4,931 research outputs found
A method for optimal image subtraction
We present a new method designed for optimal subtraction of two images with
different seeing. Using image subtraction appears to be essential for the full
analysis of the microlensing survey images, however a perfect subtraction of
two images is not easy as it requires the derivation of an extremely accurate
convolution kernel. Some empirical attempts to find the kernel have used the
Fourier transform of bright stars, but solving the statistical problem of
finding the best kernel solution has never really been tackled. We demonstrate
that it is possible to derive an optimal kernel solution from a simple least
square analysis using all the pixels of both images, and also show that it is
possible to fit the differential background variation at the same time. We also
show that PSF variations can also be easily handled by the method. To
demonstrate the practical efficiency of the method, we analyzed some images
from a Galactic Bulge field monitored by the OGLE II project.
We find that the residuals in the subtracted images are very close to the
photon noise expectations. We also present some light curves of variable stars,
and show that, despite high crowding levels, we get an error distribution close
to that expected from photon noise alone. We thus demonstrate that nearly
optimal differential photometry can be achieved even in very crowded fields. We
suggest that this algorithm might be particularly important for microlensing
surveys, where the photometric accuracy and completeness levels could be very
significantly improved by using this method.Comment: 8,pages, 4 Postscript figures, emulateapj.sty include
Digital computer processing of X-ray photographs
Enhanced digital computer processing of X-ray photographs by image subtraction or filterin
Real time image subtraction and "exclusive or" operation using a self-pumped phase conjugate mirror
Real time "exclusive or" operation with an interferometer using a self-pumped phase conjugate mirror is reported. Also, results of image subtraction and intensity inversion are shown
Photometry of SN 2002bo with template image subtraction
VRI photometry of the type Ia supernova 2002bo is presented. This SN exploded
in a dusty region of the host galaxy NGC 3190, thus, subtraction of a template
frame was necessary to obtain reliable photometry. We used a template frame of
NGC 3190 taken during the course of our galaxy imaging project, fortunately,
just a few days before SN 2002bo was discovered. The aim of this project is to
collect template frames of nearby galaxies that are potential hosts of bright
SNe. Subtraction of pre-SN images helped us to exclude the background light
contamination of the host galaxy. The maximum occurred at JD 2452346, with
maximal V brightness of 13.58. MLCS analysis led to T0(B)=JD 2452346.1 pm 0.8
(fiducial B-maximum), E(B-V)=0.24 pm 0.02, mu0=32.46 pm 0.06, Delta=-0.14 pm
0.04. E(B-V)=0.24(2) indicates a significant extinction in the host galaxy as
the galactic reddening is negligible toward NGC 3190. The accepted value of
Delta indicates that SN 2002bo was a slightly overluminous SN by about 0.14
relative to fiducial SN Type Ia. The distance turned out to be 31.0 pm 3 Mpc.
In addition, the heavily obscured SN 2002cv was also detected on the I frame
taken on JD 2452434 (June 8, 2002), and a variable star is found in the field,
very close to the host galaxy.Comment: accepted by Astronomy and Astrophysic
Intermediate Palomar Transient Factory: Realtime Image Subtraction Pipeline
A fast-turnaround pipeline for realtime data reduction plays an essential
role in discovering and permitting follow-up observations to young supernovae
and fast-evolving transients in modern time-domain surveys. In this paper, we
present the realtime image subtraction pipeline in the intermediate Palomar
Transient Factory. By using high-performance computing, efficient database, and
machine learning algorithms, this pipeline manages to reliably deliver
transient candidates within ten minutes of images being taken. Our experience
in using high performance computing resources to process big data in astronomy
serves as a trailblazer to dealing with data from large-scale time-domain
facilities in near future.Comment: 18 pages, 6 figures, accepted for publication in PAS
Digital computer processing of X-ray photos
Digital computers correct various distortions in medical and biological photographs. One of the principal methods of computer enhancement involves the use of a two-dimensional digital filter to modify the frequency spectrum of the picture. Another computer processing method is image subtraction
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