98 research outputs found
A High Precision, Optical Polarimeter to Measure Inclinations of High Mass X-Ray Binaries
We present commissioning data for the POLISH instrument obtained on the Hale
5-m telescope. The goal of this high precision polarimeter is to constrain
orbital inclination of high mass X-ray binaries and to therefore obtain
independent mass estimates for their black hole companions. We have obtained
photon shot noise limited precision on standard stars, and we have measured the
polarization of bright stars at the part per million level on a nightly basis.
Systematic effects have been reduced to less than 1% of the measured
polarization for polarized sources and to the part per million level for weakly
polarized sources. The high sensitivity of this instrument to asymmetry
suggests that valuable contributions will be made in many other fields,
including studies of extrasolar planets, debris disks, and stellar
astrophysics.Comment: 35 pages, 10 figures, accepted for publication in PAS
A Multiple Scattering Polarized Radiative Transfer Model: Application to HD 189733b
We present a multiple scattering vector radiative transfer model which
produces disk integrated, full phase polarized light curves for reflected light
from an exoplanetary atmosphere. We validate our model against results from
published analytical and computational models and discuss a small number of
cases relevant to the existing and possible near-future observations of the
exoplanet HD 189733b. HD 189733b is arguably the most well observed exoplanet
to date and the only exoplanet to be observed in polarized light, yet it is
debated if the planet's atmosphere is cloudy or clear. We model reflected light
from clear atmospheres with Rayleigh scattering, and cloudy or hazy atmospheres
with Mie and fractal aggregate particles. We show that clear and cloudy
atmospheres have large differences in polarized light as compared to simple
flux measurements, though existing observations are insufficient to make this
distinction. Futhermore, we show that atmospheres that are spatially
inhomogeneous, such as being partially covered by clouds or hazes, exhibit
larger contrasts in polarized light when compared to clear atmospheres. This
effect can potentially be used to identify patchy clouds in exoplanets. Given a
set of full phase polarimetric measurements, this model can constrain the
geometric albedo, properties of scattering particles in the atmosphere and the
longitude of the ascending node of the orbit. The model is used to interpret
new polarimetric observations of HD 189733b in a companion paper.Comment: 13 pages, 13 figures. Accepted for publication in Ap
A Ground-Based Albedo Upper Limit for HD 189733b from Polarimetry
We present 50 nights of polarimetric observations of HD 189733 in band
using the POLISH2 aperture-integrated polarimeter at the Lick Observatory Shane
3-m telescope. This instrument, commissioned in 2011, is designed to search for
Rayleigh scattering from short-period exoplanets due to the polarized nature of
scattered light. Since these planets are spatially unresolvable from their host
stars, the relative contribution of the planet-to-total system polarization is
expected to vary with an amplitude of order 10 parts per million (ppm) over the
course of the orbit. Non-zero and also variable at the 10 ppm level, the
inherent polarization of the Lick 3-m telescope limits the accuracy of our
measurements and currently inhibits conclusive detection of scattered light
from this exoplanet. However, the amplitude of observed variability
conservatively sets a upper limit to the planet-induced polarization
of the system of 58 ppm in band, which is consistent with a previous upper
limit from the POLISH instrument at the Palomar Observatory 5-m telescope
(Wiktorowicz 2009). A physically-motivated Rayleigh scattering model, which
includes the depolarizing effects of multiple scattering, is used to
conservatively set a upper limit to the geometric albedo of HD
189733b of . This value is consistent with the value derived from occultation observations with HST STIS (Evans et al.
2013), but it is inconsistent with the large albedo
reported by (Berdyugina et al. 2011).Comment: 10 pages, 9 figures, submitted to Ap
The PHASES Differential Astrometry Data Archive. I. Measurements and Description
The Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES)
monitored 51 sub-arcsecond binary systems to determine precision binary orbits,
study the geometries of triple and quadruple star systems, and discover
previously unknown faint astrometric companions as small as giant planets.
PHASES measurements made with the Palomar Testbed Interferometer (PTI) from
2002 until PTI ceased normal operations in late 2008 are presented. Infrared
differential photometry of several PHASES targets were measured with Keck
Adaptive Optics and are presented.Comment: 33 pages emulateapj, Accepted to A
Masses, luminosities, and orbital coplanarities of the ” Orionis quadruple-star system from phases differential astrometry
ÎŒ Orionis was identified by spectroscopic studies as a quadruple-star system. Seventeen high-precision differential astrometry measurements of ÎŒ Ori have been collected by the Palomar High-precision Astrometric Search for Exoplanet Systems (PHASES). These show both the motion of the long-period binary orbit and short-period perturbations superimposed on that caused by each of the components in the long-period system being themselves binaries. The new measurements enable the orientations of the long-period binary and short-period subsystems to be determined. Recent theoretical work predicts the distribution of relative inclinations between inner and outer orbits of hierarchical systems to peak near 40 and 140 degrees. The degree of coplanarity of this complex system is determined, and the angle between the planes of the AâB and AaâAb orbits is found to be 136.7 ± 8.3 degrees, near the predicted distribution peak at 140 degrees; this result is discussed in the context of the handful of systems with established mutual inclinations. The system distance and masses for each component are obtained from a combined fit of the PHASES astrometry and archival radial velocity observations. The component masses have relative precisions of 5% (component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The median size of the minor axes of the uncertainty ellipses for the new measurements is 20 micro-arcseconds (ÎŒas). Updated orbits for ÎŽ Equulei, Îș Pegasi, and V819 Herculis are also presented
Masses of Astrometrically-Discovered and Imaged Binaries: G 78-28AB and GJ 231.1BC
The Stellar Planet Survey (STEPS) is an ongoing astrometric search for giant
planets and brown dwarfs around a sample of ~30 M-dwarfs. We have discovered
several low-mass companions by measuring the motion of our target stars
relative to their reference frames. The highest mass discovery thus far is G
78-28B, a companion to the M-dwarf G 78-28A. The orbital period is 4.18 +/-
0.03 y, the system mass is 0.565 +/- 0.055 Msolar, and the semi-major axis is
2.19 +/- 0.10 AU. Imaging observations with the Keck laser guide star adaptive
optics (LGSAO) and the Palomar AO instruments resolved the system and also
yielded JHK-band delta magnitudes. We use the orbital solution, light ratios,
and mass-luminosity relationships to derive component masses of MA = 0.370 +/-
0.034 Msolar and MB = 0.195 +/- 0.021 Msolar. G 78-28B is of type M4 V based
upon its colors and mass. We also discovered GJ 231.1C, a companion to GJ
231.1B, with STEPS and imaged the companion with LGSAO and Palomar AO, but the
orbital period is longer than our observing baseline; thus the system
parameters are less constrained. In GJ 231.1BC the masses are MB = 0.25 +/-
0.06 Msolar and MC =0.12 +/- 0.02 Msolar. The inferred spectral type of GJ
231.1C is M5 V. We demonstrate the results of the current state of mass
estimation techniques with our data.Comment: 25 pages, 8 figures, accepted for Ap
Experimental Design for the Gemini Planet Imager
The Gemini Planet Imager (GPI) is a high performance adaptive optics system
being designed and built for the Gemini Observatory. GPI is optimized for high
contrast imaging, combining precise and accurate wavefront control, diffraction
suppression, and a speckle-suppressing science camera with integral field and
polarimetry capabilities. The primary science goal for GPI is the direct
detection and characterization of young, Jovian-mass exoplanets. For plausible
assumptions about the distribution of gas giant properties at large semi-major
axes, GPI will be capable of detecting more than 10% of gas giants more massive
than 0.5 M_J around stars younger than 100 Myr and nearer than 75 parsecs. For
systems younger than 1 Gyr, gas giants more massive than 8 M_J and with
semi-major axes greater than 15 AU are detected with completeness greater than
50%. A survey targeting young stars in the solar neighborhood will help
determine the formation mechanism of gas giant planets by studying them at ages
where planet brightness depends upon formation mechanism. Such a survey will
also be sensitive to planets at semi-major axes comparable to the gas giants in
our own solar system. In the simple, and idealized, situation in which planets
formed by either the "hot-start" model of Burrows et al. (2003) or the core
accretion model of Marley et al. (2007), a few tens of detected planets are
sufficient to distinguish how planets form.Comment: 15 pages, 9 figures, revised after referee's comments and resubmitted
to PAS
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