EVIDENCE OF PHOTOEVAPORATION AND SPATIAL VARIATION OF GRAIN SIZES IN THE ORION 114-426 PROTOPLANETARY DISK (original) (raw)
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Formation and Evolution of Planetary Systems: Properties of Debris Dust Around Solar-Type Stars
The Astrophysical Journal Supplement Series, 2009
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr-3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24 μm, and 21 sources with excesses at 70 μm. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24 μm excess greater than 10.2% above the photosphere is 15% for ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the 70 μm fractional luminosity appears to decline over a similar age range. The characteristic temperature of the debris inferred from the IRS spectra range between 60 and 180 K, with evidence for the presence of cooler dust to account for the strength of the 70 μm excess emission. No strong correlation is found between dust temperature and stellar age. Comparison of the observational data with disk models containing a power-law distribution of silicate grains suggests that the typical inner-disk radius is 10 AU. Although the interpretation is not unique, the lack of excess emission shortward of 16 μm and the relatively flat distribution of the 24 μm excess for ages 300 Myr is consistent with steady-state collisional models.
2008
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems (FEPS) Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24um, and 21 sources with excesses at 70um. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the 70um fractional luminosity appears to decline over a similar age range. The characteristic temperature of the debris inferred from the IRS spectra range between 60 and...
The structure of the protoplanetary disk surrounding three young intermediate mass stars
Astronomy and Astrophysics, 2008
Aims. We present the first direct comparison of the distribution of the gas, as traced by the [O i] 6300Å emission, and the dust, as traced by the 10 µm emission, in the planet-forming region of proto-planetary disks around three intermediate-mass stars: HD 101412, HD 135344 B and HD 179218. Methods. N-band visibilities were obtained with VLTI/MIDI. Simple geometrical models are used to compare the dust emission to high-resolution optical spectra in the 6300 Å [O i] line of the same targets. Results. HD 101412 and HD 135344 B show compact (< 2 AU) 10 µm emission while the [O i] brightness profile shows a double peaked structure. The inner peak is strongest and is consistent with the location of the dust, the outer peak is fainter and is located at 5-10 AU. In both systems, spatially extended PAH emission is found. HD 179218 shows a double ring-like 10 µm emission with the first ring peaking at ∼ 1 AU and the second at ∼ 20 AU. The [O i] emitting region is more compact, peaking between 3-6 AU. Conclusions. The disks around HD 101412 and HD 135344 B appear strongly flared in the gas, but self-shadowed in the dust beyond ∼ 2 AU. The difference in the gas and dust vertical structure beyond 2 AU might be the first observational evidence of gas-dust decoupling in protoplanetary disks. The disk around HD 179218 is flared in the dust. The 10 µm emission emerges from the inner rim and from the flared surface of the disk at larger radii. No dust emission is detected between ∼ 3-15 AU. The oxygen emission seems also to come from a flared structure, however, the bulk of this emission is produced between ∼ 1-10 AU. This could indicate a lack of gas in the outer disk or could be due to chemical effects which reduce the abundance of OH-the parent molecule of the observed [O i] emission-further away from the star. It may also be a contrast effect if the [O i] emission is much stronger in the inner disk. We suggest that the three systems, HD 179218, HD 135344 B and HD 101412, may form an evolutionary sequence: the disk initially flared becomes flat under the combined action of gas-dust decoupling, grain growth and dust settling.
Evidence of grain growth in the disk of the bipolar proto-planetary nebula M 1–92
Astronomy and Astrophysics, 2010
Aims. We investigate the dust grain size and dust shell structure of the bipolar proto-planetary nebula M 1-92. Methods. We performed radiative transfer modeling of the dust shells of M 1-92. Our models consists of a disk and bipolar lobes that are surrounded by an AGB shell, each component having different dust characteristics. The model parameters were constrained with the previously obtained spectral energy distribution, the intensity images, the polarization images based on HST/NICMOS archived data as well as the previous radio observations in the CO emission line. Results. Our model geometries with the optically thick disk and lobes with a hollow structure reproduce the bright bipolar lobes of M 1-92. The upper limit of the grain size a max in the lobes is estimated to be 0.5 μm from the polarization value in the bipolar lobe. The a max value of the disk is constrained with the disk mass (0.2 M), which was estimated from a previous CO emission line observation. We find a good model with a max = 1000.0 μm, which provides an approximated disk mass of 0.15 M. Even taking into account uncertainties such as the gas-to-dust mass ratio, a significantly larger dust of a max > 100.0 μm, comparing to the dust in the lobe, is expected. We also estimated the disk inner radius, the disk outer radius, the mass-loss rate, and the envelope mass to be 30 R (=9 AU), 4500 AU, 7.5 × 10 −6 [v exp km s −1 ] M yr −1 , and 4 M , respectively, where v exp is the expansion velocity. Conclusions. If the dust existing in the lobes in large separations from the central star undergoes little dust processing, the dust sizes preserves the ones in the dust formation. Submicron-sized grains are found in many objects besides M 1-92, suggesting that the size does not depend much on the object properties, such as initial mass of the central star and chemical composition of the stellar system. On the other hand, the grain sizes in the disk do. Evidence of large grains has been reported in many bipolar PPNs, including M 1-92. This result suggests that disks play an important role in grain growth.
