Spitzer IRS Spectra Research Articles

A “Wonderful” Reference Dataset of Mira Variables

The conditions in Mira variable atmospheres make them wonderful laboratories to study a variety of stellar physics such as molecule–grain formation, dust production, shock chemistry, stellar winds, mass loss, opacity-driven pulsation, and shocks. We were awarded an NSF grant to analyze over a decade of synoptic observations from the Palomar Testbed Interferometer (PTI) of 106 Miras to curate a Mira Reference Dataset. The Miras included in this dataset include M-types, S-types, and C-types, and span a wide range of pulsation periods. PTI measured K-band angular sizes that when combined with a distance allow us to directly determine fundamental stellar parameters such as effective temperature, radial size, and bolometric flux. Supplementing observations with interferometric measurements of the stars opens the Mira laboratory to a wealth of different experiments. We provide two case studies to serve as examples of the power of the Mira Reference Dataset. The first case study describes combining PTI measurements with Spitzer IRS spectra of M-type Miras, which allowed us to fully characterize CO2 gas in their atmospheres. The second case study examines how PTI narrow-band data can be used to study phase-dependent pulsation effects on the stellar atmosphere. We provide a list of all the Miras (with coordinates) included in the set for anyone who would like to add them to their observing programs. All the data we produce and collate for this Mira Reference Dataset will be hosted and curated on a website open to the public so that other researchers and citizen scientists can participate in expanding the utility and body of knowledge on this set of “wonderful” stars.

Identification and Parameter Determination of F-type Herbig Stars from LAMOST DR8

We identify 20 F-type Herbig stars and provide a list of 22 pre-main-sequence candidates from LAMOST DR8. The effective temperature, distance, extinction, stellar luminosity, mass, age, and radius are derived for each Herbig star based on optical spectra, photometry, Gaia EDR3 parallaxes, and pre-main-sequence evolutionary tracks. According to spectral energy distribution, 19 F-type Herbig stars belong to Class II YSOs, and one belongs to the flat-spectrum class. Four have Spitzer IRS spectra, of which three show extremely weak polycyclic aromatic hydrocarbon emissions, and three with both amorphous and crystalline silicate emissions share similar parameters and are at the same evolutionary stage. We detect a solar-nearby outbursting EXor Herbig star J034344.48+314309.3, a possible precursor of a Herbig Ae star. Intense emission lines of H i, He i, O i, Na i, and Ca ii originating from the rapid accretion during the outbursts are detected in its optical spectra, and silicate emission features are detected in its infrared spectrum. We also conduct a statistical analysis of the disk properties of all known Herbig stars using the defined infrared spectral indices ( and ). The proportion of Herbig stars with moderate infrared excesses decreases as effective temperature increases. The majority of the precursors (F, G, or K type) have moderate infrared excesses. Hotter Herbig stars tend to have a larger proportion with large infrared excesses. The trends may be due to the fact that hotter stars have larger areas of re-emitting dust, although there is some scatter due to the particularities of each disk.

A Catalog of Early-type Hα Emission-line Stars and 62 Newly Confirmed Herbig Ae/Be Stars from LAMOST Data Release 7

Abstract We derive a catalog of early-type emission-line stars including 30,023 spectra of 25,867 stars from LAMOST Data Release 7, in which 4189 have Simbad records. The spectra are classified into three morphological types (10 subtypes) based on Hα emission-line profiles. Some spectra contaminated by nebula emission lines such as from H ii regions are flagged in the catalog. We also provide a specific catalog of 20 stars with stellar winds or accretion flows by calculating the terminal and peak velocities based on P-Cygni or inverse P-Cygni profiles. More important, with two color–color diagrams, (H-Ks, J-H) and (Ks-W1, H-Ks), of a collection of known Herbig Ae/Be stars (HAeBes) and classical Ae/Be stars (CAeBes), we propose an updated criterion to separate HAeBes from CAeBes. By the criterion, we select 118 HAeBe candidates and 2636 CAeBe candidates from the sample. We confirm 71 of the 118 HAeBes based on the data from LAMOST (optical spectra) and WISE (photometry and images), 62 of which are newly identified. The 71 identified HAeBes are compiled into a specific catalog, and their SEDs and MIR images are also presented. The distances of 76% confirmed HAeBes are further than 1 kpc, which enlarges the number of known HAeBes in further distance. Most of the 71 HAeBes are located in the Galactic disk while 6 of them have ∣Z gal∣ > 400 pc. Four HAeBes show the forbidden emission lines of [Fe ii] and [O i], in which J051425.20+411310.7 is a newly discovered B[e]. In addition, four HAeBes having Spitzer IRS spectra all show PAH features.

