Molecular Clouds, HII Regions, Interstellar Medium and Dust

129

Molecular Clouds, HII Regions, Interstellar Medium and Dust

Poster Session

Essex Ballroom

8:00 AM - 7:00 PM

In the past 15 years, there has been considerable effort to estimate the mass of H2 from dust FIR measurements in order to constrain the star formation law in low metallcity galaxies, where the low dust abundance and subsequent lack of shielding from ambient radiation makes photo-dissociated CO an ineffective tracer of molecular gas. This method relies on an estimate of the gas-to-dust ratio (GDR) from gas H I 21 cm, CO, and dust FIR observations either in diffuse regions where no H2 is expected to exist, or in the densest regions where CO is known to trace H2 and the value of the X factor can be derived simultaneously with the GDR. Thus, the GDR is assumed to be independent of local environment and density. In reality, dust destruction by shocks in the diffuse ISM, mantling in the dense ISM, and variations in the dust production rate with star formation activity can lead to significant (factor 2-3) variations in the GDR and bias this estimate of the H2 mass. In addition, the dust emissivity is assumed to be constant, although it actually depends on density because grain growth in dense molecular clouds increases the emissivity by a factor of a few. Here, we investigate systematic variations of the GDR, dust emissivity, and X factor with column density, radiation field, and star formation activity based on the correlation between gas mass derived from CO and H I 21 cm observations and FIR emission from the HERschel Inventory of The Agents of Galactic Evolution (HERITAGE) project in the Magellanic Clouds. We show that the dust-gas correlation cannot be explained by a single GDR, dust emissivity, or X factor, and we use a simple model of GDR and dust emissivity variations with column density of explain the observed trends.

129.02

Level Crossing Analysis of the I-GALFA H I 21-cm Line Maps of the Galaxy

Geumsook Park¹, B. Koo¹, S. J. Gibson², J. Kang³, K. A. Douglas³, J. E. G. Peek⁴, E. J. Korpela⁵, C. E. Heiles^5
1Seoul National University, Korea, Republic of, ²Western Kentucky University, ³Arecibo Observatory, Puerto Rico, ⁴Columbia University, ⁵University of California.

8:00 AM - 7:00 PM

Recent high-resolution observations reveal that the HI structure of the Galaxy is quite complex with numerous filaments and clumps. Statistical techniques are essential to describe and compare these complex morphologies, which can give insights on how the energy is injected and dissipated in the interstellar medium. We use the level-crossing statistics (LCS) to examine the HI structure in the I-GALFA HI survey data. The LCS is complimentary to the genus statistics. Like the Genus, the LCS can discriminate specific topologies such as clumpy or hole-like field, but in addition it can describe aligned or filamentary structures. The I-GALFA HI survey covers the first quadrant of the Galaxy including significant latitude range (about 12 degree up and down the plane) with high resolution (about 3.35 arcmin), so that it provides a great opportunity to observe the fine details of HI both in the inner and outer Galaxy. We select sample regions of spiral arms in the inner and outer Galaxy and derive their LCS properties. The LCS curves of most areas show positive tails and large skewnesses, which implies that the HI morphology is significantly clumpy. In the outer spiral arm, the LCS curves in longitude and latitude directions show considerable difference and indicate that the HI gases are aligned along the Galactic plane. This appears to be consistent with the low stellar activity in the outer Galaxy. We will also present the LCS properties with varying spatial scales.

129.03

Testing Extinction Distances to Massive Star-Forming Regions Against Maser Parallax Distances

Jonathan B. Foster¹, J. Stead², R. Benjamin³, J. Jackson^1
1Boston University, ²University of Leeds, United Kingdom, ³University of Wisconsin Madison.

8:00 AM - 7:00 PM

Accurate distances to massive star-forming regions are critical for converting observed values into physical quantities. Recent parallax measurements of masers within massive star-forming regions have established a reliable set of distances to a number of clouds in the first quadrant, ranging from 1 to 6 kpc. Unfortunately, maser parallax measurements are difficult to make and only possible in regions which exhibit bright masers. We report on a study using these distances to validate and calibrate two different near-infrared extinction distance methods which combine a galactic model with UKIDSS/GPS and 2MASS data. One method uses star counts of blue foreground stars, and the other uses red giant stars as standard candles. We also compare the parallax and extinction distances to kinematic distances using a variety of rotation curves. Support for this project provided by a grant from NASA.

