Mid‐Infrared Spectra of Dust Debris around Main‐Sequence Stars (original) (raw)
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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.
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.
DUST IN THE INNER REGIONS OF DEBRIS DISKS AROUND A STARS
The Astrophysical Journal, 2009
We present infrared interferometric observations of the inner regions of two A-star debris disks, β Leo and ζ Lep, using the FLUOR instrument at the CHARA interferometer on both short (30 m) and long (> 200 m) baselines. For the target stars, the short-baseline visibilities are lower than expected for the stellar photosphere alone, while those of a check star, δ Leo, are not. We interpret this visibility offset of a few percent as a near-infrared (NIR) excess arising from dust grains which, due to the instrumental field of view, must be located within several AU of the central star. For β Leo, the NIR excess-producing grains are spatially distinct from the dust which produces the previously known mid-infrared (MIR) excess. For ζ Lep, the NIR excess may be spatially associated with the MIR excess-producing material. We present simple geometric models which are consistent with the NIR and MIR excesses and show that for both objects, the NIR-producing material is most consistent with a thin ring of dust near the sublimation radius, with typical grain sizes smaller than the nominal radiation pressure blowout radius. Finally, we discuss possible origins of the NIR-emitting dust in the context of debris disk evolution 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...
Frequency of Debris Disks around Solar‐Type Stars: First Results from a Spitzer MIPS Survey
The Astrophysical Journal, 2006
We have searched for infrared excesses around a well-defined sample of 69 FGK main-sequence field stars. These stars were selected without regard to their age, metallicity, or any previous detection of IR excess; they have a median age of 4Gyr.Wehavedetected70mexcessesaroundsevenstarsatthe3confidencelevel.Thisextraemissionisproducedbycoolmaterial(<100K)locatedbeyond10AU,welloutsidethe′′habitablezones′′ofthesesystemsandconsistentwiththepresenceofKuiperBeltanalogswith4 Gyr. We have detected 70 m excesses around seven stars at the 3 confidence level. This extra emission is produced by cool material (<100 K) located beyond 10 AU, well outside the ''habitable zones'' of these systems and consistent with the presence of Kuiper Belt analogs with 4Gyr.Wehavedetected70mexcessesaroundsevenstarsatthe3confidencelevel.Thisextraemissionisproducedbycoolmaterial(<100K)locatedbeyond10AU,welloutsidethe′′habitablezones′′ofthesesystemsandconsistentwiththepresenceofKuiperBeltanalogswith100 times more emitting surface area than in our own planetary system. Only one star, HD 69830, shows excess emission at 24 m, corresponding to dust with temperatures k300 K located inside of 1 AU. While debris disks with L dust /L ? ! 10 À3 are rare around old FGK stars, we find that the disk frequency increases from 2% AE 2% for L dust /L ? ! 10 À4 to 12% AE 5% for L dust /L ? ! 10 À5 . This trend in the disk luminosity distribution is consistent with the estimated dust in our solar system being within an order of magnitude greater or less than the typical level around similar nearby stars. Although there is no correlation of IR excess with metallicity or spectral type, there is a weak correlation with stellar age, with stars younger than a gigayear more likely to have excess emission.
Dust Characteristics of Massive Star‐forming Sites in the Mid‐Infrared
The Astrophysical Journal, 2001
Four massive star-forming regions were imaged in the mid-infrared with the MIRAC3 instrument : W51 IRS 2, Mon R2, DR 21, and S140. We obtained high spatial resolution (D1A) images at several wavelengths from 7.8 to 13.2 km with the circular variable Ðlter, as well as narrow-band continuum images at 12.5 and 20.6 km toward each region. In each massive star-forming region, one or more sources show deep silicate absorption. For at least two of the massive star-forming regions, W51 IRS 2 and Mon R2, the absorbing material is highly localized and may be circumstellar material in disks or shells. The silicate absorption occurs at least as often around massive young stars as around young stars of lower mass (which are more often observed). The estimated optical depths of the silicate features are consistent with those predicted by radiative transfer models toward ultracompact H II regions, but substantially higher than observed toward T Tauri stars and other low-mass young stellar objects. There is no consistent correspondence between silicate absorption and either the dust color temperature or the 12.5 km opacity. In W51 IRS 2, the two previously known mid-infrared sources have been resolved into at least six subsources. Infrared counterparts are newly reported for two radio-continuum sources in S140. Also, new mid-infrared sources have been detected in both W51 IRS 2 and S140. We suggest that the infrared source in the southwest of DR 21 may not be self-luminous, but may instead be heated by the three nearby radio continuum sources. The gas density in the ring at Mon R2 supports the blister scenario for the IRS 1 H II region.
DUst around NEarby Stars. The survey observational results
Astronomy & Astrophysics, 2013
Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 µm were obtained, complemented in some cases with observations at 70 µm, and at 250, 350 and 500 µm using SPIRE. The observing strategy was to integrate as deep as possible at 100 µm to detect the stellar photosphere.
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.
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.
Dust formation by massive stars studied by infrared observations with AKARI/IRC and Subaru/COMICS
2010
Recent AKARI/IRC observations of SN2008ax in NGC4490 on the day 98 has revealed the presence of near-infrared excess emission. This emission can be interpreted as the re-radiation from the pre-existing circumstellar amorphous carbon dust of a color temperature of 767±45 K and the mass of 1.2 +0.4 −0.3 × 10 −5 M or silicate dust of 885±60 K and 6.8 +2.5 −1.7 × 10 −5 M , which may have been formed in the mass loss wind from the OB/WR progenitor in an interacting binary system. In order to investigate the ongoing dust formation by WR binary systems, the mid-infrared observations of the Galactic WR binary WR140 were carried out with Subaru/COMICS on 1st August 2009. 11.7µm image of WR140 has shown that the dust cloud formed during the previous periastron passage in 2001