590 research outputs found
Kinematics of subluminous O and B stars by surface helium abundance
The majority of hot subdwarf stars are low-mass core-helium-burning stars. Their atmospheres are generally helium deficient; however, a minority have extremely helium-rich surfaces. An additional fraction have an intermediate surface-helium abundance, occasionally accompanied by peculiar abundances of other elements. We have identified a sample of 88 hot subdwarfs including 38 helium-deficient, 27 intermediate-helium and 23 extreme-helium stars for which radial-velocity and proper-motion measurements, together with distances, allow a calculation of galactic space velocities. We have investigated the kinematics of these three groups to determine whether they belong to similar or different Galactic populations. The majority of helium-deficient subdwarfs in our sample show a kinematic distribution similar to that of thick disc stars. Helium-rich sdBs show a more diverse kinematic distribution. Although the majority are probably disc stars, a minority show a much higher velocity dispersion consistent with membership of a Galactic halo population. Several of the halo subdwarfs are members of the class of âheavy-metalâ subdwarfs discovered by Naslim et al
An analysis of ultraviolet spectra of Extreme Helium Stars and new clues to their origins
Abundances of about 18 elements including the heavy elements Y and Zr are
determined from Hubble Space Telescope Space Telescope Imaging Spectrograph
ultraviolet spectra of seven extreme helium stars (EHes): LSE 78, BD+10 2179,
V1920 Cyg, HD 124448, PV Tel, LS IV -1 2, and FQ Aqr. New optical spectra of
the three stars -- BD+10 2179, V1920 Cyg, and HD 124448 were analysed. The
abundance analyses is done using LTE line formation and LTE model atmospheres
especially constructed for these EHe stars. The stellar parameters derived from
an EHe's UV spectrum are in satisfactory agreement with those derived from its
optical spectrum. Adopted abundances for the seven EHes are from a combination
of the UV and optical analyses. Published results for an additional ten EHes
provide abundances obtained in a nearly uniform manner for a total of 17 EHes,
the largest sample on record. The initial metallicity of an EHe is indicated by
the abundance of elements from Al to Ni; Fe is adopted to be the representative
of initial metallicity. Iron abundances range from approximately solar to about
one-hundredth of solar. Clues to EHe evolution are contained within the H, He,
C, N, O, Y, and Zr abundances. Two novel results are (i) the O abundance for
some stars is close to the predicted initial abundance yet the N abundance
indicates almost complete conversion of initial C, N, and O to N by the
CNO-cycles; (ii) three of the seven stars with UV spectra show a strong
enhancement of Y and Zr attributable to an s-process. The observed compositions
are discussed in light of expectations from accretion of a He white dwarf by a
CO white dwarf.Comment: 126 pages, 15 figures, 20 Tables, accepted for publication in the Ap
Abundance analyses of cool extreme helium stars
Extreme helium stars (EHe) with effective temperatures from 8000K to 13000K
are among the coolest EHe stars and overlap the hotter R CrB stars in effective
temperature. The cool EHes may represent an evolutionary link between the hot
EHes and the R CrBs. Abundance analyses of four cool EHes are presented. To
test for an evolutionary connection, the chemical compositions of cool EHes are
compared with those of hot EHes and R CrBs. Relative to Fe, the N abundance of
these stars is intermediate between those of hot EHes and R CrBs. For the R
CrBs, the metallicity M derived from the mean of Si and S appears to be more
consistent with the kinematics than that derived from Fe. When metallicity M
derived from Si and S replaces Fe, the observed N abundances of EHes and R CrBs
fall at or below the upper limit corresponding to thorough conversion of
initial C and O to N. There is an apparent difference between the composition
of R CrBs and EHes; the former having systematically higher [N/M] ratios. The
material present in the atmospheres of many R CrBs is heavily CN- and
ON-cycled. Most of the EHes have only CN-cycled material in their atmospheres.
There is an indication that the CN- and ON-cycled N in EHes was partially
converted to Ne by -captures. If EHes are to evolve to R CrBs, fresh C
in EHes has to be converted to N. If Ne is found to be normal in R CrBs, the
proposal that EHes evolve to R CrBs fails. The idea that R CrBs evolve to EHes
is ruled out; the N abundance in R CrBs has to be reduced to the level of EHes,
as the C/He which is observed to be uniform across EHes, has to be maintained.
Hence, the inferred [N/M], C/He, [Ne/M], and the H-abundances of these two
groups indicate that the EHes and the R CrBs may not be on the same
evolutionary path.Comment: 24 pages (MNRAS Journal style), 7 tables, 19 figures, Accepted for
publication in MNRA
Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction
With the unprecedented photometric precision of the Kepler Spacecraft,
significant systematic and stochastic errors on transit signal levels are
observable in the Kepler photometric data. These errors, which include
discontinuities, outliers, systematic trends and other instrumental signatures,
obscure astrophysical signals. The Presearch Data Conditioning (PDC) module of
the Kepler data analysis pipeline tries to remove these errors while preserving
planet transits and other astrophysically interesting signals. The completely
new noise and stellar variability regime observed in Kepler data poses a
significant problem to standard cotrending methods such as SYSREM and TFA.
