Infrared Space Observatory Research Articles

Calibration of the AKARI Far-Infrared Imaging Fourier-Transform Spectrometer

The Far-Infrared Surveyor (FIS) onboard the AKARI satellite has a spectroscopic capability provided by a Fourier transform spectrometer (FIS–FTS). FIS–FTS is the first space-borne imaging FTS dedicated to far-infrared astronomical observations. We describe the calibration process of the FIS–FTS, and discuss its accuracy and reliability. The calibration is based on observational data of bright astronomical sources as well as two instrumental sources. We have compared the FIS–FTS spectra with the spectra obtained from the Long Wavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO), having a similar spectral coverage. The present calibration method accurately reproduces the spectra of several solar system objects having a reliable spectral model. Under this condition the relative uncertainty of the calibration of the continuum is estimated to be $\pm$ 15% for SW, $\pm$ 10% for 70–85 cm$^{-1}$ of LW, and $\pm$ 20% for 60–70 cm$^{-1}$ of LW; and the absolute uncertainty is estimated to be $+$35%/$-$55% for SW, $+$35%/$-$55% for 70–85 cm$^{-1}$ of LW, and $+$40%/$-$60% for 60–70 cm$^{-1}$ of LW. These values have been confirmed by comparisons with theoretical models and previous observations by the ISO / LWS.

COBEAND THE GALACTIC INTERSTELLAR MEDIUM: GEOMETRY OF THE SPIRAL ARMS FROM FIR COOLING LINES

We present a new model for the spiral structure of the Milky Way based upon the essentially all-sky intensity maps of the [C II] 158 {mu}m and [N II] 205 {mu}m lines of the interstellar medium (ISM) obtained by the FIRAS instrument of the Cosmic Background Explorer (COBE), with ancillary data from the Balloon-borne Infrared Carbon Explorer, and Infrared Space Observatory. These lines are important coolants of the ISM and strong tracers of the spiral structure. The model provides the volume emissivity of these species as a function of position within the Galaxy. Two-, three-, and four-arm models are examined, using a number of spiral functional forms. Two-arm models are found to be inconsistent with the COBE/FIRAS data. A three-arm model can be constructed that reproduces the [C II] and [N II] intensity profiles along the Galactic plane. This model, however, is discounted by historical observations of the Perseus and Cygnus ('Outer') arms. A four-arm model, with arms defined by logarithmic spiral forms, reproduce the observations extremely well. Models of the Milky Way's spiral geometry proposed from {approx}1980 to the present are examined in light of the COBE data and compared with the model presented herein. The preponderance of themore » evidence supports the existence of four well-defined logarithmic spiral arms in the gaseous component of the ISM. We note that essentially all two-arm models proposed since the mid-1980s are based upon observations of older evolved stars. We address the question of why studies based upon observations of stellar densities yield two-arm models while models based upon observations of more traditional tracers of spiral arms, i.e., enhanced gas and dust densities, star formation, and young stellar populations, yield four-arm models.« less

Mapping and spectroscopy of the planetary nebula NGC 7009 in the visual and infrared

