217 research outputs found
The Na I D resonance lines in main sequence late-type stars
We study the sodium D lines (D1: 5895.92 \AA; D2: 5889.95 \AA) in late-type
dwarf stars. The stars have spectral types between F6 and M5.5 (B-V between
0.457 and 1.807) and metallicity between [Fe/H] = -0.82 and 0.6. We obtained
medium resolution echelle spectra using the 2.15-m telescope at the argentinian
observatory CASLEO. The observations have been performed periodically since
1999. The spectra were calibrated in wavelength and in flux. A definition of
the pseudo-continuum level is found for all our observations. We also define a
continuum level for calibration purposes. The equivalent width of the D lines
is computed in detail for all our spectra and related to the colour index (B-V)
of the stars. When possible, we perform a careful comparison with previous
studies. Finally, we construct a spectral index (R_D') as the ratio between the
flux in the D lines, and the bolometric flux. We find that, once corrected for
the photospheric contribution, this index can be used as a chromospheric
activity indicator in stars with a high level of activity. Additionally, we
find that combining some of our results, we obtain a method to calibrate in
flux stars of unknown colour.Comment: 12 pages, including 14 figures and 4 tables. Accepted for publication
in MNRA
The Large Quasar Reference Frame (LQRF) - an optical representation of the ICRS
The large number and all-sky distribution of quasars from different surveys,
along with their presence in large, deep astrometric catalogs,enables the
building of an optical materialization of the ICRS following its defining
principles. Namely: that it is kinematically non-rotating with respect to the
ensemble of distant extragalactic objects; aligned with the mean equator and
dynamical equinox of J2000; and realized by a list of adopted coordinates of
extragalatic sources. Starting from the updated and presumably complete LQAC
list of QSOs, the initial optical positions of those quasars are found in the
USNO B1.0 and GSC2.3 catalogs, and from the SDSS DR5. The initial positions are
next placed onto UCAC2-based reference frames, following by an alignment with
the ICRF, to which were added the most precise sources from the VLBA calibrator
list and the VLA calibrator list - when reliable optical counterparts exist.
Finally, the LQRF axes are inspected through spherical harmonics, contemplating
to define right ascension, declination and magnitude terms. The LQRF contains
J2000 referred equatorial coordinates for 100,165 quasars, well represented
across the sky, from -83.5 to +88.5 degrees in declination, and with 10 arcmin
being the average distance between adjacent elements. The global alignment with
the ICRF is 1.5 mas, and the individual position accuracies are represented by
a Poisson distribution that peaks at 139 mas in right ascension and 130 mas in
declination. It is complemented by redshift and photometry information from the
LQAC. The LQRF is designed to be an astrometric frame, but it is also the basis
for the GAIA mission initial quasars' list, and can be used as a test bench for
quasars' space distribution and luminosity function studies.Comment: 23 pages, 23 figures, 6 tables Accepted for publication by Astronomy
& Astrophysics, on 25 May 200
Mg II h + k emission lines as stellar activity indicators of main sequence F-K stars
The main purpose of this study is to use the IUE spectra in the analysis of
magnetic activity of main sequence F-K stars. Combining IUE observations of
MgII and optical spectroscopy of Ca II, the registry of ctivity of stars can be
extended in time. We retrieved all the high-resolution spectra of F, G, and K
main sequence stars observed by IUE (i.e. 1623 spectra of 259 F to K dwarf
stars). We obtained the continuum surface flux near the Mg II h+k lines near
2800 \AA and the MgII line-core surface flux from the IUE spectra. We obtained
a relation between the mean continuum flux near the MgII lines with the colour
of the star. For a set of 117 nearly simultaneous observations of Mg II
and Ca II fluxes of 21 F5 to K3 main sequence stars, we obtained a colour
dependent relation between the Mount Wilson CaII S-index and the MgII emission
line-core flux. As an application of this calibration, we computed the Mount
Wilson index for all the dF to dK stars which have high resolution IUE spectra.
