The Experts below are selected from a list of 16071 Experts worldwide ranked by ideXlab platform
S. Wolf - One of the best experts on this subject based on the ideXlab platform.
-
Magnetic fields in Circumstellar Disks: The potential of Zeeman observations
Astronomy & Astrophysics, 2017Co-Authors: Robert Brauer, S. Wolf, Mario FlockAbstract:Context. Recent high angular resolution polarimetric continuum observations of Circumstellar Disks provide new insights into their magnetic field. However, direct constraints are limited to the plane of sky component of the magnetic field. Observations of Zeeman split spectral lines are a potential approach to enhance these insights by providing complementary information. Aims. We investigate which constraints for magnetic fields in Circumstellar Disks can be obtained from Zeeman observations of the $113~\mathrm{GHz}$ CN lines. Furthermore, we analyze the requirements to perform these observations and their dependence on selected quantities. Methods. We simulate the Zeeman splitting with the radiative transfer (RT) code POLARIS (Reissl et al. 2016) extended by our Zeeman splitting RT extension ZRAD (Brauer et al. 2017), which is based on the line RT code Mol3D (Ober et al. 2015). Results. We find that Zeeman observations of the $113~\mathrm{GHz}$ CN lines provide significant insights into the magnetic field of Circumstellar Disks. However, with the capabilities of recent and upcoming instrument/observatories, even spatially unresolved observations would be challenging. Nevertheless, these observations are feasible for the most massive Disks with a strong magnetic field and high abundance of CN/H. The most restrictive quantity is the magnetic field strength, which should be at least in the order of $\sim1~\mathrm{mG}$. In addition, the inclination of the disk should be around $60\deg$ to preserve the ability to derive the line-of-sight (LOS) magnetic field strength and to obtain a sufficiently high circularly polarized flux.
-
Impact of an inhomogeneous density distribution on selected observational characteristics of Circumstellar Disks
Astronomy & Astrophysics, 2015Co-Authors: Robert Brauer, S. WolfAbstract:Context. Analysis of observations of Circumstellar Disks around young stellar objects is often based on disk models with smooth and continuous density distribution. However, spatially resolved observations with increasing angular resolution and dynamical models indicate that Circumstellar Disks are highly structured. Aims. We investigate the influence of different clumpy density distributions on selected physical properties and on the observable characteristics of Circumstellar Disks. In particular, these are the temperature distribution, the spectral energy distribution (SED), the radial brightness profile and the degree of polarization of scattered stellar radiation. Methods. Based on radiative transfer modeling we calculated the temperature structure of the disk and simulate observational quantities in the thermal re-emission and scattering regime. The clumpy density distributions are realized using a two-phase medium approach with phases for the clumps and the medium in between. We compared our results to those obtained for a smooth and continuous density distribution to quantify the influence of clumps on internal physical parameters and observable quantities of Circumstellar Disks. Results. Within the considered model space, the clumpiness has a significant impact on the disk temperature distribution. For instance, in the transition region from the optically thin upper disk layers to the disk interior, it causes a decrease in the mean temperature by up to 12 K (corresponding to ~15%), if compared to continuous Disks. In addition, Circumstellar Disks with clumpy density distributions generally feature a lower spectral index in the submm/mm range of the SED than continuous Disks. The strength of this decrease can be varied by changing the dust mass or grain size, but not by changing the inclination of the disk. As a consequence of the lower spectral index, the dust grain size derived from the submm/mm-slope of the SED may be overestimated, if the inhomogeneity of the disk density distribution is not taken into account. Furthermore, the scattered light brightness distribution of clumpy Disks shows a steeper radial decrease than in the case of continuous Disks. The azimuthal variations in the scattered flux, resulting from inhomogeneous density distributions, have their maximum at the medium radial extent of the Disks. Additionally, clumpy density distributions change the degree of polarization of the scattered light in the optical compared to continuous Disks. The quantitative level of this variation increases with the optical depth of the clumps.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, Richard D. Alexander, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observatories is outlined.
