Mean Surface Gravity Research Articles

A Photometric Study of ZZ Microscopium

ABSTRACTNew photometric (uvbyβ) observations of ZZ Mic are described. Reddening values E(b - y) = 0.00 mag and [Fe/H] = -0.078 were derived from the photometry. Intrinsic (b - y) and c1 values indicate a mean effective temperature of 〈Teff〉 = 7780 K and a mean surface gravity of 〈 log g〉 = 3.84. Theoretical evolutionary tracks yielded a mass of 1.75 M⊙ and an age of 0.56 Gyr. However, the pulsation mass was determined as 1.0 M⊙. ZZ Mic in most respects resembles a typical Population I dwarf Cepheid. We collected 34 times of maximum light from the literature and our observation in order to investigate the variations of the O - C values, and we confirmed a sign that the period is increasing.

A ballistics analysis of the Deep Impact ejecta plume: Determining Comet Tempel 1's gravity, mass, and density

In July of 2005, the Deep Impact mission collided a 366 kg impactor with the nucleus of Comet 9P/Tempel 1, at a closing speed of 10.2 km s −1. In this work, we develop a first-order, three-dimensional, forward model of the ejecta plume behavior resulting from this cratering event, and then adjust the model parameters to match the flyby-spacecraft observations of the actual ejecta plume, image by image. This modeling exercise indicates Deep Impact to have been a reasonably “well-behaved” oblique impact, in which the impactor–spacecraft apparently struck a small, westward-facing slope of roughly 1 / 3 – 1 / 2 the size of the final crater produced (determined from initial ejecta plume geometry), and possessing an effective strength of not more than Y ¯ = 1 – 10 kPa . The resulting ejecta plume followed well-established scaling relationships for cratering in a medium-to-high porosity target, consistent with a transient crater of not more than 85–140 m diameter, formed in not more than 250–550 s, for the case of Y ¯ = 0 Pa (gravity-dominated cratering); and not less than 22–26 m diameter, formed in not less than 1–3 s, for the case of Y ¯ = 10 kPa (strength-dominated cratering). At Y ¯ = 0 Pa , an upper limit to the total ejected mass of 1.8 × 10 7 kg ( 1.5 – 2.2 × 10 7 kg ) is consistent with measurements made via long-range remote sensing, after taking into account that 90% of this mass would have stayed close to the surface and then landed within 45 min of the impact. However, at Y ¯ = 10 kPa , a lower limit to the total ejected mass of 2.3 × 10 5 kg ( 1.5 – 2.9 × 10 5 kg ) is also consistent with these measurements. The expansion rate of the ejecta plume imaged during the look-back phase of observations leads to an estimate of the comet's mean surface gravity of g ¯ = 0.34 mm s −2 (0.17–0.90 mm s −2), which corresponds to a comet mass of m t = 4.5 × 10 13 kg ( 2.3 – 12.0 × 10 13 kg ) and a bulk density of ρ t = 400 kg m −3 (200–1000 kg m −3), where the large high-end error is due to uncertainties in the magnitude of coma gas pressure effects on the ejecta particles in flight.

Chemical Composition and Differential Time-Series CCD Photometry of V2314 Ophiuchi: A New λ Bootis-Type Star

We investigated V2314 Oph using high-resolution (R = 45,000) spectral observations. The atmospheric parameters were determined using iron-line abundance analysis. We derived a mean effective temperature of Teff = 7510 K, mean surface gravity of log g = 3.30, metallicity of [Fe/H] = -0.59, and rotation velocity of v sin i = 38 km s-1. The abundances of 19 chemical elements were determined. The abundance pattern of V2314 Oph was found to be similar to that of λ Bootis-type stars. V2314 Oph is also a variable star, as are a majority of λ Bootis stars. A frequency analysis of 10 selected nights of precise differential photometry has preliminarily revealed four pulsational modes. The multiperiodic solution of the light curve is probably more similar to a low-amplitude Population I δ Scuti variable pattern, as is apparent for many λ Bootis stars. For asteroseismic investigations of the star it is necessary to obtain more prolonged, continuous time-series observations. These features, as well as the small proper motion and relatively large rotational velocity of V2314 Oph, specify the star as not likely to be a field SX Phoenicis Population II variable, as was suggested previously.

