演化晚期恒星中的结晶硅酸盐尘埃

硅酸盐是宇宙尘埃的主要成分之一。20世纪60年代,在演化晚期恒星中就曾发现硅酸盐尘埃的辐射特征,并且与实验室无定形硅酸盐的光谱特征非常吻合。到20世纪90年代,演化晚期恒星中的结晶硅酸盐特征首次在ISO卫星拍摄的光谱中探测到,其后随着更多的红外空间天文台(Spitzer、Herschel等)的发射,发现了大量具有结晶硅酸盐特征的恒星,尤其是演化晚期恒星,几乎涵盖了演化晚期的各个阶段(红巨星、渐近巨星支星、原行星状星云、行星状星云、红超巨星等)。结晶硅酸盐尘埃的特征广泛分布在10～70μm波长范围内,表现为多个丰富的谱带。阐述了演化晚期恒星中结晶硅酸盐尘埃的发现、谱特征、观测特性、结晶度和形成机制。     

行星状星云NGC 2242的红外辐射

被Zwicky等人列为星系的NGC 2242,后来刘继英等人发现它具有发射特征并认为可能是行星状星云。前原英夫等人用有缝光谱肯定了它是一个行星状星云。我们证认它是IRAS06304+4448。根据IRAS Point Source Catalog所提供的25μm和60μm的辐射流量,我们得到了这一行星状星云的尘埃温度T_d=130K,光学厚度τ_(25μm)=1.98×10~(-7)和尘埃的总质量M_d=1.0×10~(-7)到1.8×10~(-6)M_⊙之间。     

行星形成方式的探讨

行星形成的方式,目前主要有两种见解:一种认为,行星是星子集聚而成,另一种认为,行星是由星云物质经过势井聚集为原行星而形成。笔者认为,角动量守恒定律,是认识太阳系起源和行星、卫星形成方式的重要钥匙。某一行星区的星云物质绕太阳转动的角动量总和(A_c)减去该区今日行星轨道角动量(A_p)应当等于该区行星自转角动量(A_r),即A_c-A_p=△A=A_r。但计算结果,A_c-A_p=△A>A_r。这就证明,行星是经过星云环形成的。文中计算了星云环内外边界的位置,即星云环的宽度,并提出一些新的看法,可能为行星形成方式的研究提供一些有益的线索。     

星际红外消光律

该文综述了星际尘埃在红外波段的消光律。现有的观测表明,在0.7μm≤λ≤5μm范围内的星际消光可以近似用幂律函数来拟合,而对5μm≤A≤8μm范围内的星际消光争论比较多,但现在已明确该范围内消光律是随视线方向的变化而变化,这与以往认为在整个0.7μm≤λ≤8μm范围内星际消光为各处一致的结论是相左的。在8μm≤λ≤30μm范围内的消光主要由硅酸盐在9.7μm和18μm处的吸收特征所决定,其中9.7μm处的吸收所引起的消光强度(相对可见光波段消光)在太阳邻近弥漫星云和银心方向上有较大变化,其原因仍有争论;同时,由脂肪族碳氢化合物的C-H键伸缩振动引起的在3.4μm处的谱特征强度也和9.7μm硅酸盐谱特征类似,在太阳邻近弥漫星云和银心方向有较大变化。在λ≥30μm以上的远红外范围,由于观测的限制,人们主要利用尘埃红外辐射理论来间接研究消光率,不同尘埃模型给出的红外辐射明显地不同,对λ≥30μm的红外观测将提高该范围内消光律的准确性。     

CO分子转动谱线的天体物理研究方法和近期进展

ＣＯ的射电转动谱线揭示了光学不可见的冷宇宙、银河系最大天体－巨分子云和恒星形成过程中的一个普遍存在的重要的相－双极外流。ＣＯ在６７～１８６ｕｍ波段的转动谱线是探测动能温度数百度以上的热天体（诸如富碳、富氧演化星包层,行星状星云、年轻星和恒星形成区复合体）物理条件的重要探针。对ＣＯ分子转动谱线的天体物理研究方法和在该领域的近期进展作了简单的评述。     

