Gas and dust in the TW Hydrae association as seen by theHerschelSpace Observatory (original) (raw)
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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
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.
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.
Modeling the IR spectrum of the dust shell around the [WC] star: V605 AQL
Astrophysics and Space Science, 2001
Nebulae around low mass Wolf-Rayet [WC] stars often show a strong midand near infrared (MN-IR) emission which cannot be explained with asingle grain size and an equilibrium temperature model. Weinvestigated the effect of the grain size, radiation density, andtemperature fluctuations of small dust grains on the spectral energydistribution (SED) in the infrared.A model of ISOCAM and IRAS measurements of V605
Multiwavelength studies of the gas and dust disc of IRAS 04158+2805
Astronomy and Astrophysics, 2008
We present a study of the circumstellar environment of IRAS 04158+2805 based on multi-wavelength observations and models. Images in the optical and near-infrared, a polarisation map in the optical, and mid-infrared spectra were obtained with VLT-FORS1, CFHT-IR, and Spitzer-IRS. Additionally we used an X-ray spectrum observed with Chandra. We interpret the observations in terms of a central star surrounded by an axisymmetric circumstellar disc, but without an envelope, to test the validity of this simple geometry. We estimate the structural properties of the disc and its gas and dust content. We modelled the dust disc with a 3D continuum radiative transfer code, MCFOST, based on a Monte-Carlo method that provides synthetic scattered light images and polarisation maps, as well as spectral energy distributions. We find that the disc images and spectral energy distribution narrowly constrain many of the disc model parameters, such as a total dust mass of 1.0−1.75 × 10 −4 M and an inclination of 62 • −63 •. The maximum grain size required to fit all available data is of the order of 1.6−2.8 μm although the upper end of this range is loosely constrained. The observed optical polarisation map is reproduced well by the same disc model, suggesting that the geometry we find is adequate and the optical properties are representative of the visible dust content. We compare the inferred dust column density to the gas column density derived from the X-ray spectrum and find a gas-to-dust ratio along the line of sight that is consistent with the ISM value. To our knowledge, this measurement is the first to directly compare dust and gas column densities in a protoplanetary disc.
Constraints on the nature of dust particles by infrared observations
Monthly Notices of the Royal Astronomical Society, 2006
The far-infrared (FIR) emissivity of dust is an important parameter characterizing the physical properties of the grains. With the availability of stellar databases and far-infrared data from Infrared Space Observatory (ISO) it is possible to compare the optical and infrared properties of dust, and derive the far-infrared emissivity with respect to the optical extinction. In this paper we present the results of a systematic analysis of the FIR emissivity of interstellar clouds observed with ISOPHOT (the photometer onboard ISO) at least at two infrared wavelengths, one close to ∼100µm and one at 200µm. We constructed FIR emission maps, determined dust temperatures, created extinction maps using 2MASS survey data, and calculated far-infrared emissivity for each of these clouds. We present the largest homogeneously reduced database constructed so far for this purpose. During the data analysis special care was taken on possible systematic errors. We find that far-infrared emissivity has a clear dependence on temperature. The emissivity is enhanced by a factor of usually less than 2 in the low dust temperature regime of 12K≤T d ≤14K. This result suggests larger grain sizes in those regions. However, the emissivity increase of typically below 2 restricts the possible grain growth processes to ice-mantle formation and coagulation of silicate grains, and excludes the coagulation of carbonaceous particles on the scales of the regions we investigated. In the temperature range 14 K ≤ T d ≤ 16 K a systematic decrease of emissivity is observed with respect to the values of the diffuse interstellar matter. Possible scenarios for this behaviour are discussed in the paper.
STUDY OF DUST PROPERTIES AROUND THE WHITE DWARF WD0011-399 IN IRIS, AKARI AND WISE SURVEYS
Department of Physics, Tri-Chandra Multiple Campus, Tribhuvan University, 2022
This research project is focused on the study of an isolated dust structure near the white dwarf WD0011-399 located at R.A. (J2000) 00h 13m 47.48s and Dec. (J2000) -39◦ 37′ 24.28′′ using Improved Reprocessing of the IRAS (IRIS), AKARI and Wide-field Infrared Survey Explorer (WISE) surveys from SkyView Virtual Observatory along with SIMBAD Astronomical Database and Gaia Archive of ESA. The size of the cavity under study is 5.42 pc×2.75 pc, 1.87 pc×0.87 pc and 1.03 pc×0.51 pc with inclination angle of 62.32◦ , 65.57◦ and 62.27◦ respectively in IRIS, AKARI and WISE data suggesting that the cavity is neither a face-on nor an edge-on. The relative flux density of the region has been studied through pixel extraction of FIR images (0.5◦ , 30 pixels) and dust color temperature along with dust mass has been calculated. Using IRIS data the temperature of the dust structure is found between a maximum value of 36.82±4.30 K to a minimum of 22.59±2.32 K with an offset of 14.23 K. The average temperature of the region is 28.22±0.18 K. Following similar procedures for AKARI data, the temperature is found between a maximum of 26.37±3.56 K and a minimum of 16.32±1.47 K with an offset of 10.06 K. The average temperature is 19.25±0.15 K. Similarly, using WISE data, the temperature is found between a maximum of 353.72±18.54 K and a minimum of 307.24±4.69 K with an offset of 46.48 K. The average temperature is 316.62±0.81 K. The high value of offset temperature suggests that the structure might be evolving with disruptions from background radiative sources. Approximately Gaussian distribution of the temperature in all the surveys implies that the region might be tending towards local thermodynamic equilibrium. The total mass of the isolated structure is estimated to be around 0.03 M⊙, 1.6×10−3 M⊙ and 10−7 M⊙ using IRIS, AKARI, and WISE data respectively. The Jean’s mass of the structure was calculated assuming the structure a non-degenerate gas, which was estimated around 2001.93 M⊙, 178.44 M⊙, and 121.47 M⊙ using IRIS, AKARI, and WISE data. Since Jean’s mass is much greater than the mass of the structure there seems no possibility of star formation within the region of interest. The color maps show identical distribution for all wavelengths however, no significant relation was observed between dust color temperature and dust mass.
