arXiv subjects

D. Miller

Publications and source records attributed to D. Miller.

At least 19 recordsLinked to original sources

arXiv2023

Near-Infrared Observations of Outflows and YSOs in the Massive Star-Forming Region AFGL 5180

Methods: Broad- and narrow-band imaging of AFGL 5180 was made in the NIR with the LBT, in both seeing-limited ($\sim0.5\arcsec$) and high angular resolution ($\sim0.09\arcsec$) Adaptive Optics (AO) modes, as well as with HST. Archival ALMA continuum data was also utilized. Results: At least 40 jet knots were identified via NIR emission from H$_2$ and [FeII] tracing shocked gas. Bright jet knots outflowing from the central most massive protostar, S4, are detected towards the east of the source and are resolved in fine detail with the AO imaging. Additional knots are distributed throughout the field, likely indicating the presence of multiple driving sources. Sub-millimeter sources detected by ALMA are shown to be grouped in two main complexes, AFGL 5180 M and a small cluster $\sim15\arcsec$ to the south, AFGL 5180 S. From our NIR continuum images we identify YSO candidates down to masses of $\sim 0.1\:M_\odot$. Combined with the sub-mm sources, this yields a surface number density of such YSOs of $N_* \sim 10^3 {\rm pc}^{-2}$ within a projected radius of about 0.1 pc. Such a value is similar to those predicted by models of both Core Accretion from a turbulent clump environment and Competitive Accretion. The radial profile of $N_*$ is relatively flat on scales out to 0.2~pc, with only modest enhancement around the massive protostar inside 0.05~pc. Conclusions: This study demonstrates the utility of high-resolution NIR imaging, in particular with AO, for detecting outflow activity and YSOs in distant regions. The presented images reveal the complex morphology of outflow-shocked gas within the large-scale bipolar flow of a massive protostar, as well as clear evidence for several other outflow driving sources in the region. Finally, this work presents a novel approach to compare the observed YSO surface number density from our study against different models of massive star formation.

astro-ph.SR↗

arXiv2023

The SOUL view of IRAS20126+4104. Kinematics and variability of the H$_2$ jet from a massive protostar

We exploit the increased sensitivity of the recently installed AO SOUL at the LBT to obtain new high-spatial-resolution NIR images of the massive young stellar object IRAS20126+4104 and its outflow. We aim to derive the jet proper motions and kinematics, as well as to study its photometric variability by combining the novel performances of SOUL together with previous NIR images. We used both broad-band ($K_{s}$, $K'$) and narrow-band (Br$\gamma$, H2) observations from a number of NIR cameras (UKIRT/UFTI,SUBARU/CIAO,TNG/NICS,LBT/PISCES,and LBT/LUCI1) to derive maps of the continuum and the H$_2$ emission in the 2.12 $\mu$m line. Three sets of images, obtained with AO systems (CIAO,2003; FLAO,2012; SOUL,2020), allowed us to derive the proper motions of a large number of H$_2$ knots along the jet. Photometry from all images was used to study the jet variability. We derived knot proper motions in the range of 1.7-20.3 mas yr$^{-1}$ (i.e. 13-158 km s$^{-1}$ at 1.64 kpc, avg. outflow tangential velocity $\sim$ 80 km s$^{-1}$). The derived knot dynamical age spans a $\sim$ 200-4000 yr interval. A ring-like H$_2$ feature near the protostar location exhibits peculiar kinematics and may represent the outcome of a wide-angle wind impinging on the outflow cavity. Both H$_2$ geometry and velocities agree with those inferred from proper motions of the H$_2$O masers, located at a smaller distance from the protostar. Although the total H$_2$ line emission from the knots does not exhibit time variations at a $\widetilde{>}$ 0.3 mag level, we have found a clear continuum flux variation (radiation scattered by the dust in the cavity opened by the jet) which is anti-correlated between the blue-shifted and red-shifted lobes and may be periodic (with a period of $\sim$ 12-18 yr). We suggest that the continuum variability might be related to inner-disc oscillations which have also caused the jet precession.

