Polarization due to dust scattering in the planetary nebula Cn1-1

The peculiar emission-line object Cn1-1 (=HDE330036=PK330+4 degrees 1), classified both as a symbiotic star and as a planetary nebula, was detected by the Infrared Astronomical Satellite (IRAS) as a strong source of far-infrared dust in the system. Bhatt and Mallik (1986) discussed the nature of the dust in Cn1-1 and argued that the object is a Type I protoplanetary nebula in a binary system. The argument presented here is that the polarization is intrinsic to Cn1-1 and is due to scattering by large (compared to interstellar) dust grains in the protoplanetary nebula that are asymmetrically distributed around the central star. The large degree of polarization (approximately 3 percent for the Cn1-1 distance of approximately 450 pc) with a large lambda(sub max) is naturally explained if it is caused by scattering by large dust grains in the Cn1-1 nebula. Since the H(sub alpha) line is also polarized at the same level and position angle as the continuum, the dust must be asymmetrically distributed around the central star. The morphology of the protoplanetary nebula in Cn1-1 may be bipolar. Thus, the polarization observations support the suggestion that Cn1-1 is a bipolar Type I planetary nebula

Heitler-London model for acceptor-acceptor interactions in doped semiconductors

The interactions between acceptors in semiconductors are often treated in qualitatively the same manner as those between donors. Acceptor wave functions are taken to be approximately hydrogenic and the standard hydrogen molecule Heitler-London model is used to describe acceptor-acceptor interactions. But due to valence band degeneracy and spin-orbit coupling, acceptor states can be far more complex than those of hydrogen atoms, which brings into question the validity of this approximation. To address this issue, we develop an acceptor-acceptor Heitler-London model using single-acceptor wave functions of the form proposed by Baldereschi and Lipari, which more accurately capture the physics of the acceptor states. We calculate the resulting acceptor-pair energy levels and find, in contrast to the two-level singlet-triplet splitting of the hydrogen molecule, a rich ten-level energy spectrum. Our results, computed as a function of inter-acceptor distance and spin-orbit coupling strength, suggest that acceptor-acceptor interactions can be qualitatively different from donor-donor interactions, and should therefore be relevant to the control of two-qubit interactions in acceptor-based qubit implementations, as well as the magnetic properties of a variety of p-doped semiconductor systems. Further insight is drawn by fitting numerical results to closed-form energy-level expressions obtained via an acceptor-acceptor Hubbard model.Comment: 19 pages, 10 figures, text revised, figure quality improved, additional references adde

X-ray emission from O-type stars : DH Cep and HD 97434

We present X-ray emission characteristics of the massive O-type stars DH Cep and HD 97434 using archival XMM-Newton observations. There is no convincing evidence for short term variability in the X-ray intensity during the observations. However, the analysis of their spectra reveals X-ray structure being consistent with two-temperature plasma model. The hydrogen column densities derived from X-ray spectra of DH Cep and HD 97434 are in agreement with the reddening measurements for their corresponding host clusters NGC 7380 and Trumpler 18, indicating that the absorption by stellar wind is negligible. The X-ray emission from these hot stars is interpreted in terms of the standard instability-driven wind shock model.Comment: 13 pages ; 2 figures; 2 tables (Accepted for publication in New Astronomy