Results for "R. M. Rich"

total 288155took 0.19s
Abundances of Stars in the Galactic Bulge Obtained Using the Keck TelescopeMay 06 2000We report on detailed abundances of giants in the Galactic bulge, measured with the HIRES echelle spectrograph on the 10-m Keck telescope. We also review other work on the bulge field population and globular clusters using Keck/HIRES. Our new spectra ... More
3-Dimensional Kinematics in low foreground extinction windows of the Galactic Bulge: Radial Velocities for 6 bulge fieldsFeb 27 2012The detailed structure of the Galactic bulge still remain uncertain. The strong difficulties of obtaining observations of stars in the Galactic bulge have hindered the acquisition of a kinematic representation for the inner kpc of the Milky Way. The observation ... More
High resolution infrared spectra of NGC 6440 and NGC 6441: two massive Bulge Globular ClustersMay 22 2008Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the 1.5-1.8 micron range for giant stars in the massive bulge globular clusters NGC6440 and NGC6441. We report the first high dispersion abundance for NGC6440, ... More
High resolution near-IR spectra of NGC 6624 and NGC 6569Mar 01 2011We present the first abundances analysis based on high-resolution infrared (IR) echelle spectra of NGC 6569 and NGC 6624, two moderately reddened globular clusters located in the outer bulge of the Galaxy. We find [Fe/H]=-0.79$\pm$0.02 dex and [Fe/H]=-0.69$\pm$0.02 ... More
The Stellar Content of the Southern Tail of NGC 4038/9 and a Revised DistanceNov 09 2003We have used the Hubble Space Telescope and Wide Field Planetary Camera 2 to image the putative tidal dwarf galaxy located at the tip of the Southern tidal tail of NGC 4038/9, the Antennae. We resolve individual stars, and identify two stellar populations. ... More
High resolution infrared spectra of NGC 6342 and NGC 6528: two moderately reddened Bulge Globular ClustersOct 21 2004Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the range 1.5-1.8 micron for the moderately reddened bulge globular clusters NGC 6342 and NGC 6528, finding [Fe/H]= -0.60 and -0.17 dex, respectively. We measure ... More
K Giants in Baade's Window. I. Velocity and Line-strength MeasurementsAug 23 1995This is the first in a series of papers in which we analyze medium--resolution spectra of over 400 K and M giants in Baade's Window. Our sample was selected from the proper motion study of Spaenhauer et al. [AJ, 103, 297 (1992)]. We have measured radial ... More
Local Group Dwarf Elliptical Galaxies: I. Mapping the Dynamics of NGC 205 Beyond the Tidal RadiusSep 19 2005NGC 205 is the nearest example of a dwarf elliptical (dE) galaxy and the prototype of this enigmatic galaxy class. Photometric evidence suggests that NGC 205, a close satellite of the M31 galaxy, is tidally interacting with its parent galaxy. We present ... More
High resolution infrared spectroscopy of the old open cluster NGC6791Apr 03 2006We report abundance analysis for 6 M giant members of the old open cluster NGC6791, based on infrared spectroscopy (1.5-1.8 micron) at R=25,000, using the NIRSPEC spectrograph at the Keck II telescope. We find the iron abundance <[Fe/H]>= +0.35 +/- 0.02$, ... More
Near-Infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity Bulge Globular ClustersAug 05 2005Using the SofI imager at ESO/NTT and NIRSPEC spectrograph at KeckII, we have obtained J,K images and echelle spectra covering the range 1.5 - 1.8 micron for the intermediate metallicity Bulge globular clusters NGC6539 and UKS1. We find [Fe/H]=-0.76 and ... More
K Giants in Baade's Window. II. The Abundance DistributionApr 10 1996This is the second in a series of papers in which we analyze spectra of over 400 K and M giants in Baade's Window, including most of the stars with proper motions measured by Spaenhauer et al. [AJ, 103, 297 (1992)]. In our first paper, we measured line--strength ... More
