Extremely low period gas giants

[danielj]

Hubble discovered last year,planets that revolve around the star in question of hours,instead of days.These planets are ovals(elipticals?) and have some kind of cometlike tail.Your surface temparature is 1650 degrees Celsius and are tidally locked to the star.Why no one try to modelate this planet?It??s certain that the custom gas giants textures are not suitable for this kind of planet.I saw this in the January 2007 editon of Astronomy magazine.
Also,Hybble and other telescopes measure the composition of some planet??s atmosphere.I think the extrasolar.ssc needs a MAJOR improvement!

[ajtribick]

Presumably you are referring to the SWEEPS survey. Of those, only two (SWEEPS-04 and SWEEPS-11) have been confirmed to be planets from radial velocity measurements. The others (including the ultra-short period planets you mention) have not been confirmed. However the distances to the stars involved are not known, so we can't model the systems in Celestia.

The cometlike tails for these planets are only depicted by analogy to the known evaporation tail of HD 209458 b (a planet which IS included in Celestia, however the tail is not modelled: not sure if it would actually be seen in visible light either). I guess an ultra-short-period planet might appear quite oblate (assuming the density is low), but if it has a massive core it might not.

As for saying the textures are not suitable, do you have any references to back you up - what is the upper temperature limit for silicate clouds anyway?

[eburacum45]

Strangely enough the comet tail of HD 209458 b is modelled, (at least in the latest version of Celestia) but it isn't in the same place as the planet.
I managed to get them to line up for this shot (which is processed slightly to make the tail blurred)
http://img239.imageshack.us/my.php?imag ... 8bbbg0.jpg
but unless I have forgotten doing it myself, the comet tail is there.

[ajtribick]

Hmmm... you sure about that? I'm using the latest version of extrasolar.ssc and am not finding a comet tail.

I remember writing a small add-on which I posted on these forums which put a comet in the same place as HD 209458 b. However since then the orbital elements have been refined, which means if you use the add-on the tail will be in the wrong place.

Are you sure you haven't got a file in your extras directory putting a comet in the system?

[Hungry4info]

The SWEEPS planets are all near the centre of the galaxy anyway. Celestia cannot display them due to that problem with displaying objects too far away, which should have been fixed long ago.

[ajtribick]

Actually, the site I linked gives a distance of ~2000 parsecs, which corresponds to ~6500 light years. That's closer than some of the OGLE stars which are implemented... I guess we could implement SWEEPS-11 and SWEEPS-04, however matching apparent/absolute magnitudes at that distance is complicated by absorption by interstellar dust.

[Hungry4info]

Those very sites you linked to give the visual magnitudes of SWEEPS-04 and SWEEPS-11 as V=18.8 and V=19.83 respectively. I'm not so sure that there would be much difference if interstellar gas and dust were taken into account, because the image of the Hubble SWEEPS field doesn't seem to have much dust (you may have already seen this image):
http://antwrp.gsfc.nasa.gov/apod/image/ ... 16_hst.jpg

As I understand it, the area was called the "Sagittarius Window" because it was an area devoid of gas and dust, allowing many stars to be seen. So I'm not sure that the visual magnitudes given by exoplanet.eu are all that unreliable.

However, I'm not entirely sure about all this, and am certainly able to be wrong.

[ajtribick]

Nah, the visual apparent magnitudes (which are given there) are fine: we know how bright they appear from Earth on account of the fact that we are observing from Earth. It's the question of how bright they'd appear in the vicinity.

Then again, the actual discovery paper uses a distance modulus of 14.3 which would put the stars at ~20000 light years, which is outside Celestia's limit.

[eburacum45]

Hmmm... you sure about that? I'm using the latest version of extrasolar.ssc and am not finding a comet tail.

I remember writing a small add-on which I posted on these forums which put a comet in the same place as HD 209458 b. However since then the orbital elements have been refined, which means if you use the add-on the tail will be in the wrong place.

Are you sure you haven't got a file in your extras directory putting a comet in the system?

Yes; it is your add-on; thanks mate! I'll adjust it as necessary.

[Arnavion]

I can't find HD 209458 !!!

[bh]

I've got it! BTW chaos... love your landscapes on DA skip.

[ajtribick]

The add-on is here, but you'll need to update the parameters - in the time since I made it, the comet model has been changed, and the planet parameters have been altered. The following looks quite good in my setup (v1.4.1, Windows, extrasolar.ssc v1.82):

Code: Select all

"b Atmosphere Evaporation" "HD 209458"   # V376 Peg

{
   Class "comet"
   Mesh "empty.3ds"
   Radius 0.45         # to get the comet tail the right size

   InfoURL "http://www2.iap.fr/exoplanetes/index_en.html"

   EllipticalOrbit {
      Period          0.0097
      SemiMajorAxis   0.046
      Eccentricity    0
      Inclination     71.3
      AscendingNode   325.9
      ArgOfPericenter 122
      MeanAnomaly     141
   }

   Albedo 0
}

Save it to a ssc file (e.g. hd209458.ssc) in the extras directory.

You may also want the empty.3ds mesh from http://www.lns.cornell.edu/~seb/celesti ... /empty.3ds

Note that this is in no way an accurate attempt to model the atmosphere evaporation! I leave that to the mathematical modelling gurus around here

Regarding my DA page, cheers bh.

[Arnavion]

I don't mean that. I can't search for the HD number (pressing ENTER and typing the number), though I can search using the name V376 Peg. In fact, many HD and HIP numbers can't be searched for, despite my having them. How do I rectify this ?

[selden]

Just because an object's designation isn't shown by the tab-completion code does not mean you can't use [return]name[return] to select that designation. Type in the object's entire name and the object will be selected.

Please read the "Preliminary User's FAQ', especially Q/A #28. It's a "sticky" near the top of the Users Forum.

Only names which are in an object's quoted textual name string in a textual catalog (SSC, STC or DSC) are listed by the tab-completion code. Strings which only match an entry in the binary stars.dat database or in one of the cross-index databases are not shown. There are too many of them.

Only a few Stars happen to have HIP or HD designations included in their STC quoted textual name strings.

[Arnavion]

Thanks Selden, I found it now.