Abstract
The massive evolved star
η
Carinae is the most luminous star in the Milky Way and has the highest steady wind mass-loss rate of any known star. Radiative transfer models of the spectrum by ...Hillier et al. predict that H
α
is mostly emitted in regions of the wind at radii of 6–60 au from the star (2.5–25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ∼ 25 mas) with Magellan adaptive optics in two epochs, showing that
η
Carinae consistently appears ∼2.5–3 mas wider in H
α
emission compared to the adjacent 643 nm continuum. This implies that the H
α
line-forming region may have a characteristic emitting radius of 12 mas or ∼30 au, in very good agreement with the Hillier stellar-wind model. This provides direct confirmation that the physical wind parameters of that model are roughly correct, including the mass-loss rate of
, plus the clumping factor, and the terminal velocity. Comparison of the H
α
images (ellipticity and PA) to the continuum images reveals no significant asymmetries at H
α
. Hence, any asymmetry induced by a companion or by the primary’s rotation do not strongly influence the global H
α
emission in the outer wind.
NaSt1 (aka Wolf-Rayet 122) is a peculiar emission-line star embedded in an extended nebula of Nii emission with a compact dusty core. The object was previously characterized as a Wolf-Rayet (WR) star ...cloaked in an opaque nebula of CNO-processed material, perhaps analogous to ... Car and its Homunculus nebula, albeit with a hotter central source. To discern the morphology of the Nii nebula we performed narrow-band imaging using the Hubble Space Telescope and Wide-field Camera 3. The images reveal that the nebula has a disc-like geometry tilted ...12 degree from edge-on, composed of a bright central ellipsoid surrounded by a larger clumpy ring. Ground-based spectroscopy reveals radial velocity structure ( plus or minus 10 km s...) near the outer portions of the nebula's major axis, which is likely to be the imprint of outflowing gas. Near-infrared adaptive-optics imaging with Magellan AO has resolved a compact ellipsoid of K ...-band emission aligned with the larger Nii nebula, which we suspect is the result of scattered He i line emission (...2.06 mu m). Observations with the Chandra X-ray Observatory have revealed an X-ray point source at the core of the nebula that is heavily absorbed at energies <1 keV and has properties consistent with WR stars and colliding-wind binaries. We suggest that NaSt1 is a WR binary embedded in an equatorial outflow that formed as the result of non-conservative mass transfer. NaSt1 thus appears to be a rare and important example of a stripped-envelope WR forming through binary interaction, caught in the brief Roche lobe overflow phase. (ProQuest: ... denotes formulae/symbols omitted.)
We present the first results from the polarimetry mode of the Gemini Planet Imager (GPI), which uses a new integral field polarimetry architecture to provide high contrast linear polarimetry with ...minimal systematic biases between the orthogonal polarizations. We describe the design, data reduction methods, and performance of polarimetry with GPI. Point-spread function (PSF) subtraction via differential polarimetry suppresses unpolarized starlight by a factor of over 100, and provides sensitivity to circumstellar dust reaching the photon noise limit for these observations. In the case of the circumstellar disk around HR 4796A, GPI's advanced adaptive optics system reveals the disk clearly even prior to PSF subtraction. In polarized light, the disk is seen all the way in to its semi-minor axis for the first time. The disk exhibits surprisingly strong asymmetry in polarized intensity, with the west side > ~9 times brighter than the east side despite the fact that the east side is slightly brighter in total intensity. Based on a synthesis of the total and polarized intensities, we now believe that the west side is closer to us, contrary to most prior interpretations. Forward scattering by relatively large silicate dust particles leads to the strong polarized intensity on the west side, and the ring must be slightly optically thick in order to explain the lower brightness in total intensity there. These findings suggest that the ring is geometrically narrow and dynamically cold, perhaps shepherded by larger bodies in the same manner as Saturn's F ring.
ABSTRACT We present Gemini Planet Imager (GPI) observations of AU Microscopii, a young M dwarf with an edge-on, dusty debris disk. Integral field spectroscopy and broadband imaging polarimetry were ...obtained during the commissioning of GPI. In our broadband imaging polarimetry observations, we detect the disk only in total intensity and find asymmetries in the morphology of the disk between the southeast (SE) and northwest (NW) sides. The SE side of the disk exhibits a bump at 1″ (10 AU projected separation) that is three times more vertically extended and three times fainter in peak surface brightness than the NW side at similar separations. This part of the disk is also vertically offset by 69 30 mas to the northeast at 1″ when compared to the established disk midplane and is consistent with prior Atacama Large Millimeter/submillimeter Array and Hubble Space Telescope/Space Telescope Imaging Spectrograph observations. We see hints that the SE bump might be a result of detecting a horizontal sliver feature above the main disk that could be the disk backside. Alternatively, when including the morphology of the NW side, where the disk midplane is offset in the opposite direction ∼50 mas between 0 4 and 1 2, the asymmetries suggest a warp-like feature. Using our integral field spectroscopy data to search for planets, we are 50% complete for ∼4 MJup planets at 4 AU. We detect a source, resolved only along the disk plane, that could either be a candidate planetary mass companion or a compact clump in the disk.
Young giant exoplanets are a unique laboratory for understanding cool, low-gravity atmospheres. A quintessential example is the massive extrasolar planet β Pic b, which is 9 AU from and embedded in ...the debris disk of the young nearby A6V star β Pictoris. We observed the system with first light of the Magellan Adaptive Optics (MagAO) system. In Paper I we presented the first CCD detection of this planet with MagAO+VisAO. Here we present four MagAO+Clio images of β Pic b at 3.1 μm, 3.3 μm, L′, and M{sup ′}, including the first observation in the fundamental CH{sub 4} band. To remove systematic errors from the spectral energy distribution (SED), we re-calibrate the literature photometry and combine it with our own data, for a total of 22 independent measurements at 16 passbands from 0.99 to 4.8 μm. Atmosphere models demonstrate the planet is cloudy but are degenerate in effective temperature and radius. The measured SED now covers >80% of the planet’s energy, so we approach the bolometric luminosity empirically. We calculate the luminosity by extending the measured SED with a blackbody and integrating to find log(L{sub bol}/L{sub ⊙}) = −3.78±0.03. From our bolometric luminosity and an age of 23 ± 3 Myr, hot-start evolutionary tracks give a mass of 12.7 ± 0.3 M{sub Jup}, radius of 1.45 ± 0.02 R{sub Jup}, and T{sub eff} of 1708 ± 23 K (model-dependent errors not included). Our empirically determined luminosity is in agreement with values from atmospheric models (typically −3.8 dex), but brighter than values from the field-dwarf bolometric correction (typically −3.9 dex), illustrating the limitations in comparing young exoplanets to old brown dwarfs.
•Radar confirms asteroid 16 Psyche to be the largest metal asteroid in the main belt.•A Psyche shape model was generated using radar, adaptive optics, and occultation data.•The shape model of Psyche ...shows evidence of large scale features.•Psyche displays significant variations in radar and optical albedo with rotation.
Using the S-band radar at Arecibo Observatory, we observed 16 Psyche, the largest M-class asteroid in the main belt. We obtained 18 radar imaging and 6 continuous wave runs in November and December 2015, and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images (Drummond et al., 2016) to generate a three-dimensional shape model of Psyche. Our model is consistent with a previously published AO image (Hanus et al., 2013) and three multi-chord occultations. Our shape model has dimensions 279 × 232 × 189km (± 10%), Deff= 226 ± 23km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves (Hanus et al., 2013). Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ∼50–70km wide depressions near its south pole. Our size and published masses lead to an overall bulk density estimate of 4500 ± 1400kgm−3. Psyche's mean radar albedo of 0.37 ± 0.09 is consistent with a near-surface regolith composed largely of iron-nickel and ∼40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface. The variations in radar albedo appear to correlate with large and small-scale shape features. Our size and Psyche's published absolute magnitude lead to an optical albedo of pv= 0.15 ± 0.03, and there is evidence for albedo variegations that correlate with shape features.
Abstract
We present spectrophotometry spanning 1–5
μ
m of 51 Eridani b, a 2–10
planet discovered by the Gemini Planet Imager Exoplanet Survey. In this study, we present new
K
1 (1.90–2.19
μ
m) and
K
...2 (2.10–2.40
μ
m) spectra taken with the Gemini Planet Imager as well as an updated
L
P
(3.76
μ
m) and new
M
S
(4.67
μ
m) photometry from the NIRC2 Narrow camera. The new data were combined with
J
(1.13–1.35
μ
m) and
H
(1.50–1.80
μ
m) 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 (
), 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
.
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