Discovery of a nearby halo white dwarf with proper motion mu=2.55 arcsec/yrOct 04 2005We report the discovery of PM J13420-3415, a faint (V=17) white dwarf with a very high proper motion mu = 2.55 arcsec/yr. The star was found in the southern sky extension of the SUPERBLINK proper motion survey. A red spectrum shows the classical signature ... More
New Photometry for the Intermediate-age LMC Globular Cluster NGC 2121 and the Nature of the LMC Age GapMay 31 2001We report new photometry for the cluster NGC 2121 in the Large Magellanic Cloud, which shows a prominent hydrogen core exhaustion gap at the turnoff, and a descending subgiant branch remniscent of Galactic open clusters. We achieve an excellent fit using ... More
A Consistent Microlensing Model for the Galactic BarDec 11 1995We compute a microlensing map for the Galactic bar. The predicted event rate and event duration distribution are consistent with the $55$ events recently reported by the MACHO and OGLE collaborations. Most of the events are due to lensing by stars in ... More
LSR1610-0040: the first early-type L subdwarfMay 29 2003Jun 11 2003We report the discovery of LSR1610-0040, a previously unreported r=17.5 star with a very high proper motion mu=1.46"/yr. This very cool star (b-i=6.3) is found to have a peculiar spectrum that does not fit into the standard sequence of late-M dwarfs and ... More
Spectroscopy of New High Proper Motion Stars in the Northern Sky. I. New Nearby Stars, New High Velocity Stars, and an Enhanced Classification Scheme for M DwarfsSep 14 2002Nov 15 2002We define an enhanced spectral classification scheme for M dwarf stars, and use it to derive spectral classification of 104 northern stars with proper motions larger than 0.5"/yr which we discovered in a survey of high proper motion stars at low galactic ... More
New High Proper Motion Stars from the Digitized Sky Survey. II. Northern Stars with 0.5<mu<2.0 arcsec/yr at High Galactic LatitudesJun 25 2003In a continuation of our systematic search for high proper motion stars in the Digitized Sky Survey, we have completed the analysis of northern sky fields at galactic latitudes above 25 degrees. With the help of our SUPERBLINK software, a powerful automated ... More
Discovery of an ultra-cool subdwarf: LSR1425+7102, first star with spectral type sdM8.0Jan 17 2003We report the discovery of the coolest subdwarf reported to date. The star LSR1425+7102 was discovered in our survey for faint high proper motion stars in the northern sky. Follow-up spectroscopy revealed the star to be a very red object with the characteristic ... More
Andromeda and its satellites - a kinematic perspectiveJan 10 2012Jan 16 2012Using spectroscopic data taken with Keck II DEIMOS by the Z-PAndAS team in the Andromeda-Triangulum region, I present a comparison of the disc and satellite systems of Andromeda with those of our own Galaxy. I discuss the observed discrepancies between ... More
High-resolution CRIRES spectra of Terzan1: a metal-poor globular cluster toward the inner bulgeDec 05 2014Containing the oldest stars in the Galaxy, globular clusters toward the bulge can be used to trace its dynamical and chemical evolution. In the bulge direction, there are ~50 clusters, but only about 20% have been subject of high-resolution spectroscopic ... More
New High Proper Motion Stars from the Digitized Sky Survey. I. Northern Stars with proper motion between 0.5 and 2.0 arcsec/yr at Low Galactic LatitudesJul 23 2002We have conducted a systematic search for high proper motion stars in the Digitized Sky Survey, in the area of the sky north of -2.8 degrees in declination and within 25 degrees of the galactic plane. Using the SUPERBLINK software, a powerful automated ... More
New distant companions to known nearby stars: I. GJ 4047B, GJ 718B, GJ 747.2C, GJ 4100B, and GJ 4153BMar 11 2002In an ongoing survey for high proper motion stars at low galactic latitudes, we have identified 5 previously uncatalogued common proper motion companions to stars listed in the Preliminary Version of the Third Catalogue of Nearby Stars (GJ stars). For ... More
