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Spitzer Microlensing parallax reveals two isolated stars in the Galactic bulge
Weicheng Zang, Yossi Shvartzvald, Tianshu Wang +90
We report the mass and distance measurements of two single-lens events from the 2017 Spitzer microlensing campaign. The ground-based observations yield the detection of finite-sour…
Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic Disk
Sun-Ju Chung, Andrew Gould, Jan Skowron +60
We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1 =…
A Distant Sample of Halo Wide Binaries from SDSS
Johanna Coronado, María Paz Sepúlveda, Andrew Gould +1
Samples of reliably identified halo wide binaries are scarce. If reasonably free from selection effects and with a small degree of contamination by chance alignments, these wide bi…
TGAS Error Renormalization from the RR Lyrae Period-Luminosity Relation
Andrew Gould, Juna A. Kollmeier, Branimir Sesar
The Gaia team has applied a renormalization to their internally-derived parallax errors $$ σ_{tgas}(π) = \sqrt{[Aσ_{int}(π)]^2 + σ_0^2}; \ \ \ \ (A,σ_0) = (1.4,0.2…
Predicted Information Content of Gaia-Hipparcos
Andrew Gould, Juna A. Kollmeier
The Gaia-Tycho release, scheduled for 14 September, is forecast to yield parallax errors of as for about 2 million Tycho stars. We show analytically that the actua…
Gaia Parallax Zero Point From RR Lyrae Stars
Andrew Gould, Juna A. Kollmeier
Like Hipparcos, Gaia is designed to give absolute parallaxes, independent of any astrophysical reference system. And indeed, Gaia's internal zero-point error for parallaxes is like…
Slingshot Mechanism in Orion: Kinematic Evidence For Ejection of Protostars by Filaments
Amelia M. Stutz, Andrew Gould
By comparing 3 constituents of Orion A (gas, protostars, and pre-main-sequence stars), both morhologically and kinematically, we derive the following. The gas surface density near…
WFIRST Ultra-Precise Astrometry II: Asteroseismology
A. Gould, D. Huber, M. Penny +1
WFIRST microlensing observations will return high-precision parallaxes, sigma(pi) < 0.3 microarcsec, for the roughly 1 million stars with H<14 in its 2.8 deg^2 field toward the Gal…
Microlens Masses from 1-D Parallaxes and Heliocentric Proper Motions
Andrew Gould
One-dimensional (1-D) microlens parallaxes can be combined with heliocentric lens-source relative proper motion measurements to derive the lens mass and distance, as suggested by G…
A New Method to Calibrate the Stellar Color/Surface-Brightness Relation
Andrew Gould
I show that the standard microlensing technique to measure the angular radius of a star using color/surface-brightness relations can be inverted, via late-time proper motion measur…
Three New Cool Brown Dwarfs Discovered with the Wide-field Infrared Survey Explorer (WISE) and an Improved Spectrum of the Y0 Dwarf WISE J041022.71+150248.4
Michael C. Cushing, J. Davy Kirkpatrick, Christopher R. Gelino +3
As part of a larger search of Wide-field Infrared Survey Explorer (WISE) data for cool brown dwarfs with effective temperatures less than 1000 K, we present the discovery of three…
Reanalysis of the Gravitational Microlensing Event MACHO-97-BLG-41 based on Combined Data
Youn Kil Jung, Cheongho Han, Andrew Gould +1
MACHO-97-BLG-41 is a gravitational microlensing event produced by a lens composed of multiple masses detected by the first-generation lensing experiment. For the event, there exist…
A Second Kelvin-Helmholtz Timescale of Post Helium-Flash Evolution
Andrew Gould
I show that after the "helium flash" abruptly ends its first ascent red giant evolution, a solar-type star is powered primarily by gravitational contraction of its helium core, rat…
Gravitational Pulse Astronomy
Andrew Gould
Thompson has argued that the Kozai mechanism is primarily responsible for driving white-dwarf binary mergers and so generating type Ia supernovae (SNe). If so, the gravitational wa…
Limits on Unresolved Planetary Companions to White Dwarf Remnants of 14 Intermediate-Mass Stars
Mukremin Kilic, Andrew Gould, Detlev Koester
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 pho…