2,600 research outputs found
Spectral variability of planetary nebulae and related objects
The results of long-term spectral observations were used to search for
changes in planetary nebulae and emission-line stars. Significant increase of
excitation degree is found in two objects: M1-6 and M1-11
SMEI observations of previously unseen pulsation frequencies in γ Doradus
Aims. As g-mode pulsators, gamma-Doradus-class stars may naïvely be expected to show a large number of modes. Taking advantage of the long photometric time-series generated by the solar mass ejection imager (SMEI) instrument, we have studied the star gamma Doradus to determine whether any other modes than the three already known are present at observable amplitude.
Methods. High-precision photometric data from SMEI taken between April 2003 and March 2006 were subjected to periodogram analysis with the PERIOD04 package.
Results. We confidently determine three additional frequencies at 1.39, 1.87, and 2.743 d−1. These are above and beyond the known frequencies of 1.320, 1.364, and 1.47 d−1.
Conclusions. Two of the new frequencies, at 1.39 and 1.87 d−1, are speculated to be additional modes of oscillation, with the third frequency at 2.743−1 a possible combination frequency
White dwarf spins from low mass stellar evolution models
The prediction of the spins of the compact remnants is a fundamental goal of
the theory of stellar evolution. Here, we confront the predictions for white
dwarf spins from evolutionary models including rotation with observational
constraints. We perform stellar evolution calculations for stars in the mass
range 1... 3\mso, including the physics of rotation, from the zero age main
sequence into the TP-AGB stage. We calculate two sets of model sequences, with
and without inclusion of magnetic fields. From the final computed models of
each sequence, we deduce the angular momenta and rotational velocities of the
emerging white dwarfs. While models including magnetic torques predict white
dwarf rotational velocities between 2 and 10 km s, those from the
non-magnetic sequences are found to be one to two orders of magnitude larger,
well above empirical upper limits. We find the situation analogous to that in
the neutron star progenitor mass range, and conclude that magnetic torques may
be required in order to understand the slow rotation of compact stellar
remnants in general.Comment: Accepted for A&A Letter
Studying the photometric and spectroscopic variability of the magnetic hot supergiant Orionis Aa
Massive stars play a significant role in the chemical and dynamical evolution
of galaxies. However, much of their variability, particularly during their
evolved supergiant stage, is poorly understood. To understand the variability
of evolved massive stars in more detail, we present a study of the O9.2Ib
supergiant Ori Aa, the only currently confirmed supergiant to host a
magnetic field. We have obtained two-color space-based BRIght Target Explorer
photometry (BRITE) for Ori Aa during two observing campaigns, as well
as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We
perform a detailed frequency analysis to detect and characterize the star's
periodic variability. We detect two significant, independent frequencies, their
higher harmonics, and combination frequencies: the stellar rotation period
d, most likely related to the presence of the
stable magnetic poles, and a variation with a period of d
attributed to circumstellar environment, also detected in the H and
several He I lines, yet absent in the purely photospheric lines. We confirm the
variability with /4, likely caused by surface
inhomogeneities, being the possible photospheric drivers of the discrete
absorption components. No stellar pulsations were detected in the data. The
level of circumstellar activity clearly differs between the two BRITE observing
campaigns. We demonstrate that Ori Aa is a highly variable star with
both periodic and non-periodic variations, as well as episodic events. The
rotation period we determined agrees well with the spectropolarimetric value
from the literature. The changing activity level observed with BRITE could
explain why the rotational modulation of the magnetic measurements was not
clearly detected at all epochs.Comment: 20 pages, 5 tables, 12 figures, accepted for publication in A&
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
Conditional embryonic lethality to improve the sterile insect technique in Ceratitis capitata (Diptera: Tephritidae)