A New Model for the Milky Way BarSep 05 2012We use Schwarzschild's orbit-superposition technique to construct self-consistent models of the Galactic bar. Using $\chi^2$ minimisation, we find that the best-fit Galactic bar model has a pattern speed $\Omega_{\rm p}=60 \rm{km s^{-1} kpc^{-1}}$, disk ... More
Revised metallicity classes for low-mass stars: dwarfs (dM), subdwarfs (sdM), extreme subdwarfs (esdM), and ultra subdwarfs (usdM)Jul 20 2007The current classification system of M stars on the main sequence distinguishes three metallicity classes (dwarfs - dM, subdwarfs - sdM, and extreme subdwarfs - esdM). The spectroscopic definition of these classes is based on the relative strength of ... More
LSR0602+3910 - Discovery of a Bright Nearby L-type Brown DwarfJan 15 2003Feb 14 2003We report the discovery of LSR0602+3910, an L dwarf of class L1. The object was initially identified by Lepine et al. (2002) as a new high proper motion star lying close to the Galactic plane. Its 2MASS J-K_s=1.43 is consistent with an L dwarf, which ... More
Signatures of Bulge Triaxiality from Kinematics in Baade's Window/Sep 12 1994We study a sample of 62 Baade's Window (1,-4) K giants that have published proper motions, radial velocity and metallicity. We construct the velocity ellipsoids for the metal rich stars and metal poor stars. We find a vertex deviation characteristic of ... More
The Large Synoptic Survey Telescope and Milky Way ScienceDec 07 2017The Large Synoptic Survey Telescope (LSST) surveys have initially been optimized to omit the inner part of the Milky Way disk/bar from deep and cadence observations. However it is now clear that the LSST will be powerful for Galactic astronomy and may ... More
The Bulge Radial Velocity/Abundance AssayAug 30 2011The Bulge Radial Velocity/Abundance Assay (BRAVA) has accomplished a survey of 10,000 red giants in the Southern Galactic bulge, approximately spanning -8 deg. < l < +8 deg. and -3 deg. <b < -8 deg., a region within roughly 1 kpc from the nucleus. We ... More
The Age of the Galactic BulgeAug 07 2001The dominant stellar population of the central bulge of the Milky Way is old, with roughly solar metallicity. The age is very similar to that of the old metal rich bulge globular clusters and to 47 Tucanae, which has an age of 13 Gyr. Stellar composition ... More
A Radial Velocity and Calcium Triplet abundance survey of field Small Magellanic Cloud giantsMar 31 2010Apr 01 2010We present the results of a pilot wide-field radial velocity and metal abundance survey of red giants in ten fields in the Small Magellanic Cloud (SMC). The targets lie at projected distances of 0.9 and 1.9 kpc from the SMC centre ($m-M=18.79$) to the ... More
Halos of Spiral Galaxies. III. Metallicity DistributionsOct 09 2005(Abriged) We report results of a campaign to image the stellar populations in the halos of highly inclined spiral galaxies, with the fields roughly 10 kpc (projected) from the nuclei. We use the F814W (I) and F606W (V) filters in the Wide Field Planetary ... More
Halos of Spiral Galaxies. I. The Tip of the Red Giant Branch as a Distance IndicatorOct 09 2005We have imaged the halo populations of a sample of nearby spiral galaxies using the Wide Field Planetary Camera 2 on broad the Hubble Space Telescope with the aim of studying the stellar population properties and relating them to those of the host galaxies. ... More
Halos of Spiral Galaxies. II. halo metallicity-luminosity relationOct 09 2005Using the Hubble Space Telescope, we have resolved individual red-giant branch stars in the halos of eight nearby spiral galaxies. The fields lie at projected distances between 2 and 13 kpc along the galaxies' minor axes. The data set allows a first look ... More
WFPC2 Observations of Star Clusters in the Magellanic Clouds: I. The LMC Globular Cluster Hodge 11Mar 19 1996We present our analysis of Hubble Space Telescope Wide Field Planetary Camera 2 observations in F555W (broadband V) and F450W (broadband B) of the globular cluster Hodge 11 in the Large Magellanic Cloud galaxy. The resulting V vs. (B-V) color-magnitude ... More
