1,455 research outputs found
Absolute Flux Calibration of the IRAC Instrument on the Spitzer Space Telescope using Hubble Space Telescope Flux Standards
The absolute flux calibration of the James Webb Space Telescope will be based
on a set of stars observed by the Hubble and Spitzer Space Telescopes. In order
to cross-calibrate the two facilities, several A, G, and white dwarf (WD) stars
are observed with both Spitzer and Hubble and are the prototypes for a set of
JWST calibration standards. The flux calibration constants for the four Spitzer
IRAC bands 1-4 are derived from these stars and are 2.3, 1.9, 2.0, and 0.5%
lower than the official cold-mission IRAC calibration of Reach et al. (2005),
i.e. in agreement within their estimated errors of ~2%. The causes of these
differences lie primarily in the IRAC data reduction and secondarily in the
SEDs of our standard stars. The independent IRAC 8 micron band-4 fluxes of
Rieke et al. (2008) are about 1.5 +/- 2% higher than those of Reach et al. and
are also in agreement with our 8 micron result.Comment: 16 pages, 6 figure
Writing New Rites: John Donne\u27s and John Milton\u27s Elegies as Mourning Ritual
In this study, I read John Donne\u27s The Anniversaries and John Milton\u27s Lycidas in the context of the changing funeral and mourning ritual since the Reformation and England\u27s turn to Protestantism, approximately begun in the 1540s. In Donne\u27sAnniversaries, I find that he is exploring how the body can sign spiritual health or sickness, as well as negotiating how the dead (body and spirit) might be exemplum for the living. I argue that this negotiation is particularly Protestant in that the body, despite conventional notions about Protestantism\u27s tendency to privilege the soul, is still important in divining the quality of the soul. In Lycidas, the speaker\u27s concern for the dead body of Lycidas is striking, although as an imagined absence/presence, rather than as a spokesperson for the soul. I argue that Milton\u27s Lycidas, although attempting new Protestant mourning rites, also exhibits reluctant continuity with some of the funeral and mourning rituals that were practiced before the Reformation in England, such as the obit, a ceremony where funeral services were repeated on the anniversary of death (or burial), including an empty casket. This thesis works to challenge typical periodization, as it is possible to see funeral and mourning rituals continue in these early modern elegies
The rocket ultraviolet spectrum of the planetary nebula NGC 7027
An ultraviolet spectrum of NGC 7027 was obtained with a rocket-borne telescope. The observed fluxes are given on an absolute basis and upper limits are given for the strongest predicted lines which were not observed. The extinction correction was made on the basis of the observed and calculated line ratios for the hydrogenic recombination line of He 2 at 1640A to H beta. The extinction is in agreement with ground based determinations. When corrected for extinction the C 4 resonance line at 1549A is in good agreement with the intensity calculated from models, but the C 3 intercombination line at 1909A is a factor of ten too bright. The addition of dielectronic recombination to the models sufficiently changes the C 3 concentration to reduce the discrepancy to a factor of four. The abundance of carbon is assumed to be 2 x 0.0001 that of hydrogen. Using carbon abundances for the sun, this discrepancy disappears and there must be attenuation in the C 4 line. Since the optical depth is approximately 10,000 at the line center, no appreciable number of absorbing grains can exist in the C 4 producing region of the nebula
Risk homeostasis theory - A study of intrinsic compensation
Risk homeostasis theory (RHT) suggests that changes made to the intrinsic risk of environments are negated in one of three ways: behavioural adjustments within the environment, mode migration, and avoidance of the physical risk. To date, this three-way model of RHT has little empirical support, whilst research findings on RHT have at times been diametrically opposed. A reconciliation of apparently opposing findings might be possible by suggesting that extrinsic compensation fails to restore previously existing levels of actual risk in cases where behavioural adjustments within the environment are incapable of negating intrinsic risk changes. This paper reports a study in which behavioural adjustments within the physical risk-taking environment are capable of reconciling target with actual risk. The results provide positive support for RHT in the form of overcompensation for the intrinsic risk change on specific driver behaviours
Faint NUV/FUV Standards from Swift/UVOT, GALEX and SDSS Photometry
At present, the precision of deep ultraviolet photometry is somewhat limited
by the dearth of faint ultraviolet standard stars. In an effort to improve this
situation, we present a uniform catalog of eleven new faint (u sim17)
ultraviolet standard stars. High-precision photometry of these stars has been
taken from the Sloan Digital Sky Survey and Galaxy Evolution Explorer and
combined with new data from the Swift Ultraviolet Optical Telescope to provide
precise photometric measures extending from the Near Infrared to the Far
Ultraviolet. These stars were chosen because they are known to be hot (20,000 <
T_eff < 50,000 K) DA white dwarfs with published Sloan spectra that should be
photometrically stable. This careful selection allows us to compare the
combined photometry and Sloan spectroscopy to models of pure hydrogen
atmospheres to both constrain the underlying properties of the white dwarfs and
test the ability of white dwarf models to predict the photometric measures. We
find that the photometry provides good constraint on white dwarf temperatures,
which demonstrates the ability of Swift/UVOT to investigate the properties of
hot luminous stars. We further find that the models reproduce the photometric
measures in all eleven passbands to within their systematic uncertainties.
