Monthly Notices of the Royal Astronomical Society, Dec 6, 2022
The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Wa... more The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in 𝑅 0 limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses. While measurements of 𝑅 0 have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of 𝑅 0 being somewhere within 8.0 to 8.5 kpc. The most precise measurements to date have to assume that Sgr A * is at rest at the Galactic center, which may not be the case. In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity 𝑣 𝑇 and the quadrupolar signature in radial velocity 𝑣 𝑅 expected for stars orbiting in a bar. From the minimum in 𝑣 𝑇 , we measure 𝑅 0 = 8.23 ± 0.12 kpc. We validate our measurement using realistic 𝑁-body simulations of the Milky Way. We further measure the pattern speed of the bar to be Ω bar = 40.08 ± 1.78 km s -1 kpc -1 . Because the bar forms out of the disk, its center is manifestly the barycenter of the bar+disc system and our measurement is therefore the most robust and accurate measurement of 𝑅 0 to date.
The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Wa... more The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in 𝑅 0 limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses. While measurements of 𝑅 0 have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of 𝑅 0 being somewhere within 8.0 to 8.5 kpc. The most precise measurements to date have to assume that Sgr A * is at rest at the Galactic center, which may not be the case. In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity 𝑣 𝑇 and the quadrupolar signature in radial velocity 𝑣 𝑅 expected for stars orbiting in a bar. From the minimum in 𝑣 𝑇 , we measure 𝑅 0 = 8.23 ± 0.12 kpc. We validate our measurement using realistic 𝑁-body simulations of the Milky Way. We further measure the pattern speed of the bar to be Ω bar = 40.08 ± 1.78 km s -1 kpc -1 . Because the bar forms out of the disk, its center is manifestly the barycenter of the bar+disc system and our measurement is therefore the most robust and accurate measurement of 𝑅 0 to date.
Over two years 8,859 high-resolution H-band spectra of 3,493 young (1 -10 Myr) stars were gathere... more Over two years 8,859 high-resolution H-band spectra of 3,493 young (1 -10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of that SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition we present accurate extinctions by measuring the E(J-H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely the extinction-corrected J-band magnitude, the surface gravity and the R sin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger R sin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.
We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky ... more We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] vs. [Mg/H] with a 2-process model, which decomposes abundance patterns into a "prompt" component tracing core collapse supernovae and a "delayed" component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals ∆[X/H] from this two-parameter fit. The rms residuals range from ∼ 0.01 -0.03 dex for the most precisely measured APOGEE abundances to ∼ 0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3 -13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15 -17 kpc), 0.05-0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4-1 dex) of multiple elements in ω Cen. Residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.
During an imaging survey of the Chamaeleon I star-forming region with the Advanced Camera for Sur... more During an imaging survey of the Chamaeleon I star-forming region with the Advanced Camera for Surveys aboard the Hubble Space Telescope, we have discovered a candidate substellar companion to the young low-mass star CHXR 73 (τ ∼ 2 Myr, M ∼ 0.35 M ⊙ ). We measure a projected separation of 1. ′′ 30 ± 0. ′′ 03 for the companion, CHXR 73 B, which corresponds to 210 AU at the distance of the cluster. A near-infrared spectrum of this source obtained with the Cornell Massachusetts Slit Spectrograph at the Magellan II telescope exhibits strong steam absorption that confirms its latetype nature ( M9.5). In addition, the gravity-sensitive shapes of the H-and K-band continua demonstrate that CHXR 73 B is a young, pre-main-sequence object rather than a field star. The probability that CHXR 73 A and B are unrelated members of Chamaeleon I is ∼ 0.001. We estimate the masses of CHXR 73 B and other known substellar companions in young clusters with a method that is consistent with the dynamical measurements of the eclipsing binary brown dwarf 2M 0535-0546, which consists of a comparison of the bolometric luminosities of the companions to the values predicted by the evolutionary models of Chabrier & coworkers and Burrows & coworkers. We arrive at mass estimates of 0.003-0.004, 0.024 ± 0.012, 0.011 +0.01 -0.003 , and 0.012 +0.008 -0.005 M ⊙ for 2M 1207-3932 B, GQ Lup B, DH Tau B, and CHXR 73 B, respectively. Thus, DH Tau B and CHXR 73 B appear to be the least massive companions to stars outside the solar system that have been detected in direct images, and may have masses that are within the range observed for extrasolar planetary companions (M 0.015 M ⊙ ). However, because these two objects (as well as 2M 1207-3932 B) probably did not form within circumstellar disks around their primaries, we suggest that they should be viewed as brown dwarf companions rather than planets.
