VLA observations of hydrogen and carbon recombination lines toward W3A at 1.4 GHz

We present high-sensitivity, high-resolution VLA observations of the W3 complex of H II regions in the 168α recombination lines of hydrogen, carbon, and sulphur. The H 168α line from W3A consists of two components: a broad line (width ~27 km s-1) and a narrow line (width ~7 km s-1). The narrow hydrogen and carbon line emissions over W3A, although overlapping, are not entirely coextensive. The carbon line is possibly correlated with the molecular gas near W3A. Stimulated emission is the main mechanism for the narrow hydrogen line emission. The width of the H0 line gives an upper limit of ~1000 K for the electron temperature of the partially ionized gas. The electron density ranges from 10 to 80 cm-3 in the narrow hydrogen line region and from 10 to 60 cm-3 in the carbon-line region. We determined the electron temperature of the classical H II region W3A from the continuum brightness to be ~9000 K. The rms ne of this H II region is ~2200 cm-3, and the true ne, determined from a pressure-broadened profile of the H 171η (8.6 GHz) line, is ~2 × 104 cm-3. Using these two values of electron densities, we determine a lower limit to the filling factor (0.01). Such a low value can be interpreted as an effect of density inhomogeneities in the medium

VLA observations of carbon 91α recombination line emission in W49 north

We have detected C91α (8.5891 GHz) emission toward four ultracompact H II regions (UCHs; W49G, J, L, and C) in the W49 North massive star-forming region with the Very Large Array (VLA) at 3" resolution. No carbon line emission was detected toward UCHs W49F, A, O, S, and Q at this frequency to a 3 σ level of 2 mJy. We also observed the same region in the C75α line (15.3 GHz) with no detection at a 3 σ level of 6 mJy with a 1".7 beam. Detection of line emission toward these sources add supporting data to the 2005 result of Roshi et al. that many UCHs have an associated photodissociation region (PDR). The similarity of the LSR velocities of carbon recombination lines and H2CO absorption toward UCHs in W49 North suggests that the PDRs reside in the dense interface zone surrounding these H II regions. Combining the observed carbon line parameters at 8.6 GHz with the upper limits on line emission at 15.3 GHz, we obtain constraints on the physical properties of the PDRs associated with W49G and J. The upper limit on the number density of hydrogen molecule obtained from carbon line models is ~5 × 106 cm-3

Carbon Recombination Lines from the Galactic Plane at 34.5 & 328 MHz

We present results of a search for carbon recombination lines in the Galaxy at 34.5 MHz (C$575\alpha$) made using the dipole array at Gauribidanur near Bangalore. Observations made towards 32 directions, led to detections of lines in absorption at nine positions. Followup observations at 328 MHz (C$272\alpha$) using the Ooty Radio Telescope detected these lines in emission. A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10' for the angular size of the line forming region. The longitude-velocity distribution of the observed carbon lines indicate that the line forming region are located mainly between 4 kpc and 7 kpc from the Galactic centre. Combining our results with published carbon recombination line data near 76 MHz (\nocite{erickson:95} Erickson \et 1995) we obtain constraints on the physical parameters of the line forming regions. We find that if the angular size of the line forming regions is $\ge 4^{\circ}$, then the range of parameters that fit the data are: \Te $= 20-40$ K, \ne $\sim 0.1-0.3$ \cm3 and pathlengths $\sim 0.07-0.9$ pc which may correspond to thin photo-dissociated regions around molecular clouds. On the other hand, if the line forming regions are $\sim 2^{\circ}$ in extent, then warmer gas (\Te $\sim 60-300$ K) with lower electron densities (\ne $\sim 0.03-0.05$ \cm3) extending over several tens of parsecs along the line of sight and possibly associated with atomic \HI gas can fit the data. Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation regions.Comment: To appear in Journal of Astrophysics & Astronomy, March 200

Cytochromeâ P450â Induced Ordering of Microsomal Membranes Modulates Affinity for Drugs

