In this century, increasing concentrations of carbon dioxide (CO2) and other greenhouse gases in the Earth's atmosphere are expected to cause warmer surface temperatures and changes in precipitation patterns. At the same time, reactive nitrogen is entering natural systems at unprecedented rates. These global environmental changes have consequences for the functioning of natural ecosystems, and responses of these systems may feed back to affect climate and atmospheric composition. Here, we report plant growth responses of an ecosystem exposed to factorial combinations of four expected global environmental changes. We exposed California grassland to elevated CO2, temperature, precipitation, and nitrogen deposition for five years. Root and shoot production did not respond to elevated CO2 or modest warming. Supplemental precipitation led to increases in shoot production and offsetting decreases in root production. Supplemental nitrate deposition increased total production by an average of 26%, primarily by stimulating shoot growth. Interactions among the main treatments were rare. Together, these results suggest that production in this grassland will respond minimally to changes in CO2 and winter precipitation, and to small amounts of warming. Increased nitrate deposition would have stronger effects on the grassland. Aside from this nitrate response, expectations that a changing atmosphere and climate would promote carbon storage by increasing plant growth appear unlikely to be realized in this system.

Leaf dark respiration (R-dark) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R-dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in R-dark. Area-based R-dark at the prevailing average daily growth temperature (T) of each siteincreased only twofold from the Arctic to the tropics, despite a 20 degrees C increase in growing T (8-28 degrees C). By contrast, R-dark at a standard T (25 degrees C, R-dark(25)) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R-dark(25) at a given photosynthetic capacity (V-cmax(25)) or leaf nitrogen concentration ([N]) than species at warmer sites. R-dark(25) values at any given V-cmax(25) or [N] were higher in herbs than in woody plants. The results highlight variation in R-dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R-dark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).

The Magellan Echellette (MagE) spectrograph is a single-object optical echellette spectrograph for the Magellan Clay telescope. MagE has been designed to have high throughput in the blue; the peak throughput is 22% at 5600 angstrom including the telescope. The wavelength coverage includes the entire optical window (3100 angstrom - 1 mu m). The spectral resolution for a 1" slit is R similar to 4100. MagE is a very simple spectrograph with only four moving parts, prism cross-dispersion, and a vacuum Schmidt camera. The instrument saw first light in November 2007 and is now routinely taking science observations.

The Carnegie Planet Finder Spectrograph (PFS) has been constructed for use with the Magellan telescopes at Las Campanas Observatory in Chile. PFS has been optimized for high-precision measurement of stellar radial velocities in order to support an ongoing search for extrasolar planets. PFS uses an R4 echelle grating and a, prism cross-disperser in a Littrow arrangement to provide complete wavelength coverage between 390 and 620 nm distributed across 58 orders. Spectral resolution is 38,000 when using a 1 arcsec slit. An iodine absorption cell is included in the pre-slit module to allow the superimposition of well-defined absorption features on the stellar spectra. To improve velocity stability, the echelle grating is enclosed in a small vacuum tank with the cross-dispersing prism acting as the vacuum window. The spectrograph is mounted on an invar optical bench that is surrounded by an insulated enclosure with circulating liquid temperature control. Fabrication and assembly have been completed, and testing will soon be underway. Delivery to Las Campanas Observatory is scheduled for late 2008.

A detailed high-resolution spectroscopic analysis is presented for the carbon-rich low-metallicity Galactic halo object CS 22964-161. We have discovered that CS 22964-161 is a double-lined spectroscopic binary and have derived accurate orbital components for the system. From a model atmosphere analysis we show that both components are near the metal-poor main-sequence turnoff. Both stars are very enriched in carbon and in neutron-capture elements that can be created in the s-process, including lead. The primary star also possesses an abundance of lithium close to the value of the "Spite plateau.'' The simplest interpretation is that the binary members seen today were the recipients of these anomalous abundances from a third star that was losing mass as part of its AGB evolution. We compare the observed CS 22964-161 abundance set with nucleosynthesis predictions of AGB stars, discuss issues of envelope stability in the observed stars under mass transfer conditions, and consider the dynamical stability of the alleged original triple star. Finally, we consider the circumstances that permit survival of lithium, whatever its origin, in the spectrum of this extraordinary system.

We present spectroscopic and photometric observations of the eclipsing binary V32 located in the central field of the globular cluster NGC 6397. The variable is a single-line spectroscopic binary with an orbital period of 9.8783 days and a large eccentricity of e = 0.32. Its systemic velocity (gamma = 20.7 km s(-1)) and metallicity ([Fe/H]similar to -1.9) are both consistent with cluster membership. The primary component of the binary is located at the top of the main-sequence turnoff on the cluster color - magnitude diagram. Only a shallow primary eclipse is observed in the light curve. Based on stellar models for an age of 12 Gyr and the mass function derived from the radial velocity curve, we estimate the masses to be M-p = 0.79 M circle dot and M-s = 0.23 M circle dot. The light curve of V32 can be reproduced by adopting R-p = 1.569 R circle dot and R-s = 0.236 R circle dot for the radii and i = 85.44 deg for the system inclination. The system geometry precludes observations of the secondary eclipse. The large eccentricity of the orbit is puzzling given that for metal-poor, halo binaries the transition from circular to eccentric orbit occurs at an orbital period of about 20 days. We suppose that the orbit of V32 was modified relatively recently by dynamical interaction with other cluster star(s). An alternative explanation of the observed eccentricity calls for the presence of a third body in the system.