The post-Herschel view of intrinsic AGN emission: constructing templates for galaxy and AGN emission at IR wavelengths

ABSTRACT Measuring the star-forming properties of active galactic nucleus (AGN) hosts is key to our understanding of galaxy formation and evolution. However, this topic remains debated, partly due to the difficulties in separating the infrared (i.e. 1–1000 ${\rm \mu m}$) emission into AGN and star-forming components. Taking advantage of archival far-infrared data from Herschel, we present a new set of AGN and galaxy infrared templates and introduce the spectral energy distribution fitting code iragnsep. Both can be used to measure infrared host galaxy properties, free of AGN contamination. To build these, we used a sample of 100 local (z < 0.3), low-to-high luminosity AGNs (i.e. Lbol$\ \sim \ 10^{42-46}$ erg s−1), selected from the 105-month Swift–BAT X-ray survey, which have archival Spitzer–IRS spectra and Herschel photometry. We first built a set of seven galaxy templates using a sample of 55 star-forming galaxies selected via infrared diagnostics. Using these templates, combined with a flexible model for the AGN contribution, we extracted the intrinsic infrared emission of our AGN sample. We further demonstrate that we can reduce the diversity in the intrinsic shapes of AGN spectral energy distributions down to a set of three AGN templates, of which two represent AGN continuum, and one represents silicate emission. Our results indicate that, on average, the contribution of AGNs to the far-infrared (λ ≳ 50 ${\rm \mu m}$) is not as high as suggested by some recent work. We further show that the need for two infrared AGN continuum templates could be related to nuclear obscuration, where one of our templates appears dominated by the emission of the extended polar dust.

Unveiling the stellar origin of the Wolf–Rayet nebula NGC 6888 through infrared observations

ABSTRACT We present a comprehensive infrared (IR) study of the iconic Wolf–Rayet (WR) wind-blown bubble NGC 6888 around WR 136. We use Wide-field Infrared Survey Explorer, Spitzer IRAC, and MIPS and Herschel PACS IR images to produce a sharp view of the distribution of dust around WR 136. We complement these IR photometric observations with Spitzer IRS spectra in the 5–38-μm wavelength range. The unprecedented high-resolution IR images allowed us to produce a clean spectral energy distribution, free of contamination from material along the line of sight, to model the properties of the dust in NGC 6888. We use the spectral synthesis code cloudy to produce a model for NGC 6888 that consistently reproduces its optical and IR properties. Our best model requires a double distribution with the inner shell composed only of gas, whilst the outer shell requires a mix of gas and dust. The dust consists of two populations of grain sizes, one with small-sized grains asmall = [0.002–0.008] $\mu$m and another one with large-sized grains abig = [0.05–0.5] $\mu$m. The population of big grains is similar to that reported for other red supergiants stars and dominates the total dust mass, which leads us to suggest that the current mass of NGC 6888 is purely due to material ejected from WR 136, with a negligible contribution of the swept up interstellar medium. The total mass of this model is 25.5$^{+4.7}_{-2.8}$ M⊙, a dust mass of $M_\mathrm{dust} = 0.14^{+0.03}_{-0.01}$ M⊙, for a dust-to-gas ratio of 5.6 × 10−3. Accordingly, we suggest that the initial stellar mass of WR 136 was ≲50 M⊙, consistent with current single stellar evolution models.

