B2 Region Research Articles

OBSERVATIONAL RESULTS OF A MULTI-TELESCOPE CAMPAIGN IN SEARCH OF INTERSTELLAR UREA [(NH2)2CO

In this paper, we present the results of an observational search for gas phase urea [(NH$_2$)$_2$CO] observed towards the Sgr B2(N-LMH) region. We show data covering urea transitions from $\sim$100 GHz to 250 GHz from five different observational facilities: BIMA, CARMA, the NRAO 12 m telescope, the IRAM 30 m telescope, and SEST. The results show that the features ascribed to urea can be reproduced across the entire observed bandwidth and all facilities by best fit column density, temperature, and source size parameters which vary by less than a factor of 2 between observations merely by adjusting for telescope-specific parameters. Interferometric observations show that the emission arising from these transitions is cospatial and compact, consistent with the derived source sizes and emission from a single species. Despite this evidence, the spectral complexity, both of (NH$_2$)$_2$CO and of Sgr B2(N), makes the definitive identification of this molecule challenging. We present observational spectra, laboratory data, and models, and discuss our results in the context of a possible molecular detection of urea.

FLICKERING OF 1.3 cm SOURCES IN SGR B2: TOWARD A SOLUTION TO THE ULTRACOMPACT H II REGION LIFETIME PROBLEM

Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing radiation, alternately exposing and confining their H II regions. As a result, the H II regions are predicted to flicker in flux density over periods of decades to centuries rather than increase monotonically in size as predicted by simple Spitzer solutions. We have recently observed the Sgr B2 region at 1.3 cm with the Very Large Array in its three hybrid configurations (DnC, CnB, and BnA) at a resolution of ~025. These observations were made to compare in detail with matched continuum observations from 1989. At 025 resolution, Sgr B2 contains 41 ultracompact (UC) H II regions, 6 of which are hypercompact. The new observations of Sgr B2 allow comparison of relative peak flux densities for the H II regions in Sgr B2 over a 23 year time baseline (1989-2012) in one of the most source-rich massive star forming regions in the Milky Way. The new 1.3 cm continuum images indicate that four of the 41 UC H II regions exhibit significant changes in their peak flux density, with one source (K3) dropping in peak flux density, and the other three sources (F10.303, F1, and F3) increasing in peak flux density. The results are consistent with statistical predictions from simulations of high mass star formation, suggesting that they offer a solution to the lifetime problem for UC H II regions.

Submillimeter continuum observations of Sagittarius B2 at subarcsecond spatial resolution

We report the first high spatial resolution submillimeter continuum observations of the Sagittarius B2 cloud complex using the Submillimeter Array (SMA). With the subarcsecond resolution provided by the SMA, the two massive star-forming clumps Sgr B2(N) and Sgr B2(M) are resolved into multiple compact sources. In total, twelve submillimeter cores are identified in the Sgr B2(M) region, while only two components are observed in the Sgr B2(N) clump. The gas mass and column density are estimated from the dust continuum emission. We find that most of the cores have gas masses in excess of 100 M⊙ and column densities above 1025 cm-2. The very fragmented appearance of Sgr B2(M), in contrast to the monolithic structure of Sgr B2 (N), suggests that the former is more evolved. The density profile of the Sgr B2(N)-SMA1 core is well fitted by a Plummer density distribution. This would lead one to believe that in the evolutionary sequence of the Sgr B2 cloud complex, a massive star forms first in an homogeneous core, and the rest of the cluster forms subsequently in the then fragmenting structure.

