54 research outputs found
Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)
We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand
2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet
at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo
2.3m optical spectroscopy, and analysed using a spherical, non-LTE,
line-blanketed code. Our study reveals exceptional stellar parameters:
T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt
a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and
O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination
line studies. We confirm that Sand 2 is more chemically enriched in carbon than
LMC WC stars, and is expected to undergo a supernova explosion within the next
50,000 yr.Comment: 17 pages, 4 figures, AASTeX preprint format. This paper will appear
in a special issue of ApJ Letters devoted to the first scientific results
from the FUSE missio
Optical Structure and Proper-Motion Age of the Oxygen-rich Supernova Remnant 1E 0102-7219 in the Small Magellanic Cloud
We present new optical emission-line images of the young SNR 1E 0102-7219
(E0102) in the SMC obtained with the HST Advanced Camera for Surveys (ACS).
E0102 is a member of the oxygen-rich class of SNRs showing strong oxygen, neon
, and other metal-line emissions in its optical and X-ray spectra, and an
absence of H and He. The progenitor of E0102 may have been a Wolf-Rayet star
that underwent considerable mass loss prior to exploding as a Type Ib/c or
IIL/b SN. The ejecta in this SNR are fast-moving (V > 1000 km/s) and emit as
they are compressed and heated in the reverse shock. In 2003, we obtained
optical [O III], H-alpha, and continuum images with the ACS Wide Field Camera.
The [O III] image captures the full velocity range of the ejecta, and shows
considerable high-velocity emission projected in the middle of the SNR that was
Doppler-shifted out of the narrow F502N bandpass of a previous Wide Field and
Planetary Camera 2 image from 1995. Using these two epochs separated by ~8.5
years, we measure the transverse expansion of the ejecta around the outer rim
in this SNR for the first time at visible wavelengths. From proper-motion
measurements of 12 ejecta filaments, we estimate a mean expansion velocity for
the bright ejecta of ~2000 km/s and an inferred kinematic age for the SNR of
\~2050 +/- 600 years. The age we derive from HST data is about twice that
inferred by Hughes et al.(2000) from X-ray data, though our 1-sigma error bars
overlap. Our proper-motion age is consistent with an independent optical
kinematic age derived by Eriksen et al.(2003) using spatially resolved [O III]
radial-velocity data. We derive an expansion center that lies very close to
X-ray and radio hotspots, which could indicate the presence of a compact
remnant (neutron star or black hole).Comment: 28 pages, 8 figures. Accepted to the Astrophysical Journal, to appear
in 20 April 2006 issue. Full resolution figures are posted at:
http://stevenf.asu.edu/figure
Overview of the Far Ultraviolet Spectroscopic Explorer Mission
The Far Ultraviolet Spectroscopic Explorer satellite observes light in the
far-ultraviolet spectral region, 905 - 1187 A with high spectral resolution.
The instrument consists of four coaligned prime-focus telescopes and Rowland
spectrographs with microchannel plate detectors. Two of the telescope channels
use Al:LiF coatings for optimum reflectivity from approximately 1000 to 1187 A
and the other two use SiC coatings for optimized throughput between 905 and
1105 A. The gratings are holographically ruled to largely correct for
astigmatism and to minimize scattered light. The microchannel plate detectors
have KBr photocathodes and use photon counting to achieve good quantum
efficiency with low background signal. The sensitivity is sufficient to examine
reddened lines of sight within the Milky Way as well as active galactic nuclei
and QSOs for absorption line studies of both Milky Way and extra-galactic gas
clouds. This spectral region contains a number of key scientific diagnostics,
including O VI, H I, D I and the strong electronic transitions of H2 and HD.Comment: To appear in FUSE special issue of the Astrophysical Journal Letters.
