We present chemical abundances in a sample of luminous cool stars located within 30 pc of the Galactic Center. Abundances of carbon, nitrogen, oxygen, calcium, and iron were derived from high-resolution infrared spectra in the H- and K-bands. The abundance results indicate that both [O/Fe] and [Ca/Fe] are enhanced respectively by averages of +0.2 and +0.3 dex, relative to either the Sun or the Milky Way disk at near solar Fe abundances. The Galactic Center stars show a nearly uniform and nearly solar iron abundance. The mean value of A(Fe) = 7.59 +- 0.06 agrees well with previous work. The total range in Fe abundance among Galactic Center stars, 0.16 dex, is significantly narrower than the iron abundance distributions found in the literature for the older bulge population. Our snapshot of the current-day Fe abundance within 30 pc of the Galactic Center samples stars with an age less than 1 Gyr; a larger sample in time (or space) may find a wider spread in abundances.
Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) dominate the star formation rate budget of the universe at z > 1, yet no local measurements of their heavy element abundances exist. We measure nuclear or near-nuclear oxygen abundances in a sample of 100 star-forming LIRGs and ULIRGs using new, previously published, and archival spectroscopy of strong emission lines (including [O II] 3727, 3729 A) in galaxies with redshifts <z> ~ 0.1. When compared to local emission-line galaxies of similar luminosity and mass (using the near-infrared luminosity-metallicity and mass-metallicity r…
We examine the effects of cooling flows on the T_X-L_Bol relation for a sample of the most X-ray luminous (L_Bol > 10^45 erg/s) clusters of galaxies known. Using high-quality ASCA X-ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X-ray properties of the clusters and show that this reduces the previously-noted dispersion in the T_X-L_Bol relationship. More importantly, the slope of the relationship is flattened from L_Bol \propto T_{X}^3 to approximately L_Bol\propto T_{X}^2, in agreement with recent theoretical models which include the effects of shoc…
Using broadband optical imaging and Chandra X-ray data for a sample of 46 cluster central dominant galaxies (CDGs), we investigate the connection between star formation, the intracluster medium (ICM), and the central active galactic nucleus (AGN). We report the discovery of a remarkably sharp threshold for the onset of star formation that occurs when the central cooling time of the hot atmosphere falls below ~ 5x10^8 yr, or equivalently when the central entropy falls below ~ 30 keV cm^2. In addition to this criterion, star formation in cooling flows also appears to require that the X-ray and g…
We derive oxygen abundances for a sample of 40 luminous (M_{B} < -19), star-forming, mostly disk, field galaxies with redshifts in the range 0.2 < z < 0.8$, with a median of <z> = 0.45. Oxygen abundances, relative to hydrogen, of the interstellar emitting gas are estimated by means of the empirically calibrated strong emission line ratio technique. The derived (12+log(O/H)) values range from 8.4 to 9.0, with a median of 8.7. Twenty of these galaxies have securely measured rotation velocities, in the range 50--244 km/s. The measured emission line equivalent widths and diagnostic ratios for the …
FUSE ultraviolet spectra of 8 giant and supergiant stars reveal that high temperature (3 X 10^5 K) atmospheres are common in luminous cool stars and extend across the color-magnitude diagram from Alpha Car (F0 II) to the cool giant Alpha Tau (K5 III). Emission present in these spectra includes chromospheric H-Lyman Beta, Fe II, C I, and transition region lines of C III, O VI, Si III, Si IV. Emission lines of Fe XVIII and Fe XIX signaling temperatures of ~10^7 K and coronal material are found in the most active stars, Beta Cet and 31 Com. A short-term flux variation, perhaps a flare, was detect…
We discuss the nature of non-LTE effects affecting abundance analysis of cool stars. The departures from LTE of importance for the B I lines in solar-type stars are described and some new results are presented. Boron abundances derived under the LTE assumption have significant systematic errors, especially for metal-poor stars. For beryllium, current results suggest that departures from LTE will not affect abundance analysis significantly.
