94 research outputs found
Our Future Water Supply Needs Your Help Now
Not too long ago I floated on rivers for a living.
As a wilderness educator and whitewater river guide, I plied rafts through torrents of whitewater and along miles of placid riverscape. I drank from them, carefully decanting the layers of sediment collected over hundreds of miles. I slept on sandbars that stretched for hundreds of yards, as millions of gallons of water quietly shifted them down stream
The Effect to Human Performance and Wellbeing of Air Traffic Management Operational Staff Through the COVID-19 Pandemic
The Covid-19 pandemic reduced air traffic levels in Europe by up to 95% and the system had to respond quickly to preserve safety, maintain efficiency and performance. Operators were significantly affected both in terms of individual and team performance, as well as the longer-term impact to skills and attitudes. Human Performance data from Operators has been collected through this period. The impact to safety risk due to underloading of human performance, as well as the longer-term impact to wellbeing and competencies of operators was analysed. The largest impact to staff was reduced performance because of anxiety and uncertainty around the future as well as changing job roles. Results also demonstrated the positive effect of systems already place to protect human performance
Connecting to the Natural World is Important to Our Personal Development
I have vivid memories from my childhood of traipsing through the woods near our house, a forest that had yet to be razed and developed, as it would be decades later. The pines and maples grew thick and laid down a soft bed of leaves to walk along
The Earth Does Not Need Us, but We Most Certainly Need a Healthy Planet
A few weeks ago I stood at Yaki Point on the edge of the Grand Canyon watching the sunset. A cold desert wind rushed up the cliff sides, sucking the last remaining heat from the sandstone below. The rustle of pinyons and junipers gave sound to the silence of the setting sun
Now More Than Ever We Need to Protect Our Public Lands
I spent nearly a year of my life walking within the borders of what is now designated as the Bears Ears National Monument in southern Utah. I covered hundreds of miles hiking across plateaus, climbing into canyons, and scrambling up cliff walls as a wilderness educator, guide and recreationist. I stumbled upon countless Native American artifacts and sites, giving me a glimpse into the ancient history of native people of the region. My first steps on the land were as a student and eventually I came full circle and became an educator
Help is Here if You Are Experiencing the \u27Fear of Missing Out\u27
Technology is an amazing thing
The Missing Luminous Blue Variables and the Bistability Jump
We discuss an interesting feature of the distribution of luminous blue
variables on the H-R diagram, and we propose a connection with the bistability
jump in the winds of early-type supergiants. There appears to be a deficiency
of quiescent LBVs on the S Dor instability strip at luminosities between log
L/Lsun = 5.6 and 5.8. The upper boundary, is also where the
temperature-dependent S Dor instability strip intersects the bistability jump
at about 21,000 K. Due to increased opacity, winds of early-type supergiants
are slower and denser on the cool side of the bistability jump, and we
postulate that this may trigger optically-thick winds that inhibit quiescent
LBVs from residing there. We conduct numerical simulations of radiation-driven
winds for a range of temperatures, masses, and velocity laws at log L/Lsun=5.7
to see what effect the bistability jump should have. We find that for
relatively low stellar masses the increase in wind density at the bistability
jump leads to the formation of a modest to strong pseudo photosphere -- enough
to make an early B-type star appear as a yellow hypergiant. Thus, the proposed
mechanism will be most relevant for LBVs that are post-red supergiants. Yellow
hypergiants like IRC+10420 and rho Cas occupy the same luminosity range as the
``missing'' LBVs, and show apparent temperature variations at constant
luminosity. If these yellow hypergiants do eventually become Wolf-Rayet stars,
we speculate that they may skip the normal LBV phase, at least as far as their
apparent positions on the HR diagram are concerned.Comment: 20 pages, 4 figs, accepted by Ap
Red supergiants as potential Type IIn supernova progenitors: Spatially resolved 4.6 micron CO emission around VY CMa and Betelgeuse
We present high-resolution 4.6micron CO spectra of the circumstellar
environments of two RSGs that are potential SN progenitors: Betelgeuse and VY
CMa. Around Betelgeuse, 12CO emission within 3arcsec follows a mildly clumpy
but otherwise spherical shell, smaller than its 55arcsec shell in KI
lambda7699. In stark contrast, 4.6micron CO emission around VY CMa is
coincident with bright KI in its clumpy asymmetric reflection nebula, within
