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Context.The variable pre-white dwarf PG 1159 stars (GW Vir) are g-mode non-radial pulsators. Asteroseismology puts strong constraints on their global parameters and internal structure. PG 0122+200 defines the red edge of the instability strip and its evolutionary timescale is predicted to be dominated by neutrino emission. Its study offers the opportunity to better understand the instability mechanism and to validate the physics of the neutrino production in dense plasma.

In this article we present the results of 215 h of time-series photometry on the rapidly pulsating subdwarf B star PG 1325+101 (Teff= 35 000 K, $\log g$= 5.8, $\log$N(He)/N(H) = –1.7), obtained during 25 days of observation in Spring 2003 from nine different sites. As in previous observations, the temporal spectrum is dominated by the main peak at 7255.55 μHz, with an amplitude of about 2.7% which, however, is dropped to about 1.7% in February 2005. No secondary peaks close to the dominant pulsation mode are clearly detected. In addition, at least fourteen more pulsation frequencies are found: three of them at 7704.92, 9380.17 and 14511.10 μHz were already present in the discovery run with small differences in frequency, probably due to 1-day aliasing effects. The peak at 7704.92 μHz belongs to a triplet of almost equally spaced frequencies that could be due to rotational splitting and would imply a rotational period of about 1.6 days. Based on the results of this article, a detailed asteroseismic analysis of PG 1325+101 is presented in a separate paper (Charpinet et al. 2006b, A&A, 459, 565, Paper II).

We present a detailed analysis of the rapidly pulsating subdwarf B star (or EC14026 star) PG 1325+101. This analysis exploits the outcome of dedicated multisite observations using time-series photometry that revealed the presence of (at least) 15 periodicities in the luminosity modulation of this star (Silvotti et al. 2006, A&A, 459, 557, Paper I). Based on high-$S/N$, medium-resolution spectra obtained at the Steward Observatory's 2.3 m Telescope and at the 6.5 m MMT Telescope, new NLTE spectroscopic derivations of the atmospheric parameters of PG 1325+101 are presented. The mean values of $T_{\rm eff} = 35\,050 \pm 220$K, $\log g=5.81 \pm 0.04$, and $\log N({\rm He})/N({\rm H}) = -1.70\pm 0.02$are in agreement with previous determinations, but are significantly more accurate. These improved spectroscopic parameters are essential for isolating a unique asteroseismic model solution for the observed pulsation spectrum of PG 1325+101. Using the “forward modeling” approach, our combined spectroscopic and asteroseismic analysis leads objectively to the identification of the (k, $\ell$) indices of the 12 independent modes observed in this star, and to the determination of its structural parameters. The periods correspond to low-order acoustic modes with adjacent values of kand having degrees $\ell=0{-}4$. They define a band of unstable modes, in agreement with nonadiabatic pulsation theory. The average dispersion achieved between the observed periods and the periods of the corresponding theoretical modes of the optimal model is only ~0.46% (∼0.54 s), comparable to the results from similar analyses of other EC14026 stars analysed to date. The inferred structural parameters of PG 1325+101 are $T_{{\rm eff}}= 35\,050 \pm 220$K, $\log g=5.811\pm0.004$, $\log M_{{\rm env}}/M_{*}=-4.18\pm0.10$, $M_{*}=0.50\pm0.01$$M_{\odot}$(i.e., close to the canonical mass of extreme horizontal branch stars), $R/R_{\odot}=0.145\pm0.002$, and $L/L_{\odot}=28.3\pm1.5$. In addition, by combining detailed model atmosphere calculations with $V=14.019\pm0.012$, we estimate that this star has an absolute visual magnitude $M_{\rm V}=4.45\pm0.04$and is located at a distance of $d=820\pm21$pc. Finally, the presence of fine structure in the observed period spectrum suggests a rotation period of $P=1.6\pm0.2$days, leading to an equatorial velocity of $V_{{\rm eq}}=4.6\pm0.6$km s-1. Hence, asteroseismic evidence suggests that PG 1325+101 is a slow rotator, a conclusion reinforced by the limit $V\sin i < 20{-}30$km s-1, which we determined by modeling the He I 4471 line in our 1 Å-resolution MMT spectrum.

This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 μHz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of $\ell=1$and $\ell=2$non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately “thick” hydrogen mass fraction log $q_{\rm H} \geq -7.0$. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

We observed the pulsating hydrogen atmosphere white dwarf G 185–32 with the Whole Earth Telescope in 1992. We report on a weighted Fourier transform of the data detecting 18 periodicities in its light curve. Using the Hubble Space Telescope Faint Object Spectrograph time resolved spectroscopy, and the wavelength dependence of the relative amplitudes, we identify the spherical harmonic degree ($\ell$) for 14 pulsation signals. We also compare the determinations of effective temperature and surface gravity using the excited modes and atmospheric methods, obtaining $T_{{\rm eff}}=11\,960$±80 K, $\log g=8.02$±0.04 and $M=0.617$±$0.024~M_{\odot}$.

We report the discovery of a new eclipsing system less than one arcminute south of the pulsating DB white dwarf KUV 05134+2605. The object could be identified with the point source 2MASS J0516288+260738published by the Two Micron All Sky Survey. We present and discuss the first light curves as well as some additional colour and spectral information. The eclipse period of the system is 1.29 d, and, assuming this to be identical to the orbital period, the best light curve solution yields a mass ratio of $m_2/m_1=0.11$, a radius ratio of $r_2/r_1\approx 1$and an inclination of 74°. The spectral anaylsis results in a $T_{\rm eff}=4200$K for the primary. On this basis, we suggest that the new system probably consists of a late K + Brown dwarf (which would imply a system considerably younger than ≈0.01 Gyr to have $r_2/r_1\approx 1$), and outline possible future observations.

