A fluffy disk around a baby star

Aug 23, 2013
Figure 1: Artist’s rendition of the "fluffy" layer associated with the protoplanetary disk of RY Tau, including jets coming from the star. Although typical young stars like RY Tau are often associated with jets, they are not visible in the HiCIAO observations at this time. Credit: NAOJ

An international team of astronomers that are members of the Strategic Exploration of Exoplanets and Disks with Subaru Telescope (SEEDS) Project has used Subaru Telescope's High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) to observe a disk around the young star RY Tau (Tauri). The team's analysis of the disk shows that a "fluffy" layer above it is responsible for the scattered light observed in the infrared image. Detailed comparisons with computer simulations of scattered light from the disk reveal that this layer appears to be a remnant of material from an earlier phase of stellar and disk development, when dust and gas were falling onto the disk.

Since 2009, the five-year SEEDS Project has focused on direct imaging of , i.e., planets orbiting stars outside of our Solar System, and disks around a targeted total of 500 stars. Planet formation, an exciting and active area for , has long fascinated many scientists. Disks of dust and gas that rotate around young stars are of particular interest, because astronomers think that these are the sites where planets form—in these so-called "protoplanetary disks." Since and disks are born in , giant and gas, the role of dust becomes an important feature of understanding ; it relates not only to the formation of rocky, Earth-like planets and the cores of giant Jupiter-like planets but also to that of moons, planetary rings, comets, and asteroids.

As a part of the SEEDS Project, the current team of researchers used HiCIAO mounted on the Subaru Telescope to observe a possible planet-forming disk around the young star RY Tau. This star is about 460 light years away from Earth in the constellation Taurus and is around half a million years old. The disk has a radius of about 70 AU (10 billion kilometers), which is a few times larger than the orbit of Neptune in our own Solar System.

Figure 2: (left) An image in the near infrared (1.65 μm) around RY Tau, using a special mode of the HiCIAO coronagraph, the polarized intensity image. This type of observation is preferred for faint emissions associated with scattered light around planet-forming disks, as there is less light from the much brighter star. The colors indicate the strength of the emission (blue, yellow and red from faint to bright). A coronagraphic mask in the telescope optics blocks the central star, with its position marked at the center. A white ellipse shows the position of the midplane of the disk, which is observed at millimeter wavelengths. Scattered light observed in the near infrared is offset to the top of the image compared with the denser millimeter disk. (right) Schematic view of the observed infrared light. The light from the star is scattered in the upper dust layer, and it makes the observed light offset from the midplane. Credit: NAOJ

Astronomers have developed powerful instruments to obtain images of protoplanetary disks, and Subaru Telescope's HiCIAO is one of them. HiCIAO uses a mask to block out the light of the central star, which may be a million times brighter than its disk. They can then observe light from the star that has been reflected from the surface of the disk. The will reveal the structure of the surface of the disk, which is very small in scale and difficult to observe, even with large telescopes. Observers use HiCIAO with a 188 element system to reduce the blurring effects of the Earth?s atmosphere, making the images significantly sharper.

This team succeeded in capturing a near- (1.65 ?m) associated with the RY Tau disk. Unlike many other protoplanetary disks, the disk emission is offset from the centre of the star (Figure 2, left). In contrast to longer wavelength observations, which are associated with the midplane of the disk, near-infrared, scattered light coming from the surface of the disk produced this offset (Figure 2, right), which provides information about the vertical structure of the disk.

Figure 3: Computer simulation for dust scattering for RY Tau. The color indicates the strength of the modeled flux (blue, yellow and red for faint to bright). The white contours show the image observed using Subaru Telescope's HiCIAO. This modeled disk has a disk with a fluffy layer and closely matches the image in shape and brightness. Credit: NAOJ

Changes in structure perpendicular to the surface of a disk are much harder to investigate because there are few good examples to study. Therefore, the information about vertical structure that this image provides is a contribution to understanding the formation of planets, which depends strongly on the structure of the disk, including structures such as spirals and rings, as well as height.

The team performed extensive of the scattered light, for disks with different masses, shapes, and types of dust (Figure 3). They found that the scattered light is probably not associated with the main surface of the disk, which is the usual explanation for the scattered light image (Figure 4a). Instead, the observed infrared emission can be explained if the emission is associated with a fluffy upper layer, which is almost transparent and not completely transparent (Figure 4b). The team estimated the dust mass in this layer to be about half the mass of Earth?s Moon.

Figure 4: Schematic views of the structure of the protoplanetary disk. The disk is transparent at millimeter wavelengths, and as a result, the observed millimeter emission is associated with the densest region (the midplane). In contrast, the disk is opaque in the infrared in even at the upper layer. Researchers often assume that the near-infrared emission is due to scattered light from its surface like figure (a). Figure (b) shows the revised schematic view through this study for RY Tau. There is another layer above the two layers in (a). This layer is almost transparent in the near-infrared, but not completely. The team concludes that the scattered emission observed using Subaru Telescope's HiCIAO is mainly due to scattering in this layer. Credit: NAOJ

Why is this fluffy layer observed in this disk, but not in many other possible planet-forming disks? The team suspects that this layer is a remnant of the dust that fell onto the star and the disk during earlier stages of formation. In most stars, unlike RY Tau, this layer dissipates by this stage in the formation of the star, but RY Tau may still have it because of its youth. It may act as a special comforter to warm the inside of the disk for baby planets being born there. This may affect the number, size, and composition of the planets being born in this system.