Despite its importance for understanding the nature of early stellar generations and for constrai... more Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, highresolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] -1.7), including two that are very metal-poor [Fe/H] ∼ -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the α-elements O, Mg, and Si without significant α-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.
This paper seeks to synthesize much recent work on the HTSC materials around the latest energy re... more This paper seeks to synthesize much recent work on the HTSC materials around the latest energy resolved scanning tunnelling microscopy (STM) results from Davis and coworkers. The STM conductance diffuse scattering results in particular are employed as point of entry to discuss bosonic modes, both of condensed and uncondensed form. The bosonic mode picture is essential to understanding an ever growing range of observations within the HTSC field. The work is expounded within the context of the site-inhomogeneous negative-U boson-fermion modelling long advocated by the author. This general approach is presently seeing much theoretical development, into which I have looked to couple many of the experimental advances. While this formal theory is not yet sufficiently detailed to cover adequately all the experimental complexities presented by the real cuprate systems, it is clear it affords very appreciable support to the line taken. An attempt is made throughout to clarify why and how it is that these novel circumstances and phenomena are tied so very closely to this particular set of materials.
Recent photoemission work on underdoped cuprates between Tc and T*, the pseudogap temperature, ar... more Recent photoemission work on underdoped cuprates between Tc and T*, the pseudogap temperature, are interpreted within the framework of a previously developed negative-U scenario. From this exposition, incorporating a developed 2q diagonal striping model, detailed understanding follows of the ARPES results, together with certain STM and far infrared optical data. Identification of the origin of the magnetic circular dichroism and related effects exhibited by such materials below T* also appears to have been achieved.
Recently, interest has emerged in investigating the potential for use of advanced materials in de... more Recently, interest has emerged in investigating the potential for use of advanced materials in developing new and innovative structural response modification devices for seismic applications, such as for seismic isolator and damping systems. Shape memory alloys (SMAs) are a class of metals that have the capability to dissipate energy through repeated cycling loading without significant permanent deformations. They have a high usable strain range (up to about 8%) compared to other metals, and thus require a smaller volume of material in order to produce the same damping capacity. They also possess an inherent ability to provide stiff elastic resistance at large displacements. One of the most promising of these alloys is a material composed of essentially equal percentages of nickel and titanium (Nitinol). Although relatively commonplace in other fields such as biomedical applications, the development of SMA devices for seismic applications is still in the infancy stages. Consequently...
Symposium - International Astronomical Union, 2003
We present new M and L-dwarfs confirmed through follow-up of 2MASS color-selected objects with th... more We present new M and L-dwarfs confirmed through follow-up of 2MASS color-selected objects with the CorMASS near-infrared spectrograph (R ˜ 300) on the Palomar 60-inch telescope as part of a continuing follow-up survey. Most of the objects are bright…
Symposium - International Astronomical Union, 2003
The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% compl... more The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary sys...
The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a co... more The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a common mount. Coherent combination of these two AO-corrected apertures via the LBT Interferometer (LBTI) produces Fizeau interferometric images with a spatial resolution equivalent to that of a 22.8-meter telescope and the lightgathering power of single 11.8-meter mirror. Capitalizing on these unique capabilities, we used LBTI/LMIRcam to image thermal radiation from volcanic activity on the surface of Io at M-Band (4.8 µm) over a range of parallactic angles. We compare two deconvolution routines in order to recover the full spatial resolution of the combined images, resolving at least fifteen known volcanic hot spots. Coupling these observations with advanced image reconstruction algorithms demonstrates the versatility of Fizeau interferometry and realizes the LBT as the first in a series of extremely large telescopes.
