1,262 research outputs found
Spatial study with the VLT of a new resolved edge-on circumstellar dust disk discovered at the periphery of the rho Ophiuchi dark cloud
We report the discovery in NIR with SofI at the NTT of a resolved
circumstellar dust disk around a 2MASS source at the periphery of the rho
Ophiuchi dark cloud. We present follow-up observations in J, H, and Ks-band
obtained with ISAAC at the VLT, under 0.4"-seeing conditions, which unveil a
dark dust lane oriented East-West between two characteristic northern and
southern reflection nebulae. This new circumstellar dust disk has a radius of
2.15" (300 AU at 140 pc), and a width of 1.2" (170 AU at 140 pc). Thanks to its
location at the periphery of the dense cores, it suffers small foreground
visual extinction (Av=2.1\pm2.6 mag). Although this disk is seen close to
edge-on, the two reflection nebulae display very different colors. We introduce
a new NIR data visualization called ``Pixel NIR Color Mapping'', which allows
to visualize directly the NIR colors of the nebula pixels. Thanks to this
method we identify a ridge, 0.3" (40 AU at 140 pc) to the north of the dark
lane and parallel to it, which displays a NIR color excess. This ridge
corresponds to an unusual increase of brightness from J to Ks, which is also
visible in the NTT observation obtained 130 days before the VLT one. We also
find that the northern nebula shows ~3 mag more extinction than the southern
nebula. We compute axisymmetric disk models to reproduce the VLT scattered
light images and the spectral energy distribution from optical to NIR. Our best
model, with a disk inclination i=86\pm1 deg, correctly reproduces the extension
of the southern reflection nebula, but it is not able to reproduce either the
observed NIR color excess in the northern nebula or the extinction difference
between the two reflection nebulae. We discuss the possible origin of the
peculiar asymmetrical NIR color properties of this object.Comment: 11 pages, 8 figures, 2 tables. Accepted for publication in ApJ (vol.
586, March 20, 2003). Table 2 appears now correctly in the postscript versio
New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS
We carried out a survey of infrared star clusters and stellar groups on the
2MASS J, H and K_s all-sky release Atlas in the Northern and Equatorial Milky
Way (350 < l < 360, 0 < l < 230). The search in this zone complements that in
the Southern Milky Way (Dutra et al. 2003a). The method concentrates efforts on
the directions of known optical and radio nebulae. The present study provides
167 new infrared clusters, stellar groups and candidates. Combining the two
studies for the whole Milky Way, 346 infrared clusters, stellar groups and
candidates were discovered, whereas 315 objects were previously known. They
constitute an important new sample for future detailed studies.Comment: Accepted to Astronomy and Astrophysic
The NGC 7129 Young Stellar Cluster: A Combined Spitzer, MMT, and 2MASS Census of Disks, Protostars, and Outflows
We present the analysis of seven band (1.2 to 8 micron) ground and
space-based imaging of the NGC 7129 young stellar cluster from FLAMINGOS on
MMT, 2MASS, and the Infrared Array Camera (IRAC) on the Spitzer Space
Telescope. An analysis of the H-[4.5] vs. J-H colors reveals 84 objects with
circumstellar disks. Of these, 42 are located within the cluster core, a 0.5 pc
(100'') radius region of enhanced stellar surface density. From a luminosity
and extinction limited sample of the stars within the cluster core boundary we
have determined that 54% +/- 14% have circumstellar disks. Finally, we report
the detection of several resolved outflows in the IRAC 4.5 micron mosaic.Comment: 13 pages, 4 figures. Accepted to the Spitzer special issue of ApJS.
