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Title: Microlensing Constraints on the Mass of Single Stars from HST Astrometric Measurements

Here, we report on the first results from a large-scale observing campaign aiming to use astrometric microlensing to detect and place limits on the mass of single objects, including stellar remnants. We used the Hubble Space Telescope to monitor stars near the Galactic Center for three years, and we measured the brightness and positions of ~2 million stars at each observing epoch. In addition to this, we monitored the same pointings using the VIMOS imager on the Very Large Telescope. The stars we monitored include several bright microlensing events observed from the ground by the OGLE collaboration. In this paper, we present the analysis of our photometric and astrometric measurements for six of these events, and derive mass constraints for the lens in each of them. Although these constraints are limited by the photometric precision of ground-based data, and our ability to determine the lens distance, we were able to constrain the size of the Einstein ring radius thanks to our precise astrometric measurements—the first routine measurements of this type from a large-scale observing program. In conclusion, this demonstrates the power of astrometric microlensing as a tool to constrain the masses of stars, stellar remnants, and, in the future, extrasolarmore » planets, using precise ground- and space-based observations.« less
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ;  [1] ; ORCiD logo [1] ;  [2] ;  [3] ; ORCiD logo [4] ; ORCiD logo [5] ;  [6] ; ORCiD logo [7] ; ORCiD logo [8] ; ORCiD logo [9] ;  [10] ;  [11] ; ORCiD logo [12]
  1. Space Telescope Science Inst., Baltimore, MD (United States)
  2. Warsaw Univ. Observatory, Warsaw (Poland)
  3. Pontificia Universidad Catolica de Chile, Santiago (Chile). Inst. de Astrofisica; Millennium Inst. of Astrophysics, Santiago (Chile)
  4. Space Telescope Science Inst., Baltimore, MD (United States); Pennsylvania State Univ., University Park, PA (United States). Dept of Astronomy & Astrophysics
  5. Univ. of Canterbury, Christchurch (New Zealand). Dept. of Physics and Astronomy
  6. Massey Univ., Auckland (New Zealand). Inst. of Natural and Mathematical Sciences
  7. Space Telescope Science Inst., Baltimore, MD (United States)
  8. Univ. of St Andrews, St Andrews (United Kingdom). SUPA, School of Physics & Astronomy
  9. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  10. Univ. of Nevada, Las Vegas, NV (United States). Dept. of Physics and Astronomy
  11. Chinese Academy of Sciences, Beijing (China). National Astronomical Observatories
  12. European Southern Observatory, Garching (Germany)
Publication Date:
Report Number(s):
Journal ID: ISSN 1538-4357; TRN: US1800641
Grant/Contract Number:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 843; Journal Issue: 2; Journal ID: ISSN 1538-4357
Institute of Physics (IOP)
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; astrometry; gravitational lensing micro; stars black holes; stars general
OSTI Identifier: