N. R. Erickson

University of Massachusetts Amherst, Amherst Center, Massachusetts, United States

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Publications (162)336.27 Total impact

  • A. A. Danylov · A. R. Light · J. Waldman · N. Erickson
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    ABSTRACT: Measurements of the frequency stability of a far-infrared molecular laser have been made by mixing the harmonic of an ultrastable microwave source with a portion of the laser output signal in a terahertz (THz) Schottky diode balanced mixer. A 3 GHz difference-frequency signal was used in a frequency discriminator circuit to lock the laser to the microwave source. Comparisons of the short- and long-term laser frequency stability under free-running and locked conditions show a significant improvement with locking. Short-term frequency jitter was reduced by an order of magnitude, from approximately 40 to 4 kHz, and long-term drift was reduced by more than three orders of magnitude, from approximately 250 kHz to 80 Hz. The results, enabled by the efficient Schottky diode balanced mixer downconverter, demonstrate that ultrastable microwave-based frequency stabilization of THz optically pumped lasers (OPLs) will now be possible at frequencies extending well above 4.0 THz.
    No preview · Article · Dec 2015 · Applied Optics

  • No preview · Article · Nov 2015 · Optics Letters
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    ABSTRACT: The 23rd and 31st harmonics of a microwave signal generated in a novel THz balanced Schottky diode mixer were used as a frequency stable reference source to phase lock solid-nitrogen-cooled 2.324 and 2.959 THz quantum cascade lasers. Hertz-level frequency stability was achieved, which was maintained for several hours.
    No preview · Article · Oct 2015 · Optics Letters
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    ABSTRACT: An understanding of the mass build-up in galaxies over time necessitates tracing the evolution of cold gas (molecular and atomic) in galaxies. To that end, we have conducted a pilot study called CO Observations with the LMT of the Blind Ultra-Deep H I Environment Survey (COOL BUDHIES). We have observed 23 galaxies in and around the two clusters Abell 2192 (z = 0.188) and Abell 963 (z = 0.206), where 12 are cluster members and 11 are slightly in the foreground or background, using about 28 total hours on the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT) to measure the $^{12}$CO J = 1 --> 0 emission line and obtain molecular gas masses. These new observations provide a unique opportunity to probe both the molecular and atomic components of galaxies as a function of environment beyond the local Universe. For our sample of 23 galaxies, nine have reliable detections (S/N$\geq$3.6) of the $^{12}$CO line, and another six have marginal detections (2.0 < S/N < 3.6). For the remaining eight targets we can place upper limits on molecular gas masses roughly between $10^9$ and $10^{10} M_\odot$. Comparing our results to other studies of molecular gas, we find that our sample is significantly more abundant in molecular gas overall, when compared to the stellar and the atomic gas component, and our median molecular gas fraction lies about $1\sigma$ above the upper limits of proposed redshift evolution in earlier studies. We discuss possible reasons for this discrepancy, with the most likely conclusion being target selection and Eddington bias.
    No preview · Article · Oct 2015 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Measuring redshifted CO line emission is an unambiguous method for obtaining an accurate redshift and total cold gas content of optically faint, dusty starburst systems. Here, we report the first successful spectroscopic redshift determination of AzTEC J095942.9+022938 (‘COSMOS AzTEC-1’), the brightest 1.1 mm continuum source found in the AzTEC/James Clerk Maxwell Telescope survey (Scott et al.), through a clear detection of the redshifted CO (4–3) and CO (5–4) lines using the Redshift Search Receiver on the Large Millimeter Telescope. The CO redshift of z = 4.3420 ± 0.0004 is confirmed by the detection of the redshifted 158 μm [C ii] line using the Submillimeter Array. The new redshift and Herschel photometry yield LFIR = (1.1 ± 0.1) × 1013 L⊙ and SFR ≈ 1300 M⊙ yr−1. Its molecular gas mass derived using the ultraluminous infrared galaxy conversion factor is 1.4 ± 0.2 × 1011M⊙ while the total interstellar medium mass derived from the 1.1 mm dust continuum is 3.7 ± 0.7 × 1011M⊙ assuming Td = 35 K. Our dynamical mass analysis suggests that the compact gas disc (r ≈ 1.1 kpc, inferred from dust continuum and spectral energy distribution analysis) has to be nearly face-on, providing a natural explanation for the uncommonly bright, compact stellar light seen by the HST. The [C ii] line luminosity $L_{\rm [C\,\small {II}]}= 7.8\pm 1.1 \times 10^9 \,\mathrm{L}_{\odot }$ is remarkably high, but it is only 0.04 per cent of the total IR luminosity. AzTEC COSMOS-1 and other high redshift sources with a spatially resolved size extend the tight trend seen between [C ii]/FIR ratio and ΣFIR among IR-bright galaxies reported by Díaz-Santos et al. by more than an order of magnitude, supporting the explanation that the higher intensity of the IR radiation field is responsible for the ‘[C ii] deficiency’ seen among luminous starburst galaxies.
