14,665 research outputs found
Enhancing the Visible with the Invisible: Exploiting Near-Infrared to Advance Computational Photography and Computer Vision
Silicon-based digital camera sensors exhibit significant sensitivity beyond the visible spectrum (400-700nm). They are able to capture wavelengths up to 1100 nm, i.e., they are sensitive to near-infrared (NIR) radiation. This additional information is conventionally treated as noise and is absorbed by a NIR-blocking filter affixed to the sensor. We show that retaining instead of removing NIR information can significantly improve certain computational photography and computer vision tasks. Indeed, intrinsic properties of the NIR wavelength band guarantee that images can be sharper, less affected by man-made colorants, and more resilient to changing light conditions. The benefits of using NIR images in conjunction with standard color images in applications such as haze removal, skin smoothing, single and multiple illuminant detection, shadow detection, and material classification is discussed
Triggered star formation and Young Stellar Population in Bright-Rimmed Cloud SFO 38
We have investigated the young stellar population in and around SFO 38, one
of the massive globules located in the northern part of the Galactic HII region
IC 1396, using the Spitzer IRAC and MIPS observations (3.6 to 24 micron) and
followed up with ground based optical photometric and spectroscopic
observations. Based on the IRAC and MIPS colors and H-alpha emission we
identify ~45 Young Stellar Objects (Classes 0/I/II) and 13 probable Pre Main
Sequence candidates. We derive the spectral types (mostly K- and M-type stars),
effective temperatures and individual extinction of the relatively bright and
optically visible Class II objects. Based on optical photometry and theoretical
isochrones, we estimate the spread in stellar ages to be between 1--8 Myr with
a median age of 3 Myr and a mass distribution of 0.3--2.2 Msun with a median
value around 0.5 Msun. Using the width of the H-alpha emission line measured at
10% peak intensity, we derive the mass accretion rates of individual objects to
be between 10^{-10} to 10^{-8} Msun/yr. From the continuum-subtracted H-alpha
line image, we find that the H-alpha emission of the globule is not spatially
symmetric with respect to the O type ionizing star HD 206267. We clearly detect
an enhanced concentration of YSOs closer to the southern rim of SFO~38 and
identify an evolutionary sequence of YSOs from the rim to the dense core of the
cloud, with most of the Class II objects located at the bright rim. The YSOs
appear to be aligned along two different directions towards the O6.5V type star
HD 206267 and the B0V type star HD 206773. This is consistent with the
Radiation Driven Implosion (RDI) model for triggered star formation. (Abridged)Comment: Accepted for publication in Ap
Embedded Star Formation in the Eagle Nebula with Spitzer/GLIMPSE
We present new Spitzer photometry of the Eagle Nebula (M16, containing the
optical cluster NGC 6611) combined with near-infrared photometry from 2MASS. We
use dust radiative transfer models, mid-infrared and near-infrared color-color
analysis, and mid-infrared spectral indices to analyze point source spectral
energy distributions, select candidate young stellar objects (YSOs), and
constrain their mass and evolutionary state. Comparison of the different
protostellar selection methods shows that mid-infrared methods are consistent,
but as has been known for some time, near-infrared-only analysis misses some
young objects. We reveal more than 400 protostellar candidates, including one
massive young stellar object (YSO) that has not been previously highlighted.
The YSO distribution supports a picture of distributed low-level star
formation, with no strong evidence of triggered star formation in the
``pillars''. We confirm the youth of NGC 6611 by a large fraction of
infrared-excess sources, and reveal a younger cluster of YSOs in the nearby
molecular cloud. Analysis of the YSO clustering properties shows a possible
imprint of the molecular cloud's Jeans length. Multiwavelength mid-IR imaging
thus allows us to analyze the protostellar population, to measure the dust
temperature and column density, and to relate these in a consistent picture of
star formation in M16.Comment: 16p preprint - ApJ accepte
2MASS NIR photometry for 693 candidate globular clusters in M31 and the Revised Bologna Catalogue
We have identified in the 2MASS database 693 known and candidate globular
clusters in M31. The 2MASS J,H,K magnitudes of these objects have been
transformed to the same homogeneous photometric system of existing near
infrared photometry of M31 globulars, finally yielding J,H,K integrated
photometry for 279 confirmed M31 clusters, 406 unconfirmed candidates and 8
objects with controversial classification. Of these objects 529 lacked any
previous estimate of their near infrared magnitudes. The newly assembled near
infrared dataset has been implemented into a revised version of the Bologna
Catalogue of M31 globulars, with updated optical (UBVRI) photometry taken, when
possible, from the most recent sources of CCD photometry available in the
literature and transformed to a common photometric system. The final Revised
Bologna Catalogue (available in electronic form) is the most comprehensive list
presently available of confirmed and candidate M31 globular clusters, with a
total of 1164 entries. In particular, it includes 337 confirmed GCs, 688 GC
candidates, 10 objects with controversial classification, 70 confirmed
galaxies, 55 confirmed stars, and 4 HII regions lying within ~3 deg. from the
center of the M31 galaxy. Using the newly assembled database we show that the
V-K color provides a powerful tool to discriminate between M31 clusters and
background galaxies, and we identify a sample of 83 globular cluster
