1,673 research outputs found
Age spreads and the temperature dependence of age estimates in Upper Sco
Past estimates for the age of the Upper Sco Association are typically 11-13
Myr for intermediate-mass stars and 4-5 Myr for low-mass stars. In this study,
we simulate populations of young stars to investigate whether this apparent
dependence of estimated age on spectral type may be explained by the star
formation history of the association. Solar and intermediate mass stars begin
their pre-main sequence evolution on the Hayashi track, with fully convective
interiors and cool photospheres. Intermediate mass stars quickly heat up and
transition onto the radiative Henyey track. As a consequence, for clusters in
which star formation occurs on a similar timescale as the transition from a
convective to a radiative interior, discrepancies in ages will arise when ages
are calculated as a function of temperature instead of mass. Simple simulations
of a cluster with constant star formation over several Myr may explain about
half of the difference in inferred ages versus photospheric temperature;
speculative constructions that consist of a constant star formation followed by
a large supernova-driven burst could fully explain the differences, including
those between F and G stars where evolutionary tracks may be more accurate. The
age spreads of low-mass stars predicted from these prescriptions for star
formation are consistent with the observed luminosity spread of Upper Sco. The
conclusion that a lengthy star formation history will yield a temperature
dependence in ages is expected from the basic physics of pre-main sequence
evolution and is qualitatively robust to the large uncertainties in pre-main
sequence evolutionary models.Comment: 13 pages, accepted by Ap
Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect
We discuss different physical effects related to the uniform acceleration of
atoms in vacuum, in the framework of quantum electrodynamics. We first
investigate the van der Waals/Casimir-Polder dispersion and resonance
interactions between two uniformly accelerated atoms in vacuum. We show that
the atomic acceleration significantly affects the van der Waals force, yielding
a different scaling of the interaction with the interatomic distance and an
explicit time dependence of the interaction energy. We argue how these results
could allow for an indirect detection of the Unruh effect through dispersion
interactions between atoms. We then consider the resonance interaction between
two accelerated atoms, prepared in a correlated Bell-type state, and
interacting with the electromagnetic field in the vacuum state, separating
vacuum fluctuations and radiation reaction contributions, both in the
free-space and in the presence of a perfectly reflecting plate. We show that
nonthermal effects of acceleration manifest in the resonance interaction,
yielding a change of the distance dependence of the resonance interaction
energy. This suggests that the equivalence between temperature and acceleration
does not apply to all radiative properties of accelerated atoms. To further
explore this aspect, we evaluate the resonance interaction between two atoms in
non inertial motion in the coaccelerated (Rindler) frame and show that in this
case the assumption of an Unruh temperature for the field is not required for a
complete equivalence of locally inertial and coaccelerated points of views.Comment: 8 pages, Proceedings of the Eighth International Workshop DICE 2016
Spacetime - Matter - Quantum Mechanic
Gender in the Construction Industry: Literature Review and Comparative Survey of Men’s and Women’s Perceptions in UK Construction Consultancies
For more than two decades, construction industry leaders have made attempts to attract more women into professional roles to ease skills shortages and diversify the workforce. However, the number of women working in the industry has not improved significantly. This paper reviews previous literature on gender diversity in the construction industry and disseminates findings from a survey that investigated whether there are significant differences in self-perception between men and women in construction consultancies operating in the United Kingdom (UK). The survey questionnaire was completed by 60 men and 57 women. Analysis of the results confirmed that women tend to follow “zig-zag” career development paths and that “global self-worth” of women over the age of 40 is the lowest among all ages. However, little variation was found on initiatives to improve retention of women in construction consultancies. The results reveal that both men and women regarded improved flexible working-arrangements, transparent promotion criteria, return-to-work training, and outreach programs to schools the most crucial initiatives to retain women. This reinforces the call for organizations to introduce innovative strategic plans to change the masculine culture of the construction profession and modernize working practice away from the existing rather outdated traditional structure
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New Insights into the Charge-Transfer-to-Solvent Spectrum of Aqueous Iodide: Surface versus Bulk.
Liquid phase charge-transfer-to-solvent (CTTS) transitions are important, as they serve as photochemical routes to solvated electrons. In this work, broadband deep-ultraviolet electronic sum frequency generation (DUV-ESFG) and two-photon absorption (2PA) spectroscopic techniques were used to assign and compare the nature of the aqueous iodide CTTS excitations at the air/water interface and in bulk solution. In the one-photon absorption (1PA) spectrum, excitation to the 6s Rydberg-like orbital (5p → 6s) gives rise to a pair of spin-orbit split iodine states, 2P3/2 and 2P1/2. In the 2PA spectra, the lower-energy 2P3/2 peak is absent and the observed 2PA peak, which is ∼0.14 eV blue-shifted relative to the upper 2P1/2 CTTS peak seen in 1PA, arises from 5p → 6p electronic promotion. The band observed in the ESFG spectrum is attributed to mixing of excited states involving 5p → 6p and 5p → 6s promotions caused by both vibronic coupling and the external electric field generated by asymmetric interfacial solvation
WISE Circumstellar Disks in the Young Sco-Cen Association
We present an analysis of the WISE photometric data for 829 stars in the
Sco-Cen OB2 association, using the latest high-mass membership probabilities.
We detect infrared excesses associated with 135 BAF-type stars, 99 of which are
secure Sco-Cen members. There is a clear increase in excess fraction with
membership probability, which can be fitted linearly. We infer that 41+-5% of
Sco-Cen OB2 BAF stars to have excesses, while the field star excess fraction is
consistent with zero. This is the first time that the probability of
non-membership has been used in the calculation of excess fractions for young
stars. We do not observe any significant change in excess fraction between the
three subgroups. Within our sample, we have observed that B-type association
members have a significantly smaller excess fraction than A and F-type
association members.Comment: 5 Pages, 3 figure, 4 tables. Complete table 1 included. Accepted to
MNRAS Letter
The Mass-Radius Relation Of Young Stars. I. Usco 5, An M4.5 Eclipsing Binary In Upper Scorpius Observed By K2
We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M-tot sin(i) = 0.64M(circle dot)), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M-A = 0.329 +/- 0.002 M-circle dot, R-A = 0.834 +/- 0.006 R-circle dot, M-B = 0.317 +/- 0.002 M-circle dot, and R-B = 0.810 +/- 0.006 R-circle dot. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%-50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT-T-eff scale. The simplest modification to the models (changing T-eff to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (tau similar to 11 Myr).NASA Science Mission directorateW. M. Keck FoundationAstronom
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