Multiwavelength Observations of the Infrared Dust Bubble N75 and its Surroundings

Infrared dust bubbles play an important role in the study of star formation and the evolution of the interstellar medium.In this work,we study the infrared dust bubble N75 and the infrared dark cloud G38.93 mainly using the tracers C^(18)O,HCO^(+),HNC and N_(2)H^(+)observed by the 30 m IRAM telescope.We also study the targets using data from large-scale surveys:GLIMPSE,MIPSGAL,GRS,NRAO VLA Sky Survey and Bolocam Galactic Plane Survey.We found that the C^(18)O emission is morphologically similar to the Spitzer IRAC 8.0μm emission.The1.1 mm cold dust emission of G38.93 shows an elongated structure from southwest to northeast.The ionized gas from G38.93 is surrounded by polycyclic aromatic hydrocarbon emission,which may be excited by radiation from G38.93.We found that the identified young stellar objects tend to cluster around G38.93 and are mostly in class II with several class I cases distributed around N75,but no class II examples.We also found evidence of expanding feedback,which could have triggered star formation.

Star formation associated with the infrared dust bubble N68

We investigated the environment of the infrared dust bubble N68 and searched for evidence of triggered star formation in its surroundings. We performed a multiwavelength study of the nebula with data taken from several large-scale surveys： GLIMPSE, MIPSGAL, IRAS, NVSS, GRS and JCMT. We analyzed the spectral pro- file and the distribution of the molecular gas （13CO J -- 1 - 0 and J -- 3 - 2）, and the dust in the environment of N68. The position-velocity diagram clearly shows that N68 may be expanding outward. We used two three-color images of the mid-infrared emis- sion to explore the physical environment, and one color-color diagram to investigate the distribution of young stellar objects （YSOs）. We found that the 24 p^m emission is surrounded by the 8.0 ~m emission. Morphologically, the 1.4 GHz continuum strongly correlates with the 24 gm emission, and the 13CO J -- 1 - 0 and J -- 3 - 2 emissions correlate well with the 8.0 p^m emission. We investigated two compact cores located in the shell of N68. The spectral intensity ratios of 13CO J -- 3 - 2 to J = 1 - 0 range from 5 to 0.3. In addition, YSOs, masers, IRAS and UC HII regions are distributed in the shell of the bubble. The active region may be triggered by the expansion of the bubble N68.

The Role of Jets in Exploding Supernovae and in Shaping their Remnants

I review studies of core collapse supernovae(CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosion mechanism that I take to power most CCSN explosions. Neutrino heating does play a role in boosting the jets. I compare the morphologies of some CCSN remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. I then discuss CCSNe that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets(with small jittering) that shape bipolar ejecta. A large fraction of the bipolar CCSNe are superluminous supernovae(SLSNe). I conclude that modeling of SLSN light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter(CSM). I connect the properties of bipolar CCSNe to common envelope jets supernovae(CEJSNe) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. I discuss how jets can shape the pre-explosion CSM, as in Supernova 1987A, and can power pre-explosion outbursts(precursors)in binary system progenitors of CCSNe and CEJSNe. Binary interaction also facilitates the launching of postexplosion jets.

WISE Infrared Search for Young Stellar Objects Associated with Starless Cores

This study presents the results of an infrared search of young stellar objects (YSOs) associated with cores with high optical extinction and no associated infrared IRAS source. Four hundred YSO candidates were identified in the WISE photometric catalog based on the infrared excess attributed to the circumstellar materials and proto-planetary disks. One-hundred and forty-nine cores do not have YSO candidates. Whereas, 32 cores harbor only Class I candidates and 107 cores have Class II candidates. Ninety-one cores that were previously identified as starless cores, were found to contain YSOs. The ratio of the number of starless cores to the number of star-forming cores suggests that the typical timescale from molecular cloud core formation to the birth of a star is in the range of 0.5 - 1.4 Myr.

Investigation of star formation toward the Sharpless 155 H II region

We present a comprehensive study of star formation toward the H II re- gion Sharpless 155 （$155）. Star-formation activities therein were investigated based on multi-wavelength data from optical to the far-infrared. The surface density distri- bution of selected 2MASS sources toward S 155 indicates the existence of a compact cluster, which is spatially consistent with the position of the exciting source of the Htt region, HD 217086. A sample of more than 200 sources with excessive emission in the infrared were selected based on their 2MASS color indices. The spatial distri- bution of the sample sources reveals the existence of three young subclusters in this region, among which subcluster A is spatially coincident with the bright rim of the H II region. In addition, photometric data from the WISE survey were used to identify and classify young stellar objects （YSOs）. To further explore the evolutionary stages of the candidate YSOs, we fit the spectral energy distributions of 44 sources, which led to the identification of 14 Class I, 27 Class II and 3 Class Ⅲ YSOs. The spatial distribu- tion of the classified YSOs at different evolutionary stages presents a spatiotemporal gradient, which is consistent with a scenario of sequential star formation. On the other hand, Herschel PACS observations toward the interface between S 155 and the ambi- ent molecular cloud disclose an arc-shaped dust layer, the origin of which could be attributed to the UV dissipation from early type stars, e.g. HD 217061, in S155. Four dusty cores were revealed by the Herschel data, which hints at new generations of star formation.

