Jeffrey Paul Morgenthaler

A High Spectral Resolution Observation of the Soft X-Ray Diffuse Background with Thermal Detectors

A high spectral resolution observation of the diffuse X-ray background in the 60–1000 eV energy range has been made using an array of 36 1 mm 2 microcalorimeters flown on a sounding rocket. Detector energy resolution ranged from 5 to 12 eV FWHM, and a composite spectrum of � 1 sr of the background centered at l ¼ 90 � , b ¼þ 60 � was obtained with a net resolution of � 9 eV. The target area includes bright 1 keV regions but avoids Loop I and the North Polar Spur. Lines of C vi ,O vii, and O viii are clearly detected with intensities of 5:4 � 2:3, 4:8 � 0:8, and 1:6 � 0:4 photons cm � 2 s � 1 sr � 1 , respectively. The oxygen lines alone account for a majority of the diffuse background observed in the ROSAT R4 band that is not due to resolved extragalactic discrete sources. We also have a positive detection of the Fe-M line complex near 70 eV at an intensity consistent with previous upper limits that indicate substantial gas-phase depletion of iron. We include a detailed description of the instrument and its detectors. Subject headings: instrumentation: detectors — instrumentation: spectrographs — intergalactic medium — space vehicles: instruments — X-rays: diffuse background — X-rays: ISM

Large-aperture [O I] 6300 Å photometry of comet Hale-Bopp: Implications for the photochemistry of OH

Large-aperture photometric observations of comet Hale-Bopp (C/1995 O1) in the forbidden red line of neutral oxygen ([O I] 6300 with the 150 mm dual-etalon spectrometer that comprises the Ae ) Fabry-Pec rot

Sunlit Io atmospheric [O I] 6300 Å emission and the plasma torus

A large database of sunlit Io [O I] 6300 A emission, acquired over the period 1990–1999, with extensive coverage of Io orbital phase angle ϕ and System III longitude λIII, exhibits significant long-term and short-term variations in [O I] 6300 A emission intensities. The long-term average intensity shows a clear dependence on λIII, which establishes conclusively that the emission is produced by the interaction between Ios atmosphere and the plasma torus. Two prominent average intensity maxima, 70° to 90° wide, are centered at λIII ≈ 130° and λIII ≈ 295°. A comparison of data from October 1998 with a three-dimensional plasma torus model, based upon electron impact excitation of atomic oxygen, suggests a basis for study of the torus interaction with Ios atmosphere. The observed short-term, erratic [O I] 6300 A intensity variations fluctuate ∼20–50% on a timescale of tens of minutes with less frequent fluctuations of a factor of ∼2. The most likely candidate to produce these fluctuations is a time-variable energy flux of field-aligned nonthermal electrons identified recently in Galileo plasma science data. If true, the short-term [O I] intensity fluctuations may be related to variable field-aligned currents driven by inward and outward torus plasma transport and/or transient high-latitude, field-aligned potential drops. A correlation between the intensity and emission line width indicates molecular dissociation may contribute significantly to the [O I] 6300 A emission. The nonthermal electron energy flux may produce O(1D) by electron impact dissociation of SO2 and SO, with the excess energy going into excitation of O and its kinetic energy. The [O I] 6300 A emission database establishes Io as a valuable probe of the torus, responding to local conditions at Ios position.

Thermal calorimeters for high resolution X-ray spectroscopy

Abstract Thermal detection of individual X-ray photons by small (0.5×0.5 mm) calorimeters has been used to achieve an energy resolution as good as 7.5 eV FWHM for 6 keV X-rays. Such detectors should have interesting applications in X-ray astronomy as well as laboratory spectroscopy, and they promise a high tolerance for embedded sources. Ideally, it should be possible to improve the resolution greatly by making smaller detectors or operating them at lower temperatures than the 50–100 mK currently used. However, there appear to be fairly fundamental limitations when semiconductor thermistors are used as the thermometer. When trying to achieve energy resolution of 0.1% or better, fluctuations in the thermalization efficiency of the detector must also be considered, and this places additional restrictions on suitable detector materials.

Spectra of the ¼ keV X-Ray Diffuse Background from the Diffuse X-Ray Spectrometer Experiment

The Diffuse X-ray Spectrometer (DXS) flew as an attached payload on the STS-54 mission of the space shuttle Endeavour in 1993 January and obtained spectra of the soft X-ray diffuse background in the 148-284 eV (84-44 ?) band using a Bragg-crystal spectrometer. The spectra show strong emission lines, indicating that the emission is primarily thermal. Since the observations were made at low Galactic latitude, this thermal emission must arise from a nearby hot component of the interstellar medium, most likely the Local Hot Bubble, a region within ~100 pc of the Sun characterized by an absence of dense neutral gas. The DXS spectrum of the hot interstellar medium is not consistent with either collisional equilibrium models or with nonequilibrium ionization models of the X-ray emission from astrophysical plasmas. Models of X-ray emission processes appear not yet adequate for detailed interpretation of these data. The DXS data are most nearly consistent with models of thermal emission from a plasma with a temperature of 106.1 K and depletions of refractory elements magnesium, silicon, and iron to levels ~30% of solar.

A sounding rocket payload for X-ray astronomy employing high-resolution microcalorimeters

Abstract We have completed a sounding rocket payload that will use a 36 element array of microcalorimeters to obtain a high-resolution spectrum of the diffuse X-ray background between 0.1 and 1 keV. This experiment uses only mechanical collimation of the incoming X-rays, but the cryostat and detector assembly have been designed to be placed at the focus of a conical foil imaging mirror which will be employed on subsequent flights to do spatially resolved spectroscopy of supernova remnants and other extended objects. The detector system is a monolithic array of silicon calorimeters with ion-implanted thermometers and HgTe X-ray absorbers. The 1 mm 2 pixels achieve a resolution of about 8 eV FWHM operating at 60 mK.

