Infrared mapping of the dust disc around Vega     

Heinrichsen  Walker  & Klaas 《Monthly notices of the Royal Astronomical Society》1998,293(4):L78-L82

ISOPHOT has been used to perform high-resolution 60-μm scans of Vega, and these have been compared with those from γDra, to obtain a Gaussian width of 22±2 arcsec. The dust disc around Vega has been mapped, resolving it at 60 and 90 μm with ISOPHOT. At 90 μm a Gaussian width of 36±3 arsec has been derived. In addition, multi-filter photometry is presented, at 25, 60, 80, 100, 120, 150, 170 and 200 μm. The data are fitted by a modified blackbody with a temperature of 73 K [ Q (λ)∝1/λ^1.1]. The dust disc has a luminosity L _IR/ L _*∼3×10⁻⁵. Using a distance of 7.8 pc, 22 arcsec corresponds to a distance of 86 au, and 36 arcsec to a distance of 140 au.  相似文献   

The K-band Hubble diagram for brightest cluster galaxies in X-ray clusters     

Collins  & Mann 《Monthly notices of the Royal Astronomical Society》1998,297(1):128-142

  相似文献   

The equatorial disc of the Be star X Persei     

Telting  Waters  Roche  Boogert  Clark  de Martino  & Persi 《Monthly notices of the Royal Astronomical Society》1998,296(4):785-799

  相似文献   

The ortho- to para- ratio of H₂ in the starburst of NGC 253     

Andrew Harrison  Phil Puxley  Adrian Russell  & Peter Brand 《Monthly notices of the Royal Astronomical Society》1998,297(2):624-632

We present measurements of several near-infrared emission lines from the nearby galaxy NGC 253. We have been able to measure four H₂ lines across the circumnuclear starburst, from which we estimate the ortho- to para- ratio of excited H₂ to be ∼2. This indicates that the bulk of the H₂ emission arises from photodissociation regions (PDRs), rather than from shocks. This is the case across the entire region of active star formation.
As the H₂ emission arises from PDRs, it is likely that the ratio of H₂ to Brγ (the bright hydrogen recombination line) is a measure of the relative geometry of O and B stars and PDRs. Towards the nucleus of NGC 253 the geometry is deduced to be tightly clustered O and B stars in a few giant H  II regions that are encompassed by PDRs. Away from the nuclear region, the geometry becomes that of PDRs bathed in a relatively diffuse ultraviolet radiation field.
The rotation curves of 1–0 S(1) and Brγ suggest that the ionized gas is tracing a kinetic system different from that of the molecular gas in NGC 253, particularly away from the nucleus.  相似文献   

Estimates for the luminosity function of galaxies and its evolution     

Volker Springel  & Simon D. M. White 《Monthly notices of the Royal Astronomical Society》1998,298(1):143-152

A new method is presented to obtain a non-parametric maximum likelihood estimate of the luminosity function and the selection function of a flux-limited redshift survey. The method parametrizes the selection function as a series of stepwise power laws and allows possible evolution of the luminosity function. We also propose a new technique to estimate the rate of evolution of the luminosity function. This is based on a minimization of the observed large-scale power with respect to the evolutionary model. We use an ensemble of mock surveys extracted from an N -body simulation to verify the power of this method. We apply our estimators to the 1.2-Jy survey of IRAS galaxies. We find a far-infrared luminosity function in good agreement with previously published results and evidence for rather strong evolution. If the comoving number density of IRAS galaxies is assumed to scale ∝ (1 +  z ) ^P , we estimate P  = 4.3 ± 1.4.  相似文献   

Optical, infrared and radio observations of the Seyfert galaxy Markarian 315     

M. Nonino  J. P. Henry  C. Fanti  R. Fanti  & J. Davies 《Monthly notices of the Royal Astronomical Society》1998,299(2):332-340

We report on new optical, infrared and radio observations of the Seyfert galaxy Markarian 315. We confirm the detection at all wavelengths of a secondary peak of emission, which lies ≈ 2 arcsec east of the Seyfert nucleus. Moreover, we detect a chain-like structure which surrounds the active nucleus, with peculiar behaviour westward of the nucleus. We consider different interpretations for the origin of the secondary peak emission.  相似文献   

Mid-infrared imaging of WL 16: the spatial distribution of the hydrocarbon emission features     

