The Chemical Composition of the Field Zero-Age Star HD77407

High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of the star is determined by fitting the H α line wings. The parameters derived for this star are Teff=5900K, log g=4.47 and [Fe/H] = 0.07. It is found that the derived iron content is slightly higher than what is given in the published literature. This star shows a relative overabundances of Ca and Ba, and underabundances of Na, V and Ni with respect to the solar mix. Activity of the star is indicated by the filled in Hα and Ca II triplet line cores. It has been confirmed that our spectroscopic approach yields fairly reliable and consistent results for active stars.     

Time-dependent Behaviour of the Low Amplitude δ Scuti Star HD 52788

Wavelet transform is applied to reanalyze the low amplitude δ Scuti star HD 52788, which exhibits complex light variations with uncertain frequency solutions. We gain an insight into the strong instability of pulsation present in the star. Based on an estimate of the star‘s physical parameters, its evolutionary status is determined. An attempt of asteroseismic modelling failed to predict the observed dense frequencies. Because of its varying pulsation spectrum, HD 52788 is a distinctive and very interesting object among δ Sct stars for testing current models of stellar evolution and pulsation.     

The physics of turbulent and dynamically unstable Herbig–Haro jets

The overall properties of the Herbig–Haro objects such as centerline velocity, transversal profile of velocity, flow of mass, and flow of energy are explained adopting two models for the turbulent jet. The complex shapes of the Herbig–Haro objects, such as the arc in HH34, can be explained by introducing the combination of different kinematic effects such as velocity behavior along the main direction of the jet and the velocity of the star in the interstellar medium. The behavior of the intensity or brightness of the line of emission is explored in three different cases: transversal one-dimensional (1D) cut, longitudinal 1D cut, and 2D map. An analytical explanation for the enhancement in intensity or brightness such as usually modeled by the bow shock is given by a careful analysis of the geometrical properties of the torus.     

On the Carbon—Star Status of Five Stars in a New Carbon Star Catalog

We find that five sources listed in the new carbon star catalog are not really carbon-rich objects but oxygen-rich stars, because they all have the prominent 10μm silicate features in absorption and the 1612MHz OH maser emission or/and the SiO molecular features. These objects were considered as carbon stars in the catalog based only on their locations in the infrared two-color diagram. Therefore to use the infrared two-color diagram to distinguish carbon-rich stars from oxygenrich stars must be done with caution, because, in general, it has only a statistical meaning.     

Herbig Ae/Be星的尘埃壳层形态研究

我们使用Kurucz恒星大气模型以及黑体模型对22颗Herbig Ae/Be星的紫外数据、IRAS观测数据、地面光学及近红外测光数据资料等进行了拟合计算,用能量平衡方法进行了统计分析,得出Herbig Ae/Be星的尘埃壳层为盘状的结论.     

Herbig Ae／Be星的尘埃壳层形态研究

我们使用Ｋｕｒｕｃｚ恒星大气模型以及黑体模型对２２颗ＨｅｒｂｉｇＡｅ／Ｂｅ星的紫外数据，ＩＲＡＳ观测数据，地面光学及近红外测光数据资料等进行了拟合计算，用能量平衡方法进行了统计分析得出ＨｅｒｂｉｇＡｅ／Ｂｅ星的尘埃壳层为盘状的结论。     

On the nature of the proposed blob in the inner preplanetary disk of the Herbig Ae/Be star HD141569: evidence for a giant vortex?

Recently, Brittain and Rettig, using the cryogenic echelle spectrograph at the Infrared Telescope Facility to study the infrared emission from the inner preplanetary disk of the Herbig Ae/Be star HD141569, detected CO and H₃⁺ ion emission. This emission has been tentatively interpreted as due to the existence of a forming gas giant planet. The suggested protoplanetary blob appears to be orbiting its host star at about 7 AU being perhaps 2 AU across and roughly five times the mass of Jupiter. Based on numerical modeling of the evolution of the dust disk we show that their observational results are compatible with the presence of an evolved giant vortex in the disk. Our calculations suggest that vortices formed in disks similar to the one found around HD141569 are more effective at capturing solid material than equivalent structures around solar-like stars. On the other hand, we investigate the possibility to find evidence for large-scale vortices in preplanetary disks by submillimeter interferometry. Disks around Herbig Ae/Be stars may be primary targets for giant vortex detection using this technique.     

