16310685
Young Stellar Groups around Herbig Ae/Be Stars: A Low-Mass YSO Census
We present near-IR and mid-IR observations of eight embedded young stellar groups around Herbig Ae/Be stars (HAEBEs) using archived Spitzer IRAC data and 2MASS data. These young stellar groups are nearby (≤1 kpc) and still embedded within their molecular clouds. In order to identify the young stellar objects in our sample, we use the color-color diagram of J - [3.6] versus Ks - [4.5]. The Spitzer images of our sample show that the groups around HAEBEs, spectral types earlier than B8, are usually associated with bright infrared nebulosity. Within this, there are normally 10-50 young stars distributed close to the HAEBEs (<1 pc). Not only are there young stars around the HAEBEs, there are also young stellar populations throughout the whole cloud, some of which are distributed and some of which are clumped. The groups around the HAEBEs are substructures of the large young population within the molecular cloud. The sizes of groups are also comparable with those substructures seen in massive clusters. Young stars in groups around HAEBEs have generally larger SED slopes compared to those outside, which suggests that the young stars in groups are probably younger than the distributed systems. This might imply that there is usually a higher and more continuous star-forming rate in groups, that the formation of groups initiates later, or that low-mass stars in groups form slower than those outside. Finally, there is no obvious trend between the SED slopes and the distance to the HAEBEs for those young stars within the groups. This suggests that the clustering of young stars dominates over the effect of massive stars on the low-mass young stars at the scale of our study.
17153677
Dense Molecular Gas in a Young Cluster around MWC 1080: Rule of the Massive Star
We present CS -->J = 2→ 1,13CO -->J = 1→ 0, and C18O -->J = 1→ 0, observations with the 10 element Berkeley Illinois Maryland Association (BIMA) array toward the young cluster around the Be star MWC 1080. These observations reveal a biconical outflow cavity with size ~0.3 and 0.05 pc for the semimajor and semiminor axis and ~45° position angle. These transitions trace the dense gas, which is likely the swept-up gas of the outflow cavity, rather than the remaining natal gas or the outflow gas. The gas is clumpy; 32 clumps are identified. The identified clumps are approximately gravitationally bound and consistent with a standard isothermal sphere density, which suggests that they are likely collapsing protostellar cores. The gas kinematics suggests that velocity gradients exist that imply effects from the inclination of the cavity and MWC 1080. The kinematics of dense gas has also been affected by either outflows or stellar winds from MWC 1080, and lower mass clumps are possibly under stronger effects from MWC 1080 than higher mass clumps. In addition, low-mass cluster members tend to be formed in the denser and more turbulent cores, compared to isolated low-mass star-forming cores. This results from the contributions of nearby forming massive stars, such as outflows or stellar winds. Therefore, we conclude that in clusters like the MWC 1080 system, effects from massive stars dominate the star-forming environment in both the kinematics and dynamics of the natal cloud and the formation of low-mass cluster members. This study provides insights into the effects of MWC 1080 on its natal cloud, and suggests a different low-mass star-forming environment in clusters compared to isolated star formation.
17710652
Colliding Clouds: The Star Formation Trigger of the Stellar Cluster around BD +40 4124
We present BIMA and SCUBA observations of the young cluster associated with BD +40 4124 in the dense molecular gas tracer CS J = 2 → 1 and the continuum dust emission at λ = 3.1 mm and 850 μm. The dense gas and dust in the system are aligned in a long ridge morphology extending ~0.4 pc with 16 gas clumps of estimated masses ranging from 0.14 to 1.8 M☉. A north-south variation in the CS center line velocity can be explained with a two-cloud model. We posit that the BD +40 4124 stellar cluster formed from a cloud-cloud collision. The largest line widths occur near V1318 Cyg S, a massive star affecting its natal environment. In contrast, the dense gas near the other, more evolved, massive stars displays no evidence for disruption; the material must either be processed into the star, dissipate, or relax fairly quickly. The more evolved low-mass protostars are more likely to be found near the massive stars. If the majority of low-mass stars are coeval, the seemingly evolved low-mass protostars are not older: the massive stars have eroded their structures. Finally, at the highest resolution, the λ = 3.1 mm dust emission is resolved into a flattened structure 3100 × 1500 AU with an estimated mass of 3.4 M☉. The continuum and CS emission are offset by 11 from the southern binary source. A simple estimate of the extinction due to the continuum emission structure is AV ~ 700 mag. From the offset and because the southern source is detected in the optical, the continuum emission is from a previously unknown very young, intermediate-mass, embedded stellar object.