Although membrane environment is known to boost drug metabolism by mammalian cytochromeâ P450s, the factors that stabilize the structural folding and enhance protein function are unclear. In this study, we use peptideâ based lipid nanodiscs to â trapâ the lipid boundaries of microsomal cytochromeâ P450 2B4. We report the first evidence that CYP2B4 is able to induce the formation of raft domains in a biomimetic compound of the endoplasmic reticulum. NMR experiments were used to identify and quantitatively determine the lipids present in nanodiscs. A combination of biophysical experiments and molecular dynamics simulations revealed a sphingomyelin binding region in CYP2B4. The proteinâ induced lipid raft formation increased the thermal stability of P450 and dramatically altered ligand binding kinetics of the hydrophilic ligand BHT. These results unveil membrane/protein dynamics that contribute to the delicate mechanism of redox catalysis in lipid membrane.Redox catalysis in the lipid membrane: A novel application of peptide nanodiscs shows that cytochromeâ P450 2B4 is able to induce the formation of lipid raft domains in a biomimetic compound of the endoplasmic reticulum (ER). The proteinâ induced lipid rafts increase the thermal stability cytochromeâ P450 and dramatically alter the ligandâ binding kinetics of the hydrophilic ligand BHT.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142960/1/anie201713167.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142960/2/anie201713167_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142960/3/anie201713167-sup-0001-misc_information.pd

A Minimal Functional Complex of Cytochrome P450 and FBD of Cytochrome P450 Reductase in Nanodiscs

Structural interactions that enable electron transfer to cytochromeâ P450 (CYP450) from its redox partner CYP450â reductase (CPR) are a vital prerequisite for its catalytic mechanism. The first structural model for the membraneâ bound functional complex to reveal interactions between the fullâ length CYP450 and a minimal domain of CPR is now reported. The results suggest that anchorage of the proteins in a lipid bilayer is a minimal requirement for CYP450 catalytic function. Akin to cytochromeâ b5 (cytâ b5), Argâ 125 on the Câ helix of CYP450s is found to be important for effective electron transfer, thus supporting the competitive behavior of redox partners for CYP450s. A general approach is presented to study proteinâ protein interactions combining the use of nanodiscs with NMR spectroscopy and SAXS. Linking structural details to the mechanism will help unravel the xenobiotic metabolism of diverse microsomal CYP450s in their native environment and facilitate the design of new drug entities.Solving a structure of the cytochrome P450 (CYP450) complex with its redox partner is a vital prerequisite to understand the selective route of electron transfer. Structural interactions of CYP450â redox partner complex anchored in lipid membrane are a minimal requirement for functionality (electron transfer). This study unravels the drug/xenobiotic metabolism by diverse microsomal CYPs in their native membrane environment.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144586/1/anie201802210.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144586/2/anie201802210_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144586/3/anie201802210-sup-0001-misc_information.pd

Anomalous Radio-Wave Scattering from Interstellar Plasma Structures

This paper considers scattering screens that have arbitrary spatial variations of scattering strength transverse to the line of sight, including screens that are spatially well confined, such as disks and filaments. We calculate the scattered image of a point source and the observed pulse shape of a scattered impulse. The consequences of screen confinement include: (1) Source image shapes that are determined by the physical extent of the screen rather than by the shapes of much-smaller diffracting microirregularities. These include image elongations and orientations that are frequency dependent. (2) Variation with frequency of angular broadening that is much weaker than the trademark \nu^{-2} scaling law (for a cold, unmagnetized plasma), including frequency-independent cases; and (3) Similar departure of the pulse broadening time from the usually expected \nu^{-4} scaling law. We briefly discuss applications that include scattering of pulses from the Crab pulsar by filaments in the Crab Nebula; image asymmetries from Galactic scattering of the sources Cyg X-3, Sgr A*, and NGC 6334B; and scattering of background active galactic nuclei by intervening galaxies. We also address the consequences for inferences about the shape of the wavenumber spectrum of electron density irregularities, which depend on scaling laws for the image size and the pulse broadening. Future low-frequency (< 100 MHz) array observations will also be strongly affected by the Galactic structure of scattering material. Our formalism is derived in the context of radio scattering by plasma density fluctuations. It is also applicable to optical, UV and X-ray scattering by grains in the interstellar medium.Comment: 21 pages, LaTeX2e with AASTeX-4.0, 6 PostScript figures, accepted by ApJ, revised version has minor changes to respond to referee comments and suggestion

Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center

The scattering diameters of Sgr A* and several nearby OH masers (~ 1" at 1 GHz) indicate that a region of enhanced scattering is along the line of sight to the Galactic center. We combine radio-wave scattering data and free-free emission and absorption measurements in a likelihood analysis that constrains the following parameters of the GC scattering region: The GC-scattering region separation, d; the angular extent of the region, \psi_l; the outer scale on which density fluctuations occur, l_0; and the gas temperature, T. The maximum likelihood estimates of these parameters are d = 133_{-80}^{+200} pc, 0.5 degrees <= \psi_l <~ 1 degrees, and (l_0/1 pc)^{2/3}T^{-1/2} = 10^{-7 +/- 0.8}. As host media for the scattering, we consider the photoionized surface layers of molecular clouds and the interfaces between molecular clouds and the 10^7 K ambient gas. We are unable to make an unambiguous determination, but we favor an interface model in which the scattering medium is hot (T ~ 10^6 K) and dense (n_e ~ 10 cm^{-3}). The GC scattering region produces a 1 GHz scattering diameter for an extragalactic source of 90", if the region is a single screen, or 180", if the region wraps around the GC, as appears probable. We modify the Taylor-Cordes model for the Galactic distribution of free electrons in order to include an explicit GC component. Pulsars seen through this region will have a dispersion measure of approximately 2000 pc cm^{-3}, of which 75% arises from the GC component. We stress the uniqueness of the GC scattering region, probably resulting from the high-pressure environment in the GC.Comment: 39 pages with 9 PostScript figures; LaTeX2e with AASTeX macro aaspp4, to be published in Ap

Finding Radio Pulsars in and Beyond the Galactic Center

Radio-wave scattering is enhanced dramatically for Galactic center sources in a region with radius >~ 15 arc min. Using scattering from Sgr A* and other sources, we show that pulse broadening for pulsars in the Galactic center is {\em at least} 6.3 \nu^{-4} seconds (\nu = radio frequency in GHz) and is most likely 50--200 times larger because the relevant scattering screen appears to be within the Galactic center region itself. Pulsars beyond---but viewed through---the Galactic center suffer even greater pulse broadening and are angularly broadened by <~ 2 {\em arc min}. Periodicity searches at radio frequencies are likely to find only long period pulsars and, then, only if optimized by using frequencies >~ 7 GHz and by testing for small numbers of harmonics in the power spectrum. The optimal frequency is $\nu ~ 7.3 GHz (\Delta_{0.1}P\sqrt{\alpha})^{-1/4}$ where \Delta_{0.1} is the distance of the scattering region from Sgr A* in units of 0.1 kpc, P is the period (seconds), and \alpha is the spectral index. A search for compact sources using aperture synthesis may be far more successful than searches for periodicities because the angular broadening is not so large as to desensitize the survey. We estimate that the number of {\em detectable} pulsars in the Galactic center may range from <= 1 to 100, with the larger values resulting from recent, vigorous starbursts. Such pulsars provide unique opportunities for probing the ionized gas, gravitational potential, and stellar population near Sgr A*.Comment: 13 pages, 4 PS figures, LaTeX and requires AASTeX macro aas2pp4, accepted by ApJ, also available as http://astrosun.tn.cornell.edu/SPIGOT/papers/pulsar/gc_psr.web

High-Resolution, Wide-Field Imaging of the Galactic Center Region at 330 MHz

We present a wide field, sub-arcminute resolution VLA image of the Galactic Center region at 330 MHz. With a resolution of ~ 7" X 12" and an RMS noise of 1.6 mJy/beam, this image represents a significant increase in resolution and sensitivity over the previously published VLA image at this frequency. The improved sensitivity has more than tripled the census of small diameter sources in the region, has resulted in the detection of two new Non Thermal Filaments (NTFs), 18 NTF candidates, 30 pulsar candidates, reveals previously known extended sources in greater detail, and has resulted in the first detection of Sagittarius A* in this frequency range. A version of this paper containing full resolution images may be found at http://lwa.nrl.navy.mil/nord/AAAB.pdf.Comment: Astronomical Journal, Accepted 62 Pages, 21 Figure