THE BM Ori system. IV. A new component of the system

Cross correlations between observed and synthetic spectra are used to discover yet another satellite of BM Ori with the following characteristics: effective temperature T_eff = 4000 K, radius R = 16R_⊙, mass M = 1.8M_⊙, spectral type K7 III, absolute bolometric stellar magnitude M_b = + 4^m·0, axial rotation velocity V sini = 85 km/s, and relative luminosity 0.005 near the V band. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 111–120 (February 2006).     

The system Bm Ori. V. Improved photometric elements

The times of individual minima taken from the literature are used to plot the dependence of O-C on revolution number for the eclipsing star BM Ori. A least squares fit of this plot yields the following photometric elements: Min I=JD2440265.331(5)+6.470524(3)·E. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 501–503 (August 2008).     

The BM Ori System. I. Anomaly in the Radial Velocity

The radial velocities of the star BM Ori are determined from spectra obtained by the HST and IUE satellites, as well as from spectra obtained with the BTA telescope. An analysis of this data shows that the radial velocities of the main star and its satellite experience an irregular positive shift by 20-30 km/s. This fact can only be interpreted in terms of the presence of yet another star in the binary system. The new observations have made it possible to significantly improve the accuracy of the spectroscopic elements of the orbit of the close binary system and to estimate the orbital characteristics of the third body. The preliminary values of the elements are: Ep=JD2444744, P=1302^d, =11km/s, e=0.92, K=20km/s, and =1.6rad.     

The BM Ori System. III. The Depth of the Minimum in the Infrared

The depth of the minimum of the BM Ori eclipsing system is studied in the infrared. For this purpose, observations have been made in the JHKLM bands outside the eclipse and in the JHKL bands near the central phase of the eclipse. The depth of the minimum is found to have a complicated wavelength dependence. In the short wavelength region of the spectrum this depth decreases from the U band to the R band (λ=0.36–0.71 mm), which is explained in terms of eclipsing of the principal star by a dust cloud surrounding the companion and by the disk of the companion. In the IR the depth of the minimum increases sharply from the I to the L band (λ=0.97–3.5 mm). This effect can be explained by partial obscuring of the hot region of the dust cloud by the disk of the companion. __________ Translated from Astrofizika, Vol. 48, No. 4, pp. 565–573 (November 2005).     

Searches for HH-objects and Emission Stars in Star Formation Regions. II. The Region of GM1-61 and V453 Ori

Observations of objects lying in the dark cloud L1582A, which contains the cometary nebulae GM1-61 and V453 Ori, are reported. Five previously unknown HH-objects are discovered in this region; they appear to form several flows. The morphology of the nebulae is examined and possible sources of the HH-flows are discussed. Another reflecting nebula is found that is visible mainly in the infrared.     

Analysis of the Historical Light Curve of the UX Ori Star CQ Tau

An historical light curve for the UX Ori star CQ Tau is constructed for the period from 1939 through 2003. The star’s photometric behavior includes a cyclical component with a period of about 21 years. An analysis of the periodogram reveals a shorter cycle with a duration of about 1020 days after this cycle is subtracted. Since the photometric activity of UX Ori type stars is caused by variations in the circumstellar extinction, both of these cycles indicate the existence of large-scale deviations from axial symmetry in the distribution of matter in the circumstellar disk of CQ Tau. The orbiting of these inhomogeneities about the star also causes oscillatory variations in its brightness. An analysis of the color-magnitude diagrams reveals differences in the optical parameters of the circumstellar dust along the line of sight in various phases of the 21-year cycle: absorption by larger particles predominates near the brightness maximum of CQ Tau. This means that the reduced circumstellar extinction in this part of the circumstellar disk is the result of a smaller contribution from small particles; this may be evidence of the onset of a process of coagulation of the dust particles and their conversion into large-scale bodies and planetesimals.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 165–174 (May 2005).     

AGB星氦燃烧壳层源出现非稳定热核反应的判据

建立了热脉动AGB星氦燃烧壳层源出现非稳定热核反应的判据,新判据包含 了丰富的物理信息,它不仅与热脉动AGB星氦燃烧壳层源的几何性质有关,而且与氦燃 烧壳层源的力学、热学和化学的性质都有关． 提出了热脉动AGB星氦燃烧壳层源非稳定热核反应的发生和消失的机理,它可表述 为:热脉动AGB星氦燃烧壳层源的局部区域出现对流不稳定区会触发非稳定热核反应的 发生,非稳定热核反应会促使氦燃烧壳层源急速膨胀,氦燃烧壳层源的急速几何形变会消 除非稳定热核反应． 用改进后的Kippenhahn恒星演化程序对5M(?)恒星进行了从主序星到热脉动AGB 星的演化模型计算,结果表明新判据能很好地反映5M(?)AGB星氦燃烧壳层源的热核反应 情况．并得出5M(?)热脉动AGB星在第6次热脉动周期阶段,被挖掘到热脉动AGB星 表面的元素主要是在温度lgT2／K<8．155和密度4．0相似文献   

