# Planets at HW Virginis?

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## Planets at HW Virginis?

A new paper has appeared in the Extrasolar Planets Encyclopaedia's Bibliography.

LEE ET AL. , 2008 (update : 08 August 2008)
The sdB+M Eclipsing System HW Virginis and its Circumbinary Planets
Astron. J. , - , -
submitted

This should be interesting. Note the use of a plural noun.

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Sirius_Alpha

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## Re: Planets at HW Virginis?

I wonder whether that term is being used to include the brown dwarf companion previously reported?

Lazarus
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## Re: Planets at HW Virginis?

A paper from 2000, Spectrophotometry and period analysis of the sdB eclipsing binary HW Virginis, says,

paper wrote:1. New photometric observations are presented revealing the recent period change of HW Vir. The O-C diagram covering 17 years does not support earlier suggestions of a possible light-time effect, but can be very well described by two linear branches. There are also additional smooth period changes.

Lazarus wrote:I wonder whether that term is being used to include the brown dwarf companion previously reported?
I don't know how accurate transit timing is, so I would guess planets would have to be fairly massive to be detected this way. Perhaps one of them are a brown dwarf.

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## Re: Planets at HW Virginis?

Brown dwarf I was referring to is described in İbanoǧlu et al. (2004)

Timing is sensitive to massive planets on wide orbits, as these cause the timed system (e.g. pulsar, eclipsing binary, etc.) to move in wider orbits around the centre-of-mass.

Lazarus
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## Re: Planets at HW Virginis?

We all eagerly wait for the discovery paper...

Edasich
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## Re: Planets at HW Virginis?

Does anyone know the separation of the two HW Virginis stars?

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## Re: Planets at HW Virginis?

 System Period: 0.116795 days Semimajor axis: 0.853 solar radii sdB star Mass: 0.48 solar masses Radius: 0.197 solar radii Temperature: 28700 K dM star Mass: 0.14 solar masses Radius: 0.181 solar radii Temperature: 3300 K Albedo: 0.73 (B-band) 0.98 (V-band)

Lazarus
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## Re: Planets at HW Virginis?

Ooh! I've been waiting for a circumbinary planet to be found.

NuclearVacuum
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## Re: Planets at HW Virginis?

NuclearVacuum wrote:Ooh! I've been waiting for a circumbinary planet to be found.

Wait no longer!
PSR B1620-26
Circumbinary planet orbiting a white dwarf and a pulsar =D.

But yeah, I, too, have been waiting for another circumbinary planet. I was hoping for one that didn't orbit some pulsar or white dwarf or some other sort of non main-sequence star. Oh well.

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Sirius_Alpha

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## Re: Planets at HW Virginis?

I already knew about PSR B1620-26 c. But I have the mental capacity that I don't really register pulsar planets (only normal stars). But I know what you mean I've been waiting for a circumbinary planet to be found around stars like Delta Trianguli, CM Draconis, and HD 98800 ^_^

NuclearVacuum
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## Re: Planets at HW Virginis?

Well, something around CM Dra is supposed to be present, but it needs confirmation. About Delta Trianguli, it seems there's nothing so far and TV Crateris (HD 98800) seems quite a tight multiple to host even "torch orbit" jovians.

Edasich
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## Re: Planets at HW Virginis?

I have a good question. I have good feelings that the planet will be designated "HW Virginis c" (because the planet orbits two stars ["a" and "b"]). But if a brown dwarf was also discovered orbiting the stars, could the planet be skipped to "d" or be designated "ABc"?

NuclearVacuum
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## Re: Planets at HW Virginis?

HW Vir c will probably be used, yes. The brown dwarf would likely be given a capital C, if we don't consider it a superjovian.

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## Re: Planets at HW Virginis?

Sirius_Alpha wrote:HW Vir c will probably be used, yes. The brown dwarf would likely be given a capital C, if we don't consider it a superjovian.

Unless it turns out a superjovian...

Edasich
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## Re: Planets at HW Virginis?

Edasich wrote:
Sirius_Alpha wrote:HW Vir c will probably be used, yes. The brown dwarf would likely be given a capital C, if we don't consider it a superjovian.

Unless it turns out a superjovian...

Is there a difference between a 14-Jupiter mass planet and a 14-Jupiter mass brown dwarf?

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Sirius_Alpha

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## Re: Planets at HW Virginis?

A circumbinary planet around a W UMa-type eclipsing binary would be cool (alike 44 Bootis B-C or even W Ursae Majoris, both nearby ones...)

Edasich
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## Re: Planets at HW Virginis?

If you work out the luminosities of the two stars, the sdB star is about 7000 times more luminous than the dM star.

The reflected light of the sdB star from the dM star probably outshines the dM star itself.

Lazarus
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## Re: Planets at HW Virginis?

This paper, Spectrophotometry and period analysis of the sdB eclipsing binary HW Virginis, would seem to agree. In the abstract, it talks about the dM star's heating due to the primary.

From the abstract:
The magnitude of the reflection effect was used to estimate the mean effective temperature of the illuminated hemisphere of the secondary. The result is 13300\pm200 K or 11000\pm200 K, depending on the primary temperature (35000 K or 26000 K). An albedo near unity is implied for the cool component.

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## Re: Planets at HW Virginis?

