620 research outputs found
Line profile analysis of the Delta Scuti star HD2724=BB Phe: mode identification and amplitude variations
The line profile variations of the Delta Scuti star HD 2724=BB Phe were
studied on the basis of new 189 high-resolution spectrograms covering 52 hours
of observations on a baseline of 8.3 days. By combining these results with
those of a previous campaign 13 pulsation modes were identified: 5 of them are
both photometric and spectroscopic, 3 are purely spectroscopic and 5 purely
photometric. For the first time it was possible to compare spectroscopic data
taken in two different seasons: 6 modes were found to be common to both
datasets and furthermore strong amplitude variations of the excited modes were
detected. The fit of the line profile variations with a model of non-radial
pulsating star allowed us to obtain a reasonable estimate of the inclination of
the rotational axis and to propose the l,m typing of the spectroscopic modes.
The frequency content resembles that of 4 CVn, a delta Sct star with similar
physical parameters.Comment: 7 pages (in A&A style), 5 ps figures (Fig. 4 in colour) Accepted for
A&A Main Journa
Search for second overtone Cepheids in the Magellanic Clouds. I. Study of three candidates in the SMC
Accurate CCD observations of three Cepheids in the SMC were made with the
purpose of confirming their nature of second overtone mode Cepheids. The stars
were suspected pulsating in the second overtone mode owing to the unusual light
curve and short period reported by Payne-Gaposchkin & Gaposchkin (1966). The
analysis of the new data shows that for two stars the previous periods are
wrong, and in the three cases the new light curves are normal. According to the
new observations, HV 1353 is a fundamental mode pulsator with small amplitude,
and HV 1777 and HV 1779 are first overtone mode pulsators.
Also the star HV 1763, whose nature was unknown, was observed in the field of
HV 1777. The new data show that it is a first overtone mode Cepheid with
P=2.117d.Comment: 6 pages, 8 figures. To be published in A&A Suppl.Se
Coefficient of thermal expansion of nanostructured tungsten based coatings assessed by thermally induced substrate curvature method
The in plane coefficient of thermal expansion (CTE) and the residual stress
of nanostructured W based coatings are extensively investigated. The CTE and
the residual stresses are derived by means of an optimized ad-hoc developed
experimental setup based on the detection of the substrate curvature by a laser
system. The nanostructured coatings are deposited by Pulsed Laser Deposition.
Thanks to its versatility, nanocrystalline W metallic coatings,
ultra-nano-crystalline pure W and W-Tantalum coatings and amorphous-like W
coatings are obtained. The correlation between the nanostructure, the residual
stress and the CTE of the coatings are thus elucidated. We find that all the
samples show a compressive state of stress that decreases as the structure goes
from columnar nanocrystalline to amorphous-like. The CTE of all the coatings is
higher than the one of the corresponding bulk W form. In particular, as the
grain size shrinks, the CTE increases from 5.1 10 K for
nanocrystalline W to 6.6 10 K in the ultra-nano-crystalline
region. When dealing with amorphous W, the further increase of the CTE is
attributed to a higher porosity degree of the samples. The CTE trend is also
investigated as function of materials stiffness. In this case, as W coatings
become softer, the easier they thermally expand.Comment: The research leading to these results has also received funding from
the European Research Council Consolidator Grant ENSURE (ERC-2014-CoG No.
647554
Search for low instability strip variables in the young open cluster NGC 2516
In this paper we revise and complete the photometric survey of the
instability strip of the southern open cluster NGC 2516 published by Antonello
and Mantegazza (1986). No variable stars with amplitudes larger than
were found. However by means of an accurate analysis based on a new statistical
method two groups of small amplitude variables have been disentangled: one with
periods (probably Scuti stars) and one with periods
. The position in the HR diagram and the apparent time-scale may
suggest that the stars of the second group belong to a recently discovered new
class of variables, named Dor variables. They certainly deserve
further study. We also present a comparison between the results of the
photometric survey and the available pointed ROSAT observations of this
cluster.Comment: 7 pages, 2 ps figures. Accepted for P.A.S.
