Planet around WD+dM binary NN Serpentis?

Lazarus wrote:

Take a look at the picture on the penultimate slide... looks familiar to anyone?

I noticed that!

Well, waiting for some kind of abstract or preprint, perhaps.

Now and in the Encyclopedia.
http://exoplanet.eu/star.php?st=NN+Ser+(ab)

Welcome back!

Who knows if they're even planning the "revanche" for QS Virginis

Seems to have set a new naming convention for circumbinary planets: planet designations start at "c". Wonder if the other circumbinary systems will get updated to match this?

I don't know how comfortable this designation is. I think this may create more confusion calling binary components as "a" and "b", likely to be disguised as planets.

Weren't capital letters ("A" and "B") enough clear to distinguish star from substellar companions?

As for me I prefer naming them NN Ser b and c

Well it does restore the property of planet designations that, if it turns out that the object is actually a star in a nearly face-on orbit, you can change the designation to uppercase without causing conflicts. Also having designations that differ only by case makes searching difficult.

Use of the lowercase "a" designation for the host stars is rare, but it definitely happens.

I think capital letters are enough to distinguish stars from planet.

Well imagine you have a system with stars "A", "B", planets "b", "c".

It then turns out that planet "b" was in fact a star in a nearly face-on orbit. You can't convert the designation to "B", because that conflicts with the designation of the star that is already called "B". If you change it to "C", your typical case-insensitive search won't find the previous references to the object when it was designated b.

After all, one reason planet designations around single stars start at "b" not "a" is to avoid this kind of naming conflict. If case is sufficient to distinguish the two, why not start the planets at "a"?

Lazarus wrote:

Well imagine you have a system with stars "A", "B", planets "b", "c".

It then turns out that planet "b" was in fact a star in a nearly face-on orbit. You can't convert the designation to "B", because that conflicts with the designation of the star that is already called "B". If you change it to "C", your typical case-insensitive search won't find the previous references to the object when it was designated b.

After all, one reason planet designations around single stars start at "b" not "a" is to avoid this kind of naming conflict. If case is sufficient to distinguish the two, why not start the planets at "a"?

Aa-Ab or Ba-Bb is already provided, not? As for Sigma Coronae Borealis: Sig1 CrB and Sig2 CrB Aa-Ab, a RS CVn-type binary. No conflict.

However, for instance, if NN ser b and c turned out low mass stars, I think they may be named C and D without problem.

Rather an objection may arise considering NN Serpentis as binary system and then dubbing substellar companions as "ABb" and "ABc", since circumbinary objects. However NN Ser b and c should not look so complicated. It's just my opinion.

Is it too late to entirely scrap the current planetary designation system? These sort of problems were entirely predictable from the start.

One obvious designation system would be calling the planets STAR DESIGNATION p1, p2, p3 etc. -- or if you wanting an auto-ordering list then STAR DESIGNATION p(n1), p(n2), p(n3) where n1, n2, n3 indicate the planet's orbital period. For example:

55 Cnc p14 (2004 McArthur, Endl, Cochran, Benedict, Fischer, Marcy, Butler, Naef, Mayor, Queloz, Udry, Harrison) = 55 Cnc e
55 Cnc p22 (1996 Butler, Marcy, Williams, Hauser, Shirts) = 55 Cnc b
55 Cnc p26 (2002 Marcy, Butler, Fischer, Laughlin, Vogt, Henry, Pourbaix) = 55 Cnc c
55 Cnc p34 (2007 Fischer, Marcy, Butler, Vogt, Laughlin, Henry, Abouav, Peek, Wright, Johnson, McCarthey, Isaacson) = 55 Cnc f
55 Cnc p47 (2002 Marcy, Butler, Fischer, Laughlin, Vogt, Henry, Pourbaix) = 55 Cnc d

where the integer after the "p" represents ten times the base-10 logarithm of the planetary period in days, plus ten (to ensure that the integer is always positive). I also added the year of publication of the discovery paper, and the discovery team, in parentheses, since the period, discovery date, and discovery team are the three pieces of information that we know about almost every known planet. This follows the standard nomenclature in biology where the year of description, and the describer, are part of the official species name.

That doesn't handle uncertainty on the orbital period very well. For some long-period planets there are substantial error values. Changing the designation of the object makes a literature search very difficult. (Unlike changing the case, as the most common implementations of search are case-insensitive by default)

And what about wide-separation objects such as 2M1207b discovered by direct imaging, or planets discovered via microlensing, for which orbital motion is unknown?

As far as I can see, designation based on orbital periods would lead to worse confusion than the current system.

Not to make matters worse.

There are stars that have Name A & Name B that are not even in the same system.
It just depends on what catalog you use.

