arXiv subjects

D. Miller

Publications and source records attributed to D. Miller.

At least 37 records · Page 2Linked to original sources

arXiv2014

Performance of the Caltech Submillimeter Observatory Dual-Color 180-720 GHz Balanced SIS Receivers

We report on balanced SIS receivers covering the astronomical important 180-720 GHz submillimeter atmospheric window. To facilitate remote observations and automated spectral line surveys, fully synthesized local oscillators are employed. High-current-density Nb-AlN-Nb superconducting-insulating-superconducting (SIS) tunnel junctions are used as the mixing element. The measured double-sideband (DSB) 230 GHz receiver noise temperature, uncorrected for optics loss, ranges from 50K at 185 GHz, 33K at 246 GHz, to 51K at 280 GHz. In this frequency range the mixer has a DSB conversion gain of 0 +- 1.5 dB. The measured 460 GHz double-sideband receiver noise temperature, uncorrected for optics loss, is 32K at 400 GHz, 34K at 460 GHz, and 61K at 520 GHz. Similar to the 230 GHz balanced mixer, the DSB mixer conversion gain is 1 +- 1 dB. To help optimize performance, the mixer IF circuits and bias injection are entirely planar by design. Dual-frequency observation, by means of separating the incoming circular polarized electric field into two orthogonal components, is another important mode of operation offered by the new facility instrumentation. Instrumental stability is excellent supporting the LO noise cancellation properties of the balanced mixer configuration. In the spring of 2012 the dual-frequency 230/460 SIS receiver was successfully installed at Caltech Submillimeter Observatory (CSO), Mauna Kea, HI.

astro-ph.IM↗

arXiv2012

LBT observations of the HR 8799 planetary system: First detection of HR8799e in H band

We have performed H and Ks band observations of the planetary system around HR 8799 using the new AO system at the Large Binocular Telescope and the PISCES Camera. The excellent instrument performance (Strehl ratios up to 80% in H band) enabled detection the inner planet HR8799e in the H band for the first time. The H and Ks magnitudes of HR8799e are similar to those of planets c and d, with planet e slightly brighter. Therefore, HR8799e is likely slightly more massive than c and d. We also explored possible orbital configurations and their orbital stability. We confirm that the orbits of planets b, c and e are consistent with being circular and coplanar; planet d should have either an orbital eccentricity of about 0.1 or be non-coplanar with respect to b and c. Planet e can not be in circular and coplanar orbit in a 4:2:1 mean motion resonances with c and d, while coplanar and circular orbits are allowed for a 5:2 resonance. The analysis of dynamical stability shows that the system is highly unstable or chaotic when planetary masses of about 5 MJup for b and 7 MJup for the other planets are adopted. Significant regions of dynamical stability for timescales of tens of Myr are found when adopting planetary masses of about 3.5, 5, 5, and 5 Mjup for HR 8799 b, c, d, and e respectively. These masses are below the current estimates based on the stellar age (30 Myr) and theoretical models of substellar objects.

astro-ph.EP↗

arXiv2012

Using the Parkes Pulsar Data Archive

The Parkes Pulsar Data Archive currently provides access to 165,755 data files obtained from observations carried out at the Parkes Observatory since the year 1991. Data files and access methods are compliant with the Virtual Observatory protocol. This paper provides a tutorial on how to make use of the Parkes Pulsar Data Archive and provides example queries using on-line interfaces.

astro-ph.IM↗

arXiv2012

Technology Development for the Caltech Submillimeter Observatory Balanced Receivers

The Caltech Submillimeter Observatory (CSO) is located on top of Mauna Kea, Hawaii, at an altitude of 4.2 km. The existing suite of facility heterodyne receivers covering the submillimeter band is rapidly aging and in need of replacement. To facilitate deep integrations and automated spectral line surveys, a family of remote programmable, synthesized, dual-frequency balanced receivers covering the astronomical important 180 - 720 GHz atmospheric windows is in an advanced stage of development. Installation of the first set of receivers is expected in the spring of 2012. Dual-frequency observation will be an important mode of operation offered by the new facility instrumentation. Two band observations are accomplished by separating the H and V polarizations of the incoming signal and routing them via folded optics to the appropriate polarization sensitive balanced mixer. Scientifically this observation mode facilitates pointing for the higher receiver band under mediocre weather conditions and a doubling of scientific throughput (2 x 4 GHz) under good weather conditions.

