463 research outputs found
The Absolute Magnitude of RRc Variables From Statistical Parallax
We present the first definitive measurement of the absolute magnitude of RR
Lyrae c-type variable stars (RRc) determined purely from statistical parallax.
We use a sample of 247 RRc selected from the All Sky Automated Survey (ASAS)
for which high-quality light curves, photometry and proper motions are
available. We obtain high-resolution echelle spectra for these objects to
determine radial velocities and abundances as part of the Carnegie RR Lyrae
Survey (CARRS). We find that M_(V,RRc) = 0.52 +/- 0.11 at a mean metallicity of
[Fe/H] = -1.59. This is to be compared with previous estimates for RRab stars
(M_(V,RRab) = 0.75 +/- 0.13 and the only direct measurement of an RRc absolute
magnitude (RZ Cephei, M_(V, RRc) = 0.27 +/- 0.17). We find the bulk velocity of
the halo to be (W_pi, W_theta, W_z) = (10.9,34.9,7.2) km/s in the radial,
rotational and vertical directions with dispersions (sigma_(W_pi),
sigma_(W_theta), sigma_(W_z)) = (154.7, 103.6, 93.8) km/s. For the disk, we
find (W_pi, W_theta, W_z) = (8.5, 213.2, -22.1) km/s with dispersions
(sigma_(W_pi), sigma_(W_theta), sigma_(W_z)) = (63.5, 49.6, 51.3) km/s.
Finally, we suggest that UCAC2 proper motion errors may be overestimated by
about 25%Comment: Submitted to ApJ. 11 pages including 6 figure
Kepler Mission Stellar and Instrument Noise Properties
Kepler Mission results are rapidly contributing to fundamentally new
discoveries in both the exoplanet and asteroseismology fields. The data
returned from Kepler are unique in terms of the number of stars observed,
precision of photometry for time series observations, and the temporal extent
of high duty cycle observations. As the first mission to provide extensive time
series measurements on thousands of stars over months to years at a level
hitherto possible only for the Sun, the results from Kepler will vastly
increase our knowledge of stellar variability for quiet solar-type stars. Here
we report on the stellar noise inferred on the timescale of a few hours of most
interest for detection of exoplanets via transits. By design the data from
moderately bright Kepler stars are expected to have roughly comparable levels
of noise intrinsic to the stars and arising from a combination of fundamental
limitations such as Poisson statistics and any instrument noise. The noise
levels attained by Kepler on-orbit exceed by some 50% the target levels for
solar-type, quiet stars. We provide a decomposition of observed noise for an
ensemble of 12th magnitude stars arising from fundamental terms (Poisson and
readout noise), added noise due to the instrument and that intrinsic to the
stars. The largest factor in the modestly higher than anticipated noise follows
from intrinsic stellar noise. We show that using stellar parameters from
galactic stellar synthesis models, and projections to stellar rotation,
activity and hence noise levels reproduces the primary intrinsic stellar noise
features.Comment: Accepted by ApJ; 26 pages, 20 figure
Advection-Dominated Accretion and the Spectral States of Black Hole X-Ray Binaries: Application to Nova Muscae 1991
We present a self-consistent model of accretion flows which unifies four
distinct spectral states observed in black hole X-ray binaries: quiescent, low,
intermediate and high states. In the quiescent, low and intermediate states,
the flow consists of an inner hot advection-dominated part extending from the
black hole horizon to a transition radius and an outer thin disk. In the high
state the thin disk is present at all radii. The model is essentially
parameter-free and treats consistently the dynamics of the accretion flow, the
thermal balance of the ions and electrons, and the radiation processes in the
accreting gas. With increasing mass accretion rate, the model goes through a
sequence of stages for which the computed spectra resemble very well
observations of the four spectral states; in particular, the low-to-high state
transition observed in black hole binaries is naturally explained as resulting
from a decrease in the transition radius. We also make a tentative proposal for
the very high state, but this aspect of the model is less secure.
