Infrared Space Observatory Short-Wavelength Spectrometer Research Articles

High-Ionization Mid-Infrared Lines as Black Hole Mass and Bolometric Luminosity Indicators in Active Galactic Nuclei

We present relations of the black hole mass and the optical luminosity with the velocity dispersion and the luminosity of the [Ne v] and the [O iv] high-ionization lines in the mid-infrared (MIR) for 28 reverberation-mapped active galactic nuclei. We used high-resolution Spitzer Infrared Spectrograph and Infrared Space Observatory Short Wavelength Spectrometer data to fit the profiles of these MIR emission lines that originate from the narrow-line region of the nucleus. We find that the lines are often resolved and that the velocity dispersion of [Ne v] and [O iv] follows a relation similar to that between the black hole mass and the bulge stellar velocity dispersion found for local galaxies. The luminosity of the [Ne v] and the [O iv] lines in these sources is correlated with that of the optical 5100 continuum and with the black hole mass. Our results provide a means to derive °A black hole properties in various types of active galactic nuclei, including highly obscured systems.

Search for 17 μm H2Pure Rotational Emission from Circumstellar Disks

We report the negative detection of the S(1) pure rotational line emission of molecular hydrogen at 17.035 μm for four young stars, HD 163296, MWC 863, CQ Tau, and LkCa 15, for which Infrared Space Observatory (ISO) observations detected the S(1) emission, with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2 m Subaru Telescope. We did not detect the line emission toward the central star nor within 15'' of the central star along the slit for any of the present targets. Upper limits of the present observations are much smaller than previous line flux estimates based on ISO Short Wavelength Spectrometer ( SWS) observations, irrespective of the intrinsic line width. The present results indicate that the emission detected by the ISO SWS is not concentrated within the disk. Our detection limit of the H2 S(1) emission corresponds to upper limits of the disk masses of (0.72-3.8) × 10-4 M☉ within a radius of ~30-45 AU for the optically thin emission from the gas of 150 K. The upper limits of the disk masses are significantly lower than those of the warm molecular hydrogen mass predicted by the model (Chiang & Goldreich 1997), suggesting that the optically thick emission from dust dominates in the radiation from the disks in the mid-infrared wavelength. We point out that detectability of the H2 emission in young stars depends on the evolution of the disks, particularly in the sedimentation and growth of dust grains in the disk.

The Disk Atmospheres of Three Herbig Ae/Be Stars

We present infrared (IR) spectrophotometry (R 180) of three Herbig Ae/Be stars surrounded by possible protoplanetary disks: HD 150193, HD 100546, and HD 179218. We construct a mid-IR spectral energy distributions (SEDs) for each object by using 7.6-13.2 μm HIFOGS spectra, 2.4-45 μm spectrophotometry from the Infrared Space Observatory Short-Wavelength Spectrometer, the 12, 25, 60, and 100 μm photometric points from IRAS, and for HD 179218, photometric bolometric data points from the Mount Lemmon Observing Facility. The SEDs are modeled by using an expanded version of the Chiang & Goldreich two-layer, radiative and hydrostatic equilibrium, passive disk. This expanded version includes the emission from Mg-pure crystalline olivine (forsterite) grains in the disk surface layer. Each of the three objects studied vary in the amount of crystals evident from their spectrophotometry. HD 150193 contains no crystals, while HD 100546 and HD 179218, respectively, show evidence of having crystalline silicates in the surface layers of their disks. We find that the inner region of HD 100546 has a 37% higher crystalline-to-amorphous silicate ratio in its inner disk region (≤5 AU) than in the outer disk region, while the inner disk region of HD 179218 has a 84% higher crystalline-to-amorphous silicate ratio in its inner disk region (≤5 AU) than in the outer region. All three objects are best fitted using a grain-size distribution power law that falls as a-3.5. HD 150193 is best fitted by a small disk (~5 AU in radius), while HD 100546 and HD 179218 are best fitted by larger disks (~150 AU in radius). Furthermore, HD 100546's disk flares larger than those of HD 150193 (25% more at 5 AU) and HD 179218 (80% more at 5 AU). We discuss the implications of our results and compare them with other modeling efforts.

