852 research outputs found
Sun-like Stars Shed Light on Solar Climate Forcing
Recently published, precise stellar photometry of 72 Sun-like stars obtained
at the Fairborn Observatory between 1993 and 2017 is used to set limits on the
solar forcing of Earth's atmosphere of 4.5 W m since 1750. This
compares with the +2.2 1.1 W m IPCC estimate for anthropogenic
forcing. Three critical assumptions are made. In decreasing order of importance
they are: (a) most of the brightness variations occur within the average
time-series length of 17 years; (b) the Sun seen from the ecliptic
behaves as an ensemble of middle-aged solar-like stars; and (c) narrow-band
photometry in the Str\"omgren and bands are linearly proportional to
the total solar irradiance. Assumption (a) can best be relaxed and tested by
obtaining more photometric data of Sun-like stars, especially those already
observed. Eight stars with near-solar parameters have been observed from 1999,
and two since 1993. Our work reveals the importance of continuing and expanding
ground-based photometry, to complement expensive solar irradiance measurements
from space.Comment: 6 pages, 6 figures, accepted to The Astrophysical Journal Letter
Impact of Rubin Observatory LSST Template Acquisition Strategies on Early Science from the Transients and Variable Stars Science Collaboration: Non-time-critical Science Cases
Vera C. Rubin Observatory Legacy Survey of Space and Time, LSST, will revolutionize modern astronomy by producing an extremely deep (coadded depth ~27 mag) depth-limited survey of the entire southern sky (LSST Science Collaboration et al. 2009). The 8.4 m large-aperture, wide-field telescope, which is based in Cerro Pachón, will image the entire Southern sky every three nights in multiple bands (SDSS-u, g, r, i, z, y) and produce a fire-hose of data, 20 Tb each night, concluding in a 60 petabyte data set as the legacy of the 10 yr survey.
Extracting meaningful light curves from variable objects requires difference imaging to both identify variability and calibrate light curve data products. Templates, co-added groups of visits that act as an image of the "static" sky, are a key component of Difference Imaging Analysis (DIA) and as such are of paramount importance for all science that involves variable objects. As the "non-time-critical" science cases discussed here are mostly periodic, they generally do not depend upon the survey alert stream; however, templates are still crucial for performing science and calibrations during the first year. We provide recommendations for observing strategies for template acquisition starting from commissioning and through Year 1 of the survey
The spherical probe electric field and wave experiment
The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonlinear processes that result in acceleration of plasma, and the analysis of large scale phenomena where all four spacecraft are needed
The role of (de-)essentialisation within siting conflicts: an interdisciplinary approach
Large-scale renewable energy and associated technologies (RET), such as high voltage power lines (HVPL), often meet opposition from the local communities living nearby. Research has suggested that one of the main aspects that might contribute to this is the fact that RET are represented as industrial and urban, and thus, as having a different essence from rural landscapes, where they are usually deployed and which are represented as natural and unspoilt. However, this 'hypothesis' of landscape essentialisation shaping people's responses to RET has not been explicitly examined. By drawing upon research from Social Psychology and Human Geography on essentialisation, we will examine if and how landscape (de-)essentialisation plays a role in people's responses to RET. Namely, by examining it as a rhetorical construction that can be strategically used to negotiate and legitimize given relations with place and associated responses to RET.Focus groups were conducted in the UK and Norway with members of local communities to be affected by the construction of HVPLs that will connect to new low carbon energy technologies. Analyses show that participants present British and Norwegian rural landscapes in general and HVPL as having two different essences, which justifies opposition to those infrastructures. However, analyses also show that essentialisation of the countryside is strategically used. Namely, participants also present the countryside in the place where they live as having more of the essence of the British or Norwegian countryside than other areas of the UK and Norway. In turn, this allows them to legitimize claims that whereas HVPL are 'out of place' in the countryside in general, they are more so in the place where they live.The implications of these results for the definition of acceptable locations for RET and for research on people-place relations and responses to place change, are discussed.info:eu-repo/semantics/acceptedVersio
Photospheric and chromospheric magnetic activity of seismic solar analogs. Observational inputs on the solar/stellar connection from Kepler and Hermes
We identify a set of 18 solar analogs among the seismic sample of solar-like
stars observed by the Kepler satellite rotating between 10 and 40 days. This
set is constructed using the asteroseismic stellar properties derived using
either the global oscillation properties or the individual acoustic
frequencies. We measure the magnetic activity properties of these stars using
observations collected by the photometric Kepler satellite and by the
ground-based, high-resolution Hermes spectrograph mounted on the Mercator
telescope. The photospheric (Sph) and chromospheric (S index) magnetic activity
levels of these seismic solar analogs are estimated and compared in relation to
the solar activity. We show that the activity of the Sun is comparable to the
