Publications (50)
Discovery and Spectroscopic Characterization of a Distant, Compact Milky Way Satellite in Gemini
K. Overdeck, W. Cerny, C. Y. Tan +27
We present the discovery of a compact Milky Way satellite in the constellation of Gemini. This system was discovered by cross-matching detections from two independent search algori…
The Southern Stellar Stream Spectroscopic Survey (): Overview, Target Selection, Data Reduction, Validation, and Early Science
T. S. Li, S. E. Koposov, D. B. Zucker +29
We introduce the Southern Stellar Stream Spectroscopy Survey (), an on-going program to map the kinematics and chemistry of stellar streams in the Southern Hemisphere. The i…
The MACHO Project: Microlensing Results from 5.7 Years of LMC Observations
The MACHO collaboration, C. Alcock, R. A. Allsman +23
We report on our search for microlensing towards the Large Magellanic Cloud (LMC). Analysis of 5.7 years of photometry on 11.9 million stars in the LMC reveals 13 - 17 microlensing…
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: II. Rotating Versus Non-Rotating Dwarfs
M. Geha, P. Guhathakurta, R. van der Marel
We present spatially-resolved internal kinematics and stellar chemical abundances for a sample of dwarf elliptical (dE) galaxies in the Virgo Cluster observed with Keck/ESI. We fin…
Stellar Kinematics and Metallicities in the Ultra-Faint Dwarf Galaxy Reticulum II
J. D. Simon, A. Drlica-Wagner, T. S. Li +69
We present Magellan/M2FS, VLT/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member stars s…
DELVE 6: An Ancient, Ultra-Faint Star Cluster on the Outskirts of the Magellanic Clouds
W. Cerny, A. Drlica-Wagner, T. S. Li +23
We present the discovery of DELVE 6, an ultra-faint stellar system identified in the second data release of the DECam Local Volume Exploration (DELVE) survey. Based on a maximum-li…
NGC 770: A Counter-Rotating Core in a Low-Luminosity Elliptical Galaxy
M. Geha, P. Guhathakurta, R. van der Marel
We present evidence for a counter-rotating core in the low-luminosity (M_B = -18.2) elliptical galaxy NGC 770 based on internal stellar kinematic data. This counter-rotating core i…
Microlensing Optical Depth towards the Galactic Bulge Using Clump Giants from the MACHO Survey
P. Popowski, K. Griest, C. L. Thomas +20
Using 7 years of MACHO survey data, we present a new determination of the optical depth to microlensing towards the Galactic bulge. We select the sample of 62 microlensing events (…
The MACHO project: Microlensing Optical Depth towards the Galactic Bulge from Difference Image Analysis
C. Alcock, R. A. Allsman, D. R. Alves +21
We present the microlensing optical depth towards the Galactic bulge based on the detection of 99 events found in our Difference Image Analysis (DIA) survey. This analysis encompas…
MACHO 96-LMC-2: Lensing of a Binary Source in the LMC and Constraints on the Lensing Object
C. Alcock, R. A. Allsman, D. R. Alves +21
We present photometry and analysis of the microlensing alert MACHO 96-LMC-2. The ~3% photometry provided by the Global Microlensing Alert Network follow--up effort reveals a period…
The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud
C. Alcock, R. A. Allsman, D. R. Alves +23
We present a 9 million star color-magnitude diagram (9M CMD) of the LMC bar. The 9M CMD reveals a complex superposition of different age and metallicity stellar populations, with i…
Blue Variable Stars from the MACHO database I: Photometry and Spectroscopy of the LMC sample
Stefan C. Keller, M. S. Bessell, K. H. Cook +2
We present the photometric properties of 1279 blue variable stars within the LMC. Photometry is derived from the MACHO database. The lightcurves of the sample exhibit a variety of…
A 421 d Activity Cycle in the BeX Recurrent Transient A0538-66 from MACHO monitoring
C. Alcock, R. A. Allsman, D. R. Alves +23
We present a ~ 5-yr optical light curve of the recurrent Be/X-ray transient A0538-66 obtained as a by-product of the MACHO Project. These data reveal both a long-term modulation at…
Internal Dynamics, Structure and Formation of Dwarf Elliptical Galaxies: I. A Keck/HST Study of Six Virgo Cluster Dwarfs
M. Geha, P. Guhathakurta, R. van der Marel
Keck/ESI spectroscopy is presented for six Virgo Cluster dwarf elliptical (dE) galaxies. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radiu…
Keck Spectroscopy of Dwarf Elliptical Galaxies in the Virgo Cluster
M. Geha, P. Guhathakurta, R. van der Marel
Keck spectroscopy is presented for four dwarf elliptical galaxies in the Virgo Cluster. At this distance, the mean velocity and velocity dispersion are well resolved as a function…
The MACHO Project LMC Variable Star Inventory. IX. Frequency Analysis of the First Overtone RR Lyrae Stars and the Indication for Nonradial Pulsations
C. Alcock, R. Allsman, D. R. Alves +26