    Full-text · Article · Aug 2015 · Monthly Notices of the Royal Astronomical Society
  • X. Qian · A.A. Danylov · A.R. Light · J. Waldman · N. Erickson
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    ABSTRACT: This paper introduces the continuously tunable THz radiation through sideband generation of a free running and solidnitrogen- cooled THz quantum cascade laser. The 2.324 THz QCL operating in a single longitudinal mode (SLM) in continuous-wave (cw) was mixed with a swept synthesized microwave signal by a THz Schottky-diode-balanced mixer. Through sideband generation, two frequency branches were observed at low and high frequency, characterized with a Fourier-transform spectrometer. At low frequency, the sideband generates frequencies from -50 GHz to +50 GHz. At high frequency, it generates sideband frequencies from 70 GHz to 115 GHz. The total ±100 GHz tuning range can be further expanded with higher frequency millimeter wave amplifier/multiplier source. The sideband generates total 1 μW of output power at both upper and lower frequency with 200 μW of driven power from the THz QCL, showing a power conversion efficiency of 5 × 10-3. The demonstration of this SM, continuously tunable THz source enables its applications where SM, spatially coherent beam is required.
    No preview · Article · Jan 2015 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We present a new high-fidelity method of calibrating a cross-track scanning microwave radiometer using Global Positioning System (GPS) radio occultation (GPSRO) measurements. The radiometer and GPSRO receiver periodically observe the same volume of atmosphere near the Earth's limb, and these overlapping measurements are used to calibrate the radiometer. Performance analyses show that absolute calibration accuracy better than 0.25 K is achievable for temperature sounding channels in the 50–60-GHz band for a total-power radiometer using a weakly coupled noise diode for frequent calibration and proximal GPSRO measurements for infrequent (approximately daily) calibration. The method requires GPSRO penetration depth only down to the stratosphere, thus permitting the use of a relatively small GPS antenna. Furthermore, only coarse spacecraft angular knowledge (approximately one degree rms) is required for the technique, as more precise angular knowledge can be retrieved directly from the combined radiometer and GPSRO data, assuming that the radiometer angular sampling is uniform. These features make the technique particularly well suited for implementation on a low-cost CubeSat hosting both radiometer and GPSRO receiver systems on the same spacecraft. We describe a validation platform for this calibration method, the Microwave Radiometer Technology Acceleration (MiRaTA) CubeSat, currently in development for the National Aeronautics and Space Administration (NASA) Earth Science Technology Office. MiRaTA will fly a multiband radiometer and the Compact TEC/Atmosphere GPS Sensor in 2015.
    No preview · Article · Sep 2014 · IEEE Transactions on Geoscience and Remote Sensing
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    ABSTRACT: A compact, tunable, ultranarrowband terahertz source, Δν∼1 MHz, is demonstrated by upconversion of a 2.324 THz, free-running quantum cascade laser with a THz Schottky-diode-balanced mixer using a swept, synthesized microwave source to drive the nonlinearity. Continuously tunable radiation of 1 μW power is demonstrated in two frequency regions: νLaser±0 to 50 GHz and νLaser±70 to 115 GHz. The sideband spectra were characterized with a Fourier-transform spectrometer, and the radiation was tuned through CO, HDO, and D2O rotational transitions.
