Faint Object Infrared Camera For The SOFIA Telescope Research Articles

A thermophysical and dynamical study of the Hildas, (1162) Larissa, and (1911) Schubart

ABSTRACT The Hilda asteroids are among the least studied populations in the asteroid belt, despite their potential importance as markers of Jupiter’s migration in the early Solar system. We present new mid-infrared observations of two notable Hildas, (1162) Larissa, and (1911) Schubart, obtained using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), and use these to characterize their thermal inertia and physical properties. For (1162) Larissa, we obtain an effective diameter of 46.5$^{+2.3}_{-1.7}$ km, an albedo of 0.12 ± 0.02, and a thermal inertia of 15$^{+10}_{-8}$ Jm−2 s1/2 K−1. In addition, our Larissa thermal measurements are well matched with an ellipsoidal shape with an axial ratio a/b = 1.2 for the most-likely spin properties. Our modelling of (1911) Schubart is not as refined, but the thermal data point towards a high-obliquity spin-pole, with a best fit a/b = 1.3 ellipsoidal shape. This spin-shape solution is yielding a diameter of 72$^{+3}_{-4}$ km, an albedo of 0.039± 0.02, and a thermal inertia below 30 Jm−2 s1/2 K−1 (or 10$^{+20}_{-5}$ Jm−2 s1/2 K−1). As with (1162) Larissa, our results suggest that (1911) Schubart is aspherical, and likely elongated in shape. Detailed dynamical simulations of the two Hildas reveal that both exhibit strong dynamical stability, behaviour that suggests that they are primordial, rather than captured objects. The differences in their albedos, along with their divergent taxonomical classification, suggests that despite their common origin, the two have experienced markedly different histories.

SOFIA/FORCAST resolves 30–40 μm extended dust emission in nearby active galactic nuclei

We present arcsecond-scale observations of the active galactic nuclei (AGNs) of seven nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the 31.5 and 37.1 um filters of the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We isolate unresolved emission from the torus and find extended diffuse emission in six 37.1 um residual images in our sample. Using Spitzer/IRS spectra, we determine the dominant mid-infrared (MIR) extended emission source and attribute it to dust in the narrow line region (NLR) or star formation. We compare the optical NLR and radio jet axes to the extended 37.1 um emission and find coincident axes for three sources. For those AGNs with extended emission coincident with the optical axis, we find that spatial scales of the residual images are consistent with 0.1 - 1 kpc scale distances to which dust can be heated by the AGN. Using previously published subarcsecond 1 - 20 um imaging and spectroscopic data along with our new observations, we construct broadband spectral energy distributions (SEDs) of the AGNs at wavelengths 1 - 40 um. We find that three AGNs in our sample tentatively show a turnover in the SED between 30 - 40 um. Using results from Clumpy torus models and the Bayesian inference tool BayesClumpy, we find that the posterior outputs for AGNs with MIR turnover revealed by SOFIA/FORCAST have smaller uncertainties than AGNs that do not show a turnover.

FORCAST: A Mid-Infrared Camera for SOFIA

We describe the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) which is presently operating as a facility instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). FORCAST provides imaging and moderate resolution spectroscopy capability over the 5–40[Formula: see text][Formula: see text]m wavelength range. In imaging mode, FORCAST has a 3.4[Formula: see text] field-of-view with 0.768[Formula: see text] pixels. Using grisms, FORCAST provides long-slit low-resolution ([Formula: see text]–300) and short-slit, cross-dispersed medium-resolution spectroscopic modes ([Formula: see text]–1200) over select wavelengths. Preceded by both Spitzer and Herschel, the discovery phase space for FORCAST lies in providing unique photometric bands and/or spectroscopic coverage, higher spatial resolution and exploration of the brightest sources which typically saturate space observatories.

SOFIA/FORCAST Observations of the Luminous Blue Variable Candidates MN 90 and HD 168625

Abstract We present Stratospheric Observatory for Infrared Astronomy (SOFIA)/Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) imaging of the circumstellar dust shells surrounding the luminous blue variable candidates MN 90 and HD 168625 to quantify the mineral abundances of the dust and to constrain the evolutionary state of these objects. Our image at 37.1 μm of MN 90 shows a limb-brightened, spherical dust shell. A least-squares fit to the spectral energy distribution of MN 90 yields a dust temperature of 59 ± 10 K, with the peak of the emission at 42.7 μm. Using 2-Dust radiative transfer code, we estimate for MN 90 that mass loss occurred at a rate of (7.3 ± 0.4) × 10−7 × (v exp/50 ) to create a dust shell with a dust mass of (3.2 ± 0.1) × 10−2 . Our images between 7.7 and 37.1 μm of HD 168625 complement previously obtained mid-IR imaging of its bipolar nebulae. The SOFIA/FORCAST imaging of HD 168625 shows evidence for the limb-brightened peaks of an equatorial torus. We estimate a dust temperature of 170 ± 40 K for the equatorial dust surrounding HD 168625, with the peak of the emission at 18.3 μm. Our 2-Dust model for HD 168625 estimates that mass loss occurred at a rate of (3.2 ± 0.2) × 10−7 to create a dust torus/shell with a dust mass of (2.5 ± 0.1) × 10−3 .

