HL Tau - Imaged protoplanetary disk

Not looking particularly good for this one...

From Carrasco-González et al. (2009)...

Quote :

As can be seen in Figure 1a, we have not detected 7 mm emission at the position of the proto-planet candidate, with a 3-σ upper limit level of ∼0.15 mJy. This upper limit and the 1.3 cm flux density of Greaves et al. (2008) implies a spectral index <1, suggesting free-free rather than dust emission. On the other hand, the spectral index of 2.5 between 1.3 cm and 1.4 mm obtained by Greaves et al. (2008) would imply a 7 mm flux density of 0.5 mJy, well above our 3-σ upper limit. Additional, high angular resolution observations in the mm range are necessary to clarify the true nature of this source.

And today's arXiv... Kwon et al. (2011)

Quote :

As shown in the panels, the candidate position is within the dust thermal emission region of the disk at λ = 1.3 mm; however, subtraction of the axi-symmetric disk model removes essentially all flux. Before model subtraction the flux at the position is ∼16 mJy beam⁻¹; after subtraction the position has a negative flux at a level of 2σ. Therefore, our λ = 1.3 mm image provides no support for the candidate protoplanetary condensation.

Nevertheless there do seem to be hints of potentially-interesting structures in the disc, I guess the story is not done yet...

That's... wow...

Never expected to see this kind of thing at that level of detail. Amazing to see the progress being made.

ALMA has proved itself to be extremely capable. I expect the will be many more exquisite debris disk images to come.

I wonder if this image is going to get analysed for what it shows of the dynamics of the disk. The distribution of gaps and rings towards the outer edge of the disk seem rather complex indeed.

They used between 25 and 30 antennas...(At 1.28 mm wavelength)
ALMA has now 66 antennas : guess the futur !

Attempts to constrain the mass of the planets.

Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau
http://arxiv.org/abs/1502.05099

ALMA Partnership, "First Results from High Angular Resolution ALMA Observations Toward the HL Tau Region"
http://arxiv.org/abs/1503.02649

Also observations of XZ Tauri AB and LkHα358

http://www.eurekalert.org/pub_releases/2015-05/uot-uot050515.php

The team, led by Daniel Tamayo from the Centre for Planetary Science at U of T Scarborough and the Canadian Institute for Theoretical Astrophysics, found that circular gaps in a disk of dust and gas swirling around the young star HL Tau are in fact made by forming planets

http://arxiv.org/abs/1505.00882

Evidence of fast pebble growth near condensation fronts in the HL Tau protoplanetary disk

Water and simple organic molecular ices dominate the mass of solid materials available for planetesimal and planet formation beyond the water snow line. Here we analyze ALMA long Baseline 2.9, 1.3 and 0.87mm continuum images of the young star HL Tau, and suggest that the emission dips observed are due to rapid pebble growth around the condensation fronts of abundant volatile species. Specifically, we show that the prominent innermost dip at 13AU is spatially resolved in the 0.87mm image, and its center radius is coincident with the expected mid-plane condensation front of water ice. In addition, two other prominent dips, at distances of 32 and 63 AU, cover the mid-plane condensation fronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially with CO and N2) formed from amorphous water ice. The spectral index map of HL Tau between 1.3 and 0.87mm shows that the flux ratios inside the dips are statistically larger than those of nearby regions in the disk. This variation can be explained by a model with two dust populations, where most of solid mass resides in a component that has grown into decimeter size scales inside the dips. Such growth is in accord with recent numerical simulations of volatile condensation, dust coagulation and settling.

http://www.skyandtelescope.com/astronomy-news/searching-for-exoplanets-around-hl-tau-10192015/

With or without gas observations, planets are really the only plausible explanation for the disk gaps, says Alan Boss (Carnegie Institution for Science). “There is no alternative that I can conceive.”
But will ALMA or other telescopes be able to find these planets? Testi notes that in order to find smaller planets 70 a.u. from HL Tau, astronomers will need to improve the contrast in their infrared imaging by 3 to 4 magnitudes at only 0.5 arcseconds from the central star, something still out of reach for current scopes.
“I am sure that there will be other attempts to look at HL Tau to find planets,” Testi says, “but the real breakthrough will come with the generation of the 30- to 40-meter telescopes — it will take a few years, alas.”

http://arxiv.org/abs/1511.04822

Planetary System Formation in Protoplanetary Disk around HL Tauri

We re-process the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. As shown by the previous work, we confirm that the high spatial resolution (~ 0."019, corresponding to ~ 2.7 AU) dust continuum images at \lambda = 0.87, 1.3, and 2.9 mm exhibit a multiple ring-like gap structure in the circumstellar disk. Assuming that the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on following two approaches; the Hill radius analysis and a more elaborated approach developed from the angular momentum transfer analysis in gas disks. For the former, the measured gap widths are used for calibrating the mass of the bodies, while for the latter, the measured gap depths are utilized. We show that their masses are likely comparable to or less than the mass of Jovian planets, and then discuss an origin of the observed gap structure….

The VLA view of the HL Tau Disk - Disk Mass, Grain Evolution, and Early Planet Formation

Quote :

The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the Karl G. Jansky Very Large Array at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. We obtain a total disk dust mass of 0.001 - 0.003 Msun, depending on the assumed opacity and disk temperature. Our optically thin data also indicate fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright rings.

[Phys.org]Speedy planet birth: Astronomers observe a clump of dust in the disk around star HL Tauri



Maybe should we fuse this thread with this one?