In this paper we present a novel, quadruple well process developed in a modern 0.18 µm CMOS techn... more In this paper we present a novel, quadruple well process developed in a modern 0.18 µm CMOS technology called INMAPS. On top of the standard process, we have added a deep P implant that can be used to form a deep P-well and provide screening of N-wells from the P-doped epitaxial layer. This prevents the collection of radiation-induced charge by unrelated N-wells, typically ones where PMOS transistors are integrated. The design of a
Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter, 2006
We describe the optical and mechanical design of a simple hand-held near infra-red spectrograph c... more We describe the optical and mechanical design of a simple hand-held near infra-red spectrograph constructed to produce observations of the spectrum of scrambled light from the Earth from aboard the International Space Station. Observing the Earth in this manner simulates the changing perspective on an extra-solar terrestrial planet observed as a point source by the Terrestrial Planet Finder. A Sensors Unlimited, Inc. SU320-M InGaAs(0.86 − 1.72µm) camera detects the dispersed spectrum and outputs NTSC video to be recorded and also permits frame grabbing. One of the three copies of the instrument is currently aboard the International Space Station. The optical and mechanical design was conceived and executed by graduate and undergraduate students at the University of Virginia.
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 2012
We diamond fly cut 2 sets of germanium grisms for the LMIRcam 3-5 micron Fizeau imager for the co... more We diamond fly cut 2 sets of germanium grisms for the LMIRcam 3-5 micron Fizeau imager for the combined focus of the Large Binocular Telescope (LBT). The grisms mount in a filter wheel near a pupil to enable moderate resolution (R~300) spectroscopy. Both sets have a measured blaze angle of 2.9º. The first set has a groove period of 40 lines/mm and will be used in first order with peak efficiency at 3.6 µm. The second set has 32 lines/mm. It can operate in first order with an efficiency peak near 4.4 µm and in second order with a peak near 2.3 µm. First results from testing the grisms in the instrument on the sky with the LBT are presented.
The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb −1... more The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb −1 of pp collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → J/ψ(→ µ + µ −)π + π − decay mode, and probes ψ(2S) mesons with transverse momenta in the range 10 ≤ p T < 100 GeV and rapidity |y| < 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production.
Additional jet activity in dijet events is measured using pp collisions at ATLAS at a centre-of-m... more Additional jet activity in dijet events is measured using pp collisions at ATLAS at a centre-of-mass energy of 7 TeV, for jets reconstructed using the anti-k t algorithm with radius parameter R = 0.6. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijets. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the scalar average of the transverse momenta of the dijets and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijets. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to powheg, interfaced to the pythia 8 and herwig parton shower generators, as well as to hej with and without interfacing it to the ariadne parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, powheg+pythia 8 and hej+ariadne are found to provide the best agreement with the data. These measurements use the full data sample collected with the ATLAS detector in 7 TeV pp collisions at the LHC and correspond to integrated luminosities of 36.1 pb −1 and 4.5 fb −1 for data collected during 2010 and 2011, respectively.
A detailed exposition is made of recent transport and 'quantum oscillation' results fro... more A detailed exposition is made of recent transport and 'quantum oscillation' results from HTSC systems covering the full range from overdoped to underdoped material. This now very extensive and high quality data set is interpreted here within the framework developed by the author of local pairs and boson-fermion resonance, arising in the context of negative-U behaviour in an inhomogeneous electronic environment. The strong inhomogeneity comes with the mixed-valent condition of these materials, which when underdoped lie in close proximity to the Mott-Anderson transition. The observed intense scattering is presented as resulting from pair formation and electron-boson collisions in the resonant crossover circumstance. The high level of scattering brings the systems to incoherence in the pseudogapped state, p < pc (= 0.183). In a high magnetic field the striped partition of the inhomogeneous charge distribution is much strengthened and regularized. Magnetization and resistan...
