Observations of interstellar linear polarization in the spectral range 0.35È2.2 km are presented for several stars reddened by dust in the Taurus region. Combined with a previously published study by Whittet et al., these results represent the most comprehensive data set available on the spectral dependence of interstellar polarization in this nearby dark cloud (a total of 27 sight lines). Extinction data for these and other reddened stars in Taurus are assembled for the same spectral range, combining

We present new observations with the Infrared Spectrograph on board the Spitzer Space Telescope of the solid-CO 2 absorption feature near 15 m in the spectra of eight field stars behind the Taurus complex of dark clouds. Solid CO 2 is detected in six lines of sight. New results are combined with previous data to investigate the correlation of CO 2 column density with those of other major ice constituents (H 2 O and CO) and with extinction. CO 2 is shown to display a ''threshold extinction'' effect, i.e., a minimum extinction (A 0 ¼ 4:3 AE 1:0 mag) required for detection, behavior similar to that previously reported for H 2 O and CO. We find a particularly tight correlation through the origin between N(CO 2 ) and N(H 2 O), confirming that these species form in tandem and coexist in the same (polar) ice layer on the grains. The observed composition of the mantles is broadly consistent with the predictions of photochemical models with diffusive surface chemistry proposed by Ruffle & Herbst. Comparison of our results for Taurus with published data for Serpens indicates significant differences in ice composition consistent with enhanced CO 2 production in the latter cloud. Our results also place constraints on the distribution of elemental oxygen between ices and other potential reservoirs. Assuming a constant N(H) to extinction ratio, we show that~65% of the solar O abundance is accounted for by summing the contributions of ices (~26%), refractory dust (~30%) and gas-phase CO (~9%). If the Sun is an appropriate standard for the interstellar medium, the ''missing'' oxygen may reside in atomic O i gas and/or (undetected) O 2 within the ices.

Widespread hydration was detected on the lunar surface through observations of a characteristic absorption feature at 3 µm by three independent spacecraft 1-3. Whether the hydration is molecular water (H 2 O) or other hydroxyl (OH) compounds is unknown and there are no established methods to distinguish the two using the 3 µm band 4. However, a fundamental vibration of molecular water produces a spectral signature at 6 µm that is not shared by other hydroxyl compounds 5. Here, we present observations of the Moon at 6 µm using the NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA). Observations reveal a 6 µm emission feature at high lunar latitudes due to the presence of molecular water on the lunar surface. On the basis of the strength of the 6 µm band, we estimate abundances of about 100 to 400 µg g −1 H 2 O. We find that the distribution of water over the small latitude range is a result of local geology and is probably not a global phenomenon. Lastly, we suggest that a majority of the water we detect must be stored within glasses or in voids between grains sheltered from the harsh lunar environment, allowing the water to remain on the lunar surface. Using SOFIA and the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) instrument, we conducted observations of the lunar surface at 6 µm on 31 August 2018 in a search for molecular water. FORCAST is well suited to look for 6 µm lunar water due to its wavelength coverage from 5 to 8 µm, spectral resolution of R = 200 and high signal-to-noise ratios. The FORCAST entrance slit that defines the portion of the Moon observed is 2.4 × 191 arcsec sampled with 248 pixels. At the lunar centre of disk the slit has a spatial extent of 4.8 × 1.5 km 2 (the spatial resolution near the limb is lower due to foreshortening). During the observations, the Moon was at a phase angle of 57.5°. We observed a region at high southern latitudes near Clavius crater and a low-latitude portion of Mare Serenitatis (Extended Data Fig. 1). Details regarding observations, site selection and data reduction can be found in the Methods. Data from SOFIA reveal a strong 6 µm emission band at Clavius crater and the surrounding terrain (Fig. 1) relative to the control location near the lunar equator, which shows low hydration in some analyses (see Methods). All spectra from the Clavius region exhibit this 6 µm emission feature. The majority of these emission peaks (98%) exceed 2σ significance relative to the background noise, and about 20% exceed 4σ significance (Extended Data Fig. 2). To determine whether the spectral properties of the lunar 6 µm band are consistent with spectra of particulate water-bearing materials, we examined other planetary materials that show a 6 µm

MIPSGAL is a 278 deg 2 survey of the inner Galactic plane using the Multiband Infrared Photometer for Spitzer aboard the Spitzer Space Telescope. The survey field was imaged in two passbands, 24 and 70 μm with resolutions of 6″ and 18″, respectively. The survey was designed to provide a uniform, well-calibrated and well-characterized data set for general inquiry of the inner Galactic plane and as a longer-wavelength complement to the shorter-wavelength Spitzer survey of the Galactic plane: Galactic Plane Infrared Mapping Survey Extraordinaire. The primary science drivers of the current survey are to identify all high-mass (M > 5 M ⊙) protostars in the inner Galactic disk and to probe the distribution, energetics, and properties of interstellar dust in the Galactic disk. The observations were planned to minimize data artifacts due to image latents at 24 μm and to provide full coverage at 70 μm. Observations at ecliptic latitudes within 15°of the ecliptic plane were taken at multiple epochs to help reject asteroids. The data for the survey were collected in three epochs, 2005 September-October, 2006 April, and 2006 October with all of the data available to the public. The estimated point-source sensitivities of the survey are 2 and 75 mJy (3 σ) at 24 and 70 μm, respectively. Additional data processing was needed to mitigate image artifacts due to bright sources at 24 μm and detector responsivity variations at 70 μm due to the large dynamic range of the Galactic plane. Enhanced data products including artifact-mitigated mosaics and point-source catalogs are being produced with the 24 μm mosaics already publicly available from the NASA/IPAC Infrared Science Archive. Some preliminary results using the enhanced data products are described.

We present a catalog of 416 extended, resolved, disk and ringlike objects as detected in the MIPSGAL 24 μm survey of the Galactic plane. This catalog is the result of a search in the MIPSGAL image data for generally circularly symmetric, extended "bubbles" without prior knowledge or expectation of their physical nature. Most of the objects have no extended counterpart at 8 μm or 70 μm, with less than 20% detections at each wavelength. For the 54 objects with central point sources, the sources are nearly always seen in all Infrared Array Camera bands. About 70 objects (16%) have been previously identified, with another 35 listed as Infrared Astronomical Satellite sources. Among the identified objects, those with central sources are mostly listed as emission-line stars, but with other source types including supernova remnants (SNRs), luminous blue variables, and planetary nebulae (PNe). The 57 identified objects (of 362) without central sources are nearly all PNe (∼90%), which suggests that a large fraction of the 300+ unidentified objects in this category are also PNe. These identifications suggest that this is primarily a catalog of evolved stars. Also included in the catalog are two filamentary objects that are almost certainly SNRs, and 10 unusual compact extended objects discovered in the search. Two of these show remarkable spiral structure at both 8 μm and 24 μm. These are likely background galaxies previously hidden by the intervening Galactic plane.

The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO 2 near 15 μm has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature to be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for ∼85% of the CO 2 in the line of sight. We compare for the first time 15 μm profiles in three widely separated dark clouds (Taurus, Serpens, and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO 2 /H 2 O ratio in the three clouds have little or no effect on the 15 μm profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H 2 O, CO 2 , and CO) in the ices.

No abstract

The Vulpecula OB association, Vul OB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of Vul OB1, and search for signatures of past triggering events. We make a census of Young Stellar Objects (YSO) in Vul OB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in Vul OB1 is rather homogeneous -ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ∼ 8%. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation.