166 research outputs found
Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- III. Two new low-mass systems with rapidly evolving spots
We present the results of our spectroscopic and photometric analysis of two
newly discovered low-mass detached eclipsing binaries found in the All-Sky
Automated Survey (ASAS) catalogue: ASAS J093814-0104.4 and ASAS J212954-5620.1.
Using the GIRAFFE instrument on the 1.9-m Radcliffe telescope at SAAO and the
UCLES spectrograph on the 3.9-m Anglo-Australian Telescope, we obtained
high-resolution spectra of both objects and derived their radial velocities
(RVs) at various orbital phases. The RVs of both objects were measured with the
TODCOR technique using synthetic template spectra as references. We also
obtained V and I band photometry using the 1.0-m Elizabeth telescope at SAAO
and the 0.4-m PROMPT instruments located at the CTIO. The orbital and physical
parameters of the systems were derived with PHOEBE and JKTEBOP codes. We
compared our results with several sets of widely-used isochrones. Our
multi-epoch photometric observations demonstrate that both objects show
significant out-of-eclipse modulations, which vary in time. We believe that
this effect is caused by stellar spots, which evolve on time scales of tens of
days. For this reason, we constructed our models on the basis of photometric
observations spanning short time scales (less than a month). Our modeling
indicates that (1) ASAS-09 is a main sequence active system with nearly-twin
components with masses of M1 = 0.771(33) Msun, M2 = 0.768(21) Msun and radii of
R1 = 0.772(12) Rsun and R2 = 0.769(13) Rsun. (2) ASAS-21 is a main sequence
active binary with component masses of M1 = 0.833(17) Msun, M2 = 0.703(13) Msun
and radii of R1 = 0.845(12) Rsun and R2 = 0.718(17) Rsun. Both systems confirm
the characteristic of active low-mass stars, for which the observed radii are
larger and the temperatures lower than predicted by evolutionary models. Other
parameters agree within errors with the models of main sequence stars.Comment: 15 pages, 7 figures, 7 tables, to appear in A&
Confirmation of the Luminous Blue Variable status of MWC 930
We present spectroscopic and photometric observations of the emission-line
star MWC 930 (V446 Sct) during its long-term optical brightening in 2006--2013.
Based on our earlier data we suggested that the object has features found in
Luminous Blue Variables (LBV), such as a high luminosity (~3 10^5 Lsun, a low
wind terminal velocity (~ 140 km/s), and a tendency to show strong brightness
variations (~1 mag over 20 years). For the last ~7 years it has been exhibiting
a continuous optical and near-IR brightening along with a change of the
emission-line spectrum appearance and cooling of the star's photosphere. We
present the object's --band light curve, analyze the spectral variations,
and compare the observed properties with those of other recognized Galactic
LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide
Galactic LBV that is currently in the middle of an S Dor cycle.Comment: 12 pages, 7 figure
PROMPT Observations of the Early-Time Optical Afterglow of GRB 060607A
PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes)
observed the early-time optical afterglow of GRB 060607A and obtained a densely
sampled multiwavelength light curve that begins only tens of seconds after the
GRB. Located at Cerro Tololo Inter-American Observatory in Chile, PROMPT is
designed to observe the afterglows of gamma-ray bursts using multiple automated
0.4-m telescopes that image simultaneously in many filters when the afterglow
is bright and may be highly variable. The data span the interval from 44
seconds after the GRB trigger to 3.3 hours in the Bgri filters. We observe an
initial peak in the light curve at approximately three minutes, followed by
rebrightenings peaking around 40 minutes and again at 66 minutes. Although our
data overlap with the early Swift gamma-ray and x-ray light curves, we do not
see a correlation between the optical and high-energy flares. We do not find
evidence for spectral evolution throughout the observations. We model the
variations in the light curves and find that the most likely cause of the
rebrightening episodes is a refreshment of the forward shock preceded by a
rapidly fading reverse shock component, although other explanations are
plausible.Comment: 23 pages, 3 figures, accepted to Ap
The CHilean Automatic Supernova sEarch (CHASE)
The CHASE project started in 2007 with the aim of providing young southern
supernovae (SNe) to the Carnegie Supernova Project (CSP) and Millennium Center
for Supernova Studies (MCSS) follow-up programs. So far CHASE has discovered 33
SNe with an average of more than 2.5 SNe per month in 2008. In addition to the
search we are carrying out a follow-up program targeting bright SNe. Our fully
automated data reduction allows us to follow the evolution on the light curve
in real time, triggering further observations if something potentially
interesting is detectedComment: 4 pages, 2 figures, conference proceedin
IGR J19552+0044: A new asynchronous short period polar: "Filling the gap between intermediate and ordinary polars"
Based on XMM--Newton X-ray observations IGR J19552+0044 appears to be either
a pre-polar or an asynchronous polar. We conducted follow-up optical
observations to identify the sources and periods of variability precisely and
to classify this X-ray source correctly. Extensive multicolor photometric and
medium- to high-resolution spectroscopy observations were performed and period
search codes were applied to sort out the complex variability of the object. We
found firm evidence of discording spectroscopic (81.29+/-0.01m) and photometric
(83.599+/-0.002m) periods that we ascribe to the white dwarf (WD)\ spin period
and binary orbital period, respectively. This confirms that IGR J19552+0044 is
an asynchronous polar. Wavelength-dependent variability and its continuously
changing shape point at a cyclotron emission from a magnetic WD with a
relatively low magnetic field below 20 MG.
