Spitzer Observations of the λ Orionis Cluster. I. The Frequency of Young Debris Disks at 5 Myr (original) (raw)
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Spitzerobservations of the Λ Orionis Cluster. II. Disks Around Solar-Type and Low-Mass Stars
The Astrophysical Journal, 2010
We present IRAC/MIPS Spitzer Space Telescope observations of the solar-type and the low-mass stellar population of the young (∼5 Myr) λ Orionis cluster. Combining optical and Two Micron All Sky Survey photometry, we identify 436 stars as probable members of the cluster. Given the distance (450 pc) and the age of the cluster, our sample ranges in mass from 2 M to objects below the substellar limit. With the addition of the Spitzer mid-infrared data, we have identified 49 stars bearing disks in the stellar cluster. Using spectral energy distribution slopes, we place objects in several classes: non-excess stars (diskless), stars with optically thick disks, stars with "evolved disks" (with smaller excesses than optically thick disk systems), and "transitional disk" candidates (in which the inner disk is partially or fully cleared). The disk fraction depends on the stellar mass, ranging from ∼6% for K-type stars (R C − J < 2) to ∼27% for stars with spectral-type M5 or later (R C − J > 4). We confirm the dependence of disk fraction on stellar mass in this age range found in other studies. Regarding clustering levels, the overall fraction of disks in the λ Orionis cluster is similar to those reported in other stellar groups with ages normally quoted as ∼5 Myr.
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%
A Spitzer Space Telescope Study of Disks in the Young sigma Orionis Cluster
Astrophysical Journal, 2007
We report new Spitzer Space Telescope observations from the IRAC and MIPS instruments of the young (~ 3 Myr) sigma Orionis cluster. 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. As in other young stellar populations, the fraction of disks depends on the stellar mass, ranging from ~10% for stars in the Herbig Ae/Be mass range (>2 msun) to ~35% in the T Tauri mass range (1-0.1 msun). We find that the disk fraction does not decrease significantly toward the brown dwarf candidates (<0.1 msun). The IRAC infrared excesses found in stellar clusters and associations with and without central high mass stars are similar, suggesting that external photoevaporation is not very important in many clusters. Finally, we find no correlation between the X-ray luminosity and the disk infrared excess, suggesting that the X-rays are not strongly affected by disk accretion.
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.
SpitzerObservations of the Orion OB1 Association: Disk Census in the Low‐Mass Stars
The Astrophysical Journal, 2007
We present new Spitzer Space Telescope observations of two fields in the Orion OB1 association. We report here IRAC/MIPS observations for 115 confirmed members and 41 photometric candidates of the ∼10 Myr 25 Orionis aggregate in the OB1a subassociation, and 106 confirmed members and 65 photometric candidates of the 5 Myr region located in the OB1b subassociation. The 25 Orionis aggregate shows a disk frequency of 6 % while the field in the OB1b subassociation shows a disk frequency of 13 %. Combining IRAC, MIPS and 2MASS photometry we place stars bearing disks in several classes: stars with optically thick disks (class II systems), stars with an inner transitional disks (transitional disk candidates) and stars with "evolved disks"; the last exhibit smaller IRAC/MIPS excesses than class II systems. In all, we identify 1 transitional disk candidate in the 25 Orionis aggregate and 3 in the OB1b field; this represents ∼10% of the disk bearing stars, indicating that the transitional disk phase can be relatively fast. We find that the frequency of disks is a function of the stellar mass, suggesting a maximum around stars with spectral type M0. Comparing the infrared excess in the IRAC bands among several stellar groups we find that inner disk emission decays with stellar age, showing a correlation with the respective disk frequencies. The disk emission at the IRAC and MIPS bands in several stellar groups indicates that disk dissipation takes place faster in the inner region of the disks. Comparison with models of irradiated accretion
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.
Astrophysical Journal, 2008
We report detection with the Spitzer Space Telescope of cool dust surrounding solar type stars. The observations were performed as part of the Legacy Science Program, "Formation and Evolution of Planetary Systems" (F EP S). From the overall F EP S sample of 328 stars having ages ∼0.003-3 Gyr we have selected sources with 70 µm flux densities indicating excess in their spectral energy distributions above expected photospheric emission. Six strong excess sources are likely primordial circumstellar disks, remnants of the star formation process. Another 25 sources having ≥ 3σ excesses are associated with dusty debris disks, generated by collisions within planetesimal belts that are possibly stirred by existing planets. We draw attention to six additional sources with ≥ 2σ excesses which require confirmation as debris disks. In our analysis, most (>80%) of the debris disks identified via 70 µm excesses have ≥ 3σ excesses at 33 µm as well, while only a minority (<40%) have ≥ 3σ excesses at 24 µm.
