104 research outputs found
The beta Pictoris phenomena among young stars, II. UV observations of the Herbig Ae star UX Orionis
Observations of 51 Ophiuchi with MIDI at the VLTI
We present interferometric observations of the Be star 51 Ophiuchi. These
observations were obtained during the science demonstration phase of the MIDI
instrument at the Very Large Telescope Interferometer (VLTI). Using MIDI, a
Michelson 2 beam combiner that operates at the N band (8 to 13 microns), we
obtained for the first time observations of 51 Oph in the mid-infrared at
high-angular resolution. It is currently known that this object presents a
circumstellar dust and gas disk that shows a very different composition from
other Herbig Ae disks. The nature of the 51 Oph system is still a mystery to be
solved. Does it have a companion? Is it a protoplanetary system? We still don't
know. Observations with MIDI at the VLTI allowed us to reach high-angular
resolution (20 mas).We have several uv points that allowed us to constrain the
disk model. We have modeled 51 Oph visibilities and were able to constrain the
size and geometry of the 51 Oph circumstellar disk.Comment: 5 pages, 3 figures, 2 tables, to be published in the proceedings of
"The Power of Optical / IR Interferometry: Recent Scientific Results and 2nd
Generation VLTI Instrumentation", Garching, April 4-8, 200
High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity
Planet formation studies are often focused on solar-type stars, implicitly
considering our Sun as reference point. This approach overlooks, however, that
Herbig Ae/Be stars are in some sense much better targets to study planet
formation processes empirically, with their disks generally being larger,
brighter and simply easier to observe across a large wavelength range. In
addition, massive gas giant planets have been found on wide orbits around early
type stars, triggering the question if these objects did indeed form there and,
if so, by what process. In the following I briefly review what we currently
know about the occurrence rate of planets around intermediate mass stars,
before discussing recent results from Herbig Ae/Be stars in the context of
planet formation. The main emphasis is put on spatially resolved polarized
light images of potentially planet forming disks and how these images - in
combination with other data - can be used to empirically constrain (parts of)
the planet formation process. Of particular interest are two objects, HD100546
and HD169142, where, in addition to intriguing morphological structures in the
disks, direct observational evidence for (very) young planets has been
reported. I conclude with an outlook, what further progress we can expect in
the very near future with the next generation of high-contrast imagers at 8-m
class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in
special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables
and reference
The Architecture of the LkCa 15 Transitional Disk Revealed By High-Contrast Imaging
We present four new epochs of Ks-band images of the young pre-transitional disk around LkCa 15 and perform extensive forward modeling to derive the physical parameters of the disk. We find indications of strongly anisotropic scattering (Henyey-Greenstein g = 0.67 (+0.18/0.11)) and a significantly tapered gap edge ("round wall") but see no evidence that the inner disk, whose existence is predicted by the spectral energy distribution, shadows the outer regions of the disk visible in our images.We marginally confirm the existence of an offset between the disk center and the star along the line of nodes; however, the magnitude of this offset (x = 27 (+19/20) mas) is notably lower than that found in our earlier H-band images. Intriguingly, we also find an offset of y = 69 (+49/25) mas perpendicular to the line of nodes at high significance. If confirmed by future observations, this would imply a highly elliptical - or otherwise asymmetric - disk gap with an effective eccentricity of e 0.3. Such asymmetry would most likely be the result of dynamical sculpting by one or more unseen planets in the system. Finally, we find that the bright arc of scattered light we see in direct imaging observations originates from the near side of the disk and appears brighter than the far side because of strong forward scattering
Imaging of a Transitional Disk Gap in Reflected Light: Indications of Planet Formation Around the Young Solar Analog LkCa 15
We present H- and Ks-band imaging data resolving the gap in the transitional
disk around LkCa 15, revealing the surrounding nebulosity. We detect sharp
elliptical contours delimiting the nebulosity on the inside as well as the
outside, consistent with the shape, size, ellipticity, and orientation of
starlight reflected from the far-side disk wall, whereas the near-side wall is
shielded from view by the disk's optically thick bulk. We note that
forward-scattering of starlight on the near-side disk surface could provide an
alternate interpretation of the nebulosity. In either case, this discovery
provides confirmation of the disk geometry that has been proposed to explain
the spectral energy distributions (SED) of such systems, comprising an
optically thick outer disk with an inner truncation radius of ~46 AU enclosing
a largely evacuated gap. Our data show an offset of the nebulosity contours
along the major axis, likely corresponding to a physical pericenter offset of
the disk gap. This reinforces the leading theory that dynamical clearing by at
least one orbiting body is the cause of the gap. Based on evolutionary models,
our high-contrast imagery imposes an upper limit of 21 Jupiter masses on
companions at separations outside of 0.1" and of 13 Jupiter masses outside of
0.2". Thus, we find that a planetary system around LkCa 15 is the most likely
explanation for the disk architecture.Comment: 5 pages, 4 figures, accepted for publication in ApJ Letters. Minor
change to Figure
Observational diagnostics of gas in protoplanetary disks
Protoplanetary disks are composed primarily of gas (99% of the mass).