astro-ph.SR↗

arXiv2020

Spectroscopic study of $^{47}$Ca from the $\beta^-$ decay of $^{47}$K

The $\beta^-$ decay of $^{47}$K to $^{47}$Ca is an appropriate mechanism for benchmarking interactions spanning the $sd$ and $pf$ shells, but current knowledge of the $\beta^-$-decay scheme is limited. We have performed a high-resolution, high-efficiency study of the $\beta^-$-decay of $^{47}$K with the GRIFFIN spectrometer at TRIUMF-ISAC. The study revealed 48 new transitions, a more precise value for the $^{47}$K half-life (17.38(3)~s), and new spin and parity assignments for eight excited states. Levels placed for the first time here raise the highest state observed in $\beta^-$ decay to within 568(3) keV of the $Q$-value and confirm the previously measured large $\beta^-$-decay branching ratios to the low-lying states. Previously unobserved $\beta^-$-feeding to 3/2$^+$ states between 4.5 and 6.1~MeV excitation energy was identified with a total $\beta^-$-feeding intensity of 1.29(2)\%. The sum of the $B(GT)$ values for these states indicates that the $1s_{1/2}$ proton hole strength near this excitation energy is comparable to the previously known $1s_{1/2}$ proton and neutron hole strengths near 2.6 MeV.

nucl-ex↗

arXiv2020

Single-particle structure in neutron-rich Sr isotopes approaching the N = 60 shape transition

Background: Neutron-rich nuclei around neutron number N = 60 show a dramatic shape transition from spherical ground states to prolate deformation in 98Sr and heavier nuclei. Purpose: The purpose of this study is to investigate the single-particle structure approaching the shape transitional region. Method: The level structures of neutron-rich 93,94,95Sr were studied via the d(94,95,96Sr,t) one-neutron stripping reactions at TRIUMF using a beam energy of 5.5 AMeV. {\gamma}-rays emitted from excited states and recoiling charged particles were detected by using the TIGRESS and SHARC arrays, respectively. States were identified by gating on the excitation energy and, if possible, the coincident {\gamma} radiation. Results: Triton angular distributions for the reactions populating states in ejectile nuclei 93,94,95Sr were compared with distorted wave Born approximation calculations to assign and revise spin and parity quantum numbers and extract spectroscopic factors. The results were compared with shell model calculations and the reverse (d,p) reactions and good agreement was obtained. Conclusions: The results for the d(94Sr,t)93Sr and d(95Sr,t)94Sr reactions are in good agreement with shell model calculations. A two level mixing analysis for the 0+ states in 94Sr suggest strong mixing of two shapes. For the d(96Sr,t)95Sr reaction the agreement with the shell model is less good. The configuration of the ground state of 96Sr is already more complex than predicted, and therefore indications for the shape transition can already be observed before N = 60.

nucl-ex↗

arXiv2020

First candidates for {\gamma} vibrational bands built on the [505]11/2- neutron orbital in odd-A Dy isotopes

Rotational structures have been measured using the Jurogam II and GAMMASPHERE arrays at low spin following the 155Gd({\alpha},2n)157Dy and 148Nd(12C, 5n)155Dy reactions at 25 and 65 MeV, respectively. We report high-K bands, which are conjectured to be the first candidates of a K{\pi}= 2+ {\gamma} vibrational band, built on the [505]11/2- neutron orbital, in both odd-A 155, 157Dy isotopes. The coupling of the first excited K=0+ states or the so-called \b{eta} vibrational bands at 661 and 676 keV in 154Dy and 156Dy to the [505]11/2- orbital, to produce a K{\pi}=11/2- band, was not observed in both 155Dy and 157Dy, respectively. The implication of these findings on the interpretation of the first excited 0+ states in the core nuclei 154Dy and 156Dy are also discussed.

nucl-ex↗

arXiv2020

Observation of $\gamma$-vibrations and alignments built on non-ground-state configurations in 156Dy

