Joseph B. Jensen

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This paper presents the basic design of the Gemini Near-Infrared Imager (NIRI) and discusses its capabilities. NIRI offers three different pixel scales to match different operating modes of the Gemini telescope and allows polarimetric and spectroscopic observations. It is equipped with an infrared on-instrument wave-front sensor (OIWFS) to allow tip-tilt(More)
We describe a simple and cost-effective concept for implementing a Ground Layer Adaptive Optics (GLAO) system on Gemini that will feed all instruments mounted at the Cassegrain focus. The design concept can provide a GLAO correction to any of the current or future seeing-limited optical or near-infrared Gemini instruments. The GLAO design uses an adaptive(More)
Surface brightness fluctuations (SBFs) are much brighter in the infrared than they are at optical wavelengths, making it possible to measure greater distances using IR SBFs. We report new K ′ (2.1μm) SBF measurements of nine galaxies in the Fornax and Eridanus clusters using a 10242-pixel HgCdTe array. We used improved analysis techniques to remove(More)
We present a deep H-band image of the field of a candidate z=10 galaxy magnified by the foreground (z=0.25) cluster Abell 1835. The image was obtained with NIRI on Gemini North to better constrain the photometry and investigate the morphology of the source. The image is approximately one magnitude deeper and has better spatial resolution (seeing was 0.4-0.5(More)
To empirically calibrate the IR surface brightness uctuation (SBF) distance scale and probe the properties of unresolved stellar populations, we measured uctuations in 65 galaxies using NICMOS on the Hubble Space Telescope. The early-type galaxies in this sample include elliptical and S0 galaxies and spiral bulges in a variety of environments. Absolute(More)
A simple and high-sensitivity differential scanning calorimeter (DSC) unit operating under magnetic field has been built for indirect determination of the magnetocaloric effect. The principle of the measuring unit in the calorimeter is based on Peltier elements as heat flow sensors. The high sensitivity of the apparatus combined with a suitable calibration(More)
At the present time, several new Gemini instruments are being delivered and commissioned. The Near-Infrared Coronagraph has been extensively tested and commissioned on the Gemini-South telescope, and will soon begin a large survey to discover extrasolar planets. The FLAMINGOS-2 near-IR multi-object spectrograph is nearing completion at the University of(More)
To empirically calibrate the IR surface brightness fluctuation (SBF) distance scale and probe the properties of unresolved stellar populations, we measured fluctuations in 65 galaxies using NICMOS on the Hubble Space Telescope. The early-type galaxies in this sample include elliptical and S0 galaxies and spiral bulges in a variety of environments. Absolute(More)
We present IR surface brightness fluctuation (SBF) distance measurements to NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster. We explicitly corrected for the contributions to the fluctuations from globular clusters, background galaxies, and residual background variance. We measured a distance of 85± 10 Mpc to NGC 4889 and a(More)