Accreting protoplanets in the LkCa 15 transition disk

LkCa 15: A Young Exoplanet Caught at Formation?
http://arxiv.org/abs/1110.3808

Quote :

Young and directly imaged exoplanets offer critical tests of planet-formation models that are not matched by RV surveys of mature stars. These targets have been extremely elusive to date, with no exoplanets younger than 10--20 Myr and only a handful of direct-imaged exoplanets at all ages. We report the direct imaging discovery of a likely (proto)planet around the young (~2 Myr) solar analog LkCa 15, located inside a known gap in the protoplanetary disk (a "transitional disk"). Our observations use non-redundant aperture masking interferometry at 3 epochs to reveal a faint and relatively blue point source ($M_K'=9.1+/-0.2, K'-L'=0.98+/-0.22), flanked by approximately co-orbital emission that is red and resolved into at least two sources (M_L'=7.5+/-0.2, K'-L'=2.7+/-0.3; M_L'=7.4+/-0.2, K'-L'=1.94+/-0.16). We propose that the most likely geometry consists of a newly-formed (proto)planet that is surrounded by dusty material. The nominal estimated mass is ~6 M_{Jup} according to the 1 Myr hot-start models. However, we argue based on its luminosity, color, and the presence of circumplanetary material that the planet has likely been caught at its epoch of assembly, and hence this mass is an upper limit due to its extreme youth and flux contributed by accretion. The projected separations (71.9 +/- 1.6 mas, 100.7 +/- 1.9 mas, and 88.2 +/- 1.8 mas) and deprojected orbital radii (16, 21, and 19 AU) correspond to the center of the disk gap, but are too close to the primary star for a circular orbit to account for the observed inner edge of the outer disk, so an alternate explanation (i.e., additional planets or an eccentric orbit) is likely required. This discovery is the first direct evidence that at least some transitional disks do indeed host newly-formed (or forming) exoplanetary systems, and the observed properties provide crucial insight into the gas giant formation process.

A Closer Look at the LkCa 15 Protoplanetary Disk
http://arxiv.org/abs/1110.3865

Quote :

We present 870 micron observations of dust continuum emission from the LkCa 15 protoplanetary disk at high angular resolution (with a characteristic scale of 0.25" = 35 AU), obtained with the IRAM Plateau de Bure interferometer and supplemented by slightly lower resolution observations from the Submillimeter Array. We fit these data with simple morphological models to characterize the spectacular ring-like emission structure of this disk. Our analysis indicates that a small amount of 870 micron dust emission (~5 mJy) originates inside a large (40-50 AU radius) low optical depth cavity. This result can be interpreted either in the context of an abrupt decrease by a factor of ~5 in the radial distribution of millimeter-sized dust grains or as indirect evidence for a gap in the disk, in agreement with previous inferences from the unresolved infrared spectrum and scattered light images. A preliminary model focused on the latter possibility suggests the presence of a low-mass (planetary) companion, having properties commensurate with those inferred from the recent discovery of LkCa 15b.

Searching for circumplanetary disks around LkCa 15
http://arxiv.org/abs/1404.5627

Quote :

We present Karl G. Jansky Very Large Array (VLA) observations of the 7 mm continuum emission from the disk surrounding the young star LkCa 15. The observations achieve an angular resolution of 70 mas and spatially resolve the circumstellar emission on a spatial scale of 9 AU. The continuum emission traces a dusty annulus of 45 AU in radius that is consistent with the dust morphology observed at shorter wavelengths. The VLA observations also reveal a compact source at the center of the disk, possibly due to thermal emission from hot dust or ionized gas located within a few AU from the central star. No emission is observed between the star and the dusty ring, and, in particular, at the position of the candidate protoplanet LkCa 15 b. By comparing the observations with theoretical models for circumplanetary disk emission, we find that if LkCa~15~b is a massive planet (>5 M_J) accreting at a rate greater than 1.e-6 M_J yr^{-1}, then its circumplanetary disk is less massive than 0.1 M_J, or smaller than 0.4 Hill radii. Similar constraints are derived for any possible circumplanetary disk orbiting within 45 AU from the central star. The mass estimate are uncertain by at least one order of magnitude due to the uncertainties on the mass opacity. Future ALMA observations of this system might be able to detect circumplanetary disks down to a mass of 5.e-4 M_J and as small as 0.2 AU, providing crucial constraints on the presence of giant planets in the act of forming around this young star.