Spitzer: Accretion in Low-Mass Stars and Brown Dwarfs in the lambda Orionis Cluster
Astrophysical Journal, 2007
We present multi-wavelength optical and infrared photometry of 170 previously known low mass stars and brown dwarfs of the 5 Myr Collinder 69 cluster (Lambda Orionis). The new photometry supports cluster membership for most of them, with less than 15% of the previous candidates identified as probable non-members. The near infrared photometry allows us to identify stars with IR excesses, and we find that the Class II population is very large, around 25% for stars (in the spectral range M0 - M6.5) and 40% for brown dwarfs, down to 0.04 Msun, despite the fact that the H(alpha) equivalent width is low for a significant fraction of them. In addition, there are a number of substellar objects, classified as Class III, that have optically thin disks. The Class II members are distributed in an inhomogeneous way, lying preferentially in a filament running toward the south-east. The IR excesses for the Collinder 69 members range from pure Class II (flat or nearly flat spectra longward of 1 micron), to transition disks with no near-IR excess but excesses beginning within the IRAC wavelength range, to two stars with excess only detected at 24 micron. Collinder 69 thus appears to be at an age where it provides a natural laboratory for the study of primordial disks and their dissipation.
2007
(abbreviated) We report detection with the Spitzer Space Telescope of cool dust surrounding solar type stars. The observations were performed as part of the Legacy Science Program, ``Formation and Evolution of Planetary Systems'' (FEPS). From the overall FEPS sample (Meyer et al. 2006) of 328 stars having ages ~0.003-3 Gyr we have selected sources with 70 um flux densities indicating excess in their spectral energy distributions above expected photospheric emission........ .....The rising spectral energy distributions towards - and perhaps beyond - 70 um imply dust temperatures T_dust <45-85 K for debris in equilibrium with the stellar radiation field. We infer bulk properties such as characteristic temperature, location, fractional luminosity, and mass of the dust from fitted single temperature blackbody models. For >1/3 of the debris sources we find that multiple temperature components are suggested, implying a spatial distribution of dust extending over many tens of AU. Because the disks are dominated by collisional processes, the parent body (planetesimal) belts may be extended as well. Preliminary assessment of the statistics of cold debris around sun-like stars shows that ~10% of FEPS targets with masses between 0.6 and 1.8 Msun and ages between 30 Myr and 3 Gyr exhibit 70 um emission in excess of the expected photospheric flux density. We find that fractional excess amplitudes appear higher for younger stars and that there may be a trend in 70 um excess frequency with stellar mass.
The Astronomical Journal, 2005
Fluxes and upper limits in the wavelength range from 3.6 to 70 µm from the Spitzer Space Telescope are provided for twenty solar-mass Pleiades members. One of these stars shows a probable mid-IR excess and two others have possible excesses, presumably due to circumstellar debris disks. For the star with the largest, most secure excess flux at MIPS wavelengths, HII1101, we derive Log(L dust /L * ) ∼ -3.8 and an estimated debris disk mass of 4.2×10 −5 M(Earth) for an assumed uniform dust grain size of 10µm. If the stars with detected excesses are interpreted as stars with relatively recent, large collision events producing a transient excess of small dust particles, the frequency of such disk transients is about ∼10% for our ∼100 Myr, Pleiades G dwarf sample. For the stars without detected 24-70µm excesses, the upper limits to their fluxes correspond to approximate 3σ upper limits to their disk masses of 6×10 −6 M(Earth) using the MIPS 24µm upper limit, or 2×10 −4 M(Earth) using the MIPS 70µm limit. These upper limit disk masses (for "warm" and "cold" dust, respectively) are roughly consistent, but somewhat lower than, predictions of a heuristic model for the evolution of an "average" solar-mass star's debris disk based on extrapolation backwards in time from current properties of the Sun's Kuiper belt.