P. W. Morris

An oxygen-rich dust disk surrounding an evolved star in the Red Rectangle

The Red Rectangle is the prototype of a class of carbon-rich reflection nebulae surrounding low-mass stars in the final stages of evolution. The central star of this nebula has ejected most of its layers (during the red-giant phase), which now form the surrounding cloud, and is rapidly evolving to a white dwarf. This star is also a member of a wide binary system, which is surrounded by a thick, dusty disk of material,. Here we report infrared observations of the Red Rectangle that reveal the presence of oxygen-rich material: prominent emission bands from crystalline silicates, and absorption lines arising from carbon dioxide. The oxygen-rich material is located in the circumbinary disk, in contrast to the previously known carbon-rich dust, which is found mainly in the extended nebula,. The properties of the oxygen-rich dust are similar to those of dusty disks surrounding young stars, which are believed to be the sites of planet formation. Grain processing, and perhaps even planet formation, may therefore also be occurring in the circumbinary disk of this evolved star.

Herschel observations of EXtra-Ordinary Sources (HEXOS):The present and future of spectral surveys with Herschel/HIFI

We present initial results from the Herschel GT key program: Herschel observations of EXtra-Ordinary Sources (HEXOS) and outline the promise and potential of spectral surveys with Herschel/HIFI. The HIFI instrument offers unprecedented sensitivity, as well as continuous spectral coverage across the gaps imposed by the atmosphere, opening up a largely unexplored wavelength regime to high-resolution spectroscopy. We show the spectrum of Orion KL between 480 and 560 GHz and from 1.06 to 1.115 THz. From these data, we confirm that HIFI separately measures the dust continuum and spectrally resolves emission lines in Orion KL. Based on this capability we demonstrate that the line contribution to the broad-band continuum in this molecule-rich source is ~20-40% below 1 THz and declines to a few percent at higher frequencies. We also tentatively identify multiple transitions of HD18O in the spectra. The first detection of this rare isotopologue in the interstellar medium suggests that HDO emission is optically thick in the Orion hot core with HDO/H2O ~ 0.02. We discuss the implications of this detection for the water D/H ratio in hot cores. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Figure 2 (page 6) is also available in electronic form at http://www.aanda.org

New Infrared Emission Features and Spectral Variations in Ngc 7023

We observed the reflection nebula NGC 7023, with the Short-High module and the long-slit Short-Low and Long-Low modules of the Infrared Spectrograph on the Spitzer Space Telescope. We also present Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) images of NGC 7023 at 3.6, 4.5, 8.0, and 24 μm. We observe the aromatic emission features (AEFs) at 6.2, 7.7, 8.6, 11.3, and 12.7 μm, plus a wealth of weaker features. We find new unidentified interstellar emission features at 6.7, 10.1, 15.8, 17.4, and 19.0 μm. Possible identifications include aromatic hydrocarbons or nanoparticles of unknown mineralogy. We see variations in relative feature strengths, central wavelengths, and feature widths, in the AEFs and weaker emission features, depending on both distance from the star and nebular position (southeast vs. northwest).

Mid-Infrared Spectra of Polycyclic Aromatic Hydrocarbon Emission in Herbig Ae/Be Stars

We present spectra of four Herbig Ae/Be stars obtained with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 μm emission feature shifted to 6.3 μm and the strongest C–C skeletal-mode feature occurring at 7.9 μm instead of at 7.7 μm, as is often seen. Remarkably, none of the four stars has silicate emission. The strength of the 7.9 μm feature varies with respect to the 11.3 μm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 μm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 μm that may be related to the 12.7 μm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7-9 μm region, with the peak emission to the red of 8.0 μm and no 8.6 μm PAH feature.We present spectra of four Herbig AeBe stars obtained with the Infrared Spectrograph (IRS) 1 on the Spitzer Space Telescope. All four of the sources show strong emission from polycyclic aromatic hydrocarbons (PAHs), with the 6.2 µm emission feature shifted to 6.3 µm and the strongest C C skeletal-mode feature occuring at 7.9 µm instead of at 7.7 µm as is often seen. Remarkably, none of the four stars have silicate emission. The strength of the 7.9 µm feature varies with respect to the 11.3 µm feature among the sources, indicating that we have observed PAHs with a range of ionization fractions. The ionization fraction is higher for systems with hotter and brighter central stars. Two sources, HD 34282 and HD 169142, show emission features from aliphatic hydrocarbons at 6.85 and 7.25 µm. The spectrum of HD 141569 shows a previously undetected emission feature at 12.4 µm which may be related to the 12.7 µm PAH feature. The spectrum of HD 135344, the coolest star in our sample, shows an unusual profile in the 7–9 µm region, with the peak emission to the red of 8.0 µm and no 8.6 µm PAH feature. Subject headings: stars: chemically peculiar — infrared: stars

OBSERVATIONS OF ULTRALUMINOUS INFRARED GALAXIES WITH THE INFRARED SPECTROGRAPH (IRS) ON THE SPITZER SPACE TELESCOPE: EARLY RESULTS ON MARKARIAN 1014, MARKARIAN 463, AND UGC 5101

We present spectra taken with the Infrared Spectrograph on the Spitzer Space Telescope covering the 5-38 μm region of three ultraluminous infrared galaxies (ULIRGs): Mrk 1014 (z = 0.163), Mrk 463 (z = 0.051), and UGC 5101 (z = 0.039). The continua of UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant optical depths to the nuclei at 10 μm. UGC 5101 also shows the clear presence of water ice in absorption. Polycyclic aromatic hydrocarbon (PAH) emission features are seen in both Mrk 1014 and UGC 5101, including the 16.4 μm line in UGC 5101. The fine-structure lines are consistent with dominant active galactic nucleus (AGN) power sources in both Mrk 1014 and Mrk 463. In UGC 5101 we detect the [Ne V] 14.3 μm emission line, providing the first direct evidence for a buried AGN in the mid-infrared. The detection of the 9.66 μm and 17.03 μm H2 emission lines in both UGC 5101 and Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the total molecular gas masses in these galaxies.

