bluuebunny/crossref_metadata_2025_split huggingface dataset:
OH masers and magnetic fields in massive star-forming regions: ON1
Authors: Nammahachak S. , Asanok K. , Kramer B. Hutawarakorn , Cohen R. J. , Muanwong O. , Gasiprong N. 
Published: April 2007

AbstractOH masers are sensitive probes of the kinematics and physical conditions, and give unique information on the magnetic field through their polarization. Zeeman splitting of the OH lines can give the magnetic field strength and direction. Observing OH masers with MERLIN we studied the bipolar outflow in the star-forming region ON1, which hosts one of the earliest known ultra-compact (UC) HII regions. The strongest masers lie near the southern edge of the UCHII region in an elongated distribution. The maser distribution is orthogonal to the bipolar outflow seen in HCO+, suggesting that the OH masers may be embedded in a molecular disk or torus around a young B0.3 star, most likely tracing a shock front. An isolated group of 1720-MHz masers is also seen to the East. The magnetic field deduced from Zeeman splitting of the OH maser lines shows a large-scale order, with field values ranging from -0.4 to -4.6 mG. These results add to the growing body of evidence for OH masers associated with molecular disks or tori at the centre of bipolar outflow from massive young stars, and for a significant role played by the magnetic field in generating or channeling the bipolar outflow. Further details are presented by Nammahachak et al. 2006.
Subaru high-dispersion spectroscopy of Hα and [NII] 6584 Å emission in the HL Tau jet
Authors: Nishikawa Takayuki , Takami Michihiro , Hayashi Masahiko 
Published: April 2007

AbstractWe present slit-scan observations of the Hα and [NII] 6584 Å emission lines toward the HL Tau jet with the 8.2m Subaru Telescope. HL Tau is an active young star in transitional phase from an embedded class I protostar to a class II pre-main-sequence star, and it is located in the northeastern part of the L1551 dark cloud. The slit-scan technique at high spectral resolution (R=3.6×104) allowed for studying kinematics of individual features in unprecedented details. The Hα emission shows the main jet component (VLSR ~ −180 km s−1) and distinct lower velocity components (∣VLSR∣<120 km s−1). The [NII] emission is primarily associated with the jet within 10 arcsecond from the source, and also knot B and C ~30 arcsecond away from the source. These are associated with the main jet component, and absent in the lower velocity components. The velocity of Hα and [NII] emissions in the main jet component well matches each other.Our high-resolution spectra do not show the evidence for the presence of turbulent mixing layers between the jet and surrounding gas. The lower velocity components are associated with individual knots, and explained as the lateral of bow shocks. Their line profiles suggest that shock velocity of the knots A-C is 120~130 km s−1 (Hartigan et al. 1987). The observed [NII]/Hα flux ratio markedly differ between regions: 0.1-0.7 in base of the jet; less than 0.1 in knot A; ~0.2 in knot B; ~0.4 in knot C; and ~0.7 in knot D. Shock models predict that the [NII]/Hα flux ratio reflects the ionization of the preshock gas. This results from enhancement of N+ via the charge exchange reaction (Osterbrock 1989; Bacciotti & Eislöffel 1999). We perform more detailed comparisons between models and observations (Hartigan et al. 1987; Morse et al. 1994). The base of the jet and knot D show high [NII]/Hα flux ratios, indicating that the ambient gas surrounding the jet is considerably ionized, or the preshock density of the ambient gas is significantly low. In contrast, the knots A-C exhibit low [NII]/Hα flux ratios, indicating that the ambient gas surrounding the jet is almost neutral, or the preshock density of the ambient gas is significantly high. The [NII]/Hα flux ratio increases from knot A (0.1) to knot D (~0.7). This suggests that the ionization fraction of the ambient gas increases away from the source, or the preshock density of the ambient gas decreases away from the source.
Luminosity functions of YSO clusters in Sh-2 255, W3 Main and NGC 7538 star forming regions
Authors: Ojha Devendra , Tamura Motohide ,   SIRIUS Team
Published: April 2007

