bluuebunny/crossref_metadata_2025_split huggingface dataset:
The high latitude low mass star forming region Cometary Globule 12: two compact cores and a C18O hot spot
Authors: Haikala L. K. , Juvela M. , Harju J. , Lehtinen K. , Mattila K. , Olberg M. , Dumke M. 
Published: April 2007

AbstractCometary globule CG 12 lies at the distance of 630 pc more than 200 pc above the Galactic plane. The cloud's structure could be due to the passage of a supernova blast wave. Curiously, the cometary tail points at the galactic plane which would put the putative supernova even farther above the Galactic plane than the globule. The globule contains a low/intermediate mass stellar cluster with at least 9 members (Williams et al. 1977). The head of CG 12 has been observed using NIR imaging (NTT SOFI), mm continuum (SEST SIMBA) and sub mm (APEX) and mm (SEST) spectroscopy (Haikala & Olberg 2006, Haikala et al.). The molecular material is distributed in a North-South 10' long elongated lane with two compact maxima separated by 3'. Strong C18O (3-2), (2-1) and (1-0) emission is detected in both maxima and both have an associated compact 1.2 mm continuum source. The Northern core, CG 12 N, is cold and is possibly still pre-stellar. A dense and compact core is observed in DCO+ and CS emission in the direction of the Southern core, CG 12 S. A remarkable C18O hot spot was detected in CG 12 S. This is the first detection of such a compact, warm object in a low mass star forming region. The hot spot can be modelled with a 60″ to 80″ diameter (~0.2 pc) hot (80 K ≲ Tex≲ 100 K) 1.6 solar mass clump (Haikala et al. 2006). The hot spot lies at the edge of a dense cloud core and on the axis of a highly collimated bipolar molecular outflow (White 1993). The driving source of the outflow is most probably embedded in the dense core. NIR imaging reveals a bright cone like feature with a faint counter cone in the centre of CG 12 S. The size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than 100 solar masses are comparable to those of other nearby low/intermediate mass star formation regions.
Diffuse X-ray emission from the Carina Nebula observed with Suzaku
Authors: Hamaguchi K. , Petre R. ,   the Suzaku η Carina team
Published: April 2007

AbstractThe Carina Nebula possesses the brightest soft diffuse X-ray emission among the Galactic giant HII regions, but the origin has not been known yet. The XIS1 back-illuminated CCD camera onboard the Suzaku X-ray observatory has the best spectral resolution for extended soft sources so far, and is therefore capable of measuring these key emission lines in the soft diffuse plasma. Suzaku observed the Carina nebula on 2005 Aug. 29. The XIS1 spectra of the Carina nebula clearly showed spatial variations in emission line strengths. In the south, the spectrum showed strong L-shell lines of iron ions and K-shell lines of silicon ions, while in the north these lines were much weaker. Fitting the spectra with an absorbed thin-thermal plasma model with kT ~ 0.2, 0.6 keV and NH ~ −2 × 1021 cm−2 showed that the silicon and iron abundance is about 2–3 times higher in the south than in the north. Because of its large size (~40 pc), the diffuse emission in the Carina nebula might have been produced by an old supernova, or a super shell produced by multiple supernovae.
Discovery of large-scale masers in W3(OH)
Authors: Harvey-Smith L. , Cohen R. J. 
Published: April 2007

AbstractWe report a vast filament of hydroxyl and methanol maser emission surrounding the ultra-compact HII region W3(OH). The filament stretches 3100 AU and has a linear velocity gradient. By studying the velocity structure, line profiles and extended methanol maser structures we believe we have located the position of the central star and detected around it a circumstellar disc with a large velocity gradient of 47 km s−1 arcsec−1.
IRSF/SIRIUS near-infrared survey of the Magellanic Clouds: triggered star formation in N11 in the Large Magellanic Cloud
Authors: Hatano H. , Kadowaki R. , Kato D. , Sato S. ,   the IRSF/SIRIUS group
Published: April 2007

AbstractA near-infrared survey of the Magellanic Clouds has been carried out with IRSF/SIRIUS. As a part of the results, we present a study of triggered star formation in N11 in the LMC.
A (Sub)Millimeter survey of massive star-forming regions identified by the ISOPHOT Serendipity Survey (ISOSS)
Authors: Hennemann Martin , Birkmann Stephan M. , Krause Oliver , Lemke Dietrich 
Published: April 2007