129.04

Detection of Thermal 2 cm and 1 cm Formaldehyde Emission in NGC 7538

Liang Yuan¹, E. D. Araya¹, P. Hofner², S. Kurtz³, Y. Pihlstrom^4
1Western Illinois University, ²New Mexico Tech, ³CRyA, Universidad Autonoma de Mexico, Mexico, ⁴University of New Mexico.

8:00 AM - 7:00 PM

Formaldehyde is a tracer of high density gas in massive star forming regions. The K-doublet lines from the three lowest rotational energy levels of ortho-formaldehyde correspond to wavelengths of 6, 2 and 1 cm. Thermal emission of these transitions is rare, and maser emission has only been detected in the 6 cm line. NGC 7538 is an active site of massive star formation in the Galaxy, and one of only a few regions known to harbor 6 cm formaldehyde (H₂CO) masers. Using the NRAO 100 m Green Bank Telescope (GBT), we detected 2 cm H₂CO emission toward NGC 7538 IRS1. The velocity of the 2 cm H₂CO line is very similar to the velocity of one of the 6 cm H₂CO masers but the linewidth is greater. To investigate the nature of the 2 cm emission, we conducted observations of the 1 cm H₂CO transition, and obtained a cross-scan map of the 2 cm line. We detected 1 cm emission and found that the 2 cm emission is extended (greater than 30"), which implies brightness temperatures of ∼0.2 K. Assuming optically thin emission, LTE, and that the 1 cm and 2 cm lines originate from the same volume of gas, both these detections are consistent with thermal emission of gas at ∼30 K. We conclude that the 1 cm and 2 cm H₂CO lines detected with the GBT are thermal, which implies molecular densities above ∼10⁵ cm^-3. LY acknowledges support from WIU. PH acknowledges partial support from NSF grant AST-0908901.

129.05

8:00 AM - 7:00 PM

Massive stars are formed in warm, dense condensations in molecular clouds known as hot molecular cores (HMCs). Despite their importance, the role that HMCs play in the evolution of massive stars is currently not well understood due to a lack of observational data and hence physical properties. Molecular transitions in the HMCs are used to deduce the physical properties of these regions. In this study, observations of CH3CN in the J=12-11 transition in the 1mm band for 9 massive star forming regions were made using the Arizona Radio Observatory 10m Telescope on Mt. Graham, AZ (SMT). We report results of the derivation of column densities and temperatures of the observed sources using the population diagram technique, as well as a kinematic analysis based on our high resolution spectra. This research is supported by NSF grant AST-0908901.

129.06

Simulations of High Velocity Clouds: High-Velocity High-Stage Ions

Kyujin Kwak¹, D. B. Henley¹, R. L. Shelton^1
1Univ. of Georgia.

8:00 AM - 7:00 PM

We present the results of hydrodynamic simulations of high velocity clouds (HVCs) carried out using FLASH. The simulations self-consistently trace the non-equilibrium ionization evolution of carbon, nitrogen, and oxygen in a realistic HVC geometry, in which a cool dense spherical cloud moves through hot, tenuous halo gas. In our simulations, H I is ablated from the clouds through shear instabilities and undergoes turbulent mixing with the hot ambient gas. High-stage ions (C IV, N V, and O VI) are abundant in these turbulent mixing layers. We investigate a suite of models with a range of model parameters (cloud size, cloud velocity, cloud density). The simulations run for 60-240 Myr, depending on the model parameters. We find that the cloud's initial velocity does not affect the rates of H I ablation or ionization or high-stage ion production over a wide range of velocities, from subsonic through transonic to supersonic. However, we find that the cloud's initial size does affect the rate at which cloud material is ablated and/or ionized: a smaller cloud loses its H I mass relative to its initial mass more rapidly than a larger cloud. We also find that large HVCs are able to survive as far as the Galactic disk in the form of neutral hydrogen and thus fuel star formation. Our models compare well with Complex C observations in terms of the observed high-stage ion column densities, the trend between N(O VI)/N(H I) and N(H I), the ion-to-H I ratios, and the ion-to-ion ratios.

