Paul Goldsmith - Academia.edu (original) (raw)
Papers by Paul Goldsmith
Astronomy & Astrophysics, 2016
Context. The past decade has witnessed a large number of Galactic plane surveys at angular resolu... more Context. The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20. However, no comparable high-resolution survey exists at long radio wavelengths around 21 cm in line and continuum emission. Aims. We remedy this situation by studying the northern Galactic plane at ∼20 resolution in emission of atomic, molecular, and ionized gas. Methods. Employing the Karl G. Jansky Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21 cm line, four OH lines, nineteen Hnα radio recombination lines as well as the continuum emission from 1 to 2 GHz in full polarization over a large part of the first Galactic quadrant. Results. Covering Galactic longitudes from 14.5 to 67.4 deg and latitudes between ±1.25 deg, we image all of these lines and the continuum at ∼20 resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Hnα radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page. Conclusions. The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from Hii regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing the different datasets will allow us to address many open questions.
![Research paper thumbnail of Photon-Dominated Region Modeling of the [C I], [C II], and Co Line Emission from a Boundary in the Taurus Molecular Cloud](https://attachments.academia-assets.com/107106310/thumbnails/1.jpg)
](The Astrophysical Journal, 2014
We present [C i] and [C ii] observations of a linear edge region in the Taurus molecular cloud, a... more We present [C i] and [C ii] observations of a linear edge region in the Taurus molecular cloud, and model this region as a cylindrically symmetric PDR exposed to a low-intensity UV radiation field. The sharp, long profile of the linear edge makes it an ideal case to test PDR models and determine cloud parameters. We compare observations of the [C i], 3 P 1 → 3 P 0 (492 GHz), [C i] 3 P 2 → 3 P 1 (809 GHz), and [C ii] 2 P 3/2 → 2 P 1/2 (1900 GHz) transitions, as well as the lowest rotational transitions of 12 CO and 13 CO, with line intensities produced by the RATRAN radiative transfer code from the results of the Meudon PDR code. We constrain the density structure of the cloud by fitting a cylindrical density function to visual extinction data. We study the effects of variation of the FUV field, 12 C/ 13 C isotopic abundance ratio, sulfur depletion, cosmic ray ionization rate, and inclination of the filament relative to the sky-plane on the chemical network of the PDR model and resulting line emission. We also consider the role of suprathermal chemistry and density inhomogeneities. We find good agreement between the model and observations, and that the integrated line intensities can be explained by a PDR model with an external FUV field of 0.05 G 0 , a low ratio of 12 C to 13 C ∼ 43, a highly depleted sulfur abundance (by a factor of at least 50), a cosmic ray ionization rate (3 − 6) × 10 −17 s −1 , and without significant effects from inclination, clumping or suprathermal chemistry.
The Astrophysical Journal, 2002
We report the tentative detection of molecular oxygen in the interstellar medium. Deep integratio... more We report the tentative detection of molecular oxygen in the interstellar medium. Deep integrations using the Submillimeter Wave Astronomy (SWAS) satellite of the Oph A cloud have resulted in a detection of an emission feature consistent with the N J ¼ 3 3 ! 1 2 transition of O 2 at a local standard of rest velocity of 6.0 km s À1. The line width and velocity are suggestive of the redshifted wing emission seen in species that trace the molecular outflows seen in this region. The fractional abundance of O 2 relative to H 2 in this high-velocity gas is approximately 10 À5. The fractional abundance of ortho-H 2 O in this material is 8  10 À8 , somewhat higher than found in quiescent material by earlier SWAS observations but less than that found in younger outflows. We suggest a unified scenario that explains the low O 2 abundance in cloud cores previously reported ½X ðO 2 Þ few  10 À7 , along with the much enhanced abundance in the outflow region. In this picture, quiescent clouds are characterized by significant depletion of gas-phase oxygen, which ends up largely as water ice on the dust grains. A shock associated with the outflow results in almost all oxygen being processed into gas-phase water. In the cool postshock gas, the standard gas-phase chemistry reasserts itself, and after an elapsed time of a few times 10 5 yr, the O 2 abundance has increased to the point that this species is one of the main repositories of oxygen atoms. At the same time, the gas-phase water abundance drops drastically, in agreement with the SWAS observations that we report here. On a somewhat longer timescale, depletion again dominates and the gas-phase abundance of O 2 drops by several orders of magnitude, with a significant fraction of oxygen remaining in atomic form.
