Can Turbulent, High-density Gas Form Stars in Molecular Clouds: A Case Study in Ophiuchus

Star formation is governed by the interplay between gravity and turbulence in most of molecular clouds.Recent theoretical works assume that dense gas,whose column density is above a critical value in the column density probability distribution function(N-PDF),where gravity starts to overcome turbulence,becomes star-forming gas and will collapse to form stars.However,these high-density gases will include some very turbulent areas in the clouds.Will these dense but turbulent gases also form stars?We test this scenario in Ophiuchus molecular cloud using N-PDF analysis and find that at least in some regions,the turbulent,dense gas is not forming stars.We identified two isolated high-density structures in Ophiuchus,which are gravitationally unbound and show no sign of star formation.Their high densities may come from turbulence.

Mid-Infrared Diagnostic Diagrams and the Starburst-AGN Connection

The mid infrared regime is little affected by extinction, and it contains a plethora of spectroscopic information. The Infrared Space Observatory (ISO) has provided access to this wealth of information. Here I present new results from a study of ISO SWS spectra of about 30 AGNs, concentrating on diagnostic digrams to distinguish between star formation and AGNs as energy source in dusty galaxies (such as ULIRGs), and to discuss the Starburst AGN connection in general. Further results and all details of this study can be found in Sturm et al. (2002).

AGN: The Gamma-Ray Status after CGRO

By detecting more than 100 AGN at γ ray energies, the experiments aboard CGRO finally opened the field of extragalactic γ ray astronomy. A general picture has developed which is briefly summarized.

New insights into AGNs with low-mass black holes and high accretion rates:the case of narrow-line Seyfert 1 galaxies

Narrow-line Seyfert 1(NLS1) galaxies are believed to harbor low-mass black holes accreting at high rates,and they are therefore important targets when studying the nature of black hole growth,galaxy evolution,and accretion physics.We have rigorously studied the physical properties of a sample of NLS1 galaxies.We briefly review previous findings and present new results,including:(1) The locus of NLS1 galaxies on the MBH-σ plane,which we find to follow the relation of non-active galaxies after removing objects obviously dominated by outflows.(2) The presence of "blue outliers" which hint at extreme outflows as they would be predicted from merger models.(3) More subtle evidence for winds and outflows across the whole NLS1 population.(4) New correlations and trends which link black hole mass,Eddington ratio and physical parameters of the emission-line region.A new element is added to the eigenvector 1 space based on a principal component analysis,which aims at identifying the main drivers of AGN correlation properties.

More than softer-when-brighter: The X-ray powerlaw spectral variability in NGC 4051

The powerlaw X-ray spectra of active galactic nuclei at moderate to high accretion rates normally appear softer when they brighten,for which the underlying mechanisms are yet unclear.Utilizing XMM-Newton observations and excluding photons<2 keV to avoid contamination from the soft excess,in this work we scrutinize the powerlaw spectral variability of NCG 4051 from two new aspects.We first find that a best-fit"softer-when-brighter"relation is statistically insufficient to explain the observed spectral variabilities,and intervals deviated from the empirical relation are clearly visible in the light curve of 2-4 ke V/4-10 keV count rate ratio.The deviations are seen not only between but also within individual XMM-Newton exposures,consistent with random variations of the corona geometry or inner structure(with timescales as short as^1 ks),in addition to those behind the smooth"softer-when-brighter"trend.We further find the"softer-when-brighter"trend gradually weakens with the decreasing timescale(from^100 ks down to 0.5 ks).These findings indicate that the powerlaw spectral slope is not solely determined by its brightness.We propose a two-tier geometry,including flares/nano-flares on top of the inner disc and an embedding extended corona(heated by the flares,in analogy to solar corona)to explain the observations together with other observational clues in literature.Rapid spectral variabilities could be due to individual flares/nano-flares,while slow ones are driven by the variations in the global activity of inner disc region(akin to the variation of solar activity,but not the accretion rate)accompanied with heating/cooling and inflation/contraction of the extended corona.

Millimeter gap contrast as a probe for turbulence level in protoplanetary disks

Turbulent motions are believed to regulate angular momentum transport and influence dust evolution in protoplanetary disks.Measuring the strength of turbulence is challenging through gas line observations because of the requirement for high spatial and spectral resolution data,and an exquisite determination of the temperature.In this work,taking the well-known HD 163296 disk as an example,we investigated the contrast of gaps identified in high angular resolution continuum images as a probe for the level of turbulence.With self-consistent radiative transfer models,we simultaneously analyzed the radial brightness profiles along the disk major and minor axes,and the azimuthal brightness profiles of the B67 and B100 rings.By fitting all the gap contrasts measured from these profiles,we constrained the gas-to-dust scale height ratioΛto be 3.0^(+0.3)_(−0.8),1.2^(+0.1)_(−0.1),and≥6.5 for the D48,B67,and B100 regions,respectively.The varying gas-to-dust scale height ratios indicate that the degree of dust settling changes with radius.The inferred values forΛtranslate into a turbulence level of α_(turb)<3×10^(−3) in the D48 and B100 regions,which is consistent with previous upper limits set by gas line observations.However,turbulent motions in the B67 ring are strong with α_(turb)∼1.2×10^(−2).Due to the degeneracy betweenΛand the depth of dust surface density drops,the turbulence strength in the D86 gap region is not constrained.

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

从星系中星际介质（ISM）的观察到自一致模拟

2002年的“欧洲和国家联合天文学会议（JENAM）”在葡萄牙举行，会议的主题为：从星系中星际介质（ISM）的观察到自一致模拟，会议上的报告发表在2004年的《天体物理和空间科学》杂志289卷，3～4期，本书为该期的重新出版本。