129.07

Simulations of High Velocity Clouds: X-ray Signatures

Robin L. Shelton¹, K. Kwak¹, D. Henley^1
1Univ. of Georgia.

8:00 AM - 7:00 PM

High velocity clouds (HVCs) have been observed in a variety of wavebands, from radio to ultraviolet. Even excess X-rays have been reported near some HVCs. Here, we examine possible production scenarios for the HVC-induced X-rays. Using detailed hydrodynamic and magnetohydrodynamic simulations of HVCs interacting with environmental gas, we examine two scenarios. In the first, the

129.08
Parker Instabilities with Magnetic Cross Field Diffusion of Cosmic Rays

8:00 AM - 7:00 PM

Parker instability arises from the presence of magnetic fields in a plasma in a gravitational field such as the interstellar medium (ISM), wherein the magnetic buoyant pressure expels the gas and causes the gas to move along the field lines. The subsequent gravitational collapse of the plasma gas is thought to be responsible for the formation of giant molecular clouds in the Galaxy. The process of mixing in the ISM near the Galactic plane is investigated. The initial ISM is assumed to consist of two fluids: plasma gas and cosmic-ray particles, in hydrostatic equilibrium, coupled with a uniform, azimuthally-aligned magnetic field. After a small perturbation, the unstable gas aggregates at the bottom of the magnetic loops and forms dense blobs. The growth rate of the instability decreases as the coupling between the cosmic rays and the plama becomes stronger (meaning a smaller cosmic-ray diffusion coefficient). The mixing is enhanced by the cosmic-ray diffusion, while the shape of the condensed gas depends sensitively on the initial equilibrium conditions. The perpendicular or cross field lines diffusion coefficient kappa_cross is often substantially smaller than the parallel coefficient kappa_0, only around 2%-4% of kappa_0. However, even with the minimum cross field diffusion, the mixing is significantly enhanced. The galactic wind flow perpendicular to the galactic disk may be greatly facilitated by Parker instabilities through the cross field diffusion of cosmic rays.

129.09

A Survey of N2H+ Toward the Serpens Molecular Cloud

Kevin Hardegree-Ullman¹, Y. L. Shirley^1
1University of Arizona.

8:00 AM - 7:00 PM

The Serpens Molecular Cloud, at a distance of ~230pc, is star forming region containing 35 dense protostellar and starless cores, as identified in the c2d 1.1mm continuum survey (Enoch et al. 2007, ApJ, 666, 982). These cores are in the process of forming low and intermediate-mass stars, so they provide a unique test bed to study gas phase evolution in molecular clouds. Using the Arizona 12-m radio telescope, we observed the J=1-0 rotational transition of N2H+ in order to calculate column densities in the cloud. We mapped N2H+ abundance in the vicinity of three major star forming filaments, previously identified in the 1.1mm survey, and found N2H+ in protostellar cores is enhanced by three times compared to that of starless cores. Comparison of N2H+ distribution with that of 12CO and 13CO found by Bieging et al. (in prep) will shed further light on gas phase evolution within Serpens. This research is supported by the Arizona NASA Space Grant Consortium.

129.10

Pairwise Correlations Of Eight Strong DIBs And N(H), N(H2), And E(B-V)

Scott David Friedman¹, D. G. York², B. J. McCall³, J. Dahlstrom⁴, P. Sonnentrucker¹, D. E. Welty³, M. M. Drosback⁵, L. M. Hobbs⁶, B. L. Rachford⁷, T. P. Snow^8
1STScI, ²University of Chicago, ³University of Illinois, ⁴Carthage College, ⁵University of Virginia, ⁶Yerkes Observatory, ⁷Embry-Riddle Aeronautical University, ⁸University of Colorado.

8:00 AM - 7:00 PM

129.11

8:00 AM - 7:00 PM

Chemical evolution of organic molecules essential to life begins in cold, pre-stellar molecular cloud cores. Given the relative lack of incident radiation, chemical reactions in these cores are dependent on interactions between their gas phase material and dust/ices. C18O and N2H+ in particular are two constituents in many pre-stellar cores that are detectable in their gas phase at radio wavelengths. Using data collected with the Swedish-ESO Submillimeter Telescope (SEST), we have observed the abundance and distribution of molecular gasses in a cold (10-13 K), starless core in the vicinity of Rossano cloud B (Corona Australis) which we have designated Object 42. We calculated and mapped C18O and N2H+ column densities and investigated the possibility of gas phase depletion in the core, which can occur as volatiles freeze out onto dust grains. This research is supported by Rensselaer Polytechnic Institute and the New York Center for Astrobiology which is a member of the NASA Astrobiology Institute.

