459 research outputs found
Seismology of Procyon A: determination of mode frequencies, amplitudes, lifetimes, and granulation noise
The F5 IV-V star Procyon A (aCMi) was observed in January 2001 by means of
the high resolution spectrograph SARG operating with the TNG 3.5m Italian
telescope (Telescopio Nazionale Galileo) at Canary Islands, exploiting the
iodine cell technique. The time-series of about 950 spectra carried out during
6 observation nights and a preliminary data analysis were presented in Claudi
et al. 2005. These measurements showed a significant excess of power between
0.5 and 1.5 mHz, with ~ 1 m/s peak amplitude. Here we present a more detailed
analysis of the time-series, based on both radial velocity and line equivalent
width analyses. From the power spectrum we found a typical p-mode frequency
comb-like structure, identified with a good margin of certainty 11 frequencies
in the interval 0.5-1400 mHz of modes with l=0,1,2 and 7< n < 22, and
determined large and small frequency separations, Dn = 55.90 \pm 0.08 muHz and
dnu_02=7.1 \pm 1.3 muHz, respectively. The mean amplitude per mode (l=0,1) at
peak power results to be 0.45 \pm 0.07 m/s, twice larger than the solar one,
and the mode lifetime 2 \pm 0.4 d, that indicates a non-coherent, stochastic
source of mode excitation. Line equivalent width measurements do not show a
significant excess of power in the examined spectral region but allowed us to
infer an upper limit to the granulation noise.Comment: 10 pages, 15 figures, 4 tables. Accepted for publication in A&
Solar-like oscillations in the G9.5 subgiant beta Aquilae
An interesting asteroseismic target is the G9.5 IV solar-like star beta Aql.
This is an ideal target for asteroseismic investigations, because precise
astrometric measurements are available from Hipparcos that greatly help in
constraining the theoretical interpretation of the results. The star was
observed during six nights in August 2009 by means of the high-resolution
\'echelle spectrograph SARG operating with the TNG 3.58 m Italian telescope on
the Canary Islands, exploiting the iodine cell technique. We present the result
and the detailed analysis of high-precision radial velocity measurements, where
the possibility of detecting time individual p-mode frequencies for the first
and deriving their corresponding asymptotic values will be discussed. The
time-series analysis carried out from \sim 800 collected spectra shows the
typical p-mode frequency pattern with a maximum centered at 416 \muHz. In the
frequency range 300 - 600 \muHz we identified for the first time six high S/N
(\gtrsim 3.5) modes with l = 0,2 and 11 < n < 16 and three possible candidates
for mixed modes (l = 1), although the p-mode identification for this type of
star appears to be quite difficult owing to a substantial presence of avoided
crossings. The large frequency separation and the surface term from the set of
identified modes by means of the asymptotic relation were derived for the first
time. Their values are \Delta \nu = 29.56 \pm 0.10 \muHz and \epsilon = 1.29
\pm 0.04, consistent with expectations. The most likely value for the small
separation is \delta\nu_{02} = 2.55 \pm 0.71 \muHz.Comment: 8 pages, 8 figures, 3 tables, accepted by A&
First spectroscopic investigation of Anomalous Cepheid variables
Anomalous Cepheids (ACEPs) are intermediate mass metal-poor pulsators mostly
discovered in dwarf galaxies of the Local Group. However, recent Galactic
surveys, including the Gaia DR3, found a few hundreds of ACEPs in the Milky
Way. Their origin is not well understood. We aim to investigate the origin and
evolution of Galactic ACEPs by studying for the first time the chemical
composition of their atmospheres. We used UVES@VLT to obtain high-resolution
spectra for a sample of 9 ACEPs belonging to the Galactic halo. We derived the
abundances of 12 elements, including C, Na, Mg, Si, Ca, Sc, Ti, Cr, Fe, Ni, Y,
and Ba. We complemented these data with literature abundances for an additional
three ACEPs that were previously incorrectly classified as type II Cepheids,
thus increasing the sample to a total of 12 stars. All the investigated ACEPs
have an iron abundance [Fe/H] dex as expected from theoretical
predictions for these pulsators. The abundance ratios of the different elements
to iron show that the ACEP's chemical composition is generally consistent with
that of the Galactic halo field stars, except the Sodium, which is found
overabundant in 9 out of the 11 ACEPs where it was measured, in close
similarity with second-generation stars in the Galactic Globular Clusters. The
same comparison with dwarf and ultra-faint satellites of the Milky Way reveals
more differences than similarities so it is unlikely that the bulk of Galactic
ACEPs originated in such a kind of galaxies which subsequently dissolved in the
Galactic halo. The principal finding of this work is the unexpected
overabundance of Sodium in ACEPs. We explored several hypotheses to explain
this feature, finding that the most promising scenario is the evolution of
low-mass stars in a binary system with either mass transfer or merging.
Detailed modelling is needed to confirm this hypothesis.Comment: 15 Figures, 4 Tables, Accepted for publication on Astronomy &
Astrophysic
Oscillations in Procyon A: First results from a multi-site campaign
Procyon A is a bright F5IV star in a binary system. Although the distance,
mass and angular diameter of this star are all known with high precision, the
exact evolutionary state is still unclear. Evolutionary tracks with different
ages and different mass fractions of hydrogen in the core pass, within the
errors, through the observed position of Procyon A in the Hertzsprung-Russell
diagram. For more than 15 years several different groups have studied the
solar-like oscillations in Procyon A to determine its evolutionary state.