http://www.space.com/31146-alien-planet-formation-photographed.html

"It's exciting, because it's the first time that we've been able to image forming planets directly," study lead author Stephanie Sallum
(…)

The team confirmed the existence of LkCA 15b, imaging it directly in hydrogen-alpha photons, a type of light that's emitted when superheated material accretes onto a newly forming world. (Like newborn stars, newborn planets are surrounded by disks of feeder material.)
Other LBT observations revealed the presence of another newborn planet, LkCA 15c, inside the gap and suggested that a third (LkCA 15d) exists there as well, study team members report online today (Nov. 18) in the journal Nature



See also : https://solar-flux.forumotion.com/t954-protoplanet-imaged-at-lkca-15

Here's the paper, but I don't have access to it. Figure 1 helps make sense of the protoplanet orbits to me.

Accreting protoplanets in the LkCa 15 transition disk
http://www.nature.com/nature/journal/v527/n7578/full/nature15761.html

And now finally free to access on arXiv.
http://arxiv.org/abs/1511.07456

Some slides from Davos meeting
New results with SPHERE/VLT :

[URL=http://imgbox.com/cSCGnCrV]

Paper on the SPHERE results:

Thalmann et al. "Resolving the planet-hosting inner regions of the LkCa 15 disk"
http://arxiv.org/abs/1608.08642

There may be a case for "b" being a protoplanet but "c" and "d" may actually be accounted for by the inner disc.

Spectro-astrometry of the pre-transitional star LkCa 15 does not reveal an accreting planet but extended Hα emission
https://arxiv.org/abs/1810.04181

Quote :

(Abridged) The detection of forming planets in disks around young stars remains elusive, and state-of-the-art observational techniques provide somewhat ambiguous results. It has been reported that the pre-transitional T Tauri star LkCa 15 could host three planets; candidate planet b is in the process of formation, as inferred from its Hα emission. However, a more recent work casts doubts on the planetary nature of the previous detections. We have observed LkCa 15 with ISIS/WHT. The spectrograph's slit was oriented towards the last reported position of LkCa 15 b (parallel direction) and 90degr from that (perpendicular). The photocenter and full width half maximum (FWHM) of the Gaussians fitting the spatial distribution at Hα and the adjacent continuum were measured. A well-known binary (GU CMa) was used as a calibrator to test the spectro-astrometric performance of ISIS/WHT, recovering consistent photocenter and FWHM signals. However, the photocenter shift predicted for LkCa 15 b is not detected, but the FWHM in Hα is broader than in the continuum for both slit positions. Our simulations show that the photocenter and FWHM observations cannot be explained simultaneously by an accreting planet. In turn, both spectro-astrometric observations are naturally reproduced from a roughly symmetric Halpha emitting region centered on the star and extent comparable to the orbit originally attributed to the planet at several au. The extended Hα emission around LkCa 15 could be related to a variable disk wind, but additional multi-epoch data and detailed modeling are necessary to understand its physical nature. Spectro-astrometry in Hα is able to test the presence of accreting planets and can be used as a complementary technique to survey planet formation in circumstellar disks.

Another strike against:

Currie et al. "No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals"
https://arxiv.org/abs/1905.04322

Long et al. (2022) "ALMA Detection of Dust Trapping around Lagrangian Points in the LkCa 15 Disk"
https://iopscience.iop.org/article/10.3847/2041-8213/ac8b10

Two excess emission features separated by 120° and a faint ring at 42 au from the star, suggestive of material trapped in the Trojan points of a ~Neptune–Saturn mass planet, which remains undetected.