SPITZER SPACE TELESCOPE SPECTROSCOPY OF ICES TOWARD LOW-MASS EMBEDDED PROTOSTARS

Sensitive 5-38 μm Spitzer Space Telescope and ground-based 3-5 μm spectra of the embedded low-mass protostars B5 IRS1 and HH 46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO_2 bending mode at 15 μm is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN^- bands, however. The observed CO2 profile indicates an intimate mixture with H_(2)O, but not necessarily with CH_(3)OH, in contrast to some high-mass protostars. This is consistent with the low CH_(3)OH abundance derived from the ground-based L-band spectra. The CO_2 : H_(2)O column density ratios are high in both B5 IRS1 and HH 46 IRS (~35%). Clearly, the Spitzer spectra are essential for studying ice evolution in low-mass protostellar environments and for eventually determining the relation between interstellar and solar system ices.

Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6-0.4 (W31C), W49N, and W51

We report the detection of the ground state N, J = 1, 3/2 → 1, 1/2 doublet of the methylidyne radical CH at ∼532 GHz and ∼536 GHz with the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO + in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO + deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with [CCH]/[H2] ∼3.2 ± 1.1 × 10 −8 . The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities nH = n(H) + 2n(H2) ranging between 100 and 1000 cm −3 .

Mid-Infrared Spectroscopy of Disks around Classical T Tauri Stars

We present the first Spitzer Space Telescope Infrared Spectrograph observations of the disks around classical T Tauri stars: spectra in the 5.2-30 μm range of six stars. The spectra are dominated by emission features from amorphous silicate dust, and a continuous component from 5 to 8 μm that in most cases comprises an excess above the photosphere throughout our spectral range. There is considerable variation in the silicate feature/continuum ratio, which implies variations of inclination, disk flaring, and stellar mass accretion rate. In most of our stars, structure in the silicate feature suggests the presence of a crystalline component. In one, CoKu Tau/4, no excess above the photosphere appears at wavelengths shortward of the silicate features, similar to 10 Myr old TW Hya, Hen 3-600, and HR 4796A. This indicates the optically thick inner disk is largely absent. The silicate emission features with peaks at 9.7 and 18 μm indicate small dust grains are present. The extremely low 10-20 μm color temperature of the dust excess, 135 K, indicates these grains are located more than 10 AU from the star. These features are suggestive of gravitational influence by planets or close stellar companions and grain growth in the region within 10 AU of the star, somewhat surprising for a star this young (1 Myr).

The formation and evolution of planetary systems: Placing our solar system in context with Spitzer

We provide an overview of the Spitzer Legacy Program, Formation and Evolution of Planetary Systems, that was proposed in 2000, begun in 2001, and executed aboard the Spitzer Space Telescope between 2003 and 2006. This program exploits the sensitivity of Spitzer to carry out mid-infrared spectrophotometric observations of solar-type stars. With a sample of ~328 stars ranging in age from ~3 Myr to ~3 Gyr, we trace the evolution of circumstellar gas and dust from primordial planet-building stages in young circumstellar disks through to older collisionally generated debris disks. When completed, our program will help define the timescales over which terrestrial and gas giant planets are built, constrain the frequency of planetesimal collisions as a function of time, and establish the diversity of mature planetary architectures. In addition to the observational program, we have coordinated a concomitant theoretical effort aimed at understanding the dynamics of circumstellar dust with and without the effects of embedded planets, dust spectral energy distributions, and atomic and molecular gas line emission. Together with the observations, these efforts will provide an astronomical context for understanding whether our solar system—and its habitable planet—is a common or a rare circumstance. Additional information about the FEPS project can be found on the team Web site.

CH+(1-0) and 13CH+(1-0) absorption lines in the direction of massive star-forming regions

We report the detection of the ground-state rotational transition of the methylidyne cation CH+ and its isotopologue 13CH+ toward the remote massive star-forming regions W33A, W49N, and W51 with the HIFI instrument onboard the Herschel satellite. Both lines are seen only in absorption against the dust continuum emission of the star-forming regions. The CH+ absorption is saturated over almost the entire velocity ranges sampled by the lines-of-sight that include gas associated with the star-forming regions (SFR) and Galactic foreground material. The CH+ column densities are inferred from the optically thin components. A lower limit of the isotopic ratio [ 12CH+] /[ 13CH+] > 35.5 is derived from the absorptions of foreground material toward W49N. The column density ratio, N(CH+)/N(HCO+), is found to vary by at least a factor 10, between 4 and >40, in the Galactic foreground material. Line-of-sight 12CH+ average abundances relative to total hydrogen are estimated. Their average value, N(CH+)/NH > 2.6×10-8, is higher than that observed in the solar neighborhood and confirms the high abundances of CH+ in the Galactic interstellar medium. We compare this result to the predictions of turbulent dissipation regions (TDR) models and find that these high abundances can be reproduced for the inner Galaxy conditions. It is remarkable that the range of predicted N(CH+)/N(HCO+) ratios, from 1 to ~50, is comparable to that observed. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix (page 6) is only available in electronic form at http://www.aanda.org