A. Dutrey - One of the best experts on this subject based on the ideXlab platform.
-
Spread of the dust temperature distribution in Circumstellar Disks
Astronomy and Astrophysics - A&A, 2017Co-Authors: S. Heese, A. Dutrey, S Wolf, S. GuilloteauAbstract:Accurate temperature calculations for Circumstellar Disks are particularly important for their chemical evolution. Their temperature distribution is determined by the optical properties of the dust grains, which, among other parameters, depend on their radius. However, in most disk studies, only average optical properties and thus an average temperature is assumed to account for an ensemble of grains with different radii. We investigate the impact of subdividing the grain radius distribution into multiple sub-intervals on the resulting dust temperature distribution and spectral energy distribution (SED). These quantities were computed for two different scenarios: (1) Radius distribution represented by 16 logarithmically distributed radius intervals, and (2) radius distribution represented by a single grain species with averaged optical properties (reference). Within the considered parameter range, i.e., of grain radii between 5 nm and 1 mm and an optically thin and thick disk with a parameterized density distribution, we obtain the following results: In optically thin disk regions, the temperature spread can be as large as ~63% and the relative grain surface below a certain temperature is lower than in the reference disk. With increasing optical depth, the difference in the midplane temperature and the relative grain surface below a certain temperature decreases. Furthermore, below ~20K, this fraction is higher for the reference disk than for the case of multiple grain radii, while it shows the opposite behavior for temperatures above this threshold. The thermal emission in the case of multiple grain radii at short wavelengths is stronger than for the reference disk. The freeze-out radius is a function of grain radius, spanning a radial range between the coldest and warmest grain species of ~30AU.
-
Circumstellar Disks and planets
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, Richard D. Alexander, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observatories is outlined.
-
Millimetre/Sub-millimetre Observations of Circumstellar Disks
2011Co-Authors: A. DutreyAbstract:TTauri Disks located in nearby star-forming regions (e.g. Taurus-Auriga at 140 pc) are thought to be the site of planet formation, since proto-planetary Disks orbiting around active (still accreting) TTauri stars should contain, in many cases, enough gas to form giant gaseous planets. As such, Circumstellar Disks are ideal laboratories to study planet formation, provided the gas and dust observations have enough sensitivity and resolving power. I will focus in these proceedings, on recent results of molecular observations which unveil the physical conditions of gas Disks and reveal the weakness of our current understanding and modeling.
Hubert Klahr - One of the best experts on this subject based on the ideXlab platform.
-
the concentration and growth of solids in fragmenting Circumstellar Disks
arXiv: Earth and Planetary Astrophysics, 2019Co-Authors: Hans Baehr, Hubert KlahrAbstract:Due to the gas rich environments of early Circumstellar Disks, the gravitational collapse of cool, dense regions of the disk form fragments largely composed of gas. During formation, disk fragments may attain increased metallicities as they interact with the surrounding disk material, whether through particle migration to pressure maxima or through mutual gravitational interaction. In this paper, we investigate the ability of fragments to collect and retain a significant solid component through gas-particle interactions in high-resolution 3D self-gravitating shearing box simulations. The formation of axissymmetric perturbations associated with gravitational instabilities allows particles of intermediate sizes to concentrate through aerodynamic drag forces. By the onset of fragmentation, the mass of local particle concentrations within the fragment are comparable to that of the gas component and the sebsequent gravitational collapse results in the formation of a solid core. We find that these cores can be up to several tens of Earth masses, depending on grain size, before the fragment center reaches temperatures which would sublimate solids. The solid fraction and total mass of the fragment also depend on the metallicity of the young parent protoplanetary disk, with higher initial metallicities resulting in larger fragments and larger solid cores. Additionally, the extended atmospheres of these soon-to-be gas giants or brown dwarfs are occasionally enriched above the initial metallicity, provided no solid core forms in the center and are otherwise lacking in heavier elements when a core does form.
-
tracing planet induced structures in Circumstellar Disks using molecular lines
Astronomy and Astrophysics, 2015Co-Authors: F Ober, S Wolf, Ana Uribe, Hubert KlahrAbstract:Context. Circumstellar Disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. Aims. We investigate the feasibility of using molecular lines to trace planet-induced structures in Circumstellar Disks. Methods. Based on 3D hydrodynamic simulations of planet-disk interactions obtained with the PLUTO code, we perform selfconsistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these Disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, five disk masses, seven disk radii, and two different typical pre-main-sequence host stars (T Tauri, Herbig Ae) at a distance of 140 pc. We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques (12C16O, 12C18O, HCO, HCN, and CS) in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. Results. We find that the majority of protoplanetary Disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. By comparison with simulated observations of undisturbed Disks we identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Conclusions. Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection of planet-induced gaps is possible under certain conditions.