5arcsec of the star. Our CO data reveal redshifted features not seen in KI
spectra of VY CMa, indicating a more isotropic distribution of gas punctuated
by randomly distributed asymmetric clumps. The relative CO and KI distribution
in Betelgeuse arises from ionization effects within a steady wind, whereas in
VY CMa, KI is emitted from skins of CO cloudlets resulting from episodic mass
ejections 500--1000 yr ago. In both cases, CO and KI trace potential pre-SN
circumstellar matter: we conclude that an extreme RSG like VY CMa might produce
a Type IIn event like SN1988Z if it were to explode in its current state, but
Betelgeuse will not. VY CMa demonstrates that LBVs are not necessarily the only
progenitors of SNe IIn, but it underscores the requirement that SNe IIn suffer
enhanced episodic mass loss shortly before exploding.Comment: 16 pages, AJ accepte
Nearby Supernova Rates from the Lick Observatory Supernova Search. II. The Observed Luminosity Functions and Fractions of Supernovae in a Complete Sample
This is the second paper of a series in which we present new measurements of
the observed rates of supernovae (SNe) in the local Universe, determined from
the Lick Observatory Supernova Search (LOSS). In this paper, a complete SN
sample is constructed, and the observed (uncorrected for host-galaxy
extinction) luminosity functions (LFs) of SNe are derived. These LFs solve two
issues that have plagued previous rate calculations for nearby SNe: the
luminosity distribution of SNe and the host-galaxy extinction. We select a
volume-limited sample of 175 SNe, collect photometry for every object, and fit
a family of light curves to constrain the peak magnitudes and light-curve
shapes. The volume-limited LFs show that they are not well represented by a
Gaussian distribution. There are notable differences in the LFs for galaxies of
different Hubble types (especially for SNe Ia). We derive the observed
fractions for the different subclasses in a complete SN sample, and find
significant fractions of SNe II-L (10%), IIb (12%), and IIn (9%) in the SN II
sample. Furthermore, we derive the LFs and the observed fractions of different
SN subclasses in a magnitude-limited survey with different observation
intervals, and find that the LFs are enhanced at the high-luminosity end and
appear more "standard" with smaller scatter, and that the LFs and fractions of
SNe do not change significantly when the observation interval is shorter than
10 days. We also discuss the LFs in different galaxy sizes and inclinations,
and for different SN subclasses. Some notable results are ... (abridged).Comment: Minor revisions after the referee's report. MNRAS accepted (Paper II
of a series). For high-res figures, latex source, landscape tables, and
online data, please visit http://astro.berkeley.edu/~weidong/rate
Chandra spectroscopy of the hot star beta Crucis and the discovery of a pre-main-sequence companion
In order to test the O star wind-shock scenario for X-ray production in less
luminous stars with weaker winds, we made a pointed 74 ks observation of the
nearby early B giant, beta Cru (B0.5 III), with the Chandra HETGS. We find that
the X-ray spectrum is quite soft, with a dominant thermal component near 3
million K, and that the emission lines are resolved but quite narrow, with
half-widths of 150 km/s. The forbidden-to-intercombination line ratios of Ne IX
and Mg XI indicate that the hot plasma is distributed in the wind, rather than
confined near the photosphere. It is difficult to understand the X-ray data in
the context of the standard wind-shock paradigm for OB stars, primarily because
of the narrow lines, but also because of the high X-ray production efficiency.
A scenario in which the bulk of the outer wind is shock heated is broadly
consistent with the data, but not very well motivated theoretically. It is
possible that magnetic channeling could explain the X-ray properties, although
no field has been detected on beta Cru. We detected periodic variability in the
hard (hnu > 1 keV) X-rays, modulated on the known optical period of 4.58 hours,
which is the period of the primary beta Cep pulsation mode for this star. We
also have detected, for the first time, an apparent companion to beta Cru at a
projected separation of 4 arcsec. This companion was likely never seen in
optical images because of the presumed very high contrast between it and beta
Cru in the optical. However, the brightness contrast in the X-ray is only 3:1,
which is consistent with the companion being an X-ray active low-mass
pre-main-sequence star. The companion's X-ray spectrum is relatively hard and
variable, as would be expected from a post T Tauri star.Comment: Accepted for publication in MNRAS; 19 pages, 15 figures, some in
color; version with higher-resolution figures available at
http://astro.swarthmore.edu/~cohen/papers/bcru_mnras2008.pd
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