Brorfelde Schmidt CCD Catalog (BSCC)

The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars, north of +49 deg Declination with precise positions and V, R photometry. The catalog has been constructed from the reductions of 18,667 CCD frames observed with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog was used for astrometric and photometric reference stars. Errors of individual positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range. External comparisons with 2MASS and SDSS reveal possible small systematic errors in the BSCC of up to about 30 mas. The catalog is supplemented with J, H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550 MB ASCII, compressed) will be made available at the Strasbourg Data Center (CDS).Comment: 16 pages, 22 figures, 2 tables, accepted by A

Magnetic field diagnostics and spatio-temporal variability of the solar transition region

Magnetic field diagnostics of the transition region from the chromosphere to the corona faces us with the problem that one has to apply extreme UV spectro-polarimetry. While for coronal diagnostic techniques already exist through infrared coronagraphy above the limb and radio observations on the disk, for the transition region one has to investigate extreme UV observations. However, so far the success of such observations has been limited, but there are various projects to get spectro-polarimetric data in the extreme UV in the near future. Therefore it is timely to study the polarimetric signals we can expect for such observations through realistic forward modeling. We employ a 3D MHD forward model of the solar corona and synthesize the Stokes I and Stokes V profiles of C IV 1548 A. A signal well above 0.001 in Stokes V can be expected, even when integrating for several minutes in order to reach the required signal-to-noise ratio, despite the fact that the intensity in the model is rapidly changing (just as in observations). Often this variability of the intensity is used as an argument against transition region magnetic diagnostics which requires exposure times of minutes. However, the magnetic field is evolving much slower than the intensity, and thus when integrating in time the degree of (circular) polarization remains rather constant. Our study shows the feasibility to measure the transition region magnetic field, if a polarimetric accuracy on the order of 0.001 can be reached, which we can expect from planned instrumentation.Comment: Accepted for publication in Solar Physics (4.Mar.2013), 19 pages, 9 figure

Molecular Beams

Contains research objectives and reports on four research projects.Lincoln Laboratory, Purchase Order DDL B-00306U. S. ArmyU. S. NavyU. S. Air Force under Air Force Contract AF19(604)-740

Optical properties of structurally-relaxed Si/SiO2_2 superlattices: the role of bonding at interfaces

We have constructed microscopic, structurally-relaxed atomistic models of Si/SiO$_2$ superlattices. The structural distortion and oxidation-state characteristics of the interface Si atoms are examined in detail. The role played by the interface Si suboxides in raising the band gap and producing dispersionless energy bands is established. The suboxide atoms are shown to generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and optical-absorption calculations at the Fermi Golden rule level are used to demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue shift in the spectrum, and (c) an enhancement of the absorption intensity in the threshold-energy region. Some aspects of this behaviour appear not only in the symmetry direction associated with the superlattice axis, but also in the orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO$_2$ superlattices show clear optical enhancement and a shift of the optical spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B

Hubble Space Telescope Imaging of the Outburst Site of M31 RV

M31 RV is a luminous red variable star that appeared for several months in the bulge of M31 during 1988. Unlike classical novae, M31 RV was cool throughout its outburst. Interest in this object has revived recently because of its strong resemblance to V838 Mon, a luminous Galactic variable star that appeared in 2002 and is illuminating a spectacular light echo, and has evolved to ever-cooler surface temperatures. V4332 Sgr is a third object which was also a red supergiant throughout its eruption. We have examined archival Hubble Space Telescope (HST) images of the site of M31 RV, obtained fortuitously in 1999 with the WFPC2 camera in parallel mode during spectroscopic observations of the nucleus of M31. We located the site of M31 RV in the HST frames precisely through astrometric registration with ground-based CCD images, including several taken during the outburst. No light echo is seen at the M31 RV site, implying that M31 RV is not surrounded by circumstellar (or interstellar) dust similar to that around V838 Mon, or that its extent is less than ~1.7 pc. The stellar population at the outburst site consists purely of old red giants; there is no young population, such as seen around V838 Mon. There are no stars of unusual color at the site, suggesting that M31 RV had faded below HST detectability in the 11 years since outburst, that it is an unresolved companion of one of the red giants in the field, or that it is one of the red giants. We suggest future observations that may help decide among these possibilities.Comment: 16 pages, 3 figures, 2 tables; AJ accepte