Two planets orbiting the recently formed post-common envelope binary NN Serpentis
http://arxiv.org/abs/1010.3608

Quote :

Planets orbiting post-common envelope binaries provide fundamental information on planet formation and evolution. We searched for such planets in NN Ser ab, an eclipsing short-period binary that shows long-term eclipse time variations. Using published, reanalysed, and new mid-eclipse times of NN Ser ab obtained between 1988 and 2010, we find excellent agreement with the light-travel-time effect by two additional bodies superposed on the linear ephemeris of the binary. Our multi-parameter fits accompanied by N-body simulations yield a best fit for the objects NN Ser (ab)c and d locked in a 2:1 mean motion resonance, with orbital periods P_c=15.5 yrs and P_d=7.7 yrs, masses M_c sin i_c = 6.9 M_Jup and M_d sin i_d = 2.2 M_Jup, and eccentricities e_c=0 and e_d=0.20. A secondary chi**2 minimum corresponds to an alternative solution with a period ratio of 5:2. We estimate that the progenitor binary consisted of an A star with ~2 M_Sun and the present M dwarf secondary at an orbital separation of ~1.5 AU. The survival of two planets through the common-envelope phase that created the present white dwarf requires fine tuning between the gravitational force and the drag force experienced by them in the expanding envelope. The alternative is a second-generation origin in a circumbinary disk created at the end of this phase. In that case, the planets would be extremely young with ages not exceeding the cooling age of the white dwarf of 10**6 yrs.

The resonance is quite notable, especially since the binary is evolved and therefore underwent signficant mass loss that would have affected the orbits of the planets. Pity about the large distance of the system, this would be one where direct detection of the planets might be able to confirm second generation planet formation.

A Detailed Investigation of the Proposed NN Serpentis Planetary System

Turns out that unlike the proposed 2-planet systems around HU Aqr and HW Vir, this one is dynamically stable provided the eccentricity of the more massive planet is fixed to zero.

More support for a stable system at NN Ser. The two planets appear to be in a 2:1 MMR
http://arxiv.org/abs/1305.6494

Unfortunately looks like it will be a while before the effect of planet-planet interactions become noticeable. Especially since there have been quite a few issues raised against the circumbinary planet interpretation for timing variations in PCEBs.

Main-sequence progenitor configurations of the NN Ser candidate circumbinary planetary system are dynamically unstable
http://arxiv.org/abs/1309.3881

Quote :

...we conclude that the planets are not survivors from before the Common Envelope phase, implying that either they formed recently out of material ejected from the primary, or that the observed signals are of non-planetary origin.

The latter being their preferred interpretation, given the results from other PCEB "planets".

I still prefer Peryt (2010)'s hypothesis of 2nd generation planets...

New data further strengthens case for two-planet system, but fewer models that fit the data are stable.
http://arxiv.org/abs/1310.1391

However, newer data is making it harder to fit a stable model.

Quote :

The planet model for NN Ser also survives the test of dynamical stability which has cut down so many other claims. Although we have challenged the methodology of these tests, we suspect that the general implication of implausibly unstable orbits found for many systems will prove to be correct. This is not the case for NN Ser yet, although it perhaps might be when further data are acquired, because the addition of new data has consistently made it harder to locate long-lived solutions. Around 50% of viable orbits fitted to the data of Beuermann et al (2010) (with circular outer orbits) were long-lived. With our new data, this droppedto 0.2%, prompting us to allow for eccentric outer orbits. Even allowing for eccentricity, we found a similar drop from 7.6% to 0.7% when we added the two ULTRACAM points from July 2013.

To me the most interesting part of this is the criticism of the methodology used to determine that the other PCEB planetary systems are unstable (section 4.1), though given the prevalence of intersecting orbits and the like I don't see much prospect for altered conclusions for many cases.

Timing variations in the secondary eclipse of NN Ser
 

Quote :

The eclipsing white dwarf plus main-sequence binary NN Serpentis provides one of the most convincing cases for the existence of circumbinary planets around evolved binaries. The exquisite timing precision provided by the deep eclipse of the white dwarf has revealed complex variations in the eclipse arrival times over the last few decades. These variations have been interpreted as the influence of two planets in orbit around the binary. Recent studies have proved that such a system is dynamically stable over the current lifetime of the binary. However, the existence of such planets is by no means proven and several alternative mechanisms have been proposed that could drive similar variations. One of these is apsidal precession, which causes the eclipse times of eccentric binaries to vary sinusoidally on many year timescales. In this paper we present timing data for the secondary eclipse of NN Ser and show that they follow the same trend seen in the primary eclipse times, ruling out apsidal precession as a possible cause for the variations. This result leaves no alternatives to the planetary interpretation for the observed period variations, although we still do not consider their existence as proven. Our data limits the eccentricity of NN Ser to e<0.001. We also detect a 3.3+/-1.0 second delay in the arrival times of the secondary eclipses relative to the best planetary model. This delay is consistent with the expected 2.84+/-0.04 second Romer delay of the binary, and is the first time this effect has been detected in a white dwarf plus M dwarf system.

According to this, second-generation planet formation from the ejecta of the common envelope system is feasible.

Schleicher and Dreizler, "Planet formation from the ejecta of common envelopes"
http://arxiv.org/abs/1312.3479

If so, the planets in the NN Serpentis system could be among the youngest detected planets. Determining whether or not they were "seeded" from pre-existing planets is not going to be easy though!

If so one could expect inflated radii. Could an imaging campaing be feasible too?