Abundance analysis of the cool extreme helium (EHe) star LSS 3378 is presented. The abundance analysis is done using LTE line formation and LTE model atmospheres constructed for EHe stars. The atmosphere of LSS 3378 shows evidence of H-burning, He-burning, and s-process nucleosynthesis. The derived abundances of iron-peak and alpha-elements indicate absence of selective fractionation or any other processes that can distort chemical composition of these elements. Hence, the Fe abundance (log epsilon(Fe) = 6.1) is adopted as an initial metallicity indicator. The measured abundances of LSS 3378 a…
We review the field of abundance determinations of elements in cool stars, with special interest paid to determinations based on analyses of high-resolution, 1-5 micron spectra. We discuss the current status, problems, and challenges of exploring high-resolution, near-infrared spectra. In particular, advantages and drawbacks are pointed out. A few examples of current, chemical-abundance determinations are high-lighted and, finally, we discuss the development
We identified a possible origin of the difficulty in abundance analysis of cool luminous stars. We found purely empirically that there is a limit of logW/nu = -4.75 (W: equivalent width, nu: wavenumber) above which the observed lines do not follow the line formation theory based on the classical micro-turbulent model and that the abundance analysis can be done only with the lines of logW/nu < -4.75. The C, O, and their isotopic abundances determined from such weak lines of CO and OH in 23 K - M giants are roughly consistent with the predictions of evolutionary models. However, the stronger lin…
We present [Ffe/H] abundance results that involve a sample of stars with a wide range in luminosity from luminous giants to stars near the turnoff in a globular cluster. Our sample of 25 stars in M71 includes 10 giant stars more luminous than the RHB, 3 horizontal branch stars, 9 giant stars less luminous than the RHB, and 3 stars near the turnoff. We analyzed both Fe I and Fe II lines in high dispersion spectra observed with HIRES at the W. M. Keck Observatory. We find that the [Fe/H] abundances from both Fe I and Fe II lines agree with each other and with earlier determinations. Also the [Fe…
Iron abundance distribution is now known for 12 clusters of galaxies. For some clusters (e.g. Centaurus) the observed abundance increases toward the cluster center, while for the others (e.g. Coma and Hydra-A) no significant inhomogeneity was observed. In order to understand this difference, we investigate the influence of cooling flow and turbulence produced by galactic motion on the iron abundance distribution by simple spherical models. We show that the cooling flow has a significant effect to flatten the iron abundance distribution if the flow velocity is sufficiently large. Further, by ap…
We have derived azimuthally-averaged radial iron abundance profiles of the X-ray gas contained within 12 clusters of galaxies with redshift 0.03 < z < 0.2 observed with BeppoSAX. We find evidence for a negative metal abundance gradient in most of the clusters, particularly significant in clusters that possess cooling flows. The composite profile from the 12 clusters resembles that of cluster simulations of Metzler & Evrard (1997). This abundance gradient could be the result of the spatial distribution of gas-losing galaxies within the cluster being more centrally condensed than the primordial …
We report on new VLA radio observations of the distant cluster RX J1347.5-1145, which is the most luminous in X-rays. We aim at investigating the possible presence of diffuse and extended radio emission in this very peculiar system which shows both a massive cooling flow and merging signatures. New low resolution (~18 arcsec) VLA radio observations of this cluster are combined with higher resolution (~2 arcsec) data available in the VLA archive. We discover the presence of a diffuse and extended (~500 kpc) radio source centered on the cluster, unrelated to the radio emission of the central AGN…
The present study of spectra of twelve metal-rich cool dwarf stars, carefully selected in order to cover a range of temperatures (~4400 - 6000 K), is a follow up on Feltzing & Gustafsson (1998, A&AS 129, 237) with the aim to understand the apparent over-ionization and anomalous elemental abundances found by them for the K dwarf stars in their sample. Our method of analysis employs synthetic spectra of the full spectrum both to constrain the continuum level and to derive abundances. It is shown that by using this method and imposing a strict excitation equilibrium (possible to do because of the…
We analyze the Ginga LAC and Einstein SSS spectra of four cooling flow clusters, A496, A1795, A2142 and A2199, each of which shows firm evidence of a relatively cool component. The inclusion of such cool spectral components in joint fits of SSS and LAC data leads to somewhat higher global temperatures than are derived from the high energy LAC data alone. We find little evidence of cool emission outside the SSS field of view. Metal abundances appear to be centrally enhanced in all four cluster, with varying degrees of model dependence and statistical significance: the evidence is statistically …
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…
We report the first identification of the Eu III lambda 6666.317 line in optical spectra of CP stars. This line is clearly present in the spectra of HR 4816, 73 Dra, HR 7575, and beta CrB, while it is marginally present or absent in spectra of the roAp stars alpha Cir, gamma Equ, BI Mic, 33 Lib, and HD 24712.
