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We present 5--14~$\mu$m spectra at two different positions across the Orion Bar photodissociation region (PDR) obtained with the Infrared Spectrograph onboard the Spitzer Space Telescope and 3.3~$\mu$m PAH observations obtained with the Stratospheric Observatory for Infrared Astronomy (SOFIA). We aim to characterize emission from Polycyclic Aromatic Hydrocarbon (PAH), dust, atomic and molecular hydrogen, argon, sulfur, and neon as a function of distance from the primary illuminating source. We find that all the major PAH bands peak between the ionization front and the PDR front, as traced by H$_{2}$, while variations between these bands become more pronounced moving away from this peak into the face-on PDRs behind the PDR front and at the backside of the \HII\, region. While the relative PAH intensities are consistent with established PAH characteristics, we report unusual behaviours and attribute these to the PDR viewing angle and the strength of the FUV radiation field impinging on the PDRs. We determine the average PAH size which varies across the Orion Bar. We discuss subtle differences seen between the cationic PAH bands and highlight the photo-chemical evolution of carbonaceous species in this PDR environment. We find that PAHs are a good tracer of environmental properties such as the strength of the FUV radiation field and the PAH ionization parameter., Comment: 25 pages, 19 Figures. To be published in MNRAS

The heart of the Large Magellanic Cloud, 30 Doradus, is a complex region with a clear core-halo structure. Feedback from the stellar cluster R$\,$136 has been shown to be the main source of energy creating multiple pc-scale expanding-shells in the outer region, and carving a nebula core in the proximity of the ionization source. We present the morphology and strength of the magnetic fields (B-fields) of 30 Doradus inferred from the far-infrared polarimetric observations by SOFIA/HAWC+ at 89, 154, and 214$\,\mu$m. The B-field morphology is complex, showing bending structures around R$\,$136. In addition, we use high spectral and angular resolution [\textsc{CII}] observations from SOFIA/GREAT and CO(2-1) from APEX. The kinematic structure of the region correlates with the B-field morphology and shows evidence of multiple expanding shells. Our B-field strength maps, estimated using the Davis-Chandrasekhar-Fermi method and structure-function, show variations across the cloud within a maximum of 600, 450, and 350$\,\mu$G at 89, 154, and 214$\,\mu$m, respectively. We estimated that the majority of the 30 Doradus clouds are sub-critical and sub-Alfv\'enic. The probability distribution function of the gas density shows that the turbulence is mainly compressively driven, while the plasma beta parameter indicates supersonic turbulence. We show that the B-field is sufficient to hold the cloud structure integrity under feedback from R$\,$136. We suggest that supersonic compressive turbulence enables the local gravitational collapse and triggers a new generation of stars to form. The velocity gradient technique (VGT) using [\textsc{CII}] and CO(2-1) is likely to confirm these results., Comment: 26 pages, 17 figures, 3 tables, accepted to ApJ

MWC 297 is a young, early-type star driving an ionized outflow and surrounded by warm, entrained dust. Previous analyses of near- and mid-IR interferometric images suggest that the emission at these wavelengths arises from a compact accretion disk with a moderate ($i < 40$ degrees) inclination. We have obtained 5-40 micron images of MWC 297 with FORCAST on SOFIA, as well as near-infrared spectra acquired with SpeX on the IRTF and radio data obtained with the VLA and BIMA, and supplemented these with archival data from Herschel/PACS and SPIRE. The FORCAST images, combined with the VLA data, indicate that the outflow lobes are aligned nearly north-south and are well separated. Simple geometrical modeling of the FORCAST images suggests that the disk driving the outflow has an inclination of $55\pm 5$ degrees, in disagreement with the results of the interferometric analyses. Analysis of the SpeX data, with a wind model, suggests the the mass loss rate is on the order of $6.0 \pm ^{3.7}_{1.7} \times 10^{-7} M_\odot ~\mathrm{yr}^{-1}$ and the extinction to the source is $A_V \sim 8.1 \pm^{2.5}_{1.5}$ mag. We have combined our data with values from the literature to generate the spectral energy distribution of the source from $0.35~ μ$m to $6$ cm and estimate the total luminosity. We find the total luminosity to be about $7900 ~ L_\odot$, if we include emission from an extended region around the star, only slightly below that expected for a B1.5V star. The reddening must be produced by dust along the line of sight, but distant from the star., 30 pages, 16 figures, accepted for publication in ApJ

Determining the efficiency with which gas is converted into stars in galaxies requires an accurate determination of the total reservoir of molecular gas mass. However, despite being the most abundant molecule in the Universe, H$_2$ is challenging to detect through direct observations and indirect methods have to be used to estimate the total molecular gas reservoir. These are often based on scaling relations from tracers such as CO or dust, and are generally calibrated in the Milky Way. Yet, evidence that these scaling relations are environmentally dependent is growing. In particular, the commonly used CO-to-H$_2$ conversion factor (X$_{\rm CO}$) is expected to be higher in metal-poor and/or strongly UV-irradiated environments. We use new SOFIA/FIFI-LS observations of far-infrared fine structure lines from the ionised and neutral gas and the Meudon photodissociation region model to constrain the physical properties and the structure of the gas in the massive star-forming region of 30 Doradus in the Large Magellanic Cloud, and determine the spatially resolved distribution of the total reservoir of molecular gas in the proximity of the young massive cluster R136. We compare this value with the molecular gas mass inferred from ground-based CO observations and dust-based estimates to quantify the impact of this extreme environment on commonly used tracers of the molecular gas. We find that the strong radiation field combined with the half-solar metallicity of the surrounding gas are responsible for a large reservoir of "CO-dark" molecular gas, leaving a large fraction of the total H$_2$ gas (> 75%) undetected when adopting a standard X$_{\rm CO}$ factor in this massive star-forming region., 14 pages, 7 figures. Accepted for publication in MNRAS (April 16, 2020)