AbstractA sample of potential massive starforming regions identified at 170 m by ISO was observed in the submillimeter and millimeter regime. These observations allow us to infer physical properties of the molecular cloud cores. Two sources are presented in detail: ISOSS J23053+5953 and J183640221 show viable candidates for massive protocluster cores. Our analysis shows very low temperatures and low levels of turbulence of the major mass fraction in the molecular cloud cores besides active star formation at an early evolutionary stage. These conditions seem similar to the low mass case and may precede phases of luminous infrared emission observed towards young massive protostars.
Non-symmetrical protoplanetary disks destroyed by UV photoevaporation
Authors: Hetem A. , Gregorio-Hetem J. 
Published: April 2007

AbstractWe have developed geometric disk models to study the circumstellar geometries by fitting the spectral energy distribution (SED) of T Tauri and Herbig Ae/Be stars. The simulations provide means to recognize the signatures of different disk structures, including the effects due to external UV photoevaporation.Following Chiang & Goldreich (1997) and Dullemond et al. (2001), we used hydrostatic, radiative equilibrium models for passive, reprocessing flared disks. The grains in the surface of the disk are directly exposed to the radiation from the star and the interior of the disk is heated by diffusion from the surface. Adopting this two-layers disk structure, our disk model was improved in order to optimize the parameters estimated by using a calculation technique based on genetic algorithms presented by Bentley & Corne (2002).In the present work, we apply the code to model the SED of protoplanetary disks, which have being destroyed by photoevaporation due to the presence of ionizing OB stars, as the example of Trapezium region in the Orion Nebula. We compare geometric disk characteristics and physical conditions evaluated by our method to those obtained to the “proplyds” studied by Scally & Clarke (2001), Robberto et al. (2002) and Smith et al. (2005), among others. We also conclude that the parameter estimation by genetic algorithms assures accurate and efficient calculations.
Giant Molecular Associations in M51
Authors: Hitschfeld M. , Kramer C. , Schuster K. , Garcia-Burillo S. , Stutzki J. 
Published: April 2007

AbstractWe present a 12CO 2-1 map of M51 (Schuster et al. 2006) at 11″ resolution observed with HERA at the IRAM-30m telescope. The map covers the companion galaxy NGC5195 as well as the south-western arm out to 12 kpc. Using the IRAM-30m data and the clump finding procedure GAUSSCLUMPS (Stutzki et al. 1990), we obtain the masses, positions, peak temperatures and more intrinsic properties as i.e. deconvolved sizes of Giant Molecular Associations (GMAs) in M51 (Hitschfeld et al. 2007, in prep.).
High-resolution mapping of interstellar clouds with near-infrared scattered light
Authors: Juvela M. , Pelkonen V.-M. , Padoan P. , Mattila K. 
Published: April 2007

AbstractWe examine the intensity of scattered near-infrared (NIR) light in the case of interstellar clouds illuminated by the normal interstellar radiation field. We have developed a way to convert the observed surface brightness into estimates of the column density and have estimated the accuracy of the new method. The NIR intensities can be converted into reliable estimates of the column density in regions with AV up to almost 20 magnitudes. The errors can be further reduced with detailed radiative transfer modelling and by using the lower resolution information that is provided by the colour excess data of background stars. Therefore, NIR scattered light is a promising new way to map quiescent interstellar clouds at a high, even sub-arcsecond resolution.
3D Spectroscopy of the Blue Compact Dwarf Galaxies IZw18 and IIZw70
Authors: Kehrig C. , Vílchez J. M. , Sanchez S. F. , Lopez-Martin L. , Telles E. , Martin-Gordón D. 
Published: April 2007