<p>Abstract</p> <p>Background</p> <p>The sterile insect technique (SIT) is an environment-friendly method used in area-wide pest management of the Mediterranean fruit fly <it>Ceratitis capitata </it>(Wiedemann; Diptera: Tephritidae). Ionizing radiation used to generate reproductive sterility in the mass-reared populations before release leads to reduction of competitiveness.</p> <p>Results</p> <p>Here, we present a first alternative reproductive sterility system for medfly based on transgenic embryonic lethality. This system is dependent on newly isolated medfly promoter/enhancer elements of cellularization-specifically-expressed genes. These elements act differently in expression strength and their ability to drive lethal effector gene activation. Moreover, position effects strongly influence the efficiency of the system. Out of 60 combinations of driver and effector construct integrations, several lines resulted in larval and pupal lethality with one line showing complete embryonic lethality. This line was highly competitive to wildtype medfly in laboratory and field cage tests.</p> <p>Conclusion</p> <p>The high competitiveness of the transgenic lines and the achieved 100% embryonic lethality causing reproductive sterility without the need of irradiation can improve the efficacy of operational medfly SIT programs.</p
The Nainital-Cape Survey -- II:Report for pulsation in five chemically peculiar A-type stars and presentation of 140 null results
To search photometric variability in chemically peculiar A type stars in the
northern hemisphere. High-speed photometric observations of Ap and Am star
candidates have been carried out from ARIES (Manora Peak, Nainital) using a
three-channel fast photometer attached to the ARIES 104-cm Sampurnanand
telescope. This paper presents three new variables: HD 113878, HD 118660 and HD
207561. During the time span of the survey (1999 December to 2004 January)
pulsations of the Sct type were also found for the two evolved Am
stars HD 102480 and HD 98851, as reported in Joshi et al. (2002, 2003).
Additionally, we present 140 null results of the survey for this time span. The
star HD 113878 pulsates with a period of 2.31 hr, which is typical of
Sct stars. HD 118660 exhibits multi-periodic variability with a prominent
period of nearly 1 hr. These periods need to be investigated and make HD 118660
a particularly interesting target for further observations. For HD 207561, a
star classified as Am, a probable pulsation with a period of 6 min was found in
the light curves obtained on two consecutive nights. Both HD 102480 and HD
98851 exhibit unusual alternating high and low amplitude maxima, with a period
ratio of 2:1. The analysis of the null results confirms the photometric quality
of the NainitalComment: 14 pages, 13 figures, Accepted for publication in A&
The 2003-4 multisite photometric campaign for the Beta Cephei and eclipsing star 16 (EN) Lacertae with an Appendix on 2 Andromedae, the variable comparison star
A multisite photometric campaign for the Beta Cephei and eclipsing variable
16 Lacertae is reported. 749 h of high-quality differential photoelectric
Stromgren, Johnson and Geneva time-series photometry were obtained with ten
telescopes during 185 nights. After removing the pulsation contribution, an
attempt was made to solve the resulting eclipse light curve by means of the
computer program EBOP. Although a unique solution was not obtained, the range
of solutions could be constrained by comparing computed positions of the
secondary component in the Hertzsprung-Russell diagram with evolutionary
tracks.
For three high-amplitude pulsation modes, the uvy and the Geneva UBG
amplitude ratios are derived and compared with the theoretical ones for
spherical-harmonic degrees l <= 4. The highest degree, l = 4, is shown to be
incompatible with the observations. One mode is found to be radial, one is l =
1, while in the remaining case l = 2 or 3.
The present multisite observations are combined with the archival photometry
in order to investigate the long-term variation of the amplitudes and phases of
the three high-amplitude pulsation modes. The radial mode shows a
non-sinusoidal variation on a time-scale of 73 yr. The l = 1 mode is a triplet
with unequal frequency spacing, giving rise to two beat-periods, 720.7 d and
29.1 yr. The amplitude and phase of the l = 2 or 3 mode vary on time-scales of
380.5 d and 43 yr.
The light variation of 2 And, one of the comparison stars, is discussed in
the Appendix.Comment: 18 pages, 19 figures, accepted for publication in MNRA
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