We present mid infrared imaging of two young clusters, the Coronet in the CrA cloud core and B59 in the Pipe Nebula, using the FORCAST camera on the Stratospheric Observatory for Infrared Astronomy. We also analyze Herschel Space Observatory PACS and SPIRE images of the associated clouds. The two clusters are at similar, and very close, distances. Star formation is ongoing in the Coronet, which hosts at least one Class 0 source and several pre-stellar cores, which may collapse and form stars. The B59 cluster is older, although it still has a few Class I sources, and is less compact. The CrA cloud has a diameter of about 0.16 pc, and we determine a dust temperature of 15.7 K and a star formation efficiency of about 27 %, while the B59 core is approximately twice as large, has a dust temperature of about 11.4 K and a star formation efficiency of about 14 %. We infer that the gas densities are much higher in the Coronet, which has also formed intermediate mass stars, while B59 has only formed low-mass stars., 15 pages, 6 figures, Accepted for publication in The Astrophysical Journal

On UT 29 June 2015, the occultation by Pluto of a bright star (r′ = 11.9) was observed from the Stratospheric Observatory for Infrared Astronomy (SOFIA) and several ground-based stations in New Zealand and Australia. Pre-event astrometry allowed for an in-flight update to the SOFIA team with the result that SOFIA was deep within the central flash zone (~22 km from center). Analysis of the combined data leads to the result that Pluto's middle atmosphere is essentially unchanged from 2011 and 2013 (Person et al. 2013; Bosh et al. 2015); there has been no significant expansion or contraction of the atmosphere. Additionally, our multi-wavelength observations allow us to conclude that a haze component in the atmosphere is required to reproduce the light curves obtained. This haze scenario has implications for understanding the photochemistry of Pluto's atmosphere.

We present observations from the First Light Infrared TEst CAMera (FLITECAM) on board the Stratospheric Observatory for Infrared Astronomy (SOFIA), the Spitzer Infrared Array Camera (IRAC) and the Spitzer Infrared Spectrograph (IRS) SH mode in three well-known Photodissocation Regions (PDRs), the reflection nebulae (RNe) NGC 7023 and NGC 2023 and to the southeast of the Orion Bar, which are well suited to probe emission from Polycyclic Aromatic Hydrocarbon molecules (PAHs). We investigate the spatial behaviour of the FLITECAM 3.3 um filter as a proxy for the 3.3 um PAH band, the integrated 11.2 um PAH band, and the IRAC 8.0 um filter as a proxy for the sum of the 7.7 and 8.6 um PAH bands. The resulting ratios of 11.2/3.3 and IRAC 8.0/11.2 provide an approximate measure of the average PAH size and PAH ionization respectively. In both RNe, we find that the relative PAH ionization and the average PAH size increases with decreasing distance to the illuminating source. The average PAH sizes derived for NGC 2023 are greater than those found for NGC 7023 at all points. Both results indicate that PAH size is dependent on the radiation field intensity. These results provide additional evidence of a rich carbon-based chemistry driven by the photo-chemical evolution of the omnipresent PAH molecules within the interstellar medium. In contrast, we did not detect a significant variation in the average PAH size found in the region southeast of the Orion Bar and report a peculiar PAH ionization radial profile., 20 pages, 11 figures, accepted for publication in ApJ

Located in the Large Magellanic cloud and mostly irradiated by a massive-star cluster R$\,$136, 30 Doradus is an ideal target to test the leading theory of the grain alignment and rotational disruption by RAdiative Torques (RATs). Here, we use publicly available polarized thermal dust emission observations of 30 Doradus at 89, 154, and 214$\,\mu$m using SOFIA/HAWC+. We analyse the variation of the dust polarization degree ($p$) with the total emission intensity ($I$), the dust temperature ($T_{\rm d}$), and the gas column density ($N_{\rm H}$) constructed from ${\it Herschel}$ data. The 30 Doradus complex is divided into two main regions relative to R$\,$136, namely North and South. In the North, we find that the polarization degree first decreases and then increases before decreasing again when the dust temperature increases toward the irradiating cluster R$\,$136. The first depolarization likely arises from the decrease of grain alignment efficiency toward the dense medium due to the attenuation of the interstellar radiation field and the increase of the gas density. The second trend (the increase of $p$ with $T_{\rm d}$) is consistent with the RAT alignment theory. The final trend (the decrease of $p$ with $T_{\rm d}$) is consistent with the RAT alignment theory only when the grain rotational disruption by RATs is taken into account. In the South, we find that the polarization degree is nearly independent of the dust temperature, while the grain alignment efficiency is higher around the peak of the gas column density and decreases toward the radiation source. The latter feature is also consistent with the prediction of the rotational disruption by RATs., Comment: 19 pages, 13 figures, 1 table, accepted to ApJ

We report NASA-DLR SOFIA upGREAT circumstellar [O i] 63.2 μm and [C ii] 157.7 μm emission profiles and FIFI-LS [O i] 63.2 μm, [O i] 145.5 μm, and [C ii] 157.7 μm fluxes obtained shortly after Betelgeuse’s 2019/2020 Great Dimming event. Haas et al. noted a potential correlation between the [O i] 63.2 μm flux and V magnitude based on three Kuiper Airborne Observatory observations made with the CGS and FIFI instruments. The FIFI observation was obtained when V ≃ 0.88 and revealed a 3σ non-detection at a quarter of the previous CGS flux measurement made when V ≃ 0.35. A potential explanation could be a change in dust-gas drag heating by circumstellar silicates caused by variations in the photospheric radiation field. SOFIA observations provide a unique test of this correlation because the V-band brightness went to its lowest value on record, V ≃ 1.61, with the SOFIA observations being made when V FIFI−LS ≃ 1.51 and V upGREAT ≃ 1.36. The upGREAT spectra show a [O i] 63.2 μm flux larger than previous space observatory measurements obtained when V ≃ 0.58. The profile is consistent with formation in the slower, more turbulent inner S1 outflow, while the [C ii] 157.7 μm profile is consistent with formation farther out in the faster S2 outflow. Modeling of dust-gas drag heating, combined with 25 yr of Wing three-filter and V photometry, reveals that it is unlikely that the S1 circumstellar envelope and [O i] 63.2 μm fluxes are dominated by the dust-gas drag heating and that another heating source is also active. The [O i] 63.2 μm profile is hard to reconcile with existing outflow velocity models.