candidates, which is not likely to be contaminated by misclassified galaxies.Comment: 9 pages,5 figures,accepted for publication in Astronomy &
Astrophysics ASCII (commented) version of the tables 2,3,4 are available at
http://www.bo.astro.it/M3
A near-infrared variability campaign of TMR-1: New light on the nature of the candidate protoplanet TMR-1C
(abridged) We present a near-infrared (NIR) photometric variability study of
the candidate protoplanet, TMR-1C, located at a separation of about 10" (~1000
AU) from the Class I protobinary TMR-1AB in the Taurus molecular cloud. Our
campaign was conducted between October, 2011, and January, 2012. We were able
to obtain 44 epochs of observations in each of the H and Ks filters. Based on
the final accuracy of our observations, we do not find any strong evidence of
short-term NIR variability at amplitudes of >0.15-0.2 mag for TMR-1C or
TMR-1AB. Our present observations, however, have reconfirmed the
large-amplitude long-term variations in the NIR emission for TMR-1C, which were
earlier observed between 1998 and 2002, and have also shown that no particular
correlation exists between the brightness and the color changes. TMR-1C became
brighter in the H-band by ~1.8 mag between 1998 and 2002, and then fainter
again by ~0.7 mag between 2002 and 2011. In contrast, it has persistently
become brighter in the Ks-band in the period between 1998 and 2011. The (H-Ks)
color for TMR-1C shows large variations, from a red value of 1.3+/-0.07 and
1.6+/-0.05 mag in 1998 and 2000, to a much bluer color of -0.1+/-0.5 mag in
2002, and then again a red color of 1.1+/-0.08 mag in 2011. The observed
variability from 1998 to 2011 suggests that TMR-1C becomes fainter when it gets
redder, as expected from variable extinction, while the brightening observed in
the Ks-band could be due to physical variations in its inner disk structure.
The NIR colors for TMR-1C obtained using the high precision photometry from
1998, 2000, and 2011 observations are similar to the protostars in Taurus,
suggesting that it could be a faint dusty Class I source. Our study has also
revealed two new variable sources in the vicinity of TMR-1AB, which show
long-term variations of ~1-2 mag in the NIR colors between 2002 and 2011.Comment: Accepted in A&
Hunting Galaxies to (and for) Extinction
In studies of star-forming regions, near-infrared excess (NIRX)
sources--objects with intrinsic colors redder than normal stars--constitute
both signal (young stars) and noise (e.g. background galaxies). We hunt down
(identify) galaxies using near-infrared observations in the Perseus
star-forming region by combining structural information, colors, and number
density estimates. Galaxies at moderate redshifts (z = 0.1 - 0.5) have colors
similar to young stellar objects (YSOs) at both near- and mid-infrared (e.g.
Spitzer) wavelengths, which limits our ability to identify YSOs from colors
alone. Structural information from high-quality near-infrared observations
allows us to better separate YSOs from galaxies, rejecting 2/5 of the YSO
candidates identified from Spitzer observations of our regions and potentially
extending the YSO luminosity function below K of 15 magnitudes where galaxy
contamination dominates. Once they are identified we use galaxies as valuable
extra signal for making extinction maps of molecular clouds. Our new iterative
procedure: the Galaxies Near Infrared Color Excess method Revisited (GNICER),
uses the mean colors of galaxies as a function of magnitude to include them in
extinction maps in an unbiased way. GNICER increases the number of background
sources used to probe the structure of a cloud, decreasing the noise and
increasing the resolution of extinction maps made far from the galactic plane.Comment: 16 pages and 16 figures. Accepted for publication in ApJ. Full
resolution version at
http://www.cfa.harvard.edu/COMPLETE/papers/Foster_HuntingGalaxies.pd
A Spitzer IRS Spectral Atlas of Luminous 8 micron Sources in the Large Magellanic Cloud
We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS)
spectra of highly luminous, compact mid-infrared sources in the Large
Magellanic Cloud. Sources were selected on the basis of infrared colors and 8
micron (MSX) fluxes indicative of highly evolved, intermediate- to high-mass
stars with current or recent mass loss at large rates. We determine the
chemistry of the circumstellar envelope from the mid-IR continuum and spectral
features and classify the spectral types of the stars. In the sample of 60
sources, we find 21 Red Supergiants (RSGs), 16 C-rich Asymptotic Giant Branch
(AGB) stars, 11 HII regions, 4 likely O-rich AGB stars, 4 Galactic O-rich AGB
stars, 2 OH/IR stars, and 2 B[e] supergiants with peculiar IR spectra. We find
that the overwhelming majority of the sample AGB stars (with typical IR
luminosities ~1.0E4 L_sun) have C-rich envelopes, while the O-rich objects are
predominantly luminous RSGs with L_IR ~ 1.0E5 L_sun. We determine mean
bolometric corrections to the stellar K-band flux densities and find that for
carbon stars, the bolometric corrections depend on the infrared color, whereas
for RSGs, the bolometric correction is independent of IR color. Our results
reveal that objects previously classified as PNe on the basis of IR colors are
in fact compact HII regions with very red IRS spectra that include strong
atomic recombination lines and PAH emission features. We demonstrate that the
IRS spectral classes in our sample separate clearly in infrared color-color
diagrams that use combinations of 2MASS data and synthetic IRAC/MIPS fluxes
derived from the IRS spectra. On this basis, we suggest diagnostics to identify
and classify, with high confidence levels, IR-luminous evolved stars and HII
regions in nearby galaxies using Spitzer and near-infrared photometry.Comment: 46 pages, 9 figures; accepted for publication in AJ; abstract
abridge
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