30 research outputs found
Asteroseismology of the Beta Cephei star Nu Eridani -- IV. The 2003-4 multisite photometric campaign and the combined 2002-4 data
The second multisite photometric campaign devoted to Nu Eri is reported. For
Nu Eri, analysis of the new data adds four independent frequencies to the nine
derived previously from the 2002-3 data, three in the range from 7.20 to 7.93
c/d, and a low one, equal to 0.614 c/d. Combining the new and the old data
results in two further independent frequencies, equal to 6.7322 and 6.2236 c/d.
Altogether, the oscillation spectrum is shown to consist of 12 high frequencies
and two low ones. The latter have u amplitudes about twice as large as the v
and y amplitudes, a signature of high radial-order g modes. Thus, the
suggestion that Nu Eri is both a Beta Cephei and an SPB star, put forward on
the basis of the first campaign's data, is confirmed.
Nine of the 12 high frequencies form three triplets, of which two are new.
The triplets represent rotationally split l=1 modes, although in case of the
smallest-amplitude one this may be questioned. Mean separations and asymmetries
of the triplets are derived with accuracy sufficient for meaningful comparison
with models.
The first comparison star, Mu Eri, is shown to be an SPB variable with an
oscillation spectrum consisting of six frequencies, three of which are
equidistant in period. The star is also found to be an eclipsing variable. The
eclipse is a transit, probably total, the secondary is fainter than the primary
by several magnitudes, and the system is widely detached.
The second comparison star, Xi Eri, is confirmed to be a Delta Scuti
variable. To the frequency of 10.8742 c/d seen already in the first campaign's
data, another one, equal to 17.2524 c/d, is added.Comment: 13 pages, 8 figures, MNRAS, in pres
A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph
We report a multisite photometric campaign for the Beta Cep stars V2052 Oph
and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with eight telescopes
on five continents during 182 nights. Frequency analyses of the V2052 Oph data
enabled the detection of three pulsation frequencies, the first harmonic of the
strongest signal, and the rotation frequency with its first harmonic.
Pulsational mode identification from analysing the colour amplitude ratios
confirms the dominant mode as being radial, whereas the other two oscillations
are most likely l=4. Combining seismic constraints on the inclination of the
rotation axis with published magnetic field analyses we conclude that the
radial mode must be the fundamental. The rotational light modulation is in
phase with published spectroscopic variability, and consistent with an oblique
rotator for which both magnetic poles pass through the line of sight. The
inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o
<beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is
discussed. The photometric amplitudes of the single oscillation of V986 Oph are
most consistent with an l=3 mode, but this identification is uncertain.
Additional intrinsic, apparently temporally incoherent, light variations of
V986 Oph are reported. Different interpretations thereof cannot be
distinguished at this point, but this kind of variability appears to be present
in many OB stars. The prospects of obtaining asteroseismic information for more
rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are
briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres
Asteroseismology of the Beta Cephei star Nu Eridani: photometric observations and pulsational frequency analysis
We undertook a multisite photometric campaign for the Beta Cephei star Nu
Eridani. More than 600 hours of differential photoelectric uvyV photometry were
obtained with 11 telescopes during 148 clear nights. The frequency analysis of
our measurements shows that the variability of Nu Eri can be decomposed into 23
sinusoidal components, eight of which correspond to independent pulsation
frequencies between 5 - 8 c/d. Some of these are arranged in multiplets, which
suggests rotational m-mode splitting of nonradial pulsation modes as the cause.
If so, the rotation period of the star must be between 30 - 60 d. One of the
signals in the light curves of Nu Eri has a very low frequency of 0.432 c/d. It
can be a high-order combination frequency or, more likely, an independent
pulsation mode. In the latter case Nu Eri would be both a Beta Cephei star and
a slowly pulsating B (SPB) star. The photometric amplitudes of the individual
pulsation modes of Nu Eri appear to have increased by about 20 per cent over
the last 40 years. So do the amplitudes of the dominant combination frequencies
of the star. Among the latter, we only could identify sum frequencies with
certainty, not difference frequencies, which suggests that neither light-curve
distortion in its simplest form nor resonant mode coupling are their single
cause. One of our comparison stars, Mu Eridani, turned out to be variable with
a dominant time scale of 1.62 d. We believe that it is either an SPB star just
leaving its instability strip or that its variations are of rotational origin.Comment: 10 pages, 5 figure
A photometric study of the southern Blazhko star SS For Unambiguous detection of quintuplet components
We present our analysis of photometric data in the Johnson B and V filter of
the southern Blazhko star SS For. In parallel, we analyzed the V observations
obtained with the ASAS-3 photometry of the star gathered between 2000 and 2008.
In the frequency spectra resulting from a Fourier analysis of our data, the
triplet structure is detectable up to high order, both in the B and V data.
Moreover, we find evidence for quintuplet components. We confirm from our data
that the modulation components decrease less steeply than the harmonics of the
main frequency. We derived the variations of the Fourier parameters quantifying
the light curve shape over the Blazhko cycle. There is good agreement between
the spectroscopic abundance and the metallicity determined from the Fourier
parameters of the average light curve. SS For is peculiar as a Blazhko star
because of its strong variations around minimum light.Comment: 15 pages, 14 figures, accepted for publication in MNRA
Johnson photometry of southern Blazhko targets
We report on differential photomultiplier photometry in the Johnson B and V filters of five southern Blazhko stars (RU Cet, RY Col, V674 Cen, AR Ser, RV Cap). The data were gathered from the South African Astronomical Observatory (SAAO) in Sutherland, South Africa, in the course of 2004 and 2005. To find the most reliable values for the periods, we combined our V data with ASAS photometry. For some stars, this enabled us to constrain their Blazhko period with unprecedented accuracy.status: publishe
Photometric observations of southern Blazhko Stars
In the years 2004 and 2005, we obtained Johnson B and V photometry of 7 southern Blazhko RR Lyrae stars at the South African Astronomical Observatory (SAAO) and Siding Spring Observatory (SSO), Australia. Using the new data in combination with the ASAS data, Blazhko periods could be determined with unprecedented accuracy.status: publishe
Johnson photometry of southern Blazhko targets. Veröffentlichungen der Kommission für Astronomie|Communications in Asteroseismology|Communications in Asteroseismology 153 153|
CCD Measurements of Hipparcos Wide Visual Double Stars
International audienceWe present final astrometric and photometric results of CCD observations of HIPPARCOS visual double stars obtained with the Kryonerion 1.2m telescope. The new measurements together with several hundreds more obtained during the last two years in both hemispheres, will permit the determination of the physical pairs in the sample
Energy dispersive x-ray fluorescence analysis of pre and post-1850 historical documents obtained from the national library of South Africa
Energy dispersive X-ray fluorescence technique was used to study the elemental composition of some historical paper samples obtained from the National Library of South Africa. Six elements namely Fe, Cu, Mn, Ca, K and S were detected. It was found that older documents had higher concentrations of Ca and hence a considerable alkaline buffer than recent documents. It was also observed that the levels of Ca dropped significantly between 1800 and 1890 coinciding with the period paper making technology also changed. The concentrations of K and S also decreased around 1890. Iron remained fairly high and was detected in all the samples. Copper and manganese were found to be at very low concentrations compared to Fe. This research shows that Fe has the potential to impact negatively on paper permanency unless de-acidification is undertaken because of its relative abundance compared to Cu
The Nainital-Cape Survey: IV. A search for pulsational variability in 108 chemically peculiar stars⋆
Context. The Nainital-Cape Survey is a dedicated ongoing survey program to search for and study pulsational variability in chemically peculiar (CP) stars to understand their internal structure and evolution