417 research outputs found
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
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
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
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
Multisite photometry of the pulsating Herbig Ae star V346 Ori
CONTEXT: The study of pulsation in Pre--Main--Sequence intermediate-mass
stars represents an important tool for deriving information on fundamental
stellar parameters and internal structure, as well as for testing current
theoretical models. Interest in this class of variable stars has significantly
increased during the last decade and about 30 members are presently known in
the literature. AIMS: We have constructed the frequency spectrum of the
oscillations in V346 Ori. We apply asteroseismic tools to these data to
estimate the intrinsic parameters (mass, luminosity, effective temperature) of
V346 Ori and to obtain information on its internal structure. METHODS: CCD time
series photometry in the Johnson V filter has been obtained for a total of
145.7 h of observations distributed over 36 nights. The resulting light curves
have been subjected to a detailed frequency analysis using updated numerical
techniques. Photometric and spectroscopic data have also been acquired to
determine reliable estimates of the stellar properties. RESULTS: We have
identified 13 oscillation frequencies, 6 of which with higher significance.
These have been compared with the predictions of non-radial adiabatic models.
The resulting best fit model has a mass of 2.10.2 , luminosity
, and effective temperature
7300200 K. These values are marginally consistent with the association of
V346 Ori to Orion OB1a. Alternatively, V346 Ori could be placed at a slightly
larger distance than previously estimated.Comment: Accepted for publication on A&A. 14 Pages, 11 Figure
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
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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