12,800 research outputs found
Feasibility of transit photometry of nearby debris discs
Dust in debris discs is constantly replenished by collisions between larger
objects. In this paper, we investigate a method to detect these collisions. We
generate models based on recent results on the Fomalhaut debris disc, where we
simulate a background star transiting behind the disc, due to the proper motion
of Fomalhaut. By simulating the expanding dust clouds caused by the collisions
in the debris disc, we investigate whether it is possible to observe changes in
the brightness of the background star. We conclude that in the case of the
Fomalhaut debris disc, changes in the optical depth can be observed, with
values of the optical depth ranging from for the densest dust
clouds to for the most diffuse clouds with respect to the background
optical depth of .Comment: 19 pages, 15 figures, accepted for publication in MNRA
Registration of Airborne Infrared Images using Platform Attitude Information
In current warfare scenario stealth and passive threat detection capabilities are considered as prime requirements to accomplish desired mission by the fighter aircrafts. To improve the stealth of an aircraft, the trend is towards detecting threats with the help of passive sensors (Electro Optic or Infrared). Current situation caters for systems like Infra-red Search and Track (IRST) and Passive Missile Warning Systems (PMWS). IRST system is a passive target detection system, used for detecting aerial & ground targets. PMWS is a threat detection system used for detecting missiles approaching towards aircraft. Both of these systems detect targets of interest by processing IR images acquired in mid-IR region. The prime challenge in IRST system or PMWS is detecting a moving target of size typically 1~2 pixels in acquired image sequences. The temporal change caused by moving target in consecutive frames can be considered as one important factor to detect them. The temporal change caused by moving target is identified through absolute frame differencing of successive frames. This principle has limitation in application to IRST & PMWS as the imaging sensor with the aircraft is moving. This motion also imparts temporal change in the acquired images. In this paper authors are proposing a method for removing the temporal change caused by the platform motion in two consequently acquired frames using registration process. The proposed method uses the platform attitude information at frame sampling times. Authors have analyzed the sensitivity of registration process to noisy platform attitude information.Defence Science Journal, 2014, 64(2), pp. 130-135. DOI: http://dx.doi.org/10.14429/dsj.64.546
NICMOS Snapshot Survey of Damped Lyman Alpha Quasars
We image 19 quasars with 22 damped Lyman alpha (DLA) systems using the F160W
filter and the Near-Infrared Camera and Multiobject Spectrograph aboard the
Hubble Space Telescope, in both direct and coronagraphic modes. We reach 5
sigma detection limits of ~H=22 in the majority of our images. We compare our
observations to the observed Lyman-break population of high-redshift galaxies,
as well as Bruzual & Charlot evolutionary models of present-day galaxies
redshifted to the distances of the absorption systems. We predict H magnitudes
for our DLAs, assuming they are producing stars like an L* Lyman-break galaxy
(LBG) at their redshift. Comparing these predictions to our sensitivity, we
find that we should be able to detect a galaxy around 0.5-1.0 L* (LBG) for most
of our observations. We find only one new possible candidate, that near
LBQS0010-0012. This scarcity of candidates leads us to the conclusion that most
DLA systems are not drawn from a normal LBG luminosity function nor a local
galaxy luminosity function placed at these high redshifts.Comment: 31 pages, 8 figures, Accepted for Feb. 10 issue of Ap
Optical tracking of deep-space spacecraft in Halo L2 orbits and beyond: the Gaia mission as a pilot case
We tackle the problem of accurate optical tracking of distant man-made
probes, on Halo orbit around the Earth-Sun libration point L2 and beyond, along
interplanetary transfers. The improved performance of on-target tracking,
especially when observing with small-class telescopes is assessed providing a
general estimate of the expected S/N ratio in spacecraft detection. The
on-going Gaia mission is taken as a pilot case for our analysis, reporting on
fresh literature and original optical photometry and astrometric results. The
probe has been located, along its projected nominal path, within 0.13 +/- 0.09
arcsec, or 0.9 +/- 0.6 km. Spacecraft color appears to be red, with (V-R_c) =
1.1 +/- 0.2 and a bolometric correction to the R_c band of (Bol-R_c) = -1.1 +/-
0.2. The apparent magnitude, R_c = 20.8 +/- 0.2, is much fainter than
originally expected. These features lead to suggest a lower limit for the Bond
albedo a = 0.11 +/- 0.05 and confirm that incident Sun light is strongly
reddened by Gaia through its on-board MLI blankets covering the solar shield.
Relying on the Gaia figures, we found that VLT-class telescopes could yet be
able to probe distant spacecraft heading Mars, up to 30 million km away, while
a broader optical coverage of the forthcoming missions to Venus and Mars could
be envisaged, providing to deal with space vehicles of minimum effective area
Aeff >= 10^6 cm^2. In addition to L2 surveys, 2m-class telescopes could also
effectively flank standard radar-ranging techniques in deep-space probe
tracking along Earth's gravity-assist maneuvers for interplanetary missions.Comment: In press for Advances in Space Research (w/ 15 colour figures and 1
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