On the Origin of Near-Infrared Extragalactic Background Light Anisotropy

Extragalactic background light (EBL) anisotropy traces variations in the total production of photons over cosmic history, and may contain faint, extended components missed in galaxy point source surveys. Infrared EBL fluctuations have been attributed to primordial galaxies and black holes at the epoch of reionization (EOR), or alternately, intra-halo light (IHL) from stars tidally stripped from their parent galaxies at low redshift. We report new EBL anisotropy measurements from a specialized sounding rocket experiment at 1.1 and 1.6 micrometers. The observed fluctuations exceed the amplitude from known galaxy populations, are inconsistent with EOR galaxies and black holes, and are largely explained by IHL emission. The measured fluctuations are associated with an EBL intensity that is comparable to the background from known galaxies measured through number counts, and therefore a substantial contribution to the energy contained in photons in the cosmos.Comment: 65 pages, 29 figures, Published in Science Nov 7 2014 (includes supplementary material

Two Transistor Current Mode Active Pixel Sensor

A novel current mode active pixel sensor for high resolution imaging is presented. The photo pixel is composed of a photodiode and two transistors: reset and transconductance amplifier transistor. The switch transistor is moved outside the pixel, allowing for lower pixel pitch and increased linearity of the output photocurrent. The increased linearity of the image sensor has greatly reduced spatial variations across the image after correlated double sampling and the column fix pattern noise is 0.35% of the saturated current. A discussion on theoretical temporal noise limitations of this design is also presented

Low Fixed Pattern Noise Current-mode Imager Using Velocity Saturated Readout Transistors

This paper described a novel current-mode active pixel sensor (APS) imager. Conversion of photodiode voltage to output current is done using transistors operating in velocity saturation region. The high output impedance of this region makes it more suitable for current-sourcing operation than the linear region. The transistors also exhibit high linearity, allowing us to suppress fixed pattern noise (FPN) by correcting for both offset and gain variations among pixels. Experimental results on the fabricated 110×200 pixel array are presented. With conventional correlated double sampling (CDS), FPN is reduced from 3.8% to 0.85%. Further reduction requires compensation of gain variations, and results in a final FPN of 0.19%. A triple sampling approach is introduced to implement the described correction in hardware

Gemini multi-conjugate adaptive optics system review II: Commissioning, operation and overall performance

The Gemini Multi-conjugate Adaptive Optics System - GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near diffraction limited images at near infrared wavelengths (0.95 microns- 2.5 microns) over a field of view of 120 arc seconds. GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 arc seconds square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.Comment: 20 pages, 11 figures, accepted for publication in MNRA

Linear Current-Mode Active Pixel Sensor

A current mode CMOS active pixel sensor (APS) providing linear light-to-current conversion with inherently low fixed pattern noise (FPN) is presented. The pixel features adjustable-gain current output using a pMOS readout transistor in the linear region of operation. This paper discusses the pixel’s design and operation, and presents an analysis of the pixel’s temporal noise and FPN. Results for zero and first-order pixel mismatch are presented. The pixel was implemented in a both a 3.3 V 0.35 µm and a 1.8 V 0.18 µm CMOS process. The 0.35 µm process pixel had an uncorrected FPN of 1.4%/0.7% with/without column readout mismatch. The 0.18 µm process pixel had 0.4% FPN after delta-reset sampling (DRS). The pixel size in both processes was 10 X 10 µm2, with fill factors of 26% and 66%, respectively

A CMOS Linear Voltage/Current Dual-Mode Imager

We present a CMOS image sensor capable of both voltage- and current-mode operations. Each pixel on the image has a single transistor acting as either source follower for voltage readout, or transconductor for current readout. The two modes share the same readout lines, but have their own correlated double sampling (CDS) units for noise suppression. We also propose a novel current-mode readout technique using a velocity saturated short-channel transistor, which achieves high linearity. The 300x200 image array is a mixture of 3 types of pixels with identical photodiodes and access switches; while the readout transistors are sized for their designated mode of operation. This ensures a fair comparison on the performance of the different modes

Design and construction of a Cherenkov imager for charge measurement of nuclear cosmic rays

A proximity focusing Cherenkov imager called CHERCAM, has been built for the charge measurement of nuclear cosmic rays with the CREAM instrument. It consists of a silica aerogel radiator plane across from a detector plane equipped with 1,600 1" diameter photomultipliers. The two planes are separated by a ring expansion gap. The Cherenkov light yield is proportional to the charge squared of the incident particle. The expected relative light collection accuracy is in the few percents range. It leads to an expected single element separation over the range of nuclear charge Z of main interest 1 < Z < 26. CHERCAM is designed to fly with the CREAM balloon experiment. The design of the instrument and the implemented technical solutions allowing its safe operation in high altitude conditions (radiations, low pressure, cold) are presented.Comment: 24 pages, 19 figure

Implications of the Cosmic Background Imager Polarization Data

We present new measurements of the power spectra of the E-mode of CMB polarization, the temperature T, the cross-correlation of E and T, and upper limits on the B-mode from 2.5 years of dedicated Cosmic Background Imager (CBI) observations. Both raw maps and optimal signal images in the uv-plane and real space show strong detections of the E-mode (11.7 sigma for the EE power spectrum overall) and no detection of the B-mode. The power spectra are used to constrain parameters of the flat tilted adiabatic Lambda-CDM models: those determined from EE and TE bandpowers agree with those from TT, a powerful consistency check. There is little tolerance for shifting polarization peaks from the TT-forecast locations, as measured by the angular sound crossing scale theta = 100 ell_s = 1.03 +/- 0.02 from EE and TE cf. 1.044 +/- 0.005 with the TT data included. The scope for extra out-of-phase peaks from subdominant isocurvature modes is also curtailed. The EE and TE measurements of CBI, DASI and BOOMERANG are mutually consistent, and, taken together rather than singly, give enhanced leverage for these tests.Comment: 15 pages, 9 figures, submitted to ApJ -- Accepted version. The fine-bin spectrum, covariance matrix, and window functions are now available on the web (suitable for use in COSMOMC) at: http://www.astro.caltech.edu/~tjp/CBI/data2006/index.html The pipeline in the previous version inadvertently omitted one antenna, so the new spectrum contains ~15% more data. We emphasize that previous results were in no way biased, and that the (small) changes to the spectrum solely reflect the inclusion of the additional data. Numbers and figures in the paper have been updated correspondingly. All maps now have color bar

A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C

The characterization of a physically-diverse set of transiting exoplanets is an important and necessary step towards establishing the physical properties linked to the production of obscuring clouds or hazes. It is those planets with identifiable spectroscopic features that can most effectively enhance our understanding of atmospheric chemistry and metallicity. The newly-commissioned LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed fringing in the red optical, thus advancing the search for the spectroscopic signature of water in exoplanetary atmospheres from the ground. Using data acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b. Our measured spectrum is best explained by the presence of water vapor, a lack of potassium, and either a high-metallicity, cloud-free atmosphere or a solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of multi-scale-height spectral features in our data suggests that future observations at higher precision could break this degeneracy and reveal the planet's atmospheric chemical abundances. We also update HAT-P-26b's transit ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p = 4.2345023(7) days.Comment: 9 pages, 8 figures, Accepted for publication in Ap