Bipolar outflows as a repulsive gravitational phenomenon——Azimuthally Symmetric Theory of Gravitation(Ⅱ)

This paper is part of a series on the Azimuthally Symmetric Theory of Gravitation （ASTG）. This theory is built on Laplace-Poisson＇s well known equation and it has been shown that the ASTG is capable of explaining, from a purely classical physics standpoint, the precession of the perihelion of solar planets as a consequence of the azimuthal symmetry emerging from the spin of the Sun. This symmetry has and must have an influence on the emergent gravitational field. We show herein that the emergent equations from the ASTG, under some critical conditions determined by the spin, do possess repulsive gravitational fields in the polar regions of the gravitating body in question. This places the ASTG on an interesting pedestal to infer the origins of outflows as a repulsive gravitational phenomenon. Outflows are a ubiquitous phenomenon found in star forming systems and their true origin is a question yet to be settled. Given the current thinking on their origin, the direction that the present paper takes is nothing short of an asymptotic break from conventional wisdom; at the very least, it is a complete paradigm shift because gravitation is not at all associated with this process, but rather it is thought to be an all-attractive force that only tries to squash matter together onto a single point. Additionally, we show that the emergent Azimuthally Symmetric Gravitational Field from the ASTG strongly suggests a solution to the supposed Radiation Problem that is thought to be faced by massive stars in their process of formation. That is, at ,- 8-10M⊙, radiation from the nascent star is expected to halt the accretion of matter. We show that in-falling material will fall onto the equatorial disk and from there, this material will be channeled onto the forming star via the equatorial plane, thus accretion of mass continues well past the value of - 8-10M⊙, albeit via the disk. Along the equatorial plane, the net force （with the radiation force included） on any material there-on right up to the surface of the star is directed toward the forming star, hence accretion of mass by the nascent star is un-hampered.

Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912

Near-infrared images and K-band spectroscopy of the massive star-formingregion IRAS 23151+5912 are presented. The JHK′ images reveal an embedded infrared clusterassociated with infrared nebula, and the H_2 (2.12 μm) narrowband image provides for the first timeevidence of outflow activity associated with the cluster. That the cluster is young can be shown bythe high percentage of infrared excess sources and the outflow activity. We suggest an age of thecluster of ～ 10~6 yr. Eight young stars are found in the bright nebular core around IRAS23151+5912. By the color-magnitude diagrams of the cluster, we found five high-mass YSOs and fourintermediate-mass YSOs in the cluster. Eight H_2 emission features are discovered in the region witha scattered and non-axisymmetric distribution, indicating the existence of multiple outflows drivenby the cluster. Diffuse H_2 emission detected to the north and to the west of the cluster mayresult from UV leakage of the cluster. Brγ, H_2, and CIV emission lines are found in the K-bandspectrum of the brightest source, NIRS 19, indicating the presence of envelope, stellar wind, andshock in the circumstellar environment. We have estimated an O7-O9 spectral type for the centralmassive YSO (20 ～ 30 solar mass), with an age of less than 1 x 10~6 yr.

Molecular Gas and Dust in the Massive Star Forming Region S 233 IR

The massive star forming region S 233 IR is observed in the molecular lines CO J = 2–1, 3–2, NH3 (1,1), (2,2) and the 870 um dust continuum. Four submillimeter continuum sources, labelled SMM 1–4, are revealed in the 870 um dust emission. The main core, SMM1, is found to be associated with a deeply embedded near infrared cluster in the northeast; while the weaker source SMM2 coincides with a more evolved cluster in the southwest. The best fit spectral energy distribution of SMM1 gives an emissivity of β = 1.6, and temperatures of 32 K and 92 K for the cold- and hot-dust components. An SMM1 core mass of 246 M☉, and a total mass of 445 M☉ are estimated from the 870 um dust continuum emission. SMM1 is found to have a temperature gradient decreasing from inside out, indicative of the presence of interior heating sources. The total outflow gas mass as traced by the CO J = 3–2 emission is estimated to be 35 M☉. Low velocity outflows are also found in the NH3 (1,1) emission. The non-thermal dominant NH3 line width as well as the substantial core mass suggest that the SMM1 core is a ``turbulent, massive dense core', in the process of forming a group or a cluster of stars. The much higher star formation efficiency found in the southwest cluster supports the suggestion that this cluster is more evolved than the northeast one. Large near infrared photometric variations found in the source PCS-IR93, a previously found highly polarized nebulosity, indicate an underlying star showing the FU Orionis type of behavior.

