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Bond, H. E.

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

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The Size Evolution of Passive Galaxies: Observations From the Wide-Field Camera 3 Early Release Science Program

We present the size evolution of passively evolving galaxies at z approximately 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z greater than approximately 1.5. We identify 30 galaxies in approximately 40 arcmin(sup 2) to H less than 25 mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 micrometers less than approximately lambda (sub obs) 1.6 micrometers with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of approximately 0.033(1+z).We determine effective radii from Sersic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M(sub ∗) approximately 10(sup 11) solar mass) undergo the strongest evolution from z approximately 2 to the present. Parameterizing the size evolution as (1 + z)(sup - alpha), we find a tentative scaling of alpha approximately equals (−0.6 plus or minus 0.7) + (0.9 plus or minus 0.4) log(M(sub ∗)/10(sup 9 solar mass), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of highredshift systems. We discuss the implications of this result for the redshift evolution of the M(sub ∗)-R(sub e) relation for red galaxies.

fundamental parameters↗
NASA NTRS2012

Stellar Populations of Lyman Break Galaxies at z approx. to 1-3 in the HST/WFC3 Early Release Science Observations

We analyze the spectral energy distributions (SEDs) of Lyman break galaxies . (LBGs) at z approx = 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST /WFC3 obse,rvations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z approx = 1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope f3 is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at .z approx = 1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1a uncertainties. This could imply that identical dropout selection technique, at all. redshifts, find physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of approx 0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of approx 0.90. These relations hold true - within luminosities probed in this study - for LBGs from z approx = 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z approx = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z approx = 2 is essential. The future HST UV surveys,. both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

Hathi, N. P.↗
NASA NTRS2010

HST WFC3 Early Release Science: Emission-Line Galaxies from IR Grism Observations

We present grism spectra of emission line galaxies (ELGs) from 0.6-1.6 microns from the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). These new infrared grism data augment previous optical Advanced Camera for Surveys G800L (0.6-0.95 micron) grism data in GOODS South, extending the wavelength coverage well past the G800L red cutoff. The ERS grism field was observed at a depth of 2 orbits per grism, yielding spectra of hundreds of faint objects, a subset of which are presented here. ELGs are studied via the Ha, [O III ], and [OII] emission lines detected in the redshift ranges 0.2 less than or equal to z less than or equal to 1.6, 1.2 less than or equal to z less than or equal to 2.4 and 2.0 less than or equal to z less than or equal to 3.6 respectively in the G102 (0.8-1.1 microns; R approximately 210) and C141 (1.1-1.6 microns; R approximately 130) grisms. The higher spectral resolution afforded by the WFC3 grisms also reveals emission lines not detectable with the G800L grism (e.g., [S II] and [S III] lines). From these relatively shallow observations, line luminosities, star formation rates, and grism spectroscopic redshifts are determined for a total of 25 ELGs to M(sub AB)(F098M) approximately 25 mag. The faintest source in our sample with a strong but unidentified emission line--is MAB(F098M)=26.9 mag. We also detect the expected trend of lower specific star formation rates for the highest mass galaxies in the sample, indicative of downsizing and discovered previously from large surveys. These results demonstrate the remarkable efficiency and capability of the WFC3 NIR grisms for measuring galaxy properties to faint magnitudes.

Straughn, A. N.↗
NASA NTRS1986

UV observations of blue stragglers and population 2 K dwarfs

Blue stragglers are stars, found usually in either open or globular clusters, that appear to lie on the main sequence, but are brighter and bluer than the cluster turn-off. Currently, two rival models are invoked to explain this apparently pathological behavior: internal mixing (so that fresh fuel is brought into the stellar core); and mass transfer (by which a normal main sequence star acquires mass from an evolving nearby companion and so moves up the main sequence). The latter model predicts that in the absence of complete mass transfer (i.e., coalescence), blue stragglers should be binary systems with the fainter star in a post-main sequence evolutionary state. It is important to ascertain the cause of this phenomenon since stellar evolution models of main sequence stars play such a vital role in astronomy. If mass transfer is involved, one may easily exclude binaries from age determinations of clusters, but if mixing is the cause, our age determinations will be much less accurate unless we can determine whether all stars or only some mix, and what causes the mixing to occur at all.

Carney, B. W.↗
NASA NTRS1985

Extremely metal-deficient red giants. IV - Equivalent widths for 36 halo giants

Further work on a study of 36 metal-poor field red giants is reported. Chemical abundances previously determined were based on model stellar atmosphere analyses of equivalent widths from photographic image-tube echelle spectrograms obtained with with 4-m reflectors at Kitt Peak and Cerro Tololo. A tabulation of the equivalent-width data (a total of 18, 275 equivalent widths) is presented.

Luck, R. E.↗
NASA NTRS1985

TT Arietis - The low state

A comprehensive photometric and spectroscopic study of the low state of the novalike variable TT Ari has been made with observations spanning the UV to IR spectral regions. The roughly 5 mag drop in the system's luminosity from the high state indicates that the mass-transfer rate decreased by more than two orders of magnitude. The drastic reduction in the luminosity of the accretion disk between the high and low states enabled the white dwarf component to be directly observed for the first time. The broad absorption profiles at various lines and the UV energy distribution are best fitted by a hot white dwarf. A lower limit of 200 pc for the distance to TT Ari is derived, and the behavior of TT Ari is compared to that of another novalike variable, MV Lyr. The long-term photometric behavior of TT Ari makes it a typical member of the VY Scl subclass of novalike variables.

