226 research outputs found
PANIC: A Near-infrared Camera for the Magellan Telescopes
PANIC (Persson's Auxiliary Nasmyth Infrared Camera) is a near-infrared camera
designed to operate at any one of the f/11 folded ports of the 6.5m Magellan
telescopes at Las Campanas Observatory, Chile. The instrument is built around a
simple, all-refractive design that reimages the Magellan focal plane to a plate
scale of 0.125'' pixel^{-1} onto a Rockwell 1024x1024 HgCdTe detector. The
design goals for PANIC included excellent image quality to sample the superb
seeing measured with the Magellan telescopes, high throughput, a relatively
short construction time, and low cost. PANIC has now been in regular operation
for over one year and has proved to be highly reliable and produce excellent
images. The best recorded image quality has been ~0.2'' FWHM.Comment: 8 pages, 5 figures. To appear in "Astronomical Telescopes and
Instrumentation," Proc SPIE (Glasgow), June 2004. Version with higher
resolution figures is available at
http://cfa-www.harvard.edu/~pmartini/professional/publications/panic.pd
Background-Limited Imaging in the Near-Infrared with Warm InGaAs Sensors: Applications for Time-Domain Astronomy
We describe test observations made with a customized 640 x 512 pixel Indium
Gallium Arsenide (InGaAs) prototype astronomical camera on the 100" DuPont
telescope. This is the first test of InGaAs as a cost-effective alternative to
HgCdTe for research-grade astronomical observations. The camera exhibits an
instrument background of 113 e-/sec/pixel (dark + thermal) at an operating
temperature of -40C for the sensor, maintained by a simple thermo-electric
cooler. The optical train and mechanical structure float at ambient temperature
with no cold stop, in contrast to most IR instruments which must be cooled to
mitigate thermal backgrounds. Measurements of the night sky using a reimager
with plate scale of 0.4 arc seconds / pixel show that the sky flux in Y is
comparable to the dark current. At J the sky brightness exceeds dark current by
a factor of four, and hence dominates the noise budget. The sensor read noise
of ~43e- falls below sky+dark noise for exposures of t>7 seconds in Y and 3.5
seconds in J. We present test observations of several selected science targets,
including high-significance detections of a lensed Type Ia supernova, a type
IIb supernova, and a z=6.3 quasar. Deeper images are obtained for two local
galaxies monitored for IR transients, and a galaxy cluster at z=0.87. Finally,
we observe a partial transit of the hot JupiterHATS34b, demonstrating the
photometric stability required over several hours to detect a 1.2% transit
depth at high significance. A tiling of available larger-format sensors would
produce an IR survey instrument with significant cost savings relative to
HgCdTe-based cameras, if one is willing to forego the K band. Such a camera
would be sensitive for a week or more to isotropic emission from r-process
kilonova ejecta similar to that observed in GW170817, over the full 190 Mpc
horizon of Advanced LIGO's design sensitivity for neutron star mergers.Comment: 13 pages, 12 figures, submitted to A
Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data
The Southern Abell Redshift Survey contains 39 clusters of galaxies with
redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z =
0.0845. SARS covers the region 0 21h (while
avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the
Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected
from the Automatic Plate Measuring Facility galaxy catalog with
extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the
Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects
concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are
reported in the fields of these 39 clusters of galaxies.Comment: 20 pages, 5 figures, accepted for publication in the Astronomical
Journal, Table 2 can be downloaded in its entirety from
http://trotsky.arc.nasa.gov/~mway/SARS1/sars1-table2.cs
Chain Galaxies are Edge-On Low Surface Brightness Galaxies
Deep HST WFPC2 images have revealed a population of very narrow blue galaxies
which Cowie et al. (1996) have interpreted as being a new morphological class
of intrinsically linear star forming galaxies at . We show that the
same population exists in large numbers at low redshifts (z=0.03) and are
actually the edge-on manifestation of low surface brightness disk galaxies.Comment: 18 pages + 3 pages of figures. Uuencoded, gzipped, tar file of 1
latex file, 5 figures, and 2 latex style files. To appear in the
Astrophysical Journal Letter
Demonstrating Diversity in Star Formation Histories with the CSI Survey
We present coarse but robust star formation histories (SFHs) derived from
spectro-photometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494
galaxies at 0.3<z<0.9 with stellar masses of 10^9 Msun to 10^12 Msun. Our study
moves beyond "average" SFHs and distribution functions of specific star
formation rates (sSFRs) to individually measured SFHs for tens of thousands of
galaxies. By comparing star formation rates (SFRs) with timescales of 10^10,
10^9, and 10^8 years, we find a wide diversity of SFHs: 'old galaxies' that
formed most or all of their stars early; galaxies that formed stars with
declining or constant SFRs over a Hubble time, and genuinely 'young galaxies'
that formed most of their stars since z=1. This sequence is one of decreasing
stellar mass, but, remarkably, each type is found over a mass range of a factor
of 10. Conversely, galaxies at any given mass follow a wide range of SFHs,
leading us to conclude that: (1) halo mass does not uniquely determine SFHs;
(2) there is no 'typical' evolutionary track; and (3) "abundance matching" has
limitations as a tool for inferring physics. Our observations imply that SFHs
are set at an early epoch, and that--for most galaxies--the decline and
cessation of star formation occurs over a Hubble-time, without distinct
"quenching" events. SFH diversity is inconsistent with models where galaxy
mass, at any given epoch, grows simply along relations between SFR and stellar
mass, but is consistent with a 2-parameter lognormal form, lending credence to
this model from a new and independent perspective.Comment: 17 pages, 10 figures; accepted by ApJ; version 2 - no substantive
changes; clarifications and correction
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