A multi-transition molecular line study of infrared dark cloud G331.71+00.59

Using archive data from the Millimeter Astronomy Legacy Team Survey at 90 GHz （MALT90）, carried out using the Mopra 22-m telescope, we made the first multi-transition molecular line study of infrared dark cloud （IRDC） MSXDC G331.71＋00.59. Two molecular cores were found embedded in this IRDC. Each of these cores is associated with a known extended green object （EGO）, indicating places of massive star formation. The HCO＋ （1-0） and HNC （1-0） transitions show promi- nent blue or red asymmetric structures, suggesting outflow and inflow activities of young stellar objects （YSOs）. Other detected molecular lines include H13CO＋ （1- 0）, C2H （1-0）, HC3N （10-9）, HNCO（40,4-30,3） and SiO （2-1）, which are typical of hot cores and outflows. We regard the two EGOs as evolving from the IRDC to hot cores. Using public GLIMPS data, we investigate the spectral energy distribution of EGO G331.71＋0.60. Our results support this EGO being a massive YSO driving the outflow. G331.71＋0.58 may be at an earlier evolutionary stage.

CSO CO(2–1) and Spitzer IRAC observations of a bipolar outflow in high-mass star-forming region IRAS 22506+5944

We present Caltech Submillimeter Observatory CO （2-1） and Spitzer IRAC observations toward IRAS 22506＋5944, which is a 104 Lo massive star-forming region. The CO （2-1） maps show an east-west bipolar molecular outflow originating from the 3 mm dust continuum peak. The Spitzer IRAC color-composite image reveals a pair of bow-shaped tips which are prominent in excess 4.5 p.m emission and are located at the leading fronts of the bipolar outflow, providing compelling evidence for the existence of bow-shocks as the driving agents of the molecular outflow. By comparing our CO （2- 1） observations with previously published CO （1-0） data, we find that the CO （2-1）/（1-0） line ratio increases from low （-5 km s- 1） to moderate （- 8-12 km s- 1） velocities, and then decreases at higher velocities. This is qualitatively consistent with the scenario that the molecular outflow is driven by multiple bow-shocks. We also revisit the position-velocity diagram of the CO （1-0） data, and find two spur structures along the outflow axis, which are further evidence for the presence of multiple jet bow- shocks. Finally, power-law fittings to the mass spectrum of the outflow gives power law indexes more consistent with the jet bow-shock model than the wide-angle wind model.

Near-Infrared Imaging Observations of the Orion A-W Star Forming Region

We carried out near-infrared imaging observations of the Ori A-W region using the Italian 1.5 m TIRGO infrared telescope at Gornergrat. A group of infrared objects is visible on the K band image, including an IRAS source (IRS 1). From its IRAS flux density the IRAS luminosity is derived to be 45L⊙, which shows that IRS 1 is a low-mass protostar. By superimposing the position of the VLA H2O maser on the K image, we can identify the less evolved object IRS 1 as the excitation source of the H2O maser, within a projected distance of 470AU. This would be evidence that the maser effect is associated with the youngest phase of stellar evolution. The first probable HH object candidate in the Ori A-W region is discovered from the H2S(1)1-0 observation. Comparing the position of the H2O maser with the direction of the molecular hydrogen emission in the region, we suggest that the observed H2O maser could be tracing the circumstellar disk of IRS 1.

A Search for High-velocity Gas Associated H_2O Masers and Ultracompact HII Regions

With the objective of studying the relationships between high-velocity gas and water maser emissions the results of a search from 95 IRAS sources for high-velocity gas associated with star forming molecular clouds are reported. 21 sources have been identified as molecular outflow candidates.

