Arcsecond Resolution Research Articles

Monte Carlo simulation of stellar intensity interferometry

Stellar intensity interferometers will achieve stellar imaging with a tenth of a milli- arcsecond resolution in the optical band by taking advantage of the large light collect- ing area and broad range of inter-telescope distances offered by future gamma-ray Air Cherenkov Telescope (ACT) arrays. Up to now, studies characterizing the capabilities of intensity interferometers using ACTs have not accounted for realistic effects such as telescope mirror extension, detailed photodetector time response, excess noise, and night sky contamination. In this paper, we present the semi-classical quantum optics Monte-Carlo simulation we developed in order to investigate these experimental limi- tations. In order to validate the simulation algorithm, we compare our first results to models for sensitivity and signal degradation resulting from mirror extension, pulse shape, detector excess noise, and night sky contamination.

Size magnification as a complement to cosmic shear

We investigate the extent to which cosmic size magnification may be used to com- plement cosmic shear in weak gravitational lensing surveys, with a view to obtaining high-precision estimates of cosmological parameters. Using simulated galaxy images, we find that size estimation can be an excellent complement, finding that unbiased estimation of the convergence field is possible with galaxies with angular sizes larger than the point-spread function (PSF) and signal-to-noise ratio in excess of 10. The statistical power is similar to, but not quite as good as, cosmic shear, and it is subject to different systematic effects. Application to ground-based data will be challeng- ing, with relatively large empirical corrections required to account for with biases for galaxies which are smaller than the PSF, but for space-based data with 0.1 arcsecond resolution, the size distribution of galaxies brighter than i=24 is ideal for accurate estimation of cosmic size magnification.

NEARSHORE WAVE PREDICTIONS ALONG THE OREGON AND SOUTHWEST WASHINGTON COAST

A nearshore wave forecasting system was implemented to elevate the ocean information resources in the US Pacific Northwest region. This implementation brings the US State of Oregon and the Southwest region of the state of Washington to the same level of prediction as the neighboring state of California and other regions of the country. It was achieved using the Wavewatch III numerical wave model, which was validated in intermediate to shallow waters. The forecasting system provides data at a 30 arc-second resolution from the shelf break up to a depth of 20 meters. The data is distributed to the public at no cost as part of a greater initiative put together by the Networked Association of Ocean Observing Systems. Information generated by this implementation is presently being used to provide boundary conditions to localized applications in the region as well as to beach users.

H II REGIONS, EMBEDDED PROTOSTARS, AND STARLESS CORES IN SHARPLESS 2-157

We present arcsecond resolution 1.4mm observations of the high mass star forming region, Sharpless 2-157, that reveal the cool dust associated with the first stages of star formation. These data are compared with archival images at optical, infrared, and radio wavelengths, and complemented with new arcsecond resolution mid-infrared data. We identify a dusty young HII region, numerous infrared sources within the cluster envelope, and four starless condensations. Three of the cores lie in a line to the south of the cluster peak, but the most massive one is right at the center and associated with a jumble of bright radio and infrared sources. This presents an interesting juxtaposition of high and low mass star formation within the same cluster which we compare with similar observations of other high mass star forming regions and discuss in the context of cluster formation theory.

Infrared surface photometry of dwarf galaxies in Fornax

Despite its utility in exploring possible spatial variations in the stellar populations in galaxies, infrared surface photometry of low-luminosity dwarf elliptical (dE) galaxies is generally lacking, due to the technical difficulties in observing low surface brightness objects against the bright infrared sky. Here we attempt to remedy this shortfall to some extent by presenting K-band photometry at arcsecond resolution, including radial profiles, 1D and 2D model fits and the quantification of nuclear components, for a small sample of dE galaxies, with absolute magnitudes MB?-15 to -13, in the Fornax Cluster. In the second part of the paper, we explore the comparison of these data with corresponding optical observations and attempt to interpret this in terms of stellar population models and their radial trends. A significant range of global opticalinfrared colours is present in our sample, but radial colour gradients in the galaxies are usually small. However, while the nuclear regions tend to be bluer in optical colours, they are systematically redder than the surrounding galaxy in (R-K). The stellar population modelling suggests that these colour differences are probably an effect of both higher metallicity and younger age in the nuclei. Excluding the nuclear regions, the global colour profiles typically change in the same direction, again indicating older, more metal-poor stellar populations in the outskirts of the galaxies.

