37 research outputs found
Physical Conditions in the Narrow-Line Region of Markarian 3. I. Observational Results
We use Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS)
longslit low-resolution spectroscopy from 1150A to 10,300A to study the
physical conditions in the narrow-line region (NLR) of the Seyfert 2 galaxy
Markarian 3. We find from the HeII 1640/4686 line ratio and the Balmer
decrement that the extinction within Markarian 3 along the line-of-sight to the
NLR is best characterized by a Large Magellanic Cloud (LMC) type extinction
curve. We observe an extinction gradient increasing from west to east along the
STIS slit in both line and continuum emission. We infer from this gradient that
the host galaxy disk is tilted towards the observer in the east: the
line-of-sight to the eastern emission-line cone intersects more dust in the
plane of the galaxy than that to the western cone. We model the observed
continuum as a combination of reddened host galaxy light from an old stellar
population, reddened H+ and He++ recombination continua, and less reddened
scattered light from the central engine with spectral index alpha=1 (L(nu)
proportional to nu^(-alpha)). The host galaxy to scattered-light ratio is
estimated to be 3:1 at 8125 A in 0.1 X 1.8 square-arcsecond aperture. We
estimate that the amount of intrinsic non-ionizing UV continuum scattered into
our line-of-sight is 0.04%. This is consistent with our estimate of the
scattering fraction for broad CIV 1548,1551 emission.Comment: 57 pages, 21 Figures; LaTeX; accepted for publication in Ap
Small Platforms, High Return: The Need to Enhance Investment in Small Satellites for Focused Science, Career Development, and Improved Equity
In the next decade, there is an opportunity for very high return on
investment of relatively small budgets by elevating the priority of smallsat
funding in heliophysics. We've learned in the past decade that these missions
perform exceptionally well by traditional metrics, e.g., papers/year/\$M
(Spence et al. 2022 -- arXiv:2206.02968). It is also well established that
there is a "leaky pipeline" resulting in too little diversity in leadership
positions (see the National Academies Report at
https://www.nationalacademies.org/our-work/increasing-diversity-in-the-leadership-of-competed-space-missions).
Prioritizing smallsat funding would significantly increase the number of
opportunities for new leaders to learn -- a crucial patch for the pipeline and
an essential phase of career development. At present, however, there are far
more proposers than the available funding can support, leading to selection
ratios that can be as low as 6% -- in the bottom 0.5th percentile of selection
ratios across the history of ROSES. Prioritizing SmallSat funding and
substantially increasing that selection ratio are the fundamental
recommendations being made by this white paper.Comment: White paper submitted to the Decadal Survey for Solar and Space
Physics (Heliophysics) 2024-2033; 6 pages, 1 figur
Energetic electron precipitation driven by electromagnetic ion cyclotron waves from ELFIN's low altitude perspective
We review comprehensive observations of electromagnetic ion cyclotron (EMIC)
wave-driven energetic electron precipitation using data from the energetic
electron detector on the Electron Losses and Fields InvestigatioN (ELFIN)
mission, two polar-orbiting low-altitude spinning CubeSats, measuring 50-5000
keV electrons with good pitch-angle and energy resolution. EMIC wave-driven
precipitation exhibits a distinct signature in energy-spectrograms of the
precipitating-to-trapped flux ratio: peaks at 0.5 MeV which are abrupt (bursty)
with significant substructure (occasionally down to sub-second timescale).
Multiple ELFIN passes over the same MLT sector allow us to study the spatial
and temporal evolution of the EMIC wave - electron interaction region. Using
two years of ELFIN data, we assemble a statistical database of 50 events of
strong EMIC wave-driven precipitation. Most reside at L=5-7 at dusk, while a
smaller subset exists at L=8-12 at post-midnight. The energies of the
peak-precipitation ratio and of the half-peak precipitation ratio (our proxy
for the minimum resonance energy) exhibit an L-shell dependence in good
agreement with theoretical estimates based on prior statistical observations of
EMIC wave power spectra. The precipitation ratio's spectral shape for the most
intense events has an exponential falloff away from the peak (i.e., on either
side of 1.45 MeV). It too agrees well with quasi-linear diffusion theory based
on prior statistics of wave spectra. Sub-MeV electron precipitation observed
concurrently with strong EMIC wave-driven 1MeV precipitation has a spectral
shape that is consistent with efficient pitch-angle scattering down to 200-300
keV by much less intense higher frequency EMIC waves. These results confirm the
critical role of EMIC waves in driving relativistic electron losses. Nonlinear
effects may abound and require further investigation
The James Webb Space Telescope Mission
Twenty-six years ago a small committee report, building on earlier studies,
expounded a compelling and poetic vision for the future of astronomy, calling
for an infrared-optimized space telescope with an aperture of at least .