The exact nature of the lowest $K^\pi =2_\gamma ^+$ rotational bands in all deformed nuclei remains obscure. Traditionally they are assumed to be collective vibrations of the nuclear shape in the $\gamma$ degree of freedom perpendicular to the nuclear symmetry axis. Very few such $\gamma$-bands have been traced past the usual back-bending rotational alignments of high-j nucleons. We have investigated the structure of positive-parity bands in the N=90 nucleus 156Dy, using the 148Nd(12C,4n)156Dy reaction at 65 MeV, observing the resulting ${\gamma}$-ray transitions with the Gammasphere array. The even- and odd-spin members of the $K^\pi =2_\gamma^+$ $\gamma$-band are observed to 32+ and 31+ respectively. This rotational band faithfully tracks the ground-state configuration to the highest spins. The members of a possible $\gamma$-vibration built on the aligned yrast S-band are observed to spins 28+ and 27+. An even-spin positive-parity band, observed to spin 24+, is a candidate for an aligned S-band built on the seniority-zero configuration of the $0_2^+$ state at 676 keV. The crossing of this band with the $0_2^+$ band is at $\hbar\omega$= 0.28(1) MeV and is consistent with the configuration of the $0_2^+$ band not producing any blocking of the monopole pairing.

nucl-ex↗

arXiv2019

Detailed spectroscopy of $^{46}$Ca: A study of the $\beta^-$ decay of $^{46}$K

We report on high-statistics data from the $\beta^-$ decay of the $^{46}$K $J^{\pi}$ = 2$^-$ ground state taken with the GRIFFIN spectrometer located at the TRIUMF-ISAC facility. In total, 199 $\gamma$ rays and 42 excited states were placed in the level scheme, and from the observed $\beta$ feeding and angular correlations of pairs of cascading $\gamma$ rays, it was possible to assign spins and parities to excited states and determine mixing ratios for selected $\gamma$ rays. The level structure of $^{46}$Ca is compared to theoretical predictions from a microscopic valence-space Hamiltonian derived from two- (NN) and three-nucleon (3N) forces. These calculations are in reasonable agreement with the experimental data and indicate that the protons in this region are not as inert as would be expected for semi-magic nuclei.

nucl-ex↗

arXiv2019

Single-Particle Structure of Neutron-Rich Sr Isotopes Via d( 94,95,96 Sr, p) Reactions

The region around neutron number N = 60 in the neutron-rich Sr and Zr nuclei is one of the most dramatic examples of a ground state shape transition from (near) spherical below N = 60 to strongly deformed shapes in the heavier isotopes. The single-particle structure of 95-97Sr approaching the ground state shape transition at 98 Sr has been investigated via single-neutron transfer reactions using the (d, p) reaction in inverse kinematics. These reactions selectively populate states with a large overlap of the projectile ground state coupled to a neutron in a single-particle orbital. Radioactive 94,95,96Sr nuclei with energies of 5.5 AMeV were used to bombard a CD 2 target. Recoiling light charged particles and {\gamma} rays were detected using a quasi-4{\pi} silicon strip detector array and a 12 element Ge array. The excitation energy of states populated was reconstructed employing the missing mass method combined with {\gamma}-ray tagging and differential cross sections for final states were extracted. A reaction model analysis of the angular distributions allowed for firm spin assignments to be made for the low-lying 352, 556 and 681 keV excited states in 95Sr and a constraint has been placed on the spin of the higher-lying 1666 keV state. Angular distributions have been extracted for 10 states populated in the d(95Sr,p)96Sr reaction, and constraints have been provided for the spins and parities of several final states. Results are compared to shell model calculations in several model spaces and the structure of low-lying states in 94Sr and 95Sr is well-described. The spectroscopic strength of the 0+ and 2 states in 96Sr is significantly more fragmented than predicted.

nucl-ex↗

arXiv2019

3C 294 revisited: Deep Large Binocular Telescope AO NIR images and optical spectroscopy

Context. High redshift radio galaxies are among the most massive galaxies at their redshift, are often found at the center of protoclusters of galaxies, and are expected to evolve into the present day massive central cluster galaxies. Thus they are a useful tool to explore structure formation in the young Universe. Aims. 3C~294 is a powerful FR II type radio galaxy at z = 1.786. Past studies have identified a clumpy structure, possibly indicative of a merging system, as well as tentative evidence that 3C~294 hosts a dual active galactic nucleus (AGN). Due to its proximity to a bright star, it has been subject to various adaptive optics imaging studies. Method. In order to distinguish between the various scenarios for 3C~294 we performed deep, high-resolution adaptive optics near-infrared imaging and optical spectroscopy of 3C~294 with the Large Binocular Telescope. Results. We resolve the 3C~294 system into three distinct components separated by a few tenths of an arcsecond on our images. One is compact, the other two are extended, and all appear to be non-stellar. The nature of each component is unclear. The two extended components could be a galaxy with an internal absorption feature, a galaxy merger, or two galaxies at different redshifts. We can now uniquely associate the radio source of 3C~294 with one of the extended components. Based on our spectroscopy, we determined a redshift of z = 1.784+-0.001, which is similar to the one previously cited. In addition we found a previously unreported emission line at $\lambda$6749.4 \AA\ in our spectra. It is not clear that it originates from 3C~294. It could be the Ne [IV] doublet lambda 2424/2426 AA at z = 1.783, or belong to the compact component at a redshift of z ~ 4.56. We thus cannot unambiguously determine whether 3C~294 hosts a dual AGN or a projected pair of AGNs.