Observations of the CH3OH 42-51E Line Toward the Sgr B2 Region

The <TEX>$CH_3OH$</TEX> <TEX>$4_2-5_1$</TEX> E transition was observed toward the Sgr B2 region, including the Principal Cloud and its surroundings. This methanol transition shows an extended emission along the 2'N cloud, which is believed to be colliding with the Principal Cloud and may trigger the massive star formation in this cloud. This extended methanol emission may also suggest that the 2'N cloud is under shocks. We derive total methanol column density <TEX>$N(CH_3OH)\;=\;2.9{\pm}0.3{\times}10^{14}\;cm^{-2}$</TEX> toward the peak position of the extended emission. The fractional abundance of methanol is about 10.9, relative to the estimated total <TEX>$H_2$</TEX> abundance, which is similar to the methanol abundances in quiet gas phase.

The Submillimeter Array 1.3 mm line survey of Arp 220

We present the first aperture synthesis unbiased spectral line survey toward an extragalactic object. The survey covered the 40 GHz frequency range between 202 and 242 GHz of the 1.3 mm atmospheric window. We find that 80% of the observed band shows molecular emission, with 73 features identified from 15 molecular species and 6 isotopologues. The 13C isotopic substitutions of HC3N and transitions from H2(18)O, 29SiO, and CH2CO are detected for the first time outside the Galaxy. Within the broad observed band, we estimate that 28% of the total measured flux is due to the molecular line contribution, with CO only contributing 9% to the overall flux. We present maps of the CO emission at a resolution of 2.9"x1.9" which, though not enough to resolve the two nuclei, recover all the single-dish flux. The 40 GHz spectral scan has been modelled assuming LTE conditions and abundances are derived for all identified species. The chemical composition of Arp 220 shows no clear evidence of an AGN impact on the molecular emission but seems indicative of a purely starburst-heated ISM. The overabundance of H2S and the low isotopic ratios observed suggest a chemically enriched environment by consecutive bursts of star formation, with an ongoing burst at an early evolutionary stage. The large abundance of water (~10^-5), derived from the isotopologue H2(18)O, as well as the vibrationally excited emission from HC3N and CH3CN are claimed to be evidence of massive star forming regions within Arp 220. Moreover, the observations put strong constraints on the compactness of the starburst event in Arp 220. We estimate that such emission would require ~2-8x10^6 hot cores, similar to those found in the Sgr B2 region in the Galactic center, concentrated within the central 700 pc of Arp 220.

THE MOLECULAR OUTFLOWS IN THE ρ OPHIUCHI MAIN CLOUD: IMPLICATIONS FOR TURBULENCE GENERATION

We present the results of CO (J=3-2) and CO (J=1-0) mapping observations toward the active cluster forming clump, L1688, in the rho Ophiuchi molecular cloud. From the CO (J=3-2) and CO (J=1-0) data cubes, we identify five outflows, whose driving sources are VLA 1623, EL 32, LFAM 26, EL 29, and IRS 44. Among the identified outflows, the most luminous outflow is the one from the prototypical Class 0 source, VLA 1623. We also discover that the EL 32 outflow located in the Oph B2 region has very extended blueshifted and redshifted lobes with wide opening angles. This outflow is most massive and have the largest momentum among the identified outflows in the CO (J=1-0) map. We estimate the total energy injection rate due to the molecular outflows identified by the present and previous studies to be about 0.2 L_solar, larger than or at least comparable to the turbulence dissipation rate [~(0.03 - 0.1) L_solar]. Therefore, we conclude that the protostellar outflows are likely to play a significant role in replenishing the supersonic turbulence in this clump.

