A Spitzer IRS Survey of NGC 1333: Insights into disk evolution from a very young cluster (original) (raw)
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Spitzer observations of NGC 2264: the nature of the disk population
Astronomy & Astrophysics, 2012
Aims. NGC 2264 is a young cluster with a rich circumstellar disk population which makes it an ideal target for studying the evolution of stellar clusters. Our goal is to study the star formation history of NGC 2264 and to analyse the primordial disk evolution of its members.
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...
Infrared Spectrograph Characterization of a Debris Disk Around an M-Type Star in NGC 2547
The Astrophysical Journal, 2009
We present 5 to 15 µm Spitzer Infrared Spectrograph (IRS) low resolution spectral data of a candidate debris disk around an M4.5 star identified as a likely member of the ∼40 Myr old cluster NGC 2547. The IRS spectrum shows a silicate emission feature, indicating the presence of warm, small, (sub)micron-sized dust grains in the disk. Of the fifteen previously known candidate debris disks around M-type stars, the one we discuss in this paper is the first to have an observed mid-infrared spectrum and is also the first to have measured silicate emission. We combined the IRS data with ancillary data (optical, JHK s , and Spitzer InfraRed Array Camera and 24 µm data) to build the spectral energy distribution (SED) of the source. Monte Carlo radiation transfer modeling of the SED characterized the dust disk as being very flat (h 100 =2 AU) and extending inward within at least 0.13 AU of the central star. Our analysis shows that the disk is collisionally dominated and is likely a debris disk.
Spitzer Observations of NGC 2547: The Disk Population at 25 Million Years
The Astrophysical Journal Supplement Series, 2004
We present Spitzer observations of the young cluster NGC 2547, obtaining photometry at 3. 6, 4.5, 5.8, 8.0, and 24 m, reaching significantly fainter infrared sensitivities than previous studies. With these observations, we investigate the disk frequency in this cluster. A total of 3770, 2408, 1988, 1238, and 1123 sources were detected in the common region of the five respective bands. The detection limits were 14.9, 14.0, 13.5, 13.3, and 12.0 mag, respectively. The large majority of sources are associated with 2MASS objects. From this large ensemble, we utilize the criteria of Naylor et al. to identify 184 likely members of the cluster. The analyses in this paper are focused on these likely members. Of the 184 candidates, 162 were detected in at least one Infrared Array Camera (IRAC) band. These objects form a well-defined family in the J À K; K À½3:6 color-color diagram. There is no evidence for excess emission at 3.6 m for cluster candidates with J À K < 0:8, corresponding to spectral types earlier than late K. For later type stars, only 12 have evidence for a 3.6 m excess. Hence, we derive a 3.6 m emitting disk fraction of less than 7%. The lack of excess for the more massive stars may indicate a difference in the disk dissipation timescales for different mass stars. At 24 m, 32 of the sources are detected. Most of them have photospheric K À½3:6 and K À½24 colors, but approximately a quarter show an excess at 24 m. This observation may be evidence for cool disks with central holes.
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.
Spitzer /IRAC‐MIPS Survey of NGC 2244: Protostellar Disk Survival in the Vicinity of Hot Stars
Astrophysical Journal, 2007
We present the results from a survey of NGC 2244 from 3.6 to 24 µm with the Spitzer Space Telescope. The 24µm-8µm-3.6µm color composite image of the region shows that the central cavity surrounding the multiple O and B stars of NGC2244 contains a large amount of cool dust visible only at 24µm. Our survey gives a detailed look at disk survivability within the hot-star-dominated environment in this cavity. Using mid infrared two color diagrams ([3.6]-[4.5] vs [5.8]-[8.0]) we identified 337 class II and 25 class I objects out of 1084 objects detected in all four of these bands with photometric uncertainty better than 10%. Including the 24 µm data, we found 213 class II and 20 class I sources out of 279 stars detected also at this latter band. The center of the class II density contours is in very good agreement with the center of the cluster detected in the 2MASS images. We studied the distribution of the class II sources relative to the O stars and found that the effect of high mass stars on the circumstellar disks is significant only in their immediate vicinity.
