红外相机OASIS的偏振器设计

介绍为日本冈山天文台１．８８ｍ镜红外相机（ＯＡＳＩＳ）研制的红外偏振器．该偏振器与ＯＡＳＩＳ配备可实现～４．１′视场的近红外成像偏振观测．偏振器包括可旋转的消色差半波片和固定的致冷偏振片,通过旋转半波片对入射光的调制取得线偏振测量．实际观测给出ＪＨＫ波段的偏振效率分别为８６．３％、９７．０％和９７．５％．并给出了ＯＡＳＩＳ偏振观测与前人观测结果的比较     

分子外流源L1211中近红外HH天体的发现

报告分子外流源Ｌ１２１１ 中新发现的１２ 个近红外ＨＨ 天体．在Ｌ１２１１ 的～４’区域,取得了ＪＨＫ’宽带和Ｈ２ 　ｖ ＝ １０ 　Ｓ（１） 发射线窄带的近红外图像．分析表明,新探测到的许多红外源与浓密分子云物理成协,其中有２０ 多个源表现出典型的Ｔ Ｔａｕｒｉ 星、Ｈｅｒｂｉｇ Ａｅ／Ｂｅ星和原恒星的红外超．Ｌ１２１１ 中的ＩＲＡＳ点源没有被观测到,可能是更深地埋于分子云中．对红外观测和分子线观测消光估计的比较显示,小于２μｍ 的近红外观测还不足以揭示深埋于分子云的整个年轻星团．根据近红外ＨＨ 天体的形态分布和红外源性质,能进一步证认这些ＨＨ 天体的激发源．其结果表明,Ｌ１２１１ 分子云中具有多个红外源驱动的多个外流活动     

The obscured growth of massive black holes

The mass density of massive black holes observed locally is consistent with the hard X-ray background provided that most of the radiation produced during their growth was absorbed by surrounding gas. A simple model is proposed here for the formation of galaxy bulges and central black holes in which young spheroidal galaxies have a significant distributed component of cold dusty clouds, which accounts for the absorption. The central accreting black hole is assumed to emit both a quasar-like spectrum, which is absorbed by the surrounding gas, and a slow wind. The power in both is less than the Eddington limit for the black hole. The wind, however, exerts the most force on the gas and, as earlier suggested by Silk & Rees, when the black hole reaches a critical mass it is powerful enough to eject the cold gas from the galaxy, so terminating the growth of both black hole and galaxy. In the present model this point occurs when the Thomson depth in the surrounding gas has dropped to about unity and results in the mass of the black hole being proportional to the mass of the spheroid, with the normalization agreeing with that found for local galaxies by Magorrian et al. for reasonable wind parameters. The model predicts a new population of hard X-ray and submm sources at redshifts above 1, which are powered by black holes in their main growth phase.     

A Spitzer survey of young stellar objects in the Rosette Molecular Cloud

We present results from a survey of the Rosette Molecular Cloud (RMC) using both the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) onboard the Spitzer Space Telescope . We have mapped a region of active star formation covering an area approximately 1° by 1.5° including several previously known clusters. Spectral energy distributions (SEDs) fitted to our data combined with that from Two Micron All Sky Survey (2MASS) are used to identify young stellar objects (YSOs) with infrared (IR) excesses. We find that roughly 50 per cent of the sources are forming in clustered environments and identify seven clusters of IR excess sources including four that were previously unknown. We investigate evidence for triggering of star formation due to the ionization front, identified in Brackett-α emission, associated with the young open cluster NGC 2244. Although the position of several of the clusters of IR excess sources are coincident with the ionization front, the bulk of the youngest YSOs are located far from the ionization front, in clusters located along the mid-plane of the cloud. We conclude that although triggering from the H  ii nebula is a possible origin for some of the recent star formation, the majority of the active star formation is occurring in already dense regions of the cloud not compressed by the expansion of the H  ii region.     

Properties of dusty tori in active galactic nuclei – I. The case of SWIRE/SDSS quasars

We derive the properties of dusty tori in active galactic nuclei from the comparison of observed spectral energy distributions (SEDs) of SDSS quasars and a precomputed grid of torus models. The observed SEDs comprise SDSS photometry, Two-Micron All-Sky Survey J , H and K data, whenever available, and mid-infrared (mid-IR) data from the Spitzer Wide-area InfraRed Extragalactic Survey. The adopted model is that of Fritz, Franceschini & Hatziminaoglou. The fit is performed by standard  χ²  -minimization; the model, however, can be a multicomponent comprising a stellar and a starburst component, whenever necessary. Models with low equatorial optical depth, τ_9.7, were allowed as well as 'traditional' models with  τ_9.7≥ 1.0  , corresponding to   A _V≥ 22  and the results were compared. Fits using high optical depth tori models only produced dust more compactly distributed than in the configuration where all τ_9.7 models were permitted. Tori with decreasing dust density with the distance from the centre were favoured while there was no clear preference for models with or without angular variation of the dust density. The computed outer radii of the tori are of some tens of parsecs large but can reach, in a few cases, a few hundreds of parsecs. The mass of dust, M _Dust, and IR luminosity, L _IR, integrated in the wavelength range between 1 and 1000 μm, do not show significant variations with redshift, once the observational biases are taken into account. Objects with 70-μm detections, representing 25 per cent of the sample, are studied separately and the starburst contribution (whenever present) to the IR luminosity can reach, in the most extreme but very few cases, 80 per cent.     

The long-term stability of a possible aqueous ammonium sulfate ocean inside Titan

We model the thermal evolution of a subsurface ocean of aqueous ammonium sulfate inside Titan using a parameterized convection scheme. The cooling and crystallization of such an ocean depends on its heat flux balance, and is governed by the pressure-dependent melting temperatures at the top and bottom of the ocean. Using recent observations and previous experimental data, we present a nominal model which predicts the thickness of the ocean throughout the evolution of Titan; after 4.5 Ga we expect an aqueous ammonium sulfate ocean 56 km thick, overlain by a thick (176 km) heterogeneous crust of methane clathrate, ice I and ammonium sulfate. Underplating of the crust by ice I will give rise to compositional diapirs that are capable of rising through the crust and providing a mechanism for cryovolcanism at the surface. We have conducted a parameter space survey to account for possible variations in the nominal model, and find that for a wide range of plausible conditions, an ocean of aqueous ammonium sulfate can survive to the present day, which is consistent with the recent observations of Titan's spin state from Cassini radar data [Lorenz, R.D., Stiles, B.W., Kirk, R.L., Allison, M.D., del Marmo, P.P., Iess, L., Lunine, J.I., Ostro, S.J., Hensley, S., 2008. Science 319, 1649-1651].