129.12

New Interstellar Ammonia Maser Emission in NGC 7538: Expanded Very Large Array and Green Bank Telescope Observations

Stella Seojin Kim¹, I. M. Hoffman^1
1St. Paul's School.

8:00 AM - 7:00 PM

Using the Expanded Very Large Array and the Green Bank Telescope, we have observed the ammonia maser in NGC 7538 for the first time since its discovery in 1984. We present the first interferometric observations of the maser, demonstrating the nonthermal nature of the emission and providing a precise location for the maser in the star-forming complex. We also detect several new maser components that have appeared in the last 25 years. This maser is the nonmetastable (J,K) = (9,6) transition of ammonia at 18.5 GHz.

129.13

8:00 AM - 7:00 PM

Observations by the Hubble Space Telescope have revealed a wealth of super star clusters (SSCs) in lower extinction areas between dust lanes of starburst galaxies. These SSCs may be present-day analogues of young globular clusters, and are thought to form directly from giant molecular clouds. The mode of formation (efficient compression from shocks vs. slow compression within super giant molecular clouds), however, is still not well-understood. We report on high-spatial resolution CO(2-1) observations of the Antennae Galaxies with the Submillimeter Array (SMA) and the IRAM Plateau de Bure Interferometer (PdBI). We discuss the implications of our results on the various formation scenarios of SSCs in starburst galaxies.

129.14

Far-ultraviolet Observation Of The Aquila Rift With Fims Instrument

Sung-Joon Park¹, K. Min², K. Seon¹, W. Han¹, D. Lee¹, J. Edelstein^3
1Korea Astronomy and Space Science Institute, Korea, Republic of, ²Korea Advanced Institute of Science and Technology, Korea, Republic of, ³Space Sciences Lab., University of California, Berkeley.

8:00 AM - 7:00 PM

We present the first FUV observation of the Aquila Rift region near the Galactic plane by the FIMS instrument flown aboard the STSAT-1. Various wavelength datasets are used to compare with our FUV observation. While the core of the Aquila Rift suffers heavy dust extinction, the FUV continuum emission outside the Aquila Rift is found to be proportional to the certain amount of dust. The FUV Intensity clearly correlates with the dust extinction for E(B-V) < 0.3,, while anti-correlation is seen for E(B-V) > 0.3, which is in agreement with Hurwitz (1994) and Luhman & Jaffe (1996). Our entire field of view basically consists of inside and outside of Aquila Rift. The “Aquila-East,” “Aquila-Serpens,” and “Aquila-West,” are the inside sub-regions, and the “Scutum,” “Halo,” “Ophiuchus,” and “Hercules” are the outside. The CLOUD model and the calculation of H2 fluorescent line intensities are applied to investigate the physical conditions of each inside sub-region. Based on the velocity break (l ~ 33°) in CO emission and our result that the H2 fluorescent emission is poor in the “Aquila-East” region compared to the “Aquila-Serpens” and “Aquila-West” regions although the ``Aquila-East'' is similar to the other two inside sub-regions, we conclude the east region of Aquila is different in molecular condition or dust distribution, which may be related with the fact that the “Aquila-East” region is lack of star-forming regions. Furthermore, by calculating the line ratio of H2 fluorescent emissions, the characteristics of temperature and amount of dust can be expected for each sub-region.

129.15

8:00 AM - 7:00 PM

We present the first resolved magnetic field strength map for the quiescent molecular cloud GRSMC 45.60+0.30. GRSMC 45.60+0.30 subtends approximately 40 pc at a distance of 1.88 kpc. Polarization data were taken using the 1.8m Perkins telescope with the Mimir instrument. The data were processed using the custom IDL reduction pipeline for the GPIPS project, returning starlight polarization information in and around the cloud. Using the Chandrasekhar-Fermi method, the polarization angle dispersions were combined with the cloud radius, peak intensity, and velocity dispersion from the 13CO Galactic Ring Survey to create a resolved magnetic field map. An average magnetic field strength of approximately 4 microgauss was found across the cloud, with increases to around 13 microgauss in the 7 'magnetic cores.' This work was partially supported by NSF AST 09-07790.