AbstractBlue compact dwarf (BCD) galaxies are low-metallicity objects undergoing violent star formation (Searle & Sargent 1972). We present our ongoing work on integral field spectroscopy (IFS) of the two prototypical BCD galaxies IIZw70 and IZw18 (Papaderos et al. 2002). Two-dimensional spectroscopy allows us to collect simultaneously the spectra of many different regions of an extended object, combining photometry and spectroscopy in the same data set. The great advantage of using IFS for the investigation of galaxies is that it allows us to obtain data on the galaxies' positions, velocity fields and star-forming properties all in one data cube. The observations were taken with the instruments INTEGRAL/WYFFOS at the WHT (ORM, La Palma) and PMAS installed on the 3.5m telescope at the CAHA, covering a spectral range from λ 3600 to 6800 Å. The data are mainly used to study the ionized gas and stellar clusters. Our main goal is to investigate the presence of spatial variations in ionization structure indicators, physical conditions and gaseous metal abundances, in these galaxies (Vílchez & Iglesias-Páramo 1998). We also study the kinematical properties of the ionized gas, as well as systematic variations of ionization structure and physical-chemical parameters as a function of the surface-brightness in Hα emission. Maps of the relevant emission lines are presented.
ASTE observations of dense molecular gas in galaxies
Authors: Kohno K. , Muraoka K. , Nakanishi K. , Tosaki T. , Kuno N. , Miura R. , Sawada T. , Sorai K. , Okuda T. , Kamegai K. , Tanaka K. , Endo A. , Hatsukade B. , Ezawa H. , Sakamoto S. , Cortes J. , Yamaguchi N. , Matsuo H. , Kawabe R. 
Published: April 2007

AbstractAtacama Submillimeter Telescope Experiment (ASTE) is a joint project between Japan and Chile for installing and operating a 10 m high precision telescope in the Atacama Desert in order to explore the southern sky through the submillimeter wavelength. We have achieved an accuracy of 19 μm (rms) for the main reflector surface and a stable radio pointing accuracy of about 2 arcsec (rms). A 350 GHz cartridge type SIS mixer receiver achieves good performance with a typical system noise temperature of 150 ~ 250 K in DSB and a main beam efficiency of 0.6 ~ 0.7 during winter nights.A large scale CO(3-2) imaging survey of nearby galaxies using ASTE is now in progress. One of our goals is to compare our wide area CO(3-2) images with existing CO(1-0) data as well as distributions of massive star formation tracers (i.e., Hα and radio continuum emission) in order to understand the physical mechanism which controls the global star formation properties such as star formation efficiency. Initial CO(3-2) maps of some sample galaxies (M 83, NGC 604 in M 33, NGC 1672, & NGC 7130) are reported.
Three-dimensional MHD simulations of magnetized molecular cloud fragmentation with turbulence and ion-neutral friction
Authors: Kudoh T. , Basu S. 
Published: April 2007

AbstractWe perform a 3D-MHD simulation of a self-gravitating isothermal gas layer that is initially penetrated by a uniform magnetic field. The strength of the initial magnetic field is such that the cloud is slightly subcritical. In this system, we input random supersonic turbulence initially. Ion-neutral friction is also introduced in the magnetized gas so that the magnetic diffusion allows gas to go across the magnetic field and form self-gravitating cores. We found that self-gravitating cores are formed in the dense region enhanced by the shock waves if ion-neutral friction is introduced. The time scale of core formation is on the order of the 106 years, which is faster than the usual magnetic diffusion time (107 years) estimated from the initial condition. Our result is consistent with the results of 2D-MHD simulations by Li & Nakamura (2004).
Triggered cluster formation in the RMC
Authors: Li Jin Zeng , Smith Michael D. 
Published: April 2007

AbstractA comprehensive study of clustered star formation in the Rosette Molecular Complex was carried out based on archived data from the 2 Micron All Sky Survey. We presented strong evidence that triggered formation of embedded clusters and stellar aggregates took place in the working shells of the Rosette Nebula, a spectacular HII region excavated by the dozens of OB stars of the emerging massive cluster NGC 2244. Surprisingly, we have identified, within the confines of NGC 2244, a distinct congregation of young stellar objects showing prominent NIR excess that forms an arc like structure in appearance. Its location right to the south-east of the center of the main cluster and its strange morphology indicate most likely an origin from a former working shell of the HII region. This relic arc and the large, fragmented working surface layer of Rosette with the ambient cloud roughly show a concentric origin in morphology. This implies also a common origin of the clusters or stellar aggregates in association. The formation of massive star clusters was evidenced further into the heart of the molecular complex, and structured clustering star formation seemed to have taken place toward the south-east edge of the complex.
Dependence of radio halos on underlying star formation activity and galaxy mass
Authors: Lisenfeld U. , Dahlem M. , Rossa J. 
Published: April 2007