Large-scale groundwater modeling using global datasets: a test case for the Rhine-Meuse basin

Abstract. The current generation of large-scale hydrological models does not include a groundwater flow component. Large-scale groundwater models, involving aquifers and basins of multiple countries, are still rare mainly due to a lack of hydro-geological data which are usually only available in developed countries. In this study, we propose a novel approach to construct large-scale groundwater models by using global datasets that are readily available. As the test-bed, we use the combined Rhine-Meuse basin that contains groundwater head data used to verify the model output. We start by building a distributed land surface model (30 arc-second resolution) to estimate groundwater recharge and river discharge. Subsequently, a MODFLOW transient groundwater model is built and forced by the recharge and surface water levels calculated by the land surface model. Results are promising despite the fact that we still use an offline procedure to couple the land surface and MODFLOW groundwater models (i.e. the simulations of both models are separately performed). The simulated river discharges compare well to the observations. Moreover, based on our sensitivity analysis, in which we run several groundwater model scenarios with various hydro-geological parameter settings, we observe that the model can reasonably well reproduce the observed groundwater head time series. However, we note that there are still some limitations in the current approach, specifically because the offline-coupling technique simplifies the dynamic feedbacks between surface water levels and groundwater heads, and between soil moisture states and groundwater heads. Also the current sensitivity analysis ignores the uncertainty of the land surface model output. Despite these limitations, we argue that the results of the current model show a promise for large-scale groundwater modeling practices, including for data-poor environments and at the global scale.

Direct Imaging of Bridged Twin Protoplanetary Disks in a Young Multiple Star

AbstractProtoplanetary disks are ubiquitously observed around young solar-mass stars and are considered to be not only natural by-products of stellar evolution but also precursors of planet formation. If a forming star has close companions, the protoplanetary disk may be seriously influenced. It is important to consider this effect because most stars form as multiples. Thus, studies of protoplanetary disks in multiple systems are essential to describe the general processes of star and planet formation.We present the direct image of an interacting binary protoplanetary system. We obtained an infrared image of a young multiple circumstellar disk system, SR24, with the Subaru 8.2-m Telescope. Both circumprimary and circumsecondary disks are clearly resolved with a 0.1 arcsecond resolution. The binary system exhibits a bridge of infrared emission connecting the two disks and a long spiral arm extending from the circumprimary disk. A spiral arm would suggest that the SR24 system rotates counter-clockwise. The orbital period of the binary is 15,000 yr. Numerical simulations reveal that the bridge corresponds to gas flow and a shock wave caused by the collision of gas rotating around the primary and secondary stars. The simulations also show that fresh material streams along the spiral arm, confirming the theoretical proposal that gas is replenished from a circum-multiple reservoir. These results reveal the mechanism of interacting protoplanetary disks in young multiple systems. Furthermore, our observations provide the first direct image that enables a comparison with theoretical models of mass accretion in binary systems. The observations of this binary system provide a great opportunity to test and refine theoretical models of star and planet formation in binary systems.

STAR-FORMING CLOUD COMPLEXES IN THE CENTRAL MOLECULAR ZONE OF NGC 253

We report 350 and 230 GHz observations of molecular gas and dust in the starburst nucleus of NGC 253 at 20-40 pc (1"-2") resolution. The data contain CO(3-2), HCN(4-3), CO(2-1), 13CO(2-1), C18O(2-1), and continuum at 0.87 mm and 1.3 mm toward the central kiloparsec. The CO(2-1) size of the galaxy's central molecular zone (CMZ) is measured to be about 300 pc x 100 pc at the half maximum of intensity. Five clumps of dense and warm gas stand out in the CMZ at arcsecond resolution, and they are associated with compact radio sources due to recent massive star formation. They contribute one third of the CO emission in the central 300 pc and have 12CO peak brightness temperatures around 50 K, molecular gas column densities on the order of 10^{4} Msun pc^{-2}, gas masses on the order of 10^{7} Msun in the size scale of 20 pc, volume-averaged gas densities of n(H2) ~ 4000 cm^{-3}, and high HCN-to-CO ratios suggestive of higher fractions of dense gas than in the surrounding environment. It is suggested that these are natal molecular cloud complexes of massive star formation. The CMZ of NGC 253 is also compared with that of our Galaxy in CO(2-1) at the same 20 pc resolution. Their overall gas distributions are strikingly similar. The five molecular cloud complexes appear to be akin to such molecular complexes as Sgr A, Sgr B2, Sgr C, and the l=1.3deg cloud in the Galactic center. On the other hand, the starburst CMZ in NGC 253 has higher temperatures and higher surface (and presumably volume) densities than its non-starburst cousin.

