Crystal structure and second harmonic generation in Bi₂TeO₅: An X-N study from synchrotron and neutron diffraction data

Ló,pez, C.A.,Bâ,ati, E.,Ferná,ndez-Dí,az, M.T.,Saouma, F.O.,Jang, J.I.,Alonso, J.A. Academic Press 2019 Journal of solid state chemistry Vol.276 No.-

<P><B>Abstract</B></P> <P>Bi<SUB>2</SUB>TeO<SUB>5</SUB> has been obtained in polycrystalline form via solid state reaction and structurally characterized from both synchrotron and neutron powder diffraction data, enabling the precise determination of the atomic positions. The crystal structure is defined in the acentric <I>Amb</I>2 space group, containing three crystallographically unequivalent Bi atoms. The position of the stereochemically active electron lone pairs of both Bi<SUP>3+</SUP> and Te<SUP>4+</SUP> ions is inferred to be opposite to the strongly covalent BiO and TeO chemical bonds; the global electron polarization arises from the non-compensated Bi<SUP>3+</SUP> lone electron pairs. Additionally, from difference Fourier maps between synchrotron and neutron diffraction data (X-N technique) it was possible to observe experimental evidence of the lone electron pair for Bi<SUP>3+</SUP>. Nonlinear optical measurements display highly active second harmonic generation response, comparable to that of reference AgGaSe<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The crystal structure is defined in the non-centrosymmetric <I>Amb</I>2 space group. </LI> <LI> Fourier maps between synchrotron and neutron diffraction data (X-N technique). </LI> <LI> Experimental evidence of Bi<SUP>3+</SUP>lone electron pair from X-N study. </LI> <LI> Nonlinear optical measurements display highly active SHG response. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

THE THICK DISK IN THE GALAXY NGC 4244 FROM S⁴G IMAGING

Comer&oacute,n, Sé,bastien,Knapen, Johan H.,Sheth, Kartik,Regan, Michael W.,Hinz, Joannah L.,Gil de Paz, Armando,Mené,ndez-Delmestre, Karí,n,Muñ,oz-Mateos, Juan-Carlos,Seibert, IOP Publishing 2011 The Astrophysical journal Vol.729 No.1

<P>If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G) we have identified signs of two disk components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244 can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous accretion after the formation of the galaxy.</P>

THE UNUSUAL VERTICAL MASS DISTRIBUTION OF NGC 4013 SEEN THROUGH THE <i>SPITZER</i> SURVEY OF STELLAR STRUCTURE IN GALAXIES (S ⁴ G)

Comer&oacute,n, Sé,bastien,Elmegreen, Bruce G.,Knapen, Johan H.,Sheth, Kartik,Hinz, Joannah L.,Regan, Michael W.,Gil de Paz, Armando,Muñ,oz-Mateos, Juan-Carlos,Mené,ndez-Delmestre, K IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.738 No.2

<P>NGC 4013 is a nearby Sb edge-on galaxy known for its 'prodigious' Hi warp and its 'giant' tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6 mu m images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scale height z(EC) similar to 3 kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains similar to 20% of the total mass of all three stellar components. We argue it is unlikely to be related to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in which the thick disk and the extended component were formed in a two-stage process, in which an initially thick disk has been dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it.</P>

KINEMATICS OF THE ENVELOPE AND TWO BIPOLAR JETS IN THE CLASS 0 PROTOSTELLAR SYSTEM L1157

Kwon, Woojin,Ferná,ndez-Ló,pez, Manuel,Stephens, Ian W.,Looney, Leslie W. IOP Publishing 2015 The Astrophysical journal Vol.814 No.1

<P>A massive envelope and a strong bipolar outflow are the two main structures characterizing the youngest protostellar systems. In order to understand the physical properties of a bipolar outflow and the relationship with those of the envelope, we obtained a mosaic map covering the whole bipolar outflow of the youngest protostellar system L1157 with about 5 '' angular resolution in CO J = 2-1 using the Combined Array for Research in Millimeter-wave Astronomy. By utilizing these observations of the whole bipolar outflow, we estimate its physical properties and show that they are consistent with multiple jets. We also constrain a preferred precession direction. In addition, we observed the central envelope structure with 2' resolution in the lambda = 1.3 and 3 mm continua and various molecular lines: (CO)-O-17, (CO)-O-18, (13)CO3 CS, CN, N2H+, CH3OH, H2O, SO, and SO2. All of the CO isotopes and CS, CN, and N2H+ have been detected and imaged. We marginally detected the features that can be interpreted as a rotating inner envelope in (CO)-O-17 and (CO)-O-18 and as an infalling outer envelope in N2H+. We also estimated the envelope and central protostellar masses and found that the dust-opacity spectral index changes with radius.</P>

