arXiv subjects

H. Edelmann

Publications and source records attributed to H. Edelmann.

23 records · Page 2Linked to original sources

arXiv2003

Simultaneous time-series spectroscopy and multi-band photometry of the sdBV PG 1605+072

We present time-series spectroscopy and multi-band photometry of the sdBV PG 1605+072 carried out simultaneously at the Calar Alto 2.2m and 3.5m telescopes. The periodogram analysis of the radial velocity curves reveals three frequencies at 2.078, 2.756, and 1.985 mHz for Hbeta and at 2.076, 2.753, and 1.978 mHz for Hgamma. The corresponding radial velocity amplitudes are 12.7, 8.0, and 7.9 km/s for Hbeta and 14.3, 6.5, and 7.2 km/s for Hgamma. Furthermore, we found five frequencies that are present in all wavelength bands of the BUSCA photometer. The frequencies detected in the radial velocity curves are recovered by the photometric measurements. Moreover, additional frequencies were present in the periodograms which could not be identified in all four bands simultaneously. The comparison of the amplitudes presented here with previous results from radial velocity and photometric observations of PG 1605+072 shows a significant change or even switch in the power of the modes within short time scales, i. e. about one year. No changes in frequency were registered and the phases of the modes show no wavelength dependency within our multi-band photometry.

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arXiv2003

Spectral analysis of sdB stars from the Hamburg Quasar Survey

We present the results of a spectral analysis of a large sample of subdwarf B stars selected from follow-up observations of candidates from the Hamburg Quasar Survey. Fundamental parameters (effective temperature, gravity, and helium abundance) were determined by matching synthetic line profiles calculated from model atmospheres to all hydrogen and helium absorption lines present in the observed optical spectra. The derived helium abundances are compared with the atmospheric parameters to search forpossible trends. We discovered a correlation between the helium abundance and the effective temperature: the larger the temperature, the larger the photospheric helium content of sdB stars. Additionally, a separation into two sequences of sdB stars in the effective temperature - helium abundance plane is detected. We compared our analysis results with data from the literature. The stars from our sample are found to be somewhat more luminous. This can only partlybe explained by NLTE effects. Three apparently normal B stars were discovered, which could be massive stars far away from the galactic plane (7-19kpc). Radial velocities were measured for 23 stars from which we discovered a new radial velocity variable sdB star.

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arXiv2002

Discovery of A New Class of Pulsating Stars: Gravity-mode Pulsators among Subdwarf B Stars

During the course of an ongoing CCD monitoring program to investigate low-level light variations in subdwarf B (sdB) stars, we have serendipitously discovered a new class of low amplitude, multimode sdB pulsators with periods of the order of an hour. These periods are more than a factor of ten longer than those of previously known multimode sdB pulsators (EC 14026 stars), implying that they are due to gravity modes rather than pressure modes. The longer period pulsators are found only among cooler sdB stars, where they are surprisingly common. The iron opacity instability that drives the short period EC 14026 stars is effective only in hot sdB's, leaving the driving mechanism for the deeper gravity modes in cool sdB's currently unknown. We present the first observational results for our newly identified sdB variables, and discuss possible implications.

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arXiv2001

Early type stars at high galactic latitudes II. Four evolved B-type stars of unusual chemical composition

We present the result of differential spectral analyses of a further four apparently normal B-type stars. Abundance anomalies (e.g. He, C, N enrichment), slow rotation and/or high gravities suggest that the programme stars are evolved low-mass B-type stars. In order to trace their evolutionary status several scenarios are discussed. Post-AGB evolution can be ruled out. PG 0229+064 and PG 1400+389 could be horizontal branch (HB) stars, while HD 76431 and SB 939 have already evolved away from the extreme HB (EHB). The low helium abundance of HD 76431 is consistent with post-EHB evolution. The enrichment in helium, carbon and nitrogen of the remaining stars can be explained either by deep mixing of nuclearly processed material to the surface or by diffusion processes modified by magnetic fields and/or stellar winds. A kinematic study of their galactic orbits indicates that the stars belong to an old disk population.

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arXiv2001

Binaries discovered by the SPY project I. HE 1047-0436: a subdwarf B + white dwarf system

In the course of our search for double degenerate binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY) we discovered that the sdB star HE 1047-0436 is radial velocity variable. The orbital period of 1.213253d, a semi-amplitude of 94km/s, and a minimum mass of the invisible companion of 0.44Msol are derived from the analysis of the radial velocity curve. We use an upper limit on the projected rotational velocity of the sdB star to constrain the system inclination and the companion mass to M>0.71Msol, bringing the total mass of the system closer to the Chandrasekhar limit. However, the system will merge due to loss of angular momentum via gravitational wave radiation only after several Hubble times. Atmospheric parameters and metal abundances are also derived. The resulting values are typical for sdB stars.

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