148 research outputs found
A comprehensive study of Kepler phase curves and secondary eclipses -- temperatures and albedos of confirmed Kepler giant planets
We present a comprehensive study of phase curves and secondary eclipses in
the Kepler data set using all data from 16 quarters that were available in
2013-2014. Our sample consists of 20 confirmed planets with R_p > 4 R_e ,P <
10d, V_mag < 15. Here we derive their temperatures and albedos, with an eye
towards constraining models for the formation and evolution of such planets.
Where there was overlap our results confirm parameters derived by previous
studies, whereas we present new results for Kepler 1b-8b, 12b-15b, 17b, 40b,
41b, 43b, 44b, 76b, 77b, and 412b derived in a consistent manner. We also
present lightcurve analyses for Kepler 91b and Kepler 74b, which both show
extra dimmings at times other than from the expected primary and secondary
eclipses. Corrected for thermal emission we find most of the massive planets
from our sample to be low in albedo (<0.1) with a few having higher albedo
(>0.1).Comment: 50 pages, 7 figures - PASP accepte
The Purple Haze of Eta Carinae: Binary-Induced Variability?
Asymmetric variability in ultraviolet images of the Homunculus obtained with
the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space
Telescope suggests that Eta Carinae is indeed a binary system. Images obtained
before, during, and after the recent ``spectroscopic event'' in 2003.5 show
alternating patterns of bright spots and shadows on opposite sides of the star
before and after the event, providing a strong geometric argument for an
azimuthally-evolving, asymmetric UV radiation field as one might predict in
some binary models. The simplest interpretation of these UV images, where
excess UV escapes from the secondary star in the direction away from the
primary, places the major axis of the eccentric orbit roughly perpendicular to
our line of sight, sharing the same equatorial plane as the Homunculus, and
with apastron for the hot secondary star oriented toward the southwest of the
primary. However, other orbital orientations may be allowed with more
complicated geometries. Selective UV illumination of the wind and ejecta may be
partly responsible for line profile variations seen in spectra. The brightness
asymmetries cannot be explained plausibly with delays due to light travel time
alone, so a single-star model would require a seriously asymmetric shell
ejection.Comment: 8 pages, fig 1 in color, accepted by ApJ Letter
FUV and X-ray Observations of the Reverse Shock in the SMC SNR 1E 0102.2-7219
We present FUSE and XMM-Newton data for the reverse shock of the O-rich SNR
1E0102.2-7219 in the SMC. The FUSE observations cover three regions with
significantly different optical [O III] intensities, all associated with the
relatively bright part of the X-ray ring. Emission lines of O VI 1032, 1038 are
clearly detected in the FUSE spectra. By combining this O VI doublet emission
with the O VII triplet and O VIII Lyalpha fluxes from the XMM-Newton spectra
and assuming a non-equilibrium ionization model with a single ionization
timescale for the spectra, we are able to find a narrow range of temperatures
and ionization timescales that are consistent with the respective line ratios.