The Astrophysical Journal, 2007
![Research paper thumbnail of Collisional Excitation of the [C II] Fine Structure Transition in Interstellar Clouds](https://attachments.academia-assets.com/107106307/thumbnails/1.jpg)
](The Astrophysical Journal Supplement Series, 2012
We analyze the collisional excitation of the 158 µm (1900.5 GHz) fine structure transition of ion... more We analyze the collisional excitation of the 158 µm (1900.5 GHz) fine structure transition of ionized carbon in terms of line intensities produced by simple cloud models. The single C + fine structure transition is a very important coolant of the atomic interstellar medium and of photon dominated regions in which carbon is partially or completely in ionized form. The [CII] line is widely used as a tracer of star formation in the Milky Way and other galaxies. Excitation of the [CII] fine structure transition can be via collisions with hydrogen molecules, atoms, and electrons. Analysis of [CII] observations is complicated by the fact that it is difficult to determine the optical depth of the line. We discuss the excitation of the [CII] line, deriving analytic results for several limiting cases and carry out numerical solutions using a large velocity gradient model for a more inclusive analysis. For antenna temperatures up to 1/3 of the brightness temperature of the gas kinetic temperature, the antenna temperature is linearly proportional to the column density of C + irrespective of the optical depth of the transition. This is appropriately referred to as the effectively optically thin (EOT) approximation. We review the critical densities for excitation of the [CII] line by various collision partners, briefly analyze C + absorption, and conclude with a discussion of C + cooling and how the considerations for line intensities affect the behavior of this important coolant of the ISM.
![Research paper thumbnail of AHerschel[C ii] Galactic plane survey](https://attachments.academia-assets.com/107106280/thumbnails/1.jpg)
](Astronomy & Astrophysics, 2013
Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interste... more Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interstellar matter. Ionized carbon is present in a variety of phases of the interstellar medium (ISM), including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions. Aims. Velocity-resolved observations of [C ii] are the most powerful technique available to disentangle the emission produced by these components. These observations can also be used to trace CO-dark H 2 gas and determine the total mass of the ISM. Methods. The Galactic Observations of Terahertz C+ (GOT C+) project surveys the [C ii] 158 μm line over the entire Galactic disk with velocity-resolved observations using the Herschel/HIFI instrument. We present the first longitude-velocity maps of the [C ii] emission for Galactic latitudes b = 0 • , ±0.5 • , and ±1.0 •. We combine these maps with those of H i, 12 CO, and 13 CO to separate the different phases of the ISM and study their properties and distribution in the Galactic plane. Results. [C ii] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc. It traces the envelopes of evolved clouds as well as clouds that are in the transition between atomic and molecular. We estimate that most of the observed [C ii] emission is produced by dense photon dominated regions (∼47%), with smaller contributions from COdark H 2 gas (∼28%), cold atomic gas (∼21%), and ionized gas (∼4%). Atomic gas inside the Solar radius is mostly in the form of cold neutral medium (CNM), while the warm neutral medium gas dominates the outer galaxy. The average fraction of CNM relative to total atomic gas is ∼43%. We find that the warm and diffuse CO-dark H 2 is distributed over a larger range of Galactocentric distances (4−11 kpc) than the cold and dense H 2 gas traced by 12 CO and 13 CO (4−8 kpc). The fraction of CO-dark H 2 to total H 2 increases with Galactocentric distance, ranging from ∼20% at 4 kpc to ∼80% at 10 kpc. On average, CO-dark H 2 accounts for ∼30% of the molecular mass of the Milky Way. When the CO-dark H 2 component is included, the radial distribution of the CO-to-H 2 conversion factor is steeper than that when only molecular gas traced by CO is considered. Most of the observed [C ii] emission emerging from dense photon dominated regions is associated with modest far-ultraviolet fields in the range χ 0 1−30.
