Engineering topics

Bond, Howard E.

Publications and source records attributed to Bond, Howard E..

15 records

DOE OSTI2023

Spectroscopic survey of faint planetary-nebula nuclei – II. The subdwarf O central star of Fr 2-30

Fr 2-30 = PN? G126.8−15.5 is a faint emission nebula, hosting a 14th-mag central star that we identify here for the first time. Deep Hα and [O III ] images reveal a roughly elliptical nebula with dimensions of at least 22 arcmin × 14 arcmin, fading into a surrounding network of even fainter emission. Optical spectrograms of the central star show it to have a subdwarf O spectral type, with a Gaia parallax distance of 890 pc. A model-atmosphere analysis gives parameters of T eff = 60 000 K, log g = 6.0, and a low helium content of n He /n H = 0.0017. The location of the central star in the log g–T eff plane is inconsistent with a post-asymptotic-giant-branch evolutionary status. Two alternatives are that it is a helium-burning post-extreme-horizontal-branch object, or a hydrogen-burning post-red-giant-branch star. In either case, the evolutionary ages are so long that a detectable planetary nebula (PN) should not be present. We find evidence for a variable radial velocity (RV), suggesting that the star is a close binary. However, there are no photometric variations, and the spectral-energy distribution rules out a companion earlier than M2 V. The RVs of the star and surrounding nebula are discordant, and the nebula lacks typical PN morphology. We suggest that Fr 2-30 is a ‘PN mimic’ – the result of a chance encounter between the hot sdO star and an interstellar cloud. However, we note the puzzling fact that there are several nuclei of genuine PNe that are known to be in evolutionary states similar to that of the Fr 2-30 central star.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

The Stars of the HETDEX Survey. I. Radial Velocities and Metal-poor Stars from Low-resolution Stellar Spectra

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution ( R ~ 750) spectra of Ly α emitters. In its search for these galaxies, HETDEX will also observe a few times 10 5 stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between 10 < G < 22 spread across the HETDEX footprint at relatively high ( b ~ 60°) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for ~42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1 σ precision of 28.0 km s -1 and bias of 3.5 km s -1 with respect to the Large Sky Area Multi-Object Fibre Spectroscopic Telescope surveys and 1 σ precision of 27.5 km s -1 and bias of 14.0 km s -1 compared to the Sloan Extension for Galactic Understanding and Exploration survey. Since these RVs are for faint ( G ≥ 16) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (tSNE), we also demonstrate that the HETDEX spectra can be used to determine a star’s T eff , and log g and its [Fe/H]. With the tSNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] < -1 dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys.

Astronomy & Astrophysics↗

DOE OSTI2021

Two Luminous Post-AGB Stars in the Galactic Globular Cluster M19

We report the discovery of a luminous “yellow” post–asymptotic giant branch (PAGB) star in the globular cluster (GC) M19 (NGC 6273), identified during our uBVI survey of Galactic GCs. The uBVI photometric system is optimized to detect stars with large Balmer discontinuities, indicating very low surface gravities and high luminosities. The spectral energy distribution (SED) of the star is consistent with an effective temperature of about 6250 K and a surface gravity of logg=0.5. We use Gaia data to show that the star’s proper motion and radial velocity are consistent with cluster membership. One aim of our program is to test yellow PAGB stars as candidate Population II standard candles for determining extragalactic distances. We derive a visual absolute magnitude of M {sub V} = − 3.39 ± 0.09 for the M19 star. This is in close agreement with the M {sub V} values found for yellow PAGB stars in the GCs ω Cen, NGC 5986, and M79, indicating a very narrow luminosity function. These objects are 4 mag brighter than RR Lyrae variables, and they can largely avoid the issues of interstellar extinction that are a problem for Population I distance indicators. We also identified a second luminous PAGB object in M19, this one a hotter “UV-bright” star. Its SED is consistent with an effective temperature of about 11,750 K and logg=2.0. The two objects have nearly identical bolometric luminosities, logL/L{sub ⊙}=3.24 and 3.22, respectively.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2020

