249 research outputs found
New observational techniques and analysis tools for wide field CCD surveys and high resolution astrometry
(Abridged) In the first part of this thesis, a general methodology for
applying image deconvolution to wide-field CCD imagery. Results show that
wavelet-based deconvolution can increase limiting magnitude up to 0.6 mag and
improve limiting resolution 1 pixel with respect to original image with no
astrometric accuracy degradation.
In the second part, a new observational technique based on CCD fast drift
scanning has been proposed for lunar occultations (LO) and speckle
interferometry. This enables all kind of professional and high-end amateur
observatories to perform such kind of observations.
For LO, 16 new binaries up to 2mas of projected separation were detected and
stellar diameters measurements in the 7 mas regime were obtained with that CCD
and IR subarray based techniques. A new wavelet-based LO reduction pipeline was
implemented.
For speckle, CCD fast drift scanning technique was validated with the
observation of four binary systems with well determined orbits. The results of
separation, position angle and magnitude difference are in accordance with
published measurements. A new approach for calibrating speckle transfer
function from the binary power spectrum itself has been introduced. It does not
require point source observations, which gives a more effective use of
observation time.Comment: This is the abstract of my PhD Thesis at University of Barcelona.
Abridged and complete summary available from astro-ph. Full thesis (22Mb) in
separate chapters and with a summary in Catalan is available from:
http://www.tesisenxarxa.net/TDX-0330106-125745/index_an.htm
TFAW: wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys
There have been many efforts to correct systematic effects in astronomical
light curves to improve the detection and characterization of planetary
transits and astrophysical variability. Algorithms like the Trend Filtering
Algorithm (TFA) use simultaneously-observed stars to remove systematic effects,
and binning is used to reduce high-frequency random noise. We present TFAW, a
wavelet-based modified version of TFA. TFAW aims to increase the periodic
signal detection and to return a detrended and denoised signal without
modifying its intrinsic characteristics. We modify TFA's frequency analysis
step adding a Stationary Wavelet Transform filter to perform an initial noise
and outlier removal and increase the detection of variable signals. A wavelet
filter is added to TFA's signal reconstruction to perform an adaptive
characterization of the noise- and trend-free signal and the noise contribution
at each iteration while preserving astrophysical signals. We carried out tests
over simulated sinusoidal and transit-like signals to assess the effectiveness
of the method and applied TFAW to real light curves from TFRM. We also studied
TFAW's application to simulated multiperiodic signals, improving their
characterization. TFAW improves the signal detection rate by increasing the
signal detection efficiency (SDE) up to a factor ~2.5x for low SNR light
curves. For simulated transits, the transit detection rate improves by a factor
~2-5x in the low-SNR regime compared to TFA. TFAW signal approximation performs
up to a factor ~2x better than bin averaging for planetary transits. The
standard deviations of simulated and real TFAW light curves are ~40x better
than TFA. TFAW yields better MCMC posterior distributions and returns lower
uncertainties, less biased transit parameters and narrower (~10x) credibility
intervals for simulated transits. We present a newly-discovered variable star
from TFRM.Comment: Accepted for publication by A&A. 13 pages, 16 figures and 5 table
New high-sensitivity, milliarcsecond resolution results from routine observations of lunar occultations at the ESO VLT
(Abridged) Lunar occultations (LO) are a very efficient and powerful
technique, that achieves the best combination of high angular resolution and
sensitivity possible today at near-infrared wavelengths. Given that the events
are fixed in time, that the sources are occulted randomly, and that the
telescope use is minimal, the technique is very well suited for service mode
observations. We have established a program of routine LO observations at the
VLT observatory, especially designed to take advantage of short breaks
available in-between other programs. We have used the ISAAC instrument in burst
mode, capable of producing continuous read-outs at millisecond rates on a
suitable subwindow. Given the random nature of the source selection, our aim
has been primarily the investigation of a large number of stellar sources at
the highest angular resolution in order to detect new binaries. Serendipitous
results such as resolved sources and detection of circumstellar components were
also anticipated. We have recorded the signal from background stars for a few
seconds, around the predicted time of occultation by the Moon's dark limb. At
millisecond time resolution, a characteristic diffraction pattern can be
observed. Patterns for two or more sources superimpose linearly, and this
property is used for the detection of binary stars. The detailed analysis of
the diffraction fringes can be used to measure specific properties such as the
stellar angular size and the presence of extended light sources such as a
circumstellar shell. We present a list of 191 stars for which LO data could be
recorded and analyzed. Results include the detection of 16 binary and 2 triple
stars, all but one of which were previously unknown. The projected angular
separations are as small as 4 milliarcseconds and magnitude differences as high
as ?K=5.8 mag...Comment: 10 pages, 3 figures, to be published in A&
Evidence of coupling between the thermal and nonthermal emission in the gamma-ray binary LS I +61 303
The gamma-ray binary LS I +61 303 is composed of a Be star and a compact
companion orbiting in an eccentric orbit. Variable flux modulated with the
orbital period of ~26.5 d has been detected from radio to very high-energy
gamma rays. In addition, the system presents a superorbital variability of the
phase and amplitude of the radio outburst with a period of ~4.6 yr. We present
optical photometric observations of LS I +61 303 spanning ~1.5 yr and
contemporaneous Halpha equivalent width (EW Halpha) data. The optical
photometry shows, for the first time, that the known orbital modulation suffers
a positive orbital phase shift and an increase in flux for data obtained 1-yr
apart. This behavior is similar to that already known at radio wavelengths,
indicating that the optical flux follows the superorbital variability as well.
The orbital modulation of the EW Halpha presents the already known superorbital
flux variability but shows, also for the first time, a positive orbital phase
shift. In addition, the optical photometry exhibits a lag of ~0.1-0.2 in
orbital phase with respect to the EW Halpha measurements at similar
superorbital phases, and presents a lag of ~0.1 and ~0.3 orbital phases with
respect noncontemperaneous radio and X-ray outbursts, respectively. The phase
shifts detected in the orbital modulation of thermal indicators, such as the
optical flux and the EW Halpha, are in line with the observed behavior for
nonthermal indicators, such as X-ray or radio emission. This shows that there
is a strong coupling between the thermal and nonthermal emission processes in
the gamma-ray binary LS I +61 303. The orbital phase lag between the optical
flux and the EW Halpha is naturally explained considering different emitting
regions in the circumstellar disk, whereas the secular evolution might be
caused by the presence of a moving one-armed spiral density wave in the disk.Comment: 4 pages, 3 figures, accepted for publication in A&A (this version
matches the published version
Infrared and visual lunar occultations measurements of stellar diameters and new binary stars detections at the Calar Alto 1.5m telescope
We present a program of routine lunar occultations, at optical and near-IR
wavelengths, recently started at the 1.5m Spanish telescope at the Calar Alto
Observatory. Both a CCD and an infrared array detector are used. The program is
aimed mainly at the detection and investigation of binary systems, although
results in other areas of stellar research are also anticipated.
Occultations are reported for a total of 40 stars. Among these, SAO 164567,
SAO 78258 and AG+24 788 have been discovered to be binaries, with projected
separations as small as 0.006". Furthermore, binarity is suspected in the case
of SAO 78119 and SAO 79251. Additionally, the angular diameter of the late-type
giant 30 Psc and of the infrared star V349 Gem have been accurately measured,
this latter for the first time.
We finally evaluate the instrumentation performance in terms of limiting
magnitude and angular resolution, and discuss applications to larger
telescopes.Comment: 15 pages, 3 figures, LaTeX, uses aa.cls. Accepted for publication in
A&
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