More than 1300 variables classified provisionally as first overtone RR Lyrae pulsators in the MACHO variable star database of the Large Magellanic Cloud (LMC) have been subjected t…
The MACHO Project Hubble Space Telescope Follow-Up: Preliminary Results on the Location of the Large Magellanic Cloud Microlensing Source Stars
C. Alcock, R. A. Allsman, D. R. Alves +21
We attempt to determine whether the MACHO microlensing source stars are drawn from the average population of the LMC or from a population behind the LMC by examining the HST color-…
MACHO Project Analysis of the Galactic Bulge Microlensing Events with Clump Giants as Sources
P. Popowski, T. Vandehei, K. Griest +19
We present preliminary results of the analysis of 5 years of MACHO data on the Galactic bulge microlensing events with clump giants as sources. This class of events allows one to o…
Gravitational Microlensing Events Due to Stellar Mass Black Holes
D. P. Bennett, A. C. Becker, J. L. Quinn +28
We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find 6 events that exhibi…
A Stellar Mass Threshold for Quenching of Field Galaxies
M. Geha, M. Blanton, R. Yan +1
We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atla…
Illuminating the Darkest Galaxies
J. D. Simon, M. Geha
Low luminosity dwarf galaxies provide stringent constraints on the nature of dark matter. Establishing these constraints depends on precise kinematic measurements of individual sta…
Searching for periodicities in the MACHO light curve of LMC X-2
C. Alcock, R. A. Allsman, D. R. Alves +23
Using the exceptional long-term monitoring capabilities of the MACHO project, we present here the optical history of LMC X-2 for a continuous 6-yr period. These data were used to i…
The MACHO Project Large Magellanic Cloud Variable Star Inventory. XIII. Fourier Parameters for the First Overtone RR Lyrae Variables and the LMC Distance
C. Alcock, D. R. Alves, T. S. Axelrod +21
Fourier coefficents have been derived for the and light curves of 785 overtone RR Lyrae variables in 16 MACHO fields near the bar of the LMC. The and coe…
HST/ACS Direct Ages of the Dwarf Elliptical Galaxies NGC 147 and NGC 185
M. Geha, D. Weisz, A. Grocholski +3
We present the deepest optical photometry for any dwarf elliptical (dE) galaxy based on Hubble Space Telescope ACS observations of the Local Group dE galaxies NGC 147 and NGC 185.…
Chemical Analysis of the Ultra-Faint Dwarf Galaxy Grus~II. Signature of high-mass stellar nucleosynthesis
T. T. Hansen, J. L. Marshall, J. D. Simon +59
We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultra-faint dwarf galaxy Grus~II. All stars exhibit a higher than…
The Stellar Initial Mass Function of Ultra-Faint Dwarf Galaxies: Evidence for IMF Variations with Galactic Environment
M. Geha, T. M. Brown, J. Tumlinson +8
We present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep HST/ACS imaging. The Hercules and Leo…
The BigBOSS Experiment
D. Schlegel, F. Abdalla, T. Abraham +138
BigBOSS is a Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy and quasar redshift survey…
The MACHO Project HST Follow-Up: The Large Magellanic Cloud Microlensing Source Stars
C. A. Nelson, A. J. Drake, K. H. Cook +21
We present Hubble Space Telescope (HST) WFPC2 photometry of 13 microlensed source stars from the 5.7 year Large Magellanic Cloud (LMC) survey conducted by the MACHO Project. The mi…
Structure and Dynamics of the Globular Cluster Palomar 13
J. D. Bradford, M. Geha, R. Munoz +6
We present Keck/DEIMOS spectroscopy and CFHT/MegaCam photometry for the Milky Way globular cluster Palomar 13. We triple the number of spectroscopically confirmed members, includin…
The MACHO Project Large Magellanic Cloud variable star inventory. XI. Frequency analysis of the fundamental mode RR Lyrae stars
C. Alcock, D. R. Alves, A. Becker +20
We have frequency analyzed 6391 variables classified earlier as fundamental mode RR Lyrae (RR0) stars in the MACHO database on the Large Magellanic Cloud (LMC). The overwhelming ma…
A Pride of Satellites in the Constellation Leo? Discovery of the Leo VI Milky Way Satellite Galaxy with DELVE Early Data Release 3
C. Y. Tan, W. Cerny, A. Drlica-Wagner +32
We report the discovery and spectroscopic confirmation of an ultra-faint Milky Way (MW) satellite in the constellation of Leo. This system was discovered as a spatial overdensity o…
Six More Ultra-Faint Milky Way Companions Discovered in the DECam Local Volume Exploration Survey
W. Cerny, C. E. MartÃnez-Vázquez, A. Drlica-Wagner +28
We report the discovery of six ultra-faint Milky Way satellites discovered through matched-filter searches conducted using Dark Energy Camera (DECam) data processed as part of the…
The MACHO Project LMC Variable Star Inventory: X. The R Coronae Borealis Stars
C. Alcock, R. A. Allsman, D. R. Alves +26
We report the discovery of eight new R Coronae Borealis (RCB) stars in the Large Magellanic Cloud (LMC) using the MACHO project photometry database. The discovery of these new star…
