A Spitzer Survey of Protoplanetary Disk Dust in the Young Serpens Cloud: How Do Dust Characteristics Evolve With Time? (original) (raw)
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DUST EVOLUTION IN PROTOPLANETARY DISKS AROUND HERBIG Ae/Be STARS—THE SPITZER VIEW
The Astrophysical Journal, 2010
In this paper we present mid-infrared spectra of a comprehensive set of Herbig Ae/Be stars observed with the Spitzer Space Telescope. The signal-to-noise ratio of these spectra is very high, ranging between about a hundred and several hundreds. During the analysis of these data we tested the validity of standard protoplanetary dust models and studied grain growth and crystal formation. On the basis of the analyzed spectra, the major constituents of protoplanetary dust around Herbig Ae/Be stars are amorphous silicates with olivine and pyroxene stoichiometry, crystalline forsterite and enstatite and silica. No other solid state features, indicating other abundant dust species, are present in the Spitzer spectra. Deviations of the synthetic spectra from the observations are most likely related to grain shape effects and uncertainties in the iron content of the dust grains. Our analysis revealed that larger grains are more abundant in the disk atmosphere of flatter disks than in that of flared disks, indicating that grain growth and sedimentation decrease the disk flaring. We did not find, however, correlations between the value of crystallinity and any of the investigated system parameters. Our analysis shows that enstatite is more concentrated toward the warm inner disk than forsterite, in contrast to predictions of equilibrium condensation models. None of the three crystal formation mechanisms proposed so far can alone explain all our findings. It is very likely that all three play at least some role in the formation of crystalline silicates.
Astromineralogy of protoplanetary disks
Proceedings of the International Astronomical Union, 2007
We review mid-infrared N-band spectra (8–13 μm) for a sample of 28 targets, obtained with the TIMMI2 camera at La Silla Observatory. The sample contains 5 FU Orionis stars, 6 Herbig Ae/Be objects, 7 T Tauri stars and 10 Vega-type main sequence objects. All targets show infrared excess, but for several the proof of circumstellar matter was lacking up to our observations. We model the N-band emission features with a mixture of silicates consisting of different grain sizes and composition, and determine the status of dust processing in these disks. While for some targets the emission spectrum resembles those of known pre-main sequence stars of evolved dust, other objects show strong isolated PAH bands but no silicate emission. For the first time we find evidence of PAH processing occurring in a T Tauri star. The Vega-type object HD 113766 exhibits highly-processed secondary generation dust, likely released by the collision of planetesimal-sized bodies. The findings of our dust analysis...
A Spitzer Study of Dusty Disks around Nearby, Young Stars
The Astrophysical Journal, 2005
We have obtained Spitzer Space Telescope MIPS (Multiband Imaging Photometer for Spitzer) observations of 39 A-through M-type dwarfs, with estimated ages between 12 and 600 Myr; IRAC observations for a subset of 11 stars; and follow-up CSO SHARC II 350 m observations for a subset of two stars. None of the objects observed with IRAC possess infrared excesses at 3.6-8.0 m; however, seven objects observed with MIPS possess 24 and/or 70 m excesses. Four objects ( Phe, HD 92945, HD 119124, and AU Mic), with estimated ages 12-200 Myr, possess strong 70 m excesses, !100% larger than their predicted photospheres, and no 24 m excesses, suggesting that the dust grains in these systems are cold. One object (HD 112429) possesses moderate 24 and 70 m excesses with a color temperature, T gr ¼ 100 K. Two objects ( 1 Lib and HD 177724) possess such strong 24 m excesses that their 12, 24, and 70 m fluxes cannot be self-consistently modeled using a modified blackbody despite a 70 m excess >2 times greater than the photosphere around 1 Lib. The strong 24 m excesses may be the result of emission in spectral features, as observed toward the Hale-Bopp star HD 69830.
Effects of dust evolution on protoplanetary disks in the mid-infrared
Astronomy & Astrophysics, 2019
In this paper, we couple the dust evolution code two-pop-py with the thermochemical disk modelling code ProDiMo. We create a series of thermochemical disk models that simulate the evolution of dust over time from 0.018 to 10 Myr, including the radial drift, growth, and settling of dust grains. We examine the effects of this dust evolution on mid-infrared gas emission, focusing on the mid-infrared spectral lines of C2H2, CO2, HCN, NH3, OH, and H2O, which are readily observable with Spitzer and the upcoming E-ELT and JWST. The addition of dust evolution acts to increase line fluxes by reducing the population of small dust grains. We find that the spectral lines of all species except C2H2 respond strongly to dust evolution; line fluxes increase by more than an order of magnitude across the model series as the density of small dust grains decreases over time. The C2H2 line fluxes are extremely low because of a low abundance in the infrared line-emitting regions, even though C2H2 is comm...
