-
L. Inno,
G. Bono,
N. Matsunaga,
M. Romaniello,
F. Primas,
R. Buonanno,
F. Caputo,
K. Genovali,
C. D. Laney, M. Marconi,
A. Pietrinferni
[show abstract]
[hide abstract]
ABSTRACT: We present new estimates of the relative distance of the Magellanic Clouds
(MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The
relative distances are independent of uncertainties affecting the zero-point of
the PW relations, but do depend on the adopted pivot periods. We estimated the
pivot periods for fundamental (FU) and first overtone (FO) Cepheids on the
basis of their period distributions. We found that log P=0.5 (FU) and log P=0.3
(FO) are solid choices, since they trace a main peak and a shoulder in LMC and
SMC period distributions. By using the above pivot periods and ten PW
relations, we found MC relative distances of 0.53$\pm$0.06 (FU) and
0.53$\pm$0.07 (FO) mag. Moreover, we investigated the possibility to use
mixed-mode (FU/FO, FO/SO) Cepheids as distance indicators and we found that
they follow quite well the PW relations defined by single mode MC Cepheids,
with deviations typically smaller than 0.3{\sigma}.
04/2013;
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L. Inno,
N. Matsunaga,
G. Bono,
F. Caputo,
R. Buonanno,
K. Genovali,
C. D. Laney, M. Marconi,
A. M. Piersimoni,
F. Primas,
M. Romaniello
[show abstract]
[hide abstract]
ABSTRACT: We present the largest near-infrared (NIR) data sets, $JHKs$, ever collected
for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental
(FU) and first overtone (FO) pulsators, and found 4150 (2571 FU, 1579 FO)
Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large
Magellanic Cloud (LMC). Current sample is 2--3 times larger than any sample
used in previous investigations with NIR photometry. We also discuss optical
$VI$ photometry from OGLE-III. NIR and optical--NIR Period-Wesenheit (PW)
relations are linear over the entire period range ($0.0<\log P_{\rm FU} \le1.65
$) and their slopes are, within the intrinsic dispersions, common between the
MCs. These are consistent with recent results from pulsation models and
observations suggesting that the PW relations are minimally affected by the
metal content. The new FU and FO PW relations were calibrated using a sample of
Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid
pulsation models. By using FU Cepheids we found a true distance moduli of
$18.45\pm0.02{\rm(random)}\pm0.10{\rm(systematic)}$ mag (LMC) and
$18.93\pm0.02{\rm(random)}\pm0.10{\rm(systematic)}$ mag (SMC). These estimates
are the weighted mean over ten PW relations and the systematic errors account
for uncertainties in the zero-point and in the reddening law. We found similar
distances using FO Cepheids
($18.60\pm0.03{\rm(random)}\pm0.10{\rm(systematic)}$ mag [LMC] and
$19.12\pm0.03{\rm(random)}\pm0.10{\rm(systematic)}$ mag [SMC]). These new MC
distances lead to the relative distance, $\Delta\mu=0.48\pm0.03$ mag (FU, $\log
P=1$) and $\Delta\mu=0.52\pm0.03$ mag (FO, $\log P=0.5$),which agrees quite
well with previous estimates based on robust distance indicators.
12/2012;
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V. Ripepi,
S. Leccia,
A. Baglin,
A. Ruoppo,
S. Bernabei,
K. Zwintz,
F. Cusano,
D. Gandolfi,
E. W. Guenter,
S. Alencar, [......],
M. Deluil,
F. Favata,
M. Fernandez,
J. Gregorio-Hetem,
J. D. R. Lepine,
F. J. G. Pinheiro,
P. G. Prada Moroni,
G. Quast,
C. A. O. Torres,
W. Weiss
[show abstract]
[hide abstract]
ABSTRACT: We present some preliminary results based on the CoRoT observations of the young distant cluster Dolidze25. The light curve for the 28 stars observed by the satellite have been analyzed and the relevant periodogram presented. As a result we have found two binary, three Pulsating Be, three SPB, two Spotted and one ellipsoidal variables. Noteworthy, we have also identified one PMS δ Scuti candidate.