Moore  Emerson  Skinner  Meixner  Arens  & Jernigan 《Monthly notices of the Royal Astronomical Society》1998,299(4):1209-1214

We present arcsec-resolution images at 8.2, 10.0 and 11.3 μm of the unusual young object WL 16 in Ophiuchus, which has an extended envelope of fluorescing hydrocarbon molecules. To the limit of achieved sensitivity, the faint 10.0-μm continuum has a surface-brightness distribution that is not distinguishable from those at 8.2 and 11.3 μm, where the luminosity is known to be dominated by the polycyclic aromatic hydrocarbon (PAH) emission features. We conclude that the 10-μm continuum either arises from non-equilibrium heating of small dust grains that are well mixed with the hydrocarbons or is quasi-continuous emission from the PAH particles themselves, rather than thermal equilibrium emission from macroscopic dust grains, and that there is no significant silicate absorption variation across the source. The extended hydrocarbon emission may trace a flattened, equatorial distribution of circumstellar material or arise in bipolar lobes. The former case is slightly favoured, based on currently available data, and would imply that WL 16 is a relatively evolved Herbig Ae star, the equatorial plane of which has been almost cleared of normal dust, leaving only fluorescing hydrocarbons and larger coagulated particles as a possibly transient fossil of the original circumstellar disc.  相似文献   

利用ERBE和ISCCP资料反演青藏高原地表短波吸收辐射场   总被引：7，自引：1，他引：6  

高歌  翁笃鸣 《南京气象学院学报》1998,21(1):8-14

利用ＥＲＢＥ和ＩＳＣＣＰ卫星辐射及总云量资料,结合青藏高原地面日射资料,讨论了并提出了该地区地表短波吸收气候反演方法,该法的似合精度较高,平均误差为９．８Ｗ．ｍ＾－２据此计算出７５°Ｅ－９５°豚２５°Ｅ－４０°Ｎ间２．５°＊２．５°经纬网格点和高原６３个站点的各月平均地面吸收辐射通量密度,给制出其在高原的分布图,揭示其基本特征。  相似文献   

Detecting Arctic snow and ice cover with FY-1D global data     

References： 《极地研究(英文版)》2007,18(1):54-62

Chinese meteorological satellite FY-1D can obtain global data from four spectral channels which include visible channel(0.58-0.68 μm) and infrared channels(0.84-0.89 μm,10.3-11.3 μm,11.5-12.5 μm).2366 snow and ice samples,2024 cloud samples,1602 land samples and 1648 water samples were selected randomly from Arctic imageries.Land and water can be detected by spectral features.Snow-ice and cloud can be classified by textural features.The classifier is Bayes classifier.By synthesizing five d ays classifying result of Arctic snow and ice cover area,complete Arctic snow and ice cover area can be obtained.The result agrees with NOAA/NESDIS IMS products up to 70%.  相似文献   

Long-term infrared variability of the UX Ori-type star SV Cep     

A. Juhász  T. Prusti  P. Ábrahám  C. P. Dullemond 《Monthly notices of the Royal Astronomical Society》2007,374(4):1242-1252

We investigate the long-term optical–infrared variability of SV Cep and explain it in the context of an existing UX Ori (UXOR) model. A 25-month monitoring programme was completed with the Infrared Space Observatory in the 3.3–100 μm wavelength range. Following a careful data reduction, the infrared light curves were correlated with the variations of SV Cep in the V band. A remarkable correlation was found between the optical and the far-infrared light curves. In the mid-infrared regime, the amplitude of variations is lower, with a hint for a weak anti-correlation with the optical changes. In order to interpret the observations, we modelled the spectral energy distribution of SV Cep assuming a self-shadowed disc with a puffed-up inner rim, using a two-dimensional radiative transfer code. We found that modifying the height of the inner rim, the wavelength dependence of the long-term optical–infrared variations is well reproduced, except the mid-infrared domain. The origin of variation of the rim height might be fluctuation in the accretion rate in the outer disc. In order to model the mid-infrared behaviour, we tested adding an optically thin envelope to the system, but this model failed to explain the far-infrared variability. Infrared variability is a powerful tool to discriminate between models of the circumstellar environment. The proposed mechanism of variable rim height may not be restricted to UXOR stars, but might be a general characteristic of intermediate-mass young stars.  相似文献