728 research outputs found
A search for p-modes and other variability in the binary system 85 Pegasi using MOST photometry
Context: Asteroseismology has great potential for the study of metal-poor
stars due to its sensitivity to determine stellar ages. Aims: Our goal was to
detect p-mode oscillations in the metal-poor sub-dwarf 85 Peg A and to search
for other variability on longer timescales. Methods: We have obtained
continuous high-precision photometry of the binary system 85 Pegasi with the
MOST space telescope in two seasons (2005 & 2007). Furthermore, we redetermined
vsini for 85 Peg A using high resolution spectra obtained through the ESO
archive, and used photometric spot modeling to interpret long periodic
variations. Results: Our frequency analysis yields no convincing evidence for
p-modes significantly above a noise level of 4 ppm. Using simulated p-mode
patterns we provide upper RMS amplitude limits for 85 Peg A. The light curve
shows evidence for variability with a period of about 11 d and this periodicity
is also seen in the follow up run in 2007; however, as different methods to
remove instrumental trends in the 2005 run yield vastly different results, the
exact shape and periodicity of the 2005 variability remain uncertain. Our
re-determined vsini value for 85 Peg A is comparable to previous studies and we
provide realistic uncertainties for this parameter. Using these values in
combination with simple photometric spot models we are able to reconstruct the
observed variations. Conclusions: The null-detection of p-modes in 85 Peg A is
consistent with theoretical values for pulsation amplitudes in this star. The
detected long-periodic variation must await confirmation by further
observations with similar or better precision and long-term stability. If the
11 d periodicity is real, rotational modulation of surface features on one of
the components is the most likely explanation.Comment: 11 pages, 9 figures, accepted for publication in A&
Impact of rural-to-urban migration on family and gender values in China
Drawing on data from the 2006 China General Social Survey, propensity score matching was used to investigate the impact of rural-to-urban migration on family and gender values in China at distinct stages of the migratory process. Little evidence of ideational difference is found between rural natives who intend to migrate to urban areas and those who intend to stay in rural China. However, rural-to-urban migration has significant, diverse and gendered impacts on various domains of family and gender values at distinct migratory stages. The results also cast light on the important roles played by hukou status and various forms of socioeconomic and cultural status, such as education and occupation, in mediating the impact of rural-to-urban migration on family and gender values. The ideational impact of migration is shown to be shaped by China’s distinctive institutional features
Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy
The transit of Venus in 2004 offered the rare possibility to remotely sense a
well-known planetary atmosphere using ground-based observations for absorption
spectroscopy. Transmission spectra of Venus' atmosphere were obtained in the
near infrared using the Vacuum Tower Telescope (VTT) in Tenerife. Since the
instrument was designed to measure the very bright photosphere of the Sun,
extracting Venus' atmosphere was challenging. CO_2 absorption lines could be
identified in the upper Venus atmosphere. Moreover, the relative abundance of
the three most abundant CO_2 isotopologues could be determined. The
observations resolved Venus' limb, showing Doppler-shifted absorption lines
that are probably caused by high-altitude winds.