Astrophysics and Space Science 04/2012; 328(1):119-122. · 1.69 Impact Factor
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M. Fabrizio,
T. Merle,
F. Thévenin,
M. Nonino,
G. Bono,
P. B. Stetson,
I. Ferraro,
G. Iannicola,
M. Monelli,
A. R. Walker, [......],
S. Degl'Innocenti,
P. François,
R. Gilmozzi, M. Marconi,
A. Pietrinferni,
P. G. Prada Moroni,
F. Primas,
L. Pulone,
V. Ripepi,
M. Romaniello
[show abstract]
[hide abstract]
ABSTRACT: We have performed accurate iron abundance measurements for 44 red giants
(RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival,
high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in
slit mode (5) or in fiber mode (39, FLAMES/GIRAFFE-UVES). The sample is more
than a factor of four larger than any previous spectroscopic investigation of
stars in dSphs based on high-resolution (R>38,000) spectra. We did not impose
the ionization equilibrium between neutral and singly-ionized iron lines. The
effective temperatures and the surface gravities were estimated by fitting
stellar isochrones in the V, B-V color-magnitude diagram. To measure the iron
abundance of individual lines we applied the LTE spectrum synthesis fitting
method using MARCS model atmospheres of appropriate metallicity. We found
evidence of NLTE effects between neutral and singly-ionized iron abundances.
Assuming that the FeII abundances are minimally affected by NLTE effects, we
corrected the FeI stellar abundances using a linear fit between FeI and FeII
stellar abundance determinations.
We found that the Carina metallicity distribution based on the corrected FeI
abundances (44 RGs) has a weighted mean metallicity of [Fe/H]=-1.80 and a
weighted standard deviation of sigma=0.24 dex. The Carina metallicity
distribution based on the FeII abundances (27 RGs) gives similar estimates
([Fe/H]=-1.72, sigma=0.24 dex). The current weighted mean metallicities are
slightly more metal poor when compared with similar estimates available in the
literature. Furthermore, if we restrict our analysis to stars with the most
accurate iron abundances, ~20 FeI and at least three FeII measurements (15
stars), we found that the range in iron abundances covered by Carina RGs (~1
dex) agrees quite well with similar estimates based on high-resolution spectra.
04/2012;
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V. Ripepi,
M. I. Moretti, M. Marconi,
G. Clementini,
M. R. Cioni,
J. B. Marquette,
L. Girardi,
S. Rubele,
M. A. T. Groenewegen,
R. de Grijs,
B. K. Gibson,
J. M. Oliveira,
J. Th. van Loon,
J. P. Emerson
[show abstract]
[hide abstract]
ABSTRACT: The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep
Ks-band time-series photometry of the pulsating variable stars hosted by the
system formed by the two Magellanic Clouds (MCs) and the "bridge" connecting
them. In this paper we present the first results for Classical Cepheids, from
the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC
Ks-band light curves of the Cepheids are well sampled (12-epochs) and of
excellent precision. We were able to measure for the first time the Ks
magnitude of the faintest Classical Cepheids in the LMC (Ks\sim17.5 mag), which
are mostly pulsating in the First Overtone (FO) mode, and to obtain FO
Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color
(PLC) relations, spanning the full period range from 0.25 to 6 day. Since the
longest period Cepheid in our dataset has a variability period of 23 day, we
have complemented our sample with literature data for brighter F Cepheids. On
this basis we have built a PL relation in the Ks band that, for the first time,
includes short period pulsators, and spans the whole range from 1.6 to 100 days
in period. We also provide the first ever empirical PW and PLC relations using
the (V-Ks) color and time-series Ks photometry. The very small dispersion
(\sim0.07 mag) of these relations makes them very well suited to study the
three-dimensional (3D) geometry of the Magellanic system. The use of "direct"
(parallax- and Baade-Wesselink- based) distance measurements to both Galactic
and LMC Cepheids, allowed us to calibrate the zero points of the PL, PW, and
PLC relations obtained in this paper, and in turn to estimate an absolute
distance modulus of (m-M)0=18.46\pm0.03 for the LMC. This result is in
agreement with most of the latest literature determinations based on Classical
Cepheids.
