55 research outputs found
Binary central stars of planetary nebulae with long orbits: the radial velocity orbit of BD+33.2642 (PN G052.7+50.7) and the orbital motion of HD112313 (PN LoTr5)
We study the impact of binary interaction processes on the evolution of low-
and intermediate-mass stars using long-term monitoring of their radial
velocity.
Here we report on our results on the central stars of two planetary nebulae
(PNe): the well-studied spectrophotometric standard BD+33.2642 (central star of
PNG 052.7+50.7) and HD112313 (central star of PN LoTr5), the optical light of
which is dominated by a rapidly rotating G star.
The high-resolution spectra were cross-correlated with carefully selected
masks of spectral lines. The individual masks were optimised for the spectral
signatures of the dominant contributor of the optical light.
We report on the first detection of orbital motion in these two objects. For
BD+33.2642 we sampled 1.5 cycles of the 1105 +/- 24 day orbital period. For HD
112313 a full period is not yet covered, despite our 1807 days of monitoring.
The radial-velocity amplitude shows that it is unlikely that the orbital plane
is co-planar with the one defined by the nebular waist of the bipolar nebula.
To our knowledge these are the first detections of orbits in PNe that are in a
range from several weeks to a few years.
The orbital properties and chemical composition of BD+33.2642 are similar to
what is found in post-AGB binaries with circumbinary discs. The latter are
probably progenitors of these PNe. For LoTr5 the Ba-rich central star and the
long orbital period are similar to the Ba star giants, which hence serve as
natural progeny. In contrast to the central star in LoTr5, normal Ba stars are
slow rotators. The orbits of these systems have a low probability of occurrence
according to recent population synthesis calculations.Comment: 4 pages, 3 figures, Astronomy and Astrophysics, letter
A novel technique to characterize the spatial intra-pixel sensitivity variations in a CMOS image sensor
To understand the scientific imaging capability, one must characterize the
intra-pixel sensitivity variation (IPSV) of the CMOS image sensor. Extracting
an IPSV map contributes to an improved detector calibration that allows to
eliminate some of the uncertainty in the spatial response of the system. This
paper reports the measurement of the sub-pixel sensitivity variation and the
extraction of the 2D IPSV map of a front-side illuminated CMOS image sensor
with a pixel pitch of 6 {\mu}m. Our optical measurement setup focuses a
collimated beam onto the imaging surface with a microscope objective. The spot
was scanned in a raster over a single pixel and its immediate neighbors in
order to probe its response at selected (sub-pixel) positions. In this work we
introduced a novel technique to extract the IPSV map by fitting (forward
modeling) the measured data to a mathematical model of the image, generated in
a single pixel that allows for a spatially varying sensitivity
Asgard/NOTT: L-band nulling interferometry at the VLTI I. Simulating the expected high-contrast performance
Context: NOTT (formerly Hi-5) is a new high-contrast L' band (3.5-4.0 \textmu
m) beam combiner for the VLTI with the ambitious goal to be sensitive to young
giant exoplanets down to 5 mas separation around nearby stars. The performance
of nulling interferometers in these wavelengths is affected both by fundamental
noise from the background and by the contributions of instrumental noises. This
motivates the development of end-to-end simulations to optimize these
instruments. Aims: To enable the performance evaluation and inform the design
of such instruments on the current and future infrastructures, taking into
account the different sources of noise, and their correlation. Methods:
SCIFYsim is an end-to-end simulator for single mode filtered beam combiners,
with an emphasis on nulling interferometers. It is used to compute a covariance
matrix of the errors. Statistical detection tests based on likelihood ratios
are then used to compute compound detection limits for the instrument. Results:
With the current assumptions on the performance of the wavefront correction
systems, the errors are dominated by correlated instrumental errors down to
stars of magnitude 6-7 in the L band, beyond which thermal background from the
telescopes and relay system becomes dominant. Conclusions: SCIFYsim is suited
to anticipate some of the challenges of design, tuning, operation and signal
processing for integrated optics beam combiners. The detection limits found for
this early version of NOTT simulation with the unit telescopes are compatible
with detections at contrasts up to in the L band at separations of 5 to
80 mas around bright stars
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