High-angular resolution observations of methanol in the infrared dark cloud core G11.11-0.12P1

Recent studies suggest that infrared dark clouds (IRDCs) have the potential of harboring the earliest stages of massive star formation and indeed evidence for this is found toward distinct regions within them. We present a study with the Plateau de Bure Interferometer of a core in the archetypal filamentary IRDC G11.11-0.12 at few arcsecond resolution to determine its physical and chemical structure. The data consist of continuum and line observations covering the C34S 2-1 line and the methanol 2_k-1_k v_t=0 lines at 3mm and the methanol 5_k-4_k v_t =0 lines at 1mm. Our observations show extended emission in the continuum at 1 and 3 mm. The methanol 2_k-1_k v_t=0 emission presents three maxima extending over 1 pc scale (when merged with single-dish short-spacing observations); one of the maxima is spatially coincident with the continuum emission. The fitting results show enhanced methanol fractional abundance (~3x10^-8) at the central peak with respect to the other two peaks, where it decreases by about an order of magnitude (~4-6x10^-9). Evidence of extended 4.5 microns emission, "wings" in the CH3OH 2_k-1_k spectra, and CH3OH abundance enhancement point to the presence of an outflow in the East-West direction. In addition, we find a gradient of ~4 km/s in the same direction, which we interpret as being produced by an outflow(s)-cloud interaction.

Catalogue of known Galactic SNRs uncovered in Hα light

During detailed searches for new Galactic supernova remnants (SNRs) in the Anglo Australian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) HAlpha survey of the southern Galactic plane, we also uncovered, for the first time, possible associated HAlpha emission in the vicinity of about 24 known Galactic SNRs previously known solely from radio or X-ray observations.The possible optical counterparts to these known SNR were detected due to the 1 arcsecond resolution and 5 Rayleigh sensitivity of this HAlpha survey. The newly discovered emission frequently exhibits the typical filamentary form of other optically detected SNRs although sometimes the HAlpha emission clouds or fragmented filaments largely inside an SNR extend over the radio border. It is true that superposition of general diffuse and extended Galactic emission in the region of these remnants is a complicating factor, but for many optical candidates the HAlpha emission provides an excellent morphological and positional match to the observed radio emission so that an association seems clear. We have already published HAlpha images and confirmatory spectral observations for several of the best optical counterparts to known SNRs but for completeness and convenience we include them in our complete catalogue of previously known radio detected SNRs for which we have now uncovered HAlpha optical emission. For better visualisation of the optical emissions from these faint supernova remnants and to enhance some low surface-brightness features we also present quotient images of the HAlpha data divided by the accompanying broad-band short red (SR) data. Out of 274 Galactic SNRs currently catalogued and detected in the radio only ~20 had previous optical counterparts. We may have now increased this by a further third by adding a further 24 candidate optical counterparts.

AN OVERALL PICTURE OF THE GAS FLOW IN A MASSIVE CLUSTER-FORMING REGION: THE CASE OF G10.6–0.4

The massive clump G10.6-0.4 is an OB cluster forming region, in which multiple UC HII regions have been identified. In the present study, we report arcsecond resolution observations of the CS (1-0) transition, the NH$_{3}$ (3,3) main hyperfine inversion transition, the CH$_{3}$OH J=5 transitions, and the centimeter free-free continuum emissions in this region. The comparisons of the molecular line emissions with the free--free continuum emissions reveal a 0.5 pc scale massive molecular envelope which is being partially dispersed by the dynamically-expanding bipolar ionized cavity. The massive envelope is rotationally flattened and has an enhanced molecular density in the mid-plane. In the center of this massive clump lies a compact ($<$0.1 pc) hot ($\gtrsim$100 K) toroid, in which a cluster of O--type stars has formed. This overall geometry is analogous to the standard core collapse picture in the low-mass star forming region, with a central (proto-)stellar object, a disk, an envelope, and a bipolar outflow and outflow cavity. However, G10.6-0.4 has a much larger physical size scale ($\le$0.1 pc for typical low--mass star forming core). Based on the observations, we propose a schematic picture of the OB cluster forming region, which incorporates the various physical mechanisms. This model will be tested with the observations of other embedded OB clusters, and with numerical simulations.

