325 research outputs found
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
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
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
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
Measurement of double beta decay of ¹⁰⁰Mo to excited states in the NEMO 3 experiment
The double beta decay of ¹⁰⁰Mo to the 0_{1}^{+} and 2_{1}^{+} excited states of ¹⁰⁰Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of ¹⁰⁰Mo to the excited 0_{1}^{+} state is measured to be T_{1/2}^{2v} = [5.7_{-0.9}^{+1.3} (stat.) ± 0.8 (syst.)] x 10²⁰ y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0_{1}^{+} state has been found. The corresponding half-life limit is T_{1/2}^{0v} (0⁺→0_{1}^{+}) > 8.9 x 10²² y (at 90% C.L.). The search for the double beta decay to the 2_{1}^{+} excited state has allowed the determination of limits on the half-life for the two neutrino mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.1 x 10²¹ y (at 90% C.L.) and for the neutrinoless mode T_{1/2}^{0v} (0⁺→2_{1}^{+}) > 1.6 x 10²³ y (at 90% C.L.)
The star formation in the L1615/L1616 cometary cloud
The present work aims at performing a comprehensive census and
characterisation of the pre-main sequence (PMS) population in the cometary
cloud L1615/L1616, in order to assess the significance of the triggered star
formation scenario and investigate the impact of massive stars on its star
formation history and mass spectrum. Our study is based on UBVRcIc and JHKs
photometry, as well as optical multi-object spectroscopy. We performed a
physical parametrisation of the young stellar population in L1615/L1616. We
identified 25 new T Tauri stars mainly projected on the dense head of the
cometary cloud, almost doubling the current number of known members. We studied
the spatial distribution of the cloud members as a function of the age and
H emission. The star formation efficiency in the cloud is about 7-8 %,
as expected for molecular clouds in the vicinity of OB associations. The slope
of the initial mass function (IMF), in the mass range 0.1<M<5.5 , is
consistent with that of other T and OB associations, providing further support
of an universal IMF down to the hydrogen burning limit, regardless of
environmental conditions. The cometary appearance, as well as the high star
formation efficiency, can be explained in terms of triggered star formation
induced by the strong UV radiation from OB stars or supernovae shockwaves. The
age spread as well as both the spatial and age distribution of the PMS objects
provide strong evidence of sequential, multiple events and possibly still
ongoing star formation activity in the cloud.Comment: 59 pages, 14 figures, accepted for publication in Ap
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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