The VMC Survey

Context. Variability is a key property of stars on the asymptotic giant branch (AGB). Their pulsation period is related to the luminosity and mass-loss rate of the star. Long-period variables (LPVs) and Mira variables are the most prominent of all types of variability of evolved stars. The reddest, most obscured AGB stars are too faint in the optical and have eluded large variability surveys. Aims. We obtained a sample of LPVs by analysing K-band light curves (LCs) of a large number of sources in the direction of the Magellanic Clouds with the colours expected for red AGB stars ((J − K) > 3 mag or equivalent in other colour combinations). Methods. Selection criteria were derived based on colour-colour and colour-magnitude diagrams from the combination of the VISTA Magellanic Cloud (VMC) survey, Spitzer IRAC and AllWISE data. After eliminating LPVs with known periods shorter than 450 days, a sample of 1299 candidate obscured AGB stars was selected. K-band LCs were constructed by combining the epoch photometry available in the VMC survey with literature data, were analysed for variability, and fitted with a single period sine curve to derive mean magnitudes, amplitudes, and periods. A subset of 254 stars are either new variables, known variables where the period we find is better determined than the literature value, or variables with periods longer than 1000 days. The spectral energy distributions (SEDs) of these stars were fitted to a large number of templates. For this purpose the SEDs and Spitzer IRS spectra of some non-AGB stars (Be stars, HII regions and young stellar objects – YSOs) were also fitted to have templates of the most likely contaminants in the sample. Results. A sample of 217 likely LPVs is found. Thirty-four stars have periods longer than 1000 days, although some of them have alternative shorter periods. The longest period of a known Mira in the Magellanic Clouds from Optical Gravitational Lensing Experiment data (with P = 1810 d) is derived to have a period of 2075 d based on its infrared LC. Two stars are found to have longer periods, but both have lower luminosities and smaller pulsation amplitudes than expected for Miras. Mass-loss rates and luminosities are estimated from the template fitting. Period-luminosity relations are presented for carbon (C-) and oxygen (O-) rich Miras that appear to be extensions of relations derived in the literature for shorter periods. The fit for the C stars is particularly well defined (with 182 objects) and reads Mbol = (−2.27 ± 0.20) ⋅ log P + (1.45 ± 0.54) mag with an rms of 0.41 mag. Thirty-four stars show pulsation properties typical of Miras while the SEDs indicate that they are not. Overall, the results of the LC fitting are presented for over 200 stars that are associated with YSOs.

Fullerenes in the IC 348 star cluster of the Perseus Molecular Cloud

Abstract We present the detection of fullerenes C60 and C70 in the star-forming region IC 348 of the Perseus molecular cloud. Mid-IR vibrational transitions of C60 and C70 in emission are found in Spitzer IRS spectra of individual stars (LRLL 1, 2, 58), in the averaged spectrum of three other cluster stars (LRLL 21, 31 and 67) and in spectra obtained at four interstellar locations distributed across the IC 348 region. Fullerene bands appear widely distributed in this region with higher strength in the lines-of-sight of stars at the core of the cluster. Emission features consistent with three most intense bands of the C$_{60}^+$ and with one of C$_{60}^-$ are also found in several spectra, and if ascribed to these ionized species it would imply ionization fractions at 20 and 10 %, respectively. The stars under consideration host protoplanetary disks, however the spatial resolution of the spectra is not sufficient to disentangle the presence of fullerenes in them. If fullerene abundances in the cloud were representative of IC 348 protoplanetary disks, C60, the most abundant of the two species, could host ∼ 0.1 % of the total available carbon in the disks. This should encourage dedicated searches in young disks with upcoming facilities as JWST. Fullerenes provide a reservoir of pentagonal and hexagonal carbon rings which could be important as building blocks of prebiotic molecules. Accretion of these robust molecules in early phases of planet formation may contribute to the formation of complex organic molecules in young planets.

