| 1. |
- Cataldi, Gianni, et al.
(författare)
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The Surprisingly Low Carbon Mass in the Debris Disk around HD 32297
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 892:2
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Tidskriftsartikel (refereegranskat)abstract
- Gas has been detected in a number of debris disks. It is likely secondary, i.e., produced by colliding solids. Here, we report ALMA Band 8 observations of neutral carbon in the CO-rich debris disk around the 15-30 Myr old A-type star HD 32297. We find that C-0 is located in a ring at similar to 110 au with an FWHM of similar to 80 au and has a mass of (3.5 0.2) x 10(-3) M-circle plus. Naively, such a surprisingly small mass can be accumulated from CO photodissociation in a time as short as similar to 10(4) yr. We develop a simple model for gas production and destruction in this system, properly accounting for CO self-shielding and shielding by neutral carbon, and introducing a removal mechanism for carbon gas. We find that the most likely scenario to explain both C-0 and CO observations is one where the carbon gas is rapidly removed on a timescale of order a thousand years and the system maintains a very high CO production rate of similar to 15 M-circle plus Myr(-1), much higher than the rate of dust grind-down. We propose a possible scenario to meet these peculiar conditions: the capture of carbon onto dust grains, followed by rapid CO re-formation and rerelease. In steady state, CO would continuously be recycled, producing a CO-rich gas ring that shows no appreciable spreading over time. This picture might be extended to explain other gas-rich debris disks.
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| 2. |
- Currie, Thayne, et al.
(författare)
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SCExAO/CHARIS Direct Imaging Discovery of a 20 au Separation, Low-mass Ratio Brown Dwarf Companion to an Accelerating Sun-like Star
- 2020
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 904:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the direct imaging discovery of a substellar companion to the nearby Sun-like star, HD 33632 Aa, at a projected separation of similar to 20 au, obtained with SCExAO/CHARIS integral field spectroscopy complemented by Keck/NIRC2 thermal infrared imaging. The companion, HD 33632 Ab, induces a 10.5 sigma astrometric acceleration on the star as detected with the Gaia and Hipparcos satellites. SCExAO/CHARIS JHK (1.1-2.4 mu m) spectra and Keck/NIRC2 L-p (3.78 mu m) photometry are best matched by a field L/T transition object: an older, higher-gravity, and less dusty counterpart to HR 8799 cde. Combining our astrometry with Gaia/Hipparcos data and archival Lick Observatory radial velocities, we measure a dynamical mass of 46.4 8 M-J and an eccentricity of e < 0.46 at 95% confidence. HD 33632 Ab's mass and mass ratio (4.0% 0.7%) are comparable to the low-mass brown dwarf GJ 758 B and intermediate between the more massive brown dwarf HD 19467 B and the (near-)planet-mass companions to HR 2562 and GJ 504. Using Gaia to select for direct imaging observations with the newest extreme adaptive optics systems can reveal substellar or even planet-mass companions on solar system-like scales at an increased frequency compared to blind surveys.
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| 3. |
- Hinkley, Sasha, et al.
(författare)
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The JWST Early Release Science Program for the Direct Imaging and Spectroscopy of Exoplanetary Systems
- 2022
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 134:1039
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Tidskriftsartikel (refereegranskat)abstract
- The direct characterization of exoplanetary systems with high-contrast imaging is among the highest priorities for the broader exoplanet community. As large space missions will be necessary for detecting and characterizing exo-Earth twins, developing the techniques and technology for direct imaging of exoplanets is a driving focus for the community. For the first time, JWST will directly observe extrasolar planets at mid-infrared wavelengths beyond 5 μm, deliver detailed spectroscopy revealing much more precise chemical abundances and atmospheric conditions, and provide sensitivity to analogs of our solar system ice-giant planets at wide orbital separations, an entirely new class of exoplanet. However, in order to maximize the scientific output over the lifetime of the mission, an exquisite understanding of the instrumental performance of JWST is needed as early in the mission as possible. In this paper, we describe our 55 hr Early Release Science Program that will utilize all four JWST instruments to extend the characterization of planetary-mass companions to ∼15 μm as well as image a circumstellar disk in the mid-infrared with unprecedented sensitivity. Our program will also assess the performance of the observatory in the key modes expected to be commonly used for exoplanet direct imaging and spectroscopy, optimize data calibration and processing, and generate representative data sets that will enable a broad user base to effectively plan for general observing programs in future Cycles.
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| 4. |
- Mayama, Satoshi, et al.
(författare)
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Subaru Near-infrared Imaging Polarimetry of Misaligned Disks around the SR 24 Hierarchical Triple System
- 2020
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 159:1
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Tidskriftsartikel (refereegranskat)abstract
- The SR 24 multistar system hosts both circumprimary and circumsecondary disks, which are strongly misaligned with each other. The circumsecondary disk is circumbinary in nature. Interestingly, both disks are interacting, and they possibly rotate in opposite directions. To investigate the nature of this unique twin disk system, we present 01 resolution near-infrared polarized intensity images of the circumstellar structures around SR 24, obtained with HiCIAO mounted on the Subaru 8.2 m telescope. Both the circumprimary disk and the circumsecondary disk are resolved and have elongated features. While the position angle of the major axis and radius of the near-IR (NIR) polarization disk around SR 24S are 55° and 137 au, respectively, those around SR 24N are 110° and 34 au, respectively. With regard to overall morphology, the circumprimary disk around SR 24S shows strong asymmetry, whereas the circumsecondary disk around SR 24N shows relatively strong symmetry. Our NIR observations confirm the previous claim that the circumprimary and circumsecondary disks are misaligned from each other. Both the circumprimary and circumsecondary disks show similar structures in 12CO observations in terms of its size and elongation direction. This consistency is because both NIR and 12CO are tracing surface layers of the flared disks. As the radius of the polarization disk around SR 24N is roughly consistent with the size of the outer Roche lobe, it is natural to interpret the polarization disk around SR 24N as a circumbinary disk surrounding the SR 24Nb–Nc system.
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| 5. |
- Yang, Yi, et al.
(författare)
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High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A : Possible Streamers in Misaligned Circumbinary Disk System
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 889:2
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Tidskriftsartikel (refereegranskat)abstract
- We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high -contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2-1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to similar to 240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19-5.64 km s(-1). Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17-16.43 km s(-1). From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.
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| 6. |
- Youngblood, Allison, et al.
(författare)
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A Radiatively Driven Wind from the η Tel Debris Disk
- 2021
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 162:6
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Tidskriftsartikel (refereegranskat)abstract
- We present far- and near-ultraviolet absorption spectroscopy of the ∼23 Myr edge-on debris disk surrounding the A0V star η Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C i, C ii, O i, Mg ii, Al ii, Si ii, S ii, Mn ii, Fe ii, and marginally N i. The lines show two clear absorption components at −22.7 ± 0.5 km s−1 and −17.8 ± 0.7 km s−1, which we attribute to circumstellar (CS) and interstellar gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by −16.9 ± 2.6 km s−1 in the star's reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the η Tel CS gas is significantly higher than the solar ratio, as is the case in the β Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the η Tel CS gas is consistent with the solar value. Our analysis shows that because η Tel is an earlier type star than β Pic and 49 Cet, with more substantial radiation pressure at the dominant C ii transitions, this species cannot bind the CS gas disk to the star as it does for β Pic and 49 Cet, resulting in the disk wind.
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