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 Model Atmosphere Analysis of the F6V Star π3 Ori

Model atmosphere analysis, based on Kurucz models has been applied to study the F6V star π³ Ori (=BS1543=HD30652). The following values of the effective temperature, surface gravity and microturbulence velocity were obtained: = 6270±200 K, log g = 3.80.2, ξ_t =3.5±0.5 km/s. The abundances of 10 elements were determined. The resulting element abundances for the π³ Ori were found to be about three times lower with respect to the Sun. From evolutionary calculations we derived a mass, radius and luminosity for π³ Ori of M =1.3 M_⊙, R =2.38 R_⊙, L =7.9 L_⊙. Hence this star should be classified F6IV instead of F6 V. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spectral Observations of Subfuors (Exors). II. V1143 Ori

Spectral observations of the subfuor (exor) V 1143 Ori during the outburst of 1992-93 are reported. Data on the behavior of the Ca II infrared triplet before and during the outburst are presented for the first time. The amplitudes of the outbursts during 1982-94 show that their maxima do not vary greatly on the average. Between outbursts, when the star is in the minimum of its active period, the spectrum of V 1143 Ori is typical of a WTTS and during an outburst, of a CTTS.     

A population of very young brown dwarfs and free-floating planets in Orion

We describe the results of a very deep imaging survey of the Trapezium cluster in the IJH bands, using the UKIRT high-resolution camera UFTI. Approximately 32 per cent of the 515 point sources detected are brown dwarf candidates, including several free-floating objects with masses below the deuterium-burning (planetary) threshold at 0.013 M_⊙, which are detectable because of their extreme youth. We have confidence that almost all the sources detected are cluster members, since foreground contamination is minimal in the 33-arcmin² area surveyed, and the dense backdrop of OMC-1 obscures all background stars at these wavelengths. Extinction is calculated from the ( J − H ) colours, permitting accurate luminosity estimates, and temperatures are derived from the dereddened ( I − J ) colours. There is some evidence for a cut-off in the luminosity function below the level corresponding to several Jupiter masses, which may represent the bottom end of the initial mass function . Since star formation is complete in the Trapezium, this limit could have wide significance, if confirmed. However, it could well be an effect of the dispersal of the molecular cloud by the central O-type stars, a process for which the time-scale will vary between star formation regions.     

氦白矮星与小质量主序星并合及脉动热亚矮星的形成

sdBVrs型热亚矮星是一类特殊的热亚矮星,观测显示它们同时具有p模和g模的脉动.目前这一类热亚矮星的演化起源仍然缺乏完备的解释.对氦白矮星与小质量主序星并合模型进行详细计算表明,并合模型的结果符合sdBVrs型热亚矮星的表面有效温度、重力加速度等观测特征,并且能够激发出稳定的p模和g模脉动.因此,氦白矮星与小质量主序星并合是形成sdBVrs型热亚矮星可能的渠道之一.     

The unique frequency spectrum of the Blazhko RRc Star LS Her

The Blazhko effect in RR Lyrae stars is still poorly understood theoretically. Stars with multiple Blazhko periods or in which the Blazhko effect itself varies are particularly challenging. This study investigates the Blazhko effect in the RRc star LS Her. Detailed CCD photometry in the   V , R _C  and I _C band has been performed on 63 nights during six months. LS Her is confirmed to have a Blazhko period of  12.75 ± 0.02  d. However, where normally the side frequencies of the Blazhko triplet are expected, an equidistant group of three frequencies is found on both sides of the main pulsation frequency. As a consequence, the period and amplitude of the Blazhko effect itself vary in a cycle of  109 ± 4  d. LS Her is a unique object turning out to be very important in the verification of the theories for the Blazhko effect.     

Star formation in the Cepheus Flare region – II. A-type stars associated with IRAS sources

In order to reveal the star-forming history of the molecular cloud complex we studied the intermediate mass stellar population in the Cepheus Flare region. (Paper I dealt with the distance and the young stellar object candidates of the region.) Correlating the IRAS Point Source Catalogue and Faint Source Catalogue positions with those of 1214 B8–A8 and 1760 F0–F5 type stars brighter than     and classified during an objective prism survey, we identified 19 stars showing far-infrared excess emission in the Cepheus Flare region. In addition to the 16 stars whose counterparts are given in the IRAS catalogues, we found three more stars with infrared excess not recognized before. In order to identify the young medium-mass stars associated with the Cepheus Flare molecular clouds we observed the optical spectra of the IR-excess stars, and using published optical photometry and the IRAS data we examined their spectral energy distributions (SEDs) and IRAS two-colour diagram. The observations resulted in the discovery of a new Herbig Ae/Be star, BD +68°1118, coinciding with IRAS 21169+6842. More evolved HAe/Be stars may be SAO 19953, BD +67°1314 and BD +69°1231, whose H α lines showed weak emission components. Possible β Pictoris- or Vega-type stars may be HD 203854, HD 212826 and HD 216486, whereas the far-infrared fluxes at the positions of BD +72°1018, HD 210806 and HD 217903 can be attributed to the heating of the interstellar environment. We used distances and radial velocities of the stars derived from the spectroscopy and published optical photometry as indicators of their relations to the clouds. Information on the environment of the observed stars deduced from the diffuse interstellar band at λ 6613 is briefly discussed.     

