Circumstellar disk

Prinn, R. G. (1993) Chemistry and evolution of gaseous circumstellar disks. In Protostars and Planets III, eds. Levy, E. H. and Lunine, J. I. Tucson University of Arizona Press, pp. 1005-1028. 

SEDs) demonstrate that massive disks often extend to hundreds of astronomical units. A lower estimate for the initial mass distribution of our Solar System is provided by the minimum mass solar nebula (MMSN) model, which is the minimum mass required to produce the observed distribution of solids from a disk with solar composition. This analysis predicts a disk mass between 0.01 and 0.07 M extending out to 40 AU. Mass estimates for circumstellar disks derived from submillimeter and longer-wavelength observations are consistent with the range estimated for the MMSN (e.g. Beckwith et al. 1990 Williams etal. 2005). 

The initial mass and lifetime of gas in circumstellar disks affect both the formation of giant planets as well as the formation of terrestrial planets. According to the widely accepted scenario of giant-planet formation, rocky cores need to reach several M before being able to accumulate a substantial amount of gas from the protoplanetary disk. Current models require from a few to 10 million years to form Jupiter-like planets at 5AU (see e.g. Lissauer Stevenson 2007), meaning that primordial... 

The daughter nuclide may be stable or unstable (radioactive), debris disk a circumstellar disk in which the majority of the dust is not derived from the collapsing molecular cloud, but from the collisions of minor bodies in the disk. The typical masses and optical depths of these disks are several orders of magnitudes lower than those typical to accretion disks, desorption changing from an adsorbed state on a surface to a gaseous or liquid state. 

Herbig Ae/Be star intermediate-mass ( 1.5-6 M ) star with a circumstellar disk, typically younger than 5-7 Myr. 

Over the past decade these exciting advances have transformed our understanding of the origins of planetary systems. Astronomers provide exquisite observations of nascent planetary systems. Cosmochemists reconstruct the detailed history of the first ten million years of the Solar System. Circumstellar disks and, in particular,... 

Beckwith S. V. W., Sargent A. 1., Chini R. S., and Gusten R. (1990) A survey for circumstellar disks around young stellar objects. Astron, J. 99, 924-945. 

Roughly half of young T Tauri stars with ages <10Myr are observed to have optically thick disks of gas and dust with masses of 0.001-IM (Beckwith et al., 1990 Strom, 1994). These disks have spectra containing absorption features caused by the presence of water ice and silicates. Ultraviolet and visible emission lines indicate that the central stars are accreting mass from their disks at rates of 10 -10 Mo yr (Hartmann et al., 1998). Optically thick circumstellar disks are not observed around stars older than —10 Myr (Strom, 1995), which provides an approximate upper limit for the lifetime of the Sun s protoplanetary nebula. 

The finite hfetime of circumstellar disks, and the fact that young stars are observed to be accreting material, has given rise to a model which views the protoplanetary nebula as a viscous accretion disk in which material was transported radially inwards, ultimately falling onto the Sun (Lynden-Bell and Pringle, 1974). As a consequence of this accretion, the mass of the... 

Analytic estimates suggest that lOM cores were unlikely to accrete in a minimum mass nebula on a timescale comparable to the lifetime of circumstellar disks. However, such cores could have formed if the surface density of solids at 5 AU was 5-10 times that of a minimum mass nebula (Lissauer, 1987). Numerical models of planetary accretion support this conclusion... 

Therefore, from all of the recent examples of modeling and observations of circumstellar disks a number of mechanisms can be considered that might contribute to very early heating and depletion of moderately volatile elements at 1 AU. However, some of these are localized processes and the timescales for heating are expected to be short in the midplane. 

McCaughrean M. J. and O Dell C. R. (1996) Direct imaging of circumstellar disks in the Orion nebula. Astronom. J. Ill,... 

Memos imaging of the HR 4796A circumstellar disk. Astrophys. J. 513, L127-L130. 

