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Context.PG 1159-035, a pre-white dwarf with $T_{{\rm eff}}$$\simeq$140 000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star.

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.

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 report on the analysis of multisite time-series photometry of the pulsating pre-white dwarf (GW Vir star) PG 1707+427, obtained by the Whole Earth Telescope collaboration. This is the last of the known GW Vir stars without surrounding nebulae to be resolved by multisite data. Successful resolution of the pulsation spectrum resulted from the combination of high signal-to-noise observations with a large telescope and wide coverage in longitude with smaller telescopes. We find a series of 8 pulsation frequencies (along with two nonlinear combination frequencies), and identify 7 of them as part of a sequence of $\ell=1$modes, with a common period spacing of 23.0 s. This spacing implies that the mass of PG 1707+427 is $0.57~M_{\odot}$. Preliminary model fits suggest that the mass determined via asteroseismology is consistent with the mass determined from spectroscopy combined with evolutionary tracks.

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.

The acute effect of i.v. spironolactone dissolved in ethanol on renal digoxin clearance was studied in 10 dogs. All dogs received i.v. digoxin (0.02 micrograms/kg/min) and 0.9% saline (30 ml/kg of bolus and 0.1 ml/kg/min for maintenance) throughout the study. After 2 hr of equilibration, four 15-min urine collections were made. The dogs then received, over 1 hr, a loading infusion of 4 mg/kg of spironolactone in ethanol (group 1, N = 6) or ethanol alone (group 2, N = 4). Thereafter the infusion was maintained at one-tenth the initial rate for eight 15-min periods. Three additional control dogs received ethanol plus spironolactone without digoxin. Digoxin radioimmunoassay of plasma and urine from these control animals did not reveal any significant cross-reactivity between spironolactone and the antibody of the digoxin radioimmunoassay. The digoxin clearance (CDIG) and ratio of CDIG to inulin clearance (CDIG/CIN) increased insignificantly with ethanol alone, but were respectively reduced by 21 and 28% with spironolactone (P less than .05). The reductions of CDIG and CDIG/CIN were observed immediately after the spironolactone loading infusion and were associated with a sudden rise in plasma digoxin. The changes in digoxin handling with spironolactone appeared to be temporally dissociated from the antimineralocorticoid activity of spironolactone. We conclude that spironolactone inhibits renal CDIG by a mechanism that may be independent of its antimineralocorticoid activity.

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.