CARMA LARGE AREA STAR FORMATION SURVEY: DENSE GAS IN THE YOUNG L1451 REGION OF PERSEUS

Storm, Shaye,Mundy, Lee G.,Lee, Katherine I.,Ferná,ndez-Ló,pez, Manuel,Looney, Leslie W.,Teuben, Peter,Arce, Hé,ctor G.,Rosolowsky, Erik W.,Meisner, Aaron M.,Isella, Andrea,Kauffmann American Astronomical Society 2016 The Astrophysical journal Vol.830 No.2

<P>We present a 3 mm spectral line and continuum survey of L1451 in the Perseus Molecular Cloud. These observations are from the CARMA Large Area Star Formation Survey (CLASSy), which also imaged Barnard. 1, NGC 1333, Serpens Main, and Serpens South. L1451 is the survey region with the lowest level of star formation activity-it contains no confirmed protostars. HCO+, HCN, and N2H+ (J = 1 -> 0). are all detected throughout the region, with HCO+ being the most spatially widespread, and molecular emission seen toward 90% of the area above N(H-2) column densities of 1.9 x 10(21) cm(-2). HCO+ has the broadest velocity dispersion, near 0.3 km s(-1) on average, compared with similar to 0.15 km s(-1) for the other molecules, thus representing a range of subsonic to supersonic gas motions. Our non-binary dendrogram analysis reveals that the dense gas traced by each molecule has a similar hierarchical structure, and that gas surrounding the candidate first hydrostatic core (FHSC), L1451-mm, and other previously detected single-dish continuum clumps has similar hierarchical structure; this suggests that different subregions of L1451 are fragmenting on the pathway to forming young stars. We determined that the three-dimensional morphology of the largest detectable dense-gas structures was relatively ellipsoidal compared with other CLASSy regions, which appeared more flattened at the largest scales. A virial analysis shows that the most centrally condensed dust structures are likely unstable against collapse. Additionally, we identify a new spherical, centrally condensed N2H+ feature that could be a new FHSC candidate. The overall results suggest that L1451 is a young region starting to form its generation of stars within turbulent, hierarchical structures.</P>

ALMA Observations of Polarized 872 <i>μ</i>m Dust Emission from the Protostellar Systems VLA 1623 and L1527

Harris, Robert J.,Cox, Erin G.,Looney, Leslie W.,Li, Zhi-Yun,Yang, Haifeng,Ferná,ndez-Ló,pez, Manuel,Kwon, Woojin,Sadavoy, Sarah,Segura-Cox, Dominique,Stephens, Ian,Tobin, John American Astronomical Society 2018 The Astrophysical journal Vol.861 No.2

<P>We present high-sensitivity (sigma(I) similar to 0.2-0.5 mJy, sigma(QU) similar to 0.05 mJy), high-resolution (similar to 0.'' 12-0.'' 2) observations of polarized 872 mu m dust emission from the young multiple system VLA 1623 in rho Ophiuchus and the protostar L1527 in Taurus. We detect the circumstellar material of VLA 1623A, the extended Keplerian disk surrounding VLA 1623A that we call VLA 1623CBdisk, VLA 1623B, VLA 1623W, and L1527 strongly in the polarized emission, at the similar to 1%-3% level. We spatially resolve VLA 1623A into two sources, VLA 1623Aa and VLA 1623Ab, separated by similar to 30 au and located within a cavity of radius similar to 50 au within the circumbinary Keplerian disk, as well as the edge-on disk of VLA 1623W. The polarization angle of the emission is uniform across each protostellar source and nearly coincides with each disk's minor axis. The offsets between the minor axis position angle and the polarization angle are not uniformly distributed at the P less than or similar to 2 x 10(-4) level. The circumbinary disk surrounding VLA 1623Aab is azimuthally symmetrically polarized. Each compact source's emission is partially optically thick (tau greater than or similar to 1) at 872 mu m, complicating interpretations of polarization involving aligned grains. We find evidence against alignment by radiative flux in each source, particularly in the edge-on VLA 1623W and L1527. We detect astrometric offsets between the polarized emission and the total intensity in VLA 1623Aa, VLA 1623Ab, and VLA 1623B, as predicted if self-scattering in the optically thick limit operates. We conclude that self-scattering is likely responsible for disk-scale polarization at 872 mu m in these systems.</P>

