Planet around WD+dM binary NN Serpentis?

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Planet around WD+dM binary NN Serpentis?

Post by Edasich on 3rd November 2009, 5:00 am

Amongst unconfirmed objects, though

http://exoplanet.eu/star.php?st=NN+Ser

Typo shows period of 7.56 days rather 7.56 years.
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Re: Planet around WD+dM binary NN Serpentis?

Post by Lazarus on 3rd November 2009, 4:03 pm

Another pre-cataclysmic binary eh? If confirmed this could be another case where the planet may have accreted substantial amounts of mass from the matter lost from the red giant star. Wonder what impact that would have on any moon system.
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 3rd November 2009, 4:35 pm

I would imagine the increased mass of the planet, plus drag from the moon orbiting within the expelled RGB envelope would lower the moon's orbit quite a bit.

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 3rd November 2009, 4:37 pm

Lazarus wrote:Another pre-cataclysmic binary eh? If confirmed this could be another case where the planet may have accreted substantial amounts of mass from the matter lost from the red giant star. Wonder what impact that would have on any moon system.

It seems there is another one hiding. OV Carinae seems likely to host a 16 Mj object at 17 AUs and it's quite a CV
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 3rd November 2009, 4:43 pm

So, since SWIFT J1756.9-2508 (planetary-mass white dwarf + accreting pulsar) is considered a WD + pulsar, would a planet that has accreted enough mass to raise it into the brown dwarf regime still count as a planet?

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Re: Planet around WD+dM binary NN Serpentis?

Post by Lazarus on 3rd November 2009, 5:15 pm

Sirius_Alpha wrote:So, since SWIFT J1756.9-2508 (planetary-mass white dwarf + accreting pulsar) is considered a WD + pulsar, would a planet that has accreted enough mass to raise it into the brown dwarf regime still count as a planet?
What do you mean by the "brown dwarf regime" - fusion of deuterium (which I'd argue does not make a useful boundary between planets and BDs anyway, despite what the IAU WGESP says) or the far side of the brown dwarf desert? Smile
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 3rd November 2009, 5:27 pm

Yeah I was thinking the 13 M_j + range. But... yeah....

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 6th November 2009, 3:28 pm

http://en.wikipedia.org/wiki/NN_Serpentis

Been edited by me.

There is a correction: I get a luminosity of 4.2 Solar for the white dwarf. Thus water zone would be located at 2 AUs. So the planet would be fairly habitable? At the moment...
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 6th November 2009, 10:04 pm

That's odd, I always assumed white dwarfs had sub-solar luminosities.

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 7th November 2009, 5:11 am

http://adsabs.harvard.edu/abs/2009arXiv0909.4307P

It is a recent article and gives me Teff=57,000 K and radius=0.021 Solar. Doing the math I get 4.17 Solar luminosities.

Probably because it's a post-AGB star alike V391 Pegasi.
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Re: Planet around WD+dM binary NN Serpentis?

Post by Lazarus on 7th November 2009, 6:11 am

...or it is a very young white dwarf.

Note the quoted radius of the white dwarf is roughly 10 times smaller than V391 Peg and the sdB star in HW Virginis.
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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 7th November 2009, 6:49 am

Lazarus wrote:...or it is a very young white dwarf.

Note the quoted radius of the white dwarf is roughly 10 times smaller than V391 Peg and the sdB star in HW Virginis.

True, but Teff is much higher (57,000 K)
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 7th November 2009, 10:05 am

Yeah now I'm a bit confused. With the lower radius of a white dwarf, would this mean there is less surface area from which to emit radiation, translating to less irradiation of planets despite the Teff?

Or does the white dwarf's epic gravity relativistically play with the light to cause it to lose energy before reaching a planet?

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Re: Planet around WD+dM binary NN Serpentis?

Post by Sedna on 7th November 2009, 10:21 am

Sirius_Alpha wrote:Yeah now I'm a bit confused. With the lower radius of a white dwarf, would this mean there is less surface area from which to emit radiation, translating to less irradiation of planets despite the Teff?

Or does the white dwarf's epic gravity relativistically play with the light to cause it to lose energy before reaching a planet?

At first sight, everybody could think like you. But, looking at the formula, the luminosity strongly depends on the temperature (which is raised at the 4th power, while the radius is raised at the 2nd power). So, despite the radius of the WD is 47-48 times smaller than the Sun's and the temperature is only 10 times greater, the temp is "heavier" than the radius.


Last edited by Sedna on 7th November 2009, 2:52 pm; edited 1 time in total

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 7th November 2009, 10:49 am

Moreover, as author states, it is a pre-cataclysmic variable, so it's likely the WD is young and thus hotter.
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 7th November 2009, 3:25 pm

Sedna wrote:But, looking at the formula, the luminosity strongly depends on the temperature (which is raised at the 4th power, while the radius is raised at the 2nd power).
This applies even for degenerate stars?

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Re: Planet around WD+dM binary NN Serpentis?

Post by Lazarus on 7th November 2009, 3:48 pm

It's a result that applies to blackbody radiation (the Stefan-Boltzmann law).
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sedna on 7th November 2009, 5:41 pm

I have no proof that it cannot be applied for such stars, so...

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 7th November 2009, 5:45 pm

However with a luminosity of 4.2 LSolar the planet "temporarily" lies in a comfortable zone for liquid water.
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Two planets orbiting NN Serpentis?

Post by Borislav on 1st September 2010, 10:38 am

http://astro.uni-tuebingen.de/~rauch/EUROWD10/Talks/2010-08-20_Friday/1130_dreizler.ppt

Nice that discovery made very young astronomers.

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Re: Planet around WD+dM binary NN Serpentis?

Post by Edasich on 1st September 2010, 11:24 am

Yeah, noticed that one. Cool find.
There is even something about a white dwarf EC... something.
I prefer call it QU Telescopii
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Re: Planet around WD+dM binary NN Serpentis?

Post by Sirius_Alpha on 1st September 2010, 12:09 pm

Borislav wrote:It is possible to merge with earlier themes?
Merged the two threads that are mainly about NN Ser, left the QS Vir one alone.

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Re: Planet around WD+dM binary NN Serpentis?

Post by Lazarus on 1st September 2010, 12:58 pm

Take a look at the picture on the penultimate slide... looks familiar to anyone? Wink
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Re: Planet around WD+dM binary NN Serpentis?

Post by Borislav on 1st September 2010, 1:26 pm

http://exoplanet.eu/star.php?st=NN+Ser
Why not upgrade? After the presentation dates back to August 20.

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Re: Planet around WD+dM binary NN Serpentis?

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