An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris

Abstract The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the most extensively studied stars on the AGB. R Scl is a carbon star with a massive circumstellar shell (M shell ∼ 7.3 × 10−3 M ⊙) that is thought to have been produced during a thermal pulse event ∼2200 years ago. To study the thermal dust emission associated with its circumstellar material, observations were taken with the Faint Object InfraRed CAMera for the SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 μm. Maps of the infrared emission at these wavelengths were used to study the morphology and temperature structure of the spatially extended dust emission. Using the radiative-transfer code DUSTY, and fitting the spatial profile of the emission, we find that a geometrically thin dust shell cannot reproduce the observed spatially resolved emission. Instead, a second dust component in addition to the shell is needed to reproduce the observed emission. This component, which lies interior to the dust shell, traces the circumstellar envelope of R Scl. It is best fit by a density profile with n ∝ r α , where and a dust mass of . The strong departure from an r −2 law indicates that the mass-loss rate of R Scl has not been constant. This result is consistent with a slow decline in the post-pulse mass loss that has been inferred from observations of the molecular gas.

The Power of SOFIA/FORCAST in Estimating Internal Luminosities of Low-mass Class 0/I Protostars

Abstract With the Stratospheric Observatory for Infrared Astronomy (SOFIA) routinely operating science flights, we demonstrate that observations with the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) can provide reliable estimates of the internal luminosities, L int, of protostars. We have developed a technique to estimate L int using a pair of FORCAST filters: one “short-wavelength” filter centered within 19.7–25.3 μm, and one “long-wavelength” filter within 31.5–37.1 μm. These L int estimates are reliable to within 30%–40% for 67% of protostars and to within a factor of 2.3–2.6 for 99% of protostars. The filter pair comprised of F 25.3 μm and F 37.1 μm achieves the best sensitivity and most constrained results. We evaluate several assumptions that could lead to systematic uncertainties. The OH5 dust opacity matches observational constraints for protostellar environments best, although not perfectly; we find that any improved dust model will have a small impact of 5%–10% on the L int estimates. For protostellar envelopes, the TSC84 model yields masses that are twice those of the Ulrich model, but we conclude that this mass difference does not significantly impact results at the mid-infrared wavelengths probed by FORCAST. Thus, FORCAST is a powerful instrument for luminosity studies targeting newly discovered protostars or suspected protostars lacking detections longward of 24 μm. Furthermore, with its dynamic range and greater angular resolution, FORCAST may be used to characterize protostars that were either saturated or merged with other sources in previous surveys using the Spitzer Space Telescope or the Herschel Space Observatory.

EVIDENCE FROM SOFIA IMAGING OF POLYCYCLIC AROMATIC HYDROCARBON FORMATION ALONG A RECENT OUTFLOW IN NGC 7027

ABSTRACT We report spatially resolved (FWHM ∼ 3.″8–4.″6) mid-IR imaging observations of the planetary nebula (PN) NGC 7027 taken with the 2.5 m telescope on board the Stratospheric Observatory for Infrared Astronomy (SOFIA). Images of NGC 7027 were acquired at 6.3, 6.6, 11.1, 19.7, 24.2, 33.6, and 37.1 using the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST). The observations reveal emission from polycyclic aromatic hydrocarbons (PAHs) and warm dust ( K) from the illuminated inner edge of the molecular envelope surrounding the ionized gas and central star. The DustEM code was used to fit the spectral energy distribution of fluxes obtained by FORCAST and the archival infrared spectrum of NGC 7027 acquired by the Short Wavelength Spectrometer (SWS) on the Infrared Space Observatory (ISO). Best-fit dust models provide a total dust mass of , where carbonaceous large (a = 1.5 μm) and very small ( ) grains, and PAHs ( ) compose 96.5, 2.2, and 1.3% of the dust by mass, respectively. The 37 μm optical depth map shows minima in the dust column density at regions in the envelope that are coincident with a previously identified collimated outflow from the central star. The optical depth minima are also spatially coincident with enhancements in the 6.2 μm PAH feature, which is derived from the 6.3 and 6.6 μm maps. We interpret the spatial anti-correlation of the dust optical depth and PAH 6.2 μm feature strength and their alignment with the outflow from the central star as evidence of dust processing and rapid PAH formation via grain–grain collisions in the post-shock environment of the dense ( ) photo-dissociation region and molecular envelope.