Although several studies independently detected power excess in the
periodogram, there is no agreement on the actual oscillation frequencies yet.
This is probably due to either insufficient high-quality data (i.e., aliasing)
or due to intrinsic properties of the star (i.e., short mode lifetimes). Now a
spectroscopic multi-site campaign using 10 telescopes world-wide (minimizing
aliasing effects) with a total time span of nearly 4 weeks (increase the
frequency resolution) is performed to identify frequencies in this star and
finally determine its properties and evolutionary state.Comment: 7 pages, 4 figures to be published in the proceedings of HELAS II
International Conference: Helioseismology, Asteroseismology and MHD
Connections published in the Journal of Physics: Conference Series. High
resolution colour figures can be provided on reques
Study of 2 beta-decay of Mo-100 and Se-82 using the NEMO3 detector
After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of Mo-100 (T-1/2 > 3.1 x 10(23) y, 90% CL) and Se-82 (T-1/2 > 1.4 x 10(23) y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: 1.4 x 10(22) y (90% CL) for Mo-100 and T-1/2 > 1.2 x 10(22) y (90% CL) for Se-82. Corresponding bounds on the Majoron-neutrino coupling constant are < (0.5-0.9) x 10(- 4) and <(0.7-1.6) x 10(- 4). Two-neutrino 2beta-decay half-lives have been measured with a high accuracy, (T1/2Mo)-Mo-100 = [7.68 +/- 0.02(stat) +/- 0.54(syst)] x 10(18) y and (T1/2Se)-Se-82 = [10.3 +/- 0.3(stat) +/- 0.7(syst)] x 10(19) y. (C) 2004 MAIK "Nauka/Interperiodica"
Technical design and performance of the NEMO3 detector
The development of the NEMO3 detector, which is now running in the Frejus
Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun
more than ten years ago. The NEMO3 detector uses a tracking-calorimeter
technique in order to investigate double beta decay processes for several
isotopes. The technical description of the detector is followed by the
presentation of its performance.Comment: Preprint submitted to Nucl. Instrum. Methods A Corresponding author:
Corinne Augier ([email protected]
Kepler observations of Am stars
We present an analysis of high-resolution spectra for two pulsating Am stars in the Kepler field. The stellar parameters derived in this way are important because parameters derived from narrow-band photometry may be affected by the strong metal lines in these stars. We analyse the Kepler time series of ten known Am stars and find that six of them clearly show δ Scuti pulsations. The other four appear to be non-pulsating. We derive fundamental parameters for all known pulsating Am stars from ground-based observations and also for the Kepler Am stars to investigate the location of the instability strip for pulsating Am stars. We find that there is not much difference between the Am-star instability strip and the δ Scuti instability strip. We find that the observed location of pulsating Am stars in the HR diagram does not agree with the location predicted from diffusion calculation
Study of 2b-decay of Mo-100 and Se-82 using the NEMO3 detector
After analysis of 5797 h of data from the detector NEMO3, new limits on
neutrinoless double beta decay of Mo-100 (T_{1/2} > 3.1 10^{23} y, 90% CL) and
Se-82 (T_{1/2} > 1.4 10^{23} y, 90% CL) have been obtained. The corresponding
limits on the effective majorana neutrino mass are: m < (0.8-1.2) eV and m <
(1.5-3.1) eV, respectively. Also the limits on double-beta decay with Majoron
emission are: T_{1/2} > 1.4 10^{22} y (90% CL) for Mo-100 and T_{1/2}> 1.2
10^{22} y (90%CL) for Se-82. Corresponding bounds on the Majoron-neutrino
coupling constant are g < (0.5-0.9) 10^{-4} and < (0.7-1.6) 10^{-4}.
Two-neutrino 2b-decay half-lives have been measured with a high accuracy,
T_{1/2} Mo-100 = [7.68 +- 0.02(stat) +- 0.54(syst) ] 10^{18} y and T_{1/2}
Se-82 = [10.3 +- 0.3(stat) +- 0.7(syst) ] 10^{19} y.Comment: 5 pages, 4 figure
Asteroseismology of Procyon A with SARG at TNG
We present high precision radial velocity measurements on the F5 IV star
alpha CMi obtained by the SARG spectrograph at TNG (Telescopio Nazionale
Galileo) exploiting the iodine cell technique. The time series of about 950
spectra of Procyon A taken during 6 observation nights are affected by an
individual error of 1.3 m/s. Thanks to the iodine cell technique, the
spectrograph contribution to the Doppler shift measurement error is quite
negligible and our error is dominated by the photon statistics Brown et al
1994. An excess of power between 0.5 and 1.5 mHz, detected also by Martic et
al. 2004 has been found. We determined a large separation frequency Delta nu0 =
56\pm 2 microHz, consistent with both theoretical estimates Chaboyer et al.
1999 and previous observations Martic et al. 2004.Comment: 4 pages, 5 figures, accepted to be published in A&A Letter
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