We report on the measurements of telluric water vapor made with the instrument FIFI-LS on SOFIA. Since November 2018, FIFI-LS has measured the water vapor overburden with the same measurement setup on each science flight with about 10 data points throughout the flight. This created a large sample of 469 measurements at different locations, flight altitudes and seasons. The paper describes the measurement principle in detail and provides some trend analysis on the 3 parameters. This presents the first systematic analysis with SOFIA based on in situ observations., 15 pages, 7 figures, 1 tables, accepted for publication in Publications of the Astronomical Society of the Pacific (PASP)

SOFIA is an airborne observatory for far-infrared astronomy. Although SOFIA flies at altitudes of ∼41,000 feet, any far-infrared observations from within the Earth’s atmosphere are nevertheless hampered by water vapor absorbing the astronomical signal. The atmospheric parameter governing absorption is the total upward precipitable water vapor, PWV. In this paper we investigated if data of the Earth’s atmosphere provided by the European Centre for Medium-Range Weather Forecasts, ECMWF, can be used to determine spatially and time-resolved PWV data to allow a more precise calibration of far-infrared data taken with SOFIA along its flight path. We found that PWV values obtained from ECMWF correlate extremely well with independently determined PWV values obtained with the FIFI-LS instrument onboard SOFIA. We determined maximum observing time intervals (depending on the pressure altitude SOFIA is flying at) within which the upward PWV value changes inflight by less than a certain amount. We also present a new calibration method which enhances data quality and observing efficiency with FIFI-LS significantly. Furthermore our new method is universal and may be applied to data from all of SOFIA's instruments.

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.

The HIgh-Resolution Mid-infrarEd Spectrometer (HIRMES) is the 3rd Generation Instrument for the Stratospheric Observatory For Infrared Astronomy (SOFIA), currently in development at the NASA Goddard Space Flight Center (GSFC), and due for commissioning in 2019. By combining direct-detection Transition Edge Sensor (TES) bolometer arrays, grating-dispersive spectroscopy, and a host of Fabry-Perot tunable filters, HIRMES will provide the ability for high resolution ([Formula: see text]), mid-resolution ([Formula: see text]), and low-resolution ([Formula: see text]) slit-spectroscopy, and 2D Spectral Imaging ([Formula: see text] at selected wavelengths) over the 25–122[Formula: see text][Formula: see text]m mid to far infrared waveband. The driving science application is the evolution of proto-planetary systems via measurements of water-vapor, water-ice, deuterated hydrogen (HD), and neutral oxygen lines. However, HIRMES has been designed to be as flexible as possible to cover a wide range of science cases that fall within its phase-space, all whilst reaching sensitivities and observing powers not yet seen thus far on SOFIA, providing unique observing capabilities which will remain unmatched for decades.

We present SOFIA/FIFI-LS observations of the [CII] 158${\mu}$m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H I data to compare [CII] emission to dust properties, star formation rate (SFR), H$_2$, and HI at 560pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute $73\%$ of the [CII] luminosity to arms, and $19\%$ and $8\%$ to the center and interarm region, respectively. [CII]/TIR, [CII]/CO, and [CII]/PAH radial profiles are largely constant, but rise at large radii ($\gtrsim$8kpc) and drop in the center ("[CII] deficit"). This increase at large radii and the observed decline with the 70${\mu}$m/100${\mu}$m dust color are likely driven by radiation field hardness. We find a near proportional [CII]-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. [CII] also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of [CII] as an H$_2$ and SFR tracer in such regimes. Finally, based on the observed [CII] and CO radial profiles and different models, we find ${\alpha}_{CO}$ to increase with radius, in line with the observed metallicity gradient. The low ${\alpha}_{CO}$ (galaxy average $\lesssim2\,M_{sun}\,pc^{-2}\,(K\,km\,s^{-1})^{-1}$) and low [CII]/CO ratios ($\sim$400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way., Comment: 12 pages, 6 Figures, published in ApJ

We analyze a [C II] 158 micron map obtained with the L2 GREAT receiver on SOFIA of the emission/reflection nebula illuminated by the early B star S1 in the rho-OphA cloud core. This data set has been complemented with maps of CO(3-2), 13CO(3-2) and C18O(3-2), observed as a part of the JCMT Gould Belt Survey, with archival HCO^+(4-3) JCMT data, as well as with [O I] 63 and 145 micron imaging with Herschel/PACS. The [C II] emission is completely dominated by the strong PDR emission from the nebula surrounding S1 expanding into the dense Oph A molecular cloud west and south of S1. The [C II] emission is significantly blue shifted relative to the CO spectra and also relative to the systemic velocity, particularly in the northwestern part of the nebula. The [C II] lines are broader towards the center of the S1 nebula and narrower towards the PDR shell. The [C II] lines are strongly self-absorbed over an extended region in the S1 PDR. Based on the strength of the [13C II] F = 2-1 hyperfine component, [C II] is significantly optically thick over most of the nebula. CO and 13CO(3-2) spectra are strongly self-absorbed, while C18O(3-2) is single peaked and centered in the middle of the self-absorption. We have used a simple two-layer LTE model to characterize the background and foreground cloud contributing to the [C II] emission. From this analysis we estimate the extinction due to the foreground cloud to be ~9.9 mag, which is slightly less than the reddening estimated towards S1. Since some of the hot gas in the PDR is not traced by low J CO emission, this result appears quite plausible. Using a plane parallel PDR model with the observed [OI(145)]/[C II] brightness ratio and an estimated FUV intensity of 3100-5000 G0 suggests that the density of the [C II] emitting gas is ~3-4x10^3 cm^-3., Accepted for publication in Astronomy & Astrophysics

