Johnson, Jennifer A., Dong, Subo, Gould, Andrew
Finite source effects can be important in observations of gravitational microlensing of stars. Near caustic crossings, for example, some parts of the source star will be more highly magnified than...
Gould, Andrew, Dong, Subo, Bennett, David P., Bond, Ian A., Udalski, Andrzej, Kozlowski, Szymon
At present, microlensing light curves from different telescopes and filters are photometrically aligned by fitting them to a common model. We present a second method based on photometry of common...
Chemical Composition of Faint (I~21 mag) Microlensed Bulge Dwarf OGLE-2007-BLG-514S (2009)
Epstein, Courtney R., Johnson, Jennifer A., Dong, Subo, Udalski, Andrzej, Gould, Andrew, Becker, George
We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff = 5600 +/- 180 K. This I~21 mag star was magnified by a factor ranging from...
Kilic, Mukremin, Gould, Andrew, Koester, Detlev
We present Spitzer IRAC photometry of white dwarf remnants of 14 stars with M = 3-5 Msol. We do not detect mid-infrared excess around any of our targets. By demanding a 3 sigma photometric excess at...
Spectroscopic Confirmation of the Pisces Overdensity (2009)
Kollmeier, Juna A., Gould, Andrew, Shectman, Stephen, Thompson, Ian B., Preston, George W., Simon, Joshua D., ...
We present spectroscopic confirmation of the "Pisces Overdensity", also known as "Structure J", a photometric overdensity of RR Lyrae stars discovered by the Sloan Digital Sky Survey (SDSS) at an...
Lyman-alpha Emission From Cosmic Structure I: Fluorescence (2009)
Kollmeier, Juna A., Zheng, Zheng, Davé, Romeel, Gould, Andrew, Katz, Neal, Miralda-Escudé, Jordi, ...
We present predictions for the fluorescent Lyman-alpha emission signature arising from photoionized, optically thick structures in Smoothed Particle Hydrodynamic (SPH) cosmological simulations of a...
Cohen, Judith G., Thompson, Ian B., Sumi, Takahiro, Bond, Ian, Gould, Andrew, Johnson, Jennifer A., ...
We present abundance analyses based on high dispersion and high signal-to-noise ratio Magellan spectra of two highly microlensed Galactic bulge stars in the region of the main-sequence turnoff with...
OGLE-2005-BLG-071Lb, the Most Massive M Dwarf Planetary Companion? (2009)
Dong, Subo, Gould, Andrew, Udalski, Andrzej, Anderson, Jay, Christie, G. W., Gaudi, B. S., ...
We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include...
Cohen, Judith G., Thompson, Ian B., Sumi, Takahiro, Bond, Ian, Gould, Andrew, Johnson, Jennifer A., ...
We present abundance analyses based on high dispersion and high signal-to-noise ratio Magellan spectra of two highly microlensed Galactic bulge stars in the region of the main sequence turnoff with...
Detectability of Terrestrial Planets in Multi-Planet Systems: Preliminary Report (2009)
Traub, Wesley A., Beichman, Charles, Boden, Andrew F., Boss, Alan P., Casertano, Stefano, Catanzarite, Joseph, ...
We ask if Earth-like planets (terrestrial mass and habitable-zone orbit) can be detected in multi-planet systems, using astrometric and radial velocity observations. We report here the preliminary...
Gaudi, B. Scott, Bennett, David P., Bond, Ian A., Dong, Subo, Gould, Andrew, ...
In the currently-favored paradigm of planet formation, the location of the snow line in the protoplanetary disk plays a crucial role. Determining the demographics of planets beyond the snow line of...
Wide Field Imager in Space for Dark Energy and Planets (2009)
A wide-field imager in space could make remarkable progress in two very different frontiers of astronomy: dark energy and extra-solar planets. Embedding such an imager on a much larger and more...
Guest Essay Class Politics is Dead! Long Live Class Politics! A Political Economy Perspective (2008)
Anthony M. Messina, Lucas González, Naunihal Singh, Andrew Gould, Frances Hagopian, ...
on the New Partisan Politics There is broad agreement among comparativists that political conflict in the rich democracies has moved away from “old ” issues of state ownership, redistribution...
Old-Population Hypervelocity Stars from the Galactic Center: Limits from the SDSS (2008)
Kollmeier, Juna A., Gould, Andrew, Knapp, Gillian, Beers, Timothy C.
We present limits on the ejection of old-population HVS from a sample of over 290,000 stars selected from the SDSS. We derive the speed at the solar circle from the measured positions and radial...
Astrometric and radial-velocity planet detections track very similar motions, and one generally expects that the statistical properties of the detections would also be similar after they are scaled...
OGLE-2005-BLG-071Lb, the Most Massive M-Dwarf Planetary Companion? (2008)
Dong, Subo, Gould, Andrew, Udalski, Andrzej, Anderson, Jay, Christie, G. W., Gaudi, B. S., ...
We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include...
Recent Developments in Gravitational Microlensing (2008)
Twenty-one years after Bohdan's seminal paper launched the field of gravitational microlensing, it has radically diversified from a method narrowly focused on finding dark matter to a very general...
Keller, and William Protheroe. (2008)
Darren Depoy, Jay Frogel, Andrew Gould, Jordi Miralda-escudé, Gerald Newsom, Patrick Osmer, ...
this report, the regular academic staff of the Department of Astronomy included Richard Boyd, Darren DePoy, Jay Frogel, Andrew Gould, Eric Herbst, Jordi Miralda-Escude , Gerald Newsom, Patrick Osmer...
Clues to the Metallicity Distribution in the Galactic Bulge: Abundances in OGLE-2007_BLG-349S (2008)
Cohen, Judith G., Huang, Wenjin, Udalski, A., Gould, Andrew, Johnson, Jennifer
We present an abundance analysis based on high dispersion and high signal-to-noise ratio Keck spectra of a very highly microlensed Galactic bulge dwarf, OGLE-2007-BLG-349S, with Teff ~ 5400 K. The...
