The discovery of a jovian mass planet around a metal poor horizontal branch star in a kinematic stream of stars, possibly originating from a merger with a dwarf galaxy, is an interesting conundrum.
With bonus updates and links.
HIP 13044 is a 10th magnitude, F2 horizontal branch star.
It is about 600 700 pc away, has high proper motion and is associated with a tidal stream, and may therefore have originated in a dwarf galaxy that merged with the Milky Way a long time ago.
stellar tidal stream in Milky Way model
tidal stream formation from hos
As an HB star, it has gone through a red giant phase, shedding its hydrogen envelope as it expanded to maybe 100 million kilometer radius, and is now a compact short lived helium burning star, which will likely expand again as an asymptotic giant branch star to an even bigger size before fizzling out as a white dwarf, a few hundred million years from now.
Its progenitor, as an old, high proper motion halo star, ought to have been metal poor.
Likely had metallicity between 1/10th and 1/100th of the Sun, possibly a bit lower.
It has a planet, paper is coming out in Science (subscription), I'll add a link tomorrow.
1.25 MJ/sin(i)
16.2 d orbital period
high eccentricity (e=0.25)
HB star is a rapid rotator (estimate 5 day rotation period)
PS: 10th magnitude (V)
metallicity -2.1 !!!
velocity half amplitude of 120 m/sec.
semi-major axis 0.116 AU
periastron 0.087 AU - dipping in close there
star is in galactic anti-center
detected using FEROS on the ESO 2.2m
Huh.
PS: ok, so having read the paper, and the supplementary material which is quite relevant in this case, I am surprisingly more inclined to believe the claim, but with some reservation.
The star is really over on the red side of the horizontal branch, with a radius of a bit over 6 solar radii! So it has retained substantial fraction of the hydrogen envelope, maybe 0.2 solar masses or so. Star is about 0.8 solar masses.
The putative planet is orbiting at just a few stellar radii and the velocity signal is not subtle.
They looked at bisectors, and photometric variability - it is a known pulsator at 1.4 and 3.5 days, and rotation looks plausible at 5.2 days.
Looks ok I guess
It could be a halo star heated by the putative galaxy merger that might have created the Helmi stream, or it could have come from the dwarf galaxy that did the merger.
Actually detailed metallicity analysis might help decide that, look at s-process elements and alpha/iron ratios and compare it with other kinematic ally grouped stars
A Just So Story: origins looks a bit less contrived now - I'd bet on there having been originally 2 or more planets, both jovian mass, orbiting near 2:1 resonance out around 0.5-1 AU - probably inside the 2:1 resonance in near circular orbits to begin with
when the star got some way up the RGB two things happen - the inner planet starts feeling drag, and the planetary orbits expand due to stellar mass loss - so the relative orbital frequency of the planets shifts and they come into resonance
this would lead to scatter from planet-planet perturbation, including sharp increase in planetary eccentricity and maybe explains the current weird configuration
1) It is possible the other planet went inward and erged with the star and is responsible for its apparent rapid rotation. The observed planet is then the outer of the two and got partially dragged inwards but not all the way, and its eccentricity is partially circularized, but this would then NOT be a coincidence because the same even lead to the expulsion of the RGB envelope and the termination of the giant branch ascent.
2)Alternatively, but in my opinion somewhat less likely, the observed planet is the inner planet, and there is another Jovian in an eccentric orbit out beyond this one, which never came into contact - it'd have an orbital period ~ 3-10 times longer than the observed planet, and since they have 300 days of data it should already be showing in the data, and I don't see any residuals at tens of m/sec
'course having one jovian around ~ solar mass halo star with Z= -2.1 is bad enough,
if you had to have 2 of them, inside 1 AU it raises all new questions
END PS
Well, it is good to get another Jovian planet form Pop II stars to join 1620-26
This should do some damage to the mass-metallicity relationship for exoplanets.
Also a bit suggestive that the Cameron mechanism for direct collapse to form giant planets may work in some circumstances, maybe.
I don't understand how it is in its current orbit - a "touch-n-go" orbit which tidally coupled to the RGB envelope just as it detached is possible for shrinking the orbit starting from something like a ~ 1 AU orbit.
But...
how did it end up eccentric?
The HB rapid rotation is suggestive of angular momentum transfer, so possible there was a second giant planet which was swallowed - if there was scattering during this process, maybe it could explain the current orbit, but this is a bit contrived, even for me, and I love contrived "just so" stories to explain exotic planets.
I'll update after I digest the paper.
Interesting.
Someone needs to take independent confirming data on a bigger telescope
Cute video below - star should be bluer and the orbit shape just does not look right.
Focus folks!
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My guess is that there's something wrong with these numbers (Setiawan's last first-author discovery--a planet around TW Hydrae, Nature result--seems not to really exist, Figueira et al. 2010). Perhaps most likely is that there's another planet in the system, giving a false eccentricity to the planet's orbit. I haven't read the paper yet, so we'll see.
How do you determine [Fe/H] if most of the H has been either burned or blown off?
Ando now a detection of a fourth planet around HR 8799... how does the probable membership of the Columba association affect the blue straggler hypothesis you mentioned in previous blog posts about this system?
@Lab - the metal abundance that is measured is the photospheric abundance. This particular star has a fairly thick residual hydrogen envelope which was convectively mixed while on the giant branch.
But, the do consider both differential mass loss - radiative expulsion of metal dust grains - and settling.
@andy - well, I haven't gone back and checked if there is new data, but the original paper cites kinematic similarity to two members of the group, but, as I recall, from Simbad data, the metallicity is off by a factor of 3 or so, which makes common membership very unlikely.
I really do like HR8799 for a blue straggler, for broader reasons that cannot be explicated in the narrow comment section... I'd ideally like to work it into a section of a paper that is plodding along, but it may have to be worked into a short separate paper. Just doesn't feel like something worth a whole paper by itself.
Hi,Im expert in Astronomy and I work actuali in the jet propution laboratory,so If there is a planet from an other galaxy how they know it comes from another galaxy they bean there "NO" so it comes from omega centaury with my obtervations I can see that it moves and with my calculations it comes from the direction of omega centaury a glubuler star of 1000 stars.thans
How about a pre-existing star plunging into an already condensing cloud of thick gas to create the unusually heavy planet?
@aackb - no, extremely unlikely because of requirement to conserve energy and momentum
@ronyto - Omega Cen has closer to 10,000,000 stars.
It is relatively metal rich, order of magnitude more than HIP13044, and is a disk object closer to the galactic centre whereas HIP13044 is a halo object at the anti-centre.
So rather unlikely to be related, though I'd be impressed if you can show a kinematic model backtracking them to a common origin. Omega Cen does have full 3D motion and so in fact does HIP 13044.
Regarding the metallicity difference between HR 8799 and the Columba association, are there known examples of Lambda Boötis stars in stellar clusters, and if so what are the metallicities like relative to the parent cluster?