Evolution of H2O, CO, and CO2 production in Comet C/2009 P1 Garradd during the 2011-2012 apparition

Abstract We present analysis of high spectral resolution NIR spectra of CO and H2O in Comet C/2009 P1 (Garradd) taken during its 2011–2012 apparition with the CSHELL instrument on NASA’s Infrared Telescope Facility (IRTF). We also present analysis of observations of atomic oxygen in Comet Garradd obtained with the ARCES echelle spectrometer mounted on the ARC 3.5-m telescope at Apache Point Observatory and the Tull Coude spectrograph on the Harlan J. Smith 2.7-m telescope at McDonald Observatory. The observations of atomic oxygen serve as a proxy for H2O and CO2. We confirm the high CO abundance in Comet Garradd and the asymmetry in the CO/H2O ratio with respect to perihelion reported by previous studies. From the oxygen observations, we infer that the CO2/H2O ratio decreased as the comet moved towards the Sun, which is expected based on current sublimation models. We also infer that the CO2/H2O ratio was higher pre-perihelion than post-perihelion. We observe evidence for the icy grain source of H2O reported by several studies pre-perihelion, and argue that this source is significantly less abundant post-perihelion. Since H2O, CO2, and CO are the primary ices in comets, they drive the activity. We use our measurements of these important volatiles in an attempt to explain the evolution of Garradd’s activity over the apparition.

Large Aperture O I 6300 Å Observations of Comet Hyakutake: Implications for the Photochemistry of OH and O I Production in Comet Hale-Bopp

In previous work (Morgenthaler et al. and Glinski et al.), we proposed a revision to the standard OH photochemistry of van Dishoeck & Dalgarno in order to explain the anomalously bright [O I] 6300 A emission observed by several instruments in comet C/1995 O1 (Hale-Bopp). In order to test the validity of revisions to the OH photochemistry, we present wide-field Fabry-Perot [O I] 6300 A observations of comet C/1996 B2 (Hyakutake) and review similar observations recorded for 1P/Halley and 1989 c1 (Austin). Conventional long-slit spectroscopic observations of several comets in [O I] are also reviewed. The bulk of the evidence suggests that the OH photochemical rates of van Dishoeck & Dalgarno are, on the whole, correct and that the bright [O I] emission observed in Hale-Bopp, particularly at cometocentric distances beyond ~3 × 104 km, was unique to that comet, or possibly any comet with such a large production rate.

Measurements of [C I] Emission from Comet Hale-Bopp

We present quantitative measurements of cometary [C I] 9850 A emission obtained during observations of comet Hale-Bopp (C/1995 O1) in 1997 March and April. The observations were carried out using a high-resolution (λ/Δλ ≈ 40,000) Fabry-Perot/CCD spectrometer at the McMath-Pierce Solar telescope on Kitt Peak. This forbidden line, the carbon analog of [O I] 6300 A, is emitted in the radiative decay of C(1D) atoms. In the absence of other sources and sinks, [C I] 9850 A emission can be used as a direct tracer of CO photodissociation in comets. However, in Hale-Bopps large, dense coma, other processes, such as collisional excitation of ground-state C(3P), dissociative recombination of CO+, and collisional dissociation of CO and CO2 may produce significant amounts of C(1D). The long C(1D) radiative lifetime (~4000 s) makes collisional deexcitation (quenching) the primary loss mechanism in the inner coma. Thus, a detailed, self-consistent global model of collisional and photochemical interactions is necessary to fully account for [C I] 9850 A emission in comet Hale-Bopp.

Production, Outflow, Velocity, and Radial Distribution of H2O and OH in the Coma of Comet C/1995 O1 (Hale-Bopp) from Wide-field Imaging of OH

Observations of OH are a useful proxy of the water production rate (Q) and outflow velocity (V) in comets. From wide-field images taken on 1997 March 28 and April 8 that capture the entire scale length of the OH coma of comet C/1995 O1 (Hale-Bopp), we obtain QOH from the model-independent method of aperture summation and Q from the OH photochemical branching ratio, BROH. Using an adaptive ring summation algorithm, we extract the radial brightness distribution of OH 0-0 band emission out to cometocentric distances of up to 106 km, both as azimuthal averages and in quadrants covering different position angles relative to the comet-Sun line. These profiles are fitted using both fixed and variable velocity two-component spherical expansion models to estimate VOH with increasing distance from the nucleus. The OH coma of Hale-Bopp was more spatially extended than those of previous comets, and this extension is best matched by a variable acceleration of H2O and OH that acted across the entire coma, but was strongest within 1-2 × 104 km from the nucleus. Our models indicate that VOH at the edge of our detectable field of view (106 km) was ~2-3 times greater in Hale-Bopp than for a 1P/Halley class comet at 1 AU, which is consistent with the results of more sophisticated gas-kinetic models, extrapolation from previous observations of OH in comets with Q > 1029 s-1, and direct radio measurements of the outer coma Hale-Bopp OH velocity. The likely source of this acceleration is thermalization of the excess energy of dissociation of H2O and OH over an extended collisional coma. When the coma is broken down by quadrants in position angle, we find an azimuthal asymmetry in the radial distribution that is characterized by an increase in the spatial extent of OH in the region between the orbit-trailing and anti-Sunward directions. Model fits specific to this area and comparison with radio OH measurements suggest greater acceleration here, with VOH ~ 1.5 times greater at a 106 km cometocentric distance than elsewhere in the coma. We discuss several mechanisms that may have acted within the coma to produce the observed effect.