Variable stars are often of particular astrophysical interest so the
preservation of their signals is of significant importance to the astrophysical
community. We present a Bayesian Maximum A Posteriori (MAP) approach where a
subset of highly correlated and quiet stars is used to generate a cotrending
basis vector set which is in turn used to establish a range of "reasonable"
robust fit parameters. These robust fit parameters are then used to generate a
Bayesian Prior and a Bayesian Posterior Probability Distribution Function (PDF)
which when maximized finds the best fit that simultaneously removes systematic
effects while reducing the signal distortion and noise injection which commonly
afflicts simple least-squares (LS) fitting. A numerical and empirical approach
is taken where the Bayesian Prior PDFs are generated from fits to the light
curve distributions themselves.Comment: 43 pages, 21 figures, Submitted for publication in PASP. Also see
companion paper "Kepler Presearch Data Conditioning I - Architecture and
Algorithms for Error Correction in Kepler Light Curves" by Martin C. Stumpe,
et a
A Novel Splice-Site Mutation in VEGFC Is Associated with Congenital Primary Lymphoedema of Gordon.
Lymphedema is characterized by chronic swelling of any body part caused by malfunctioning or obstruction in the lymphatic system. Primary lymphedema is often considered genetic in origin. VEGFC, which is a gene encoding the ligand for the vascular endothelial growth factor receptor 3 (VEGFR3/FLT4) and important for lymph vessel development during lymphangiogenesis, has been associated with a specific subtype of primary lymphedema. Through Sanger sequencing of a proband with bilateral congenital pedal edema resembling Milroy disease, we identified a novel mutation (NM_005429.2; c.361+5G>A) in VEGFC. The mutation induced skipping of exon 2 of VEGFC resulting in a frameshift and the introduction of a premature stop codon (p.Ala50ValfsTer18). The mutation leads to a loss of the entire VEGF-homology domain and the C-terminus. Expression of this Vegfc variant in the zebrafish floorplate showed that the splice-site variant significantly reduces the biological activity of the protein. Our findings confirm that the splice-site variant, c.361+5G>A, causes the primary lymphedema phenotype in the proband. We examine the mutations and clinical phenotypes of the previously reported cases to review the current knowledge in this area
Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
UVO 0825+15 is a hot bright helium-rich subdwarf which lies in K2 Field 5 and in a sample of intermediate helium-rich subdwarfs observed the Subaru High Dispersion Spectrograph. The K2 light curve shows low-amplitude variations, whilst the Subaru spectrum shows PbâIV absorption lines, indicative of a very high lead overabundance. UVO 0825+15 also has a high proper motion with kinematics typical for a thick disc star. Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion and provide fundamental atmospheric parameters of Teff=38 900±270 K, logg/cmsâ2=5.97±0.11, logânHe/nH = â0.57 ± 0.01, EB â V â 0.03, and angular radius Ξ = 1.062 ± 0.006 Ă 10â11 radians (formal errors). The high-resolution spectrum shows that carbon is \u3e2 dex subsolar, iron is approximately solar, and all other elements heavier than argon are at least 2â4 dex overabundant, including germanium, yttrium and lead. Approximately 150 lines in the blue-optical spectrum remain unidentified. The chemical structure of the photosphere is presumed to be determined by radiatively dominated diffusion. The K2 light curve shows a dominant period around 10.8 h, with a variable amplitude, its first harmonic, and another period at 13.3 h. The preferred explanation is multiperiodic non-radial oscillation due to g modes with very high radial order, although this presents difficulties for pulsation theory. Alternative explanations fail for lack of radial-velocity evidence. UVO 0825+15 represents the fourth member of a group of hot subdwarfs having helium-enriched photospheres and 3â4 dex overabundances of trans-iron elements and is the first lead-rich subdwarf to show evidence of pulsations
Discovery of a variable lead-rich hot subdwarf: UVO 0825+15
UVO 0825+15 is a hot bright helium-rich subdwarf which lies in K2 Field 5 and in a sample of intermediate helium-rich subdwarfs observed the Subaru High Dispersion Spectrograph. The K2 light curve shows low-amplitude variations, whilst the Subaru spectrum shows PbâIV absorption lines, indicative of a very high lead overabundance. UVO 0825+15 also has a high proper motion with kinematics typical for a thick disc star. Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion and provide fundamental atmospheric parameters of Teff=38 900±270 K, logg/cmsâ2=5.97±0.11, logânHe/nH = â0.57 ± 0.01, EB â V â 0.03, and angular radius Ξ = 1.062 ± 0.006 Ă 10â11 radians (formal errors). The high-resolution spectrum shows that carbon is \u3e2 dex subsolar, iron is approximately solar, and all other elements heavier than argon are at least 2â4 dex overabundant, including germanium, yttrium and lead. Approximately 150 lines in the blue-optical spectrum remain unidentified. The chemical structure of the photosphere is presumed to be determined by radiatively dominated diffusion. The K2 light curve shows a dominant period around 10.8 h, with a variable amplitude, its first harmonic, and another period at 13.3 h. The preferred explanation is multiperiodic non-radial oscillation due to g modes with very high radial order, although this presents difficulties for pulsation theory. Alternative explanations fail for lack of radial-velocity evidence. UVO 0825+15 represents the fourth member of a group of hot subdwarfs having helium-enriched photospheres and 3â4 dex overabundances of trans-iron elements and is the first lead-rich subdwarf to show evidence of pulsations
Kepler Presearch Data Conditioning I - Architecture and Algorithms for Error Correction in Kepler Light Curves
Kepler provides light curves of 156,000 stars with unprecedented precision.
