Image at 7 mm wavelength of the
dusty disk around the star HD 169142 obtained with the Very Large Array
(VLA) at 7 mm wavelength. The positions of the protoplanet candidates
are marked with plus signs (+) (Osorio et al. 2014, ApJ, 791, L36). The
insert in the upper right corner shows, at the same scale, the bright
infrared source in the inner disk cavity, as observed with the Very
Large Telescope (VLT) at 3.8 micron wavelength (Reggiani et al. 2014,
ApJ, 792, L23).
Young star HD169142 displays a disk of gas and dust with two annular gaps possibly due to the formation of planets
Planets are formed from disks of gas and dust that orbit around young
stars. Once the “seed” of the planet —composed of a small aggregate of
dust— is formed, it will continue to gather material and it will carve
out a cavity or gap in the disk along its orbital path.
This transitional stage between the original disk and the planetary
system, difficult to study and as yet little known, is precisely what
has been observed in the star HD169142 and is discussed in two articles
published in The Astrophysical Journal Letters.
"Although in recent years more than seventeen hundred extrasolar
planets have been discovered, few of them have been directly imaged, and
so far we have never been able to capture an unequivocal image of an
still-forming planet”, says Mayra Osorio, researcher at the Institute of
Astrophysics of Andalusia (IAA-CSIC) heading one of the articles. “In
HD 169142 we may be seeing indeed those seeds of gas and dust which will
later become planets."
HD169142 is a young star with twice the mass of the Sun and whose disk
extends up to two hundred and fifty astronomical units (an astronomical
unit, or AU, is a unit equivalent to the distance between the Sun and
the Earth: one hundred and fifty million kilometers). The system is in
an optimal orientation for the study of planet formation because the
disk is seen face-on.
The first article explores the disk of HD169142 with the Very Large Array radio
telescope, which can detect centimeter-sized dust grains. The results,
combined with infrared data which trace the presence of microscopic
dust, reveal two gaps in the disk, one in the inner region (between 0.7
and 20 AU) and another, farther out and less developed, between 30 and
70 AU.
"This structure already suggested that the disk was being modified by
two planets or sub-stellar objects, but, additionally, the radio data
reveal the existence of a clump of material within the external gap,
located approximately at the distance of Neptune’s orbit, which points
to the existence of a forming planet”, says Mayra Osorio (IAA-CSIC).
The second study focused on searching for infrared sources in the gaps of the disk, using the Very Large Telescope.
They found a bright signal in the inner gap, which could correspond to a
still-forming planet or to a young brown dwarf (a sort of failed star
that never reached the threshold mass to trigger the nuclear reactions
characteristic of stars).
Infrared data did not, however, corroborate the presence of an object
in the outer gap as radio observations suggested. This non detection
could be due to technical limitations: the researchers have calculated
that an object with a mass between one tenth and 18 times the Jupiter’s
mass surrounded by a cold envelope may well remain undetected at the
observed wavelength.
"In future observations we will be able to verify whether the disk
harbors one or two objects. In any case, HD 169142 remains as a
promising object since it is one of the few known transitional disks and
it is revealing to us the environment where planets are formed", says
Mayra Osorio (IAA-CSIC).
An artist's impression of a protoplanetary disk
Credit: ESO/L. Calçada
Reference:
M. Osorio et al. "Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm". The Astrophysical Journal ApJ 791 L36. DOI: 10.1088/2041-8205/791/2/L36
M. Reggiani et al. "Discovery of a companion candidate in the HD169142
transition disk and the possibility of multiple planet formation". The Astrophysical Journal. 792, L23, DOI: 10.1088/2041-8205/792/1/L23
Contact:
Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - Email: sll@iaa.es - 958230532
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - Email: sll@iaa.es - 958230532
Instituto de Astrofísica de Andalucía - (IAA- CSIC)
http://www-divulgacion.iaa.es
