70 research outputs found
Gemini Planet Imager Observational Calibrations III: Empirical Measurement Methods and Applications of High-Resolution Microlens PSFs
The newly commissioned Gemini Planet Imager (GPI) combines extreme adaptive
optics, an advanced coronagraph, precision wavefront control and a
lenslet-based integral field spectrograph (IFS) to measure the spectra of young
extrasolar giant planets between 0.9-2.5 um. Each GPI detector image, when in
spectral model, consists of ~37,000 microspectra which are under or critically
sampled in the spatial direction. This paper demonstrates how to obtain
high-resolution microlens PSFs and discusses their use in enhancing the
wavelength calibration, flexure compensation and spectral extraction. This
method is generally applicable to any lenslet-based integral field spectrograph
including proposed future instrument concepts for space missions.Comment: 10 pages, 6 figures. Proceedings of the SPIE, 9147-282 v2: reference
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HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-H 569
We present new HST ACS observations and detailed models for a recently
discovered edge-on protoplanetary disk around ESO H 569 (a low-mass T
Tauri star in the Cha I star forming region). Using radiative transfer models
we probe the distribution of the grains and overall shape of the disk
(inclination, scale height, dust mass, flaring exponent and surface/volume
density exponent) by model fitting to multiwavelength (F606W and F814W) HST
observations together with a literature compiled spectral energy distribution.
A new tool set was developed for finding optimal fits of MCFOST radiative
transfer models using the MCMC code emcee to efficiently explore the high
dimensional parameter space. It is able to self-consistently and simultaneously
fit a wide variety of observables in order to place constraints on the physical
properties of a given disk, while also rigorously assessing the uncertainties
in those derived properties. We confirm that ESO H 569 is an optically
thick nearly edge-on protoplanetary disk. The shape of the disk is well
described by a flared disk model with an exponentially tapered outer edge,
consistent with models previously advocated on theoretical grounds and
supported by millimeter interferometry. The scattered light images and spectral
energy distribution are best fit by an unusually high total disk mass (gas+dust
assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap
An upper limit on the mass of the circumplanetary disk for DH Tau b
DH Tau is a young (1 Myr) classical T Tauri star. It is one of the few
young PMS stars known to be associated with a planetary mass companion, DH Tau
b, orbiting at large separation and detected by direct imaging. DH Tau b is
thought to be accreting based on copious H emission and exhibits
variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place
constraints on the disk dust mass for both DH Tau b and the primary in a regime
where the disks will appear optically thin. We estimate a disk dust mass for
the primary, DH Tau A of , which gives a disk-to-star
mass ratio of 0.014 (assuming the usual Gas-to-Dust mass ratio of 100 in the
disk). We find a conservative disk dust mass upper limit of 0.42
for DH Tau b, assuming that the disk temperature is dominated by irradiation
from DH Tau b itself. Given the environment of the circumplanetary disk,
variable illumination from the primary or the equilibrium temperature of the
surrounding cloud would lead to even lower disk mass estimates. A MCFOST
radiative transfer model including heating of the circumplanetary disk by DH
Tau b and DH Tau A suggests that a mass averaged disk temperature of 22 K is
more realistic, resulting in a dust disk mass upper limit of 0.09
for DH Tau b. We place DH Tau b in context with similar objects and discuss the
consequences for planet formation models.Comment: accepted for publication in A
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
JWST/NIRCam Imaging of Young Stellar Objects. II. Deep Constraints on Giant Planets and a Planet Candidate Outside of the Spiral Disk Around SAO 206462
We present JWST/NIRCam F187N, F200W, F405N and F410M direct imaging data of
the disk surrounding SAO 206462. Previous images show a very structured disk,
with a pair of spiral arms thought to be launched by one or more external
perturbers. The spiral features are visible in three of the four filters, with
the non-detection in F410M due to the large detector saturation radius. We
detect with a signal-to-noise ratio of 4.4 a companion candidate (CC1) that, if
on a coplanar circular orbit, would orbit SAO 206462 at a separation of
au, away from the predicted separation for the driver of
the eastern spiral. According to the BEX models, CC1 has a mass of
. No other companion candidates were
detected. At the location predicted by simulations of both spirals generated by
a single massive companion, the NIRCam data exclude objects more massive than
assuming the BEX evolutionary models. In terms of
temperatures, the data are sensitive to objects with
K, when assuming planets emit like blackbodies
( between 1 and ). From these results, we
conclude that if the spirals are driven by gas giants, these must be either
cold or embedded in circumplanetary material. In addition, the NIRCam data
provide tight constraints on ongoing accretion processes. In the low extinction
scenario we are sensitive to mass accretion rates of the order
yr. Thanks to the longer wavelengths
used to search for emission lines, we reach unprecedented sensitivities to
processes with yr even towards highly
extincted environments (~mag).Comment: 18 pages, 8 figures, 3 table
Constraints on the architecture of the HD 95086 planetary system with the Gemini Planet Imager
We present astrometric monitoring of the young exoplanet HD 95086 b obtained
with the Gemini Planet Imager between 2013 and 2016. A small but significant
position angle change is detected at constant separation; the orbital motion is
confirmed with literature measurements. Efficient Monte Carlo techniques place
preliminary constraints on the orbital parameters of HD 95086 b. With 68%
confidence, a semimajor axis of 61.7^{+20.7}_{-8.4} au and an inclination of
153.0^{+9.7}_{-13.5} deg are favored, with eccentricity less than 0.21. Under
the assumption of a co-planar planet-disk system, the periastron of HD 95086 b
is beyond 51 au with 68% confidence. Therefore HD 95086 b cannot carve the
entire gap inferred from the measured infrared excess in the SED of HD 95086.