However, the raw data as they come from the spacecraft contain significant
systematic and stochastic errors. These errors, which include discontinuities,
systematic trends, and outliers, obscure the astrophysical signals in the light
curves. To correct these errors is the task of the Presearch Data Conditioning
(PDC) module of the Kepler data analysis pipeline. The original version of PDC
in Kepler did not meet the extremely high performance requirements for the
detection of miniscule planet transits or highly accurate analysis of stellar
activity and rotation. One particular deficiency was that astrophysical
features were often removed as a side-effect to removal of errors. In this
paper we introduce the completely new and significantly improved version of PDC
which was implemented in Kepler SOC 8.0. This new PDC version, which utilizes a
Bayesian approach for removal of systematics, reliably corrects errors in the
light curves while at the same time preserving planet transits and other
astrophysically interesting signals. We describe the architecture and the
algorithms of this new PDC module, show typical errors encountered in Kepler
data, and illustrate the corrections using real light curve examples.Comment: Submitted to PASP. Also see companion paper "Kepler Presearch Data
Conditioning II - A Bayesian Approach to Systematic Error Correction" by Jeff
C. Smith et a
Spectroscopic abundance analysis of dwarfs in young open cluster IC 4665
We report a detailed spectroscopic abundance analysis for a sample of 18 F-K
dwarfs of the young open cluster IC 4665. Stellar parameters and element
abundances of Li, O, Mg, Si, Ca, Ti, Cr, Fe and Ni have been derived using the
spectroscopic synthesis tool SME (Spectroscopy Made Easy). Within the
measurement uncertainties the iron abundance is uniform with a standard
deviation of 0.04 dex. No correlation is found between the iron abundance and
the mass of the stellar convective zone, and between the Li abundance and the
Fe abundance. In other words, our results do not reveal any signature of
accretion and therefore do not support the scenario that stars with planets
(SWPs) acquire their on the average higher metallicity compared to field stars
via accretion of metal-rich planetary material. Instead the higher metallicity
of SWPs may simply reflect the fact that planet formation is more efficient in
high metallicity environs. However, since that many details of the planet
system formation processes remain poorly understood, further studies are needed
for a final settlement of the problem of the high metallicity of SWPs.
The standard deviation of [Fe/H] deduced from our observations, taken as an
upper limit on the metallicity dispersion amongst the IC 4665 member stars, has
been used to constrain proto-planetary disk evolution, terrestrial and giant
planets formation and evolution processes. Our results do not support the
possibility that the migration of gas giants and the circularization of
terrestrial planets' orbits are regulated by their interaction with a residual
population of planetesimals and dust particles.Comment: 18 pages, 6 figures, accepted for publication in Ap
A combined chemometric and quantitative NMR analysis of HIV/AIDS serum discloses metabolic alterations associated with disease status
Individuals infected with the human immunodeficiency virus (HIV) often suffer from concomitant metabolic
complications. Treatment with antiretroviral therapy has also been shown to alter the metabolism of patients.
Although chemometric analysis of nuclear magnetic resonance (NMR) spectra of human sera can distinguish
normal sera (HIVneg) from HIV-infected sera (HIVpos) and sera from HIV-infected patients on antiretroviral
therapy (ART), quantitative analysis of the discriminating metabolites and their relationship to disease status has
yet to be determined. The objectives of the study were to analyze NMR spectra of HIVneg, HIVpos, and ART
serum samples with a combination of chemometric and quantitative methods and to compare the NMR data
with disease status as measured by viral load and CD4 count. High-resolution magic angle spinning (HRMAS)
NMR spectroscopy was performed on HIVneg (N = 10), HIVpos (N = 10), and ART (N = 10) serum samples.
Chemometric linear discriminant analysis classified the three groups of spectra with 100% accuracy.
Concentrations of 12 metabolites were determined with a semi-parametric metabolite quantification method
named high-resolution quantum estimation (HR-QUEST). CD4 count was directly associated with alanine (p =
0.008), and inversely correlated with both glutamine (p = 0.017) and glucose (p = 0.022) concentrations. A
multivariate linear model using alanine, glutamine and glucose as covariates demonstrated an association with
CD4 count (p = 0.038). The combined chemometric and quantitative analysis of the data disclosed previously
unknown associations between specific metabolites and disease status. The observed associations with CD4
count are consistent with metabolic disorders that are commonly seen in HIV-infected patients.http://www.rsc.org/molecularbiosystemsam201
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