129.16

PAHs in Translucent Interstellar Clouds

Farid Salama¹, G. Galazutdinov², J. Krelowski³, L. Biennier⁴, Y. Beletsky⁵, I. Song^6
1NASA Ames Research Center, Space Science & Astrobiology Division, ²Instituto de Astronomia, Universidad Catolica del Norte, Chile, ³Center for Astronomy, Nicolaus Copernicus University, Poland, ⁴Institut de Physique de Rennes, UMR 6251 du CNRS, France, ⁵European Southern Observatory, Chile, ⁶Korea Science Academy, Korea Advanced Institute of Science and Technology, Korea, Republic of.

8:00 AM - 7:00 PM

We discuss the proposal of relating the origin of some of the diffuse interstellar bands (DIBs) to neutral polycyclic aromatic hydrocarbons (PAHs) present in translucent interstellar clouds. The spectra of several cold, isolated gas-phase PAHs have been measured in the laboratory under experimental conditions that mimic the interstellar conditions and are compared with an extensive set of astronomical spectra of reddened, early type stars. This comparison provides - for the first time - accurate upper limits for the abundances of specific PAH molecules along specific lines-of-sight. Something that is not attainable from IR observations alone. The comparison of these unique laboratory data with high resolution, high S/N ratio astronomical observations leads to two major findings: (1) a finding specific to the individual molecules that were probed in this study and, which leads to the clear and unambiguous conclusion that the abundance of these specific neutral PAHs must be very low in the individual translucent interstellar clouds that were probed in this survey (PAH features remain below the level of detection) and, (2) a general finding that neutral PAHs exhibit intrinsic band profiles that are similar to the profile of the narrow DIBs indicating that the carriers of the narrow DIBs must have close molecular structure and characteristics. This study is the first quantitative survey of neutral PAHs in the optical range and it opens the way for unambiguous quantitative searches of PAHs in a variety of interstellar and circumstellar environments.

129.17

8:00 AM - 7:00 PM

The Rosette Nebula is an apparently spherical HII region which, though approximately 5000 light years distant, spans approximately 1.5 degrees of sky. Larger and much less luminous than the nearby Orion nebula, its faintness and angular size have made examination of the physical processes driving its shape, structure, and dynamics difficult. The spatial morphology of the nebula, which interacts with the associated Rosette Molecular Cloud complex, is obscured by the interstellar dust produced by previous generations of star formation. Our research seeks to construct a multispectral data set for the nebula and its environment, and through that to develop an observationally informed three dimensional model for the gas and dust densities, temperature, composition and motion. The distinctive ring of the Rosette is thought to be caused by radiation and winds from a central cluster of recently formed hot (OB) stars. The interaction of these stars with the nebula may be modeled based on physical first principles with CLOUDY and CLOUDY3D, thereby yielding a self-consistent understanding of the flow of energy from its stars and its appearance across the full spectrum from the ultraviolet to the radio. We are searching for evidence of prior episodes of star formation, and an understanding of the development of the heavy elements, molecules, and dust that are precursors to Earth-like planet formation. We have acquired narrow band images and long-slit spectra using wide-field instrumentation at Moore Observatory of the University of Louisville as the first phase of this project. Mosaics of the entire Rosette nebula with a 3.8 degree field of view and 4 arcsecond resolution have been produced in Hα, Hß, [OIII], and [SII]. Additionally, an initial characterization of the dust density of the region achieved through analysis of the Hα/Hß line ratio from these images is presented.

129.18

8:00 AM - 7:00 PM

We report the discovery of 6.035 GHz hydroxyl (OH) maser flares toward the massive young stellar object IRAS 18566+0408, which is the only region known to show periodic formaldehyde (4.8 GHz H₂CO) and methanol (6.7 GHz CH₃OH) maser flares. The observations were conducted between October 2008 and January 2010 with the 305m Arecibo Telescope in Puerto Rico. We detected two flare events, one in March 2009 and the other in September to November 2009. The 6.035 GHz OH flares are not simultaneous with the H₂CO flares; the peak of the OH flares appears to be delayed by 1 to 3 months with respect to the formaldehyde flares. On the other hand, the OH flares occurred simultaneously with CH₃OH flares from maser components that have approximately the same LSR velocity as the OH. The correlated variability of OH and CH₃OH masers in IRAS 18566+0408 supports a common excitation mechanism (IR pumping) as predicted by theory. EA acknowledges support from the WIU OSP. PH acknowledges partial support from NSF grant AST-0908901.