A chemical confirmation of the faint Bootes II dwarf Spheroidal GalaxyAug 15 2014We present a chemical abundance study of the brightest confirmed member star of the ultrafaint dwarf galaxy Bootes II from Keck/HIRES high-resolution spectroscopy at moderate signal-to-noise ratios. At [Fe/H] = -2.93 +/- 0.03 (stat.) +/- 0.17 (sys.) this ... More
A statistical analysis of the late-type stellar content in the Andromeda haloApr 06 2010We present a statistical characterization of the carbon-star to M-giant (C/M) ratio in the halo of M31. Based on application of pseudo-filter band passes to our Keck/DEIMOS spectra we measure the 81-77-color index of 1288 stars in the giant stellar stream ... More
Star Formation Signatures in Optically Quiescent Early-type GalaxiesApr 12 2010In recent years argument has been made that a high fraction of early-type galaxies in the local universe experience low levels (< 1 M_sun/yr) of star formation (SF) that causes strong excess in UV flux, yet leaves the optical colors red. Many of these ... More
HST/WFPC2 proper motions in two bulge fields: kinematics and stellar population of the Galactic bulgeJul 04 2002Jul 08 2002We report proper motion dispersions for stars in the direction of two fields of the Galactic bulge, using HST/WFPC2 images taken six years apart. Our two fields are Baade's Window (l,b)=(1.13,-3.77) and Sgr I (l,b)=(1.25 ,-2.65). Our proper motion dispersions ... More
Spatiotemporal dynamics in 2D Kolmogorov flow over large domainsAug 15 2013May 13 2014Kolmogorov flow in two dimensions - the two-dimensional Navier-Stokes equations with a sinusoidal body force - is considered over extended periodic domains to reveal localised spatiotemporal complexity. The flow response mimicks the forcing at small forcing ... More
Exhausting the background approach for bounding the heat transport in Rayleigh-Bénard convectionJun 08 2019We revisit the optimal heat transport problem for Rayleigh-B\'enard convection in which a rigorous upper bound on the Nusselt number, $Nu$, is sought as a function of the Rayleigh number $Ra$. Concentrating on the 2-dimensional problem with stress-free ... More
Searching turbulence for periodic orbits with dynamic mode decompositionJun 04 2019We present a new method for generating robust guesses for unstable periodic orbits (UPOs) by post-processing turbulent data using dynamic mode decomposition (DMD). The approach relies on the identification of near-neutral, repeated harmonics in the DMD ... More
Koopman mode expansions between simple invariant solutionsNov 14 2018A Koopman decomposition is a powerful method of analysis for fluid flows leading to an apparently linear description of nonlinear dynamics in which the flow is expressed as a superposition of fixed spatial structures with exponential time dependence. ... More
New Neighbors: Parallaxes of 18 nearby stars selected from the LSPM-north catalogJan 23 2009Feb 26 2009We present astrometric parallaxes for 18 suspected nearby stars selected from the LSPM-north proper motion catalog. Sixteen objects are confirmed to be main sequence M dwarfs within 16 parsecs of the Sun, including three stars (LSPM J0011+5908, LSPM J0330+5413, ... More
An HST search for planets in the lower Main Sequence of the globular cluster NGC 6397Feb 23 2012Nov 09 2012Searches for planetary transits carried out in open and globular clusters have yielded to date only a handful of weak, unconfirmed candidates. These results have been interpreted either as being insignificant, or as evidence that the cluster chemical ... More
High resolution infrared spectra of bulge globular clusters: The extreme chemical abundances of Terzan 4 and Terzan 5Feb 09 2004May 08 2004Using the NIRSPEC spectrograph at Keck II, we have obtained infrared echelle spectra covering the range $1.5-1.8 \mu \rm m$ for the highly reddened bulge globular clusters Terzan 4 and Terzan 5. The clusters are of interest because a blue horizontal branch ... More
Somos Sequence Near-Addition Formulas and Modular Theta FunctionsMar 15 2007We have discovered conjectural near-addition formulas for Somos sequences. We have preliminary evidence suggesting the existence of modular theta functions.