Nevertheless, relatively few observational constraints exist for the gas in
disks. In this review, I discuss several observational diagnostics in the UV,
optical, near-IR, mid-IR, and (sub)-mm wavelengths that have been employed to
study the gas in the disks of young stellar objects. I concentrate in
diagnostics that probe the inner 20 AU of the disk, the region where planets
are expected to form. I discuss the potential and limitations of each gas
tracer and present prospects for future research.Comment: Review written for the proceedings of the conference "Origin and
Evolution of Planets 2008", Ascona, Switzerland, June 29 - July 4, 2008. Date
manuscript: October 2008. 17 Pages, 6 graphics, 134 reference
Optical photometry of GM Cep: evidence for UXor type of variability
Results from optical photometric observations of the pre-main sequence star
GM Cep are reported in the paper. The star is located in the field of the young
open cluster Trumpler 37 - a region of active star formation. GM Cep shows a
large amplitude rapid variability interpreted as a possible outburst from EXor
type in previous studies. Our data from BVRI CCD photometric observations of
the star are collected from June 2008 to February 2011 in Rozhen observatory
(Bulgaria) and Skinakas observatory (Crete, Greece). A sequence of sixteen
comparison stars in the field of GM Cep was calibrated in the BVRI bands. Our
photometric data for a 2.5 years period show a high amplitude variations (Delta
V ~ 2.3m) and two deep minimums in brightness are observed. The analysis of
collected multicolor photometric data shows the typical of UX Ori variables a
color reversal during the minimums in brightness. On the other hand, high
amplitude rapid variations in brightness typical for the Classical T Tauri
stars also present on the light curve of GM Cep. Comparing our results with
results published in the literature, we conclude that changes in brightness are
caused by superposition of both: (1) magnetically channeled accretion from the
circumstellar disk, and (2) occultation from circumstellar clouds of dust or
from features of a circumstellar disk.Comment: 7 pages, 3 figures, accepted for publication in Ap&S
Dynamical evidence of a spiral arm-driving planet in the MWC 758 protoplanetary disk
Stars and planetary system
The parent?infant dyad and the construction of the subjective self
Developmental psychology and psychopathology has in the past been more concerned with the quality of self-representation than with the development of the subjective agency which underpins our experience of feeling, thought and action, a key function of mentalisation. This review begins by contrasting a Cartesian view of pre-wired introspective subjectivity with a constructionist model based on the assumption of an innate contingency detector which orients the infant towards aspects of the social world that react congruently and in a specifically cued informative manner that expresses and facilitates the assimilation of cultural knowledge. Research on the neural mechanisms associated with mentalisation and social influences on its development are reviewed. It is suggested that the infant focuses on the attachment figure as a source of reliable information about the world. The construction of the sense of a subjective self is then an aspect of acquiring knowledge about the world through the caregiver's pedagogical communicative displays which in this context focuses on the child's thoughts and feelings. We argue that a number of possible mechanisms, including complementary activation of attachment and mentalisation, the disruptive effect of maltreatment on parent-child communication, the biobehavioural overlap of cues for learning and cues for attachment, may have a role in ensuring that the quality of relationship with the caregiver influences the development of the child's experience of thoughts and feelings
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