On the Observability of Giant Protoplanets in Circumstellar Disks

We investigate the possibility to detect giant planets that are still embedded in young circumstellar disks. Based on models with different stellar, planetary, and disk masses, and different radial positions of the planet we analyze the resulting submillimeter appearance of these systems. We find that the influence of the planet on the spectral energy distribution could not be distinguished from that of other disk parameters. However, dust reemission images of the disks show that the hot region in the proximity of a young planet, along with the gap, could indeed be detected and mapped with the Atacama Large Millimeter Array in the case of nearby circumstellar disks (d<100pc) in approximate face-on orientation.Comment: ApJ, in pres

Large-scale Vortices in Protoplanetary Disks: On the observability of possible early stages of planet formation

We investigate the possibility of mapping large-scale anti-cyclonic vortices, resulting from a global baroclinic instability, as pre-cursors of planet formation in proto-planetary disks with the planned Atacama Large Millimeter Array (ALMA). On the basis of three-dimensional radiative transfer simulations, images of a hydrodynamically calculated disk are derived which provide the basis for the simulation of ALMA. We find that ALMA will be able to trace the theoretically predicted large-scale anti-cyclonic vortex and will therefore allow testing of existing models of this very early stage of planet formation in circumstellar disks.Comment: Accepted by ApJ (Letters section). A preprint version with high-quality figures can be downloaded from http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/ vortex.ps.g

Large-scale magnetic fields in Bok globules

Context: The role of magnetic fields in the star formation process is a contentious matter of debate. In particular, no clear observational proof exists of a general influence by magnetic fields during the initial collapse of molecular clouds. Aims: Our aim is to examine magnetic fields and their influence on a wide range of spatial scales in low-mass star-forming regions. Method: We trace the large-scale magnetic field structure on scales of 10^3-10^5 AU in the local environment of Bok globules through optical and near-infrared polarimetry and combine these measurements with existing submillimeter measurements, thereby characterizing the small-scale magnetic field structure on scales of 10^2-10^3 AU. Results: For the first time, we present polarimetric observations in the optical and near-infrared of the three Bok globules B335, CB68, and CB54, combined with archival observations in the submillimeter and the optical. We find a significant polarization signal (P>=2%, P/sigma(P)>3) in the optical and near-infrared for all three globules. Additionally, we detect a connection between the structure on scales of 10^2-10^3 AU to 10^3-10^4 AU for both B335 and CB68. Furthermore, for CB54, we trace ordered polarization vectors on scales of ~10^5 AU. We determine a magnetic field orientation that is aligned with the CO outflow in the case of CB54, but nearly perpendicular to the CO outflow for CB68. For B335 we find a change in the magnetic field oriented toward the outflow direction, from the inner core to the outer regions. Conclusion: We find strongly aligned polarization vectors that indicate dominant magnetic fields on a wide range of spatial scales.Comment: 9 pages, 7 figures, accepted by A&

Sadder but fitter. The evolutionary function of depressive symptoms following fetal loss

A literature review about an evolutionary model of fetal loss depression is presented. This model conceptualizes depression following miscarriage or stillbirth as an evolutionary protective mechanism to avoid further fetal loss. It postulates that depressive symptoms delay the next reproduction and save maternal resources. These symptoms along with hypochondric symptoms of depression which lead to a search for causes and reappraisal of environmental factors, are probably adaptations to causes of further fetal loss (e.g. epidemics, famines, infections, environmental toxins)

The Circumstellar Disk of the Butterfly Star in Taurus

We present a model of the circumstellar environment of the so-called ``Butterfly Star'' in Taurus (IRAS 04302+2247). The appearance of this young stellar object is dominated by a large circumstellar disk seen edge-on and the light scattering lobes above the disk. The model is based on multi-wavelength continuum observations: Millimeter maps and high-resolution near-infrared images obtained with HST/NICMOS. It was found that the disk and envelope parameters are comparable with those of the circumstellar environment of other young stellar objects. A main result is that the dust properties must be different in the circumstellar disk and in the envelope: While a grain size distribution with grain radii up to 100 micron is required to reproduce the millimeter observations of the disk, the envelope is dominated by smaller grains similar to those of the interstellar medium. Preprint with high figure quality available at: http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/i04302.psComment: 32 pages, 9 figure

Spectropolarimetry and Modeling of the Eclipsing T Tauri Star KH 15D

KH 15D is a strongly variable T Tauri star in the young star cluster NGC 2264 that shows a decrease in flux of 3.5 magnitudes lasting for 18 days and repeating every 48 days. The eclipsing material is likely due to orbiting dust or rocky bodies in a partial ring or warped disk that periodically occults the star. We measured the polarized spectrum in and out of eclipse at the Keck and Palomar observatories. Outside of the eclipse, the star exhibited low polarization consistent with zero. During eclipse, the polarization increased dramatically to ~2% across the optical spectrum, while the spectrum had the same continuum shape as outside of eclipse and exhibited emission lines of much larger equivalent width, as previously seen. From the data, we conclude that (a) the scattering region is uneclipsed; (b) the scattering is nearly achromatic; (c) the star is likely completely eclipsed so that the flux during eclipse is entirely due to scattered light, a conclusion also argued for by the shape of the ingress and egress. We argue that the scattering is not due to electrons, but may be due to large dust grains of size ~10 micron, similar to the interplanetary grains which scatter the zodiacal light. We construct a warped-disk model with an extended dusty atmosphere which reproduces the main features of the lightcurve, namely (a) a gradual decrease before ingress due to extinction in the atmosphere (similar for egress); (b) a sharper decrease within ingress due to the optically-thick base of the atmosphere; (c) a polarized flux during eclipse which is 0.1% of the total flux outside of eclipse, which requires no fine-tuning of the model. (abridged)Comment: 9 pages, 7 figures, accepted for publication in ApJ, MPEG simulation available at http://www.astro.washington.edu/agol/scatter2.mp

Signatures of Planets in Spatially Unresolved Disks

Main sequence stars are commonly surrounded by debris disks, composed of cold dust continuously replenished by a reservoir of undetected dust-producing planetesimals. In a planetary system with a belt of planetesimals (like the Solar System's Kuiper Belt) and one or more interior giant planets, the trapping of dust particles in the mean motion resonances with the planets can create structure in the dust disk, as the particles accumulate at certain semimajor axes. Sufficiently massive planets may also scatter and eject dust particles out of a planetary system, creating a dust depleted region inside the orbit of the planet. In anticipation of future observations of spatially unresolved debris disks with the Spitzer Space Telescope, we are interested in studying how the structure carved by planets affects the shape of the disk's spectral energy distribution (SED), and consequently if the SED can be used to infer the presence of planets. We numerically calculate the equilibrium spatial density distributions and SEDs of dust disks originated by a belt of planetesimals in the presence of interior giant planets in different planetary configurations, and for a representative sample of chemical compositions. The dynamical models are necessary to estimate the enhancement of particles near the mean motion resonances with the planets, and to determine how many particles drift inside the planet's orbit. Based on the SEDs and predicted $\it{Spitzer}$ colors we discuss what types of planetary systems can be distinguishable from one another and the main parameter degeneracies in the model SEDs.Comment: 40 pages (pre-print form), including 16 figures. Published in ApJ 200