Eighteenth International Symposium on …, 2007
Submillimeter astronomy from space offers many advantages, due to completely avoiding the attenua... more Submillimeter astronomy from space offers many advantages, due to completely avoiding the attenuations and noise from the Earth's atmosphere. For spectroscopy in the 60 to 670 micron range, the Herschel Space Observatory offers important new capabilities in terms of angular resolution, sensitivity, and over much of this range, for high spectral resolution observations. Herschel builds on the success of two earlier space missions devoted to submillimeter spectroscopy: SWAS and Odin. In this paper, I briefly highlight the results from those missions. I then discuss the capabilities of the three instruments on the Herschel Space Observatory, known by their acronyms HIFI, SPIRE, and PACS, focusing on spectroscopic observations. I conclude with a short summary of some of the astrophysical highlights that may be anticipated when Herschel is operational, which should be about 6 months after launch, currently scheduled for September 2008.
Zone plate lenses are a type of focusing element which function essentially as differential phase... more Zone plate lenses are a type of focusing element which function essentially as differential phase shifters, having a relatively few, coarsely quantized phase delays across the incident beam of radiation. The major advantages are ease of fabrication and much reduced thickness, compared to conventional refractive focusing elements. These considerations are both of particular importance for the submillimeter range, in which manufacturing tolerances for curved optical elements can pose significant problems, and where the absorption of readily available dielectric materials is quite large. In this presentation we briefly review the theory of zone plate lens operation, present a relatively simple method for calculating the aperture efficiency of zone plate lenses used as antennas, and show some theoretical and measured results in the 100 GHz range.
In this paper, we present measurements of a prototype metamaterial flat lens. Flat, lenses with s... more In this paper, we present measurements of a prototype metamaterial flat lens. Flat, lenses with short focal lengths are of particular interest due to their potential use in quasi-optical observing in space-based cubesat applications. Our metamaterial flat lens was manufactured by using 11 layers of RO3003 circuit board laminate with etched sub-wavelengthsized copper patterning. The copper patterning is designed in such a way as to maximize the transmittance of the lens while applying the correct phase shift across the lens plane to give the lens its focusing properties. The lens was measured by scanning a receiver horn through one axis of the image plane of a transmitting horn. This measurement demonstrated that the waist of the focused gaussian beam is 30% wider than ideal. It is suspected that this non-ideality is caused by phase error in the design process, though simulations would be necessary to confirm this. Further measurements will be useful to fully characterize the lens’s ...
Quasioptical Systems, 2009
Ground-based and Airborne Telescopes VI, 2016
We present the details of the optical design, corrector system, mechanical layout, tolerances, po... more We present the details of the optical design, corrector system, mechanical layout, tolerances, pointing requirements, and overall performance of the sub-millimeter wavelength Large Balloon Reflector telescope (LBR).
IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium
ABSTRACT
IEEE Antennas and Propagation Society International Symposium 1992 Digest, 1992
The basic principles used in the Keck telescope have been applied to the design of a large segmen... more The basic principles used in the Keck telescope have been applied to the design of a large segmented millimeter-wave radio telescope. The Large Millimeter Telescope is envisioned as a 50 m-diameter instrument operating at wavelengths as short as 1 mm, with a peak gain approached 100 dB. A geometry for the surface that has 126 hexagonal segments in a classical
2014 39th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2014
Use the ground state Water line at 557 GHz to probe the formation of planetary systems. Goal 2: E... more Use the ground state Water line at 557 GHz to probe the formation of planetary systems. Goal 2: External Galaxies: Use the ground state Water line at 557 GHz to probe the chemistry and physical conditions in Normal, Starburst, & High z galaxies. Goal 3: Cosmic Evolution: Use the LiH line at 444 GHz to determine the lithium abundance along multiple lines of sight through the Galaxy. The Large Balloon Reflector (LBR) is a gamechanging concept to use the aluminized halfhemisphere of a balloon to form a 10 meter stratospheric observatory. The spherical balloon reflector is deployed within a larger carrier balloon that serves both as a launch vehicle and radome. Such a telescope could study the origins of stars, planets, molecular clouds, and galaxies; providing a much needed means of following-up on tantalizing results from recent successful missions such as Spitzer, Herschel, and SOFIA. LBR will perform high spectral/spatial resolution observations in astrophysically important atomic and molecular spectral lines only accessible from near space or from orbit. The proposed effort directly addresses NASA's Strategic Goals 2, 3, 5, and 6. Data Products: Spectroscopic data base of water and LiH lines toward a variety of galactic and extragalactic objects.
