146 research outputs found
Gemini Planet Imager Observational Calibrations VI: Photometric and Spectroscopic Calibration for the Integral Field Spectrograph
The Gemini Planet Imager (GPI) is a new facility instrument for the Gemini
Observatory designed to provide direct detection and characterization of
planets and debris disks around stars in the solar neighborhood. In addition to
its extreme adaptive optics and corona graphic systems which give access to
high angular resolution and high-contrast imaging capabilities, GPI contains an
integral field spectrograph providing low resolution spectroscopy across five
bands between 0.95 and 2.5 m. This paper describes the sequence of
processing steps required for the spectro-photometric calibration of GPI
science data, and the necessary calibration files. Based on calibration
observations of the white dwarf HD 8049B we estimate that the systematic error
in spectra extracted from GPI observations is less than 5%. The flux ratio of
the occulted star and fiducial satellite spots within coronagraphic GPI
observations, required to estimate the magnitude difference between a target
and any resolved companions, was measured in the -band to be in laboratory measurements and using
on-sky observations. Laboratory measurements for the , , and
filters are also presented. The total throughput of GPI, Gemini South and the
atmosphere of the Earth was also measured in each photometric passband, with a
typical throughput in -band of 18% in the non-coronagraphic mode, with some
variation observed over the six-month period for which observations were
available. We also report ongoing development and improvement of the data cube
extraction algorithm.Comment: 15 pages, 6 figures. Proceedings of the SPIE, 9147-30
Accretion onto a Supermassive Black Hole Binary Before Merger
While supermassive binary black holes (SMBBHs) inspiral toward merger they
may also accrete significant amounts of matter. To study the dynamics of such a
system requires simultaneously describing the evolving spacetime and the
dynamics of magnetized plasma. Here we present the first relativistic
calculation simulating two equal-mass, non-spinning black holes as they
inspiral from an initial separation of () almost to merger,
, while accreting gas from a surrounding disk, where is the
total binary mass. We find that the accretion rate onto the black
holes first decreases during this period and then reaches a plateau, dropping
by only a factor of despite its rapid inspiral. An estimated
bolometric light curve follows the same profile. The minidisks through which
the accretion reaches the black holes are very non-standard. Reynolds, not
Maxwell, stresses dominate, and they oscillate between two distinct structural
states. In one part of the cycle, ``sloshing" streams transfer mass from one
minidisk to the other through the L1 point at a rate the
accretion rate, carrying kinetic energy at a rate that can be as large as the
peak minidisk bolometric luminosity. We also discover that the minidisks have
time-varying tilts with respect to the orbital plane similar in magnitude to
the circumbinary disk's aspect ratio. The unsigned poloidal flux on the black
hole event horizon is roughly constant at a dimensionless level ,
but doubles just before merger; if the black holes had significant spin, this
flux could support jets whose power could approach the radiated luminosity.
This simulation is the first to employ our multipatch infrastructure \pwmhd,
decreasing computational expense per physical time to of similar
runs using conventional single-grid methods.Comment: Comments welcom
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