Engineering topics

Low, Frank J.

Publications and source records attributed to Low, Frank J..

12 records

NASA NTRS1994

A survey of the Large Magellanic Cloud in the (C II) 158 micron line

We have mapped the Large Magellanic Cloud (the LMC) in the (C II) 158 microns fine-structure line with the Balloon-borne Infrared Carbon Explorer (BICE) system. The (C II) line emission was detected over most of the LMC. The mean (C II)/CO (J = 1-0) line intensity ratio was 23,000 18 times larger than the typical value observed in the Galactic plane (1300). This result implies that each clump of the molecular clouds in the LMC has a larger C(+) envelope relative to its CO core than those in our Galaxy. Lower dust abundance due to its lower metallicity allows UV photons, which convert CO molecules into C(+) ions, to penetrate deeper into the clumps in the LMC than in our Galaxy.

Mochizuki, Kenji↗

NASA NTRS1994

IRAS F15307+3252: A hyperluminous infrared galaxy at z = 0.93

A new hyperluminous infrared galaxy in the Infrared Astronomy Satellite (IRAS) Faint Source Catalog is identified at a redshift of 0.93. This object has a bolometric luminosity of approximately 10(exp 13) solar luminosity, a very large ratio of infrared-to-optical luminosity, warm dust emission, a ratio of infrared-to-radio flux densities consistent with other infrared galaxies, and an optical spectrum similar to a Seyfert 2 galaxy. IRAS F15307+3552 shares these characteristics and its radio-to-optical spectral energy distribution with two other infrared galaxies, F10214+4724 and P09104+4109. Discovery of a third object with these properties defines an extreme subclass of ultraluminous galaxies powered primarily by star formation. The systematic method used to find this object begins the process of determining the space density of these most luminous examples of the infrared galaxy phenomenon.

Cutri, Roc M.↗

NASA NTRS1993

A joint program with Japanese investigators to map carbon 2 line emission from the galaxy

A large portion of the inner galactic plane has been mapped in the far-infrared (C II) line using a balloon-borne survey instrument. Complete coverage is reported from 25 degrees north to 80 degrees south of the galactic center and extending a few degrees on each side of the plane. Effective resolution is 14.1 acrmin (FWHM) and contour levels begin at 2 E -5 ergs/(s x sq. cm x ster). When compared with 100 micron dust emission observed by IRAS the (C II) appears well correlated with the dust emission except for a 10 degree region centered on the galactic center where emission from the gas is much weaker than that from the dust.

Low, Frank J.↗

NASA NTRS1993

Photometric calibration of NGS/POSS and ESO/SRC plates using the NOAO PDS measuring engine. II - Surface photometry

In this paper we present a method to calibrate surface photometry of faint sources measured from direct photographic plates, such as those of the NGS/POSS and ESO/SRC Sky Survey. This calibration procedure does not require scanning sensitometer spots on the plates, but instead uses measurements of the brightness profiles of many faint stars of known brightness to fit a linearized approximation to the characteristic curve. The approximation is valid for only low- to medium-density emulsions, so this technique is appropriate only for relatively faint emission. Comparison between measurements of representative extended sources on the NGS/POSS and CCD images indicates that surface photometry can be obtained from the Sky Survey plates accurate to 0.1-0.3 mag in the range mu(B) between 23 and 27 and mu(R) between 22 and 26 mag/sq arcsec.

Cutri, Roc M.↗

NASA NTRS1992

Photometric calibration of NGS/POSS and ESO/SRC plates using the NOAO PDS measuring engine. I - Stellar photometry

The PDS/Monet measuring engine at the National Optical Astronomy Observatory was used to obtain photometry of nearly 10,000 stars on the NGS/POSS and 2000 stars on the ESO/SRC Survey glass plates. These measurements have been used to show that global transformation functions exist that allow calibration of stellar photometry from any blue or red plate to equivalent Johnson B and Cousins R photoelectric magnitudes. The four transformation functions appropriate for the POSS O and E and ESO/SRC J and R plates were characterized, and it was found that, within the measurement uncertainties, they vary from plate to plate only by photometric zero-point offsets. A method is described to correct for the zero-point shifts and to obtain calibrated B and R photometry of stellar sources to an average accuracy of 0.3-0.4 mag within the range R between values of 8 and 19.5 for red plates in both surveys, B between values of 9 and 20.5 on POSS blue plates, and B between values of 10 and 20.5 on ESO/SRC blue plates. This calibration procedure makes it possible to obtain rapid photometry of very large numbers of stellar sources.

