We present high resolution spectro-astrometry of a sample of 28 Herbig Ae/Be and 3 F-type pre-main sequence stars. The spectro-astrometry, which is essentially the study of unresolved features in long-slit spectra, is shown from both empirical and simulated data to be capable of detecting binary companions that are fainter by up to 6 magnitudes at separations larger than ∼ 0.1 arcsec. The nine ...

We report on a sub-stellar companion search utilizing interferometric fringe-tracking astrometry acquired with Fine Guidance Sensor 3 (FGS 3) on the Hubble Space Telescope. Our targets were Proxima Centauri and Barnard’s Star. We obtain absolute parallax values for Proxima Cen πabs = 0. 7687± 0. 0003 and for Barnard’s Star πabs = 0. 5454± 0. 0003. Once low-amplitude instrumental systematic erro...

Improved quantum sensing of photons from astronomical objects could provide high resolution observations in the optical benefiting numerous fields, including general relativity, dark matter studies, and cosmology. It has been recently proposed that stations interferometers would not require a phase-stable link if instead sources quantum-mechanically entangled pairs be provided to them, potentia...

We present 5 GHz space-VLBI observations of the quasar pair B 1342+662 / B 1342+663 that demonstrate the feasibility of phase-reference techniques using an antenna in space. The space-based data were taken by the satellite HALCA, of the space-VLBI mission VSOP. From residual (referenced) phases we derive an upper bound of 10 meters to the uncertainty of the spacecraft orbit reconstruction. An a...

The Tycho–2 Catalogue, released in February 2000, is based on the ESA Hipparcos space mission data and various ground–based catalogs for proper motions. An external comparison of the Tycho–2 astrometry is presented here using the first U.S. Naval Observatory CCD As-trograph Catalog (UCAC1). The UCAC1 data were obtained from observations performed at CTIO between February 1998 and November 1999,...

In this document we present fits for the distortion of the LRIS-R and LRIS-B instrument focal plane applicable to the determination of astrometric coordinates from imaeges taken with the LRIS at the Keck I Telescope. Coefficients were determined for LRIS-R and LRIS-B with the ADC in use and without the ADC in the beam based on images taken in the time period Jan. to March, 2007. These are utili...

In very crowded fields, the modulation of the background by the sea of unresolved faint sources induces centroid shifts. The errors increase with the number of sources per beam. Even the most optimistic simulations of imaging data show that position errors can become severe (on the order of the beam size) at flux levels at which images contain 1/100 to 1/20 sources per beam, depending on the sl...

We discuss the prospect of deblending microlensing events by observing astrometric shifts of the lensed stars. Since microlensing searches are generally performed in very crowded fields, it is expected that stars will be confusion limited rather than limited by photon statistics. By performing simulations of events in crowded fields, we find that if we assume a dark lens and that the lensed sta...