The age of the young bulge-like population in the stellar system Terzan5: linking the Galactic bulge to the high-z UniverseSep 06 2016The Galactic bulge is dominated by an old, metal rich stellar population. The possible presence and the amount of a young (a few Gyr old) minor component is one of the major issues debated in the literature. Recently, the bulge stellar system Terzan 5 ... More
The Terzan 5 puzzle: discovery of a third, metal-poor componentNov 07 2013We report on the discovery of 3 metal-poor giant stars in Terzan 5, a complex stellar system in the the Galactic bulge, known to have two populations at [Fe/H]=-0.25 and +0.3. For these 3 stars we present new echelle spectra obtained with NIRSPEC at Keck ... More
Spatial/Spectral Resolution of a Galactic Bulge K3 Giant Stellar Atmosphere via Gravitational MicrolensingJan 02 2001We present two Keck HIRES spectra (R=40,000) of a bulge K3 giant taken on successive nights during the second caustic crossing of the binary microlensing event EROS BLG-2000-5. This caustic crossing served to effectively resolve the surface of the source ... More
Optimising energy growth as a tool for finding exact coherent structuresJan 31 2017We discuss how searching for finite amplitude disturbances of a given energy which maximise their subsequent energy growth after a certain later time $T$ can be used to probe phase space around a reference state and ultimately to find other nearby solutions. ... More
Koopman analysis of Burgers equationDec 18 2017Jun 29 2018The emergence of Dynamic Mode Decomposition (DMD) as a practical way to attempt a Koopman mode decomposition of a nonlinear PDE presents exciting prospects for identifying invariant sets and slowly decaying transient structures buried in the PDE dynamics. ... More
The Once and Future Andromeda StreamNov 28 2007Jan 12 2008The interaction between an accreting satellite and the Andromeda galaxy (M31) has been studied analytically and numerically, using a high-resolution N-body simulation with $4\times10^7$ particles. For the first time, we show the self-gravitating response ... More
The Proper Motion of NGC 6522 in Baade's WindowOct 30 1997We have detected seven stars with a common proper motion which are located within 2.5 arcminutes of the globular cluster NGC 6522 in the Baade's Window field of the Galactic bulge. We argue that these stars are members of the cluster, and derive a weighted ... More
Detailed near-IR stellar abundances of red giants in the Inner Bulge and Galactic CenterAug 30 2017Owing to their extreme crowding and high and variable extinction, stars in the Galactic Bulge, within +-2 degrees of the Galactic plane, and especially those in the Nuclear Star Cluster, have only rarely been targeted for an analyses of their detailed ... More
A New All-Sky Catalog of Stars with Large Proper MotionsMay 30 2008Oct 06 2008A new all-sky catalog of stars with proper motions pm>0.15"/yr is presented. The catalog is largely a product of the SUPERBLINK survey, a data-mining initiative in which the entire Digitized Sky Surveys are searched for moving stellar sources. Findings ... More
Detailed Abundances for the Old Population near the Galactic Center: I. Metallicity distribution of the Nuclear Star ClusterOct 23 2017We report the first high spectral resolution study of 17 M giants kinematically confirmed to lie within a few parsecs of the Galactic Center, using R=24,000 spectroscopy from Keck/NIRSPEC and a new linelist for the infrared K band. We consider their luminosities ... More
Nova Sagittarii 1994 #1 (V4332 Sagittarii): The Discovery and Evolution of an Unusual Luminous Red Variable StarMay 04 1999We report photometry and spectroscopy of the evolution of Nova Sagittarii 1994 #1 (V4332 Sagittarii) during outburst. We compare the photometric and spectral evolution of this outburst to known classes of outbursts -- including classical novae and outbursts ... More
Chemical evolution of the inner 2 degrees of the Milky Way bulge: [alpha/Fe] trends and metallicity gradientsOct 09 2015The structure, formation, and evolution of the Milky Way bulge is a matter of debate. Important diagnostics for discriminating between bulge models include alpha-abundance trends with metallicity, and spatial abundance and metallicity gradients. Due to ... More
On the helium content of Galactic globular clusters via the R parameterMar 01 2000We estimate the empirical R parameter in 26 Galactic Globular Clusters covering a wide metallicity range, imaged by WFPC2 on board the HST. The improved spatial resolution permits a large fraction of the evolved stars to be measured and permits accurate ... More