Hot, X-ray emitting gaseous halos around massive elliptical galaxies are a result of both stellar mass loss and inflow toward the overdensity from which giant ellipticals and their associated galaxy groups formed. The metal abundance in this gas contains important information about early star formation and past supernova activity. We find that Type II supernovae based on a Salpeter IMF, plus a small number of additional Type Ia supernovae, can explain the the density, temperature and abundance profiles currently observed in gaseous halos around massive ellipticals. Within the central, opticall…
We have analyzed a sample of nearby cool and warm infrared (IR) galaxies using photometric and structural parameters. The set of measures include far-infrared color ($C = \log_{10}[S_{60μm}/S_{100μm}]$), total IR luminosity ($L_{TIR}$), radio surface brightness as well as radio, near-infrared, and optical sizes. In a given luminosity range cool and warm galaxies are considered as those sources that are found approximately $1 σ$ below and above the mean color in the far-infrared $C - L_{TIR}$ diagram. We find that galaxy radio surface brightness is well correlated with color whereas size is les…
We present Gemini near-infrared spectroscopic observations of six luminous quasars at z=5.8$\sim$6.3. Five of them were observed using Gemini-South/GNIRS, which provides a simultaneous wavelength coverage of 0.9--2.5 $μ$m in cross dispersion mode. The other source was observed in K band with Gemini-North/NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar with a typical value of $\sim$4 Z_{\sun}, and a comparison with low-redshift observations shows…
Although only about 5 percent of the total baryonic mass in luminous elliptical galaxies is in the form of cooled interstellar gas, it is concentrated within the optical effective radius r_e where it influences the local dynamical mass. The mass of cooled gas must be spatially distributed since it greatly exceeds the masses of central black holes. We explore here the proposition that a population of low mass, optically dark stars is created from the cooled gas. We consider a wide variety of radial distributions for the interstellar cooling, but only a few are consistent with observed X-ray sur…
We present a small data base of homogeneously derived photospheric element abundances of DZ white dwarfs and related objects. Our previous investigations are supplemented with the analysis of ultraviolet spectra for nine white dwarfs. Of particular interest is the detection of Lalpha absorption in van Maanen 2 and a determination of the effective temperature of this star. The new value is about 1000K lower than previous results due to the strong ultraviolet absorption by metals which has to be considered consistently. The metal abundances of our sample stars are compatible with the predictions…
We present far-UV spectroscopy of the giant elliptical galaxy NGC 1399, obtained with the Far Ultraviolet Spectroscopic Explorer. Of all quiescent ellipticals, NGC 1399 has the strongest known ``UV upturn'' -- a sharp spectral rise shortward of 2500 A. It is now well-established that this emission comes from hot horizontal branch (HB) stars and their progeny; however, the chemical composition of these stars has been the subject of a long-standing debate. For the first time in observations of any elliptical galaxy, our spectra clearly show photospheric metallic absorption lines within the UV up…
Oxygen abundances [12+log(O/H)] in the interstellar medium of a large sample of distant (z>0.4) luminous infrared galaxies (LIRGs) were estimated from their extinction corrected emission-line ratios, on the basis of the VLT/FORS2 spectra with good S/N and moderate resolution. These LIRGs were selected from ISOCAM deep survey fields (CFRS, UDSR, UDSF). They show oxygen abundances ranging from 8.36 to 8.93, with a median value of 8.67, which is 0.5 lower than that of the local bright disks (i.e., L*) at the given magnitude. A significant fraction of distant large disks are indeed LIRGs. Such mas…
Recent observations with TRACE reveal that the time delay between the appearance of a cooling loop in different EUV temperature filters is proportional to the loop length, dt_12 ~ L. We model this cooling delay in terms of radiative loss and confirm this linear relationship theoretically. We derive an expression that can be used to constrain the coronal iron enhancement alpha_Fe=A_Fe^cor/A_Fe^Ph relative to the photospheric value as function of the cooling delay dt_12, flux F_2, loop width w, and filling factor q_w < 1. With this relation we find upper limits on the iron abundance enhancement …