NGC 7009 is a fascinating example of a high-excitation, elliptical planetary nebula (PN) containing circumnebular rings, and FLIERs and jets along the major axis. We present visual spectroscopy along multiple position angles through the nucleus, taken with the Observatorio Astronomico Nacional (Mexico); mid-infrared (MIR) spectroscopy and imaging acquired using the Infrared Space Observatory (ISO) and Spitzer Space Telescope (SST), and narrow-band imaging obtained using the Hubble Space Telescope (HST). The data show that the mid-infrared (MIR) continuum is dominated by a broad ≈100 K continuum, and a strong excess attributable to crystalline silicate emission. The primary peaks in this excess are similar to those observed in Forsterite and clino- and ortho-enstatite. The MIR images, by contrast, appear to be dominated by ionic transitions, with the 8.991 μm transition of [Ar iii] being important in the 8.0-μm band. The morphology and size of the envelope are found to vary with wavelength, with the largest dimensions occurring at 8.0 μm – a trend which is also reflected in an increase in the 8.0 μm/4.5 μm and 5.8 μm/4.5 μm ratios with distance from the nucleus. The visual spectroscopy permits us to map density and temperature throughout the shell, and confirm that the lowest values of ne are located close to the ansae, where densities appear to be of the order of 900–2600 cm−3. We provide mean line intensities for 116 transitions in six regions of the shell, and use mapping to confirm a systematic increase in excitation in the outer portions of the envelope. We finally use the ground-based spectroscopy, and ratioing of HST images to investigate the presence of shocks in the ansae and interior envelope. It is concluded that line ratios in the ansae may be partially consistent with shock excitation, although these features are primarily dominated by photoionization. We also note evidence for shock excitation at the limits of the interior elliptical shell, and for multiple bow-shock structures centred upon the ansae. The orientations of the easterly bow-shocks may have varied over time, indicating precession of the collimating engine at a rate of deg yr−1, whilst the outward splaying of the westerly ‘jet’ appears consistent with shock refraction modelling. We finally note that HST observations of the halo rings show them to have widths of the order of ∼1–3 arcsec, and steep changes in surface brightness consistent with local shock activity.

Chemical and radiative transfer modelling of the ISO-LWS Fabry-Perot spectra of Orion-KL water lines

We present chemical and radiative transfer models for the many far-IR ortho- and para-H2O lines that were observed from the Orion-KL region in high resolution Fabry-Perot (FP) mode by the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The chemistry of the region was first studied by simulating the conditions in the different known components of Orion-KL: chemical models for a hot core, a plateau and a ridge were coupled with an accelerated Lambda$-iteration (ALI) radiative transfer model to predict H2O line fluxes and profiles. Our models include the first 45 energy levels of ortho- and para-H2O. We find that lines arising from energy levels below 560 K were best reproduced by a gas of density 3x10^5 cm^-3 at a temperature of 70-90 K, expanding at a velocity of 30 km s^-1 and with a H2O/H2 abundance ratio of the order of 2 - 3 x 10^-5, similar to the abundance derived by Cernicharo et al. (2006). However, the model that best reproduces the fluxes and profiles of H2O lines arising from energy levels above 560 K has a significantly higher H2O/H2 abundance, 1 - 5 x 10^-4, originating from gas of similar density, in the Plateau region, that has been heated to 300 K, relaxing to 90-100 K. We conclude that the observed water lines do not originate from high temperature shocks.

The source of 3-μm absorption in Jupiter’s clouds: Reanalysis of ISO observations using new NH 3 absorption models

A prominent characteristic of jovian near-IR spectra is the widely distributed presence of a strong absorption at wavelengths from about 2.9 μm to 3.1 μm, first noticed in a 3-μm spectrum obtained by the Infrared Space Observatory (ISO) in 1996. While Brooke et al. (Brooke, T.Y., Knacke, R.F., Encrenaz, T., Drossart, P., Crisp, D., Feuchtgruber, H. [1998]. Icarus 136, 1–13) were able to fit the ISO spectrum very well using ammonia ice as the sole source of particulate absorption, Irwin et al. (Irwin, P.G.J., Weir, A.L., Taylor, F.W., Calcutt, S.B., Carlson, R.W. [2001]. Icarus 149, 397–415) noted that their best-fit cloud model implied a strong absorption at 2 μm that was not observed in Galileo NIMS spectra, raising questions about the source of the absorption. Subsequent significant revisions in ammonia gas absorption models (Bowles, N., Calcutt, S., Irwin, P., Temple, J. [2008]. Icarus 196, 612–614) also raised questions about these conclusions because ammonia gas absorption overlaps regions of ammonia ice absorption. Our reanalysis, based on improved ammonia absorption models, finds that the ISO spectrum can be well fit by models that include both NH 3 ice and solid NH 4SH, with the latter substance providing most of the absorption. The component due to NH 3 is very possibly due to NH 3 present as a coating on either large ( r ∼ 15 μm) NH 4SH particles in a deeper layer at ∼550 mb or on small ( r ∼ 0.3 μm) photochemical haze particles in a lower pressure layer at ∼370 mb. Neither option creates conflict with the lack of significant NH 3 absorption features at thermal wavelengths.