AbstractWe have conducted deep near-infrared surveys of the Sh-2 255, W3 Main and NGC 7538 massive star forming regions using simultaneous observations of the JHKs-band with the near-infrared camera SIRIUS on the UH 88-inch telescope and with SUBARU. The near-infrared surveys cover a total area of ~ 72 arcmin2 of three regions with 10-σ limiting magnitudes of ~ 19.5, 18.4 and 17.3 in J, H and Ks-band, respectively. Based on the color-color and color-magnitude diagrams and their clustering properties, the candidate young stellar objects are identified and their luminosity functions are constructed in Sh-2 255, W3 Main and NGC 7538 star forming regions. A large number of previously unreported red sources (H-K > 2) have also been detected around these regions. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. The detected young stellar objects show a clear clustering pattern in each region: the Class I-like sources are mostly clustered in molecular cloud region, while the Class II-like sources are in or around more evolved optical HII regions. We find that the slopes of the Ks-band luminosity functions of Sh-2 255, W3 Main and NGC 7538 are lower than the typical values reported for the young embedded clusters, and their stellar populations are primarily composed of low mass pre-main-sequence stars. From the slopes of the Ks-band luminosity functions, we infer that Sh-2 255, W3 Main and NGC 7538 star forming regions are rather young (age ≤ 1 Myr).
The conditions for star formation at low metallicity: results from the LMC
Authors: Oliveira J. M. , van Loon J. Th. , Stanimirović S. 
Published: April 2007

AbstractWe present our recent work on the conditions under which star formation occurs in a metal-poor environment, the Large Magellanic Cloud ([Fe/H] ~ −0.4). Water masers are used as beacons of the current star formation in H II regions. Comparing their location with the dust morphology imaged with the Spitzer Space Telescope, and additional Hα imaging and groundbased near-infrared observations, we conclude that the LMC environment seems favourable to sequential star formation triggered by massive star feedback (Oliveira et al. 2006). Good examples of this are 30 Doradus and N 113. There are also H II regions, such as N 105A, where feedback may not be responsible for the current star formation although the nature of one young stellar object (YSO) suggests that feedback may soon start making an impact. The chemistry in one YSO hints at a stronger influence from irradiation effects in a metal-poor environment where shielding by dust is suppressed (van Loon 2005).
Thermal and non thermal components of interstellar medium at sub-kiloparsec scales in galaxies
Authors: Paladino Rosita 
Published: April 2007

AbstractWe present the result of the analysis of the point-by-point correlation between the radio continuum (RC) and CO intensities from kpc to sub-kpc scales in 22 BIMA SONG galaxies and the point-by-point correlation at sub-kpc scales between the RC, CO and 24 μm-IR emissions in 6 galaxies for which Spitzer images have been recently released. We found that there is no significant variation of the slope and the scatter of the correlations at this spatial resolution. All three correlations are comparably tight with scatter of less than a factor of two.
Degree scale high resolution mapping of CO J=2-1 and 3-2 in giant molecular clouds
Authors: Peters W. L. , Bieging J. H. , Groppi C. E. , Kulesa C. A. , Walker C. K. , Hedden A. S. , Puetz P. S. 
Published: April 2007

AbstractWe present the first results from a project to map Giant Molecular Clouds (GMCs) in the 12CO J=2-1, 13CO J=2-1, and 12CO J=3-2 lines using the Heinrich Hertz Submillimeter Telescope (HHT) at the University of Arizona. We mapped nearly 2.5 sq. deg of W3 and 1.0 sq. deg of W51 in the J=2-1 lines. We have begun mapping in the J=3-2 line. We achieve angular resolutions of 33″ and 24″ in the J=2-1 and J=3-2 lines with 1.3 and 0.9 km s−1 resolution.
Triggered star formation in the isolated cluster CB 34?
Authors: Peterson Dawn E. , Gutermuth R. A. , Skrutskie M. F. , Megeath S. T. , Pipher J. L. , Allen L. E. , Myers P. C. 
Published: April 2007

AbstractBok globules, optically opaque small dark clouds, are classical examples of isolated star formation. However, the collapse mechanism for these cold, dense clouds of gas and dust is not well understood. Observations of Bok globules include some which appear to be starless while others harbor single stars, binaries and even small groups of forming stars. One example of a Bok globule forming a group of stars is CB 34, observed with both the IRAC and MIPS instruments as part of the Spitzer Young Cluster Survey. Based on initial analysis of 1-8 μm photometry from IRAC and the Two Micron All Sky Survey (2MASS), we identified 9 Class 0/I and 14 Class II young stellar objects within the small, 4.5′ × 4.5′ region encompassing CB 34. This unusually high number of protostars compared with Class II sources is intriguing because it implies a high rate of star formation. Therefore we have begun a larger study of this region in order to determine why and how CB 34 started forming stars at such a high rate. Is CB 34 embedded within a larger HII region which may have triggered its collapse or does it appear to have collapsed in isolation from outside influences?
Evolutionary sequence of expanding Hydrogen shells
Authors: Relaño M. , Beckman J. E. , Daigle O. , Carignan C. 
Published: April 2007