04/2012;
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M. Dall'Ora,
K. Kinemuchi,
V. Ripepi,
C. T. Rodgers,
G. Clementini,
L. Di Fabrizio,
H. A. Smith, M. Marconi,
I. Musella,
C. Greco,
C. A. Kuehn,
M. Catelan,
B. J. Pritzl,
T. C. Beers
[show abstract]
[hide abstract]
ABSTRACT: We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf
satellite Ursa Major II (UMa II), spanning the magnitude range from V ~ 15 to V
~ 23.5 mag and extending over a 18 {\times} 18 arcmin2 area centered on the
galaxy. Our photometry goes down to about 2 magnitudes below the galaxy's main
sequence turn-off, that we detected at V ~ 21.5 mag. We have discovered a
bona-fide RR Lyrae variable star in UMa II, which we use to estimate a
conservative dereddened distance modulus for the galaxy of (m-M)0 =
17.70{\pm}0.04{\pm}0.12 mag, where the first error accounts for the
uncertainties of the calibrated photometry, and the second reflects our lack of
information on the metallicity of the star. The corresponding distance to UMa
II is 34.7 {\pm} 0.6 ({\pm} 2.0) kpc. Our photometry shows evidence of a spread
in the galaxy subgiant branch, compatible with a spread in metal abundance in
the range between Z=0.0001 and Z=0.001. Based on our estimate of the distance,
a comparison of the fiducial lines of the Galactic globular clusters (GCs) M68
and M5 ([Fe/H]=-2.27 {\pm} 0.04 dex and -1.33 {\pm} 0.02 dex, respectively),
with the position on the CMD of spectroscopically confirmed galaxy members, may
suggest the existence of stellar populations of different metal abundance/age
in the central region of UMa II.
03/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting
$K_S$-band time series photometry of the system formed by the two Magellanic
Clouds (MC) and the "bridge" that connects them. These data are used to build
$K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and
determine absolute distances and the 3D geometry of the whole system using the
$K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$)
and the Wesenhiet relations applicable to these types of variables. As an
example of the survey potential we present results from the VMC observations of
two fields centered respectively on the South Ecliptic Pole and the 30 Doradus
star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light
curves of the RR Lyrae stars in these two regions have very good photometric
quality with typical errors for the individual data points in the range of
$\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical
errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types
of variables were used to derive $PLK_S$ relations that are in general good
agreement within the errors with the literature data, and show a smaller
scatter than previous studies.
02/2012;
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L. A. Balona,
P. Lenz,
V. Antoci,
S. Bernabei,
G. Catanzaro,
J. Daszyńska-Daszkiewicz,
M. Di Criscienzo,
A. Grigahcène,
G. Handler,
D. W. Kurtz, [......],
J. M. Nemec,
A. Pigulski,
D. Pricopi,
V. Ripepi,
B. Smalley,
J. C. Suárez,
M. Suran,
J. R. Hall,
K. Kinemuchi,
T. C. Klaus
[show abstract]
[hide abstract]
ABSTRACT: We analyse Kepler observations of the high-amplitude δ Scuti (HADS) star V2367 Cyg (KIC 9408694). The variations are dominated by a mode with frequency f1= 5.6611 d−1. Two other independent modes with f2= 7.1490 d−1 and f3= 7.7756 d−1 have amplitudes an order of magnitude smaller than f1. Nearly all the light variation is due to these three modes and their combination frequencies, but several hundred other frequencies of very low amplitude are also present. The amplitudes of the principal modes may vary slightly with time. The star has twice the projected rotational velocity of any other HADS star, which makes it unusual. We find a correlation between the phases of the combination frequencies and their pulsation frequencies, which is not understood. Since modes of highest amplitude in HADS stars are normally radial modes, we assumed that this would also be true in this star. However, attempts to model the observed frequencies as radial modes without mode interaction were not successful. For a star with such a relatively high rotational velocity, it is important to consider the effect of mode interaction. Indeed, when this was done, we were able to obtain a model in which a good match with f1 and f2 is obtained, with f1 being the fundamental radial mode.
