413 research outputs found
The CoRoT star ID100866999: a hybrid gamma Doradus - delta Scuti star in an eclipsing binary system
The presence of g- and p-modes allows testing stellar models from the core to
the envelope. Moreover, binarity in an eclipsing system constrains the physical
parameters of the pulsating star. CoRot ID 100866999 is a relatively
large-amplitude hybrid gDor - dSct star with two clearly distinct frequency
domains. The large number of detected frequencies allows a detailed study of
the interaction between them. In addition, we can derive the fundamental
parameters of both components from the study of the eclipsing light curve.
After removing the eclipsing phases, we analyzed the data with the Period04
package up to S/N=4. The light curve was then prewhitened with these
oscillation frequencies to derive the fundamental parameters of the two
components. The eclipsing light curve analysis results in a (1.8+1.1)\,Mo
system, both components being main sequence stars. We detect 124 frequencies
related to luminosity variations of the primary. They are present in two
well-separated domains: 89 frequencies in the interval [0.30;3.64]/d and 35 in
the interval [14.57; 33.96]/d. There are 22 gDor frequencies separated by a
constant period interval Delta P = 0.03493 d. These frequencies correspond to a
series of g-modes of degree ell=1 with successive radial orders k. We identify
21 linear combinations between the first nine gDor frequencies. The dSct domain
is dominated by a large-amplitude frequency F=16.9803 /d. The eight first gDor
frequencies f_i are present with much lower amplitude in the delta Scuti domain
as F +/- f_i. These interactions between g- and p-modes confirm the phenomenon
we detected in another CoRoT star. The amplitude and the phase of the main
frequency F shows a double-wave modulation along the orbital phase, giving rise
to series of combination frequencies. Such combination frequencies are also
detected, with lower amplitude, for the first gDor modes.Comment: Table 2 is available electronically from CD
First Results of the EDELWEISS WIMP Search using a 320 g Heat-and-Ionization Ge Detector
The EDELWEISS collaboration has performed a direct search for WIMP dark
matter using a 320 g heat-and-ionization cryogenic Ge detector operated in a
low-background environment in the Laboratoire Souterrain de Modane. No nuclear
recoils are observed in the fiducial volume in the 30-200 keV energy range
during an effective exposure of 4.53 kg.days. Limits for the cross-section for
the spin-independent interaction of WIMPs and nucleons are set in the framework
of the Minimal Supersymmetric Standard Model (MSSM). The central value of the
signal reported by the experiment DAMA is excluded at 90% CL.Comment: 14 pages, Latex, 4 figures. Submitted to Phys. Lett.
Spectroscopic Pulsational Frequency Identification and Mode Determination of Gamma Doradus Star HD135825
We present the mode identification of frequencies found in spectroscopic
observations of the Gamma Doradus star HD135825. Four frequencies were
successfully identified: 1.3150 +/- 0.0003 1/d; 0.2902 +/- 0.0004 1/d; 1.4045
+/- 0.0005 1/d; and 1.8829 +/- 0.0005 1/d. These correspond to (l, m) modes of
(1,1), (2,-2), (4,0) and (1,1) respectively. Additional frequencies were found
but they were below the signal-to-noise limit of the Fourier spectrum and not
suitable for mode identification. The rotational axis inclination and vsini of
the star were determined to be 87 degrees (nearly edge-on) and 39.7 km/s
(moderate for Gamma Doradus stars) respectively. A simultaneous fit of these
four modes to the line profile variations in the data gives a reduced chi
square of 12.7. We confirm, based on the frequencies found, that HD135825 is a
bona fide Gamma Doradus star.Comment: Accepted to MNRAS 2012 March
A photometric mode identification method, including an improved non-adiabatic treatment of the atmosphere
We present an improved version of the method of photometric mode
identification of Heynderickx et al. (1994). Our new version is based on the
inclusion of precise non-adiabatic eigenfunctions determined in the outer
stellar atmosphere according to the formalism recently proposed by Dupret et
al.(2002). Our improved photometric mode identification technique is therefore
no longer dependent on ad hoc parameters for the non-adiabatic effects. It
contains the complete physical conditions of the outer atmosphere of the star,
provided that rotation does not play a key role. We apply our improved method
to the two slowly pulsating B stars HD 74560 and HD 138764 and to the beta
Cephei star EN (16) Lac. Besides identifying the degree l of the pulsating
stars, our method is also a tool for improving the knowledge of stellar
interiors and atmospheres, by imposing constraints on parameters such as the
metallicity and the mixing-length parameter alpha (a procedure we label
non-adiabatic asteroseismology).Comment: 10 pages, 9 figures Accepted for publication in Astronomy and
Astrophysic
gamma Doradus stars in the COROT exoplanets fields: first inspection
We present here preliminary results concerning 32 stars identified as main
gamma Doradus candidates by the COROT Variable Classifier (CVC) among the 4
first fields of the exoplanet CCDs.Comment: To appear in "Stellar Pulsation: Challenges for Theory and
Observation", AI
Strong interactions between g- and p-modes in the hybrid gamma Doradus-delta Scuti CoRoT star ID105733033
CoRoT ID 105733033 is an excellent example of hybrid pulsators as it shows g-
and p-modes with almost similar amplitudes in two clearly distinct frequency
domains.