Detailed abundance analysis of a metal-poor giant in the Galactic CenterAug 26 2016We report the first results from our program to examine the metallicity distribution of the Milky Way nuclear star cluster connected to SgrA*, with the goal of inferring the star formation and enrichment history of this system, as well as its connection ... More
Composition of the Galactic bulgeDec 27 2003We present detailed abundance results for 9 Galactic bulge stars in Baade's Window, based on HIRES (R=45,000--60,000) spectra taken with the Keck I telescope. The alpha elements show non-uniform enhancements relative to the Solar neighborhood trends: ... More
Localization in a spanwise-extended model of plane Couette flowOct 08 2014We consider a 9-PDE (1-space and 1-time) model of plane Couette flow in which the degrees of freedom are severely restricted in the streamwise and cross-stream directions to study spanwise localisation in detail. Of the many steady Eckhaus (spanwise modulational) ... More
The First Detailed Abundances for M giants in Baade's Window from Infrared SpectroscopyJun 02 2005We report the first abundance analysis of 14 M giant stars in the Galactic bulge, based on R=25,000 infrared spectroscopy (1.5-1.8um) using NIRSPEC at the Keck II telescope. Because some of the bulge M giants reach high luminosities and have very late ... More
The Andromeda Project. I. Deep HST-WFPC2 V,I photometry of 16 fields toward the disk and the halo of the M31 galaxy. Probing the stellar content and metallicity distributionDec 23 2002HST-WFPC2 F555W and F814W photometry were obtained for 16 fields of the luminous nearby spiral galaxy M31, sampling the stellar content of the disk and the halo at different distances from the center, from ~ 20 to ~ 150 arcmin (i.e. ~ 4.5 to 35 kpc), ... More
HST NICMOS Photometry of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4Jul 24 2001We present results from NICMOS Hubble Space Telescope observations of the reddened bulge globular clusters NGC 6528, Terzan 5, Liller 1, UKS 1 and Terzan 4, obtained through the filters F110W and F160W (nearly equivalent to J and H). For the first time ... More
A Survey of M31 Globular Clusters using WFPC2 on board HSTJun 01 2001We report new, as yet unpublished HST/WFPC2 V, I photometry of 9 globular clusters in M31. These are part of a total sample of 19 clusters on M31 with well observed CMDs from HST. The clusters have the full range of horizontal branch morphologies from ... More
High-Resolution Abundance Analysis of Very Metal-Rich Stars in the Solar NeighborhoodApr 22 1997We report detailed analysis of high-resolution spectra of nine high velocity metal-rich dwarfs in the solar neighborhood. The stars are super metal-rich and 5 of them have [Fe/H]>=+0.4, making them the most metal-rich stars currently known. We find that ... More
The inner two degrees of the Milky Way. Evidence of a chemical difference between the Galactic Center and the surrounding inner bulge stellar populationsJun 19 2019Although there have been numerous studies of chemical abundances in the Galactic bulge, the central two degrees have been relatively unexplored due to the heavy and variable interstellar extinction, extreme stellar crowding, and the presence of complex ... More
High-resolution HI Mapping of NGC 4038/9 ("The Antennae") and its Tidal Dwarf Galaxy CandidatesOct 26 2001We present new VLA C+D-array HI observations and optical and NIR imaging of the well known interacting system NGC 4038/9, ``The Antennae''. The radio data reveal a wealth of gaseous sub-structure both within the main bodies of the galaxies and along the ... More
SiO Masers in the Galactic Bulge and Disk: Kinematics from the BAaDE SurveyMay 11 2018We present the first results from the BAaDE (Bulge Asymmetries and Dynamic Evolution) survey. Though only a subset of the complete survey ($\sim$2700 out of $\sim$20000 final sources), our data comprise the largest radio kinematic survey to date of stellar ... More
The GALEX UV emission in shell galaxies: tracing galaxy "rejuvenation" episodesJul 19 2007We present the GALEX far FUV and near NUV ultraviolet imaging of three nearby shell galaxies, namely NGC 2865, NGC 5018 and NGC 7135. The system of shells and fine structures visible in the optical is detected in the NUV image of NGC 2865 and in both ... More
Detections of massive stars in the cluster MCM2005b77, in the star-forming regions GRS G331.34$-$00.36 (S62) and GRS G337.92$-$00.48 (S36)Jun 20 2018Large infrared and millimeter wavelength surveys of the Galactic plane have unveiled more than 600 new bubble HII regions and more than 3000 candidate star clusters. We present a study of the candidate clusters MCM2005b72, DBS2003-157, DBS2003-172, and ... More