The field-imaging far-infrared line spectrometer (FIFI-LS) is a science instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA). FIFI-LS allows simultaneous observations in two spectral channels. The “blue” channel is sensitive from 51[Formula: see text][Formula: see text]m to 125[Formula: see text][Formula: see text]m and the “red” channel from 115[Formula: see text][Formula: see text]m to 203[Formula: see text][Formula: see text]m. The instantaneous spectral coverage is 1000–3000[Formula: see text]km/s in the blue and 800–2500[Formula: see text]km/s in the red channel with a spectral resolution between 150[Formula: see text]km/s and 600[Formula: see text]km/s. Each spectral channel observes a field of five by five spatial pixels on the sky. The pixel size in the blue channel is 6.14 by 6.25 square arc seconds and it is 12.2 by 12.5 square arc seconds in the red channel. FIFI-LS has been operating on SOFIA since 2014. It is available to the astronomical community as a facility science instrument. We present the results of the spectral and spatial characterization of the instrument based on laboratory measurements. This includes the measured spectral resolution and examples of the line spread function in the spectral domain. In the spatial domain, a model of the instrument’s point spread function (PSF) and the description of a second pass ghost are presented. We also provide an overview of the procedures used to measure the instrument’s field of view geometry and spectral calibration. The spectral calibration yields an accuracy of 15–60[Formula: see text]km/s depending on wavelength.

We describe the design of the Field-Imaging Far-Infrared Line Spectrometer (FIFI-LS), operated as a Facility-Class instrument on the Stratospheric Observatory for Infrared Astronomy (SOFIA). FIFI-LS is an imaging spectrometer for medium resolution spectroscopy. Since being commissioned in 2014, it has performed over 50 SOFIA commissioning and science flights. After operating as a principal investigator instrument in 2014 and early 2015, it was accepted as a Facility Science Instrument in 2015. In addition to the description of the design, we report on the in-flight performance and the concept of operation. We also provide an overview of the science opportunities with FIFI-LS and describe how FIFI-LS observations complement and complete observations with the PACS instrument on the Herschel observatory.

We present infrared spectroscopy of the classical nova V339 Delphini, obtained over a $\sim2$ year period. The infrared emission lines were initially symmetrical, with HWHM velocities of 525 km s$^{-1}$. In later ($t\gtrsim77$days, where $t$ is the time from outburst) spectra however, the lines displayed a distinct asymmetry, with a much stronger blue wing, possibly due to obscuration of the receding component by dust. Dust formation commenced at $\sim$ day 34.75 at a condensation temperature of $1480\pm20$K, consistent with graphitic carbon. Thereafter the dust temperature declined with time as $T_{\rm d}\propto{t}^{-0.346}$, also consistent with graphitic carbon. The mass of dust initally rose, as a result of an increase in grain size and/or number, peaked at $\sim$ day 100, and then declined precipitously. This decline was most likely caused by grain shattering due to electrostatic stress after the dust was exposed to X-radiation. An Appendix summarises Planck Means for carbon, and the determination of grain mass and radius for a carbon dust shell., Accepted by MNRAS on 19 December 2016. 19 pages

The benchmark exoplanet GJ 1214b is one of the best studied transiting planets in the transition zone between rocky Earth-sized planets and gas or ice giants. This class of super-Earth/mini-Neptune planets is unknown in our Solar System, yet is one of the most frequently detected classes of exoplanets. Understanding the transition from rocky to gaseous planets is a crucial step in the exploration of extrasolar planetary systems, in particular with regard to the potential habitability of this class of planets. GJ 1214b has already been studied in detail from various platforms at many different wavelengths. Our airborne observations with SOFIA add information in the Paschen-alpha cont. 1.9 micron infrared wavelength band, which is not accessible by any other current ground- or space-based instrument due to telluric absorption or limited spectral coverage. We used FLIPO and FPI+ on SOFIA to comprehensively analyse the transmission signal of the possible water-world GJ 1214b through photometric observations during transit in three optical and one infrared channels. We present four simultaneous light curves and corresponding transit depths in three optical and one infrared channel, which we compare to previous observations and state-of-the-art synthetic atmospheric models of GJ 1214b. The final precision in transit depth is between 1.5 and 2.5 times the theoretical photon noise limit, not sensitive enough to constrain the theoretical models any better than previous observations. This is the first exoplanet observation with SOFIA that uses its full set of instruments available to exoplanet spectrophotometry. Therefore we use these results to evaluate SOFIA's potential in this field and suggest future improvements., Comment: Accepted for publication in Astronomy and Astrophysics