The Long-term Survival Chances of Young Massive Star Clusters

We review the long-term survival chances of young massive star clusters (YMCs), hallmarks of intense starburst episodes often associated with violent galaxy interactions. We address the key question as to whether at least some of these YMCs can be considered proto- globular clusters (GCs), in which case these would be expected to evolve into counterparts of the ubiquitous old GCs believed to be among the oldest galactic building blocks. In the absence of significant external perturbations, the key factor determining a cluster's long-term survival chances is the shape of its stellar initial mass function (IMF). It is, however, not straightforward to assess the IMF shape in unresolved extragalactic YMCs. We discuss in detail the promise of using high-resolution spectroscopy to make progress towards this goal, as well as the numerous pitfalls associated with this approach. We also discuss the latest progress in worldwide efforts to better understand the evolution of entire cluster systems, the disruption processes they are affected by, and whether we can use recently gained insights to determine the nature of at least some of the YMCs observed in extragalactic starbursts as proto-GCs. We conclude that there is an increasing body of evidence that GC formation appears to be continuing until today; their long-term evolution crucially depends on their environmental conditions, however.     

The Chemical Classification of the AGB Star IRAS 17515-2407

The chemical classification of IRAS 17515-2407 has been debated for a long time. Up to now there are two contenders, oxygen-rich or carbon-rich. We believe that IRAS 17515-2407 is an oxygen-rich source: because (ⅰ) it shows the silicate self-absorbed emission; (ⅱ) in the near infrared-IRAS diagram it is located in the oxygen-rich object region and (ⅲ) particularly, it has detected SiO maser emission.     

A Study of the Energy Sources of Herbig—Haro Objects

1 INTRODUCTIONHerbig-Haro objects are a kind of semi-sta]c, semi-nebuIa objects associated with star fOrm-ing regions. Although such objects were noticed by Burnham as early as l890s, they did notattract much attention until the late 1940s until their independent rediscovery by Herbig andHaro in NGC 1999. A few years later, these objects were named Herbig-Haro objects fOr thefirst time by Ambartsumian (Reipurth 1997). In the fOllowing half century, the observationand theoretical res…     

Optical spectrum of the post-AGB Star HD56126 in the wavelength interval 4010-8790 Å Å

The optical spectrum of the post-AGB star HD56126 identified with the infrared source IRAS07134+1005 is studied in detail using high spectral resolution observations (R = 25000 and 60000) performed with the echelle spectrographs of the 6-m telescope. A total of about one and a half thousand absorptions of neutral atoms and ions, absorption bands of C₂, CN, and CH molecules, and interstellar bands (DIBs) are identified in the 4012 to 8790 Å Å wavelength interval, and the depths and radial velocities of these spectral features are measured. Differences are revealed between the variations of the radial velocities measured from spectral features of different excitation. In addition to the well-known variability of the Hα profile, we found variations in the profiles of a number of FeII, YII, and BaII lines. We also produce an atlas of the spectrum of HD56126 and its comparison star α Per. The full version of the Atlas is available in electronic form from: http://www.sao.ru/hq/ssl/Atlas/Atlas.html.     

The destruction of the cometary nucleus – The case of 73P/Schwassmann-Wachmann

The paper presents an analysis of the actual brightness change of comet 73P/Schwassmann-Wachmann, which took place in 1995. The consequence of a cometary outburst is the destruction of a fragment of its surface. This causes the emission of comet material from both the surface and from exposed subsurface layers. Therefore, the calculations take into account the scattering cross-sections that come from ice and dust particles. It was assumed that the dust particles are silicates which are characterized by high irregularity of their structure. This assumption is a consequence of the analysis of the results provided by the Rosetta mission to the comet 67P/Churyumov-Gerasimenko. The main factor determining the amplitude of a cometary outburst is the mass ejected as well as the loss of ice that holds the individual nucleus structures together. Consequently, this phenomenon can significantly contribute to the destruction and even decay of the cometary nucleus.     

Large－Scale Distribution of Herbig－Haro Objects in Taurus

We report our new results on Herbig-Haro (HH) objects in the star forming region of Taurus from a wide-field survey with the 60/90 cm Schmidt telescope of the Beijing Astronomical Observatory. This survey using CCD imaging with a narrow band [SII] filter and an intermediate band [BATC10] filter covered approximately 30 square degrees in Taurus. Besides confirming the known HH Objects in the region, we discovered seven new HH candidates, and groups. Six of these are HH 701A-B, HH 702A-D, HH 703, HH 704A-D, HH 705, HH 706 and the seventh is a group, a new component of HH 319, labeled HH 319B-D. Based on the large-scale distribution of pre-main-sequence (PMS) stars in Taurus, we analyze statistically the most probable distance from the HH objects to each PMS star, from which we estimate the typical timescale of these HH objects to be between (1.3 - 2.0) ×104 yrs; and we also obtain the birth rates of HH objects: 0.447±0.198 for Class Ⅰ PMS stars, 0.360±0.222 for Class Ⅱ PMS stars, and -0.148±0.234 fo     

