26 research outputs found
A search for p-modes and other variability in the binary system 85 Pegasi using MOST photometry
Context: Asteroseismology has great potential for the study of metal-poor
stars due to its sensitivity to determine stellar ages. Aims: Our goal was to
detect p-mode oscillations in the metal-poor sub-dwarf 85 Peg A and to search
for other variability on longer timescales. Methods: We have obtained
continuous high-precision photometry of the binary system 85 Pegasi with the
MOST space telescope in two seasons (2005 & 2007). Furthermore, we redetermined
vsini for 85 Peg A using high resolution spectra obtained through the ESO
archive, and used photometric spot modeling to interpret long periodic
variations. Results: Our frequency analysis yields no convincing evidence for
p-modes significantly above a noise level of 4 ppm. Using simulated p-mode
patterns we provide upper RMS amplitude limits for 85 Peg A. The light curve
shows evidence for variability with a period of about 11 d and this periodicity
is also seen in the follow up run in 2007; however, as different methods to
remove instrumental trends in the 2005 run yield vastly different results, the
exact shape and periodicity of the 2005 variability remain uncertain. Our
re-determined vsini value for 85 Peg A is comparable to previous studies and we
provide realistic uncertainties for this parameter. Using these values in
combination with simple photometric spot models we are able to reconstruct the
observed variations. Conclusions: The null-detection of p-modes in 85 Peg A is
consistent with theoretical values for pulsation amplitudes in this star. The
detected long-periodic variation must await confirmation by further
observations with similar or better precision and long-term stability. If the
11 d periodicity is real, rotational modulation of surface features on one of
the components is the most likely explanation.Comment: 11 pages, 9 figures, accepted for publication in A&
New SPB stars in the field of the young open cluster NGC 2244 discovered by the MOST photometric satellite
During two weeks of nearly continuous optical photometry of the young open
cluster NGC 2244 obtained by the MOST satellite, we discovered two new SPB
stars, GSC 00154-00785 and GSC 00154-01871. We present frequency analyses of
the MOST light curves of these stars, which reveal two oscillation frequencies
(0.61 and 0.71 c/d) in GSC 00154-00785 and two (0.40 and 0.51 c/d) in GSC
00154-01871. These frequency ranges are consistent with g-modes of excited in models of main-sequence or pre-main-sequence (PMS) stars of
masses 4.5 - 5 and solar composition .
Published proper motion measurements and radial velocities are insufficient to
establish unambiguously cluster membership for these two stars. However, the
PMS models which fit best their eigenspectra have ages consistent with NGC
2244. If cluster membership can be confirmed, these would be the first known
PMS SPB stars, and would open a new window on testing asteroseismically the
interior structures of PMS stars.Comment: accepted for publication in MNRA
The VMC survey - XX. Identification of new Cepheids in the Small Magellanic Cloud
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © : 2016 M. I. Moretti, et al., Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We present Ks-band light curves for 299 Cepheids in the Small Magellanic Cloud (SMC) of which 288 are new discoveries that we have identified using multi-epoch near-infrared photometry obtained by the VISTA survey of the Magellanic Clouds system (VMC). The new Cepheids have periods in the range from 0.34 to 9.1 d and cover the magnitude interval 12.9 = 〈Ks〉 = 17.6 mag. Our method was developed using variable stars previously identified by the optical microlensing survey OGLE.We focus on searching newCepheids in external regions of the SMC for which complete VMC Ks-band observations are available and no comprehensive identification of different types of variable stars from other surveys exists yet.Peer reviewe
Asteroseismic analysis of the CoRoT \delta-Scuti star HD174936
We present an analysis of the \delta-Scuti star object HD 174936 (ID 7613)
observed by CoRoT during the first short run SRc01 (27 days). A total number of
422 frequencies we are extracted from the light curve using standard
prewhitening techniques. This number of frequencies was obtained by considering
a spectral significance limit of sig = 10 using the software package SigSpec.