We use the analysis of the heavy element abundances (C, N, O, S) in circumstellar nebulae around Luminous Blue Variables to infer the evolutionary phase in which the material has been ejected. (1) We discuss the different effects that may have changed the gas composition of the nebula since it was ejected (2) We calculate the expected abundance changes at the stellar surface due to envelope convection in the red supergiant phase. If the observed LBV nebulae are ejected during the RSG phase, the abundances of the LBV nebulae require a significantly smaller amount of mass to be lost than assumed…
We present a Chandra study of 38 X-ray luminous clusters of galaxies in the ROSAT Brightest Cluster Sample (BCS) that lie at z~0.15-0.4. We find that the majority of clusters at moderate redshift generally have smooth, relaxed morphologies with some evidence for mild substructure perhaps indicative of recent minor merger activity. Using spatially-resolved spectral analyses, cool cores appear to still be common at these redshifts. At a radius of 50 kpc, we find that at least 55 per cent of the clusters in our sample exhibit signs of mild cooling [t(cool)<10 Gyr], while in the central bin at lea…
We perform a spatially resolved X-ray spectroscopic study of a set of 18 relaxed clusters of galaxies with gas temperatures below 4 keV. Spectral analysis was done using ASCA/SIS data coupled with the spatial information contained in ROSAT/PSPC and Einstein/IPC observations. We derive the temperature profiles using single-temperature fits and also correct for the presence of cold gas at the cluster centers. For all of the clusters in the sample, we derive Si and Fe abundance profiles. For a few of the clusters, we also derive Ne and S abundance profiles. We present a comparison of the elementa…
Extreme helium stars (EHe) with effective temperatures from 8000K to 13000K are among the coolest EHe stars and overlap the hotter R CrB stars in effective temperature. The cool EHes may represent an evolutionary link between the hot EHes and the R CrBs. Abundance analyses of four cool EHes are presented. To test for an evolutionary connection, the chemical compositions of cool EHes are compared with those of hot EHes and R CrBs. Relative to Fe, the N abundance of these stars is intermediate between those of hot EHes and R CrBs. For the R CrBs, the metallicity M derived from the mean of Si and…
We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC 1313, which contains two "ultra-luminous" X-ray (ULX) sources. We measure isotropic luminosities of L_X = 2.0 * 10^(40) erg/s and L_X = 6.6 * 10^(39) erg/s for NGC 1313 X-1 and X-2 (0.2-10.0 keV, assuming a distance of 3.7 Mpc). The spectra statistically require soft and hard spectral components to describe the continuum emission; some prior studies of ULXs have claimed cool soft components with lower statistics. The improvement over several single-component models exceeds the 8 sigma level of confidence for X-1; the im…
We review observations on the chemical enrichment of the intracluster medium (ICM) performed using BeppoSAX MECS data. The picture emerging is that non-cooling flow clusters have flat metallicity profiles, whereas a strong enhancement in the abundance is found in the central regions of the cooling flow clusters. All the non-cooling flow clusters present evidence of recent merger activity suggesting that the merger events redistributes efficiently the metal content of the ICM. The observed abundance excess in the central regions of cooling flow clusters is probably due to metals ejected from th…
We have studied the infrared properties of the brightest cluster galaxies (BCGs) located in the cores of X-ray-luminous clusters at 0.15 < z < 0.35. The majority of the BCGs are not particularly infrared-luminous compared with other massive early-type galaxies, suggesting that the cluster environment has little influence on the infrared luminosities of the BCGs. The exceptions, however, are the BCGs in the three X-ray-brightest clusters in the sample, A1835, Z3146, and A2390. These BCGs have a prominent far-infrared peak in their spectral energy distributions (SEDs), and two of them (those in …
We present an analysis of CH band strengths in Keck LRIS spectra of a sample of 81 stars in M13 within 2 magnitudes of the main-sequence turnoff. The subgiants clearly exhibit a substantial (a factor of ~ 6) spread in [C/Fe]. Moreover, the bulk of the subgiants possess C abundances larger than those found among their more luminous counterparts. The turnoff stars themselves are too warm for appreciable CH formation, but the relatively small range in the observed CH band strength for stars just below the turnoff nevertheless translates into this same spread in [C/Fe]. Still fainter, the sample s…