Polycyclic Aromatic Hydrocarbons and Crystalline Silicates in the Bipolar Post–Asymptotic Giant Branch Star IRAS 16279−4757

IRAS 16279-4757 belongs to a group of post-asymptotic giant branch (post-AGB) stars showing both polycyclic aromatic hydrocarbon (PAH) bands and crystalline silicates. We present mid-infrared images that resolve the object for the first time. The morphology is similar to that of the Red Rectangle (HD 44179), the prototype object with PAHs and crystalline silicates. A two-component model and images suggest a dense oxygen-rich torus, an inner, low-density, carbon-rich region, and a carbon-rich bipolar outflow. The PAH bands are enhanced at the outflow, while the continuum emission is concentrated toward the center. Our findings support the suggestion that mixed chemistry and morphology are closely related. We discuss the Infrared Space Observatory Short-Wavelength Spectrometer (ISO SWS) spectra of IRAS 16279-4757. Several bands in the ISO SWS spectrum show a match with anorthite: this would be the first detection of this mineral outside the solar system. Compared to HD 44179, the shapes of PAH bands are closer to those of planetary nebulae, possibly related to a population of small PAHs present in HD 44179 but absent around IRAS 16279-4757. Detailed examination of the spectra shows the individual character of these two objects. The comparison suggests that the torus found in IRAS 16279-4757 may have formed more recently than that in HD 44179.

Far-infrared spectroscopy of the giant planets: measurements of ammonia and phosphine at Jupiter and Saturn and the continuum of Neptune

We detected rotational transition features of ammonia and phosphine in the far-infrared spectra of Jupiter and Saturn and measured the far-infrared continuum of Neptune with high photometric accuracy. These observations were made with the long-wavelength spectrometer (LWS) aboard the infrared space observatory (ISO). The LWS covered the wavelength region between 43 and 197 μm (51–233 cm −1) with both medium and high spectral resolving power. Also Neptune's continuum was measured with the LWS and at shorter wavelengths with the ISO short-wavelength spectrometer (SWS). The spectra observed in the far-infrared are compared to synthetic spectra calculated from atmospheric radiative transfer models using expected values for the constituent vertical concentration profiles.

Neptune's far-infrared spectrum from the ISO long-wavelength and short-wavelength spectrometers

Neptune was observed by the Infrared Space Observatory (ISO) Long-Wavelength Spectrometer (LWS) between 46 and 185 μm. At wavelengths between 50 and 110 μm the accuracy of these measurements is ⩽0.3 K. Observations of this planet made by the ISO Short-Wavelength Spectrometer between 28 and 44 μm were combined with the LWS data to determine a disk-averaged temperature profile and derive several physical quantities. The combined spectra are matched best by a He/(H 2+He) mass ratio of 26.4 +2.6 −3.5%, reflecting a He molar fraction of 14.9 +1.7 −2.2%, assuming the molar fraction of CH 4 to be 2% in the troposphere. This He abundance is consistent with one derived from analysis of joint Voyager-2 IRIS and radio occultation experiment data, a technique whose accuracy has recently been called into question. For a disk average, the para-H 2 fraction is found to be no more than ∼1.5% different from its equilibrium value, and the N 2 mixing ratio is probably less than 0.7%. The composite spectrum is best fit by invoking a CH 4 ice condensate cloud. Using a Mie approximation to particle scattering and absorption, best-fit particle sizes lie between 15 and 40 μm. The composite spectra are relatively insensitive to the vertical distribution of the cloud, but the particle scale height must be greater than 5% of the gas scale height. The best models are consistent with an effective temperature for Neptune that is 59.5±0.6 K, a value slightly lower than derived by the Voyager IRIS experiment—possibly Neptune's mid- and far-infrared emission has changed during the seven years that lie between its encounter with Voyager 2 and the first spectra taken of this planet with ISO. The model spectra are also ostensibly lower than ground-based observations in the spectral range of 17–24 μm, but this discrepancy can be relieved by perturbing the temperature of the lower stratosphere where the LWS spectrum is not particularly sensitive, combined with the uncertainty in the absolute calibration of the ground-based measurements.