The formation processes and the exact appearance of the dust torus and broad line region (BLR) of active galactic nuclei (AGN) are under debate. Theoretical studies show a possible connection between the dust torus and BLR through a common origin in the accretion disk. However observationally the dust torus and BLR are typically studied separately. NGC~4151 is possibly one of the best suited Seyfert~1 galaxies for simultaneous examinations because of its high number of both photometric and spectroscopic observations in the past. Here we compare changes of the dust radius to shape variations of broad emission lines (BEL). While the radius of the dust torus decreased by almost a factor of two from 2004 to 2006 shape variations can be seen in the red wing of BELs of NGC~4151. These simultaneous changes are discussed in a dust and BEL formation scheme. We also use the BEL shape variations to assess possible cloud distributions, especially in azimuthal direction, which could be responsible for the observed variations. Our findings can best be explained in the framework of a dust inflated accretion disk. The changes in the BELs suggest that this dusty cloud formation does not happen continuously, and over the whole accretion disk, but on the contrary in spatially confined areas over rather short amount of times. We derive limits to the azimuthal extension of the observed localized BEL flux enhancement event., Comment: accepted for publication in A&A

FORCAST is a mid-infrared (5–40 μm) facility instrument for the Stratospheric Observatory for Infrared Astronomy (SOFIA). After achieving first light flight in 2010 May, FORCAST has completed two observatory characterization flights and thirteen science flights on SOFIA. In this paper we describe the photometric calibration of FORCAST which involves some subtleties in correction for array artifacts and uncertainties due to the airborne environment. At present FORCAST is able to achieve approximately 20% (3σ) uncertainty in the calibration.

Effective stray light control is a key requirement for wide dynamic range performance of scientific optical and infrared systems. SOFIA now has over 325 mission flights including extended southern hemisphere deployments; science campaigns using 7 different instrument configurations have been completed. The research observations accomplished on these missions indicate that the telescope and cavity designs are effective at suppressing stray light. Stray light performance impacts, such as optical surface contamination, from cavity environment conditions during mission flight cycles and while on-ground, have proved to be particularly benign. When compared with earlier estimates, far fewer large optics re-coatings are now anticipated, providing greater facility efficiency.

We estimate the dynamical masses of several young (~10 Myr) massive star clusters in two interacting galaxies, NGC 4038/4039 ("The Antennae") and NGC 1487, under the assumption of virial equilibrium. These are compared with photometric mass estimates from K-band photometry and assuming a standard Kroupa IMF. The clusters were selected to have near-infrared colors dominated by red supergiants, and hence to be old enough to have survived the earliest phases of cluster evolution when the interstellar medium is rapidly swept out from the cluster, supported by the fact that there is no obvious Halpha emission associated with the clusters. All but one of the Antennae clusters have dynamical and photometric mass estimates which are within a factor ~2 of one another, implying both that standard IMFs provide a good approximation to the IMF of these clusters, and that there is no significant extra-virial motion, as would be expected if they were rapidly dispersing. These results suggest that almost all of the Antennae clusters in our sample have survived the gas removal phase as bound or marginally bound objects. Two of the three NGC 1487 clusters studied here have M_dyn estimates which are significantly larger than the photometric mass estimates. At least one of these two clusters, and one in the Antennae, may be actively in the process of dissolving. The process of dissolution contributes a component of non-virial motion to the integrated velocity measurements, resulting in an estimated M_dyn which is too high relative to the amount of measured stellar light. The dissolution candidates in both galaxies are amongst the clusters with the lowest pressures/densities measured in our sample., 17 pages, 14 Figures, A&A accepted

We present low resolution multi-object spectroscopy of an I-band magnitude limited (I_{AB} ~ 23--23.5) sample of galaxies located in an area centered on the Hubble Deep Field-South (HDFS). The observations were obtained using the Focal Reducer low dispersion Spectrograph (FORS) on the ESO Very Large Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were supplemented with galaxies detected in the Infrared Space Observatory's survey of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100 galaxies for spectroscopic observations. Based on detections of several emission lines, such as [OII]3727, H_beta and [OIII]5007, or other spectroscopic features, we have measured accurate redshifts for 50 objects in the central HDFS and flanking fields. The redshift range of the current sample of galaxies is 0.6--1.2, with a median redshift of 1.13 (at I ~ 23.5 not corrected for completeness). The sample is dominated by starburst galaxies with only a small fraction of ellipticals (~10%). For the emission line objects, the extinction corrected [OII]3727 line strengths yield estimates of star formation rates in the range 0.5--30 M_solar/yr. We have used the present data to derive the [OII]3727 luminosity function up to redshift of 1.2. When combined with [OII]3727 luminosity densities for the local and high redshift Universe, our results confirm the steep rise in the star formation rate (SFR) to z ~ 1.3., Comment: Tables 2 and 3 provided as separate files. Accepted for publication by Astronomy and Astrophysics

We estimate the dynamical masses of several young (≈ 10 Myr) massive star clusters in two interacting galaxies, NGC 4038/4039 (“The Antennae”) and NGC 1487, under the assumption of virial equilibrium. These are compared with photometric mass estimates. A dynamical mass substantially higher than the photometric estimate could indicate non-virial motion of the stars in the cluster, and potentially lead to cluster disruption. All but one of the Antennae clusters have dynamical and photometric mass estimates which are within a factor ≈ 2 of one another, implying both that standard IMFs provide a good approximation to the IMF of these clusters, and that there is no significant extra-virial motion, as would be expected if they were rapidly dispersing. These results suggest that almost all of the clusters in our sample have survived the gas removal phase as bound or marginally bound objects. But a few targets (two in NGC 1487 and one in the Antennae) have Mdyn estimates which are significantly larger than the photometric mass estimates. At least two of those clusters may be actively in the process of dissolving. The dissolution candidates in both galaxies are amongst the clusters with the lowest pressures/densities measured in our sample. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present ground-based infrared photometry, JHK spectroscopy, and 5-28 micron SOFIA FORCAST spectroscopy documenting the early temporal development of Nova Delphini 2013 (V339 Del). We derive a distance of ˜4.5 kpc using data available from the early expansion of the fireball. This distance gives an outburst luminosity of ˜8.3 × 10^5 solar luminosities making V339 Del the most luminous CO nova on record. Our data provide new constraints on the ejected gas mass and the dust yield in fast CO novae. The ejected gas mass as estimated by the cutoff wavelength during the free-free emission phase is ˜7.5 × 10^-5 solar masses. There is evidence for the formation of ˜1.2(±0.4) × 10^-7 solar masses of dust about 102 days after outburst. The gas to dust ratio of ˜470/1-940/1 implies that dust production was much less efficient in V339 Del than is the case for most CO novae.