C₆₀ dimers connected through pleiadene bridges: fullerenes talking to each other

Sastre-Santos, Á,ngela,Parejo, Concepci&oacute,n,Martí,n-Gomis, Luis,Ohkubo, Kei,Ferná,ndez-Lá,zaro, Fernando,Fukuzumi, Shunichi Royal Society of Chemistry 2011 Journal of materials chemistry Vol.21 No.5

<P>New C<SUB>60</SUB> dimers 1, 2 and 3 that differ in the distance between the two balls, connected through pleiadene bridges have been synthesized. Different synthetic strategies have been used to prepare C<SUB>60</SUB> dimers 1–3. A diastereoisomeric mixture was obtained for C<SUB>60</SUB> dimer 1, which was separated by column chromatography and characterized by NMR. By CV measurements, no interaction between the two balls was found in the ground state in any type of C<SUB>60</SUB> dimer. By reduction with dimeric benzylnicotinamide [(BNA)<SUB>2</SUB>], a two electron reductant, the interaction between both C<SUB>60</SUB> units has been analyzed using electron paramagnetic resonance (EPR). For C<SUB>60</SUB> dimer 3, upon addition of 1 equivalent (BNA)<SUB>2</SUB> no electronic interaction in the C<SUB>60</SUB>˙<SUP>−</SUP>–C<SUB>60</SUB>˙<SUP>−</SUP> was observed due to the long distance between the C<SUB>60</SUB> balls (20 Å). However, for C<SUB>60</SUB> dimer 1, where the distance between radicals is shorter, 10 Å, the electronic interaction in the di(radical anion), C<SUB>60</SUB>˙<SUP>−</SUP>–C<SUB>60</SUB>˙<SUP>−</SUP> in the presence of 1 equivalent of (BNA)<SUB>2</SUB> was observed by EPR, corresponding to a triplet biradical.</P> <P>Graphic Abstract</P><P>Addition of 1 equivalent of (BNA)<SUB>2</SUB> to dimer 1 yields the C<SUB>60</SUB>˙<SUP>−</SUP>–C<SUB>60</SUB>˙<SUP>−</SUP> triplet biradical where electronic interaction is observed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0jm02635b'> </P>

Electrically controlled nuclear polarization of individual atoms

Yang, Kai,Willke, Philip,Bae, Yujeong,Ferr&oacute,n, Alejandro,Lado, Jose L.,Ardavan, Arzhang,Ferná,ndez-Rossier, Joaquí,n,Heinrich, Andreas J.,Lutz, Christopher P. Nature Publishing Group 2018 Nature nanotechnology Vol.13 No.12

The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign

Baran, A.,Oreiro, R.,Pigulski, A.,Herná,ndez, F. Pé,rez,Ulla, A.,Reed, M. D.,Rodrí,guez-Ló,pez, C.,Moskalik, P.,Kim, S.-L.,Chen, W.-P.,Crowe, R.,Siwak, M.,Armendarez, L.,Binder Blackwell Publishing Ltd 2009 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.392 No.3