Spectral imaging of the Sagittarius B2 region in multiple 7-mm molecular lines

We have undertaken a spectral-line imaging survey of a 6 × 6 arcmin2 area around Sagittarius (Sgr) B2 near the centre of the Galaxy, in the range from 30 to 50 GHz, using the Mopra telescope. The spatial resolution varies from 1.0 to 1.4 arcmin and the spectral resolution varies from 1.6 to 2.7 km s−1 over the frequency range. We present velocity-integrated emission images for 47 lines: 38 molecular lines and nine radio recombination lines. There are significant differences between the distributions of different molecules, in part due to spatial differences in chemical abundance across the complex. For example, HNCO and HOCO+ are found preferentially in the north cloud, and CH2NH near Sgr B2 (N). Some of the differences between lines are due to excitation differences, as shown by the 36.17- and 44.07-GHz lines of CH3OH, which have maser emission, compared to the 48.37-GHz line of CH3OH. Other major differences in integrated molecular line distribution are due to absorption of the 7-mm free–free continuum emission (spatially traced by the radio recombination line emission) by cool intervening molecular material, causing a central dip in the molecular line distributions. These line distribution similarities and differences have been statistically described by Principal Component Analysis and interpreted in terms of simple Sgr B2 physical components of the cooler, lower density envelope, and dense, hot cores Sgr B2 (N), (M) and (S).

Characterization of two-phase B2–HCP alloys in the Ru–Al–Cr system

Alloys of Ru–Al–Cr produced by arc-melting and by directional solidification at 20 mm/h were heat treated at 1100 °C and 1500 °C. Partial isothermal sections at 1100 °C and 1500 °C were constructed using the results from scanning (SEM) and transmission (TEM) electron microscopy. Both isothermal sections displayed a large B2 region with a composition extending towards Ru–20Al–38Cr at%. The directionally solidified Ru–6Al–38Cr and Ru–4Al–41Cr (at%) alloys exhibited uniformly distributed B2 precipitates in an HCP matrix after heat treatment at 1100 °C for 200 h. The Burgers orientation relationship of ( ( 0001 ) HCP / / ( 011 ) B 2 , [ 2 1 ¯ 1 ¯ 0 ] HCP / / [ 1 1 ¯ 1 ] B 2 ) was found between the HCP matrix and the semicoherent B2 precipitates by TEM. A uniform Al compositional profile within the B2 precipitates was found using STEM while limited solubility was detected in the matrix.

A positron annihilation study of two Fe-Al alloys in the B2 region

In order to investigate the nature of defects in the B2( h) and B2( l) regions of Fe–Al phase diagram, two alloys with aluminum contents of 40 at.% and 45 at.% have been quenched from temperatures in the range 950 °C–600 °C. Positron annihilation spectroscopy and Vickers microhardness have been used to follow the changes produced by the quenching treatments. Two different behaviours could be distinguished in the evolution of the positron lifetime for both alloys. Between 950 °C and 800 °C the lifetime remains constant and it drastically falls down at 750 °C. Between 600 °C and 750 °C the lifetime monotonically increased with the quenching temperature. A dependence with the Al content was also observed; higher positron lifetimes were obtained for the alloy with a 45 at.% of Al over all the temperature range. The constant lifetime value obtained between 800 °C and 950 °C has been assigned to the presence of a triple defect formed by two Fe vacancies bound to a Fe on an Al site as main defect. The stage from 600 °C to 750 °C has been assigned to the presence of Fe vacancies and an increasing number with the quenching temperature of triple defect. The detected step between 750 °C and 800 °C is in good agreement with the solvus line between B2( h) and B2( l) regions.

Time Variability of the Neutral Iron Lines from the Sagittarius B2 Region and Its Implication of a Past Outburst of Sagittarius A$^\ast$

Abstract We investigated long-term X-ray behavior from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra, and ASCA. The observed region of the Sgr B2 complex included two prominent spots in the FeI K$\alpha$ line at 6.40 keV, a giant molecular cloud, M0.66$-$0.02, known as the “Sgr B2 cloud” and an unusual X-ray source, G0.570$-$0.018. Although these 6.40 keV spots have spatial extensions of a few parsec scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the Fe XXV K$\alpha$ line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M0.66$-$0.02; the 6.40 keV line flux declined in 2001, and decreased to 60% in the time span 1994–2005. The other spot, G0.570$-$0.018, is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability ($\sim$10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A$^\ast$ was X-ray bright in the past 300 years, and exhibited a time variability with a period of a few years.

