1,935 research outputs found
Teaching interdisciplinary sustainability science teamwork skills to graduate students using in-person and web-based interactions
Interdisciplinary sustainability science teamwork skills are essential for addressing the world’s most pressing and complex sustainability problems, which inherently have social, natural, and engineering science dimensions. Further, because sustainability science problems exist at global scales, interdisciplinary science teams will need to consist of international members who communicate and work together effectively. Students trained in international interdisciplinary science skills will be able to hit the ground running when they obtain jobs requiring them to tackle sustainability problems. While many universities now have sustainability science programs, few offer courses that are interdisciplinary and international in scope. In the fall semester of 2013, we piloted a course for graduate students entitled “Principles of Interdisciplinary Sustainability Research” at Michigan Technological University. This course was part of our United States National Science Foundation Partnerships in International Research and Education project on bioenergy development impacts across the Americas. In this case study, we describe the course development and implementation, share critical insights from our experience teaching the course and student learning outcomes, and give recommendations for future similar course
Constraints of a pulsation frequency on stellar parameters in the eclipsing spectroscopic binary system: V577 Oph
We present a preliminary spectroscopic analysis of the binary system V577Oph,
observed during the summer of 2007 on the 2.6m NOT telescope on La Palma. We
have obtained time series spectroscopic observations, which show clear binary
motion as well as radial velocity variations due to pulsation in the primary
star. By modelling the radial velocities we determine a full orbital solution
of the system, which yields M_A sin^3 i = 1.562 +/- 0.012 M_solar and M_B sin^3
i = 1.461 +/- 0.020 M_solar. An estimate of inclination from photometry yields
a primary mass of 1.6 M_solar. Using this derived mass, and the known pulsation
frequency we can impose a lower limit of 1 Gyr on the age of the system, and
constrain the parameters of the oscillation mode. We show that with further
analysis of the spectra (extracting the atmospheric parameters), tighter
constraints could be imposed on the age, metallicity and the mode parameters.
This work emphasizes the power that a single pulsation frequency can have for
constraining stellar parameters in an eclipsing binary system.Comment: Accepted by A
Analysis of IUE spectra of helium-rich white dwarf stars
We studied the class of DB white dwarf stars, using re-calibrated UV spectra
for thirty four DBs obtained with the IUE satellite. By comparing the observed
energy distributions with model atmospheres, we simultaneously determine
spectroscopic distances (d), effective temperature (Teff), and surface
gravities (log g). Using parallax measurements and previous determinations of
Teff and log g from optical spectra, we can study whether the atmospheres of
eleven DB stars are consistent with pure He or have a small amount of H
contamination. We also report on our observations of seventeen stars with Teff
close to the DB instability strip through time series photometry and found them
to be non variable within our detection limits.Comment: 8 pages, 5 figure
The Three Most Important Factors Every Orientation and Mobility Instructor Needs to Know when Working with Guide Dogs
Climate change adaptation strategies and approaches for outdoor recreation
Climate change will alter opportunities and demand for outdoor recreation through altered winter weather conditions and season length, climate-driven changes in user preferences, and damage to recreational infrastructure, among other factors. To ensure that outdoor recreation remains sustainable in the face of these challenges, natural resource managers may need to adapt their recreation management. One of the major challenges of adapting recreation to climate change is translating broad concepts into specific, tangible actions. Using a combination of in-depth interviews of recreational managers and a review of peer-reviewed literature and government reports, we developed a synthesis of impacts, strategies, and approaches, and a tiered structure that organizes this information. Six broad climate adaptation strategies and 25 more specific approaches were identified and organized into a “recreation menu”. The recreation menu was tested with two national forests in the US in multi-day workshops designed to integrate these concepts into real-world projects that were at the beginning stages of the planning process. We found that the recreation menu was broad yet specific enough to be applied to recreation-focused projects with different objectives and climate change impacts. These strategies and approaches serve as stepping stones to enable natural resource and recreation managers to translate broad concepts into targeted and prescriptive actions for implementing adaptation
Massive pulsating stars observed by BRITE-Constellation. I. The triple system Beta Centauri (Agena)
This paper aims to precisely determine the masses and detect pulsation modes
in the two massive components of Beta Cen with BRITE-Constellation photometry.
In addition, seismic models for the components are considered and the effects
of fast rotation are discussed. This is done to test the limitations of seismic
modeling for this very difficult case. A simultaneous fit of visual and
spectroscopic orbits is used to self-consistently derive the orbital
parameters, and subsequently the masses, of the components. The derived masses
are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the
wider, A - B system, presently approaching periastron passage, are constrained.