Recent high energy observations of Cas A suggests the presence of synchrotron radiation, implying... more Recent high energy observations of Cas A suggests the presence of synchrotron radiation, implying acceleration of cosmic rays by young supernova remnants. We detect synchrotron emission from Cas A in the near-infrared using Two Micron All Sky Survey (2MASS) and Palomar 200 inch PFIRCAM observations. The remnant is detected in J, H, and K s bands using 2MASS: K s band is the brightest, H is moderate and J is faint. In the J and H bands, bright [Fe II] lines (1.24µm and 1.64µm) are detected spectroscopically. The Palomar observations include K s continuum, narrowband 1.64 µm (centered on [Fe II]) and 2.12µm (centered on H 2 (1-0)) images. While the narrow-band 1.64 µm image shows filamentary and knotty structures, similar to the optical image, the K s image shows a relatively smooth, diffuse shell, remarkably similar to the radio image. The H 2 image is identical to the K s continuum image with surface brightness reduced as expected for the ratio of filter bandwidths, showing no contribution of H 2 lines to the K s-band image. The broad-band near-infrared fluxes of Cas A are generally consistent with, but a few tens of percent higher than, an extrapolation of the radio fluxes. The hardening to higher frequencies is possibly due to nonlinear shock acceleration and/or spectral index variation across the remnant. We show evidence of spectral index variation across Cas A using the 'spectral tomography' technique. The presence of near-infrared synchrotron radiation requires the roll-off frequency to be higher than 1.5 × 10 14 Hz, implying that electrons are accelerated to-2energies of at least E = 0.3B −1/2 mG erg or 0.2 TeV. The morphological similarity in diffuse emission between the radio and K s band images implies that synchrotron losses are not dominant, or we would expect to see a greater concentration in knots. We also show dust continuum is not significant in the near-infrared emission of Cas A. Our observations show unambiguous evidence that the near-infrared K s band emission of Cas A is from synchrotron emission by accelerated cosmic-ray electrons.
We report 0.8-2.5 m spectrophotometry of CI Aquilae at eight epochs between 2000 May 9 and 2001 J... more We report 0.8-2.5 m spectrophotometry of CI Aquilae at eight epochs between 2000 May 9 and 2001 June 2 UT, corresponding to approximately 3 and 391 days after peak brightness. Near peak brightness, the spectra showed emission lines that were characteristic of a low-excitation, nitrogen-rich shell. Within a few weeks, the spectra began to show higher excitation/ionization emission lines indicative of a harder illuminating source: the neutral metal lines faded, leaving only lines of H i, He i, and He ii and the emerging coronal lines. A month after peak brightness, the [Ca viii] coronal line at 2.3205 m appeared and persisted until the last of our observations, on day +391. From the O i line ratios, we deduced a reddening of E BÀV = 1.5 AE 0.1 and a visual extinction of A V = 4.6 AE 0.2. Along with the rate of decline from the light curve (t 2), we derived a distance of 2.6 AE 1.3 kpc. The frequently observed unidentified novae lines were present in CI Aquilae along with a potentially new member of the group at 2.425 AE 0.002 m.
Monthly Notices of the Royal Astronomical Society, Dec 6, 2022
The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Wa... more The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in 𝑅 0 limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses. While measurements of 𝑅 0 have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of 𝑅 0 being somewhere within 8.0 to 8.5 kpc. The most precise measurements to date have to assume that Sgr A * is at rest at the Galactic center, which may not be the case. In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity 𝑣 𝑇 and the quadrupolar signature in radial velocity 𝑣 𝑅 expected for stars orbiting in a bar. From the minimum in 𝑣 𝑇 , we measure 𝑅 0 = 8.23 ± 0.12 kpc. We validate our measurement using realistic 𝑁-body simulations of the Milky Way. We further measure the pattern speed of the bar to be Ω bar = 40.08 ± 1.78 km s -1 kpc -1 . Because the bar forms out of the disk, its center is manifestly the barycenter of the bar+disc system and our measurement is therefore the most robust and accurate measurement of 𝑅 0 to date.
The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Wa... more The distance to the Galactic center 𝑅 0 is a fundamental parameter for understanding the Milky Way, because all observations of our Galaxy are made from our heliocentric reference point. The uncertainty in 𝑅 0 limits our knowledge of many aspects of the Milky Way, including its total mass and the relative mass of its major components, and any orbital parameters of stars employed in chemo-dynamical analyses. While measurements of 𝑅 0 have been improving over a century, measurements in the past few years from a variety of methods still find a wide range of 𝑅 0 being somewhere within 8.0 to 8.5 kpc. The most precise measurements to date have to assume that Sgr A * is at rest at the Galactic center, which may not be the case. In this paper, we use maps of the kinematics of stars in the Galactic bar derived from APOGEE DR17 and Gaia EDR3 data augmented with spectro-photometric distances from the astroNN neural-network method. These maps clearly display the minimum in the rotational velocity 𝑣 𝑇 and the quadrupolar signature in radial velocity 𝑣 𝑅 expected for stars orbiting in a bar. From the minimum in 𝑣 𝑇 , we measure 𝑅 0 = 8.23 ± 0.12 kpc. We validate our measurement using realistic 𝑁-body simulations of the Milky Way. We further measure the pattern speed of the bar to be Ω bar = 40.08 ± 1.78 km s -1 kpc -1 . Because the bar forms out of the disk, its center is manifestly the barycenter of the bar+disc system and our measurement is therefore the most robust and accurate measurement of 𝑅 0 to date.
