The Ages of Stars

The age of an individual star cannot be measured, only estimated through mostly model-dependent or empirical methods, and no single method works well for a broad range of stellar types or for a full range in age. This review presents a summary of the available techniques for age-dating stars and ensembles of stars, their realms of applicability, and their strengths and weaknesses. My emphasis is on low-mass stars because they are present from all epochs of star formation in the Galaxy and because they present both special opportunities and problems. The ages of open clusters are important for understanding the limitations of stellar models and for calibrating empirical age indicators. For individual stars, a hierarchy of quality for the available age-dating methods is described. Although our present ability to determine the ages of even the nearest stars is mediocre, the next few years hold great promise as asteroseismology probes beyond stellar surfaces and starts to provide precise interior properties of stars and as models continue to improve when stressed by better observations.Comment: To appear in the 2010 volume of Annual Reviews of Astronomy and Astrophysics

Mars polar volatiles: Topographic and geologic setting

Progress on a project to elucidate the geological and topographic setting of the Martian polar volatiles is reported. The following accomplishments are enumerated: (1) all of the Mariner 9 imaging data sets available through JPL were acquired and copied; (2) Mariner 9 imagery was investigated in terms of the accuracy of the imaging footprints, dark current, and residual image; (3) the transfer functions of both vidicons were investigated; and (4) the magnitude of the atmospheric scattering was examined

Differences between proposed Apollo sites - Far infrared emissivity evidence

Infrared emissivity spectra comparison of lunar surface area

Fine structure of the chromospheric activity in Solar-type stars - The Halpha Line

A calibration of H-alpha as both a chromospheric diagnostic and an age indicator is presented, complementing the works previously done on this subject (Herbig 1985, Pasquini & Pallavicini 1991. The chromospheric diagnostic was built with a statistically significant sample, covering nine years of observations, and including 175 solar neighborhood stars. Regarding the age indicator, the presence of stars for which very accurate ages are determined, such as those belonging to clusters and kinematic groups, lends confidence to our analysis. We also investigate the possibility that stars of the same age might have gone through different tracks of chromospheric decay, identifying - within the same age range - effects of metallicity and mass. These parameters, however, as well as age, seem to be significant only for dwarf stars, losing their meaning when we analyze stars in the subgiant branch. This result suggests that, in these evolved stars, the emission mechanism cannot be magnetohydrodynamical in nature, in agreement with recent models (Fawzy et al. 2002c, and references therein). The Sun is found to be a typical star in its H-alpha chromospheric flux, for its age, mass and metallicity. As a byproduct of this work, we developed an automatic method to determine temperatures from the wings of H-alpha, which means the suppression of the error inherent to the visual procedure used in the literature.Comment: 10 pages, 10 figures, accepted for publication in Astronomy & Astrophysics. Nature of replacement: match astro-ph and ADS title (greek letter

Progressive Saxonism: The Construction of Anglo-Saxonism in Jack London\u27s The Valley of the Moon and Frank Norris\u27s McTeague

The purpose of my thesis seeks to uncover the constructed nature of the Anglo-Saxon ethnicity within two works of fiction. My thesis utilizes London’s The Valley of the Moon (1913) and Norris’s McTeague (1899) because they were published in a similar era. Both authors lived and wrote in the Bay Area during the Progressive Era of American politics. Therefore, there is political, stylistic, and regional proximity. Although Anglo-Saxonism has always been present in the United States, the construction of race was changing in the 1900s. The Valley of the Moon and McTeague both contain intriguing (and antiquated) notions of whiteness that further exacerbate the class struggle in California. This thesis describes the convergence of Progressive politics, eugenics, and Marxism within a unique chapter of American history. Through an exploration of Anglo-Saxonism, this examination of racial classifications is an attempt to reveal the inner workings of oppression in America

Lithium abundances from the 6104A line in cool Pleiades stars

Lithium abundances determined by spectral synthesis from both the 6708A resonance line and the 6104 subordinate line are reported for 11 late-type Pleiades stars, including spectra previously analysed by Russell (1996). We report a 0.7 dex scatter in the abundances from 6708A, and a scatter at least as large from the 6104A line. We find a reasonable correllation between the 6104A and 6708A Li abundances, although four stars have 6104A-determined abundances which are significantly larger than the 6708-determined values, by up to 0.5 dex, suggesting problems with the homogeneous, one-dimensional atmospheres being used. We show that these discrepancies can be explained, although probably not uniquely, by the presence of star spots with plausible coverage fractions. The addition of spots does not significantly reduce the apparent scatter in Li abundances, leaving open the possibility that at least some of the spread is caused by real star-to-star differences in pre-main- sequence Li depletion.Comment: 13 pages, 7 figures; Accepted by A&A 17/05/0

The Age Related Properties of Solar Type Stars

The studies of lithium in solar-type stars in clusters of a wide range of ages has provided critical information on a tracer of convective processes, especially among very young stars. Our most recent work has been on a pre-main sequence cluster (NGC 2264) that took place after this grant expired, but was founded on it. The spread seen in Li in Zero-Age Main Sequence clusters like the Pleiades is huge and possibly related to rotation. No clear spread in seen in NGC 2264, so it does not have its origins in the conditions of formation but is instead a result of processes occurring during PMS evolution. Our observations of M67 were particularly interesting because this cluster is the same age as the Sun, i.e.,very old. Clear evidence was seen for a spread in Li there too, indicating that the spread seen in very young stars perpetuates itself into old age

The young, active binary star EK Draconis

EK Dra (HD 129333) is a young, active, nearby star that is orbited by a low mass companion. By combining new speckle observations with old and new radial velocity measurements we find that the orbit is highly eccentric with e=0.82\pm0.03, and we derive the true masses of both components. The masses are $0.9\pm0.1 {\rm M}_\odot$ and $0.5\pm0.1 {\rm M}_\odot$, for the primary and secondary, respectively. From high resolution spectra we derive a new $T_{\rm eff}$ of $5700\pm70$ K, and a $\log g$ of $4.37\pm0.10$, which is different to previous estimates. However, the new spectroscopic distance differs by only 5.8% to the distance derived by parallax measurement of the Hipparcos satellite and thus the stellar parameters are presumably more realistic than older determinations. We derive a somewhat higher value for the metallicity of $[Fe/H]=-0.16\pm0.07$. EK Dra turns out to be one of the few nearby young stars which will evolve similar to the sun. The precise radial velocity measurements taken in the course of this program also allows us to shed more light on to the activity of this star. In 2001 and 2002 we find a periodic signal of the radial velocity variations with a period of $2.767\pm0.005$ days which we interpret as the rotation period. This signal vanishes in 2003. However the signal can be recovered if only the spectra in which the photospheric lines are asymmetric are used. On the other hand, we do not find a close correlation between the asymmetry of photospheric lines and the radial velocity.Comment: 10 pages, 11 figures, accepted by A&