79 research outputs found
Gaia photometry for white dwarfs
Context. White dwarfs can be used to study the structure and evolution of the Galaxy by analysing their luminosity function and initial mass function. Among them, the very cool white dwarfs provide the information for the early ages of each population. Because white dwarfs are intrinsically faint only the nearby (~ 20 pc) sample is reasonably complete. The Gaia space mission will drastically increase the sample of known white dwarfs through its 5-6 years survey of the whole sky up to magnitude V = 20-25. Aims. We provide a characterisation of Gaia photometry for white dwarfs to better prepare for the analysis of the scientific output of the mission. Transformations between some of the most common photometric systems and Gaia passbands are derived. We also give estimates of the number of white dwarfs of the different galactic populations that will be observed. Methods. Using synthetic spectral energy distributions and the most recent Gaia transmission curves, we computed colours of three different types of white dwarfs (pure hydrogen, pure helium, and mixed composition with H/He = 0.1). With these colours we derived transformations to other common photometric systems (Johnson-Cousins, Sloan Digital Sky Survey, and 2MASS). We also present numbers of white dwarfs predicted to be observed by Gaia. Results. We provide relationships and colour-colour diagrams among different photometric systems to allow the prediction and/or study of the Gaia white dwarf colours. We also include estimates of the number of sources expected in every galactic population and with a maximum parallax error. Gaia will increase the sample of known white dwarfs tenfold to about 200 000. Gaia will be able to observe thousands of very cool white dwarfs for the first time, which will greatly improve our understanding of these stars and early phases of star formation in our Galaxy
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
Abridged: We estimate the distances to ~48 million stars detected by the
Sloan Digital Sky Survey and map their 3D number density distribution in 100 <
D < 20 kpc range over 6,500 deg^2 of sky. The data show strong evidence for a
Galaxy consisting of an oblate halo, a disk component, and a number of
localized overdensities with exponential disk parameters (bias-corrected for an
assumed 35% binary fraction) H_1 = 300 pc, L_1 = 2600 pc, H_2 = 900 pc, L_2 =
3600 pc, and local density normalization of 12%. We find the halo to be oblate,
with best-fit axis ratio c/a = 0.64, r^{-2.8} profile, and the local
halo-to-thin disk normalization of 0.5%. We estimate the errors of derived
model parameters to be no larger than ~20% (disk scales) and ~10% (thick disk
normalization). While generally consistent with the above model, the density
distribution shows a number of statistically significant localized deviations.
We detect two overdensities in the thick disk region at (R, Z) ~ (6.5, 1.5)kpc
and (R, Z) ~ (9.5, 0.8) kpc, and a remarkable density enhancement in the halo
covering >1000deg^2 of sky towards the constellation of Virgo, at distances of
~6-20 kpc. Compared to a region symmetric with respect to the l=0 line, the
Virgo overdensity is responsible for a factor of 2 number density excess and
may be a nearby tidal stream or a low-surface brightness dwarf galaxy merging
with the Milky Way. After removal of the resolved overdensities, the remaining
data are consistent with a smooth density distribution; we detect no evidence
of further unresolved clumpy substructure at scales ranging from ~50pc in the
disk, to ~1 - 2 kpc in the halo.Comment: 60 pages, 46 figures (reduced resolution; see the ApJ for hi-res
version
Seeding Science, Courting Conclusions: Reexamining the Intersection of Science, Corporate Cash, and the Law
Social scientists have expressed strong views on corporate influences over science, but most attention has been devoted to broad, Black/White arguments, rather than to actual mechanisms of influence. This paper summarizes an experience where involvement in a lawsuit led to the discovery of an unexpected mechanism: A large corporation facing a multibillion-dollar court judgment quietly provided generous funding to well-known scientists (including at least one Nobel prize winner) who would submit articles to "open," peer-reviewed journals, so that their "unbiased science" could be cited in an appeal to the Supreme Court. On balance, the corporation's most effective techniques of influence may have been provided not by overt pressure, but by encouraging scientists to continue thinking of themselves as independent and impartial
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Genome-wide analysis of 53,400 people with irritable bowel syndrome highlights shared genetic pathways with mood and anxiety disorders
Funder: Kennedy Trust Rheumatology Research Prize StudentshipFunder: DFG Cluster of Excellence “Precision Medicine in Chronic In-flammation” (PMI; ID: EXC2167)Funder: EC | EC Seventh Framework Programm | FP7 Ideas: European Research Council (FP7-IDEAS-ERC - Specific Programme: “Ideas” Implementing the Seventh Framework Programme of the European Community for Research, Technological Development and Demonstration Activities (2007 to 2013)); doi: https://doi.org/10.13039/100011199; Grant(s): 715772Funder: NWO-VIDI grant 016.178.056, the Netherlands Heart Foundation CVON grant 2018-27, and NWO Gravitation grant ExposomeNLFunder: Li Ka Shing Foundation (Li Ka Shing Foundation Limited); doi: https://doi.org/10.13039/100007421Abstract: Irritable bowel syndrome (IBS) results from disordered brain–gut interactions. Identifying susceptibility genes could highlight the underlying pathophysiological mechanisms. We designed a digestive health questionnaire for UK Biobank and combined identified cases with IBS with independent cohorts. We conducted a genome-wide association study with 53,400 cases and 433,201 controls and replicated significant associations in a 23andMe panel (205,252 cases and 1,384,055 controls). Our study identified and confirmed six genetic susceptibility loci for IBS. Implicated genes included NCAM1, CADM2, PHF2/FAM120A, DOCK9, CKAP2/TPTE2P3 and BAG6. The first four are associated with mood and anxiety disorders, expressed in the nervous system, or both. Mirroring this, we also found strong genome-wide correlation between the risk of IBS and anxiety, neuroticism and depression (rg > 0.5). Additional analyses suggested this arises due to shared pathogenic pathways rather than, for example, anxiety causing abdominal symptoms. Implicated mechanisms require further exploration to help understand the altered brain–gut interactions underlying IBS
i Housing for Youth Aging Out of Foster Care ACKNOWLEDGMENTS
The authors gratefully acknowledge the valuable contributions others have made to this study. We particularly appreciate the excellent guidance of Anne Fletcher in the Office of Polic
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