A coarse spectroscopic analysis is presented of the faint blue stars JL87 and JL111, which are rather different despite their nearly identical UBV colors. JL87 is shown to be a helium-rich subluminous B star. Its abundance ratio nHe/nH = 0.2 is abnormally high compared to the bulk of the sdB stars that have strongly helium-depleted atmospheres relative to the sun. Observers are urged to look for a magnetic field in this star that could have caused the abundance anomaly. The other star, JL111, appears to be a quite normal, slightly hotter sdB.
Time-series photometry is reported that shows that KUV 05134 + 2605 is a pulsating DB white dwarf. The light curve shows sharply peaked pulses with a complicated mode structure including periods between 350 and 900 sec. The optical spectrum appears to be that of a star near the hot end of the DB sequence, consistent with theoretical predictions and the temperature range estimated empirically for previously known DBV stars.
Optical photometry is presented for the quadruple gravitational lens PG1115+080. A preliminary reduction of data taken from November 1995 to June 1996 gives component ``C'' leading component ``B'' by 23.7+/-3.4 days and components ``A1'' and ``A2'' by 9.4 days. A range of models has been fit to the image positions, none of which gives an adequate fit. The best fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km/s/Mpc for Omega=1, with an observational uncertainty of 14%, as computed from the B-C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0=64 km/sec/Mpc while taking the galaxy to be a point mass gives H0=84 km/sec/Mpc. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned HST observations.
The ENEAR project is an all-sky survey of nearby early-type galaxies. About 2200 new spectra and R-band images of over 1500 galaxies together with published data were assembled into a large catalog containing over 2000 objects with cz, sigma, photometric data, and line strengths on a uniform system. From this extensive database a magnitude-limited sample has been drawn comprising ~ 1400 galaxies brighter than m_B = 14.5, cz < 7000 km/s, and type T -2 or less with measured distances (ENEARf) and about 500 early-type galaxies in 28 clusters/groups (ENEARc) to derive an internally consistent D_n-sigma relation to estimate galaxy distances. In this contribution we discuss some general properties of ENEAR and briefly describe some preliminary results.
The EFAR project is a study of 736 candidate early-type galaxies in 84 clusters lying in two regions towards Hercules-Corona Borealis and Perseus-Cetus at distances $cz \approx 6000-15000$ km/s. In this paper we describe a new method of galaxy photometry adopted to derive the photometric parameters of the EFAR galaxies. The algorithm fits the circularized surface brightness profiles as the sum of two seeing-convolved components, an $R^{1/4}$ and an exponential law. This approach allows us to fit the large variety of luminosity profiles displayed by the EFAR galaxies homogeneously and to derive (for at least a subset of these) bulge and disk parameters. Multiple exposures of the same objects are optimally combined and an optional sky-fitting procedure has been developed to correct for sky subtraction errors. Extensive Monte Carlo simulations are analyzed to test the performance of the algorithm and estimate the size of random and {\it systematic} errors. Random errors are small, provided that the global signal-to-noise ratio of the fitted profiles is larger than $\approx 300$. Systematic errors can result from 1) errors in the sky subtraction, 2) the limited radial extent of the fitted profiles, 3) the lack of resolution due to seeing convolution and pixel sampling, 4) the use of circularized profiles for very flattened objects seen edge-on and 5) a poor match of the fitting functions to the object profiles. Large systematic errors are generated by the widely used simple $R^{1/4}$ law to fit luminosity profiles when a disk component, as small as 20% of the total light, is present.
The gravitational redshift is one of Einstein’s three original tests of General Relativity and derives from time’s slowing near a massive body. For velocities well below c, this is represented with sufficient accuracy by: As detailed by Will (1981), Schiff’s conjecture argues that the gravitational redshift actually tests the principle of equivalence rather than the gravitational field equations. For low redshifts, solar system tests give highest accuracy. LoPresto & Pierce (1986) have shown that the redshift at the Sun’s limb is good to about ±3%. Rocket experiments produce an accuracy of ±0.02% (Vessot et al . 1980), while for 40 Eri B the best white dwarf, the observed and predicted V RS agree to only about ±_5% (Wegner 1980).
Differential measurements of the radial velocities of the DA white dwarf omicron/sup 2/ Eri B and its M4Ve companion, omicron/sup 2/ Eri C, using the coude spectrograph of the 100-in. Mount Wilson telescope, yield a new gravitational redshift of V/sub RS/=+23.9 +- 1.3 (s.d.) km s/sup -1/. Corrections for the binary's orbital motion, the small gravitational redshift of the nondegenerate companion, and atmospheric refraction have been included in the reduction. At the present level of accuracy, the redshift, mass, and radius are inconsistent, but reconsideration of the errors and a slight lowering of the parallax to ..pi..=+0''.204 +- 0''.006 (s.d.) partially removes this problem. The radius is more insensitive to the parallax than the mass in the redshift-radius diagram. After a re-discussion of the radius, a value of 100R/R/sub sun/=1.30 +- 0.03 is found. Using this, the position of omicron/sup 2/ Eri B seems to agree with the Hamada and Salpeter mass-radius relations and stellar evolutionary theory, which predicts a carbon-oxygen core. The possibility of an iron core for omicron/sup 2/ Eri B now seems doubtful.
We derive central values and logarithmic gradients for the Hbeta, Mg and Fe indices of 35 early-type galaxies in the Coma cluster. We find that pure elliptical galaxies have on average slightly higher velocity dispersions, lower Hbeta, and higher metallic line-strengths than galaxies with disks (S0). The gradients strongly correlate with the gradients of sigma, but only weakly with the central index values and galaxy velocity dispersion. Using stellar population models with variable element abundance ratios from Thomas, Maraston & Bender (2003a) we derive average ages, metallicities and [alpha/Fe] ratios in the center and at the effective radius. We find that the [alpha/Fe] ratio correlates with velocity dispersion and drives 30% of the Mg-sigma relation, the remaining 70% being caused by metallicity variations. We derive negative metallicity gradients (-0.16 dex per decade) that are significantly flatter than what is expected from gaseous monolithic collapse models, pointing to the importance of mergers in the galaxy formation history. The gradients in age are negligible, implying that no significant residual star formation has occurred either in the center or in the outer parts of the galaxies, and that the stellar populations at different radii must have formed at a common epoch. For the first time we derive the gradients of the [alpha/Fe] ratio and find them very small on the mean. Hence, [alpha/Fe] enhancement is not restricted to galaxy centers but it is a global phenomenon. Our results imply that the Mg-sigma local relation inside a galaxy, unlike the global Mg-sigma relation, must be primarily driven by metallicity variations alone.
Visual wavelength spectroscopic and photoelectric observations confirm the identification of HD 149499B as a new hot white dwarf with a nearly continuous spectrum. Therefore it probably is a hydrogen-deficient object.
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