The field of computer vision has greatly matured in the past decade, and many of the methods and techniques can be useful for astronomical applications. One example is in searching large imaging ...surveys for objects of interest, especially when it is difficult to specify the characteristics of the objects being searched for. We have developed a method using contour finding and convolution neural networks (CNNs) to search for Infrared Dark Clouds (IRDCs) in the Spitzer Galactic plane survey data. IRDCs can vary in size, shape, orientation, and optical depth, and are often located near regions with complex emission from molecular clouds and star formation, which can make the IRDCs difficult to reliably identify. False positives can occur in regions where emission is absent, rather than from a foreground IRDC. The contour finding algorithm we implemented found most closed figures in the mosaic and we developed rules to filter out some of the false positive before allowing the CNNs to analyze them. The method was applied to the Spitzer data in the Galactic plane surveys, and we have constructed a catalog of IRDCs which includes additional parts of the Galactic plane that were not included in earlier surveys.
We have conducted an N-band survey of 14 young stars in the approx30 Myr old Tucana-Horologium association to search for evidence of warm, circumstellar dust disks. Using the MIRAC-BLINC camera on ...the Magellan I (Baade) 6.5 m telescope, we find that none of the stars have a statistically significant N-band excess compared to the predicted stellar photospheric flux. Using three different sets of assumptions, this null result rules out the existence of the following around these post-T Tauri stars: (1) optically thick disks with inner hole radii of ~0.1 AU, (2) optically thin disks with masses of less than 10 super(-6) M sub(o+) (in approx1 mu m sized grains) within ~10 AU of these stars, and (3) scaled-up analogs of the solar system zodiacal dust cloud with more than 4000 times the emitting area. Our survey was sensitive to dust disks in the terrestrial planet zone with fractional luminosity of log(L sub(dust)/L sub(*)) approx 10 super(-2.9), yet none were found. Combined with results from previous surveys, these data suggest that circumstellar dust disks become so optically thin as to be undetectable at N band before age approx20 Myr. We also present N-band photometry for several members of other young associations and a subsample of targets that will be observed with the Spitzer Space Telescope by the Formation and Evolution of Planetary Systems Legacy Science Program. Finally, we present an absolute calibration of MIRAC-BLINC for four filters (L, N, 11.6, and Q sub(s)) on the Cohen-Walker-Witteborn system.
We present Spitzer IRAC, NOAO 2.1 m Flamingos, Keck NIRC, and FCRAO SEQUOIA observations of the massive star-forming complex S254-S258, covering an area of image. Using a combination of the IRAC and ...NIR data, we identify and classify the young stellar objects (YSOs) in the complex. We detect 510 sources with near- or mid-IR excess, and we classify 87 Class I and 165 Class II sources. The YSOs are found in clusters surrounded by isolated YSOs in a low-density distributed population. The ratio of clustered to total YSOs is 0.8. We identify six new clusters in the complex. One of them, G192.63-00, is located around the ionizing star of the H ii region S255. We hypothesize that the ionizing star of S255 was formed in this cluster. We also detect a southern component of the cluster in H ii region S256. The cluster G192.54- 0.15, located inside H ii region S254 has a image of 17 km s super(-1) with respect to the main cloud, and we conclude that it is located in the background of the complex. The structure of the molecular cloud is examined using image and image, as well as a near-IR extinction map. The main body of the molecular cloud has image between 5 and 9 km s super(-1). The arc-shaped structure of the molecular cloud following the border of the H ii regions and the high column density in the border of the H ii regions support the idea that the material has been swept up by the expansion of the H ii regions.