AbstractWe investigate the relation between the existence and size of radio halos, which are believed to be created by star formation (SF) related energy input into the interstellar medium, and other galaxy properties, most importantly star formation activity and galaxy mass. Based on radio continuum and Hα observations of a sample of seven galaxies we find a direct, linear correlation of the radial extent of gaseous halos on the size of the actively star-forming parts of the galaxy disks. Data of a larger sample of 22 galaxies indicate that the threshold energy input rate into the disk ISM per unit surface area for the creation of a gaseous halo depends on the mass surface density of the galaxy, in the sense that a higher (lower) threshold has to be surpassed for galaxies with a higher (lower) surface density. Because of the good prediction of the existence of a radio halo from these two parameters, we conclude that they are important, albeit not the only contributors. The compactness of the SF-related energy input is also found to be a relevant factor. Galaxies with relatively compact SF distributions are more likely to have gaseous halos than others with more widespread SF activity. These results quantify the so-called “break-out” condition for matter to escape from galaxy disks, as used in all current models of the interstellar medium.More details can be found Dahlem, Lisenfeld & Rossa, 2006, A&A 457, 121.
Triggered star formation in spiral arms
Authors: Martínez-García Eric E. , González-Lópezlira Rosa Amelia , Bruzual-A. Gustavo 
Published: April 2007

AbstractWe present preliminary results for six spiral galaxies from a sample of 25, where we have used the method developed by González & Graham (1996) to search for and analyze azimuthal color gradients across spiral arms. The six galaxies analyzed here are NGC 1703 (SBrb), NGC 3001 (SABrsbc), NGC 3059 (SBrsbc), NGC 3513 (SBrsc), NGC 4593 (RSBrsb), and NGC 4603 (SAsc).NGC 1703: We found one azimuthal color gradient in NGC 1703. Star formation was traced with the reddening free parameter Q, and the dust lane was located with the (g – J) color. This gradient lies at a distance of 1.45 kpc from the center of the galaxy. In order to get some physical parameters of the star formation processes that are taking place in the spiral arms of the galaxies in our sample, we compared the observed Q profiles with the stellar population synthesis models of Bruzual & Charlot (2003). The fitted Q model is shown in figure 1. If one assumes that stars form in the site of the shock, and that they age as they move away from this birthsite, then distance from the dust lane (at constant radius) parameterizes stellar age. In fact, stretching the model Q to the fit the data fixes the ratio between the distance and the age of the stellar population. If, in addition, the rotational velocity is known, it is possible to find the angular velocity of the spiral pattern. The spiral pattern speeds derived from the gradients (under the assumption that star formation is triggered by the density wave) yield theoretical resonance positions that are coincident with the observed spiral end points, in 3 out of 6 spirals. It would be hard to avoid the conclusion that disk dynamics and star formation are fundamentally related in these objects.
SUBARU near-infrared multi-color images of Class II Young Stellar Object, RNO91
Authors: Mayama Satoshi , Tamura Motohide , Hayashi Masahiko 
Published: April 2007

AbstractRNO91 is class II source currently in a transition phase between a protostar and a main-sequence star. It is known as a source of complex molecular outflows. Previous studies suggested that RNO91 was associated with a reflection nebula, a CO outflow, shock-excited H2 emission, and disk type structure. But the geometry of RNO91, especially its inner region, is not well confirmed yet. High resolution imaging is needed to understand the nature of RNO91 and its interaction with outflow. Thus, we conducted near-infrared imaging observations of RNO91 with the infrared camera CIAO mounted on the Subaru 8.2-m Telescope. We presented JHK band and optical images which resolved a complex asymmetrical circumstellar structure. We examined the color of RNO91 nebula and compared the geometry of the system suggested by our data with that already proposed on the basis of other studies. Our main results are as follows; 1. The K-band images show significant halo emission detected within ~2″ around the peak position while less halo emission is seen in shorter wavelength images such as J and optical. The nebula appears to become more circular and more diffuse with increasing wavelengths. The cut-off at 300AU derived from our radial surface brightness is consistent with the size of the polarization disk suggested by Draper & Tadhunter (1993). These consistencies indicate that this optically thick region is attributed to a disk-like structure.2. At J and optical, several bluer knot-like structures are detected around and beyond the halo emission. These bluer knots seen in our images are comparable to the size of the envelope detected in HCO+ emission surrounding RNO91 (Lee & Ho 2005). It is thus natural to suggest that these bluer knots are the near-infrared light scattered by an envelope structure which is disrupted by molecular outflows.3. The pseudo-true color composite image has an appearance of arc-shaped emission extending to the north and to the east through RNO91. On the counter part of this arc-shaped structure, the nebula appears to become more extended to the southwest from the central peak position in J band and optical images. We interpret these whole structures as a bottom of bipolar cavity seen relatively edge-on opening to the north and south directions.
Chemical structure of the massive protobinary-forming hot core, W3(H2O)
Authors: Minh Y. C. , Chen H.-R. 
Published: April 2007

