1,154 research outputs found
Evolved solar systems in Praesepe
"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics." Original paper can be found at: http://scitation.aip.org/"We have obtained near-IR photometry for the 11 Praesepe white dwarfs, to search for an excess indicative of a dusty debris disk. All the white dwarfs are in the DAZ temperature regime, however we find no indications of a disk around any white dwarf. We have, however determined that the radial velocity variable white dwarf WD0837+185 could have an unresolved T8 dwarf companion that would not be seen as a near-IR excess.Final Accepted Versio
The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds: III. The Serpens Cloud in CO J=2-1 and 13CO J=2-1 Emission
We mapped 12CO and 13CO J = 2-1 emission over 1.04 square deg of the Serpens
molecular cloud with 38 arcsec spatial and 0.3 km/s spectral resolution using
the Arizona Radio Observatory Heinrich Hertz Submillimeter telescope. Our maps
resolve kinematic properties for the entire Serpens cloud. We also compare our
velocity moment maps with known positions of Young Stellar Objects (YSOs) and
1.1 mm continuum emission. We find that 12CO is self-absorbed and 13CO is
optically thick in the Serpens core. Outside of the Serpens core, gas appears
in filamentary structures having LSR velocities which are blue-shifted by up to
2 km/s relative to the 8 km/s systemic velocity of the Serpens cloud. We show
that the known Class I, Flat, and Class II YSOs in the Serpens core most likely
formed at the same spatial location and have since drifted apart. The spatial
and velocity structure of the 12CO line ratios implies that a detailed
3-dimensional radiative transfer model of the cloud will be necessary for full
interpretation of our spectral data. The starless cores region of the cloud is
likely to be the next site of star formation in Serpens.Comment: 41 pages, 15 figure
Detection limits for close eclipsing and transiting sub-stellar and planetary companions to white dwarfs in the WASP survey
We used photometric data from the WASP (Wide-Angle Search for Planets) survey
to explore the possibility of detecting eclipses and transit signals of brown
dwarfs, gas giants and terrestrial companions in close orbit around white
dwarfs. We performed extensive Monte Carlo simulations and we found that for
Gaussian random noise WASP is sensitive to companions as small as the Moon
orbiting a 12 white dwarf. For fainter stars WASP is sensitive to
increasingly larger bodies. Our sensitivity drops in the presence of co-variant
noise structure in the data, nevertheless Earth-size bodies remain readily
detectable in relatively low S/N data. We searched for eclipses and transit
signals in a sample of 194 white dwarfs in the WASP archive however, no
evidence for companions was found. We used our results to place tentative upper
limits to the frequency of such systems. While we can only place weak limits on
the likely frequency of Earth-sized or smaller companions; brown dwarfs and gas
giants (radius R) with periods 0.2 days must certainly be
rare (). More stringent constraints requires significantly larger white
dwarf samples, higher observing cadence and continuous coverage. The short
duration of eclipses and transits of white dwarfs compared to the cadence of
WASP observations appears to be one of the main factors limiting the detection
rate in a survey optimised for planetary transits of main sequence stars.Comment: 8 pages, 3 figure
Irradiated brown dwarfs
We have observed the post common envelope binary WD0137-349 in the near
infrared , and bands and have determined that the photometry varies
on the system period (116 min). The amplitude of the variability increases with
increasing wavelength, indicating that the brown dwarf in the system is likely
being irradiated by its 16500 K white dwarf companion. The effect of the
(primarily) UV irradiation on the brown dwarf atmosphere is unknown, but it is
possible that stratospheric hazes are formed. It is also possible that the
brown dwarf (an L-T transition object) itself is variable due to patchy cloud
cover. Both these scenarios are discussed, and suggestions for further study
are made.Comment: 5 pages, 2 figures. Proceedings from "Brown dwarfs come of age"
meeting in Fuerteventura 201
Hubble Space Telescope Imaging and Spectroscopy of the Sirius-Like Triple Star System HD 217411
We present Hubble Space Telescope imaging and spectroscopy of HD 217411, a G3
V star associated with the extreme ultraviolet excess source (EUV 2RE
J2300-07.0). This star is revealed to be a triple system with a G 3V primary
(HD 217411 A) separated by ~1.1" from a secondary that is in turn composed of
an unresolved K0 V star (HD 217411 Ba) and a hot DA white dwarf (HD 217411 Bb).