We test the model against observations of the soft X-ray transient Nova
Muscae during its 1991 outburst. The model reproduces the observed lightcurves
and spectra surprisingly well, and makes a number of predictions which can be
tested with future observations.Comment: 68 pages, LaTeX, includes 1 table (forgotten in the previous version)
and 14 figures; submitted to The Astrophysical Journa
The specificity and patterns of staining in human cells and tissues of p16INK4a antibodies demonstrate variant antigen binding
The validity of the identification and classification of human cancer using antibodies to detect biomarker proteins depends upon antibody specificity. Antibodies that bind to the tumour-suppressor protein p16INK4a are widely used for cancer diagnosis and research. In this study we examined the specificity of four commercially available anti-p16INK4a antibodies in four immunological applications. The antibodies H-156 and JC8 detected the same 16 kDa protein in western blot and immunoprecipitation tests, whereas the antibody F-12 did not detect any protein in western blot analysis or capture a protein that could be recognised by the H-156 antibody. In immunocytochemistry tests, the antibodies JC8 and H-156 detected a predominately cytoplasmic localised antigen, whose signal was depleted in p16INK4a siRNA experiments. F-12, in contrast, detected a predominately nuclear located antigen and there was no noticeable reduction in this signal after siRNA knockdown. Furthermore in immunohistochemistry tests, F-12 generated a different pattern of staining compared to the JC8 and E6H4 antibodies. These results demonstrate that three out of four commercially available p16INK4a antibodies are specific to, and indicate a mainly cytoplasmic localisation for, the p16INK4a protein. The F-12 antibody, which has been widely used in previous studies, gave different results to the other antibodies and did not demonstrate specificity to human p16INK4a. This work emphasizes the importance of the validation of commercial antibodies, aside to the previously reported use, for the full verification of immunoreaction specificity
Weak Lensing with SDSS Commissioning Data: The Galaxy-Mass Correlation Function To 1/h Mpc
(abridged) We present measurements of galaxy-galaxy lensing from early
commissioning imaging data from the Sloan Digital Sky Survey (SDSS). We measure
a mean tangential shear around a stacked sample of foreground galaxies in three
bandpasses out to angular radii of 600'', detecting the shear signal at very
high statistical significance. The shear profile is well described by a
power-law. A variety of rigorous tests demonstrate the reality of the
gravitational lensing signal and confirm the uncertainty estimates. We
interpret our results by modeling the mass distributions of the foreground
galaxies as approximately isothermal spheres characterized by a velocity
dispersion and a truncation radius. The velocity dispersion is constrained to
be 150-190 km/s at 95% confidence (145-195 km/s including systematic
uncertainties), consistent with previous determinations but with smaller error
bars. Our detection of shear at large angular radii sets a 95% confidence lower
limit , corresponding to a physical radius of
kpc, implying that galaxy halos extend to very large radii. However, it is
likely that this is being biased high by diffuse matter in the halos of groups
and clusters. We also present a preliminary determination of the galaxy-mass
correlation function finding a correlation length similar to the galaxy
autocorrelation function and consistency with a low matter density universe
with modest bias. The full SDSS will cover an area 44 times larger and provide
spectroscopic redshifts for the foreground galaxies, making it possible to
greatly improve the precision of these constraints, measure additional
parameters such as halo shape, and measure the properties of dark matter halos
separately for many different classes of galaxies.Comment: 28 pages, 11 figures, submitted to A
Expanding the horizon of research into the pathogenesis of the white matter diseases: Proceedings of the 2021 Annual Workshop of the Albert Research Institute for White Matter and Cognition
White matter pathologies are critically involved in the etiology of vascular cognitive impairment–dementia (VCID), Alzheimer’s disease (AD), and Alzheimer’s disease and related diseases (ADRD), and therefore need to be considered a treatable target (Roseborough A, Hachinski V, Whitehead S. White matter degeneration - a treatable target? Roseborough et al. JAMA Neurol [Internet]. 2020 Apr 27;77(7):793–4, [1]. To help address this often-missed area of research, several workshops have been sponsored by the Leo and Anne Albert Charitable Trust since 2015, resulting in the incorporation of “The Albert Research Institute for White Matter and Cognition” in 2020. The first annual “Institute” meeting was held virtually on March 3–4, 2021. The Institute provides a forum and workspace for communication and support of the advancement of white matter science and research to better understand the evolution and prevention of dementia. It serves as a platform for young investigator development, to introduce new data and debate biology mechanisms and new ideas, and to encourage and support new research collaborations and directions to clarify how white matter changes, with other genetic and health risk factors, contribute to cognitive impairment. Similar to previous Albert Trust–sponsored workshops (Barone et al. in J Transl Med 14:1–14, [2]; Sorond et al. in GeroScience 42:81–96, [3]), established expert investigators were identified and invited to present. Opportunities to attend and present were also extended by invitation to talented research fellows and younger scientists. Also, updates on institute-funded research collaborations were provided and discussed. The summary that follows is a synopsis of topics and discussion covered in the workshop
Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
We report the distribution of planets as a function of planet radius (R_p),
orbital period (P), and stellar effective temperature (Teff) for P < 50 day
orbits around GK stars. These results are based on the 1,235 planets (formally
"planet candidates") from the Kepler mission that include a nearly complete set
of detected planets as small as 2 Earth radii (Re). For each of the 156,000
target stars we assess the detectability of planets as a function of R_p and P.
