PRELIMINARY MEASUREMENTS OF THE ACCURACY OF MANUAL OPTICAL SIGHTING AT THE CENTER OF A PLANETARY DISK
Accuracy of manual optical theodolite sighting of the center of a planetary disk
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Observational studies of the clearing phase in proto-planetary disk systems
A summary of the work completed during the first year of a 5 year program to observationally study the clearing phase of proto-planetary disks is presented. Analysis of archival and current IUE data, together with supporting optical observations has resulted in the identification of 6 new proto-planetary disk systems associated with Herbig Ae/Be stars, the evolutionary precursors of the beta Pictoris system. These systems exhibit large amplitude light and optical color variations which enable us to identify additional systems which are viewed through their circumstellar disks including a number of classical T Tauri stars. On-going IUE observations of Herbig Ae/Be and T Tauri stars with this orientation have enabled us to detect bipolar emission plausibly associated with disk winds. Preliminary circumstellar extinction studies were completed for one star, UX Ori. Intercomparison of the available sample of edge-on systems, with stars ranging from 1-6 solar masses, suggests that the signatures of accreting gas, disk winds, and bipolar flows and the prominence of a dust-scattered light contribution to the integrated light of the system decreases with decreasing IR excess.
Grady, Carol A.↗
Radio maps of Jupiter's radiation belts and planetary disk at lambda 6 cm
Two-dimensional maps of Jupiter's radio emission were made in April 1978 at a frequency of 4885 MHz (6 cm) using the Westerbork telescope in the Netherlands. Pictures in the Stokes parameters I, Q and U have been obtained every 15 deg in longitude, each smeared over 20 deg of the planet's rotation. The half power beam width was approximately 1/6 of the disk diameter in right ascension and approximately 1/2 in declination. The planetary disk shows little or no limb darkening at this wavelength and has a temperature of 220 + or - 8 K. The radiation belts clearly show a kind of plateau or flattening in intensity in the outer part of the belt. A comparison with 21 and 50 cm maps indicate no difference in the width and form of the emission regions with wavelength.
De Pater, I.↗
The Detection and Study of Pre-Planetary Disks
A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun, before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve.
Pre-Planetary↗
Understanding Giant-Planet Formation in Proto-Planetary Disks with Dust-Growth Model [Slides]
Abstract not provided.
79 ASTRONOMY AND ASTROPHYSICS↗
Externally Illuminated Proto-Planetary Disks
We used the Hubble Space Telescope (HST) to obtain high angular resolution images and the first UV spectra of young stars and their circumstellar environments embedded within the Orion Nebula. The observations consists of: Direct imaging of young stars, their disks, and the surrounding environments with the Planetary Camera (PC) portion of Wide Field and Planetary Camera (WFPC2) using narrow band interference filters; The first UV imaging of these objects with the Faint Object Camera (FOC); and The first UV spectroscopy of these objects using the Faint Object Spectrograph (FOS).
Bally, John↗
The detection and study of pre-planetary disks
A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that surrounded the Sun before the formation of the planets. The properties of these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over the last decade, it is now possible to detect and study the circumstellar environments of the very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system. For example, millimeter-wave aperture synthesis imaging provides a direct means of studying in detail the morphology, temperature and density distributions, velocity field and chemical constituents in the outer disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly reflecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.
Sargent, A. I.↗
Observational Studies of the Clearing Phase in Proto-Planetary Disks Surrounding Intermediate Mass Stars
A detailed study of circumstellar gas associated with young, intermediate-mass stars has demonstrated that, far from being unique or an infrequently occurring phenomenon, beta Pic-like infall activity is routinely observed in stars younger than 10-50 Myr when the observer's line of sight lies within 15 degrees of the disk mid-plane. Detailed studies of 2 Herbig Ae/Be stars, AB Aur and HD 163296 demonstrate that enhanced infall episodes last 20-60 hours, comparable to the duration of similar episodes in beta Pictoris. The infall activity is consistent with detection of the comae of swarms of star-grazing bodies of asteroidal to cometary composition. Episodic fluctuations in the infall activity are clearly present by approximately 6 Myr, and may indicate the presence of massive planets within the disk. This study has therefore, directly contributed to NASA's Origins of Planetary Systems theme by identifying under what conditions extra-solar planetesimals can be remotely sensed, indicating that such bodies appear to be routinely detectable among young stars in the 1-10 Myr range, and suggesting that temporal studies of spectroscopic variability may provide a means of identifying those systems harboring massive planets. This study has resulted in 2 refereed review papers, 13 other refereed papers, and 17 conference papers.
Grady, Carol A.↗
Observational studies of the clearing phase in proto-planetary disk systems
Progress in this study is summarized for its second year. An extensive program of high dispersion UV spectral studies using the IUE (International Ultraviolet Explorer) has resulted in acquisition of 40 Herbig Ae/Be star and related object spectra. We find that accreting, circumstellar gas is detected with velocities consistent with material in free-fall toward the stars in approximately 38% of the sample. With acquisition of optical measurements of the projected stellar rotational velocities, we find that the systems with accreting gas exhibit systematically higher projected rotational velocities than the systems showing signatures of outflowing material only. When combined with polarimetric and photometric data, the IUE spectra for these stars indicate that accretion in intermediate-mass pre-main sequence stars is confined to the plane of the circumstellar dust disk. This is in contrast to lower-mass PMS stars where accretion, persumably along magnetic field lines, is seen at polar latitudes. Our data also support significant clearing of the central regions of these circumstellar disks, as originally suggested. The model which most closely matches the observational data is accretion from a disk envelope, as developed by Calvet et al. (1994).
Grady, Carol A.↗
Gravitational instabilities in a proto-planetary disk including the effects of magnetic fields
We investigate the gravitational instability of a thin, Keplerian protoplanetary disk including the effects of a largely azimuthal magnetic field. The model follows that of our previous work (Noh, Vishniac, & Cochran 1991) except for the inclusion of a magnetic field. The disk is assumed to consist of neutral and ionized gas and neutral dust which are coupled by gravity and friction. The growth rates and eigenfunctions are calculated numerically using nonaxisymmetric linear perturbation methods. The results show that the growth rate has a maximum at some intermediate azimuthal number m, but for each value of m it is reduced relative to the unmagnetized case. The effects of the magnetic field appear more strongly on small scales. As the strength of the equilibrium magnetic field increases the growth rates decrease, and the maximum instability occurs at a lower value on m due to the increasing magnetic pressure. The response of each component to the magnetic field is discussed using the behavior of the eigenfunctions in the radial direction. With the inclusion of the magnetic field, the effects of the ionization fraction and friction on the growth rates also appear to be important for high m modes. Increasing the ionization fraction or the friction suppresses instability, but only slightly changes the maximally unstable azimuthal scales. The enhanced growth rates due to a dust component for which thermal pressure is negligible are somewhat reduced by the inclusion of a magnetic field. The effects of different boundary conditions (reflecting and transmitting) on the growth rates are also shown.
Noh, Hyerim↗
SPICES: Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems - From Planetary Disks To Nearby Super Earths
SPICES (Spectro-Polarimetric Imaging and Characterization of Exoplanetary Systems) is a five-year M-class mission proposed to ESA Cosmic Vision. Its purpose is to image and characterize long-period extrasolar planets and circumstellar disks in the visible (450-900 nm) at a spectral resolution of about 40 using both spectroscopy and polarimetry. By 2020/2022, present and near-term instruments will have found several tens of planets that SPICES will be able to observe and study in detail. Equipped with a 1.5 m telescope, SPICES can preferentially access exoplanets located at several AUs (0.5-10 AU) from nearby stars (less than 25 pc) with masses ranging from a few Jupiter masses to Super Earths (approximately 2 Earth radii, approximately 10 mass compared to Earth) as well as circumstellar disks as faint as a few times the zodiacal light in the Solar System.
Boccaletti, Anthony↗
Collisional dynamics of perturbed particle disks in the solar system
Theoretical and computational studies were carried out on galactic and planetary disks. With the goal of addressing important open questions centered on galactic structure, the cloudy interstellar medium, giant molecular clouds, and star formation in galactic disks and the collisional dynamics of perturbed particulate matter in planetary disks, focus was largely on the self-gravitational effects, dissipative effects, and collisional dynamics of cloud-particle disks. N-body, 'cloud-particle' computational algorithms were developed for the purpose of isolating the role of gaseous self gravity from the roles of other dominant physical mechanisms and dynamical processes, e.g. the collisional dynamics and dissipative processes. The efforts focused largely on galactic disks show that observational constraints provide stringent tests of the numerical simulation techniques developed. Self gravitational effects of the galactic interstellar medium's gas clouds are included by means of Fourier Transform technique.
Roberts, William W., Jr.↗
Disk Detective: Discovery of New Circumstellar Disk Candidates Through Citizen Science
The Disk Detective citizen science project aims to find new stars with 22 micron excess emission from circumstellar dust using data from NASAs Wide-field Infrared Survey Explorer (WISE) mission. Initial cuts on the AllWISE catalog provide an input catalog of 277,686 sources. Volunteers then view images of each source online in 10different bands to identify false positives (galaxies, interstellar matter, image artifacts, etc.). Sources that survive this online vetting are followed up with spectroscopy on the FLWO Tillinghast telescope. This approach should allow us to unleash the full potential of WISE for finding new debris disks and proto planetary disks. We announce a first list of 37 new disk candidates discovered by the project, and we describe our vetting and follow-up process. One of these systems appears to contain the first debris disk discovered around a star with a white dwarf companion: HD 74389. We also report four newly discovered classical Be stars (HD 6612, HD 7406, HD 164137,and HD 218546) and a new detection of 22 micron excess around the previously known debris disk host star HD 22128.