8106823
THE X-RAY ORIGIN OF HERBIG AeBe SYSTEMS: NEW INSIGHTS
We present a statistical study of the X-ray emission toward 22 Herbig AeBe stars (HAEBE) using the Chandra archive. We probe the origin of the X-rays toward Herbig stars: are they intrinsic?This question is addressed by correlations between the physical stellar properties and the X-ray emission. There is a weak correlation between the continuum radio emission at λ = 3.6 cm and L X, which suggests that the X-ray emission depends upon the source. On the other hand, no correlation was found with the stellar rotational period, but that only excludes solar-like magnetic activity as the origin of the X-rays. Most importantly, the X-ray luminosity of HAEBE has a different distribution from that of T Tauri stars, suggesting that X-ray emission from an unseen late-type star companion can be ruled out with an 80% confidence level. This implies that the HAEBE must have magnetic activity. In addition, we report the observation of five sources for the first time, in three detections.
118404940
THE ABUNDANCE OF H2O AND HDO IN ORION KL FROM HERSCHEL/HIFI*
Using a broadband, high spectral resolution survey toward the Orion Kleinmann-Low nebula acquired with Herschel/HIFI as part of the Herschel Observations of Extra-Ordinary Sources key program, we derive the abundances of H2O and HDO in the different spatial/velocity components associated with this massive star-forming region: the Hot Core, Compact Ridge, and Plateau. A total of 20 transitions of H2 18O, 14 of H2 17O, 37 of HD16O, 6 of HD18O, and 6 of D2O are used in the analysis, spanning from ground state transitions to over 1200?K in upper-state energy. Low-excitation lines are detected in multiple components, but the highest-excitation lines (Eu > 500?K) are well modeled as emitting from a small (~2'') clump with a high abundance of H2O (? = 6.5 ? 10?4 relative to H2) and a HDO/H2O ratio of 0.003. Using high spatial resolution (1.''5 ? 1.''1) images of two transitions of HDO measured by the Atacama Large Millimeter/Submillimeter Array as part of its science verification phase, we identify this component as located near, but not directly coincident with, known continuum sources in the Hot Core region. Significant HDO/H2O fractionation is also seen in the Compact Ridge and Plateau components. The outflowing gas, observed with both emission and absorption components, has a lower HDO/H2O ratio than the compact components in Orion Kleinmann-Low, which we propose could be due to modification by gas-phase shock chemistry.
118143387
Chern Simons Theory and the volume of 3-manifolds
We give some applications of the Chern Simons gauge theory to the study of the set ${\rm vol}(N,G)$ of volumes of all representations $\rho\co\pi_1N\to G$, where $N$ is a closed oriented three-manifold and $G$ is either ${\rm Iso}_e\t{\rm SL_2(\R)}$, the isometry group of the Seifert geometry, or ${\rm Iso}_+{\Hi}^3$, the orientation preserving isometry group of the hyperbolic 3-space. We focus on three natural questions: 
(1) How to find non-zero values in ${\rm vol}(N, G)$? or weakly how to find non-zero elements in ${\rm vol}(\t N, G)$ for some finite cover $\t N$ of $N$? 
(2) Do these volumes satisfy the covering property in the sense of Thurston? 
(3) What kind of topological information is enclosed in the elements of ${\rm vol}(N, G)$? 
We determine ${\rm vol}(N, G)$ when $N$ supports the Seifert geometry, and we find some non-zero values in ${\rm vol}(N,G)$ for certain 3-manifolds with non-trivial geometric decomposition for either $G={\rm Iso}_+{\Hi}^3$ or ${\rm Iso}_e\t{\rm SL_2(\R)}$. Moreover we will show that unlike the Gromov simplicial volume, these non-zero elements carry the gluing information between the geometric pieces of $N$. 
For a large class 3-manifolds $N$, including all rational homology 3-spheres, we prove that $N$ has a positive Gromov simplicial volume iff it admits a finite covering $\t N$ with ${\rm vol}(\t N,{\rm Iso}_+{\Hi}^3)\ne \{0\}$. On the other hand, among such class, there are some $N$ with positive simplicial volume but ${\rm vol}(N,{\rm Iso}_+{\Hi}^3)=\{0\}$, yielding a negative answer to question (2) for hyperbolic volume.
118374115
Possible origin of the Damocloids: the scattered disk or a new region?
The Damocloids are a group of unusual asteroids that recently added a new member: 2010 EJ104. The dynamical evolution of the Damocloids may reveal a connection from the Main Belt to the Kuiper Belt and beyond the scattered disk. According to our simulations, two regions may be considered as possible origins of the Damocloids: the scattered disk, or a part of the Oort cloud, which will be perturbed to a transient region located between 700 AU and 1000 AU. Based on their potential origin, the Damocloids can be classified into two types, depending on their semi-major axes, and about 65.5% of the Damocloids are classified into type I which mainly originate from the Oort cloud. Whether the Damocloids are inactive nuclei of the Halley Family of Comets may depend on their origin.
