4,952 research outputs found
MOST observations of the roAp stars HD 9289, HD 99563, and HD 134214
We report on the analysis of high-precision space-based photometry of the
roAp (rapidly oscillating Ap) stars HD 9289, HD 99563, and HD134214. All three
stars were observed by the MOST satellite for more than 25 days, allowing
unprecedented views of their pulsation. We find previously unknown candidate
frequencies in all three stars. We establish the rotation period of HD 9289
(8.5 d) for the first time and show that the star is pulsating in two modes
that show different mode geometries. We present a detailed analysis of HD
99563's mode multiplet and find a new candidate frequency which appears
independent of the previously known mode. Finally, we report on 11 detected
pulsation frequencies in HD 134214, 9 of which were never before detected in
photometry, and 3 of which are completely new detections. Thanks to the
unprecedentedly small frequency uncertainties, the p-mode spectrum of HD 134214
can be seen to have a well-defined large frequency spacing similar to the
well-studied roAp star HD 24712 (HR 1217).Comment: 11 pages, 12 figures, accepted for publication in A&
A Tight Upper Limit on Oscillations in the Ap star Epsilon Ursae Majoris from WIRE Photometry
Observations of Epsilon UMa obtained with the star tracker on the Wide Field
Infrared Explorer (WIRE) satellite during a month in mid-2000 are analyzed.
This is one of the most precise photometry of an Ap star. The amplitude
spectrum is used to set an upper limit of 75 parts per million for the
amplitude of stellar pulsations in this star unless it accidentally oscillates
with a single mode at the satellite orbit, its harmonics or their one day
aliases. This is the tightest limit put on the amplitude of oscillations in an
Ap star. As the rotation period of Epsilon UMa is relatively short (5.1 d), it
cannot be argued that the observations were made at a wrong rotational phase.
Our results thus support the idea that some Ap stars do not pulsate at all.Comment: 4 pages, 4 figures, 2 style files, accepted for publication in ApJ
Discovery of unusual pulsations in the cool, evolved Am stars HD 98851 and HD 102480
The chemically peculiar (CP) stars HD 98851 and HD 102480 have been
discovered to be unusual pulsators during the ``Naini Tal Cape Survey''
programme to search for pulsational variability in CP stars. Time series
photometric and spectroscopic observations of these newly discovered stars are
reported here. Fourier analyses of the time series photometry reveal that HD
98851 is pulsating mainly with frequencies 0.208 mHz and 0.103 mHz, and HD
102480 is pulsating with frequencies 0.107 mHz, 0.156 mHz and 0.198 mHz. The
frequency identifications are all subject to 1 d cycle count
ambiguities. We have matched the observed low resolution spectra of HD 98851
and HD 102480 in the range 3500-7400 \AA with theoretical synthetic spectra
using Kurucz models with solar metallicity and a micro-turbulent velocity 2 km
s. These yield K, log for HD 98851
and K, log for HD 102480. We
determined the equivalent H-line spectral class of these stars to be F1 IV and
F3 III/IV, respectively. A comparison of the location of HD 98851 and HD 102480
in the HR diagram with theoretical stellar evolutionary tracks indicates that
both stars are about 1-Gyr-old, 2- stars that lie towards the red
edge of the Sct instability strip. We conclude that HD 98851 and HD
102480 are cool, evolved Am pulsators. The light curves of these pulsating
stars have alternating high and low amplitudes, nearly harmonic (or
sub-harmonic) period ratios, high pulsational overtones and Am spectral types.
This is unusual for both Am and Sct pulsators, making these stars
interesting objects.Comment: 9 pages, 6 Figures, Accepted for publication in MNRA
Suppression of superconductivity in nanowires by bulk superconductors
Transport measurements were made on a system consisting of a zinc nanowire
array sandwiched between two bulk superconducting electrodes (Sn or In). It was
found that the superconductivity of Zn nanowires of 40 nm diameter is
suppressed either completely or partially by the superconducting electrodes.
When the electrodes are driven into their normal state by a magnetic field, the
nanowires switch back to their superconducting state. This phenomenon is
significantly weakened when one of the two superconducting electrodes is
replaced by a normal metal. The phenomenon is not seen in wires with diameters
equal to and thicker than 70 nm.Comment: 4 pages, 5 figure
The Emerging Scholarly Brain
It is now a commonplace observation that human society is becoming a coherent
super-organism, and that the information infrastructure forms its emerging
brain. Perhaps, as the underlying technologies are likely to become billions of
times more powerful than those we have today, we could say that we are now
building the lizard brain for the future organism.Comment: to appear in Future Professional Communication in Astronomy-II
(FPCA-II) editors A. Heck and A. Accomazz
A spectroscopic analysis of the chemically peculiar star HD207561
In this paper we present a high-resolution spectroscopic analysis of the
chemically peculiar star HD207561. During a survey programme to search for new
roAp stars in the Northern hemisphere, Joshi et al. (2006) observed significant
photometric variability on two consecutive nights in the year 2000. The
amplitude spectra of the light curves obtained on these two nights showed
oscillations with a frequency of 2.79 mHz [P~6-min]. However, subsequent
follow-up observations could not confirm any rapid variability. In order to
determine the spectroscopic nature of HD207561, high-resolution spectroscopic
and spectro-polarimetric observations were carried out. A reasonable fit of the
calculated Hbeta line profile to the observed one yields the effective
temperature (Teff) and surface gravity (log g) as 7300 K and 3.7 dex,
respectively. The derived projected rotational velocity (vsin i) for HD207561
is 74 km/sec indicative of a relatively fast rotator. The position of HD207561
in the H-R diagram implies that this is slightly evolved from the main-sequence
and located well within the delta-Scuti instability strip. The abundance
analysis indicates the star has slight under-abundances of Ca and Sc and mild
over-abundances of iron-peak elements. The spectro-polarimetric study of
HD207561 shows that the effective magnetic field is within the observational
error of 100 gauss (G). The spectroscopic analysis revealed that the star has
most of the characteristics similar to an Am star, rather than an Ap star, and
that it lies in the delta-Scuti instability strip; hence roAp pulsations are
not expected in HD207561, but low-overtone modes might be excited.Comment: 8 pages, 7 figures, 3 tables. Accepted for pubblication in MNRA
High power arcjet
The activities on the development of the high power arc jet HIPARC, the thrust balance, and plasma diagnostic probes are discussed. Modifications of the HIPARC design and a synopsis of the materials used are given. Further experimental results with the TT30 thruster in the 50 kW range are presented. Some first calibration measurements of the thrust balance are also included. Progress concerning the development of plasma diagnostic devices is documented
Radiation hardness of Ga0.5In0.5 P/GaAs tandem solar cells
The radiation hardness of a two-junction monolithic Ga sub 0.5 In sub 0.5 P/GaAs cell with tunnel junction interconnect was investigated. Related single junction cells were also studied to identify the origins of the radiation losses. The optimal design of the cell is discussed. The air mass efficiency of an optimized tandem cell after irradiation with 10(exp 15) cm (-2) 1 MeV electrons is estimated to be 20 percent using currently available technology
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