NuclearVacuum wrote:I have a good question. I have good feelings that the planet will be designated "HW Virginis c" (because the planet orbits two stars ["a" and "b"]). But if a brown dwarf was also discovered orbiting the stars, could the planet be skipped to "d" or be designated "ABc"?

Well SIMBAD lists the designation of the planet in the PSR B1620-26 system as "PSR B1620-26 b", which is presumably the official designation for now.

Alternatively they might avoid the designation issue like every paper on the PSR B1620-26 planet has done so far...

Lazarus
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## Re: Planets at HW Virginis?

More on the properties of the HW Vir system...

HW Vir's Companion: a M-type Dwarf, or maybe a giant rotating spherical Mirror?

Lazarus
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## Re: Planets at HW Virginis?

We've got two planets!

The sdB+M Eclipsing Binary System HW Virginis and its Circumbinary Planets
http://arxiv.org/abs/0811.3807

Abstract wrote:For the very short-period sdB eclipsing binary HW Vir, we present new CCD photometry made from 2000 through 2008. In order to obtain consistency of the binary parameters, our new light curves were analyzed simultaneously with previously published radial-velocity data. The secondary star parameters of $M_2$=0.14 M$_\odot$, $R_2$=0.18 R$_\odot$, and $T_2$=3,084 K are consistent with those of an M6-7 main sequence star. More than 250 times of minimum light, including our 41 timings and spanning more than 24 yrs, were used for a period study. From a detailed analysis of the $O$--$C$ diagram, it emerged that the orbital period of HW Vir has varied as a combination of a downward-opening parabola and two sinusoidal variations, with cycle lengths of $P_3$=15.8 yr and $P_4$=9.1 yr and semi-amplitudes of $K_3$=77 s and $K_4$=23 s, respectively. The continuous period decrease with a rate of $-8.28\times10^{-9}$ d yr$^{-1}$ may be produced by angular momentum loss due to magnetic stellar wind braking but not by gravitational radiation. Of the possible causes of the cyclical components of the period change, apsidal motion and magnetic period modulation can be ruled out. The most reasonable explanation of both cyclical variations is a pair of light-travel-time effects driven by the presence of two substellar companions with projected masses of $M_3 \sin i_3$=19.2 M$\rm_{Jup}$ and $M_4 \sin i_4$=8.5 M$\rm_{Jup}$. The two objects are the first circumbinary planets known to have been formed in a protoplanetary disk as well the first ones discovered by using the eclipse-timing method. The detection implies that planets could be common around binary stars just as are planets around single stars and demonstrates that planetary systems formed in a circumbinary disk can survive over long time scales.

HW Vir c (the outermost planet)
Mass = 19.2 M_j
Period = 15.8 yr.
e=0.46
i=81 degrees (assuming coplanarity with the host stars)
a = 5.3 AU

HW Vir d (the innermost planet)
Mass = 8.5 M_j
Period = 9.1 yr.
e = 0.31
i = 81 degrees (again, assuming coplanarity)
a = 3.6 AU.

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Sirius_Alpha

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## Re: Planets at HW Virginis?

The paper seems to avoid the discussion of designations for the planets: refers to them as the third and fourth components (so HW Vir 3, HW Vir 4?) Note also the same thing for the primary and secondary... (HW Vir 1, HW Vir 2?) EPE uses b, c but then they use b,c,d instead of A,B,C for PSR B1257+12...

Lazarus
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## Re: Planets at HW Virginis?

Well, this is really a great confirmation. The presence of at least one substellar companion was already suspected since 2003 (right-click and save directly).

Moreover SIMBAD lists HW Vir as Algol-type binary. Would this one be the 1st exoplanetary system around an Algol-type pair?
It would the first circumbinary one of course (excluding HD 202206).

Edasich
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## Re: Planets at HW Virginis?

Either my eyes are bad, or I can't find anything that says what the planets are named. I can't find anything that says they are numbered. Where is it?

NuclearVacuum
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## Re: Planets at HW Virginis?

Well the paper refers to the properties of each companion with numeric subscripts (e.g. M3, M4) but this doesn't really count for much.

As far as I am aware the current precedent is set by SIMBAD's use of "b" for the planet around PSR B1620-26, which would make the HW Vir planets "b" and "c" for outer and inner companions respectively. However this designation is (as far as I can see) not used at all in any papers about this object. All the papers seem to totally avoid the designations issue for circumbinary planets. Even the logic that "a" refers to the primary star, it isn't clear: do the primary and secondary become "a" and "b" or "aa" and "ab"? The SIMBAD precedent of designating the planets starting at "b" leads to the potential for confusion in systems with more than two components - how would you designate a companion orbiting component B of a multi-star system where component B is itself a double star (e.g. Xi UMa B) and how would you distinguish that from the secondary star of the double (which would presumably be Xi UMa Bb)?

The literature doesn't appear to use designations, they merely set up the context so you can refer to them as the "third component", "fourth component", etc. (In fact I don't see the usage of A or B to refer to the stellar components of this system, they seem to just use "primary" and "secondary".

In short, there are no universal systems for designations, there is no widely-accepted precedent for circumbinary planets, and the system used for designating planets starts to fail once systems of more than one star are considered.

(And then you can have even more fun when it is not clear which component to describe as the primary: e.g. Capella where the visually brighter component is the spectroscopic secondary...)

Lazarus
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