D. R. Alves
A5106762436- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- History and Developments in Astronomy
- Astrophysical Phenomena and Observations
- Geophysics and Gravity Measurements
- Scientific Research and Discoveries
- Pulsars and Gravitational Waves Research
- Photocathodes and Microchannel Plates
- Cosmology and Gravitation Theories
- Distributed and Parallel Computing Systems
- Advanced optical system design
- Impact of Light on Environment and Health
- Astrophysics and Cosmic Phenomena
- Advanced Measurement and Metrology Techniques
- Magnetic Bearings and Levitation Dynamics
- Optical measurement and interference techniques
- Calibration and Measurement Techniques
- Quantum chaos and dynamical systems
- Hydraulic Fracturing and Reservoir Analysis
University of Chile
2021-2024
Millennium Institute of Astrophysics
2022-2024
Centro de Astrofísica y Tecnologías Afines
2022-2024
Queen Mary University of London
2023
University of Warwick
2022
Institute of Astrophysics and Space Sciences
2020
University of Lisbon
2020
Lawrence Livermore National Laboratory
1995-2007
Goddard Space Flight Center
2005
Columbia University
2002-2004
We report on our search for microlensing towards the Large Magellanic Cloud (LMC). Analysis of 5.7 years photometry 11.9 million stars in LMC reveals 13 - 17 events. This is significantly more than $\sim$ 2 to 4 events expected from lensing by known stellar populations. The timescales ($\that$) range 34 230 days. estimate optical depth with $2 < \that 400$ days be 1.2 ^{+0.4}_ {-0.3} \ten{-7}$, an additional 20% 30% systematic error. spatial distribution mildly inconsistent LMC/LMC disk...
The MACHO Project is a search for dark matter in the form of massive compact halo objects (MACHOs). Photometric monitoring millions stars Large Magellanic Cloud (LMC), Small (SMC), and Galactic bulge used to gravitational microlensing events caused by these otherwise invisible objects. Analysis first 2.1 yr photometry 8.5 million LMC reveals eight candidate events. This substantially more than number expected (~1.1) from lensing known stellar populations. timescales (t) range 34 145 days. We...
Determining the architecture of multi-planetary systems is one cornerstones understanding planet formation and evolution. Resonant are especially important as fragility their orbital configuration ensures that no significant scattering or collisional event has taken place since earliest phase when parent protoplanetary disc was still present. In this context, TOI-178 been subject particular attention first TESS observations hinted at a 2:3:3 resonant chain. Here we report results from...
The EROS and MACHO collaborations have each published upper limits on the amount of planetary mass dark matter in Galactic Halo obtained from gravitational microlensing searches. In this paper two are combined to give a much stronger constraint abundance low MACHOs.
We present the first detection of parallax effects in a gravitational microlensing event. Parallax event observed only from Earth appears as distortion (otherwise symmetrical) light curve arising motion around Sun. This can be detected if duration is not much less than year and projected velocity lens larger orbital about The presented here has (or Einstein diameter crossing time) = 220 days clearly shows resulting Earth's motion. find that 75 ± 5 km s-1 at an angle 28° 4° direction...
We report the detection of 45 candidate microlensing events in fields toward Galactic bulge. These come from analysis 24 containing 12.6 million stars observed for 190 days 1993. Many these are extremely high signal-to-noise ratio and remarkable examples gravitational microlensing. The distribution peak magnifications is shown to be consistent with interpretation events. Using a subsample 1.3 "clump giant" whose distance efficiency well known, we find 13 estimate optical depth bulge as...
We report on a search for long duration microlensing events towards the Large Magellanic Cloud. find none, and therefore put limits contribution of high mass objects to Galactic dark matter. At 95% confidence level we exclude in range 0.3 solar masses 30.0 from contributing more than 4 times 10^11 halo. Combined with earlier results, this means that under 30 cannot make up entire matter halo if is typical size. For halo, 10 contribute less 40%
We present the microlensing optical depth toward Galactic bulge based on detection of 99 events found in our Difference Image Analysis (DIA) survey. This analysis encompasses 3 yr data, covering ~17 million stars ~4 deg2, to a source-star baseline magnitude limit V = 23. The DIA technique improves quality photometry crowded fields, and allows us detect more with faint source stars. find that this method increases number by 85% compared standard technique. light curves are presented, fit...
We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event toward the Galactic bulge whose peak magnification departs significantly from standard point-source model. 95-30 was observed in real time by Global Microlensing Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout event. interpret light-curve "fine structure" as indicating transit lens across extended face source star. This signifies resolution star several...
Using 7 years of MACHO survey data, we present a new determination the optical depth to microlensing towards Galactic bulge. We select sample 62 events (60 unique) on clump giant sources and perform detailed efficiency analysis. use only because these are bright bulge stars not as strongly affected by blending other events. subsample 42 concentrated in just 4.5 square degrees, find tau = 2.17^{+0.47}_{-0.38} x 10^{-6} at (l,b) (1.50, -2.68), somewhat smaller than found most previous studies,...
We present an analysis of the longest timescale microlensing events discovered by MACHO Collaboration during a 7 year survey Galactic bulge. find 6 that exhibit very strong parallax signals due, in part, to accurate photometric data from GMAN and MPS collaborations. The fit parameters are used likelihood analysis, which is able estimate distance masses lens objects based upon standard model velocity distribution. This indicates most likely 5 lenses > 1 Msun, suggests substantial fraction...
More than 1300 variables classified provisionally as first-overtone RR Lyrae pulsators in the MACHO variable-star database of Large Magellanic Cloud (LMC) have been subjected to standard frequency analysis. Based on remnant power prewhitened spectra, we found 70% total population be monoperiodic. The remaining 30% (411 stars) are one nine types according their spectra. Several pulsational behavior clearly identified here for first time. Together with earlier discovered double-mode...