We present a preliminary survey of 58 radio sources within the isoplanatic patches (r < 25") of bright (111) that are now within the capabilities of the current generation of AO-fed integral-field spectrographs. These objects constitute a unique sample that can be used for detailed ground-based AO studies of galactic structure, evolution, and AGN formation at high redshift., Comment: 41 pages, 29 figures, accepted to ApJS

IC 2144 is a small reflection nebula located in the zone of avoidance near the Galactic anticenter. It has been investigated here largely on the basis of Keck/HIRES optical spectroscopy (R ~ 48,000) and a SpeX spectrogram in the near-IR (R = 2000) obtained at the NASA IRTF. The only star in the nebula that is obvious in the optical or near-IR is the peculiar emission-line object MWC 778 (V = 12.8), which resembles a T Tauri star in some respects. What appear to be F- or G-type absorption features are detectable in its optical region under the very complex emission line spectrum; their radial velocity agrees with the CO velocity of the larger cloud in which IC 2144 is embedded. There are significant differences between the spectrum of the brightest area of the nebula and of MWC 778, the presumed illuminator, an issue discussed in some detail. The distance of IC 2144 is inferred to be about 1.0 kpc by reference to other star-forming regions in the vicinity. The extinction is large, as demonstrated by [Fe II] emission line ratios in the near-IR and by the strength of the diffuse interstellar band spectrum; a provisional value of A_V of 3.0 mag was assumed. The SED of MWC 778 rises steeply beyond about 1 $\mu$m, with a slope characteristic of a Class I source. Integration of the flux distribution leads to an IR luminosity of about 510 L_solar. If MWC 778 is indeed a F- or G-type pre--main-sequence star several magnitudes above the ZAMS, a population of faint emission Halpha stars would be expected in the vicinity. Such a search, like other investigations that are recommended in this paper, has yet to be carried out., Comment: 36 pages, 13 figures, accepted by AJ

We present an analysis of the 0.95-14.5 micron spectral energy distributions of nine field ultracool dwarfs with spectral types ranging from L1 to T4.5. Effective temperatures, gravities, and condensate cloud sedimentation efficiencies are derived by comparing the data to synthetic spectra computed from atmospheric models that self-consistently include the formation of condensate clouds. Derived effective temperatures decrease steadily through the L1 to T4.5 spectral types and we confirm that the effective temperatures of ultracool dwarfs at the L/T transition are nearly constant, decreasing by only ~200 K from spectral types L7.5 to T4.5. The two objects in our sample with very red J-Ks colors are best fitted with synthetic spectra that have thick clouds which hints at a possible correlation between the near-infrared colors of L dwarfs and the condensate cloud properties. The fits to the two T dwarfs in our sample (T2 and T4.5) also suggest that the clouds become thinner in this spectral class, in agreement with previous studies. Restricting the fits to narrower wavelength ranges (i.e., individual photometric bands) almost always yields excellent agreement between the data and models. Limitations in our knowledge of the opacities of key absorbers such as FeH, VO, and CH4 at certain wavelengths remain obvious, however. The effective temperatures obtained by fitting the narrower wavelength ranges can show a large scatter compared to the values derived by fitting the full spectral energy distributions; deviations are typically ~200 K and in the worst cases, up to 700 K.

We present high spectral resolution (~3 km/s) observations of the nu_2 ro-vibrational band of H2O in the 6.086--6.135 micron range toward the massive protostar AFGL 2591 using the Echelon-Cross-Echelle Spectrograph (EXES) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). Ten absorption features are detected in total, with seven caused by transitions in the nu_2 band of H2O, two by transitions in the first vibrationally excited nu_2 band of H2O, and one by a transition in the nu_2 band of H2{18}O. Among the detected transitions is the nu_2 1(1,1)--0(0,0) line which probes the lowest lying rotational level of para-H2O. The stronger transitions appear to be optically thick, but reach maximum absorption at a depth of about 25%, suggesting that the background source is only partially covered by the absorbing gas, or that the absorption arises within the 6 micron emitting photosphere. Assuming a covering fraction of 25%, the H2O column density and rotational temperature that best fit the observed absorption lines are N(H2O)=(1.3+-0.3)*10^{19} cm^{-2} and T=640+-80 K., Comment: 6 pages, 3 figures, 1 table, accepted for publication in ApJL