Hexadecapole Approximation in Planetary Microlensing (2008)
The frequency of microlensing planet detections, particularly in difficult-to-model high-magnification events, is increasing. Their analysis can require tens of thousands of processor hours or more,...
A High-Resolution Spectrum of the Highly Magnified Bulge G-Dwarf MOA-2006-BLG-099S (2008)
Johnson, Jennifer A., Gaudi, B. Scott, Sumi, Takahiro, Bond, Ian A., Gould, Andrew
We analyze a high-resolution spectrum of a microlensed G-dwarf in the Galactic bulge, acquired when the star was magnified by a factor of 110. We measure a spectroscopic temperature, derived from the...
The Initial Mass Function of the Galactic Bulge Down to (2007)
Manuela Zoccali Santi, Santi Cassisi, Jay A. Frogel, Andrew Gould, Sergio Ortolani, Alvio Renzini, ...
We present a luminosity function (LF) for lower main sequence stars in the Galactic bulge near (l; b) = (0 ffi ; \Gamma6 ffi ) to J = 24, corresponding to M J 9:3. This LF is derived from Hubble...
Finding Planets Around White Dwarf Remnants of Massive Stars (2007)
Gould, Andrew, Kilic, Mukremin
Planet frequency shows a strong positive correlation with host mass from the hydrogen-burning limit to M ~ 2Msun. No search has yet been conducted for planets of higher-mass hosts because all...
Investigation of the Contamination of the Gould (2003) Halo Sample (2007)
A recent astroph posting argued that the Gould (2003a) halo sample is substantially contaminated with thick-disk stars, which would then ``wash out'' any signature of granularity in the halo velocity...
Microlens Parallax Measurements with a Warm Spitzer (2007)
Because Spitzer is an Earth-trailing orbit, losing about 0.1 AU/yr, it is excellently located to perform microlens parallax observations toward the Magellanic Clouds (LMC/SMC) and the Galactic bulge....
Ground-based Microlensing Surveys (2007)
Gould, Andrew, Gaudi, B. Scott, Bennett, David P.
Microlensing is a proven extrasolar planet search method that has already yielded the detection of four exoplanets. These detections have changed our understanding of planet formation ``beyond the...
Discovery of a Very Bright, Nearby Gravitational Microlensing Event (2007)
Gaudi, B. Scott, Patterson, Joseph, Spiegel, David S., Krajci, Thomas, Koff, R., Pojmanski, G., ...
We report the serendipitous detection of a very bright, very nearby microlensing event. In late October 2006, an otherwise unremarkable A0 star at a distance ~1 kpc (GSC 3656-1328) brightened...
A High-Resolution Spectrum of the Extremely Metal-rich Bulge G Dwarf OGLE-2006-BLG-265 (2007)
Johnson, Jennifer A., Gal-Yam, Avishay, Leonard, Douglas C., Simon, Joshua D., Udalski, Andrzej, Gould, Andrew
We present an R = 45,000 Keck spectrum of the microlensed Galactic bulge G dwarf OGLE-2006-BLG-265, which has high (~60) signal-to-noise ratio despite its short (15 minute) exposure time, because the...
Where are the Old-Population High Velocity Stars? (2007)
Kollmeier, Juna A., Gould, Andrew
To date, all of the reported high velocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young. Old-population HVSs could be much...
Photometric Selection of QSO Candidates From GALEX Sources (2006)
Atlee, David W., Gould, Andrew
We present a catalog of 36,120 QSO candidates from the Galaxy Evolution Explorer (GALEX) Release Two (GR2) UV catalog and the USNO-A2.0 optical catalog. The selection criteria are established using...
Origin of the Break and Mass-Dependence in the Wide-Binary Projected-Separation Distribution (2006)
The distribution of Galactic-disk wide binaries shows a clear break in slope at projected separations of about r_\perp ~ 2500 AU in two basically independent surveys by Chaname & Gould and Lepine &...
A High-Resolution Spectrum of the Extremely Metal-Rich Bulge G-Dwarf OGLE-2006-BLG-265 (2006)
Johnson, Jennifer A., Gal-Yam, Avishay, Leonard, Douglas C., Simon, Joshua D., Udalski, Andrzej, Gould, Andrew
We present an R=45,000 Keck spectrum of the microlensed Galactic bulge G-dwarf OGLE-2006-BLG-265, which has a high (~60) signal-to-noise ratio despite its short (15 min) exposure time because the...
Identification of the OGLE-2003-BLG-235/MOA-2003-BLG-53 Planetary Host Star (2006)
Bennett, David P., Anderson, Jay, Bond, Ian A., Udalski, Andrzej, Gould, Andrew
We present the results of HST observations of the host star for the first definitive extrasolar planet detected by microlensing. The light curve model for this event predicts that the lens star...
Gould, Andrew, Dorsher, Susan, Gaudi, B. Scott, Udalski, Andrzej
We derive the frequencies of hot Jupiters (HJs) with 3--5 day periods and very hot Jupiters (VHJs) with 1-3 day periods by comparing the planets actually detected in the OGLE-III survey with those...
Gould, Andrew, Dorsher, Susan, Gaudi, B. Scott, Udalski, Andrzej
We derive the frequencies of hot Jupiters (HJs) with 3--5 day periods and very hot Jupiters (VHJs) with 1-3 day periods by comparing the planets actually detected in the OGLE-III survey with those...
Gould, Andrew, Dorsher, Susan, Gaudi, B. Scott, Udalski, Andrzej
We derive the frequencies of hot Jupiters (HJs) with 3--5 day periods and very hot Jupiters (VHJs) with 1-3 day periods by comparing the planets actually detected in the OGLE-III survey with those...
Black Hole Masses and Eddington Ratios at 0.3 (2005)
Kollmeier, Juna A., Onken, Christopher A., Kochanek, Christopher S., Gould, Andrew, Weinberg, David H., Dietrich, Matthias, ...
