151 research outputs found
Examining Type Ia Supernova Progenitors from Local Event Rates
We present the recalculation of the rates of supernovae in local, low redshift (z ≤ 0.1) from the Nearby Galaxies Supernovae Search Project (Strolger, 2003) using an improved baseline designed to maximize SNe yield. Approximately 15 additional SNe of various types and ages have been discovered from the dataset and added to the 42 SNe already detected. This sample is sufficient to obtain an accurate rate of SNe in the local universe. The rates are weighted by volume, total light, and host galaxy type. Further spectroscopic data for the progenitor galaxies of each event will allow us to compare the rates using various galaxy properties. Contributions included an estimate of the precision and depth of the survey with false supernovae, and estimated luminosity function using literature estimates, and determining the control times for the survey to correct for the cadence and sensitivity of the survey. We present a detailed description of the resurveying of the NGSS dataset, the rate calculations, and the preliminary results. We obtain a B-band rate of 0.220century−1[1010L⊙(B)]−1. This roughly corresponds to 1 SNe Ia every 400 - 500 years in a galaxy like the Milky Way. Keywords: Physics, Astronomy, Astrophysics, Extragalactic, Type Ia Supernova, Lo- cal Galaxie
Characterizing the Evolution of Circumstellar Systems with the Hubble Space Telescope and the Gemini Planet Imager
The study of circumstellar disks at a variety of evolutionary stages is essential to understand the physical processes leading to planet formation. As the earliest stage of planet formation, massive, optically thick, and gas rich protoplanetary disks give information about the distribution and composition of the dust grains that will eventually coalesce into planetesimal bodies, while the later stages of the planet formation process (debris disks) demonstrate the interactions that the dust particles in disks have with the planetary bodies.
The recent development of high contrast instruments designed to directly image the structures surrounding nearby stars (e.g. Gemini Planet Imager) and coronagraphic data from the Hubble Space Telescope (HST) have made detailed studies of circumstellar systems possible. As a member of the Gemini Planet Imager (GPI) exoplanet survey team, I have developed the wavelength calibration for the lenslet-based integral field spectrograph. This work has enabled some incredible science, namely the spectral characterization of one of the lowest mass extrasolar planets ever discovered via direct imaging, 51 Eridani b. The second part of this work details the observations and characterization of three systems. I obtained GPI polarization data for the transition disk, PDS 66, which shows a double ring and gap structure and a temporally variable azimuthal asymmetry. This evolved morphology could indicate shadowing from some feature in the innermost regions of the disk, a gap-clearing planet, or a localized change in the dust properties of the disk. Millimeter continuum data of the DH Tau system places limits on the dust mass that is contributing to the strong accretion signature on the wide-separation planetary mass companion, DH Tau b. The lower than expected dust mass constrains the possible formation mechanism, with core accretion followed by dynamical scattering being the most likely. Finally, I present HST observations of the flared, edge-on protoplanetary disk ESO Halpha 569. Using a covariance-based MCMC software toolkit I developed, I combine the scattered light image with a spectral energy distribution to model the key structural parameters such as the geometry (disk outer radius, vertical scale height, radial flaring profile), total mass, and dust grain properties in the disk using the radiative transfer code MCFOST
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
Five Debris Disks Newly Revealed in Scattered Light from the HST NICMOS Archive
We have spatially resolved five debris disks (HD 30447, HD 35841, HD 141943,
HD 191089, and HD 202917) for the first time in near-infrared scattered light
by reanalyzing archival Hubble Space Telescope (HST)/NICMOS coronagraphic
images obtained between 1999 and 2006. One of these disks (HD 202917) was
previously resolved at visible wavelengths using HST/Advanced Camera for
Surveys. To obtain these new disk images, we performed advanced point-spread
function subtraction based on the Karhunen-Loeve Image Projection (KLIP)