We fit the data for binary lens microlensing event MACHO 98-SMC-1 from five different collaborations and find two distinct solutions characterized by separation d mass ratio q: (d,q) = (0.54,0.50) (3.65,0.36), where is in units of Einstein radius. However, relative proper motion very similar solutions, 1.30 km s-1 kpc-1 1.48 kpc-1, thus confirming that Small Magellanic Cloud. The close can be either rotating or approximately static but wide must at to its maximum allowed rate consistent with...
We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and 38. is a bright ($T = 8.5$ mag), high proper motion ($\sim\,200$ mas yr$^{-1}$), low metallicity ([Fe/H]$\approx\,-0.28$) K-dwarf with mass $0.68\pm0.05$ M$_{\odot}$ radius $0.67\pm0.01$ R$_{\odot}$. obtain photometric follow-up observations variety facilities, we use these data-sets to determine that inner planet, b, $1.70\pm0.07$ R$_{\oplus}$ super-Earth in 3.82 day orbit,...
We present the light curves of 21 gravitational microlensing events from first six years MACHO Project survey that are likely examples lensing by binary systems. These were manually selected a total sample ~350 candidate either detected Alert System or discovered through retrospective analyses database. At least 14 these exhibit strong (caustic) features, and four well fit with large mass ratio (brown dwarf planetary) systems, although fits not necessarily unique. The event rate is roughly...
We have frequency-analyzed 6391 variables classified earlier as fundamental-mode RR Lyrae (RR0) stars in the MACHO database on Large Magellanic Cloud (LMC). The overwhelming majority (i.e., 96%) of these been proved to be indeed RR0 stars, whereas remaining ones fallen into one following categories: single- and double-mode Cepheids, binaries, first-overtone nonclassified variables. Special attention has paid properties amplitude- phase-modulated (the Blazhko stars). found altogether 731...
We report the discovery of RV Tauri stars in Large Magellanic Cloud (LMC). In light- and color-curve behavior, appear to be a direct extension type II Cepheids longer periods. A single period-luminosity-color relationship is seen describe both LMC. derive relation V0 = 17.89(±0.20)-2.95(±0.12) log P + 5.49(±0.35)⟨(V - R)0⟩, which valid for period range 0.9 < 1.75. Assuming distance modulus LMC 18.5, terms absolute luminosities becomes MV -0.61(±0.20)-2.95(±0.12) R)0⟩.
view Abstract Citations (85) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The MACHO Project LMC Variable Star Inventory.V.Classification and Orbits of 611 Eclipsing Binary Stars Alcock, C. ; Allsman, R. A. Alves, D. Axelrod, T. S. Becker, Bennett, P. Cook, K. H. Freeman, Griest, Lacy, Lehner, M. J. Marshall, L. Minniti, Peterson, B. Pratt, Quinn, Rodgers, W. Stubbs, Sutherland, Welch, We report the characteristics eclipsing binary stars in...
We present a 9 million star color-magnitude diagram (9M CMD) of the LMC bar. The 9M CMD reveals complex superposition different age and metallicity stellar populations, with important evolutionary phases occurring over 3 orders magnitude in number density. First, we count non-variable supergiants, associated Cepheids, measure effective temperatures defining instability strip. Lifetime predictions evolution theory are tested, implications for origin low-luminosity Cepheids. highly-evolved AGB...
ABSTRACT We report the discovery of a brown dwarf orbiting M1 host star. first identified within Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. confirmed follow-up photometry from South African Astronomical Observatory, SPECULOOS-S, TRAPPIST-S, radial velocity measurements HARPS, which allowed us to characterize system. find an orbital period ∼1.25 d, mass $69.0^{+5.3}_{-4.8}$ MJ, close hydrogen burning limit, radius 0.95 ± 0.05 RJ....
We report the discovery of 73 double-mode RR Lyrae (RRd) stars in fields near bar LMC. The are detected among MACHO database short-period variables that currently contains about 7900 stars. Fundamental periods (P_0) for these found range 0.46-0.55 days and first overtone-to-fundamental period ratios to be 0.742 < P_1/P_0 0.748. A significant fraction our current sample have smaller than any previously discovered RRd variables. present mean magnitudes, colors, lightcurve properties all LMC...
The MACHO Project: Microlensing Detection Efficiency, C. Alcock, R. A. Allsman, D. Alves, T. S. Axelrod, Becker, P. Bennett, K. H. Cook, J. Drake, Freeman, M. Geha, Griest, Lehner, L. Marshall, Minniti, Nelson, B. Peterson, Popowski, Pratt, Quinn, W. Stubbs, Sutherland, Tomaney, Vandehei, Welch, (The Collaboration)
By cross-correlating the results of two recent large-scale surveys, general properties a well-defined sample semiregular variable stars have been determined. ISOGAL mid-infrared photometry (7 and 15 μm) MACHO V R light curves are assembled for approximately 300 in Baade's windows low extinction toward Galactic bulge. These mainly giants late M spectral type, evolving along asymptotic giant branch (AGB). They found to possess wide continuous distribution pulsation periods obey an approximate...
We report the first discovery of a gravitational microlensing candidate toward new population source stars, Small Magellanic Cloud (SMC). The event's light curve shows no variation for 3 yr before an upward excursion lasting ~217 days that peaks around 1997 January 11 at magnification ~2.1. Microlensing events Large and Galactic bulge have allowed important conclusions to be reached on stellar dark matter content Milky Way. SMC gives line sight through Way is expected prove useful in...