101 research outputs found
Characterizing 51 Eri b from 1 to 5 μm: A Partly Cloudy Exoplanet
We present spectrophotometry spanning 1–5 μm of 51 Eridani b, a 2–10 M_(Jup) planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new K1 (1.90–2.19 μm) and K2 (2.10–2.40 μm) spectra taken with the Gemini Planet Imager as well as an updated L_P (3.76 μm) and new M_S (4.67 μm) photometry from the NIRC2 Narrow camera. The new data were combined with J (1.13–1.35 μm) and H (1.50–1.80 μm) spectra from the discovery epoch with the goal of better characterizing the planet properties. The 51 Eri b photometry is redder than field brown dwarfs as well as known young T-dwarfs with similar spectral type (between T4 and T8), and we propose that 51 Eri b might be in the process of undergoing the transition from L-type to T-type. We used two complementary atmosphere model grids including either deep iron/silicate clouds or sulfide/salt clouds in the photosphere, spanning a range of cloud properties, including fully cloudy, cloud-free, and patchy/intermediate-opacity clouds. The model fits suggest that 51 Eri b has an effective temperature ranging between 605 and 737 K, a solar metallicity, and a surface gravity of log(g) = 3.5–4.0 dex, and the atmosphere requires a patchy cloud atmosphere to model the spectral energy distribution (SED). From the model atmospheres, we infer a luminosity for the planet of −5.83 to −5.93 (log L/L_⊙), leaving 51 Eri b in the unique position of being one of the only directly imaged planets consistent with having formed via a cold-start scenario. Comparisons of the planet SED against warm-start models indicate that the planet luminosity is best reproduced by a planet formed via core accretion with a core mass between 15 and 127 M_⊕
Archival Legacy Investigations of Circumstellar Environments: Overview and First Results
We are currently conducting a comprehensive and consistent re-processing of
archival HST-NICMOS coronagraphic surveys using advanced PSF subtraction
methods, entitled the Archival Legacy Investigations of Circumstellar
Environments program (ALICE, HST/AR 12652). This virtual campaign of about 400
targets has already produced numerous new detections of previously unidentified
point sources and circumstellar structures. We present five newly spatially
resolved debris disks revealed in scattered light by our analysis of the
archival data. These images provide new views of material around young
solar-type stars at ages corresponding to the period of terrestrial planet
formation in our solar system. We have also detected several new candidate
substellar companions, for which there are ongoing followup campaigns (HST/WFC3
and VLT/SINFONI in ADI mode). Since the methods developed as part of ALICE are
directly applicable to future missions (JWST, AFTA coronagraph) we emphasize
the importance of devising optimal PSF subtraction methods for upcoming
coronagraphic imaging missions. We describe efforts in defining direct imaging
high-level science products (HLSP) standards that can be applicable to other
coronagraphic campaigns, including ground-based (e.g., Gemini Planet Imager),
and future space instruments (e.g., JWST). ALICE will deliver a first release
of HLSPs to the community through the MAST archive at STScI in 2014.Comment: Proceedings of the SPIE, 9143-199. 17 pages, 11 figure
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
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
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
HST/WFC3 Observations of Low-mass Globular Clusters AM 4 and Palomar 13: Physical Properties and Implications for Mass Loss
We investigate the loss of low-mass stars in two of the faintest globular clusters known, AM 4 and Palomar 13 (Pal 13), using HST/WFC3 F606W and F814W photometry. To determine the physical properties of each cluster—age, mass, metallicity, extinction, and present day mass function (MF)—we use the maximum likelihood color–magnitude diagram (CMD) fitting program MATCH and the Dartmouth, Padova, and BaSTI stellar evolution models. For AM 4, the Dartmouth models provide the best match to the CMD and yield an age of >13 Gyr, metallicity log Z/Z_☉ = −1.68 ± 0.08, a distance modulus (m − M)V = 17.47 ± 0.03, and reddening AV = 0.19 ± 0.02. For Pal 13 the Dartmouth models give an age of 13.4 ± 0.5 Gyr, log Z/Z_☉ = −1.55 ± 0.06, (m − M)V = 17.17 ± 0.02, and AV = 0.43 ± 0.01. We find that the systematic uncertainties due to choice in assumed stellar model greatly exceed the random uncertainties, highlighting the importance of using multiple stellar models when analyzing stellar populations. Assuming a single-sloped power-law MF, we find that AM 4 and Pal 13 have spectral indices α = +0.68 ± 0.34 and α = −1.67 ± 0.25 (where a Salpeter MF has α = +1.35), respectively. Comparing our derived slopes with literature measurements of cluster integrated magnitude (MV) and MF slope indicates that AM 4 is an outlier. Its MF slope is substantially steeper than clusters of comparable luminosity, while Pal 13 has an MF in line with the general trend. We discuss both primordial and dynamical origins for the unusual MF slope of AM 4 and tentatively favor the dynamical scenario. However, MF slopes of more low luminosity clusters are needed to verify this hypothesis
High contrast imaging at the LBT: the LEECH exoplanet imaging survey
In Spring 2013, the LEECH (LBTI Exozodi Exoplanet Common Hunt) survey began
its 130-night campaign from the Large Binocular Telescope (LBT) atop Mt
Graham, Arizona. This survey benefits from the many technological achievements
of the LBT, including two 8.4-meter mirrors on a single fixed mount, dual
adaptive secondary mirrors for high Strehl performance, and a cold beam
combiner to dramatically reduce the telescope's overall background emissivity.
LEECH neatly complements other high-contrast planet imaging efforts by
observing stars at L' (3.8 m), as opposed to the shorter wavelength
near-infrared bands (1-2.4 m) of other surveys. This portion of the
spectrum offers deep mass sensitivity, especially around nearby adolescent
(0.1-1 Gyr) stars. LEECH's contrast is competitive with other extreme
adaptive optics systems, while providing an alternative survey strategy.
Additionally, LEECH is characterizing known exoplanetary systems with
observations from 3-5m in preparation for JWST.Comment: 12 pages, 5 figures. Proceedings of the SPIE, 9148-2
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
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