astro-ph.IM↗

arXiv2011

Synchrotron radiation based beam diagnostics at the Fermilab Tevatron

Synchrotron radiation has been used for many years as a beam diagnostic at electron accelerators. It is not normally associated with proton accelerators as the intensity of the radiation is too weak to make detection practical. However, if one utilizes the radiation originating near the edge of a bending magnet, or from a short magnet, the rapidly changing magnetic field serves to enhance the wavelengths shorter than the cutoff wavelength, which for more recent high energy proton accelerators such as Fermilab's Tevatron, tends to be visible light. This paper discusses the implementation at the Tevatron of two devices. A transverse beam profile monitor images the synchrotron radiation coming from the proton and antiproton beams separately and provides profile data for each bunch. A second monitor measures the low-level intensity of beam in the abort gaps which poses a danger to both the accelerator's superconducting magnets and the silicon detectors of the high energy physics experiments. Comparisons of measurements from the profile monitor to measurements from the flying wire profile systems are presented as are a number of examples of the application of the profile and abort gap intensity measurements to the modelling of Tevatron beam dynamics.

physics.ins-det↗

arXiv2011

The Parkes Observatory Pulsar Data Archive

The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 10^5 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.

astro-ph.IM↗

arXiv2010

Observation of isotonic symmetry for enhanced quadrupole collectivity in neutron-rich 62,64,66Fe isotopes at N=40

The transition rates for the 2_{1}^{+} states in 62,64,66Fe were studied using the Recoil Distance Doppler-Shift technique applied to projectile Coulomb excitation reactions. The deduced E2 strengths illustrate the enhanced collectivity of the neutron-rich Fe isotopes up to N=40. The results are interpreted by the generalized concept of valence proton symmetry which describes the evolution of nuclear structure around N=40 as governed by the number of valence protons with respect to Z~30. The deformation suggested by the experimental data is reproduced by state-of-the-art shell calculations with a new effective interaction developed for the fpgd valence space.

nucl-ex↗

arXiv2009

Search for 14.4 keV solar axions emitted in the M1-transition of 57Fe nuclei with CAST

We have searched for 14.4 keV solar axions or more general axion-like particles (ALPs), that may be emitted in the M1 nuclear transition of 57Fe, by using the axion-to-photon conversion in the CERN Axion Solar Telescope (CAST) with evacuated magnet bores (Phase I). From the absence of excess of the monoenergetic X-rays when the magnet was pointing to the Sun, we set model-independent constraints on the coupling constants of pseudoscalar particles that couple to two photons and to a nucleon g_{aγ} |-1.19 g_{aN}^{0}+g_{aN}^{3}|<1.36\times 10^{-16} GeV^{-1} for m_{a}<0.03 eV at the 95% confidence level.

hep-ex↗

arXiv2009

Probing eV-scale axions with CAST

We have searched for solar axions or other pseudoscalar particles that couple to two photons by using the CERN Axion Solar Telescope (CAST) setup. Whereas we previously have reported results from CAST with evacuated magnet bores (Phase I), setting limits on lower mass axions, here we report results from CAST where the magnet bores were filled with \hefour gas (Phase II) of variable pressure. The introduction of gas generated a refractive photon mass $m_γ$, thereby achieving the maximum possible conversion rate for those axion masses \ma that match $m_γ$. With 160 different pressure settings we have scanned \ma up to about 0.4 eV, taking approximately 2 h of data for each setting. From the absence of excess X-rays when the magnet was pointing to the Sun, we set a typical upper limit on the axion-photon coupling of $\gag\lesssim 2.17\times 10^{-10} {\rm GeV}^{-1}$ at 95% CL for $\ma \lesssim 0.4$ eV, the exact result depending on the pressure setting. The excluded parameter range covers realistic axion models with a Peccei-Quinn scale in the neighborhood of $f_{\rm a}\sim10^{7}$ GeV. Currently in the second part of CAST Phase II, we are searching for axions with masses up to about 1.2 eV using \hethree as a buffer gas.

