68 research outputs found
Similar health economic outcomes in low-risk and high-risk malnourished inpatients as screened by the Malnutrition Screening Tool after delivery of oral nutritional supplements
Notes Toward a Theory of Dialogue
Multiple dimensions of dialogue as pedagogical practice are examined in the following three essays. In the first piece, âWhen Life Imitates Art: Notes on the Nature of Dialogue,â poet and essayist Jane Vanderbosch reflects about the politics of silence and voice in graduate school. She analyzes how power and politics charge the atmosphere of the classroom. In âThe Pedagogy of Dialogue: A Relation Between Means and End,â Grace Deniston-Trochta focuses on self-examining the possibility of dialogue in a large âpitâ classroom. She proposes teacher as listener/learner, a teacher who is self-reflective and respectful. In the final essay, âManaging the Silence of Children,â Ed Check considers how power and control are mediated in the lives of students and teachers. He implicates himself in his discussion as he reflects on a conversation with his nephew. Throughout, the writers dissect pedagogy as dialogue through the personal as political. Each reveals how telling oneâs truths is a site to rethink institutionalized strategies and self-imposed silences
The Rapid Rotation of the Strongly Magnetic Ultramassive White Dwarf EGGR 156
The distribution of white dwarf rotation periods provides a means for
constraining angular momentum evolution during the late stages of stellar
evolution, as well as insight into the physics and remnants of double
degenerate mergers. Although the rotational distribution of low mass white
dwarfs is relatively well constrained via asteroseismology, that of high mass
white dwarfs, which can arise from either intermediate mass stellar evolution
or white dwarf mergers, is not. Photometric variability in white dwarfs due to
rotation of a spotted star is rapidly increasing the sample size of high mass
white dwarfs with measured rotation periods. We present the discovery of 22.4
minute photometric variability in the lightcurve of EGGR 156, a strongly
magnetic, ultramassive white dwarf. We interpret this variability as rapid
rotation, and our data suggest that EGGR 156 is the remnant of a double
degenerate merger. Finally, we calculate the rate of period change in rapidly
rotating, massive, magnetic WDs due to magnetic dipole radiation. In many
cases, including EGGR 156, the period change is not currently detectable over
reasonable timescales, indicating that these WDs could be very precise clocks.
For the most highly magnetic, rapidly rotating massive WDs, such as ZTF
J1901+1450 and RE J0317853, the period change should be detectable and may
help constrain the structure and evolution of these exotic white dwarfs.Comment: Replaced to correct two typos in equations on page 12. No
calculations or conclusions affected. 15 pages, 5 figures, accepted for
publication in the Astronomical Journa
Destroying Aliases from the Ground and Space: Super-Nyquist ZZ Cetis in K2 Long Cadence Data
With typical periods of order 10 minutes, the pulsation signatures of ZZ Ceti
variables (pulsating hydrogen-atmosphere white dwarf stars) are severely
undersampled by long-cadence (29.42 minutes per exposure) K2 observations.
Nyquist aliasing renders the intrinsic frequencies ambiguous, stifling
precision asteroseismology. We report the discovery of two new ZZ Cetis in
long-cadence K2 data: EPIC 210377280 and EPIC 220274129. Guided by 3-4 nights
of follow-up, high-speed (<=30 s) photometry from McDonald Observatory, we
recover accurate pulsation frequencies for K2 signals that reflected 4-5 times
off the Nyquist with the full precision of over 70 days of monitoring (~0.01
muHz). In turn, the K2 observations enable us to select the correct peaks from
the alias structure of the ground-based signals caused by gaps in the
observations. We identify at least seven independent pulsation modes in the
light curves of each of these stars. For EPIC 220274129, we detect three
complete sets of rotationally split ell=1 (dipole mode) triplets, which we use
to asteroseismically infer the stellar rotation period of 12.7+/-1.3 hr. We
also detect two sub-Nyquist K2 signals that are likely combination (difference)
frequencies. We attribute our inability to match some of the K2 signals to the
ground-based data to changes in pulsation amplitudes between epochs of
observation. Model fits to SOAR spectroscopy place both EPIC 210377280 and EPIC
220274129 near the middle of the ZZ Ceti instability strip, with Teff =
11590+/-200 K and 11810+/-210 K, and masses 0.57+/-0.03 Msun and 0.62+/-0.03
Msun, respectively.Comment: 13 pages, 9 figures, 7 tables; accepted for publication in Ap
The pulsating helium-atmosphere white dwarfs : I. New DBVs from the Sloan Digital Sky Survey