Monthly Notices of the Royal Astronomical Society 02/2012; 419(4):3028 - 3038. · 4.90 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We used Optical, Near Infrared photometry and radial velocity data for a
sample of 11 Cepheids belonging to the young LMC blue populous cluster NGC 1866
to estimate their radii and distances on the basis of the CORS Baade-Wesselink
method. This technique, based on an accurate calibration of the surface
brightness as a function of (U-B), (V-K) colors, allows us to estimate,
simultaneously, the linear radius and the angular diameter of Cepheid
variables, and consequently to derive their distance. A rigorous error estimate
on radius and distances was derived by using Monte Carlo simulations. Our
analysis gives a distance modulus for NGC 1866 of 18.51+/-0.03 mag, which is in
agreement with several independent results.
01/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The mid-infrared period-luminosity (P-L) relation for Cepheids will be
important in the JWST era, as it holds the promise of deriving the Hubble
constant within 2% accuracy. We present the synthetic P-L and period-color
(P-C) relations, derived from a series of stellar pulsation models with varying
helium and metallicity abundance, in the Spitzer IRAC bands. Selected synthetic
P-L and P-C relations were compared to the empirical relations derived from
Galactic and Large Magellanic Cloud Cepheids. We also present the empirical P-L
relations based on the latest distance measurements using infrared surface
brightness techniques.
11/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The evolutionary properties and spatial distribution of I Zwicky 18 stellar
populations are analyzed by means of HST/ACS deep and accurate photometry. The
comparison of the resulting Colour- Magnitude diagrams with stellar evolution
models indicates that stars of all ages are present in all the system
components, including ob jects possibly up to 13 Gyr old, intermediate age
stars and very young ones. The Colour-Magnitude diagrams show evidence of
thermally pulsing asymptotic giant branch and carbon stars. Classical and
ultra-long period Cepheids, as well as long period variables have been
measured. About 20 ob jects could be unresolved star clusters, and are mostly
concentrated in the North-West (NW) portion of the Main Body (MB). If
interpreted with simple stellar population models, these ob jects indicate a
particularly active star formation over the past hundred Myr in IZw 18. The
stellar spatial distribution shows that the younger ones are more centrally
concentrated, while old and intermediate age stars are distributed
homogeneously over the two bodies, although more easily detectable at the
system periphery. The oldest stars are best visible in the Secondary Body (SB)
and in the South East (SE) portion of the MB, where crowding is less severe,
but are present also in the rest of the MB, although measured with larger
uncertainties. The youngest stars are a few Myr old, are located predominantly
in the MB and mostly concentrated in its NW portion. The SE portion of the MB
appears to be in a similar, but not as young evolutionary stage as the NW,
while the SB stars are older than at least 10 Myr. There is then a sequence of
decreasing age of the younger stars from the Secondary Body to the SE portion
of the MB to the NW portion. All our results suggest that IZw18 is not atypical
compared to other BCDs.
06/2011;
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[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of the time series observations of CoRoT\,102699796
obtained by the CoRoT satellite that show the presence of five independent
oscillation frequencies in the range 3.6-5 c/d. Using spectra acquired with
FLAMES@VLT, we derive the following stellar parameters: spectral type F1V,
T$_{\rm eff}$=7000$\pm$200 K, log(g)=$3.8\pm0.4$, [M/H]=$-1.1\pm0.2$,
$v$sin$i$=$50\pm5$ km/s, L/L$_{\odot}$=21$^{+21}_{-11}$. Thus, for the first
time we report the existence of a metal poor, intermediate-mass PMS pulsating
star. Ground-based and satellite data are used to derive the spectral energy
distribution of CoRoT\,102699796 extending from the optical to mid-infrared
wavelengths. The SED shows a significant IR excess at wavelengths greater than
$\sim5 \mu$. We conclude that CoRoT\,102699796 is a young Herbig Ae (F1Ve) star
with a transitional disk, likely associated to the HII region [FT96]213.1-2.2.
The pulsation frequencies have been interpreted in the light of the
non-radial pulsation theory, using the LOSC code in conjunction with static and
rotational evolutionary tracks. A minimization algorithm was used to find the
best-fit model with M=1.84 M$_{\odot}$, T$_{\rm eff}$=6900 K which imply an
isochronal age of t$\sim$2.5 Myr. This result is based on the interpretation of
the detected frequencies as $g$-modes of low-moderate $n$-value. To our
knowledge, this is the first time that such modes are identified in a
intermediate-mass PMS pulsating star. Since CoRoT\,102699796 lies in the region
of the HR diagram where the $\delta$ Sct and $\gamma$ Dor instability strips
intersect, we argue that the observed pulsation characteristics are
intermediate between these classes of variables, i.e. CoRoT\,102699796 is
likely the first PMS hybrid $\gamma$ Dor-$\delta$ Sct pulsator ever studied.