和原行星状星云成协的致密反射星云

对从IRAS点源表中选择出来的原行星状星云的光学证认和有缝光谱、CCD直接成像观测表明,其中三个与致密的反射星云成协,即PPN No.34=IRAS16559—2957、PPN No.35=IRAS16552—3050和PPN No.38=IRAS17150—3224。本文根据球对称尘埃壳层模型,计算了中心星光度和颜色的变化,反射星云的可见期等。认为近距的原行星状星云在早中期阶段将有致密的反射星云与它成协。     

CO67—186μm谱线在天体物理研究中的作用

采用球型大速度梯度模型,对ＩＲＣ＋ １０２１６ 、ＡＦＧＬ２６８８ 和ＮＧＣ７０２７ 等经ＩＳＯ 发表的首次数据证明有相对强的ＣＯ６７ － １８６ μｍ 发射线的天体作模型计算．统计平衡辐射转移计算共覆盖低于能量４８６３ ｃｍ －１（ｖ ＝ ０ ,Ｊ＝ ０ 能级的能量为０） 的全部能级,即ｖ ＝ ０ 、Ｊ＝ ０ －５０ ,ｖ ＝ １ 、Ｊ＝ ０ － ３７ 和ｖ ＝ ２ 、Ｊ＝ ０ － １７ 的１０７ 个能级．计算表明ＣＯ 谱线的流量相对值对于上能级转动量子数Ｊｕ 的分布函数,是该谱线发射区物理条件的良好探针．ＩＲＣ＋ １０２１６ 的ＣＯ远红外发射线主要由中央星激发形成,而ＡＦＧＬ２６８８ 和ＮＧＣ７０２７ 区则是因温暖和致密的冲击气体所致．对ＩＳＯ 首次数据涉及的其他天体的ＣＯ 谱线激发机制,也作了一些讨论。ＣＯ 的谱线是在６７ － １８６ μｍ 波段探测动能温度数百度以上的热天体,诸如富碳、富氧演化星包层,行星状星云、年轻星和恒星形成区复合体物理条件的重要探针     

寻找AKARI/FIS观测到的长寿命原行星盘

基于日本红外卫星AKARI/FIS的年轻恒星体样本,通过匹配Hipparcos(High Precision Parallax Collecting Satellite)的数据库共计得到21个太阳系附近的年轻恒星体,可靠性为90%.恒星的光谱类型从B型到M型星.利用Hipparcos精确的三角视差测量,定出源在赫罗图位置分布,进而与理论的演化轨迹等时线比较估算恒星的年龄.结果发现样本中存在两个年龄大于10 Myr的年轻恒星体.光学至红外能谱分布表明这两个源是II型年轻恒星体,即有原行星盘.通过进一步的能谱拟合表明这两个源的年龄分别为(14.1±4.2)Myr和(16.8±4.4)Myr.长寿命原行星盘与行星形成关系紧密,是理想的原行星诞生地.     

IRAS 19227+1700:富碳星还是富氧星?

IRASl9227 1700作为富碳星列于新版碳星星表中．然而该星在IRAS红外双色图上处于典型的有较厚富氧拱星包层区域中，而不处于硅酸盐碳星通常所处的区域．而且有证据表明该星不但有主线和伴线羟基脉泽发射，还有靠近中心星的水脉泽发射．其IRASLRS谱在9—12μm范围有尘埃发射特征，近红外的观测又证实它确实存在热的拱星包层．因此IRAS19227 1700的拱星包层应该全是富氧性质的，它的中心星是富氧的可能性也极大．     

英仙座软木塞星云M76

行星状星云M76(NGC650及651)因其外貌像两只相对着的软木塞而被称为软木塞星云,但实际上和M27一样也是一个哑铃状的天体。它的赤道坐标为:赤经1时42.4分,赤纬+51°34′;视星等10.1;角直径67″;距离3900光年。梅西叶在1780年10月21日观察它时有这样的记述:这个天体是我的年轻同事梅襄(PjerreMechain)在1780年9月5日首先发现的,它是靠近     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work,     

Alkali and halogen chemistry in volcanic gases on Io

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10⁻⁶ to 10⁺¹ bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I₂ (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.     