hep-ex↗

arXiv2008

Solar axion search with the CAST experiment

The CAST (CERN Axion Solar Telescope) experiment is searching for solar axions by their conversion into photons inside the magnet pipe of an LHC dipole. The analysis of the data recorded during the first phase of the experiment with vacuum in the magnet pipes has resulted in the most restrictive experimental limit on the coupling constant of axions to photons. In the second phase, CAST is operating with a buffer gas inside the magnet pipes in order to extent the sensitivity of the experiment to higher axion masses. We will present the first results on the $^{4}{\rm He}$ data taking as well as the system upgrades that have been operated in the last year in order to adapt the experiment for the $^{3}{\rm He}$ data taking. Expected sensitivities on the coupling constant of axions to photons will be given for the recent $^{3}{\rm He}$ run just started in March 2008.

hep-ex↗

arXiv2008

Search for low Energy solar Axions with CAST

We have started the development of a detector system, sensitive to single photons in the eV energy range, to be suitably coupled to one of the CAST magnet ports. This system should open to CAST a window on possible detection of low energy Axion Like Particles emitted by the sun. Preliminary tests have involved a cooled photomultiplier tube coupled to the CAST magnet via a Galileian telescope and a switched 40 m long optical fiber. This system has reached the limit background level of the detector alone in ideal conditions, and two solar tracking runs have been performed with it at CAST. Such a measurement has never been done before with an axion helioscope. We will present results from these runs and briefly discuss future detector developments.

hep-ex↗

arXiv2007

Linear polarization sensitivity of SeGA detectors

Parity is a key observable in nuclear spectroscopy. Linear polarization measurements of $γ$-rays are a probe to access the parities of energy levels. Utilizing the segmentation of detectors in the Segmented Germanium Array (SeGA) at the NSCL and analyzing the positions of interaction therein allows the detectors to be used as Compton polarimeters. Unlike other segmented detectors, SeGA detectors are irradiated from the side to utilize the transversal segmentation for better Doppler corrections. Sensitivity in such an orientation has previously been untested. A linear polarization sensitivity $Q \approx 0.14$ has been measured in the 350-keV energy range for SeGA detectors using $α$-$γ$ correlations from a \nuc{249}{Cf} source.

nucl-ex↗

arXiv2007

Shape and structure of N=Z 64Ge; Electromagnetic transition rates from the application of the Recoil Distance Method to knock-out reaction

Transition rate measurements are reported for the first and the second 2+ states in N=Z 64Ge. The experimental results are in excellent agreement with large-scale Shell Model calculations applying the recently developed GXPF1A interactions. Theoretical analysis suggests that 64Ge is a collective gamma-soft anharmonic vibrator. The measurement was done using the Recoil Distance Method (RDM) and a unique combination of state-of-the-art instruments at the National Superconducting Cyclotron Laboratory (NSCL). States of interest were populated via an intermediate-energy single-neutron knock-out reaction. RDM studies of knock-out and fragmentation reaction products hold the promise of reaching far from stability and providing lifetime information for excited states in a wide range of nuclei.

nucl-ex↗

arXiv2007

Clock and Trigger Synchronization between Several Chassis of Digital Data Acquisition Modules

In applications with segmented high purity Ge detectors or other detector arrays with tens or hundreds of channels, where the high development cost and limited flexibility of application specific integrated circuits outweigh their benefits of low power and small size, the readout electronics typically consist of multi-channel data acquisition modules in a common chassis for power, clock and trigger distribution, and data readout. As arrays become larger and reach several hundred channels, the readout electronics have to be divided over several chassis, but still must maintain precise synchronization of clocks and trigger signals across all channels. This division becomes necessary not only because of limits given by the instrumentation standards on module size and chassis slot numbers, but also because data readout times increase when more modules share the same data bus and because power requirements approach the limits of readily available power supplies. In this paper, we present a method for distributing clocks and triggers between 4 PXI chassis containing DGF Pixie-16 modules with up to 226 acquisition channels per chassis in a data acquisition system intended to instrument the over 600 channels of the SeGA detector array at the National Superconducting Cyclotron Laboratory. Our solution is designed to achieve synchronous acquisition of detector waveforms from all channels with a jitter of less then 1 ns, and can be extended to a larger number of chassis if desired.