The source of widespread 3-μm absorption in Jupiter’s clouds: Constraints from 2000 Cassini VIMS observations

The Cassini flyby of Jupiter in 2000 provided spatially resolved spectra of Jupiter’s atmosphere using the Visual and Infrared Mapping Spectrometer (VIMS). A prominent characteristic of these spectra is the presence of a strong absorption at wavelengths from about 2.9 μm to 3.1 μm, previously noticed in a 3-μm spectrum obtained by the Infrared Space Observatory (ISO) in 1996. While Brooke et al. (Brooke, T.Y., Knacke, R.F., Encrenaz, T., Drossart, P., Crisp, D., Feuchtgruber, H. [1998]. Icarus 136, 1–13) were able to fit the ISO spectrum very well using ammonia ice as the sole source of particulate absorption, Sromovsky and Fry (Sromovsky, L.A., Fry, P.M. [2010]. Icarus 210, 211–229), using significantly revised NH 3 gas absorption models, showed that ammonium hydrosulfide (NH 4SH) provided a better fit to the ISO spectrum than NH 3, but that the best fit was obtained when both NH 3 and NH 4SH were present in the clouds. Although the large FOV of the ISO instrument precluded identification of the spatial distribution of these two components, the VIMS spectra at low and intermediate phase angles show that 3-μm absorption is present in zones and belts, in every region investigated, and both low- and high-opacity samples are best fit with a combination of NH 4SH and NH 3 particles at all locations. The best fits are obtained with a layer of small ammonia-coated particles ( r ∼ 0.3 μm) overlying but often close to an optically thicker but still modest layer of much larger NH 4SH particles ( r ∼ 10 μm), with a deeper optically thicker layer, which might also be composed of NH 4SH. Although these fits put NH 3 ice at pressures less than 500 mb, this is not inconsistent with the lack of prominent NH 3 features in Jupiter’s longwave spectrum because the reflectivity of the core particles strongly suppresses the NH 3 absorption features, at both near-IR and thermal wavelengths. Unlike Jupiter, Saturn lacks the broad 3-μm absorption feature, but does exhibit a small absorption near 2.965 μm, which resembles a similar jovian feature and suggests that both planets contain upper tropospheric clouds of sub-micron particles containing ammonia as a minor fraction.

Preparation for the solar system observations with Herschel: Simulation of Jupiter observations with PACS

Observations of the water inventory as well as other chemically important species on Jupiter will be performed in the frame of the guaranteed time key project of the Herschel Space Observatory entitled “Water and related chemistry in the Solar system”. Among other onboard instruments, PACS (Photodetector Array Camera and Spectrometer) will provide new data of the spectral atlas in a wide region covering the far-infrared and submillimetre domains, with an improved spectral resolution and a higher sensitivity compared to previous observations carried out by Cassini/CIRS (Composite InfraRed Spectrometer) and by ISO (Infrared Space Observatory). In order to optimise the observational plan and to prepare for the data analysis, we have simulated the expected spectra of PACS Jupiter observations. Our simulation shows that PACS will promisingly detect several H 2O emission lines. As PACS is capable of spatially resolving the Jovian disk, we will be able to discern the external oxygen sources in the giant planets by exploring the horizontal distribution of water. In addition to H 2O lines, some absorption lines due to tropospheric CH 4, HD, PH 3 and NH 3 lines will be observed with PACS. Furthermore, owing to the high sensitivity of the instrument, the current upper limit on the abundance of hydrogen halides such as HCl will be also improved.