We present the results of a search for dwarf novae (DNe) in globular clusters (GCs). It is based on the largest available homogeneous sample of observations, in terms of the timespan, number of observations and number of clusters. It includes 16 Galactic GCs and yielded two new certain DNe: M55-CV1 and M22-CV2. All previously known systems located in our fields were recovered, too. We surveyed M4, M5, M10, M12, M22, M30, M55, NGC 288, NGC 362, NGC 2808, NGC 320 1, NGC 4372, NGC 6362, NGC 6752, (o Centauri (NGC 5139) and 47 Tucanae (NGC 104). The discovery of two DNe, namely M55-CV1 and M22-CV2, was already reported by Kaluzny et al. and Pietrukowicz et al., respectively. In the remaining 14 GCs, we found no certain new DNe. Our result raises the total number of known DNe in the Galactic GCs to 12 DNe, distributed among seven clusters. Our survey recovered all three already known erupting cataclysmic variables (CVs) located in our fields, namely M5-V101, M22-CV1, and V4 in the foreground of M30. To assess the efficiency of the survey, we analysed images with inserted artificial stars mimicking outbursts of the prototype DNe SS Cygni and U Geminorum. Depending on the conditions, we recovered between 16-100 per cent of these artificial stars. The efficiency seems to be predominantly affected by duty cycle/time-sampling and much less by distance/magnitude. Except for saturated tiny collapsed cores of M30, NGC 362 and NGC 6752 (and also the dense core of NGC 2808), crowding effects in the V band were avoided by our image subtraction technique augmented with auxiliary unsaturated B-band images. Our results clearly demonstrate that in GCs common types of DNe are very rare indeed. However, great care must be taken before these conclusions can be extended to the CV population in GCs.

We present an analysis of NGC2204-S892 - a new detached eclipsing binary composed of two late K dwarfs. Based on three photometric campaigns launched in 2008 we obtained five light Curves (three in V, one in B and one in I), and derived an orbital period. We also obtained 20 VLT/UVES spectra, enabling accurate radial velocity measurements. The derived masses and radii of the components are consistent with the empirical mass-radius relationship established recently for lower main sequence stars in binary systems; in particular we find that both stars are oversized compared to theoretical models. NGC2204-S892 is very active: both components show variable emission in H alpha and H beta and are heavily spotted, causing the light curve to show appreciable changes on a timescale of weeks. Our results add to the increasing evidence that the observed inflation of the radii of K and M stars is related to high levels of magnetic activity.

We report time-series photometry for 16 variable stars located in the central part of the globular cluster NGC 6752. The sample includes 13 newly identified objects. The precision of our differential photometry ranges from 1 mmag at V = 14.0 mag to 10 mmag at V = 18.0 mag. We detected four low amplitude variables located on the extended horizontal branch (EHB) of the cluster. They are candidate binary stars harboring sdB subdwarfs. A candidate degenerate binary was detected about 2 mag below the faint end of the EHB. The star is blue and its light curve is modulated with a period of 0.47 d. We argue that some of the identified variable red/blue stragglers are ellipsoidal binaries harboring degenerate stars. They have low amplitude sine-like light curves and periods from a few hours to a few days. Spectroscopic observations of such objects may lead to the detection of detached inactive binaries harboring stellar mass black holes or neutron stars. No binaries of this kind are known so far in globular clusters although their existence is expected based on the common occurrence of accreting LMXBs and millisecond pulsars. An eclipsing SB1 type binary was identified on the upper main sequence of the cluster. We detected variability of optical counterparts to two X-ray sources located in the core region of NGC 6752. The already known cataclysmic variable Bl=CX4 experienced a dwarf nova type outburst. The light curve of an optical counterpart to the X-ray source CX19 exhibited modulation with a period of 0.113 d. The same periodicity was detected in the HST-ACS data. The variable is located on the upper main sequence of the cluster. It is an excellent candidate for a close degenerate binary observed in quiescence.

Aims. Our aims are twofold. First we aim to evaluate the robustness and accuracy of stellar parameters and detailed elemental abundances that can be derived from high-resolution spectroscopic observations of microlensed dwarf and subgiant stars. We then aim to use microlensed dwarf and subgiant stars to investigate the abundance structure and chemical evolution of the Milky Way Bulge. Contrary to the cool giant stars, with their extremely crowded spectra, the dwarf stars are hotter, their spectra are cleaner, and the elemental abundances of the atmospheres of dwarf and subgiant stars are largely untouched by the internal nuclear processes of the star.