astro-ph.GA↗

arXiv2018

The GRIFFIN Facility for Decay-Spectroscopy Studies at TRIUMF-ISAC

Gamma-Ray Infrastructure For Fundamental Investigations of Nuclei, GRIFFIN, is a new high-efficiency $\gamma$-ray spectrometer designed for use in decay spectroscopy experiments with low-energy radioactive ion beams provided by TRIUMF's Isotope Separator and Accelerator (ISAC-I) facility. GRIFFIN is composed of sixteen Compton-suppressed large-volume clover-type high-purity germanium (HPGe) $\gamma$-ray detectors combined with a suite of ancillary detection systems and coupled to a custom digital data acquisition system. The infrastructure and detectors of the spectrometer as well as the performance characteristics and the analysis techniques applied to the experimental data are described.

physics.ins-det↗

arXiv2018

Shape Coexistence and Mixing of Low-Lying $0^+$ States in $^{96}$Sr

The low energy excited $0_{2,3}^+$ states in $^{96}$Sr are amongst the most prominent examples of shape coexistence across the nuclear landscape. In this work, the neutron $[2s_{1/2}]^2$ content of the $0_{1,2,3}^+$ states in $^{96}$Sr was determined by means of the d($^{95}$Sr,p) transfer reaction at the TRIUMF-ISAC2 facility using the SHARC and TIGRESS arrays. Spectroscopic factors of 0.19(3) and 0.22(3) were extracted for the $^{96}$Sr ground and 1229~keV $0^+$ states, respectively, by fitting the experimental angular distributions to DWBA reaction model calculations. A detailed analysis of the $\gamma$-decay of the isomeric $0_3^+$ state was used to determine a spectroscopic factor of 0.33(13). The experimental results are compared to shell model calculations, which predict negligible spectroscopic strength for the excited $0^+$ states in $^{96}$Sr. The strengths of the excited $0_{2,3}^+$ states were also analyzed within a two-level mixing model and are consistent with a mixing strength of $a^2$=0.40(14) and a difference in intrinsic deformations of $|\Delta \beta|=0.31(3)$. These results suggest coexistence of three different configurations in $^{96}$Sr and strong shape mixing of the two excited $0^+$ states.

nucl-ex↗

arXiv2017

The nuclear force imprints revealed on the elastic scattering of protons with $^{10}$C

How does nature hold together protons and neutrons to form the wide variety of complex nuclei in the universe? Describing many-nucleon systems from the fundamental theory of quantum chromodynamics has been the greatest challenge in answering this question. The chiral effective field theory description of the nuclear force now makes this possible but requires certain parameters that are not uniquely determined. Defining the nuclear force needs identification of observables sensitive to the different parametrizations. From a measurement of proton elastic scattering on $^{10}$C at TRIUMF and ab initio nuclear reaction calculations we show that the shape and magnitude of the measured differential cross section is strongly sensitive to the nuclear force prescription.

nucl-ex↗

arXiv2016

The Pan-STARRS1 distant z>5.6 quasar survey: more than 100 quasars within the first Gyr of the universe

Luminous quasars at z>5.6 can be studied in detail with the current generation of telescopes and provide us with unique information on the first gigayear of the universe. Thus far these studies have been statistically limited by the number of quasars known at these redshifts. Such quasars are rare and therefore wide-field surveys are required to identify them and multiwavelength data are needed to separate them efficiently from their main contaminants, the far more numerous cool dwarfs. In this paper, we update and extend the selection for z~6 quasars presented in Banados et al. (2014) using the Pan-STARRS1 (PS1) survey. We present the PS1 distant quasar sample, which currently consists of 124 quasars in the redshift range 5.6 5.6 presented in this work almost double the quasars previously known at these redshifts, marking a transition phase from studies of individual sources to statistical studies of the high-redshift quasar population, which was impossible with earlier, smaller samples.

