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Hemenway, P. D.

Publications and source records attributed to Hemenway, P. D..

11 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Distributions and motions of nearby stars defined by objective prism surveys and Hipparcos data

Material and objective prism spectral classification work is used to determine the space density distribution of nearby common stars to the limits of objective prism spectral surveys. The aim is to extend the knowledge of the local densities of specific spectral types from a radius of 25 pc from the sun, as limited in the Gliese catalog of nearby stars, to 50 pc or more. Future plans for the application of these results to studies of the kinematic and dynamical properties of stars in the solar neighborhood as a function of their physical properties and ages are described.

Hemenway, P. D.↗
NASA NTRS1994

Astrometry with Hubble Space Telescope Fine Guidance Sensor number 3: Position-mode stability and precision

We report results from a test exploring the long- and short-term astrometric stability of Hubble Space Telescope Fine Guidance Sensor (FGS) #3. A test field was observed 40 times over 522 days to determine the precision and accuracy of FGS astrometry and to measure the character and magnitude of possible secular scale changes. We examine the astrometric data and the associated guide-star data to determine random errors. These data are also explored to find sources of systematic error. After correcting for some systematic effects we obtain a precision of 0.002 arcsec (2 mas) per observation (RSS of x and y). This is relative astrometry within a central 2.5 arcmin FGS field of view for any orientation. We find that the scale varies over time and confirm the sense of the trend with independent data. From the 40 observation sets we produce a catalog of an astrometry test field containing eight stars whose relative positions are known to an average 0.7 and 0.9 mas in x and y. One reference star has a relative parallax of 3.1 plus or minus 0.5 mas. Finally, we report that eleven observation sets acquired over 387 days produce parallaxes and relative positions with 1-mas precision.

Benedict, G. F.↗
NASA NTRS1993

Periodic low-amplitude variations in the brightness of Proxima Centauri

Using data acquired with Fine Guidance Sensor No. 3 on board the Hubble Space Telescope we find that the brightness of Proxima Centauri varies with an amplitude of 0.01 mag and a period P = 41.6 +/- 0.6 days. We interpret this variation as rotational modulation of star spots or bright regions in the photosphere of Proxima Cen. In a total of 89.36 min of monitoring over 212 days, we detected one major flare and three post-flare brightenings.

Benedict, G. F.↗
NASA NTRS1993

NGC 4314. II - Hubble Space Telescope I-band surface photometry of the nuclear region

We present an HST I-band Planetary Camera image of the nuclear region of NGC 4314, an anemic barred galaxy with recent star formation confined to a nuclear ring. These data resolve the nuclear ring into multiple sites of new star formation and resolve associated dust lanes into discrete clouds. Deconvolution results in at least 0.13 arcsec resolution, as demonstrated by the de Vaucouleurs r exp 1/4 law. Contrasted with similar studies of M87 and NGC 7457, we find no photometric evidence for an extreme concentration of stars in the center of NGC 4314. We identify an oval distortion of length 8 arcsec in the nuclear region, using ellipse-fitting routines and the unsharp masked frame. This nuclear bar has newer stars near its ends. We catalog 14 star clusters associated with H II regions in the nuclear ring. As an additional demonstration of the resolution achieved, the integral size distribution of these clusters is described by an exponential relationship which prevails down to 0.14 arcsec.

Benedict, G. F.↗
NASA NTRS1992

Astrometric performance characteristics of the Hubble Space Telescope fine guidance sensors

Each of the three fine guidance sensors for the Hubble Space Telescope constitutes a sixth science instrument to be used for astrometry. We detail the tests and results used in choosing one of the three sensors to be the prime astrometer. The Astrometry Science Team has chosen Fine Guidance Sensor (FGS) 3. FGS 3 produces position measurements on a star with V = 17 with a peraxis precision of 0.003 arcsec. The interferometer response function should permit double-star astrometry at least down to V = 16 for the central region of FGS 3. In a 10-h test of the stability of POS-mode astrometric measurements made in FGS 3, we found no scale or orientation variations greater than two parts in 100,000. During this same time period, we found no statistically significant systematic guide-star radial separation changes. Spacecraft jitter is found to be the prime determinant of astrometry success or failure.

Benedict, G. F.↗
NASA NTRS1991

Astrometry using the Hubble Space Telescope fine guidance sensors

Plans for the use of the three fine guidance sensors (FGSs) of the NASA Hubble Space Telescope for direct astrometric observations are reviewed. Topics addressed include the optical elements and detectors of the FGSs, the basic and astrometric operating modes of the FGSs, spacecraft pointing control during astrometric observations, and the astrometric data-reduction software provided to HST users. Particular attention is given to the calibration procedures for optical-field angle distortion, the plate scale, filter-wedge errors, lateral color effects, secular changes, velocity aberration, and transfer function. Also discussed are the steps being taken to verify the HST orbit. It is pointed out that the performance of the interferometric FGSs should not be affected by the focusing problems of the main HST instrument.

Duncombe, Raynor L.↗
NASA NTRS1988

Using the Hubble Space Telescope to relate the Hipparcos and extragalactic reference frames

The Hipparcos satellite will produce positions, motions, and parallaxes of celestial objects with previously unattained accuracy. This Hipparcos Instrumental System, however, will have an unknown solid body rotation with respect to an inertial reference frame. One aspect of the program of astrometric observations with the Hubble Space Telescope is to determine the rotation of the Hipparcos reference frame with respect to an extragalactic reference system.

Hemenway, P. D.↗
NASA NTRS1985

Prospects for astrometry with the Hubble Space Telescope

The Hubble Space Telescope (HST), a large optical telescope having an aperture of 2.4 meters and a length of 8.8 meters, is being developed by NASA. This telescope will be placed into earth orbit by the Space Shuttle. Astrometric observations with the HST are made using a Fine Guidance Sensor which is capable of measuring the position of one object relative to another with an accuracy of + or - 0.002 arcseconds. The astrometric user of HST will be provided with an Astrometric Data Reduction Software package. The variety of astrometric problems to be investigated with HST is discussed.

Jefferys, W. H.↗
NASA NTRS1985

Using Space Telescope to tie the HIPPARCOS and extragalactic reference frames together

Hubble Space Telescope observations will be made to tie the HIPPARCOS Instrumental System (HIS) to extragalactic objects, to determine the overall rotation of the HIS with respect to a set of extragalactic objects; to compare the HIS to an accurate radio reference frame; and to look for motions in the optical centroids of compact extragalactic objects at the level of 0.001 arcseconds per year. About 75 radio sources and extragalactic objects will be chosen from the initial group of 414 pairs. The egos will have their positions and proper motions determined relative to the HIPPARCOS Input Catalog stars. The candidate stars are being screened by ground based speckle interferometry to select a final set.

Hemenway, P. D.↗
NASA NTRS1982

Astrometric observations with the Space Telescope

Astrometry with the Space Telescope (ST) is performed using one of the fine guidance sensors (FGS). The FGS, which is based on a pair of Koester's prism interferometers, one for each axis, is capable of measuring the position of one object relative to another with an accuracy of 0.002 arcseconds. Astrometric Data Reduction Software (ADRS) available to the astrometric user of ST is described. The kinds of problems the space telescope astrometry team plans to investigate using ST are discussed.

Duncombe, R. L.↗