The WARPS team reviews the properties and history of discovery of ClJ0152.7-1357, an X-ray luminous, rich cluster of galaxies at z=0.833. At L_X = 8 x 10^44 h^(-2) erg/s (0.5-2.0 keV) ClJ0152.7-1357 is the most X-ray luminous cluster known at redshifts z>0.55. The high X-ray luminosity of the system suggests that massive clusters may begin to form at redshifts considerably greater than unity. This scenario is supported by the high degree of optical and X-ray substructure in ClJ0152.7-1357, which is similarly complex as that of other X-ray selected distant clusters and consistent with the pictu…
Calculations of the statistical equilibrium of magnesium in the solar photosphere have shown that NLTE populations hardly affect Mg line formation in the Sun. However, in metal-poor dwarfs and giants the influence of electron collisions is reduced, and the ultraviolet radiation field, enhanced due to reduced background line opacity, results in more pronounced NLTE effects. In thephotosphere of a cool star excitation and ionization due to collisions with neutral hydrogen can outweigh electron collisions. Analyses based on NLTE populations lead to significantly higher Mg abundances than those ca…
We present the X-ray properties and scaling relations of a flux-limited morphology-unbiased sample of 12 X-ray luminous galaxy clusters at redshift around 0.2 based on XMM-Newton observations. The scaled radial profiles are characterized by a self-similar behavior at radii outside the cluster cores (>0.2 r500) for the temperature, surface brightness, entropy, gas mass and total mass. The cluster cores contribute up to 70% of the bolometric X-ray luminosity. The X-ray scaling relations and their scatter are sensitive to the presence of the cool cores. Using the X-ray luminosity corrected for th…
Hydrodynamical SPH simulations of galaxy clusters are used to investigate the metal enrichment of the intracluster medium. The final metallicity abundances of the simulated clusters are determined according to the numerical resolution and a number of model parameters. For a fiducial set of model prescriptions the results of the simulations indicate iron abundances in broad agreement with data. Final X-ray properties are not sensitive to the heating of the ICM. This supports a scenario where the ICM evolution of cool clusters is driven by radiative cooling.
The high resolution spectra of a R CrB type star Z UMi are analysed. The atmospheric parameters of Z UMi are estimated: Teff=5250+/-250K and log g=0.5+/-0.3. This places Z UMi among the coolest R CrB stars. The hydrogen deficiency of Z UMi is confirmed. The abundances of other elements resemble those found for the minority group of R CrB stars. We note very low iron abundance, [Fe/H]=-1.85, and an excess of lithium, [Li/Fe]=+1.9.
From high resolution spectra of 61 cool dwarfs and giants, Mg isotopic abundance ratios 24Mg:25Mg:26Mg are derived from spectral synthesis of the MgH A-X lines near 5140A. Our sample spans the range -2.5 < [Fe/H] < 0.1, including the first measurements of Mg isotope ratios in stars with metallicities below [Fe/H]=-2.0. We confirm the decrease in 25,26Mg/24Mg with decreasing [Fe/H] as predicted by recent models of Galactic chemical evolution where the Mg isotopes are produced in massive stars. A subset of kinematically identified thin disk stars have Mg isotope ratios in excellent agreement wit…
We study the formation of B I lines in a grid of cool stellar model atmospheres without the assumption of local thermodynamic equilibrium (LTE). The non-LTE modelling includes the effect of other lines blending with the B I resonance lines. Except for the cases where the B I lines are very strong, the departures from LTE relevant for the resonance lines can be described as an overionisation effect and an optical-pumping effect. This causes the lines to be weaker than in LTE so that an abundance analysis assuming LTE will underestimate stellar boron abundances. We present non-LTE abundance corr…
We explore the formation of alpha-enhanced and metal-rich stellar populations in the nuclei of luminous ellipticals under the assumption of two extreme galaxy formation scenarios based on hierarchical clustering, namely a fast clumpy collapse and the merger of two spirals. We investigate the parameter space of star formation time-scale, IMF slope, and stellar yields. In particular, the latter add a huge uncertainty in constraining time-scales and IMF slopes. We find that -- for Thielemann, Nomoto & Hashimoto nucleosynthesis -- in a fast clumpy collapse scenario an [alpha/Fe] overabundance of a…
Based on a new and large sample of optical and near-infrared spectra obtained at the Mount Stromlo and Siding Spring Observatories (Lancon & Wood 1998; Lancon & Wood, in preparation), spectrophotometric properties of cool oxygen- and carbon-rich Long Period Variables and supergiants are presented. Temperatures of oxygen-rich stars are assigned by comparison with synthetic spectra computed from up-to-date oxygen-rich model atmosphere grids. The existence of reliable optical and near-infrared temperature indicators is investigated. A narrow relation between the bolometric correction BC(I) and th…