-
tracing planet induced structures in Circumstellar Disks using molecular lines
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: F Ober, S Wolf, Ana Uribe, Hubert KlahrAbstract:Circumstellar Disks are considered to be the birthplace of planets. Specific structures like spiral arms, gaps, and cavities are characteristic indicators of planet-disk interaction. Investigating these structures can provide insights into the growth of protoplanets and the physical properties of the disk. We investigate the feasibility of using molecular lines to trace planet-induced structures in Circumstellar Disks. Based on 3D hydrodynamic simulations of planet-disk interactions, we perform self-consistent temperature calculations and produce N-LTE molecular line velocity-channel maps and spectra of these Disks using our new N-LTE line radiative transfer code Mol3D. Subsequently, we simulate ALMA observations using the CASA simulator. We consider two nearly face-on inclinations, 5 disk masses, 7 disk radii, and 2 different typical pre-main-sequence host stars (T Tauri, Herbig Ae). We calculate up to 141 individual velocity-channel maps for five molecules/isotopoloques in a total of 32 rotational transitions to investigate the frequency dependence of the structures indicated above. We find that the majority of protoplanetary Disks in our parameter space could be detected in the molecular lines considered. However, unlike the continuum case, gap detection is not straightforward in lines. For example, gaps are not seen in symmetric rings but are masked by the pattern caused by the global (Keplerian) velocity field. We identify specific regions in the velocity-channel maps that are characteristic of planet-induced structures. Simulations of high angular resolution molecular line observations demonstrate the potential of ALMA to provide complementary information about the planet-disk interaction as compared to continuum observations. In particular, the detection of planet-induced gaps is possible under certain conditions.(abridged)
-
tracing large scale structures in Circumstellar Disks with alma
Astronomy and Astrophysics, 2013Co-Authors: Jan Philipp Ruge, S Wolf, Ana Uribe, Hubert KlahrAbstract:Context. Planets are supposed to form in Circumstellar Disks. The additional gravitational potential of a planet perturbs the disk and leads to characteristic structures, i.e. spiral waves and gaps, in the disk’s density profile. Aims. We perform a large-scale parameter study of the observability of these planet-induced structures in Circumstellar Disks in the (sub)mm wavelength range for the Atacama Large (Sub)Millimeter Array (ALMA). Methods. On the basis of hydrodynamical and magneto-hydrodynamical simulations of star-disk-planet models, we calculated the disk temperature structure and (sub)mm images of these systems. These were used to derive simulated ALMA images. Because appropriate objects are frequent in the Taurus-Auriga region, we focused on a distance of 140 pc and a declination of ≈20 ◦ .T he explored range of star-disk-planet configurations consists of six hydrodynamical simulations (including magnetic fields and different planet masses), nine disk sizes with outer radii ranging from 9 AU to 225 AU, 15 total disk masses in the range between 2.67 × 10 −7 M� and 4.10 × 10 −2 M� ,s ix different central stars, and two different grain size distributions, resulting in 10 000 disk models.
-
tracing large scale structures in Circumstellar Disks with alma
arXiv: Solar and Stellar Astrophysics, 2012Co-Authors: Jan Philipp Ruge, S Wolf, Ana Uribe, Hubert KlahrAbstract:Planets are supposed to form in Circumstellar Disks. The gravitational potential of a planet perturbs the disk and leads to characteristic structures, i.e. spiral waves and gaps, in the disk's density profile. We perform a large-scale parameter study of the observability of these planet-induced structures in Circumstellar Disks with ALMA. On the basis of HD and MHD simulations, we calculated the disk temperature structure and (sub)mm images of these systems. These were used to derive simulated ALMA images. Because appropriate objects are frequent in Taurus, we focused on a distance of 140pc and a declination of 20{\deg}. The explored range of star-disk-planet configurations consists of 6 HD simulations (including magnetic fields and different planet masses), 9 disk sizes, 15 total disk masses, 6 different central stars, and two different grain size distributions. On almost all scales and in particular down to a scale of a few AU, ALMA is able to trace disk structures induced by planet-disk interaction or by the influence of magnetic fields on the wavelength range between 0.4 and 2.0mm. In most cases, the optimum angular resolution is limited by the sensitivity. However, within the range of typical masses of protoplanetary Disks (0.1-0.001Msun) the disk mass has a minor impact on the observability. It is possible to resolve Disks down to 2.67e-6Msun and trace gaps induced by a planet with M_p/M_s = 0.001 in Disks with 2.67e-4Msun with a signal-to-noise ratio greater than three. The central star has a major impact on the observability of gaps, as well as the considered maximum grainsize of the dust in the disk. In general, it is more likely to trace planet-induced gaps in our MHD models, because gaps are wider in the presence of magnetic fields. We also find that zonal flows resulting from MRI create gap-like structures in the disk's re-emission radiation, which are observable with ALMA.