Depletion of molecules from the gas phase onto surfaces of dust grains is becoming increasingly w... more Depletion of molecules from the gas phase onto surfaces of dust grains is becoming increasingly well-established observationally. The reduction in the abundance of key gas phase coolants will inevitably reduce the cooling rate and tend to increase the gas temperature in the central, well-shielded regions of dark clouds. The increased temperature would have the effect of limiting the depletion. We investigate this effect of depletion by calculating the gas phase cooling rate as a function of depletion factor. The SWAS determination of the surprisingly low abundances of molecular oxygen and water help define the important coolants. The cooling is only weakly dependent on the molecular depletion, due to the large optical depths of the key cooling lines, particularly the lower rotational transitions of carbon monoxide. The coupling with dust grains is included in a calculation of thermal balance, and we find that in well-shielded regions, at densities above 104 cm-3, the coupling of gas...
The Astrophysical Journal, 1972
ABSTRACT
Astronomy & Astrophysics, 2016
Context. The past decade has witnessed a large number of Galactic plane surveys at angular resolu... more Context. The past decade has witnessed a large number of Galactic plane surveys at angular resolutions below 20. However, no comparable high-resolution survey exists at long radio wavelengths around 21 cm in line and continuum emission. Aims. We remedy this situation by studying the northern Galactic plane at ∼20 resolution in emission of atomic, molecular, and ionized gas. Methods. Employing the Karl G. Jansky Very Large Array (VLA) in the C-array configuration and a large program, we observe the HI 21 cm line, four OH lines, nineteen Hnα radio recombination lines as well as the continuum emission from 1 to 2 GHz in full polarization over a large part of the first Galactic quadrant. Results. Covering Galactic longitudes from 14.5 to 67.4 deg and latitudes between ±1.25 deg, we image all of these lines and the continuum at ∼20 resolution. These data allow us to study the various components of the interstellar medium (ISM): from the atomic phase, traced by the HI line, to the molecular phase, observed by the OH transitions, to the ionized medium, revealed by the cm continuum and the Hnα radio recombination lines. Furthermore, the polarized continuum emission enables magnetic field studies. In this overview paper, we discuss the survey outline and present the first data release as well as early results from the different datasets. We now release the first half of the survey; the second half will follow later after the ongoing data processing has been completed. The data in fits format (continuum images and line data cubes) can be accessed through the project web-page. Conclusions. The HI/OH/Recombination line survey of the Milky Way (THOR) opens a new window to the different parts of the ISM. It enables detailed studies of molecular cloud formation, conversion of atomic to molecular gas, and feedback from Hii regions as well as the magnetic field in the Milky Way. It is highly complementary to other surveys of our Galaxy, and comparing the different datasets will allow us to address many open questions.
