149 research outputs found
Development of high-performance light-weight electrodes for hydrogen-oxygen fuel cells Second quarterly report, Jul. 6 - Oct. 5, 1965
High performance lightweight electrodes for hydrogen-oxygen fuel cell
Development of high-performance lightweight electrodes for hydrogen-oxygen fuel cells Third quarterly report, 6 Oct. 1965 - 5 Jan. 1966
High performance, lightweight electrodes for hydrogen-oxygen fuel cell
High-performance light-weight electrodes for hydrogen-oxygen fuel cells
High performance light weight electrodes for hydrogen oxygen fuel cell
Research and development of high-performance light-weight fuel cell electrodes final report, nov. 1, 1963 - oct. 31, 1964
High performance light weight fuel cell electrode developmen
A Spectroscopic Survey of a Sample of Active M Dwarfs
A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray
selected M dwarfs with photometric distances less than 25 pc is presented.
Radial and rotation velocities have been measured by fits to the H-alpha
profiles. Radial velocities have been measured by cross correlation. Artificial
broadening of an observed spectrum has produced a relationship between H-alpha
FWHM and rotation speed, which we use to infer rotation speeds for the entire
sample by measurement of the H-alpha emission line. We find 3 ultra-fast
rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The
UFRs have variable emission. Cross-correlation velocities measured for
ultra-fast rotators (UFRs) are shown to depend on rotation speed and the
filtering used. The radial velocity dispersion of the sample is 17 km/s. A new
double emission line spectroscopic binary with a period of 3.55 days has been
discovered, and another known one is in the sample. Three other objects are
suspected spectroscopic binaries, and at least six are visual doubles. The only
star in the sample observed to have significant lithium is a known TW Hya
Association member, TWA 8A. These results show that there are a number of young
(< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar
neighbourhood. The H-alpha activity strength does not depend on rotation speed.
Our fast rotators are less luminous than similarly fast rotators in the
Pleiades. They are either younger than the Pleiades, or gained angular momentum
in a different way.Comment: 38 pages incl. 14 figures and 4 tables, plus 12 pages of table for
electronic journal only; LaTeX, aastex.cls. Accepted 07/18/02 for publication
in The Astronomical Journa
Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo
We report the results of a high temporal resolution spectroscopic monitoring
of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in
the optical range using the Isaac Newton Telescope (INT) and the Intermediate
Dispersion Spectrograph (IDS). We have observed a large number of short and
weak flares occurring very frequently (flare activity > 0.71 hours-1). This is
in favour of the very important role that flares can play in stellar coronal
heating. The detected flares are non white-light flares and, though most of
solar flares belong to this kind, very few such events had been previously
observed on stars. The behaviour of different chromospheric lines (Balmer
series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I
D_3) has been studied in detail for a total of 14 flares. We have also
estimated the physical parameters of the flaring plasma by using a procedure
which assumes a simplified slab model of flares. All the obtained physical
parameters are consistent with previously derived values for stellar flares,
and the areas - less than 2.3% of the stellar surface - are comparable with the
size inferred for other solar and stellar flares. Finally, we have studied the
relationships between the physical parameters and the area, duration, maximum
flux and energy released during the detected flares.Comment: Latex file with 17 pages, 11 figures. Available at
http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted
for publication in: Astronomy & Astrophysics (A&A
Integrated transcriptome catalogue and organ-specific profiling of gene expression in fertile garlic (Allium sativum L.)
New periodic variable stars coincident with ROSAT sources discovered using SuperWASP
We present optical lightcurves of 428 periodic variable stars coincident with ROSAT X-ray sources, detected using the first run of the SuperWASP photometric survey. Only 68 of these were previously recognised as periodic variables. A further 30 of these objects are previously known pre-main sequence stars, for which we detect a modulation period for the first time. Amongst the newly identified periodic variables, many appear to be close eclipsing binaries, their X-ray emission is presumably the result of RS CVn type behaviour. Others are probably BY Dra stars, pre-main sequence stars and other rapid rotators displaying enhanced coronal activity. A number of previously catalogued pulsating variables (RR Lyr stars and Cepheids) coincident with X-ray sources are also seen, but we show hat these are likely to be misclassifications. We identify four objects which are probable low mass eclipsing binary stars, based on
their very red colour and light curve morphology
The effect of magnetic activity saturation in chromospheric flux-flux relationships
We present a homogeneous study of chromospheric and coronal flux-flux
relationships using a sample of 298 late-type dwarf active stars with spectral
types F to M. The chromospheric lines were observed simultaneously in each star
to avoid spread due to long term variability. Unlike other works, we subtract
the basal chromospheric contribution in all the spectral lines studied. For the
first time, we quantify the departure of dMe stars from the general relations.
We show that dK and dKe stars also deviate from the general trend. Studying the
flux-colour diagrams we demonstrate that the stars deviating from the general
relations are those with saturated X-ray emission and that those stars also
present saturation in the H line. Using several age spectral
indicators, we show that they are younger stars than those following the
general relationships. The non-universality of flux-flux relationships found in
this work should be taken into account when converting between fluxes in
different chromospheric activity indicators.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Societ
Chromospheric activity, lithium and radial velocities of single late-type stars possible members of young moving groups
We present here high resolution echelle spectra taken during three observing
runs of 14 single late-type stars identified in our previous studies (Montes et
al. 2001b, hereafter Paper I) as possible members of different young stellar
kinematic groups (Local Association (20 - 150 Myr), Ursa Major group (300 Myr),
Hyades supercluster (600 Myr), and IC 2391 supercluster (35 Myr)). Radial
velocities have been determined by cross correlation with radial velocity
standard stars and used together with precise measurements of proper motions
and parallaxes taken from Hipparcos and Tycho-2 Catalogues, to calculate
Galactic space motions (U, V, W) and to apply Eggen's kinematic criteria. The
chromospheric activity level of these stars have been analysed using the
information provided for several optical spectroscopic features (from the Ca II
H & K to Ca II IRT lines) that are formed at different heights in the
chromosphere. The Li I 6707.8 AA line equivalent width (EW) has been determined
and compared in the EW(Li I) versus spectral type diagram with the EW(Li I) of
stars members of well known young open clusters of different ages, in order to
obtain an age estimation. All these data allow us to analyse in more detail the
membership of these stars in the different young stellar kinematic groups.
Using both kinematic and spectroscopic criteria we have confirmed PW And, V368
Cep, V383 Lac, EP Eri, DX Leo, HD 77407, and EK Dra as members of the Local
Association and V834 Tau, pi^{1} UMa, and GJ 503.2 as members of the Ursa Major
group. A clear rotation-activity dependence has been found in these stars.Comment: Latex file with 19 pages, 7 figures tar'ed gzip'ed. Full postscript
(text, figures and tables) available at
http://www.ucm.es/info/Astrof/p_skg_stars_I_fv.ps.gz Accepted for publication
in: Astronomy & Astrophysics (A&A
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