Source counts at 15 microns from the AKARI NEP survey

We present galaxy counts at 15 microns using the Japanese AKARI satellite's NEP-deep and NEP-wide legacy surveys at the North Ecliptic Pole. The total number of sources detected are approximately 6700 and 10,700 down to limiting fluxes of 117 and 250 microJy (5 sigma) for the NEP-deep and NEP-wide survey respectively. We construct the Euclidean normalized differential source counts for both data sets (assuming 80 percent completeness levels of 200 and 270 microJy respectively) to produce the widest and deepest contiguous survey at 15 microns to date covering the entire flux range from the deepest to shallowest surveys made with the Infrared Space Observatory (ISO) over areas sufficiently significant to overcome cosmic variance, detecting six times as many sources as the largest survey carried out with ISO.We compare the results from AKARI with the previous surveys with ISO at the same wavelength and the Spitzer observations at 16 microns using the peek-up camera on its IRS instrument. The AKARI source counts are consistent with other results to date reproducing the steep evolutionary rise at fluxes less than a milliJansky and super-Euclidean slopes. We find the the AKARI source counts show a slight excess at fluxes fainter than 200 microJanskys which is not predicted by previous source count models at 15 microns. However, we caution that at this level we may be suffering from the effects of source confusion in our data. At brighter fluxes greater than a milliJansky, the NEP-wide survey source counts agree with the Northern ISO-ELAIS field results, resolving the discrepancy of the bright end calibration in the ISO 15 micron source counts.

Neptune's atmospheric composition from AKARI infrared spectroscopy

<i>Aims. <i/>Disk-averaged infrared spectra of Neptune between 1.8 and 13 <i>μ<i/>m, obtained by the AKARI infrared camera (IRC) in May 2007, have been analysed to (a) determine the globally-averaged stratospheric temperature structure; (b) derive the abundances of stratospheric hydrocarbons; and (c) detect fluorescent emission from CO at 4.7 <i>μ<i/>m.<i>Methods. <i/>Mid-infrared spectra (SG1 and SG2 channels of AKARI/IRC), with spectral resolutions of 47 and 34 respectively, were modelled using a line-by-line radiative transfer code to determine the temperature structure between 1–1000 <i>μ<i/>bar and the abundances of CH<sub>4<sub/>, CH<sub>3<sub/>D and higher-order hydrocarbons. A full non-LTE radiative model was then used to determine the best fitting CO profile to reproduce the fluorescent emission observed at 4.7 <i>μ<i/>m in the NG channel (with a spectral resolution of 135).<i>Results. <i/>The globally-averaged stratospheric temperature structure is quasi-isothermal between 1–1000 <i>μ<i/>bar, which suggests little variation in global stratospheric conditions since studies by the Infrared Space Observatory a decade earlier. The derived CH<sub>4<sub/> mole fraction of (9.0 <i>±<i/> 3.0)× 10<sup>-4<sup/> at 50 mbar, decreasing to (0.9 <i>±<i/> 0.3)× 10<sup>-4<sup/> at 1 <i>μ<i/>bar, is larger than that expected if the tropopause at 56 K acts as an efficient cold trap, but consistent with the hypothesis that CH<sub>4<sub/> leaking through the warm south polar tropopause (62–66 K) is globally redistributed by stratospheric motion. The ratio of D/H in CH<sub>4<sub/> of 3.0 <i>±<i/> 1.0 × 10<sup>-4<sup/> supports the conclusion that Neptune is enriched in deuterium relative to the other giant planets. We determine a mole fraction of ethane of (8.5 <i>±<i/> 2.1)× 10<sup>-7<sup/> at 0.3 mbar, consistent with previous studies, and a mole fraction of ethylene of 5.0 × 10<sup>-7<sup/> at 2.8 <i>μ<i/>bar. An emission peak at 4.7 <i>μ<i/>m is interpreted as a fluorescent emission of CO, and requires a vertical distribution with both external and internal sources of CO. Finally, comparisons to previous <i>L<i/>-band studies indicate significant variability of Neptune's flux densities in the 3.5–4.1 <i>μ<i/>m range, related to changes in solar energy deposition.

