42 research outputs found
Evolution of Molecular Abundance in Protoplanetary Disks
We investigate the evolution of molecular abundance in quiescent
protoplanetary disks which are presumed to be around weak-line T Tauri stars.
In the region of surface density less than g cm (distance from
the star AU in the minimum- mass solar nebula), cosmic rays are
barely attenuated even in the midplane of the disk and produce chemically
active ions such as He and H. Through reactions with these ions CO
and N are finally transformed into CO, NH, and HCN. In the region
where the temperature is low enough for these products to freeze onto grains,
considerable amount of carbon and nitrogen is locked up in the ice mantle and
is depleted from the gas phase in a time scale yr.
Oxidized (CO) ice and reduced (NH and hydrocarbon) ice naturally
coexist in this part of the disk. The molecular abundance both in the gas phase
and in ice mantle varies significantly with the distance from the central star.Comment: 7 pages latex file (using aas2pp4.sty), 3 figures (ps file), to
appear in the Astrophysical Journal Letter
Magnetorotational Instability in Protoplanetary Disks. II. Ionization State and Unstable Regions
We investigate where in protoplanetary disks magnetorotational instability
operates, which can cause angular momentum transport in the disks. We
investigate the spatial distribution of various charged particles and the
unstable regions for a variety of models for protoplanetary disks taking into
account the recombination of ions and electrons at grain surfaces, which is an
important process in most parts of the disks. We find that for all the models
there is an inner region which is magnetorotationally stable due to ohmic
dissipation. This must make the accretion onto the central star non-steady. For
the model of the minimum-mass solar nebula, the critical radius, inside of
which the disk is stable, is about 20 AU, and the mass accretion rate just
outside the critical radius is 10^{-7} - 10^{-6} M_{\odot} yr^{-1}. The stable
region is smaller in a disk of lower column density. Dust grains in
protoplanetary disks may grow by mutual sticking and may sediment toward the
midplane of the disks. We find that the stable region shrinks as the grain size
increases or the sedimentation proceeds. Therefore in the late evolutionary
stages, protoplanetary disks can be magnetorotationally unstable even in the
inner regions.Comment: 23 pages + 16 figures + 3 tables, accepted for publication in Ap
Subaru near infrared coronagraphic images of T Tauri
High angular resolution near-infrared (JHK) adaptive optics images of T Tau were obtained with the infrared camera Coronagraphic Imager with Adaptive Optics (CIAO) mounted on the 8.2m Subaru Telescope in 2002 and 2004. The images resolve a complex circumstellar structure around a multiple system. We resolved T Tau Sa and Sb as well as T Tau N and S. The estimated orbit of T Tau Sb indicates that it is probably bound to T Tau Sa. The K band flux of T Tau S decreased by ˜ 1.7 Jy in 2002 November compared with that in 2001 mainly because T Tau Sa became fainter. The arc-like ridge detected in our near-infrared images is consistent with what is seen at visible wavelengths, supporting the interpretation in previous studies that the arc is part of the cavity wall seen relatively pole-on. Halo emission is detected out to ˜2\u27\u27from T Tau N. This may be light scattered off the common envelope surrounding the T Tauri multiple system
Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk around PDS 70: Observations of the disk
We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14
AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk
around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of
28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly
resolved for the first time, and the radius of the gap is ~70 AU. Our data show
that the geometric center of the disk shifts by ~6 AU toward the minor axis. We
confirm that the brown dwarf companion candidate to the north of PDS 70 is a
background star based on its proper motion. As a result of SED fitting by Monte
Carlo radiative transfer modeling, we infer the existence of an optically thick
inner disk at a few AU. Combining our observations and modeling, we classify
the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the
analysis of L'-band imaging data, we put an upper limit mass of companions at
~30 to ~50MJ within the gap. Taking account of the presence of the large and
sharp gap, we suggest that the gap could be formed by dynamical interactions of
sub-stellar companions or multiple unseen giant planets in the gap.Comment: accepted by APJ
A Young Brown Dwarf Companion to DH Tauri
We present the detection of a young brown dwarf companion DH Tau B associated
with the classical T Tauri star DH Tau. Near-infrared coronagraphic
observations with CIAO on the Subaru Telescope have revealed DH Tau B with H =
\~15 mag located at 2.3" (330 AU) away from the primary DH Tau A. Comparing its
position with a Hubble Space Telescope archive image, we confirmed that DH Tau
A and B share the common proper motion, suggesting that they are physically
associated with each other. The near-infrared color of DH Tau B is consistent
with those of young stellar objects. The near-infrared spectra of DH Tau B show
deep water absorption bands, a strong K I absorption line, and a moderate Na I
absorption line. We derived its effective temperature and surface gravity of
Teff = 2700 -- 2800 K and log g = 4.0--4.5, respectively, by comparing the
observed spectra with synthesized spectra of low-mass objects. The location of
DH Tau B on the HR diagram gives its mass of 30 -- 50 M_Jupiter.Comment: 10 pages, 14 figures, 1 table, accepted for publication in Ap
Constraining the Movement of the Spiral Features and the Locations of Planetary Bodies within the AB Aur System
We present new analysis of multi-epoch, H-band, scattered light images of the
AB Aur system. We used a Monte Carlo, radiative transfer code to simultaneously
model the system's SED and H-band polarized intensity imagery. We find that a
disk-dominated model, as opposed to one that is envelope dominated, can
plausibly reproduce AB Aur's SED and near-IR imagery. This is consistent with
previous modeling attempts presented in the literature and supports the idea
that at least a subset of AB Aur's spirals originate within the disk. In light
of this, we also analyzed the movement of spiral structures in multi-epoch
H-band total light and polarized intensity imagery of the disk. We detect no
significant rotation or change in spatial location of the spiral structures in
these data, which span a 5.8 year baseline. If such structures are caused by
disk-planet interactions, the lack of observed rotation constrains the location
of the orbit of planetary perturbers to be >47 AU.Comment: 8 pages, 3 figures, 1 table, Accepted to Ap
Coincidence analysis to search for inspiraling compact binaries using TAMA300 and LISM data
Japanese laser interferometric gravitational wave detectors, TAMA300 and
LISM, performed a coincident observation during 2001. We perform a coincidence
analysis to search for inspiraling compact binaries. The length of data used
for the coincidence analysis is 275 hours when both TAMA300 and LISM detectors
are operated simultaneously. TAMA300 and LISM data are analyzed by matched
filtering, and candidates for gravitational wave events are obtained. If there
is a true gravitational wave signal, it should appear in both data of detectors
with consistent waveforms characterized by masses of stars, amplitude of the
signal, the coalescence time and so on. We introduce a set of coincidence
conditions of the parameters, and search for coincident events. This procedure
reduces the number of fake events considerably, by a factor
compared with the number of fake events in single detector analysis. We find
that the number of events after imposing the coincidence conditions is
consistent with the number of accidental coincidences produced purely by noise.
We thus find no evidence of gravitational wave signals. We obtain an upper
limit of 0.046 /hours (CL ) to the Galactic event rate within 1kpc from
the Earth. The method used in this paper can be applied straightforwardly to
the case of coincidence observations with more than two detectors with
arbitrary arm directions.Comment: 28 pages, 17 figures, Replaced with the version to be published in
Physical Review