The pulsating PG 1159 planetary nebula central star RXJ 2117+3412 has been observed over three successive seasons of a multisite photometric campaign. The asteroseismological analysis of the data, based on the 37 identified $\ell=1$modes among the 48 independent pulsation frequencies detected in the power spectrum, leads to the derivation of the rotational splitting, the period spacing and the mode trapping cycle and amplitude, from which a number of fundamental parameters can be deduced. The average rotation period is $1.16\pm 0.05$days. The trend for the rotational splitting to decrease with increasing periods is incompatible with a solid body rotation. The total mass is 0.56$^{+0.02}_{-0.04}$$M_{\odot}$and the He-rich envelope mass fraction is in the range 0.013–0.078 $M_{*}$. The luminosity derived from asteroseismology is log($L/L_{\odot})= 4.05$$^{+0.23}_{-0.32}$and the distance 760 $^{+230}_{-235}$pc. At such a distance, the linear size of the planetary nebulae is $2.9\pm 0.9$pc. The role of mass loss on the excitation mechanism and its consequence on the amplitude variations is discussed.

A detailed proof is given to the previously published result, concerning the local symmetry groups relating distinct solutions of the Einstein equations. The maximal local symmetry group associated with the exterior metric of rotating bodies is proved to be three-parametric.

Optical observations of HZ Her made in the spring and summer of 1973 are presented. Some of the observations are practically coincident with estimated turn-on times for Her X-1 and others are simultaneous with X-ray observations made using the Copernicus satellite. Eight magnitudes were also measured from old plates for the epoch 1953-60; these measurements confirm the long-term variations for that epoch reported by Jones, Forman, and Liller (1973). An interesting theoretical explanation by Fabian, Pringle, and Rees (1973) for the persistence of large optical variations throughout the 35-day X-ray period is ruled out by simultaneous UHURU (X-ray) and Wise Observatory (optical) observations.

Observation of g-mode pulsations in the variable pre-white dwarf (GW Virginis) stars provides a unique means to probe their interiors and to study the late stages of stellar evolution. Multisite campaigns have in several cases proved highly successful in decoding pre-white dwarf light curves. Three previous attempts to untangle the pulsation spectrum of the coolest GW Virginis star, PG 0122+200, confirmed the existence of multiple g-modes but left the fundamental period spacing and therefore the star's mass and luminosity in doubt. We present an analysis based on new observations of PG 0122+200 obtained during a Whole Earth Telescope (WET) campaign conducted in the fall of 1996. Although our coverage was, because of bad weather, far poorer than in previous WET campaigns, we confirm the previous result that PG 0122+200 rotates once in 1.6 ± 0.1 days. The most likely period spacing supported by the data implies a mass of 0.69±0.03 M?. Based on the best seismology we can currently do, the cooling of PG 0122+200 is dominated by neutrino losses. This is not true for all pre-white dwarf stars and makes PG 0122+200 the prime candidate for learning useful physics. Constraints placed on the cooling rate of PG 0122+200 by future measurement of d?/dtcould provide a unique test of the standard theory of lepton interactions in the (experimentally unexplored) region of phase-space appropriate to pre-white dwarf interiors.

The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post-main-sequence evolution, along with their cooling rates, which will allow us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DA variables (DAVs), which have not been explored previously through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning 10 yr, we explore the pulsation spectrum of the cool DAV, G29-38 and find an underlying structure of 19 (not including multiplet components) normal-mode, probably =1 pulsations amidst an abundance of time variability and linear combination modes. Modeling results are incomplete, but we suggest possible starting directions and discuss probable values for the stellar mass and hydrogen layer size. For the first time, we have made sense out of the complicated power spectra of a large-amplitude DA pulsator. We have shown that its seemingly erratic set of observed frequencies can be understood in terms of a recurring set of normal-mode pulsations and their linear combinations. With this result, we have opened the interior secrets of the DAVs to future asteroseismological modeling, thereby joining the rest of the known white dwarf pulsators.

The article offers a personal narrative of experiences of actor and singer Brie Larson, when she danced with English singer-songwriter, multi-instrumentalist, and composer Paul McCartney of the English rock band Beatles at a party attended by music industry artists and recording company executives.

The V, (B - V), and (U - B) color indices of 26 stars in the immediate neighborhood of V1343 Aql are presented, with a finding chart. The magnitudes of the standard stars are in the range of the variability of SS 433.

Line identifications and radial velocities ofNova Sgr 1974 (= V3888 Sgr) determined from spectrograms taken in October and November 1974 in Israel and Australia are presented. The spectra and the fading rate of the light curve indicate that Nova Sgr 1974 was discovered approximately 2 or 3 magnitudes beyond maximum light. Provided the initial phases of evolution of the nova were normal, it may have been as bright as m 6 or 7 at maximum light. Both the measured radial velocities and an upper limit for the outburst amplitude indicate that Nova Sgr 1974 was a fast nova with t3 10 days. Alternatively, the nova was not typical of other observed Galactic novae. Key words: nova - radial velocity