algorithm on recently reprocessed NICMOS data with improved detector artifact
removal (Legacy Archive PSF Library And Circumstellar Environments Legacy
program). Three of the disks (HD 30447, HD 35841, and HD 141943) appear
edge-on, while the other two (HD 191089 and HD 202917) appear inclined. The
inclined disks have been sculpted into rings; in particular, the disk around HD
202917 exhibits strong asymmetries. All five host stars are young (8-40 Myr),
nearby (40-100 pc) F and G stars, and one (HD 141943) is a close analog to the
young sun during the epoch of terrestrial planet formation. Our discoveries
increase the number of debris disks resolved in scattered light from 19 to 23
(a 21% increase). Given their youth, proximity, and brightness (V = 7.2 to
8.5), these targets are excellent candidates for follow-up investigations of
planet formation at visible wavelengths using the HST/STIS coronagraph, at
near-infrared wavelengths with the Gemini Planet Imager (GPI) and Very Large
Telescope (VLT)/SPHERE, and at thermal infrared wavelengths with the James Webb
Space Telescope NIRCam and MIRI coronagraphs.Comment: 6 pages, 1 figure, 1 tabl
Discovery of a Companion Candidate in the HD169142 Transition Disk and the Possibility of Multiple Planet Formation
We present L' and J-band high-contrast observations of HD169142, obtained
with the VLT/NACO AGPM vector vortex coronagraph and the Gemini Planet Imager,
respectively. A source located at 0".156+/-0".032 north of the host star
(PA=7.4+/-11.3 degrees) appears in the final reduced L' image. At the distance
of the star (~145 pc), this angular separation corresponds to a physical
separation of 22.7+/-4.7 AU, locating the source within the recently resolved
inner cavity of the transition disk. The source has a brightness of
L'=12.2+/-0.5 mag, whereas it is not detected in the J band (J>13.8 mag). If
its L' brightness arose solely from the photosphere of a companion and given
the J-L' color constraints, it would correspond to a 28-32 MJupiter object at
the age of the star, according to the COND models. Ongoing accretion activity
of the star suggests, however, that gas is left in the inner disk cavity from
which the companion could also be accreting. In this case the object could be
lower in mass and its luminosity enhanced by the accretion process and by a
circumplanetary disk. A lower mass object is more consistent with the observed
cavity width. Finally, the observations enable us to place an upper limit on
the L'-band flux of a second companion candidate orbiting in the disk annular
gap at ~50 AU, as suggested by millimeter observations. If the second companion
is also confirmed, HD169142 might be forming a planetary system, with at least
two companions opening gaps and possibly interacting with each other.Comment: Accepted to ApJL, see also Biller et al. 201
Bringing "The Moth" to Light: A Planet-Sculpting Scenario for the HD 61005 Debris Disk
The HD 61005 debris disk ("The Moth") stands out from the growing collection
of spatially resolved circumstellar disks by virtue of its unusual swept-back
morphology, brightness asymmetries, and dust ring offset. Despite several
suggestions for the physical mechanisms creating these features, no definitive
answer has been found. In this work, we demonstrate the plausibility of a
scenario in which the disk material is shaped dynamically by an eccentric,
inclined planet. We present new Keck NIRC2 scattered-light angular differential
imaging of the disk at 1.2-2.3 microns that further constrains its outer
morphology (projected separations of 27-135 AU). We also present complementary
Gemini Planet Imager 1.6 micron total intensity and polarized light detections
that probe down to projected separations less than 10 AU. To test our
planet-sculpting hypothesis, we employed secular perturbation theory to
construct parent body and dust distributions that informed scattered-light
models. We found that this method produced models with morphological and
photometric features similar to those seen in the data, supporting the premise
of a planet-perturbed disk. Briefly, our results indicate a disk parent body
population with a semimajor axis of 40-52 AU and an interior planet with an
eccentricity of at least 0.2. Many permutations of planet mass and semimajor
axis are allowed, ranging from an Earth mass at 35 AU to a Jupiter mass at 5
AU.Comment: Accepted to AJ; added Figure 5 and minor text edit
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