activity of the seismic solar analogs, within the maximum-to-minimum temporal
variations of the 11-year solar activity cycle 23. In agreement with previous
studies, the youngest stars and fastest rotators in our sample are actually the
most active. The activity of stars older than the Sun seems to not evolve much
with age. Furthermore, the comparison of the photospheric, Sph, with the
well-established chromospheric, S index, indicates that the Sph index can be
used to provide a suitable magnetic activity proxy which can be easily
estimated for a large number of stars from space photometric observations.Comment: Accepted for publication in A&
Lars Vegard:key communicator and pioneer crystallographer
The Norwegian physicist Lars Vegard studied with William H. Bragg in Leeds and then with Wilhelm Wien in Würzburg. There, in 1912, he heard a lecture by Max Laue describing the first X-ray diffraction experiments and took accurate notes which he promptly sent to Bragg. Although now remembered mainly for his work on the physics of the aurora borealis, Vegard also did important pioneering work in three areas of crystallography. He derived chemical insight from a series of related crystal structures that he determined, Vegard's Law relates the unit-cell dimensions of mixed crystals to those of the pure components, and he determined some of the first crystal structures of gases solidified at cryogenic temperatures
Magnetic variability in the young solar analog KIC 10644253: Observations from the Kepler satellite and the HERMES spectrograph
The continuous photometric observations collected by the Kepler satellite
over 4 years provide a whelm of data with an unequalled quantity and quality
for the study of stellar evolution of more than 200000 stars. Moreover, the
length of the dataset provide a unique source of information to detect magnetic
activity and associated temporal variability in the acoustic oscillations. In
this regards, the Kepler mission was awaited with great expectation. The search
for the signature of magnetic activity variability in solar-like pulsations
still remained unfruitful more than 2 years after the end of the nominal
mission. Here, however, we report the discovery of temporal variability in the
low-degree acoustic frequencies of the young (1 Gyr-old) solar analog KIC
10644253 with a modulation of about 1.5 years with significant temporal
variations along the duration of the Kepler observations. The variations are in
agreement with the derived photometric activity. The frequency shifts extracted
for KIC 10644253 are shown to result from the same physical mechanisms involved
in the inner sub-surface layers as in the Sun. In parallel, a detailed
spectroscopic analysis of KIC 10644253 is performed based on complementary
ground-based, high-resolution observations collected by the HERMES instrument
mounted on the MERCATOR telescope. Its lithium abundance and chromospheric
activity S-index confirm that KIC 10644253 is a young and more active star than
the Sun.Comment: Accepted for publication in A&A, 12 pages, 8 figure
In situ oligonucleotide synthesis on poly(dimethylsiloxane): a flexible substrate for microarray fabrication
In this paper, we demonstrate in situ synthesis of oligonucleotide probes on poly(dimethylsiloxane) (PDMS) microchannels through use of conventional phosphoramidite chemistry. PDMS polymer was moulded into a series of microchannels using standard soft lithography (micro-moulding), with dimensions <100 μm. The surface of the PDMS was derivatized by exposure to ultraviolet/ozone followed by vapour phase deposition of glycidoxypropyltrimethoxysilane and reaction with poly(ethylene glycol) spacer, resulting in a reactive surface for oligonucleotide coupling. High, reproducible yields were achieved for both 6mer and 21mer probes as assessed by hybridization to fluorescent oligonucleotides. Oligonucleotide surface density was comparable with that obtained on glass substrates. These results suggest PDMS as a stable and flexible alternative to glass as a suitable substrate in the fabrication and synthesis of DNA microarrays
Covariations of chromospheric and photometric variability of the young Sun analogue HD 30495: evidence for and interpretation of mid-term periodicities
This study reports the synchronization between the chromospheric and photometric variability at time-scale of about 1.6–1.8 yr as observed for the young, rapidly rotating solar analogue HD 30495. In addition, HD 30495 may be presenting evidence of surface differential rotation at time-scales of about 11 d and 21 d, as well as the sunspot-like decadal cycles at 11–12 yr or so. We apply a new gapped wavelet method of time–frequency analysis for studying the variability in a new composite of the chromospheric S-index (1967–2018) and the longest photometric Δ(b + y)/2 index (1993–2018). We discuss and interpret our results in relation to other observed mid-term periodicities roughly of the same time-scales that had been found recently from not only chromospheric and photospheric activity indices but also from coronal X-ray emissions as observed in a considerably large set of stellar samples including those young Sun analogues from the Kepler satellite project. Thus, there is an apparent universality of such mid-term activity modulation time-scales as this solar-stellar magnetic phenomenon is well observed directly for a host of solar activity related indices covering the photopsheric, chromospheric, coronal, and even the heliospheric (utilizing the measures of incoming galactic cosmic rays as a probe of activity variations) activity records. This is why we made a further attempt to interpret the results in search of a realistic generation mechanism as well as spatio-temporal persistency of the phenomenon under a wide scenario of dynamo simulations
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