704 research outputs found
Time-resolved photometry of the young dipper RX~J1604.3-2130A:Unveiling the structure and mass transport through the innermost disk
Context. RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk, with respect to its face-on outer disk. Aims. We aim to study the eclipses to constrain the inner disk properties. Methods. We used time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and infrared data to track accretion, rotation, and changes in disk structure. Results. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5 d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (similar to 0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such an amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE infrared variability reveal variations in the dust content in the innermost disk on a timescale of a few years, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v sin i = 16 km s(-1) confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.Science & Technology Facilities Council (STFC): ST/S000399/1.
ESO fellowship.
European Union (EU): 823 823.
German Research Foundation (DFG): FOR 2634/1 TE 1024/1-1.
French National Research Agency (ANR): ANR-16-CE31-0013.
Alexander von Humboldt Foundation.
European Research Council (ERC): 678 194.
European Research Council (ERC): 742 095.
National Aeronautics & Space Administration (NASA).
National Science Foundation (NSF).
National Aeronautics & Space Administration (NASA): NNG05GF22G.
National Science Foundation (NSF): AST-0909182, AST-1 313 422
Strengthening extended Gravity constraints with combined systems:\\ \texorpdfstring{}{} bounds from Cosmology and the Galactic Center
MOdified Gravity (MoG)) is widely constrained in different astrophysical and
astronomical systems. Since these different systems are based on different
scales it is not trivial to get a combined constraint that is based on
different phenomenology. Here, for the first time (to the best of our
knowledge), we combine constraints for MoG from late time Cosmology and the
orbital motion of the stars around the galactic center. MoG give different
potentials that are tested directly in the galactic center. The cosmological
data set includes the type Ia supernova and baryon acoustic oscillations. For
the galactic star center data set we use the published orbital measurements of
the S2 star. The constraints on the universal parameter from the
combined system give: for the Hu-Sawicki model,
while for the Starobinsky model. These results
improve on the cosmological results we obtain. The results show that {{\it
combined constraint}} from different systems yields a stronger constraint for
different theories under consideration. Future measurements from the galactic
center and from cosmology will give better constraints on MoG.Comment: 8 pages, 2 figure
Refined masses and distance of the young binary Haro 1-14 C
We aim to refine the dynamical masses of the individual component of the
low-mass pre-main sequence binary Haro 1-14 C. We combine the data of the
preliminary orbit presented previously with new interferometric observations
obtained with the four 8m telescopes of the Very Large Telescope
Interferometer. The derived masses are M_a=0.905\pm0.043\,\Msun and
M_b=0.308\pm0.011\,\Msun for the primary and secondary components,
respectively. This is about five times better than the uncertainties of the
preliminary orbit. Moreover, the possibility of larger masses is now securely
discarded. The new dynamical distance, pc, is smaller than the
distance to the Ophiuchus core with a significance of . Fitting
the spectral energy distribution yields apparent diameters of
\phi_a=0.13\pm0.01\mas and \phi_b=0.10\pm0.01\mas (corresponding to
\Ra=1.50\,\Rsun and \Rb=1.13\,\Rsun) and a visual extinction of
. Although the revised orbit has a nearly edge-on geometry, the
system is unlikely to be a long-period eclipsing binary. The secondary in
Haro~1-14C is one of the few low-mass, pre-main sequence stars with an
accurately determined dynamical mass and distance
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Milli-arcsecond images of the Herbig Ae star HD 163296
The very close environments of young stars are the hosts of fundamental
physical processes, such as planet formation, star-disk interactions, mass
accretion, and ejection. The complex morphological structure of these
environments has been confirmed by the now quite rich data sets obtained for a
few objects by near-infrared long-baseline interferometry. We gathered numerous
interferometric measurements for the young star HD163296 with various
interferometers (VLTI, IOTA, KeckI and CHARA), allowing for the first time an
image independent of any a priori model to be reconstructed. Using the
Multi-aperture image Reconstruction Algorithm (MiRA), we reconstruct images of
HD 163296 in the H and K bands. We compare these images with reconstructed
images obtained from simulated data using a physical model of the environment
of HD 163296. We obtain model-independent and -band images of the
surroundings of HD 163296. The images present several significant features that
we can relate to an inclined asymmetric flared disk around HD 163296 with the
strongest intensity at about 4-5 mas. Because of the incomplete spatial
frequency coverage, we cannot state whether each of them individually is
peculiar in any way. For the first time, milli-arcsecond images of the
environment of a young star are produced. These images confirm that the
morphology of the close environment of young stars is more complex than the
simple models used in the literature so far.Comment: 11 pages, 10 figures, accepted A&A pape
The complex morphology of the young disk MWC 758: Spirals and dust clumps around a large cavity
We present Atacama Large Millimeter Array (ALMA) observations at an angular
resolution of 0.1-0.2" of the disk surrounding the young Herbig Ae star MWC
758. The data consist of images of the dust continuum emission recorded at 0.88
millimeter, as well as images of the 13CO and C18O J = 3-2 emission lines. The
dust continuum emission is characterized by a large cavity of roughly 40 au in
radius which might contain a mildly inner warped disk. The outer disk features
two bright emission clumps at radii of about 47 and 82 au that present
azimuthal extensions and form a double-ring structure. The comparison with