129.19

8:00 AM - 7:00 PM

We present the results of a ~ 250 arcmin² mapping of the 205 μm [NII] fine-structure emission over the northern Carina Nebula, including the Car I and Car II HII regions. Spectra were obtained using the South Pole Imaging Fabry-Perot Interferometer (SPIFI) at the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) at South Pole. We supplement the 205 μm data with new reductions of far-IR fine-structure spectra from the Infrared Space Observatory (ISO) in 63 μm [OI], 122 μm [NII], 146 μm [OI], and 158 μm [CII]. Morphological comparisons are made with optical, radio continuum and CO maps. The 122 [NII] / 205 [NII] line ratio is used to probe the density of the low-ionization gas, and the 158 [C II] / 205 [NII] line ratio is used to probe the fraction of C+ arising from photodissociation regions (PDRs). From the [OI] and [CII] data, we construct a PDR model of Carina following Kaufman et al. (1999). When the PDR properties are compared with other sources, Carina is found to be more akin to 30 Doradus than Galactic star-forming regions such as the Orion Bar, M17, or W49; this is consistent with the view of Carina as a more evolved region, where much of the parent molecular cloud has been ionized or swept away. These data constitute the first ever ground-based detection of the 205 μm [NII] line, and only the third detection overall since those of the COBE FIRAS and the KAO in the early 1990s.

129.20

8:00 AM - 7:00 PM

The I-GALFA survey mapping all the H I in the inner Galactic disk visible to the Arecibo 305m telescope within 10 degrees of the Galactic plane (longitudes of 32 to 77 degrees at b = 0) completed observations in 2009 September and will soon be made publicly available. The high (3.4 arcmin) resolution and tremendous sensitivity of the survey offer a great opportunity to observe the fine details of H I both in the inner and in the far outer Galaxy. The reduced HI column density maps show that the HI structure is highly filamentary and clumpy, pervaded by shell-like structures, vertical filaments, and small clumps. By inspecting individual maps, we have found 36 shell candidates of angular sizes ranging from 0.4 to 12 degrees, half of which appear to be expanding. In order to characterize the filamentary/clumpy morphology of the HI structure, we have carried out statistical analyses of selected areas representing the spiral arms in the inner and outer Galaxy. Genus statistics that can distinguish the ``meatball'' and ``swiss-cheese'' topologies show that the HI topology is clump-like in most regions. The two-dimensional Fourier analysis further shows the HI structures are filamentary and mainly parallel to the plane in the outer Galaxy. We also examine the level-crossing statistics, the results of which are described in detail in an accompanying poster by Park et al.

129.21

Automatic Searching Algorithm For Galactic HI At Forbidden Velocities In The Inner-Galaxy ALFA Low-Latitude HI (I-GALFA) Survey

Ji-hyun Kang¹, B. Koo², S. J. Gibson³, K. A. Douglas¹, G. Park², J. E. G. Peek⁴, E. J. Korpela⁵, C. E. Heiles^6
1NAIC/Arecibo Observatory, ²Seoul National University, Korea, Republic of, ³Western Kentucky University, ⁴Columbia University, ⁵University of Exeter, United Kingdom, ⁶University of California - Berkeley.

8:00 AM - 7:00 PM

The faint wing-like features at velocities beyond the velocity boundaries of the Galactic rotation (Forbidden-Velocity Wings, FVWs) in the large-scale position-velocity diagrams of the HI surveys are thought to be associated with dynamical Galactic events. The primary candidates of these FVWs are rapidly expanding HI shells of the old Galactic supernova remnants (SNRs), which are too faint to be visible in other frequencies. The unprecedented sensitivity and resolution of the I-GALFA survey enable detection of "all" HI shells of Galactic SNRs at forbidden velocities predicted by Koo and Kang (2004). Therefore, comparing the distribution of the FVWs visible in the I-GALFA survey and that of the model will improve our understanding on the interstellar medium and the evolution of SNRs. We have been developing an automatic searching algorithm for FVWs in the I-GALFA survey to minimize the selection effects of visual inspection used in the previous FVW study. We present the searching mechanism for FVWs and the statistical properties of the automatically searched FVWs. Also, we discuss the similarities and the differences between the distribution of the identified FVWs and that of the SNRs predicted by Koo and Kang (2004).