NASAs Wide-field Infrared Survey Explorer (WISE) m↗
Far-infrared spectral observations of Saturn and its rings
The spectrum of Saturn and its rings between 45 and 115 microns has been measured at an average resolving power of 14 from the NASA Lear Jet. The combined brightness temperature of the rings and planetary disk decreases beyond 65 microns, in disagreement with previous results. A brightness temperature of 65 + or - 10 K is obtained for the planetary disk in the 80-110-micron wavelength range if a large-particle, constant-emissivity model is assumed for the rings. The possible effects of small particles in the rings are briefly considered.
Ward, D. B.↗
Disk Tides and Accretion Runaway
It is suggested that tidal interaction of an accreting planetary embryo with the gaseous pre-planetary disk may provide a mechanism to breach the so-called runaway limit during the formation of the giant planet cores.
accretion↗
Postrefurbishment mission Hubble Space Telescope images of the core of the Orion Nebula: Proplyds, Herbig-Haro objects, and measurements of a circumstellar disk
We report on observations of M42 made with the Hubble Space Telescope (HST) immediately after the successful repair and refurbishment mission. Images were made in the strongest optical emission lines of H I, (N II), and (O III) and in a bandpass close to V. In a previous paper, the term proplyd was introduced to describe young stars surrounded by circumstellar material rendered visible by being in an H II region. We confirm the proplyd nature of 17 of 18 objects found earlier with the HST, incorporate 13 previously known sources into the class on the basis of their emission-line appearance, and find 26 additional members not seen previously in other wavelengths. Half of the 110 stars brighter than V = 21 show proplyd structure, which implies that more than half of the stars have circumstellar material since nebular structures are more difficult to detect than stars. The highly variable forms of the proplyds can be explained on the basis of balance of ambient stellar gas pressure and radial pressure arising from the stellar wind and radiation pressure of the dominant stars in the region. Arguments are presented explaining the proplyds as disks or flattened envelopes surrounding young stars, hence they are possible planetary disks. The characteristic mass of ionized material is 2 x 10(exp 28) g, which becomes a lower limit to the total mass of the proplyds. A new, coordinate-based, designation scheme for compact sources and stars in the vicinity of M42 is proposed and applied. Evidence is presented that one of the previously known bright Herbig-Haro objects (HH 203) may be the result of a stream of material coming from a proplyd shocking against the neutral lid that covers M42. One object, 183-405, is a proplyd seen only in silhouette against the bright nebular background. It is elliptical, with dimensions 0.9 sec by 1.2 sec and surrounds a pre-main-sequence star of at least 0.2 solar mass. The outer parts of this stellar disk are optically thin and allow column mass densities to be determined. We set a lower limit to this disk to be 0.1-4.4 x 10(exp 28) g, dependent on the assumed gas to dust mass ratio.
O'Dell, C. R.↗
Interpretation of the variation of polarization over the disk of Venus
The polarization of reflected sunlight is computed for model atmospheres of Venus as a function of location on the apparent planetary disk. The calculations are for both homogeneous and layered models, as required to investigate the vertical distribution of particles. The results are compared with available observations. It is shown that the Rayleigh scattering observed in the polarization of Venus originates primarily from within the visible clouds, rather than from above the clouds. The visible 'clouds' are actually a very diffuse hazy region, and this visible-cloud layer extends at least up to the level where the pressure is of the order of 10 mb. The results indicate that the atmosphere behaves more nearly as the so-called 'homogeneous model' than as the 'reflecting-layer model'. However, there is some indication in the data that the turbidity increases with depth into the atmosphere. This conclusion receives stronger support from a comparison of particle number densities obtained from the polarization data with the number densities obtained from other observations which refer on the average to higher and lower levels in the atmosphere.
Kawabata, K.↗
Axisymmetric Two-Dimensional Computation of Magnetic Field Dragging in Accretion Disks
In this paper we model a geometrically thin accretion disk interacting with an externally imposed, uniform, vertical magnetic field. The accretion flow in the disk drags and distorts field lines, amplifying the magnetic field in the process. Inside the disk the radial component of the field is sheared into a toroidal component. The aim of this work is to establish the character of the resultant magnetic field and its dependence on the disk's parameters. We concentrate on alpha-disks driven by turbulent viscosity. Axisymmetric, two-dimensional solutions are obtained without taking into account the back-reaction of the magnetic field on the structure of the disk. The character of the magnetic field depends strongly on the magnitude of the magnetic Prandtl number, P . We present two illustrative examples of viscous disks: a so-called 'standard' steady state model of a disk around a compact star (e.g., cataclysmic variable), and a steady state model of a proto-planetary disk. In both cases, P = 1, P = 10(sup -1), and P = 10(sup -2) scenarios are calculated. Significant bending and magnification of the magnetic field is possible only for disks characterized by P of the order of 10(sup -2). In such a case, the field lines are bent sufficiently to allow the development of a centrifugally driven wind. Inside the disk the field is dominated by its toroidal component. We also investigate the dragging of the magnetic field by a nonviscous protoplanetary disk described by a phenomenological model. This scenario leads to large distortion and magnification of the magnetic field.
Reyes-Ruiz, Mauricio↗