Atomic ordering and magnetic properties in the Ni45Co5Mn36.7In13.3 metamagnetic shape memory alloy

The effects of chemical order on the phase stability and magnetic properties of the metamagnetic shape memory alloy Ni45Co5Mn36.7In13.3 were investigated. Alloys quenched from the B2 and L21 phase regions were found to transform to the L10 and 6M martensite phases, respectively. For alloys quenched from the B2 region the martensitic transformation starting temperature is about 80 K higher than that for alloys quenched from the L21 region. The Curie temperature of the parent phase and the magnetization of the martensite phase were both lower for the alloy quenched from the B2 region than those for the alloy quenched from L21 region.

A New 100-GHz Band Front-End System with a Waveguide-Type Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio Telescope

Abstract We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100-GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode transducer and two sideband-separating SIS mixers, which are both based on a waveguide technique. The receiver has four intermediate frequency (IF) bands of 4.0–8.0 GHz. Over the radio frequency range of 80–120 GHz, the single-sideband receiver noise temperatures are 50–100 K, and the image rejection ratios (IRRs) are greater than 10 dB. We developed new matching optics for the telescope beam as well as new IF chains for the four IF signals. The new receiver system was installed in the telescope, and we successfully observed the12CO,13CO, and C18O emission lines simultaneously toward the Sagittarius B2 region to confirm the performance of the receiver system. The SSB noise temperature of the system, including the atmosphere, became approximately half of that of the previous receiver system. The IRRs of the two 2SB mixers were estimated from the12CO and HCO+ spectra from the W 51 giant molecular cloud, resulting in &amp;gt;20 dB for one polarization and &amp;gt;12 dB for the other polarization.

The kinetic temperature of a molecular cloud at redshift 0.9: ammonia in the gravitational lens PKS 1830–211

Using the Green Bank Telescope (GBT), we have detected the (J,K) = (1,1) to (10,10) ammonia inversion lines, up to 1030 K above the ground state, in a face-on spiral galaxy viewed against the radio continuum of the lensed background source PKS 1830-211. The ammonia absorption lines, seen at redshift 0.886, appear to be optically thin with absolute peak flux densities up to 2.5 percent of the total continuum of the background source. Measured intensities are consistent with a kinetic temperature of 80 K for 80-90 percent of the ammonia column. The remaining gas is warmer, reaching at least 600 K. Column density and fractional abundance are of order (5-10) x 10^14 cm^-2 and (1.5-3.0) x 10^-8. Similarities with a hot ammonia absorption component observed toward the Sgr B2 region close to the Galactic center may suggest that the Sgr B2 component also originates from warm diffuse low-density molecular gas. The warm ammonia column observed toward PKS 1830-211 is unique in the sense that it originates in a spiral arm.

Spectral imaging of the Sagittarius B2 region in multiple 3-mm molecular lines with the Mopra telescope

Using the Mopra telescope, we have undertaken a 3-mm spectral-line imaging survey of a 5 x 5 arcmin^2 area around Sgr B2. We covered almost the complete spectral the range from 81.7 to 113.5 GHz, with 2.2 MHz wide spectral channels or ~ 6 km/s, and have observed 24 lines, with 0.033 MHz wide, or ~ 0.1 km/s channels. We discuss the distribution of around 50 lines, and present velocity-integrated emission images for 38 of the lines. In addition, we have detected around 120 more lines, mostly concentrated at the particularly spectral line-rich Sgr B2(N) source. There are significant differences in molecular emission, pointing to both abundance and excitation differences throughout the region. Seven distinct spatial locations are identified for the emitting species, including peaks near the prominent star forming cores of Sgr B2(N), (M) and (S) that are seen in IR-to-radio continuum images. The other features are a 'North Ridge' and a 'North Cloud' to the north of the Sgr B2 N-M-S cores, a 'South-East Peak' and a 'West Ridge'. The column density, as evident through C^{18}O, peaks at the Sgr B2(N) and (M) cores, where strong absorption is also evident in otherwise generally bright lines such as HCO^{+}, HCN and HNC. Most molecules trace a ridge line to the west of the Sgr B2 N-M-S cores, wrapping around the cores and extending NE to the North Cloud. This is most clearly evident in the species HC_{3}N, CH_{3}CN, CH_{3}OH and OCS. They are found to be closer in distribution to the cooler dust traced by the sub-mm continuum than either the warmer dust seen in the mid-IR or to the radio continuum. The molecule CN, in contrast, is reasonably uniform over the entire region mapped, aside from strong absorption at the positions of the Sgr B2(N) and (M) cores.