With the support of their governments in the US, Europe, and Canada, 20,000
people realized that vision as the James Webb Space Telescope. A
generation of astronomers will celebrate their accomplishments for the life of
the mission, potentially as long as 20 years, and beyond. This report and the
scientific discoveries that follow are extended thank-you notes to the 20,000
team members. The telescope is working perfectly, with much better image
quality than expected. In this and accompanying papers, we give a brief
history, describe the observatory, outline its objectives and current observing
program, and discuss the inventions and people who made it possible. We cite
detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space
Telescope Overview, 29 pages, 4 figure
The ELFIN mission
The Electron Loss and Fields Investigation with a Spatio-Temporal Ambiguity-Resolving option (ELFIN-STAR, or heretoforth simply: ELFIN) mission comprises two identical 3-Unit (3U) CubeSats on a polar (∼93∘ inclination), nearly circular, low-Earth (∼450 km altitude) orbit. Launched on September 15, 2018, ELFIN is expected to have a >2.5 year lifetime. Its primary science objective is to resolve the mechanism of storm-time relativistic electron precipitation, for which electromagnetic ion cyclotron (EMIC) waves are a prime candidate. From its ionospheric vantage point, ELFIN uses its unique pitch-angle-resolving capability to determine whether measured relativistic electron pitch-angle and energy spectra within the loss cone bear the characteristic signatures of scattering by EMIC waves or whether such scattering may be due to other processes. Pairing identical ELFIN satellites with slowly-variable along-track separation allows disambiguation of spatial and temporal evolution of the precipitation over minutes-to-tens-of-minutes timescales, faster than the orbit period of a single low-altitude satellite (Torbit ∼ 90 min). Each satellite carries an energetic particle detector for electrons (EPDE) that measures 50 keV to 5 MeV electrons with Δ E/E 1 MeV. This broad energy range of precipitation indicates that multiple waves are providing scattering concurrently. Many observed events show significant backscattered fluxes, which in the past were hard to resolve by equatorial spacecraft or non-pitch-angle-resolving ionospheric missions. These observations suggest that the ionosphere plays a significant role in modifying magnetospheric electron fluxes and wave-particle interactions. Routine data captures starting in February 2020 and lasting for at least another year, approximately the remainder of the mission lifetime, are expected to provide a very rich dataset to address questions even beyond the primary mission science objective.Published versio
Woman in profile wearing a red head scarf and dress, probably 1909 /
Title devised by cataloguer based on inscription.; Part of the collection: Album presented to Lord Chelmsford as congratulations, New South Wales, 1909.; Also available online at: http://nla.gov.au/nla.pic-vn6570571-s29
In search of the big fish: Investigating the coexistence of the big-fish-little-pond effect with the positive effects of upward comparisons
International audienceBlanton, Buunk, Gibbons, and Kuyper (1999) and Huguet, Dumas, Monteil, and Genestoux (2001) found that children nominated a social comparison target who slightly outperformed them in class with a beneficial effect on course grades - an assimilation effect, but with no effects on self-evaluation. However, big-fish-little-pond effect (BFLPE) research has shown that attending a high-ability school has a negative effect on academic self-concept - a contrast effect. To resolve this apparent conflict, the present investigation (1) tested the BFLPE in the Netherlands and France, using nationally representative samples (Study 1) and (2) further analysed (using more sophisticated analyses) the Dutch (Blanton et al.) study (Study 2) and the French (Huguet et al.) study including new French data (Study 3), to examine whether the BFLPE coexisted with, or was moderated by, the beneficial impact of upward comparisons. In support of the BFLPE, all studies found the negative effects of school-or class-average ability on self-evaluation, demonstrating that these assimilation and contrast effects can coexist
The positive effects of upward comparison : can they coexist with the big-fish-little-pond effect?
Social comparison research has demonstrated that upward comparisons can enhance academic performance (Blanton, Buunk, Gibbons & Kuyper, 1999; Huguet, Dumas, Monteil & Genestoux, 2001). Conversely, educational research on the big-fish-little-pond effect (BFLPE) has implied that upward comparisons result in lowered self-evaluations of academic ability (Craven, Marsh & Print, 2000; Davis, 1966; Marsh & Hau, 2003; Marsh, Koller & Baumert., 2001). By re-analysing data from the Blanton et al. study, and the Huguet et al. study, the present investigation aimed to ascertain whether upward comparisons could simultaneously enhance academic performance, and produce lower self-evaluations as predicted by the BFLPE. Participants were Dutch and French high school students, who completed a questionnaire assessing academic self-evaluation and comparison choices. Performance was measured by accessing end of semester grades. Using a multi-level modelling approach, a BFLPE emerged. Implications for educational policy were discussed
The auroral ionosphere - Comparison of a time-dependent model with composition measurements
A time-dependent model of the auroral ionosphere including the odd nitrogen species, NO, N(D-2), and N(S-4), is used for comparison with data from a coordinated rocket-satellite measurement of an auroral event. The chemical scheme and the adopted rate coefficients have been shown to be compatible with daytime mid-latitude ionospheric chemistry. The electron flux and neutral atmospheric parameters measured on the satellite are used to compute the appropriate ionization and dissociation rates. The calculated NO(plus), O2(plus), O(plus), Ne, and NO densities agree well with the rocket measurements. The calculated N2(plus) densities are larger than the measured densities by a factor of 3 at most altitudes. The calculations show that the nitric oxide content of the aurora (about 1.2 times 10 to the 9th NO molecules/cu cm at 105 km) is below the saturation value