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1.
We present high-resolution observations made with the Very Large Array (VLA) in its A configuration at frequencies between 5 and 43 GHz of a sample of five massive young stellar objects (YSOs): Lk Hα101, NGC 2024-IRS2, S106-IR, W75N and S140-IRS1. The resolution varied from 0.04 arcsec (at 43 GHz) to 0.5 arcsec (at 5 GHz), corresponding to a linear resolution as high as 17 au for our nearest source. A MERLIN observation of S106-IR at 23 GHz with 0.03-arcsec resolution is also presented. S106-IR and S140-IRS1 are elongated at 43 GHz perpendicular to their large-scale bipolar outflows. This confirms the equatorial wind picture for these sources seen previously in MERLIN 5-GHz observations. The other sources are marginally resolved at 43 GHz. The spectral indices we derive for the sources in our sample range from +0.2 to +0.8, generally consistent with ionized stellar winds. We have modelled our sources as uniform, isothermal spherical winds, with Lk Hα101 and NGC 2024-IRS2 yielding the best fits. However, in all cases our fits give wind temperatures of only 2000–5000 K, much less than the effective temperatures of main-sequence stars of the same luminosity, a result which is likely due to the clumpy nature of the winds.  相似文献   

2.
Observations of two infrared objects embedded in molecular clouds near the supernova remnant W44 are presented. W44-IRS1 offers compelling evidence that it is a star whose formation was recently induced by expansion of the supernova remnant. W44-IRS2 lies beyond the remnant, possibly apart from the region of its influence.Paper presented at the Conference on Protostars and Planets, held at the Planetary Science Institute, University of Arizona, Tucson, Arizona, between January 3 and 17, 1978.Kitt Peak National Observatory which is operated by AURA. Inc. under contract with the National Science Foundation.  相似文献   

3.
We present a new set of diagnostics which allow us to trace and classify in a statistical manner the mid-IR emission produced by active galactic nuclei (AGN) and star-forming regions. We construct a diagram based on the strength of the unidentified infrared band (UIB)at 6.2 μm, and the intensity of the continuum at short (6 μm) and long wavelengths (15 μm). We interpret the integrated mid-IR emission in late-type galaxies as resulting from three individual contributions coming from HII regions, diffuse/photodissociation regions (PDRs), and AGN. Based on this assumption, our diagnostic diagram provides a quantitative estimate of the AGN and starburst contribution to an observed mid-IR spectrum. We show that UIB emission is very faint or absent in regions harbouring intense and hard radiation fields as in the case of AGN or ‘pure’ HII starburst regions where UIB carriers can be destroyed by photodissociation. However, contrary to starburst spectra, typical AGN spectra present a strong hot continuum below 9 μm originating from hot dust heated by the AGN radiation field. An extrapolation of this diagnostic towards other mid-IR observations should improve our knowledge of the AGN/starburst connection. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

4.
Using photometric data from the Two-Micron All-Sky Survey (2MASS) and GLIMPSE catalogues, I investigate the incidence of mid-infrared (mid-IR) excesses  (∼10 μm)  in G and K stars of luminosity class III. In order to obtain a large sample size, stars are selected using a near-IR colour–magnitude diagram. Sources which are candidates for showing mid-IR excess are carefully examined and modelled to determined whether they are likely to be G/K giants. It is found that mid-IR excesses are present at a level of  (1.8 ± 0.4) × 10−3  . While the origin of these excesses remains uncertain, it is plausible that they arise from debris discs around these stars. I note that the measured incidence is consistent with a scenario in which dust lifetimes in debris discs are determined by Poynting–Robertson drag rather than by collisions.  相似文献   

5.
We present basic observational strategies for ASTRO-F [also known as the Infra-Red Imaging Surveyor (IRIS) ] to be launched in 2004 by the Japanese Institute of Space and Astronautical Science (ISAS). We examine two survey scenarios, a deep ∼1 deg2 survey reaching sensitivities an order of magnitude below all but the deepest surveys performed by ISO in the mid-IR, and a shallow ∼18  deg2 mid-IR (7–25μm in six bands) covering an area greater than the entire area covered by all ISO mid-IR surveys. Using two cosmological models, the number of galaxies predicted for each survey is calculated. The first model uses an enhancement of a classical (1+ z )3.1 pure luminosity evolution model by Pearson & Rowan-Robinson. The second model incorporates a strongly evolving ultraluminous infrared galaxy component. For the deep survey, between 20 000 and 30 000 galaxies should be detected in the shortest wavebands, and ≈5000 in the longest (25-μm) band. It is predicted that the shallow survey will detect of the order of 100 000–150 000 sources. We find that for both ASTRO-F and other small-aperture space telescopes, confusion due to faint sources may be severe, especially at the longest mid-IR wavelengths. Using the exceptional range of observational options provided by ASTRO-F (nine wavelength filters and spectroscopic ability from 2.2 to 25 μm), we show that by combining the mid-IR observations with the near-IR camera on ASTRO-F , both the different galaxy populations and rough photometric redshifts can be distinguished in the colour–colour plane. In its role as a surveyor (plus near-IR spectroscopic ability) ASTRO-F will complement well the SIRTF space observatory mission.  相似文献   

