356 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&
Detection of solar-like oscillations in the G5 subgiant mu-Herculis
A clear detection of excess of power, providing a substantial evidence for
solar-like oscillations in the G5 subgiant \muher{}, is presented. This star
was observed over seven nights with the SARG echelle spectrograph operating
with the 3.6-m Italian TNG Telescope, using an iodine absorption cell as a
velocity reference. A clear excess of power centered at 1.2 mHz, with peak
amplitudes of about 0.9 \ms in the amplitude spectrum is present. Fitting the
asymptotic relation to the power spectrum, a mode identification for the
modes in the frequency range 900-1600 \muHz is derived. The
most likely value for the large separation turns out to be 56.5 \muHz,
consistent with theoretical expectations. The mean amplitude per mode ()
at peak power results to be , almost three times larger than
the solar one.Comment: 8 pages, 6 figures, ApJ to appea
HD344787: a true Polaris analogue?
Classical Cepheids (DCEPs) are the most important primary indicators for the
extragalactic distance scale, but they are also important objects per se,
allowing us to put constraints on the physics of intermediate-mass stars and
the pulsation theories. We have investigated the peculiar DCEP HD 344787, which
is known to exhibit the fastest positive period change among DCEPs along with a
quenching amplitude of the light variation. We have used high-resolution
spectra obtained with HARPS-N@TNG for HD 344787 and the more famous Polaris
DCEP, to infer their detailed chemical abundances. Results from the analysis of
new time-series photometry of HD 344787 obtained by the TESS satellite are also
reported. The double mode nature of HD344787 pulsation is confirmed by analysis
of the TESS light curve, although with rather tiny amplitudes of a few tens of
millimag. This is an indication that HD344787 is on the verge of quenching the
pulsation. Analysis of the HARPS-N@TNG spectra reveals an almost solar
abundance and no depletion of carbon and oxygen. Hence, the star appears to
have not gone through the first dredge-up. Similar results are obtained for
Polaris. Polaris and HD344787 are confirmed to be both most likely at their
first crossing of the instability strip (IS). The two stars are likely at the
opposite borders of the IS for first overtone DCEPs with metal abundance
Z=0.008. A comparison with other DCEPs which are also thought to be at their
first crossing allows us to speculate that the differences we see in the
Hertzsprung-Russell diagram might be due to differences in the properties of
the DCEP progenitors during the main sequence phase.Comment: 9 pages, 6 figures, Astronomy & Astrophysics in press. Version
corrected by Language Edito
V363 Cas: a new lithium rich Galactic Cepheid
Classical Cepheids (DCEPs) are important astrophysical objects not only as
standard candles in the determination of the cosmic distance ladder, but also
as a testbed for the stellar evolution theory, thanks to the strict connection
between their pulsation [period(s), amplitudes] and stellar (luminosity, mass,
effective temperature, metallicity) parameters. We aim at unveiling the nature
of the Galactic DCEP V363 Cas and other DCEPs showing cosmic abundances of
lithium in their atmospheres. We have collected three epochs high-resolution
spectroscopy for V363 Cas with HARPS-N@TNG. Accurate stellar parameters:
effective temperatures, gravities, micro-turbulences, radial velocities, and
metal abundances were measured for this star. We detected a lithium abundance
of A(Li)=2.86+-0.10 dex, along with iron, carbon and oxygen abundances of
[Fe/H]=-0.30+-0.12 dex, [C/H]=-0.06+-0.15 dex and [O/H]=0.00+-0.12 dex. V363
Cas is the fifth among the Milky Way DCEPs to exhibit a Li-rich feature. An
analysis of historical time-series spanning a hundred year interval shows that
the period of V363 Cas is increasing, with a sharp acceleration after
HJD=2453000. This is a clear hint of first crossing of the instability strip.
Our results favour the scenario in which the five Galactic Li-rich DCEPs are
first-crossing the instability strip having had slowly-rotating progenitors
during their main sequence phase.Comment: Accepted on Astronomy and Astrophysics (Letter). 5 Page
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 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
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