30-micron sources in galaxies with different metallicities

Aims. We present an analysis and comparison of the 30 μm dust features seen in the Spitzer Space Telescope spectra of 207 carbon-rich asymptotic giant branch (AGB) stars, post-AGB objects, and planetary nebulae (PNe) located in the Milky Way, the Magellanic Clouds (MCs), or the Sagittarius dwarf spheroidal galaxy (Sgr dSph), which are characterised by different average metallicities. We investigated whether the formation of the 30 μm feature carrier may be a function of the metallicity. Through this study we expect to better understand the late stages of stellar evolution of carbon-rich stars in these galaxies. Methods. Our analysis uses the “Manchester method” as a basis for estimating the temperature of dust for the carbon-rich AGB stars and the PNe in our sample. For post-AGB objects we changed the wavelength ranges used for temperature estimation, because of the presence of the 21 μm feature on the short wavelength edge of the 30 μm feature. We used a black-body function with a single temperature deduced from the Manchester method or its modification to approximate the continuum under the 30 μm feature. Results. We find that the strength of the 30 μm feature increases until dust temperature drops below 400 K. Below this temperature, the large loss of mass and probably the self-absorption effect reduces the strength of the feature. During the post-AGB phase, when the intense mass-loss has terminated, the optical depth of the circumstellar envelope is smaller, and the 30 μm feature becomes visible again, showing variety of values for post-AGB objects and PNe, and being comparable with the strengths of AGB stars. In addition, the AGB stars and post-AGB objects show similar values of central wavelengths – usually between 28.5 and 29.5 μm. However, in case of PNe the shift of the central wavelength towards longer wavelengths is visible. The normalised median profiles for AGB stars look uniformly for various ranges of dust temperature, and different galaxies. We analysed the profiles of post-AGB objects and PNe only within one dust temperature range (below 200 K), and they were also similar in different galaxies. In the spectra of 17 PNe and five post-AGB objects we found the broad 16–24 μm feature. Two objects among the PNe group are the new detections: SMP LMC 51, and SMP LMC 79, whereas in the case of post-AGBs the new detections are: IRAS 05370-7019, IRAS 05537-7015, and IRAS 21546+4721. In addition, in the spectra of nine PNe we found the new detections of 16–18 μm feature. We also find that the Galactic post-AGB object IRAS 11339-6004 has a 21 μm emission. Finally, we have produced online catalogues of photometric data and Spitzer IRS spectra for all objects that show the 30 μm feature. These resources are available online for use by the community. Conclusions. The most important conclusion of our work is the fact that the formation of the 30 μm feature is affected by metallicity. Specifically that, as opposed to more metal-poor samples of AGB stars in the MCs, the feature is seen at lower mass-loss rates, higher temperatures, and has seen to be more prominent in Galactic carbon stars. The averaged feature (profile) in the AGB, post-AGB objects, and PNe seems unaffected by metallicity at least between a fifth and solar metallicity, but in the case of PNe it is shifted to significantly longer wavelengths.

Broad-band X-ray analysis of local mid-infrared-selected Compton-thick AGN candidates

The estimate of the number and space density of obscured AGN over cosmic time still represents an open issue. While the obscured AGN population is a key ingredient of the X-ray background synthesis models and is needed to reproduce its shape, a complete census of obscured AGN is still missing. Here we test the selection of obscured sources among the local 12-micron sample of Seyfert galaxies. Our selection is based on a difference up to three orders of magnitude in the ratio between the AGN bolometric luminosity, derived from the spectral energy distribution (SED) decomposition, and the same quantity obtained by the published XMM-Newton 2-10 keV luminosity. The selected sources are UGC05101, NGC1194 and NGC3079 for which the available X-ray wide bandpass, from Chandra and XMM-Newton plus NuSTAR data, extending to energies up to ~30-45 keV, allows us an accurate determination of the column density, and hence of the true intrinsic power. The newly derived NH values clearly indicate heavy obscuration (about 1.2, 2.1 and 2.4 x10^{24} cm-2 for UGC05101, NGC1194 and NGC3079, respectively) and are consistent with the prominent silicate absorption feature observed in the Spitzer-IRS spectra of these sources (at 9.7 micron rest frame). We finally checked that the resulting X-ray luminosities in the 2-10 keV band are in good agreement with those derived from the mid-IR band through empirical L_MIR-L_X relations.

Modelling gas and dust around carbon stars in the Large Magellanic Cloud

AbstractIn order to investigate the effect of dust production on the molecular absorption, we model the dust continuum and the 7.5 and 13.7 μm acetylene absorption features in the Spitzer IRS spectra of 148 carbon stars in the Large Magellanic Cloud (LMC). Our preliminary investigation does not find a strong correlation between the dust-production rate and the column density of acetylene for the LMC sample. However, we will construct more models at high optical depths and probe a larger range of dust properties for more robust results.

Herschel PACS Observations of 4–10 Myr Old Classical T Tauri Stars in Orion OB1

Abstract We present Herschel PACS observations of eight classical T Tauri Stars in the ∼7–10 Myr old OB1a and the ∼4–5 Myr old OB1b Orion subassociations. Detailed modeling of the broadband spectral energy distributions, particularly the strong silicate emission at 10 μm, shows that these objects are (pre-)transitional disks with some amount of small optically thin dust inside their cavities, ranging from ∼4 to ∼90 au in size. We analyzed Spitzer IRS spectra for two objects in the sample: CVSO-107 and CVSO-109. The IRS spectrum of CVSO-107 indicates the presence of crystalline material inside its gap, while the silicate feature of CVSO-109 is characterized by a pristine profile produced by amorphous silicates; the mechanisms creating the optically thin dust seem to depend on disk local conditions. Using millimeter photometry, we estimated dust disk masses for CVSO-107 and CVSO-109 lower than the minimum mass of solids needed to form the planets in our solar system, which suggests that giant planet formation should be over in these disks. We speculate that the presence and maintenance of optically thick material in the inner regions of these pre-transitional disks might point to low-mass planet formation.