Classical Fourier analysis allows the dectection of frequencies with an
amplitude as small as 0.1 mmag up to 50c/d. The frequency spectrum of CoRoT ID
105733033 clearly consists of two distinct ranges, which are typical of gamma
Doradus and delta Scuti pulsation. Focus was placed on the identification of
linear combinations and frequencies due to the coupling between gamma Doradus
and delta Scuti modes.
We detect 198 gamma Doradus type frequencies in the range [0.25;4]c/d, of
which 180 are not combination frequencies, and 24 of them are separated by a
constant period-interval Delta P=0.03074d. According to the asymptotic theory,
these 24 frequencies correspond to a series of g-modes of the same ell-degree
and different radial orders n. We also detect 246 delta Scuti type frequencies
in the range [10.1;63.4]c/d. The dominant frequency F=12.6759c/d was identified
as the fundamental radial mode. Our most noteworthy result is that all the main
gamma Doradus frequencies f_i are also detected in the delta Scuti domain as F
+- f_i with four times smaller amplitudes. Once these frequencies were removed,
only 59 can be considered as individual delta Scuti frequencies.
A coupling between g- and p-modes is proposed to be a tool for detecting
g-modes in the Sun, but this coupling has never yet been observed. Our present
study may be valuable input to theoretical studies, addressing the mutual
influence of g- and p-mode cavities and the deviation from classical theory.
Furthermore, we identify a sequence of g-modes belonging to the same ell but
with consecutive orders n
HD 173977: An ellipsoidal d Scuti star variable
Astronomy and Astrophysics, v. 426, p. 247-252, 2004. http://dx.doi.org/10.1051/0004-6361:20034068International audienc
Measurement of the response of heat-and-ionization germanium detectors to nuclear recoils
The heat quenching factor Q' (the ratio of the heat signals produced by
nuclear and electron recoils of equal energy) of the heat-and-ionization
germanium bolometers used by the EDELWEISS collaboration has been measured. It
is explained how this factor affects the energy scale and the effective
quenching factor observed in calibrations with neutron sources. This effective
quenching effect is found to be equal to Q/Q', where Q is the quenching factor
of the ionization yield. To measure Q', a precise EDELWEISS measurement of Q/Q'
is combined with values of Q obtained from a review of all available
measurements of this quantity in tagged neutron beam experiments. The
systematic uncertainties associated with this method to evaluate Q' are
discussed in detail. For recoil energies between 20 and 100 keV, the resulting
heat quenching factor is Q' = 0.91+-0.03+-0.04, where the two errors are the
contributions from the Q and Q/Q' measurements, respectively. The present
compilation of Q values and evaluation of Q' represent one of the most precise
determinations of the absolute energy scale for any detector used in direct
searches for dark matter.Comment: 28 pages, 7 figures. Submitted to Phys. Rev.
Background discrimination capabilities of a heat and ionization germanium cryogenic detector
The discrimination capabilities of a 70 g heat and ionization Ge bolometer
are studied. This first prototype has been used by the EDELWEISS Dark Matter
experiment, installed in the Laboratoire Souterrain de Modane, for direct
detection of WIMPs. Gamma and neutron calibrations demonstrate that this type
of detector is able to reject more than 99.6% of the background while retaining
95% of the signal, provided that the background events distribution is not
biased towards the surface of the Ge crystal. However, the 1.17 kg.day of data
taken in a relatively important radioactive environment show an extra
population slightly overlapping the signal. This background is likely due to
interactions of low energy photons or electrons near the surface of the
crystal, and is somewhat reduced by applying a higher charge-collecting inverse
bias voltage (-6 V instead of -2 V) to the Ge diode. Despite this
contamination, more than 98% of the background can be rejected while retaining
50% of the signal. This yields a conservative upper limit of 0.7
event.day^{-1}.kg^{-1}.keV^{-1}_{recoil} at 90% confidence level in the 15-45
keV recoil energy interval; the present sensitivity appears to be limited by
the fast ambient neutrons. Upgrades in progress on the installation are
summarized.Comment: Submitted to Astroparticle Physics, 14 page
Event categories in the EDELWEISS WIMP search experiment
Four categories of events have been identified in the EDELWEISS-I dark matter
experiment using germanium cryogenic detectors measuring simultaneously charge
and heat signals. These categories of events are interpreted as electron and
nuclear interactions occurring in the volume of the detector, and electron and
nuclear interactions occurring close to the surface of the detectors(10-20 mu-m
of the surface). We discuss the hypothesis that low energy surface nuclear
recoils,which seem to have been unnoticed by previous WIMP searches, may
provide an interpretation of the anomalous events recorded by the UKDMC and
Saclay NaI experiments. The present analysis points to the necessity of taking
into account surface nuclear and electron recoil interactions for a reliable
estimate of background rejection factors.Comment: 11 pages, submitted to Phys. Lett.
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