154 research outputs found
The Central Star Candidate of the Planetary Nebula Sh2-71: Photometric and Spectroscopic Variability
We present the analysis of several newly obtained and archived photometric
and spectroscopic datasets of the intriguing and yet poorly understood 13.5-mag
central star candidate of the bipolar planetary nebula Sh2-71. Photometric
observations confirmed the previously determined quasi-sinusoidal lightcurve
with a period of 68 days and also indicated periodic sharp brightness dips,
possibly eclipses, with a period of 17.2 days. In addition, the comparison
between U and V lightcurves revealed that the 68-day brightness variations are
accompanied by a variable reddening effect of .
Spectroscopic datasets demonstrated pronounced variations in spectral profiles
of Balmer, helium and singly ionised metal lines and indicated that these
variations occur on a time-scale of a few days. The most accurate verification
to date revealed that spectral variability is not correlated with the 68-day
brightness variations. The mean radial velocity of the observed star was
measured to be 26 km/s with an amplitude of 40 km/s. The spectral
type was determined to be B8V through spectral comparison with synthetic and
standard spectra. The newly proposed model for the central star candidate is a
Be binary with a misaligned precessing disc.Comment: 9 pages, 6 figures (main article). 7 pages, 6 figures (appendix).
Accepted for publication in MNRA
Reverberation Mapping of IC4329A
We present the results of a new reverberation mapping campaign for the
broad-lined active galactic nucleus (AGN) in the edge-on spiral IC4329A.
Monitoring of the optical continuum with band photometry and broad
emission-line flux variability with moderate-resolution spectroscopy allowed
emission-line light curves to be measured for H, H, and HeII
. We find a time delay of days for H,
a similar time delay of days for H, and an
unresolved time delay of days for HeII. The time delay for
H is consistent with the predicted value from the relationship between
AGN luminosity and broad line region radius, after correction for the
mag of intrinsic extinction at 5100A. Combining the measured time
delay for H with the broad emission line width and an adopted value of
, we find a central supermassive black hole mass of
. Velocity-resolved time
delays were measured across the broad H emission-line profile and may be
consistent with an ''M''-like shape. Modeling of the full reverberation
response of H was able to provide only modest constraints on some
parameters, but does exhibit agreement with the black hole mass and average
time delay. The models also suggest that the AGN structure is misaligned by a
large amount from the edge-on galaxy disk. This is consistent with expectations
from the unified model of AGNs, in which broad emission lines are expected to
be visible only for AGNs that are viewed at relatively face-on inclinations.Comment: 12 pages, 6 figures, 3 tables; accepted for publication in Ap
Simulator for Microlens Planet Surveys
We summarize the status of a computer simulator for microlens planet surveys.
The simulator generates synthetic light curves of microlensing events observed
with specified networks of telescopes over specified periods of time.
Particular attention is paid to models for sky brightness and seeing,
calibrated by fitting to data from the OGLE survey and RoboNet observations in
2011. Time intervals during which events are observable are identified by
accounting for positions of the Sun and the Moon, and other restrictions on
telescope pointing. Simulated observations are then generated for an algorithm
that adjusts target priorities in real time with the aim of maximizing planet
detection zone area summed over all the available events. The exoplanet
detection capability of observations was compared for several telescopes.Comment: Proc. IAU Symp. No. 293 "Formation, detection, and characterization
of extrasolar habitable planets", ed. by N. Haghighipour. 4 pages, in pres
Statistical Searches for Microlensing Events in Large, Non-Uniformly Sampled Time-Domain Surveys: A Test Using Palomar Transient Factory Data
Many photometric time-domain surveys are driven by specific goals, such as
searches for supernovae or transiting exoplanets, which set the cadence with
which fields are re-imaged. In the case of the Palomar Transient Factory (PTF),
several sub-surveys are conducted in parallel, leading to non-uniform sampling
over its footprint. While the median PTF field has been imaged 40 times in \textit{R}-band,
have been observed 100 times. We use PTF data to
study the trade-off between searching for microlensing events in a survey whose
footprint is much larger than that of typical microlensing searches, but with
far-from-optimal time sampling. To examine the probability that microlensing
events can be recovered in these data, we test statistics used on uniformly
sampled data to identify variables and transients. We find that the von Neumann
ratio performs best for identifying simulated microlensing events in our data.
We develop a selection method using this statistic and apply it to data from
fields with 10 -band observations, light curves,
uncovering three candidate microlensing events. We lack simultaneous,
multi-color photometry to confirm these as microlensing events. However, their
number is consistent with predictions for the event rate in the PTF footprint
over the survey's three years of operations, as estimated from near-field
microlensing models. This work can help constrain all-sky event rate
predictions and tests microlensing signal recovery in large data sets, which
will be useful to future time-domain surveys, such as that planned with the
Large Synoptic Survey Telescope.Comment: 13 pages, 14 figures; accepted for publication in ApJ. fixed author
lis
Velocity-Resolved Reverberation Mapping of NGC 3227
We describe the results of a new reverberation mapping program focused on the
nearby Seyfert galaxy NGC 3227. Photometric and spectroscopic monitoring were
carried out from 2022 December to 2023 June with the Las Cumbres Observatory
network of telescopes. We detected time delays in several optical broad
emission lines, with H having the longest delay at days and He II having the shortest delay with
days. We also detect velocity-resolved
behavior of the H emission line, with different line-of-sight velocities
corresponding to different observed time delays. Combining the integrated
H time delay with the width of the variable component of the emission
line and a standard scale factor suggests a black hole mass of . Modeling of the full
velocity-resolved response of the H emission line with the
phenomenological code CARAMEL finds a similar mass of , and suggests that the
H-emitting broad line region (BLR) may be represented by a biconical or
flared disk structure that we are viewing at an inclination angle of and with gas motions that are dominated by rotation. The
new photoionization-based BLR modeling tool BELMAC finds general agreement with
the observations when assuming the best-fit CARAMEL results, however BELMAC
prefers a thick disk geometry and kinematics that are equally comprised of
rotation and inflow. Both codes infer a radially extended and flattened BLR
that is not outflowing.Comment: 16 pages, 9 figures, 4 tables; submitted to Ap
Results from the Wide Angle Search for Planets Prototype (WASP0) II: Stellar Variability in the Pegasus Field
Recent wide-field photometric surveys which target a specific field for long
durations are ideal for studying both long and short period stellar
variability. Here we report on 75 variable stars detected during observations
of a field in Pegasus using the WASP0 instrument, 73 of which are new
discoveries. The variables detected include 16 delta Scuti stars, 34 eclipsing
binaries, 3 BY Draconis stars, and 4 RR Lyraes. We estimate that the fraction
of stars in the field brighter than V ~ 13.5 exhibiting variable behaviour with
an amplitude greater than 0.6% rms is ~ 0.4%. These results are compared with
other wide-field stellar variability surveys and implications for detecting
transits due to extra-solar planets are discussed.Comment: 10 pages, 8 figures, published in MNRA
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