DUST ABUNDANCE AND PROPERTIES IN THE NEARBY DWARF GALAXIES NGC 147 AND NGC 185

We present new mid- to far-infrared images of the two dwarf compact elliptical galaxies that are satellites of M31, NGC 185, and NGC 147, obtained with the Spitzer Space Telescope. Spitzer's high sensitivity and spatial resolution enable us for the first time to look directly into the detailed spatial structure and properties of the dust in these systems. The images of NGC 185 at 8 and 24 μm display a mixed morphology characterized by a shell-like diffuse emission region surrounding a central concentration of more intense infrared emission. The lower resolution images at longer wavelengths show the same spatial distribution within the central 50 but beyond this radius, the 160 μm emission is more extended than that at 24 and 70 μm. On the other hand, the dwarf galaxy NGC 147, located only a small distance away from NGC 185, shows no significant infrared emission beyond 24 μm and therefore its diffuse infrared emission is mainly stellar in origin. For NGC 185, the derived dust mass based on the best fit to the spectral energy distribution is 1.9 × 10^3 M_⊙, implying a gas mass of 3.0 × 10^5 M_⊙. These values are in agreement with those previously estimated from infrared as well as CO and H I observations and are consistent with the predicted mass return from dying stars based on the last burst of star formation 1 × 10^9 yr ago. Based on the 70-160 μm flux density ratio, we estimate a temperature for the dust of ~17 K. For NGC 147, we obtain an upper limit for the dust mass of 4.5 × 10^2 M_⊙ at 160 μm (assuming a temperature of ~20 K), a value consistent with the previous upper limit derived using Infrared Space Observatory observations of this galaxy. In the case of NGC 185, we also present full 5-38 μm low-resolution (R ~ 100) spectra of the main emission regions. The Infrared Spectrograph spectra of NGC 185 show strong polycyclic aromatic hydrocarbons emission, deep silicate absorption features and H_2 pure rotational line ratios consistent with having the dust and molecular gas inside the dust cloud being impinged by the far-ultraviolet radiation field of a relatively young stellar population. Therefore, based on its infrared spectral properties, NGC 185 shows signatures of recent star formation (a few ×10^8 yr ago), although its current star formation rate is quite low.

Testing PDR models againstISOfine structure line data for extragalactic sources

Far-infrared [C ii] 158 micron, [O i] 145 micron and [O i] 63 micron fine structure emission line fluxes were measured from archival Infrared Space Observatory Long Wavelength Spectrometer spectra of 46 extragalactic sources, with 28 sources providing detections in all three lines. For 12 of the sources, the contribution to the [C ii] 158 micron line flux from H ii regions could be estimated from their detected [N ii] 122 micron line fluxes. The measured [C ii]/[O i] and [O i] 63/145 micron line flux ratios were compared with those from a grid of PDR models previously computed using the UCL PDR code. Persistent offsets between the observed and modelled line ratios could be partly attributed to the effects of [O i] 63 micron self-absorption. Using the SMMOL code, we calculated model [O i] line profiles and found that the strength of the [O i] 63 micron line was reduced by 20-80%, depending on the PDR parameters. We conclude that high PDR densities and radiation field strengths, coupled with the effects of [O i] 63 micron self-absorption, are likely to provide the best match to the observed line flux ratios.

