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Detecting the signature of planets at millimeter wavelengths
F. Ramos-Stierle, D.H. Hughes, E. L. Chapin (INAOE, Mexico), G.A. Blake ??? [email protected]
The study of planet formation mechanisms is a central part of our search for an understanding of the origin of the Earth and Solar System. The motivation to study the
environments of planet formation has become more intense since the discovery of the first giant planets around nearby solar-type stars using the Doppler planetdetection technique. One of the most intriguing results of searches for exoplanets (and a challenge to the new theories of planetary formation), is the discovery that the
formation process gives rise to considerable diversity. Surveys of young stars at infrared and millimeter wavelengths show that most exhibit thermal emission from small
heated particles distributed in disks (PROPLYDs) , with properties similar to those of the young Solar System. Models of their spectral energy distributions (SEDs) and
imaging indicate disk sizes of tens to hundreds of AU. These dusty and gas-rich disks are believed to provide the material for proto-stellar sources, as well as the
reservoirs of mass for the formation of planetary systems. Although there is now abundant evidence for the existence of circumstellar disks around young low-mass
stars, our understanding of the detailed properties of disks, in particular at distances (< 30 AU) associated with planet formation, is still in its early stages. With the
combination of high angular resolution and sensitivity in new millimeter experiments (e.g. ALMA and LMT) , we will be able to image the detailed structure of nearby
disks, and detect the gaps and inner-holes (both spectrally and spatially) created by the clearing of material during the planet formation process.
Modelling the thermal emission from PROPLYDs
HST imaging of PROPLYDs
(25 to 500 AU) around YSOs
in Orion (D=400pc).
Massive planets orbiting a
star cause a change in the
radial velocity. This Doppler
method currently provides
the most efficient planet
detection method.
We know about the existence of PROPLYDs and planets, but we are still
waiting for clear proof that both are related. We present optically thin
thermal models of the multi-wavelength emission from PROPLYDs, to
generate realistic simulated images of the gaps and holes in disks
associated with planet formation. Disks contain a mixture of gas and dust.
Even though the dust mass is 1% (or less) of the mass in PROPLYD
environments, virtually all the continuum radiation from the infrared to the
millimeter is due to thermal radiation from dust. Dust warmed by the
starlight radiates as a blackbody modified by the emissivity of the grains.
The dust temperatures depend on the distance of a grain from the star, and
since a continuous disk contains particles over a wide range of distances
from the star (out to several hundred AU), dust temperatures range from
the sublimation temperature (approximately 1500 K) to a few Kelvin. The
result is a broad spectrum of thermal emission from ~ 1 μm to 1000 μm.
The composite SED (black line)
from a disk with thermal
emission at different radii, and
different temperatures. The
contribution from the individual
annuli are shown in colour.
Gaps in disks
Physical gaps in the disk can be created by the presence of a
proto-planet which clears dusty and gaseous material.
Removing this material will also reduce the thermal contribution
from the region. The gap will therefore produce a depression in
the SED at wavelengths that correspond to the temperature of
the “missing” dust .
Inner-holes in disks
A 15 – 35 AU gap in the PROPLYD caused by
the clearance of dust due to proto-planets.
The maximum intensity was clipped to show
better the effect.
Composite SEDs showing the
impact of gaps of different
widths which are created in a
continuous disk.
A 40 AU inner-hole caused by the clearance of
dust from the collective influence of all planets
in a young solar system.
Composite SEDs calculated
for different sizes of innerholes. The stellar contribution
is shown in yellow.
While only the largest proto-planets may form gaps of sufficient
width to be imaged directly, smaller bodies can produce
detectable inner-holes once the bulk of disk material interior to
their orbits has been accreted. After sufficient evolution, the
entire planetary system can clear all material out to the most
distant planet.
Telescope simulations
Individual detector signals are generated
by an instrument and telescope simulator2
that passes an array of pixels across a
composite of the "idealised" maps.
The following effects eare included:
 telescope primary aperture
 beam shape
 array geometry and sensitivity
 scan pattern and pointing errors
 atmospheric noise and attenuation
 detector time constant and 1/f drift
 Poisson noise
 integration time
Simulated 100AU PROPLYD (D=3pc), at
an inclination 45°, with an inner-hole of
40AU, observed with the BOLOCAM-II
camera operating at 1.1mm on the LMT.
Background is a segment of Saturn’s rings.
True image of dust
emission around ε Eri at a
wavelength of 850μm,
using SCUBA at the JCMT
(Greaves et al. 1998)3 .
A simulation of dust emission
around ε Eri at a wavelength of
850μm, observed with the
SCUBA camera operating on
the 15-m JCMT.
This figure shows the same
PROPLYD (Mdust = 5.5 Mℂ, 5%
the initial dust of the minimum
solar-nebula)4 observed at
1.1mm with ALMA using the
smallest baselines (150m).
Francisco Ramos Stierle : [email protected]
David Hughes
: [email protected]
Edward Chapin
: [email protected]
In these simulations we tune
interferometer to optimize the
synthesized beam size and
sensitivity to the structure of
interest. Left figure: We choose
a maximum baseline of 150m
(beamsize 1’’) in order to map
the extended structure of the
dust disk, and measure the
total dust mass. Right figure:
ALMA observations with longer
baselines (3.5km – beamsize
0.06’’) in order to spatially
resolve a gap in a disk at a
distance of 20pc.
A simulated 100AU PROPLYD (D=20 pc) at 45°
inclination with a gap between 3.2 and 11AU
(corresponding to the clearance by the orbits of
Jupiter + Saturn), observed with ALMA for 3hrs
using 3.5km baselines. The lower panel shows a
slice though the disk, clearly showing the
presence of the gaps. The huge intensity peak is
caused by the hot dust located close to the star.
2. Chapin et al. 2001, astro-ph/109330
3. Greaves et al. 1998, ApJ 506:L133-L137
4. Ramos-Stierle 2003, MSc thesis