06/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present new and accurate near-infrared (NIR) J, K-band time series data
for the Galactic globular cluster (GC) M5 = NGC5904. Data were collected with
SOFI at the NTT (71 J + 120 K images) and with NICS at the TNG (25 J + 22 K
images) and cover two orthogonal strips across the center of the cluster of
\approx 5 \times 10 arcmin^{2} each. These data allowed us to derive accurate
mean K-band magnitudes for 52 fundamental (RR_{ab}) and 24 first overtone
(RR_{c}) RR Lyrae stars. Using this sample of RR Lyrae stars, we find that the
slope of the K-band Period Luminosity (PLK) relation (-2.33 \pm 0.08) agrees
quite well with similar estimates available in the literature. We also find,
using both theoretical and empirical calibrations of the PLK relation, a true
distance to M5 of (14.44 \pm 0.02) mag. This distance modulus agrees very well
(1\sigma) with distances based on main sequence fitting method and on kinematic
method (14.44 \pm 0.41 mag, \citealt{rees_1996}), while is systematically
smaller than the distance based on the white dwarf cooling sequence (14.67 \pm
0.18 mag, \citealt{layden2005}), even if with a difference slightly larger than
1\sigma. The true distance modulus to M5 based on the PLJ relation (14.50 \pm
0.08 mag) is in quite good agreement with the distance based on the PLK
relation further supporting the use of NIR PL relations for RR Lyrae stars to
improve the precision of the GC distance scale.
Monthly Notices of the Royal Astronomical Society 05/2011; 416(2). · 4.90 Impact Factor
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G. Catanzaro,
V. Ripepi,
S. Bernabei, M. Marconi,
L. Balona,
D. W. Kurtz,
B. Smalley,
W. J. Borucki,
H. Bruntt,
J. Christensen-Dalsgaard,
A. Grigahcene,
H. Kjeldsen,
D. G. Koch,
M. J. P. F. G. Monteiro,
J. C. Suarez,
R. Szabo,
K. Uytterhoeven
[show abstract]
[hide abstract]
ABSTRACT: We report spectroscopic observations for 19 $\delta$\,Sct candidates observed by the {\it Kepler} satellite both in long and short cadence mode. For all these stars, by using spectral synthesis, we derive the effective temperature, the surface gravity and the projected rotational velocity. An equivalent spectral type classification has been also performed for all stars in the sample. These determinations are fundamental for modelling the frequency spectra that will be extracted from the {\it Kepler} data for asteroseismic inference. For all the 19 stars, we present also periodograms obtained from {\it Kepler} data. We find that all stars show peaks in both low- ($\gamma$\,Dor; g mode) and high-frequency ($\delta$\,Sct; p mode) regions. Using the amplitudes and considering 5\,c/d as a boundary frequency, we classified 3 stars as pure $\gamma$\,Dor, 4 as $\gamma$\,Dor\,-\,$\delta$\ hybrid, Sct, 5 as $\delta$\,Sct\,-\,$\gamma$\,Dor hybrid, and 6 as pure $\delta$\,Sct. The only exception is the star KIC\,05296877 which we suggest could be a binary. Comment: 11 pages, 6 figures, MNRAS main journal
Monthly Notices of the Royal Astronomical Society 01/2011; 411:1167. · 4.90 Impact Factor
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M. -R. L. Cioni,
G. Clementini,
L. Girardi,
R. Guandalini,
M. Gullieuszik,
B. Miszalski,
M. -I. Moretti,
V. Ripepi,
S. Rubele,
G. Bagheri, [......],
C. Mastropietro,
B. Moore,
R. Napiwotzki,
T. Naylor,
J. M. Oliveira,
M. Read,
E. Sutorius,
J. Th. van Loon,
M. I. Wilkinson,
P. R. Wood
[show abstract]
[hide abstract]
ABSTRACT: The new VISual and Infrared Telescope for Astronomy (VISTA) has started
operations. Over its first five years it will be collecting data for six public
surveys, one of these is the near-infrared YJKsVISTA survey of the Magellanic
Clouds system (VMC). This survey comprises the LMC, the SMC, the Bridge
connecting the two galaxies and two fields in the Stream. This paper provides
an overview of the VMC survey strategy and presents first science results. The
main goals of the VMC survey are the determination of the spatially resolved
SFH and 3D structure of the Magellanic system. Therefore, the VMC survey is
designed to reach stars as faint as the oldest main sequence turn-off point and
to constrain the mean magnitude of pulsating variable stars such as RR Lyrae
stars and Cepheids. This paper focuses on observations of VMC fields in the LMC
obtained between November 2009 and March 2010. These observations correspond to
a 7% completeness of the LMC fields. The VMC observations consist of
multi-epoch measurements organised following a specific structure. The data
were reduced using the VISTA Data Flow System pipeline whose source catalogues
were produced and made available via the VISTA Science Archive. The analysis of
the data shows that the sensitivity in each wave band agrees with expectations.