Over two years 8,859 high-resolution H-band spectra of 3,493 young (1 -10 Myr) stars were gathere... more Over two years 8,859 high-resolution H-band spectra of 3,493 young (1 -10 Myr) stars were gathered by the multi-object spectrograph of the APOGEE project as part of the IN-SYNC ancillary program of that SDSS-III survey. Here we present the forward modeling approach used to derive effective temperatures, surface gravities, radial velocities, rotational velocities, and H-band veiling from these near-infrared spectra. We discuss in detail the statistical and systematic uncertainties in these stellar parameters. In addition we present accurate extinctions by measuring the E(J-H) of these young stars with respect to the single-star photometric locus in the Pleiades. Finally we identify an intrinsic stellar radius spread of about 25% for late-type stars in IC 348 using three (nearly) independent measures of stellar radius, namely the extinction-corrected J-band magnitude, the surface gravity and the R sin i from the rotational velocities and literature rotation periods. We exclude that this spread is caused by uncertainties in the stellar parameters by showing that the three estimators of stellar radius are correlated, so that brighter stars tend to have lower surface gravities and larger R sin i than fainter stars at the same effective temperature. Tables providing the spectral and photometric parameters for the Pleiades and IC 348 have been provided online.
We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky ... more We apply a novel statistical analysis to measurements of 16 elemental abundances in 34,410 Milky Way disk stars from the final data release (DR17) of APOGEE-2. Building on recent work, we fit median abundance ratio trends [X/Mg] vs. [Mg/H] with a 2-process model, which decomposes abundance patterns into a "prompt" component tracing core collapse supernovae and a "delayed" component tracing Type Ia supernovae. For each sample star, we fit the amplitudes of these two components, then compute the residuals ∆[X/H] from this two-parameter fit. The rms residuals range from ∼ 0.01 -0.03 dex for the most precisely measured APOGEE abundances to ∼ 0.1 dex for Na, V, and Ce. The correlations of residuals reveal a complex underlying structure, including a correlated element group comprised of Ca, Na, Al, K, Cr, and Ce and a separate group comprised of Ni, V, Mn, and Co. Selecting stars poorly fit by the 2-process model reveals a rich variety of physical outliers and sometimes subtle measurement errors. Residual abundances allow comparison of populations controlled for differences in metallicity and [α/Fe]. Relative to the main disk (R = 3 -13 kpc), we find nearly identical abundance patterns in the outer disk (R = 15 -17 kpc), 0.05-0.2 dex depressions of multiple elements in LMC and Gaia Sausage/Enceladus stars, and wild deviations (0.4-1 dex) of multiple elements in ω Cen. Residual abundance analysis opens new opportunities for discovering chemically distinctive stars and stellar populations, for empirically constraining nucleosynthetic yields, and for testing chemical evolution models that include stochasticity in the production and redistribution of elements.