Spectroscopic Survey of {\gamma} Doradus Stars I. Comprehensive atmospheric parameters and abundance analysis of {\gamma} Doradus stars
We present a spectroscopic survey of known and candidate \,Doradus
stars. The high-resolution, high signal-to-noise spectra of 52 objects were
collected by five different spectrographs. The spectral classification,
atmospheric parameters (\teff, , ), and chemical
composition of the stars were derived. The stellar spectral and luminosity
classes were found between G0-A7 and IV-V, respectively. The initial values for
\teff\ and \logg\ were determined from the photometric indices and spectral
energy distribution. Those parameters were improved by the analysis of hydrogen
lines. The final values of \teff, \logg\ and were derived from the iron
lines analysis. The \teff\ values were found between 6000\,K and 7900\,K, while
\logg\,values range from 3.8 to 4.5\,dex. Chemical abundances and
values were derived by the spectrum synthesis method. The values were
found between 5 and 240\,km\,s. The chemical abundance pattern of
\,Doradus stars were compared with the pattern of non-pulsating stars.
It turned out that there is no significant difference in abundance patterns
between these two groups. Additionally, the relations between the atmospheric
parameters and the pulsation quantities were checked. A strong correlation
between the and the pulsation periods of \,Doradus variables
was obtained. The accurate positions of the analysed stars in the H-R diagram
have been shown. Most of our objects are located inside or close to the blue
edge of the theoretical instability strip of \,Doradus.Comment: 18 pages, 13 figure
V39: an unusual object in the field of IC 1613
The variable star V39 in the field of IC 1613 is discussed in the light of
the available photometric and new spectroscopic data. It has strong emission
Balmer lines, and the observed characteristics could be explained by a W Vir
pulsating star with a period of 14.341 d, located at more than 115 kpc, that is
in the very outer halo of our Galaxy. It should have an apparent companion, a
long period (1118d) red variable, belonging to IC 1613. The main uncertainty in
this interpretation is an emission feature at 668.4 nm, which we tentatively
identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic
Probable nonradial g-mode pulsation in early A-type stars
A survey for line profile variability in early A-type stars has been
performed in order to detect nonradial pulsation signatures. The star HR 6139,
with spectral type A2V and estimated T_eff=8800 K, shows evident line profile
variations that can be explained by oscillations in prograde g-modes. This
feature and the known photometric variability are similar to those observed in
the Slowly Pulsating B-type stars. However HR 6139 is much cooler than the cool
border of the instability strip of such variables, and it is hotter than the
blue edge of the delta Scuti instability strip. There are indications of a tiny
variability also in other four objects, whose nature is not yet clear.Comment: 4 pages, 5 figures; accepted for publication in A&A (letter
Variable stars in nearby galaxies. VI. Frequency-period distribution of Cepheids in IC 1613 and other galaxies of the Local Group
The frequency--period distribution and other properties of Cepheids in IC
1613 are discussed and compared with those of stars in our Galaxy (Milky Way),
LMC, SMC, M31 and M33. Taking into account the observational limitations and
related incompleteness, it is concluded that the frequency-period distribution
of Cepheids in IC 1613 is similar to that of SMC; we suspect that a much larger
number of stars exist in IC 1613 with a period of less than 2 d that have not
yet been detected. A discussion of the deficiency of fundamental mode Cepheids
with periods in the range 8 - 10 d in the Milky Way, M31 and M33 is reported.
The present data are not sufficient to verify if this is produced by a real
bimodal frequency--period distribution or whether depends on the lack of
pulsating stars in such a period range due to pulsational stability reasons.
Some arguments are presented in favor of a bimodal distribution that is a
function of the average metallicity. The Milky Way, M31 and M33 have the two
maxima located at the same periods, about 5 and 13 d, respectively. A comment
on very long period Cepheids is also given.Comment: 6 pages; accepted for publication in Astronomy and Astrophysic
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