The Atacama Large Millimeter/Submillimeter Array (ALMA), a superb international millimeter/submillimeter telescope, will soon be making extensive observations of protoplanetary disks, which will allow scientists to directly observe ongoing planet formation in the midplane of a disk. By comparing SEEDS and ALMA observations scientists may be able to understand the details of how planets form, something that has raised fascinating questions for centuries.

Explore further: Spitzer discovers young stars with a 'hula hoop'

More information: Takami, M. et al, 2013, High-Contrast Near-Infrared Imaging Polarimetry of the Protoplanetary Disk around RY Tau, Astrophysical Journal, Vol. 772, paper 145.

Related Stories

Dust grains highlight the path to planet formation

Nov 28, 2012

(Phys.org)—An international team of researchers from the National Astronomical Observatory of Japan (NAOJ) and the Japanese universities of Kobe, Hyogo, and Saitama used the Subaru Telescope to capture ...

Spiral structure of disk may reveal planets

Dec 20, 2012

(Phys.org)—An international team of astronomers has used HiCIAO (High Contrast Instrument for the Subaru Next Generation Optics) to observe a disk around the young star SAO 206462. They succeeded in capturing ...

Spitzer discovers young stars with a 'hula hoop'

Jul 31, 2013

(Phys.org) —Astronomers using NASA's Spitzer Space Telescope have spotted a young stellar system that "blinks" every 93 days. Called YLW 16A, the system likely consists of three developing stars, two of ...

Recommended for you

Quest for extraterrestrial life not over, experts say

Apr 18, 2014

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

Protoplasmix
1.9 / 5 (9) Aug 23, 2013
Definitely looking forward to seeing what ALMA can make out. 500k years is pretty young for a star.
Q-Star
3.7 / 5 (6) Aug 23, 2013
Definitely looking forward to seeing what ALMA can make out. 500k years is pretty young for a star.


Yes it is and if was a serendipitous find. This is the sort of thing ALMA excels at. (If the strike down there doesn't throw the observation schedule out for too long.)
rug
1 / 5 (6) Aug 23, 2013
Am I the only one that is really, really glad this wasn't closer and pointed at us?
megmaltese
1.4 / 5 (9) Aug 24, 2013
Am I the only one that is really, really glad this wasn't closer and pointed at us?


Uh why? This is nothing dangerous, for what I know.

BTW I hope technology will allow me to see some star system with good resolution before I die. I would love it so much.
Torbjorn_Larsson_OM
4.2 / 5 (5) Aug 24, 2013
@rug: Maybe you are mistaking the protoplanetary system jets for black hole disk or neutron star jets?

They are somewhat analogous but much more weak x ray jets, as it is a young and in comparison larger star with much weaker and diffuse magnetic field driving the jets.

They are not harmful what I know. Instead they are the birth pangs of new systems, something joyous to see IMO.
rug
1.6 / 5 (7) Aug 25, 2013
Ah, I was thinking for some reason these jets would have the same gamma radiation a neutron star would have. Still, even extra x-rays seem like a bad idea.
Fleetfoot
5 / 5 (2) Sep 16, 2013
Ah, I was thinking for some reason these jets would have the same gamma radiation a neutron star would have. Still, even extra x-rays seem like a bad idea.


There are no jets involved here, we are seeing just the surface glow and reflected starlight from a flat disc. The radiation is infra-red and completely harmless, below the wavelength where infra-red themometers operate.
yyz
5 / 5 (2) Sep 16, 2013
While this current near-IR study of the dusty disk surrounding RY Tau found no evidence of jets, a recent Gemini study did find bipolar optical jets originating from the star: http://iopscience....web.pdf

Observations with the Chandra X-ray Observatory have also found possible evidence of a weak x-ray jet associated with RY Tau: http://arxiv.org/abs/1105.5125

But as TLOM points out, these jets are weak, low-power analogs of astrophysical jets associated with black holes and gamma ray bursts.

"The birth pangs of new systems".

Joyous indeed.

More news stories

Another fireball explodes over Russia

Why does Russia seem to get so many bright meteors? Well at 6.6 million square miles it's by far the largest country in the world plus, with dashboard-mounted cameras being so commonplace (partly to help ...

ISEE-3 comes to visit Earth

(Phys.org) —It launched in 1978. It was the first satellite to study the constant flow of solar wind streaming toward Earth from a stable orbit point between our planet and the sun known as the Lagrangian ...

NASA's MMS observatories stacked for testing

(Phys.org) —Engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., accomplished another first. Using a large overhead crane, they mated two Magnetospheric Multiscale, or MMS, observatories – ...