2012
We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the PACS instrument on the Herschel Space Observatory. This Open Time Key Program, known as GASPS (Gas Survey of Protoplan-etary Systems), targeted ∼250 young stars in narrow wavelength regions covering the [OI] fine structure line at 63µm, the brightest far-infrared line in such objects. A subset of the bright-est targets were also surveyed in [OI] 145µm, [CII] at 157µm, as well as several transitions of H2O and high-excitation CO lines at selected wavelengths between 78 and 180µm. Additionally, GASPS included continuum photometry at 70, 100 and 160µm, around the peak of the dust emission. The targets were SED Class II-III T Tauri stars and debris disks from 7 nearby young associations, along with a comparable sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide sample of circumstellar disks, c...
GASPS—A Herschel Survey of Gas and Dust in Protoplanetary Disks: Summary and Initial Statistics
Publications of the Astronomical Society of the Pacific, 2013
We describe a large-scale far-infrared line and continuum survey of protoplanetary disk through to young debris disk systems carried out using the PACS instrument on the Herschel Space Observatory. This Open Time Key Program, known as GASPS (Gas Survey of Protoplanetary Systems), targeted ∼250 young stars in narrow wavelength regions covering the [OI] fine structure line at 63µm, the brightest far-infrared line in such objects. A subset of the brightest targets were also surveyed in [OI] 145µm, [CII] at 157µm, as well as several transitions of H 2 O and high-excitation CO lines at selected wavelengths between 78 and 180µm. Additionally, GASPS included continuum photometry at 70, 100 and 160µm, around the peak of the dust emission. The targets were SED Class II-III T Tauri stars and debris disks from 7 nearby young associations, along with a comparable sample of isolated Herbig AeBe stars. The aim was to study the global gas and dust content in a wide sample of circumstellar disks, combining the results with models in a systematic way. In this overview paper we review the scientific aims, target selection and observing strategy. We summarise some of the initial results, showing line identifications, listing the detections, and giving a first statistical study of line detectability.
The Physical Structure of Protoplanetary Disks: The Serpens Cluster Compared with Other Regions
The Astrophysical Journal, 2013
Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud, based on photometry and Spitzer IRS spectra. Most of the stars have spectroscopically determined spectral types. Taking a distance to the cloud of 415 pc rather than 259 pc, the distribution of ages is shifted to lower values, in the 1 -3 Myr range, with a tail up to 10 Myr. The mass distribution spans 0.2 -1.2 M ⊙ , with median mass of 0.7 M ⊙ . The distribution of fractional disk luminosities in Serpens resembles that of the young Taurus Molecular Cloud, with most disks consistent with optically thick, passively irradiated disks in a variety of disk geometries (L disk /L star ∼ 0.1). In contrast, the distributions for the older Upper Scorpius and η Chamaeleontis clusters are dominated by optically thin lower luminosity disks (L disk /L star ∼ 0.02). This evolution in fractional disk luminosities is concurrent with that of disk fractions: with time disks become fainter and the disk fractions decrease. The actively accreting and non-accreting stars (based on Hα data) in Serpens show very similar distributions in fractional disk luminosities, differing only in the brighter tail dominated by strongly accreting stars. In contrast with a sample of Herbig Ae/Be stars, the T Tauri stars in Serpens do not have a clear separation in fractional disk luminosities for different disk geometries: both flared and flat disks present wider, overlapping distributions. This result is consistent with previous suggestions of a faster evolution for disks around Herbig Ae/Be stars. Furthermore, the results for the mineralogy of the dust in the disk surface (grain sizes, temperatures and crystallinity fractions, as derived from Spitzer IRS spectra) do not show any correlation to either stellar and disk characteristics or mean cluster age in the 1 -10 Myr range probed here. A possible explanation for the lack of correlation is that the processes affecting the dust within disks have short timescales, happening repeatedly, making it difficult to distinguish long lasting evolutionary effects.