Uncertainties and completeness of the data are also derived. The first science
results, aimed at assessing the science quality of the VMC data, include an
overview of the distribution of stars in colour-magnitude and colour-colour
diagrams, the detection of planetary nebulae and of stellar clusters, and the
Ks band light-curve of variable stars. The VMC survey represents a tremendous
improvement, in spatial resolution and sensitivity, on previous panoramic
observations of the Magellanic system in the near-infrared and complements
nicely the deep observations at other wavelengths. (Abridged)
12/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a new derivation of the CORS Baade-Wesselink method in the Walraven photometric system. We solved the complete Baade-Wesselink equation by calibrating the surface brightness function with a recent grid of atmosphere models. The new approach was adopted to estimate the mean radii of a sample of Galactic Cepheids for which are available precise light curves in the Walraven bands. Current radii agree, within the errors, quite well with Cepheid radii based on recent optical and near-infrared interferometric measurements. We also tested the impact of the projection factor on the Period-Radius relation using two different values (p=1.36, p=1.27) that bracket the estimates available in the literature. We found that the agreement of our Period-Radius relation with similar empirical and theoretical Period-Radius relations in the recent literature, improves by changing the projection factor from p=1.36 to p=1.27. Our Period-Radius relation is log(R)=(0.75\pm 0.03)log(P)+(1.10 \pm 0.03), with a rms=0.03 dex. Thanks to accurate estimates of the effective temperature of the selected Cepheids, we also derived the Period-Luminosity relation in the V band and we found Mv=(-2.78 \pm 0.11)log(P)+(-1.42 \pm 0.11) with rms=0.13 mag, for p=1.27. It agrees quite well with recent results in the literature, while the relation for p=1.36 deviates by more than 2sigma. We conclude that, even taking into account the intrinsic dispersion of the obtained Period-Luminosity relations, that is roughly of the same order of magnitude as the effect of the projection factor, the results of this paper seem to favour the value p = 1.27. Comment: 17 pages, 14 figures, accepted for publication in MNRAS
12/2010;
-
M. Breger,
L. Balona,
P. Lenz,
J. K. Hollek,
D. W. Kurtz,
G. Catanzaro, M. Marconi,
A. A. Pamyatnykh,
B. Smalley,
J. C. Suarez,
R. Szabo,
K. Uytterhoeven,
V. Ripepi,
J. Christensen-Dalsgaard,
H. Kjeldsen,
M. N. Fanelli,
K. A. Ibrahim,
K. Uddin
[show abstract]
[hide abstract]
ABSTRACT: In the faint star KIC 9700322 observed by the Kepler satellite, 76
frequencies with amplitudes from 14 to 29000 ppm were detected. The two
dominant frequencies at 9.79 and 12.57 c/d (113.3 and 145.5 \mu Hz),
interpreted to be radial modes, are accompanied by a large number of
combination frequencies. A small additional modulation with a 0.16 c/d
frequency is also seen; this is interpreted to be the rotation frequency of the
star. The corresponding prediction of slow rotation is confirmed by a spectrum
from which v sin i = 19 \pm 1 km/s is obtained. The analysis of the spectrum
shows that the star is one of the coolest {\delta} Sct variables. We also
determine Teff = 6700 \pm 100 K and log g = 3.7 \pm 0.1, compatible with the
observed frequencies of the radial modes. Normal solar abundances are found. An
\ell = 2 frequency quintuplet is also detected with a frequency separation
consistent with predictions from the measured rotation rate. A remarkable
result is the absence of additional independent frequencies down to an
amplitude limit near 14 ppm, suggesting that the star is stable against most
forms of nonradial pulsation. The frequency spectrum of this star emphasizes
the need for caution in interpreting low frequencies in {\delta} Sct stars as
independent gravity modes. A low frequency peak at 2.7763 c/d in KIC 9700322
is, in fact, the frequency difference between the two dominant modes and is
repeated over and over in various frequency combinations involving the two
dominant modes. The relative phases of the combination frequencies show a
strong correlation with frequency, but the physical significance of this result
is not clear.