Infrared Spectroscopy of HR 4796A's Bright Outer Cometary Ring + Tenuous Inner Hot Dust Cloud

Abstract We have obtained new NASA/IRTF SpeX spectra of the HR 4796A debris ring system. We find a unique red excess flux that extends out to ∼9 μm in Spitzer IRS spectra, where thermal emission from cold, ∼100 K dust from the system’s ring at ∼75 au takes over. Matching imaging ring photometry, we find the excess consists of NIR reflectance from the ring, which is as red as that of old, processed comet nuclei, plus a tenuous thermal emission component from close-in, T ∼ 850 K circumstellar material evincing an organic/silicate emission feature complex at 7–13 μm. Unusual, emission-like features due to atomic Si, S, Ca, and Sr were found at 0.96–1.07 μm, likely sourced by rocky dust evaporating in the 850 K component. An empirical cometary dust phase function can reproduce the scattered light excess and 1:5 balance of scattered versus thermal energy for the ring with optical depth in an 8 au wide belt of 4 au vertical height and M dust > 0.1–0.7 M Mars. Our results are consistent with HR 4796A, consisting of a narrow shepherded ring of devolatilized cometary material associated with multiple rocky planetesimal subcores and a small steady stream of dust inflowing from this belt to a rock sublimation zone at ∼1 au from the primary. These subcores were built from comets that have been actively emitting large, reddish dust for >0.4 Myr at ∼100 K, the temperature at which cometary activity onset is seen in our solar system.

Ground-based Mid-infrared Study of the Compton-thick AGN in M51 at 10–100 pc Scale*

Abstract We performed near-diffraction-limited ( FWHM) N-band imaging of one of the nearest active galactic nuclei (AGNs) in M51 with the 8.2 m Subaru Telescope to study the nuclear structure and spectral energy distribution (SED) at 8–13 μm. We found that the nucleus is composed of an unresolved core (at pc resolution, orintrinsic size corrected for the instrumental effect of pc) and an extended halo (at a few tens of parsec scale), and each of their SEDs is almost flat. We examined the SED by comparing with the archival Spitzer IRS spectrum processed to mimic our chopping observation of the nucleus and the published radiative transfer model SEDs of the AGN clumpy dusty torus. The halo SED is likely due to circumnuclear star formation showing deficient polycyclic aromatic hydrocarbon emission due to the AGN. The core SED is likely dominated by the AGN because of the following two reasons. First, the clumpy torus model SEDs can reproduce the red mid-infrared continuum with apparently moderate silicate 9.7 μm absorption. Second, the core 12 μm luminosity and the absorption-corrected X-ray luminosity at 2–10 keV in the literature follow the mid-infrared–X-ray luminosity correlation known for the nearby AGNs, including the Compton-thick ones.

THE DEPLETION OF WATER DURING DISPERSAL OF PLANET-FORMING DISK REGIONS

ABSTRACT We present a new velocity-resolved survey of 2.9 μm spectra of hot H2O and OH gas emission from protoplanetary disks, obtained with the Cryogenic Infrared Echelle Spectrometer at the VLT (R ∼ 96,000). With the addition of archival Spitzer-IRS spectra, this is the most comprehensive spectral data set of water vapor emission from disks ever assembled. We provide line fluxes at 2.9–33 μm that probe from the dust sublimation radius at ∼0.05 au out to the region of the water snow line. With a combined data set for 55 disks, we find a new correlation between H2O line fluxes and the radius of CO gas emission, as measured in velocity-resolved 4.7 μm spectra (R ), which probes molecular gaps in inner disks. We find that H2O emission disappears from 2.9 μm (hotter water) to 33 μm (colder water) as increases and expands out to the snow line radius. These results suggest that the infrared water spectrum is a tracer of inside-out water depletion within the snow line. It also helps clarify an unsolved discrepancy between water observations and models by finding that disks around stars of generally have inner gaps with depleted molecular gas content. We measure radial trends in H2O, OH, and CO line fluxes that can be used as benchmarks for models to study the chemical composition and evolution of planet-forming disk regions at 0.05–20 au. We propose that JWST spectroscopy of molecular gas may be used as a probe of inner disk gas depletion, complementary to the larger gaps and holes detected by direct imaging and by ALMA.

