John T. McGraw

The pattern speeds of m51, m83 and ngc 6946 using co and the tremaine-Weinberg method

In spiral galaxies in which the molecular phase dominates the ISM, the molecular gas as traced by CO emission will approximately obey the continuity equation on orbital timescales. The Tremaine-Weinberg method can then be used to determine the pattern speed of such galaxies. We have applied the method to single-dish CO maps of three nearby spirals, M51, M83, and NGC 6946, to obtain estimates of their pattern speeds: 38 ± 7, 45 ± 8, and 39 ± 8 km s-1 kpc-1, respectively, and we compare these results to previous measurements. We also analyze the major sources of systematic errors in applying the Tremaine-Weinberg method to maps of CO emission.

The luminosity function at the end of the main sequence: Results of a deep, large-area, CCD survey for cool dwarfs

The luminosity function at the end of the main sequence is determined from V, R, and I data taken by the charge coupled devices (CCD)/Transit Instrument, a dedicated telescope surveying an 8.25 min wide strip of sky centered at delta = +28 deg, thus sampling Galactic latitudes of +90 deg down to -35 deg. A selection of 133 objects chosen via R - I and V - I colors has been observed spectroscopically at the 4.5 m Multiple Mirror Telescope to assess contributions by giants and subdwarfs and to verify that the reddest targets are objects of extremely late spectral class. Eighteen dwarfs of type M6 or later have been discovered, with the latest being of type M8.5. Data used for the determination of the luminosity function cover 27.3 sq. deg down to a completeness limit of R = 19.0. This luminosity function, computed at V, I, and bolometric magnitudes, shows an increase at the lowest luminosities, corresponding to spectral types later than M6- an effect suggested in earlier work by Reid & Gilmore and Legget & Hawkins. When the luminosity function is segregated into north Galactic and south Galactic portions, it is found that the upturn at faint magnitudes exists only in the southern sample. In fact, no dwarfs with M(sub I) is greater than or equal to 12.0 are found within the limiting volume of the 19.4 sq deg northern sample, in stark contrast to the smaller 7.9 sq deg area at southerly latitudes where seven such dwarfs are found. This fact, combined with the fact that the Sun is located approximately 10-40 pc north of the midplane, suggests that the latest dwarfs are part of a young population with a scale height much smaller than the 350 pc value generally adopted for other M dwarfs. These objects comprise a young population either because the lower metallicities prevelant at earlier epochs inhibited the formation of late M dwarfs or because the older counterparts of this population have cooled beyond current detection limits. The latter scenario would hold if these late-type M dwarfs are substellar. The luminosity function data together with an empirical derivation of the mass-luminosity relation (from Henry & McCarthy) are used to compute a mass function independent of theory. This mass function increases toward the end of the main sequence, but the observed density of M dwarfs is still insufficient to account for the missing mass. If the increases seen in the luminosity and mass functions are indicative of a large, unseen, substellar population, brown dwarfs may yet add significantly to the mass of the Galaxy.

High-speed photometric observations of the pulsating DA white dwarf GD 165

New high-speed photometric observations of the pulsating DA white dwarf GD 165 are presented. The Fourier spectrum of the light curve of GD 165 exhibits two main regions of power at 120 and 193 s. The presence of a high-amplitude long period mode near ∼1800 s reported by Bergeron and McGraw is not confirmed by these new observations. Light curves obtained with the Canada-France-Hawaii Telescope reveal previously undetected low-amplitude harmonic oscillations. Observations with the Whole Earth Telescope are used to resolve the two principal regions of power. The 120 and 193 s peaks are shown to be multiplets composed of at least three, and possibly five frequency components. The most likely explanation is that these two peaks correspond to nonradial gravity modes with different values of the radial order k and with l=1 or 2 split into 2l+1 components by slow rotation

A Search for Binary Hot Subdwarfs. II. Infrared Photometry of Palomar‐Green Survey sdO Stars

Eight sdO binary candidates have been identified through IR photometry of 25 type O hot subdwarfs. Five of the eight binary candidates are identified for the first time. These new binary candidates complement a list of nine optically identified sdO binary candidates discovered in an earlier portion of this project. The new candidates are identified on the basis of IR color excesses in two-color plots of extinction-corrected data. We estimate that at least 64% of the Palomar-Green Survey sdOC hot subdwarfs are binary.