AbstractThe hot molecular core, W3(H2O), contains a massive protobinary system that is cocooned by dense gas (n(H2) ~ 107 cm−3), with about 1 arcsec (~ 2000 AU) separation of the binary system. We investigate chemical properties of the gas components around this binary system using the mm-wave transitions of complex molecules, CH3CN, SiO, HNCO, and CH3CH2CN, observed with the BIMA array. The two protostellar objects, A and C in W3(H2O), can be distinguished using chemical properties, suggesting that the source A may be younger than the source C within the time scale of less than 104 years. The hot core around the source C, traced by CH3CH2CN and the K=6 component of CH3CN, seems to have more time for chemical evolution than the source A. The SiO emission in this region suggests that there was an influence from the outside of the W3(H2O) and W3(OH) hot cores. The nitrogen chemistry may be more active in the later stage than the oxygen chemistry, but the chemical evolution of the protostellar envelopes may not be monotonic as previously suggested.
Radiation driven implosion model for star formations near an H II region
Authors: Motoyama K. , Umemoto T. , Shang H. 
Published: April 2007

AbstractWe performed numerical simulation including UV radiation transfer, and investigated effects of radiation driven implosion on star formation processes. We also observed two bright-rimmed clouds with C12O(J=1-0) and C13O(J=1-0) in order to compare density distributions between numerical results and observational results. Density profiles of bright-rimmed clouds are consistent with those of numerical simulations. These facts insist that star formations in bright-rimmed clouds are triggered by radiation driven implosion.
ASTE CO(3-2) observations of M 83: Correlation between CO(3-2)/CO(1-0) ratios and star formation efficiencies
Authors: Muraoka K. , Kohno K. , Tosaki T. , Kuno N. , Nakanishi K. , Sorai K. , Sakamoto S. 
Published: April 2007

AbstractWe have performed CO(J=3−2) emission observations with the Atacama Submillimeter Telescope Experiment (ASTE) toward the 5′ × 5′ (or 6.6 × 6.6 kpc at the distance D = 4.5 Mpc) region of the nearby barred spiral galaxy M 83. We successfully resolved the major structures, i.e., the nuclear starburst region, bar, and inner spiral arms in CO(J=3−2) emission at a resolution of 22'' (or 480 pc), showing a good spatial coincidence between CO(J=3−2) and 6 cm continuum emissions.From a comparison of CO(J=3−2) data with CO(J=1−0) intensities measured with Nobeyama 45-m telescope, we found that the radial profile of CO(J=3−2)/CO(J=1−0) integrated intensity ratio R3−2/1−0 is almost unity in the central region (r<0.25 kpc), whereas it drops to a constant value, 0.6–0.7, in the disk region. The radial profile of star formation efficiencies (SFEs), determined from 6 cm radio continuum and CO(J=1−0) emission, shows the same trend as that of R3−2/1−0. At the bar-end (r ~ 2.4 kpc), the amounts of molecular gas and the massive stars are enhanced when compared with other disk regions, whereas there is no excess of R3−2/1−0 and SFE in that region. This means that a simple summation of the star forming regions at the bar-end and the disk cannot reproduce the nuclear starburst of M 83, implying that the spatial variation of the dense gas fraction traced by R3−2/1−0 governs the spatial variation of SFE in M 83.