Photometric observations of selected, optically bright quasars for Space Interferometry Mission and other future celestial reference frames

Photometric observations of 235 extragalactic objects that are potential targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R, I magnitudes at the 5% level are obtained at 1 - 4 epochs between 2005 and 2007 using the 1-m telescopes at Cerro Tololo Inter-American Observatory and Naval Observatory Flagstaff Station. Of the 134 sources which have V magnitudes in the Veron & Veron-Cetty catalog a difference of over 1.0 mag is found for the observed-catalog magnitudes for about 36% of the common sources, and 10 sources show over 3 mag difference. Our first set of observations presented here form the basis of a long-term photometric variability study of the selected reference frame sources to assist in mission target selection and to support in general QSO multi-color photometric variability studies.Comment: 40 pages, 13 figures, 4 table

USNO Analysis Center for Source Structure Report

This report summarizes the activities of the United States Naval Observatory Analysis Center for Source Structure for the 2012 calendar year and the activities planned for the year 2013

Astrophysics of Reference Frame Tie Objects

The Astrophysics of Reference Frame Tie Objects Key Science program will investigate the underlying physics of SIM grid objects. Extragalactic objects in the SIM grid will be used to tie the SIM reference frame to the quasi-inertial reference frame defined by extragalactic objects and to remove any residual frame rotation with respect to the extragalactic frame. The current realization of the extragalactic frame is the International Celestial Reference Frame (ICRF). The ICRF is defined by the radio positions of 212 extragalactic objects and is the IAU sanctioned fundamental astronomical reference frame. This key project will advance our knowledge of the physics of the objects which will make up the SIM grid, such as quasars and chromospherically active stars, and relates directly to the stability of the SIM reference frame. The following questions concerning the physics of reference frame tie objects will be investigated

Four-dimensional String Compactifications with D-Branes, Orientifolds and Fluxes

This review article provides a pedagogical introduction into various classes of chiral string compactifications to four dimensions with D-branes and fluxes. The main concern is to provide all necessary technical tools to explicitly construct four-dimensional orientifold vacua, with the final aim to come as close as possible to the supersymmetric Standard Model. Furthermore, we outline the available methods to derive the resulting four-dimensional effective action. Finally, we summarize recent attempts to address the string vacuum problem via the statistical approach to D-brane models.Comment: 331 pages, 7 figures, review prepared for Physics Reports, please send constructive comments to: [email protected], v2: refs added, v3: final version to appear in Phys. Rep

Search for supersymmetry in events with a photon, a lepton, and missing transverse momentum in pp collisions at root s=8 TeV

Peer reviewe

ICRF-3 Overview

No abstract availabl

Revisiting the VLBA Calibrator Surveys for ICRF3

International audiencehe original VLBA Calibrator (VCS) surveys were a set of 24 24-hr VLBA sessions between 1994 and 2007 in which ~2600 compact radio sources were observed in X/S bands to obtain precise positions and snapsot images. Most were observed in only one session but they vastly expanded the pool of calibrator sources available for phase-referencing VLBI. These sources were later incorporated into ICRF2, but within ICRF2 they became a second class compared to the other ICRF2 sources observed in regular Mark3/Mark4/RDV VLBI geodesy and astrometry sessions over nearly 30 years. The VCS sources represented 2/3 of ICRF2, but they had formal errors approximately 5 times greater, on average, than the other 1/3. In order to reduce this 2 class distinction, the VCS-II team was formed to re-observe these sources for ICRF3 and improve their usefulness as phase-referencing calibrators. We report here on the re-observations of 2400 of these sources in 8 VLBA sessions in 2014 and 2015. The new observations were made at 2 GBits/sec versus the 128 MBits/sec of the original VCS sessions, and thus are considerably more sensitive. Some 2000 'old' VCS sources have been re-observed and their formal position errors have improved by an average factor of 3.6 in RA and Dec. And ~300 'new' sources (not detected in the original VCS analysis) have also now been detected. Mapping of these sources is also being performed and we anticipate being able to compute structure indices for them as well

Revisiting the VLBA Calibrator Surveys for ICRF3

he original VLBA Calibrator (VCS) surveys were a set of 24 24-hr VLBA sessions between 1994 and 2007 in which ~2600 compact radio sources were observed in X/S bands to obtain precise positions and snapsot images. Most were observed in only one session but they vastly expanded the pool of calibrator sources available for phase-referencing VLBI. These sources were later incorporated into ICRF2, but within ICRF2 they became a second class compared to the other ICRF2 sources observed in regular Mark3/Mark4/RDV VLBI geodesy and astrometry sessions over nearly 30 years. The VCS sources represented 2/3 of ICRF2, but they had formal errors approximately 5 times greater, on average, than the other 1/3. In order to reduce this 2 class distinction, the VCS-II team was formed to re-observe these sources for ICRF3 and improve their usefulness as phase-referencing calibrators. We report here on the re-observations of 2400 of these sources in 8 VLBA sessions in 2014 and 2015. The new observations were made at 2 GBits/sec versus the 128 MBits/sec of the original VCS sessions, and thus are considerably more sensitive. Some 2000 'old' VCS sources have been re-observed and their formal position errors have improved by an average factor of 3.6 in RA and Dec. And ~300 'new' sources (not detected in the original VCS analysis) have also now been detected. Mapping of these sources is also being performed and we anticipate being able to compute structure indices for them as well