F. Pont - One of the best experts on this subject based on the ideXlab platform.
-
Circumstellar Disks and planets
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
The Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, Richard D. Alexander, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observations is outlined.
-
Circumstellar Disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers
Astronomy and Astrophysics Review, 2012Co-Authors: S. Wolf, F. Malbet, R. Alexander, J.-p. Berger, M. Creech-eakman, G. Duchêne, A. Dutrey, C. Mordasini, E. Pantin, F. PontAbstract:We present a review of the interplay between the evolution of Circumstellar Disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of Circumstellar Disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observatories is outlined.
Mark J. Mccaughrean - One of the best experts on this subject based on the ideXlab platform.
-
X-Ray Emission from Orion Nebula Cluster Stars with Circumstellar Disks and Jets
Astronomy and Astrophysics Supplement Series, 2005Co-Authors: Joel Kastner, Mark J. Mccaughrean, John Bally, Geoffrey Franz, Nicolas Grosso, Konstantin V. Getman, Eric D. Feigelson, Norbert SchulzAbstract:We investigate the X-ray and near-infrared emission properties of a sample of pre-main-sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for Circumstellar Disks (``proplyds'') and optical jets in Hubble Space Telescope (HST) imaging. Our study uses X-ray data acquired during Chandra Orion Ultradeep Program (COUP) observations, as well as complementary optical and near-infrared data recently acquired with HST and the Very Large Telescope (VLT), respectively. Approximately 70% of ~140 proplyds were detected as X-ray sources in the 838 ks COUP observation of the ONC, including ~25% of proplyds that do not display central stars in HST imaging. In near-infrared imaging, the detection rate of proplyd central stars is 〉90%. Many proplyds display near-infrared excesses, suggesting disk accretion is ongoing onto the central, PMS stars. About 50% of Circumstellar Disks that are detected in absorption in HST imaging contain X-ray sources. For these sources, we find that X-ray absorbing column and apparent disk inclination are well correlated, providing insight into the disk scale heights and metal abundances of UV- and X-ray-irradiated protoplanetary Disks. Approximately 2/3 of the ~30 proplyds and PMS stars exhibiting jets in Hubble images have COUP X-ray counterparts. These jet sources display some of the largest near-infrared excesses among the proplyds, suggesting that the origin of the jets is closely related to ongoing, PMS stellar accretion. One morphologically complex jet source, d181-825, displays a double-peaked X-ray spectral energy distribution with a prominent soft component that is indicative of strong shocks in the jet collimation region. A handful of similar objects also display X-ray spectra that are suggestive of shocks near the jet source. These results support models in which Circumstellar Disks collimate and/or launch jets from young stellar objects and, furthermore, demonstrate that star-disk-jet interactions may contribute to PMS X-ray emission.