New insights on the interior of solar-like pulsators thanks to CoRoT: the case of HD 49385

The high performance photometric data obtained with space mission CoRoT offer the opportunity to efficiently constrain our models for the stellar interior of solar-like pulsating stars. On the occasion of the analysis of the oscillations of solar-like pulsator HD 49385, a G0-type star in an advanced stage of evolution, we revisit the phenomenon of the avoided crossings. Christensen-Dalgaard proposed a simple analogy to describe an avoided crossing between two modes. We here present an extension of this analogy to the case of n modes, and show that it should lead, in certain cases, to a characteristic behavior of the eigenfrequencies, significantly different from the n=2 case. This type of behavior seems to be observed in HD 49385, from which we infer that the star should be in a Post Main Sequence phase.     

The many faces of pulsars – the case of PSR B0833-45

A review of observational properties of the Vela pulsar across a wide energy spectrum is given. Then current approaches to the modelling of pulsars and their wind zones are briefly presented. The challenges posed to the models by the diversity of Vela’s light curves in different energy ranges are discussed.     

Scientific Analysis within SEPServer – New Perspectives in Solar Energetic Particle Research: The Case Study of the 13 July 2005 Event

Solar energetic particle (SEP) events are a key ingredient of solar?Cterrestrial physics both for fundamental research and space weather applications. Multi-satellite observations are an important and incompletely exploited tool for studying the acceleration and the coronal and interplanetary propagation of the particles. While STEREO uses for this diagnostic two identical sets of instrumentation, there are many earlier observations carried out with different spacecraft. It is the aim of the SEPServer project to make these data and analysis tools available to a broad user community. The consortium will carry out data-driven analysis and simulation-based data analysis capable of deconvolving the effects of interplanetary transport and solar injection from SEP observations, and will compare the results with the electromagnetic signatures. The tools and results will be provided on the web server of the project in order to facilitate further analysis by the research community. This paper describes the data products and analysis strategies with one specific event, the case study of 13 July 2005. The release time of protons and electrons are derived using data-driven and simulation-based analyses, and compared with hard X-ray and radio signatures. The interconnection of the experimental and the simulation-based results are discussed in detail.     

Identification of absorption lines of rare-earth elements in the region of the spectrum λλ 610.25–610.57 nm roAp stars,HD 101065, HD 134214, HD 137949, and HD 24712

In the spectral region λλ = 610.25−610.57 nm of the roAp star HD 101065, we performed the identification of the rare-earth element absorption lines absent from the atomic spectral line databases VALD and DREAM. The identified lines were used for calculating the synthetic spectra of the roAp stars HD 137949, HD 134214, and HD 24712. The upper limit of the identified line estimates was determined. The rotation/pulsation parameter νsini and magnetic field modulus were determined using the lines Nd III 669.083 nm and Ca I 616.217 nm. The element abundance in the roAp stars HD 134214 and HD 24712 was determined for the first time using Nd III lines. Calculations were carried out with the help of the code SynthM developed by S.A. Khan.     

The coupling of solar convection and rotation – (Invited Review)

In recent years, helioseismology has provided an unprecedented look at the dynamics of the solar interior. These new insights have been accompanied by tremendous advances in high-performance computing technology, prompting increasingly sophisticated and realistic numerical models of solar convection. Among the most important helioseismic constraints on global-scale convection models is the mean differential rotation profile of the solar envelope, which is established by convection under the influence of rotation. The highly turbulent nature of solar convection makes this rotational influence difficult to determine and model. I will begin this review by discussing the solar rotation profile inferred from helioseismic measurements and various theoretical and numerical approaches to account for it. Computational constraints limited early numerical models to relatively laminar flow regimes but more recent investigations have begun to explore the distinct nature of turbulent convection. After a brief overview of empirical and numerical results on the related Rayleigh-Bernard system, I will outline the current state of numerical modeling of turbulent convection in rotating, stratified fluids, first in Cartesian and then in spherical geometries. The emphasis throughout will be on how rotation influences the structure, evolution, and transport processes of turbulent convection and what type of differential rotation can result.