This paper illustrates the ability of ground-based measurements to examine
atmospheric constituents of a terrestrial planet atmosphere which might be
applied in future to terrestrial extrasolar planets.Comment: 7 pages, 5 figures, 1 tabl
MOST detects variability on tau Bootis possibly induced by its planetary companion
(abridged) There is considerable interest in the possible interaction between
parent stars and giant planetary companions in 51 Peg-type systems. We
demonstrate from MOST satellite photometry and Ca II K line emission that there
has been a persistent, variable region on the surface of tau Boo A which
tracked its giant planetary companion for some 440 planetary revolutions and
lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves
are folded on a range of periods centered on the planetary orbital period and
phase dependent variability is quantified by Fourier methods and by the mean
absolute deviation (MAD) of the folded data for both the photometry and the Ca
II K line reversals. The region varies in brightness on the time scale of a
rotation by ~1 mmag. In 2004 it resembled a dark spot of variable depth, while
in 2005 it varied between bright and dark. Over the 123 planetary orbits
spanned by the photometry the variable region detected in 2004 and in 2005 are
synchronised to the planetary orbital period within 0.0015 d. The Ca II K line
in 2001, 2002 and 2003 also shows enhanced K-line variability centered on
phi=0.8, extending coverage to some 440 planetary revolutions. The apparently
constant rotation period of the variable region and its rapid variation make an
explanation in terms of conventional star spots unlikely. The lack of
complementary variability at phi=0.3 and the detection of the variable region
so far in advance of the sub-planetary point excludes tidal excitation, but the
combined photometric and Ca II K line reversal results make a good case for an
active region induced magnetically on the surface of tau Boo A by its planetary
companion.Comment: 7 pages, 7 figures; accepted for publication in A&
Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters
Bisectors of the HARPS cross-correlation function (CCF) can discern between
planetary radial-velocity (RV) signals and spurious RV signals from stellar
magnetic activity variations. However, little is known about the effects of the
stellar atmosphere on CCF bisectors or how these effects vary with spectral
type and luminosity class. Here we investigate the variations in the shapes of
HARPS CCF bisectors across the HR diagram in order to relate these to the basic
stellar parameters, surface gravity and temperature. We use archive spectra of
67 well studied stars observed with HARPS and extract mean CCF bisectors. We
derive previously defined bisector measures (BIS, v_bot, c_b) and we define and
derive a new measure called the CCF Bisector Span (CBS) from the minimum radius
of curvature on direct fits to the CCF bisector. We show that the bisector
measures correlate differently, and non-linearly with log g and T_eff. The
resulting correlations allow for the estimation of log g and T_eff from the
bisector measures. We compare our results with 3D stellar atmosphere models and
show that we can reproduce the shape of the CCF bisector for the Sun.Comment: 13 pages, 20 figures. Accepted by A&
Why growth equals power - and why it shouldn't : constructing visions of China
When discussing the success of China's transition from socialism, there is a tendency to focus on growth figures as an indication of performance. Whilst these figures are
indeed impressive, we should not confuse growth with development and assume that the former necessarily automatically generates the latter. Much has been done to
reduce poverty in China, but the task is not as complete as some observers would suggest; particularly in terms of access to health, education and welfare, and also in
dealing with relative (rather than absolute) depravation and poverty. Visions of China have been constructed that exaggerate Chinese development and power in the global
system partly to serve political interests, but partly due to the failure to consider the relationship between growth and development, partly due to the failure to disaggregate
who gets what in China, and partly due to the persistence of inter-national conceptions of globalised production, trade, and financial flows
Family and Gender Values in China
Previous research has reported on structural changes in Chinese families. However, questions remain as to whether/how social change has influenced family and gender values and how this differs across generations, regions, and gender in China. Drawing on 2006 data from the China General Social Survey, we find that values pertaining to filial piety are traditional, whereas patrilineal and gender values are less traditional. Historic events/policies provide the context for how social change can shape differential generational, geographic, and gender perspectives. Our hypothesis that generation, region, and gender associations will differ across the various ideational domains is confirmed. We find significant interaction effects in how generation and geography differ by gender in patrilineal, filial piety, and gender values; and higher education erodes patrilineal and traditional gender values but enhances filial piety. Such findings indicate that family values should be understood in the specific sociocultural contexts governing Chinese families across time and place.</jats:p
Preparation of Kepler lightcurves for asteroseismic analyses
The Kepler mission is providing photometric data of exquisite quality for the
asteroseismic study of different classes of pulsating stars. These analyses
place particular demands on the pre-processing of the data, over a range of
timescales from minutes to months. Here, we describe processing procedures
developed by the Kepler Asteroseismic Science Consortium (KASC) to prepare
light curves that are optimized for the asteroseismic study of solar-like
oscillating stars in which outliers, jumps and drifts are corrected.Comment: Accepted for publication in MNRAS. 5 pages, 2 figure
Transiting Disintegrating Planetary Debris around WD 1145+017
More than a decade after astronomers realized that disrupted planetary
material likely pollutes the surfaces of many white dwarf stars, the discovery
of transiting debris orbiting the white dwarf WD 1145+017 has opened the door
to new explorations of this process. We describe the observational evidence for
transiting planetary material and the current theoretical understanding (and in
some cases lack thereof) of the phenomenon.Comment: Invited review chapter. Accepted March 23, 2017 and published October
7, 2017 in the Handbook of Exoplanets. 15 pages, 10 figure
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