Planet around WD+dM binary NN Serpentis?

Amongst unconfirmed objects, though

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

Typo shows period of 7.56 days rather 7.56 years.

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.

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.

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

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?

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?

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

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...

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

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.

...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.

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)

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 T_eff?

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

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 T_eff?

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.

Moreover, as author states, it is a pre-cataclysmic variable, so it's likely the WD is young and thus hotter.