Shafter, A. W.↗
NASA NTRS1985

Two-phase ultraviolet spectrophotometry of the pulsating white dwarf ZZ Piscium

Spectra of the pulsating white dwarf ZZ Psc (= G29-38) were obtained using the International Ultraviolet Explorer. By using a multiple-exposure technique in conjunction with simultaneous ground-based exposure-metering photometry, it was possible to obtain mean on-pulse and off-pulse spectra in the 1950-1310 A wavelength range. The ratio of the time-averaged on-pulse to off-pulse spectra is best fitted by a temperature variation that is in phase with the optical light variation. This result is consistent with the hypothesis that the observed variation is due to a high-order nonradial pulsation. Conventional ultraviolet spectra of ZZ Psc showed broad absorption features at 1390 and 1600 A. These features are also found in the spectra of the cool DA-type white dwarfs G226-29 and G67-23, and appear to increase in strength with decreasing temperature. A possible explanation for the 1600 A feature is absorption by the satellite band of resonance-broadened hydrogen Ly-alpha. Such absorption would also help explain a discrepancy between the observed pulsation amplitude shortward of 1650 A and the predicted amplitudes based on model atmospheres.

Bond, H. E.↗
NASA NTRS1984

Two new extremely hot pulsating white dwarfs

High speed photometry of the extremely hot, nearly degenerate stars PG 1707 + 427 and PG 2131 + 066 reveals that they are low-amplitude pulsating variables. Power spectral analysis shows both to be multiperiodic, with dominant periods of 7.5 and 6.4-6.9 minutes, respectively. Together with the known pulsators PG 1159 - 035 and the central star of the planetary nebula Kohoutek 1-16, these objects define a new pulsational instability strip at the hot edge of the H-R diagram. The variations of these objects closely resemble those of the much cooler pulsating ZZ Ceti DA white dwarfs; both groups are probably nonradial g-mode pulsators. Evolutionary contraction of the PG 1159 - 035 variables may lead to period changes that would be detectable in as little as 1 year. The optical and IUE spectra of the PG 1159 - 035 variables are characterized by absorption lines of C IV and other CNO ions, indicating radiative levitation of species heavier than helium. He II is also present in the spectra, but the hydrogen Balmer lines are absent. Effective temperatures near 100,000 K are required, and the He II 4686 A profiles indicate log g greater than 6. These helium-rich pulsators form the hottest known subgroup of the DO white dwarfs.

Bond, H. E.↗
NASA NTRS1984

E2003 + 225 - A 3h 42m AM Herculis type binary system

The bright soft X-ray source E2003 + 225, originally discovered by the HEAO 1 low-energy detectors, has been found to be a new AM Herculis type binary. The optical counterpart shows a rich emission spectrum of He II, He I, and H as well as circular and linear polarization. Larger polarization in the near-infrared than in the ultraviolet argues for its origin as high harmonic cyclotron emission. Optical photometry, polarimetry, spectroscopy, and the X-ray light curves are all consistent with an orbital period of 222.51 m, the longest period known for AM Herculis systems, and only the second on the long side of the 2-3 hour cataclysmic variable period gap.

Takalo, L. O.↗
NASA NTRS1984

Light variations of the population II F-type supergiant HD 46703

Photometric monitoring has revealed brightness variations of 0.1 m on a time scale of weeks for HD 46703, a metal-deficient F-type field analog of the stars lying above the horizontal branch in globular clusters. It is suggested that HD 46703 belongs to the '89 Her' class of luminous F-type variables. Since HD 46703 is unquestionably a halo object, it is almost certainly a low-mass star. It is suggested that it, and probably the other 89 Her variables, are masquerading as supergiants during their final evolution off the asymptotic giant branch.

Bond, H. E.↗
NASA NTRS1982

The noncompact binary X-ray source 4U 2129+47

The 5.2 hr X-ray binary 4U 2129+47 was observed for a full orbital cycle using the imaging proportional counter detector and the monitor proportional counter detector aboard the Einstein Observatory, as well as a 0.9 m reflector for 5 hrs continuous optical photometry. The X-ray and optical light curves, the X-ray spectrum, and the times of optical and X-ray minimum were determined. The shape of the 5.2 hr X-ray light curve is independent of energy. A partial X-ray eclipse occurred which was centered on the time of optical minimum and which lasted 20 percent of the orbital period. During this interval the X-ray intensity varied smoothly by a factor of three, and the light curve was symmetric relative to the time of minimum. These findings argue that the X-ray emitting region is extended and highly ionized. A model is presented in which an accretion disk corona scatters radiation from a central accreting neutron star.

Mcclintock, J. E.↗
NASA NTRS1982

A search for cataclysmic binaries containing strongly magnetic white dwarfs

The AM Herculis type binaries which contain accreting white dwarfs with surface magnetic fields of a few times 10 to the seventh power gauss were studied. If white dwarfs in cataclysmic binaries have a range of field strengths similar to that among single white dwarfs. AM Her like systems should exist with fields as high as 3 x 10 to the eighth power gauss. It is suggested that such objects will not have the strong optical polarization of the AM Her variables; however, they exhibit high harmonic cyclotron emission, making them spectacular UV sources. We made IUE observations of seven candidate cataclysmic variables selected for optical similarity to AM Her binaries. Although all seven objects were detected in the UV, none display unusually strong UV continua. It is suggested that the distribution of magnetic field strengths among single white dwarfs may be different from that among binaries.

Bond, H. E.↗