The climatic and physiographic controls of the eastern Mediterranean over the late Pleistocene climates in the southern Levant and its neighboring deserts

Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr^− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant.     

Active hot star shells

Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells. Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fitting X-ray Afterglow Light curves of Gamma-ray Bursts by Using the Magnetar Energy Injection Model

The central compact object for some gamma-ray bursts (GRBs) may be a strongly magnetized millisecond pulsar. It can inject energy to the outer shock of the GRB by through the magnetic dipole radiation, and therefore causes the shallow decay of the early afterglow. Recently, from a large number of GRB X-ray afterglows observed by Swift/XRT(X-ray telescope), it is revealed that many of them exhibit the shallow decay about 10²∼10⁴ s after the burst prompt emission. We have fitted the X-ray afterglow light curves of 11 GRBs by using the energy injection model of a magnetar with the rotation period in the millisecond order of magnitude. The obtained result shows the validity and universality of the magnetar energy injection model in explaining the shallow decay of afterglows, and simultaneously provides some constraints on the magnetic field strength and rotation period of the central magnetar.     

Dynamical study of wide pairs of stars based on data from the WDS catalog

Using the method of apparent motion parameters, we have studied the relative motion of the components in 561 pairs of wide (ρ > 2″) and relatively nearby (Hipparcos parallaxes > 0.01″) visual double stars based on data from the WDS catalog. The minimum masses of the double stars have been calculated at given parallaxes. We have identified 358 optical pairs. For 11 stellar pairs, we have found the minimum mass to exceed the estimate corresponding to their spectral types and luminosities. This excess is 5–7 M _⊙ for two stars, ADS 7446 and 9701.     

Microscopic black hole detection in UHECR: the double bang signature

According to recent conjectures on the existence of large extra dimensions in our universe, black holes could be produced during the interaction of Ultra High Energy Cosmic Rays with the atmosphere. However, and so far, the proposed signatures are based on statistical effects, not allowing identification on an event by event basis, and may lead to large uncertainties. In this note, events with a double bang topology, where the production and instantaneous decay of a microscopic black hole (first bang) is followed, at a measurable distance, by the decay of an energetic tau lepton (second bang) are proposed as an almost background free signature. The characteristics of these events and the capability of large cosmic ray experiments to detect them are discussed.     

Solar-cycle Time Delay of Rotating Sunspots

As shown by statistical results, in the 23rd solar activity cycle the variation of the latitudes of rotating sunspots with time exhibits a butterfly pattern. We have studied the variations with phase for the mean square errors among the 4 fitting curves of the 2 wings of the butterfly diagram of sunspots and the 2 wings of the butterfly diagram of rotating sunspots in the 23rd solar activity cycle. The results show that a systematic time delay exists not only between the northern and southern hemispheres of the butterfly diagram of sunspots, but also between the northern and southern hemispheres of the butterfly diagram of rotating sunspots, even between the butterfly diagrams of the sunspots and rotating sunspots in the same hemisphere. This means that the 23rd-cycle sunspot activities in the northern and southern hemispheres happened not simultaneously, that a systematic time delay or advance (phase difference) exists between the northern and southern hemispheres, that the southern hemisphere lags behind the northern hemisphere, that a phase difference exists between the butterfly diagram of rotating sunspots and the butterfly diagram of sunspots in the 23rd cycle, and that the butterfly diagram of rotating sunspots lags behind that of sunspots. The observed delay is a little less than the theoretical value predicted by the dynamo model.