6.
We present high angular resolution (1.2), narrow band (/=0.1) images of the nucleus of NGC253 at three wavelengths in the mid-IR (8.5, 10.0, and 12.5 m). We find that most of the mid-IR flux in the nucleus of NGC253 derives from a very small region 120 pc in diameter. Within this small region there are three spatially and spectrally distinct IR components: two bright compact sources, and a surrounding envelope of low level, diffuse emission. The mid-IR and 6cm radio are loosely correlated in position but not in brightness. The implication is that the mid-IR - radio correlation may begin to break down on small spatial scales relevant to individual star forming regions and large individual sources. These variations in the mid-IR spectra and in the radio-IR correlation imply that the nuclear emission is excited by more than one mechanism and source type.  相似文献   

7.
The near and mid-IR properties of barred and unbarred spiral galaxies are discussed on the basis of complete samples that were compiled earlier. The two types of spirals are shown not to differ from one another in emission power in the near and mid-IR ranges. Multiple regression and principal component analysis have been applied to investigate near and mid-IR properties of SB and SA galaxies, particularly their relation to X-ray and radio continuum emissions. There are definite differences between SB and SA spirals in the near and mid-IR. In the case of SB galaxies, the compactness of 10 m emission is closely related to the J - H color index, and the redder J - H color corresponds to relatively more extended emission at 10 m. It is assumed that these are caused by the bar itself, which stimulates enhanced star formation in a barred galaxy with respect to unbarred spiral.  相似文献   

8.
We present the main characteristics of a new mid-IR camera, TIRCAM, operating at the 1.5 m Italian Infrared Telescope.  相似文献   

9.
We study the 37 brightest radio sources in the Subaru/ XMM–Newton Deep Field. We have spectroscopic redshifts for 24 of 37 objects and photometric redshifts for the remainder, yielding a median redshift z med for the whole sample of   z med≃ 1.1  and a median radio luminosity close to the 'Fanaroff–Riley type I/type II (FR I/FR II)' luminosity divide. Using mid-infrared (mid-IR) ( Spitzer MIPS 24 μm) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the FR I/FR II radio luminosity break most of the radio sources are associated with objects that have excess mid-IR emission, only some of which are broad-line objects, although there is one clear low-accretion-rate object with an FR I radio structure. For extended steep-spectrum radio sources, the fraction of objects with mid-IR excess drops dramatically below the FR I/FR II luminosity break, although there exists at least one high-accretion-rate 'radio-quiet' QSO. We have therefore shown that the strong link between radio luminosity (or radio structure) and accretion properties, well known at z ∼ 0.1, persists to z ∼ 1. Investigation of mid-IR and blue excesses shows that they are correlated as predicted by a model in which, when significant accretion exists, a torus of dust absorbs ∼30 per cent of the light, and the dust above and below the torus scatters ≳1 per cent of the light.  相似文献   

10.
We have studied the panchromatic broad-band properties from the FUV to the MIR of a sample of 808 post-starburst galaxies. We find that in the optical and near-IR bands post-starburst galaxies (PSGs) form a remarkably uniform class of objects and that, on average, simple populations synthesis models (SSP) reproduce very well the SEDs of PSGs over a broad wavelength range, but not in the UV. We also find that, while the photometric variance in the optical and near-IR properties of the sample is small and comparable to the observational errors, both in the UV and the mid-IR the observed variance is much larger than the errors. We find a strong correlation between the UV fluxes and those in the mid-IR, indicating that the large variance in UV properties of PSGs could be related to a non-uniform distribution of dust covering the intermediate age populations. The disagreement between models and observations in the UV could be due to inadequate modelling; to the contribution of AGB and post-AGB stars; or to a non-uniform distribution of dust; possibly all three. Further progress in understanding this important class of galaxies, therefore, requires at the same time better modelling and better observations in the UV and mid-IR.  相似文献   

11.
We investigate in this contribution emissivity properties of the [Fe ii] near-IR lines and their application to the study of jets in young stars. We report a model-independent method to determine the gas phase abundance in jets. Then, we present synthetic maps deduced from a recent self-consistent MHD cold disk wind model from which the thermal solution has been solved a posteriori. Kinematics is compared with observations in the [Fe ii] near-IR lines of L1551-IRS5. General kinematical behaviour is well reproduced, the existence of two velocity components in particular. However, we note a relative deficit in emission at intermediate velocity as observed in the jets from optically visible T Tauri stars. We examine predicted rotation signatures for various types of MHD disk winds. Compared to observations of DG Tau, warm disk winds reproduce quite well observed velocity shifts, whereas cold solutions predict too high toroidal velocities by a factor 2–3.  相似文献   

12.
Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.  相似文献   

13.
Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5 % with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 μm, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths.  相似文献   