12/2010;
-
K. Uytterhoeven,
M. Briquet,
H. Bruntt,
P. De Cat,
S. Frandsen,
J. Gutiérrez-Soto,
L. Kiss,
D.W. Kurtz, M. Marconi,
J. Molenda-Żakowicz,
R. Østensen,
S. Randall,
J. Southworth,
R. Szabó,
KASC Working Groups on ground‐based observations
[show abstract]
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ABSTRACT: The Kepler space mission, successfully launched in March 2009, is providing continuous and high-precision photometry of thousands of stars simultaneously. The uninterrupted time-series of stars of all known pulsation types are a precious source for asteroseismic studies. The Kepler data do not provide information on the physical parameters, such as log g, metallicity, and v sin i, which are crucial for successful asteroseismic modelling. Additional ground-based time-series data are needed to characterize mode parameters in several types of pulsating stars. Therefore, ground-based multi-colour photometry and mid/high-resolution spectroscopy are needed to complement the space data. We present ground-based activities within KASC on selected asteroseismic Kepler targets of several pulsation types (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Astronomische Nachrichten 11/2010; 331(9‐10):993 - 997. · 1.01 Impact Factor
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ABSTRACT: We present B, V and I CCD light curves for 101 variable stars belonging to the globular cluster NGC2419, 60 of which are new discoveries, based on datasets obtained at the TNG, SUBARU and HST telescopes. The sample includes 75 RR Lyrae stars (of which 38 RRab, 36 RRc and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, 2 DeltaScuti stars, 3 binary systems, 5 long-period variables, and 3 variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistent with the low metal abundance and the cluster horizontal branch morphology,disfavoring (but not totally ruling out) an extragalactic hypotesis for the origin of NGC2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is mo(NGC2419)=19.71+/-0.08mag (D= 87.5+/-3.3kpc), with E(B-V)=0.08+/-0.01mag, [Fe/H]=-2.1dex in the Zinn & West metallicity scale, and a value of Mv that sets mo(LMC)=18.52mag. This value is in good agreement with most recent literature estimates of the distance to NGC 2419. Comment: 26 pages, 16 figures, 4 tables; accepted for publication in AJ
11/2010;
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A. Grigahcène,
K. Uytterhoeven,
V. Antoci,
L. Balona,
G. Catanzaro,
J. Daszyńska-Daszkiewicz,
J.A. Guzik,
G. Handler,
G. Houdek,
D.W. Kurtz, [......],
S. Martín-Ruiz,
P. Mathias,
J. Molenda-Żakowicz,
J.M. Nemec,
J. Nuspl,
M. Paparó,
M. Roth,
R. Szabó,
M.D. Suran,
R. Ventura
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ABSTRACT: Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence -γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2–2.5 M⊙ are particularly interesting for asteroseismic study. The -γ Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The δ Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of ‘hybrid’ stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of -γ Dor and δ Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The Kepler satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of Kepler data of hundreds of -γ Dor and δ Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the δ Sct and -γ Dor frequency range. As these results show that there are practically no pure δ Sct or -γ Dor pulsators, a new observational classification scheme is proposed by Grigahcène et al. (2010). We present their results and characterize 234 stars in terms of δ Sct, -γ Dor, δ Sct/-γ Dor or -γ Dor/δ Sct hybrids (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Astronomische Nachrichten 11/2010; 331(9‐10):989 - 992. · 1.01 Impact Factor