However, if we assume a plane-parallel shock model with a distribution of
ionization timescales, the O VI emission appears to be inconsistent with O VII
and O VIII in X-rays. We also analyze the total XMM-Newton EPIC-MOS 1/2 spectra
for the three regions. The X-ray spectra are dominated by strong emission lines
of O, Ne, and Mg, however, we detect an emission component that accounts for 14
- 25% of the flux and can be attributed to shocked ISM. We find that there is
no consistent set of values for the temperature and ionization timescale which
can explain the observed line ratios for O, Ne, and Mg. This would be
consistent with a structured distribution of the ejecta as the O, Ne, Mg would
have interacted with the reverse shock at different times.Comment: 28 pages, 5 figues, Fig. 1 as JPEG. To be published in ApJ (01 May
2006, v. 642, 1 issue
Kinematics of X-ray Emitting Components in Cassiopeia A
We present high-resolution X-ray proper motion measurements of Cassiopeia A
using Chandra observations from 2000 and 2002. We separate the emission into
four spectrally distinct classes: Si-dominated, Fe-dominated,
low-energy-enhanced, and continuum-dominated. These classes also represent
distinct spatial and kinematic components. The Si- and Fe-dominated classes are
ejecta and have a mean expansion rate of 0.2%/yr. This is the same as for the
forward shock filaments but less than the 0.3%/yr characteristic of optical
ejecta. The low-energy-enhanced spectral class possibly illuminates a clumpy
circumstellar component and has a mean expansion rate of 0.05%/yr. The
continuum-dominated emission likely represents the forward shock and consists
of diffuse circumstellar material which is seen as a circular ring around the
periphery of the remnant as well as projected across the center.Comment: 15 pages, 3 figures, accepted to Ap
Hubble Space Telescope Observations of Oxygen-rich Supernova Remnants in the Magellanic Clouds. III. WFPC2 Imaging of the Young, Crab-like Supernova Remnant SNRO540-69.3
Hubble Space Telescope images with the Wide Field Planetary Camera 2 of the young, oxygen-rich, Crab-like supernova remnant SNR0540-69.3 in the Large Magellanic Cloud (LMC) reveal details of the emission distribution and the relationship between the expanding ejecta and synchrotron nebula. The emission distributions appear very similar to those seen in the Crab nebula, with the ejecta located in a thin envelope surrounding the synchrotron nebula. The [O III] emission is more extended than other tracers, forming a faint "skin" around the denser filaments and synchrotron nebula, as also observed in the Crab. The [O III] exhibits somewhat different kinematic structure in long-slit spectra, including a more extended high-velocity emission halo not seen in images. Yet even the fastest expansion speeds in SNR 0540 s halo are slow when compared to most other young supernova remnants, though the Crab nebula has similar slow expansion speeds. We show a striking correspondence between the morphology of the synchrotron nebula observed in an optical continuum filter with that recently resolved in Chandra X-ray images. We argue that the multi-component kinematics and filamentary morphology of the optical emission-line features likely result from magnetic Rayleigh-Taylor instabilities that form as the synchrotron nebula expands and sweeps up ejecta, as seen in the Crab nebula. Our images and spectra help to refine our understanding of SNR 0540 in several more detailed respects: they confirm the identification of H(alpha)+[N II] in the red spectrum, they show that the systemic velocity of SNR 0540 is not significantly different from that of the LMC, and they hint at a lower Ne abundance than the Crab (potentially indicating a more massive progenitor star)
Hubble Space Telescope WFPC-2 Imaging of Cassiopeia A
The young SNR Cassiopeia A was imaged with WFPC-2 through four filters
selected to capture the complete velocity range of the remnant's main shell in
several important emission lines. Primary lines detected were [O III]
4959,5007, [N II] 6583, [S II] 6716,6731 + [O II] 7319,7330 + [O I] 6300,6364,
and [S III] 9069,9532. About 3/4th of the remnant's main shell was imaged in
all four filters. Considerable detail is observed in the reverse-shocked ejecta
with typical knot scale lengths of 0.2"-0.4" (1 - 2 x 10^16 cm). Both bright
and faint emission features appear highly clumped. Large differences in [S III]
and [O III] line intensities indicating chemical abundance differences are also
seen, particularly in knots located along the bright northern limb and near the
base of the northeast jet. A line of curved overlapping filament in the
remnant's northwestern rim appears to mark the location of the remnant's
reverse shock front in this region. Finger-like ejecta structures elsewhere
suggest cases where the reverse shock front is encountering the remnant's
clumped ejecta. Narrow-band [N II] images of the remnant's circumstellar knots
("QSFs") reveal them to be 0.1"-0.6" thick knots and filaments, often with
diffuse edges facing away from the center of expansion. Three color composite
images of the whole remnant and certain sections along with individual filter
enlargements of selected regions of the bright optical shell are presented and
discussed.Comment: 26 pages, 12 figures Accepted to the Astronomical Journa
NGC 7582: The Prototype Narrow-Line X-ray Galaxy
NGC 7582 is a candidate prototype of the Narrow Line X-ray Galaxies (NLXGs)
found in deep X-ray surveys. An ASCA observation shows the hard (> 3 keV) X-ray
continuum of NGC 7582 drops 40% in ~6 ks, implying an AGN, while the soft band
(< 3 keV) does not drop in concert with the hard continuum, requiring a
separate component. The X-ray spectrum of NGC 7582 also shows a clear 0.5-2 keV
soft (kT = 0.8 (+0.9,-0.3) keV or Gamma = 2.4 +/- 0.6; L(X) = 6 x 10**40 ergs
s**-1) low--energy component, in addition to a heavily absorbed [N(H) = (6 +/-
2)\times 10**22 cm**-2 ] and variable 2-10 keV power law [Gamma = 0.7
(+0.3,-0.4); L(X) = (1.7-2.3) x 10**42 ergs s**-1]. This is one of the flattest
2-10 keV slopes in any AGN observed with ASCA. (The ROSAT HRI image of NGC 7582
further suggests extent to the SE.)