A New Generation of Cool White Dwarf Atmosphere Models. III. WD J2356$-$209: Accretion of a Planetesimal with an Unusual CompositionFeb 08 2019WD J2356$-$209 is a cool metal-polluted white dwarf whose visible spectrum is dominated by a strong and broad sodium feature. Although discovered nearly two decades ago, no detailed and realistic analysis of this star had yet been realized. In the absence ... More
UV Morphology and Star Formation in the Tidal Tails of NGC 4038/39Nov 12 2004We present GALEX FUV (1530 A) and NUV (2310 A) observations of the archetypal merging system NGC 4038/39, ``The Antennae". Both tails are relatively bright in the UV, especially in the vicinity of the Tidal Dwarf Galaxy candidates at the end of the southern ... More
An astrometric companion to the nearby metal-poor, low-mass star LHS 1589Mar 15 2007Jul 20 2007We report the discovery of a companion to the high proper motion star LHS 1589, a nearby high-velocity, low-mass subdwarf. The companion (LHS 1589B) is located 0.224+/-0.004" to the southwest of the primary (LHS 1589A), and is 0.5 magnitude fainter than ... More
Stellar Companions and the Age of HD 141569 and its Circumstellar DiskJul 12 2000We investigate the stellar environment of the Beta Pictoris-like star HD 141569 with optical spectroscopy and near infrared imaging. The B9.5Ve primary, and an M2 and an M4 type star both located in projection less than nine arseconds away have the same ... More
Star cluster formation and evolution in Mrk 930: properties of a metal-poor starburstMar 29 2011We present a HST multiband analysis of the large population of star clusters in the blue compact galaxy (BCG) Mrk 930. We have reconstructed the spectral energy distributions of the star clusters and estimated age, mass, and extinction for a representative ... More
The Slow Death (or Rebirth?) of Extended Star Formation in z~0.1 Green Valley Early-Type GalaxiesOct 22 2012Oct 24 2012UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. We present resolved UV-optical photometry of a sample of 19 SDSS early-type galaxies at z~0.1 ... More
Discovery of an M8.5 Dwarf With Proper Motion mu=2.38 arcsec/yrNov 07 2002We report the discovery of LSR1826+3014, a very faint (V=19.36) star with a very large proper motion (mu=2.38 arcsec/yr). A low resolution red spectrum reveals that LSR1826+3014 is an ultra-cool red dwarf with spectral type M8.5 V and with a radial velocity ... More
Mayall II = G1 in M31: Giant Globular Cluster or Core of a Dwarf Elliptical Galaxy ?May 01 2001(Abridged version) Mayall II = G1 is one of the brightest globular clusters belonging to M31, the Andromeda galaxy. Our observations with HST/WFPC2 provide data for the (I vs. V-I) and (V vs. V-I) color-magnitude diagrams. From model fitting, we determine ... More
The Dearth of Massive, Helium-Rich White Dwarfs in Young Open Star ClustersSep 07 2004Dec 07 2004Spectra have been obtained of 21 white dwarfs (WDs) in the direction of the young, rich open star cluster NGC 2099. This represents an appreciable fraction (>30%) of the cluster's total WD population. The mean derived mass of the sample is 0.8 Msun - ... More
The dynamics of Andromeda's dwarf galaxies and stellar streamsMay 11 2016As part of the Z-PAndAS Keck II DEIMOS survey of resolved stars in our neighboring galaxy, Andromeda (M31), we have built up a unique data set of measured velocities and chemistries for thousands of stars in the Andromeda stellar halo, particularly probing ... More
A Large Proper-Motion Survey in Plaut's Low-Extinction WindowJul 25 1996We present preliminary results from the deepest and largest photographic proper-motion survey ever undertaken of the Galactic bulge. Our first-epoch plate material (from 1972-3) goes deep enough (V_lim = 22) to reach below the bulge main-sequence turnoff. ... More
The Evolution of Oxygen and Magnesium in the Bulge and Disk of the Milky WayAug 29 2007We show that the Galactic bulge and disk share a similar, strong, decline in [O/Mg] ratio with [Mg/H]. The similarity of the [O/Mg] trend in these two, markedly different, populations suggests a metallicity-dependent modulation of the stellar yields from ... More
HST/WFPC2 Color-Magnitude Diagrams for Globular Clusters in M31Feb 09 2005We report new HST/WFPC2 photometry for 10 globular clusters (GC) in M31 observed in F5555W(V) and F814W(I). Additionally we have reanalyzed HST archival data of comparable quality for 2 more GCs. Extraordinary care is taken to account for the effects ... More
Galaxy-scale Star Formation on the Red Sequence: the Continued Growth of S0s and the Quiescence of EllipticalsJun 25 2012This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at z~0.1. A sample is drawn from bulge-dominated GALEX/SDSS galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. ... More