Recent Microlensing Results from the MACHO Project
P. Popowski, C. A. Nelson, D. P. Bennett +19
We describe a few recent microlensing results from the MACHO Collaboration. The aim of the MACHO Project was the identification and quantitative description of dark and luminous ma…
Discovery and Spectroscopic Confirmation of Aquarius III: A Low-Mass Milky Way Satellite Galaxy
W. Cerny, A. Chiti, M. Geha +37
We present the discovery of Aquarius III, an ultra-faint Milky Way satellite galaxy identified in the second data release of the DECam Local Volume Exploration (DELVE) survey. Base…
Variability-Selected Quasars in MACHO Project Magellanic Cloud Fields
M. Geha, C. Alcock, R. A. Allsman +22
We present 47 spectroscopically-confirmed quasars discovered behind the Magellanic Clouds identified via photometric variability in the MACHO database. Thirty-eight quasars lie beh…
The MACHO Project: Microlensing Detection Efficiency
The MACHO collaboration, C. Alcock, R. A. Allsman +22
The MACHO project is a search for dark matter in the form of massive compact halo objects (MACHOs). The project has photometrically monitored tens of millions of stars in the Large…
The Baryon Content of Extremely Low Mass Dwarf Galaxies
M. Geha, M. R. Blanton, M. Masjedi +1
We investigate the gas content and baryonic Tully-Fisher relationship for extremely low luminosity dwarf galaxies in the absolute magnitude range -13.5 > Mr > -16. The sample is se…
Local Group Dwarf Elliptical Galaxies: II. Stellar Kinematics to Large Radii in NGC 147 and NGC 185
M. Geha, R. P. van der Marel, P. Guhathakurta +3
We present kinematic and metallicity profiles for the M31 dwarf elliptical (dE) satellite galaxies NGC 147 and NGC 185. The profiles represent the most extensive spectroscopic radi…
Darwin Tames an Andromeda Dwarf: Unraveling the Orbit of NGC 205 Using a Genetic Algorithm
K. M. Howley, M. Geha, P. Guhathakurta +3
NGC 205, a close satellite of the M31 galaxy, is our nearest example of a dwarf elliptical galaxy. Photometric and kinematic observations suggest that NGC 205 is undergoing tidal d…
Main Sequence Star Populations in the Virgo Overdensity Region
H. Jerjen, G. S. Da Costa, B. Willman +12
We present deep CMDs for two Subaru Suprime-Cam fields in the Virgo Stellar Stream(VSS)/Virgo Overdensity(VOD) and compare them to a field centred on the highest concentration of S…
Measuring Sizes of Ultra-Faint Dwarf Galaxies
R. R. Munoz, N. Padmanabhan, M. Geha
The discovery of Ultra-Faint Dwarf (UFD) galaxies in the halo of the Milky Way extends the faint end of the galaxy luminosity function to a few hundred solar luminosities. This ext…
Mass-Losing Semiregular Variable Stars in Baade's Windows
C. Alard, J. Blommaert, C. Cesarsky +38
By cross-correlating the results of two recent large-scale surveys, the general properties of a well defined sample of semi-regular variable stars have been determined. ISOGAL mid-…
MACHO Project Limits on Black Hole Dark Matter in the 1-30 Solar Mass Range
The Macho collaboration, C. Alcock, R. A. Allsman +22
We report on a search for long duration microlensing events towards the Large Magellanic Cloud. We find none, and therefore put limits on the contribution of high mass objects to t…
Metallicity Evolution of the Six Most Luminous M31 Dwarf Satellites
N. Ho, M. Geha, E. Tollerud +3
We present global metallicity properties, metallicity distribution functions (MDFs) and radial metallicity profiles for the six most luminous M31 dwarf galaxy satellites: M32, NGC…
Local Group Dwarf Elliptical Galaxies: I. Mapping the Dynamics of NGC 205 Beyond the Tidal Radius
M. Geha, P. Guhathakurta, R. M. Rich +1
NGC 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…
AGN All the Way Down? AGN-like Line Ratios are Common In the Lowest-Mass Isolated Quiescent Galaxies
C. Dickey, M. Geha, A. Wetzel +1
We investigate the lowest-mass quiescent galaxies known to exist in isolated environments (; 1.5 Mpc from a more massive galaxy). This popula…
The Proper Motion of the Large Magellanic Cloud using HST
Nitya Kallivayalil, Roeland P. van der Marel, Charles Alcock +4
We present a measurement of the systemic proper motion of the Large Magellanic Cloud (LMC) from astrometry with the High Resolution Camera (HRC) of the Advanced Camera for Surveys…
Galactic Bulge Microlensing Events with Clump Giants as Sources
P. Popowski, C. Alcock, R. A. Allsman +21
We present preliminary results of the analysis of 5 years of MACHO data on the Galactic bulge microlensing events with clump giants as sources. In particular, we discuss: 1) the se…
Galactic Bulge Microlensing Events from the MACHO Collaboration
C. L. Thomas, K. Griest, P. Popowski +21
We present a catalog of 450 high signal-to-noise microlensing events observed by the MACHO collaboration between 1993 and 1999. The events are distributed throughout our fields and…