In February 2013, the first Austrian nanosatellite BRITE-Austria/TUGSAT‑1 was launched into orbit to observe the brightness variations of massive luminous stars. Although the mission was originally ...planned to last only two years, BRITE-Austria has been providing scientific data at a high quality standard for more than eight years. The natural degradation of the systems on board over time as well as the impact of radiation, especially on the light-sensitive detectors, led to a decrease in efficiency and data quality. To ensure the continuous operation and a high level of data quality, several countermeasures were successfully introduced over the years, some of which are highlighted in this paper.
The BRITE mission has shown impressively that, with the help of small and inexpensive satellites, even highly demanding scientific objectives can be achieved. The BRITE satellites have delivered new insights into the physical nature of stars, their pulsations, and “heartbeats”, as described in numerous publications, and even observed the complete development of a nova in the Carina field.
BRITE-Constellation is devoted to high-precision optical photometric monitoring of bright stars, distributed all over the Milky Way, in red and/or blue passbands. Photometry from space avoids the ...turbulent and absorbing terrestrial atmosphere and allows for very long and continuous observing runs with high time resolution and thus provides the data necessary for understanding various processes inside stars (e.g., asteroseismology) and in their immediate environment. While the first astronomical observations from space focused on the spectral regions not accessible from the ground it soon became obvious around 1970 that avoiding the turbulent terrestrial atmosphere significantly improved the accuracy of photometry and satellites explicitly dedicated to high-quality photometry were launched. A perfect example is BRITE-Constellation, which is the result of a very successful cooperation between Austria, Canada and Poland. Research highlights for targets distributed nearly over the entire HRD are presented, but focus primarily on massive and hot stars.
As a continuation of our previous studies in 2007 and 2008, new photometric observations of the T Tauri star TW Hya obtained by the MOST satellite and the All Sky Automated Survey (ASAS) project over ...40 d in 2009 with temporal resolution of 0.2 d are presented. A wavelet analysis of the combined MOST-ASAS data provides a rich picture of coherent, intermittent, variable-period oscillations, similarly as discovered in the 2008 data. The periods (1.3-10 d) and systematic period shortening on time-scales of weeks can be interpreted within the model of magnetorotationally controlled accretion processes in the inner accretion disc around the star. Within this model and depending on the assumed visibility of plasma parcels causing the oscillations, the observed shortest oscillation period may indicate the stellar rotation period of 1.3 or 2.6 d, synchronized with the disc at 4.5 or 7.1 R⊙, respectively.
The system is the closest known stellar system with directly detected gas giant planets, an edge-on circumstellar disc, and evidence of falling sublimating bodies and transiting exocomets. The inner ...planet has also been indirectly detected with radial velocity (RV) measurements. The star is a known pulsator, and the long-term stability of these pulsations opens up the possibility of indirectly detecting the gas giant planets through time delays of the pulsations due to a varying light travel time. We search for phase shifts in the pulsations consistent with the known planets and c and carry out an analysis of the stellar pulsations of beta Pictoris over a multi-year timescale. We used photometric data collected by the BRITE-Constellation, bRing, ASTEP, and TESS to derive a list of the strongest and most significant pulsations. We carried out an analysis with the open-source python package maelstrom to study the stability of the pulsation modes of beta Pictoris in order to determine the long-term trends in the observed pulsations. We did not detect the expected signal for or . The expected time delay is 6 seconds for and 24 seconds for . With simulations, we determined that the photometric noise in all the combined data sets cannot reach the sensitivity needed to detect the expected timing drifts. An analysis of the pulsational modes of beta Pictoris using maelstrom showed that the modes themselves drift on the timescale of a year, fundamentally limiting our ability to detect exoplanets around beta Pictoris via pulsation timing.
A SUPER-EARTH TRANSITING A NAKED-EYE STAR Winn, Joshua N.; Matthews, Jaymie M.; Dawson, Rebekah I. ...
Astrophysical journal. Letters,
08/2011, Letnik:
737, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We have detected transits of the innermost planet 'e' orbiting 55 Cnc (V = 6.0), based on two weeks of nearly continuous photometric monitoring with the MOST space telescope. The transits occur with ...the period (0.74 days) and phase that had been predicted by Dawson & Fabrycky, and with the expected duration and depth for the crossing of a Sun-like star by a hot super-Earth. Assuming the star's mass and radius to be 0.963+0.051 -- 0.029 M and 0.943 ? 0.010 R , the planet's mass, radius, and mean density are 8.63 ? 0.35 M {circled plus}, 2.00 ? 0.14 R {circled plus}, and 5.9+1.5 -- 1.1 g cm--3, respectively. The mean density is comparable to that of Earth, despite the greater mass and consequently greater compression of the interior of 55 Cnc e. This suggests a rock-iron composition supplemented by a significant mass of water, gas, or other light elements. Outside of transits, we detected a sinusoidal signal resembling the expected signal due to the changing illuminated phase of the planet, but with a full range (168 ? 70 ppm) too large to be reflected light or thermal emission. This signal has no straightforward interpretation and should be checked with further observations. The host star of 55 Cnc e is brighter than that of any other known transiting planet, which will facilitate future investigations.
Abstract
In order to explore how the ubiquitous short-term stochastic variability in the photometric observations of Wolf–Rayet (WR) stars is related to various stellar characteristics, we examined a ...sample of 50 Galactic WR stars using 122 lightcurves obtained by the BRIght Target Explorer-Constellation, Transiting Exoplanet Survey Satellite and Microvariability and Oscillations of Stars satellites. We found that the periodograms resulting from a discrete Fourier transform of all our detrended lightcurves are characterized by a forest of random peaks showing an increase in power starting from ∼0.5 day
−1
down to ∼0.1 day
−1
. After fitting the periodograms with a semi-Lorentzian function representing a combination of white and red noise, we investigated possible correlations between the fitted parameters and various stellar and wind characteristics. Seven correlations were observed, the strongest and only significant one being between the amplitude of variability,
α
0
, observed for hydrogen-free WR stars, while WNh stars exhibit correlations between
α
0
and the stellar temperature,
T
*
, and also between the characteristic frequency of the variations,
ν
char
, and both
T
*
and
v
∞
. We report that stars observed more than once show significantly different variability parameters, indicating an epoch-dependent measurement. We also find that the observed characteristic frequencies for the variations generally lie between
−
0.5
<
log
10
ν
char
<
0.5
, and that the values of the steepness of the amplitude spectrum are typically found in the range
−
0.1
<
log
10
γ
<
0.5
. We discuss various physical processes that can lead to this correlation.
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