A Wide-field Survey of Two Z~0.5 Galaxy Clusters: Identifying the Physical Processes Responsible for the Observed Transformation of Spirals into S0sJul 27 2007We present new results from our comprehensive comparative survey of two massive, intermediate redshift galaxy clusters, Cl0024+17 (z=0.39) and MS0451-03 (z=0.54). We identify and study several key classes of `transition objects' whose stellar populations ... More
A tidally distorted dwarf galaxy near NGC 4449Feb 10 2012NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs. It is wreathed in an extraordinary neutral hydrogen (H I) ... More
Kinematics and Metallicity of M31 Red Giants: The Giant Southern Stream and Discovery of a Second Cold Component at R = 20 kpcDec 06 2005We present spectroscopic observations of red giant branch (RGB) stars in the Andromeda spiral galaxy (M31), acquired with the DEIMOS instrument on the Keck II 10-m telescope. The three fields targeted in this study are in the M31 spheroid, outer disk, ... More
Morphologies of local Lyman break galaxy analogs II: A Comparison with galaxies at z=2-4 in ACS and WFC3 images of the Hubble Ultra Deep FieldNov 06 2009Dec 24 2009Lyman break galaxies (LBGs) display a range in structures (from single/compact to clumpy/extended) that is different from typical local star-forming galaxies. Recently, we have introduced a sample of rare, nearby (z<0.3) starbursts that appear to be good ... More
A Slowly Precessing Disk in the Nucleus of M31 as the Feeding Mechanism for a Central StarburstOct 03 2017Jan 24 2018We present a kinematic study of the nuclear stellar disk in M31 at infrared wavelengths using high spatial resolution integral field spectroscopy. The spatial resolution achieved, FWHM = 0."12 (0.45 pc at the distance of M31), has only previously been ... More
HST Observations of Galactic Globular Cluster Cores. II. NGC 6273 and the Problem of Horizontal-Branch GapsJun 16 1999We present observations of the center of the Galactic globular cluster NGC 6273, obtained with the HST/WFPC2 camera as part of the snapshot program GO-7470. A B, V color-magnitude diagram (CMD) for ~28,000 stars is presented and discussed. The most prominent ... More
Spectroscopy Unveils the Complex Nature of Terzan 5Dec 09 2010We present the chemical abundance analysis of 33 red giant stars belonging to the complex stellar system Terzan 5. We confirm the discovery of two stellar populations (Ferraro et al. 2009, Nature, 462,483) with distinct iron abundances: a relatively metal-poor ... More
Evidence against anomalous compositions for giants in the Galactic Nuclear Star ClusterAug 22 2018Very strong Sc I lines have been found recently in cool M giants in the Nuclear Star Cluster in the Galactic Center. Interpreting these as anomalously high scandium abundances in the Galactic Center would imply a unique enhancement signature and chemical ... More
An empirical mass-loss law for Population II giants from the Spitzer-IRAC survey of Galactic globular clustersMar 17 2014The main aim of the present work is to derive an empirical mass-loss (ML) law for Population II stars in first and second ascent red giant branches. We used the Spitzer InfraRed Array Camera (IRAC) photometry obtained in the 3.6-8 micron range of a carefully ... More
The near-IR luminosity-metallicity relationship for dwarf irregular galaxiesOct 15 2003Dec 06 2003We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and a preliminary ... More
Proper motions in Terzan 5: membership of the multi-iron sub-populations and first constrain to the orbitJul 10 2015By exploiting two sets of high-resolution images obtained with HST ACS/WFC over a baseline of ~10 years we have measured relative proper motions of ~70,000 stars in the stellar system Terzan 5. The results confirm the membership of the three sub-populations ... More
Deep near-IR observations of the Globular Cluster M4: Hunting for Brown DwarfsJun 03 2015Nov 16 2015We present an analysis of deep HST/WFC3 near-IR (NIR) imaging data of the globular cluster M4. The best-photometry NIR colour-magnitude diagram (CMD) clearly shows the main sequence extending towards the expected end of the Hydrogen-burning limit and ... More
Hubble Space Telescope analysis of stellar populations within the globular cluster G1 (Mayall II) in M31Mar 01 2019In this paper we present a multi-wavelength analysis of the complex stellar populations within the massive globular cluster Mayall II (G1), a satellite of the nearby Andromeda galaxy projected at a distance of 40 kpc. We used images collected with the ... More
The Initial Mass Function of the Galactic Bulge Down to ~0.15 MsunJun 28 1999Aug 23 1999We present a luminosity function (LF) for lower main sequence stars in the Galactic bulge near (l,b)=(0,-6) to J=24, corresponding to M_J~9.3. This LF is derived from HST + NICMOS observations with the F110W and F160W filters. The main sequence locus ... More