Stars of extragalactic origin in the solar neighborhood

For 77 main-sequence F–G stars in the solar neighborhood with published iron, magnesium, and europium abundances determined from high-dispersion spectra and with the ages estimated from theoretical isochrones, we calculated the spatial velocities using Hipparcos data and the Galactic orbital elements. A comparison with the orbital elements of the globular clusters that are known to have been accreted by our Galaxy in the past reveals stars of extragalactic origin. We show that the abundance ratios of r-and α-elements in all the accreted stars differ sharply from those in the stars that are genetically associated with the Galaxy. According to current theoretical models, europium is produced mainly in low-mass type-II supernovae (SNe II), while magnesium is synthesized in large quantities in high-mass SN II progenitors. Since all the old accreted stars of our sample exhibit a significant Eu overabundance relative to Mg, we conclude that the maximum masses of the SN II progenitors outside the Galaxy were much lower than those inside it. On the other hand, only a small number of young accreted stars exhibit low negative ratios [Eu/Mg]<0. This can be explained by the delay of primordial star formation and the explosions of high-mass SNe II in a relatively small part of extragalactic space. We provide evidence that the interstellar medium was weakly mixed at the early evolutionary stages of the Galaxy formed from a single protogalactic cloud, and that the maximum mass of the SN II progenitors increased in it with time simultaneously with the increase in mean metallicity.     

CEMP星HE1005-1439中子俘获元素天体物理来源的研究

HE1005-1439是一颗金属丰度极低([Fe/H] ~ - 3.0)的碳增丰贫金属星(Carbon Enhanced Metal-Poor,CEMP), 该星的s-过程元素显著超丰([Ba/Fe] = 1.16±0.31, [Pb/Fe] = 1.98±0.19), 而r-过程元素温和超丰([Eu/Fe] = 0.46±0.22), 使用单一的s-过程模型和i-过程模型均不能拟合该星中子俘获丰度分布. 采用丰度分解的方法探究该星化学元素的天体物理来源可有助于理解CEMP星的形成和化学演化. 利用s-过程和r-过程的混合模型对其中子俘获元素的丰度分布进行拟合, 发现该星的中子俘获元素主要来源于低质量低金属丰度AGB伴星的s-过程核合成, 而r-过程核合成也有贡献.     

Spectral and photometric observations of the star Y Ori

Data are presented from a spectral and photometric study of the long-period variable star Y Ori, which we have classified as a type M7IIIe near its brightness minimum. In the blue part of the spectrum, features from a star of an earlier spectral class are superimposed on the spectrum of a cool giant, so that a variable excess emission is observed at wavelengths of 4000–4200 Å. As opposed to the monotonically decreasing intensity of the Balmer lines (EWHα > EWHβ > EWHγ > EWHδ) in normal stars belonging to the earlier spectral classes, a reverse relationship, with EWHγ < EWHδ is detected in Y Ori. Translated from Astrofizika, Vol. 51, No. 4, pp. 567–575 (November 2008).     

ROSAT PSPC observations of the Orion Trapezium area II. Source variability and revised source list

A deep ROSAT PSPC image centred on the Orion Trapezium has been reduceda second time using an improved version of the PSF to fit the data. The outer rim of the field of view was also included. The new catalogue contains 316 X‐ray sources which are easily identified with pre‐main sequence stars of the Ori OB1 Ic and Id association. All 316 sources were tested for variability. No variations were found inside the single exposures of about 45 minutes length each. Between the 4 exposures spaced over 5 days about 1/3 of the sources show signs of activities of various forms. As above 25% of these have somewhat regular lights curves (monotonically rising or falling or hill‐shaped) we infer that at least some outbursts with time scales longer than a day are present and that past searches for X‐ray flares of pre‐main sequence stars were biased towards shorter time scales.     

A near-infrared fabry-perot imager at CRL 1.5m telescope and the structure and velocity field of shocked H2 emission in orion KL region

We have developed a near-infrared Fabry-Perot imager at the Nasmyth focus of the Communications Research Laboratory (CRL) 1.5 m telescope at Tokyo. Using this wide field Fabry-Perot imager, we obtained continuum-subtracted images of the H₂ v=1–0 S(1) line for the Orion KL region.