星际水脉泽源中高速气体的CO巡测

用射电天文联合实验室紫金山天文台青海站１３．７米望远镜，于１９９７年４月对９７个水脉泽源做了ＣＯ（Ｊ＝１－０）的巡测及部分成图观测，结果表明８１个源的谱线适于作成协星体活动分析．经初步证认有外向流候选者３３个，全部为首次给出高速范围．对其轮廓特点及与Ｈ２Ｏ脉泽辐射的关系作了简要讨论．ＣＯ高速气体和Ｈ２Ｏ脉泽的速度范围和峰值速度在多数情况下分别相符，这说明两者的激发可能相关．

年轻星天体喷流的近红外成像观测进展

分子氢的红外振动发射线是显现年轻星质量外流的重要谱线之一．自Ｇａｕｔｉｅｒ等人１９７６年在猎户座发现年轻星质量外流的分子氢发射开始，人们在银河系内几乎所有的恒星形成区都发现了这种线发射。研究表明，分子氢发射与年轻星周围的其它活动现象（如分子外流和光学喷流）之间有着非常密切的联系．红外和光学喷流代表了年轻星剧烈活动的两个侧面，是喷流与周围介质相互作用强弱不同的表现，这种作用还拖带周围介质，产生分子外流。光 学、红外喷流和分子外流组成了恒星形成区壮观的景象，它们是恒星形成活动的重要标志。 随着红外探测技术的飞速发展，对年轻星外流活动现象的观测越来越丰富和详细，使 人们对这种现象的本质越来越了解。在２０世纪９０年代ＮＩＣＭＯＳ等大阵列红外探测器投入 使用后，红外成像观测有了长足的进步．目前已在７０个左右的区域里发现了Ｈ２发射，这 一数字还在迅速增加。今后的研究主要可能向两个方向发展。其一是高分辨观测，进一步了 解Ｈ２发射的结构以及与光学喷流和分子外流之间的关系；其二是巡天观测，了解银河系内 的恒星形成区Ｈ２发射的大尺度结构和恒星形成的统计分布规律。

红外源IRAS05437-0001和IRAS05351+3549的CO分子谱线观测研究

利用紫金山天文台青海观测站13 .7 米射电望远镜对红外源IRAS054370001 和IRAS05351 + 3549 附近区域进行了CO(J= 1 - 0) 的分子谱线观测.发现在这两个源的方向都有很强的CO 发射,CO 谱线还有明显的线翼成分,这暗示两个红外源存在分子外流.同时还获得了每个源5′×5′的成图.通过对高速气体的空间分布的观测和分析,认为这两个源为分子外流源.其中IRAS054370001 附近区域的外流结构比较复杂,可能这一区域的外流是多极的.IRAS05351 + 3549 附近的外流结构较简单.从两个源的红外光谱分类以及外流的动力学时标得出都是年轻星( 年龄～105 yrs) .通过对这两个外流源的参数估算,得出两个外流源的质量损失率.

大质量星形成区的高速气体搜寻

在红外天文卫星点源表中选取了具有陡远红外谱的９７个源及其它８个红外源，用射电天文联合实验室紫金山天文台青海站的１３７ｍ望远镜，进行了ＣＯ（Ｊ＝１－０）的观测．结果在１０２个源中测到了ＣＯ辐射，有９个源参考位置难以确定，２１个源有多重成分，在其余７２个源中有２９个具有高速气体，其中１８个是新测到的双极外向流候选者，对其性质及与年轻星体的关系作了简要讨论．

IRAS 20231+3440区外流激发源的性质研究

给出红外点源IRAS20231+3440附近恒星形成区近红外JHK’和H_2成像观测结果,以及与该IRAS点源成协的近红外点源IRS1的K波段分光观测结果。JHK’观测显示该区域存在嵌埋的年轻星天体,H_2窄波段观测揭示了若干个氢分子发射结点,其中有几个结点排列成线形,暗示分子氢喷流的存在。喷流的北部与已知观测的分子外流成协,表明二者之间存在联系。喷流的走向提示IRS1可能是其激发源,对IRS1的K波段分光观测给出了进一步的证据。从近红外、MSX及IRAS资料估计出IRS1的能谱分布,表明它是一个处于ClassⅠ状态的中等质量的年轻星天体。

大质量恒星形成的观测和研究

对于大质量星的形成，由于区域的遥远和结构的复杂以及过程的特殊，研究相对迟缓．对可能形成大质量星的云核和大质量年轻星体的活动，进行了多波段搜寻和研究．取得了相应的进展．

高准直双极分子外流速度的“哈勃”律

在高准直双极分子外流中，气体速度和离中心恒星距离的“哈勃”关系，可能是分子外流物理性质中最关键的特征．高速喷流驱动弓激波的方式能够解释这种速度结构．本文建立起一组喷射角可变的微分方程组．用数值方法得出分子外流的速度结构。

新单极高速分子外向流源IRAS19282+1814

12COJ=1-0成图观测表明在IRAS19282+1814附近存在着一个蓝向单极高速分子外流.计算了其基本参量并进行了分析.它的成协红外源IRAS19282+1814可能是大质量年轻星体,其IRAS波段色指数表明该源深埋于气体和尘埃物质之中.由60-100μm流量密度获得尘埃温度为30K.它的附近没有其他的源,所以IRAS19282+1814可能是外向流的驱动源.