For some of the most frequently observed main sequence stars, we analysed the
Mount Wilson index S from the IUE spectra, together with the ones derived from
visible spectra. We confirm the cyclic chromospheric activity of epsilon Eri
(HD 22049) and beta Hydri (HD 2151), and we find a magnetic cycle in alpha Cen
B (HD 128621). Complete abstract in the paper.Comment: 10 pages, accepted for publication in Astronomy and Astrophysic
Correlating corneal arcus with atherosclerosis in familial hypercholesterolemia
Abstract Background A relationship between corneal arcus and atherosclerosis has long been suspected but is controversial. The homozygous familial hypercholesterolemia patients in this study present a unique opportunity to assess this issue. They have both advanced atherosclerosis and corneal arcus. Methods This is a cross-sectional study of 17 patients homozygous for familial hypercholesterolemia presenting to the Clinical Center of the National Institutes of Health. Plasma lipoproteins, circumferential extent of arcus, thoracic aorta and coronary calcific atherosclerosis score, and Achilles tendon width were measured at the National Institutes of Health. Results Patients with corneal arcus had higher scores for calcific atherosclerosis (mean 2865 compared to 412), cholesterol-year score (mean 11830 mg-yr/dl compared to 5707 mg-yr/dl), and Achilles tendon width (mean 2.54 cm compared to 1.41 cm) than those without. Corneal arcus and Achilles tendon width were strongly correlated and predictive of each other. Although corneal arcus was correlated with calcific atherosclerosis (r = 0.67; p = 0.004), it was not as highly correlated as was the Achilles tendon width (r = 0.855; p Conclusion Corneal arcus reflects widespread tissue lipid deposition and is correlated with both calcific atherosclerosis and xanthomatosis in these patients. Patients with more severe arcus tend to have more severe calcific atherosclerosis. Corneal arcus is not as good an indicator of calcific atherosclerosis as Achilles tendon thickness, but its presence suggests increased atherosclerosis in these hypercholesterolemic patients.</p
On the relative merits of simple and advanced constitutive models in dynamic analysis of tunnels
OGLE-II High Proper Motion Stars towards the Galactic centre
The photometry data base of the second phase of the OGLE microlensing
experiment, OGLE-II, is a rich source of information about the kinematics and
structure of the Galaxy. In this work we use the OGLE-II proper motion
catalogue to identify candidate stars which have high proper motions. 521 stars
with proper motion mu > 50 mas/yr in the OGLE-II proper motion catalogue (Sumi
2004) were cross-identified with stars in the MACHO high proper motion
catalogue, and the DENIS and 2MASS infra-red photometry catalogues. Photometric
distances were computed for stars with colours consistent with G/K and M type
stars. 6 stars were newly identified as possible nearby (< 50 pc) M dwarfs.Comment: 7 figures and 4 tables, MNRAS, accepte
Subjects with Molecularly Defined Familial Hypercholesterolemia or Familial Defective apoB-100 Are Not Being Adequately Treated
To study whether subjects with a molecular genetic diagnosis of familial hypercholesterolemia (FH) or familial defective apoB-100 (FDB) are being adequately treated.A questionnaire regarding medical history was sent to 2611 subjects who had been provided with a molecular genetic diagnosis of FH or FDB, and a blood sample was obtained for lipid measurements.956 (36.6%) of the 2611 subjects participated. The mean age for starting lipid-lowering therapy was 33.4 (±12.1) years. Among those below 18 years of age, only 20.4% were on lipid-lowering drugs, whereas 89.1% of those aged 18 and above were on lipid-lowering drugs. The mean levels of total serum cholesterol and LDL-cholesterol were 5.7 (±1.5) mmol/l and 3.9 (±1.3) mmol/l, respectively. Among those who were on lipid-lowering drugs, 29.0% and 12.2% had levels of LDL cholesterol below 3.0 mmol/l and 2.6 mmol/l, respectively. Only 47.3% of the 956 subjects were considered as being adequately treated largely due to a failure to titrate their drug regimens. From the use of cholesterol-years score, lipid-lowering therapy must start before the age of 20 in order to prevent the subjects from contracting premature coronary heart disease.The majority of FH/FDB subjects are being diagnosed late in life and are not being adequately treated. In order to prevent them from contracting premature coronary heart disease, it is key that levels of LDL cholesterol are normalized from a young age and that sufficient doses of lipid-lowering drugs are being used
Long-term chromospheric activity of non-eclipsing RS CVn-type stars
Context. The IUE database provides a large number of UV high and
low-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular,
many of these stars were monitored continuously during several seasons by IUE.
Aims. Our main purpose is to study the short and long-term chromospheric
activity of the RS CVn systems most observed by IUE: HD 22468 (V711 Tau, HR
1099, K1IV+G5V), HD 21242 (UX Ari, K0IV+G5V) and HD 224085 (II Peg, K2IV).
Methods. We first obtain the Mount Wilson index S from the IUE high and
low-resolution spectra. Secondly, we analyse with the Lomb-Scargle periodogram
the mean annual index S and the amplitude of its rotational modulation.
Results. For HD 22468 (V711 Tau, HR 1099), we found a possible chromospheric
cycle with a period of 18 years and a shorter cycle with a period of 3 years,
which could be associated to a chromospheric "flip-flop" cycle. The data of HD
224085 (II Peg) also suggest a chromospheric cycle of 21 years and a flip-flop
cycle of 9 years. Finally, we obtained a possible chromospheric cycle of 7
years for HD 21242 (UX Ari).Comment: accepted for publication in Astronomy and Astrophysic
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