Solange V. Ramirez

Abundances in Stars from the Red Giant Branch Tip to Near the Main-Sequence Turnoff in M71. III. Abundance Ratios*

We present [Fe/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, three horizontal branch stars, nine giant stars less luminous than the RHB, and three 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/H] obtained from Fe I and Fe II lines is constant within the rather small uncertainties for this group of stars over the full range in Teff and luminosity, suggesting that non-LTE effects are negligible in our iron abundance determination. In this globular cluster, there is no difference among the mean [Fe/H] of giant stars located at or above the RHB, RHB stars, giant stars located below the RHB and stars near the turnoff.

The NASA Exoplanet Archive: Data and Tools for Exoplanet Research

ABSTRACT.We describe the contents and functionality of the NASA Exoplanet Archive, a database and toolset funded by NASA to support astronomers in the exoplanet community. The current content of the database includes interactive tables containing properties of all published exoplanets, Kepler planet candidates, threshold-crossing events, data validation reports and target stellar parameters, light curves from the Kepler and CoRoT missions and from several ground-based surveys, and spectra and radial velocity measurements from the literature. Tools provided to work with these data include a transit ephemeris predictor, both for single planets and for observing locations, light curve viewing and normalization utilities, and a periodogram and phased light curve service. The archive can be accessed at http://exoplanetarchive.ipac.caltech.edu.

Near-Infrared and Optical Morphology of Spiral Galaxies

We announce the initial release of data from the Ohio State University (OSU) Bright Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications from Sa through Scd appear about one T type earlier in the H band than in the B band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B- and H-band images for a set of 17 galaxies chosen as type examples and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength.

PLANETARY CANDIDATES OBSERVED BYKEPLER. VI. PLANET SAMPLE FROM Q1–Q16 (47 MONTHS)

We provide updates to the Kepler planet candidate sample based upon nearly two years of high-precision photometry (i.e., Q1-Q8). From an initial list of nearly 13,400 threshold crossing events, 480 new host stars are identified from their flux time series as consistent with hosting transiting planets. Potential transit signals are subjected to further analysis using the pixel-level data, which allows background eclipsing binaries to be identified through small image position shifts during transit. We also re-evaluate Kepler Objects of Interest (KOIs) 1-1609, which were identified early in the mission, using substantially more data to test for background false positives and to find additional multiple systems. Combining the new and previous KOI samples, we provide updated parameters for 2738 Kepler planet candidates distributed across 2017 host stars. From the combined Kepler planet candidates, 472 are new from the Q1-Q8 data examined in this study. The new Kepler planet candidates represent ~40% of the sample with R P ~ 1 R ? and represent ~40% of the low equilibrium temperature (T eq < 300?K) sample. We review the known biases in the current sample of Kepler planet candidates relevant to evaluating planet population statistics with the current Kepler planet candidate sample.

CHEMICAL ABUNDANCES OF LUMINOUS COOL STARS IN THE GALACTIC CENTER FROM HIGH-RESOLUTION INFRARED SPECTROSCOPY

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.

Characterizing the Variability of Stars with Early-release Kepler Data

We present a variability analysis of the early-release first quarter of data publicly released by the Kepler project. Using the stellar parameters from the Kepler Input Catalog, we have separated the sample into 129,000 dwarfs and 17,000 giants and further sub-divided the luminosity classes into temperature bins corresponding approximately to the spectral classes A, F, G, K, and M. Utilizing the inherent sampling and time baseline of the public data set (30 minute sampling and 33.5 day baseline), we have explored the variability of the stellar sample. The overall variability rate of the dwarfs is 25% for the entire sample, but can reach 100% for the brightest groups of stars in the sample. G dwarfs are found to be the most stable with a dispersion floor of σ ~ 0.04 mmag. At the precision of Kepler, >95% of the giant stars are variable with a noise floor of ~0.1 mmag, 0.3 mmag, and 10 mmag for the G giants, K giants, and M giants, respectively. The photometric dispersion of the giants is consistent with acoustic variations of the photosphere; the photometrically derived predicted radial velocity distribution for the K giants is in agreement with the measured radial velocity distribution. We have also briefly explored the variability fraction as a function of data set baseline (1-33 days), at the native 30 minute sampling of the public Kepler data. To within the limitations of the data, we find that the overall variability fractions increase as the data set baseline is increased from 1 day to 33 days, in particular for the most variable stars. The lower mass M dwarf, K dwarf, and G dwarf stars increase their variability more significantly than the higher mass F dwarf and A dwarf stars as the time baseline is increased, indicating that the variability of the lower mass stars is mostly characterized by timescales of weeks while the variability of the higher mass stars is mostly characterized by timescales of days. A study of the distribution of the variability as a function of galactic latitude suggests that sources closer to the galactic plane are more variable. This may be the result of sampling differing populations (i.e., ages) as a function of latitude or may be the result of higher background contamination that is inflating the variability fractions at lower latitudes. A comparison of the M dwarf statistics to the variability of 29 known bright M dwarfs indicates that the M dwarfs are primarily variable on timescales of weeks or longer presumably dominated by spots and binarity. On shorter timescales of hours, which are relevant for planetary transit detection, the stars are significantly less variable, with ~80% having 12 hr dispersions of 0.5 mmag or less.