Are curved focal planes necessary for wide-field survey telescopes?

The last decade has seen significant interest in wide field of view (FOV) telescopes for sky survey and space surveillance applications. Prompted by this interest, a multitude of wide-field designs have emerged. While all designs result from optimization of competing constraints, one of the more controversial design choices is whether such telescopes require flat or curved focal planes. For imaging applications, curved focal planes are not an obvious choice. Thirty years ago with mostly analytic design tools, the solution to wide-field image quality appeared to be curved focal planes. Today however, with computer aided optimization, high image quality can be achieved over flat focal surfaces. For most designs, the small gains in performance offered by curved focal planes are more than offset by the complexities and cost of curved CCDs. Modern design techniques incorporating reflective and refractive correctors appear to make a curved focal surface an unnecessary complication. Examination of seven current, wide FOV projects (SDSS, MMT, DCT, LSST, PanStarrs, HyperSuprime and DARPA SST) suggests there is little to be gained from a curved focal plane. The one exception might be the HyperSuprime instrument where performance goals are severely stressing refractive prime-focus corrector capabilities.

RR Lyrae Variable Stars In The CCD/Transit Instrument Survey.

Abstract : RR Lyrae variable stars have long been recognized as important tools in probing the mass, chemical distribution and kinematics of the Galaxy from the inner recesses of the nuclear bulge to the outer environs of the distant Galactic halo. This dissertation chronicles an RR Lyrae variable star survey from a thorough description of the initial observations with the CCD/Transit Instrument (CTI), to an examination of RR Lyrae space density and the Galactic mass using the discovered RR Lyrae stars. The RR Lyrae space density as a function f Galactocentric distance is shown to be a power-law function (R-3 to -3.5) and consistent with an ellipsoidal distribution in the nuclear bulge and more spherically symmetric distribution in the Galactic halo. The unique area of the CTI survey and comparison to other RR Lyrae surveys verifies this function is valid throughout the Galactic halo and over the range of Galactocentric distances sampled (0.6 < R < 40 kpc). Local underdensities and overdensities of RR Lyrae stars are discussed, including a possible resonance with the Magallenic Clouds (R 50 kpc).

Near-field calibration of an objective spectrophotometer to NISTradiometric standards for the creation and maintenance of standardstars for ground- and space-based applications

NIST-calibrated detectors will be used by the ground-based 100mm diameter Astronomical Extinction Spectrophotometer (AESoP) to calibrate the spectral energy distributions of bright stars to sub-1% per 1nm spectral resolution element accuracy. AESoP will produce about a hundred spectroradiometrically calibrated stars for use by ground- and space-based sensors. This will require accurate and near-continuous NIST calibration of AESoP, an equatorially mounted objective spectrophotometer operating over the wavelength range 350nm – 1050nm using a CCD detector. To provide continuous NIST calibration of AESoP in the field a near-identical, removable 100mm diameter transfer standard telescope (CAL) is mounted physically parallel to AESoP. The CAL transfer standard is calibrated by NIST end-to-end, wavelength-by-wavelength at ~ 1nm spectral resolution. In the field, CAL is used in a near-field configuration to calibrate AESoP. Between AESoP science observations, AESoP and CAL simultaneously observe clear sub-apertures of a 400mm diameter calibration collimator. Monochromatic light measured simultaneously by AESoP and CAL is dispersed by the objective grating onto the AESoP pixels measuring the same wavelength of starlight, thus calibrating both wavelength and instrumental throughput, and simultaneously onto a unique low-noise CAL detector providing the required throughput measurement. System sensitivity variations are measured by vertically translating the AESoP/CAL pair so that CAL can observe the AESoP sub-aperture. Details of this system fundamental to the calibration of the spectral energy distributions of stars are discussed and its operation is described. System performance will be demonstrated, and a plan of action to extend these techniques firstly into the near infrared, then to fainter stars will be described.