    No preview · Article · Jul 2014 · Applied Optics
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    ABSTRACT: The design, packaging, and characterization of a 70-95 GHz downconverter with 25 GHz of instantaneous bandwidth is presented. The circuit features a novel LO pass-through feature, making it suitable for integration in two-dimensional focal plane arrays with large-N. The chip has been packaged in a waveguide module and, in the packaged configuration, has a noise temperature below 2000 K (9 dB NF) and greater than 23 dB conversion gain, 8 dB input return loss, and 13 dB output return loss over the entire frequency range. The circuit operates with an LO power of just -5 dBm and has a DC power consumption of 170 mW.
    No preview · Conference Paper · Jun 2014
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    ABSTRACT: We present 12CO (J = 1 → 0) observations of a sample of local galaxies (0.04 < z < 0.08) with a large neutral hydrogen reservoir, or ‘H i monsters’. The data were obtained using the redshift search receiver on the five college radio astronomy observatory (FCRAO) 14 m telescope. The sample consists of 20 H i-massive galaxies with MH i > 3 × 1010 M⊙ from the Arecibo Legacy Fast ALFA (ALFALFA) survey and 8 low surface brightness galaxies (LSBs) with a comparable MH i(>1.5 × 1010 M⊙). Our sample selection is purely based on the amount of neutral hydrogen, thereby providing a chance to study how atomic and molecular gas relate to each other in these H i-massive systems. We have detected CO in 15 out of 20 ALFALFA selected galaxies and 4 out of 8 LSBs with molecular gas mass MH2 of (1–11)× 109 M⊙. Their total cold gas masses of (2–7) × 1010 M⊙ make them some of the most gas-massive galaxies identified to date in the Local Universe. Observed trends associated with H i, H2, and stellar properties of the H i massive galaxies and the field comparison sample are analysed in the context of theoretical models of galaxy cold gas content and evolution, and the importance of total gas content and improved recipes for handling spatially differentiated behaviours of disc and halo gas are identified as potential areas of improvement for the modelling.
    Preview · Article · Apr 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: form only given. A novel compact radiometer observing nine channels near the 118.75GHz oxygen absorption line is introduced. The radiometer is designed as the payload for the Micro-sized Microwave Atmospheric Satellite (MicroMAS). MicroMAS is a dual-spinning 3U CubeSat that aims to address the need for low-cost, mission-flexible, and rapidly deployable spaceborne sensors. The focus of the current MicroMAS mission is to observe convective thunderstorms, tropical cyclones, and hurricanes from a near-equatorial orbit. As a low cost platform, MicroMAS offers the potential to deploy multiple satellites, in a constellation, that can provide near-continuous views of severe weather. The existing architecture of few, high-cost platforms, infrequently view the same earth area which can miss rapid changes in the strength and direction of evolving storms thus degrading forecast accuracy. MicroMAS is a scalable CubeSat-based system that will pave the path towards improved revisit rates over critical earth regions, and achieve state-of-the-art performance relative to current systems with respect to spatial, spectral, and radiometric resolution. The current MicroMAS mission will demonstrate the viability of CubeSats for high-fidelity environmental monitoring and space control that would provide profound advances by reducing costs, by at least an order of magnitude, while increasing robustness to launch and sensor failures. This discourse focuses on the compact radiometer designed for this CubeSat mission. The radiometer is housed in a 1U (10 × 10 × 10 cm) payload section of the 3U (10 × 10 × 30 cm) MicroMAS CubeSat. The payload is scanned about the spacecraft's velocity vector as the spacecraft orbits the earth, creating crosstrack scans across the