A ballistics analysis of the Deep Impact ejecta plume: Determining Comet Tempel 1's gravity, mass, and density

In July of 2005, the Deep Impact mission collided a 366 kg impactor with the nucleus of Comet 9P/Tempel 1, at a closing speed of 10.2 km s −1. In this work, we develop a first-order, three-dimensional, forward model of the ejecta plume behavior resulting from this cratering event, and then adjust the model parameters to match the flyby-spacecraft observations of the actual ejecta plume, image by image. This modeling exercise indicates Deep Impact to have been a reasonably “well-behaved” oblique impact, in which the impactor–spacecraft apparently struck a small, westward-facing slope of roughly 1 / 3 – 1 / 2 the size of the final crater produced (determined from initial ejecta plume geometry), and possessing an effective strength of not more than Y ¯ = 1 – 10 kPa . The resulting ejecta plume followed well-established scaling relationships for cratering in a medium-to-high porosity target, consistent with a transient crater of not more than 85–140 m diameter, formed in not more than 250–550 s, for the case of Y ¯ = 0 Pa (gravity-dominated cratering); and not less than 22–26 m diameter, formed in not less than 1–3 s, for the case of Y ¯ = 10 kPa (strength-dominated cratering). At Y ¯ = 0 Pa , an upper limit to the total ejected mass of 1.8 × 10 7 kg ( 1.5 – 2.2 × 10 7 kg ) is consistent with measurements made via long-range remote sensing, after taking into account that 90% of this mass would have stayed close to the surface and then landed within 45 min of the impact. However, at Y ¯ = 10 kPa , a lower limit to the total ejected mass of 2.3 × 10 5 kg ( 1.5 – 2.9 × 10 5 kg ) is also consistent with these measurements. The expansion rate of the ejecta plume imaged during the look-back phase of observations leads to an estimate of the comet's mean surface gravity of g ¯ = 0.34 mm s −2 (0.17–0.90 mm s −2), which corresponds to a comet mass of m t = 4.5 × 10 13 kg ( 2.3 – 12.0 × 10 13 kg ) and a bulk density of ρ t = 400 kg m −3 (200–1000 kg m −3), where the large high-end error is due to uncertainties in the magnitude of coma gas pressure effects on the ejecta particles in flight.

Photometric Studies of δ Scuti Stars. II. V1162 Orionis

ABSTRACTNew photometric (uvbyβ) observations of V1162 Orionis are reported. We derive a reddening value of E(b - y) = 0.021 mag and a metallicity of[Fe/H] = +0.1. Intrinsic (b - y) and c1 values indicate a mean effective temperature,〈Teff〉 = 7540 K, and a mean surface gravity,〈log g〉 = 3.96. Theoretical evolutionary tracks, along with pulsation models, indicate the mass of V1162 Ori is 1.8 M⊙ and the age is 0.60 Gyr. New V magnitude CCD observations are also reported. A time of maximum light analysis shows that V1162 Ori has experienced a period break. In addition, the amplitude has dropped from ΔV = 0.2 before the period break to ΔV = 0.1 after the break.

Photometric Studies of δ Scuti Stars. I. IP Virginis

ABSTRACTWe report 15 new times of maximum light for the δ Scuti star IP Virginis (formerly known as SA 106‐1024). An analysis of all times of maximum light indicates that IP Vir has been decreasing in period at a constant rate of −7.4 × 10-9 days day−1. Evidence is also presented that IP Vir is a double‐mode variable with a period ratio of π1/π0 = 0.774. This period ratio predicts a [Fe/H] value of −0.3. From photometric (uvbyβ) observations, we find a foreground reddening of E(b - y) = 0.008 mag and a metallicity of[Fe/H] = +0.05. It is shown that [Fe/H] = −0.3 is most likely the correct value. Intrinsic (b - y)‐ and c1‐values, plotted in a model atmosphere grid, indicate a mean effective temperature,〈Teff〉 = 7400 K, and a mean surface gravity,〈log g〉 = 3.89. All of these physical parameters support Landolt's initial conclusion that IP Vir is an ordinary δ Sct star.

A PHOTOMETRIC STUDY OF V798 CYGNI

ABSTRACT New photometric (uvbyβ) observations of the intrinsic variable star V798 Cyg have been secured and used to derive values of foreground reddening, E(b - y) = 0\\fm117, and metallicity, [Fe/H] = 0.64. Intrinsic (b - y) and c1 values indicate a mean effective temperature, < Teff > = 7150 K, and a mean surface gravity, < log g > = 3.39. Pulsation theory and theoretical evolutionary tracks yield a mass of 2.3M⊙ and an age of 0.63 Gyrs. Although V798 Cyg has been described as being multi-periodic, this conclusion is not confirmed by our observations. V798 Cyg in most respects resembles a typical population I dwarf Cepheid.

A Photometric and Spectrographic Study of SX Phœnicis

AbstractNew simultaneous photometric (uvbyβ) and spectrographic observations of SX Phe are described. Analysis of the light variation frequency spectrum is performed and the oscillation modes are investigated. After separating the light curves and radial velocity curve, atmospheric and physical parameters corresponding to each different oscillation mode were determined. Intrinsic (b – y), m1, and c1 values used in conjunction with a model-atmosphere grid yield a mean effective temperature &lt; Teff &gt; = 7590K, a mean surface gravity, &lt; logg &gt; = 4.02, and [Fe/H]= -0.47 for the first period. The pulsation theory and stellar model sequences yield bolometric magnitude of mass of 1.4 M⊙ and age of 2.0 Gyrs. It was found that these atmospheric parameters are almost independent upon different oscillation mode. The radial-velocity data indicates a mean radial velocity of -37km/s and a total velocity amplitude range of 38km/s.