Space-based photometric precision from ground-based telescopes

Ground-based telescopes supported by lidar and spectrophotometric auxiliary instrumentation can attain space-based precision for all-sky photometry, with uncertainties dominated by fundamental photon counting statistics. Earths atmosphere is a wavelength-, directionally- and time-dependent turbid refractive element for every ground-based telescope, and is the primary factor limiting photometric measurement precision. To correct accurately for the transmission of the atmosphere requires direct measurements of the wavelength-dependent transmission in the direction and at the time that the supported photometric telescope is acquiring its data. While considerable resources have been devoted to correcting the effects of the atmosphere on angular resolution, the effects on precision photometry have largely been ignored. We describe the facility-class lidar that observes the stable stratosphere, and a spectrophotometer that observes NIST absolutely calibrated standard stars, the combination of which enables fundamentally statistically limited photometric precision. This inexpensive and replicable instrument suite provides the lidar-determined monochromatic absolute transmission of Earths atmosphere at visible and near-infrared wavelengths to 0.25% per airmass and the wavelengthdependent transparency to less than 1% uncertainty per minute. The atmospheric data are merged to create a metadata stream that allows throughput corrections from data acquired at the time of the scientific observations to be applied to broadband and spectrophotometric scientific data. This new technique replaces the classical use of nightly mean atmospheric extinction coefficients, which invoke a stationary and plane-parallel atmosphere. We demonstrate application of this instrument suite to stellar photometry, and discuss the enhanced value of routinely provably precise photometry obtained with existing and future ground-based telescopes.

Comparison of Adaptive Resonance Theory Neural Networks for Astronomical Region of Interest Detection and Noise Characterization

While learning algorithms have been used for astronomical data analysis, the vast majority of those algorithms have used supervised learning. In a continuation of the work described in Young et ah [18] we examine the use of unsupervised learning for this task with two types of Adaptive Resonance Theory (ART) neural networks. Using synthetic astronomical data from SkyMaker[2], [3] which was designed to mimic the dynamic range of the CTI-[14] telescope, we compared the ability of the ART-1 neural network[4] and the ART-1 neural network with category theoretic modiflcation[9], [11] to detect regions of interest and to characterize noise. We show a difference in the geometries of the templates created by each architecture. We also show an analysis of the two architectures over a range of parameter settings. The results provided show that ART neural networks and unsupervised learning algorithms in general should not be overlooked for astronomical data analysis.

Structural Design of a Unique Passive Telescope

Most telescopes designed today assume that, as the telescope is pointed at different locations on the celestial sphere, there will be some interactive human or computationally-activated mechanical adjustment for defocus or misalignment during routine use. As part of a collaboration between the University of New Mexico and the University of Texas at Austin, design of the second iteration of the CCD/Transit Instrument (CTI-II) is underway. With a one degree square scientific focal plane mosaic of charged coupled devices (CCDs) operated in the time-delay and integrate readout mode, the stationary, 1.8-m telescope will accomplish a multi-bandpass photometric and astrometric imaging survey of more than 300 square degrees of the sky. The structural design goal for CTI-II is to make the telescope as passive as possible, so that little or no physical human or computationally-activated mechanical adjustment is required during routine use. Because the telescope will never be repositioned during normal operations, structural deformations due to the earth’s gravity will not vary during operation. We are designing the telescope so that its optical behavior will be as nearly as possible thermally invariant, and we are also attempting to minimize vibrations due to wind and ambient seismicity. The structural design philosophy, methodology, and provisions for thermally and optically tuning the telescope (hopefully an infrequent operation) are discussed.