EFFECTS OF FORSTERITE GRAIN SHAPE ON INFRARED SPECTRA

The Infrared Space Observatory (ISO) detected several sharp infrared features around young stars, comets, and evolved stars. These sharp features were identified as Mg-rich crystalline silicates of forsterite and enstatite by comparison with spectra from laboratory data. However, certain infrared emission bands in the observed spectra cannot be identified because they appear at slightly shorter wavelengths than the peaks in forsterite laboratory spectra, where the shapes of forsterite particles are irregular. To solve this problem, we measured infrared spectra of forsterite grains of various shapes (irregular, plate-like with no sharp edges, elliptical, cauliflower, and spherical) in the infrared spectral region between 5 and 100 μm. The spectra depend on particle shape. The spectra of the 11, 19, 23, and 33 μm bands, in particular, are extremely sensitive to particle shape, whereas some peaks such as the 11.9, 49, and 69 μm bands remained almost unchanged despite different particle shapes. This becomes most evident from the spectra of near-spherical particles produced by annealing an originally amorphous silicate sample at temperature from 600 to 1150 ◦ C. The spectra of these samples differ strongly from those of other ones, showing peaks at much shorter wavelengths. At a higher annealing temperature of 1200 ◦ C, the particle shapes changed drastically from spherical to irregular and the spectra became similar to those of forsterite particles with irregular shapes. Based on ISO data and other observational data, the spectra of outflow sources and disk sources may correspond to differences in forsterite shape, and further some unidentified peaks, such as those at 32.8 or 32.5 μm, may be due to spherical or spherical-like forsterite.

ISOobservation of molecular hydrogen and fine-structure lines in the photodissociation region IC���63

We wish to constrain the main physical properties of the photodissociation region (PDR) IC 63. We present the results of a survey for the lowest pure-rotational lines of H_2 with the Short Wavelength Spectrometer and for the major fine-structure cooling lines of O i at 63 and 145 μm and C ii at 157.7 μm with the Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO) in the high-density PDR IC 63. The observations are compared with available photochemical models based on optical absorption and/or millimetre emission line data with and without enhanced H_2 formation rate on grain surfaces. The cloud density n_H is constrained by the fine-structure lines. The models include both collisional excitation and ultraviolet (UV) pumping of the H_2 ro-vibrational levels. Molecular pure-rotational lines up to S(5) are detected. The inferred column density of warm H_2 at 106 ± 11 K is (5.9 ± 1.8)^(+0.9)_(−0.7) × 10^(21) cm^(−2), while that of the hot component at 685 ± 68 K is (1.2 ± 0.4) × 10^(19) cm^(−2). Fine-structure lines are also detected in the far-infrared spectrum of IC 63. The fine-structure lines constrain the density of the PDR to be (1–5) × 10^3 cm^(−3). The impinging UV field on the PDR is enhanced by a factor of 10^3 compared to the mean interstellar field and is consistent with direct measurements in the UV. PDR models that include an enhanced H2 formation at high dust temperature give higher H_2 intensities than models without enhancement. However, the predicted intensities are still lower than the observed intensities.

Testing PDR models against ISO fine structure line data for extragalactic sources

AbstractStudies of our own Galaxy and observations of external galaxies have suggested that stellar ultraviolet radiation can ionize vast volumes of a galaxy and that far-ultraviolet radiation impinging on neutral cloud surfaces is responsible for a large fraction of the observed far-infrared (FIR) spectral line emission that cools the gas (Crawford &amp; al. (1985)). Fine structure (FS) emission lines can be used as tracers of nebular conditions such as density, excitation and ionization. By virtue of their different excitation potentials and critical densities, FS emission lines provide an insight into the energetics and chemical composition of the regions from which they originate. The far infrared [C ii]158 μm, [O i]145 μm and [O i]63 μm fine structure emission lines obtained with the Infrared Space Observatory (ISO) from 35 extragalactic sources are examined to investigate the chemical abundances and large scales physical properties of these sources. Line fluxes are compared with a grid of PDR models previously computed using the UCL_PDR code. We overplotted our model predictions against flux ratios from the [C ii]158 μm and [O i]63 μm and 145 μm ISO LWS fluxes. In this section we will only discuss the sensitivity of the ratios to changes in the input parameters. We find that the average radiation field G0 is 60–8 × 102 and the average density nH 104−9 × 104 cm−3. While ionised carbon, because of its ionisation potential, can be found in both neutral gas and ionised gas clouds, species such as ionised nitrogen [N ii], with ionisation potential of 14.53 eV, can arise only from H ii regions. The 11 sources that have detections of both [C ii] 158 μm and [N ii] 122 μm have mean and median [C ii]158/[N ii]122 flux ratios of 10.2 and 5.9 respectively. A H ii region [C ii]158/[N ii]122 ratio of 1.6 implies that H ii region contribute only 16% (mean case) and 27% (median case) of the overall [C ii] 158 μm flux that is observed. We used the above predicted H ii region [C ii]158/[N ii]122 ratio of 1.6 along with the observed [N ii] 122 μm fluxes, to correct the observed [C ii] 158 μm flux of these 11 sources for H ii region contributions. We estimate that 10-60% of the [C ii] is excited in ionised regions. When accounting for the contribution to the [C ii] 158 μm by H ii regions we found that our models fitted better the observations. We modeled the oxygen emission line profile emitted from an ensemble of PDRs and found a clear [O i] 63 μm self-absorbed profile. We estimate that approximately 20-70% of the [O i] 63 μm intensity may be suppressed through oxygen self-absorption depending on the physical parameters of the PDR regions. This work has been submitted for publication to MNRAS, Vasta et al. (2009).