The Astrophysical Journal, 2014
We present [C i] and [C ii] observations of a linear edge region in the Taurus molecular cloud, a... more We present [C i] and [C ii] observations of a linear edge region in the Taurus molecular cloud, and model this region as a cylindrically symmetric PDR exposed to a low-intensity UV radiation field. The sharp, long profile of the linear edge makes it an ideal case to test PDR models and determine cloud parameters. We compare observations of the [C i], 3 P 1 → 3 P 0 (492 GHz), [C i] 3 P 2 → 3 P 1 (809 GHz), and [C ii] 2 P 3/2 → 2 P 1/2 (1900 GHz) transitions, as well as the lowest rotational transitions of 12 CO and 13 CO, with line intensities produced by the RATRAN radiative transfer code from the results of the Meudon PDR code. We constrain the density structure of the cloud by fitting a cylindrical density function to visual extinction data. We study the effects of variation of the FUV field, 12 C/ 13 C isotopic abundance ratio, sulfur depletion, cosmic ray ionization rate, and inclination of the filament relative to the sky-plane on the chemical network of the PDR model and resulting line emission. We also consider the role of suprathermal chemistry and density inhomogeneities. We find good agreement between the model and observations, and that the integrated line intensities can be explained by a PDR model with an external FUV field of 0.05 G 0 , a low ratio of 12 C to 13 C ∼ 43, a highly depleted sulfur abundance (by a factor of at least 50), a cosmic ray ionization rate (3 − 6) × 10 −17 s −1 , and without significant effects from inclination, clumping or suprathermal chemistry.
The Astrophysical Journal, 2002
We report the tentative detection of molecular oxygen in the interstellar medium. Deep integratio... more We report the tentative detection of molecular oxygen in the interstellar medium. Deep integrations using the Submillimeter Wave Astronomy (SWAS) satellite of the Oph A cloud have resulted in a detection of an emission feature consistent with the N J ¼ 3 3 ! 1 2 transition of O 2 at a local standard of rest velocity of 6.0 km s À1. The line width and velocity are suggestive of the redshifted wing emission seen in species that trace the molecular outflows seen in this region. The fractional abundance of O 2 relative to H 2 in this high-velocity gas is approximately 10 À5. The fractional abundance of ortho-H 2 O in this material is 8  10 À8 , somewhat higher than found in quiescent material by earlier SWAS observations but less than that found in younger outflows. We suggest a unified scenario that explains the low O 2 abundance in cloud cores previously reported ½X ðO 2 Þ few  10 À7 , along with the much enhanced abundance in the outflow region. In this picture, quiescent clouds are characterized by significant depletion of gas-phase oxygen, which ends up largely as water ice on the dust grains. A shock associated with the outflow results in almost all oxygen being processed into gas-phase water. In the cool postshock gas, the standard gas-phase chemistry reasserts itself, and after an elapsed time of a few times 10 5 yr, the O 2 abundance has increased to the point that this species is one of the main repositories of oxygen atoms. At the same time, the gas-phase water abundance drops drastically, in agreement with the SWAS observations that we report here. On a somewhat longer timescale, depletion again dominates and the gas-phase abundance of O 2 drops by several orders of magnitude, with a significant fraction of oxygen remaining in atomic form.
The Astrophysical Journal, 2007
The Astrophysical Journal Supplement Series, 2012
We analyze the collisional excitation of the 158 µm (1900.5 GHz) fine structure transition of ion... more We analyze the collisional excitation of the 158 µm (1900.5 GHz) fine structure transition of ionized carbon in terms of line intensities produced by simple cloud models. The single C + fine structure transition is a very important coolant of the atomic interstellar medium and of photon dominated regions in which carbon is partially or completely in ionized form. The [CII] line is widely used as a tracer of star formation in the Milky Way and other galaxies. Excitation of the [CII] fine structure transition can be via collisions with hydrogen molecules, atoms, and electrons. Analysis of [CII] observations is complicated by the fact that it is difficult to determine the optical depth of the line. We discuss the excitation of the [CII] line, deriving analytic results for several limiting cases and carry out numerical solutions using a large velocity gradient model for a more inclusive analysis. For antenna temperatures up to 1/3 of the brightness temperature of the gas kinetic temperature, the antenna temperature is linearly proportional to the column density of C + irrespective of the optical depth of the transition. This is appropriately referred to as the effectively optically thin (EOT) approximation. We review the critical densities for excitation of the [CII] line by various collision partners, briefly analyze C + absorption, and conclude with a discussion of C + cooling and how the considerations for line intensities affect the behavior of this important coolant of the ISM.