Monthly Notices of the Royal Astronomical Society, 1996
We study star formation processes in the disc of the weakly barred grand design spiral galaxy M100 (NGC 4321) from a variety of images tracing recent massive star formation, old and young stars, dust, and neutral hydrogen. Differences between arm and interarm regions are specifically studied by decomposing the images into arm and non-arm zones. We find from a comparison of the morphology in Hα, H i and dust that while the first two are coincident over most of the disc, they are offset from the dust lanes especially along the inner parts of the spiral arms: a picture which is indicative of a density wave shock moving through the arms. H i is formed near the young massive stars as a result of photo-dissociation. From radial profiles we find that in the region of the star-forming spiral arms the exponential scale lengths for Hα, blue and near-infrared light, and 21 cm radio continuum are equal within the fitting errors. The scale lengths for the interarm region are also equal for all these tracers, but the arm scale lengths are significantly longer. This points to a common origin of the profiles in star formation, with little or no influence from radial population gradients or dust in the disc of this galaxy. The longer arm scale lengths are equivalent to an outwardly increasing arm-interarm contrast. We argue that the radial profiles of radio continuum and H i, as well as CO, are also directly regulated by star formation, and discuss the possible implications of this result for the interpretation of observed CO intensities in and outside spiral arms. We discuss the radial atomic hydrogen profile in some detail. Its almost perfectly flat shape in the region of the star-forming spiral arms may be explained by photodissociation and recombination processes in the presence of a limited quantity of interstellar dust, controlling the equilibrium between the molecular and atomic form of hydrogen. Over most of the inner part of the disc, Hi seems to be a product of the star formation processes, rather than the cause of enhanced star formation.
The Astrophysical Journal, 2006
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low resolution) observations for 314 stars in the Formation and Evolution of Planetary Systems Legacy program. These data are used to investigate the properties and evolution of circumstellar dust around solar-type stars spanning ages from approximately 3 Myr-3 Gyr. We identify 46 sources that exhibit excess infrared emission above the stellar photosphere at 24 μm, and 21 sources with excesses at 70 μm. Five sources with an infrared excess have characteristics of optically thick primordial disks, while the remaining sources have properties akin to debris systems. The fraction of systems exhibiting a 24 μm excess greater than 10.2% above the photosphere is 15% for ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the 70 μm fractional luminosity appears to decline over a similar age range. The characteristic temperature of the debris inferred from the IRS spectra range between 60 and 180 K, with evidence for the presence of cooler dust to account for the strength of the 70 μm excess emission. No strong correlation is found between dust temperature and stellar age. Comparison of the observational data with disk models containing a power-law distribution of silicate grains suggests that the typical inner-disk radius is 10 AU. Although the interpretation is not unique, the lack of excess emission shortward of 16 μm and the relatively flat distribution of the 24 μm excess for ages 300 Myr is consistent with steady-state collisional models.
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Cygnus OB2 is the most massive stellar association within 2 kpc from the Sun. Given its large content of massive stars, counting tens of O and 3 WR stars, and thousands of young low mass stars, Cygnus OB2 is the best target to study how massive stars affect the star formation process in the parental cloud and the evolution of nearby protoplanetary disks.<br> I will present the results of our study on the feedback provided by the environment in Cygnus OB2 on disk evolution, combining the X-ray data from the 1.08 Msec Chandra Cygnus OB2 Legacy Project (P.I. J. J. Drake) with an extensive set of optical and infrared data of the association. I will analyze and compare the destructive feedback provided by disk photoevaporation induced by the intense local UV field and close encounters between members of the association, and I will show evidence indicating that disk evolution in an environment similar to Cygnus OB2 is seriously affected by externally induced photoevaporation while c...