebulosity. They're very young white dwarfs.

The apparent magnitude of a star depends on how far away it is, how much material is between it and us, and other factors. As a result, there is no typical value for AppMag.

I think it'd be easier if you used the absolute magnitude (AbsMag), which is a measure of how bright a star would be if it were 10 parsecs away with no intervening matter. White Dwarf stars tend to be rather dim, with absolute magnitudes between 10 and 13 or so.

There are spectral classifications which are specific to White Dwarfs, depending on what elements are visible in their spectra. In Celestia you can just use "WD" if you want.

You might find the "McCook-Sion White Dwarf Catalog" of interest. See
http://heasarc.gsfc.nasa.gov/W3Browse/all/mcksion.html
and
http://heasarc.gsfc.nasa.gov/db-perl/W3Browse/w3table.pl?tablehead=name%3Dmcksion&Action=More+Options

[Cham]

Thanks Selden.

Is there any White Dwarfs catalog for Celestia, a bit like your pulsars addon ?

[selden]

Unfortunately, the distances to most white dwarf stars are unknown.

There's one in Grant's nearstars.stc.

I found 22 in the Hipparcos catalog. They're already in Celestia. The STC file below makes them visible by setting their AbsMag to be extremely bright. I'll leave it to you to create an appropriate marker script.

I suspect the distances calculated by my program will be slightly different from the ones used by Celestia.

The spectral codes shown below are taken directly from the Hipparcos catalog. It looks like two of them may be misidentified: HIP 10267 and HIP 11644.

I think the white dwarf spectral types in Celestia have been updated to use current white dwarf classifications.

Code: Select all

#STC catalog of Hipparcos WD stars
 #converted to STC format by s.ball 16Dec04
   3829 {RA 012.28823784 Dec   5.39519787
         Distance     14.3715930551
         SpectralType "DG          " AbsMag -13 }
   8709 {RA 028.01232553 Dec   47.0015488
         Distance     51.7062920945
         SpectralType "DAs         " AbsMag -13 }
  10267 {RA 033.04014839 Dec   63.4983673
         Distance    290.4392816521
         SpectralType "DF          " AbsMag -13 }
  11644 {RA 037.55697441 Dec  -25.1865177
         Distance    347.3517444884
         SpectralType "DAn...      " AbsMag -13 }
  11650 {RA 037.56909300 Dec   5.26414061
         Distance     79.2620383732
         SpectralType "DA          " AbsMag -13 }
  12031 {RA 038.78144144 Dec   3.73243046
         Distance    242.6810343626
         SpectralType "DAwe...     " AbsMag -13 }
  14754 {RA 047.62898313 Dec  -68.6006851
         Distance     33.1130253807
         SpectralType "DA          " AbsMag -13 }
  23692 {RA 076.37752362 Dec   52.8313179
         Distance    224.4757783855
         SpectralType "DAw...      " AbsMag -13 }
  32560 {RA 101.90899326 Dec   37.5181313
         Distance     50.2485413031
         SpectralType "DAn         " AbsMag -13 }
  51280 {RA 157.11365720 Dec   5.81580782
         Distance    119.7368952792
         SpectralType "DA:         " AbsMag -13 }
  56662 {RA 174.27168180 Dec   29.7995529
         Distance     49.9637417431
         SpectralType "DA          " AbsMag -13 }
  57367 {RA 176.41359792 Dec  -64.8406754
         Distance     15.0722416451
         SpectralType "DC:         " AbsMag -13 }
  65877 {RA 202.55955416 Dec  -8.57370281
         Distance     58.7681621622
         SpectralType "DA          " AbsMag -13 }
  66578 {RA 204.71321916 Dec   70.2855148
         Distance     80.8736139825
         SpectralType "DA:         " AbsMag -13 }
  80300 {RA 245.89074946 Dec  -39.2294884
         Distance     41.7943741893
         SpectralType "DA          " AbsMag -13 }
  82257 {RA 252.10618044 Dec   59.0570183
         Distance     35.7909919708
         SpectralType "DA          " AbsMag -13 }
  95071 {RA 290.14566329 Dec  -7.66629124
         Distance     36.6146490004
         SpectralType "DAw...      " AbsMag -13 }
  97394 {RA 296.91877292 Dec  -42.0072327
         Distance    358.0277851722
         SpectralType "DB:p        " AbsMag -13 }
 101516 {RA 308.59226795 Dec   25.0651894
         Distance     48.2133470278
         SpectralType "DA          " AbsMag -13 }
 102207 {RA 310.64387351 Dec  -20.0764141
         Distance     68.8253437858
         SpectralType "DAw         " AbsMag -13 }
 107968 {RA 328.10570848 Dec   2.38950205
         Distance     81.8682978792
         SpectralType "DA:         " AbsMag -13 }
 115195 {RA 349.99335153 Dec  -5.16560078
         Distance    583.4763704774
         SpectralType "DA:         " AbsMag -13 }