The stellar populations of early-type galaxies as a function of their environment

Gravity-sensitive spectral indices in the blue spectral region were used to study the mean stellar surface gravity of early-type galaxies in a variety of galaxian environments. The findings confirm earlier work that the mean surface gravity in integrated light is high for isolated and Virgo Cluster E/S0 galaxies, but there is evidence to suggest that the mean surface gravity for similar galaxies in rich clusters is significantly lower. This indicates that galaxies in dense environments may be older on average than their counterparts in lower-density regions. Possible selection effects and systematic errors are discussed. It is concluded that star formation in galaxies was truncated at an earlier epoch (on average) in dense environments. However, the strength of this result would be weakened if there were large age gradients within these galaxies. 31 refs.

A PHOTOMETRIC AND SPECTROGRAPHIC STUDY OF BP PEGASI

ABSTRACT Photometric (uvby beta) and spectrographic observations of the dwarf Cepheid BP Peg are discussed. The observations are used to derive a reddening value of E(b-y) = 0.067 m. An effective temperature of 7470 K, a mean surface gravity, log g = 3.85, and a Fe/H abundance ratio of - 0.08 are obtained. Pulsation theory and stellar model sequences yield Mbol = 1.4 m, mass = 1.85 solar masses, and age = 1.3 X 10 to the 9th yrs. Also, the radial-velocity data show a mean radial velocity of - 30 km/s and a total velocity range of 36 km/s.

Metal-abundance determinations from near-UV spectra - Application to the mean metal abundance of M32

view Abstract Citations (30) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Metal Abundance Determinations from Near-UV Spectra: Application to the Mean Metal Abundance of M32 Boulade, Olivier ; Rose, James A. ; Vigroux, Laurent Abstract Near-UV spectra have been obtained for the nucleus of the elliptical galaxy M32 and for 60 field stars covering a range in T_eff_, luminosity class, and [Fe/H] using the UV prime-focus spectrograph on the Canada-France-Hawaii Telescope. The spectra cover the wavelength interval λλ3200-3900A at a resolution of 2.5 A FWHM. A number of quantitative spectral indices have been defined that are sensitive to surface gravity and/or metal abundance. In particular, a depression in the pseudocontinuum shortward of 3504 A is shown to be highly sensitive to metal abundance. The spectral indices have been used to determine the luminosity-weighted mean metal abundance and surface gravity of M32 at 3500 A. The following results have been obtained: (1) The luminosity- weighted mean metal abundance for M32 at 3500 A is [Fe/H] ~ -0.1, in very close agreement with determinations made at red wavelengths. The derived metal abundance is shown to be largely insensitive to the amount of giant-branch light that contaminates the near-UV integrated light of M32. (2) The luminosity-weighted mean surface gravity for M32 at 3500 A indicates that the giant branch contributes slightly less than 30% of the light at 4000 A. (3) On the basis of an index characterizing the NH λ 3360 A feature, it is found that the luminosity-weighted [N/Fe] is approximately equal to that of solar neighborhood stars, indicating that M32 has had a chemical-enrichment history similar to that of the solar neighborhood. The close agreement between metal-abundance determinations in the near UV and in the red appears to rule out the possibility that the integrated spectrum of M32 can be synthesized with a coeval population of stars covering a range in metal abundance and indicates that a substantial age spread is required. Publication: The Astronomical Journal Pub Date: October 1988 DOI: 10.1086/114881 Bibcode: 1988AJ.....96.1319B Keywords: Abundance; Elliptical Galaxies; Galactic Nuclei; Metallicity; Near Ultraviolet Radiation; Ultraviolet Spectra; Chemical Composition; Solar Neighborhood; Stellar Luminosity; Stellar Spectra; Astrophysics; GALAXIES: INDIVIDUAL; GALAXIES: LOCAL GROUP; GALAXIES: NUCLEI; GALAXIES: ABUNDANCES full text sources ADS | data products SIMBAD (58) NED (1)

The Integrated Spectra of Metal-Rich Galactic Globular Clusters: A Two-Parameter Family