New Debris Disks Around Young, Low-Mass Stars Discovered with the Spitzer Space Telescope
The Astrophysical Journal, 2009
We present 24 µm and 70 µm Multiband Imaging Photometer for Spitzer (MIPS) observations of 70 A through M-type dwarfs with estimated ages from 8 Myr to 1.1 Gyr, as part of a Spitzer guaranteed time program, including a re-analysis of some previously published source photometry. Our sample is selected from stars with common youth indicators such as lithium abundance, X-ray activity, chromospheric activity, and rapid rotation. We compare our MIPS observations to empirically derived K s -[24] colors as a function of the stellar effective temperature to identify 24 µm and 70 µm excesses. We place constraints or upper limits on dust temperatures and fractional infrared luminosities with a simple blackbody dust model. We confirm the previously published 70 µm excesses for HD 92945, HD 112429, and AU Mic, and provide updated flux density measurements for these sources. We present the discovery of 70 µm excesses for five stars: HD 7590, HD 10008, HD 59967, HD 73350, and HD 135599. HD 135599 is also a known Spitzer IRS (InfraRed Spectrograph) excess source, and we confirm the excess at 24 µm. We also present the detection of 24 µm excesses for 10 stars: HD 10008, GJ 3400A, HD 73350, HD 112429, HD 123998, HD 175742, AT Mic, BO Mic, HD 358623 and Gl 907.1. We find that large 70 µm excesses are less common around stars with effective temperatures of less than 5000 K (3.7 +7.6 −1.1 %) than around stars with effective temperatures between 5000 K and 6000 K (21.4 +9.5 −5.7 %), despite the cooler stars having a younger median age in our sample (12 Myr vs. 340 Myr). We find that the previously reported excess for TWA 13A at 70 µm is due to a nearby background galaxy, and the previously reported excess for HD 177724 is due to saturation of the near-infrared photometry used to predict the mid-infrared stellar flux contribution. In the Appendix, we present an updated analysis of dust grain removal timescales due to grain-grain collisions and radiation pressure, Poynting-Robertson (P-R) drag, stellar wind drag, and planet-dust dynamical interaction. We find that drag forces can be important for disk dynamics relative to grain-grain collisions for L IR /L * < 10 −4 , and that stellar wind drag is more important than P-R drag for K and M dwarfs, and possibly for young (<1 Gyr) G dwarfs as well.
Astronomy and Astrophysics, 2010
We present the most sensitive 3 mm-survey to date of protoplanetary disks carried in the Taurus-Auriga star forming region (average rms of about 0.3 mJy), using the IRAM PdBI. With our high detection rate of 17/19, we provide the first detections at wavelengths longer than about 1 mm for 12 sources. This enables us to study statistically the mm SED slopes and dust properties of faint disks and compare them to brighter disks using a uniform analysis method. With these new data and literature measurements at sub-millimeter and millimeter wavelengths, we analyze the dust properties of a sample of 21 isolated disks around T Tauri stars in the Taurus-Auriga star forming region. Together with the information about the disks spatial extension from sub/mm-mm interferometric studies, we derive from the observed sub-mm/mm spectral energy distribution constraints on the dust opacity law at these wavelengths, using two-layer flared disk models and a self-consistent dust model that takes properly into account the variation of the dust opacity with grain growth. We find evidence for the presence in the disk midplane of dust particles that have grown to sizes as large as at least 1 millimeter in all the disks of our sample, confirming what was previously observed on smaller brighter objects. This indicates that the dust coagulation from ISM dust to mm-sized grains is a very fast process in protoplanetary disks, that appears to occur before a young stellar object enters the Class II evolutionary stage. Also, the amount of these large grains in the disk outer regions is stationary throughout all the Class II evolutionary stage, indicating that mechanisms slowing down the dust inward migration are playing an important role in the Taurus-Auriga protoplanetary disks. Another result is that the spectral index between 1 and 3 mm for the 6 faintest disks in our sample is on average smaller than for the brighter disks, indicating either that these fainter, yet unmapped, disks are spatially much less extended than the brighter spatially resolved disks, or that fainter disks have typically larger dust grains in their outer regions. Considering that these fainter disks are more representative of the bulk of the disk population than the brighter ones, this may have important consequences for the theories of planetesimal formation and disk formation and evolution. Finally, we investigate the relations between the derived dust properties, namely dust mass and grain growth, and the properties of the central star, like its mass, age and mass accretion rate.
Mid‐Infrared Spectra of Dust Debris around Main‐Sequence Stars
The Astrophysical Journal Supplement Series, 2004
We report spectra obtained with the Spitzer Space Telescope in the λ = 14-35 µm range of 19 nearby main-sequence stars with infrared excesses. The six stars with strong dust emission show no recognizable spectral features, suggesting that the bulk of the emitting particles have diameters larger than 10 µm. If the observed dust results from collisional grinding of larger solids, we infer minimum masses of the parent body population between 0.004 M ⊕ and 0.06 M ⊕. We estimate grain production rates of ∼10 10 g s −1 around λ Boo and HR 1570; selective accretion of this matter may help explain their peculiar surface abundances.