Indications of a Large Fraction of Spectroscopic Binaries Among Nuclei of Planetary Nebulae

Previous work indicates that about 10% of planetary-nebula nuclei (PNNi) are photometrically variable short-period binaries with periods of hours to a few days. These systems have most likely descended from common-envelope (CE) interactions in initially much wider binaries. Population-synthesis studies suggest that these very close pairs could be the short-period tail of a much larger post-CE binary population with periods of up to a few months. We have initiated a radial-velocity (RV) survey of PNNi with the WIYN 3.5-m telescope and Hydra spectrograph, which is aimed at discovering these intermediate-period binaries. We present initial results showing that 10 out of 11 well-observed PNNi have variable RVs, suggesting that a significant binary population may be present. However, further observations are required because we have as yet been unable to fit our sparse measurements with definite orbital periods, and because some of the RV variability might be due to variations in the stellar winds of some of our PNNi.Comment: 11 pages, 1 table, no figures. Accepted by the Astrophysical Journal Letter

Asteroseismological studies of three Beta Cephei stars: IL Vel, V433 Car and KZ Mus

We have acquired between 127 and 150 h of time-resolved multicolour photometry for each of the three Beta Cephei stars IL Vel, V433 Car and KZ Mus over a time span of four months from two observatories. All three objects are multiperiodic with at least three modes of pulsation. Mode identification from the relative colour amplitudes is performed. We obtain unambiguous results for the two highest-amplitude modes of IL Vel (both are l=1) and the three strongest modes of KZ Mus (l=2,0 and 1), but none for V433 Car. Spectroscopy shows the latter star to be a fast rotator (v sin i = 240 km/s), whereas the other two have moderate v sin i (65 and 47 km/s, respectively). We performed model calculations with the Warsaw-New Jersey stellar evolution and pulsation code. We find that IL Vel is an object of about 12 Msun in the second half of its main sequence evolutionary track. Its two dipole modes are most likely rotationally split components of the mode originating as p1 on the ZAMS; one of these modes is m=0. V433 Car is suggested to be an unevolved 13 Msun star just entering the Beta Cephei instability strip. KZ Mus seems less massive (about 12.7 Msun) and somewhat more evolved, and its radial mode is probably the fundamental one. In this case its quadrupole mode would be the one originating as g1, and its dipole mode would be p1. It is suggested that mode identification of slowly rotating Beta Cephei stars based on photometric colour amplitudes is reliable; we estimate that a relative accuracy of 3% in the amplitudes is sufficient for unambiguous identifications. Due to the good agreement of our theoretical and observational results we conclude that the prospects for asteroseismology of multiperiodic slowly rotating Beta Cephei star are good.Comment: 16 pages, 16 figures, MNRAS, in pres

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

Particle decay branching ratios for states of astrophysical importance in 19Ne

We have measured proton and alpha-particle branching ratios of excited states in 19Ne formed using the 19F(3He,t) reaction at a beam energy of 25 MeV. These ratios have a large impact on the astrophysical reaction rates of 15O(alpha,gamma), 18F(p,gamma) and 18F(p,alpha), which are of interest in understanding energy generation in x-ray bursts and in interpreting anticipated gamma-ray observations of novae. We detect decay protons and alpha-particles using a silicon detector array in coincidence with tritons measured in the focal plane detector of our Enge split-pole spectrograph. The silicon array consists of five strip detectors of the type used in the Louvain-Edinburgh Detector Array, subtending angles from 130 degrees to 165 degrees with approximately 14% lab efficiency. The correlation angular distributions give additional confidence in some prior spin-parity assignments that were based on gamma branchings. We measure Gamma_p/Gamma=0.387+-0.016 for the 665 keV proton resonance, which agrees well with the direct measurement of Bardayan et al.Comment: 5 pages, 2 figures, 3 tables. Prepared using RevTex 4 and BibTex. Further minor revisions, incl. fig. 1 font size increase, 1 table removal, and minor changes to the tex

Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295

We have discovered both intermediate-order gravity mode and low-order pressure mode pulsation in the same star, HD 209295. It is therefore both a Gamma Doradus and a Delta Scuti star, which makes it the first pulsating star to be a member of two classes. The star is a single-lined spectroscopic binary with an orbital period of 3.10575 d and an eccentricity of 0.352. Weak pulsational signals are found in both the radial velocity and line-profile variations, allowing us to show that the two highest-amplitude Gamma Doradus pulsation modes are consistent with l=1 and |m|=1. In our 280 h of BVI multi-site photometry we detected ten frequencies in the light variations, one in the Delta Scuti regime and nine in the Gamma Doradus domain. Five of the Gamma Doradus frequencies are exact integer multiples of the orbital frequency. This observation leads us to suspect they are tidally excited. Results of theoretical modeling (stability analysis, tidal excitation) were consistent with the observations. We could not detect the secondary component of the system in infrared photometry, suggesting that it may not be a main-sequence star. Archival data of HD 209295 show a strong ultraviolet excess, the origin of which is not known. The orbit of the primary is consistent with a secondary mass of M > 1.04 Msun indicative of a neutron star or a white dwarf companion.Comment: 18 pages, 18 figures, accepted for publication in MNRAS, shortened abstrac

The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode

We undertook a time-series photometric multi-site campaign for the rapidly oscillating Ap star HD 99563 and also acquired mean light observations over two seasons. The pulsations of the star, that show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 microHertz and some first harmonics of these. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 +/- 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break the distorted oscillation mode up into its pure spherical harmonic components and find it is dominated by the l=1 pulsation, and also has a notable l=3 contribution, with weak l=0 and 2 components. The geometrical configuration of the star allows one to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes was modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the Delta Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03 solar mass object, seen at a rotational inclination of 44 degrees, which then predicts a magnetic obliquity of 86.4 degrees.Comment: 10 pages, 6 figures, accepted for publication by MNRA