BD+14°3061: A Luminous Yellow Post-AGB Star in the Galactic Halo

I report the discovery that the ninth-mag Galactic-halo star BD+14°3061 is a member of the rare class of luminous metal-poor “yellow post-AGB” stars. Its Gaia DR2 parallax implies an absolute magnitude of M V = -3.44 ± 0.27, and it is a very high-velocity star moving in a retrograde Galactic orbit. BD+14°3061 is a field analog of the half-dozen yellow PAGB stars known in Galactic globular clusters, which have closely similar absolute magnitudes. These objects are the visually brightest members of old stellar populations; their apparently narrow luminosity function makes them potentially useful as Population II standard candles. The spectral-energy distribution of BD+14°3061 out to 22 μm shows no evidence for circumstellar dust. The star is a low-amplitude semiregular pulsating variable, with typical periods of 30–32 days. A radial-velocity study suggests that it is a spectroscopic binary with a period of 429.6 days, making it similar to known binary yellow PAGB stars such as HD 46703 and BD+39°4926.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2015

Hubble Space Telescope Astrometry of the Procyon System

The nearby star Procyon is a visual binary containing the F5 IV-V subgiant Procyon A, orbited in a 40.84-year period by the faint DQZ white dwarf (WD) Procyon B. Using images obtained over two decades with the Hubble Space Telescope, and historical measurements back to the 19th century, we have determined precise orbital elements. Combined with measurements of the parallax and the motion of the A component, these elements yield dynamical masses of 1.478 plus or minus 0.012M and 0.592 plus or minus 0.006M for A and B, respectively. The mass of Procyon A agrees well with theoretical predictions based on asteroseismology and its temperature and luminosity. Use of a standard core-overshoot model agrees best for a surprisingly high amount of core overshoot. Under these modeling assumptions, Procyon A's age is approximately 2.7 Gyr. Procyon B's location in the H-R diagram is in excellent agreement with theoretical cooling tracks for WDs of its dynamical mass. Its position in the mass-radius plane is also consistent with theory, assuming a carbon-oxygen core and a helium-dominated atmosphere. Its progenitor's mass was 1.9-2.2M, depending on its amount of core overshoot. Several astrophysical puzzles remain. In the progenitor system, the stars at periastron were separated by only approximately AU, which might have led to tidal interactions and even mass transfer; yet there is no direct evidence that these have occurred. Moreover the orbital eccentricity has remained high (approximately 0.40). The mass of Procyon B is somewhat lower than anticipated from the initial-to-final-mass relation seen in open clusters. The presence of heavy elements in its atmosphere requires ongoing accretion, but the place of origin is uncertain.

PROCYON↗

NASA NTRS2012

The Resolved Stellar Population in 50 Regions of M83 from HST/WFC3 Early Release Science Observations

We present a multi-wavelength photometric study of approximately 15,000 resolved stars in the nearby spiral galaxy M83 (NGC 5236, D = 4.61 Mpc) based on Hubble Space Telescope Wide Field Camera 3 observations using four filters: F336W, F438W, F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in the spiral arm and inter-arm areas of M83 and determine the age distribution of the luminous stellar populations in each region. This is accomplished by correcting for extinction toward each individual star by comparing its colors with predictions from stellar isochrones.We compare the resulting luminosity-weighted mean ages of the luminous stars in the 50 regions with those determined from several independent methods, including the number ratio of red-to-blue supergiants, morphological appearance of the regions, surface brightness fluctuations, and the ages of clusters in the regions. We find reasonably good agreement between these methods. We also find that young stars are much more likely to be found in concentrated aggregates along spiral arms, while older stars are more dispersed. These results are consistent with the scenario that star formation is associated with the spiral arms, and stars form primarily in star clusters and then disperse on short timescales to form the field population. The locations ofWolf-Rayet stars are found to correlate with the positions of many of the youngest regions, providing additional support for our ability to accurately estimate ages. We address the effects of spatial resolution on the measured colors, magnitudes, and age estimates. While individual stars can occasionally show measurable differences in the colors and magnitudes, the age estimates for entire regions are only slightly affected.