During an imaging survey of the Chamaeleon I star-forming region with the Advanced Camera for Sur... more During an imaging survey of the Chamaeleon I star-forming region with the Advanced Camera for Surveys aboard the Hubble Space Telescope, we have discovered a candidate substellar companion to the young low-mass star CHXR 73 (τ ∼ 2 Myr, M ∼ 0.35 M ⊙ ). We measure a projected separation of 1. ′′ 30 ± 0. ′′ 03 for the companion, CHXR 73 B, which corresponds to 210 AU at the distance of the cluster. A near-infrared spectrum of this source obtained with the Cornell Massachusetts Slit Spectrograph at the Magellan II telescope exhibits strong steam absorption that confirms its latetype nature ( M9.5). In addition, the gravity-sensitive shapes of the H-and K-band continua demonstrate that CHXR 73 B is a young, pre-main-sequence object rather than a field star. The probability that CHXR 73 A and B are unrelated members of Chamaeleon I is ∼ 0.001. We estimate the masses of CHXR 73 B and other known substellar companions in young clusters with a method that is consistent with the dynamical measurements of the eclipsing binary brown dwarf 2M 0535-0546, which consists of a comparison of the bolometric luminosities of the companions to the values predicted by the evolutionary models of Chabrier & coworkers and Burrows & coworkers. We arrive at mass estimates of 0.003-0.004, 0.024 ± 0.012, 0.011 +0.01 -0.003 , and 0.012 +0.008 -0.005 M ⊙ for 2M 1207-3932 B, GQ Lup B, DH Tau B, and CHXR 73 B, respectively. Thus, DH Tau B and CHXR 73 B appear to be the least massive companions to stars outside the solar system that have been detected in direct images, and may have masses that are within the range observed for extrasolar planetary companions (M 0.015 M ⊙ ). However, because these two objects (as well as 2M 1207-3932 B) probably did not form within circumstellar disks around their primaries, we suggest that they should be viewed as brown dwarf companions rather than planets.
Despite its importance for understanding the nature of early stellar generations and for constrai... more Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, highresolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] -1.7), including two that are very metal-poor [Fe/H] ∼ -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the α-elements O, Mg, and Si without significant α-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.
This paper seeks to synthesize much recent work on the HTSC materials around the latest energy re... more This paper seeks to synthesize much recent work on the HTSC materials around the latest energy resolved scanning tunnelling microscopy (STM) results from Davis and coworkers. The STM conductance diffuse scattering results in particular are employed as point of entry to discuss bosonic modes, both of condensed and uncondensed form. The bosonic mode picture is essential to understanding an ever growing range of observations within the HTSC field. The work is expounded within the context of the site-inhomogeneous negative-U boson-fermion modelling long advocated by the author. This general approach is presently seeing much theoretical development, into which I have looked to couple many of the experimental advances. While this formal theory is not yet sufficiently detailed to cover adequately all the experimental complexities presented by the real cuprate systems, it is clear it affords very appreciable support to the line taken. An attempt is made throughout to clarify why and how it is that these novel circumstances and phenomena are tied so very closely to this particular set of materials.
Recent photoemission work on underdoped cuprates between Tc and T*, the pseudogap temperature, ar... more Recent photoemission work on underdoped cuprates between Tc and T*, the pseudogap temperature, are interpreted within the framework of a previously developed negative-U scenario. From this exposition, incorporating a developed 2q diagonal striping model, detailed understanding follows of the ARPES results, together with certain STM and far infrared optical data. Identification of the origin of the magnetic circular dichroism and related effects exhibited by such materials below T* also appears to have been achieved.
Recently, interest has emerged in investigating the potential for use of advanced materials in de... more Recently, interest has emerged in investigating the potential for use of advanced materials in developing new and innovative structural response modification devices for seismic applications, such as for seismic isolator and damping systems. Shape memory alloys (SMAs) are a class of metals that have the capability to dissipate energy through repeated cycling loading without significant permanent deformations. They have a high usable strain range (up to about 8%) compared to other metals, and thus require a smaller volume of material in order to produce the same damping capacity. They also possess an inherent ability to provide stiff elastic resistance at large displacements. One of the most promising of these alloys is a material composed of essentially equal percentages of nickel and titanium (Nitinol). Although relatively commonplace in other fields such as biomedical applications, the development of SMA devices for seismic applications is still in the infancy stages. Consequently...