Vesta and the HED meteorites: Mid‐infrared modeling of minerals and their abundances

Abstract— We demonstrate that the use of an established spectral deconvolution algorithm with mid‐infrared spectral libraries of mineral separates of varying grain sizes is capable of identifying the known mineral compositions and abundances of a selection of howardite, eucrite, and diogenite (HED) meteorite samples. In addition, we apply the same technique to mid‐infrared spectral emissivity measurements of Vesta that have been obtained from Cornell's Mid‐Infrared Asteroid Spectroscopy (MIDAS) Survey and the Infrared Space Observatory (ISO). Each Vesta measurement was made over a different range of longitudes. Our spectral deconvolution results to the Vesta spectra corroborate that Vesta's surface is howardite or eucrite‐like in composition and heterogeneous across its surface. The spectral fits produced by the linear deconvolution algorithm yields good results for the HED samples of known composition, thus giving us a high degree of confidence that our results for Vesta are valid.

On the hardening of the ionizing radiation in H ii regions across galactic discs through softness parameters

We carry out a study of the hardness of the radiation of ionizing clusters in H ii regions. First, we explore the applicability of the softness parameter η, originally defined in the optical for pairs of consecutive ionization stages of the same species. With the advent of the infrared space observatories, this definition has been extended to the mid-infrared. We show that the softness parameters, as determined in both the optical and the mid-infrared wavelengths, are sensitive to the effective temperature using a sample of data in both spectral regimes. This is confirmed by comparing the data with a grid of photoionization models, although no complete agreement has been found even for different stellar model atmospheres. Finally, we show that both softness parameters are consistent in the search for radial variations of the hardness of the ionizing radiation of H ii regions in the discs of spiral galaxies. We find a range of trends, from galaxies showing pronounced gradients to those showing very flat ones. Although the detectability and slope of these gradients can be altered by the size and luminosity of the studied H ii regions, it looks that their existence is related to the mass and type of the galaxies and, hence, to the properties of the entire disc.

90 GHz AND 150 GHz OBSERVATIONS OF THE ORION M42 REGION. A SUBMILLIMETER TO RADIO ANALYSIS

We have used the new 90 GHz MUSTANG camera on the Robert C. Byrd Green Bank Telescope (GBT) to map the bright Huygens region of the star-forming region M42 with a resolution of 9'' and a sensitivity of 2.8 mJy beam−1. Ninety GHz is an interesting transition frequency, as MUSTANG detects both the free–free emission characteristic of the H ii region created by the Trapezium stars, normally seen at lower frequencies, and thermal dust emission from the background OMC1 molecular cloud, normally mapped at higher frequencies. We also present similar data from the 150 GHz GISMO camera taken on the IRAM 30 m telescope. This map has 15'' resolution. By combining the MUSTANG data with 1.4, 8, and 21 GHz radio data from the VLA and GBT, we derive a new estimate of the emission measure averaged electron temperature of Te = 11376 ± 1050 K by an original method relating free–free emission intensities at optically thin and optically thick frequencies. Combining Infrared Space Observatory–long wavelength spectrometer (ISO–LWS) data with our data, we derive a new estimate of the dust temperature and spectral emissivity index within the 80'' ISO–LWS beam toward Orion KL/BN, Td = 42 ± 3 K and βd = 1.3 ± 0.1. We show that both Td and βd decrease when going from the H ii region and excited OMC1 interface to the denser UV shielded part of OMC1 (Orion KL/BN, Orion S). With a model consisting of only free–free and thermal dust emission, we are able to fit data taken at frequencies from 1.5 GHz to 854 GHz (350 μm).