Neon Abundances in the HiiRegions of M33

We present neon abundances for 25 H II regions of M33, measured from line profiles of the mid-infrared transitions of [Ne II] and [Ne III] taken with the Infrared Space Observatory Short-Wavelength Spectrometer. The distribution of neon abundances as a function of galactocentric radius is best described as a step, -0.15 dex relative to the solar neon abundance from 0.7 to 4.0 kpc and -0.35 dex from 4.0 to 6.7 kpc, with estimated intrinsic scatter of 0.07 dex. The nearly flat neon abundance distribution differs from the steep oxygen abundance gradient found by previous investigators. Unless the oxygen abundance determinations are wrong, the chemical evolution of the galaxy has been radially dependent.

The Excitation and Metallicity of Galactic HiiRegions fromInfrared Space ObservatorySWS Observations of Mid‐Infrared Fine‐Structure Lines

We present mid-infrared Infrared Space Observatory Short-Wavelength Spectrometer (ISO-SWS) observations of the fine-structure emissions lines [Ne II] 12.8 ?m, [Ne III] 15.6 ?m, [Ne III] 36.0 ?m, [Ar II] 6.99 ?m, [Ar III] 8.99 ?m, [S III] 18.7 ?m, [S III] 33.5 ?m, and [S IV] 10.5 ?m and the recombination lines Br? and Br? in a sample of 112 Galactic H II regions and 37 nearby extra-Galactic H II regions in the LMC, SMC, and M33. We selected our sources from archival ISO-SWS data as those showing prominent [Ne II] 12.8 ?m or [Ne III] 15.6 ?m emissions. The Galactic sources have a wide range in galactocentric distance (0 kpc Rgal 18 kpc), which enables us to study excitation and metallicity variations over large Galactic scales. We detect a steep rise in the [Ne III] 15.6 ?m/[Ne II] 12.8 ?m, [Ar III] 8.99 ?m/[Ar II] 6.99 ?m, and [S IV] 10.5 ?m/[S III] 33.5 ?m excitation ratios from the inner Galaxy outward, and a moderate decrease in metallicity, from ~2 Z? in the inner Galaxy to ~1 Z? in the outer disk. The extra-Galactic sources in our sample show low gas density, low metallicity, and high excitation. We find a good correlation between [Ne III] 15.6 ?m/[Ne II] 12.8 ?m and [Ar III] 8.99 ?m/[Ar II] 6.99 ?m excitation ratios in our sample. The observed correlation is well reproduced by theoretical nebular models that incorporate new-generation wind-driven non-LTE model stellar atmospheres for the photoionizing stars. In particular, the non-LTE atmospheres can account for the production of [Ne III] emission in the H II regions. We have computed self-consistent nebular and stellar atmosphere models for a range of metallicities (0.5-2 Z?). We conclude that the increase in nebular excitation with galactocentric radius is due to an increase in stellar effective temperature (as opposed to a hardening of the stellar spectral energy distributions due to the metallicity gradient). We estimate an integrated [Ne III] 15.6 ?m/[Ne II] 12.8 ?m ratio for the Galaxy of 0.8, which puts it well inside the range of values for starburst galaxies. The good fit between observations and our models support the conclusion of Thornley and coworkers that the low [Ne III] 15.6 ?m/[Ne II] 12.8 ?m ratios observed in extra-Galactic sources are due to global aging effects.

The 6 Micron Feature in Protostars: Evidence for Organic Refractory Material

Data from the Infrared Space ObservatoryShort Wavelength Spectrometer have allowed abundances of many species present in interstellar ices to be determined. However, that of H 2O, the commonest of all ices, has proved controversial because of inconsistencies between results from different vibrational modes: the 6.0 mm bending mode predicts column densities systematically higher than the stretching, combination, and libration modes in several lines of sight. We show that this discrepancy can be explained by excess absorption arising in a previously unrecognized blended feature, which we attribute to organic refractory matter (ORM). The strength of the excess absorption at 6.0 mm is correlated with that of the 4.62 mm “XCN” feature, the carrier of which is thought to form when interstellar ices undergo UV photolysis or ion bombardment. Our results are thus consistent with an origin for the ORM by energetic processing of simple ices. Subject headings: infrared: ISM — ISM: abundances — ISM: molecules — line: profiles