AbstractGiant HI shells, with diameters of hundreds of parsecs and expansion velocities of 10-20 s−1 are characteristic observed features of local gas rich galaxies. Although a predictable consequence of the impact of OB associations on the ISM doubts have been raised, as OB stars are not present in the centres of the majority of these shells. Here we combine our observations of expanding ionized shells in luminous H II regions with basic dynamical models to give support to the scenario in which OB associations do produce the HI shells.
Extraplanar gas and magnetic fields in the cluster spiral galaxy NGC 4569
Authors: Ryś S. , Chyży K. T. , Weżgowiec M. , Ehle M. , Beck R. 
Published: April 2007

AbstractThe Virgo Cluster spiral NGC 4569 is known for its compact starburst in the core and unusual outflow of Hα emitting gas perpendicular to the galaxy disk. Recent radio polarimetric observations with the Effelsberg telescope reveal huge magnetized outflows. Preliminary results of our XMM-Newton observations uncover not only hot gas in the disk but also an extensive X-ray envelope around it. We investigate the possibility of starburst-induced galactic outflows in various gas phases and cluster influence on the galaxy evolution.
Infrared properties of ultracompact H II regions in the Galaxy and the LMC
Authors: Sewiło Marta , Churchwell Ed , Whitney Barbara ,   the GLIMPSE and SAGE Teams
Published: April 2007

AbstractWe report the preliminary results of the study on the infrared properties of ultracompact (UC) H II regions in our Galaxy and in the Large Magellanic Cloud (LMC) based on the GLIMPSE (the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) and SAGE (Surveying the Agents of a Galaxy's Evolution) data, respectively. We found that ~60% of the Galactic UC H II regions do not have IR counterparts. Large extinction and very strong stellar winds evacuating H II regions from dust may explain this result. The same effect is observed in the LMC. One of the goals of this research is to develop a means of identifying UC H IIs based on their mid-IR properties, e.g. positions on color-color and color-magnitude plots and/or shape of spectral energy distributions. GLIMPSE showed that bow shocks, protostellar jets/outflows, and bubbles are common phenomena in massive star formation regions (MSFRs).
Globular clusters in NGC147, 185, and 205
Authors: Sharina M. E. , Afanasiev V. L. , Puzia T. H. 
Published: April 2007

AbstractStudying the chemical compositions and color-magnitude diagrams of globular clusters in the nearby low-mass galaxies is critical to compare properties of these long-living objects situated in galaxies of different type and mass, and to establish the role of dwarf galaxies as building blocks of massive early-type and spiral galaxies. We present measurements of ages, metallicities and [α/Fe] ratios for 16 globular clusters (GC) in NGC147, NGC185, and NGC205 and for the central regions of the diffuse galaxy light in NGC185, and NGC205, based on measurements of absorption line indices as defined by the Lick standard system in spectra obtained with the SCORPIO multi-slit spectrograph at the 6-m telescope of the Russian Academy of Sciences. We include in our analysis high-quality HST/WFPC2 photometry of individual stars in the GGs to investigate the influence of their horizontal branch (HB) morphology on the spectroscopic analysis. The HB morphologies for our sample GCs follow the same behavior with metallicity as younger halo Galactic globular clusters. We show that it is unlikely that they bias our spectroscopic age estimates based on Balmer absorption-line indices. Almost all our sample GCs appear to be old (T > 8 Gyr) and metal-poor ([Z/H]<−1.1). We find that most of the GCs in the studied galaxies are weakly or not α-enhanced, in contrast to the population of GCs in nearby early-type galaxies, and to the halo population of GCs in M31 and Milky Way.
Formation and destruction of clouds and spurs in spiral galaxies
Authors: Shetty Rahul , Ostriker E. C. 
Published: April 2007