Hubble Space Telescope↗

NASA NTRS2003

Post-AGB Stars in Nearby Galaxies as Calibrators for HST

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program under Grant NAG 5-6821. The Principal Investigator is Howard E. Bond (Space Telescope Science Institute). STScI Postdoctoral Associates Laura K. Fullton (1998), David Alves (1998-2001), and Michael Siegel (2001) were partially supported by this grant. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic- giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The argument is that, in old populations, the stars that are evolving through the PAGB region of the HR diagram arise from only a single main-sequence turnoff mass. In addition, theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, PAGB stars of these spectral types are very easily identified. because of their large Balmer jumps, which are due to their very low surface gravities. Our approach is first to identify PAGB stars in Milky Way globular clusters and in other Local Group galaxies, which are at known distances, and thus to measure accurate absolute magnitudes for the PAGB stars. With this Milky Way and Local Group luminosity calibration, we will then be in a position to find PAGB stars in more distant galaxies from the ground, and ultimately from the Hubble Space Telescope. and thus derive distances. These PAGB stars are, as noted above, the visually brightest members of Population II, and hence will allow distance measurements to galaxies that do not contain Cepheids, such as elliptical galaxies, as well as distances to spirals using PAGB stars in their halos. Moreover, the method is entirely independent of Cepheids. and thus provides a direct test of the Cepheid distance scale. The program will also provide information on the evolutionary lifetimes of PAGB stars.

Bond, Howard E.↗

NASA NTRS1998

Calibration of Post-AGB Supergiants as Standard Extragalactic Candles for HST

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic-giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The reason for this belief is that in old populations, the stars that are evolving through the PAGB region of the HR (Hertzsprung-Russell) diagram arise from only a single main-sequence turnoff mass. In addition, the theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, the PAGB stars of these spectral types are very easily identified, due to their large Balmer jumps, which are due to their very low surface gravities.

Bond, Howard E.↗

NASA NTRS1995

Phase-Dependent Observations of Intermediate Polars and The Broad Emission and Absorption Line Region in NGC 3516

The Intermediate Polars (IP's) constitute a class of Cataclysmic Variables (CV's), which are binary star systems in which mass is transferred from a late-type main-sequence star to a white dwarf via Roche lobe overflow. In the IP's, the inner accretion disk is evidently disrupted by the magnetic field of the white dwarf. High-temperature shocks at the white dwarf's magnetic poles (where accretion occurs) produce X-rays, which are reprocessed into photons over a broad energy band across the electromagnetic spectrum. Because the white dwarf typically spins rapidly (rotation periods a few 10s to a few 100s of seconds), the signals due to both the X-rays and reprocessed photons are pulsed. The shape of the spectrum of pulse amplitude as a function of wavelength yields information about both the temperature and size of the pulse-emitting region. It has been noted by several investigators that the optical pulsation amplitudes rise steeply toward short wavelengths. It is therefore a fair surmise that pulsation amplitudes peak in the ultraviolet. The scientific goal of this project was to observe a representative sample of IP's, using IUE, in search of the expected strong UV pulsations, and hence to further our understanding of pulse-producing mechanisms.

Koratkar, Anuradha↗

NASA NTRS1994

Hubble Space Telescope cycle 5 call for proposals

This document invites and supports participation by the international astronomical community in the HST General Observer and Archival Research programs. These documents contain the basic procedural and technical information required for HST proposal preparation and submission, including applicable deadlines. The telescope and its instruments were built under the auspices of the NASA and the European Space Agency.