A CATALOG OF X-RAY POINT SOURCES FROM TWO MEGASECONDS OF CHANDRA OBSERVATIONS OF THE GALACTIC CENTER

We present a catalog of 9017 X-ray sources identified in Chandra observations of a 2 ◦ × 0. 8 field around the Galactic center. This enlarges the number of known X-ray sources in the region by a factor of 2.5. The catalog incorporates all of the ACIS-I observations as of 2007 August, which total 2.25 Ms of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities of 4 × 10 32 erg s −1 (0.5–8.0 keV; 90% confidence) over an area of 1 deg 2 , and up to an order of magnitude more sensitive in the deepest exposure (1.0 Ms) around Sgr A ∗ . The positions of 60% of our sources are accurate to <1 �� (95% confidence), and 20% have positions accurate to < 0. 5. We search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. We also find one source, CXOUGC J174622.7−285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. We compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8σ evidence for excesses in the numbers of X-ray sources in the region of recent star formation encompassed by the Arches, Quintuplet, and Galactic center star clusters. These excess sources are also seen in the luminosity distribution of the X-ray sources, which is flatter near the Arches and Quintuplet than elsewhere in the field. These excess point sources, along with a similar longitudinal asymmetry in the distribution of diffuse iron emission that has been reported by other authors, probably have their origin in the young stars that are prominent at l ≈ 0. 1.

Really cool stars and the star formation history at the Galactic Center

We present ?/?? = 550-1200 near-infrared H and K spectra for a magnitude-limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ?5 pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the H-R diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC. We find that (1) roughly 75% of the stars formed in the central few parsecs are older than 5 Gyr; (2) the star formation rate (SFR) is variable over time, with a roughly 4 times higher SFR in the last 100 Myr compared to the average SFR; (3) our model can match dynamical limits on the total mass of stars formed only by limiting the initial mass function to masses above 0.7 M? (this could be a signature of mass segregation or of the bias toward massive star formation from the unique star formation conditions in the GC); (4) blue supergiants account for 12% of the total sample observed, and the ratio of red to blue supergiants is roughly 1.5; and (5) models with isochrones with [Fe/H] = 0.0 over all ages fit the stars in our H-R diagram better than models with lower [Fe/H] in the oldest age bins, consistent with the finding of Ram?rez et al. that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].

Stellar Archaeology: A Keck Pilot Program on Extremely Metal-Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523

We present a detailed abundance analysis, including spectral syntheses, of a very metal-poor ([Fe/H] -2.7) peculiar main-sequence star (HE 0024-2523) detected during the course of the Keck Pilot Program. Radial velocities of this star were obtained during four different observing runs over a time span of 1.1 yr and demonstrate that it is clearly a short-period spectroscopic binary. An orbital solution was obtained, and orbital parameters were determined with high precision. The rotational velocity was also measured (vrot sin i = 9.7 ? 1.5 km s-1); rotation appears likely to be synchronous with the orbit. The abundance analysis and spectral syntheses indicate that the object is a CH star characterized by extreme s-process enrichment, likely due to mass accretion from an evolved companion that has now probably become a white dwarf. The lead (Pb) abundance of (HE 0024-2523) is very high, the same as that of the recently discovered lead-rich, metal-poor star CS 29526-110, [Pb/Fe] = +3.3. The abundance ratio of the heavy to light s-elements, as characterized by Pb and Ba, [Pb/Ba] = +1.9, is the highest yet found for any metal-poor star and is about 0.7 dex higher than that of CS 29526-110. On the basis of the measured isotopic ratio of carbon (C12/C13 ~ 6) we argue that the mass donor must have had an original mass of at least ~3 M?. The unusually short period of this CH star suggests that it underwent a past common-envelope phase with its evolved companion. Our results are compared with the latest available models for asymptotic giant branch yields and s-process nucleosynthesis. We also discuss the possible connection between HE 0024-2523, the lithium depletion of halo stars, and halo blue straggler formation.

Near- and mid-infrared photometry of the pleiades and a new list of substellar candidate members

We make use of new near- and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main-sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near- and mid-IR photometry extend effectively 2 mag deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low-mass and substellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than K_s = 14 (corresponding to 0.1 M_☉). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 M_☉. We also use new IRAC data, in particular the images obtained at 8 μm, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that—with one exception—a sample of low-mass stars recently identified as having 24 μm excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high-mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.