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We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid Beta Cep/SPB pulsator Gamma Peg. Frequency analyses reveal the presence of six g modes of high radial order together with eight low-order Beta Cep oscillations in both data sets. Mode identification shows that all pulsations have spherical degrees l = 0 - 2. An 8.5 solar mass model reproduces the observed pulsation frequencies; all theoretically predicted modes are detected. We suggest, contrary to previous authors, that Gamma Peg is a single star; the claimed orbital variations are due to g-mode pulsation. Gamma Peg is the first hybrid pulsator for which a sufficiently large number of high-order g modes and low order p and mixed modes have been detected and identified to be usable for in-depth seismic modeling., Comment: 18 pages (4 pages in journal style), 4 figures, accepted for ApJ Letters

The atmospheres of classical Cepheids cannot be represented adequately by a sequence of hydrostatic equilibrium atmospheric models (see Sasselov and Lester 1990 and references therein). Observational evidence for shocks is also available at least since Kraft (1956). Both the disequilibrium and the non-linear phenomena affect the emergent spectra and spectral line profiles of the Cepheids. In the lower amplitude variables the effects may be subtle, yet still lead to significant systematic discrepancies.We have developed the code HERMES for time-dependent treatment of hydrodynamics and non-LTE radiative transfer in the atmospheres of classical Cepheids with periods shorter than 12 days. Our approach is applicable to stars in which the formed shock waves do not dominate the energy balance of the atmosphere. Consecutive detailed calculations are performed for several multi-level model atoms, including H, Ca II, Mg II, He I and II. We use a 1-D explicit conservative upwind monotonic second-order (in time and space) Godunov-type Lagrangian hydrodynamic scheme. Being a characteristics based scheme it allows natural handling of boundary conditions. The scheme is stable and without artificial dissipation, a crucial necessity for physically meaningful radiative transfer solutions (see Roe 1990, Sasselov and Raga 1991 for more details).

We have obtained high-dispersion blue spectograms and BV photometry of the high-latitude F-supergiant HR 4912=HD 112374. As a result of our curve-of-growth analysis we conclude that it appears to have the parameters of a F-supergiant with slight metal deficiency ([Fe/H]=−0.7). The latter depends much upon the derived temperature of HR 4912, hence we pay special attention to this problem. Our blue spectra and new BV photometry made it possible to obtain four independent estimates of the temperature-better than in the previous two studies of HR 4912 in the UV and red regions.

The newly proposed UU Her-type stars are discussed; their main features being long-period variability and high galactic latitude. It is unlikely that the UU Her stars originated in the plane of the galaxy as they are now located more than a kiloparsec above it. An alternative explanation of their normal Population I characteristics must be looked for.

A general review of the group of UU Her-type stars proposed recently as a possible new type of variables is given. The available observations (spectra and photometry) reveal them as luminous Population I F-type supergiants of normal composition. This fact contradicts their great distances above the galactic plane. As there is no reason so far to distrust the results from the spectroscopic analyses and photometry, the galactic plane should be excluded as a possible birthplace of the UU Her-stars. In this respect they might probably indicate that recent star formation (though occasional) from already enriched material was possible at high galactic latitudes. Moreover, normal Main-Sequence B-stars seem now also to be found there.

We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and supernova contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of a supernova. The early afterglow light curve also shows deviations from the typical power-law decay. A supernova spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the supernova explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe., Comment: 57 pages, 13 figures, accepted by ApJ, revised per referee's comments, includes full photometry table. Data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB030329 or through WWW at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/

Considering the possibility for a low-mass celestial body to attain high luminosity, characteristic for a normal supergiant, and mimic spectroscopic and photometric behavior of the latter, a method is proposed that could be possibly used to distinguish between supergiants and their limitations. In this method, surface abundance of Na-23 was used as a probable mass indicator, deriving the sodium-to-mass relation for a sample of 34 well-observed stars. Special attention was paid to the parameter-related errors and non-LTE effects for the Na I lines in the visible. To account for the initial sodium content, all sodium abundances were normalized, using the Na/Fe relation derived from solar-type dwarfs. The plot of the normalized sodium abundance against stellar mass has revealed a direct relationship between the two parameters, suggesting a real interdependence. The classical Cepheid X Cyg, believed to be a true intermediate-mass star, was well within the highly scattered relation.

UU Her stars are often considered to be postasymptotic-giant-branch stars, which in turn implies that they should be in a state of rapid blueward evolution in the H-R diagram. A recent reviewer of theoretical models suggests an increase in effective temperature at the rate of 10 K to 40 K per year. Measurements of the (B-V) color indices of these stars over as much as 35 years, and the pulsational period of UU Her itself over 83 years are examined, and no evidence is found for detectable change in either of these quantities. This is found to constrain any rate of effective temperature change to less than 0.5 K per year and, therefore, it is concluded that most likely the UU Her stars are not post-AGB stars.