Estimating the Information and Technology Development Index (IDI) Using Nighttime Satellite Imagery

The International Telecommunication Union (ITU) has developed a tool known as the Information and Communication Technology Development Index (IDI) for measuring the development of countries as information societies. They found a close correlation between IDI and the Gross Domestic Product (GDP) per capita of countries. In this paper on the basis of this relationship we have tried to create a 30 arc-second grid of IDI. At first a disaggregated map of total economic activity was created from the Defense Meteorological Satellite Program Operational Linescan System (DMSP-OLS) merged radiance-calibrated nighttime image of 2006 and the LandScan population grid of 2006. The GDP per capita was then calculated and an attempt was made to create the IDI grid. However, at the 30 arc-second resolution the GDP per capita was found to be less in the city centers than in the areas surrounding the city centers. Thus an estimated IDI grid at 30 arc-second resolution could not be created based on the relationship between GDP per capita and official IDI. Therefore, the finest resolution at which the estimated IDI map was created was at the state level for the South-East Asian countries. In a future endeavor, we intend to create an IDI grid of much finer resolution.

THE HIGH-VELOCITY MOLECULAR OUTFLOWS IN MASSIVE CLUSTER-FORMING REGION G10.6–0.4

We report the arcsecond resolution SMA observations of the $^{12}$CO (2-1) transition in the massive cluster forming region G10.6-0.4. In these observations, the high velocity $^{12}$CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic, and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH$_{3}$OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, $\sim10^{5}$ years) is about a few percent. The total energy feedback of these high velocity outflows is higher than 10$^{47}$ erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photo-ionization.

A CATALOG OF CH 3 OH 7 0 -6 1 A + MASER SOURCES IN MASSIVE STAR-FORMING REGIONS. II. MASERS IN NGC 6334F, G8.67–0.36, AND M17

We present Very Large Array observations of the 7_0-6_1 A^+ methanol maser transition at 44 GHz towards NGC 6334F, G8.67-0.36, and M17. These arcsecond resolution observations complete a previous, larger VLA survey of this maser transition in high-mass star-forming regions reported by Kurtz et al. We confirm the presence of 44 GHz methanol maser emission in all three sources, detecting eight distinct maser components in NGC 6334F, twelve components in G8.67-0.36 and one in M17.

THE GENESIS OF AN IMPULSIVE CORONAL MASS EJECTION OBSERVED AT ULTRA-HIGH CADENCE BY AIA ON SDO

The study of fast, eruptive events in the low solar corona is one of the science objectives of the Atmospheric Imaging Assembly (AIA) imagers on the recently launched Solar Dynamics Observatory (SDO), which take full disk images in ten wavelengths with arcsecond resolution and 12 sec cadence. We study with AIA the formation of an impulsive coronal mass ejection (CME) which occurred on June 13, 2010 and was associated with an M1.0 class flare. Specifically, we analyze the formation of the CME EUV bubble and its initial dynamics and thermal evolution in the low corona using AIA images in three wavelengths (171, 193 and 211 A). We derive the first ultra-high cadence measurements of the temporal evolution of the CME bubble aspect ratio (=bubble-height/bubble-radius). Our main result is that the CME formation undergoes three phases: it starts with a slow self-similar expansion followed by a fast but short-lived (~ 70 sec) period of strong lateral over-expansion which essentially creates the CME. Then the CME undergoes another phase of self-similar expansion until it exits the AIA field of view. During the studied interval, the CME height-time profile shows a strong, short-lived, acceleration followed by deceleration. The lateral overexpansion phase coincides with the deceleration phase. The impulsive flare heating and CME acceleration are closely coupled. However, the lateral overexpansion of the CME occurs during the declining phase and is therefore not linked to flare reconnection. In addition, the multi-thermal analysis of the bubble does not show significant evidence of temperature change.

