77 research outputs found
On the variability of HD 170699 - a possible COROT target
We present the analysis of the variability of HD 170699, a COROT star showing
the characteristics of a non evolutionary Delta Scuti star with high rotational
velocity. There is a clear period of 10.45 c/d with 5.29 mmag amplitude in the
y filter. From the data, it can be seen that the star shows multi-periodicity
and it is necessary to add more frequencies to adjust the observationsComment: To appear in RevMexAA(SC) in Proceedings of XII Reunion Regional
Latinoamericana de la UAI held in Isla Margarita, Venezuela, October 22-26,
200
Long term disc variability in the Be star o Andromedae
We present 18 years of high resolution and S/N H α spectroscopy of the Be shell star o And, obtained between 1985-2002. Spectra taken during late 1985 show a pure photospheric profile, with disc re-formation commencing in 1986; a process that is found to occur over long timescales (103 days). Analysis of the evolution of the properties of the H α shell profile suggest that the disc kinematics are dominated by rotational motion. It has been shown that disc loss in o And occurs "inside out''; we find that the disc also appears to be rebuilt in a similar manner, with disc material gradually diffusing to larger radii. The long timescale for changes in the bulk properties of the disc, domination of rotational over radial velocities and manner of disc loss and formation are all consistent with the predictions of the viscous decretion disc model for Be star discs
A comprehensive study of the SX Phoenicis star BL Camelopardalis
Astronomy and Astrophysics, v. 451, p. 999-1008, 2006. http://dx.doi.org/10.1051/0004-6361:20053841International audienc
HD 173977: An ellipsoidal d Scuti star variable
Astronomy and Astrophysics, v. 426, p. 247-252, 2004. http://dx.doi.org/10.1051/0004-6361:20034068International audienc
Asteroseismology of the Beta Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification
We report a multisite photometric campaign for the Beta Cephei star 12
Lacertae. 750 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with 9 telescopes
during 190 nights. Our frequency analysis results in the detection of 23
sinusoidal signals in the light curves. Eleven of those correspond to
independent pulsation modes, and the remainder are combination frequencies. We
find some slow aperiodic variability such as that seemingly present in several
Beta Cephei stars. We perform mode identification from our colour photometry,
derive the spherical degree l for the five strongest modes unambiguously and
provide constraints on l for the weaker modes. We find a mixture of modes of 0
<= l <= 4. In particular, we prove that the previously suspected rotationally
split triplet within the modes of 12 Lac consists of modes of different l;
their equal frequency splitting must thus be accidental.
One of the periodic signals we detected in the light curves is argued to be a
linearly stable mode excited to visible amplitude by nonlinear mode coupling
via a 2:1 resonance. We also find a low-frequency signal in the light
variations whose physical nature is unclear; it could be a parent or daughter
mode resonantly coupled. The remaining combination frequencies are consistent
with simple light-curve distortions.
The range of excited pulsation frequencies of 12 Lac may be sufficiently
large that it cannot be reproduced by standard models. We suspect that the star
has a larger metal abundance in the pulsational driving zone, a hypothesis also
capable of explaining the presence of Beta Cephei stars in the LMC.Comment: 12 pages, 7 figures, MNRAS, in pres
A Giant Crater on 90 Antiope?
Mutual event observations between the two components of 90 Antiope were
carried out in 2007-2008. The pole position was refined to lambda0 =
199.5+/-0.5 eg and beta0 = 39.8+/-5 deg in J2000 ecliptic coordinates, leaving
intact the physical solution for the components, assimilated to two perfect
Roche ellipsoids, and derived after the 2005 mutual event season (Descamps et
al., 2007). Furthermore, a large-scale geological depression, located on one of
the components, was introduced to better match the observed lightcurves. This
vast geological feature of about 68 km in diameter, which could be postulated
as a bowl-shaped impact crater, is indeed responsible of the photometric
asymmetries seen on the "shoulders" of the lightcurves. The bulk density was
then recomputed to 1.28+/-0.04 gcm-3 to take into account this large-scale
non-convexity. This giant crater could be the aftermath of a tremendous
collision of a 100-km sized proto-Antiope with another Themis family member.
This statement is supported by the fact that Antiope is sufficiently porous
(~50%) to survive such an impact without being wholly destroyed. This violent
shock would have then imparted enough angular momentum for fissioning of
proto-Antiope into two equisized bodies. We calculated that the impactor must
have a diameter greater than ~17 km, for an impact velocity ranging between 1
and 4 km/s. With such a projectile, this event has a substantial 50%
probability to have occurred over the age of the Themis family.Comment: 30 pages, 3 Tables, 8 Figures. Accepted for publication in Icaru
Confirmation of simultaneous p and g mode excitation in HD 8801 and Gamma Peg from time-resolved multicolour photometry of six candidate "hybrid" pulsators
We carried out a multi-colour time-series photometric study of six stars
claimed as "hybrid" p and g mode pulsators in the literature. Gamma Peg was
confirmed to show short-period oscillations of the Beta Cep type and
simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars.
From the measured amplitude ratios in the Stromgren uvy passbands, the
stronger of the two short period pulsation modes was identified as radial; the
second is l=1. Three of the four SPB-type modes are most likely l=1 or 2.
Comparison with theoretical model calculations suggests that Gamma Peg is
either an 8.5 solar mass radial fundamental mode pulsator or a 9.6 solar mass
first radial overtone pulsator. HD 8801 was corroborated as a "hybrid" Delta
Sct Gamma Dor star; four pulsation modes of the Gamma Dor type were detected,
and two modes of the Delta Sct type were confirmed. Two pulsational signals
between the frequency domains of these two known classes of variables were
confirmed and another was newly detected. These are either previously unknown
types of pulsation, or do not originate from HD 8801. The O-type star HD 13745
showed small-amplitude slow variability on a time scale of 3.2 days. This
object may be related to the suspected new type of supergiant SPB stars, but a
rotational origin of its light variations cannot be ruled out at this point. 53
Psc is an SPB star for which two pulsation frequencies were determined and
identified with low spherical degree. The behaviour of 53 Ari and Iota Her is
consistent with non-variability during our observations, and we could not
confirm light variations of the comparison star 34 Psc previously suspected.
The use of signal-to-noise criteria in the analysis of data sets with strong
aliasing is critically discussed.Comment: 14 pages, 10 figures, accepted by MNRA
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