Cutri, Roc M.↗

NASA NTRS1992

Unfulfilled needs in IR astronomy focal-plane readout electronics

The NOAO's 8-m IR optimized telescope for Mauna Kea and NASA's SIRTF show that from 1 to 200 microns there are a number of unfulfilled needs in readout electronics. These include: extremely low readnoise, less than 10 electrons, stable operation at temperatures as low as 2 K, high well capacity, greater than 1 e 7 electrons, and integration times from 30 msec to over 100 sec. Sensors for adaptive optics systems are required with readnoise less than 10 electrons and response times of 30 msec. They should be highly efficient from 1 to 2.5 microns, but may have small formats. Ground-based imagers at these wavelengths need comparable readnoise but longer integration times, and the largest possible formats are essential. To achieve these goals improved cryogenic MOSFETS are essential and complete cryogenic CMOS circuits are highly desirable. Experimental cryoptimized MFETS promise to exceed the above noise requirements at 77 K and approach the needs at 2 K.

Low, Frank J.↗

NASA NTRS1991

An infrared/optical investigation of 100 micron 'cirrus'

IRAS Skyflux images, in conjunction with ESO/SRC photographic plates, are presently used to study a sample of 151 compact cyrrus sources. IR colors entail at least two dust components; a simple two-temperature dust model yields a mean physical temperature of 22.5 + or - 0.3 K for the warm dust, and 173 + or - 8 K for the hot dust, which constitutes 15-42 percent of total IR luminosity. A variable proportion of cold dust may contribute significantly to the optical brightness in two isolated cloud complexes.

Paley, Elizabeth S.↗

NASA NTRS1990

The detection of earth orbiting objects by IRAS

A systematic examination of 1836 images of the sky constructed from scans made by the Infrared Astronomical Satellite has resulted in the detection of 466 objects which are shown to be in earth orbit. Analysis of the spatial and size distribution and thermal properties of these objets, which may include payloads, rocket bodies and debris particles, is being conducted as one step in a feasibility study for space-based debris detection technologies.

Dow, Kimberly L.↗

NASA NTRS1989

Requirements of IR space astronomy

An introduction to a series of infrared detector technology workshops is given. The establishment of goals and new requirements is addressed in a general way. The Shuttle Infrared telescope Facility (SIRIF) goals are listed. Given that the wavelength coverage is established at 2 to 750 microns and the unvignetted field of view is 7 arcmin, the field should be fully utilized at each wavelength, diffraction should be critically sampled, and each detector should be background limited.

Low, Frank J.↗

NASA NTRS1989

Ga:Ge array development

Work at the University of Arizona and at Lawrence Berkeley Laboratory on the development of a far infrared array camera for the Multiband Imaging Photometer on the Space Infrared Telescope Facility (SIRTF) is discussed. The camera design uses stacked linear arrays of Ge:Ga photoconductors to make a full two-dimensional array. Initial results from a 1 x 16 array using a thermally isolated J-FET readout are presented. Dark currents below 300 electrons s(exp -1) and readout noises of 60 electrons were attained. Operation of these types of detectors in an ionizing radiation environment are discussed. Results of radiation testing using both low energy gamma rays and protons are given. Work on advanced C-MOS cascode readouts that promise lower temperature operation and higher levels of performance than the current J-FET based devices is described.

Young, Erick T.↗

NASA NTRS1989

A faint, dust-enshrouded carbon star at high galactic latitude

During the initial phase of a program to search for substellar candidates at high galactic in the IRAS Serendipitous Survey Catalog, one source, SSC 08546+1732, was found to have no optical couterpart on the Palomar Observatory Sky Survey plates. Ground-based positional, photometric, and spectroscopic observations have identified this source as a heavily dust-enshrouded carbon star, similar to those found in the Galactic plane. The high latitude and relative faintness of this source imply that it lies at a distance of 20-50 kpc, and is 10-30 kpc out of the plane of the Galaxy. SSC 08546+1732 and one other distant obscured carbon star found in the IRAS Point Source Catalog (Low 1987; Beichman et al. 1989) represent the first examples of such objects found in the Galactic halo. These stars may either have evolved from Population I precursors ejected from the disk, or they may be the first obscured Population II halo carbon stars to be observed. A survey for other distant enshrouded carbon stars in the IRAS Faint Source Cattalog should help to elucidate the nature of this new population.

Cutri, Roc M.↗

NASA NTRS1987

Spatial deconvolution of IRAS galaxies at 60 UM

Using IRAS in a slow scan observing mode to increase the spatial sampling rate and a deconvolution analysis to increase the spatial resolution, several bright galaxies were resolved at 60 micron. Preliminary results for M 82, NGC 1068, NGC 3079 and NGC 2623 show partially resolved emission from 10 to 26 arcsec., full width at half maximum, and extended emission from 30 to 90 arcsec. from the center. In addition, the interacting system, Arp 82, along with Mark 231 and Arp 220 were studied using the program ADDSCAN to average all available survey mode observations. The Arp 82 system is well resolved after deconvolution and its brighter component is extended; the two most luminous objects are not resolved with an upper limit of 15 arcsec. for Arp 220.

Low, Frank J.↗