We study the distribution of Eddington luminosity ratios, L_bol/L_edd, of active galactic nuclei (AGNs) discovered in the AGN and Galaxy Evolution Survey (AGES). We combine H-beta, MgII, and CIV line...
Probing the Shape of the Galactic Halo with Hyper-Velocity Stars (2005)
Gnedin, Oleg Y., Gould, Andrew, Miralda-Escude, Jordi, Zentner, Andrew R.
Precise proper motion measurements (sigma_mu ~ 10 mkas/yr) of the recently discovered hyper-velocity star (HVS) SDSS J090745.0+024507 would yield significant constraints on the axis ratios and...
Marshall, J. L., Burke, Christopher J., DePoy, D. L., Gould, Andrew, Kollmeier, Juna A.
We present metallicity estimates for seven open clusters based on spectrophotometric indices from moderate-resolution spectroscopy. Observations of field giants of known metallicity provide a...
Systematic Analysis of 22 Microlensing Parallax Candidates (2005)
Poindexter, Shawn, Afonso, Cristina, Bennett, David P., Glicenstein, Jean-Francois, Gould, Andrew, Szymanski, Michal K., ...
We attempt to identify all microlensing parallax events for which the parallax fit improves \Delta\chi^2 > 100 relative to a standard microlensing model. We outline a procedure to identify three...
E = mc^2 Without Relativity (2005)
The equivalence of mass and energy is indelibly linked with relativity, both by scientists and in the popular mind. I prove that E = mc^2 by demanding momentum conservation of an object that emits...
Probing MACHOs Toward the Galactic Bulge (2005)
If the massive compact halo object (MACHO) fraction of the Galactic dark halo is f ~ 20% as suggested by some microlensing experiments, then about 1.2% of lensing events toward the Galactic bulge are...
Systematic analysis of 22 microlensing parallax candidates (2005)
Poindexter, Shawn, Afonso, Cristina, Bennett, David P., Glicenstein, Jean-Francois, Gould, Andrew, Szymanski, Michal K., ...
We attempt to identify all microlensing parallax events for which the parallax fit improves Deltachi2>100 relative to a standard microlensing model. We outline a procedure to identify three types of...
Halo Luminosity Function From Photometric Calibration of the Revised NLTT (2004)
Gould, Andrew, Kollmeier, Juna A., Chaname, Julio, Salim, Samir
We calibrate the photographic photometry of the revised New Luyten Two-Tenths catalog (rNLTT) by matching 3448 rNLTT stars to the Sloan Digital Sky Survey (SDSS). The correction is linear in...
Microlensing Characterization of Wide-Separation Planets (2004)
Han, Cheongho, Gaudi, B. Scott, An, Jin H., Gould, Andrew
With their excellent photometric precision and dramatic increase in monitoring frequency, future microlensing survey experiments are expected to be sensitive to very short time-scale, isolated events...
Prospects for the Detection of Earth-Mass Planets (2004)
Gould, Andrew, Gaudi, B. Scott, Han, Cheongho
We compare potential state-of-the-art experiments for detecting Earth-mass planets around main-sequence stars using radial velocities, transits, astrometry, and microlensing. For...
The Mass of the MACHO-LMC-5 Lens Star (2004)
Gould, Andrew, Bennett, David P., Alves, David R.
We combine the available astrometric and photometric data for the 1993 microlensing event MACHO-LMC-5 to measure the mass of the lens, M=0.097 +/- 0.016 Msun. This is the most precise direct mass...
I present an Hipparcos color-magnitude diagram (CMD) that is color-coded by transverse velocity v_\perp. This illustrates the connection between the photometric and kinematic properties of various...
KELT: The Kilodegree Extremely Little Telescope (2004)
Pepper, Joshua, Gould, Andrew, DePoy, D. L.
Transits of bright stars offer a unique opportunity to study detailed properties of extrasolar planets that cannot be determined through radial-velocity observations. We propose a technique to find...
Testing Bimodal Planet Formation (2003)
Fields, Dale L., Gould, Andrew
We suggest that the observed break in giant-planet frequency as a function of host metallicity at Z=0.02 may be a reflection of bimodal planet formation. We search for signatures of this bimodality...
Resolution of the MACHO-LMC-5 Puzzle: The Jerk-Parallax Microlens Degeneracy (2003)
By extending the constant-acceleration analysis of Smith, Mao, & Paczynski to include jerk, I show that microlens parallax measurements are subject to a four-fold discrete degeneracy. The new...
Proper Motion Catalog From SDSS \intersect USNO-B (2003)
Gould, Andrew, Kollmeier, Juna A.
We present a catalog of 345,000 stars with proper motions \mu > 20 mas/yr and magnitudes r' 19.5, and high proper motions. We present a diagrammatic method to estimate the level of contamination in...
The mathematics of linear fits is presented in covariant form. Topics include: correlated data, covariance matrices, joint fits to multiple data sets, constraints, and extension of the formalism to...
New Hipparcos-based Parallaxes for 424 Dim Stars (2003)
We present a catalog of 424 common proper motion companions to Hipparcos stars with good (>3 sigma) parallaxes, thereby effectively providing new parallaxes for these companions. Compared to stars in...
M Dwarfs from Hubble Space Telescope Star Counts. V. The I-band Luminosity Function (2003)
Zheng, Zheng, Flynn, Chris, Gould, Andrew, Bahcall, John N., Salim, Samir
We derive the disk I-band luminosity function from the Zheng et al. sample of \~1400 disk M dwarfs observed with the Hubble Space Telescope. We adopt a Galactic-height-dependent color-magnitude...
The End of the MACHO Era: Limits on Halo Dark Matter from Stellar Halo Wide Binaries (2003)
Yoo, Jaiyul, Chaname, Julio, Gould, Andrew
We simulate the evolution of halo wide binaries in the presence of MAssive Compact Halo Objects (MACHOs) and compare our results to the sample of wide binaries of Chaname & Gould (2003). The observed...