We present a dedicated search for new pulsating helium-atmosphere (DBV) white dwarfs from the Sloan Digital Sky Survey using the McDonald 2.1 m Otto Struve Telescope. In total we observed 55 DB and DBA white dwarfs with spectroscopic temperatures between 19,000 and 35,000 K. We find 19 new DBVs and place upper limits on variability for the remaining 36 objects. In combination with previously known DBVs, we use these objects to provide an update to the empirical extent of the DB instability strip. With our sample of new DBVs, the red edge is better constrained, as we nearly double the number of DBVs known between 20,000 and 24,000 K. We do not find any new DBVs hotter than PG 0112+104, the current hottest DBV is at Teff â 31,000 K, but do find pulsations in four DBVs with temperatures between 27,000 and 30,000 K, improving empirical constraints on the poorly defined blue edge. We investigate the ensemble pulsation properties of all currently known DBVs, finding that the weighted mean period and total pulsation power exhibit trends with effective temperature that are qualitatively similar to the pulsating hydrogen-atmosphere white dwarfs
Pruning The ELM Survey: Characterizing Candidate Low-mass White Dwarfs through Photometric Variability
We assess the photometric variability of nine stars with spectroscopic T {sub eff} and log g values from the ELM Survey that locates them near the empirical extremely low-mass (ELM) white dwarf instability strip. We discover three new pulsating stars: SDSS J135512.34+195645.4, SDSS J173521.69+213440.6, and SDSS J213907.42+222708.9. However, these are among the few ELM Survey objects that do not show radial velocity (RV) variations that confirm the binary nature expected of helium-core white dwarfs. The dominant 4.31 hr pulsation in SDSS J135512.34+195645.4 far exceeds the theoretical cut-off for surface reflection in a white dwarf, and this target is likely a high-amplitude ÎŽ Scuti pulsator with an overestimated surface gravity. We estimate the probability to be less than 0.0008 that the lack of measured RV variations in four of eight other pulsating candidate ELM white dwarfs could be due to low orbital inclination. Two other targets exhibit variability as photometric binaries. Partial coverage of the 19.342 hr orbit of WD J030818.19+514011.5 reveals deep eclipses that imply a primary radius >0.4 R {sub â}âtoo large to be consistent with an ELM white dwarf. The only object for which our time series photometry adds support to ELM white dwarf classification is SDSS J105435.78â212155.9,more » which has consistent signatures of Doppler beaming and ellipsoidal variations. We conclude that the ELM Survey contains multiple false positives from another stellar population at T {sub eff}âČ9000 K, possibly related to the sdA stars recently reported from SDSS spectra.« les
The search for ZZ Ceti stars in the original Kepler mission
We report the discovery of 42 white dwarfs in the origina
The search for ZZ Ceti stars in the original Kepler mission
We report the discovery of 42 white dwarfs in the original Kepler mission
field, including nine new confirmed pulsating hydrogen-atmosphere white dwarfs
(ZZ Ceti stars). Guided by the Kepler-INT Survey (KIS), we selected white dwarf
candidates on the basis of their U-g, g-r, and r-H_alpha photometric colours.
We followed up these candidates with high-signal-to-noise optical spectroscopy
from the 4.2-m William Herschel Telescope. Using ground-based, time-series
photometry, we put our sample of new spectroscopically characterized white
dwarfs in the context of the empirical ZZ Ceti instability strip. Prior to our
search, only two pulsating white dwarfs had been observed by Kepler.
Ultimately, four of our new ZZ Cetis were observed from space. These rich
datasets are helping initiate a rapid advancement in the asteroseismic
investigation of pulsating white dwarfs, which continues with the extended
Kepler mission, K2.Comment: 9 pages, 6 figures, accepted for publication in MNRA
The pulsating helium-atmosphere white dwarfs : I. New DBVs from the Sloan Digital Sky Survey
We present a dedicated search for new pulsating helium-atmosphere (DBV) white dwarfs from the Sloan Digital Sky Survey using the McDonald 2.1 m Otto Struve Telescope. In total we observed 55 DB and DBA white dwarfs with spectroscopic temperatures between 19,000 and 35,000 K. We find 19 new DBVs and place upper limits on variability for the remaining 36 objects. In combination with previously known DBVs, we use these objects to provide an update to the empirical extent of the DB instability strip. With our sample of new DBVs, the red edge is better constrained, as we nearly double the number of DBVs known between 20,000 and 24,000 K. We do not find any new DBVs hotter than PG 0112+104, the current hottest DBV is at Teff â 31,000 K, but do find pulsations in four DBVs with temperatures between 27,000 and 30,000 K, improving empirical constraints on the poorly defined blue edge. We investigate the ensemble pulsation properties of all currently known DBVs, finding that the weighted mean period and total pulsation power exhibit trends with effective temperature that are qualitatively similar to the pulsating hydrogen-atmosphere white dwarfs
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