129.22

Through The Looking Glass: New Laboratory Spectra Of Glassy Silicates For The Comparison To Astrophysical Environments

Angela Speck¹, A. Whittington¹, A. Hofmeister^2
1Univ. of Missouri, ²Washington University.

8:00 AM - 7:00 PM

Many astrophysical environments exhibit a spectral feature at around 10 microns, which has long been attributed to amorphous silicates, but whose precise nature remains a mystery. Furthermore, the astronomically observed feature varies from location to location, and even within a given object both spatially and temporally. There have been many laboratory studies of potential cosmic dust analogs attempting to determine the exact nature of this dust, but most of those studies have failed to produce laboratory spectra that precisely match the observed astronomical spectra. We present new high-resolution spectra of a selection of silicate glasses whose compositions cover those expected to form in cosmic environments. These include synthetic endmember glasses of major mineral groups such as melilites (akermanite, gehlenite), pyroxenes (enstatite), olivines (forsterite) and silica; glasses produced by remelting natural mineral samples that contain iron and other elements; and a synthetic “cosmic” silicate glass with solar relative abundances of Mg, Si, Ca, Na and Al. Across the compositional range of 12 samples the 10 micron feature changes in peak position by more than a micron, as well as in shape. We discuss the effects of both compositional and structural factors on spectral features in these glassy silicates and we compare our new laboratory glass spectra with synthetic amorphous silicate spectra currently used in most models of dusty astrophysical environments. The synthetic spectra do not match either peak position or shape of any of our glass samples.

129.23

8:00 AM - 7:00 PM

Sulfur is abundant in the interstellar medium and its presence in grains could have important implications for extinction, yet little analysis has been done to measure the abundance of sulfur in grains. Previous abundance studies have suggested that sulfur does not contribute significantly to interstellar dust. However, studies of dust in meteorites indicate that sulfur is present in dust. We analyzed the strong S\sc{ii} 1250, 1253, 1259 \AA\ features in high-resolution STIS data to expand the sample of interstellar sulfur determinations. We present the interstellar abundance measurements of 28 sight lines for singly ionized sulfur atoms, the dominant form of sulfur in the interstellar medium. Our preliminary results indicate that sulfur is depleted into grains but does not follow the pattern of other elements in dust.

129.24

Ultraviolet Photometry of Dust Extinction in M101: Expected Results from the IMAGER Sounding Rocket

Meredith E. Danowski¹, T. A. Cook¹, K. D. Gordon², S. Chakrabarti^1
1Boston University, ²Space Telescope Science Institute.

8:00 AM - 7:00 PM

Scheduled for launch in summer 2011, the Interstellar Medium Absorption Gradient Experiment Rocket (IMAGER) will probe the correlation between ultraviolet dust extinction, and the metallicity and radiation environment in M101. IMAGER simultaneously images M101 in four 400Å-wide bandpasses, targeting UV extinction features. We present technical results from telescope and instrument calibration and integration, as well as expected science results from the unique IMAGER design.

129.25

8:00 AM - 7:00 PM

Interstellar dust (ISD) has been directly observed flowing into the Solar System. This dust has an unusual size distribution relative to typical ISD with small grains (a < 0.1 micron) deficient and large grains (about 1 micron) abundant. Such large grains are not expected to be present in warm, low density gas such as the Local Interstellar Cloud (LIC) that surrounds the Solar System. It is unclear whether the missing small grains have been excluded from the inner heliosphere by the solar wind magnetic field, or whether they are absent entirely from the LIC. If the grains are present in the LIC their density should be enhanced in the heliosheath and they should be heated by the Sun's UV radiation field. The emission from such grains may be observable and would provide a means of observing the grains that is lacking otherwise. We present the results of new models for the emission of the grains based on calculations of the trajectories of ISD grains incident on the heliosphere and resulting space densities as a function of grain size.