We present a catalog of 1147 candidate common proper motion binaries selected from the revised New Luyten Two-Tenths Catalog. Among these, we identify 999 genuine physical pairs using the measured...
Resolving the Microlens Mass Degeneracy for Earth-Mass Planets (2003)
Gould, Andrew, Gaudi, B. Scott, Han, Cheongho
Of all planet-finding techniques, microlensing is potentially the most sensitive to Earth-mass planets. However, microlensing lightcurves generically yield only the planet-star mass ratio: the mass...
An Upper Limit on the Granularity of the Local Stellar Halo (2003)
I use the statistical properties of 4588 nearby halo stars to show that if the local stellar halo is composed of cold streams from disrupted dwarf satellites as is predicted by popular cosmologies,...
Stellar Contribution to the Galactic Bulge Microlensing Optical Depth (2003)
We estimate the optical depth to self-lensing by stars in the Galactic bulge using the HST star counts of Holtzman et al and Zoccali et al as extrapolated by Gould into the brown-dwarf and remnant...
Gould, Andrew, Fischer, Debra A.
Early-type stars appear to be a difficult place to look for planets astrometrically. First, they are relatively heavy, and for fixed planetary mass the astrometric signal falls inversely as the...
Sgr A* Companion S0-2: A Probe of Very High-Mass Star Formation (2003)
Gould, Andrew, Quillen, Alice C.
The star S0-2, which is orbiting Sgr A* with a 15-yr period, almost certainly did not form in situ. We propose that it was injected into this close orbit by the tidal disruption of a massive-star...
Completeness of USNO-B for High Proper-Motion Stars (2002)
I test the completeness of USNO-B detections of high proper-motion (mu>0.18"/yr) stars and the accuracy of its measurements by comparing them to the revised NLTT (rNLTT) catalog of Salim & Gould. For...
Sensitivity of Transit Searches to Habitable Planets (2002)
Gould, Andrew, Pepper, Joshua, DePoy, D. L.
Photon-limited transit surveys in V band are in principle about 20 times more sensitive to planets of fixed size in the habitable zone around M stars than G stars. In I band the ratio is about 400....
Transit Target Selection Using Reduced Proper Motions (2002)
Gould, Andrew, Morgan, Christopher W.
In searches for planetary transits in the field, well over half of the survey stars are typically giants or other stars that are too large to permit straightforward detection of planets. For all-sky...
A 1" Telescope: The Optimal Approach to Bright-Star Planetary Transits (2002)
Pepper, Joshua, Gould, Andrew, DePoy, D. L.
Planetary transits of bright stars, V < 10, offer the best opportunity for detailed studies of extra-solar planets, such as are already being carried out for HD209458b. Since these stars are rare,...
Using All-Sky Surveys to Find Planetary Transits (2002)
Pepper, Joshua, Gould, Andrew, Depoy, D. L.
Transits of bright stars offer a unique opportunity to study detailed properties of extrasolar planets that cannot be determined through radial-velocity observations. We propose a new technique to...
Stellar Halo Parameters from 4588 Subdwarfs (2002)
Using a reduced proper motion discriminator, I obtain a sample of 4588 subdwarfs from the Revised NLTT Catalog of Salim & Gould. The ample statistics and low contamination permit much more precise...
Revised NLTT (New Luyten Catalogue of Stars With Proper Motions Larger than Two Tenths of an Arcsecond) contains improved astrometry and new optical/infrared photometry for the vast majority of NLTT...
We complete construction of a catalog containing improved astrometry and new optical/infrared photometry for the vast majority of NLTT stars lying in the overlap of regions covered by POSS I and by...
Classifying Luyten Stars Using An Optical-Infrared Reduced Proper Motion Diagram (2002)
We present a V-J reduced proper motion (RPM) diagram for stars in the New Luyten Two-Tenths (NLTT) catalog. In sharp contrast to the RPM diagram based on the original NLTT data, this optical-infrared...
Improved Astrometry and Photometry for the Luyten Catalog. I. Bright Stars (2002)
We outline the construction of an updated version of the New Luyten Two-Tenths (NLTT) catalog of high proper motion stars, which will contain improved astrometry and photometry for the vast majority...
Microlens Parallaxes of Binary Lenses Measured from a Satellite (2002)
Graff, David S., Gould, Andrew
Caustic-crossing binary lenses make up about 5% of all detected microlenses. The relative proper motion of a caustic-crossing binary lens can be measured with observations from a single terrestrial...
Millisecond Pulsars as Probes of Mass Segregation in the Galactic Center (2001)
We propose a simple test for the existence of a cluster of black hole remnants around Sgr A* that is based on a small sample of any type of Galactic Center objects, provided they are substantially...
Searching for Failed Supernovae With Astrometric Binaries (2001)
Stars in the mass range 8 Msun
Astrometry Survey Missions Beyond the Magnitude Limit (2001)
Salim, Samir, Gould, Andrew, Olling, Rob
Three planned astrometry survey satellites, FAME, DIVA, and GAIA, all aim at observing magnitude-limited samples. We argue that substantial additional scientific opportunities are within the reach of...
Microlens Mass Measurement using Triple-Peak Events (2001)
We show that one can measure the effects of microlens parallax for binary microlensing events with three well-measured peaks -- two caustic crossings plus a cusp approach, and hence derive the...
Resolving Microlens Blends Using Image Subtraction (2001)
Blended light is an important source of degeneracy in the characterization of microlensing events, particularly in binary-lens and high magnification events. We show how the techniques of image...
Applications of Microlensing to Stellar Astrophysics (2001)
Over the past decade, microlensing has developed into a powerful tool to study stellar astrophysics, especially stellar atmospheres, stellar masses, and binarity. I review this progress. Stellar...
Microlensing by Stellar Black Holes Around Sgr A* (2001)
Chaname, Julio, Gould, Andrew, Miralda-Escude, Jordi
We show that at any given time, the Galactocentric black hole Sgr A* is expected to be microlensing N(lens)=1.7 bulge stars if the threshold of detectability of the fainter image is K(thr)=21, and...