The full-resolution preprint can be obtained from
http://astro.pas.rochester.edu/~rguter/preprints/gutermuth_ngc7129_a.tar.g
HiRes deconvolution of Spitzer infrared images
Spitzer provides unprecedented sensitivity in the infrared (IR), but the spatial resolution is limited by a relatively small aperture (0.85 m) of the primary mirror. In order to maximize the scientific return it is desirable to use processing techniques which make the optimal use of the spatial information in the observations. We have developed a deconvolution technique for Spitzer images. The algorithm, "HiRes" and its implementation has been discussed by Backus et al. in 2005. Here we present examples of Spitzer IR images from the Infrared Array Camera (IRAC) and MIPS, reprocessed using this technique. Examples of HiRes processing include a variety of objects from point sources to complex extended regions. The examples include comparison of Spitzer deconvolved images with high-resolution Keck and Hubble Space Telescope images. HiRes deconvolution improves the visualization of spatial morphology by enhancing resolution (to sub-arcsecond levels in the IRAC bands) and removing the contaminating sidelobes from bright sources. The results thereby represent a significant improvement over previously-published Spitzer images. The benefits of HiRes include (a) sub-arcsec resolution (~0".6-0".8 for IRAC channels); (b) the ability to detect sources below the diffraction-limited confusion level; (c) the ability to separate blended sources, and thereby provide guidance to point-source extraction procedures; (d) an improved ability to show the spatial morphology of resolved sources. We suggest that it is a useful technique to identify features which are interesting enough for follow-up deeper analysis
Tour of the Electromagnetic Spectrum Booklet
This booklet introduces electromagnetic waves, their behaviors, and how scientists visualize these data. Each region of the spectrum is described and illustrated with examples of NASA science. It is a companion piece to the video series under the same title. Educational levels: Informal education
Elliptical Galaxy in the Making: The Dual Active Galactic Nuclei and Metal-enriched Halo of Mrk 273
A systematic analysis of the X-ray emission from the nearby ultraluminous
infrared galaxy Mrk 273 was carried out by combining new 200 ksec Chandra data
with archived 44 ksec data. The active galactic nucleus (AGN) associated with
the Southwest nucleus is confirmed by the new data, and a secondary hard X-ray
(4-8 keV) point source is detected, coincident with the Northeast nucleus at a
projected distance of 0.75 kpc from the Southwest nucleus. The hard X-ray
spectrum of the Northeast nucleus is consistent with a heavily absorbed AGN,
making Mrk 273 another example of a dual AGN in a nearby galaxy merger.
Significant 1-3 keV emission is found along the ionization cones and outflowing
gas detected in a previous study. The data also map the giant X-ray nebula
south of the host galaxy with unprecedented detail. This nebula extends on a
scale of 40 kpc 40 kpc, and is not closely related to the
well-known tidal tail seen in the optical. The X-ray emission of the nebula is
best described by a single-temperature gas model, with a temperature of
7 million K and a super-solar /Fe ratio. Further analysis suggests that
the southern nebula has most likely been heated and enriched by multiple
galactic outflows generated by the AGN and/or circumnuclear starburst in the
past, on a time scale of 0.1 Gyr, similar to the merger event itself.Comment: 25 pages, 22 figures, 4 tables, accepted for publication in the
Astrophysical Journa
4D electron diffraction reveals correlated unidirectional Behavior in zinc oxide nanowires
The confined electronic structure of nanoscale materials has increasingly been shown to induce behavior quite distinct from that of bulk analogs. Direct atomic- scale visualization of nanowires of zinc oxide was achieved through their unique pancake- type diffraction by using four- dimensional (4D) ultrafast electron crystallography. After electronic excitation of this wide- gap photonic material, the wires were found to exhibit colossal expansions, two orders of magnitude higher than that expected at thermal equilibrium; the expansion is highly anisotropic, a quasi- one- dimensional behavior, and is facilitated by the induced antibonding character. By reducing the density of nanowires, the expansions reach even larger values and occur at shorter times, suggesting a decrease of the structural constraint in transient atomic motions. This unanticipated ultrafast carrier- driven expansion highlights the optoelectronic consequences of nanoscale morphologies
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