New NTT/SOFI imaging and spectroscopy of the Wolf-Rayet population in Westerlund 1 are presented. Narrow-band near-IR imaging together with follow up spectroscopy reveals four new WR stars, of which three were independently identified recently by Groh et al., bringing the confirmed WR content to 24 (23 excluding source S) [..] A quantitative near-IR spectral classification scheme for WR stars is presented and applied to members of Westerlund 1. Late subtypes are dominant, with no subtypes earlier than WN5 or WC8 for the nitrogen and carbon sequences, respectively. A qualitative inspection of the WN stars suggests that most (75%) are highly H-deficient. The WR binary fraction is high (>62%), on the basis of dust emission from WC stars, in addition to a significant WN binary fraction from hard X-ray detections according to Clark et al. We exploit the large WN population of Westerlund 1 to reassess its distance (~5.0kpc) and extinction (A_Ks ~ 0.96 mag), such that it is located at the edge of the Galactic bar, [..]. The observed ratio of WR stars to red and yellow hypergiants, N(WR)/N(RSG+YHG)~3, favours an age of 4.5-5.0 Myr, with individual WR stars descended from progenitors of initial mass ~ 40-55 Msun. Qualitative estimates of current masses for non-dusty, H-free WR stars are presented, revealing 10-18 Msun, such that ~75% of the initial stellar mass has been removed via stellar winds or close binary evolution. We present a revision to the cluster turn-off mass for other Milky Way clusters in which WR stars are known, based upon the latest temperature calibration for OB stars. Finally, comparisons between the observed WR population and subtype distribution in Westerlund 1 and instantaneous burst evolutionary synthesis models are presented., 20 pages, 11 figures, accepted for MNRAS

We investigate the quantity and composition of unburned material in the outer layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw. Pristine matter from a white dwarf progenitor is expected to be a mixture of oxygen and carbon in approximately equal abundance. Using near-infrared (NIR, 0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is severely depleted with low upper limits in the outer third of the ejected mass. Strong features from the OI line at rest wavelength = 0.7773 microns are observed through a wide range of expansion velocities approx. 9,000 - 18,000 km/s. This large velocity domain corresponds to a physical region of the supernova with a large radial depth. We show that the ionization of C and O will be substantially the same in this region. CI lines in the NIR are expected to be 7-50 times stronger than those from OI but there is only marginal evidence of CI in the spectra and none of CII. We deduce that for these three normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000. MgII is also detected in a velocity range similar to that of OI. The presence of O and Mg combined with the absence of C indicates that for these SNe Ia, nuclear burning has reached all but the extreme outer layers; any unburned material must have expansion velocities greater than 18,000 km/s. This result favors deflagration to detonation transition (DD) models over pure deflagration models for SNe Ia., Comment: accepted for publication in ApJ

V1647 Ori is a low-mass star in the L1630 star-forming region that underwent an outburst in late 2003 and early 2004. We present postoutburst infrared spectra obtained with NIRSPEC (Keck II) and SpeX (IRTF) and compare these to spectra taken during the outburst. The results show that the temperature of the hot CO formed in the inner part of the disk has declined by ~800 K, while the water and CO ice and low-J CO gas features remained unchanged, consistent with previous assertions that the latter, low-temperature features arise in the foreground cloud. The P Cygni profiles of the Paschen series that were present in the outburst spectra taken in 2004 March disappeared by late 2004. The equivalent width of the helium absorption line at 1.0830 μm decreased from 8.9 to 3.9 A between 2004 March and November, evidence that the hot, fast wind has decreased substantially. We discuss the implications for categorizing V1647 Ori among the known classes of outbursting young stars.

(Abridged) We present high spatial resolution ultraviolet and optical spectroscopy, obtained using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, of nuclear structures within four `warm' Ultraluminous Infrared Galaxies (ULIRGs). We find an AGN in at least three, and probably all four of our sample, hosted in a compact, optically luminous `knot'. In three cases these knots were previously identified as a putative AGN nucleus from multiband optical imaging. Three of the sample also harbor a starburst in one or more knots, suggesting that the optically luminous knots seen in local ULIRGs are the most likely sites of the dust-shrouded starburst and AGN activity that power the infrared emission. The four AGN have a diverse range of properties; two are classical narrow line AGN, one shows both broad and narrow lines and evidence for lines of sight from the narrow through to the broad line regions, and one is plausibly a FeLoBAL AGN. The probable presence in one object of an FeLoBAL AGN, which are extremely rare in the QSO population, supports the idea that LoBAL AGN may be youthful systems shrouded in gas and dust rather than AGN viewed along a certain line of sight. The three starbursts for which detailed constraints are possible show a smaller range in properties; all three bursts are young with two having ages of ~4Myr and the third having an age of 20Myr, suggesting that ULIRGs undergo several bursts of star formation during their lifetimes. None of the starbursts show evidence for Initial Mass Function slopes steeper than about 3.3. The metallicities of the knots for which metallicities can be derived are all at least 1.5 times the Solar value. The properties of one further starburst knot are consistent with it being the forming core of an elliptical galaxy.

We present 0.8-5.2 micron spectroscopy of the compact source at the base of a variable nebula (McNeil's Nebula Object) in the Lynds 1630 dark cloud that went into outburst in late 2003. The spectrum of this object reveals an extremely red continuum, CO bands at 2.3-2.5 microns in emission, a deep 3.0 micron ice absorption feature, and a solid state CO absorption feature at 4.7 microns. In addition, emission lines of H, Ca II, Mg I, and Na I are present. The Paschen lines exhibit P Cygni profiles, as do two lines of He I, although the emission features are very weak in the latter. The Brackett lines, however, are seen to be purely in emission. The P Cygni profiles clearly indicate that mass outflow is occurring in a wind with a velocity of ~400 km/s. The H line ratios do not yield consistent estimates of the reddening, nor do they agree with the extinction estimated from the ice feature (A_V ~ 11). We propose that these lines are optically thick and are produced in a dense, ionized wind. The near-infrared spectrum does not appear similar to any known FUor or EXor object. However, all evidence suggests that McNeil's Nebula Object is a heavily-embedded low-mass Class I protostar, surrounded by a disk, whose brightening is due to a recent accretion event., 11 pages, 2 ps figures, accepted for publication in ApJ Letters

We describe an IDL‐based package for the reduction of spectral data obtained with SpeX, a medium‐resolution, 0.8–5.5 μm cross‐dispersed spectrograph and imager for the NASA Infrared Telescope Facility. The package, called Spextool, carries out all the procedures necessary to produce fully reduced spectra including preparation of calibration frames, processing and extraction of spectra from science frames, wavelength calibration of spectra, and flux calibration of spectra. The package incorporates an “optimal extraction” algorithm for point‐source data and also generates realistic error arrays associated with the extracted spectra. Because it is fairly quick and easy to use, requiring minimal user interaction, Spextool can be run by observers at the telescope to estimate the signal‐to‐noise ratio of their data. We describe the procedures incorporated into Spextool and show examples of extracted spectra.