ERUPTIONS FROM SOLAR EPHEMERAL REGIONS AS AN EXTENSION OF THE SIZE DISTRIBUTION OF CORONAL MASS EJECTIONS

Observations of the quiet solar corona in the 171A (~1MK) passband of the Transition Region and Coronal Explorer (TRACE) often show disruptions of the coronal part of small-scale ephemeral bipolar regions that resemble the phenomena associated with coronal mass ejections on much larger scales: ephemeral regions exhibit flare-like brightenings, rapidly rising filaments carrying absorbing material at chromospheric temperatures, or the temporary dimming of the surrounding corona. I analyze all available TRACE observing sequences between 1998/04/01 and 2009/09/30 with full-resolution 171A image sequences spanning a day or more within 500 arcsec of disk center, observing essentially quiet Sun with good exposures and relatively low background. Ten such data sets are identified between 2000 and 2008, spanning 570h of observing with a total of 17133 exposures. Eighty small-scale coronal eruptions are identified. Their size distribution forms a smooth extension of the distribution of angular widths of coronal mass ejections, suggesting that the eruption frequency for bipolar magnetic regions is essentially scale free over at least two orders of magnitude, from eruptions near the arcsecond resolution limit of TRACE to the largest coronal mass ejections observed in the inner heliosphere. This scale range may be associated with the properties of the nested set of ranges of connectivity in the magnetic field, in which increasingly large and energetic events can reach higher and higher into the corona until the heliosphere is reached.

Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS

A new 30-arc second resolution global topography/bathymetry grid (SRTM30_PLUS) has been developed from a wide variety of data sources. Land and ice topography comes from the SRTM30 and ICESat topography, respectively. Ocean bathymetry is based on a new satellite-gravity model where the gravity-to-topography ratio is calibrated using 298 million edited soundings. The main contribution of this study is the compilation and editing of the raw soundings, which come from NOAA, individual scientists, SIO, NGA, JAMSTEC, IFREMER, GEBCO, and NAVOCEANO. The gridded bathymetry is available for ftp download in the same format as the 33 tiles of SRTM30 topography. There are 33 matching tiles of source identification number to convey the provenance of every grid cell. The raw sounding data, converted to a simple common format, are also available for ftp download.

CORNISH: A 5 GHz VLA survey of the Galactic plane

AbstractThe CORNISH (Co-Ordinated Radio ‘N’ Infrared Survey for High-mass star formation) project is the radio continuum part of a series of multi-wavelength surveys of the Galactic Plane that focus on the northern GLIMPSE-I region (10° &lt; l &lt;65°, |b| &lt; 1°) observed by the SPITZER satellite in the mid-infrared (Churchwell et al. 2009). CORNISH has delivered a complementary 5 GHz arcsecond resolution, radio-continuum survey to address key questions in high-mass star formation as well as many other areas of astrophysics.

Limb Spicules from the Ground and from Space

We amassed statistics for quiet-sun chromosphere spicules at the limb using ground-based observations from the Swedish 1-m Solar Telescope on La Palma and simultaneously from NASA’s Transition Region and Coronal Explorer (TRACE) spacecraft. The observations were obtained in July 2006. With the 0.2 arcsecond resolution obtained after maximizing the ground-based resolution with the Multi-Object Multi-Frame Blind Deconvolution (MOMFBD) program, we obtained specific statistics for sizes and motions of over two dozen individual spicules, based on movies compiled at 50-second cadence for the series of five wavelengths observed in a very narrow band at Hα, on-band and at ± 0.035 nm and ± 0.070 nm (10 s at each wavelength) using the SOUP filter, and had simultaneous observations in the 160 nm EUV continuum from TRACE. The MOMFBD restoration also automatically aligned the images, facilitating the making of Dopplergrams at each off-band pair. We studied 40 Hα spicules, and 14 EUV spicules that overlapped Hα spicules; we found that their dynamical and morphological properties fit into the framework of several previous studies. From a preliminary comparison with spicule theories, our observations are consistent with a reconnection mechanism for spicule generation, and with UV spicules being a sheath region surrounding the Hα spicules.

ROTATION OF THE WARM MOLECULAR GAS SURROUNDING ULTRACOMPACT H II REGIONS

We present molecular line and 1.4 mm continuum observations towards five massive star forming regions at arcsecond resolution using the Submillimeter Array (SMA). We find that the warm molecular gas surrounding each HII region (as traced by SO_2 and OCS) appears to be undergoing bulk rotation. From the molecular line emission and thermal component of the continuum emission, we independently derived gas masses for each region which are consistent with each other. From the free-free component of the continuum emission we estimate the minimum stellar mass required to power the HII region and find that this mass, when added to the derived gas mass, is a significant fraction of the dynamical mass for that region.