We use our sensitivity to additional planets to discuss specific scenarios
presented in the literature to explain the geometry of the debris belts. We
suggest that either two planets on moderately eccentric orbits or three to four
planets with inhomogeneous masses and orbital properties are possible. The
sensitivity to additional planetary companions within the observations
presented in this study can be used to help further constrain future dynamical
simulations of the planet-disk system.Comment: Accepted for publication in ApJ
JWST/NIRCam Imaging of Young Stellar Objects. I. Constraints on Planets Exterior to The Spiral Disk Around MWC 758
MWC 758 is a young star hosting a spiral protoplanetary disk. The spirals are
likely companion-driven, and two previously-identified candidate companions
have been identified -- one at the end the Southern spiral arm at ~0.6 arcsec,
and one interior to the gap at ~0.1 arcsec. With JWST/NIRCam, we provide new
images of the disk and constraints on planets exterior to ~1". We detect the
two-armed spiral disk, a known background star, and a spatially resolved
background galaxy, but no clear companions. The candidates that have been
reported are at separations that are not probed by our data with sensitivity
sufficient to detect them -- nevertheless, these observations place new limits
on companions down to ~2 Jupiter-masses at ~150 au and ~0.5 Jupiter masses at
~600 au. Owing to the unprecedented sensitivity of JWST and youth of the
target, these are among the deepest mass-detection limits yet obtained through
direct imaging observations, and provide new insights into the system's
dynamical nature.Comment: Accepted for publication in A
Type Ia Supernova Rate Measurements To Redshift 2.5 From CANDELS: Searching For Prompt Explosions In The Early Universe
dThe Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) was a multi-cycle treasury program on the Hubble Space Telescope (HST) that surveyed a total area of -0.25 deg2 with -900 HST orbits spread across five fields over three years. Within these survey images we discovered 65 supernovae (SNe) of all types, out to z 2.5. We classify -24 of these as Type Ia SNe (SNe Ia) based on host galaxy redshifts and SN photometry (supplemented by grism spectroscopy of six SNe). Here we present a measurement of the volumetric SN Ia rate as a function of redshift, reaching for the first time beyond z =- 2 and putting new constraints on SN Ia progenitor models. Our highest redshift bin includes detections of SNe that exploded when the universe was only -3 Gyr old and near the peak of the cosmic star formation history. This gives the CANDELS high redshift sample unique leverage for evaluating the fraction of SNe Ia that explode promptly after formation ( 40 Myr. However, mild tension is apparent between ground-based low-z surveys and space-based high-z surveys. In both CANDELS and the sister HST program CLASH (Cluster Lensing And Supernova Survey with Hubble), we find a low rate of SNe Ia at z > 1. This could be a hint that prompt progenitors are in fact relatively rare, accounting for only 20% of all SN Ia explosions-though further analysis and larger samples will be needed to examine that suggestion. Key words: infrared: general - supernovae:Astronom
The Peculiar Debris Disk of HD 111520 as Resolved by the Gemini Planet Imager
Using the Gemini Planet Imager (GPI), we have resolved the circumstellar
debris disk around HD 111520 at a projected range of ~30-100 AU in both total
and polarized -band intensity. The disk is seen edge-on at a position angle
of ~165 along the spine of emission. A slight inclination or
asymmetric warping are covariant and alters the interpretation of the observed
disk emission. We employ 3 point spread function (PSF) subtraction methods to
reduce the stellar glare and instrumental artifacts to confirm that there is a
roughly 2:1 brightness asymmetry between the NW and SE extension. This specific
feature makes HD 111520 the most extreme examples of asymmetric debris disks
observed in scattered light among similar highly inclined systems, such as HD
15115 and HD 106906. We further identify a tentative localized brightness
enhancement and scale height enhancement associated with the disk at ~40 AU
away from the star on the SE extension. We also find that the fractional
polarization rises from 10 to 40% from 0.5" to 0.8" from the star. The
combination of large brightness asymmetry and symmetric polarization fraction
leads us to believe that an azimuthal dust density variation is causing the
observed asymmetry.Comment: 9 pages, 8 Figures, 1 table, Accepted to Ap
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