The hot white dwarf dominates the UV flux of the system. However; it is in turn
dominated by the K0 V component beyond 3000 {\AA}. A revised distance of 143 pc
is estimated for the system. A low level photometric modulation having a period
of 0.61 days has also been observed in this system along with a rotational
velocity on the order of 60 km s-1 in the K0 V star. Together both observations
point to a possible wind induced spin up of the K0 V star during the AGB phase
of the white dwarf. The nature of all three components is discussed as are
constraints on the orbits, system age and evolution.Comment: 11 pages, 6 figure
COVID-19: Teacher Interns’ Perspectives of an Unprecedented Year
During COVID-19, digital learning took on an unprecedented central focus in K-12 education. This study applied photovoice qualitative methodology to record and understand the lives and reality for teacher interns as they adapted to abrupt changes in the way they designed and delivered instruction while living homebound during a pandemic. Teacher interns shared their stories of transitioning to virtual or distance learning. Participants (n = 97) were a demographically and culturally diverse group of K-12 public school teacher interns from California. The findings from this study illuminate the need for U.S. public K-12 schools to develop specific professional development training to support teachers when unforeseen events may cause the physical closure of their schools. The implications of this study highlight a shift in the mindset of how to develop practices and policies to support teacher licensure candidates during times of crisis, which may affect their ability to teach and engage students in a distance learning environment. Their experiences showed that out of chaos came the development of critical thinking and unexpected skills that moved education forward for everyone involved
Phase-resolved far-ultraviolet HST spectroscopy of the peculiar magnetic white dwarf RE J0317-853
We present phase resolved FUV HST FOS spectra of the rapidly rotating, highly
magnetic white dwarf RE J0317-853. Using these data, we construct a new model
for the magnetic field morphology across the stellar surface. From an expansion
into spherical harmonics, we find the range of magnetic field strengths present
is 180-800MG. For the first time we could identify an absorption feature
present at certain phases at 1160A as a ``forbidden'' 1s_0 -> 2s_0 component,
due to the combined presence of an electric and magnetic field.Comment: 15 pages including 4 figures. Accepted for publication in ApJ Letter
Origin of electron cyclotron maser-induced radio emissions at ultra-cool dwarfs: magnetosphere-ionosphere coupling currents
A number of ultra-cool dwarfs emit circularly polarised radio waves generated
by the electron cyclotron maser instability. In the solar system such radio is
emitted from regions of strong auroral magnetic field-aligned currents. We thus
apply ideas developed for Jupiter's magnetosphere, being a well-studied
rotationally-dominated analogue in our solar system, to the case of
fast-rotating UCDs. We explain the properties of the radio emission from UCDs
by showing that it would arise from the electric currents resulting from an
angular velocity shear in the fast-rotating magnetic field and plasma, i.e. by
an extremely powerful analogue of the process which causes Jupiter's auroras.
Such a velocity gradient indicates that these bodies interact significantly
with their space environment, resulting in intense auroral emissions. These
results strongly suggest that auroras occur on bodies outside our solar system.Comment: Accepted for publication in the Astrophysical Journa
NASA ION (Interplanetary Overlay Network) Developer Course Materials
The Delay/Disruption Tolerant Networking Project created open-source software, the Interplanetary Overlay Network (ION), as an implementation of the Bundle Protocol. To aid users in understanding the architecture of ION and how best to use it, the DTN Project developed a course
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