The difference between the WD spin period and the binary orbital period
proves that IGR J19552+0044 is a polar with the largest known degree of
asynchronism (0.97 or 3%).Comment: 9 pages, 10 figures, A&A accepte
Patient-reported outcome measures for clinical decision-making in outpatient follow-up: validity and reliability of a renal disease questionnaire
Background
Patient-reported outcome measures are increasingly used by clinicians to support communication in telephone- or face-to-face consultations with patients. A renal disease questionnaire has been developed, but not sufficiently evaluated through clinimetrics in clinical setting. Hence, we aimed to evaluate the content validity, construct validity and the test–retest reliability of a renal disease questionnaire to be used for clinical decision-making.
Methods
A content, construct validity and test–retest reliability study was conducted in 3 nephrology outpatient clinics in Central Denmark Region, Denmark. Content validity (face validity, comprehensibility and relevance) was assessed among 8 patients and 6 clinicians. Reliability was assessed by asking outpatients with chronic kidney disease to complete the questionnaire twice. Reliability was assessed by kappa statistics and agreement by percentage. Construct validity was determined using 4 a priori defined hypotheses and comparing 2 known groups.
Results
Five new domains emerged, 6 items were rephrased and 3 items were removed following the content validity test. A total of 160 patients completed the questionnaire with median 8 days (IQR 2 days) between assessments. The test–retest reliability parameters of the single items in the questionnaire were substantial to almost perfect as all the observed weighted kappa values ranged from 0.61 to 0.91, 95% CI (0.34 to 0.95). In total, 61% of the single items showed almost perfect agreement. In total, 3 of the 4 hypotheses were accepted and 44% of the items showed satisfying known-group discriminative validity.
Conclusion
A renal disease questionnaire used for clinical decision-making in outpatient follow-up showed acceptable content validity and substantial to almost perfect reliability. Sufficient construct validity was not established. Incorporating the questionnaire into routine clinical practice may improve the evaluation of disease burden in patients with chronic kidney disease
Fortnightly Fluctuations in the O-C Diagram of CS 1246
Dominated by a single, large-amplitude pulsation mode, the rapidly-pulsating
hot subdwarf B star CS 1246 is a prime candidate for a long-term O-C diagram
study. We collected nearly 400 hours of photometry with the PROMPT telescopes
over a time span of 14 months to begin looking for secular variations in the
pulse timings. Interestingly, the O-C diagram is dominated by a strong
sinusoidal pattern with a period of 14.1 days and an amplitude of 10.7
light-seconds. Underneath this sine wave is a secular trend implying a decrease
in the 371.7-s pulsational period of Pdot = -1.9 x 10^-11, which we attribute
to the evolution of the star through the H-R diagram. The sinusoidal variation
could be produced by the presence of a low-mass companion, with m sin i ~ 0.12
Msun, orbiting the subdwarf B star at a distance of 20 Rsun. An analysis of the
combined light curve reveals the presence of a low-amplitude first harmonic to
the main pulsation mode.Comment: Accepted for publication in MNRAS. 11 pages, 8 figures, 5 table
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