We present the design, construction, and performance of SpeX, a medium-resolution 0.8-5.5 mm cryogenic spectrograph and imager, now in operation at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The design uses prism cross-dispersers and gratings to provide resolving powers up to R ∼ 2000 simultaneously across 0.8-2.4, 1.9-4.2, or 2.4-5.5 mm, with a 15 long slit. A high-throughput low-resolution prism mode is also provided for faint-object and occultation spectroscopy. Single-order 60 long-slit R ∼ 200 modes with resolving powers up to are available for extended objects. The spectrograph employs an R ∼ 2000

We present a method for correcting near-infrared medium-resolution spectra for telluric absorption. The method makes use of a spectrum of an A0V star, observed near in time and close in airmass to the target object, and a high-resolution model of Vega, to construct a telluric correction spectrum that is free of stellar absorption features. The technique was designed specifically to perform telluric corrections on spectra obtained with SpeX, a 0.8-5.5 micron, medium-resolution cross-dispersed spectrograph at the NASA Infrared Telescope Facility, and uses the fact that for medium resolutions there exist spectral regions uncontaminated by atmospheric absorption lines. However, it is also applicable (in a somewhat modified form) to spectra obtained with other near-infrared spectrographs. An IDL-based code that carries out the procedures is available for downloading via the World Wide Web from the IRTF website.

We present the initial results of a medium resolution, 0.8 to 4.2 μm spectroscopic survey of M, L, and T dwarfs. We have identified the most prominent molecular and atomic absorption features found in the spectra of these late-type dwarfs. We have also compared the spectra to a laboratory FeH emission spectrum and identified nearly 100 features common to the FeH spectrum and the dwarf spectra from 0.99 to 1.8 μm.

A spectrum from 1.2 to 2.5 μm of Uranus' small satellite Miranda obtained in June 1999 reveals strong water-ice signatures. It confirms the existence of a 2.0-μm water feature previously detected on Miranda and shows a strong second broad 1.5-μm water-ice absorption feature. The spectra also reveal a weak absorption band at 1.65 μm that is indicative of crystalline water ice. Reflectance models which combine the new spectra with new photometry indicate that the spectra are characteristic of a mostly water-ice surface, with a large fraction of carbonaceous or silicate contaminates, and the possible presence of ammonia hydrate, as implied by an apparent weak feature near 2.2 μm. The possible presence of other volatiles is also investigated.

To better understand the early stages of massive star cluster evolution we have obtained J,H,K', and N (10.8 micron) images of the nuclear region of the starburst galaxy He 2-10. The N-band images were obtained with the Gemini North telescope and reveal four of the five enshrouded clusters, or "ultradense HII regions" (UDHIIs), recently discovered in radio maps. None of these sources appears in either the optical HST images or the near-infrared images. They comprise about 60% of the total N-band flux from He 2-10 and, we suspect, a similar fraction of the total far infrared flux measured by IRAS. The inferred spectra of the UDHIIs are very similar to those of Galactic ultracompact HII regions and we have modeled the UDHIIs under the assumption that they are "scaled-up" versions of these objects. The bolometric luminosity of the brightest UDHII is estimated to be ~2x10^9 L_sun, and the total mass of the dust and gas is ~10^7 M_sun. The mass of the enshrouded stellar cluster must be > 2.5x10^6 M_sun and the age must be < 4.8x10^6 yr. All of the stellar clusters within the UDHIIs must have ages less than about 5x10^6 yr and masses greater than about 5x10^5 M_sun. The logarithmic ratios of the radio to far infrared flux densities for the individual UDHIIs, and He 2-10 as a whole, are significantly larger than the average for normal galaxies, but comparable to those for ultraluminous infrared galaxies. Large ratios for some starburst galaxies may indicate that a significant fraction of the far infrared flux arises from UDHIIs. If all of the far infrared flux from He 2-10 and other starbursts is produced by heavily obscured regions, the observed correlation between UV continuum slope and infrared-to-ultraviolet flux ratio in starbursts cannot be due primarily to UV reprocessing by dust in a foreground screen.

Debris disk morphology is wavelength dependent due to the wide range of particle sizes and size-dependent dynamics influenced by various forces. Resolved images of nearby debris disks reveal complex disk structures that are difficult to distinguish from their spectral energy distributions. Therefore, multi-wavelength resolved images of nearby debris systems provide an essential foundation to understand the intricate interplay between collisional, gravitational, and radiative forces that govern debris disk structures. We present the SOFIA 35 um resolved disk image of epsilon Eri, the closest debris disk around a star similar to the early Sun. Combining with the Spitzer resolved image at 24 um and 15-38 um excess spectrum, we examine two proposed origins of the inner debris in epsilon Eri: (1) in-situ planetesimal belt(s) and (2) dragged-in grains from the cold outer belt. We find that the presence of in-situ dust-producing planetesmial belt(s) is the most likely source of the excess emission in the inner 25 au region. Although a small amount of dragged-in grains from the cold belt could contribute to the excess emission in the inner region, the resolution of the SOFIA data is high enough to rule out the possibility that the entire inner warm excess results from dragged-in grains, but not enough to distinguish one broad inner disk from two narrow belts.