6 pages + 4 figure
The Detection of Wind Variability in Magellanic Cloud O Stars
We present Far Ultraviolet Explorer (FUSE) spectra for three Magellanic Cloud
O stars (Sk 80, Sk -67 05 and Sk -67 111) with repeated observations. The data
demonstrate the capabilities of FUSE to perform time-resolved spectroscopy on
extragalactic stars. The wavelength coverage of FUSE provides access to
resonance lines due to less abundant species, such as sulfur, which are
unsaturated in O supergiants. This allows us to examine wind variability at all
velocities in resonance lines for stars with higher mass loss rates than can be
studied at longer (lambda > 1150 A) wavelengths. The FUSE wavelength range also
includes resonance lines from ions which bracket the expected dominant
ionization stage of the wind. Our observations span 1-4 months with several
densely sampled intervals of 10 hours or more. These observations reveal wind
variability in all of the program stars and distinctive differences in the
ionization structure and time scales of the variability. Sk -67 111
demonstrates significant wind variability on a time scale less than 10 hours
and the coolest O star (Sk -67 05) exhibits the largest variations in O VI.Comment: 3 pages of text and 3 JPG figures. To be included in the FUSE ApJ
Letters special issu
COOL-LAMPS VI: Lens model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens
We present a strong lensing analysis of COOL J1241+2219, the brightest known
gravitationally lensed galaxy at , based on new multi-band Hubble
Space Telescope (HST) imaging data. The lensed galaxy has a redshift of
z=5.043, placing it shortly after the end of the Epoch of Reionization, and an
AB magnitude z_AB=20.47 mag (Khullar et al. 2021). As such, it serves as a
touchstone for future research of that epoch. The high spatial resolution of
HST reveals internal structure in the giant arc, from which we identify 15
constraints and construct a robust lens model. We use the lens model to extract
cluster mass and lensing magnification. We find that the mass enclosed within
the Einstein radius of the z=1.001 cluster lens is
M(<5.77'')=, significantly lower than other known
strong lensing clusters at its redshift. The average magnification of the giant
arc is , a factor of greater
than previously estimated from ground-based data; the flux-weighted average
magnification is We update the current
measurements of the stellar mass and star formation rate (SFR) of the source
for the revised magnification, and yr. The powerful lensing
magnification acting upon COOL J1241+2219 resolves the source and enables
future studies of the properties of its star formation on a clump-by-clump
basis. The lensing analysis presented here will support upcoming
multiwavelength characterization with HST and JWST data of the stellar mass
assembly and physical properties of this high-redshift lensed galaxy.Comment: Submitted to Ap
COOL-LAMPS. VI. Lens Model and New Constraints on the Properties of COOL J1241+2219, a Bright z = 5 Lyman Break Galaxy and its z = 1 Cluster Lens
We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z â„ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the âEpoch of Reionization,â and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M(<5.âł77)=1.079â0.007+0.023Ă1013Mâ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is ăÎŒ arcă = 76â20+40 , a factor of 2.4â0.7+1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is ăÎŒ arcă = 92â31+37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log(Mâ/Mâ)= 9.7 ± 0.3 and SFR = 10.3â4.4+7.0 M â yrâ1, respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy
On-Orbit Performance of the Far Ultraviolet Spectroscopic Explorer (FUSE) Satellite
Launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed
by an extensive period of calibration and characterization as part of the
preparation for normal satellite operations. Major tasks carried out during
this period include initial coalignment, focusing and characterization of the
four instrument channels, and a preliminary measurement of the resolution and
throughput performance of the instrument. We describe the results from this
test program, and present preliminary estimates of the on-orbit performance of
the FUSE satellite based on a combination of this data and prelaunch laboratory
measurements.Comment: 8 pages, including 3 figures. This paper will appear in the FUSE
special issue of ApJ Letter
A Second Chromatic Timing Event of Interstellar Origin toward PSR J1713+0747
The frequency dependence of radio pulse arrival times provides a probe of structures in the intervening media. Demorest et al. was the first to show a short-term (~100â200 days) reduction in the electron content along the line of sight to PSR J1713+0747 in data from 2008 (approximately MJD 54750) based on an apparent dip in the dispersion measure of the pulsar. We report on a similar event in 2016 (approximately MJD 57510), with average residual pulse-arrival times ââ3.0, â1.3, and â0.7 ÎŒs at 820, 1400, and 2300 MHz, respectively. Timing analyses indicate possible departures from the standard Îœ â2 dispersive-delay dependence. We discuss and rule out a wide variety of potential interpretations. We find the likeliest scenario to be lensing of the radio emission by some structure in the interstellar medium, which causes multiple frequency-dependent pulse arrival-time delays
The Effect of Mental Fatigue on Critical Power during cycling exercise
Purpose: Time-to-exhaustion (TTE) tests used in the determination of critical power (CP) and curvature constant (W) of the power-duration relationship are strongly influenced by the perception of effort (PE). This study aimed to investigate whether manipulation of the PE alters the CP and W. Methods: Eleven trained cyclists completed a series of TTE tests to establish CP and W under two conditions, following a mentally fatiguing (MF), or a control (CON) task. Both cognitive tasks lasted 30 min followed by a TTE test. Ratings of PE and heart rate (HR) were measured during each TTE. Blood lactate was taken pre and post each TTE test. Ratings of perceived mental and physical fatigue were taken pre- and post-cognitive task, and following each TTE test. Results: Perceived MF significantly increased as a result of the MF task compared to baseline and the CON task (P0.05). PE was significantly higher during TTE in the MF condition (P0.05). Neither cognitive task induced any change in CP (MF 253±51 vs. CON 247±58W; P>0.05), although W was significantly reduced in the MF condition (MF 2.3±4.5 vs. CON 2.9±6.3kJ; P<0.01). Conclusion: MF has no effect of CP, but reduces the W in trained cyclists. Lower lactate accumulation during TTE tests following MF, suggests that cyclists were not be able to fully expend W even though they exercised to volitional exhaustion
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