Integrated photographic image-tube spectra have been obtained for the central regions of a number of metal-rich Galactic globular clusters with a wavelength resolution of 2.5 å over the wavelength region λλ3400-4500 å. The spectra have been analyzed using a variety of quantitative spectral indices that compare the strengths of neighboring absorption features. Our main result is that two parameters are needed to describe the integrated spectra of metal-rich globular clusters. The second parameter is manifested in two ways:(1) In a diagnostic diagram sensitive to surface-gravity the metal-rich clusters do not form a well-defined linear sequence. Instead, we find large differences from one cluster to another in the mean surface gravity of the stars contributing to the integrated light at 4000 å. It appears that the relative amounts of light contributed by dwarfs and giants varies considerably from one cluster to another.(2) In a diagram that discriminates CN strength we find large differences from one cluster to another in the mean CN strengths of clusters having similar “spectral type”. It is inferred that the mean CN anomaly varies from one cluster to another and that the anomalous CN strengths are present in main sequence stars as well as in giants.The above two second parameter effects are shown to be strongly correlated in the sense that the “dwarf-dominated” clusters have the largest CN anomalies. Hence, our study indicates that no more than two independent parameters are required to explain the integrated spectra of metal-rich globular clusters.Details of the above findings can be found in Rose and Tripicco (1986, A.J. 92, 1610).

Developing an optimally estimated earth gravity model to degree and order 360 from a global set of 30′ by 30′ mean surface gravity anomalies

Developing an optimally estimated earth gravity model to degree and order 360 from a global set of 30′ by 30′ mean surface gravity anomalies

THE NATURE OF THE DWARF CEPHEID EH LIBRAE.

ABSTRACT Photometry (uvby beta) of EH Lib has been secured and analyzed. A small correction is made to the period in order to better predict times of light maxima. A reddening value, E(b-y) = +0.041 min is derived from standard calibrations applied to the photometry. Intrinsic (b-y) and c1 values are used to determine a mean effective temperature of 7840 K, and a mean surface gravity of 4.08. The metal abundance, Fe/H of -0.015, is determined from delta m1. Using new and previously published spectroscopic data, a mean radius of 2.4 solar radii is derived using a Wesselink method. The radius and effective temperature indicate a mean absolute bolometric magnitude, of +1.5. Also, a mass of 2.0 solar masses is derived using the radius and effective gravity. Radial-velocity data yield a mean radial velocity, gamma = -61 km/s, and a total velocity range, 2K = 35 km/s.

PHOTOMETRIC PROPERTIES OF HD 200925.

ABSTRACT Photometric observations have been carried out over ninety percent of the pulsation cycle for the variable star HD 200925. The observations were obtained using a single-channel photometer, and a photomultiplier attached to a 61-cm reflecting telescope. The instrumental indices were reduced to the standard Stromgren and beta-systems of 13 standard stars. The photometric data show that HD 200925 is multiperiodic. A reddening value of 0.040 mag was derived as the average of the variable and comparison star observations. Analysis of the intrinsic (b-y) and cl values for one primary pulsation cycle indicated a mean effective temperature of 7470 K, and a mean surface gravity of 3.87 log g. HD 200925 is found to have a somewhat higher (+0.33) Fe/H abundance ratio than stars in the Hyades. The observed magnitude and color variations of HD 200925 are reproduced in graphic form.

THE NATURE OF THE DWARF CEPHEID XX CYG.

ABSTRACT Photometry of XX Cyg in the uvby and β systems has been secured and analyzed. A reddening value, E(b - y) = + 0.m057, is derived from the photometry. Intrinsic (b - y) and c1 values are used to determine a mean effective temperature, eff> = 7530 K, and a mean surface gravity, = 3.66. XX Cyg is found to be a metal-poor dwarf cepheid with [Fe/H] = -0.49. A radius of 2.4 Rsun has been found from the Wesselink method. The radius and effective temperature indicate that bol> = + 1.7. A mass of 1.0 Msun is found from the radius and effective gravity. The radial-velocity data yield a mean radial velocity of -108 km s-1 and a total velocity range of 37 km s-1.

Masses and radii of white-dwarf stars. IV - The two-color diagram

Newly calculated model atmospheres, including both the effects of Lyman and Balmer line blanketing and the effects of convection, are used to determine the surface gravities of white-dwarf stars by the use of the separation of stars with different surface gravities in the Stroemgren and multichannel two-color diagrams. The mean surface gravity of 40 stars in the appropriate temperature range with multichannel colors is log g=8.04 +- 0.25, and the mean value for 35 stars with Stroemgren photomety is log g=7.86 +- 0.25. Comparison of all available investigations of white-dwarf masses shows that they are internally consistent with the possible exception of masses derived from gravitational redshifts, where a slight, marginally significant discrepancy may exist. The weighted mean of all mass determination is 0.75 M/sub sun/, allowing for selection effects. The 1 sigma range of white-dwarf masses extends from 0.5 M/sub sun/ to 1.0 M/sub sun/; we do not find evidence for a smaller mass range.