We also correct for the geometric probability of transit, R*/a. We consider
first stars within the "solar subset" having Teff = 4100-6100 K, logg =
4.0-4.9, and Kepler magnitude Kp < 15 mag. We include only those stars having
noise low enough to permit detection of planets down to 2 Re. We count planets
in small domains of R_p and P and divide by the included target stars to
calculate planet occurrence in each domain. Occurrence of planets varies by
more than three orders of magnitude and increases substantially down to the
smallest radius (2 Re) and out to the longest orbital period (50 days, ~0.25
AU) in our study. For P < 50 days, the radius distribution is given by a power
law, df/dlogR= k R^\alpha. This rapid increase in planet occurrence with
decreasing planet size agrees with core-accretion, but disagrees with
population synthesis models. We fit occurrence as a function of P to a power
law model with an exponential cutoff below a critical period P_0. For smaller
planets, P_0 has larger values, suggesting that the "parking distance" for
migrating planets moves outward with decreasing planet size. We also measured
planet occurrence over Teff = 3600-7100 K, spanning M0 to F2 dwarfs. The
occurrence of 2-4 Re planets in the Kepler field increases with decreasing
Teff, making these small planets seven times more abundant around cool stars
than the hottest stars in our sample. [abridged]Comment: Submitted to ApJ, 22 pages, 10 figure
The Type Ia Supernova Rate in Redshift 0.5--0.9 Galaxy Clusters
Supernova (SN) rates are potentially powerful diagnostics of metal enrichment
and SN physics, particularly in galaxy clusters with their deep,
metal-retaining potentials and relatively simple star-formation histories. We
have carried out a survey for supernovae (SNe) in galaxy clusters, at a
redshift range 0.5<z<0.9, using the Advanced Camera for Surveys (ACS) on the
Hubble Space Telescope. We reimaged a sample of 15 clusters that were
previously imaged by ACS, thus obtaining two to three epochs per cluster, in
which we discovered five likely cluster SNe, six possible cluster SNe Ia, two
hostless SN candidates, and several background and foreground events. Keck
spectra of the host galaxies were obtained to establish cluster membership. We
conducted detailed efficiency simulations, and measured the stellar
luminosities of the clusters using Subaru images. We derive a cluster SN rate
of 0.35 SNuB +0.17/-0.12 (statistical) \pm0.13 (classification) \pm0.01
(systematic) [where SNuB = SNe (100 yr 10^10 L_B_sun)^-1] and 0.112 SNuM
+0.055/-0.039 (statistical) \pm0.042 (classification) \pm0.005 (systematic)
[where SNuM = SNe (100 yr 10^10 M_sun)^-1]. As in previous measurements of
cluster SN rates, the uncertainties are dominated by small-number statistics.