M Dwarfs from Hubble Space Telescope Star Counts. IV (2001)
Zheng, Zheng, Flynn, Chris, Gould, Andrew, Bahcall, John N., Salim, Samir
We study a sample of about 1400 disk M dwarfs that are found in 148 fields observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and 162 fields observed with pre-repair Planetary...
Analytic Study of Grid Star and Reference Star Selection for the Space Interferometry Mission (2001)
Grid stars and reference stars provide the fundamental global and local astrometric reference frames for observations by the Space Interferometry Mission. They must therefore be astrometrically...
I present a somewhat selective review of microlensing theory, covering five major areas: 1) the derivation of the basic formulae, 2) the relation between the observables and the fundamental physical...
The Ratio of Total to Selective Extinction Toward Baade's Window (2000)
Gould, Andrew, Stutz, Amelia, Frogel, Jay A.
We measure the ratio of total to selective extinction, R_{VI}=A_V/E(V-I), toward Baade's Window by comparing the VIK colors of 132 Baade's Window G and K giants from Tiede, Frogel, & Terndrup with...
A Cluster of Black Holes at the Galactic Center (2000)
Miralda-Escude, Jordi, Gould, Andrew
If the stellar population of the bulge contains black holes formed in the final core collapse of ordinary stars with M \ga 30 M_{\odot}, then about 25,000 stellar mass black holes should have...
A Natural Formalism for Microlensing (2000)
If the standard microlensing geometry is inverted so that the Einstein ring is projected onto the observer plane rather than the source plane, then the relations between the observables...
Astrometric Resolution of Severely Degenerate Binary Microlensing Events (2000)
We investigate whether the "close/wide" class of degeneracies in caustic-crossing binary microlensing events can be broken astrometrically. Dominik showed that these degeneracies are particularly...
Superluminal Caustics of Close, Rapidly-Rotating Binary Microlenses (2000)
The two outer triangular caustics (regions of infinite magnification) of a close binary microlens move much faster than the components of the binary themselves, and can even exceed the speed of...
Binary Black Hole Mergers from Planet-like Migrations (1999)
Gould, Andrew, Rix, Hans-Walter
If supermassive black holes (BHs) are generically present in galaxy centers, and if galaxies are built up through hierarchical merging, BH binaries are at least temporary features of most galactic...
Can Heavy WIMPs Be Captured by the Earth? (1999)
Gould, Andrew, Alam, S. M. Khairul
If weakly interacting massive particles (WIMPs) in bound solar orbits are systematically driven into the Sun by solar-system resonances (as Farinella et al. have shown is the case for many...
Nearby Microlensing Events - Identification of the Candidates for the SIM (1999)
The Space Interferometry Mission (SIM) is the instrument of choice when it comes to observing astrometric microlensing events where nearby, usually high-proper-motion stars (``lenses''), pass in...
Stellar Mass Function From SIM Astrometry/Photometry (1999)
By combining SIM observations with ground-based photometry, one can completely solve microlensing events seen toward the Galactic bulge. One could measure the mass, distance, and transverse velocity...
Measuring the Remnant Mass Function of the Galactic Bulge (1999)
I show that by observing microlensing events both astrometrically and photometrically, the Space Interferometry Mission (SIM) can measure the mass function of stellar remnants in the Galactic bulge...
A New Kinematic Distance Estimator to the LMC (1999)
The distance to the Large Magellanic Cloud (LMC) can be directly determined by measuring three of its properties, its radial-velocity field, its mean proper motion, and the position angle \phi_ph of...
Selection of Nearby Microlensing Candidates for Observation by SIM (1999)
I investigate the prospects for using the Space Interferometry Mission (SIM) to measure the masses of nearby stars from their astrometric deflection of more distant sources, as originally suggested...
A New Argument Against An Intervening Stellar Population Toward the LMC (1999)
Zaritsky & Lin have claimed detection of an intervening population of stars toward the Large Magellanic Cloud (LMC) which, they believe, could account for a substantial fraction of the observed...
Photometric Microlens Parallaxes with SIM (1999)
Astrometric measurements of microlensing events can in principle determine both the "parallax" \tilde r_E and the "proper motion" \mu of an individual event which (combined with the Einstein time...
Faint star counts with HST (1998)
Flynn, Chris, Gould, Andrew, Bahcall, John
We describe a program of star counts in the range 19 < I < 26 made with the WFPC cameras aboard the Hubble Space Telescope. Red (V-I > 1.0) stars at these magnitudes are primarily disk and spheroid M...
Sgr A* ``Visual Binaries'': A Direct Measurement of the Galactocentric Distance (1998)
We present a new geometrical method for measuring the distance to the Galactic center (R_0) by solving for the Keplerian orbit of individual stars bound to the black hole associated with the Sgr A*...
Correlated errors in Hipparcos parallaxes towards the Pleiades and the Hyades (1998)
Narayanan, Vijay K., Gould, Andrew
We show that the errors in the Hipparcos parallaxes towards the Pleiades and the Hyades open clusters are spatially correlated over angular scales of 2 to 3 deg, with an amplitude of up to 2 mas....
Complete Parallax and Proper Motion Solutions For Halo Binary-Lens Microlensing Events (1998)
Gould, Andrew, Andronov, Nikolay
A major problem in the interpretation of microlensing events is that the only measured quantity, the Einstein time scale t_E, is a degenerate combination of the three quantities one would like to...
Empirical Calibration of Hubble Space Telescope WFPC2 F606W and F814W Photometry (1998)
Using the ground-based V and I photometry of a sample of stars from the Groth Strip, we obtain the first empirical calibration of the F606W and F814W Hubble Space Telescope WFPC2 filters for 0.5
A Precision test of Hipparcos systematics towards the Hyades (1998)
Narayanan, Vijay K., Gould, Andrew
We propose and apply a test that can detect any systematic errors in the Hipparcos parallaxes towards the Hyades cluster at the level of 0.3 mas. We show that the statistical parallax method subsumes...