AbstractWe investigate the formation of clouds and substructure in spiral galaxies using high resolution global MHD simulations, including gas self gravity. Previously, local modeling by Kim & Ostriker (2002) has shown that self gravity and magnetic fields cause the growth of high density clumps in the spiral arms rather rapidly; subsequently, these clumps result in the formation of sheared, feather like structures in the interarms, known as spurs. Recently, we performed global simulations and found that gas self-gravity can cause the growth of sheared features regardless of the strength of the external spiral potential. However, a sufficiently strong spiral potential is required to produce arm clouds as well as spurs, which are the filamentary structures distinctly associated with the spiral arms, having near-perpendicular intersections with the main dust lane. We are currently performing higher resolution simulations to study the detailed properties of the clouds and spurs; we are also including a feedback mechanism, representing turbulent forcing via supernovae, to destroy the clouds. We will thus assess the role of turbulence on the clump formation rate and properties. Further, we will also follow how subsequent arm and spur morphology develops under quasi-steady conditions.
Interaction between molecular outflows and dense gas in the cluster-forming region OMC-2/FIR4
Authors: Shimajiri Yoshito , Takahashi S. , Takakuwa S. , Saito M. , Kawabe R. 
Published: April 2007

AbstractSince most stars are born as members of clusters (Lada & Lada 2003), it is important to clarified the detailed mechanism of cluster formation for comprehensive understanding of star formation. However, our current understanding of cluster formation is limited due to the followings;
(a)Cluster forming regions are located at the far distance.(b)There are complex mixtures of outflows and dense gas in cluster forming regions.
So, we focused on the Orion Molecular Cloud 2 region (OMC-2), a famous cluster-forming region (Lada & Lada 2003) and the most nearest GMC. We observed the FIR 4 region with the Nobeyama Millimeter Array(NMA), Atacama Submillimeter Telescope Experiment (ASTE). In this region, there are 3 protostars (FIR3, FIR4, FIR5) which were identified as 1.3 mm dust continuum sources (Chini et al. 1997) and driving sources of mixed outflows, and FIR 4 is the most strongest source of 1.3 mm dust continuum in OMC-2. Molecular lines we adopted are a high density (105cm−3) gas tracer of H13CO+ (J=1-0), a molecular outflow tracer of 12CO(J=1-0) and 12CO(J=3-2), and SiO(J=2-1 v=0) as a tracer of shocks associated with an interaction between outflows and dense gas.From results of the 12CO(J=1-0) outflow, H13CO+ dense gas, and the SiO shock, the outflow from FIR 3 interacts with dense gas in the FIR 4 region. Moreover the Position-Velocity diagram along the major axis of the 12CO(J=3-2) outflow shows that the 12CO(J=1-0) and SiO emission exhibits a L shape (the line widths increase in the interacting region in morphology). This is an evidence of interaction between the outflows and dense gas (Takakuwa et al. 2003). From result of the 3 mm dust continuum, the interacted region by the molecular outflow of FIR 3 is an assemble of seven dense cores. The mass of each core is 0.1-0.8 M. This clumpy structure is evident only at FIR 4 in the entire OMC-2/3 region. There are possible that two cores are in the proto-stellar phase, because 3 mm dust continuum source correspond to NIR source or 3.6 cm f-f jet source. From these results, cores in the FIR 4 region may be potential source of the next-generation stars. In the other words, there is a possibility that the molecular outflow ejected from FIR 3 is triggering the cluster formation in the FIR 4 region.
UCHII regions in the Antennae
Authors: Snijders L. , Kewley L. J. , van der Werf P. P. , Brandl B. R. 
Published: April 2007

AbstractWe explore the physical characteristics of young stellar clusters in the Antennae by combining recent ground- and space-based mid-infrared observations with a newly developed set of diagnostic diagrams. Spitzer data give an overview of the star-forming regions extending over hundreds of parsecs, showing a dominant diffuse ISM component with a density of 102 cm−3 plus a small fraction of very compact material (106 cm−3). With its higher spatial resolution VISIR gives a close-up view of the latter component. Its emission line ratios suggest that these regions are fundamentally different from local star-forming regions. Instead of having small isolated UCHII regions, as in local star-forming regions, the average density of the medium of the whole region falls in the (ultra)compact regime, exceeding 104 cm−3 over tens of parsecs.
Study of photon dominated regions in IC 348
Authors: Sun K. , Kramer C. , Mookerjea B. , Ossenkopf V. , Röllig M. , Stutzki J. 
Published: April 2007

AbstractWe present fine structure line of neutral carbon at 492 GHz (3P1–3P0, hereafter [C I] 1–0) and 12CO 4–3 KOSMA observations. This data has been combined with FCRAO 12CO 1–0 and 13CO 1–0 data. We have used these observations to understand the emission from the photon dominated regions (PRDs) in IC 348. We confirm the anti-correlation between N(C)/N(CO) and N(H2) as seen in most Galactic PDRs (Mookerjea et al. 2006).
Survey observations of large-scale molecular outflows associated with intermediate-mass protostar candidates in the OMC-2/3 region
Authors: Takahashi Satoko , Shimajiri Y. , Takakuwa S. , Saito M. , Kawabe R. 
Published: April 2007