TEXES OBSERVATIONS OF M SUPERGIANTS: DYNAMICS AND THERMODYNAMICS OF WIND ACCELERATION

We have detected [Fe ii] 17.94 μm and 24.52 μm emission from a sample of M supergiants (μ Cep, α Sco, α Ori, CE Tau, AD Per, and α Her) using the Texas Echelon Cross Echelle Spectrograph on NASA's Infrared Telescope Facility. These low opacity emission lines are resolved at R ≃ 50, 000 and provide new diagnostics of the dynamics and thermodynamics of the stellar wind acceleration zone. The [Fe ii] lines, from the first excited term (a4F), are sensitive to the warm plasma where energy is deposited into the extended atmosphere to form the chromosphere and wind outflow. These diagnostics complement previous Kuiper Airborne Observatory and Infrared Space Observatory observations which were sensitive to the cooler and more extended circumstellar envelopes. The turbulent velocities of Vturb ≃ 12–13 km s−1 observed in the [Fe ii] a4F forbidden lines are found to be a common property of our sample, and are less than that derived from the hotter chromospheric C ii] 2325 Å lines observed in α Ori, where Vturb ≃ 17–19 km s−1. For the first time, we have dynamically resolved the motions of the dominant cool atmospheric component discovered in α Ori from multiwavelength radio interferometry by Lim et al. Surprisingly, the emission centroids are quite Gaussian and at rest with respect to the M supergiants. These constraints combined with model calculations of the infrared emission line fluxes for α Ori imply that the warm material has a low outflow velocity and is located close to the star. We have also detected narrow [Fe i] 24.04 μm emission that confirms Fe ii is the dominant ionization state in α Ori's extended atmosphere.

An infrared study of Be stars based on ISO SWS01 spectra

The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer (SWS) spectra of 10 Be stars are presented. It can be seen that the Be stars show a diversity in their ISO SWS01 spectral classifications by Kraemer et al., from naked stars, stars associated with dust, stars with warm dust shells, stars with cool dust shells to very red sources. In addition, the Bra/HI(14–6) line flux ratio derived for the sample stars is compared with that of P Cyg, and it is found that the line ratio of Be stars which were investigated show not only lower values as suggested by Waters et al., but also larger values. Therefore, the line ratio cannot be used to judge whether a star is a Be star or not.

The evolution of star formation in quasar host galaxies

We have used far-infrared data from IRAS, ISO, SWIRE, SCUBA and MAMBO to constrain statistically the mean far-infrared luminosities of quasars. Our quasar compilation at redshifts 0<z<6.5 and I-band luminosities -20<I(AB)<-32 is the first to distinguish evolution from quasar luminosity dependence in such a study. We carefully cross-calibrate IRAS against Spitzer and ISO, finding evidence that IRAS 100um fluxes at <1Jy are overestimated by ~30%. We find evidence for a correlation between star formation in quasar hosts and the quasar optical luminosities, varying as SFR proportional to L_opt^(0.44+/-0.07) at any fixed redshift below z=2. We also find evidence for evolution of the mean star formation rate in quasar host galaxies, scaling as (1+z)^(1.6+/-0.3) at z<2 for any fixed quasar I-band absolute magnitude fainter than -28. We find no evidence for any correlation between star formation rate and black hole mass at 0.5<z<4. Our data are consistent with feedback from black hole accretion regulating stellar mass assembly at all redshifts.