Symposium - International Astronomical Union, 2003
We present new M and L-dwarfs confirmed through follow-up of 2MASS color-selected objects with th... more We present new M and L-dwarfs confirmed through follow-up of 2MASS color-selected objects with the CorMASS near-infrared spectrograph (R ˜ 300) on the Palomar 60-inch telescope as part of a continuing follow-up survey. Most of the objects are bright…
Symposium - International Astronomical Union, 2003
The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% compl... more The Cornell High-order Adaptive Optics Survey for brown dwarfs (CHAOS), currently about 90% complete, uses the Palomar Hale Telescope's adaptive optics system to survey 80 bright stars out to 13 parsecs. Using the telescope's AO Science camera, brown dwarf companions 4–200 AU can be identified using coronagraphic imaging and spectroscopic modes. We will be using monte carlo simulations to create population models consistent with the CHAOS data set.Currently, we have observed 70 systems out of a target sample of 80. Five candidate companions await follow-up observations. As of now, no systems in the target sample have shown strong evidence of having brown dwarf companions. These early results support previous speculations of a “brown dwarf desert” at orbital separations out to 200 AU.While the target sources revealed no evidence of brown dwarf companions, accompanying observations of calibration stars provided evidence of an early methane dwarf candidate around the binary sys...
The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a co... more The Large Binocular Telescope (LBT) houses two 8.4-meter mirrors separated by 14.4 meters on a common mount. Coherent combination of these two AO-corrected apertures via the LBT Interferometer (LBTI) produces Fizeau interferometric images with a spatial resolution equivalent to that of a 22.8-meter telescope and the lightgathering power of single 11.8-meter mirror. Capitalizing on these unique capabilities, we used LBTI/LMIRcam to image thermal radiation from volcanic activity on the surface of Io at M-Band (4.8 µm) over a range of parallactic angles. We compare two deconvolution routines in order to recover the full spatial resolution of the combined images, resolving at least fifteen known volcanic hot spots. Coupling these observations with advanced image reconstruction algorithms demonstrates the versatility of Fizeau interferometry and realizes the LBT as the first in a series of extremely large telescopes.
In this paper we present a novel, quadruple well process developed in a modern 0.18 µm CMOS techn... more In this paper we present a novel, quadruple well process developed in a modern 0.18 µm CMOS technology called INMAPS. On top of the standard process, we have added a deep P implant that can be used to form a deep P-well and provide screening of N-wells from the P-doped epitaxial layer. This prevents the collection of radiation-induced charge by unrelated N-wells, typically ones where PMOS transistors are integrated. The design of a
Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter, 2006
We describe the optical and mechanical design of a simple hand-held near infra-red spectrograph c... more We describe the optical and mechanical design of a simple hand-held near infra-red spectrograph constructed to produce observations of the spectrum of scrambled light from the Earth from aboard the International Space Station. Observing the Earth in this manner simulates the changing perspective on an extra-solar terrestrial planet observed as a point source by the Terrestrial Planet Finder. A Sensors Unlimited, Inc. SU320-M InGaAs(0.86 − 1.72µm) camera detects the dispersed spectrum and outputs NTSC video to be recorded and also permits frame grabbing. One of the three copies of the instrument is currently aboard the International Space Station. The optical and mechanical design was conceived and executed by graduate and undergraduate students at the University of Virginia.
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 2012
We diamond fly cut 2 sets of germanium grisms for the LMIRcam 3-5 micron Fizeau imager for the co... more We diamond fly cut 2 sets of germanium grisms for the LMIRcam 3-5 micron Fizeau imager for the combined focus of the Large Binocular Telescope (LBT). The grisms mount in a filter wheel near a pupil to enable moderate resolution (R~300) spectroscopy. Both sets have a measured blaze angle of 2.9º. The first set has a groove period of 40 lines/mm and will be used in first order with peak efficiency at 3.6 µm. The second set has 32 lines/mm. It can operate in first order with an efficiency peak near 4.4 µm and in second order with a peak near 2.3 µm. First results from testing the grisms in the instrument on the sky with the LBT are presented.
The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb −1... more The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb −1 of pp collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → J/ψ(→ µ + µ −)π + π − decay mode, and probes ψ(2S) mesons with transverse momenta in the range 10 ≤ p T < 100 GeV and rapidity |y| < 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production.
Additional jet activity in dijet events is measured using pp collisions at ATLAS at a centre-of-m... more Additional jet activity in dijet events is measured using pp collisions at ATLAS at a centre-of-mass energy of 7 TeV, for jets reconstructed using the anti-k t algorithm with radius parameter R = 0.6. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijets. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the scalar average of the transverse momenta of the dijets and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijets. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to powheg, interfaced to the pythia 8 and herwig parton shower generators, as well as to hej with and without interfacing it to the ariadne parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, powheg+pythia 8 and hej+ariadne are found to provide the best agreement with the data. These measurements use the full data sample collected with the ATLAS detector in 7 TeV pp collisions at the LHC and correspond to integrated luminosities of 36.1 pb −1 and 4.5 fb −1 for data collected during 2010 and 2011, respectively.