[selden]

You might want to take a look at http://astro.estec.esa.nl/Hipparcos/venice-proc/poster03_24.pdf
"White Dwarfs Observed by Hipparcos" by Vauclair et al. They made a more careful search for white dwarfs in Hipparcos than I did just now, so their list of 20 stars is slightly different.

[Cham]

Ok, so White Dwarfs distance can't be trusted.

Selden, I placed a generic white dwarf in the center of most nebulae from your 73 Planetary_nebulae addon, under the clear hypothesis that all planetary nebulae are formed by a red giant which turn itself into a white dwarf.

[selden]

Cham,

That sounds quite reasonable.

You also could use Simbad to look up the planetary nebula. The "plot around" function might include a reference to the central star and more information about it.

[Cham]

Selden,

what exactly is the maximum distance from Sol, to put a star in Celestia ? Many of your planetary nebulae are pretty far from Sol.

[selden]

Cham,

Unless Chris has changed how it is done, stars can only be drawn reliably to a distance of about 16,000 LY. See the Preliminary User's FAQ, Q/A #12.

[Cham]

16,000 ly, that's what I believed. But then it's strange, as some of my hypothetical white dwarfs are showing at about 24,000 ly from sol (but not more), and others aren't showing at about 19,000 ly. ???

[selden]

They aren't drawn reliably. Sometimes you can see them and sometimes you can't.

[Cham]

Do you mean that a particular star, at say 20,000 ly from Sol, could be seen once, and after I restart Celestia, I may not be able to see it again ? And it may reappears if I restart Celestia another day, randomly ? Doesn't make sense to me.

Or are you saying that randomly chosen stars above the 16,000 barrier may appears and some others not ?

[selden]

I mean that as you change your viewpoint, stars which are more than 16KLY away from the sun and which should be visible (because they're bright or because they're close to your viewpoint) will appear and disappear unpredictably.

[Cham]

I didn't saw this effect.

What I saw is this : Some stars are showing normally (whatever the viewpoint), and some others just don't show themselves, whatever the viewpoint. Apparently, there's no clear limit. It appears to be spreaded between 16,000 ly and 20,000 ly. Some stars located between 16,000 and 20,000 ly are showing, some others not. It's weird.

Anyway, I placed a total of 53 white dwarfs in you planetary nebulae and they are all showing fine. The 20 other planetary nebulae doesn't accept a star (distance around 20,000 ly or more).

[Brendan]

Could it be because of the limited precision of floating point numbers? With the RA and Dec coordinates and limited precision, the density of stars allowed by the precision gets lower the further away from the origin you are. Would the recent change to xyz coordinates have any impact on that?

Brendan

[Cham]

This is a good suggestion, Brendan. It may be related.

[Cham]

I have another question for you, Selden (or any person which knows the answer).

When I created my hypothetical white dwarfs for your planetary nebulae, I had to assign them a number so Celestia could manage the stars. So, when I select one of those white dwarfs, Celestia print on screen a fake HD number, a fake SAO number and a fake TYC number as well. I feel it's misleading. Is there a way to make celestia print only the star's name, without showing those fake HD, SAO and TYC numbers ?

[selden]

If Celestia displays HD and SAO numbers, then you chose a HIP number which corresponds to a real star. Those are its real HD and SAO numbers. Celestia v1.4.0 includes the files hdindex.dat and saoindex.dat which specify which HD and SAO numbers are associated with which HIP number.

When you use Celestia v1.4.0, you do not have to specify a HIP number. You can specify just a name enclosed in quotes.

If you want to specify a fake HIP number that does not correspond to any real star, then you must specify a value between 200 000 and 1 000 000. Values less than 118322 correspond to real stars in the Hipparcos catalog. Values greater than 1 000 000 correspond to real stars in the Tycho catalog.

If you specify a HIP number which is the same as a HIP number that already is defined in Celestia, fake or real, then your new star definition replaces the previous definition.

[Cham]

Thanks a lot for the explanation, Selden. It helped much !

[selden]

You're quite welcome!