Anomaluos RR Lyrae (V-I)_0 colors in Baade's Window (1998)
Stutz, Amelia, Popowski, Piotr, Gould, Andrew
We compare (V-I)_0-(V-K)_0 color-color and (V-I)_0-log P period-color diagrams for Baade's Window and local RRab Lyrae stars. We find that for a fixed log P the Baade's Window RR Lyrae stars are...
Galactic Structure From Infrared Surveys (1998)
By combining the 2MASS and DENIS infrared surveys with the USNO-B proper-motion catalog, it will be possible to map the structure of the Galaxy in unprecedented detail. The key parameter that these...
The RR Lyrae Distance Scale (1998)
Popowski, Piotr, Gould, Andrew
We review seven methods of measuring the absolute magnitude M_V of RR Lyrae stars in light of the Hipparcos mission and other recent developments. We focus on identifying possible systematic errors...
Optimal Microlensing Observations (1998)
One of the major limitations of microlensing observations toward the Large Magellanic Cloud (LMC) is the low rate of event detection. What can be done to improve this rate? Is it better to invest...
Microlens Parallaxes with SIRTF (1998)
The Space Infrared Telescope Facility (SIRTF) will drift away from the Earth at about 0.1 AU/yr. Microlensing events will therefore have different characteristics as seen from the satellite and the...
Systematics of RR Lyrae Statistical Parallax III: Apparent Magnitudes and Extinctions (1998)
Gould, Andrew, Popowski, Piotr
We sing the praises of the central limit theorem. Having previously removed all other possible causes of significant systematic error in the statistical parallax determination of RR Lyrae absolute...
Isolating Red Giant Stars in M31's Elusive Outer Spheroid (1998)
Reitzel, David B., Guhathakurta, Puragra, Gould, Andrew
Deep UBRI images of a 15'x15' field in the M31 galaxy's outer spheroid obtained with the KPNO 4-m telescope, and Keck 10-m telescope+LRIS I-band images, are used to isolate candidate red giant branch...
Spectrophotometric Resolution of Stellar Atmospheres with Microlensing (1998)
Gaudi, B. Scott, Gould, Andrew
Microlensing is a powerful tool for studying stellar atmospheres because as the source crosses regions of formally infinite magnification (caustics) the surfaceof the star is resolved, thereby...
The Hipparcos Proper Motions in Support of the Short RR Lyrae Distance Scale (1998)
Popowski, Piotr, Gould, Andrew
In this paper we investigate whether a misestimate of proper motions could have been a source of substantial systematic errors in the statistical parallax determination of the absolute magnitude of...
Microlens Parallax Asymmetries Toward the LMC (1998)
If the microlensing events now being detected toward the Large Magellanic Cloud (LMC) are due to lenses in the Milky Way halo, then the events should typically have asymmetries of order 1% due to...
No Death Star -- For Now (1998)
A star passing within $\sim 10^4 \au$ of the Sun would trigger a comet shower that would reach the inner solar system about 0.18 Myr later. We calculate a prior probability of ~0.4% that a star has...
The Spheroid Luminosity and Mass Functions From HST Star Counts (1997)
Gould, Andrew, Flynn, Chris, Bahcall, John N.
We analyze 166 spheroid subdwarfs $(6.50.09 Msun. The spheroid therefore does not contribute significantly to microlensing unless the mass function changes slope dramatically in the substellar range....
The Proper Motion of NGC 6522 in Baade's Window (1997)
Terndrup, Donald M., Popowski, Piotr, Gould, Andrew, Rich, R. Michael, Sadler, Elaine M.
We 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...
LMC Microlenses: Dark or Luminous? (1997)
Zhao has proposed that the microlensing events observed toward the Large Magellanic Cloud (LMC) could be due to faint stars in a dwarf galaxy or tidal debris lying along the line of sight to the LMC....
Pixel Lensing Search For Bright Microlensing Events and Variables in the Galactic Bulge (1997)
We describe a new method to search for gravitational microlensing toward the Galactic bulge that employs a small camera rather than a conventional telescope and probes new regions of parameter space....
Non-Acceleration of Sgr A*: Implications for Galactic Structure (1997)
Gould, Andrew, Ramirez, Solange V.
We show that observations by Backer and collaborators over the past two decades constrain the time derivative of the proper motion of Sgr A* to be less than 0.14 mas yr^{-2}. Using this result and a...
Upper Limit to the Distance to the Large Magellanic Cloud (1997)
We remeasure the ``light echo'' times to the near and far side of the ring around SN 1987A using the method of Gould (1995) and the new reductions of the original UV spectra by Sonneborn et al....
The Zero Point of Extinction Toward Baade's Window (1997)
Gould, Andrew, Popowski, Piotr, Terndrup, Donald M.
We measure the zero point of the Stanek (1996) extinction map by comparing the observed (V-K) colors of 206 K giant stars with their intrinsic (V-K)_0 colors as derived from their H\beta indices. We...
Mathematics of Statistical Parallax and the Local Distance Scale (1997)
Popowski, Piotr, Gould, Andrew
We present a mathematical analysis of the statistical parallax method. The method yields physical insight into the maximum-likelihood determinations of the luminosity and velocity distribution and...
Microlensing: Current Results and Future Prospects (1997)
The initial results of microlensing surveys toward the Galactic bulge and the LMC are puzzling. Toward the LMC, the total mass in MACHOs is of order half that required to explain the dark matter, but...
Cepheid Luminosity Versus Galaxy Rotation Speed: L ~ v^{0.7} (1997)
Gould, Andrew, Popowski, Piotr
The distance modulus of a galaxy determined from Cepheids differs from its distance modulus determined from Tully-Fisher by an amount that is proportional to the galaxy's line width, W: Delta mu ~...