Bond, Howard E.↗

NASA NTRS1994

High-Speed Hubble Space Telescope Ultraviolet photometry of two DB white dwarfs: Nonradial and radial pulsations

We observed two DB white dwarf stars with the High Speed Photometer aboard the Hubble Space Telescope. The two targets, the nonradial pulsator GD 358, and PG 0112+104, a non-pulsating white dwarf with similar temperature, were each observed for 1800 s with a time resolution of 10 ms. We used the F140LP configuration, which gives a broadband response in the UV between 1400 and 3000 A. The data clearly show the long period (about 700 s) pulsations in GD 358. Comparison with optical observations obtained two weeks earlier shows that the amplitude of the pulsations in the UV is approximately 1.4 times higher, consistent with nonradial pulsations due solely to temperature changes at constant radius. The high time resolution of these observations allows us to search for high-frequency pulsations (such as p modes or high overtone radial modes). No firm evidencefor high-frequency pulsations was seen in either object between 1 and 12 Hz. Correlation analysis of GD 358 shows no clear signal of multifrequency high overtone radial pulsations at the 0.00075 mag level, with no individual modes above the 0.0016 mag level. Upper limits for PG 0112+104 are approximately 2 times higher than for GD 358. Implications of this study for the theory of white dwarf pulsations are discussed.

Kawaler, Steven D.↗

NASA NTRS1993

Asteroseismology of planetary nebula nuclei

Nine planetary nebula nuclei (PNNS) are now known to be pulsating variables. All of them are O VI or PG 1159-type objects, with extreme hydrogen deficiency and high abundances of C and O. They are non-radial pulsators, with typical periods of 10 to 30 min, and their probable descendants are the shorter-period GW Vir (PG 1159-035) pulsating white dwarfs whose PNe have presumably dispersed. The pulsating PNNs are promising candidates for asteroseismological study, although there are already indications that such analyses will be complicated by highly variable power spectra. We present preliminary results from two campaigns of global photometry on the pulsating nuclei of NGC 1501 and Sanduleak 3, and from ground- and space-based searches for radial-mode pulsations in PNNs and white dwarfs.

Bond, Howard E.↗

NASA NTRS1992

Ultraviolet observations of close-binary and pulsating nuclei of planetary nebulae; Winds and shells around low-mass supergiants; The close-binary nucleus of the planetary nebula HFG-1; A search for binary nuclei of planetary nebulae; UV monitoring of irregularly variable planetary nuclei; and The pulsating nucleus of the planetary nebula Lo 4

A brief summary of the research highlights is presented. The topics covered include the following: binary nuclei of planetary nebulae; other variable planetary nuclei; low-mass supergiants; and other IUE-related research.

Bond, Howard E.↗

NASA NTRS1992

The photometric period of the recurrent Nova T Pyxidis

The paper presents 1713 photometric measurements of T Pyx from 1966 to 1990. The light curve of T Pyx shows roughly sinusoidal variations with a typical amplitude of 0.09 mag and a time scale of 2 hr. Discrete Fourier transforms of data from individual nights and runs reveal a highly significant periodic modulation. This modulation is proven to be coherent only on time scales shorter than from 6 d to under 1 d. The present period for the modulation is 0.07616 +/- 0.00017 d. Since other stars have variable photometric periods (possibly related to the superhump phenomenon) which are slightly different from the orbital period, an orbital period of about 0.073 d for T Pyx is suggested.

Schaefer, Bradley E.↗

NASA NTRS1989

A compact planetary nebula around the hot white dwarf EGB 6/PG 0950 + 139

The remarkable central star (0950 + 139), a very hot DA/DAO white dwarf, of the planetary nebula EGB 6 is described. Follow-up observations relevant to the analyses of both the nebula and the stellar photosphere are presented. Three kinds of scenarios are discussed to account for the existence of this peculiar nebula, but none appears very promising. The first consideration is that the nebula was ejected from the white dwarf as a discret event. This hypothesis is heavily constrained by the nebular size, density, and expansion rate; by the low luminosity and radius of the star; and by the absence of evidence for variation in density-sensitive forbidden lines from 1978 to 1987. No plausible mechanism can cause the observed amount of mass to be lost directly from a white dwarf in a steady or sporadic wind, at outflow velocities orders of magnitude below the escape velocity. Final consideration is given to the possibility that the gas is lost from a close companion star, but there is no evidence that this is a close binary system.

Liebert, James↗