Astronomy & Astrophysics, 2013
Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interste... more Context. The [C ii] 158 μm line is an important tool for understanding the life cycle of interstellar matter. Ionized carbon is present in a variety of phases of the interstellar medium (ISM), including the diffuse ionized medium, warm and cold atomic clouds, clouds in transition from atomic to molecular, and dense and warm photon dominated regions. Aims. Velocity-resolved observations of [C ii] are the most powerful technique available to disentangle the emission produced by these components. These observations can also be used to trace CO-dark H 2 gas and determine the total mass of the ISM. Methods. The Galactic Observations of Terahertz C+ (GOT C+) project surveys the [C ii] 158 μm line over the entire Galactic disk with velocity-resolved observations using the Herschel/HIFI instrument. We present the first longitude-velocity maps of the [C ii] emission for Galactic latitudes b = 0 • , ±0.5 • , and ±1.0 •. We combine these maps with those of H i, 12 CO, and 13 CO to separate the different phases of the ISM and study their properties and distribution in the Galactic plane. Results. [C ii] emission is mostly associated with spiral arms, mainly emerging from Galactocentric distances between 4 and 10 kpc. It traces the envelopes of evolved clouds as well as clouds that are in the transition between atomic and molecular. We estimate that most of the observed [C ii] emission is produced by dense photon dominated regions (∼47%), with smaller contributions from COdark H 2 gas (∼28%), cold atomic gas (∼21%), and ionized gas (∼4%). Atomic gas inside the Solar radius is mostly in the form of cold neutral medium (CNM), while the warm neutral medium gas dominates the outer galaxy. The average fraction of CNM relative to total atomic gas is ∼43%. We find that the warm and diffuse CO-dark H 2 is distributed over a larger range of Galactocentric distances (4−11 kpc) than the cold and dense H 2 gas traced by 12 CO and 13 CO (4−8 kpc). The fraction of CO-dark H 2 to total H 2 increases with Galactocentric distance, ranging from ∼20% at 4 kpc to ∼80% at 10 kpc. On average, CO-dark H 2 accounts for ∼30% of the molecular mass of the Milky Way. When the CO-dark H 2 component is included, the radial distribution of the CO-to-H 2 conversion factor is steeper than that when only molecular gas traced by CO is considered. Most of the observed [C ii] emission emerging from dense photon dominated regions is associated with modest far-ultraviolet fields in the range χ 0 1−30.
Eighteenth International Symposium on …, 2007
Submillimeter astronomy from space offers many advantages, due to completely avoiding the attenua... more Submillimeter astronomy from space offers many advantages, due to completely avoiding the attenuations and noise from the Earth's atmosphere. For spectroscopy in the 60 to 670 micron range, the Herschel Space Observatory offers important new capabilities in terms of angular resolution, sensitivity, and over much of this range, for high spectral resolution observations. Herschel builds on the success of two earlier space missions devoted to submillimeter spectroscopy: SWAS and Odin. In this paper, I briefly highlight the results from those missions. I then discuss the capabilities of the three instruments on the Herschel Space Observatory, known by their acronyms HIFI, SPIRE, and PACS, focusing on spectroscopic observations. I conclude with a short summary of some of the astrophysical highlights that may be anticipated when Herschel is operational, which should be about 6 months after launch, currently scheduled for September 2008.
Zone plate lenses are a type of focusing element which function essentially as differential phase... more Zone plate lenses are a type of focusing element which function essentially as differential phase shifters, having a relatively few, coarsely quantized phase delays across the incident beam of radiation. The major advantages are ease of fabrication and much reduced thickness, compared to conventional refractive focusing elements. These considerations are both of particular importance for the submillimeter range, in which manufacturing tolerances for curved optical elements can pose significant problems, and where the absorption of readily available dielectric materials is quite large. In this presentation we briefly review the theory of zone plate lens operation, present a relatively simple method for calculating the aperture efficiency of zone plate lenses used as antennas, and show some theoretical and measured results in the 100 GHz range.