A Time-Variable X-Ray Echo: Indications of a Past Flare of the Galactic-Center Black Hole

Abstract A time-variability study of the neutral iron line flux at 6.40keV in the Sgr B2 region from data of Suzaku and Chandra is presented. The highly ionized iron line at 6.68keV is due to Galactic Center Diffuse X-rays, and is thus time invariable. By comparing the 6.68keV and 6.40keV line fluxes, we found that the 6.40keV flux from the Sgr B2 complex region is time variable; particularly the giant molecular cloud M 0.66$-$0.02, known as “Sgr B2 cloud” is highly variable. The variability of the 6.40keV line in intensity and spatial distribution strongly supports the scenario that the molecular clouds in the Sgr B2 region are X-ray Reflection Nebulae irradiated by the Galactic Center black hole Sgr A$^*$.

SiO IN THE SGR B2 REGION

The 2-1 and 5-4 transitions of SiO have been observed toward the Sgr B2 region, including the Principal Cloud(the GMC containing Sgr B2(M)) and its surroundings. The morphology and velocity structure of the SiO emission show a close resemblance with the HNCO Ring feature, identified by Minh & Irvine(2006), of about 10 pc in diameter, which may be expanding and colliding with the Principal Cloud. Three SiO clumps have been found around the Ring, with total column densities <TEX>$N_{SiO}{\sim}1{\times}10^{14}cm^{-2}$</TEX> at the peak positions of these clumps. The fractional SiO abundance relative to <TEX>$H_2$</TEX> has been estimated to be <TEX>${\sim}(0.5-1){\times}10^{-9}$</TEX>, which is about two orders of magnitude larger than the quiet dense cloud values. Our SiO observational result supports the existence of an expanding ring, which may be triggering active star formations in the Principal Cloud.

The Cosmic Ray Distribution in Sagittarius B

The HESS instrument has observed a diffuse flux of ~ TeV gamma rays from a large solid angle around the Galactic center (GC). This emission is correlated with the distribution of gas in the region suggesting that the gamma rays originate in collisions between cosmic ray hadrons (CRHs) and ambient matter. Of particular interest, HESS has detected gamma rays from the Sagittarius (Sgr) B Molecular Cloud Complex. Prompted by the suggestion of a hadronic origin for the gamma rays, we have examined archival 330 and 74 MHz Very Large Array radio data and 843 MHz Sydney University Molonglo Sky Survey data covering Sgr B, looking for synchrotron emission from secondary electrons and positrons (expected to be created in the same interactions that supply the observed gamma rays). Intriguingly, we have uncovered non-thermal emission, but at a level exceeding expectation. Adding to the overall picture, recent observations by the Atacama Pathfinder Experiment telescope show that the cosmic ray ionization rate is ten times greater in the Sgr B2 region of Sgr B than the local value. Lastly, Sgr B2 is also a very bright X-ray source. We examine scenarios for the spectra of CRHs and/or primary electrons that would reconcile all these different data. We determine that (i) a hard (~ E^-2.2), high-energy (> TeV) population CRHs is unavoidably required by the HESS gamma ray data and (ii) the remaining broad-band, non-thermal phenomenology is explained either by a rather steep (~ E^-2.9) spectrum of primary electrons or a (~ E^-2.7) population of CRHs. No single, power-law population of either leptons or hadrons can explain the totality of broadband, non-thermal Sgr B phenomenology.