earth's surface. The first portion of the radiometer comprises a horn-fed reflector antenna, with a full-width at half-maximum (FWHM) beamwidth of 2.4°. Hence, the scanned beam has an a- proximate footprint diameter of 20Km at nadir incidence from a nominal altitude of 500Km. The antenna system is designed for a minimum 95% beam efficiency. The next stage of the radiometer consists of superheterodyne front-end receiver electronics with single sideband (SSB) operation. The front-end electronics includes an RF preamplifier module, a mixer module, and a local oscillator (LO). The RF preamplifier module contains a low noise RF amplifier and a weakly coupled noise diode for radiometric calibration. The mixer module comprises a HEMT diode mixer and an IF preamplifier MMIC. The LO is obtained using a 30GHz dielectric resonant oscillator (DRO) and a resistive diode tripler to obtain a 90GHz LO frequency. A key technology development in the MicroMAS radiometer system is the ultra-compact intermediate frequency processor (IFP) module for channelization, detection, and analog-to-digital conversion. The antenna system, RF front-end electronics, and backend IF electronics are highly integrated, miniaturized, and optimized for low-power operation. The payload also contains microcontrollers, with one of such being in the payload interface module (PIM), to package and transmit radiometric and housekeeping data to the spacecraft bus. A voltage regulator module (VRM) was also designed for the payload to convert the input bus voltage to the required voltages for the payload electronics. The payload requires 3W (average) of power. The MicroMAS payload flight unit is currently being developed by MIT Lincoln Laboratory, and the spacecraft bus flight unit being developed by the MIT Space Systems Laboratory and the MIT Department of Earth and Planetary Sciences for a 2014 launch to be provided by the NASA CubeSat Launch Initiative program.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: Frequency stabilization of a THz quantum cascade laser (QCL) to the harmonic of a microwave source has been accomplished using a Schottky diode waveguide mixer designed for harmonic mixing. The 2.32 THz, 1.0 milliwatt CW QCL is coupled into the signal port of the mixer and a 110 GHz signal, derived from a harmonic of a microwave synthesizer, is coupled into the IF port. The difference frequency between the 21st harmonic of 110 GHz and the QCL is used in a discriminator to adjust the QCL bias current to stabilize the frequency. The short-term frequency jitter is reduced from 550 kHz to 4.5 kHz (FWHM) and the long-term frequency drift is eliminated. This performance is compared to that of several other THz QCL frequency stabilization techniques.
    No preview · Article · Dec 2012 · Optics Express
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    Aeree Chung · Min S. Yun · Gopal Naraynan · Mark Heyer · Neal R. Erickson
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    ABSTRACT: The feedback from galactic outflows is thought to play an important role in shaping the gas content, star formation history, and ultimately the stellar mass function of galaxies. Here we present evidence for massive molecular outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the co-added Redshift Search Receiver 12CO (1-0) spectrum. Our stacked spectrum of 27 ULIRGs at z = 0.043-0.11 (νrest = 110-120 GHz) shows broad wings around the CO line with ΔV(FWZI) ≈ 2000 km s–1. Its integrated line flux accounts for up to 25% ± 5% of the total CO line luminosity. When interpreted as a massive molecular outflow wind, the associated mechanical energy can be explained by a concentrated starburst with star formation rate (SFR) ≥100 M ☉ yr–1, which agrees well with their SFR derived from the FIR luminosity. Using the high signal-to-noise stacked composite spectrum, we also probe 13CO and 12CN emission in the sample and discuss how the chemical abundance of molecular gas may vary depending on the physical conditions of the nuclear region.