The interstellar medium in Andromeda's dwarf spheroidal galaxies – II. Multiphase gas content and ISM conditions

We make an inventory of the interstellar medium material in three low-metallicity dwarf spheroidal galaxies of the Local Group (NGC147, NGC185 and NGC205). Ancillary HI, CO, Spitzer IRS spectra, H{\alpha} and X-ray observations are combined to trace the atomic, cold and warm molecular, ionised and hot gas phases. We present new Nobeyama CO(1-0) observations and Herschel SPIRE FTS [CI] observations of NGC205 to revise its molecular gas content. We derive total gas masses of M_gas = 1.9-5.5x10^5 Msun for NGC185 and M_gas = 8.6-25.0x10^5 Msun for NGC205. Non-detections combine to an upper limit on the gas mass of M_gas =< 0.3-2.2x10^5 Msun for NGC147. The observed gas reservoirs are significantly lower compared to the expected gas masses based on a simple closed-box model that accounts for the gas mass returned by planetary nebulae and supernovae. The gas-to-dust mass ratios GDR~37-107 and GDR~48-139 are also considerably lower compared to the expected GDR~370 and GDR~520 for the low metal abundances in NGC 185 (0.36 Zsun) and NGC205 (0.25 Zsun), respectively. To simultaneously account for the gas deficiency and low gas-to-dust ratios, we require an efficient removal of a large gas fraction and a longer dust survival time (~1.6 Gyr). We believe that efficient galactic winds (combined with heating of gas to sufficiently high temperatures in order for it to escape from the galaxy) and/or environmental interactions with neighbouring galaxies are responsible for the gas removal from NGC147, NGC185 and NGC205.

CONSTRAINTS ON THE PRESENCE OF SiO GAS IN THE DEBRIS DISK OF HD 172555

ABSTRACT We have carried out two sets of observations to quantify the properties of SiO gas in the unusual HD 172555 debris disk: (1) a search for the J = 8–7 rotational transition from the vibrational ground state, carried out with the Atacama Pathfinder EXperiment (APEX) submillimeter telescope and heterodyne receiver at 863 μm and (2) a search at 8.3 μm for the P(17) ro-vibrational transition of gas phase SiO, carried out with the Very Large Telescope (VLT)/VISIR with a resolution, λ/Δλ, of 30,000. The APEX measurement resulted in a 3.3σ detection of an interstellar feature, but only an upper limit to emission at the radial velocity and line width expected from HD 172555. The VLT/VISIR result was also an upper limit. These were used to provide limits for the abundance of gas phase SiO for a range of temperatures. The upper limit from our APEX detection, assuming an 8000 K primary star photospheric excitation, falls more than an order of magnitude below the self-shielding stability threshold derived by Johnson et al. (2012). Our results thus favor a solid-state origin for the 8.3 μm feature seen in the Spitzer IRS spectrum of the circumstellar excess emission and the production of circumstellar O i and Si i by SiO UV photolysis. The implications of these estimates are explored in the framework of models of the HD 172555 circumstellar disk.

Comparison between 30 micron sources in different galaxies

We present an analysis and comparison of the 30 µm dust feature in the spectra of carbon-rich objects located in the Milky Way, Magellanic Clouds and the Sagittarius dwarf spheroidal galaxy. These spectra were collected by Spitzer Space Telescope. All of these galaxies are characterized by the different metallicities. We expect that some physical and chemical processes related to the formation of the feature are a function of the metallicity. Our study should allow us to better understand the mass loss process and thus late stages of stellar evolution of carbon-rich stars in these four galaxies. Our analysis uses the “Manchester method” as a basis of estimating the temperature of dust for the carbon-rich stars and the planetary nebulae in our sample. In the case of post-AGB objects we changed the spectral ranges used for the temperature estimation, because of the presence of the 21 µm feature. We used a blackbody function with a single temperature deduced from the Manchester method to approximate the continuum under the 30 µm feature.We have produced on-line catalogues of photometric and Spitzer IRS spectra for all objects that show the 30 µm feature. These resources are available on-line for use by the community.