A survey for large image-separation lensed quasars (1996)
Maoz, Dan, Rix, Hans-Walter, Gal-Yam, Avishay, Gould, Andrew
The statistics of gravitationally lensed quasars with multiple images in the 0.1''-7'' range have been measured in various surveys. Little is known, however, about lensed-quasar statistics at larger...
Signatures of Accretion Disks in Quasar Microlensing (1996)
Gould, Andrew, Miralda-Escude, Jordi
We propose that relative variability on short time-scales of the multiple images of a lensed quasar, after removal of the time delay, may be caused by hot spots or other moving structures in the...
Star Counts From HST: Implications for Dark Matter (1996)
Star counts made with the Hubble Space Telescope (HST) probe four populations that are important for dark matter: disk, halo, bulge, and intergalactic. The disk mass function falls for masses M
M Dwarfs From Hubble Space Telescope Star Counts III: The Groth Strip (1996)
Gould, Andrew, Bahcall, John N., Flynn, Chris
We analyze the disk M dwarfs found in 31 new fields observed with the Wide Field Camera (WFC2) on the Hubble Space Telescope (HST) together with the sample previously analyzed from 22 WFC2 fields and...
Microlensing: Prospects for the Future (1996)
Four ongoing microlensing experiments have produced important new results but also big puzzles, the major one being that the expected classes of lenses cannot account for the observed distribution of...
Measuring the Rotation Speed of Giant Stars From Gravitational Microlensing (1996)
During some gravitational lensing events, the lens transits the face of the star. This causes a shift in the apparent radial velocity of the star which is proportional to its rotation speed. It also...
Planet Parameters in Microlensing Events (1996)
Gaudi, B. Scott, Gould, Andrew
A planetary microlensing event occurs when a planet perturbs one of the two images created in a point-mass microlensing event, causing a deviation from the standard Paczy\'nski curve. Determination...
The Hollywood Strategy for Microlensing Detection of Planets (1996)
Follow the big stars! I review the theory of detection and parameter measurement of planetary systems by follow-up observations of ongoing microlensing events. Two parameters can generically be...
Finite Source Effects in Microlensing Events (1996)
Gould, Andrew, Gaucherel, Cedric
The computation of the magnification of a finite source by an arbitrary gravitational lens can be reduced from a two-dimensional to a one-dimensional integral using a generalization of Stoke's...
Detection Rates for Close Binaries Via Microlensing (1996)
Gaudi, B. Scott, Gould, Andrew
Microlensing is one of the most promising methods of reconstructing the stellar mass function down to masses even below the hydrogen-burning limit. The fundamental limit to this technique is the...
Femtolens Imaging of a Quasar Central Engine Using a Dwarf Star Telescope (1996)
Gould, Andrew, Gaudi, B. Scott
We show that it is possible to image the structure of a distant quasar on scales of $\sim 1\,$AU by constructing a telescope which uses a nearby dwarf star as its ``primary lens'' together with a...
Les Microlentilles Gravitationnelles (1996)
Je presente une revue des microlentilles gravitationnelles en quatre lecons. Dans un premier temps, je discute la theorie des microlentilles dans le contexte general des lentilles, en incluant les...
Einstein Radii from Binary Lensing Events (1996)
We show that the Einstein ring radius and transverse speed of a lens projected on the source plane, $\hat{r}_{\rm e}$ and $\hat{v}$, can be determined from the light curve of a binary-source event,...
Microlensing and the Stellar Mass Function (1996)
Traditional approaches to measuring the stellar mass function (MF) are fundamentally limited because objects are detected based on their luminosity, not their mass. These methods are thereby...
Extreme microlensing events, defined as events with maximum magnification $A_\max\gsim 200$ are a potentially powerful probe of the mass spectrum and spatial distribution of objects along lines of...
Luminosity Function of the Perigalactocentric Region (1996)
Narayanan, Vijay K., Gould, Andrew, DePoy, D. L.
We present H and K photometry of 42,000 stars in an area of 250 arcmin$^{2}$ centered on the Galactic center. We use the photometry to construct a dereddened K band luminosity function (LF) for this...
Hubble Deep Field Constraint on Baryonic Dark Matter (1996)
Flynn, Chris, Gould, Andrew, Bahcall, John N.
We use a new technique to search for faint red stars in the Hubble Deep Field (HDF) imaged by the Wide Field Camera (WFC2) on the {\it Hubble Space Telescope}. We construct a densely sampled stellar...
Galactic versus Extragalactic Pixel Lensing Events toward M31 (1996)
A new type of gravitational microlensing experiment toward a field where stars are not resolved is being developed observationally and theoretically: pixel lensing. When the experiment is carried out...
Satellite Parallaxes of Lensing Events Towards the Galactic Bulge (1996)
Gaudi, B. Scott, Gould, Andrew
In order to understand the nature of the lenses that generate microlensing events, one would like to measure their mass, distance, and velocity. Unfortunately, current microlensing experiments...
Imaging the Lyman-alpha Forest (1995)
Gould, Andrew, Weinberg, David H.
We show that it is now possible to image optically thick $\lya$ clouds in fluorescent $\lya$ emission with a relatively long ($\sim 20 $hr) integration on a large ($\sim 10 $m) telescope. For a broad...
Theory of Pixel Lensing (1995)
Pixel lensing, gravitational microlensing of unresolved stars, is potentially much more sensitive and much more widely applicable than is generally recognized. I give explicit expressions for the...
Monte Carlo Simulations of Macho Parallaxes From a Satellite (1995)
Boutreux, Thomas, Gould, Andrew
Three ongoing microlensing experiments have found more candidate events than expected from the known stars. These experiments measure only one parameter of the massive compact halo objects (machos),...
Limits on the Gravity Wave Background From Microlensed Quasars (1995)
The paper previously submitted under this title is incorrect in that it drastically overestimates the cumulative deflection due to a gravitational wave (GW) background. Avi Loeb gives a simple...
Macho Proper Motions From Optical/Infrared Photometry (1995)
Gould, Andrew, Welch, Douglas L.