The complete ISO spectrum of NGC 6302

We present the combined Infrared Space Observatory Short-Wavelength Spectrometer and Long- Wavelength Spectrometer 2.4{197 m spectrum of the Planetary Nebula NGC 6302 which contains in addition to strong atomic lines, a series of emission features due to solid state components. The broad wavelength coverage enables us to more accurately identify and determine the properties of both oxygen- and carbon-rich circumstellar dust. A simple model t was made to determine the abundance and typical temperature of the amorphous silicates, enstatite and forsterite. Forsterite and enstatite do have roughly the same abundance and temperature. The origin and location of the dust in a toroidal disk around the central star are discussed.

Photochemical modeling of CH3 abundances in the outer solar system

Recent measurements of methyl radicals (CH3) in the upper atmospheres of Saturn and Neptune by the Infrared Space Observatory (ISO) provide new constraints to photochemical models of hydrocarbon chemistry in the outer solar system. The derived column abundances of CH3 on Saturn above 10 mbar and Neptune above the 0.2 mbar pressure level are (2.5–6.0) × 1013 cm−2 and (0.7–2.8) × 1013 cm−2, respectively. We use the updated Caltech/Jet Propulsion Laboratory photochemical model, which incorporates hydrocarbon photochemistry, vertical molecular and bulk atmospheric eddy diffusion, and realistic radiative transfer modeling, to study the CH3 abundances in the upper atmosphere of the giant planets and Titan. We identify the key reactions that control the concentrations of CH3 in the model, such as the three‐body recombination reaction, CH3 + CH3 + M → C2H6 + M. We evaluate and extrapolate the three‐body rate constant of this reaction to the low‐temperature limit (1.8×10−16 T−3.75 e−300/T, T<300 K) and compare methyl radical abundances in five atmospheres: Jupiter, Saturn, Uranus, Neptune, and Titan. The sensitivity of our models to the rate coefficients for the reactions H + CH3 + M → CH4 + M, H + C2H3 → C2H2 + H2, 1CH2 + H2 → CH3 + H, and H + C2H5 → 2 CH3, the branching ratios of CH4 photolysis, vertical mixing in the five atmospheres, and Lyman α photon enhancement at the orbit of Neptune have all been tested. The results of our model CH3 abundances for both Saturn (5.1×1013 cm−2) and Neptune (2.2×1013 cm−2) show good agreement with ISO Short Wavelength Spectrometer measurements. Using the same chemical reaction set, our calculations also successfully generate vertical profiles of stable hydrocarbons consistent with Voyager and ground‐based measurements in these outer solar system atmospheres. Predictions of CH3 column concentrations (for p≤0.2 mbar) in the atmospheres of Jupiter (3.3×1013 cm−2), Uranus (2.5×1012 cm−2), and Titan (1.9×1015 cm−2) may be checked by future observations.

ISO-SWS Observations of Jupiter: Measurement of the Ammonia Tropospheric Profile and of the 15N/ 14N Isotopic Ratio

We present the results of the Infrared Space Observatory Short Wavelength Spectrometer (ISO-SWS) observations of Jupiter related to ammonia. We focus on two spectral regions; the first one (the 10-μm region), ranging from 9.5 to 11.5 μm, probes atmospheric levels between 1 and 0.2 bar, while the second one (the 5-μm window), ranging from 4.8 to 5.5 μm, sounds the atmosphere between 8 and 2 bar. The two spectral windows cannot be fitted with the same ammonia vertical distribution. From the 10-μm region we infer an ammonia distribution of about half the saturation profile above the 1-bar level, where the N/H ratio is roughly solar. A totally different picture is derived from the 5-μm window, where we determine an upper limit of 3.7×10 −5 at 1 bar and find an increasing NH 3 abundance at least down to 4 bar. This profile is similar to that measured by the Galileo probe. The discrepancy between the two spectral regions most likely arises from the spatial heterogeneity of Jupiter, the 5-μm window sounding dry areas unveiled by a locally thin cloud cover (the 5-μm hot spots), and the 10-μm region probing the mean jovian atmosphere above 1 bar. The 15NH 3 mixing ratio is measured around 400 mbar from ν 2 band absorptions in the 10-μm region. We find the atmosphere of Jupiter highly depleted in 15N at this pressure level [( 15N/ 14N) [formula]=1.9 +0.9 −1.0)×10 −3, while ( 15N/ 14N) ⊕=3.68×10 −3]. It is not clear whether this depletion reveals the global jovian 15N/ 14N ratio. Instead an isotopic fractionation process, taking place during the ammonia cloud condensation, is indicated as a possible mechanism. A fractionation coefficient α higher than 1.08 would explain the observed isotopic ratio, but the lack of laboratory data does not allow us to decide unambiguously on the origin of the observed low 15N/ 14N ratio.