These observations make it clear that the hard X-ray emission of NGC 7582,
the most "narrow-line" of the NLXGs, is associated with an AGN. The strong
suggestion is that all NLXGs are obscured AGNs, as hypothesized to explain the
X-ray background spectral paradox. The separate soft X-ray component makes NGC
7582 (and by extension other NLXGs) detectable as a ROSAT source.Comment: text: Latex2e 10 pages, including 1 table, and 2 postscript figures
via psfi
Nitrogen and Oxygen Abundance Variations in the Outer Ejecta of Eta Carinae: Evidence for Recent Chemical Enrichment
We present optical spectra of the ionized `Outer Ejecta' of Eta Carinae that
reveal differences in chemical composition at various positions. In particular,
young condensations just outside the dusty Homunculus Nebula show strong
nitrogen lines and little or no oxygen -- but farther away, nitrogen lines
weaken and oxygen lines become stronger. The observed variations in the
apparent N/O ratio may signify either that the various blobs were ejected with
different abundances, or more likely, that the more distant condensations are
interacting with normal-composition material. The second hypothesis is
supported by various other clues involving kinematics and X-ray emission, and
would suggest that Eta Car is enveloped in a ``cocoon'' deposited by previous
stellar-wind mass loss. In particular, all emission features where we detect
strong oxygen lines are coincident with or outside the soft X-ray shell. In
either case, the observed abundance variations suggest that Eta Car's ejection
of nitrogen-rich material is a recent phenomenon -- taking place in just the
last few thousand years. Thus, Eta Carinae may be at a critical stage of
evolution when ashes of the CNO cycle have just appeared at its surface.
Finally, these spectra reveal some extremely fast nitrogen-rich material, with
Doppler velocities up to 3200 km/s, and actual space velocities that may be
much higher. This is the fastest material yet seen in Eta Car's nebula, but
with unknown projection angles its age is uncertain.Comment: 18 pages, 5 figures, 2 tables. Accepted by ApJ, April 20 200
Structural issues affecting mixed methods studies in health research: a qualitative study
<p>Abstract</p> <p>Background</p> <p>Health researchers undertake studies which combine qualitative and quantitative methods. Little attention has been paid to the structural issues affecting this mixed methods approach. We explored the facilitators and barriers to undertaking mixed methods studies in health research.</p> <p>Methods</p> <p>Face-to-face semi-structured interviews with 20 researchers experienced in mixed methods research in health in the United Kingdom.</p> <p>Results</p> <p>Structural facilitators for undertaking mixed methods studies included a perception that funding bodies promoted this approach, and the multidisciplinary constituency of some university departments. Structural barriers to exploiting the potential of these studies included a lack of education and training in mixed methods research, and a lack of templates for reporting mixed methods articles in peer-reviewed journals. The 'hierarchy of evidence' relating to effectiveness studies in health care research, with the randomised controlled trial as the gold standard, appeared to pervade the health research infrastructure. Thus integration of data and findings from qualitative and quantitative components of mixed methods studies, and dissemination of integrated outputs, tended to occur through serendipity and effort, further highlighting the presence of structural constraints. Researchers are agents who may also support current structures - journal reviewers and editors, and directors of postgraduate training courses - and thus have the ability to improve the structural support for exploiting the potential of mixed methods research.</p> <p>Conclusion</p> <p>The environment for health research in the UK appears to be conducive to mixed methods research but not to exploiting the potential of this approach. Structural change, as well as change in researcher behaviour, will be necessary if researchers are to fully exploit the potential of using mixed methods research.</p
- …