In this paper, we present measurements of a prototype metamaterial flat lens. Flat, lenses with s... more In this paper, we present measurements of a prototype metamaterial flat lens. Flat, lenses with short focal lengths are of particular interest due to their potential use in quasi-optical observing in space-based cubesat applications. Our metamaterial flat lens was manufactured by using 11 layers of RO3003 circuit board laminate with etched sub-wavelengthsized copper patterning. The copper patterning is designed in such a way as to maximize the transmittance of the lens while applying the correct phase shift across the lens plane to give the lens its focusing properties. The lens was measured by scanning a receiver horn through one axis of the image plane of a transmitting horn. This measurement demonstrated that the waist of the focused gaussian beam is 30% wider than ideal. It is suspected that this non-ideality is caused by phase error in the design process, though simulations would be necessary to confirm this. Further measurements will be useful to fully characterize the lens’s ...
Quasioptical Systems, 2009
Ground-based and Airborne Telescopes VI, 2016
We present the details of the optical design, corrector system, mechanical layout, tolerances, po... more We present the details of the optical design, corrector system, mechanical layout, tolerances, pointing requirements, and overall performance of the sub-millimeter wavelength Large Balloon Reflector telescope (LBR).
IEEE MTT-S International Microwave Symposium digest. IEEE MTT-S International Microwave Symposium
ABSTRACT
IEEE Antennas and Propagation Society International Symposium 1992 Digest, 1992
The basic principles used in the Keck telescope have been applied to the design of a large segmen... more The basic principles used in the Keck telescope have been applied to the design of a large segmented millimeter-wave radio telescope. The Large Millimeter Telescope is envisioned as a 50 m-diameter instrument operating at wavelengths as short as 1 mm, with a peak gain approached 100 dB. A geometry for the surface that has 126 hexagonal segments in a classical
2014 39th International Conference on Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2014
Use the ground state Water line at 557 GHz to probe the formation of planetary systems. Goal 2: E... more Use the ground state Water line at 557 GHz to probe the formation of planetary systems. Goal 2: External Galaxies: Use the ground state Water line at 557 GHz to probe the chemistry and physical conditions in Normal, Starburst, & High z galaxies. Goal 3: Cosmic Evolution: Use the LiH line at 444 GHz to determine the lithium abundance along multiple lines of sight through the Galaxy. The Large Balloon Reflector (LBR) is a gamechanging concept to use the aluminized halfhemisphere of a balloon to form a 10 meter stratospheric observatory. The spherical balloon reflector is deployed within a larger carrier balloon that serves both as a launch vehicle and radome. Such a telescope could study the origins of stars, planets, molecular clouds, and galaxies; providing a much needed means of following-up on tantalizing results from recent successful missions such as Spitzer, Herschel, and SOFIA. LBR will perform high spectral/spatial resolution observations in astrophysically important atomic and molecular spectral lines only accessible from near space or from orbit. The proposed effort directly addresses NASA's Strategic Goals 2, 3, 5, and 6. Data Products: Spectroscopic data base of water and LiH lines toward a variety of galactic and extragalactic objects.
Depletion of molecules from the gas phase onto surfaces of dust grains is becoming increasingly w... more Depletion of molecules from the gas phase onto surfaces of dust grains is becoming increasingly well-established observationally. The reduction in the abundance of key gas phase coolants will inevitably reduce the cooling rate and tend to increase the gas temperature in the central, well-shielded regions of dark clouds. The increased temperature would have the effect of limiting the depletion. We investigate this effect of depletion by calculating the gas phase cooling rate as a function of depletion factor. The SWAS determination of the surprisingly low abundances of molecular oxygen and water help define the important coolants. The cooling is only weakly dependent on the molecular depletion, due to the large optical depths of the key cooling lines, particularly the lower rotational transitions of carbon monoxide. The coupling with dust grains is included in a calculation of thermal balance, and we find that in well-shielded regions, at densities above 104 cm-3, the coupling of gas...
The Astrophysical Journal, 1972
ABSTRACT