Previous studies of the Fe abundances in the hot gas of galaxies and groups have reported conflicting results with most studies finding very sub-solar Fe abundances that disagree with standard theory. To investigate the possible role of Fe abundance gradients on these measurements we present deprojection analysis of the ROSAT PSPC data of 10 of the brightest cooling flow galaxies and groups. The PSPC allows for spatially resolved spectral analysis on a half-arcminute scale, and interesting constraints on both the temperatures and Fe abundances are possible because the ~1 keV temperatures of th…
We present abundance measurements, based on high-resolution optical spectroscopic data obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on Kueyen (Very Large Telescope UT2), for ten stars in the extended blue horizontal branch of the Galactic globular cluster NGC 1904 (M79). In agreement with previous findings for other clusters, we obtain normal abundances for stars cooler than Teff ~ 11,000 K and largely anomalous abundances for hotter stars: large He depletions, and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si and Ca are roughly normal, in the hot st…
We determine X-ray temperatures and abundances for elliptical galaxies drawn from a complete, optically selected sample. The optical magnitude-limited sample consists of 43 galaxies, complete to a (corrected) B magnitude of m_B^o=11.36. Of these, 30 have enough X-ray spectral counts to allow temperature determinations. We find that the temperatures of the X-ray emitting gas in these ellipticals are correlated with the central stellar velocity dispersions: T ~ sigma^1.45; this is a shallower trend than the simple thermal relation T ~ sigma^2. The diffuse gas is substantially hotter than the kin…
We find a new two-temperature hot branch of equilibrium solutions for stationary accretion disks around black holes. In units of Eddington accretion rate defined as $10L_{\rm Edd}/c^2$, the accretion rates to which these solutions correspond are within the range $\dot{m}_1 \la \dot{m} \la 1$, here $\dot{m}_1$ is the critical rate of advecti$. In these solutions, the energy loss rate of the ions by Coulomb energy transfer between the ions and electrons is larger than the viscously heating rate and it is the advective heating together with the viscous dissipation that balances the Coulomb coolin…
We have carried out a study of the chemical abundances of $^1$H, $^4$He, $^{12}$C, $^{13}$C, $^{14}$N, $^{15}$N, $^{16}$O, $^{17}$O, $^{20}$Ne and $^{22}$Ne in symbiotic stars (SSs) by means of a population synthesis code. We find that the ratios of the number of O-rich SSs to that of C-rich SSs in our simulations are between 3.4 and 24.1, depending on the third dredge-up efficiency $λ$ and the terminal velocity of the stellar wind $v(\infty)$. The fraction of SSs with $extrinsic$ C-rich cool giants in C-rich cool giants ranges from 2.1% to 22.7%, depending on $λ$, the common envelope algorith…
We report progress in the calibration of a method to determine cool dwarf star metallicities using molecular band strength indices. The molecular band index to metallicity relation can be calibrated using chemical abundances calculated from atomic line equivalent width measurements in high resolution spectra. Building on previous work, we have measured Fe and Ti abundances in 32 additional M and K dwarf stars to extend the range of temperature and metallicity covered. A test of our analysis method using warm star - cool star binaries shows we can calculate reliable abundances for stars warmer …
We investigate the thermal and dynamical evolution of primordial gas clouds in the universe after decoupling. Comparing the time-scale of dynamical evolution with that of fragmentation, we can estimate the typical fragmentation scale. We propose the following scenario of the formation process of first luminous objects consisting of large number stars. First, by pancake collapse of the overdensity regions in the expanding universe or collision between clouds in potential wells, quasi-plane shocks form. If the shock-heated temperature is higher than about $10^4$ K, the postshock gas cools down t…
Building upon earlier observations which demonstrate substantial star-to-star differences in the carbon abundances of M13 subgiants, we present new Keck LRIS spectra reaching more that 1.5 mag below the M13 main-sequence turn-off (to V ~ 20). Our analysis reveals a distribution of C abundances similar to that found among the subgiants, implying little change in the compositions of the M13 stars at least through the main-sequence turn-off. We presume these differences to be the result of some process operating early in the cluster history. Additional spectra of previously studied bright M13 gia…