astro-ph.GA↗

arXiv2016

CUORE-0 detector: design, construction and operation

The CUORE experiment will search for neutrinoless double-beta decay of $^{130}$Te with an array of 988 TeO$_2$ bolometers arranged in 19 towers. CUORE-0, the first tower assembled according to the CUORE procedures, was built and commissioned at Laboratori Nazionali del Gran Sasso, and took data from March 2013 to March 2015. In this paper we describe the design, construction and operation of the CUORE-0 experiment, with an emphasis on the improvements made over a predecessor experiment, Cuoricino. In particular, we demonstrate with CUORE-0 data that the design goals of CUORE are within reach.

physics.ins-det↗

arXiv2015

Measurement of Lifetimes in 23Mg

Several lifetimes in 23Mg have been determined for the first time using the Doppler-shift attenuation method. A Monte Carlo simulation code has been written to model the gamma-ray line shape. An upper limit of 12 fs at the 95% C.L. has been obtained for the astrophysically important 7787 keV state.

nucl-ex↗

arXiv2015

Recent direct reaction experimental studies with radioactive tin beams

Direct reaction techniques are powerful tools to study the single-particle nature of nuclei. Performing direct reactions on short-lived nuclei requires radioactive ion beams produced either via fragmentation or the Isotope Separation OnLine (ISOL) method. Some of the most interesting regions to study with direct reactions are close to the magic numbers where changes in shell structure can be tracked. These changes can impact the final abundances of explosive nucleosynthesis. The structure of the chain of tin isotopes is strongly influenced by the Z=50 proton shell closure, as well as the neutron shell closures lying in the neutron-rich, N=82, and neutron-deficient, N=50, regions. Here we present two examples of direct reactions on exotic tin isotopes. The first uses a one-neutron transfer reaction and a low-energy reaccelerated ISOL beam to study states in 131Sn from across the N=82 shell closure. The second example utilizes a one-neutron knockout reaction on fragmentation beams of neutron-deficient 106,108Sn. In both cases, measurements of gamma rays in coincidence with charged particles proved to be invaluable.

nucl-ex↗

arXiv2015

MegaFace: A Million Faces for Recognition at Scale

Recent face recognition experiments on the LFW benchmark show that face recognition is performing stunningly well, surpassing human recognition rates. In this paper, we study face recognition at scale. Specifically, we have collected from Flickr a \textbf{Million} faces and evaluated state of the art face recognition algorithms on this dataset. We found that the performance of algorithms varies--while all perform great on LFW, once evaluated at scale recognition rates drop drastically for most algorithms. Interestingly, deep learning based approach by \cite{schroff2015facenet} performs much better, but still gets less robust at scale. We consider both verification and identification problems, and evaluate how pose affects recognition at scale. Moreover, we ran an extensive human study on Mechanical Turk to evaluate human recognition at scale, and report results. All the photos are creative commons photos and is released at \small{\url{http://megaface.cs.washington.edu/}} for research and further experiments.

cs.CV↗

arXiv2014

Proton spectroscopy of 48Ni, 46Fe, and 44Cr

Results of decay spectroscopy on nuclei in vicinity of the doubly magic 48Ni are presented. The measurements were performed with a Time Projection Chamber with optical readout which records tracks of ions and protons in the gaseous volume. Six decays of 48Ni including four events of two-proton ground-state radioactivity were recorded. An advanced reconstruction procedure yielded the 2p decay energy for 48Ni of Q2p = 1.29(4) MeV. In addition, the energy spectra of \b{eta}-delayed protons emitted in the decays of 44Cr and 46Fe, as well as half-lives and branching ratios were determined. The results were found to be consistent with the previous measurements made with Si detectors. A new proton line in the decay of 44Cr corresponding to the decay energy of 760 keV is reported. The first evidence for the \b{eta}2p decay of 46 Fe, based on one clear event, is shown.

nucl-ex↗