The SN rate in this redshift bin is consistent with the SN rate in clusters at
lower redshifts (to within the uncertainties), and shows that there is, at
most, only a slight increase of cluster SN rate with increasing redshift. The
low and fairly constant SN Ia rate out to z~1 implies that the bulk of the iron
mass in clusters was already in place by z~1. The recently observed doubling of
iron abundances in the intracluster medium between z=1 and 0, if real, is
likely the result of redistribution of existing iron, rather than new
production of iron.Comment: Accepted to ApJ. Full resolution version available at
http://kicp.uchicago.edu/~kerens/HSTclusterSNe
Recommended from our members
Adjustments in Torque Steadiness During Fatiguing Contractions Are Inversely Correlated With IQ in Persons With Multiple Sclerosis
Fatigue is one of the most debilitating symptoms of multiple sclerosis (MS), and the underlying mechanisms are poorly understood. When exposed to a physical or cognitive challenge, individuals with MS tend to exhibit greater declines in task performance (performance fatigability) and increased levels of self-reported fatigue (perceived fatigability), but these effects may be attenuated by greater intellectual capacity. The purpose of our study was to examine the influence of intelligence on fatigability in persons with MS. We hypothesized that greater intellectual capacity confers some protection against heightened levels of fatigue and fatigability associated with MS. Twelve adults with relapsing-remitting MS were compared with 12 control (CO) subjects who were matched for age, sex, and premorbid intellectual capacity. Performance fatigability was measured as the decline in maximal voluntary contraction (MVC) torque after 60 isometric contractions (10 s contraction at 25% MVC, 5 s rest) performed with the knee extensor muscles. Perceived fatigability was assessed with the modified fatigue impact scale (MFIS) questionnaire (trait fatigability) and the Borg rating of perceived exertion (RPE, state fatigability). Persons with MS reported greater MFIS scores (MS: 43 ± 14; CO: 11 ± 8, P ≤ 0.001). Initial MVC torque for the knee extensors did not differ between the groups (MS: 112 ± 38 N⋅m; CO: 107 ± 44 N⋅m) and the decline (performance fatigability) was similar for both groups (MS: -16 ± 19 N⋅m; CO: -13 ± 16 N⋅m). RPE increased during the fatiguing contraction for both groups (P < 0.001) but was significantly greater in magnitude (main effect for group, P = 0.03) and increased more for the MS group (group × time interaction, P = 0.05). Torque steadiness declined during the fatiguing contractions (main effect for time, P = 0.05) and was less steady for the MS group (main effect for group, P = 0.02). Performance and full-4 IQ was correlated with the decline in torque steadiness for the MS group (r = -0.63, P < 0.05; r = -0.64, P < 0.05). Intellectual capacity was not associated with fatigability in persons with MS but was associated with adjustments in muscle activation during the fatiguing contractions
Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
New transiting planet candidates are identified in sixteen months (May 2009 -
September 2010) of data from the Kepler spacecraft. Nearly five thousand
periodic transit-like signals are vetted against astrophysical and instrumental
false positives yielding 1,091 viable new planet candidates, bringing the total
count up to over 2,300. Improved vetting metrics are employed, contributing to
higher catalog reliability. Most notable is the noise-weighted robust averaging
of multi-quarter photo-center offsets derived from difference image analysis
which identifies likely background eclipsing binaries. Twenty-two months of
photometry are used for the purpose of characterizing each of the new
candidates. Ephemerides (transit epoch, T_0, and orbital period, P) are
tabulated as well as the products of light curve modeling: reduced radius
(Rp/R*), reduced semi-major axis (d/R*), and impact parameter (b). The largest
fractional increases are seen for the smallest planet candidates (197% for
candidates smaller than 2Re compared to 52% for candidates larger than 2Re) and
those at longer orbital periods (123% for candidates outside of 50-day orbits
versus 85% for candidates inside of 50-day orbits). The gains are larger than
expected from increasing the observing window from thirteen months (Quarter 1--
Quarter 5) to sixteen months (Quarter 1 -- Quarter 6). This demonstrates the
benefit of continued development of pipeline analysis software. The fraction of
all host stars with multiple candidates has grown from 17% to 20%, and the
paucity of short-period giant planets in multiple systems is still evident. The
progression toward smaller planets at longer orbital periods with each new
catalog release suggests that Earth-size planets in the Habitable Zone are
forthcoming if, indeed, such planets are abundant.Comment: Submitted to ApJS. Machine-readable tables are available at
http://kepler.nasa.gov, http://archive.stsci.edu/kepler/results.html, and the
NASA Exoplanet Archiv
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