Within the limits of our photometry, we find the standard stars to be
photometrically stable. This success indicates that the models can be used to
calibrate additional filters to our standard system, permitting easier
comparison of photometry from heterogeneous sources. The largest source of
uncertainty in the model fitting is the uncertainty in the foreground reddening
curve, a problem that is especially acute in the UV.Comment: Accepted for publication in Astrophysical Journal. 31 pages, 13
figures, electronic tables available from ApJ or on reques
Hubble Space Telescope Spectroscopy of the Balmer lines in Sirius B
Sirius B is the nearest and brightest of all white dwarfs, but it is very
difficult to observe at visible wavelengths due to the overwhelming scattered
light contribution from Sirius A. However, from space we can take advantage of
the superb spatial resolution of the Hubble Space Telescope to resolve the A
and B components. Since the closest approach in 1993, the separation between
the two stars has become increasingly favourable and we have recently been able
to obtain a spectrum of the complete Balmer line series for Sirius B using
HST?s Space Telescope Imaging Spectrograph (STIS). The quality of the STIS
spectra greatly exceed that of previous ground-based spectra, and can be used
to provide an important determination of the stellar temperature (Teff =
25193K) and gravity (log g = 8.556). In addition we have obtained a new, more
accurate, gravitational red-shift of 80.42 +/- 4.83 km s-1 for Sirius B.
Combining these results with the photometric data and the Hipparcos parallax we
obtain new determinations of the stellar mass for comparison with the
theoretical mass-radius relation. However, there are some disparities between
the results obtained independently from log g and the gravitational redshift
which may arise from flux losses in the narrow 50x0.2arcsec slit. Combining our
measurements of Teff and log g with the Wood (1995) evolutionary mass-radius
relation we get a best estimate for the white dwarf mass of 0.978 M. Within the
overall uncertainties, this is in agreement with a mass of 1.02 M obtained by
matching our new gravitational red-shift to the theoretical M/R relation.Comment: 11 pages, 6 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
The INES System IV: The IUE Absolute Flux Scale
This paper deals with the definition of the input fluxes used for the
calibration of the IUE Final Archive. The method adopted consists on the
determination of the shape of the detector's sensitivity curves using IUE low
resolution observations with model fluxes of the DA white dwarf G191-B2B. A
scale factor was then determined so that the IUE observations of some bright
OAO-2 standards match the original measurements from Meade (1978) in the
spectral region 2100-2300 A. The ultraviolet fluxes of six standard stars used
as input for the Final Archive photometric calibration together with the model
fluxes of G191-B2B normalized to the OAO-2 scale are given. A comparison with
the independent FOS calibration shows that the IUE flux scale for the
Ultraviolet is 7.2% lower. We consider this mainly to be caused by the
different normalization procedures. It is shown that the present flux
calibration applies to spectra processed with the INES low resolution
extraction software.Comment: 17 pages, 8 figures. To appear in Astronomy and Astrophysic
Hot Populations in M87 Globular Clusters
We have obtained HST/STIS far- and near-UV photometry of globular clusters in
four fields in the gE galaxy M87. To a limit of m(FUV) = 25 we detect a total
of 66 globular clusters (GCs) in common with the deep HST optical-band study of
Kundu et al. (1999). Despite strong overlap in V- and I-band properties, the
M87 GCs have UV/optical properties that are distinct from clusters in the Milky
Way and in M31. M87 clusters, especially metal-poor ones, produce larger hot HB
populations than do Milky Way analogues. Cluster mass is probably not a factor
in these distinctions. The most metal-rich M87 GCs in our sample are near Z_sun
and overlap the local E galaxy sample in estimated Mg_2 line indices.