Analysis of the combined blue- and red-filter BRITE-Constellation photometric
data of the system revealed the presence of 19 periodic terms, of which eight
are likely g modes, nine are p modes, and the remaining two are combination
terms. It cannot be excluded that one or two low-frequency terms are rotational
frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB
hybrids. An attempt to use the apparent changes of frequency to distinguish
which modes originate in which component did not succeed, but there is
potential for using this method when more BRITE data become available. Agena
seems to be one of very few rapidly rotating massive objects with rich p- and
g-mode spectra, and precisely known masses. It can therefore be used to gain a
better understanding of the excitation of pulsations in relatively rapidly
rotating stars and their seismic modeling. Finally, this case illustrates the
potential of BRITE-Constellation data for the detection of rich-frequency
spectra of small-amplitude modes in massive pulsating stars.Comment: 17 pages (with Appendix), 15 figures, accepted for publication in A&
The BRITE-Constellation Nanosatellite Space Mission And Its First Scientific Results
The BRIght Target Explorer (BRITE) Constellation is the first nanosatellite
mission applied to astrophysical research. Five satellites in low-Earth orbits
perform precise optical two-colour photometry of the brightest stars in the
night sky. BRITE is naturally well suited for variability studies of hot stars.
This contribution describes the basic outline of the mission and some initial
problems that needed to be overcome. Some information on BRITE data products,
how to access them, and how to join their scientific exploration is provided.
Finally, a brief summary of the first scientific results obtained by BRITE is
given.Comment: 5 pages, 1 figure, to appear in the proceedings of "Seismology of the
Sun and the Distant Stars 2016. Using Today's Successes to Prepare the
Future. Joint TASC2/KASC9 Workshop - SPACEINN/HELAS8 Conference", ed. M. J.
P. F. G. Monteir
Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field
We used extensive ground-based multisite and archival spectroscopy to derive
observational constraints for a seismic modelling of the magnetic beta Cep star
V2052 Ophiuchi. The line-profile variability is dominated by a radial mode
(f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two
non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are
also detected. The four periodicities that we found are the same as the ones
discovered from a companion multisite photometric campaign (Handler et al.
2012) and known in the literature. Using the photometric constraints on the
degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde
modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for
the mass (M \in [8.2,9.6] M_o) and central hydrogen abundance (X_c \in
[0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and
n_3=-2, and to derive an equatorial rotation velocity v_eq \in [71,75] km
s^{-1}. The model parameters are in full agreement with the effective
temperature and surface gravity deduced from spectroscopy. Only models with no
or mild core overshooting (alpha_ov \in [0,0.15] local pressure scale heights)
can account for the observed properties. Such a low overshooting is opposite to
our previous modelling results for the non-magnetic beta Cep star theta Oph
having very similar parameters, except for a slower surface rotation rate. We
discuss whether this result can be explained by the presence of a magnetic
field in V2052 Oph that inhibits mixing in its interior.Comment: 12 pages, 6 figures and 5 tables; accepted for publication in MNRAS
on 2012 August 1
Asteroseismology of the Beta Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification
We report a multisite photometric campaign for the Beta Cephei star 12
Lacertae. 750 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with 9 telescopes
during 190 nights. Our frequency analysis results in the detection of 23
sinusoidal signals in the light curves. Eleven of those correspond to
independent pulsation modes, and the remainder are combination frequencies. We
find some slow aperiodic variability such as that seemingly present in several
Beta Cephei stars. We perform mode identification from our colour photometry,
derive the spherical degree l for the five strongest modes unambiguously and
provide constraints on l for the weaker modes. We find a mixture of modes of 0
<= l <= 4. In particular, we prove that the previously suspected rotationally
split triplet within the modes of 12 Lac consists of modes of different l;
their equal frequency splitting must thus be accidental.
One of the periodic signals we detected in the light curves is argued to be a
linearly stable mode excited to visible amplitude by nonlinear mode coupling
via a 2:1 resonance. We also find a low-frequency signal in the light
variations whose physical nature is unclear; it could be a parent or daughter
mode resonantly coupled. The remaining combination frequencies are consistent
with simple light-curve distortions.
The range of excited pulsation frequencies of 12 Lac may be sufficiently
large that it cannot be reproduced by standard models. We suspect that the star
has a larger metal abundance in the pulsational driving zone, a hypothesis also
capable of explaining the presence of Beta Cephei stars in the LMC.Comment: 12 pages, 7 figures, MNRAS, in pres
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