Our analysis of the oscillation frequency spectrum reveals a spacing
periodicity of around 52 \muHz. Although modes considered here are not in the
asymptotic regime, a comparison with stellar models confirms that this
signature may stem from a quasi-periodic pattern similar to the so-called large
separation in solar-like stars.Comment: 7 pages, 7 figures, 2 tables. Accepted for publication in A&A CoRoT
Special Featur
KIC 3858884: a hybrid {\delta} Sct pulsator in a highly eccentric eclipsing binary
The analysis of eclipsing binaries containing non-radial pulsators allows: i)
to combine two different and independent sources of information on the internal
structure and evolutionary status of the components, and ii) to study the
effects of tidal forces on pulsations. KIC 3858884 is a bright Kepler target
whose light curve shows deep eclipses, complex pulsation patterns with
pulsation frequencies typical of {\delta} Sct, and a highly eccentric orbit. We
present the result of the analysis of Kepler photometry and of high resolution
phaseresolved spectroscopy. Spectroscopy yielded both the radial velocity
curves and, after spectral disentangling, the primary component effective
temperature and metallicity, and line-of-sight projected rotational velocities.
The Kepler light curve was analyzed with an iterative procedure devised to
disentangle eclipses from pulsations which takes into account the visibility of
the pulsating star during eclipses. The search for the best set of binary
parameters was performed combining the synthetic light curve models with a
genetic minimization algorithm, which yielded a robust and accurate
determination of the system parameters. The binary components have very similar
masses (1.88 and 1.86 Msun) and effective temperatures (6800 and 6600 K), but
different radii (3.45 and 3.05 Rsun). The comparison with the theoretical
models evidenced a somewhat different evolutionary status of the components and
the need of introducing overshooting in the models. The pulsation analysis
indicates a hybrid nature of the pulsating (secondary) component, the
corresponding high order g-modes might be excited by an intrinsic mechanism or
by tidal forces.Comment: 18 pages, 14 figures, accepted for publication on Astronomy &
Astrophysic
A multisite photometric campaign on the pre-main-sequence
We present the results of a photometric multisite
campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine
telescopes have been involved in the observations, with a total of
about 190 h of observations over 38 nights. Present data confirms
the multiperiodic nature of this star and leads to the identification
of at least nine pulsational frequencies. Comparison with the
predictions of linear non-adiabatic radial pulsation models allowed us
to identify only five of the nine observed frequencies, and to
constrain the position of IP Per in the HR diagram. The latter is in
good agreement with the empirical determination of the stellar
parameters obtained by Miroshnichenko et al. (2001, A&A, 377, 854). An initial interpretation of the
observed frequencies using the Aarhus non-radial pulsation code
suggests that three frequencies could be associated with non-radial
() modes. Finally, we present new evolutionary and pulsation
models at lower metallicity () to take into account the
possibility that IP Per is metal deficient, as indicated by
Miroshnichenko et al. (2001, A&A, 377, 854)
A multisite photometric campaign on the Pre-Main-Sequence delta Scuti pulsator IP Per
We present the results of a photometric multisite campaign on the Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 hours of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination of the stellar parameters obtained by Miroshnichenko et al. (2001). An initial interpretation of the observed frequencies using the Aarhus non-radial pulsation code suggests that three frequencies could be associated with non-radial (=2) modes. Finally, we present new evolutionary and pulsation models at lower metallicity (Z=0.008) to take into account the possibility that IP Per is metal deficient, as indicated by Miroshnichenko et al. (2001)
Kepler observations of rapidly oscillating Ap, δ Scuti and γ Doradus pulsations in Ap stars
Observations of the A5p star KIC 8677585 obtained during the Kepler 10-d
commissioning run with 1-min time resolution show that it is a roAp star with
several frequencies with periods near 10 min. In addition, a low frequency at
3.142 cycles/day is also clearly present. Multiperiodic gamma Doradus and delta
Scuti pulsations, never before seen in any Ap star, are present in Kepler
observations of at least three other Ap stars. Since gamma Doradus pulsations
are seen in Ap stars, it is likely that the low-frequency in KIC 8677585 is
also a gamma Doradus pulsation. The simultaneous presence of both gamma Doradus
and roAp pulsations and the unexpected detection of delta Scuti and gamma
Doradus pulsations in Ap stars present new opportunities and challenges for the
interpretation of these stars.Comment: 9 pages and 5 figure