<P>ABSTRACT</P><P>We present the results of a multisite photometric campaign on the pulsating B-type hot subdwarf star Balloon 090100001 (Bal09). The star is one of the two known hybrid hot subdwarfs with both long- and short-period oscillations, theoretically attributed to <I>g</I> and <I>p</I> modes. The campaign involved eight telescopes with three obtaining <I>UBVR</I> data, four <I>B</I>-band data and one Strömgren <I>uvby</I> photometry. The campaign covered 48 nights, providing a temporal resolution of 0.36 μHz with a detection threshold of about 0.2 mmag in <I>B</I>-filter data.</P><P>Bal09 has the richest pulsation spectrum of any known pulsating subdwarf B star, and our analysis detected 114 frequencies including 97 independent and 17 combination ones. Most of the 24 <I>g</I>-mode frequencies are between 0.1 and 0.4 mHz. Of the remaining 73, presumably <I>p</I> modes, 72 group into four distinct regions near 2.8, 3.8, 4.7 and 5.5 mHz. The density of frequencies requires that some modes must have degrees ℓ larger than 2. The modes in the 2.8 mHz region have the largest amplitudes. The strongest mode (<I>f</I><SUB>1</SUB>) is most likely radial, while the remaining ones in this region form two nearly symmetric multiplets: a triplet and quintuplet, attributed to rotationally split ℓ= 1 and 2 modes, respectively. We find clear increases of splitting in both multiplets between the 2004 and 2005 observing campaigns, amounting to ∼15 per cent on average. The observed splittings imply that the rotational rate in Bal09 depends on stellar latitude and is the fastest on the equator. We also speculate on the possible reasons for the changes of splitting. The only plausible explanation we find is torsional oscillation. This hypothesis, however, needs to be verified in the future by detailed modelling. In this context, it is very important to monitor the splittings on a longer time-scale as their behaviour may help to explain this interesting phenomenon.</P><P>The amplitudes of almost all terms detected in both 2004 and 2005 were found to vary. This is evident even during one season; for example, amplitudes of modes <I>f</I><SUB>8</SUB> and <I>f</I><SUB>C</SUB> were found to change by a factor of 2–3 within about 50 d during 2005.</P><P>We use a small grid of models to constrain the main mode (<I>f</I><SUB>1</SUB>), which most likely represents the radial fundamental pulsation. The groups of <I>p</I>-mode frequencies appear to lie in the vicinity of the consecutive radial overtones, up to the third one. Despite the large number of <I>g</I>-mode frequencies observed, we failed to identify them, most likely because of the disruption of asymptotic behaviour by mode trapping. The observed frequencies were not, however, fully exploited in terms of seismic analysis which should be done in the future with a larger grid of reliable evolutionary models of hot subdwarfs.</P>

ALMA Reveals Transition of Polarization Pattern with Wavelength in HL Tau’s Disk

Stephens, Ian W.,Yang, Haifeng,Li, Zhi-Yun,Looney, Leslie W.,Kataoka, Akimasa,Kwon, Woojin,Ferná,ndez-Ló,pez, Manuel,Hull, Charles L. H.,Hughes, Meredith,Segura-Cox, Dominique,Mundy, Lee,C American Astronomical Society 2017 The Astrophysical journal Vol.851 No.1

<P>The mechanism for producing polarized emission from protostellar disks at (sub) millimeter wavelengths is currently uncertain. Classically, polarization is expected from non-spherical grains aligned with the magnetic field. Recently, two alternatives have been suggested. One polarization mechanism is caused by self-scattering from dust grains of sizes comparable with the wavelength, while the other mechanism is due to grains aligned with their short axes along the direction of radiation anisotropy. The latter has recently been shown as a likely mechanism for causing the dust polarization detected in HL. Tau at 3.1 mm. In this paper, we present ALMA polarization observations of HL. Tau for two more wavelengths: 870 mu m and 1.3 mm. The morphology at 870 mu m matches the expectation for self-scattering, while that at 1.3 mm shows a mix between self-scattering and grains aligned with the radiation anisotropy. The observations cast doubt on the ability of (sub) millimeter continuum polarization to probe disk magnetic fields for at least HL Tau. By showing two distinct polarization morphologies at 870 mu m and 3.1 mm and a transition between the two at 1.3 mm, this paper provides definitive evidence that the dominant (sub) millimeter polarization mechanism transitions with wavelength. In addition, if the polarization at 870 mu m is due to scattering, the lack of polarization asymmetry along the minor axis of the inclined disk implies that the large grains responsible for the scattering have already settled into a geometrically thin layer, and the presence of asymmetry along the major axis indicates that the HL Tau disk is not completely axisymmetric.</P>