    Preview · Article · Mar 2011 · The Astrophysical Journal Letters
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    ABSTRACT: The 3 mm wavelength spectra of 10 galaxies have been obtained at the Five College Radio Astronomy Observatory using a new, very broadband receiver and spectrometer, called the Redshift Search Receiver (RSR). The RSR has an instantaneous bandwidth of 37 GHz covering frequencies from 74 to 111 GHz and has a spectral resolution of 31 MHz (~100 km s–1). During tests of the RSR on the FCRAO 14 m telescope the complete 3 mm spectra of the central regions of NGC 253, Maffei 2, NGC1068, IC 342, M82, NGC 3079, NGC 3690, NGC 4258, Arp 220, and NGC 6240 were obtained. Within the wavelength band covered by the RSR, 20 spectral lines from 14 different atomic and molecular species were detected. Based on simultaneous fits to the spectrum of each galaxy, a number of key molecular line ratios are derived. A simple model which assumes the emission arises from an ensemble of Milky Way like Giant Molecular Cloud cores can adequately fit the observed line ratios using molecular abundances based on Galactic molecular cloud cores. Variations seen in some line ratios, such as 13CO/HCN and HCO+/HCN, can be explained if the mean density of the molecular gas varies from galaxy to galaxy. However, NGC 3690, NGC 4258, and NGC 6240 show very large HCO+/HCN ratios and require significant abundance enhancement of HCO+ over HCN, possible due to the proximity to active galactic nucleus activity. Finally, the mass of dense molecular gas is estimated and we infer that 25%-85% of the total molecular gas in the central regions of these galaxies must have densities greater than 104 cm–3.
    Full-text · Article · Jan 2011 · The Astronomical Journal
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    ABSTRACT: The reactive molecular ions, OH+, H2O+, and H3O+, key probes of the oxygen chemistry of the interstellar gas, have been observed toward Orion KL with the Heterodyne Instrument for Far Infrared on board the Herschel Space Observatory. All three N = 1 - 0 fine-structure transitions of OH+ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H2O+ 111 - 000 transition at 1115 and 1139 GHz were detected, and an upper limit was obtained for H3O+. OH+ and H2O+ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s-1, and a broad blue shifted absorption similar to that reported recently for HF and para-H218O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH+ and H2O+ for the 9 km s-1 component of 9 ± 3 x 1012 cm-2 and 7 ± 2 x 1012 cm-2, and those in the outflow of 1.9 ± 0.7 x 1013 cm-2 and 1.0 ± 0.3 x 1013 cm-2. Upper limits of 2.4 x 1012 cm-2 and 8.7 ± 1012 cm-2 were derived for the column densities of ortho and para-H3O+ from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. A higher gas density, despite the assumption of a large ionization rate, may explain the comparatively low column densities of the ions. A part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology under contract with the National Aeronautics and Space Administration. Copyright 2010© California Institute of Technology. All rights reserved.
    Full-text · Article · Jan 2011 · Astronomy and Astrophysics
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    ABSTRACT: We report observations of the reactive molecular ions OH$^+$, H$_2$O$^+$, and H$_3$O$^+$ towards Orion KL with Herschel/HIFI. All three $N=1-0$ fine-structure transitions of OH$^+$ at 909, 971, and 1033GHz and both fine-structure components of the doublet {\it ortho}-H$_2$O$^+$ $1_{11}-0_{00}$ transition at 1115 and 1139GHz were detected; an upper limit was obtained for H$_3$O$^+$. OH$^+$ and H$_2$O$^+$ are observed purely in absorption, showing a narrow component at the source velocity of 9 kms$^{-1}$, and a broad blueshifted absorption similar to that reported recently for HF and {\it para}-H$_{2}^{18}$O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH$^+$ and H$_2$O$^+$ for the 9 km s$^{-1}$ component of $9 \pm 3 \times 10^{12}$cm$^{-2}$ and $7 \pm 2 \times 10^{12}$cm$^{-2}$, and those in the outflow of $1.9 \pm 0.7 \times 10^{13}$cm$^{-2}$ and $1.0 \pm 0.3 \times 10^{13}$cm$^{-2}$. Upper limits of $2.4\times 10^{12}$cm$^{-2}$ and $8.7\times 10^{12}$cm$^{-2}$ were derived for the column densities of {\it ortho} and {\it para}-H$_3$O$^+$ from transitions near 985 and 1657GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate. Comment: 5 pages, 1 figure. Accepted to and to be published in the Herschel HIFI special issue of A\&A Letters
    Full-text · Article · Sep 2010