AbstractWe have newly performed millimeter- and submillimeter-wave observations in the nearest GMC: the Orion Molecular Cloud -2/3 region (OMC-2/3). Here, we report results of our large-scale (22' × 14') outflow survey with the Atacama Submillimeter Telescope Experiment (ASTE) in the CO(3-2) emission. The OMC-2/3 region is one of the famous intermediate-mass star-forming regions and harbors several sources diagnosed as Class0 protostars (Chini et al. 1997). With the intensive ASTE observations, we totally identified the 8 clear, 5 probable and 6 marginal outflows in OMC-2/3. 8 clear outflows from them, MMS 2, MMS 5, MMS7, MMS9, FIR-2, FIR 3, VLA 13, and FIR 6b are associated with mm and SPITZER 24 μm sources. The others are more or less complicated, and two of which, VLA 13 and FIR 6, are newly identified. We found the interaction between the molecular outflows and the dust condensations at least in four regions. In addition, we confirmed the increment of the velocity width of the dense gas toward some of these condensations (i.e. at the termination of the outflow lobes). These results suggest that (i) the interaction between the outflows and the dense condensation occurs commonly in the OMC-2/3 region, (ii) the dense condensations in this region are compressed ubiquitously by these outflows and are receiving a part of the momentum from them. Particularly, one of the strongest millimeter sources, and hence protostar candidates, FIR4, is strongly compressed by a molecular outflow driven by FIR3 located at the north-east of FIR 4. These results suggest that the molecular outflows play an important role in the formation and evolution of stars and that the outflows are a driving mechanism of turbulence in the OMC-2/3 region.
Modeling the dust and gas temperatures near young stars
Authors: Urban Andrea , Evans Neal J. 
Published: April 2007

AbstractAs young stars form, they interact with their environment in many ways. We study the radiative interaction of a young star with its surrounding cluster environment. The change in gas temperature caused by a forming star can trigger the formation or inhibit the growth of nearby star forming cores. We calculate the gas temperature around a single star by balancing the dust-gas collisional heating, molecular cooling, and cosmic ray heating rates for a grid of models with various luminosities and density distributions. In the future, this work can be used in large-scale simulations of clustered star formation to study the effect of using a gas temperature which depends not only on density, but also on radiative environment.
Triggered star formation within the bright-rimmed cloud SFO 75
Authors: Urquhart J. S. , Thompson M. A. , Morgan L. K. , White Glenn J. 
Published: April 2007

AbstractWe present the results of a multi-wavelength line and continuum study of the bright-rimmed cloud SFO 75 in an attempt to determine whether the ionisation front and its associated shocks, driven by the nearby O star, have triggered the formation of a new generation of stars within this bright-rimmed cloud.
A turbulence study in Dwarf Irregular galaxies
Authors: Valdez-Gutiérrez Margarita , Puerari Ivânio 
Published: April 2007

AbstractWe present preliminary results of a Fourier transform power spectra analysis carried out on a sample of dwarf irregular galaxies and Local Group members. This project is intended to study turbulence and the ISM structure in irregulars as a class.
The generation of dense cores and substructure within them by MHD waves
Authors: Van Loo S. , Falle S. A. E. G. , Hartquist T. W. 
Published: April 2007

AbstractBy using 2D simulations, we examine the generation of dense cores and substructures by magnetosonic waves. We find that the excitation of slow-mode waves by fast-mode waves produces these high-density structures.
Integral field observations of distant cluster galaxies
Authors: Vergani D. , Balkowski C. , Flores H. , Cayatte V. , Hammer F. , Mei S. , Blakeslee J.P. 
Published: April 2007

AbstractWe have used the FLAMES multi-integral field unit system of the European Southern Observatory (VLT) centered on the cluster MS0451.6-0305 at z = 0.5386 to obtain the spatially resolved kinematics of the cluster members. The spectral data are supported by HST/ACS images that provide immediate morphological information of the cluster galaxies. The relevant structural parameters such as inclination, size, and orientation derived from optical high angular resolution images are compared with those derived from the kinematics. Our final goals are: 1. to derive the Tully-Fisher relation for cluster galaxies with regular kinematics. 2. to obtain the dynamical masses from resolved kinematics and stellar masses from optical images to be compared with local measurements.