A detailed exposition is made of recent transport and 'quantum oscillation' results fro... more A detailed exposition is made of recent transport and 'quantum oscillation' results from HTSC systems covering the full range from overdoped to underdoped material. This now very extensive and high quality data set is interpreted here within the framework developed by the author of local pairs and boson-fermion resonance, arising in the context of negative-U behaviour in an inhomogeneous electronic environment. The strong inhomogeneity comes with the mixed-valent condition of these materials, which when underdoped lie in close proximity to the Mott-Anderson transition. The observed intense scattering is presented as resulting from pair formation and electron-boson collisions in the resonant crossover circumstance. The high level of scattering brings the systems to incoherence in the pseudogapped state, p < pc (= 0.183). In a high magnetic field the striped partition of the inhomogeneous charge distribution is much strengthened and regularized. Magnetization and resistan...
Recent high energy observations of Cas A suggests the presence of synchrotron radiation, implying... more Recent high energy observations of Cas A suggests the presence of synchrotron radiation, implying acceleration of cosmic rays by young supernova remnants. We detect synchrotron emission from Cas A in the near-infrared using Two Micron All Sky Survey (2MASS) and Palomar 200 inch PFIRCAM observations. The remnant is detected in J, H, and K s bands using 2MASS: K s band is the brightest, H is moderate and J is faint. In the J and H bands, bright [Fe II] lines (1.24µm and 1.64µm) are detected spectroscopically. The Palomar observations include K s continuum, narrowband 1.64 µm (centered on [Fe II]) and 2.12µm (centered on H 2 (1-0)) images. While the narrow-band 1.64 µm image shows filamentary and knotty structures, similar to the optical image, the K s image shows a relatively smooth, diffuse shell, remarkably similar to the radio image. The H 2 image is identical to the K s continuum image with surface brightness reduced as expected for the ratio of filter bandwidths, showing no contribution of H 2 lines to the K s-band image. The broad-band near-infrared fluxes of Cas A are generally consistent with, but a few tens of percent higher than, an extrapolation of the radio fluxes. The hardening to higher frequencies is possibly due to nonlinear shock acceleration and/or spectral index variation across the remnant. We show evidence of spectral index variation across Cas A using the 'spectral tomography' technique. The presence of near-infrared synchrotron radiation requires the roll-off frequency to be higher than 1.5 × 10 14 Hz, implying that electrons are accelerated to-2energies of at least E = 0.3B −1/2 mG erg or 0.2 TeV. The morphological similarity in diffuse emission between the radio and K s band images implies that synchrotron losses are not dominant, or we would expect to see a greater concentration in knots. We also show dust continuum is not significant in the near-infrared emission of Cas A. Our observations show unambiguous evidence that the near-infrared K s band emission of Cas A is from synchrotron emission by accelerated cosmic-ray electrons.
We report 0.8-2.5 m spectrophotometry of CI Aquilae at eight epochs between 2000 May 9 and 2001 J... more We report 0.8-2.5 m spectrophotometry of CI Aquilae at eight epochs between 2000 May 9 and 2001 June 2 UT, corresponding to approximately 3 and 391 days after peak brightness. Near peak brightness, the spectra showed emission lines that were characteristic of a low-excitation, nitrogen-rich shell. Within a few weeks, the spectra began to show higher excitation/ionization emission lines indicative of a harder illuminating source: the neutral metal lines faded, leaving only lines of H i, He i, and He ii and the emerging coronal lines. A month after peak brightness, the [Ca viii] coronal line at 2.3205 m appeared and persisted until the last of our observations, on day +391. From the O i line ratios, we deduced a reddening of E BÀV = 1.5 AE 0.1 and a visual extinction of A V = 4.6 AE 0.2. Along with the rate of decline from the light curve (t 2), we derived a distance of 2.6 AE 1.3 kpc. The frequently observed unidentified novae lines were present in CI Aquilae along with a potentially new member of the group at 2.425 AE 0.002 m.
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Papers by John Wilson