Waelkens et al., 1996) massive pre-main sequence stars surrounded with disks of dust and gas. Herbig Ae/Be stars even show transient gas features in their spectra that have been interpreted as comets falling into the star (Beust et al., 1994). The presence of the olivine feature in comets and circumstellar disk systems and the lack of it in interstellar and molecular clouds, the parental materials for star and planetary formation, is somewhat of a conundrum. A common astronomical interpretation is that interstellar grains are amorphous silicates and when warmed in a circumstellar disk environment, they anneal to produce crystalline materials. The other possibility is that olivine in comets and disks condenses from vapor produced by evaporation of original interstellar materials. 

Strom S. E., Strom K. M., and Edwards S. (1988) Energetic winds and circumstellar disks associated with low mass young stellar objects. In Galactic and Extragalactic Star Formation (ed. R. Pudritz). NATO Advanced Study Institute, Reidel, Dordrecht, The Netherlands, pp. 53-68. 

Jets and outflows arising from low mass protostars can produce some of the most spectacular images of the star formation process. The HH 46/47 system is a striking example of a low mass protostar, surrounded by a circumstellar disk, ejecting a jet and creating a bipolar outflow perpendicular to the disk (Figure 14). The central protostar lies inside a dark cloud (known as a Bok... 

Schneider, G., Smith, B. A., Becklin, E. E. et al. (1999). NICMOS imaging of the HR 4796A circumstellar disk. Astrophysical Journal, 513, L1217-30. 

Wetherill (1990) has provided the standard model of planetary formation, based upon the planetesimal hypothesis. This model states that planets grow within a circumstellar disk, via pairwise accretion of smaller bodies known as planetesimals. It should be noted that the process of planet formation is a fundamentally different process from that of star formation. Stellar formation begins with the process of gas condensation, whereas planetary formation begins with the accumulation of solid bodies, and gas accretion takes place only at a late stage in some of the larger planets (Lissauer, 1993). 

Abstract. The intrinsic polarization of young stars contains important information about the physical state of the objects and their surroundings. In particularly, the investigations of polarimetric activity of the variable stars can throw light upon variability mechanisms. In stars surrounded by circumstellar disks unresolved with a telescope, the position angle of the intrinsic linear polarization can indicate disk orientation. The wavelength dependence of the linear polarization is a sensitive function of the optical parameters of the dust particles and can be used for their diagnostics. 

The elliptical source could correspond to a circumstellar disk with an envelope size of 200AU at 150 pc. The gaussian source can also be a circumstellar disk of 80AU at 300pc but with a different orientation with respect to the observer plane. The point source can be considered a protostar at 50pc and with a radius Rsun- As the point source size is smaller than the pixel size on the sky grid, an emissivity parameter e has to be introduced, this is... 

In the Introduction of this thesis the potential science cases that could be assessed by a Far-Infrared Spectro-Spatial Space Interferometer were introduced. This chapter focuses on one of these science cases, the Circumstellar Disks, because it is one of the major areas of focus in ground-based infrared interferometry observations. 

There is an extensive bibliography regarding protoplanetary disks and their evolution (Williams and Cieza 2011), structure (Dullemond and Monnier 2010) and composition (Wood 2008). For this reason, in Sect. 6.1 a brief introduction of the science behind the circumstellar disks focusing on the disk properties around the far infrared frequency range is given. In Sect. 6.2 a simulation of a circumstellar disk is presented. This simulated disk is fed to the instrument simulator FllnS, and the obtained results are described in Sect. 6.3 for both an ideal instrument and for a more realistic instrument. 

After about one million years (for solar-mass stars, this process is much faster for higher masses), the combination of outflow and infall disperses the majority of the envelope and the star is optically revealed, although a circumstellar disk is still present. For solar-mass stars, this is the T Tauri phase, while for intermediate masses, these stars are referred to as Herbig Ae/Be stars (Hillenbrand et al. 1992). Several million years after the primordial disk has almost disappeared. 

The protoplanetary disks, or circumstellar disks around young stars, have a very rich structure, made up of several regions where different physics apply and hence different wavelength ranges need to be observed. For this reason, the techniques used to observe these regions vary with the characteristic temperatures and scale sizes involved. 

The physical properties of circumstellar disks in terms of spatial scale, density and temperature require to use different observational techniques for different regions of the disks (Akeson 2008). Also, their basic building blocks are gas, dust and ice, which radiate predominantly in the far-infrared wavelength range. 

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