Optical/infrared photometry can double the number of proper motion measurements of Massive Compact Objects (MACHOs) relative to single band photometry. The proper motion of a MACHO can be measured by...
Lunar Occultation of MACHOs (1995)
Han, Cheongho, Narayanan, Vijay K., Gould, Andrew
Lunar occultation can be used to measure the proper motions of some of the long time scale microlensing events, $t_{e} \gsim 70$ days, now being detected toward the Galactic bulge. The long events...
Disk M Dwarf Luminosity Function From HST Star Counts (1995)
Gould, Andrew, Bahcall, John N., Flynn, Chris
We study a sample of 257 Galactic disk M dwarfs (8
Nemiroff, Robert J., Gould, Andrew
Two spacecraft separated by $\sim 1\,\au$ and equipped with gamma-ray burst (GRB) detectors could detect or rule out a cosmological density of Massive Compact Halo Objects (MACHOs) in the mass range...
Microlensing Search of $10^6$ Quasars (1995)
By monitoring $10^6$ quasars one could search for lensing by stars and Massive Compact Halo Objects (Machos) out to redshifts $z\sim 4$. If Machos have a present cosmological density...
Statistical Determination of the MACHO Mass Spectrum (1995)
The mass function of 51 Massive Compact Objects (MACHOs) detected toward the Galactic bulge is statistically estimated from Einstein ring crossing times $t_{\rm e}$. For a Gaussian mass function, the...
Search for Intra-Cluster Machos by Pixel Lensing of M87 (1995)
Intra-Cluster Machos (ICMs) are a plausible candidate for at least some of the dark matter in clusters of galaxies. ICMs can be detected by searching toward M87 for ``pixel lensing'', gravitational...
K Band Microlensing of the Inner Galaxy (1994)
Microlensing searches toward the inner galaxy $(|l|,|b|\leq 22.\hskip-2pt'5)$ have several major advantages. First, the event rate is strongly dominated by bulge-bulge lensing events where both the...
Statistics Of Microlensing Optical Depth (1994)
We show that the statistical error, $\sigma_{\tau}$, in estimating the optical depth, $\tau$, due to microlensing is substantially higher than the naive Poisson estimate: $\sigma_{\tau} = \sqrt{\eta...
A New Macho Search Strategy (1994)
I propose a radical revision in the search strategy for Massive Compact Objects (Machos) toward the Galactic bulge: monitor the entire $\sim 300$ square deg of the bulge and tune the search primarily...
Self-Lensing By Binaries (1994)
Lensing of one member of a binary by its companion is studied for several classes of binaries. For binaries in which at least one member is an ordinary (non-compact) star, the optical depths to...
The Mass Spectrum Of Machos From Parallax Measurements (1994)
We demonstrate that by making satellite-based parallax measurements of Macho events, it is possible to distinguish disk from bulge Machos and to determine individual masses of disk Machos to an...
Transverse Velocities of Galaxies From Microlens Parallaxes (1994)
The transverse velocity of a spiral galaxy can be measured to an accuracy $\sim 60\,\kms$ by making parallax observations of quasars being microlensed by stars in the disk of the galaxy. To make the...
Microlensing Events: End of the Dark Halo? (1994)
I obtain an upper limit for the optical depth to microlensing toward Baade's Window of $3\times 10^{-6}$ by assuming that all of the mass of the Galaxy interior to the Sun (and not in the bulge) is...
Macho Parallaxes From A Single Satellite (1994)
Massive Compact Objects (Machos) are currently being discovered at substantially higher rates than would be expected from standard models of known stellar populations. To determine whether they are...
Self-Lensing By A Stellar Disk (1994)
I derive a general expression for the optical depth $\tau$ for gravitational lensing of stars in a disk by Massive Compact Objects (Machos) in the same disk. For the more restricted case where the...
The Supernova Ring Revisited II: Distance to the LMC (1994)
I derive an upper limit to the distance to SN 1987A of $\dsn
Analytic Error Estimates (1994)
I present an analytic method for estimating the errors in fitting a distribution. A well-known theorem from statistics gives the minimum variance bound (MVB) for the uncertainty in estimating a set...
M Dwarfs, Microlensing, and the Mass Budget of the Galaxy (1994)
Bahcall, John N., Flynn, Chris, Gould, Andrew, Kirhakos, Sofia
We show that faint red stars do not contribute significantly to the mass budget of the Galaxy or to microlensing statistics. Our results are obtained by analyzing two long exposures of a...
Microlensing by Stars in the Disk of M31 (1994)
The optical depth to microlensing toward M31 due to known stars in the disk of M31 itself is $\tau\sim 2\times 10^{-7}e^{-r/d}$ where $d$ is the disk scale length and $r$ is the distance along the...
Weak Lensing By Nearby Structures (1994)
Gould, Andrew, Villumsen, Jens
Weak gravitational lensing due to nearby structures, such as the Coma cluster, and the Local Supercluster can be expected to polarize images of distant galaxies by ${\cal O}(0.2%\Omega)$ with...
A Spectroscopic Method to Measure Macho Proper Motions (1994)
A Massive Compact Halo Object (Macho) that lenses a background star will magnify different parts of the rotating stellar disk by varying amounts. The differential magnification will cause a shift in...
Geometry of the HST Planetary Camera Field (1993)
We present a solution for the relative positions and orientations of the four CCD chips on the Hubble Space Telescope (HST) Planetary Camera (PC). An accurate solution is required when matching HST...
MACHOs in a Flattened Halo (1993)
Sackett, Penny D., Gould, Andrew
If massive compact halo objects (\ms) are detected in ongoing searches, then \tsmctlmc, the ratio of the optical depth toward the Small and Large Magellanic Clouds, will be a robust indicator of the...
New firms and rural industrialization in East Anglia
Gould A. and Keeble D. (1984) New firms and rural industrialization in East Anglia, Reg. Studies 18, 189--201. The paper analyses key aspects of the formation of new independent manufacturing firms...