THE ORION H ii REGION AND THE ORION BAR IN THE MID-INFRARED

ABSTRACT We present mid-infrared photometry of the Orion bar obtained with the Faint Object infraRed Camera for the SOFIA Telescope (FORCAST) on board SOFIA at 6.4, 6.6, 7.7, 19.7, 31.5, and 37.1 μm. By complementing this observation with archival FORCAST and Herschel/PACS images, we are able to construct a complete infrared spectral energy distribution of the Huygens region in the Orion nebula. Comparing the infrared images with gas tracers, we find that PACS maps trace the molecular cloud, while the FORCAST data trace the photodissociation region (PDR) and the H ii region. Analysis of the energetics of the region reveal that the PDR extends for 0.28 pc along the line of sight and that the bar is inclined at an angle of 4°. The infrared and submillimeter images reveal that the Orion bar represents a swept-up shell with a thickness of 0.1 pc. The mass of the shell implies a shock velocity of ≃3 km s−1 and an age of ≃105 years for the H ii region. Our analysis shows that the UV and infrared dust opacities in the H ii region and the PDR are a factor 5 to 10 lower than in the diffuse interstellar medium. In the ionized gas, Lyα photons are a major source of dust heating at distances larger than ≃0.06 pc from θ 1 Ori C. Dust temperatures can be explained if the size of the grains is between 0.1 and 1 μm. We derive the photoelectric heating efficiency of the atomic gas in the Orion bar. The results are in good qualitative agreement with models and the quantitative differences indicate a decreased polycyclic aromatic hydrocarbon abundance in this region.

INFRARED OBSERVATIONS OF THE QUINTUPLET PROPER MEMBERS USING SOFIA/FORCAST AND GEMINI/TReCS

ABSTRACT Since their discovery, the Quintuplet proper members (QPMs) have been somewhat mysterious in nature. Originally dubbed the “cocoon stars” due to their cool featureless spectra, high-resolution near-infrared imaging observations have shown that at least two of the objects exhibit “pinwheel” nebulae consistent with binary systems with a carbon-rich Wolf–Rayet star and O/B companion. In this paper, we present 19.7, 25.2, 31.5, and 37.1 μm observations of the QPMs (with an angular resolution of 3.2″–3.8″) taken with the Faint Object Infrared Camera for the SOFIA Telescope (FORCAST) in conjunction with high-resolution (∼0.1″–0.2″) images at 8.8 and 11.7 μm from the Thermal-Region Camera Spectrograph (TReCS). DUSTY models of the thermal dust emission of two of the four detected QPMs, Q2 and Q3, are fitted by radial density profiles that are consistent with constant mass-loss rates ( ). For the two remaining sources, Q1 and Q9, extended structures (∼1″) are detected around these objects in high-resolution imaging data. Based on the fitted dust masses, Q9 has an unusually large dust reservoir ( ) compared to typical dusty Wolf–Rayet stars, which suggests that it may have recently undergone an episode of enhanced mass loss.

Investigating the dusty torus of Seyfert galaxies using SOFIA/FORCAST photometry

We present 31.5 micron imaging photometry of 11 nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We tentatively detect extended 31 micron emission for the first time in our sample. In combination with this new data set, subarcsecond resolution 1-18 micron imaging and 7.5-13 micron spectroscopic observations were used to compute the nuclear spectral energy distribution (SED) of each galaxy. We found that the turnover of the torus emission does not occur at wavelengths <31.5 micron, which we interpret as a lower-limit for the wavelength of peak emission. We used CLUMPY torus models to fit the nuclear infrared (IR) SED and infer trends in the physical parameters of the AGN torus for the galaxies in the sample. Including the 31.5 micron nuclear flux in the SED 1) reduces the number of clumpy torus models compatible with the data, and 2) modifies the model output for the outer radial extent of the torus for 10 of the 11 objects. Specifically, six (60%) objects show a decrease in radial extent while four (40%) show an increase. We find torus outer radii ranging from <1pc to 8.4 pc

FIRST SCIENCE RESULTS FROM SOFIA/FORCAST: THE MID-INFRARED VIEW OF THE COMPACT H II REGION W3A

The massive star forming region W3 was observed with the faint object infrared camera for the SOFIA telescope (FORCAST) as part of the Short Science program. The 6.4, 6.6, 7.7, 19.7, 24.2, 31.5 and 37.1 \um bandpasses were used to observe the emission of Polycyclic Aromatic Hydrocarbon (PAH) molecules, Very Small Grains and Big Grains. Optical depth and color temperature maps of W3A show that IRS2 has blown a bubble devoid of gas and dust of $\sim$0.05 pc radius. It is embedded in a dusty shell of ionized gas that contributes 40% of the total 24 \um emission of W3A. This dust component is mostly heated by far ultraviolet, rather than trapped Ly$\alpha$ photons. This shell is itself surrounded by a thin ($\sim$0.01 pc) photodissociation region where PAHs show intense emission. The infrared spectral energy distribution (SED) of three different zones located at 8, 20 and 25\arcsec from IRS2, show that the peak of the SED shifts towards longer wavelengths, when moving away from the star. Adopting the stellar radiation field for these three positions, DUSTEM model fits to these SEDs yield a dust-to-gas mass ratio in the ionized gas similar to that in the diffuse ISM. However, the ratio of the IR-to-UV opacity of the dust in the ionized shell is increased by a factor $\simeq$3 compared to the diffuse ISM.