201820079
SPECTRAL ENERGY DISTRIBUTIONS AND AGE ESTIMATES OF 104 M 31 GLOBULAR CLUSTERS
We present photometry of 104 M31 globular clusters (GCs) and GC candidates in 15 intermediate-band filters of the Beijing–Arizona–Taiwan–Connecticut photometric system. The GCs and GC candidates were selected from the Revised Bologna Catalog (v.3.5). We obtain the cluster ages by comparing the photometric data with up-to-date theoretical synthesis models. The photometric data used are Galaxy Evolution Explorer farand near-ultraviolet and Two Micron All Sky Survey near-infrared JHKs magnitudes, combined with optical photometry. The ages of our sample clusters cover a large range, although most clusters are younger than 10 Gyr. Combined with the ages obtained in our series of previous papers focusing on the M31 GC system, we present the full M31 GC age distribution. The M31 GC system contains populations of young and intermediate-age GCs, as well as the “usual” complement of well-known old GCs, i.e., GCs of similar age as the majority of the Galactic GCs. In addition, young GCs (and GC candidates) are distributed nearly uniformly in radial distance from the center of M31, while most old GCs (and GC candidates) are more strongly concentrated.
33054147
The underlying event in hard interactions at the Tevatron $\bar p p$ collider
For comparison of inclusive jet cross sections measured at hadron-hadron colliders to next-to-leading order (NLO) parton-level calculations, the energy deposited in the jet cone by spectator parton interactions must first be subtracted. The assumption made at the Tevatron is that the spectator parton interaction energy is similar to the ambient level measured in minimum bias events. In this paper, we test this assumption by measuring the ambient charged track momentum in events containing large transverse energy jets at {radical}(s)=1800 GeV and {radical}(s)=630 GeV and comparing this ambient momentum with that observed both in minimum bias events and with that predicted by two Monte Carlo models. Two cones in {eta}-{phi} space are defined, at the same pseudorapidity, {eta}, as the jet with the highest transverse energy (E{sub T}{sup (1)}), and at {+-}90{sup o} in the azimuthal direction, {phi}. The total charged track momentum inside each of the two cones is measured. The minimum momentum in the two cones is almost independent of E{sub T}{sup (1)} and is similar to the momentum observed in minimum bias events, whereas the maximum momentum increases roughly linearly with the jet E{sub T}{sup (1)} over most of the measured range. This study was carried out usingmore » data from the CDF detector taken during Run 1 (1994-1995). The study will help improve the precision of comparisons of jet cross section data and NLO perturbative QCD predictions. The distribution of the sum of the track momenta in the two cones is also examined for five different E{sub T}{sup (1)} bins. The HERWIG and PYTHIA Monte Carlo generators are reasonably successful in describing the data, but neither can describe completely all of the event properties.« less
119292283
Age and Mass Studies for Young Star Clusters in M31 from SEDS-FIT
In this paper, we present photometry for young star clusters in M31, which are selected from Caldwell et al. These star clusters have been observed as part of the Beijing–Arizona–Taiwan–Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March. The BATC images including these star clusters are taken with 15 intermediate-band filters covering 3000–10000 u Combined with photometry in the GALEX far- and near-ultraviolet, broad-band UBV RI, SDSS ugriz, and infrared JHKs of Two Micron All Sky Survey, we obtain their accurate spectral energy distributions (SEDs) from 1538 − 20000 u We derive these star clusters’ ages and masses by comparing their SEDs with stellar population synthesis models. Our results are in good agreement with previous determinations. The mean value of age and mass of young clusters (< 2 Gyr) is about 385 Myr and 2 × 10 4 M⊙, respectively. There are two distinct peaks in the age distribution, a highest peak at age ∼ 60 Myr and a secondary peak around 250 Myr, while the mass distribution shows a single peak around 10 4 M⊙. A few young star clusters have two-body relaxation times greater than their ages, indicating that those clusters have not been well dynamically relaxed and therefore have not established the thermal equilibrium. There are several regions showing aggregations of young star clusters around the 10 kpc ring and the outer ring, indicating that the distribution of the young star clusters is well correlated with M31’s star-forming regions. The young massive star clusters (age ≤ 100 Myr and mass ≥ 10 4 M⊙) show apparent concentration around the ring splitting region, suggesting a recent passage of a satellite galaxy (M32) through M31 disk. Subject headings: galaxies: individual (M31) – galaxies: young star clusters – galaxies: stellar content