A COMBINEDSPITZERANDHERSCHELINFRARED STUDY OF GAS AND DUST IN THE CIRCUMBINARY DISK ORBITING V4046 Sgr

We present results from a spectroscopic Spitzer and Herschel mid-to-far-infrared study of the circumbinary disk orbiting the evolved (age ~12-23 Myr) close binary T Tauri system V4046 Sgr. Spitzer IRS spectra show emission lines of [Ne II], H_2 S(1), CO_2 and HCN, while Herschel PACS and SPIRE spectra reveal emission from [O I], OH, and tentative detections of H_2O and high-J transitions of CO. We measure [Ne III]/[Ne II] < 0.13, which is comparable to other X-ray/EUV luminous T Tauri stars that lack jets. We use the H_2 S(1) line luminosity to estimate the gas mass in the relatively warm surface layers of the inner disk. The presence of [O I] emission suggests that CO, H_2O, and/or OH is being photodissociated, and the lack of [C I] emission suggests any excess C may be locked up in HCN, CN and other organic molecules. Modeling of silicate dust grain emission features in the mid-infrared indicates that the inner disk is composed mainly of large (r~5 um) amorphous pyroxene and olivine grains (~86% by mass) with a relatively large proportion of crystalline silicates. These results are consistent with other lines of evidence indicating that planet building is ongoing in regions of the disk within ~30 AU of the central, close binary.

AN EXTREME STARBURST IN THE CORE OF A RICH GALAXY CLUSTER ATz= 1.7

We have discovered an optically rich galaxy cluster at z = 1.7089 with star formation occurring in close proximity to the central galaxy. The system, SpARCS104922.6+564032.5, was detected within the Spitzer Adaptation of the red-sequence Cluster Survey, and confirmed through Keck-MOSFIRE spectroscopy. The rest-frame optical richness of Ngal (500 kpc) = 30 ± 8 implies a total halo mass, within 500 kpc, of ∼3.8 ± 1.2 × 1014 M⊙, comparable to other clusters at or above this redshift. There is a wealth of ancillary data available, including Canada–France–Hawaii Telescope optical, UKIRT-K, Spitzer-IRAC/MIPS, and Herschel-SPIRE. This work adds submillimeter imaging with the SCUBA2 camera on the James Clerk Maxwell Telescope and near-infrared imaging with the Hubble Space Telescope. The mid/far-infrared (M/FIR) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy, with LIR = 6.2 ± 0.9 × 1012 L⊙. The detection of polycyclic aromatic hydrocarbons at z = 1.7 in a Spitzer-IRS spectrum of the source implies the FIR luminosity is dominated by star formation (an Active Galactic Nucleus contribution of 20%) with a rate of ∼860 ± 130 M⊙ yr−1. The optical source corresponding to the IR emission is likely a chain of >10 individual clumps arranged as "beads on a string" over a linear scale of 66 kpc. Its morphology and proximity to the Brightest Cluster Galaxy (BCG) imply a gas-rich interaction at the center of the cluster triggered the star formation. This system indicates that wet mergers may be an important process in forming the stellar mass of BCGs at early times.

INFRARED AND X-RAY EVIDENCE OF AN AGN IN THE NGC 3256 SOUTHERN NUCLEUS

We investigate signs of Active Galactic Nucleus (AGN) in the luminous infrared galaxy NGC 3256 at both infrared and X-ray wavelengths. NGC 3256 has double, the Northern and Southern, nuclei (hereafter, N and S nuclei, respectively). We show that the Spitzer IRAC colors extracted at the S nucleus are AGN-like, and the Spitzer IRS spectrum is bluer at <6um than at the N nucleus. We built for the S nucleus an AGN-starburst composite model with a heavily absorbed AGN to successfully reproduce not only the IRAC and IRS specrophotometries at ~3arcsec but also the very deep silicate 9.7um absorption observed at 0.36" scale by Diaz-Santos et al. We found a 2.2um compact source at the S nucleus in a HST NICMOS image and identified its unresolved core (at 0.26" resolution) with the compact core in previous mid-infrared observations at comparable resolution. The flux of the 2.2umm core is consistent with our AGN spectral energy distribution model. We also analyzed a deeper than ever Chandra X-ray spectrum of the unresolved (at 0.5" resolution) source at the S nucleus. We found that a dual-component power-law model (for primary and scattered ones) fits an apparently very hard spectrum with a moderately large absorption on the primary component. Together with a limit on equivalent width of a fluorescent Fe-K emission line at 6.4 keV, the X-ray spectrum is consistent with a typical Compton-thin Seyfert 2. We therefore suggest that the S nucleus hosts a heavily absorbed low-luminosity AGN.