Aims. We aim at directly detecting the presence of optically thin circumstellar dust emission within the terrestrial planetary zone around main sequence stars known to harbour cold debris discs. The present study focuses on a sample of six bright A-and early F-type stars. Methods. High-precision interferometric observations have been obtained in the near-infrared K band with the FLUOR instrument installed on the CHARA Array. The measured squared visibilities are compared to the expected visibility of the stellar photospheres based on theoretical photospheric models taking into account rotational distortion. We search for potential visibility reduction at short baselines, a direct piece of evidence for resolved circumstellar emission. Results. Our observations bring to light the presence of resolved circumstellar emission around one of the six target stars (ζ Aql) at the 5σ level. The morphology of the emission source cannot be directly constrained because of the sparse spatial frequency sampling of our interferometric data. Using complementary adaptive optics observations and radial velocity measurements, we find that the presence of a low-mass companion is a likely origin for the excess emission. The potential companion is characterised by a K-band contrast of four magnitudes. It has a most probable mass of about 0.6 M and is expected to orbit between about 5.5 AU and 8 AU from its host star assuming a purely circular orbit. Nevertheless, by adjusting a physical debris disc model to the observed Spectral Energy Distribution of the ζ Aql system, we also show that the presence of hot dust within 10 AU from ζ Aql, producing a total thermal emission equal to 1.69 ± 0.31% of the photospheric flux in the K band, is another viable explanation for the observed nearinfrared excess. Our re-interpretation of archival near-to far-infrared photometric measurements shows however that cold dust is not present around ζ Aql at the sensitivity limit of the IRS and MIPS instruments onboard Spitzer, and urges us to remove ζ Aql from the category of bona fide debris disc stars. Conclusions. The hot debris disc around Vega ) currently remains our only secure resolved detection within the context of this survey, with six genuine early-type debris disc stars observed so far. Further observations will be needed to assess whether ζ Aql also belongs to this hot debris disc category.
A Herschel resolved far-infrared dust ring around HD 207129
Astronomy & Astrophysics, 2011
Context. Dusty debris discs around main sequence stars are thought to be the result of continuous collisional grinding of planetesimals in the system. The majority of these systems are unresolved and analysis of the dust properties is limited by the lack of information regarding the dust location. Aims: The Herschel DUNES key program is observing 133 nearby, Sun-like stars (<20 pc, FGK spectral type) in a volume limited survey to constrain the absolute incidence of cold dust around these stars by detection of far infrared excess emission at flux levels comparable to the Edgeworth-Kuiper belt (EKB). Methods: We have observed the Sun-like star HD 207129 with Herschel PACS and SPIRE. In all three PACS bands we resolve a ring-like structure consistent with scattered light observations. Using α Boötis as a reference point spread function (PSF), we deconvolved the images, clearly resolving the inner gap in the disc at both 70 and 100 μm. Results: We have resolved the dust-producing planetesimal belt of a debris disc at 100 μm for the first time. We measure the radial profile and fractional luminosity of the disc, and compare the values to those of discs around stars of similar age and/or spectral type, placing this disc in context of other resolved discs observed by Herschel/DUNES. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Spitzer 24 mum Survey for Dust Disks around Hot White Dwarfs
Astron J, 2011
Two types of dust disks around white dwarfs (WDs) have been reported: small dust disks around cool metal-rich WDs consisting of tidally disrupted asteroids and a large dust disk around the hot central WD of the Helix planetary nebula (PN) possibly produced by collisions among Kuiper-Belt-like objects. To search for more dust disks of the latter type, we have conducted a Spitzer MIPS 24 μm survey of 71 hot WDs or pre-WDs, among which 35 are central stars of PNe (CSPNs). Nine of these evolved stars are detected and their 24 μm flux densities are at least two orders of magnitude higher than their expected photospheric emission. Considering the bias against the detection of distant objects, the 24 μm detection rate for the sample is gsim15%. It is striking that seven, or ~20%, of the WD and pre-WDs in known PNe exhibit 24 μm excesses, while two, or 5%-6%, of the WDs not in PNe show 24 μm excesses and they have the lowest 24 μm flux densities. We have obtained follow-up Spitzer Infrared Spectrograph spectra for five objects. Four show clear continuum emission at 24 μm, and one is overwhelmed by a bright neighboring star but still shows a hint of continuum emission. In the cases of WD 0950+139 and CSPN K 1-22, a late-type companion is present, making it difficult to determine whether the excess 24 μm emission is associated with the WD or its red companion. High-resolution images in the mid-infrared are needed to establish unambiguously the stars responsible for the 24 μm excesses.