-
X-ray Emission from Orion Nebula Cluster Stars with Circumstellar Disks and Jets
The Astrophysical Journal Supplement Series, 2005Co-Authors: Joel H. Kastner, Mark J. Mccaughrean, John Bally, Geoffrey Franz, Nicolas Grosso, Konstantin V. Getman, Eric D. Feigelson, Norbert S. SchulzAbstract:We investigate the X-ray and near-infrared emission properties of a sample of pre-main sequence (PMS) stellar systems in the Orion Nebula Cluster (ONC) that display evidence for Circumstellar Disks (``proplyds'') and optical jets in Hubble Space Telescope (HST) imaging. Approximately 70% of ~140 proplyds were detected as X-ray sources in the Chandra Orion Ultradeep Program observation of the ONC, including ~25% of proplyds that do not display central stars in HST imaging. Many proplyds display near-infrared excesses, suggesting disk accretion is ongoing onto the central, PMS stars. Among Circumstellar Disks that are detected in absorption in HST imaging, we find that X-ray absorbing column and apparent disk inclination are well correlated, providing insight into the disk scale heights and metal abundances of UV- and X-ray-irradiated protoplanetary Disks. Jet sources display some of the largest near-infrared excesses among the X-ray-detected proplyds, suggesting that the origin of the jets is closely related to ongoing, PMS stellar accretion. Some jet sources display double-peaked X-ray spectral energy distributions, with soft components indicative of strong shocks in the jet collimation region. These results support models in which Circumstellar Disks collimate and/or launch jets from young stellar objects and, furthermore, demonstrate that star-disk-jet interactions may contribute to PMS X-ray emission.
-
2.12 Micron Molecular Hydrogen Emission from Circumstellar Disks Embedded in the Orion Nebula
The Astrophysical Journal, 1998Co-Authors: Hua Chen, Mark J. Mccaughrean, John Bally, C. Robert O'dell, Rodger I. Thompson, Marcia J. Rieke, Glenn Schneider, Erick T. YoungAbstract:We present narrowband images of two externally illuminated Circumstellar Disks embedded in the Orion Nebula. The images were taken with camera 2 of the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) as part of the Hubble Space Telescope Early Release Observations program. Molecular hydrogen emission is confined to the silhouettes embedded in the objects HST?10 (182-413) and HST?17 (183-419). This emission appears to trace the surfaces of nearly edge-on Circumstellar Disks and is likely to be excited by the intense far-ultraviolet (FUV) radiation field produced by nearby O stars. The presence of this emission confirms that FUV radiation penetrates to the disk surface. The absence of H -->2 emission in the region between the ionization front and the disk surface provides evidence that this medium is predominantly atomic. Our observations constitute the first demonstration that the dense Circumstellar Disks embedded in the proplyds are predominately molecular. While the central star is marginally detected at 2.15 ?m in HST?10, the central star of HST?17 is clearly detected.
-
Additional constraints on Circumstellar Disks in the Trapezium Cluster
The Astronomical Journal, 1994Co-Authors: John Stauffer, Lee Hartmann, Charles F. Prosser, Mark J. MccaughreanAbstract:We discuss the new constraints on the population of compact ionized sources in the Trapezium Cluster thought to arise from the ionization by the central OB stars of Circumstellar Disks around low-mass pre-main sequence stars. We present new Hubble Space Telescope (HST) Planetary Camera observations of two of these candidate disk sources, resolving extended nebulosity around them. One source shows a small-scale (greater than or approximately = 100 AU) bow-shock structure, previously seen on larger scales by O'Dell et al. We show that the Circumstellar disk model is the most likely one for the majority of sources, although is remains plausible that some of the larger objects could be equilibrium globules. We combine the most complete censuses of compact radio sources and stars in the core region to derive the fraction of the stellar population that may be associated with a Circumstellar disk. Our estimate of 25%-75% is comparable to that found for pre-main sequence (PMS) stars in the Taurus-Auriga dark clouds, indicating that the dense cluster environment of the Trapezium has not drastically reduced the frequency of Disks seen around PMS stars.
-
Circumstellar Disks in the Trapezium Cluster
Disks and Outflows Around Young Stars, 1Co-Authors: Mark J. Mccaughrean, John Rayner, Hans Zinnecker, John StaufferAbstract:We discuss the recent discovery and study of Circumstellar Disks in the Trapezium Cluster via two techniques. First we discuss the population of objects sometimes called ‘proplyds’, as revealed by ionizing radiation from the central massive OB stars of the Trapezium, and the fraction of these ionized objects that are associated with stars. Second, we look at the wider cluster population and the statistical occurrence of Circumstellar Disks detected through the more traditional signature of infrared excess. Both techniques reveal that a large fraction (≈50–80%) of the young stars in the Trapezium Cluster are likely surrounded by Disks.