Mid‐InfraredInfrared Space ObservatorySpectroscopy of the Prototypical LINER NGC 1052: Shocks Reconsidered

We have observed the prototypical LINER NGC 1052 with the Infrared Space Observatory Short-Wavelength Spectrometer. While we have detected the [Ne II] 12.8 μm line, we have obtained a strict upper limit for the [Ne III] 15.6 μm line. A large [Ne II]/[Ne III] line ratio and small [Ne III]/[O III] λ5007 and [Ne II]/[OIII] line ratios are consistent with slow-shock models with ~130 km s-1 shock velocity. Our results support the original suggestions of shock excitation as a dominant source for NGC 1052. We have fitted the infrared and optical line ratios with a combination of shock and photoionization models. The best combination among the simple models we considered suggests that the contribution of shock and photoionization to [O III] λ5007 emission is four-fifths and one-fifth, respectively.

SWS-Detector Glitch Effect Correction

We describe how the ISO-SWS (Infrared Space Observatory – Short Wavelength Spectrometer) software packages detect various glitch events i.e. high energy particle hits effecting the SWS detectors. A rough classification of glitch types is given. The events cause an instantaneous change in the slope of the SWS detector read outs followed by a distortion of the further samples, so called glitch tails. As a consequence the S/N ratio and photometric accuracy are reduced.Different strategies, how to remove the resulting distortion of the detectorread-out-ramp after a hit, are presented. The methods of the basic SWS software packages, the Pipeline and Interactive Analysis, will be discussed. The Pipeline has to treat glitch effects automatically. The Interactive Analysis system provides the user with a comfortable Graphical User Interface (GUI) for Trend Analysis, detailed analysis of certain glitches and the testing of new algorithms.

Water Ice, Silicate, and Polycyclic Aromatic Hydrocarbon Emission Featuresin the [ITAL]Infrared Space Observatory[/ITAL] Spectrum of the Carbon-richPlanetary Nebula CPD −56°8032

Combined Infrared Space Observatory Short-Wavelength Spectrometer and Long-Wavelength Spectrometer spectroscopy is presented of the late WC-type planetary nebula nucleus CPD -56°8032 and its carbon-rich nebula. The extremely broad coverage (2.4-197 μm) enables us to recognize the clear and simultaneous presence of emission features from both oxygen- and carbon-rich circumstellar materials. Removing a smooth continuum highlights bright emission bands characteristic of polycyclic aromatic hydrocarbons in the 3-14 μm region, bands from crystalline silicates longward of 18 μm, and the 43 and 62 μm bands of crystalline water ice. We discuss the probable evolutionary state and history of this unusual object in terms of (a) a recent transition from an O-rich to a C-rich outflow following a helium shell flash or (b) a carbon-rich nebular outflow encountering an O-rich comet cloud.

First Results and Discoveries with the ISO Short-Wavelength Spectrometer

AbstractThe Short-Wavelength Spectrometer(SWS) is one of the four instruments on-board of ESA’s Infrared Space Observatory(ISO), launched on 15 Nov. 1995. It covers the wave-length range of 2.38-45.2μm with a spectral resolution ranging from 1000-2000. An overview is given of the in-orbit performance and a summary of the main scientific results and discoveries obtained in the first 18 months of operation of the ISO-SWS.