Comparison of Velocity Fields of the Galaxies From the Catalogs RFGC and MarkIII

A distribution of matter up to 100 h ^-1 Mpc could be obtained from the large-scale galaxy peculiar motions. The best picture of such motion is given for today by two galaxy catalogs, namely MarkIII and RFGC. We compare their velocity fields and show they are very similar and have not only practically the same multipole structure but also a corresponding small-scale motions . We estimate a mean radial component of this small-scale motion as 500–700 kms. An additional comparison of distances to common galaxies is made. This revised version was published online in July 2006 with corrections to the Cover Date.     

An elemental abundance analysis of the magnetic chemically peculiar star HR 8216

An elemental abundance analysis of the cool magnetic CP star HR 8216 (= HD204411) was performed using 2.4 Å mm⁻¹ Dominion Astrophysical Observatory Reticon exposures covering  λλ3830–4770  with a typical signal-to-noise ratio of 200 taken with the long camera of the 1.22-m telescope. The spectrograms were measured interactively with the graphics computer program reduce . The fine analysis used an ATLAS9 metal-rich model atmosphere, the predictions of which best-matched the optical region fluxes and the Hγ profile. The anomalies of HR 8216 are primarily an enhancement of many iron peak elements with the rare earths elements much less enhanced than in many similar cool magnetic CP stars. Using the results of the fine analysis the spectrum was synthesized. Comparison with the observed spectrum showed that the agreement is good but did not fully account for all of the observed line spectrum.     

The carbon Cepheid RT Trianguli Australis: additional evidence of triple-α and CNO cycling

We have used echelle spectra of resolving power 35 000 to derive chemical abundances and the ¹²C/¹³C ratio in the 1.9-d carbon Cepheid RT TrA and the Cepheid U TrA, employed as a comparison star. We confirm that RT TrA is very metal-rich with [Fe/H]=+0.4. In addition, C and N are substantially in excess, and a small deficiency in O is present. We interpret these anomalies as resulting from the appearance on the stellar surface of material enriched in ¹²C by the 3- α process, followed by CNO cycling to convert ¹²C to ¹³C and ¹⁴N. In addition, some ¹⁶O has been processed to ¹⁴N. The partial processing of ¹⁶O to ¹⁴N indicates that substantial ¹⁷O may be present. Proton capture seems to have enhanced ²³Na from the Ne isotopes.     

The evolution of a rapidly accreting helium white dwarf to become a low-luminosity helium star

We have examined the evolution of merged low-mass double white dwarfs which become low-luminosity (or high-gravity) extreme helium stars. We have approximated the merging process by the rapid accretion of matter, consisting mostly of helium, on to a helium white dwarf. After a certain mass is accumulated, a helium shell flash occurs, the radius and luminosity increase and the star becomes a yellow giant. Mass accretion is stopped artificially when the total mass reaches a pre-determined value. As the helium-burning shell moves inwards with repeating shell flashes, the effective temperature gradually increases as the star evolves towards the helium main sequence. When the mass interior to the helium‐burning shell is approximately 0.25 M_⊙, the star enters a regime where it is pulsationally unstable. We have obtained radial pulsation periods for these models.
These models have properties very similar to those of the pulsating helium star V652 Her. We have compared the rate of period change of the theoretical models with that observed in V652 Her, as well as with its position on the Hertzsprung–Russell diagram. We conclude that the merger between two helium white dwarfs can produce a star with properties remarkably similar to those observed in at least one extreme helium star, and is a viable model for their evolutionary origin. Such helium stars will evolve to become hot subdwarfs close to the helium main sequence. We also discuss the number of low-luminosity helium stars in the Galaxy expected for our evolution scenario.     

TRAFICOS – an Échelle Zeeman spectrograph

We describe the TRAnsportable Flbre COupled échelle Spectrograph (TRAFICOS) equipped with a Zeeman analyzer and manufactured mainly for the observation of stellar magnetic fields. The spectrograph, designed at the Astrophysikalisches Institut Potsdam and constructed at the Thüringer Landessternwarte Tautenburg, is laid out in a quasi-Littrow configuration. The part attached to the Nasmyth focus of the 2 m telescope contains the telescope adapter for the fibre input and output of the star and calibration light, the cases for the flatfield and the wavelength calibration, and the Zeeman analyzer. The optical scheme and the reduction software are mentioned in some details and the first results of the determination of the magnetic field and radial velocity of several stars are given showing the performance of the device in comparison with existing data.