nucl-ex↗

arXiv2006

Observations of Herbig Ae Disks with Nulling Interferometry

We present the results of 10 micron nulling interferometric observations of 13 Herbig Ae stars using the Magellan I (Baade) and the MMT 6.5 m telescopes. A portion of the observations was completed with the adaptive secondary at the MMT. We have conclusively spatially resolved 3 of the 13 stars, HD 100546, AB Aur, and HD 179218, the latter two recently resolved using adaptive optics in combination with nulling interferometry. For the resolved objects we find that the 10 $μ$m emitting regions have a spatial extent of 15-30 AU in diameter. We also have some evidence for resolved emission surrounding an additional 2 stars (V892 Tau and R CrA). For those objects in our study with mid-IR SEDs classifications from Meeus et al. (2001), we find that the Group I objects (those with constant to increasing mid-IR flux) are more likely to be resolved, within our limited sample. This trend is evident in correlations in the inferred disk sizes vs. the sub-millimeter SED slope and disk size vs. fractional infrared luminosity of the systems. We explore the spatial distribution and orientation of the warm dust in the resolved systems and constrain physical models which are consistent with their observational signatures.

astro-ph↗

arXiv2006

Z=50 shell gap near $^{100}$Sn from intermediate-energy Coulomb excitations in even-mass $^{106--112}$Sn isotopes

Rare isotope beams of neutron-deficient $^{106,108,110}$Sn nuclei from the fragmentation of $^{124}$Xe were employed in an intermediate-energy Coulomb excitation experiment yielding $B(E2, 0^+_1 \to 2^+_1)$ transition strengths. The results indicate that these $B(E2,0^+_1 \to 2^+_1)$ values are much larger than predicted by current state-of-the-art shell model calculations. This discrepancy can be explained if protons from within the Z = 50 shell are contributing to the structure of low-energy excited states in this region. Such contributions imply a breaking of the doubly-magic $^{100}$Sn core in the light Sn isotopes.

nucl-ex↗

arXiv2005

Application of the Time of Flight Technique for Lifetime Measurements with Relativistic Beams of Heavy Nuclei

A novel method for picosecond lifetime measurements of excited gamma-ray emitting nuclear states has been developed for fast beams from fragmentation reactions. A test measurement was carried out with a beam of 124Xe at an energy of ~55 MeV/u. The beam ions were Coulomb excited to the first 2+ state on a movable target. Excited nuclei emerged from the target and decayed in flight after a distance related to the lifetime. A stationary degrader positioned downstream with respect to the target was used to further reduce the velocity of the excited nuclei. As a consequence, the gamma-ray decays from the 2+ excited state that occurred before or after traversing the degrader were measured at a different Doppler shift. The gamma-ray spectra were analyzed from the forward ring of the Segmented Germanium Array; this ring positioned at 37 deg. simultaneously provides the largest sensitivity to changes in velocity and the best energy resolution. The ratio of intensities in the peaks at different Doppler shifts gives information about the lifetime if the velocity is measured. The results and range of the application of the method are discussed.

nucl-ex↗

arXiv2004

Resolved Mid-Infrared Emission Around AB Aur and V892 Tau with Adaptive Optics Nulling Interferometric Observations

We present the results of adaptive optics nulling interferometric observations of two Herbig Ae stars, AB Aur and V892 Tau. Our observations at 10.3 microns show resolved circumstellar emission from both sources. Further analysis of the AB Aur emission suggests that there is an inclined disk surrounding the star. The diameter of the disk is derived to be 24 to 30 AU with an inclination of 45 to 65 degrees from face-on, and a major-axis PA of 30 +/- 15 degrees (E of N). Differences in the physical characteristics between the mid-IR emission and emission at other wavelengths (near-IR and millimeter), found in previous studies, suggest a complex structure for AB Aur's circumstellar environment, which may not be explained by a disk alone. The similarity in the observed size of AB Aur's resolved emission and that of another Herbig Ae star, HD 100546, is likely coincidental, as their respective evolutionary states and spectral energy distributions suggest significantly different circumstellar environments.

astro-ph↗