Tunnel magnetoresistance in fully epitaxial magnetic tunnel junctions with a full-Heusler alloy thin film of Co2Cr0.6Fe0.4Al and a MgO tunnel barrier

Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. Pseudo-spin-valve-type, fully epitaxial CCFA∕MgO∕Co50Fe50 MTJs with a CCFA film composition close to the stoichiometric one demonstrated high tunnel magnetoresistance (TMR) ratios of 90% at room temperature (RT) and 240% at 4.2K. These high TMR ratios were attributed to the increased spin polarization at the Fermi level due to the increased ratio of the B2 region to the A2 region in CCFA films achieved by bringing the CCFA film composition close to the stoichiometric one. Fully epitaxial CCFA∕MgO∕Co50Fe50 MTJs with exchange biasing were also fabricated, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50∕Ru∕Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10∕IrMn interface. These exchange-biased CCFA∕MgO∕Co50Fe50 MTJs exhibited further enhanced TMR ratios of 109% at RT and 317% at 4.2K. We suggested enhancement of the TMR ratio by a coherent tunneling contribution for fully epitaxial CCFA∕MgO∕Co50Fe50 MTJs.

Genetic Diversity Between Red Jungle Fowl and Domestic Chicken For BL B2 Region

Singh, A., Gupta, J., Churchil, R.R., Sharma, D. and Singh, R.V. 2007. Genetic diversity between red jungle fowl and domestic chicken for BL B2 region. J. Appl. Anim. Res., 31: 69–72. Genetic polymorphism in BL B2 gene between Red Jungle Fowl (RJF) and domesticated chicken through sequence homology comparisons was studied. A 277 bp amplicon representing second exon corresponding to β extra cellular domain of BL B2 gene was amplified using chicken specific primers and sequenced (Accession No DQ885564). Sequence homology comparisons of the 277 bp sequence of RJF showed that it had the maximum genetic similarity (93.3%) with BW1 haplotype of RJF. Among the chicken B haplotypes, B21 haplotype, irrespective of its genetic background i.e. either it is from White Leghorn or Thai native chicken, showed maximum sequence homology. Among chicken breeds, RJF showed more genetic similarity with Chinese and Korean native in comparison to Indian native chicken breed.

Thermodynamic properties of B2-AlFeNi Alloys. Part I: Investigation by knudsen effusion mass spectrometry

The vaporization of Al-Fe-Ni alloys has been investigated in the temperature range 1180 to 1508 K by Knudsen effusion mass spectrometry (KEMS). Fourteen different compositions were examined in the B2 region: 10 compositions at two fixed Al concentrations,x Al=0.45 andx Al=0.50 plus four extra compositions at constantx Ni/x Fe=1. For the first time, reliable partial pressures and thermodynamic activities of Al, Fe, and Ni have been evaluated from the measured ion intensities for both the alloy and the pure element. Gibbs energies, partial molar enthalpies, and entropies of formation for all the components have also been obtained. The relative partial molar enthalpies and entropies were found to be nearly temperature independent over the wide temperature ranges investigated. At 1400 K, the Gibbs energy of formation of Al0.50Fe0.25Ni0.25 and Al0.45Fe0.275Ni0.275, with Al(liq), Fe(fcc), and completely paramagnetic Ni(fcc,cpm) as reference states, are −37.9±0.42 kJ/mol and −38.1±0.42 kJ/mol, respectively. At the same temperature, the enthalpies of formation of Al0.50Fe0.25Ni0.25 and Al0.45Fe0.275Ni0.275, with the same reference states, are −51.5±1.7 kJ/mol and −49.2±1.7 kJ/mol, respectively.