The Astrophysical Journal, 2010
We present Spitzer IRS mid-infrared (5-35 µm) spectra of a complete fluxlimited sample (≥ 3 mJy at 8 µm) of young stellar object (YSO) candidates selected on the basis of their infrared colors in the Serpens Molecular Cloud. Spectra of 147 sources are presented and classified. Background stars (with slope consistent with a reddened stellar spectrum and silicate features in absorption), galaxies (with redshifted PAH features) and a planetary nebula (with high ionization lines) amount to 22% of contamination in this sample, leaving 115 true YSOs. Sources with rising spectra and ice absorption features, classified as embedded Stage I protostars, amount to 18% of the sample. The remaining 82% (94) of the disk sources are analyzed in terms of spectral energy distribution shapes, PAHs and silicate features. The presence, strength and shape of these silicate features are used to infer disk properties for these systems. About 8% of the disks have 30/13 µm flux ratios consistent with cold disks with inner holes or
A Spitzer space telescope study of disks in the young σ Orionis cluster
The Astrophysical …, 2007
We report new Spitzer Space Telescope observations from the IRAC and MIPS instruments of the young (∼ 3 Myr) σ Orionis cluster. The populous nature of this cluster makes it a good target for statistically-significant studies of disk emission as a function of mass. We identify 336 stars as members of the cluster using optical and near-infrared color magnitude diagrams. Using the spectral energy distribution (SED) slopes in the IRAC spectral range, we place objects in several classes: non-excess stars, stars with optically thick disks (like classical T Tauri stars), class I (protostellar) candidates, and stars with "evolved disks"; the last exhibit smaller IRAC excesses than optically thick disk systems. In general, this classification agrees with the location expected in IRAC-MIPS color-color diagrams for these objects. We find that the evolved disk systems are mostly a combination of objects with optically thick but non-flared disks, suggesting grain growth and/or settling, and transition disks, systems in which the inner disk is partially or fully cleared of small dust. In all, we identify 7 transition disk candidates and 3 possible debris disk systems. There appears to be a spatial extension of infrared excess sources to the northeast , which may be associated with the young (< 1 Myr) embedded cluster NGC 2024. As in other young stellar populations, the fraction of disks depends on the stellar mass, ranging from ∼10%
Dust Processing and Grain Growth in Protoplanetary Disks in the Taurus-Auriga Star-Forming Region
The Astrophysical Journal Supplement Series, 2009
Mid-infrared spectra of 65 T Tauri stars (TTS) taken with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope are modeled using populations of optically thin dust at two temperatures to probe the radial variation in dust composition in the uppermost layers of protoplanetary disks. Most spectra with narrow emission features associated with crystalline silicates require Mgrich minerals and silica, but a very small number suggest other components. Spectra indicating large amounts of enstatite at higher temperatures (400-500 K) also require crystalline silicates, either enstatite or forsterite, at temperatures lower (100-200 K) than those required for spectra showing high abundance of other crystalline silicates. A few spectra show 10 µm complexes of very small equivalent width. They are fit well using abundant crystalline silicates but very few large grains, inconsistent with the expectation that low peak-to-continuum ratio of the 10 µm complex always indicates grain growth. Most spectra in our sample are fit well without using the opacities of large crystalline silicate grains. If large grains grow by agglomeration of submicron grains of all dust types, the amorphous silicate components of these aggregates must typically be more abundant than the crystalline silicate components. We also find that the more there is of one crystalline dust species, the more there is of the others. This suggests extraction was used for SL and LL data, and full-column extraction was used for SH and LH data ). We used Relative Spectral Response Functions (RSRFs) to calibrate the flux (Sargent et al. 2006). For both orders of SL and for the both orders of LL (for all observations except for HBC 656), a spectral template of α Lacertae (A1 V; M. Cohen 2004, private communication) of higher spectral resolution than the templates described by Cohen et al. (2003) was used. For the LL flux calibration of HBC 656 over second, bonus, and first orders out to 36 µm wavelength, RSRFs generated from data of ξ Dra and the template for ξ Dra from Cohen et al. (2003) were used. Past 36 µm, a LL first-order RSRF generated from data of Markarian 231 and the template for Markarian 231 (J. Marshall, private communication; Marshall et al. 2007; Armus et al. 2007) were used. For SH and LH, the spectral template for ξ Dra (K2 III) by Cohen et al. (2003) and its IRS data were used to generate RSRFs. Except for GG Tau A, GG Tau B, ZZ Tau, ROXs 42C, HBC 656, and TW Cha, all RSRF-calibrated spectra are the same as presented by Watson et al. (2008).
IRS Characterization of a Debris Disk around an M-type star in NGC2547
2009
We present 5 to 15 micron Spitzer Infrared Spectrograph (IRS) low resolution spectral data of a candidate debris disk around an M4.5 star identified as a likely member of the ~40 Myr old cluster NGC2547. The IRS spectrum shows a silicate emission feature, indicating the presence of warm, small, (sub)micron-sized dust grains in the disk. Of the fifteen previously known candidate debris disks around M-type stars, the one we discuss in this paper is the first to have an observed mid-infrared spectrum and is also the first to have measured silicate emission. We combined the IRS data with ancillary data (optical, JHKs, and Spitzer InfraRed Array Camera and 24 micron data) to build the spectral energy distribution (SED) of the source. Monte Carlo radiation transfer modeling of the SED characterized the dust disk as being very flat (h100=2AU) and extending inward within at least 0.13AU of the central star. Our analysis shows that the disk is collisionally dominated and is likely a debris disk.