Nonetheless, the clusters produce much more UV light at a given Mg_2, being up
to 1 mag bluer than any gE galaxy in (FUV-V) color. The M87 GCs do not appear
to represent a transition between Milky Way-type clusters and E galaxies. The
differences are in the correct sense if the clusters are significantly older
than the E galaxies. Comparisons with Galactic open clusters indicate that the
hot stars lie on the extreme horizontal branch, rather than being blue
stragglers, and that the EHB becomes well populated for ages > 5 Gyr. We find
that 43 of our UV detections have no optical-band counterparts. Most appear to
be UV-bright background galaxies, seen through M87. Eleven NUV variable sources
detected at only one epoch in the central field are probably classical novae.
[Abridged]Comment: 70 pages, 25 figures (including 4 jpgs), 7 tables. To appear in AJ.
Full resolution version available at
http://www.astro.virginia.edu/~rwo/m87/m87-hotpops.pd
Strange magnification pattern in the large separation lens SDSS J1004+4112 from optical to X-rays
We present simultaneous XMM-Newton UV and X-ray observations of the quadruply
lensed quasar SDSS J1004+4112 (RBS 825). Simultaneously with the XMM-Newton
observations we also performed integral field spectroscopy on the two closest
lens images A and B using the Calar Alto PMAS spectrograph. In X-rays the
widely spaced components C and D are clearly resolved, while the closer pair of
images A and B is marginally resolved in the XMM-EPIC images. The integrated
X-ray flux of the system has decreased by a factor of 6 since it was observed
in the ROSAT All Sky Survey in 1990, while the X-ray spectrum became much
harder with the power law index evolving from Gamma=-2.3 to -1.86. By
deblending the X-ray images of the lensed QSO we find that the X-ray flux
ratios between the lens images A and B are significantly different from the
simultaneously obtained UV ratios and previously measured optical flux ratios.
Our optical spectrum of lens image A shows an enhancement in the blue emission
line wings, which has been observed in previous epochs as a transient feature.
We propose a scenario where intrinsic UV and X-ray variability gives rise to
line variations which are selectively magnified in image A by microlensing. The
extended emission of the lensing cluster of galaxies is clearly detected in the
EPIC images, we measure a 0.5-2.0 keV luminosity of 1.4 E44 erg/s. Based on the
cluster X-ray properties, we estimate a mass of 2-6 E14 solar masses.Comment: 11 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
How to relate the oscillator and Coulomb systems on spheres and pseudospheres?
We show that the oscillators on a sphere and pseudosphere are related, by the
so-called Bohlin transformation, with the Coulomb systems on the pseudosphere:
the even states of an oscillator yields the conventional Coulomb system on
pseudosphere, while the odd states yield the Coulomb system on pseudosphere in
the presence of magnetic flux tube generating half spin. In the higher
dimensions the oscillator and Coulomb(-like) systems are connected in the
similar way. In particular, applying the Kustaanheimo-Stiefel transformation to
the oscillators on sphere and pseudosphere, we obtained the preudospherical
generalization of MIC-Kepler problem describing three-dimensional charge-dyon
system.Comment: 12 pages, Based on talk given at XXIII Colloquium on Group
Theoretical Methods in Physics (July 31-August 5, 2000, Dubna
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