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    ABSTRACT: We present the first results of a high-spectral-resolution survey of the carbon-rich evolved star IRC+10216 that was carried out with the HIFI spectrometer onboard Herschel. This survey covers all HIFI bands, with a spectral range from 488 to 1901GHz. In this letter we focus on the band-1b spectrum, in a spectral range 554.5-636.5GHz, where we identified 130 spectral features with intensities above 0.03 K and a signal-to-noise ratio >5. Detected lines arise from HCN, SiO, SiS, CS, CO, metal-bearing species and, surprisingly, silicon dicarbide (SiC2). We identified 55 SiC2 transitions involving energy levels between 300 and 900 K. By analysing these rotational lines, we conclude that SiC2 is produced in the inner dust formation zone, with an abundance of ~2x10^-7 relative to molecular hydrogen. These SiC2 lines have been observed for the first time in space and have been used to derive an SiC2 rotational temperature of ~204 K and a source-averaged column density of ~6.4x10^15 cm^-2. Furthermore, the high quality of the HIFI data set was used to improve the spectroscopic rotational constants of SiC2. Comment: A&A HIFI Special Issue, 2010
    Full-text · Article · Aug 2010 · Astronomy and Astrophysics
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    ABSTRACT: This paper describes the current status of the Large Millimeter Telescope (LMT), the near-term plans for the telescope and the initial suite of instrumentation. The LMT is a bi-national collaboration between Mexico and the USA, led by the Instituto Nacional de Astrofísica, Óptica y Electrónica (INAOE) and the University of Massachusetts at Amherst, to construct, commission and operate a 50m-diameter millimeter-wave radio telescope. Construction activities are nearly complete at the 4600m LMT site on the summit of Volcán Sierra Negra, an extinct volcano in the Mexican state of Puebla. Full movement of the telescope, under computer control in both azimuth and elevation, has been achieved. The commissioning and scientific operation of the LMT is divided into two major phases. As part of phase 1, the installation of precision surface segments for millimeter-wave operation within the inner 32m-diameter of the LMT surface is now complete. The alignment of these surface segments is underway. The telescope (in its 32-m diameter format) will be commissioned later this year with first-light scientific observations at 1mm and 3mm expected in early 2011. In phase 2, we will continue the installation and alignment of the remainder of the reflector surface, following which the final commissioning of the full 50-m LMT will take place. The LMT antenna, outfitted with its initial complement of scientific instruments, will be a world-leading scientific research facility for millimeter-wave astronomy.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    No preview · Article · Jul 2010
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    ABSTRACT: We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H$_2^{16}$O and H$_2^{18}$O in absorption towards Sagittarius~B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of $2.35 \pm 0.35$, corresponding to a spin temperature of $\sim$27~K, towards Sagittarius~B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.
    Full-text · Article · Jul 2010 · Astronomy and Astrophysics
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    ABSTRACT: H2O+ has been observed in its ortho- and para- states toward the massive star forming core Sgr B2(M), located close to the Galactic center. The observations show absorption in all spiral arm clouds between the Sun and Sgr B2. The average o/p ratio of H2O+ in most velocity intervals is 4.8, which corresponds to a nuclear spin temperature of 21 K. The relationship of this spin temperature to the formation temperature and current physical temperature of the gas hosting H2O+ is discussed, but no firm conclusion is reached. In the velocity interval 0 to 60 km/s, an ortho/para ratio of below unity is found, but if this is due to an artifact of contamination by other species or real is not clear. Comment: A&A, HIFI special issue, accepted
    Full-text · Article · Jul 2010 · Astronomy and Astrophysics

Publication Stats

3k Citations
336.27 Total Impact Points

Institutions

  • 1981-2015
    • University of Massachusetts Amherst
      • Department of Astronomy
      Amherst Center, Massachusetts, United States
  • 1999
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, Maryland, United States
    • University of Virginia
      • Department of Electrical and Computer Engineering (ECE)
      Charlottesville, Virginia, United States
  • 1998
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, CA, United States
  • 1981-1984
    • National Radio Astronomy Observatory
      Charlottesville, Virginia, United States
  • 1980-1983
    • University of Texas at Austin
      • Department of Astronomy
      Austin, Texas, United States
  • 1977-1982
    • University of California, Berkeley
      • Department of Physics
      Berkeley, California, United States