14.
We present spatially resolved 10-μm spectra of the nucleus of IC 5063 that are near-diffraction-limited. The observations were obtained with T-ReCS, the mid-infrared (mid-IR) imager and spectrometer on the 8.1-m Gemini South telescope, with the slit aligned at a position angle on the sky along the direction of the cone of narrow-line emission. The spectra cover the nucleus and the inner reaches of the ionization cones at a spatial resolution of approximately 0.4 arcsec (90 pc). Individual spectra, extracted in steps in the spatial direction along the slit, reveal variations in continuum slope and silicate feature profile and depth on subarcsecond scales, illustrating in unprecedented detail the complexity of the circumnuclear regions of this galaxy at mid-IR wavelengths. The dust population in the vicinity of the narrow-line region, north-west of the nuclear position, is significantly warmer than that to the south-east of the nucleus. This is consistent with an observation of the cooler dust associated with the outer reaches of the postulated torus that obscures the type 1 nucleus in this object.  相似文献   

15.
From an analysis of VLBI observations of H2CO and OH maser emission in the direction of the ultra-conpact HII region NGC 7538-IRS 1, the following model is proposed: The HII region is surrounded by a thick dusty shell which breaks open at the two poles and there is a bipolar outflow. Around it is a rotating gas/dust ring and matter falls from the ring onto the surface of the HII region. The whole system, HII region and the ring, moves with a sight line velocity of −61.0 km/s inside a large cloud which moves with a sight line velocity of −57 km/s. The H2CO and OH masers occur near the poles of the HII region and within 0.2 RHII of the surface. The positions of the H2O maser and other line sources are discussed in term of this model.  相似文献   

16.
We combine Chandra and XMM–Newton X-ray data from our previous papers with new X-ray observations and with Spitzer mid-infrared (mid-IR) data in order to study the nature of the nuclei of radio galaxies and radio-loud quasars with   z < 1.0  from the 3CRR sample. The significant increase in sample size over our previous work, the reduction of bias in the sample as a result of new observations and the availability of more mid-IR data allow us to show conclusively that almost all objects classed as low-excitation radio galaxies in optical spectroscopic studies lack a radiatively efficient active nucleus. We show that the distribution of absorbing columns in the narrow-line radio galaxies differs from the population of X-ray-selected radio-quiet type 2 quasars and from that in local Seyfert 2s. We comment on the current evidence for the nature of the soft X-ray component in radio-galaxy nuclear spectra, concluding that a jet origin for this component is very hard to evade. Finally, we discuss the recently discovered 'fundamental plane' of black hole activity, showing that care must be taken when placing radio-loud active galactic nucleus (AGN) on such diagnostic diagrams.  相似文献   

17.
We present the collection of all the mid- and far-IR observations (λ=3–170 μm) of the young eruptive variable PV Cep available so far in the literature. These data allow us to confirm that flux variability is a prominent feature at mid-IR wavelength (λ=3–25 μm). Color-magnitude plots clearly indicate that the observed variability is not extinction-driven, but mainly influenced by fluctuations of the mass accretion rate. We interpret such variability as due to a hot spot created onto the stellar surface by the column of accreting matter, which heats the inner parts of the disk and determines the observed increase of the near- mid-IR luminosity. A quantitative characterization is given for both the spot itself and the additional thermal component created by it. Far-IR data (λ=60–170 μm) are consistent with the presence of a temperature stratification in a massive and quite un-evolved circumstellar disk.  相似文献   

18.
We report on the results of a time-series photometric survey of NGC 2362, carried out using the CTIO 4-m Blanco telescope and Mosaic-II detector as part of the Monitor project. Rotation periods were derived for 271 candidate cluster members over the mass range  0.1 ≲ M /M⊙≲ 1.2  . The rotation period distributions show a clear mass-dependent morphology, qualitatively similar to that in NGC 2264, as would be expected from the age of this cluster. Using models of angular momentum evolution, we show that angular momentum losses over the ∼1–5 Myr age range appear to be needed in order to reproduce the evolution of the slowest rotators in the sample from the ONC to NGC 2362, as found by many previous studies. By incorporating Spitzer IRAC mid-infrared (mid-IR) measurements, we found that three to four objects showing mid-IR excesses indicative of the presence of circumstellar discs were all slow rotators, as would be expected in the disc regulation paradigm for early pre-main-sequence angular momentum evolution, but this result is not statistically significant at present, given the extremely limited sample size.  相似文献   

19.
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20.
本文在分析研究NGC7538-IRS1致密HⅡ区H_2CO和OH脉泽辐射VLBI观测结果的基础上,指出该HⅡ区合理的模型是:HⅡ区表面为厚的尘埃层包围,尘埃层两极已被突破,并形成双极流;HⅡ区外面有一个环形转动气体-尘埃云,存在由环向HⅡ区表面的物质下落;包括环和HⅡ区在内的整个系统视向速度为-61km/s,该系统居于视向速度为-57km/s的更大分子云中。H_2CO和OH脉泽发生在HⅡ区两极附近离HⅡ区表面小于0.2R_(HⅡ)的区域内。利用上述模型,还讨论了H_2O脉泽及其他分子吸收线和发射线的发生区域。  相似文献   

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