We present infrared observations of the ultracompact H II region W3(OH) made by the FORCAST instrument aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) and by the Spitzer/Infrared ...Array Camera. We contribute new wavelength data to the spectral energy distribution (SED), which constrains the optical depth, grain size distribution, and temperature gradient of the dusty shell surrounding the H II region. We model the dust component as a spherical shell containing an inner cavity with radius ~600 AU, irradiated by a central star of type 09 and temperature ~31,000 K. The total luminosity of this system is 7.1 x 10 super(4) L sub(middot in circle). An observed excess of 2.2-4.5 mum emission in the SED can be explained by our viewing a cavity opening or dumpiness in the shell structure whereby radiation from the warm interior of the shell can escape. We claim to detect the nearby water maser source W3 (H sub(2)O) at 31.4 and 37.1 mum using beam deconvolution of the FORCAST images.
Observations of oscillations of temperature and wind in planetary atmospheres provide a means of generalizing models for atmospheric dynamics in a diverse set of planets in the Solar System and ...elsewhere. An equatorial oscillation similar to one in the Earth's atmosphere has been discovered in Jupiter. Here we report the existence of similar oscillations in Saturn's atmosphere, from an analysis of over two decades of spatially resolved observations of its 7.8- m methane and 12.2- m ethane stratospheric emissions, where we compare zonal-mean stratospheric brightness temperatures at planetographic latitudes of 3.6° and 15.5° in both the northern and the southern hemispheres. These results support the interpretation of vertical and meridional variability of temperatures in Saturn's stratosphere as a manifestation of a wave phenomenon similar to that on the Earth and in Jupiter. The period of this oscillation is 14.8 ± 1.2 terrestrial years, roughly half of Saturn's year, suggesting the influence of seasonal forcing, as is the case with the Earth's semi-annual oscillation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We determined the flux ratios of the heavy and eccentric planet XO-3b to its parent star in the four Infrared Array Camera bands of the Spitzer Space Telescope: 0.101% +- 0.004% at 3.6 {mu}m; 0.143% ...+- 0.006% at 4.5 {mu}m; 0.134% +- 0.049% at 5.8 {mu}m; and 0.150% +- 0.036% at 8.0 {mu}m. The flux ratios are within -2.2, 0.3, -0.8, and -1.7sigma of the model of XO-3b with a thermally inverted stratosphere in the 3.6 {mu}m, 4.5 {mu}m, 5.8 {mu}m, and 8.0 {mu}m channels, respectively. XO-3b has a high illumination from its parent star (F{sub p} {approx} (1.9-4.2) x 10{sup 9} erg cm{sup -2} s{sup -1}) and is thus expected to have a thermal inversion, which we indeed observe. When combined with existing data for other planets, the correlation between the presence of an atmospheric temperature inversion and the substellar flux is insufficient to explain why some high insolation planets like TrES-3 do not have stratospheric inversions and some low insolation planets like XO-1b do have inversions. Secondary factors such as sulfur chemistry, atmospheric metallicity, amounts of macroscopic mixing in the stratosphere, or even dynamical weather effects likely play a role. Using the secondary eclipse timing centroids, we determined the orbital eccentricity of XO-3b as e = 0.277 +- 0.009. The model radius-age trajectories for XO-3b imply that at least some amount of tidal heating is required to inflate the radius of XO-3b, and the tidal heating parameter of the planet is constrained to Q{sub p} {approx}< 10{sup 6}.
The dominant non-instrumental background source for space-based infrared observatories is the zodiacal light (ZL). We present Spitzer Infrared Array Camera (IRAC) measurements of the ZL at 3.6, 4.5, ...5.8, and 8.0 mu m, taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately weekly IRAC observations near the north ecliptic pole over a period of roughly 8.5 years. This long time baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk with respect to the ecliptic, which is the true signal of the ZL. This is compared to both Cosmic Background Explorer Diffuse Infrared Background Experiment data and a ZL model based thereon. Our data show a few-percent discrepancy from the Kelsall et al. model including a potential warping of the interplanetary dust disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate knowledge of the ZL is important for both extragalactic and Galactic astronomy including measurements of the cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary dust models. IRAC data can be used to further inform and test future ZL models.
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