radiative transfer models indicates that these two maxima of emission
correspond to local increases in the dust surface density of about a factor 2.5
and 6.5 for the south and north clumps, respectively. The optically thick 13CO
peak emission, which traces the temperature, and the dust continuum emission,
which probes the disk midplane, additionally reveal two spirals previously
detected in near-IR at the disk surface. The spirals seen in the dust continuum
emission present, however, a slight shift of a few au towards larger radii and
one of the spirals crosses the south dust clump. Finally, we present different
scenarios in order to explain the complex structure of the disk.Comment: 15 pages, 11 figures. The paper has been published in ApJ. References
added and typos correcte
Jets and Outflows From Star to Cloud: Observations Confront Theory
In this review we focus on the role jets and outflows play in the star and
planet formation process. Our essential question can be posed as follows: are
jets/outflows merely an epiphenomenon associated with star formation or do they
play an important role in mediating the physics of assembling stars both
individually and globally? We address this question by reviewing the current
state of observations and their key points of contact with theory. Our review
of jet/outflow phenomena is organized into three length-scale domains: Source
and Disk Scales ( au) where the connection with protostellar and disk
evolution theories is paramount; Envelope Scales ( au) where the
chemistry and propagation shed further light on the jet launching process, its
variability and its impact on the infalling envelope; Parent Cloud Scales
( au) where global momentum injection into cluster/cloud
environments become relevant. Issues of feedback are of particular importance
on the smallest scales where planet formation regions in a disk may be impacted
by the presence of disk winds, irradiation by jet shocks or shielding by the
winds. Feedback on envelope scales may determine the final stellar mass
(core-to-star efficiency) and envelope dissipation. Feedback also plays an
important role on the larger scales with outflows contributing to turbulent
support within clusters including alteration of cluster star formation
efficiencies (feedback on larger scales currently appears unlikely). A
particularly novel dimension of our review is that we consider results on jet
dynamics from the emerging field of High Energy Density Laboratory Astrophysics
(HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully
magnetized, hypersonic, radiative outflows.Comment: Accepted for publication as a chapter in Protostars and Planets VI,
University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C.
Dullemond, Th. Hennin
Planet formation in the PDS 70 system: Constraining the atmospheric chemistry of PDS 70b and c
Understanding the chemical link between protoplanetary disks and planetary
atmospheres is complicated by the fact that the popular targets in the study of
disks and planets are widely separated both in space and time. The 5 Myr PDS 70
systems offers a unique opportunity to directly compare the chemistry of a
giant planet's atmosphere to the chemistry of its natal disk. To that end, we
derive our current best physical and chemical model for the PDS 70 disk through
forward modelling of the CO, CO, and CH emission radial
profiles with the thermochemical code DALI and find a volatile C/O ratio above
unity in the outer disk. Using what we know of the PDS 70 disk today, we
analytically estimate the properties of the disk as it was 4 Myr in the past
when we assume that the giant planets started their formation, and compute a
chemical model of the disk at that time. We compute the formation of PDS 70b
and PDS 70c using the standard core accretion paradigm and account for the
accretion of volatile and refractory sources of carbon and oxygen to estimate
the resulting atmospheric carbon-to-oxygen number ratio (C/O) for these
planets. Our inferred C/O ratio of the gas in the PDS 70 disk indicates that it
is marginally carbon rich relative to the stellar C/O = 0.44 which we derive
from an empirical relation between stellar metallicity and C/O. Under the
assumption that the disk has been carbon rich for most of its lifetime, we find
that the planets acquire a super-stellar C/O in their atmospheres. If the
carbon-rich disk is a relatively recent phenomenon (i.e. developed after the
formation of the planets at Myr) then the planets should have close to
the stellar C/O in their atmospheres. This work lays the groundwork to better
understand the disk in the PDS 70 system as well as the planet formation
scenario that produce its planets.Comment: 18 pages, 14 figures, 5 tables, accepted for publication in A&
The inner radius of T Tauri disks estimated from near-infrared interferometry: the importance of scattered light
For young Herbig Ae/Be stars, near-infrared interferometric measurements have
revealed a correlation between the luminosity of the central object and the
position of the disk inner rim. This correlation breaks down for the cooler T
Tauri stars, a fact often interpreted in terms of disks with larger inner
radii. In most cases, the conversion between the observed interferometric
visibility and the calculated disk inner radius was done with a crude disk
emission model. Here, we examine how the use of models that neglect scattered
light can lead to an overestimation of the disk sizes. To do so, synthetic disk
images (and visibilities) are calculated with a full treatment of the radiative
transfer. The relative contributions of thermal emission and scattered light
are compared. We find that the latter can not be neglected for cool stars. For
further comparison, the model visibilities are also converted into inner disk
radii using the same simple disk models as found in the literature. We find
that reliable inner radii can only be estimated for Herbig Ae/Be stars with
these models. However, they lead to a systematic overestimation of the disk
size, by a factor of 2 to 3, for T Tauri stars. We suggest that including
scattered light in the models is a simple (and sufficient) explanation of the
current interferometric measurements of T Tauri stars.Comment: 4 pages, 4 figures, accepted for publication in ApJ
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